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Sample records for film-modified glassy carbon

  1. mwnts composite film modified glassy carbon electrode

    African Journals Online (AJOL)

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    ABSTRACT: A poly p-aminosalicylic acid (Poly(p-ASA)) and multiwall carbon nanotubes. (MWCNTs) composite modified glassy carbon (GC) electrode was constructed by casting the MWNTs on the GC electrode surface followed by electropolymerization of the p-ASA on the MWCNTs/GCE. The electrochemical behaviours ...

  2. Graphene/Nafion composite film modified glassy carbon electrode for simultaneous determination of paracetamol, aspirin and caffeine in pharmaceutical formulations.

    Science.gov (United States)

    Yiğit, Aydın; Yardım, Yavuz; Çelebi, Metin; Levent, Abdulkadir; Şentürk, Zühre

    2016-09-01

    A graphene-Nafion composite film was fabricated on the glassy carbon electrode (GR-NF/GCE), and used for simultaneous determination of paracetamol (PAR), aspirin (ASA) and caffeine (CAF). The electrochemical behaviors of PAR, ASA and CAF were investigated by cyclic voltammetry and square-wave adsorptive anodic stripping voltammetry. By using stripping one for simultaneous determination of PAR, ASA and CAF, their electrochemical oxidation peaks appeared at +0.64, 1.04 and 1.44V, and good linear current responses were obtained with the detection limits of 18ngmL(-1) (1.2×10(-9)M), 11.7ngmL(-1) (6.5×10(-8)M) and 7.3ngmL(-1) (3.8×10(-8)M), respectively. Finally, the proposed electrochemical sensor was successfully applied for quantifying PAR, ASA and CAF in commercial tablet formulations. Copyright © 2016 Elsevier B.V. All rights reserved.

  3. Simultaneous determination of cysteine, uric acid and tyrosine using Au-nanoparticles/poly(E)-4-(p-tolyldiazenyl)benzene-1,2,3-triol film modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Taei, M., E-mail: m.taei@ch.iut.ac.ir; Hasanpour, F.; Salavati, H.; Banitaba, S.H.; Kazemi, F.

    2016-02-01

    A novel Au nanoparticles/poly(E)-4-(p-tolyldiazenyl)benzene-1,2,3-triol (AuNPs/PTAT) film modified glassy carbon electrode (AuNPs/PTAT/GCE) was fabricated for the simultaneous determination of three antioxidants named, cysteine (Cys), uric acid (UA) and tyrosine (Tyr). The bare glassy carbon electrode (GCE) fails to separate the oxidation peak potentials of these molecules, while PTAT film modified electrode can resolve them. Electrochemical impedance spectroscopy (EIS) study indicates that the charge transfer resistance of bare electrode increased as (E)-4-(p-tolyldiazenyl)benzene-1,2,3-triol was electropolymerized at the bare electrode. Furthermore, EIS exhibits enhancement of electron transfer kinetics between analytes and electrode after electrodeposition of Au nanoparticles. Differential pulse voltammetry results show that the electrocatalytic current increases linearly in the ranges of 2–540 μmol L{sup −1} for Cys, 5–820 μmol L{sup −1} for UA and 10–560 μmol L{sup −1} for Tyr with detection limits (S/N = 3) of 0.04 μmol L{sup −1}, 0.1 μmol L{sup −1} and 2 μmol L{sup −1} for Cys, UA and Tyr, respectively. The proposed method was successfully applied for simultaneous determination of Cys, UA and Tyr in human urine samples. - Highlights: • AuNPs/PTAT/GCE was fabricated by electrodeposition and electropolymerization. • The sensor reduced the overpotential for oxidation of Cys. • This electrode was successfully used for simultaneous sensing of Cys, UA and Tyr. • This sensor was effectively used for detection Cys, UA and Tyr in real samples.

  4. Poly(3,4-ethylenedioxythiophene-co-(5-amino-2-naphthalenesulfonic acid)) (PEDOT-PANS) film modified glassy carbon electrode for selective detection of dopamine in the presence of ascorbic acid and uric acid

    International Nuclear Information System (INIS)

    Balamurugan, A.; Chen Shenming

    2007-01-01

    Poly(3,4-ethylenedioxythiophene-co-(5-amino-2-naphthalenesulfonic acid)) (PEDOT-PANS) film modified glassy carbon electrode was prepared by electrochemical polymerization technique. The properties of modified electrode was studied. It was found that the electrochemical properties of modified electrode was very much dependent on the experimental conditions, such as monomer oxidation potential and pH. The modified electrode surface was characterized by scanning electron microscopy (SEM). The PEDOT-PANS film modified electrode shows electrocatalytic activity toward oxidation of dopamine (DA) in acetate buffer solution (pH 5.0) and results in a marked enhancement of the current response. The linear sweep voltammetric (LSV) peak heights are linear with DA concentration from 2 x 10 -6 to 1 x 10 -5 M. The detection limit is 5 x 10 -7 M. More over, the interferences of ascorbic acid (AA) and uric acid (UA) were effectively diminished. This work provides a simple and easy approach for selective determination of dopamine in the presence of ascorbic acid and uric acid

  5. Electrochemical behaviors and simultaneous determination of guanine and adenine based on graphene–ionic liquid–chitosan composite film modified glassy carbon electrode

    International Nuclear Information System (INIS)

    Niu Xiuli; Yang Wu; Ren Jie; Guo Hao; Long Shijia; Chen Jiaojiao; Gao Jinzhang

    2012-01-01

    Highlights: ► This work developed a novel electrochemical biosensors for guanine and adenine detection simultaneously. ► A disposable electrode based on graphene sheets, ionic liquid and chitosan was proposed. ► The presented method was also applied to simultaneous determination of guanine and adenine in denatured DNA samples with satisfying results. ► Easy fabrication, high sensitivity, excellent reproducibility and long-term stability. - Abstract: A graphene sheets (GS), ionic liquid (IL) and chitosan (CS) modified electrode was fabricated and the modified electrode displayed excellent electrochemical catalytic activities toward guanine and adenine. The transfer electron number (n) and the charge transfer coefficient (α) were calculated with the result as n = 2, α = 0.58 for guanine, and n = 2, α = 0.51 for adenine, which indicated the electrochemical oxidation of guanine and adenine on GS/IL/CS modified electrode was a two-electron and two-proton process. The oxidation overpotentials of guanine and adenine were decreased significantly compared with those obtained at the bare glassy carbon electrode and multi-walled carbon nanotubes modified electrode. The modified electrode exhibited good analytical performance and was successfully applied for individual and simultaneous determination of guanine and adenine. Low detection limits of 0.75 μM for guanine and 0.45 μM for adenine were obtained, with the linear calibration curves over the concentration range 2.5–150 μM and 1.5–350 μM, respectively. At the same time, the proposed method was successfully applied for the determination of guanine and adenine in denatured DNA samples with satisfying results. Moreover, the GS/IL/CS modified electrode exhibited good sensitivity, long-term stability and reproducibility for the determination of guanine and adenine.

  6. Fabrication of β-cyclodextrin-coated poly (diallyldimethylammonium chloride)-functionalized graphene composite film modified glassy carbon-rotating disk electrode and its application for simultaneous electrochemical determination colorants of sunset yellow and tartrazine.

    Science.gov (United States)

    Ye, Xiaoliang; Du, Yongling; Lu, Daban; Wang, Chunming

    2013-05-24

    We proposed a green and facile approach for the synthesis of β-cyclodextrin-coated poly(diallyldimethylammonium chloride)-functionalized graphene composite film (β-CD-PDDA-Gr) by using L-ascorbic acid (L-AA) as the reducing agent at room temperature. The β-CD-PDDA-Gr composite film modified glassy carbon-rotating disk electrode (GC-RDE) was then developed for the sensitive simultaneous determination of two synthetic food colorants: sunset yellow (SY) and tartrazine (TT). By cyclic voltammetry (CV), the peak currents of SY and TT increased obviously on the developed electrochemical sensor. The kinetic parameters, such as diffusion coefficient D and standard heterogeneous rate constant kb, were estimated by linear sweep voltammetry (LSV). Under the optimal conditions, the differential pulse voltammetry (DPV) signals of SY and TT on the β-CD-PDDA-Gr modified GC-RDE were significantly enhanced. The enhanced anodic peak currents represented the excellent analytical performance of simultaneous detection of SY and TT in the range of 5.0×10(-8) to 2.0×10(-5) mol L(-1), with a low limit of detection (LOD) of 1.25×10(-8) mol L(-1) for SY and 1.43×10(-8) mol L(-1) for TT (SN(-1)=3). This proposed method displayed outstanding selectivity, good stability and acceptable repeatability and reproducibility, and also has been used to simultaneously determine SY and TT in some commercial soft drinks with satisfactory results. The obtained results were compared to HPLC of analysis for those two colorants and no significant differences were found. By the treatment of the experimental data, the electrochemical reaction mechanisms of SY and TT both involved a one-electron-one-proton-transfer process. Copyright © 2013 Elsevier B.V. All rights reserved.

  7. Fabrication of β-cyclodextrin-coated poly (diallyldimethylammonium chloride)-functionalized graphene composite film modified glassy carbon-rotating disk electrode and its application for simultaneous electrochemical determination colorants of sunset yellow and tartrazine

    International Nuclear Information System (INIS)

    Ye, Xiaoliang; Du, Yongling; Lu, Daban; Wang, Chunming

    2013-01-01

    Graphical abstract: -- Highlights: •A green and facile approach for synthesis of β-CD-PDDA-Gr at room temperature. •We present the β-CD-PDDA-Gr modified GC-RDE for simultaneous detection of SY and TT. •SY and TT's electrooxidations are both the one-electron-one-proton-transfer process. •Diffusion coefficients and standard rate constants of SY and TT were discussed. -- Abstract: We proposed a green and facile approach for the synthesis of β-cyclodextrin-coated poly(diallyldimethylammonium chloride)-functionalized graphene composite film (β-CD-PDDA-Gr) by using L-ascorbic acid (L-AA) as the reducing agent at room temperature. The β-CD-PDDA-Gr composite film modified glassy carbon-rotating disk electrode (GC-RDE) was then developed for the sensitive simultaneous determination of two synthetic food colorants: sunset yellow (SY) and tartrazine (TT). By cyclic voltammetry (CV), the peak currents of SY and TT increased obviously on the developed electrochemical sensor. The kinetic parameters, such as diffusion coefficient D and standard heterogeneous rate constant k b , were estimated by linear sweep voltammetry (LSV). Under the optimal conditions, the differential pulse voltammetry (DPV) signals of SY and TT on the β-CD-PDDA-Gr modified GC-RDE were significantly enhanced. The enhanced anodic peak currents represented the excellent analytical performance of simultaneous detection of SY and TT in the range of 5.0 × 10 −8 to 2.0 × 10 −5 mol L −1 , with a low limit of detection (LOD) of 1.25 × 10 −8 mol L −1 for SY and 1.43 × 10 −8 mol L −1 for TT (S N −1 = 3). This proposed method displayed outstanding selectivity, good stability and acceptable repeatability and reproducibility, and also has been used to simultaneously determine SY and TT in some commercial soft drinks with satisfactory results. The obtained results were compared to HPLC of analysis for those two colorants and no significant differences were found. By the treatment of the

  8. Fabrication of β-cyclodextrin-coated poly (diallyldimethylammonium chloride)-functionalized graphene composite film modified glassy carbon-rotating disk electrode and its application for simultaneous electrochemical determination colorants of sunset yellow and tartrazine

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Xiaoliang; Du, Yongling; Lu, Daban; Wang, Chunming, E-mail: wangcm@lzu.edu.cn

    2013-05-24

    Graphical abstract: -- Highlights: •A green and facile approach for synthesis of β-CD-PDDA-Gr at room temperature. •We present the β-CD-PDDA-Gr modified GC-RDE for simultaneous detection of SY and TT. •SY and TT's electrooxidations are both the one-electron-one-proton-transfer process. •Diffusion coefficients and standard rate constants of SY and TT were discussed. -- Abstract: We proposed a green and facile approach for the synthesis of β-cyclodextrin-coated poly(diallyldimethylammonium chloride)-functionalized graphene composite film (β-CD-PDDA-Gr) by using L-ascorbic acid (L-AA) as the reducing agent at room temperature. The β-CD-PDDA-Gr composite film modified glassy carbon-rotating disk electrode (GC-RDE) was then developed for the sensitive simultaneous determination of two synthetic food colorants: sunset yellow (SY) and tartrazine (TT). By cyclic voltammetry (CV), the peak currents of SY and TT increased obviously on the developed electrochemical sensor. The kinetic parameters, such as diffusion coefficient D and standard heterogeneous rate constant k{sub b}, were estimated by linear sweep voltammetry (LSV). Under the optimal conditions, the differential pulse voltammetry (DPV) signals of SY and TT on the β-CD-PDDA-Gr modified GC-RDE were significantly enhanced. The enhanced anodic peak currents represented the excellent analytical performance of simultaneous detection of SY and TT in the range of 5.0 × 10{sup −8} to 2.0 × 10{sup −5} mol L{sup −1}, with a low limit of detection (LOD) of 1.25 × 10{sup −8} mol L{sup −1} for SY and 1.43 × 10{sup −8} mol L{sup −1} for TT (S N{sup −1} = 3). This proposed method displayed outstanding selectivity, good stability and acceptable repeatability and reproducibility, and also has been used to simultaneously determine SY and TT in some commercial soft drinks with satisfactory results. The obtained results were compared to HPLC of analysis for those two colorants and no significant

  9. Electrodeposition of gold nanoclusters on overoxidized polypyrrole film modified glassy carbon electrode and its application for the simultaneous determination of epinephrine and uric acid under coexistence of ascorbic acid

    Energy Technology Data Exchange (ETDEWEB)

    Li Jing [Department of Chemistry, University of Science and Technology of China, Hefei 230026 (China); Lin Xiangqin [Department of Chemistry, University of Science and Technology of China, Hefei 230026 (China)]. E-mail: xqlin@ustc.edu.cn

    2007-07-23

    A novel biosensor was fabricated by electrochemical deposition of gold nanoclusters on ultrathin overoxidized polypyrrole (PPyox) film, formed a nano-Au/PPyox composite on glassy carbon electrode (nano-Au/PPyox/GCE). The properties of the nanocomposite have been characterized by field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and electrochemical investigations. The nano-Au/PPyox/GCE had strongly catalytic activity toward the oxidation of epinephrine (EP), uric acid (UA) and ascorbic acid (AA), and resolved the overlapping voltammetric response of EP, UA and AA into three well-defined peaks with a large anodic peak difference. The catalytic peak currents obtained from differential pulse voltammetry increased linearly with increasing EP and UA concentrations in the range of 3.0 x 10{sup -7} to 2.1 x 10{sup -5} M and 5.0 x 10{sup -8} to 2.8 x 10{sup -5} M with a detection limit of 3.0 x 10{sup -8} and 1.2 x 10{sup -8} M (s/n = 3), respectively. The results showed that the modified electrode can selectively determine EP and UA in the coexistence of a large amount of AA. In addition, the sensor exhibited excellent sensitivity, selectivity and stability. The nano-Au/PPyox/GCE has been applied to determination of EP in epinephrine hydrochloride injection and UA in urine samples with satisfactory results.

  10. Direct Quantification of Cd2+in the Presence of Cu2+by a Combination of Anodic Stripping Voltammetry Using a Bi-Film-Modified Glassy Carbon Electrode and an Artificial Neural Network.

    Science.gov (United States)

    Zhao, Guo; Wang, Hui; Liu, Gang

    2017-07-03

    Abstract : In this study, a novel method based on a Bi/glassy carbon electrode (Bi/GCE) for quantitatively and directly detecting Cd 2+ in the presence of Cu 2+ without further electrode modifications by combining square-wave anodic stripping voltammetry (SWASV) and a back-propagation artificial neural network (BP-ANN) has been proposed. The influence of the Cu 2+ concentration on the stripping response to Cd 2+ was studied. In addition, the effect of the ferrocyanide concentration on the SWASV detection of Cd 2+ in the presence of Cu 2+ was investigated. A BP-ANN with two inputs and one output was used to establish the nonlinear relationship between the concentration of Cd 2+ and the stripping peak currents of Cu 2+ and Cd 2+ . The factors affecting the SWASV detection of Cd 2+ and the key parameters of the BP-ANN were optimized. Moreover, the direct calibration model (i.e., adding 0.1 mM ferrocyanide before detection), the BP-ANN model and other prediction models were compared to verify the prediction performance of these models in terms of their mean absolute errors (MAEs), root mean square errors (RMSEs) and correlation coefficients. The BP-ANN model exhibited higher prediction accuracy than the direct calibration model and the other prediction models. Finally, the proposed method was used to detect Cd 2+ in soil samples with satisfactory results.

  11. Glassy carbon based supercapacitor stacks

    Energy Technology Data Exchange (ETDEWEB)

    Baertsch, M.; Braun, A.; Koetz, R.; Haas, O. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-06-01

    Considerable effort is being made to develop electrochemical double layer capacitors (EDLC) that store relatively large quantities of electrical energy and possess at the same time a high power density. Our previous work has shown that glassy carbon is suitable as a material for capacitor electrodes concerning low resistance and high capacity requirements. We present the development of bipolar electrochemical glassy carbon capacitor stacks of up to 3 V. Bipolar stacks are an efficient way to meet the high voltage and high power density requirements for traction applications. Impedance and cyclic voltammogram measurements are reported here and show the frequency response of a 1, 2, and 3 V stack. (author) 3 figs., 1 ref..

  12. Low temperature thermal conductivities of glassy carbons

    International Nuclear Information System (INIS)

    Anderson, A.C.

    1979-01-01

    The thermal conductivity of glassy carbon in the temperature range 0.1 to 100 0 K appears to depend only on the temperature at which the material was pyrolyzed. The thermal conductivity can be related to the microscopic structure of glassy carbon. The reticulated structure is especially useful for thermal isolation at cryogenic temperatures

  13. Glassy carbon coated graphite for nuclear applications

    International Nuclear Information System (INIS)

    Delpeux S; Cacciaguerra T; Duclaux L

    2005-01-01

    Taking into account the problems caused by the treatment of nuclear wastes, the molten salts breeder reactors are expected to a great development. They use a molten fluorinated salt (mixture of LiF, BeF 2 , ThF 4 , and UF 4 ) as fuel and coolant. The reactor core, made of graphite, is used as a neutrons moderator. Despite of its compatibility with nuclear environment, it appears crucial to improve the stability and inertness of graphite against the diffusion of chemicals species leading to its corrosion. One way is to cover the graphite surface by a protective impermeable deposit made of glassy carbon obtained by the pyrolysis of phenolic resin or polyvinyl chloride precursors. The main difficulty in the synthesis of glassy carbon is to create exclusively, in the primary pyrolysis product, a micro-porosity of about twenty Angstroms which closes later at higher temperature. Therefore, the evacuation of the volatile products occurring mainly between 330 and 600 C, must progress slowly to avoid the material to crack. In this study, the optimal parameters for the synthesis of glassy carbon as well as glassy carbon deposits on nuclear-type graphite pieces are discussed. Both thermal treatment of phenolic and PVC resins have been performed. The structure and micro-texture of glassy carbon have been investigated by X-ray diffraction, scanning and transmission electron microscopies and helium pycno-metry. Glassy carbon samples (obtained at 1200 C) show densities ranging from 1.3 to 1.55 g/cm 3 and closed pores with nano-metric size (∼ 5 to 10 nm) appear clearly on the TEM micrographs. Then, a thermal treatment to 2700 C leads to the shrinkage of the entangled graphene ribbons, in good agreement with the proposed texture model for glassy carbon. Glassy carbon deposits on nuclear graphite have been developed by an impregnation method. The uniformity of the deposit depends clearly on the surface texture and the chemistry of the graphite substrate. The deposit regions where

  14. Nano mechanical properties of carbon films modified by ion radiation

    International Nuclear Information System (INIS)

    Foerster, C.E.; Serbena, F.C.; Lepienski, C.M.; Odo, G.Y.; Zawislak, F.C.; Lopes, J.M.J.; Baptista, D.L.; Garcia, I.T.S.

    2000-01-01

    In present work it is measured hardness, Young modulus and friction coefficient values for different types of carbon films. These films were submitted to different ion bombardment conditions (energy and fluencies). The mechanical behavior was obtained by nano indentation technique and analyzed by the Oliver/Pharr method. For friction coefficient determination the nano scratch procedure is used. Pristine C 60 films (fullerenes) has a hardness of 0.33 GPa. After irradiation with different ions (He, N and Bi), the hardness raise to about 14 GPa and the Young modulus change from 20 to about 200 GPa. For photoresist film AZ-1350J irradiation with Ar and He change the hardness from 0.4 to about 14 GPa and the Young modulus raise from 4 to 80 GPa. In a-C-H the hardness change from 3.5 to 11 GPa when submitted to N irradiation. In PPA films the hardness value raise from 0.5 to 11 GPa after irradiation with Ar. These mechanical and tribological results were analyzed in terms of deposited energy by the ion irradiation and compared with those presented in the literature. (author)

  15. Thermonuclear reactor materials composed of glassy carbons

    International Nuclear Information System (INIS)

    Kazumata, Yukio.

    1979-01-01

    Purpose: To improve the durability to plasma radiation by the use of glassy carbon as the structural materials for the first wall and the blanket in thermonuclear devices. Constitution: The glassy carbon (glass-like carbon) is obtained by forming specific organic substances into a predetermined configuration and carbonizing them by heat decomposition under special conditions. They are impermeable carbon material of 1.40 - 1.70 specific gravity, less graphitizable and being almost in isotropic crystal forms in which isotropic structure such as in graphite is scarcely observed. They have an extremely high hardness, are less likely to be damaged when exposed to radiation and have great strength and corrosion resistance. Accordingly, the service life of the reactor walls and the likes can remarkably be increased by using the materials. (Horiuchi, T.)

  16. NITROANILINE FILM-HOLE MODIFIED GLASSY CARBON ...

    African Journals Online (AJOL)

    ABSTRACT. Herein, we report determination of dopamine (DA) at modified glassy carbon electrode (GCE) with a film produced by reduction of diazonium generated from p-nitroaniline (PNA). Pores were created purposely by stripping pre-deposited gold nanoparticles (AuNPs) in the modifier film. The modified electrodes.

  17. Glassy carbon electrodes modified with gelatin functionalized ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 38; Issue 7. Glassy carbon electrodes modified with gelatin functionalized reduced graphene oxide nanosheet for determination of gallic acid. Fereshteh Chekin Samira Bagheri Sharifah Bee Abd Hamid. Volume 38 Issue 7 December 2015 pp 1711-1716 ...

  18. Wafer-level microstructuring of glassy carbon

    Science.gov (United States)

    Hans, Loïc. E.; Prater, Karin; Kilchoer, Cédric; Scharf, Toralf; Herzig, Hans Peter; Hermerschmidt, Andreas

    2014-03-01

    Glassy carbon is used nowadays for a variety of applications because of its mechanical strength, thermal stability and non-sticking adhesion properties. One application is glass molding that allows to realize high resolution diffractive optical elements on large areas and at affordable price appropriate for mass production. We study glassy carbon microstructuring for future precision compression molding of low and high glass-transition temperature. For applications in optics the uniformity, surface roughness, edge definition and lateral resolution are very important parameters for a stamp and the final product. We study different methods of microstructuring of glassy carbon by etching and milling. Reactive ion etching with different protection layers such as photoresists, aluminium and titanium hard masks have been performed and will be compare with Ion beam etching. We comment on the quality of the structure definition and give process details as well as drawbacks for the different methods. In our fabrications we were able to realize optically flat diffractive structures with slope angles of 80° at typical feature sizes of 5 micron and 700 nm depth qualified for high precision glass molding.

  19. Rapid amperometric detection of coliforms based on MWNTs/Nafion composite film modified glass carbon electrode.

    Science.gov (United States)

    Cheng, Yuxiao; Liu, Yajun; Huang, Jingjing; Xian, Yuezhong; Zhang, Wen; Zhang, Zhonghai; Jin, Litong

    2008-03-15

    A multi-wall carbon nanotubes (MWNTs)/Nafion modified glassy carbon electrode (GCE) was fabricated for the rapid amperometric detection of coliforms, represented by Escherichia coli (E. coli). In the bacterial solution, beta-galactosidase which was used as an indicator of coliforms reacted with substrate, p-aminophenol-beta-galactopyranoside (PAPG), and produced p-aminophenol (PAP). PAP was detected by MWNTs/Nafion modified GCE. Due to the cation-exchange capacity of Nafion and the electrocatalytic ability of MWNTs, the detection sensitivity of PAP was improved and the detection time of coliforms was shortened. The bacterial can be detected within 5h ranging from 10 to 10(4)cfu/mL. The MWNTs/Nafion modified GCE was easy to be constructed and regenerated. To our best knowledge, it was the first time to use MWNTs/Nafion modified GCE to detect the concentration of coliforms.

  20. Glassy Carbon Coating Deposited on Hybrid Structure of Composite Materials

    Directory of Open Access Journals (Sweden)

    Posmyk A.

    2016-06-01

    Full Text Available This paper presents a method of production metal matrix composites with aluminum oxide foam covered by glassy carbon layer used as reinforcement. The glassy carbon coating was formed for decreasing of friction coefficient and reducing the wear. In first step of technology liquid glassy carbon precursor is on ceramic foam deposited, subsequently cured and carbonated at elevated temperature. In this way ceramic foam is covered with glassy carbon coating with thickness of 2-8 μm. It provides desirable amount of glassy carbon in the structure of the material. In the next step, porous spheres with carbon coating are infiltrated by liquid matrix of Al-Cu-Mg alloy. Thereby, equable distribution of glassy carbon in composite volume is achieved. Moreover, typical problems for composites reinforced by particles like sedimentation, agglomeration and clustering of particles are avoided. Tribological characteristics during friction in air versus cast iron as a counterpart were made. Produced composites with glassy carbon layer are characterised by friction coefficient between 0.08-0.20, thus meeting the typical conditions for solid lubricants.

  1. Surface-enhanced oxidation and detection of Sunset Yellow and Tartrazine using multi-walled carbon nanotubes film-modified electrode.

    Science.gov (United States)

    Zhang, Weikang; Liu, Tao; Zheng, Xiaojiang; Huang, Wensheng; Wan, Chidan

    2009-11-01

    The insoluble multi-walled carbon nanotubes (MWNT) was successfully dispersed into water in the presence of hydrophobic surfactant. After that, MWNT film-coated glassy carbon electrode (GCE) was achieved via dip-coating and evaporating water. Owing to huge surface area, high sorption capacity and subtle electronic properties, MWNT film exhibits highly efficient accumulation efficiency as well as considerable surface enhancement effects to Sunset Yellow and Tartrazine. As a result, the oxidation peak currents of Sunset Yellow and Tartrazine remarkably increase at the MWNT film-modified GCE. Based on this, a novel electrochemical method was developed for the simultaneous determination of Sunset Yellow and Tartrazine. The limits of detection are 10.0 ng mL(-1) (2.2 x 10(-8)mol L(-1)) and 0.1 microg mL(-1) (1.88 x 10(-7)mol L(-1)) for Sunset Yellow and Tartrazine. Finally, the proposed method was successfully used to detect Sunset Yellow and Tartrazine in soft drinks.

  2. Atmospheric pressure plasma treatment of glassy carbon for adhesion improvement

    DEFF Research Database (Denmark)

    Kusano, Yukihiro; Mortensen, Henrik Junge; Stenum, Bjarne

    2007-01-01

    Glassy carbon plates were treated with an atmospheric pressure dielectric barrier discharge (DBD). He gas, gas mixtures of He and reactive gases such as O2, CO2 and NH3, Ar gas and Ar/NH3 gas mixture were used as treatment gases. The oxygen and nitrogen contents on the surface as well as defect...... density increased with the plasma treatments. Adhesion test of the treated glassy carbon covered with cured epoxy showed cohesive failure, indicating strong bonding after the treatments. This is in contrast to the adhesion tests of untreated samples where the epoxy readily peeled off the glassy carbon....

  3. A study of nanostructured gold modified glassy carbon electrode for ...

    Indian Academy of Sciences (India)

    Wintec

    A study of nanostructured gold modified glassy carbon electrode for the determination of trace Cr(VI). BENZHI ... The method was applied to determine levels of chromium(VI) in tap water and sewage water. Keywords. Nanostructured gold modified ... analytical reagent-grade and double distilled water was used throughout.

  4. Glassy carbon supercapacitor: 100,000 cycles demonstrated

    Energy Technology Data Exchange (ETDEWEB)

    Baertsch, M.; Braun, A.; Schnyder, B.; Koetz, R. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1999-08-01

    A 5 V glassy carbon capacitor stack was built consisting of four bipolar and two end-plate electrodes. More than 100,000 charging/discharging cycles were applied to test the stability of the double-layer capacitor. Low and high frequency resistances were measured as a function of the number of cycles. (author) 2 figs., 1 ref.

  5. A study of nanostructured gold modified glassy carbon electrode for ...

    Indian Academy of Sciences (India)

    A nanostructured gold modified glassy carbon electrode (Aunano/GCE) was employed for the determination of trace chromium(VI). To prepare Aunano/GCE, the GCE was immersed into KAuCl4 solution and electrodeposition was conducted at the potential of -0.4 V (vs Ag/AgCl) for 600 s. Scanning electron microscopy ...

  6. Electrochemical oxidation of niclosamide at a glassy carbon ...

    African Journals Online (AJOL)

    Cyclic voltammetry, square-wave voltammetry and controlled potential electrolysis have been used to study the electrochemical oxidation behaviour of niclosamide at a glassy carbon electrode. The number of electrons transferred, the wave characteristics, the diffusion coefficient and reversibility of the reactions have been ...

  7. Voltammetric quantitation of nitazoxanide by glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    Rajeev Jain

    2013-12-01

    Full Text Available The present study reports voltammetric reduction of nitazoxanide in Britton–Robinson (B–R buffer by cyclic and square-wave voltammetry at glassy carbon electrode. A versatile fully validated voltammetric method for quantitative determination of nitazoxanide in pharmaceutical formulation has been proposed. A squrewave peak current was linear over the nitazoxanide concentration in the range of 20–140 µg/mL. The limit of detection (LOD and limit of quantification (LOQ was calculated to be 5.23 μg/mL and 17.45 μg/mL, respectively. Keywords: Nitazoxanide, Squarewave voltammetry, Glassy carbon electrode, Pharmaceutical formulation

  8. Electrocatalytic hydrazine oxidation on quinizarine modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Ardakani, Mohammad Mazloum [Department of Chemistry, Faculty of Science, Yazd University, Yazd (Iran, Islamic Republic of)]. E-mail: mazloum@yazduni.ac.ir; karami, Payam Ebrahimi [Department of Chemistry, Faculty of Science, Yazd University, Yazd (Iran, Islamic Republic of); Rahimi, Parvaneh [Department of Chemistry, Faculty of Science, Yazd University, Yazd (Iran, Islamic Republic of); Zare, Hamid Reza [Department of Chemistry, Faculty of Science, Yazd University, Yazd (Iran, Islamic Republic of); Naeimi, Hossein [Department of Chemistry, Faculty of Science, Kashan University, Kashan (Iran, Islamic Republic of)

    2007-06-10

    The electrocatalytic oxidation of hydrazine has been studied on glassy carbon modified by electrodeposition of quinizarine, using cyclic voltammetry and chronoamperometry techniques. It has been shown that the oxidation of hydrazine to nitrogen occurs at a potential where oxidation is not observed at the bare glassy carbon electrode. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode surface and immobilized quinizarine were calculated as 4.44 s{sup -1} and 0.66, respectively. The heterogenous rate constant for oxidation of hydrazine at the quinizarine modified electrode surface was also determined and found to be about 4.83 x 10{sup 3} M{sup -1} s{sup -1}. The diffusion coefficient of hydrazine was also estimated as 1.1 x 10{sup -6} cm{sup 2} s{sup -1} for the experimental conditions, using chronoamperometry.

  9. Fabrication of chronocoulometric DNA sensor based on gold nanoparticles/poly(l-lysine) modified glassy carbon electrode.

    Science.gov (United States)

    Wang, Jie; Zhang, Shaojun; Zhang, Yuzhong

    2010-01-15

    In this work, we fabricated a sensitivity chronocoulometric DNA sensor (CDS) based on gold nanoparticles (AuNPs)/poly(L-lysine) complex film modified glassy carbon electrode. Hexaammineruthenium(III) chloride ([Ru(NH3)6]3+) was used as the electroactive indicator. The assembled process was investigated by cyclic voltammetry (CV) and chronocoulometry (CC). CC is used to monitor the DNA hybridization event by measurement of electrostatic binding [Ru(NH3)6]3+. Under the optimal conditions, the signal of [Ru(NH3)6]3+ was linear with the logarithm of the concentration of the complementary oligonucleotides from 1.0 x 10(-13) to 1.0 x 10(-11) M, and the detection limit is 3.5 x 10(-14) M.

  10. In situ Raman spectroelectrochemistry of azobenzene monolayers on glassy carbon.

    Science.gov (United States)

    Itoh, Takashi; McCreery, Richard L

    2007-05-01

    In situ Raman spectra of chemisorbed azobenzene (AB) monolayers on glassy carbon (GC) electrodes were observed under potentiostatic conditions in acetonitrile (ACN) with tetrabutyl-ammonium tetrafluoroborate (TBA-BF4). The Raman intensities of these spectra were high below -1000 mV, and this is attributed to the change in absorbance of AB on GC. In this paper, we describe chemisorbed AB molecules on GC electrode surfaces under potentiostatic conditions.

  11. Magnetoresistance, electrical conductivity, and Hall effect of glassy carbon

    Energy Technology Data Exchange (ETDEWEB)

    Baker, D.F.

    1983-02-01

    These properties of glassy carbon heat treated for three hours between 1200 and 2700/sup 0/C were measured from 3 to 300/sup 0/K in magnetic fields up to 5 tesla. The magnetoresistance was generally negative and saturated with reciprocal temperature, but still increased as a function of magnetic field. The maximum negative magnetoresistance measured was 2.2% for 2700/sup 0/C material. Several models based on the negative magnetoresistance being proportional to the square of the magnetic moment were attempted; the best fit was obtained for the simplest model combining Curie and Pauli paramagnetism for heat treatments above 1600/sup 0/C. Positive magnetoresistance was found only in less than 1600/sup 0/C treated glassy carbon. The electrical conductivity, of the order of 200 (ohm-cm)/sup -1/ at room temperature, can be empirically written as sigma = A + Bexp(-CT/sup -1/4) - DT/sup -1/2. The Hall coefficient was independent of magnetic field, insensitive to temperature, but was a strong function of heat treatment temperature, crossing over from negative to positive at about 1700/sup 0/C and ranging from -0.048 to 0.126 cm/sup 3//coul. The idea of one-dimensional filaments in glassy carbon suggested by the electrical conductivity is compatible with the present consensus view of the microstructure.

  12. Xanthine oxidase/laponite nanoparticles immobilized on glassy carbon electrode: direct electron transfer and multielectrocatalysis.

    Science.gov (United States)

    Shan, Dan; Wang, Yan-Na; Xue, Huai-Guo; Cosnier, Serge; Ding, Shou-Nian

    2009-08-15

    In this work, colloidal laponite nanoparticles were further expanded into the design of the third-generation biosensor. Direct electrochemistry of the complex molybdoenzyme xanthine oxidase (XnOx) immobilized on glassy carbon electrode (GCE) by laponite nanoparticles was investigated for the first time. XnOx/laponite thin film modified electrode showed only one pair of well defined and reversible cyclic voltammetric peaks attributed to XnOx-FAD cofactor at about -0.370 V vs. SCE (pH 5). The formal potential of XnOx-FAD/FADH(2) couple varied linearly with the increase of pH in the range of 4.0-8.0 with a slope of -54.3 mV pH(-1), which indicated that two-proton transfer was accompanied with two-electron transfer in the electrochemical reaction. More interestingly, the immobilized XnOx retained its biological activity well and displayed an excellent electrocatalytic performance to both the oxidation of xanthine and the reduction of nitrate. The electrocatalytic response showed a linear dependence on the xanthine concentration ranging from 3.9 x 10(-8) to 2.1 x 10(-5)M with a detection limit of 1.0 x 10(-8)M based on S/N=3.

  13. NITROANILINE FILM-HOLE MODIFIED GLASSY CARBON ...

    African Journals Online (AJOL)

    The result showed that PNA film-hole modified GCE has a good stability and long life. Table 1. Comparison of the analytical performance of the proposed dopamine sensor with previously reported dopamine sensors. Sensor. Method LOD (µM). Ref. Co(II) complex and multi-walled carbon nanotubes modified GCE. Amp.

  14. Comparison of the voltammetric behavior of metronidazole at a DNA-modified glassy carbon electrode, a mercury thin film electrode and a glassy carbon electrode

    OpenAIRE

    Brett, Ana Maria Oliveira; Serrano, Silvia H. P.; Gutz, Ivano G. R.; La-Scalea, Mauro A.

    1997-01-01

    The electroanalytical performance at three electrodes: DNA-modified galssy carbon electrode, mercury thin film electrode and glassy carbon electrode, for the study of the electrochemical reduction of metronidazole is compared. All three electrodes showed a similar trend in the reduction mechanism for metronidazole, depenent on pH in the acid and neutral region and independent in alkaline media, although there was a shift in the peak potentials to more negative values when a bare glassy carbon...

  15. Structural and spectroscopic studies of a commercial glassy carbon

    Science.gov (United States)

    Parker, Stewart F.; Imberti, Silvia; Callear, Samantha K.; Albers, Peter W.

    2013-12-01

    Glassy carbon is a form of carbon made by heating a phenolic resin to high temperature in an inert atmosphere. It has been suggested that it is composed of fullerene-like structures. The aim of the present work was to characterize the material using both structural (neutron diffraction and transmission electron microscopy) and spectroscopic (inelastic neutron scattering, Raman and X-ray photoelectron spectroscopies) methods. We find no evidence to support the suggestion of fullerene-like material being present to a significant extent, rather the model that emerges from all of the techniques is that the material is very like amorphous carbon, consisting of regions of small graphite-like basic structural units of partly stacked but mismatched structure with the edges terminated by hydrogen or hydroxyls. We do find evidence for the presence of a small quantity of water trapped in the network and suggest that this may account for batch-to-batch variation in properties that may occur.

  16. [Preparation of OMC-Au/L-Lysine/Au modified glassy carbon electrode and the study on its detection response to hydroquinone and catechol].

    Science.gov (United States)

    Zhou, Yao-Yu; Tang, Lin; Li, Zhen; Liu, Yuan-Yuan; Yang, Gui-De; Wu, Meng-Shi; Lei, Xiao-Xia; Zheng, Guang-Ming

    2013-03-01

    Ordered mesoporous carbon-Au nanoparticles (OMC-Au) nanocomposites were synthesized by a one-step chemical reduction route, and an OMC-Au/L-Lysine/Au composite film-modified glassy carbon electrode (GCE) was constructed. The microstructure of OMC and OMC-Au/L-Lysine/Au composite films were characterized by SEM, and the preparation process of OMC-Au/L-Lysine/Au modified glassy carbon electrode was investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The electrocatalytic oxidation of hydroquinone and catechol on the modified electrode was discussed by differential pulse voltammetry in this study, and a sensor for separate determination of hydroquinone and catechol based on OMC-Au/L-Lysine/Au modified glassy carbon electrode was developed. Under the optimal conditions, the cathodic peak current was linearly related to hydroquinone concentration over ranges from 1.0 x 10(-6) mol x L(-1) to 8.0 x 10(-4) mol x L(-1) with a detection limit of 3.0 x 10(-7) mol x L(-1), and linearly related to catechol concentration from 1.0 x 10(-7) mol x L(-1) to 8.0 x 10(-5) mol x L(-1) with a detection limit of 8.0 x 10(-7) mol x L(-1).

  17. Mechanical Properties for Reliability Analysis of Structures in Glassy Carbon

    CERN Document Server

    Garion, Cédric

    2014-01-01

    Despite its good physical properties, the glassy carbon material is not widely used, especially for structural applications. Nevertheless, its transparency to particles and temperature resistance are interesting properties for the applications to vacuum chambers and components in high energy physics. For example, it has been proposed for fast shutter valve in particle accelerator [1] [2]. The mechanical properties have to be carefully determined to assess the reliability of structures in such a material. In this paper, mechanical tests have been carried out to determine the elastic parameters, the strength and toughness on commercial grades. A statistical approach, based on the Weibull’s distribution, is used to characterize the material both in tension and compression. The results are compared to the literature and the difference of properties for these two loading cases is shown. Based on a Finite Element analysis, a statistical approach is applied to define the reliability of a structural component in gl...

  18. Voltammetric pH sensing using carbon electrodes: glassy carbon behaves similarly to EPPG.

    Science.gov (United States)

    Lu, Min; Compton, Richard G

    2014-09-21

    Developing and building on recent work based on a simple sensor for pH determination using unmodified edge plane pyrolytic graphite (EPPG) electrodes, we present a voltammetric method for pH determination using a bare unmodified glassy carbon (GC) electrode. By exploiting the pH sensitive nature of quinones present on carbon edge-plane like sites within the GC, we show how GC electrodes can be used to measure pH. The electro-reduction of surface quinone groups on the glassy carbon electrode was characterised using cyclic voltammetry (CV) and optimised with square-wave voltammetry (SWV) at 298 K and 310 K. At both temperatures, a linear correlation was observed, corresponding to a 2 electron, 2 proton Nernstian response over the aqueous pH range 1.0 to 13.1. As such, unmodified glassy carbon electrodes are seen to be pH dependent, and the Nernstian response suggests its facile use for pH sensing. Given the widespread use of glassy carbon electrodes in electroanalysis, the approach offers a method for the near-simultaneous measurement and monitoring of pH during such analyses.

  19. Positron annihilation study of graphite, glassy carbon and C60/C70 fullerene

    International Nuclear Information System (INIS)

    Hasegawa, Masayuki; Kajino, Masahiro; Yamaguchi, Sadae; Iwata, Tadao; Kuramoto, Eiichi; Takenaka, Minoru.

    1992-01-01

    ACAR (Angular Correlation of Annihilation Radiation) and positron lifetime measurements have been made on, HOPG (Highly Oriented Pyrolytic Graphite), isotropic fine-grained graphite, glassy carbons and C 60 /C 70 powder. HOPG showed marked bimodality along the c-axis and anisotropy in ACAR momentum distribution, which stem from characteristic annihilation between 'interlayer' positrons and π-electrons in graphite. ACAR curves of the isotropic graphite and glassy carbons are even narrower than that of HOPG perpendicular to the c-axis. Positron lifetime of 420 and 390 - 480 psec, much longer than that of 221 psec in HOPG, were observed for the isotropic graphite and glassy carbons respectively, which are due to positron trapping in structural voids in them. Positron lifetime and ACAR width (FWHM) can be well correlated to void sizes (1.7 to 5.0 nm) of glassy carbons which have been determined by small angle neutron (SAN) scattering measurements. ACAR curves and positron lifetime of C 60 /C 70 powder agree well with those of glassy carbons. This shows that positron wave functions extend, as in the voids of glassy carbons, much wider than open spaces of the octahedral interstices of the face-centered cubic (FCC) structure of C 60 crystal and strongly suggests positron trapping in the 'soccer ball' vacancy. Possible positron states in the carbon materials are discussed with a simple model of void volume-trapping. Preliminary results on neutron irradiation damage in HOPG are also presented. (author)

  20. Activation of glassy carbon electrodes by photocatalytic pretreatment

    Energy Technology Data Exchange (ETDEWEB)

    Dumanli, Onur [Department of Chemistry, Faculty of Science and Art, Ondokuz Mayis University, Kurupelit, 55139 Samsun (Turkey); Onar, A. Nur [Department of Chemistry, Faculty of Science and Art, Ondokuz Mayis University, Kurupelit, 55139 Samsun (Turkey)], E-mail: nonar@omu.edu.tr

    2009-11-01

    This paper describes a simple and rapid photocatalytic pretreatment procedure that removes contaminants from glassy carbon (GC) surfaces. The effectiveness of TiO{sub 2} mediated photocatalytic pretreatment procedure was compared to commonly used alumina polishing procedure. Cyclic voltammetric and chronocoulometric measurements were carried out to assess the changes in electrode reactivity by using four redox systems. Electrochemical measurements obtained on photocatalytically treated GC electrodes showed a more active surface relative to polished GC. In cyclic voltammograms of epinephrine, Fe(CN){sub 6}{sup 3-/4-} and ferrocene redox systems, higher oxidation and reduction currents were observed. The heterogeneous electron transfer rate constants (k{sup o}) were calculated for Fe(CN){sub 6}{sup 3-/4-} and ferrocene which were greater for photocatalytic pretreatment. Chronocoulometry was performed in order to find the amount of adsorbed methylene blue onto the electrode and was calculated as 0.34 pmol cm{sup -2} for photocatalytically pretreated GC. The proposed photocatalytic GC electrode cleansing and activating pretreatment procedure was more effective than classical alumina polishing.

  1. Electrochemical determination of mesotrione at organoclay modified glassy carbon electrodes.

    Science.gov (United States)

    Kamga Wagheu, Josephine; Forano, Claude; Besse-Hoggan, Pascale; Tonle, Ignas K; Ngameni, Emmanuel; Mousty, Christine

    2013-01-15

    A natural Cameroonian smectite-type clay (SaNa) was exchanged with cationic surfactants, namely cetyltrimethylammonium (CTA) and didodecyldimethyl ammonium (DDA) modifying its physico-chemical properties. The resulting organoclays that have higher adsorption capacity for mesotrione than the pristine SaNa clay, have been used as modifiers of glassy carbon electrode for the electrochemical detection of this herbicide by square wave voltammetry. The stripping performances of SaNa, SaCTA and SaDDA modified electrodes were therefore evaluated and the experimental parameters were optimized. SaDDA gives the best results in deoxygenated acetate buffer solution (pH 6.0) after 2 min accumulation under open circuit conditions. Under optimal conditions, the reduction current is proportional to mesotrione concentration in the range from 0.25 to 2.5 μM with a detection limit of 0.26 μM. The fabricated electrode was also applied for the commercial formulation CALLISTO, used in European maize market. Copyright © 2012 Elsevier B.V. All rights reserved.

  2. Electrochemical behavior of ruthenium-hexacyanoferrate modified glassy carbon electrode and catalytic activity towards ethanol electro oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Wendell M.; Marques, Aldalea L.B., E-mail: aldalea.ufma@hotmail.com [Universidade Federal do Maranhao (UFMA), Sao Luis, MA (Brazil). Departamento de Quimica Tecnologica; Cardoso, William S.; Marques, Edmar P.; Bezerra, Cicero W.B. [Universidade Federal do Maranhao (UFMA), Sao Luis, MA (Brazil). Departamento de Qumica; Ferreira, Antonio Ap. P. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Araraquara, SP (Brazil). Instituto de Quimica; Song, Chaojie; Zhang, Jiujun [Energy, Mining and Environment Portfolio, National Research Council of Canada, Vancouver, BC (Canada)

    2013-04-15

    Ruthenium-based hexacyanoferrate (RuHCF) thin film modified glassy carbon electrode was prepared by drop evaporation method. The RuHCF modified electrode exhibited four redox couples in strong acidic solution (pH 1.5) attributed to Fe(CN){sub 6}{sup 3-} ion and three ruthenium forms (Ru(II), Ru(III) and Ru(IV)), characteristic of ruthenium oxide compounds. The modified electrode displayed excellent electrocatalytic activity towards ethanol oxidation in the potential region where electrochemical processes Ru(III)-O-Ru(IV) and Ru(IV)-O-Ru(VI) occur. Impedance spectroscopy data indicated that the charge transfer resistance decreased with the increase of the applied potential and ethanol concentration, indicating the use of the RuHCF modified electrode as an ethanol sensor. Under optimized conditions, the sensor responded linearly and rapidly to ethanol concentration between 0.03 and 0.4 mol L{sup -1} with a limit of detection of 0.76 mmol L{sup -1}, suggesting an adequate sensitivity in ethanol analyses. (author)

  3. Modification of glassy carbon electrode with a bilayer of multiwalled carbon nanotube/tiron-doped polypyrrole: Application to sensitive voltammetric determination of acyclovir

    Energy Technology Data Exchange (ETDEWEB)

    Shahrokhian, Saeed, E-mail: shahrokhian@sharif.edu [Department of Chemistry, Sharif University of Technology, Tehran 11155-3516 (Iran, Islamic Republic of); Institute for Nanoscience and Technology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Azimzadeh, Mahnaz [Department of Chemistry, Sharif University of Technology, Tehran 11155-3516 (Iran, Islamic Republic of); Amini, Mohammad K. [Department of Chemistry, Isfahan University, Isfahan (Iran, Islamic Republic of)

    2015-08-01

    A novel voltammetric sensor based on glassy carbon electrode (GCE) modified with a thin film of multi-walled carbon nanotubes (MWCNTs) coated with an electropolymerized layer of tiron-doped polypyrrole was developed and the resulting electrode was applied for the determination of acyclovir (ACV). The surface morphology and property of the modified electrode were characterized by field emission scanning electron microscopy and electrochemical impedance spectroscopy techniques. The electrochemical performance of the modified electrode was investigated by means of linear sweep voltammetry (LSV). The effect of several experimental variables, such as pH of the supporting electrolyte, drop size of the cast MWCNTssuspension, number of electropolymerization cycles and accumulation time was optimized by monitoring the LSV response of the modified electrode toward ACV. The best response was observed at pH 7.0 after accumulation at open circuit for 160 s. Under the optimized conditions, a significant electrochemical improvement was observed toward the electrooxidation of ACV on the modified electrode surface relative to the bare GCE, resulting in a wide linear dynamic range (0.03–10.0 μM) and a low detection limit (10.0 nM) for ACV. Besides high sensitivity, the sensor represented high stability and good reproducibility for ACV analysis, and provided satisfactory results for the determination of this compound in pharmaceutical and clinical preparations. - Highlights: • A simple method was employed to construct a thin film modified electrode. • Tiron-doped polypyrrole was electropolymerized on MWCNT precast glassy carbon electrode. • Electrode surface characterization was performed by microscopic and spectroscopic techniques. • The modified electrode showed nano-molar detection limit for acyclovir. • The modified electrode was applied for the detection of ACV in pharmaceutical and clinical preparations.

  4. Electrochemical oxidation of butein at glassy carbon electrodes.

    Science.gov (United States)

    Tesio, Alvaro Yamil; Robledo, Sebastián Noel; Fernández, Héctor; Zon, María Alicia

    2013-06-01

    The electrochemical oxidation of flavonoid butein is studied at glassy carbon electrodes in phosphate and citrate buffer solutions of different pH values, and 1M perchloric acid aqueous solutions by cyclic and square wave voltammetries. The oxidation peak corresponds to the 2e(-), 2H(+) oxidation of the 3,4-dihydroxy group in B ring of butein, given the corresponding quinone species. The overall electrode process shows a quasi-reversible behavior and an adsorption/diffusion mixed control at high butein bulk concentrations. At low butein concentrations, the electrode process shows mainly an adsorption control. Butein surface concentration values were obtained from the charge associated with the adsorbed butein oxidation peaks, which are in agreement with those values expected for the formation of a monolayer of adsorbate in the concentration range from 1 to 5μM. Square wave voltammetry was used to perform a full thermodynamic and kinetics characterization of the butein surface redox couple. Therefore, from the combination of the "quasi-reversible maximum" and the "splitting of the net square wave voltammetric peak" methods, values of (0.386±0.003) V, (0.46±0.04), and 2.7×10(2)s(-1) were calculated for the formal potential, the anodic transfer coefficient, and the formal rate constant, respectively, of the butein overall surface redox process in pH4.00 citrate buffer solutions. These results will be then used to study the interaction of butein, and other flavonoids with the deoxyribonucleic acid, in order to better understand the potential therapeutic applications of these compounds. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. Electrochemical functionalization of glassy carbon electrode by reduction of diazonium cations in protic ionic liquid

    International Nuclear Information System (INIS)

    Shul, Galyna; Ruiz, Carlos Alberto Castro; Rochefort, Dominic; Brooksby, Paula A.; Bélanger, Daniel

    2013-01-01

    Protic ionic liquid based on 2-methoxypyridine and trifluoroacetic acid was used as electrolyte for the functionalization of a glassy carbon electrode surface by electrochemical reduction of in situ generated 4-chlorobenzene diazonium and 4-nitrobenzene diazonium cations. The diazonium cations were synthesized in an electrochemical cell by reaction of the corresponding amines with NaNO 2 dissolved in protic ionic liquid. The resulting electrografted organic layers exhibit similar properties to those layers obtained by the derivatization from isolated diazonium salts dissolved in protic ionic liquid. Functionalized glassy carbon electrode surfaces were characterized by cyclic voltammetry, Fourier transform infrared and X-ray photoelectron spectroscopies. Atomic force microscopy thickness measurements revealed that, in our experimental conditions, the use of protic ionic liquid led to the formation of film with a thickness of about 1.5 nm. It is also demonstrated that the nitrobenzene chemisorbed on glassy carbon electrode or dissolved in protic ionic liquid undergoes electrochemical conversion to hydroxyaminobenzene

  6. Electrochemical Determination of Caffeine Content in Ethiopian Coffee Samples Using Lignin Modified Glassy Carbon Electrode

    OpenAIRE

    Amare, Meareg; Aklog, Senait

    2017-01-01

    Lignin film was deposited at the surface of glassy carbon electrode potentiostatically. In contrast to the unmodified glassy carbon electrode, an oxidative peak with an improved current and overpotential for caffeine at modified electrode showed catalytic activity of the modifier towards oxidation of caffeine. Linear dependence of peak current on caffeine concentration in the range 6 ? 10?6 to 100 ? 10?6?mol?L?1 with determination coefficient and method detection limit (LoD = 3?s/slope) of 0....

  7. SUPERNOVA SHOCK-WAVE-INDUCED CO-FORMATION OF GLASSY CARBON AND NANODIAMOND

    Energy Technology Data Exchange (ETDEWEB)

    Stroud, Rhonda [Naval Research Laboratory, Washington, D.C.; Chisholm, Matthew F [ORNL; Heck, Phillipp [The Field Museum, Chicago, IL; Alexander, Conel [Carnegie Institution of Washington; Nittler, Larry [Carnegie Institution of Washington

    2011-01-01

    Nanodiamond (ND) was the first extrasolar dust phase to be identified in meteorites. However, the 2 nm average size of the NDs precludes isotopic analysis of individual particles, and thus their origin(s) remains controversial. Using electron microscopy with subnanometer resolution, we show that ND separates from the Allende and Murchison meteorites are actually a two-phase mixture of ND and glassy carbon. This phase mixture is likely the product of supernova shock-wave transformation of pre-formed organics in the interstellar medium (ISM). The glassy carbon ND mixture is also a plausible contributor to the 2175 extinction feature in the diffuse ISM.

  8. SUPERNOVA SHOCK-WAVE-INDUCED CO-FORMATION OF GLASSY CARBON AND NANODIAMOND

    International Nuclear Information System (INIS)

    Stroud, Rhonda M.; Chisholm, Matthew F.; Heck, Philipp R.; Alexander, Conel M. O'D.; Nittler, Larry R.

    2011-01-01

    Nanodiamond (ND) was the first extrasolar dust phase to be identified in meteorites. However, the 2 nm average size of the NDs precludes isotopic analysis of individual particles, and thus their origin(s) remains controversial. Using electron microscopy with subnanometer resolution, we show that ND separates from the Allende and Murchison meteorites are actually a two-phase mixture of ND and glassy carbon. This phase mixture is likely the product of supernova shock-wave transformation of pre-formed organics in the interstellar medium (ISM). The glassy carbon-ND mixture is also a plausible contributor to the 2175 A extinction feature in the diffuse ISM.

  9. Electrochemical pre anodization of glassy carbon electrode and application to determine chloramphenicol

    International Nuclear Information System (INIS)

    Truc, Nguyen Minh; Mortensen, John; Anh, Nguyen Ba Hoai

    2008-01-01

    This paper suggested a method to enhance the performance of carbon electrodes for the determination of chloramphenicol (CAP). The sensitivity and the reproducibility of the carbon electrodes could be enhanced easily by electrochemical pretreatment. Some kinds of carbon material were studied including glassy carbon, graphite carbon and pyrolytic carbon. Numerous kinds of supporting electrolyte have been tried. For glassy carbon electrode, the acidic solution, H 2 SO 4 5 mM, resulted in best performance at pretreated voltage of +2.1V (vs. Ag/ AgCl) in duration of 250 second. However, for graphite and pyrolytic carbon electrodes, the phosphate buffer solution pH 6.0 gave the best performance at +1.7V (vs. Ag/ AgCl) in duration of 20 seconds. The detection limit could be at very low concentration of CAP: 0.8 ng/ ml for glassy carbon electrode, 3.5 ng/ ml for graphite carbon electrode. The method was successful applied to aqua-agriculture water sample and milk sample with simple extraction as well as direct ointment sample analysis. (author)

  10. Poly(alizarin red)/Graphene modified glassy carbon electrode for simultaneous determination of purine and pyrimidine

    Energy Technology Data Exchange (ETDEWEB)

    Ba Xi; Luo Liqiang [Department of Chemistry, Shanghai University, Shanghai 200444 (China); Ding Yaping, E-mail: wdingyp@sina.com [Department of Chemistry, Shanghai University, Shanghai 200444 (China); Zhang Zhen [Department of Chemistry, Shanghai University, Shanghai 200444 (China); Chu Yuliang [Instrumental Analysis and Research Center, Shanghai University, Shanghai 200444 (China); Wang Bijun; Ouyang Xiaoqian [Department of Chemistry, Shanghai University, Shanghai 200444 (China)

    2012-11-08

    Graphical abstract: DPVs of PAR/Graphene/GCE (a) and the bare GCE (c) in 0.1 M PBS containing 50.0 {mu}M G, 50.0 {mu}M A, 100.0 {mu}M T and 100.0 {mu}M C, (b) PAR/Graphene/GCE in 0.1 M PBS. Highlights: Black-Right-Pointing-Pointer The sensor exhibited well-separated peaks and low detection limit. Black-Right-Pointing-Pointer The sensor possesses high sensitivity and wide linear range. Black-Right-Pointing-Pointer The sensor was used for simultaneous detection of G, A, T and C successfully. Black-Right-Pointing-Pointer The sensor was applied in a fish sperm DNA sample with satisfactory results. Black-Right-Pointing-Pointer The proposed sensor has good stability and reproducibility. - Abstract: In this work, a poly(alizarin red)/Graphene composite film modified glassy carbon electrode (PAR/Graphene/GCE) was prepared for simultaneous determination of four DNA bases (guanine, adenine, thymine and cytosine) without any pretreatment. The morphology and interface property of PAR/Graphene films were examined by scanning electron microscopy and electrochemical impedance spectroscopy. The PAR/Graphene/GCE exhibited excellent electrocatalytic activity toward purine (guanine and adenine) and pyrimidine (thymine and cytosine) in 0.1 M phosphate buffer solution (pH 7.4). Under optimum conditions, differential pulse voltammetry was used to detect the oxidation of purine and pyrimidine. The results showed that PAR/Graphene/GCE exhibited well-separated peaks, low detection limit, high sensitivity and wide linear range for simultaneous detection of purine and pyrimidine. The proposed sensor also has good stability and reproducibility. Furthermore, the modified electrode was applied for the detection of DNA bases in a fish sperm DNA sample with satisfactory results.

  11. Poly(alizarin red)/Graphene modified glassy carbon electrode for simultaneous determination of purine and pyrimidine

    International Nuclear Information System (INIS)

    Ba Xi; Luo Liqiang; Ding Yaping; Zhang Zhen; Chu Yuliang; Wang Bijun; Ouyang Xiaoqian

    2012-01-01

    Graphical abstract: DPVs of PAR/Graphene/GCE (a) and the bare GCE (c) in 0.1 M PBS containing 50.0 μM G, 50.0 μM A, 100.0 μM T and 100.0 μM C, (b) PAR/Graphene/GCE in 0.1 M PBS. Highlights: ► The sensor exhibited well-separated peaks and low detection limit. ► The sensor possesses high sensitivity and wide linear range. ► The sensor was used for simultaneous detection of G, A, T and C successfully. ► The sensor was applied in a fish sperm DNA sample with satisfactory results. ► The proposed sensor has good stability and reproducibility. - Abstract: In this work, a poly(alizarin red)/Graphene composite film modified glassy carbon electrode (PAR/Graphene/GCE) was prepared for simultaneous determination of four DNA bases (guanine, adenine, thymine and cytosine) without any pretreatment. The morphology and interface property of PAR/Graphene films were examined by scanning electron microscopy and electrochemical impedance spectroscopy. The PAR/Graphene/GCE exhibited excellent electrocatalytic activity toward purine (guanine and adenine) and pyrimidine (thymine and cytosine) in 0.1 M phosphate buffer solution (pH 7.4). Under optimum conditions, differential pulse voltammetry was used to detect the oxidation of purine and pyrimidine. The results showed that PAR/Graphene/GCE exhibited well-separated peaks, low detection limit, high sensitivity and wide linear range for simultaneous detection of purine and pyrimidine. The proposed sensor also has good stability and reproducibility. Furthermore, the modified electrode was applied for the detection of DNA bases in a fish sperm DNA sample with satisfactory results.

  12. Modification of glassy carbon surfaces by atmospheric pressure cold plasma torch

    DEFF Research Database (Denmark)

    Mortensen, Henrik Junge; Kusano, Yukihiro; Leipold, Frank

    2006-01-01

    The effect of plasma treatment on glassy carbon (GC) surfaces was studied with adhesion improvement in mind. A newly constructed remote plasma source was used to treat GC plates. Pure He and a dilute NH3/He mixture were used as feed gases. Optical emission spectroscopy was performed for plasma...

  13. Development of glassy carbon electrode (Dead Sea scroll) for low energy cardiac pacing.

    Science.gov (United States)

    Katsumoto, K; Niibori, T; Takamatsu, T; Kaibara, M

    1986-11-01

    We have developed a new type of glassy carbon electrode whose smooth surface with scattered craters reduces its polarization voltage. It has both excellent antithrombogenicity and slight tissue reaction. The energy threshold curve was the lowest when compared to the Siemens (411S, 412S) and the Solin (S-100) electrodes.

  14. Preparation and characterization of dense graphite/glassy carbon composite coating for sealing application

    Science.gov (United States)

    Wang, Yang; Chen, Zhaofeng; Yu, Shengjie; Pan, Ning; Liao, Jiahao

    2017-09-01

    Glassy carbon (GC), characterized by a homogeneous structure and glass-like fracture surface once broken, has attracted increasing attention because of its excellent performance. In this paper, a dense graphite/glassy carbon composite coating with low gas permeability was introduced. In this composite coating, small graphite particles acting as second phase were wrapped by glassy carbon matrix. The composite coatings with different mass fractions of graphite particles were prepared. The mass loss of phenolic resin was determined by TG (thermogravimetry) analysis to determine the pyrolysis process. Raman spectrum analysis indicates that graphite content in composite coatings affected the G/D ratio significantly. The permeability of composite coatings with 50% and 100% graphite particles was almost same, which was ranged from 6  ×  10-13 m3 · µm/m2 · s · Pa to 3  ×  10-13 m3 · µm/m2 · s · Pa within the differential pressure from 100 kPa to 70 kPa. While the composite coating with 150% graphite particles had higher gas permeability due to the tiny micro-cracks and micro-pores produced. What was more, the densification mechanism of graphite/glassy carbon composite coating was also discussed in detail.

  15. Electrochemical investigations of Pu(IV)/Pu(III) redox reaction using graphene modified glassy carbon electrodes and a comparison to the performance of SWCNTs modified glassy carbon electrodes

    International Nuclear Information System (INIS)

    Gupta, Ruma; Gamare, Jayashree; Sharma, Manoj K.; Kamat, J.V.

    2016-01-01

    Highlights: • First report of aqueous electrochemistry of Plutonium on graphene modified electrode. • Graphene is best electrocatalytic material for Pu(IV)/Pu(III) redox couple among the reported modifiers viz. reduced graphene oxide (rGO) and SWCNT’s. • The electrochemical reversibility of Pu(IV)/Pu(III) redox couple improves significantly on graphene modified electrode compared to previously reported rGO & SWCNTs modified electrodes • Donnan interaction between plutonium species and graphene surface offers a possibility for designing a highly sensitive sensor for plutonium • Graphene modified electrode shows higher sensitivity for the determination of plutonium compared to glassy carbon and single walled carbon nanotube modified electrode - Abstract: The work reported in this paper demonstrates for the first time that graphene modified glassy carbon electrode (Gr/GC) show remarkable electrocatalysis towards Pu(IV)/Pu(III) redox reaction and the results were compared with that of single-walled carbon nanotubes modified GC (SWCNTs/GC) and glassy carbon (GC) electrodes. Graphene catalyzes the exchange of current of the Pu(IV)/Pu(III) couple by reducing both the anodic and cathodic overpotentials. The Gr/GC electrode shows higher peak currents (i p ) and smaller peak potential separation (ΔE p ) values than the SWCNTs/GC and GC electrodes. The heterogeneous electron transfer rate constants (k s ), charge transfer coefficients (α) and the diffusion coefficients (D) involved in the electrocatalytic redox reaction were determined. Our observations show that graphene is best electrocatalytic material among both the SWCNTs and GC to study Pu(IV)/Pu(III) redox reaction.

  16. Electrooxidation of DNA at glassy carbon electrodes modified with multiwall carbon nanotubes dispersed in polyethylenimine

    Energy Technology Data Exchange (ETDEWEB)

    Luque, Guillermina L.; Ferreyra, Nancy F. [INFIQC, Departamento de Fisico Quimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba (Argentina); Granero, Adrian [INFIQC, Departamento de Fisico Quimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba (Argentina); Departamento de Quimica, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Rio Cuarto (Argentina); Bollo, Soledad [Laboratorio de Bioelectroquimica, Facultad de Ciencias Quimicas y Farmaceuticas, Universidad de Chile, P.O. Box 233, Santiago (Chile); Rivas, Gustavo A., E-mail: grivas@fcq.unc.edu.ar [INFIQC, Departamento de Fisico Quimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba (Argentina)

    2011-10-30

    This work reports the electrochemical response of the complex between dsDNA and PEI formed in solution and at the surface of glassy carbon electrodes (GCE) modified with a dispersion of multi-walled carbon nanotubes in polyethylenimine (CNT-PEI). Scanning Electron Microscopy and Scanning Electrochemical Microscopy demonstrate that the dispersion covers the whole surface of the electrode although there are areas with higher density of CNT and, consequently, with higher electrochemical reactivity. The adsorption of DNA at GCE/CNT-PEI is fast and it is mainly driven by electrostatic forces. A clear oxidation signal is obtained either for dsDNA or a heterooligonucleotide of 21 bases (oligoY) at potentials smaller than those for the oxidation at bare GCE. The comparison of the behavior of DNA before and after thermal treatment demonstrated that the electrochemical response highly depends on the 3D structure of the nucleic acid.

  17. Electrooxidation of DNA at glassy carbon electrodes modified with multiwall carbon nanotubes dispersed in polyethylenimine

    International Nuclear Information System (INIS)

    Luque, Guillermina L.; Ferreyra, Nancy F.; Granero, Adrian; Bollo, Soledad; Rivas, Gustavo A.

    2011-01-01

    This work reports the electrochemical response of the complex between dsDNA and PEI formed in solution and at the surface of glassy carbon electrodes (GCE) modified with a dispersion of multi-walled carbon nanotubes in polyethylenimine (CNT-PEI). Scanning Electron Microscopy and Scanning Electrochemical Microscopy demonstrate that the dispersion covers the whole surface of the electrode although there are areas with higher density of CNT and, consequently, with higher electrochemical reactivity. The adsorption of DNA at GCE/CNT-PEI is fast and it is mainly driven by electrostatic forces. A clear oxidation signal is obtained either for dsDNA or a heterooligonucleotide of 21 bases (oligoY) at potentials smaller than those for the oxidation at bare GCE. The comparison of the behavior of DNA before and after thermal treatment demonstrated that the electrochemical response highly depends on the 3D structure of the nucleic acid.

  18. Electrochemical Determination of Glycoalkaloids Using a Carbon Nanotubes-Phenylboronic Acid Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Huiying Wang

    2013-11-01

    Full Text Available A versatile strategy for electrochemical determination of glycoalkaloids (GAs was developed by using a carbon nanotubes-phenylboronic acid (CNTs-PBA modified glassy carbon electrode. PBA reacts with α-solanine and α-chaconine to form a cyclic ester, which could be utilized to detect GAs. This method allowed GA detection from 1 μM to 28 μM and the detection limit was 0.3 μM. Affinity interaction of GAs and immobilized PBA caused an essential change of the peak current. The CNT-PBA modified electrodes were sensitive for detection of GAs, and the peak current values were in quite good agreement with those measured by the sensors.

  19. Annealing effects on the migration of ion-implanted cadmium in glassy carbon

    Energy Technology Data Exchange (ETDEWEB)

    Hlatshwayo, T.T., E-mail: thulani.hlatshwayo@up.ac.za [Physics Department, University of Pretoria, Pretoria (South Africa); Sebitla, L.D. [Physics Department, University of Pretoria, Pretoria (South Africa); Physics Department, University of Botswana, Gaborone (Botswana); Njoroge, E.G.; Mlambo, M.; Malherbe, J.B. [Physics Department, University of Pretoria, Pretoria (South Africa)

    2017-03-15

    The migration behaviour of cadmium (Cd) implanted into glassy carbon and the effects of annealing on radiation damage introduced by ion implantation were investigated. The glassy carbon substrates were implanted with Cd at a dose of 2 × 10{sup 16} ions/cm{sup 2} and energy of 360 keV. The implantation was performed at room temperature (RT), 430 °C and 600 °C. The RT implanted samples were isochronally annealed in vacuum at 350, 500 and 600 °C for 1 h and isothermally annealed at 350 °C up to 4 h. The as-implanted and annealed samples were characterized by Raman spectroscopy and Rutherford backscattering spectrometry (RBS). Raman results revealed that implantation at room temperature amorphized the glassy carbon structure while high temperature implantations resulted in slightly less radiation damage. Isochronal annealing of the RT implanted samples resulted in some recrystallization as a function of increasing temperature. The original glassy carbon structure was not achieved at the highest annealing temperature of 600 °C. Diffusion of Cd in glassy carbon was already taking place during implantation at 430 °C. This diffusion of Cd was accompanied by significant loss from the surface during implantation at 600 °C. Isochronal annealing of the room temperature implanted samples at 350 °C for 1 h caused Cd to diffuse towards the bulk while isothermal annealing at 500 and 600 °C resulted in the migration of implanted Cd toward the surface accompanied by a loss of Cd from the surface. Isothermal annealing at 350 °C for 1 h caused Cd to diffuse towards the bulk while for annealing time >1 h Cd diffused towards the surface. These results were interpreted in terms of trapping and de-trapping of implanted Cd by radiation damage.

  20. An electrochemical sensor for warfarin determination based on covalent immobilization of quantum dots onto carboxylated multiwalled carbon nanotubes and chitosan composite film modified electrode

    Energy Technology Data Exchange (ETDEWEB)

    Gholivand, Mohammad Bagher, E-mail: mbgholivand2013@gmail.com; Mohammadi-Behzad, Leila

    2015-12-01

    A method is described for the construction of a novel electrochemical warfarin sensor based on covalent immobilization of CdS-quantum dots (CdS-QDs) onto carboxylated multiwalled carbon nanotubes/chitosan (CS) composite film on the surface of a glassy carbon electrode. The CdS-QDs/CS/MWCNTs were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infra-red (FTIR) spectroscopy, XRD analysis and electrochemical impedance spectroscopy (EIS). The sensor showed optimum anodic stripping response within 90 s at an accumulation potential of 0.75 V. The modified electrode was used to detect the concentration of warfarin with a wide linear range of 0.05–80 μM and a detection limit (S/N = 3) of 8.5 nM. The proposed sensor has good storage stability, repeatability and reproducibility and was successfully applied for the determination of warfarin in real samples such as urine, serum and milk. - Highlights: • A new sensitive sensor for warfarin determination was developed. • The sensor was constructed based on covalent immobilization of CdS-QDs on the chitosan/MWCNTs/GCE. • The parameters affecting the stripping analysis of warfarin were optimized. • The proposed sensor is used for trace determination of warfarin in urine, serum and milk.

  1. Modified glassy carbon electrodes based on carbon nanostructures for ultrasensitive electrochemical determination of furazolidone

    Energy Technology Data Exchange (ETDEWEB)

    Shahrokhian, Saeed, E-mail: shahrokhian@sharif.edu [Department of Chemistry, Sharif University of Technology, Tehran 11155-9516 (Iran, Islamic Republic of); Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Naderi, Leila [Department of Chemistry, Sharif University of Technology, Tehran 11155-9516 (Iran, Islamic Republic of); Ghalkhani, Masoumeh [Department of Chemistry, Faculty of Science, Shahid Rajaee Teacher Training University, Lavizan, Tehran (Iran, Islamic Republic of); Institute for advanced technology, Shahid Rajaee Teacher Training University, Lavizan, Tehran, 16788 (Iran, Islamic Republic of)

    2016-04-01

    The electrochemical behavior of Furazolidone (Fu) was investigated on the surface of the glassy carbon electrode modified with different carbon nanomaterials, including carbon nanotubes (CNTs), carbon nanoparticles (CNPs), nanodiamond-graphite (NDG), graphene oxide (GO), reduced graphene oxide (RGO) and RGO-CNT hybrids (various ratios) using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable increase in the cathodic peak current of Fu at the RGO modified GCE, compared to other modified electrodes and also bare GCE. The surface morphology and nature of the RGO film was thoroughly characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode showed two linear dynamic ranges of 0.001–2.0 μM and 2.0–10.0 μM with a detection limit of 0.3 nM for the voltammetric determination of Fu. This sensor was used successfully for Fu determination in pharmaceutical and clinical preparations. - Highlights: • The electrochemical behavior of Furazolidone (Fu) was investigated on the surface of the modified electrode with different carbon nanomaterials by Linear sweep voltammetry. • Two linear dynamic ranges and a low detection limit were obtained. • The modified electrode was applied for the detection of Fu in pharmaceutical and clinical preparations.

  2. Trace level voltammetric determination of lead and cadmium in sediment pore water by a bismuth-oxychloride particle-multiwalled carbon nanotube composite modified glassy carbon electrode.

    Science.gov (United States)

    Cerovac, Sandra; Guzsvány, Valéria; Kónya, Zoltán; Ashrafi, Amir M; Švancara, Ivan; Rončević, Srđan; Kukovecz, Ákos; Dalmacija, Božo; Vytřas, Karel

    2015-03-01

    Two multiwalled carbon nanotubes-based composites modified with bismuth and bismuth-oxychloride particles were synthesized and attached to the glassy carbon electrode substrate. The resultant configurations, Bi/MWCNT-GCE and BiOCl/MWNT-GCE, were then characterized with respect to their physicochemical properties and electroanalytical performance in combination with square-wave anodic stripping voltammetry (SWASV). Further, some key experimental conditions and instrumental parameters were optimized; namely: the supporting electrolyte composition, accumulation potential and time, together with the parameters of the SWV-ramp. The respective method with both electrode configurations has then been examined for the trace level determination of Pb(2+) and Cd(2+) ions and the results compared to those obtained with classical bismuth-film modified GCE. The different intensities of analytical signals obtained at the three electrodes for Pb(2+) and Cd(2+) vs. the saturated calomel reference electrode had indicated that the nature of the modifiers and the choice of the supporting electrolyte influenced significantly the corresponding stripping signals. The most promising procedure involved the BiOCl/MWCNT-GCE and the acetate buffer (pH 4.0) offering limits of determination of 4.0 μg L(-1) Cd(2+) and 1.9 μg L(-1) Pb(2+) when accumulating for 120 s at a potential of -1.20 V vs. ref. The BiOCl/MWCNT electrode was tested for the determination of target ions in the pore water of a selected sediment sample and the results agreed well with those obtained by graphite furnace atomic absorption spectrometry. Copyright © 2014 Elsevier B.V. All rights reserved.

  3. Modified glassy carbon electrodes based on carbon nanostructures for ultrasensitive electrochemical determination of furazolidone.

    Science.gov (United States)

    Shahrokhian, Saeed; Naderi, Leila; Ghalkhani, Masoumeh

    2016-04-01

    The electrochemical behavior of Furazolidone (Fu) was investigated on the surface of the glassy carbon electrode modified with different carbon nanomaterials, including carbon nanotubes (CNTs), carbon nanoparticles (CNPs), nanodiamond-graphite (NDG), graphene oxide (GO), reduced graphene oxide (RGO) and RGO-CNT hybrids (various ratios) using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable increase in the cathodic peak current of Fu at the RGO modified GCE, compared to other modified electrodes and also bare GCE. The surface morphology and nature of the RGO film was thoroughly characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode showed two linear dynamic ranges of 0.001-2.0 μM and 2.0-10.0 μM with a detection limit of 0.3 nM for the voltammetric determination of Fu. This sensor was used successfully for Fu determination in pharmaceutical and clinical preparations. Copyright © 2016 Elsevier B.V. All rights reserved.

  4. Voltammetric behavior of sedative drug midazolam at glassy carbon electrode in solubilized systems

    Directory of Open Access Journals (Sweden)

    Rajeev Jain

    2012-04-01

    Full Text Available Redox behavior of midazolam was studied at a glassy carbon electrode in various buffer systems, supporting electrolytes and pH using differential pulse, square-wave and cyclic voltammetry. Based on its reduction behavior, a direct differential pulse voltammetric method has been developed and validated for the determination of midazolam in parenteral dosage. Three well-defined peaks were observed in 0.1% SLS, Britton–Robinson (BR buffer of pH 2.5. The effect of surfactants like sodium lauryl sulfate (SLS, cetyl trimethyl ammonium bromide (CTAB and Tween 20 was studied. Among these surfactants SLS showed significant enhancement in reduction peak. The cathodic peak currents were directly proportional to the concentration of midazolam with correlation coefficient of 0.99. Keywords: Midazolam, Voltammetry, Surfactant, Glassy carbon electrode, Parenteral dosage form

  5. Cytochrome C Dynamics at Gold and Glassy Carbon Surfaces Monitored by in Situ Scanning Tunnel Microscopy

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Møller, Per; Pedersen, Marianne Vind

    1995-01-01

    We have investigated the absorption of cytochrome c on gold and glassy carbon substrates by in situ scanning tunnel microscopy under potentiostatic control of both substrate and tip. Low ionic strength and potential ranges where no Faradaic current flows were used. Cyt c aggregates into flat...... composite structures of about 50 nm lateral extension at gold surfaces. The aggregates evolve in time, and structures resembling individual cyt c molecules can be distinguished in the space between the 50 nm structures. Cyt c aggregates also form at glassy carbon but have a different, unbroken character...... where cyt c both sticks well to the surface and exhibits notable mobility. The observations suggest that characteristic surface specific, internally mobile protein aggregates are formed at both surfaces and that in situ molecular resolution of the STM pictures may have been achieved....

  6. Early Stage Anodic Instability of Glassy Carbon Electrodes in Propylene Carbonate Solvent Containing Lithium Hexafluorophosphate

    Energy Technology Data Exchange (ETDEWEB)

    Carino, Emily V. [Joint; Materials; Newman, Daniel J. [Department; Connell, Justin G. [Joint; Materials; Kim, Chaerin [Department; Brushett, Fikile R. [Joint; Department

    2017-08-17

    Irreversible changes to the morphology of glassy carbon (GC) electrodes at potentials between 3.5 and 4.5 V vs Li/Li+ in propylene carbonate (PC) solvent containing lithium hexafluorophosphate (LiPF6) are reported. Analysis of cyclic voltammetry (CV) experiments in the range of 3.0 to 6.0 V shows that the capacitance of the electrochemical double -layer increased irreversibly beginning at potentials as low as 3.5 V. These changes resulted from nonfaradaic interactions, and were not due to oxidative electrochemical decomposition of the electrode and electrolyte, anion intercalation, nor caused by the presence of water, a common impurity in organic electrolyte solutions. Atomic force microscopy (AFM) images revealed that increasing the potential of a bare GC surface from 3.0 to 4.5 V resulted in a 6X increase in roughness, in good agreement with the changes in double -layer capacitance. Treating the GC surface via exposure to trichloromethylsilane vapors resulted in a stable double -layer capacitance between 3.0 and 4.5 V, and this treatment also correlated with less roughening. These results inform future efforts aimed at controlling surface composition and morphology of carbon electrodes.

  7. Structural phenomena in glassy carbon induced by cobalt ion implantation

    Czech Academy of Sciences Publication Activity Database

    Lavrentiev, Vasyl; Vacík, Jiří; Naramoto, H.

    2008-01-01

    Roč. 92, č. 3 (2008), s. 673-680 ISSN 0947-8396. [15th International Conference on Vacuum Ultraviolet Radiation Physics. Berlin, 29.07.2007-03.08.2007] Institutional research plan: CEZ:AV0Z10480505 Keywords : DIAMOND-LIKE CARBON * AMORPHOUS-CARBON * RAMAN-SCATTERING Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.884, year: 2008

  8. Gold nanoparticles directly modified glassy carbon electrode for non-enzymatic detection of glucose

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Gang; Shu, Honghui; Ji, Kai [Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Faculty of Materials Science and Engineering, Hubei University, No. 368 Youyi Avenue, Wuchang, Wuhan 430062 (China); Oyama, Munetaka [Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8520 (Japan); Liu, Xiong [Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Faculty of Materials Science and Engineering, Hubei University, No. 368 Youyi Avenue, Wuchang, Wuhan 430062 (China); He, Yunbin, E-mail: ybhe@hubu.edu.cn [Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Faculty of Materials Science and Engineering, Hubei University, No. 368 Youyi Avenue, Wuchang, Wuhan 430062 (China)

    2014-01-01

    This work describes controllable preparation of gold nanoparticles on glassy carbon electrodes by using the seed mediated growth method, which contains two steps, namely, nanoseeds attachment and nanocrystals growth. The size and the dispersion of gold nanoparticles grown on glassy carbon electrodes could be easily tuned through the growth time based on results of field-emission scanning electron microscopy. Excellent electrochemical catalytic characteristics for glucose oxidation were observed for the gold nanoparticles modified glassy carbon electrodes (AuNPs/GC), resulting from the extended active surface area provided by the dense gold nanoparticles attached. It exhibited a wide linear range from 0.1 mM to 25 mM with the sensitivity of 87.5 μA cm{sup −2} mM{sup −1} and low detection limit down to 0.05 mM for the sensing of glucose. The common interfering species such as chloride ion, ascorbic acid, uric acid and 4-acetamidophenol were verified having no interference effect on the detection of glucose. It is demonstrated that the seed mediated method is one of the facile approaches for fabricating Au nanoparticles modified substrates, which could work as one kind of promising electrode materials for the glucose nonenzymatic sensing.

  9. Potentiometric application of boron- and phosphorus-doped glassy carbon electrodes

    Directory of Open Access Journals (Sweden)

    ZORAN V. LAUSEVIC

    2001-03-01

    Full Text Available Acomparative study was carried out of the potentiometric application of boronand phosphorus-doped and undoped glassy carbon samples prepared at the same heat treatment temperature (HTT 1000°C. The electrochemical activities of the obtained electrode materials were investigated on the example of argentometric titrations. It was found that the electrochemical behaviour of the doped glassy carbon samples are very similar to a Sigri (undoped glassy carbon sample (HTT 2400°C. The experiments showed that the potentiometric response depends on the polarization mode, the nature of the sample, the pretreatment of the electrode surface, and the nature of the supporting electrolyte. The amounts of iodide, bromide, and of chloridewere determined to be 1.27 mg, 0.80 mg and 0.54 mg, respectively, with a maximum relative standard deviation of less than 1.1%. The obtained results are in good agreement with the results of comparative potentiometric titrations using a silver indicator electrode. The titrationmethod was applied to the indirect determination of pyridoxine hydrochloride, i.e., vitamin B6.

  10. Direct electron transfer from glucose oxidase immobilized on a nano-porous glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Haghighi, Behzad, E-mail: haghighi@iasbs.ac.ir [Department of Chemistry, Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-1159, Gava Zang, Zanjan (Iran, Islamic Republic of); Tabrizi, Mahmoud Amouzadeh [Department of Chemistry, Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-1159, Gava Zang, Zanjan (Iran, Islamic Republic of)

    2011-11-30

    Highlights: > A direct electron transfer reaction of glucose oxidase was observed on the surface of a nano-porous glassy carbon electrode. > A pair of well-defined and reversible redox peaks was observed at the formal potential of approximately -0.439 V. > The apparent electron transfer rate constant was measured to be 5.27 s{sup -1}. > A mechanism for the observed direct electron transfer reaction was proposed, which consists of a two-electron and a two-proton transfer. - Abstract: A pair of well-defined and reversible redox peaks was observed for the direct electron transfer (DET) reaction of an immobilized glucose oxidase (GOx) on the surface of a nano-porous glassy carbon electrode at the formal potential (E{sup o}') of -0.439 V versus Ag/AgCl/saturated KCl. The electron transfer rate constant (k{sub s}) was calculated to be 5.27 s{sup -1}. The dependence of E{sup o}' on pH indicated that the direct electron transfer of the GOx was a two-electron transfer process, coupled with two-proton transfer. The results clearly demonstrate that the nano-porous glassy carbon electrode is a cost-effective and ready-to-use scaffold for the fabrication of a glucose biosensor.

  11. Graphene oxide-mediated electrochemistry of glucose oxidase on glassy carbon electrodes.

    Science.gov (United States)

    Castrignanò, Silvia; Valetti, Francesca; Gilardi, Gianfranco; Sadeghi, Sheila J

    2016-01-01

    Glucose oxidase (GOD) was immobilized on glassy carbon electrodes in the presence of graphene oxide (GO) as a model system for the interaction between GO and biological molecules. Lyotropic properties of didodecyldimethylammonium bromide (DDAB) were used to stabilize the enzymatic layer on the electrode surface resulting in a markedly improved electrochemical response of the immobilized GOD. Transmission electron microscopy images of the GO with DDAB confirmed the distribution of the GO in a two-dimensional manner as a foil-like material. Although it is known that glassy carbon surfaces are not ideal for hydrogen peroxide detection, successful chronoamperometric titrations of the GOD in the presence of GO with β-d-glucose were performed on glassy carbon electrodes, whereas no current response was detected upon β-d-glucose addition in the absence of GO. The GOD-DDAB-GO system displayed a high turnover efficiency and substrate affinity as a glucose biosensor. The simplicity and ease of the electrode preparation procedure of this GO/DDAB system make it a good candidate for immobilizing other biomolecules for fabrication of amperometric biosensors. © 2015 International Union of Biochemistry and Molecular Biology, Inc.

  12. Electrochemical behavior and voltammetric determination of acetaminophen based on glassy carbon electrodes modified with poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite films.

    Science.gov (United States)

    Zhu, Wencai; Huang, Hui; Gao, Xiaochun; Ma, Houyi

    2014-12-01

    Poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite film modified glassy carbon electrodes (4-ABA/ERGO/GCEs) were fabricated by a two-step electrochemical method. The electrochemical behavior of acetaminophen at the modified electrode was investigated by means of cyclic voltammetry. The results indicated that 4-ABA/ERGO composite films possessed excellent electrocatalytic activity towards the oxidation of acetaminophen. The electrochemical reaction of acetaminophen at 4-ABA/ERGO/GCE is proved to be a surface-controlled process involving the same number of protons and electrons. The voltammetric determination of acetaminophen performed with the 4-ABA/ERGO modified electrode presents a good linearity in the range of 0.1-65 μM with a low detection limit of 0.01 μM (S/N=3). In the case of using the 4-ABA/ERGO/GCE, acetaminophen and dopamine can be simultaneously determined without mutual interference. Furthermore, the 4-ABA/ERGO/GCE has good reproducibility and stability, and can be used to determine acetaminophen in tablets. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. Sensitive voltammetric sensor based on isopropanol-Nafion-PSS-GR nanocomposite modified glassy carbon electrode for determination of clenbuterol in pork.

    Science.gov (United States)

    Wang, Ling; Yang, Ran; Chen, Jing; Li, Jianjun; Qu, Lingbo; de B Harrington, Peter

    2014-12-01

    In the present study, poly(sodium 4-styrenesulfonate) (PSS) functionalized graphene (GR) was synthesised via a simple one-step chemical reduction of exfoliated graphite oxides in the presence of PSS. Characterisation of as-made nanocomposite using Fourier transform infrared spectroscopy (FT-IR) and ultraviolet and visible spectroscopy (UV-vis) clearly demonstrate the successful attachment of PSS to graphene sheets. A novel clenbuterol (CLB) electrochemical sensor was fabricated based on isopropanol-Nafion-PSS-GR composite film modified glassy carbon electrode. In the Britton-Robinson buffer (pH 1.2), the sensor exhibited superior electrocatalytic activity towards the oxidation of CLB. Applying linear sweep voltammetry, a good linear relationship of the oxidation peak current with respect to concentrations of CLB cross the range of 7.5 × 10(-8)-2.5 × 10(-5)mol L(-1) and a detection limit of 2.2 × 10(-8) mol L(-1) were achieved. The proposed method was successfully applied for the determination of CLB in pork. Copyright © 2014 Elsevier Ltd. All rights reserved.

  14. Glassy carbon electrodes modified with a film of nanodiamond-graphite/chitosan: Application to the highly sensitive electrochemical determination of Azathioprine

    Energy Technology Data Exchange (ETDEWEB)

    Shahrokhian, Saeed, E-mail: shahrokhian@sharif.ed [Department of Chemistry, Sharif University of Technology, Tehran 11155-9516 (Iran, Islamic Republic of); Institute for Nanoscience and Technology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Ghalkhani, Masoumeh [Department of Chemistry, Sharif University of Technology, Tehran 11155-9516 (Iran, Islamic Republic of)

    2010-04-15

    A novel modified glassy carbon electrode with a film of nanodiamond-graphite/chitosan is constructed and used for the sensitive voltammetric determination of azathioprine (Aza). The surface morphology and thickness of the film modifier are characterized using atomic force microscopy. The electrochemical response characteristics of the electrode toward Aza are investigated by means of cyclic voltammetry. The modified electrode showed an efficient catalytic role for the electrochemical reduction of Aza, leading to a remarkable decrease in reduction overpotential and enhancement of the kinetics of the electrode reaction with a significant increase of peak current. The effects of experimental variables, such as the deposited amount of modifier suspension, the pH of the supporting electrolyte, the accumulation potential and time were investigated. Under optimal conditions, the modified electrode showed a wide linear response to the concentration of Aza in the range of 0.2-100 muM with a detection limit of 65 nM. The prepared modified electrode showed several advantages: simple preparation method, high stability and uniformity in the composite film, high sensitivity, excellent catalytic activity in physiological conditions and good reproducibility. The modified electrode can be successfully applied to the accurate determination of trace amounts of Aza in pharmaceutical and clinical preparations.

  15. Electrochemical sensing of etoposide using carbon quantum dot modified glassy carbon electrode.

    Science.gov (United States)

    Nguyen, Hoai Viet; Richtera, Lukas; Moulick, Amitava; Xhaxhiu, Kledi; Kudr, Jiri; Cernei, Natalia; Polanska, Hana; Heger, Zbynek; Masarik, Michal; Kopel, Pavel; Stiborova, Marie; Eckschlager, Tomas; Adam, Vojtech; Kizek, Rene

    2016-04-25

    In this study, enhancement of the electrochemical signals of etoposide (ETO) measured by differential pulse voltammetry (DPV) by modifying a glassy carbon electrode (GCE) with carbon quantum dots (CQDs) is demonstrated. In comparison with a bare GCE, the modified GCE exhibited a higher sensitivity towards electrochemical detection of ETO. The lowest limit of detection was observed to be 5 nM ETO. Furthermore, scanning electron microscopy (SEM), fluorescence microscopy (FM), and electrochemical impedance spectroscopy (EIS) were employed for the further study of the working electrode surface after the modification with CQDs. Finally, the GCE modified with CQDs under optimized conditions was used to analyse real samples of ETO in the prostate cancer cell line PC3. After different incubation times (1, 3, 6, 9, 12, 18 and 24 h), these samples were then prepared prior to electrochemical detection by the GCE modified with CQDs. High performance liquid chromatography with an electrochemical detection method was employed to verify the results from the GCE modified with CQDs.

  16. A Reliable Homemade Electrode Based on Glassy Polymeric Carbon

    Science.gov (United States)

    Santos, Andre L.; Takeuchi, Regina M.; Oliviero, Herilton P.; Rodriguez, Marcello G.; Zimmerman, Robert L.

    2004-01-01

    The production of a GPC-based material by submitting a cross-linked resin precursor to control thermal conditions is discussed. The precursor material is prepolymerized at 60-degree Celsius in a mold and is carbonized in inert atmosphere by slowly raising the temperature, the rise is performed to avoid change in the shape of the carbonization…

  17. Electrocatalytic oxidation of deferiprone and its determination on a carbon nanotube-modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Yadegari, H. [Department of Chemistry, Faculty of Science, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran (Iran, Islamic Republic of); Jabbari, A. [Department of Chemistry, Faculty of Science, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran (Iran, Islamic Republic of)], E-mail: jabbari@kntu.ac.ir; Heli, H.; Moosavi-Movahedi, A.A. [Institute of Biochemistry and Biophysics, University of Tehran, Tehran (Iran, Islamic Republic of); Karimian, K. [Arasto Pharmaceutical Chemicals Inc., Tehran (Iran, Islamic Republic of); Khodadadi, A. [Department of Chemical Engineering, Faculty of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of)

    2008-02-15

    The electrochemical behavior of the anti-thalassemia and anti-HIV replication drug, deferiprone, was investigated on a carbon nanotube-modified glassy carbon (GC-CNT) electrode in phosphate buffer solution, pH 7.40 (PBS). During oxidation of deferiprone, two irreversible anodic peaks, with E{sub 1}{sup 0}=452 and E{sub 2}{sup 0}=906mV, appeared, using GC-CNT. Cyclic voltammetric study indicated that the oxidation process is irreversible and diffusion controlled. The number of exchanged electrons in the electro-oxidation process was obtained, and the data indicated that deferiprone is oxidized via two two-electron steps. The results revealed that carbon nanotube (CNT) promotes the rate of oxidation by increasing the peak current, so that deferiprone is oxidized at lower potentials, which thermodynamically is more favorable. This result was confirmed by impedance measurements. The diffusion coefficient, electron-transfer coefficient and heterogeneous electron-transfer rate constant of deferiprone were found to be 1.49 x 10{sup -6} cm{sup 2} s{sup -1}, 0.44, and 3.83 x 10{sup -3} cm s{sup -1}, respectively. A sensitive, simple and time-saving differential-pulse voltammetric procedure was developed for the analysis of deferiprone. Using the proposed method, deferiprone can be determined with a detection limit of 5.25 x 10{sup -7} M. The applicability of the method to direct assays of spiked human serum and urine fluids is described.

  18. The effects of carbon dioxide exposure on permeation behavior in silicone rubber and glassy polycarbonates

    Energy Technology Data Exchange (ETDEWEB)

    Jordan, S.M.

    1989-01-01

    Permeation measurements are reported for both rubbery and glassy polymers in the presence of various pure (He, CH{sub 4}, CO{sub 2}, C{sub 2}H{sub 4}) and mixed gas (O{sub 2}/N{sub 2}, CO{sub 2}/CH{sub 4}, He/CO{sub 2}, CO{sub 2}/N{sub 2}) feed streams up to 1000 psia. The polymers studied were silicone rubber and glassy bisphenol-A polycarbonate, tetramethyl polycarbonate and hexafluoro polycarbonate. Large hysteresis was observed in permeation when comparing the pressurization and depressurization responses of the glassy samples in the presence of carbon dioxide above 300 psia exposure pressure. The magnitude of the hysteresis was related to the maximum CO{sub 2} conditioning pressure used. The conditioning treatment resulted in long-lived increases in the permeability of the conditioned films and appeared to be semi-permanent if the conditioning agent was not totally removed. For CO{sub 2}/CH{sub 4} mixed gas feed streams, the conditioning treatment resulted in enhancements in flux without a significant loss in permselectivity. For the silicone rubber sample, no permeability hysteresis was observed. Exchange experiments showed that it was possible to condition a glassy polymer with CO{sub 2} to increase its permeability and to maintain a state of increased permeability even if the CO{sub 2} was replaced by another gas of sufficient solubility such as methane or air. The CO{sub 2} conditioning treatment was not apparent if the CO{sub 2} was replaced by helium without any intervening exposure to vacuum. The inability of helium to detect the effects of the CO{sub 2}-induced conditioning sensed by larger penetrants is discussed and hypothetical explanations for these unexpected results are given.

  19. Norepinephrine-modified glassy carbon electrode for the simultaneous determination of ascorbic acid and uric acid

    International Nuclear Information System (INIS)

    Zare, H.R.; Memarzadeh, F.; Ardakani, M. Mazloum; Namazian, M.; Golabi, S.M.

    2005-01-01

    The oxidation of norepinephrine (NE) on a preactivated glassy carbon electrode leads to the formation of a deposited layer of about 4.2 x 10 -10 mol cm -2 at the surface of the electrode. The electron transfer rate constant, k s , and charge transfer coefficient, α, for electron transfer between the electrode and immobilized NE film were calculated as 44 s -1 and 0.46, respectively. The NE-modified glassy carbon electrode exhibited good electrocatalytic properties towards ascorbic acid (AA) oxidation in phosphate buffer (pH 7.0) with an overpotential of about 475 mV lower than that of the bare electrode. The electrocatalytic response was evaluated by cyclic voltammetry, chronoamperometry, amperometry and rotating disk voltammetry. The overall number of electrons involved in the catalytic oxidation of AA and the number of electrons involved in the rate-determining step are 2 and 1, respectively. The rate constant for the catalytic oxidation of AA was evaluated by RDE voltammetry and an average value of k h was found to be 8.42 x 10 3 M -1 s -1 . Amperometric determination of AA in stirred solution exhibits a linear range of 2.0-1300.0 μM (correlation coefficient 0.9999) and a detection limit of 0.076 μM. The precision of amperometry was found to be 1.9% for replicate determination of a 49.0 μM solution of AA (n = 6). In differential pulse voltammetric measurements, the NE-modified glassy carbon electrode can separate the AA and uric acid (UA) signals. Ascorbic acid oxidizes at more negative potential than UA. Also, the simultaneous determination of UA and AA is achieved at the NE-modified electrode

  20. The electrocatalytical reduction of m-nitrophenol on palladium nanoparticles modified glassy carbon electrodes

    International Nuclear Information System (INIS)

    Shi Qiaofang; Diao Guowang

    2011-01-01

    Highlights: ► The deposition of palladium on a GC electrode was performed by cyclic voltammetry. ► SEM images showed palladium nanoparticles deposited on a glassy carbon (GC) electrode. ► The Pd/GC electrode can effectively catalyze m-nitrophenol in aqueous media. ► The reduction of m-nitrophenol on the Pd/GC electrode depended on potential and pH. ► XPS spectra of the Pd/GC electrodes demonstrated the presence of palladium. - Abstract: Palladium nanoparticles modified glassy carbon electrodes (Pd/GC) were prepared via the electrodeposition of palladium on a glassy carbon (GC) electrode using cyclic voltammetry in different sweeping potential ranges. The scanning electron microscope images of palladium particles on the GC electrodes indicate that palladium particles with diameters of 20–50 nm were homogeneously dispersed on the GC electrode at the optimal deposition conditions, which can effectively catalyze the reduction of m-nitrophenol in aqueous solutions, but their catalytic activities are strongly related to the deposition conditions of Pd. The X-ray photoelectron spectroscopy spectra of the Pd/GC electrode confirmed that 37.1% Pd was contained in the surface composition of the Pd/GC electrode. The cyclic voltammograms of the Pd/GC electrode in the solution of m-nitrophenol show that the reduction peak of m-nitrophenol shifts towards the more positive potentials, accompanied with an increase in the peak current compared to the bare GC electrode. The electrocatalytic activity of the Pd/GC electrode is affected by pH values of the solution. In addition, the electrolysis of m-nitrophenol under a constant potential indicates that the reduction current of m-nitrophenol on the Pd/GC electrode is approximately 20 times larger than that on the bare GC electrode.

  1. Voltammetric behavior of sedative drug midazolam at glassy carbon electrode in solubilized systems

    OpenAIRE

    Jain, Rajeev; Yadav, Rajeev Kumar

    2012-01-01

    Redox behavior of midazolam was studied at a glassy carbon electrode in various buffer systems, supporting electrolytes and pH using differential pulse, square-wave and cyclic voltammetry. Based on its reduction behavior, a direct differential pulse voltammetric method has been developed and validated for the determination of midazolam in parenteral dosage. Three well-defined peaks were observed in 0.1% SLS, BrittonâRobinson (BR) buffer of pH 2.5. The effect of surfactants like sodium lauryl ...

  2. Voltammetric behavior of sedative drug midazolam at glassy carbon electrode in solubilized systems

    OpenAIRE

    Jain, Rajeev; Yadav, Rajeev Kumar

    2011-01-01

    Redox behavior of midazolam was studied at a glassy carbon electrode in various buffer systems, supporting electrolytes and pH using differential pulse, square-wave and cyclic voltammetry. Based on its reduction behavior, a direct differential pulse voltammetric method has been developed and validated for the determination of midazolam in parenteral dosage. Three well-defined peaks were observed in 0.1% SLS, Britton–Robinson (BR) buffer of pH 2.5. The effect of surfactants like sodium lauryl ...

  3. Electroanalysis of thiocyanate using a novel glassy carbon electrode modified by aryl radicals and cobalt tetracarboxyphthalocyanine

    Energy Technology Data Exchange (ETDEWEB)

    Matemadombo, Fungisai; Nyokong, Tebello [Rhodes University, Grahamstown (South Africa). Department of Chemistry; Westbroek, Philippe [Ghent University, Ghent (Belgium). Department of Textiles

    2007-12-01

    Electrochemical grafting of 4-nitrobenzenediazonium tetrafluoroborate onto a glassy carbon electrode (GCE) results in the formation of a nitrophenyl radical, which reacts with the surface to form a covalent bond (grafting) and results in a nitrophenyl modified electrode. The nitro group is electrochemically reduced to a NH{sub 2} group. Cobalt tetracarboxyphthalocyanine (CoTCPc) complex is then attached to the NH{sub 2} group using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling agents. The new CoTCPc modified electrode was characterized using cyclic voltammetry and then employed for the catalytic oxidation of thiocyanate. (author)

  4. Carbon nanofiber vs. carbon microparticles as modifiers of glassy carbon and gold electrodes applied in electrochemical sensing of NADH.

    Science.gov (United States)

    Pérez, Briza; Del Valle, Manel; Alegret, Salvador; Merkoçi, Arben

    2007-12-15

    Carbon materials (CMs), such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon microparticles (CMPs) are used as doping materials for electrochemical sensors. The efficiency of these materials (either before or after acidic treatments) while being used as electrocatalysts in electrochemical sensors is discussed for beta-nicotinamide adenine dinucleotide (NADH) detection using cyclic voltammetry (CV). The sensitivity of the electrodes (glassy carbon (GC) and gold (Au)) modified with both treated and untreated materials have been deeply studied. The response efficiencies of the GC and Au electrodes modified with CNF and CMP, using dimethylformamide (DMF) as dispersing agent are significantly different due to the peculiar physical and chemical characteristics of each doping material. Several differences between the electrocatalytic activities of CMs modified electrodes upon NADH oxidation have been observed. The CNF film promotes better the electron transfer of NADH minimizing the oxidation potential at +0.352 V. Moreover higher currents for the NADH oxidation peak have been observed for these electrodes. The shown differences in the electrochemical reactivities of CNF and CMP modified electrodes should be with interest for future applications in biosensors.

  5. Glucose biosensor based on a glassy carbon electrode modified with polythionine and multiwalled carbon nanotubes.

    Directory of Open Access Journals (Sweden)

    Wenwei Tang

    Full Text Available A novel glucose biosensor was fabricated. The first layer of the biosensor was polythionine, which was formed by the electrochemical polymerisation of the thionine monomer on a glassy carbon electrode. The remaining layers were coated with chitosan-MWCNTs, GOx, and the chitosan-PTFE film in sequence. The MWCNTs embedded in FAD were like "conductive wires" connecting FAD with electrode, reduced the distance between them and were propitious to fast direct electron transfer. Combining with good electrical conductivity of PTH and MWCNTs, the current response was enlarged. The sensor was a parallel multi-component reaction system (PMRS and excellent electrocatalytic performance for glucose could be obtained without a mediator. The glucose sensor had a working voltage of -0.42 V, an optimum working temperature of 25°C, an optimum working pH of 7.0, and the best percentage of polytetrafluoroethylene emulsion (PTFE in the outer composite film was 2%. Under the optimised conditions, the biosensor displayed a high sensitivity of 2.80 µA mM(-1 cm(-2 and a low detection limit of 5 µM (S/N = 3, with a response time of less than 15 s and a linear range of 0.04 mM to 2.5 mM. Furthermore, the fabricated biosensor had a good selectivity, reproducibility, and long-term stability, indicating that the novel CTS+PTFE/GOx/MWCNTs/PTH composite is a promising material for immobilization of biomolecules and fabrication of third generation biosensors.

  6. ELECTROCHEMICAL DETERMINATION OF ETHANOL, 2- PROPANOL AND 1-BUTANOL ON GLASSY CARBON ELECTRODE MODIFIED WITH NICKEL OXIDE FILM

    Directory of Open Access Journals (Sweden)

    A. Benchettara

    2014-12-01

    Full Text Available In this work, we present the modification of a glassy carbon electrode with nickel oxide film which is performed in two successive steps. In the first one, the electrochemical deposition of metallic nickel on the glassy carbon electrode (GCE is achieved in 0.1M boric acid; in the second step, the metallic deposit is anodically oxidized in 0.1M NaOH. These two operations were carried out in a three electrode cell with a filiform platinum auxiliary electrode, a SCE as potential reference and a working microelectrode of modified glassy carbon with nickel oxides. This electrode is characterized by several electrochemical techniques and is used for the catalytic determination of ethanol, 2-propanol and 1-butanol in 0.1 M NaOH. The proposed chemical mechanism shows that NiO2 acts as a mediator.

  7. Structural and surface changes in glassy carbon due to strontium implantation and heat treatment

    Science.gov (United States)

    Odutemowo, O. S.; Malherbe, J. B.; Prinsloo, L. C.; Njoroge, E. G.; Erasmus, R.; Wendler, E.; Undisz, A.; Rettenmayr, M.

    2018-01-01

    There are still questions around the microstructure of glassy carbon (GC), like the observation of the micropores. These were proposed to explain the low density of GC. This paper explains the effect of ion bombardment (200 keV Sr+, 1 × 1016 Sr+/cm2 at RT) on the microstructure of GC. TEM and AFM show that micropores in pristine GC are destroyed leading to densification of GC from 1.42 g/cm3 to 2.03 g/cm3. The amorphisation of glassy carbon was also not complete with graphitic strands embedded within the GC. These were relatively few, as Raman analysis showed that the Sr implantation resulted in a typical amorphous Raman spectrum. Annealing of the sample at 900 °C only resulted in a slight recovery of the GC structure. AFM and SEM analysis showed that the surface of the sample became rougher after Sr implantation. The roughness increased after the sample was annealed at 600 °C due to segregation of Sr towards the surface of the GC. SEM measurements of a sample with both implanted and un-implanted edges after annealing at 900 °C, showed that the high temperature heat treatment did not affect the surface topography of un-irradiated GC.

  8. Determination of trace amounts of lead and cadmium using a bismuth/glassy carbon composite electrode.

    Science.gov (United States)

    Hwang, Gil-Ho; Han, Won-Kyu; Hong, Seok-Jun; Park, Joon-Shik; Kang, Sung-Goon

    2009-02-15

    We examined the use of a bismuth-glassy carbon (Bi/C) composite electrode for the determination of trace amounts of lead and cadmium. Incorporated bismuth powder in the composite electrode was electrochemically dissolved in 0.1M acetate buffer (pH 4.5) where nanosized bismuth particles were deposited on the glassy carbon at the reduction potential. The anodic stripping voltammetry on the Bi/C composite electrode exhibited well-defined, sharp and undistorted peaks with a favorable resolution for lead and cadmium. Comparing a non-oxidized Bi/C composite electrode with an in-situ plated bismuth film electrode, the Bi/C composite electrode exhibited superior performance due to its much larger surface area. The limit of detection was 0.41 microg/L for lead and 0.49 microg/L for cadmium. Based on this study, we are able to conclude that various types of composite electrodes for electroanalytical applications can be developed with a prudent combination of electrode materials.

  9. Electrochemical Determination of Caffeine Content in Ethiopian Coffee Samples Using Lignin Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Meareg Amare

    2017-01-01

    Full Text Available Lignin film was deposited at the surface of glassy carbon electrode potentiostatically. In contrast to the unmodified glassy carbon electrode, an oxidative peak with an improved current and overpotential for caffeine at modified electrode showed catalytic activity of the modifier towards oxidation of caffeine. Linear dependence of peak current on caffeine concentration in the range 6×10-6 to 100×10-6 mol L−1 with determination coefficient and method detection limit (LoD = 3 s/slope of 0.99925 and 8.37×10-7 mol L−1, respectively, supplemented by recovery results of 93.79–102.17% validated the developed method. An attempt was made to determine the caffeine content of aqueous coffee extracts of Ethiopian coffees grown in four coffee cultivating localities (Wonbera, Wolega, Finoteselam, and Zegie and hence to evaluate the correlation between users preference and caffeine content. In agreement with reported works, caffeine contents (w/w% of 0.164 in Wonbera coffee; 0.134 in Wolega coffee; 0.097 in Finoteselam coffee; and 0.089 in Zegie coffee were detected confirming the applicability of the developed method for determination of caffeine in a complex matrix environment. The result indicated that users’ highest preference for Wonbera and least preference for Zegie cultivated coffees are in agreement with the caffeine content.

  10. Novel electroanalysis of hydroxyurea at glassy carbon and gold electrode surfaces

    Directory of Open Access Journals (Sweden)

    Keerti M. Naik

    2014-09-01

    Full Text Available A simple and a novel electroanalysis of hydroxyurea (HU drug at glassy carbon and gold electrode was investigated for the first time using cyclic, linear sweep and differential pulse voltammetric techniques. The oxidation of HU was irreversible and exhibited a diffusion controlled process on both electrodes. The oxidation mechanism was proposed. The dependence of the current on pH, the concentration, nature of buffer, and scan rate was investigated to optimize the experimental conditions for the determination of HU. It was found that the optimum buffer pH was 7.0, a physiological pH. In the range of 0.01 to 1.0 mM, the current measured by differential pulse voltammetry showed a linear relationship with HU concentration with limit of detection of 0.46 µM for glassy carbon electrode and 0.92 µM for gold electrode. In addition, reproducibility, precision and accuracy of the method were checked as well. The developed method was successfully applied to HU determination in pharmaceutical formulation and human biological fluids. The method finds its applications in quality control laboratories and pharmacokinetics.

  11. Electrochemical deposition of gold nanoparticles on carbon nanotube coated glassy carbon electrode for the improved sensing of tinidazole

    International Nuclear Information System (INIS)

    Shahrokhian, Saeed; Rastgar, Shokoufeh

    2012-01-01

    The electrochemical reduction of tinidazole (TNZ) is studied on gold-nanoparticle/carbon-nanotubes (AuNP/CNT) modified glassy carbon electrodes using the linear sweep voltammetry. An electrochemical procedure was used for the deposition of gold nanoparticles onto the carbon nanotube film pre-cast on a glassy carbon electrode surface. The resulting nanoparticles were characterized by scanning electron microscopy and cyclic voltammetry. The effect of the electrodeposition conditions, e.g., salt concentration and deposition time on the response of the electrode was studied. Also, the effect of experimental parameters, e.g., potential and time of accumulation, pH of the buffered solutions and the potential sweep rate on the response is examined. Under the optimal conditions, the modified electrode showed a wide linear response toward the concentration of TNZ in the range of 0.1–50 μM with a detection limit of 10 nM. The prepared electrode was successfully applied for the determination of TNZ in pharmaceutical and clinical samples.

  12. Comparison of glassy carbon and boron doped diamond electrodes: Resistance to biofouling

    International Nuclear Information System (INIS)

    Trouillon, Raphael; O'Hare, Danny

    2010-01-01

    Carbon based electrodes are widely used for in vivo and in vitro electrochemical studies. In particular, monoamine neurochemistry has been investigated using carbon microfibre electrodes. Similarly, glassy carbon (GC) is the preferred material for many biochemical applications, such as electrochemical detection in chromatography. More recently, boron doped diamond (BDD) has been utilized for biosensing, as its carbon sp 3 structure is expected to provide better resistance to analyte fouling. However, the main factor limiting the use of electrochemical sensors for biological studies is the effect of the biological matrix. Indeed, in vivo or in situ measurements expose the sensor to a complex matrix of proteins, which adsorb on the sensing surface and interfere with the electrochemical measurements. Here, we compare the performance of three carbon based electrodes: GC, GC with low surface oxides and BDD. The redox species ruthenium(III) hexaammine (outer-sphere), ferrocyanide (surface sensitive) and the biologically significant dopamine have been investigated in protein and blood-mimicking matrices. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to examine the effect of spectator molecules and reaction products on electrode mechanisms. Our results show that BDD generally exhibits the best performance for most conditions and reactions and should therefore be preferred for measurements in biologically fouling environments. Furthermore, surface oxides seem also to improve resistance of the GC electrode to biofouling.

  13. Raman spectra of zinc phthalocyanine monolayers absorbed on glassy carbon and gold electrodes by application of a confocal Raman microspectrometer

    NARCIS (Netherlands)

    Palys-Staron, B.J.; Palys, B.J.; Puppels, G.J.; Puppels, G.J.; van den Ham, D.M.W.; van den Ham, D.M.W.; Feil, D.; Feil, D.

    1992-01-01

    Raman spectra of zinc phthalocyanine monolayers, adsorbed on gold and on glassy carbon surfaces (electrodes), are presented. These spectra have been recorded with the electrodes inside and outside an electrochemical cell filled with an aqueous electrolyte. A confocal Raman microspectrometer was

  14. Electrocatalysis of oxygen reduction on nitrogen-containing multi-walled carbon nanotube modified glassy carbon electrodes

    International Nuclear Information System (INIS)

    Vikkisk, Merilin; Kruusenberg, Ivar; Joost, Urmas; Shulga, Eugene; Tammeveski, Kaido

    2013-01-01

    Highlights: ► Pyrolysis in the presence of urea was used for nitrogen doping of carbon nanotubes. ► N-doped carbon nanotubes were used as catalysts for the oxygen reduction reaction. ► N-doped carbon material showed a high catalytic activity for ORR in alkaline media. ► N-containing CNT material is an attractive cathode catalyst for alkaline membrane fuel cells. - Abstract: The electrochemical reduction of oxygen was studied on nitrogen-doped multi-walled carbon nanotube (NCNT) modified glassy carbon (GC) electrodes employing the rotating disk electrode (RDE) method. Nitrogen doping was achieved by simple pyrolysis of the carbon nanotube material in the presence of urea. The surface morphology and composition of the NCNT samples were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The SEM images revealed a rather uniform distribution of NCNTs on the GC electrode substrate. The XPS analysis showed a successful doping of carbon nanotubes with nitrogen species. The RDE results revealed that in alkaline solution the N-doped nanotube materials showed a remarkable electrocatalytic activity towards oxygen reduction. At low overpotentials the reduction of oxygen followed a two-electron pathway on undoped carbon nanotube modified GC electrodes, whereas on NCNT/GC electrodes a four-electron pathway of O 2 reduction predominated. The results obtained are significant for the development of nitrogen-doped carbon-based cathodes for alkaline membrane fuel cells.

  15. Using Poly-L-Histidine Modified Glassy Carbon Electrode to Trace Hydroquinone in the Sewage Water

    Directory of Open Access Journals (Sweden)

    Bin Wang

    2014-01-01

    Full Text Available A sensitive voltammetric method for trace measurements of hydroquinone in the sewage water is described. The poly-L-histidine is prepared to modify the glassy carbon electrode in order to improve the electrochemical catalysis of interesting substances such as hydroquinone. The influence of the base solution, pH value, and scanning speed on the tracing of hydroquinone is discussed, and the experimental procedures and conditions are optimized. The laboratory results show that it is possible to construct a linear calibration curve between the peak current of hydroquinone on modified electrode and its concentration at the level of 0.00001 mol/L. The potential limitation of the method is suggested by a linear peaking shift model as well. The method was successfully applied to the determination of hydroquinone in the actual sample of industrial waste water.

  16. Graphene quantum dot modified glassy carbon electrode for the determination of doxorubicin hydrochloride in human plasma.

    Science.gov (United States)

    Hashemzadeh, Nastaran; Hasanzadeh, Mohammad; Shadjou, Nasrin; Eivazi-Ziaei, Jamal; Khoubnasabjafari, Maryam; Jouyban, Abolghasem

    2016-08-01

    Low toxic graphene quantum dot (GQD) was synthesized by pyrolyzing citric acid in alkaline solution and characterized by ultraviolet--visible (UV-vis) spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), spectrofluorimetery and dynamic light scattering (DLS) techniques. GQD was used for electrode modification and electro-oxidation of doxorubicin (DOX) at low potential. A substantial decrease in the overvoltage (-0.56 V) of the DOX oxidation reaction (compared to ordinary electrodes) was observed using GQD as coating of glassy carbon electrode (GCE). Differential pulse voltammetry was used to evaluate the analytical performance of DOX in the presence of phosphate buffer solution (pH 4.0) and good limit of detection was obtained by the proposed sensor. Such ability of GQD to promote the DOX electron-transfer reaction suggests great promise for its application as an electrochemical sensor.

  17. Voltammetric behavior of sedative drug midazolam at glassy carbon electrode in solubilized systems.

    Science.gov (United States)

    Jain, Rajeev; Yadav, Rajeev Kumar

    2012-04-01

    Redox behavior of midazolam was studied at a glassy carbon electrode in various buffer systems, supporting electrolytes and pH using differential pulse, square-wave and cyclic voltammetry. Based on its reduction behavior, a direct differential pulse voltammetric method has been developed and validated for the determination of midazolam in parenteral dosage. Three well-defined peaks were observed in 0.1% SLS, Britton-Robinson (BR) buffer of pH 2.5. The effect of surfactants like sodium lauryl sulfate (SLS), cetyl trimethyl ammonium bromide (CTAB) and Tween 20 was studied. Among these surfactants SLS showed significant enhancement in reduction peak. The cathodic peak currents were directly proportional to the concentration of midazolam with correlation coefficient of 0.99.

  18. Voltammetric Determination of Salbutamol Based on Electrochemical Oxidation at Platinum and Glassy Carbon Electrodes

    OpenAIRE

    YILMAZ, Niyazi; ÖZKAN, Sibel A.; USLU, Bengi

    2014-01-01

    The oxidative behavior of salbutamol was studied as a function of pH at platinum and activated glassy carbon electrodes. Between pH 1.9 and 12.0, the drug was characterized by a single oxidation step at both electrodes. The process was found to be dependent on the nature and the pH of the supporting elctrolyte. The procedure yielded a linear concentration range of 1 \\times 10-4 to 1 \\times 10-3 M and 2 \\times 10-5 to 1 \\times 10-3 M in 0.2 M sulphuric acid and a phosphate buffer of pH 6, at p...

  19. Electrochemical Determination of Uric Acid at CdTe Quantum Dot Modified Glassy Carbon Electrodes.

    Science.gov (United States)

    Pan, Deng; Rong, Shengzhong; Zhang, Guangteng; Zhang, Yannan; Zhou, Qiang; Liu, Fenghai; Li, Miaojing; Chang, Dong; Pan, Hongzhi

    2015-01-01

    Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of uric acid (UA) at a CdTe quantum dot (QD) modified the glassy carbon electrode (GCE). CdTe QDs, as new semiconductor nanocrystals, can greatly improve the peak current of UA. The anodic peak current of UA was linear with its concentration between 1.0×10(-6) and 4.0×10(-4) M in 0.1 M pH 5.0 phosphate buffer solution. The LOD for UA at the CdTe electrode (1.0×10(-7) M) was superior to that of the GCE. In addition, we also determined the effects of scan rate, pH, and interferences of UA for the voltammetric behavior and detection. The results indicated that modified electrode possessed excellent reproducibility and stability. Finally, a new and efficient electrochemical sensor for detecting UA was developed.

  20. Polymer modified glassy carbon electrode for the electrochemical determination of caffeine in coffee.

    Science.gov (United States)

    Amare, Meareg; Admassie, Shimelis

    2012-05-15

    4-Amino-3-hydroxynaphthalene sulfonic acid (AHNSA) was electropolymerized on a glassy carbon electrode. The deposited film showed electrocatalytic activity towards the oxidation of caffeine. The polymer-modified electrode showed high sensitivity, selectivity and stability in the determination of caffeine in coffee. The peak current increased linearly with the concentration of caffeine in the range of 6 × 10(-8) to 4 × 10(-5) mol L(-1), with a detection limit of 1.37 × 10(-7) mol L(-1) (LoD = 3δ/slope). Analysis of caffeine in coffee was affected neither by sample matrices nor by structurally similar compounds. Recoveries ranging between 93.75 ± 2.32 and 100.75 ± 3.32 were achieved from coffee extracts indicating the applicability of the developed method for real sample analyses. Copyright © 2012 Elsevier B.V. All rights reserved.

  1. Determination of nitrite ion at schiff's base derivative of chitosan modified glassy carbon electrode

    International Nuclear Information System (INIS)

    Xu Zhongliang; Zhang Jianmei; Liu Shujuan; Peng Daofeng

    2007-01-01

    Chitosan react with salicyclaldehyde by schiff's base reaction in water, a polymer product S-CTS can be prepared. Glassy carbon electrode was modified with S-CTS by drop-coating method. Then, its electrocatalysis effect on the reduction of nitrite by the films of S-CTS was investigated. Experimental results showed that S-CTS modified electrode could reduce the oxidation overpotential of nitrite in pH4.5 B-R buffer solution, the peak current of reduction was proportional to the concentration of nitrite and a good linear relation from 0.20 to 81 mg/kg (r=0.9899) with a detection limit of 2.8 x 10 -7 mol/L was obtained. The methods have been applied to determining nitrite in some samples, satisfactory results were obtained. (authors)

  2. Voltammetric sensor for caffeine based on a glassy carbon electrode modified with Nafion and graphene oxide

    International Nuclear Information System (INIS)

    Zhao, F.; Wang, F.; Zhao, W.; Zhou, J.; Liu, Y.; Zou, L.; Ye, B.

    2011-01-01

    We report on a voltammetric sensor for caffeine that is based on a glassy carbon electrode modified with Nafion and graphene oxide (GO). It exhibits a good affinity for caffeine (resulting from the presence of Nafion), and excellent electrochemical response (resulting from the pressence of GO) for the oxidation of caffeine. The electrode enables the determination of caffeine in the range from 4.0 x 10 -7 to 8.0 x 10 -5 mol L -1 , with a detection limit of 2.0 x 10 -7 mol L -1 . The sensor displays good stability, reproducibility, and high sensitivity. It was successfully applied to the quantitative determination of caffeine in beverages. (author)

  3. Study of electrochemical oxidation and determination of albendazole using a glassy carbon-rotating disk electrode.

    Science.gov (United States)

    Santos, André L; Takeuchi, Regina M; Mariotti, Marcela P; De Oliveira, Marcelo F; Zanoni, Maria V B; Stradiotto, Nelson R

    2005-08-01

    In this work, electrochemical oxidation of albendazole (ABZ) was carried out using a glassy carbon-rotating disk electrode. Development of electroanalytical methodology for ABZ quantification in pharmaceutical formulations was also proposed by using linear sweep voltammetric technique. Electrochemical oxidation is observed for ABZ at E(1/2)=0.99 V vs. Ag/AgCl(sat), when an anodic wave is observed. Kinetic parameters obtained for ABZ oxidation exhibited a standard heterogeneous rate constant for the electrodic process equal to (1.51+/-0.07) x 10(-5) cm s(-1), with a alphan(a) value equal to 0.76. Limiting current dependence against ABZ concentration exhibited linearity on 5.0 x 10(-5) to 1.0 x 10(-2) mol l(-1) range, being obtained a detection limit of 2.4 x 10(-5) mol l(-1). Proposed methodology was applied to ABZ quantification in pharmaceutical formulations.

  4. Voltammetric Determination of Flunixin on Molecularly Imprinted Polypyrrole Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Abd-Elgawad Radi

    2016-01-01

    Full Text Available A novel electrochemical sensing approach, based on electropolymerization of a molecularly imprinted polypyrrole (MIPpy film onto a glassy carbon electrode (GCE surface, was developed for the detection of flunixin (FXN. The sensing conditions and the performance of the constructed sensor were assessed by cyclic, differential pulse and (DPV square wave voltammetry (SWV. The sensor exhibited high sensitivity, with linear responses in the range of 5.0 to 50.0 µM with detection limits of 1.5 and 1.0 µM for DPV and SWV, respectively. In addition, the sensor showed high selectivity towards FXN in comparison to other interferents. The sensor was successfully utilized for the direct determination of FXN in buffalo raw milk samples.

  5. Graphene quantum dot modified glassy carbon electrode for the determination of doxorubicin hydrochloride in human plasma

    Directory of Open Access Journals (Sweden)

    Nastaran Hashemzadeh

    2016-08-01

    Full Text Available Low toxic graphene quantum dot (GQD was synthesized by pyrolyzing citric acid in alkaline solution and characterized by ultraviolet--visible (UV–vis spectroscopy, X-ray diffraction (XRD, atomic force microscopy (AFM, spectrofluorimetery and dynamic light scattering (DLS techniques. GQD was used for electrode modification and electro-oxidation of doxorubicin (DOX at low potential. A substantial decrease in the overvoltage (−0.56 V of the DOX oxidation reaction (compared to ordinary electrodes was observed using GQD as coating of glassy carbon electrode (GCE. Differential pulse voltammetry was used to evaluate the analytical performance of DOX in the presence of phosphate buffer solution (pH 4.0 and good limit of detection was obtained by the proposed sensor. Such ability of GQD to promote the DOX electron-transfer reaction suggests great promise for its application as an electrochemical sensor.

  6. Wetting of a Charged Surface of Glassy Carbon by Molten Alkali-Metal Chlorides

    Science.gov (United States)

    Stepanov, V. P.

    2018-03-01

    Values of the contact angle of wetting of a surface of glassy carbon by molten chlorides of lithium, sodium, potassium, and cesium are measured by the meniscus weight method to determine the common factors of wettability of solid surfaces by ionic melts upon a change in the salt phase composition and a jump in electric potential. It is found that with a potential shift in the positive direction the shape of the curve of the contact angle's dependence on the potential varies upon substitution of one salt by another: the angle of wetting shrinks monotonously in lithium chloride but remains constant in molten cesium chloride. This phenomenon is explained by the hypothesis that the nature of the halide anion adsorption on the positively charged surface of an electrode is chemical and not electrostatic. It is shown that the adsorption process is accompanied by charge transfer through the interface, with covalent bonding between the adsorbent and adsorbate.

  7. New anode material for lithium-ion cells produced by catalytic graphitization of glassy carbon at 1000 degrees C

    Energy Technology Data Exchange (ETDEWEB)

    Skowronski, J.M. [Poznan Univ. of Technology, Poznan (Poland). Inst. of Chemistry and Technical Electrochemistry; Central Lab. of Batteries and Cells, Poznan (Poland); Knofczynski, K. [Central Lab. of Batteries and Cells, Poznan (Poland)

    2006-10-15

    This study investigated the conversion of glassy carbon into graphite at relatively low temperature of 1000 degrees C under ambient pressure using iron powder as the catalyst. The composite product of reaction was a graphite and turbostratic carbon whose use was then examined in terms of application in lithium-ion cells. Glassy, hard carbon spheres of 10 to 15 {iota}m were prepared from phenolic resin in a nitrogen atmosphere and then subjected to heat treatment with an iron powder mixture. After cooling down to ambient temperature, the carbon/iron mixture was treated with diluted HCl solution to remove metallic additives. The modified carbon was then washed with distilled water until chloride ions disappeared in a filtrate. All samples were characterized using XRD analysis. Working electrodes for electrochemical measurements were made by mixing carbons with PVDF. Cyclic voltammograms recorded for unmodified and modified carbons were consistent with XRD measurements. SEM analysis revealed that the process of graphitization begins at the external regions of glassy carbon spheres where erosion occurs when the carbon reacts with iron particles. The surface destruction of carbon spheres progresses into the interior of the spheres, resulting in their collapse followed by the transformation into pallets resembling a stack of graphite sheets. It was noted that not all unorganized carbon was conversed to graphite. Rather, only 50 per cent of turbostratic carbon existed in the product of heat treatment. The product of graphitization appeared to be a promising material for the preparation of anodes for lithium-ion cells. The discharge capacity for carbon produced by catalytic treatment was found to be approximately 5 times higher, while the discharge/charge reversibility was 23 per cent higher than values obtained for untreated carbon. The study showed that the uptake of lithium ions by the original carbon depends on the insertion/deinsertion mechanism of hard carbon as well

  8. Electrocatalytic reduction of nitrite on tetraruthenated metalloporphyrins/Nafion glassy carbon modified electrode

    Energy Technology Data Exchange (ETDEWEB)

    Calfuman, Karla [Facultad de Ciencias, Departamento de Quimica, Universidad de Chile, Las Palmeras 3425, Casilla 653, Nunoa, Santiago (Chile); Aguirre, Maria Jesus [Facultad de Quimica y Biologia, Departamento de Quimica de los Materiales, Universidad de Santiago de Chile, Santiago (Chile); Canete-Rosales, Paulina; Bollo, Soledad [Facultad de Ciencias Quimicas y Farmaceuticas, Departamento de Quimica Farmacologica y Toxicologica, Universidad de Chile, Santiago (Chile); Llusar, Rosa [Departamento de Quimica Fisica y Analitica, Universidad de Jaume I, Castellon (Spain); Isaacs, Mauricio, E-mail: misaacs@uchile.cl [Facultad de Ciencias, Departamento de Quimica, Universidad de Chile, Las Palmeras 3425, Casilla 653, Nunoa, Santiago (Chile)

    2011-10-01

    Highlights: > Preparation and characterization of modified electrodes with M(II) Tetraruthenated porphyrins onto a Nafion film. > The electrodes were characterized by SEM, TEM, AFM and SECM techniques. > The modified electrodes are active in the electrochemical reduction of nitrite at -660 mV vs Ag/AgCl. > GC/Nf/CoTRP modified electrode is more electrochemically active than their Ni and Zn analogues. - Abstract: This paper describes the electrochemical reduction of nitrite ion in neutral aqueous solution mediated by tetraruthenated metalloporphyrins (Co(II), Ni(II) and Zn(II)) electrostatically assembled onto a Nafion film previously adsorbed on glassy carbon or ITO electrodes. Scanning electron microscope (SEM-EDX) and transmission electron microscopy (TEM) results have shown that on ITO electrodes the macrocycles forms multiple layers with a disordered stacking orientation over the Nafion film occupying hydrophobic and hydrophilic sites in the polyelectrolyte. Atomic force microscopy (AFM) results demonstrated that the Nafion film is 35 nm thick and tetraruthenated metalloporphyrins layers 190 nm thick presenting a thin but compacted morphology. Scanning electrochemical microscopy (SECM) images shows that the Co(II) tetraruthenated porphyrins/Nf/GC modified electrode is more electrochemically active than their Ni and Zn analogues. These modified electrodes are able to reduce nitrite at -660 mV showing enhanced reduction current and a decrease in the required overpotential compared to bare glassy carbon electrode. Controlled potential electrolysis experiments verify the production of ammonia, hydrazine and hydroxylamine at potentials where reduction of solvent is plausible demonstrating some selectivity toward the nitrite ion. Rotating disc electrode voltammetry shows that the factor that governs the kinetics of nitrite reduction is the charge propagation in the film.

  9. Direct electron transfer of redox proteins at the bare glassy carbon electrode.

    Science.gov (United States)

    Hagen, W R

    1989-07-01

    A simple system is presented for the microscale, direct voltammetry of redox proteins, typically 25 micrograms, in the absence of mediators and/or modifiers. The sample consists of a droplet of anaerobic solution laid onto an oversized disc of nitric-acid-pretreated glassy carbon as the working electrode. Very reproducible, Nernstian responses are obtained with horse heart cytochrome c. The midpoint potential Em (pH 7.0) is dependent on the ionic strength, ranging from $293 mV in 1 mM potassium phosphate to $266 mV in 0.1 M phosphate. At fixed buffer and cytochrome concentrations the magnitude of the voltammetric response is found to be independent of pH over six pH units around neutrality. It is suggested that the response of the present system is not complicated by pH-dependent properties of the electrode surface around physiological pH and, therefore, that the use of this system is practical in biochemically oriented studies. Direct, quasi-reversible responses have also been obtained at pH 7.0 (5 mM phosphate) from Desulfovibrio vulgaris. Hildenborough strain, tetraheme cytochrome c3 (pI = 10.0 at 4 C; 3 X Em = -0.32 mV, Em = -0.26 V), and cytochrome c553 (pI = 9.3; Em = +60 mV), and from Megasphaera elsdenii rubredoxin (pI congruent to 3; Em = -353 mV). The latter protein absorbs onto the glassy carbon surface, thus forming a system with possible applications in the electrochemical study of ferredoxin-linked enzymes.

  10. Multilevel micro-structuring of glassy carbon molds for precision glass molding

    Science.gov (United States)

    Prater, Karin; Dukwen, Julia; Scharf, Toralf; Herzig, Hans Peter; Plöger, Sven; Hermerschmidt, Andreas

    2015-09-01

    Replication techniques for diffractive optical elements (DOEs) in soft materials such as plastic injection molding are state of the art. For precision glass molding in glasses with high transition temperatures, molds with extreme thermal resistivity, low chemical reactivity and high mechanical strength are needed. Glassy Carbon can be operated up to 2000°C making it possible to mold almost all glasses including Fused Silica with a transition temperatures above 1060°C. For the structuring of Glassy Carbon wafers photolithography and a RIE process is used. We have developed a process using Si as a hard mask material. If the flow rates of the etching gases O2 and SF6 are chosen properly, high selectivity of GC to Si 19:1 can be achieved, which provides excellent conditions to realize high resolution elements with feature size down to 1 micron and fulfills requirements for optical applications. We fabricated several multilevel GC molds with 8 levels of structuring. Two different optical functionalities were implemented: 6x6 array beamsplitter and 1x4 linear beamsplitter. The molds were applied for precision glass molding of a low Tg glass L-BAL 42 (from Ohara) with a transition temperature of 565°C. Their optical performance was measured. A more detailed analysis of the impact of mold fabrication defects on optical performance is done. Rigorous coupled wave analysis simulations are performed, where we included fabrication constrains such as duty cycle, edge depth errors, wall verticality and misalignment errors. We will compare the results with the design specifications and discuss the influence of fabrication errors introduced during the different process steps.

  11. Laser annealing effects of the Raman laser on nitrogen implanted glassy carbon

    Energy Technology Data Exchange (ETDEWEB)

    Barbara, D.; Prawer, S.; Jamieson, D.N. [Melbourne Univ., Parkville, VIC (Australia). School of Physics

    1996-12-31

    Raman analysis is a popular method of investigating crystallite sizes, ordering and the types of bonds that exist in ion irradiated carbon materials, namely graphite, diamond and glassy carbon (G.C.). In particular Raman spectroscopy is used in determining the tetrahedral bonding required for the elusive and potentially important new material called carbon nitride. Carbon nitride, {beta}-C{sub 3}N{sub 4}, is predicted to exist in several forms. Forming the tetrahedral bond between C and N has proved troublesome bain of many experimenters. A proven method for synthesizing novel materials is ion implantation. Thus G.C. was implanted with N at low temperatures so that diffusion of the implanted N would be hindered. G.C. is a relatively hard, chemically inert, graphitic material. The opaque property of G.C. means that Raman spectroscopy will only give information about the structures that exist at the surface and near surface layers. It was decided, after observing conflicting Raman spectra at different laser powers, that an investigation of the laser annealing effects of the Raman laser on the N implanted G.C. was warranted. The results of the preliminary investigation of the effects of increasing the Raman laser power and determining a power density threshold for high dose N implanted G.C. are discussed. 4 refs., 4 figs.

  12. Amperometric detection of carbohydrates and thiols by using a glassy carbon electrode coated with Co oxide/multi-wall carbon nanotubes catalytic system.

    Science.gov (United States)

    Buratti, Susanna; Brunetti, Barbara; Mannino, Saverio

    2008-07-15

    A glassy carbon electrode coated with cobalt oxide/multi-wall carbon nanotubes (MWCNT) system was used for the detection of carbohydrates and thiols. The modification of the glassy carbon electrode increased the anodic current response of these organic compounds and decreased their overvoltage. The amperometric responses were extremely stable with no loss of sensitivity over many days of storage. Such attractive performance characteristics indicate great promise for using this new catalytic system for monitoring in fast and simple way compounds of great interest for food industry, biotechnology and clinical diagnostics.

  13. Ion Beam Optimized Mechanical Characteristics of Glassy Polymeric Carbon for Medical Applications

    International Nuclear Information System (INIS)

    Rodrigues, M.G.; Cruz, N.C. da; Rangel, E.C.; Zimmerman, R.L.; Ila, D.; Poker, D.B.; Hensley, D.K.

    2003-01-01

    Glassy Polymeric Carbon (GPC) has medical applications owing to its inertness and biocompatible characteristics. Commercial GPC prosthetics include mitral, aortic and hydrocephalic valves. Surface treatment of GPC increases the adhesion of endothelic tissue on GPC and avoids the occurrence of thrombus in cardiac implant. In this work, ion beam was used to improve the mechanical characteristics of GPC surface. Hardness was measured as a function of depth in precursor and GPC samples heat treated from 300 to 2500 deg. C before and after bombardment with energetic ions of silicon, carbon, oxygen and gold at energies of 5, 6, 8 and 10 MeV and fluences between 1.0x1013 and 1.0x1016 ions/cm2. Comparison shows that hardness increases of the bombarded samples depend on heat treatment temperature. We verify that ion bombardment promotes carbonization due to an increased linkage between the chains of the polymeric material in lateral groups that are more numerous for samples heat treated to 700 deg. C

  14. Determination of 4-aminophenylarsonic acid using a glassy carbon electrode modified with an ionic liquid and carbon nanohorns

    International Nuclear Information System (INIS)

    Dai, Hong; Gong, Lingshan; Lu, Shuangyan; Zhang, Qingrong; Li, Yilin; Zhang, Shupei; Xu, Guifang; Li, Xiuhua; Lin, Yanyu; Chen, Guonan

    2015-01-01

    We have developed a sensor for 4-aminophenylarsonic acid (4-APhAA) by coating a glassy carbon electrode (GCE) with a composite prepared from an ionic liquid and dahlia-like carbon nanohorns (CNHs). The good electric conductivity, large surface area and high pore volume of the CNHs, and the synergistic action of the ionic liquid (which is a good dispersant with excellent ion conductivity) result in efficient electrocatalysis towards oxidation of 4-APhAA. The effect was investigated by various electrochemical methods, and the electron transfer coefficient, diffusion coefficient, standard heterogeneous rate constant and thermodynamic activation energy were determined. The response range of 4-APhAA was evaluated using an i-t plot. If operated at a working voltage of 900 mV (vs Ag/AgCl), the sensor responds to 4-APhAA over the 0.5 μM to 3.5 M concentration range. (author)

  15. Electrochemical Reduction of Oxygen on Anthraquinone/Carbon Nanotubes Nanohybrid Modified Glassy Carbon Electrode in Neutral Medium

    Directory of Open Access Journals (Sweden)

    Zheng Gong

    2013-01-01

    Full Text Available The electrochemical behaviors of monohydroxy-anthraquinone/multiwall carbon nanotubes (MHAQ/MWCNTs nanohybrid modified glassy carbon (MHAQ/MWCNTs/GC electrodes in neutral medium were investigated; also reported was their application in the electrocatalysis of oxygen reduction reaction (ORR. The resulting MHAQ/MWCNTs nanohybrid was characterized by scanning electron microscope (SEM and transmission electron microscope (TEM. It was found that the ORR at the MHAQ/MWCNTs/GC electrode occurs irreversibly at a potential about 214 mV less negative than at a bare GC electrode in pH 7.0 buffer solution. Cyclic voltammetric and rotating disk electrode (RDE techniques indicated that the MHAQ/MWCNTs nanohybrid has high electrocatalytic activity for the two-electron reduction of oxygen in the studied potential range. The kinetic parameters of ORR at the MHAQ/MWCNTs nanohybrid modified GC electrode were also determined by RDE and EIS techniques.

  16. Glassy carbon electrodes modified with multiwalled carbon nanotubes for the determination of ascorbic acid by square-wave voltammetry

    Directory of Open Access Journals (Sweden)

    Sushil Kumar

    2012-05-01

    Full Text Available Multiwalled carbon nanotubes were used to modify the surface of a glassy carbon electrode to enhance its electroactivity. Nafion served to immobilise the carbon nanotubes on the electrode surface. The modified electrode was used to develop an analytical method for the analysis of ascorbic acid (AA by square-wave voltammetry (SWV. The oxidation of ascorbic acid at the modified glassy carbon electrode showed a peak potential at 315 mV, about 80 mV lower than that observed at the bare (unmodified electrode. The peak current was about threefold higher than the response at the bare electrode. Replicate measurements of peak currents showed good precision (3% rsd. Peak currents increased with increasing ascorbic acid concentration (dynamic range = 0.0047–5.0 mmol/L and displayed good linearity (R2 = 0.994. The limit of detection was 1.4 μmol/L AA, while the limit of quantitation was 4.7 μmol/L AA. The modified electrode was applied to the determination of the amount of ascorbic acid in four brands of commercial orange-juice products. The measured content agreed well (96–104% with the product label claim for all brands tested. Recovery tests on spiked samples of orange juice showed good recovery (99–104%. The reliability of the SWV method was validated by conducting parallel experiments based on high-performance liquid chromatography (HPLC with absorbance detection. The observed mean AA contents of the commercial orange juice samples obtained by the two methods were compared statistically and were found to have no significant difference (P = 0.05.

  17. Gold nanoparticle/multi-walled carbon nanotube modified glassy carbon electrode as a sensitive voltammetric sensor for the determination of diclofenac sodium.

    Science.gov (United States)

    Afkhami, Abbas; Bahiraei, Atousa; Madrakian, Tayyebeh

    2016-02-01

    A simple and highly sensitive sensor for the determination of diclofenac sodium based on gold nanoparticle/multi-walled carbon nanotube modified glassy carbon electrode is reported. Scanning electron microscopy along with energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry was used to characterize the nanostructure and performance of the sensor and the results were compared with those obtained at the multi-walled carbon nanotube modified glassy carbon electrode and bare glassy carbon electrode. Under the optimized experimental conditions diclofenac sodium gave linear response over the range of 0.03-200μmolL(-1). The lower detection limits were found to be 0.02μmolL(-1). The effect of common interferences on the current response of DS was investigated. The practical application of the modified electrode was demonstrated by measuring the concentration of diclofenac sodium in urine and pharmaceutical samples. This revealed that the gold nanoparticle/multiwalled carbon nanotube modified glassy carbon electrode shows excellent analytical performance for the determination of diclofenac sodium in terms of a very low detection limit, high sensitivity, very good accuracy, repeatability and reproducibility. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. Chronoamperometric estimation of cognac and brandy antioxidant capacity using MWNT modified glassy carbon electrode.

    Science.gov (United States)

    Ziyatdinova, Guzel; Salikhova, Inna; Budnikov, Herman

    2014-07-01

    Cognac and brandy components are electrochemically oxidized on multi-walled carbon nanotube modified glassy carbon electrode at 0.44 and 0.59 V in 0.1 М phosphate buffer solution pH 3.0. Voltammetric behavior of the main antioxidant constituents of cognac (ellagic and gallic acids, syringaldehyde, coniferaldehyde, vanillin, 5-hydroxymethylfurfural and furfural) has been investigated. The peak at the less positive potential of cognacs is caused by oxidation of gallic acid as well as syringaldehyde- and coniferaldehyde. The second peak corresponds to ellagic acid oxidation. One-step chronoamperometry at 0.59 V for 75 s has been applied for the cognac and brandy antioxidant capacity (AOC) evaluation. Ellagic acid, being the main antioxidant of cognac, has been used as a reference substance. The chronoamperometric response of ellagic acid is linear in the range of 0.66-52.8 µM with the limit of detection and quantification at 0.19 and 0.63 µM, respectively. AOC in ellagic acid equivalents per 100mL of cognac and brandy for different denominations (11 cognacs and 11 ordinary and vintage brandies) has been estimated. AOC of cognacs and brandies increases with the age of the beverages. Positive correlations (r=0.9134-0.9703) with common parameters characterizing antioxidant properties of beverages, in particular antiradical activity, total phenolics content, total antioxidant capacity and ferric reducing power have been observed. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Core-level XPS spectra of fullerene, highly oriented pyrolitic graphite, and glassy carbon

    CERN Document Server

    Leiro, J A; Laiho, T; Batirev, I G

    2003-01-01

    The C 1s spectra of fullerene C sub 6 sub 0 , highly oriented pyrolitic graphite (HOPG) and amorphous carbon (a-C) have been measured using X-ray photoemission. The assumed background due to the inelastic scattering of electrons of these spectra has been subtracted by the Tougaard's method. The relative intensities and the energy positions for the core-level satellites have been determined. For C sub 6 sub 0 , a comparison of the low energy pi type shake-up satellites gives good agreement between theory and experiment. Also, the energies of these features for fullerene and glassy carbon are very similar, whereas the corresponding energies for HOPG are somewhat larger, presumably, because of the higher density of the latter. Moreover, the atomic force microscopy (AFM) study indicates that the C sub 6 sub 0 samples consist of a thick layer of large clusters on the Si(111) surface, which is in line with the molecular character of the XPS spectrum. Furthermore, the broad high energy satellite does not consist of ...

  20. Structural Modifications And Mechanical Degradation Of Ion Irradiated Glassy Polymer Carbon

    Science.gov (United States)

    Abunaemeh, Malek; Seif, Mohamed; Elsamadicy, Abdalla; Muntele, Claudiu; Ila, Daryush

    2011-06-01

    The TRISO fuel has been used in some of the Generation IV nuclear reactor designs. It consists of a fuel kernel of UOx coated with several layers of materials with different functions. Pyrolytic carbon (PyC) is one of the materials in the layers. In this study we investigate the possibility of using Glassy Polymeric Carbon (GPC) as an alternative to PyC. GPC is used for artificial heart valves, heat-exchangers, and other high-tech products developed for the space and medical industries. This lightweight material can maintain dimensional and chemical stability in adverse environment and very high temperatures (up to 3000 °C). In this work, we are comparing the changes in physical and microstructure properties of GPC after exposure to irradiation fluence of 5 MeV Ag equivalent to a 1 displacement per atom (dpa) at samples prepared at 1000, 1500 and 2000 °C. The GPC material is manufactured and tested at the Center for Irradiation Materials (CIM) at Alabama A&M University. Transmission electron microscopy (TEM) and Raman spectroscopy were used for analysis.

  1. Electrocatalytic behaviour and application of manganese porphyrin/gold nanoparticle- surface modified glassy carbon electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Sebarchievici, I., E-mail: incemc@incemc.ro [National Institute of Research for Electrochemistry and Condensed Matter, Aurel Paunescu Podeanu Street 144, 300569 Timisoara (Romania); Tăranu, B.O. [National Institute of Research for Electrochemistry and Condensed Matter, Aurel Paunescu Podeanu Street 144, 300569 Timisoara (Romania); Birdeanu, M. [National Institute of Research for Electrochemistry and Condensed Matter, Aurel Paunescu Podeanu Street 144, 300569 Timisoara (Romania); Institute of Chemistry Timisoara of Romanian Academy, M. Viteazul Ave. 24, 300223 Timisoara (Romania); Rus, S.F. [National Institute of Research for Electrochemistry and Condensed Matter, Aurel Paunescu Podeanu Street 144, 300569 Timisoara (Romania); Fagadar-Cosma, E., E-mail: efagadar@yahoo.com [Institute of Chemistry Timisoara of Romanian Academy, M. Viteazul Ave. 24, 300223 Timisoara (Romania)

    2016-12-30

    Highlights: • Mn-porphyrin/gold nanoparticle-modified glassy carbon electrodes were obtained. • AFM investigations of thin films display multilayer of triangular type architecture. • Oxidation and reduction processes of H{sub 2}O{sub 2} are diffusion controled. • There is a linear dependence between H{sub 2}O{sub 2} concentration and the currents intensity. • The modified electrodes show better electrochemical detection ability to H{sub 2}O{sub 2}. - Abstract: The main purpose of this research was to obtain manganese porphyrin/gold nanoparticle-modified glassy carbon electrodes and to use them for the detection of H{sub 2}O{sub 2}. Two sets of modified electrodes were prepared by drop-cast deposition of 5,10,15,20-tetra(4-methyl-phenyl)porphyrinato manganese(III) chloride alone and of the same Mn-porphyrin and gold-colloid solution and comparatively characterized by Raman, UV–vis, ellipsometry, AFM and TEM microscopy, XPS and cyclic voltammetry. XPS spectrum recorded for GC-MnP-nAu modified electrode displayed the characteristic signals of gold nanoparticles. The optical parameters have greater values for GC-MnP-nAu in comparison with GC-MnP, due to increasing charge transfer efficiency. The MnP-nAu film mediates the electron transfer between H{sub 2}O{sub 2} and GC, evidenced by an increase in the current intensity of the anodic peak, and facilitates the electrochemical regeneration of oxidized H{sub 2}O{sub 2} at cathodic potentials. From the cyclic voltammetry experiments a linear relationship between H{sub 2}O{sub 2} concentration vs oxidation and reduction currents was observed. The linear dependence between density of current and the square root of the scan rate indicates that the oxidation and reduction processes of H{sub 2}O{sub 2} are diffusion controlled. The GC-MnP-nAu modified electrode shows great potential as electrochemical sensor for determination of hydrogen peroxide.

  2. Amperometric detection of carbohydrates based on the glassy carbon electrode modified with gold nano-flake layer

    OpenAIRE

    Huy Du Nguyen; T. Thuy Luyen Nguyen; Khac Manh Nguyen; Anh Mai Nguyen; Quoc Hien Nguyen

    2015-01-01

    An electro-deposition approach was established to incorporate the gold nano-flakes onto the glassy carbon electrode in electrochemical cells (nano-Au/GC/ECCs). Using pulsed amperometric detection (PAD) without any gold oxidation for cleaning (non-oxidative PAD), the nano-Au/GC/ECCs were able to maintain their activity for oxidizing of carbohydrates in a normal alkaline medium. The reproducibility of peak area was about 2 relative standard deviation (RSD,%) for 6 consecutive injections. A dyna...

  3. Electro-oxidation of some non-steroidal anti-inflammatory drugs on an alumina nanoparticle-modified glassy carbon electrode

    OpenAIRE

    TABESHNIA, Mahla; HELI, Hossein; JABBARI, Ali

    2010-01-01

    The electro-oxidation of mefenamic acid, diclofenac, and indomethacin on glassy carbon and alumina nanoparticle-modified glassy carbon electrodes in a phosphate buffer solution at physiological pH was studied. The techniques of cyclic voltammetry, chronoamperometry, impedance spectroscopy, and steady state polarization measurements were applied. The drugs were irreversibly oxidized on bath electrodes via an anodic peak and the process was controlled by diffusion in the bulk of soluti...

  4. Manganese dioxide-graphene nanocomposite film modified electrode as a sensitive voltammetric sensor of indomethacin detection

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yuxia; Zhang, Zhenfa; Zhang, Cuizong; Huang, Wei; Liang, Caiyun; Peng, Jinyun [Guangxi Normal University for Nationalities, Chongzuo (China)

    2016-08-15

    Excess amount of analgesic and anti-inflammatory drug, such as indomethacin, often leads to serious gastrointestinal complications; therefore, amount of such active compound should be regulated in commercial drugs. This study proposes an efficient analytical technique to detect indomethacin selectively. We prepared and investigated electrochemical properties of a manganese dioxide-graphene nanocomposite film modified glassy carbon electrode (MnO{sub 2}-Gr/GCE). The behavior of the modified electrode as electrocatalyst towards indomethacin oxidation was also examined. The cyclic voltammetric results reveal that the electrocatalytic activity for the oxidation of indomethacin can significantly be enhanced on the MnO{sub 2}-Gr/GCE. Indomethacin exhibited a sensitive anodic peak at about 0.90 V at MnO{sub 2}-Gr/GCE. The data obtained from differential pulse voltammetry showed that the anodic peak currents were linearly dependent on the indomethacin concentrations in the range of 1.0 X 10{sup -7} to 2.5 X 10{sup -5} mol/L with a detection limit of 3.2 X 10{sup -8} mol/L (S/N = 3). Most importantly, the proposed method shows efficient and selective sensing of indomethacin in commercial harmaceutical formulations. This is the first report of a voltammetric sensor for indomethacin using MnO{sub 2}-Gr/GCE. We believe that this new method can be commercialized for routine applications in laboratories.

  5. Electrochemical Glucose Oxidation Using Glassy Carbon Electrodes Modified with Au-Ag Nanoparticles: Influence of Ag Content

    Directory of Open Access Journals (Sweden)

    Nancy Gabriela García-Morales

    2015-01-01

    Full Text Available This paper describes the application of glassy carbon modified electrodes bearing Aux-Agy nanoparticles to catalyze the electrochemical oxidation of glucose. In particular, the paper shows the influence of the Ag content on this oxidation process. A simple method was applied to prepare the nanoparticles, which were characterized by transmission electron microscopy, Ultraviolet-Visible spectroscopy, X-ray diffraction spectroscopy, and cyclic voltammetry. These nanoparticles were used to modify glassy carbon electrodes. The effectiveness of these electrodes for electrochemical glucose oxidation was evaluated. The modified glassy carbon electrodes are highly sensitive to glucose oxidation in alkaline media, which could be attributed to the presence of Aux-Agy nanoparticles on the electrode surface. The voltammetric results suggest that the glucose oxidation speed is controlled by the glucose diffusion to the electrode surface. These results also show that the catalytic activity of the electrodes depends on the Ag content of the nanoparticles. Best results were obtained for the Au80-Ag20 nanoparticles modified electrode. This electrode could be used for Gluconic acid (GA production.

  6. Characterization of the surface redox process of adsorbed morin at glassy carbon electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Tesio, Alvaro Yamil, E-mail: atesio@exa.unrc.edu.a [Departamento de Quimica, Facultad de Ciencias Exactas, Fisico-Quimicas y Naturales, Universidad Nacional de Rio Cuarto, Agencia Postal No 3, (5800) Rio Cuarto (Argentina); Granero, Adrian Marcelo, E-mail: agranero@exa.unrc.edu.a [Departamento de Quimica, Facultad de Ciencias Exactas, Fisico-Quimicas y Naturales, Universidad Nacional de Rio Cuarto, Agencia Postal No 3, (5800) Rio Cuarto (Argentina); Fernandez, Hector, E-mail: hfernandez@exa.unrc.edu.a [Departamento de Quimica, Facultad de Ciencias Exactas, Fisico-Quimicas y Naturales, Universidad Nacional de Rio Cuarto, Agencia Postal No 3, (5800) Rio Cuarto (Argentina); Zon, Maria Alicia, E-mail: azon@exa.unrc.edu.a [Departamento de Quimica, Facultad de Ciencias Exactas, Fisico-Quimicas y Naturales, Universidad Nacional de Rio Cuarto, Agencia Postal No 3, (5800) Rio Cuarto (Argentina)

    2011-02-01

    The thermodynamic and kinetics of the adsorption of morin (MOR) on glassy carbon (GC) electrodes in 0.2 mol dm{sup -3} phosphate buffer solutions (PBS, pH 7.00) was studied by both cyclic (CV) and square wave (SWV) voltammetries. The Frumkin adsorption isotherm was the best to describe the specific interaction of MOR with GC electrodes. The SWV allowed to characterize the thermodynamic and kinetics of surface quasi-reversible redox couple of MOR, using the combination of the 'quasi-reversible maximum' and the 'splitting of SW net peaks' methods. Average values obtained for the formal potential and the anodic transfer coefficient were (0.27 {+-} 0.02) V and (0.59 {+-} 0.09), respectively. Moreover, a value of formal rate constant (k{sub s}) of 87 s{sup -1} for the overall two-electron redox process was calculated. The SWV was also employed to generate calibration curves, which were linear in the range MOR bulk concentration (c{sub MOR}*) from 1.27 x 10{sup -7} to 2.50 x 10{sup -5} mol dm{sup -3}. The lowest concentration experimentally measured for a signal to noise ratio of 3:1 was 1.25 x 10{sup -8} mol dm{sup -3} (3 ppb).

  7. The Enhanced Photo-Electrochemical Detection of Uric Acid on Au Nanoparticles Modified Glassy Carbon Electrode

    Science.gov (United States)

    Shi, Yuting; Wang, Jin; Li, Shumin; Yan, Bo; Xu, Hui; Zhang, Ke; Du, Yukou

    2017-07-01

    In this work, a sensitive and novel method for determining uric acid (UA) has been developed, in which the glassy carbon electrode (GCE) was modified with electrodeposition Au nanoparticles and used to monitor the concentration of UA with the assistant of visible light illumination. The morphology of the Au nanoparticles deposited on GCE surface were characterized by scanning electron microscope (SEM) and the nanoparticles were found to be well-dispersed spheres with the average diameter approaching 26.1 nm. A series of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements have revealed that the introduction of visible light can greatly enhance both the strength and stability of response current due to the surface plasmon resonance (SPR). Specifically, the DPV showed a linear relationship between peak current and UA concentration in the range of 2.8 to 57.5 μM with the equation of I pa (μA) = 0.0121 c UA (μM) + 0.3122 ( R 2 = 0.9987). Herein, the visible light illuminated Au/GCE possesses a potential to be a sensitive electrochemical sensor in the future.

  8. Adsorptive Stripping Voltammetric Determination of Hydroquinone using an Electrochemically Pretreated Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Abdul Niaz1,

    2008-12-01

    Full Text Available A simple and efficient adsorptive stripping voltammetric (AdSV method was developed for the determination of hydroquinone at an electrochemically pretreated glassy carbon (GC electrode in waste water. Various parameters such as solvent system, accumulation potential, accumulation time and scan rate were optimized. The electrochemically pretreated GC electrode showed good response towards hydroquinone determination by using AdSV. Under the optimized conditions the peak current showed good linear relationship with the hydroquinone concentration in the range of 0.5-4.0mg L-1 and 5-30mg L-1. The 60/40 methanol/water composition was found to be the best solvent system and 0.05mol L-1 H2SO4 was found as useful supporting electrolyte concentration. The accumulation time was 60 s and the detection limit was 50µg L-1. The developed method was successfully applied for the determination of hydroquinone in polymeric industrial discharge samples waste photographic developer solution and cream sample without any significant effect of surface fouling.

  9. Direct chronopotentiometric analysis of riboflavin using a glassy carbon vessel as the working electrode

    Directory of Open Access Journals (Sweden)

    Brezo Tanja Ž.

    2016-01-01

    Full Text Available A new method for the determination of riboflavin (vitamin B2 was developed based on chronopotentiometry with a glassy carbon process vessel macroelectrode. The method optimisation included investigation of the most important experimental parameters: type and concentration of the supporting electrolyte, initial potential, reduction current, and the working electrode surface area. The reduction signal of riboflavin appeared at about -0.12 V vs. Ag/AgCl (3.5 mol/dm3 KCl electrode in 0.025 mol/dm3 HCl as the supporting electrolyte. A linear response was obtained in the the range of 0.05-4 mg/dm3. The limit of detection and limit of quantitation were 0.018 mg/dm3 and 0.054 mg/dm3, respectively. Due to the use of specific working electrode, a significant enhancement of the method relative sensitivity of about 10 times was achieved. The accuracy of the defined method was confirmed by HPLC analyses. The developed method was successfully applied for the quantitation of riboflavin in various pharmaceutical multivitamin preparations. [Projekat Ministarstva nauke Republike Srbije, br. III 46009

  10. Square Wave Voltammetric Determination of 2-Thiouracil in Pharmaceuticals and Real Samples Using Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Naveen M. Gokavi

    2013-01-01

    Full Text Available A simple and rapid method was developed using cyclic and square wave voltammetric techniques for the determination of trace-level sulfur containing compound, 2-thiouracil, at a glassy carbon electrode. 2-thiouracil produced two anodic peaks at 0.334 V and 1.421 V and a cathodic peak at −0.534 V. The square wave voltammetry of 2-thiouracil gave a good linear response in the range of 1–20 μM with a detection limit of 0.16 μM and quantification limit of 0.53 μM (0.0679 μg/g, which is in good agreement as per IUPAC definition of trace component analysis (100 μg/g. The obtained recoveries range from 98.10% to 102.1%. The proposed method was used successfully for its quantitative determination in pharmaceutical formulations and urine as real samples.

  11. Sensitive Electrochemical Detection of Dopamine With a Nitrogen-doped Graphene Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Wencheng Wang

    2016-09-01

    Full Text Available In this paper nitrogen-doped graphene (NG nanosheets were used as the modifier on the surface of glassy carbon electrode (GCE. The modified electrode (NG/GCE was further applied to the sensitive detection of dopamine (DA by voltammetric method. Due to the unique properties of NG such as large surface area and excellent electrocatalytic activity, electrochemical response of DA was greatly enhanced on NG/GCE with a pair of well-defined redox peaks appeared on cyclic voltammogram. Electrochemical behaviors of DA on NG/GCE were carefully investigated with the electrochemical parameters calculated. Under the selected conditions the oxidation peak currents of DA had a good linear relationship with its concentration in the range from 8.0×10–7 mol L–1 to 8.0×10–4 mol L–1 with a detection limit of 2.55×10–7 mol L–1 (3σ. The proposed method was further applied to the DA injection samples determination with satisfactory results. This work is licensed under a Creative Commons Attribution 4.0 International License.

  12. Investigations of low-energy ion irradiation influence on glassy polymeric carbon

    Science.gov (United States)

    Abidzina, V.; Tereshko, I.; Elkin, I.; Muntele, I.; Muntele, C.; Minamisawa, R. A.; Ila, D.

    2007-04-01

    Glassy polymeric carbon (GPC), which is made from phenolic resins, has a high chemical inertness and is used as high temperature and radiation resistant coatings, as high temperature heat-exchangers, as well as a biomaterial in medicine for the manufacture of heart valves and prosthetic devices [G.M. Jenkins, D. Ila, H. Maleki, Mater. Res. Soc. Symp. Proc. 394 (1995) 181]. GPC is also used for the harsh environment of space, as well as for protective coating against extreme environments such as high temperature, highly ionizing radiation, as well as corrosive environments. In this work, we present the results of our investigation of the influence of the low-energy ion irradiation in glow-discharge plasma on GPC. Chemical changes in GPC prepared at 1000 °C were studied using FTIR, micro-Raman spectroscopy and Rutherford backscattering spectrometry (RBS). Porosity changes were monitored through introducing lithium from a molten LiCl salt into GPC and using the (p, α) nuclear reaction analysis (NRA) to measure Li concentration in treated GPC.

  13. Ultrasensitive Determination of Piroxicam at Diflunisal-Derived Gold Nanoparticle-Modified Glassy Carbon Electrode

    Science.gov (United States)

    Shaikh, Tayyaba; uddin, SiraJ; Talpur, Farah N.; Khaskeli, Abdul R.; Agheem, Muhammad H.; Shah, Muhammad R.; Sherazi, Tufail H.; Siddiqui, Samia

    2017-10-01

    We present a simple and green approach for synthesis of gold nanoparticles (AuNps) using analgesic drug diflunisal (DF) as capping and stabilizing agent in aqueous solution. Characterization of the synthesized diflunisal-derived gold nanoparticles (DF-AuNps) was performed by ultraviolet-visible (UV-Vis) spectroscopy, revealing the surface plasmon absorption band at 520 nm under optimized experimental conditions. Fourier-transform infrared (FTIR) spectroscopy established the effective interaction of the capping agent with the AuNps. Topographical features of the synthesized DF-AuNps were assessed by atomic force microscopy (AFM), revealing average particle height of 29 nm to 32 nm. X-ray diffractometry was used to study the crystalline nature, revealing that the synthesized DF-AuNps possessed excellent crystalline properties. The synthesized DF-AuNps were employed to modify the surface of glassy carbon electrode (GCE) for selective determination of piroxicam (PX) using differential pulse voltammetry technique. The fabricated Nafion/DF-AuNps/GCE sensor exhibited high sensitivity compared with bare GCE. The current response of the fabricated sensor was found to be linear in the PX concentration range of 0.5 μM to 50 μM, with limit of detection (LOD) and limit of quantification (LOQ) of 50 nM and 150 nM, respectively. The proposed sensor was successfully utilized for sensitive and rapid determination of PX in human serum, urine, and pharmaceutical samples.

  14. Methionine – Au Nanoparticle Modified Glassy Carbon Electrode: a Novel Platform for Electrochemical Detection of Hydroquinone

    Directory of Open Access Journals (Sweden)

    Jiahong HE

    2014-12-01

    Full Text Available A high sensitive electrochemical sensor based on methionine/gold nanoparticles (MET/AuNPs modified glassy carbon electrode (GCE was fabricated for the quantitative detection of hydroquinone (HQ. The as-modified electrode was characterized by scanning electron microscopy (SEM and X-ray diffraction (XRD techniques. The electrochemical performance of the sensor to HQ was investigated by using cyclic and differential pulse voltammetry, which revealed its excellent electrocatalytic activity and reversibility towards HQ. The separation of anodic and cathodic peak (∆Ep was decreased from 471 mV to 75 mV. The anodic peak current achieved under the optimum conditions was linear with the HQ concentration ranging from 8 μM to 400 μM with the detection limit 0.12 μM (3σ. The as-fabricated sensor also showed a good selectivity towards HQ without demonstrating interference from other coexisting species. Furthermore, the sensor showed a good performance for HQ detection in environmental water, which suggests its potential practical application. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.6477

  15. Platinum nano-cluster thin film formed on glassy carbon and the application for methanol oxidation

    International Nuclear Information System (INIS)

    Chang, Gang; Oyama, Munetaka; Hirao, Kazuyuki

    2007-01-01

    As an interesting platinum nanostructured material, a Pt nano-cluster film (PtNCF) attached on glassy carbon (GC) is reported. Through the reduction of PtCl 4 2- by ascorbic acid in the presence of GC substrate, a Pt thin continuous film composed of small nano-clusters which had a further agglomerated nanostructure of small grains could be attached on the GC surface. It was found that the electrocatalytic ability of PtNCF for the methanol oxidation was apparently higher than those of the Pt nano-clusters dispersedly attached on GC or indium in oxides. In addition, the electrocatalytic performance of PtNCF per Pt amount was superior to that of Pt black on GC. These results indicate that, in spite of the continuous nanostructures, nano-grains of PtNCF worked effectively for the catalytic electrolysis. The present PtNCF can be regarded as an interesting thin film material, which can be easily prepared by one-step chemical reduction

  16. Investigations of low-energy ion irradiation influence on glassy polymeric carbon

    International Nuclear Information System (INIS)

    Abidzina, V.; Tereshko, I.; Elkin, I.; Muntele, I.; Muntele, C.; Minamisawa, R.A.; Ila, D.

    2007-01-01

    Glassy polymeric carbon (GPC), which is made from phenolic resins, has a high chemical inertness and is used as high temperature and radiation resistant coatings, as high temperature heat-exchangers, as well as a biomaterial in medicine for the manufacture of heart valves and prosthetic devices [G.M. Jenkins, D. Ila, H. Maleki, Mater. Res. Soc. Symp. Proc. 394 (1995) 181]. GPC is also used for the harsh environment of space, as well as for protective coating against extreme environments such as high temperature, highly ionizing radiation, as well as corrosive environments. In this work, we present the results of our investigation of the influence of the low-energy ion irradiation in glow-discharge plasma on GPC. Chemical changes in GPC prepared at 1000 deg. C were studied using FTIR, micro-Raman spectroscopy and Rutherford backscattering spectrometry (RBS). Porosity changes were monitored through introducing lithium from a molten LiCl salt into GPC and using the (p, α) nuclear reaction analysis (NRA) to measure Li concentration in treated GPC

  17. Theoretical study of the binding nature of glassy carbon with nickel(II) phthalocyanine complexes

    Energy Technology Data Exchange (ETDEWEB)

    Cortez, Luis [Laboratorio de Quimica Teorica, Facultad de Quimica y Biologia, Universidad de Santiago de Chile (USACH), Casilla 40, Correo 33, Santiago (Chile); Berrios, Cristhian [Laboratorio de Electrocatalisis, Facultad de Quimica y Biologia, Universidad de Santiago de Chile (USACH), Casilla 40, Correo 33, Santiago (Chile); Yanez, Mauricio [Laboratorio de Recursos Renovables, Centro de Biotecnologia, Universidad de Concepcion, Casilla-160 C, Concepcion (Chile); Cardenas-Jiron, Gloria I., E-mail: gloria.cardenas@usach.cl [Laboratorio de Quimica Teorica, Facultad de Quimica y Biologia, Universidad de Santiago de Chile (USACH), Casilla 40, Correo 33, Santiago (Chile)

    2009-11-26

    A theoretical study at the semiempirical RHF/PM3(tm) level (tm: transition metal) of the binding nature between a glassy carbon (GC) cluster and a nickel(II) complex (nickel(II) phthalocyanine NiPc, nickel(II) tetrasulphophthalocyanine NiTSPc) was performed. Three types of interactions for GC...NiPc (NiTSPc) were studied: (a) through an oxo (O) bridge, (b) through an hydroxo (OH) bridge, and (c) non-bridge. One layer (NiPc, NiTSPc) and two layers (NiPc...NiPc) of complex were considered. The binding energy calculated showed that in both cases NiPc and NiTSPc, the oxo structures are more stable than the hydroxo ones, and than the non-bridge systems. Charge analysis (NAO) predicted that GC gained more electrons in an oxo structure than in the analogues hydroxo. The theoretical results showed an agreement with the experimental data available, an oxo binding between GC and a nickel complex (NiPc, NiTSPc) in aqueous alkaline solutions is formed.

  18. Theoretical study of the binding nature of glassy carbon with nickel(II) phthalocyanine complexes

    International Nuclear Information System (INIS)

    Cortez, Luis; Berrios, Cristhian; Yanez, Mauricio; Cardenas-Jiron, Gloria I.

    2009-01-01

    A theoretical study at the semiempirical RHF/PM3(tm) level (tm: transition metal) of the binding nature between a glassy carbon (GC) cluster and a nickel(II) complex (nickel(II) phthalocyanine NiPc, nickel(II) tetrasulphophthalocyanine NiTSPc) was performed. Three types of interactions for GC...NiPc (NiTSPc) were studied: (a) through an oxo (O) bridge, (b) through an hydroxo (OH) bridge, and (c) non-bridge. One layer (NiPc, NiTSPc) and two layers (NiPc...NiPc) of complex were considered. The binding energy calculated showed that in both cases NiPc and NiTSPc, the oxo structures are more stable than the hydroxo ones, and than the non-bridge systems. Charge analysis (NAO) predicted that GC gained more electrons in an oxo structure than in the analogues hydroxo. The theoretical results showed an agreement with the experimental data available, an oxo binding between GC and a nickel complex (NiPc, NiTSPc) in aqueous alkaline solutions is formed.

  19. Biomedical Applications of Modified Carbon Glassy Electrode Sensor with Nanoparticles and Dendrimers

    Directory of Open Access Journals (Sweden)

    Solomon W. LEUNG

    2011-04-01

    Full Text Available We previously reported the development of a biosensor platform that is capable of measuring biometabolites and environmental sensitive species, such as peroxide and nitrate/nitrate, to concentrations in the order of ppb (parts per billion or lower. In this investigation, we modified our platform with dendrimers to enhance its performance. Zero and second generation of dendrimers were coated on the surface of a carbon glassy electrode which was then modified with l-glutamate dehydrogenase (GDH and α-keto glutarate. The resulting electrode was tested with ammonium solutions, concentrations ranged from 2 to 300 nM at pH 7.4; the results were satisfactory. Measurements at lower concentrations had better resolution than at higher concentrations and it is believed that the measurement limit can be lower than 2 nM. This biosensor platform was proven to be versatile and can be employed as a platform for ultrasensitive detecting devices in many biomedical and environmental applications.

  20. Pulse Laser Deposition Fabricating Gold Nanoclusters on a Glassy Carbon Surface for Nonenzymatic Glucose Sensing.

    Science.gov (United States)

    Shu, Honghui; Chang, Gang; Wang, Zhiqiang; Li, Pai; Zhang, Yuting; He, Yunbin

    2015-01-01

    A One-step technique for depositing gold nanoclusters (GNCs) onto the surface of a glassy carbon (GC) plate was developed by using pulse laser deposition (PLD) with appropriate process parameters. The method is simple and clean without using any templates, surfactants, or stabilizers. The experimental factors (pulse laser number and the pressure of inert gas (Ar)) that affect the morphology and structure of GNCs, and thus affect the electrocatalytic oxidation performance towards glucose were systematically investigated by means of transmission electron microscopy (TEM) and electrochemical methods (cyclic voltammograms (CV) and chronoamperometry methods). The GC electrode modified by GNCs exhibited a rapid response time (about 2 s), a broad linear range (0.1 to 20 mM), and good stability. The sensitivity was estimated to be 31.18 μA cm(-2) mM(-1) (vs. geometric area), which is higher than that of the Au bulk electrode. It has a good resistance to the common interfering species, such as ascorbic acid (AA), uric acid (UA) and 4-acetaminophen (AP). Therefore, this work has demonstrated a simple and effective sensing platform for the nonenzymatic detection of glucose, and can be used as a new material for a novel non-enzymatic glucose sensor.

  1. Determination of Mercury (II Ion on Aryl Amide-Type Podand-Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Sevgi Güney

    2011-01-01

    Full Text Available A new voltammetric sensor based on an aryl amide type podand, 1,8-bis(o-amidophenoxy-3,6-dioxaoctane, (AAP modified glassy carbon electrode, was described for the determination of trace level of mercury (II ion by cyclic voltammetry (CV and differential pulse voltammetry (DPV. A well-defined anodic peak corresponding to the oxidation of mercury on proposed electrode was obtained at 0.2 V versus Ag/AgCl reference electrode. The effect of experimental parameters on differential voltammetric peak currents was investigated in acetate buffer solution of pH 7.0 containing 1 × 10−1 mol L−1 NaCl. Mercury (II ion was preconcentrated at the modified electrode by forming complex with AAP under proper conditions and then reduced on the surface of the electrode. Interferences of Cu2+, Pb2+, Fe3+, Cd2+, and Zn2+ ions were also studied at two different concentration ratios with respect to mercury (II ions. The modified electrode was applied to the determination of mercury (II ions in seawater sample.

  2. Bottle-Brush Brushes: Cylindrical Molecular Brushes of Poly(2-oxazoline) on Glassy Carbon

    KAUST Repository

    Zhang, Ning

    2009-07-28

    We report on the synthesis of brushes of bottle-brushes of poly(2-oxazoline)s on polished glassy carbon (GC) substrates. First, homogeneous and stable poly(2-isopropenyl-2-oxazoline) (PIPOx) brush layers with thicknesses up to 160 nm were created directly onto GC by the self-initiated photografting and photopolymerization (SIPGP) of 2-isopropenyl-2-oxazoline (IPOx). Kinetic studies reveal a linear increase in thickness with the polymerization time. In a second reaction, the pendant 2-oxazoline ring of the PIPOx brushes were used for the living cationic ring-opening polymerization (LCROP) with different substituted 2-oxazoline monomers to form the side chains. Also for the second surface-initiatedLCROPfrom the surface-bound macroinitiator brushes, the thickness increase with the polymerization time was found to be linear and reproducible. Characterization of the resulting bottle-brush brushes by FTIR spectroscopy,contact angle, and AFM indicates a high side chain grafting density and quantitative reactions. Finally, we have demonstrated the possibility of functionalizing the bottle-brush brushes side chain end groups with sterically demanding molecules. © 2009 American Chemical Society.

  3. Electrochemical determination of ascorbic acid at p-phenylenediamine film-holes modified glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    Olana Bikila Nagasa

    2015-01-01

    Full Text Available In this work the determination of ascorbic acid (AA at glassy carbon electrode (GCE modified with a perforated film produced by reduction of diazonium generated in situ from p-phenylenediamine (PD is reported. Holes were intentionally created in the modifier film by stripping a pre-deposited gold nanoparticles. The modified electrodes were electrochemically characterized by common redox probes: hydroquinone, ferrocyanide and hexamineruthenium(III. The cyclic voltammetric and amperometric response of AA using the modified electrodes was compared with that of bare GCE. The bare GCE showed a linear response to AA in the concentration range of 5 mM to 45 mM with detection limit of 1.656 mM and the modified GCE showed a linear response to AA in the concentration range of 5 μM to 45 μM with detection limit of 0.123 μM. The effect of potential intereferents on amperometric signal of AA at the modified GCE was examined and found to be minimal. The inter-electrode reproducibility, stability, and accuracy were determined. The modified electrode showed excellent inter-electrode reproducibility, accuracy and stability. The modified electrode reported is a promising candidate for use in electroanalysis of AA.

  4. Analysis of diffuse scattering in neutron powder diagrams. Application to glassy carbon

    International Nuclear Information System (INIS)

    Boysen, H.

    1985-01-01

    From the quantitative analysis of the diffuse scattered intensity in powder diagrams valuable information about the disorder in crystals may be obtained. According to the dimensionality of this disorder (0D, 1D, 2D or 3D corresponding to diffuse peaks, streaks, planes or volume in reciprocal space) a characteristic modulation of the background is observed, which is described by specific functions. These are derived by averaging the appropriate cross sections over all crystallite orientations in the powder and folding with the resolution function of the instrument. If proper account is taken of all proportionality factors different components of the background can be put on one relative scale. The results are applied to two samples of glassy carbon differing in their degree of disorder. The neutron powder patterns contain contributions from 0D (00l peaks due to the stacking of graphitic layers), 1D (hkzeta streaks caused by the random orientation of these layers) and 3D (incoherent scattering, averaged thermal diffuse scattering, multiple scattering). From the fit to the observed data various parameters of the disorder like domain sizes, strains, interlayer distances, amount of incorporated hydrogen, pore sizes etc. are determined. It is shown that the omission of resolution corrections leads to false parameters. (orig.)

  5. Dihydropyridine-fused and pyridine-fused coumarins: Reduction on a glassy carbon electrode in dimethylformamide

    International Nuclear Information System (INIS)

    Nuñez-Vergara, Luis J.; Pardo-Jiménez, V.; Barrientos, C.; Olea-Azar, C.A.; Navarrete-Encina, P.A.; Squella, J.A.

    2012-01-01

    In this study, two series of dihydropyridine-fused and pyridine-fused coumarins were synthesised and electrochemically characterised in aprotic medium. In both series, the most easily reducible groups were the endocyclic carbonyl groups. The electrochemical mechanism for both types of compounds is strongly dependent on the experimental time-scale. Cyclic voltammetric (CV) reduction on a glassy carbon electrode (GCE) of the endocyclic carbonyl group of dihydropyridine-fused coumarins involves an ECEC mechanism with two electron transfer steps that are coupled with chemical reactions to produce the corresponding hemiacetal derivative. In the case of pyridine-fused coumarins, CV reduction of the endocyclic carbonyl group involves an EEC mechanism. ESR studies revealed the presence of a stabilised intermediate only for the pyridine-fused derivatives. Our theoretical study showed a spin density map of radical species delocalised mainly within the coumarin ring, indicating the reduction of the endocyclic carbonyl group. In the case of the dihydropyridine-fused derivatives, the mildly acid hydrogen of the dihydropyridine ring destabilises the radical via a father–son type reaction.

  6. Glassy carbon/multi walled carbon nanotube/cadmium sulphide photoanode for light energy storage in vanadium photoelectrochemical cell

    Science.gov (United States)

    Peimanifard, Zahra; Rashid-Nadimi, Sahar

    2015-12-01

    The aim of this study is utilizing the artificial photosynthesis, which is an attractive and challenging theme in the photoelectrocatalytic water splitting, to charge the vanadium redox flow battery (VRFB). In this work multi walled carbon nanotube/cadmium sulphide hybrid is employed as a photoanode material to oxidize VO2+ toVO2+ for charging the positive vanadium redox flow battery's half-cell. Characterization studies are also described using the scanning electron microscopic-energy-dispersive X-ray spectroscopy (SEM-EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and UV-Visible methods. The phtoelectrochemical performance is characterized by cyclic voltammetry and chronoamperometry. Applied bias photon-to-current efficiency (ABPE) is achieved for both two and three-electrode configurations. The glassy carbon/multi walled carbon nanotube/cadmium sulphide yields high maximum ABPE of 2.6% and 2.12% in three and two-electrode setups, respectively. These results provide a useful guideline in designing photoelectrochemical cells for charging the vanadium redox flow batteries by sunlight as a low cost, free and abundant energy source, which does not rely on an external power input.

  7. Determination of 8-Hydroxydeoxyguanosine: A potential biomarker of oxidative stress, using carbon-allotropic nanomaterials modified glassy carbon sensor.

    Science.gov (United States)

    Rosy; Goyal, Rajendra N

    2016-12-01

    A voltammetric sensor for the determination of 8-Hydroxydeoxyguanosine (8-OHdG); an important, sensitive and integral biomarker of oxidative stress and related pathological conditions like carcinogenesis, renal disorders, mental retardations, diabetes etc. has been fabricated. The synergistic behavior of two allotropic forms of carbon, which are electrochemically reduced graphene oxide (ErGO) and multiwalled carbon nanotubes (MWCNTs), has been exploited for the surface modification. The resulting modified surface has been characterized using Field Emission Scanning Electron Microscopy, X-ray diffraction, Electrochemical Impedance Spectroscopy and voltammetric behavior. The fabricated sensor exhibited excellent electrocatalytic effect towards oxidation of 8-OHdG and also showed substantial increment in sensitivity. The modified sensor showed a sensitivity of 0.1965µA/µM in the linear range of 3-75µM, whereas, a slope of 0.0046µA/µM was obtained for unmodified GCE. A limit of detection as low as 35nM has been obtained using the glassy carbon surface modified sensor. The proposed method was also successfully applied for the quantification of 8-OHdG in the presence of common interfering biomolecules like ascorbic acid, uric acid, xanthine, hypoxanthine etc. and also in human urine samples. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. Glassy carbon electrode modified with multi-walled carbon nanotubes sensor for the quantification of antihistamine drug pheniramine in solubilized systems

    Directory of Open Access Journals (Sweden)

    Rajeev Jain

    2012-02-01

    Full Text Available A sensitive electroanalytical method for quantification of pheniramine in pharmaceutical formulation has been investigated on the basis of the enhanced electrochemical response at glassy carbon electrode modified with multi-walled carbon nanotubes in the presence of sodium lauryl sulfate. The experimental results suggest that the pheniramine in anionic surfactant solution exhibits electrocatalytic effect resulting in a marked enhancement of the peak current response. Peak current response is linearly dependent on the concentration of pheniramine in the range 200–1500 μg/mL with correlation coefficient 0.9987. The limit of detection is 58.31 μg/mL. The modified electrode shows good sensitivity and repeatability. Keywords: Pheniramine, Sodium lauryl sulfate (SLS, Glassy carbon electrode modified with multi-walled carbon nanotubes (GCE-MWCNTs, Solubilized systems, Voltammetric quantification

  9. Cyclic voltammetric investigations of microstructured and platinum-covered glassy carbon electrodes in contact with a polymer electrolyte membrane

    Energy Technology Data Exchange (ETDEWEB)

    Scherer, G.G.; Veziridis, Z.; Staub, M. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Freimuth, H. [Inst. fuer Mikrotechnik Mainz IMM, Mainz (Germany)

    1997-06-01

    Model gas diffusion electrodes were prepared by microstructuring glassy carbon surfaces with high aspect ratios and subsequent deposition of platinum. These electrodes were characterized by hydrogen under-potential deposition (H-upd) in contact with a polymer electrolyte membrane employing cyclic voltametry. H-upd was found on platinum areas not in direct contact to the solid electrolyte, as long as a continuous platinum-path existed. A carbon surface between platinum acts as barrier for H-upd. (author) 4 figs., 5 refs.

  10. Gold nanoparticle/multi-walled carbon nanotube modified glassy carbon electrode as a sensitive voltammetric sensor for the determination of diclofenac sodium

    International Nuclear Information System (INIS)

    Afkhami, Abbas; Bahiraei, Atousa; Madrakian, Tayyebeh

    2016-01-01

    A simple and highly sensitive sensor for the determination of diclofenac sodium based on gold nanoparticle/multi-walled carbon nanotube modified glassy carbon electrode is reported. Scanning electron microscopy along with energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry was used to characterize the nanostructure and performance of the sensor and the results were compared with those obtained at the multi-walled carbon nanotube modified glassy carbon electrode and bare glassy carbon electrode. Under the optimized experimental conditions diclofenac sodium gave linear response over the range of 0.03–200 μmol L −1 . The lower detection limits were found to be 0.02 μmol L −1 . The effect of common interferences on the current response of DS was investigated. The practical application of the modified electrode was demonstrated by measuring the concentration of diclofenac sodium in urine and pharmaceutical samples. This revealed that the gold nanoparticle/multiwalled carbon nanotube modified glassy carbon electrode shows excellent analytical performance for the determination of diclofenac sodium in terms of a very low detection limit, high sensitivity, very good accuracy, repeatability and reproducibility. - Highlights: • GCE was modified with multiwalled carbon nanotube and gold nanoparticles. • AuNP/MWCNT/GCE was used for the determination of diclofenac sodium. • Modified electrode was characterized by SEM, EDS and EIS. • The proposed method showed excellent analytical figures of merit. • This sensor was used for the determination of diclofenac sodium in real samples.

  11. Gold nanoparticle/multi-walled carbon nanotube modified glassy carbon electrode as a sensitive voltammetric sensor for the determination of diclofenac sodium

    Energy Technology Data Exchange (ETDEWEB)

    Afkhami, Abbas, E-mail: afkhami@basu.ac.ir; Bahiraei, Atousa; Madrakian, Tayyebeh

    2016-02-01

    A simple and highly sensitive sensor for the determination of diclofenac sodium based on gold nanoparticle/multi-walled carbon nanotube modified glassy carbon electrode is reported. Scanning electron microscopy along with energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry was used to characterize the nanostructure and performance of the sensor and the results were compared with those obtained at the multi-walled carbon nanotube modified glassy carbon electrode and bare glassy carbon electrode. Under the optimized experimental conditions diclofenac sodium gave linear response over the range of 0.03–200 μmol L{sup −1}. The lower detection limits were found to be 0.02 μmol L{sup −1}. The effect of common interferences on the current response of DS was investigated. The practical application of the modified electrode was demonstrated by measuring the concentration of diclofenac sodium in urine and pharmaceutical samples. This revealed that the gold nanoparticle/multiwalled carbon nanotube modified glassy carbon electrode shows excellent analytical performance for the determination of diclofenac sodium in terms of a very low detection limit, high sensitivity, very good accuracy, repeatability and reproducibility. - Highlights: • GCE was modified with multiwalled carbon nanotube and gold nanoparticles. • AuNP/MWCNT/GCE was used for the determination of diclofenac sodium. • Modified electrode was characterized by SEM, EDS and EIS. • The proposed method showed excellent analytical figures of merit. • This sensor was used for the determination of diclofenac sodium in real samples.

  12. A sensitive DNA biosensor fabricated from gold nanoparticles, carbon nanotubes, and zinc oxide nanowires on a glassy carbon electrode

    International Nuclear Information System (INIS)

    Wang Jie; Li Shuping; Zhang Yuzhong

    2010-01-01

    We outline here the fabrication of a sensitive electrochemical DNA biosensor for the detection of sequence-specific target DNA. Zinc oxide nanowires (ZnONWs) were first immobilized on the surface of a glassy carbon electrode. Multi-walled carbon nanotubes (MWCNTs) with carboxyl groups were then dropped onto the surface of the ZnONWs. Gold nanoparticles (AuNPs) were subsequently introduced to the surface of the MWNTs/ZnONWs by electrochemical deposition. A single-stranded DNA probe with a thiol group at the end (HS-ssDNA) was covalently immobilized on the surface of the AuNPs by forming an Au-S bond. Scanning electron microscopy (SEM) and cyclic voltammetry (CV) were used to investigate the film assembly process. Differential pulse voltammetry (DPV) was used to monitor DNA hybridization by measuring the electrochemical signals of [Ru(NH 3 ) 6 ] 3+ bounding to double-stranded DNA (dsDNA). The incorporation of ZnONWs and MWCNTs in this sensor design significantly enhances the sensitivity and the selectivity. This DNA biosensor can detect the target DNA quantitatively in the range of 1.0 x 10 -13 to 1.0 x 10 -7 M, with a detection limit of 3.5 x 10 -14 M (S/N = 3). In addition, the DNA biosensor exhibits excellent selectivity, even for single-mismatched DNA detection.

  13. Electrocatalytic Study of Paracetamol at a Single-Walled Carbon Nanotube/Nickel Nanocomposite Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Koh Sing Ngai

    2015-01-01

    Full Text Available A rapid, simple, and sensitive method for the electrochemical determination of paracetamol was developed. A single-walled carbon nanotube/nickel (SWCNT/Ni nanocomposite was prepared and immobilized on a glassy carbon electrode (GCE surface via mechanical attachment. This paper reports the voltammetry study on the effect of paracetamol concentration, scan rate, pH, and temperature at a SWCNT/Ni-modified electrode in the determination of paracetamol. The characterization of the SWCNT/Ni/GCE was performed by cyclic voltammetry. Variable pressure scanning electron microscopy (VPSEM and energy dispersive X-ray (EDX spectrometer were used to examine the surface morphology and elemental profile of the modified electrode, respectively. Cyclic voltammetry showed significant enhancement in peak current for the determination of paracetamol at the SWCNT/Ni-modified electrode. A linear calibration curve was obtained for the paracetamol concentration between 0.05 and 0.50 mM. The SWCNT/Ni/GCE displayed a sensitivity of 64 mA M−1 and a detection limit of 1.17 × 10−7 M in paracetamol detection. The proposed electrode can be applied for the determination of paracetamol in real pharmaceutical samples with satisfactory performance. Results indicate that electrodes modified with SWCNT and nickel nanoparticles exhibit better electrocatalytic activity towards paracetamol.

  14. A novel enzymatic glucose sensor based on Pt nanoparticles-decorated hollow carbon spheres-modified glassy carbon electrode

    Science.gov (United States)

    Luhana, Charles; Bo, Xiang-Jie; Ju, Jian; Guo, Li-Ping

    2012-10-01

    A new glucose biosensor was developed based on hollow carbon spheres decorated with platinum nanoparticles (Pt/HCSs)-modified glassy carbon electrode immobilized with glucose oxidase (GOx) with the help of Nafion. The Pt nanoparticles were well dispersed on the HCSs with an average size of 2.29 nm. The detection of glucose was achieved via electrochemical detection of the enzymatically liberated H2O2 at +0.5 V versus Ag/AgCl at physiologic pH of 7.4. The Pt/HCSs-modified electrode exhibited excellent electrocatalytic activities toward both the oxidation and reduction of H2O2. The glucose biosensor showed good electrocatalytic performance in terms of high sensitivity (4.1 μA mM-1), low detection limit (1.8 μM), fast response time range (0.04-8.62 mM). The apparent Michaelis-Menten constant ( K m) and the maximum current density ( i max) values for the biosensor were 10.94 mM and 887 μA cm-2 respectively. Furthermore, this biosensor showed an acceptable reproducibility and high stability. The interfering signals from ascorbic acid and uric acid at concentration levels normally found in human blood were not much compared with the response to glucose. Blood serum samples were also tested with this biosensor and a good recovery was achieved for the two spiked serum samples.

  15. Amperometric sensing of anti-HIV drug zidovudine on Ag nanofilm-multiwalled carbon nanotubes modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Rafati, Amir Abbas, E-mail: aa_rafati@basu.ac.ir; Afraz, Ahmadreza

    2014-06-01

    The zidovudine (ZDV) is the first drug approved for the treatment of HIV virus infection. The detection and determination of this drug are very importance in human serum because of its undesirable effects. A new ZDV sensor was fabricated on the basis of nanocomposite of silver nanofilm (Ag-NF) and multiwalled carbon nanotubes (MWCNTs) immobilized on glassy carbon electrode (GCE). The modified electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) techniques. Results showed that the electrodeposited silver has a nanofilm structure and further electrochemical studies showed that the prepared nanocomposite has high electrocatalytic activity and is appropriate for using in sensors. The amperometric technique under optimal conditions is used for the determination of ZDV ranging from 0.1 to 400 ppm (0.37 μM–1.5 mM) with a low detection limit of 0.04 ppm (0.15 μM) (S/N = 3) and good sensitivity. The prepared sensor possessed accurate and rapid response to ZDV and shows an average recovery of 98.6% in real samples. - Highlights: • New anti-HIV drug sensor was fabricated on the basis of nanomaterials composite. • The GCE modified by prepared hydrophilic MWCNT silver nanoparticles. • Silver nanofilm electrodeposited on MWCNT/GCE and characterized by SEM, EDX, CV and LSV • Response of electrode to ZDV was thoroughly investigated by electrochemical techniques.

  16. An extensive study of electrochemical behavior of brimonidine and its determination at glassy carbon electrode

    International Nuclear Information System (INIS)

    Aleksić, Mara M.; Radulović, Valentina; Agbaba, Danica; Kapetanović, Vera

    2013-01-01

    Highlights: • The electrochemical behavior of BRIM was investigated by CV, DPV and SWV at GCE. • The effects of pH, scan rate and BRIM concentriation was studied. • The nature of the electrode process, and the mechanism scheme was proposed. • DPV method was developed for the estimation of BRIM in the Alphagan eye drops. -- Abstract: The electrochemical behavior of brimonidine (BRIM), an antiglaucoma agent applied in therapy for lowering high intraocular pressure, was investigated by cyclic voltammetry, differential pulse voltammetry and square wave voltammetry using a glassy carbon electrode (GCE). The reduction of BRIM occurs as one-step quasi-reversible reaction in acid and neutral medium, reaching the full reversibility in alkaline solutions. Reduction process involves the transfer of two electrons and two protons at the pyrazine ring of quinoxaline moiety, forming a dihydro-derivative. In acid and neutral solutions, brimonidine reduction product is partly oxidized to its hydroxy-derivative. BRIM is also oxidized irreversibly with the transfer of one electron and one proton at secondary amine moiety. The effects of pH of the electrolyte solution, scan rate and BRIM concentration were monitored. The nature of the electrode process was found to be controlled by the adsorption at pH > 6 and the total surface concentration of brimonidine adsorbed onto the GCE surface at pH 7, Γ BRIM = 1.35 × 10 −10 mol cm −2 was obtained. Based on this study, differential pulse voltammetric method was developed, validated and suggested for rapid electroanalytical determination of the low concentration of brimonidine. The linearity was achieved within the concentration range from 5 × 10 −7 to 5 × 10 −6 M with LOD = 1.6 × 10 −7 M and LOQ = 5.3 × 10 −7 M. The method was applied for brimonidine determination in pharmaceutical dosage form, eye drops

  17. Redox behavior of a novel menadiol derivative at glassy carbon electrode

    International Nuclear Information System (INIS)

    Munir, Shamsa; Shah, Afzal; Rauf, Abdur; Badshah, Amin; Lunsford, Suzanne K.; Zia-ur-Rehman; Hussain, Hidayat; Khan, Gul Shahzada

    2013-01-01

    Highlights: ► The electrode reaction mechanism of a novel derivative of menadiol has been established. ► Thorough electrochemical science of the analyte has been convincingly discussed. ► Sensitive modern electrochemical techniques were used for the investigation of analyte in a wide pH range. ► pK a , diffusion coefficient and heterogeneous electron transfer rate constant were determined. ► The computational and experimental results were found in very good agreement. -- Abstract: The redox behavior of a menadiol derivative, 4-hydroxy-5-methoxynaphthalene-1-yl acetate (HMNA) was investigated in a wide pH range by using modern electrochemical techniques. The techniques utilized in this study were cyclic voltammetry, square wave voltammetry and differential pulse voltammetry (CV, SWV and DPV). A sharp anodic signal in the forward scan followed by a cathodic peak (associated with the reduction of the oxidation product of HMNA) in the reverse scan produced a counter oxidation signal in the positive realm of glassy carbon electrode. Physical parameters like diffusion coefficient and heterogeneous electron transfer rate constant were determined from scan rate and concentration effects. Square wave voltammetry evidenced the quasi-reversible nature of the electrochemical process. The involvement of protons in the redox mechanism was determined from the peak potential shift as a function of pH. The redox mechanism of HMNA proposed on the basis of CV, SWV and DPV results was supported by theoretical calculations. Moreover, a detailed UV–vis spectroscopy was carried out in a wide pH range for characterization and pK a determination of HMNA

  18. In situ raman spectroelectrochemistry of electron transfer between glassy carbon and a chemisorbed nitroazobenzene monolayer.

    Science.gov (United States)

    Itoh, Takashi; McCreery, Richard L

    2002-09-11

    In situ Raman spectroscopy was used to monitor 4-nitroazobenzene (NAB) in an electrochemical cell, both as a free molecule and as a chemisorbed monolayer on a glassy carbon (GC) electrode surface. Reduction of free NAB exhibited two well-defined voltammetric couples in acetonitrile, and the accompanying spectral changes supported a mechanism involving two successive 1-e(-) transfers. Raman spectra of NAB chemisorbed to GC via diazonium ion reduction were obtained in acetonitrile with a high-sensitivity, line-focused CCD spectrometer. The chemisorbed NAB spectra were quite different from the free NAB spectra, and were sufficiently strong to monitor as a function of applied potential. In the potential range of +400 to -800 mV vs Ag/Ag(+), the intensity of the Raman bands associated with the phenyl-NO(2) moiety varied, implying an electronic interaction between the pi system of the graphitic substrate and the chemisorbed NAB molecules. Negative of -800 mV, a 1-e(-) voltammetric reduction peak was observed, which was reversible on the positive voltage scan. This peak was accompanied by significant spectral changes, particularly the loss of the N=N and NO(2) stretches. The spectra are consistent with formation of a quinoid structure containing a C=C double bond between the NAB and the graphitic surface. The electron transfer and spectral changes occurred over a wider potential range than expected for a conventional Nernstian equilibrium, but did not appear to be broadened by slow electron-transfer kinetics. The results imply a significant perturbation of electron transfer between the GC and the monolayer, caused by strong electronic coupling between the graphitic pi system and the NAB orbitals. Rather than a discrete electron transfer to a free molecule, the electron transfer to chemisorbed NAB is more gradual, and is presumably driven by the electric field at the electrode/solution interface.

  19. Annealing effect on thermal conductivity and microhardness of carbon nanotube containing Se80Te16Cu4 glassy composites

    Science.gov (United States)

    Upadhyay, A. N.; Tiwari, R. S.; Singh, Kedar

    2018-02-01

    This study deals with the effect of thermal annealing on structural/microstructural, thermal and mechanical behavior of pristine Se80Te16Cu4 and carbon nanotubes (CNTs) containing Se80Te16Cu4 glassy composites. Pristine Se80Te16Cu4, 3 and 5 wt%CNTs-Se80Te16Cu4 glassy composites are annealed in the vicinity of glass transition temperature to onset crystallization temperature (340–380 K). X-ray diffraction (XRD) pattern revealed formation of polycrystalline phases of hexagonal CuSe and trigonal selenium. The indexed d-values in XRD patterns are in well conformity with the d-values obtained after the indexing of the ring pattern of selected area electron diffraction pattern of TEM images. The SEM investigation exhibited that the grain size of the CNTs containing Se80Te16Cu4 glassy composites increased with increasing annealing temperature and decreased at further higher annealing temperature. Thermal conductivity, microhardness exhibited a substantial increase with increasing annealing temperature of 340–360 K and slightly decreases for 380 K. The variation of thermal conductivity and microhardness can be explained by cross-linking formation and voids reduction.

  20. Electrochemical determination of serotonin in urine samples based on metal oxide nanoparticles/MWCNT on modified glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    Omolola E. Fayemi

    2017-04-01

    Full Text Available The electrochemical response of serotonin on the modified electrode based on multiwalled-carbon-nanotube (MWCNT doped respectively with nickel, zinc and iron oxide nanoparticles coating on glassy carbon electrode (GCE at physiological pH 7 was determined using cyclic voltammetry (CV and square wave voltammetry (SWV. The modified GCE/MWCNT-metal oxide electrodes exhibited excellent electrocatalytic activity towards the detection of serotonin at large peak current and lower oxidation potentials compared to other electrodes investigated. The dynamic range for the serotonin determination was between 5.98 × 10−3 μM to 62.8 μM with detection limits 118, 129 and 166 nM for GCE/MWCNT-NiO, GCE/MWCNT-ZnO and GCE/MWCNT-Fe3O4 sensors respectively. GCE-MWCNT-NiO was the best electrode in terms of serotonin current response, electrode stability, resistance to fouling and limit of detection towards the analyte. The developed sensors were found to be electrochemically stable, reusable, economically effective due to their extremely low operational cost, and have demonstrated good limit of detection, sensitivity and selectivity towards serotonin determination in urine samples. Keywords: Metal oxides nanoparticles, Multiwalled carbon nanotubes, Glassy carbon electrode, Serotonin, Cyclic voltammetry, Square wave voltammetry

  1. Electrochemical evaluation and determination of antiretroviral drug fosamprenavir using boron-doped diamond and glassy carbon electrodes.

    Science.gov (United States)

    Gumustas, Mehmet; Ozkan, Sibel A

    2010-05-01

    Fosamprenavir is a pro-drug of the antiretroviral protease inhibitor amprenavir and is oxidizable at solid electrodes. The anodic oxidation behavior of fosamprenavir was investigated using cyclic and linear sweep voltammetry at boron-doped diamond and glassy carbon electrodes. In cyclic voltammetry, depending on pH values, fosamprenavir showed one sharp irreversible oxidation peak or wave depending on the working electrode. The mechanism of the oxidation process was discussed. The voltammetric study of some model compounds allowed elucidation of the possible oxidation mechanism of fosamprenavir. The aim of this study was to determine fosamprenavir levels in pharmaceutical formulations and biological samples by means of electrochemical methods. Using the sharp oxidation response, two voltammetric methods were described for the determination of fosamprenavir by differential pulse and square-wave voltammetry at the boron-doped diamond and glassy carbon electrodes. These two voltammetric techniques are 0.1 M H(2)SO(4) and phosphate buffer at pH 2.0 which allow quantitation over a 4 x 10(-6) to 8 x 10(-5) M range using boron-doped diamond and a 1 x 10(-5) to 1 x 10(-4) M range using glassy carbon electrodes, respectively, in supporting electrolyte. All necessary validation parameters were investigated and calculated. These methods were successfully applied for the analysis of fosamprenavir pharmaceutical dosage forms, human serum and urine samples. The standard addition method was used in biological media using boron-doped diamond electrode. No electroactive interferences from the tablet excipients or endogenous substances from biological material were found. The results were statistically compared with those obtained through an established HPLC-UV technique; no significant differences were found between the voltammetric and HPLC methods.

  2. A 3D Microfluidic Chip for Electrochemical Detection of Hydrolysed Nucleic Bases by a Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Jana Vlachova

    2015-01-01

    Full Text Available Modification of carbon materials, especially graphene-based materials, has wide applications in electrochemical detection such as electrochemical lab-on-chip devices. A glassy carbon electrode (GCE modified with chemically alternated graphene oxide was used as a working electrode (glassy carbon modified by graphene oxide with sulphur containing compounds and Nafion for detection of nucleobases in hydrolysed samples (HCl pH = 2.9, 100 °C, 1 h, neutralization by NaOH. It was found out that modification, especially with trithiocyanuric acid, increased the sensitivity of detection in comparison with pure GCE. All processes were finally implemented in a microfluidic chip formed with a 3D printer by fused deposition modelling technology. As a material for chip fabrication, acrylonitrile butadiene styrene was chosen because of its mechanical and chemical stability. The chip contained the one chamber for the hydrolysis of the nucleic acid and another for the electrochemical detection by the modified GCE. This chamber was fabricated to allow for replacement of the GCE.

  3. A 3D microfluidic chip for electrochemical detection of hydrolysed nucleic bases by a modified glassy carbon electrode.

    Science.gov (United States)

    Vlachova, Jana; Tmejova, Katerina; Kopel, Pavel; Korabik, Maria; Zitka, Jan; Hynek, David; Kynicky, Jindrich; Adam, Vojtech; Kizek, Rene

    2015-01-22

    Modification of carbon materials, especially graphene-based materials, has wide applications in electrochemical detection such as electrochemical lab-on-chip devices. A glassy carbon electrode (GCE) modified with chemically alternated graphene oxide was used as a working electrode (glassy carbon modified by graphene oxide with sulphur containing compounds and Nafion) for detection of nucleobases in hydrolysed samples (HCl pH = 2.9, 100 °C, 1 h, neutralization by NaOH). It was found out that modification, especially with trithiocyanuric acid, increased the sensitivity of detection in comparison with pure GCE. All processes were finally implemented in a microfluidic chip formed with a 3D printer by fused deposition modelling technology. As a material for chip fabrication, acrylonitrile butadiene styrene was chosen because of its mechanical and chemical stability. The chip contained the one chamber for the hydrolysis of the nucleic acid and another for the electrochemical detection by the modified GCE. This chamber was fabricated to allow for replacement of the GCE.

  4. Multiwall carbon nanotube modified glassy carbon electrode as voltammetric sensor for the simultaneous determination of ascorbic acid and caffeine

    International Nuclear Information System (INIS)

    Gupta, Vinod Kumar; Jain, Ajay Kumar; Shoora, Sudhir Kumar

    2013-01-01

    Highlights: ► Performance of bare and modified GCE for the study of oxidation of drugs. ► MWCNT/MGCE used for determination of AA and CAF in various samples. ► It is demonstrated that the modified electrode is better than the bare GCE. ► AA and CAF are quantified in tea leaves, coffee, cold drink, urine samples. - Abstract: Simultaneous determination of ascorbic acid (AA) and caffeine (CAF) in pharmaceutical preparation is important and it has been achieved by square wave voltammetry (SWV) using a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT). The oxidation of AA and CAF at MWCNT occurred at ∼−10 mV and ∼1103 mV at a much lower potential, than that observed (∼202 mV and ∼1402 mV) for their oxidation at bare GCE. The mechanistic study has shown that the equal number of electrons and protons are involved in the oxidation of drugs. The electrodes could be used for the determination of AA and CAF in a wide concentration range 10–500 μM, respectively, whereas the detection limit has been found to be 1.0 × 10 −2 μM and 3.52 × 10 −3 μM respectively. In view of high sensitivity for the detection of the drugs, the technique has been used for the reliable determination of AA and CAF in tea leaves, coffee, cold drink (mountain dew), pharmaceutical preparations and urine samples

  5. A novel enzymatic glucose sensor based on Pt nanoparticles-decorated hollow carbon spheres-modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Luhana, Charles; Bo Xiangjie; Ju Jian; Guo Liping, E-mail: guolp078@nenu.edu.cn [Northeast Normal University, Faculty of Chemistry (China)

    2012-10-15

    A new glucose biosensor was developed based on hollow carbon spheres decorated with platinum nanoparticles (Pt/HCSs)-modified glassy carbon electrode immobilized with glucose oxidase (GOx) with the help of Nafion. The Pt nanoparticles were well dispersed on the HCSs with an average size of 2.29 nm. The detection of glucose was achieved via electrochemical detection of the enzymatically liberated H{sub 2}O{sub 2} at +0.5 V versus Ag/AgCl at physiologic pH of 7.4. The Pt/HCSs-modified electrode exhibited excellent electrocatalytic activities toward both the oxidation and reduction of H{sub 2}O{sub 2}. The glucose biosensor showed good electrocatalytic performance in terms of high sensitivity (4.1 {mu}A mM{sup -1}), low detection limit (1.8 {mu}M), fast response time <3 s, and wide linear range (0.04-8.62 mM). The apparent Michaelis-Menten constant (K{sub m}) and the maximum current density (i{sub max}) values for the biosensor were 10.94 mM and 887 {mu}A cm{sup -2} respectively. Furthermore, this biosensor showed an acceptable reproducibility and high stability. The interfering signals from ascorbic acid and uric acid at concentration levels normally found in human blood were not much compared with the response to glucose. Blood serum samples were also tested with this biosensor and a good recovery was achieved for the two spiked serum samples.

  6. Electrochemical detection of triclosan at a glassy carbon electrode modifies with carbon nanodots and chitosan

    International Nuclear Information System (INIS)

    Dai Hong; Xu Guifang; Gong Lingshan; Yang Caiping; Lin Yanyu; Tong Yuejin; Chen Jinghua; Chen Guonan

    2012-01-01

    Herein a conspicuously simple and sensitive electrochemical sensor based on nanocomposite architecture of the one-pot synthesized carbon nanodots (CNDs) and chitosan (CS) composite film was proposed for the determination of triclosan. The electrochemical response of triclosan was examined, demonstrated the irreversible electrochemical oxidation and one electron involved process of triclosan. Due to the good conductivity, large surface area and excellent electrochemical activity of CNDs, the CS and CNDs hybrid film extremely amplified the electrochemical response of triclosan, offering a highly sensitive electrochemical platform for triclosan detection. The detection limit of this electrochemical sensor for triclosan could be down to 9.2 nM. The as-proposed sensor presented high sensitivity, low detection limit, wide dynamic response range, excellent stability and reproducibility. This simple and sensitive electrochemical sensor is promising in developing the disposable sensor for environmental monitoring and food inspection.

  7. Fabrication of calix[4]pyrrole nanofilms at the glassy carbon surface and their characterization by spectroscopic, optic and electrochemical methods

    International Nuclear Information System (INIS)

    Taner, Bilge; Ozcan, Emine; Ustuendag, Zafer; Keskin, Selda; Solak, Ali Osman; Eksi, Haslet

    2010-01-01

    meso-Octamethylcalix[4]pyrrole (CP) and meso-heptaethylcalix[4]pyrrole-meso-4-aminophenyl (4APCP) modified glassy carbon (GC) electrodes were prepared by the electrochemical oxidation in acetonitrile solution. Binding of the calix[4]pyrroles with the glassy carbon surface was investigated that it is through the etheric linkage revealed from the reflection-absorption infrared spectroscopy (RAIRS). Surface films of CP and 4APCP were investigated by cyclic voltammetry (CV), ellipsometry, X-ray photoelectron spectroscopy, RAIRS and the contact angle measurements. The thicknesses of the films were determined by ellipsometry which confirmed that the film was multilayer and homogeneous over the surface. Ellipsometric measurements also provided that the CP and 4APCP film thicknesses were 2.49 nm and 4.58 nm for 6 CV cycle modification, corresponding to 66 μF/cm 2 and 106 μF/cm 2 capacitances obtained by CV. The wetting behavior was examined by contact angle measurements and found that the hydrophobicity of the GC-4APCP surface was higher than that of GC-CP, probably due to the aromatic meso substituent present in the former.

  8. Fabrication of calix[4]pyrrole nanofilms at the glassy carbon surface and their characterization by spectroscopic, optic and electrochemical methods

    Energy Technology Data Exchange (ETDEWEB)

    Taner, Bilge; Ozcan, Emine [Selcuk University, Faculty of Science, Dept. of Chemistry, Konya (Turkey); Ustuendag, Zafer [Dumlupinar University, Faculty of Arts and Sciences, Dept. of Chemistry, Kuetahya (Turkey); Keskin, Selda [Middle East Technical University, Central Research Laboratory, Ankara (Turkey); Solak, Ali Osman, E-mail: osolak@science.ankara.edu.t [Ankara University, Faculty of Science, Department of Chemistry, Ankara (Turkey); Eksi, Haslet [Ankara University, Faculty of Science, Department of Chemistry, Ankara (Turkey)

    2010-10-29

    meso-Octamethylcalix[4]pyrrole (CP) and meso-heptaethylcalix[4]pyrrole-meso-4-aminophenyl (4APCP) modified glassy carbon (GC) electrodes were prepared by the electrochemical oxidation in acetonitrile solution. Binding of the calix[4]pyrroles with the glassy carbon surface was investigated that it is through the etheric linkage revealed from the reflection-absorption infrared spectroscopy (RAIRS). Surface films of CP and 4APCP were investigated by cyclic voltammetry (CV), ellipsometry, X-ray photoelectron spectroscopy, RAIRS and the contact angle measurements. The thicknesses of the films were determined by ellipsometry which confirmed that the film was multilayer and homogeneous over the surface. Ellipsometric measurements also provided that the CP and 4APCP film thicknesses were 2.49 nm and 4.58 nm for 6 CV cycle modification, corresponding to 66 {mu}F/cm{sup 2} and 106 {mu}F/cm{sup 2} capacitances obtained by CV. The wetting behavior was examined by contact angle measurements and found that the hydrophobicity of the GC-4APCP surface was higher than that of GC-CP, probably due to the aromatic meso substituent present in the former.

  9. An Easily Fabricated Electrochemical Sensor Based on a Graphene-Modified Glassy Carbon Electrode for Determination of Octopamine and Tyramine

    Science.gov (United States)

    Zhang, Yang; Zhang, Meiqin; Wei, Qianhui; Gao, Yongjie; Guo, Lijuan; Al-Ghanim, Khalid A.; Mahboob, Shahid; Zhang, Xueji

    2016-01-01

    A simple electrochemical sensor has been developed for highly sensitive detection of octopamine and tyramine by electrodepositing reduced graphene oxide (ERGO) nanosheets onto the surface of a glassy carbon electrode (GCE). The electrocatalytic oxidation of octopamine and tyramine is individually investigated at the surface of the ERGO modified glassy carbon electrode (ERGO/GCE) by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Several essential factors including the deposition cycle of reduced graphene oxide nanosheets and the pH of the running buffer were investigated in order to determine the optimum conditions. Furthermore, the sensor was applied to the quantification of octopamine and tyramine by DPV in the concentration ranges from 0.5 to 40 μM and 0.1 to 25 μM, respectively. In addition, the limits of detection of octopamine and tyramine were calculated to be 0.1 μM and 0.03 μM (S/N = 3), respectively. The sensor showed good reproducibility, selectivity and stability. Finally, the sensor successfully detected octopamine and tyramine in commercially available beer with satisfactory recovery ranges which were 98.5%–104.7% and 102.2%–103.1%, respectively. These results indicate the ERGO/GCE based sensor is suitable for the detection of octopamine and tyramine. PMID:27089341

  10. Highly Stable Glassy Carbon Interfaces for Long-Term Neural Stimulation and Low-Noise Recording of Brain Activity

    Science.gov (United States)

    Vomero, Maria; Castagnola, Elisa; Ciarpella, Francesca; Maggiolini, Emma; Goshi, Noah; Zucchini, Elena; Carli, Stefano; Fadiga, Luciano; Kassegne, Sam; Ricci, Davide

    2017-01-01

    We report on the superior electrochemical properties, in-vivo performance and long term stability under electrical stimulation of a new electrode material fabricated from lithographically patterned glassy carbon. For a direct comparison with conventional metal electrodes, similar ultra-flexible, micro-electrocorticography (μ-ECoG) arrays with platinum (Pt) or glassy carbon (GC) electrodes were manufactured. The GC microelectrodes have more than 70% wider electrochemical window and 70% higher CTC (charge transfer capacity) than Pt microelectrodes of similar geometry. Moreover, we demonstrate that the GC microelectrodes can withstand at least 5 million pulses at 0.45 mC/cm2 charge density with less than 7.5% impedance change, while the Pt microelectrodes delaminated after 1 million pulses. Additionally, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) was selectively electrodeposited on both sets of devices to specifically reduce their impedances for smaller diameters (<60 μm). We observed that PEDOT-PSS adhered significantly better to GC than Pt, and allowed drastic reduction of electrode size while maintaining same amount of delivered current. The electrode arrays biocompatibility was demonstrated through in-vitro cell viability experiments, while acute in vivo characterization was performed in rats and showed that GC microelectrode arrays recorded somatosensory evoked potentials (SEP) with an almost twice SNR (signal-to-noise ratio) when compared to the Pt ones.

  11. Operation of low-energy ion implanters for Si, N, C ion implantation into silicon and glassy carbon

    International Nuclear Information System (INIS)

    Carder, D.A.; Markwitz, A.

    2009-01-01

    This report details the operation of the low-energy ion implanters at GNS Science for C, N and Si implantations. Two implanters are presented, from a description of the components through to instructions for operation. Historically the implanters have been identified with the labels 'industrial' and 'experimental'. However, the machines only differ significantly in the species of ions available for implantation and sample temperature during implantation. Both machines have been custom designed for research purposes, with a wide range of ion species available for ion implantation and the ability to implant two ions into the same sample at the same time from two different ion sources. A fast sample transfer capability and homogenous scanning profiles are featured in both cases. Samples up to 13 mm 2 can be implanted, with the ability to implant at temperatures down to liquid nitrogen temperatures. The implanters have been used to implant 28 Si + , 14 N + and 12 C + into silicon and glassy carbon substrates. Rutherford backscattering spectroscopy has been used to analyse the implanted material. From the data a Si 30 C 61 N 9 layer was measured extending from the surface to a depth of about 77 ± 2 nm for (100) silicon implanted with 12 C + and 14 N + at multiple energies. Silicon and nitrogen ion implantation into glassy carbon produced a Si (40.5 %), C (38 %), N (19.5 %) and O (2%) layer centred around a depth of 50 ± 2 nm from the surface. (author). 8 refs., 20 figs

  12. Differential pulse anodic voltammetric determination of pantoprazole in pharmaceutical dosage forms and human plasma using glassy carbon electrode.

    Science.gov (United States)

    Erk, Nevin

    2003-12-01

    Pantoprazole is used as an anti-ulcer drug through inhibition of H(+), K(+)-adenosine 5(')-triphosphatase in gastric parietal cells. It reduces the gastric acid secretion regardless of the nature of stimulation. The use of differential pulse voltammetry for the determination of pantoprazole in pharmaceutical dosage forms and human plasma using a glassy carbon electrode has been examined. The best voltammetric response was reached for a glassy carbon electrode in Britton-Robinson buffer solution of pH 5.0 submitted to a scan rate of 20.0 mVs(-1) and a pulse amplitude of 50.0 mV. This electroanalytical procedure was able to determine pantoprazole in the concentration range 6.0 x 10(-6)-8.0 x 10(-4)M. Precision and accuracy of the developed method was checked with recovery studies. The limit of detection and limit of quantitation were found to be 4.0 x 10(-7) and 9.0 x 10(-7)M, respectively. Rapidity, precision, and good selectivity were also found for the determination of pantoprazole in pharmaceutical dosage forms and human plasma. For comparative purposes high-performance liquid chromatography with a diode array and UV/VIS detection at 290.0 nm determination also was developed.

  13. Glassy carbon electrode modified with poly(taurine/TiO2-graphene composite film for determination of acetaminophen and caffeine

    Directory of Open Access Journals (Sweden)

    Xiong Xiao-Qin

    2013-01-01

    Full Text Available A novel electrochemical sensor poly(taurine/TiO2-graphene nanocomposite modified glassy carbon electrode (PT/TiO2-Gr/GCE was fabricated. This sensor was based on an electrochemically polymerized taurine layer on a TiO2-graphene modified glassy carbon electrode. The electrochemical behaviors of acetaminophen and caffeine at the modified electrode were studied by cyclic voltammetry and differential pulse voltammetry. The results showed that the oxidation peak currents of acetaminophen and caffeine were linear with their concentrations in the range of 1×10-7-9×10-5 M and 2.5×10-5-2×10-4 M, respectively. The detection limits of acetaminophen and caffeine were 3.4×10-8 M and 5.0×10-7 M, respectively (S/N=3. This modified electrode showed good sensitivity and stability, which had promising potential applications in electrochemical sensors and biosensors design.

  14. Photogeneration of singlet oxygen by the phenothiazine derivatives covalently bound to the surface-modified glassy carbon

    Energy Technology Data Exchange (ETDEWEB)

    Blacha-Grzechnik, Agata, E-mail: agata.blacha@polsl.pl [Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice (Poland); Piwowar, Katarzyna; Krukiewicz, Katarzyna [Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice (Poland); Koscielniak, Piotr; Szuber, Jacek [Institute of Electronics, Silesian University of Technology, Akademicka 16, 44-100 Gliwice (Poland); Zak, Jerzy K. [Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice (Poland)

    2016-05-15

    Highlights: • The selected group of four NH{sub 2}-derivatives of phenothiazine was grafted to Glassy Carbon (GC) surface. • The grafted phenothiazines are able to generate {sup 1}O{sub 2} when activated by the radiation. • Such modified solid surfaces may find their application in the wastewater treatment. - Abstract: The selected group of four amine-derivatives of phenothiazine was covalently grafted to the glassy carbon surface in the four-step procedure consisting of the electrochemical reduction of the diazonium salt followed by the electrochemical and chemical post-modification steps. The proposed strategy involves the bonding of linker molecule to which the photosensitizer is attached. The synthesized organic layers were characterized by means of cyclic voltammetry, XPS and Raman Spectroscopy. It was shown that the phenothiazines immobilized via proposed strategy retain their photochemical properties and are able to generate {sup 1}O{sub 2} when activated by the laser radiation. The effectiveness of in situ singlet oxygen generation by those new solid photoactive materials was determined by means of UVVis spectroscopy. The reported, covalently modified solid surfaces may find their application as the singlet oxygen photogenerators in the fine chemicals’ synthesis or in the wastewater treatment.

  15. Immobilization of Nafion-ordered mesoporous carbon on a glassy carbon electrode: Application to the detection of epinephrine

    Energy Technology Data Exchange (ETDEWEB)

    Zhou Ming [Faculty of Chemistry, Northeast Normal University, Renmin Street 5268, Changchun 130024 (China); Guo Liping [Faculty of Chemistry, Northeast Normal University, Renmin Street 5268, Changchun 130024 (China)], E-mail: guolp078@nenu.edu.cn; Hou Ying; Peng Xiaojuan [Faculty of Chemistry, Northeast Normal University, Renmin Street 5268, Changchun 130024 (China)

    2008-05-01

    A stable suspension of ordered mesoporous carbon (OMC) was obtained by dispersing OMC in a solution of Nafion. By coating the suspension onto glassy carbon (GC) electrode, cyclic voltammetry was used to evaluate the electrochemical behaviors of Nafion-OMC-modified GC (Nafion-OMC/GC) electrode in 0.1 mmol L{sup -1} hexaammineruthenium(III) chloride (Ru(NH{sub 3}){sub 6}Cl{sub 3})/0.1 mol L{sup -1} KCl solution, where Nafion-OMC/GC electrode shows a faster electron transfer rate as compared with OMC/GC, Nafion/GC and GC electrodes. Due to the unique properties of Nafion-OMC, an obvious decrease in the overvoltage of the epinephrine (EP) oxidation (ca. 100 mV at pH 4.1 and 115 mV at pH 7.0) as well as a dramatic increase in the peak current (12 times at pH 4.1 and 6 times at pH 7.0) was observed at Nafion-OMC/GC electrode compared to that seen at GC electrode. By combining the advantages of OMC with those of Nafion, the anodic peak of EP and that of ascorbic acid (AA) were separated successfully (by ca. 144-270 mV) in the pH range of 2.0-10.0, which may make Nafion-OMC/GC electrode potential for selective determination of EP in the presence of AA at a broad pH range. As an EP sensor, the EP amperometric response at Nafion-OMC/GC electrode in pH 7.0 PBS is extremely stable, with 99% of the initial activity remaining (compared to 32% at GC surface) after 120 min stirring of 0.20 mmol L{sup -1} EP. And Nafion-OMC/GC electrode can be used to readily detect the physiological concentration of EP at pH 7.0. These make Nafion-OMC/GC electrode potential candidates for stable and efficient electrochemical sensor for the detection of EP. The solubilization of OMC by Nafion may provide a route to more precise manipulation, and functionalization for the construction of OMC-based sensors, as well as allowing OMC to be introduced to biologically relevant systems.

  16. Immobilization of Nafion-ordered mesoporous carbon on a glassy carbon electrode: Application to the detection of epinephrine

    International Nuclear Information System (INIS)

    Zhou Ming; Guo Liping; Hou Ying; Peng Xiaojuan

    2008-01-01

    A stable suspension of ordered mesoporous carbon (OMC) was obtained by dispersing OMC in a solution of Nafion. By coating the suspension onto glassy carbon (GC) electrode, cyclic voltammetry was used to evaluate the electrochemical behaviors of Nafion-OMC-modified GC (Nafion-OMC/GC) electrode in 0.1 mmol L -1 hexaammineruthenium(III) chloride (Ru(NH 3 ) 6 Cl 3 )/0.1 mol L -1 KCl solution, where Nafion-OMC/GC electrode shows a faster electron transfer rate as compared with OMC/GC, Nafion/GC and GC electrodes. Due to the unique properties of Nafion-OMC, an obvious decrease in the overvoltage of the epinephrine (EP) oxidation (ca. 100 mV at pH 4.1 and 115 mV at pH 7.0) as well as a dramatic increase in the peak current (12 times at pH 4.1 and 6 times at pH 7.0) was observed at Nafion-OMC/GC electrode compared to that seen at GC electrode. By combining the advantages of OMC with those of Nafion, the anodic peak of EP and that of ascorbic acid (AA) were separated successfully (by ca. 144-270 mV) in the pH range of 2.0-10.0, which may make Nafion-OMC/GC electrode potential for selective determination of EP in the presence of AA at a broad pH range. As an EP sensor, the EP amperometric response at Nafion-OMC/GC electrode in pH 7.0 PBS is extremely stable, with 99% of the initial activity remaining (compared to 32% at GC surface) after 120 min stirring of 0.20 mmol L -1 EP. And Nafion-OMC/GC electrode can be used to readily detect the physiological concentration of EP at pH 7.0. These make Nafion-OMC/GC electrode potential candidates for stable and efficient electrochemical sensor for the detection of EP. The solubilization of OMC by Nafion may provide a route to more precise manipulation, and functionalization for the construction of OMC-based sensors, as well as allowing OMC to be introduced to biologically relevant systems

  17. The redox thermodynamics and kinetics of flavonoid rutin adsorbed at glassy carbon electrodes by stripping square wave voltammetry

    Energy Technology Data Exchange (ETDEWEB)

    Aragao Catunda, Francisco Eduardo; Araujo, Marcelo Francisco de [Departamento de Quimica, Instituto de Ciencias Exactas, Universidad Federal Rural do Rio de Janeiro, BR 465 KM 07, 23890-000, Seropedica, RJ (Brazil); Granero, Adrian Marcelo; Arevalo, Fernando Javier [Departamento de Quimica, Facultad de Ciencias Exactas, Fisico-Quimicas y Naturales, Universidad Nacional de Rio Cuarto, Agencia Postal No 3 - (5800), Rio Cuarto (Argentina); Carvalho, Mario Geraldo de [Departamento de Quimica, Instituto de Ciencias Exactas, Universidad Federal Rural do Rio de Janeiro, BR 465 KM 07, 23890-000, Seropedica, RJ (Brazil); Zon, Maria Alicia, E-mail: azon@exa.unrc.edu.ar [Departamento de Quimica, Facultad de Ciencias Exactas, Fisico-Quimicas y Naturales, Universidad Nacional de Rio Cuarto, Agencia Postal No 3 - (5800), Rio Cuarto (Argentina); Fernandez, Hector, E-mail: hfernandez@exa.unrc.edu.ar [Departamento de Quimica, Facultad de Ciencias Exactas, Fisico-Quimicas y Naturales, Universidad Nacional de Rio Cuarto, Agencia Postal No 3 - (5800), Rio Cuarto (Argentina)

    2011-11-30

    Highlights: > Adsorptive accumulation of rutin is studied at glassy carbon (GC) electrodes. > The Frumkin adsorption isotherm described the specific interaction. > Gibbs free energy of adsorption and the interaction parameter were determined. > Thermodynamics and kinetics of the surface redox process were characterized by SWV. > Detection limit for rutin was 2 x 10{sup -8} mol dm{sup -3} (12 ppb). - Abstract: The adsorptive accumulation of rutin (RU) at glassy carbon (GC) electrodes in 10% ethanol + 90% 1 mol dm{sup -3} HClO{sub 4} aqueous solution is studied by using cyclic (CV) and square wave (SWV) voltammetries. The Frumkin adsorption isotherm best described the specific interaction of rutin with carbon electrodes. By fitting the experimental data, values of -31.9 kJ mol{sup -1} and 0.54 {+-} 0.02 were obtained for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the surface redox process, using a combination of the 'quasi-reversible maximum' and the 'splitting of SW peaks' methods. Average values of 0.644 {+-} 0.003 V and 0.44 {+-} 0.02 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 6.1 x 10{sup 2} s{sup -1} was obtained. SWV was also employed to generate calibration curves. The lowest concentration of RU experimentally measured for a signal-to-noise ratio of 3:1 was 2 x 10{sup -8} mol dm{sup -3} (12 ppb).

  18. Layer by layer assembly of glucose oxidase and thiourea onto glassy carbon electrode: Fabrication of glucose biosensor

    Energy Technology Data Exchange (ETDEWEB)

    Salimi, Abdollah, E-mail: absalimi@yahoo.com [Department of Chemistry, University of Kurdistsn, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Research Center for Nanotechnology, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Noorbakhsh, Abdollah [Department of Chemistry, University of Kurdistsn, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Department of Nanotechnology Engenering, Faculty of Advanced Science and Technology, University of Isfahan, 81746-73441 (Iran, Islamic Republic of)

    2011-07-01

    Highlights: > Although various enzymes immobilization have been approve for the construction of glucose biosensor, a layer by layer (LBL) technique has attracted more attention due to simplicity of the procedure, wide choice of materials that can be used, controllability of film thickness and unique mechanical properties. > In this paper, we described a novel and simple strategy for developing an amperometric glucose biosensor based on layer-by-layer self assembly of glucose oxidase on the glassy carbon electrode modified by thiourea. > Thiourea has two amino groups that the one can be immobilized on the activated glassy carbon electrode and the other can be used for the coupling of glucose oxidase enzyme. > The biosensor exhibited good performance for electrocatalytic oxidation of glucose, such as high sensitivity, low detection limit, short response time and wide concentration range. > Finally, the new method is strongly recommended for immobilization of many other enzymes or proteins containing carbaldehyde or carboxylic groups for fabricating third generation biosensors and bioelectronics devices. - Abstract: For the first time a novel, simple and facile approach is described to construct highly stable glucose oxidase (GOx) multilayer onto glassy carbon (GC) electrode using thiourea (TU) as a covalent attachment cross-linker. The layer by layer (LBL) attachment process was confirmed by cyclic voltammetry, electrochemical impedance spectroscopy and Fourier transform infrared reflection spectroscopy (FT-IR-RS) techniques. Immobilized GOx shows excellent electrocatalytic activity toward glucose oxidation using ferrocenemethanol as artificial electron transfer mediator and biosensor response was directly correlated to the number of bilayers. The surface coverage of active GOx per bilayer, heterogeneous electron transfer rate constant (k{sub s}) and Michaelis-Menten constant (K{sub M}), of immobilized GOx were 1.50 x 10{sup -12} mol cm{sup -2}, 9.2 {+-} 0.5 s{sup -1

  19. Modification of glassy carbon electrode with a polymer/mediator composite and its application for the electrochemical detection of iodate

    International Nuclear Information System (INIS)

    Li, Ta-Jen; Lin, Chia-Yu; Balamurugan, A.; Kung, Chung-Wei; Wang, Jen-Yuan; Hu, Chih-Wei; Wang, Chun-Chieh; Chen, Po-Yen; Vittal, R.; Ho, Kuo-Chuan

    2012-01-01

    Highlights: ► FAD and PEDOT are combined to modify the glassy carbon electrode for IO 3 − sensing. ► The doping of FAD into PEDOT matrix can almost be viewed as an irreversible process. ► The optimal cycle number for preparing the GCE/PEDOT/FAD electrode is found to be 9. ► The detection limit of the GCE/PEDOT/FAD electrode for IO 3 − is found to be 0.16 μM. ► The GCE/PEDOT/FAD electrode possesses enough selectivity toward IO 3 − . - Abstract: A modified glassy carbon electrode was prepared by depositing a composite of polymer and mediator on a glassy carbon electrode (GCE). The mediator, flavin adenine dinucleotide (FAD) and the polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) were electrochemically deposited as a composite on the GCE by applying cyclic voltammetry (CV). This modified electrode is hereafter designated as GCE/PEDOT/FAD. FAD was found to significantly enhance the growth of PEDOT. Electrochemical quartz crystal microbalance (EQCM) analysis was performed to study the mass changes in the electrode during the electrodeposition of PEDOT, with and without the addition of FAD. The optimal cycle number for preparing the modified electrode was determined to be 9, and the corresponding surface coverage of FAD (Γ FAD ) was ca. 5.11 × 10 −10 mol cm −2 . The amperometric detection of iodate was performed in a 100 mM buffer solution (pH 1.5). The GCE/PEDOT/FAD showed a sensitivity of 0.78 μA μM −1 cm −2 , a linear range of 4–140 μM, and a limit of detection of 0.16 μM for iodate. The interference effects of 250-fold Na + , Mg 2+ , Ca 2+ , Zn 2+ , Fe 2+ , Cl − , NO 3 − , I − , SO 4 2− and SO 3 2− , with reference to the concentration of iodate were negligible. The long-term stability of GCE/PEDOT/FAD was also investigated. The GCE/PEDOT/FAD electrode retained 82% of its initial amperometric response to iodate after 7 days. The GCE/PEDOT/FAD was also applied to determine iodate in a commercial salt.

  20. Poly(BCB)/Au-nanoparticles hybrid film modified electrode: Preparation, characterization and its application as a non-enzymatic sensor

    International Nuclear Information System (INIS)

    Kumar, S. Ashok; Wang, Sea-Fue; Chang, Yu-Tsern

    2010-01-01

    We report electrochemical preparation and characterization of poly-brilliant cresyl blue (Poly(BCB))/gold nanoparticles (Au-NPs) modified electrode. The Poly(BCB)/Au-NPs modified electrode has been used as an electrochemical sensor for the detection of hydrogen peroxide (H 2 O 2 ) at lower potential (- 0.2 V). The Poly(BCB)/Au-NPs film was characterized by scanning electron microscopy, Uv-visible spectroscopy (Uv-vis) and cyclic voltammetry. We have observed that, Au-NPs attached glassy carbon electrode (Au-NPs/GCE) significantly enhanced the polymerization of BCB compared to bare GCE. The Poly(BCB) film was irreversibly attached onto the Au-NPs modified electrode, the resulting hybrid film modified electrode was electrochemically active in the pH range from 2 to 11. Attachment of Poly(BCB)/Au-NPs hybrid film on the electrode surface was confirmed by Uv-vis spectra. In addition, electrocatalytic properties of the Poly(BCB)/Au-NPs/GCE towards reduction of H 2 O 2 have been investigated, and it was found that the sensitivity, reduction potential as well as the corresponding detection limit were improved as compared to the voltammetric response of the Poly(BCB)/GCE and Au-NPs/GCE. Based on this study, a non-enzymatic electrochemical sensor for the determination of H 2 O 2 has been reported. Moreover, analysis of commercial H 2 O 2 samples was performed using the proposed method and satisfactory results were obtained.

  1. EIS study of the redox reaction of Fe(CN)63-/4- at glassy carbon electrode via diazonium reduction in aqueous and acetonitrile solutions

    Energy Technology Data Exchange (ETDEWEB)

    Khoshroo, M.; Rostami, A. [Mazandaran Univ., Babolsar (Iran, Islamic Republic of). Dept. of Physical Chemistry

    2008-07-01

    This paper reported on a study that characterized soluble electroactive species by cyclic voltammetry to investigate the presence of grafted films and their blocking properties. In particular, the authority of the glassy carbon electrode modification conditions on the cyclic voltammetric response of Fe(CN)63-/4- oxido-reduction was examined for 2 layers grafted by electrochemical reduction of diazonium salts in acetonitrile and aqueous solutions. PAA and Fast Black K modified glassy carbon electrodes exhibited a significant blocking behaviour for oxidation and reduction reactions of the Fe(CN)63-/4- redox system in aqueous and acetonitrile solutions. The study showed that the blocking effect increased which changes in time and concentration of diazonium salts in acetonitrile solution. Electrochemical impedance spectroscopy (EIS) measurements showed that the physical barrier of grafted layers prevent the access of Fe(CN)63-/4- to the underlying glassy carbon electrode. Therefore the RCT resistance increases during the modification treatment. The substituted phenyl layers are much more compact and less permeable in a nonaqueous solvent than with an aqueous solvent. Electrochemical impedance measurements indicate that the kinetics of electron transfer slow down when the time and the concentration used to modify the glassy carbon electrode increase. 4 refs., 1 fig.

  2. A study on electrochemical redox behavior of nitric acid by using a glassy carbon fiber column electrode system

    International Nuclear Information System (INIS)

    Kim, K. W.; Song, K. C.; Lee, I. H.; Choi, I. K.; You, J. H.

    1999-01-01

    Electrochemical redox behaviors of nitric acid were studied by using a glassy carbon fiber column electrode system, and its reaction mechanism was analyzed in several ways. The electrochemical reaction in less than 2.0 M nitric acid was not observed, but in more than 2.0 M nitric acid, the reduction rate of nitric acid to produce nitrous acid was slow so that the nitric acid solution had to be contacted with electrode enough in order for a apparent reduction current of nitric acid to nitrous acid be to observed. The nitrous acid generated in more than 2.0 M nitric acid was rapidly and easily reduced to NOx through an autocatalytic reaction. Sulfamic acid was confirmed to be effective to destroy the nitrous acid. The sulfamic acid of at least 0.05M was necessary to remove the nitrous acid generated in 3.5 M nitric acid

  3. A glassy carbon electrode modified with graphene oxide and silver nanoparticles for amperometric determination of hydrogen peroxide

    International Nuclear Information System (INIS)

    Noor, An’amt Mohamed; Shahid, Muhammad Mehmood; Rameshkumar, Perumal; Huang, Nay Ming

    2016-01-01

    The article describes a glassy carbon electrode (GCE) modified with a nanocomposite consisting of graphene oxide and silver nanoparticles, and its application to amperometric determination of hydrogen peroxide (H 2 O 2 ). Cyclic voltammetry with this modified electrode reveals efficient electrocatalytic reduction of H 2 O 2 . The response to H 2 O 2 at a working potential of −0.3 V (vs. Ag/AgCl) is linear in the 100 μM to 11 mM concentration range at pH 7.2. The limit of detection is 28.3 μM (at an S/N ratio of 3). Good selectivity is observed over physiological interferents such as dopamine, ascorbic acid, uric acid and glucose. (author)

  4. A highly sensitive hydrogen peroxide sensor based on (Ag-Au NPs)/poly[o-phenylenediamine] modified glassy carbon electrode.

    Science.gov (United States)

    Shamsipur, Mojtaba; Karimi, Ziba; Amouzadeh Tabrizi, Mahmoud

    2015-11-01

    Herein, the poly(o-phenylenediamine) decorated with gold-silver nanoparticle (Ag-Au NPs) nanocomposite modified glassy carbon was used for the determination of hydrogen peroxide. Electrochemical experiments indicated that the proposed sensor possesses an excellent sensitivity toward the reduction of hydrogen peroxide. The resulting sensor exhibited a good response to hydrogen peroxide over linear range from 0.2 to 60.0μM with a limit of detection of 0.08μM, good reproducibility, long-term stability and negligible interference from ascorbic acid, uric acid and dopamine. The proposed sensor was successfully applied to the determination of hydrogen peroxide in human serum sample. Copyright © 2015 Elsevier B.V. All rights reserved.

  5. Detection of Guanine and Adenine Using an Aminated Reduced Graphene Oxide Functional Membrane-Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Di Li

    2017-07-01

    Full Text Available A new electrochemical sensor based on a Nafion, aminated reduced graphene oxide and chitosan functional membrane-modified glassy carbon electrode was proposed for the simultaneous detection of adenine and guanine. Fourier transform-infrared spectrometry (FTIR, transmission electron microscopy (TEM, and electrochemical methods were utilized for the additional characterization of the membrane materials. The prepared electrode was utilized for the detection of guanine (G and adenine (A. The anodic peak currents to G and A were linear in the concentrations ranging from 0.1 to 120 μM and 0.2 to 110 μM, respectively. The detection limits were found to be 0.1 μM and 0.2 μM, respectively. Moreover, the modified electrode could also be used to determine G and A in calf thymus DNA.

  6. Sensitive electrochemical sensor of tryptophan based on Ag-C core–shell nanocomposite modified glassy carbon electrode

    International Nuclear Information System (INIS)

    Mao Shuxian; Li Weifeng; Long Yumei; Tu Yifeng; Deng, Anping

    2012-01-01

    Graphical abstract: Ag-C and Colloidal carbon sphere modified glassy carbon electrodes were prepared. It was clear that the Ag-C/GCE exhibited enhanced electrocatalytic activity towards Trp, which could result from the synergistic effect between Ag core and carbon shell. The Ag-C/GCE showed excellent analytical properties in the determination of Trp. Highlights: ► The electrochemical behavior of Ag-C core–shell nanocomposite was firstly proposed. ► Ag-C/GC electrode exhibited favorable electrocatalytic properties towards Trp. ► The good electrocatalysis was due to the synergistic effect of Ag-core and C-shell. ► The Ag-C/GC electrode displayed excellent analytical properties in determining Trp. - Abstract: We here reported a simple electrochemical method for the detection of tryptophan (Trp) based on the Ag-C modified glassy carbon (Ag-C/GC) electrode. The Ag-C core–shell structured nanoparticles were synthesized using one-pot hydrothermal method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier transform-infrared spectroscopy (FTIR). The electrochemical behaviors of Trp on Ag-C/GC electrode were investigated and exhibited a direct electrochemical process. The favorable electrochemical properties of Ag-C/GC electrode were attributed to the synergistic effect of the Ag core and carbon shell. The carbon shell cannot only protect Ag core but also contribute to the enhanced substrate accessibility and Trp-substrate interactions, while nano-Ag core can display good electrocatalytic activity to Trp at the same time. Under the optimum experimental conditions the oxidation peak current was linearly dependent on the Trp concentration in the range of 1.0 × 10 −7 to 1.0 × 10 −4 M with a detection limit of 4.0 × 10 −8 M (S/N = 3). In addition, the proposed electrode was applied for the determination of Trp concentration in real samples and satisfactory results were obtained. The technique offers

  7. Electrocatalytical oxidation and sensitive determination of acetaminophen on glassy carbon electrode modified with graphene–chitosan composite

    International Nuclear Information System (INIS)

    Zheng, Meixia; Gao, Feng; Wang, Qingxiang; Cai, Xili; Jiang, Shulian; Huang, Lizhang; Gao, Fei

    2013-01-01

    The electrochemical behaviors of acetaminophen (ACOP) on a graphene–chitosan (GR–CS) nanocomposite modified glassy carbon electrode (GCE) were investigated by cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Electrochemical characterization showed that the GR–CS nanocomposite had excellent electrocatalytic activity and surface area effect. As compared with bare GCE, the redox signal of ACOP on GR–CS/GCE was greatly enhanced. The values of electron transfer rate constant (k s ), diffusion coefficient (D) and the surface adsorption amount (Γ ⁎ ) of ACOP on GR–CS/GCE were determined to be 0.25 s −1 , 3.61 × 10 −5 cm 2 s −1 and 1.09 × 10 −9 mol cm −2 , respectively. Additionally, a 2e − /2H + electrochemical reaction mechanism of ACOP was deduced based on the acidity experiment. Under the optimized conditions, the ACOP could be quantified in the range from 1.0 × 10 −6 to 1.0 × 10 −4 M with a low detection limit of 3.0 × 10 −7 M based on 3S/N. The interference and recovery experiments further showed that the proposed method is acceptable for the determination of ACOP in real pharmaceutical preparations. Highlights: ► A chitosan–graphene nanocomposite modified glassy carbon electrode was prepared. ► The modified electrode was electrochemically characterized by CV and EIS. ► Electro-oxidation of acetaminophen was examined on the modified electrode. ► Sensing analysis of the modified electrode toward acetaminophen was studied

  8. Functionalization of glassy carbon surface by means of aliphatic and aromatic amino acids. An experimental and theoretical integrated approach

    International Nuclear Information System (INIS)

    Vanossi, Davide; Benassi, Rois; Parenti, Francesca; Tassinari, Francesco; Giovanardi, Roberto; Florini, Nicola; De Renzi, Valentina; Arnaud, Gaelle; Fontanesi, Claudio

    2012-01-01

    Highlights: ► Glassy carbon is functionalized via electrochemical assisted grafting of amino acids. ► The grafting mechanism is suggested to involve the “zwitterionic” species. ► DFT calculations allowed to determine the electroactive species. ► An original grafting mechanism is proposed. - Abstract: Glassy carbon (GC) electrode surfaces are functionalized through electrochemical assisted grafting, in oxidation regime, of six amino acids (AA): β-alanine (β-Ala), L-aspartic acid (Asp), 11-aminoundecanoic acid (UA), 4-aminobenzoic acid (PABA), 4-(4-amino-phenyl)-butyric acid (PFB), 3-(4-amino-phenyl)-propionic acid (PFP). Thus, a GC/AA interface is produced featuring carboxylic groups facing the solution. Electrochemical (cyclic voltammetry and electrochemical impedance spectroscopy) and XPS techniques are used to experimentally characterize the grafting process and the surface state. The theoretical results are compared with the experimental evidence to determine, at a molecular level, the overall grafting mechanism. Ionization potentials, standard oxidation potentials, HOMO and electron spin distributions are calculated at the CCD/6-31G* level of the theory. The comparison of experimental and theoretical data suggests that the main electroactive species is the “zwitterionic” form for the three aliphatic amino acids, while the amino acids featuring the amino group bound to the phenyl aromatic moiety show a different behaviour. The comparison between experimental and theoretical results suggests that both the neutral and the zwitterionic forms are present in the acetonitrile solution in the case of 4-(4-amino-phenyl)-butyric acid (PFB) and 3-(4-amino-phenyl)-propionic acid.

  9. A simple and sensitive method for the determination of 4-n-octylphenol based on multi-walled carbon nanotubes modified glassy carbon electrode.

    Science.gov (United States)

    Zheng, Qiaoli; Yang, Ping; Xu, He; Liu, Jianshe; Jin, Litong

    2012-01-01

    A simple and sensitive electroanalytical method was presented for the determination of 4-n-octylphenol (OP) based on multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE). OP was directly oxidized on the MWCNTs/GCE, and the electrochemical oxidation mechanism was demonstrated by a one-electron and one-proton process in the reaction. The oxidation peak current of OP was significantly enhanced by the use of MWCNTs/GCE compared with those of bare glassy carbon electrode, suggesting that the modified electrode can remarkably improve the performance for OP determination. Factors influencing the detection processes were optimized. Under these optimal conditions, a linear relationship between concentration of OP and current response was obtained in the range of 5 x 10(-8) to 1 x 10(-5) mol/L with a detection limit of 1.5 x 10(-8) mol/L and correlation coefficient 0.9986. The modified electrode showed good selectivity, sensitivity, reproducibility and high stability.

  10. Adsorptive stripping voltammetry for simultaneous determination of hydrochlorothiazide and triamterene in hemodialysis samples using a multi-walled carbon nanotube-modified glassy carbon electrode.

    Science.gov (United States)

    Hudari, Felipe Fantinato; Souza, João Carlos; Zanoni, Maria Valnice Boldrin

    2018-03-01

    Hemodialysis is the most commonly used method for the treatment of chronic kidney disease. In this procedure, some patients use diuretics to control weight gain and blood pressure. In this work, a voltammetric sensor based on a glassy carbon electrode modified with carbon nanotubes (GCE/MWCNT) is described for the simultaneous determination of the diuretics hydrochlorothiazide (HCT) and triamterene (TRT). The oxidation of the diuretics on the GCE/MWCNT surface was observed at 1.01 and 1.17V for HCT and TRT, respectively, allowing simultaneous determination, which was not possible with the unmodified glassy carbon electrode. The GCE/MWCNT electrode provided 6-fold and 10-fold gains in anode peak intensity for HCT and TRT, respectively, compared to the unmodified electrode. After optimization of the conditions (pH, accumulation time, and accumulation potential), analytical curves were constructed for the analytes in the range from 1.0 × 10 -7 to 2.0 × 10 -5 molL -1 . The detection limits for HCT and TRT were 2.8 × 10 -8 and 2.9 × 10 -8 molL -1 , respectively. A high performance liquid chromatography method with diode array detection was also developed for the determination of HCT and TRT in hemodialysis samples, for comparison with the electroanalytical method. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. A glassy carbon electrode modified with a nickel(II) norcorrole complex and carbon nanotubes for simultaneous or individual determination of ascorbic acid, dopamine, and uric acid

    International Nuclear Information System (INIS)

    Deng, Keqin; Li, Xiaofang; Huang, Haowen

    2016-01-01

    The authors report on the synthesis of a hybrid material consisting of the porphyrinoid metal complex nickel(II) norcorrole that was noncovalently bound to carbon nanotubes (CNT-NiNC). The hybrid was characterized by UV–vis, FTIR spectroscopy, and thermogravimetric analysis. The CNT-NiNC hybrid possesses high catalytic activity and selectivity toward the oxidation of ascorbic acid, dopamine, and uric acid. It was used to modify a glassy carbon electrode which then is shown to enable simultaneous or individual determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA) at pH 6.5 and typical working potentials of −70, 200 and 380 mV (vs. SCE). The detection limits (at an SNR of 3) are 2.0 μM for AA, 0.1 μM for DA, and 0.4 μM for UA. (author)

  12. Glassy carbon electrode modified with multi-walled carbon nanotubes sensor for the quantification of antihistamine drug pheniramine in solubilized systems.

    Science.gov (United States)

    Jain, Rajeev; Sharma, Sanjay

    2012-02-01

    A sensitive electroanalytical method for quantification of pheniramine in pharmaceutical formulation has been investigated on the basis of the enhanced electrochemical response at glassy carbon electrode modified with multi-walled carbon nanotubes in the presence of sodium lauryl sulfate. The experimental results suggest that the pheniramine in anionic surfactant solution exhibits electrocatalytic effect resulting in a marked enhancement of the peak current response. Peak current response is linearly dependent on the concentration of pheniramine in the range 200-1500 μg/mL with correlation coefficient 0.9987. The limit of detection is 58.31 μg/mL. The modified electrode shows good sensitivity and repeatability.

  13. Glassy carbon electrode modified with horse radish peroxidase/organic nucleophilic-functionalized carbon nanotube composite for enhanced electrocatalytic oxidation and efficient voltammetric sensing of levodopa

    Energy Technology Data Exchange (ETDEWEB)

    Shoja, Yalda; Rafati, Amir Abbas, E-mail: aa_rafati@basu.ac.ir; Ghodsi, Javad

    2016-01-01

    A novel and selective enzymatic biosensor was designed and constructed for voltammetric determination of levodopa (L-Dopa) in aqueous media (phosphate buffer solution, pH = 7). Biosensor development was on the basis of to physically immobilizing of horse radish peroxidase (HRP) as electrochemical catalyst by sol–gel on glassy carbon electrode modified with organic nucleophilic carbon nanotube composite which in this composite p-phenylenediamine (pPDA) as organic nucleophile chemically bonded with functionalized MWCNT (MWCNT-COOH). The results of this study suggest that prepared bioorganic nucleophilic carbon nanotube composite (HRP/MWCNT-pPDA) shows fast electron transfer rate for electro oxidation of L-Dopa because of its high electrochemical catalytic activity toward the oxidation of L-Dopa, more −NH{sub 2} reactive sites and large effective surface area. Also in this work we measured L-Dopa in the presence of folic acid and uric acid as interferences. The proposed biosensor was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), FT-IR spectroscopy and cyclic voltammetry (CV). The differential pulse voltammetry (DPV) was used for determination of L-Dopa from 0.1 μM to 1.9 μM with a low detection limit of 40 nM (for S/N = 3) and sensitivity was about 35.5 μA/μM. Also this biosensor has several advantages such as rapid response, high stability and reproducibility. - Highlights: • Glassy carbon electrode modified by a novel composite in which pPDA as nucleophile is chemically attached to MWCNTs. • The developed biosensor exhibited excellent electrocatalytic activity in electrochemically determination of L-Dopa. • The biosensor showed acceptable sensitivity, reproducibility, detection limit, selectivity and stability. • MWCNT-pPDA provides a good electrical conductivity and large effective surface area for enzyme immobilization.

  14. In-Vivo Characterization of Glassy Carbon Micro-Electrode Arrays for Neural Applications and Histological Analysis of the Brain Tissue

    Science.gov (United States)

    Vomero, Maria

    The aim of this work is to fabricate and characterize glassy carbon Microelectrode Arrays (MEAs) for sensing and stimulating neural activity, and conduct histological analysis of the brain tissue after the implant to determine long-term performance. Neural applications often require robust electrical and electrochemical response over a long period of time, and for those applications we propose to replace the commonly used noble metals like platinum, gold and iridium with glassy carbon. We submit that such material has the potential to improve the performances of traditional neural prostheses, thanks to better charge transfer capabilities and higher electrochemical stability. Great interest and attention is given in this work, in particular, to the investigation of tissue response after several weeks of implants in rodents' brain motor cortex and the associated materials degradation. As part of this work, a new set of devices for Electrocorticography (ECoG) has been designed and fabricated to improve durability and quality of the previous generation of devices, designed and manufactured by the same research group in 2014. In-vivo long-term impedance measurements and brain activity recordings were performed to test the functionality of the neural devices. In-vitro electrical characterization of the carbon electrodes, as well as the study of the adhesion mechanisms between glassy carbon and different substrates is also part of the research described in this book.

  15. Electrochemical Detection of Mn(II and Cd(II Mediated by Carbon Nanotubes and Carbon Nanotubes/Li+ Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Muhammed M. Radhi

    2010-11-01

    Full Text Available Glassy carbon electrode (GCE was modified with carbon nanotubes (CNT with and without a Li+ dopant by using a mechanical attachment method; CNT/Li+/GCE was used as two working electrodes, by doping CNT/GCE with Li+. The nano-structure of the electrodes showed individual voltammetrics of Mn2+ with two reduction peaks at +800 and +100 mV. Two reduction peaks for Cd2+ appeared at +600 V and -800 mV with one oxidation peak at -600 mV. The reduction current of Mn2+ and the redox current of Cd2+ on the CNT/Li+/GCE were largely influenced by a low concentration comparison with GCE and CNT/GCE. It showed that the detection of Mn2+ and Cd2+ by CNT/Li+/GCE in an aqueous solution of 0.1M KCL, with a relative standard deviation (RSD of the electrode being very good CNT/Li+/GCE. The determination of efficiency for the best modified electrode was detected for Mn2+ and Cd2+ on CNT/Li+/GCE; it was also found to have a wide linear range and good repeatability with a relative standard deviation (RSD of ±1.9 % when this electrode was used and the limit of detection was found to be 10-4 to 10-3 mM of Mn2+ and 10-4 to 10-2 mM of Cd2+, while the range of detection was found to be 3x10-4 to 10-3 mM and 10-3 to 10 -2 mM when using the CNT/GCE for Mn2+and Cd2+, respectively, with an RSD of ±3.3 % for Mn2+ and Cd2+.

  16. A study of the electro-catalytic oxidation of methanol on a cobalt hydroxide modified glassy carbon electrode

    International Nuclear Information System (INIS)

    Jafarian, M.; Mahjani, M.G.; Heli, H.; Gobal, F.; Khajehsharifi, H.; Hamedi, M.H.

    2003-01-01

    Cobalt hydroxide modified glassy carbon electrodes (CHM/GC) prepared by the anodic deposition in presence of tartrate ions have been used for the electro-catalytic oxidation of methanol in alkaline solutions where the methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (IS) have been employed. In CV studies, in the presence of methanol the peak current of the oxidation of cobalt hydroxide increase is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of methanol is being catalysed through the mediated electron transfer across the cobalt hydroxide layer comprising of cobalt ions of various valence states. A mechanism based on the electro-chemical generation of Co(IV) active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. In this context the charge transfer resistance accessible both theoretically and through the IS studies have been used as a criteria. Under the CA regimes the reaction followed a Cottrellian behaviour

  17. Electrooxidation of sulfanilamide and its voltammetric determination in pharmaceutical formulation, human urine and serum on glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    Bruno R.L. Ferraz

    2018-02-01

    Full Text Available For the first time, sulfanilamide (SFD was determined in otologic solution, human urine and serum by electroanalytical techniques on glassy carbon electrode (GCE. The cyclic voltammetry (CV experiments showed an irreversible oxidation peak at +1.06 V in 0.1 mol/L BRBS (pH = 2.0 at 50 mV/s. Different voltammetric scan rates (from 10 to 250 mV/s suggested that the oxidation of SFD on the GCE was a diffusion-controlled process. Square-wave voltammetry (SWV method under optimized conditions showed a linear response to SFD from 5.0 to 74.7 μmol/L (R = 0.999 with detection and quantification limits of 0.92 and 3.10 μmol/L, respectively. The developed SWV method showed better results for detection limit and linear range than the chronoamperometry method. It has been successfully applied to determine SFD concentration in pharmaceutical formulation, human urine and serum samples with recovery close to 100%.

  18. Effective electrochemical method for investigation of hemoglobin unfolding based on the redox property of heme groups at glassy carbon electrodes.

    Science.gov (United States)

    Li, Xianchan; Zheng, Wei; Zhang, Limin; Yu, Ping; Lin, Yuqing; Su, Lei; Mao, Lanqun

    2009-10-15

    This study demonstrates a facile and effective electrochemical method for investigation of hemoglobin (Hb) unfolding based on the electrochemical redox property of heme groups in Hb at bare glassy carbon (GC) electrodes. In the native state, the heme groups are deeply buried in the hydrophobic pockets of Hb with a five-coordinate high-spin complex and thus show a poor electrochemical property at bare GC electrodes. Upon the unfolding of Hb induced by the denaturant of guanidine hydrochloride (GdnHCl), the fifth coordinative bond between the heme groups and the residue of the polypeptides (His-F8) is broken, and as a result, the heme groups initially buried deeply in the hydrophobic pockets dissociate from the polypeptide chains and are reduced electrochemically at GC electrodes, which can be used to probe the unfolding of Hb. The results on the GdnHCl-induced Hb unfolding obtained with the electrochemical method described here well coincide with those studied with other methods, such as UV-vis spectroscopy, fluorescence, and circular dichroism. The application of the as-established electrochemical method is illustrated to study the kinetics of GdnHCl-induced Hb unfolding, the GdnHCl-induced unfolding of another kind of hemoprotein, catalase, and the pH-induced Hb unfolding/refolding.

  19. Detection of dopamine in non-treated urine samples using glassy carbon electrodes modified with PAMAM dendrimer-Pt composites

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, M.G. [Laboratory of Bioelectrochemistry, Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, S. C., Parque Tecnologico, Queretaro, Sanfandila, Pedro Escobedo 76703, Queretaro (Mexico); Department of Chemistry, Universidad de Guanajuato, Cerro de la Venada S/N Col. Pueblito de Rocha, 36040 Guanajuato, Gto (Mexico); Armendariz, G.M.E.; Godinez, Luis A.; Torres, J. [Laboratory of Bioelectrochemistry, Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, S. C., Parque Tecnologico, Queretaro, Sanfandila, Pedro Escobedo 76703, Queretaro (Mexico); Sepulveda-Guzman, S. [Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad, San Nicolas de los Garza, Nuevo Leon, 66451 Nuevo Leon (Mexico); Bustos, E., E-mail: ebustos@cideteq.mx [Laboratory of Bioelectrochemistry, Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, S. C., Parque Tecnologico, Queretaro, Sanfandila, Pedro Escobedo 76703, Queretaro (Mexico)

    2011-09-01

    Composites of hydroxyl-terminated PAMAM dendrimers, generation 4.0 (64 peripheral OH groups) containing Pt nanoparticles were synthesized at different reaction times using a microwave reactor. The synthetic procedure resulted in dendrimer encapsulated nanoparticles of Pt (DENs-Pt) of 1.53 {+-} 0.17 nm diameter that was calculated from transmission electron microscopy, and the Pt nanoparticles had single crystal plane in (1 1 1) orientation determinate by selective area diffraction. Each composite was electrochemically immobilized on a pre-functionalized glassy carbon (GC) electrode that was incorporated as a flow injection amperometric (FIA) detector, for the selective detection and quantification of dopamine (DA) in untreated urine samples. Comparison of the analytical performance of the novel electrochemical detector revealed that the DENs-Pt modified GC electrode with the composite synthesized for 30 min in the microwave reactor, showed the best response for the detection of DA in samples of non-treated urine, being the detection and quantification limits smaller (19 and 9 ppb, respectively) than those corresponding to the naked a GC electrode (846 and 423 ppb, respectively) using the FIA detector. In addition, it was found that this electroanalytical approach suffers minimal matrix effects that arise in the analysis of DA in untreated samples of urine.

  20. Preparation and characterisation of platinum- and gold-coated copper, iron, cobalt and nickel deposits on glassy carbon substrates

    International Nuclear Information System (INIS)

    Papadimitriou, S.; Tegou, A.; Pavlidou, E.; Armyanov, S.; Valova, E.; Kokkinidis, G.; Sotiropoulos, S.

    2008-01-01

    Pt- and Au-coated Cu, Fe, Co and Ni deposits have been formed on glassy carbon (GC) substrates by electrodeposition of controlled amounts of the core metal onto the substrate and its subsequent partial replacement by Pt or Au upon immersion into a chloroplatinic or chlorolauric solution. This process resulted in a thin Pt or Au shell over the bimetallic particle as electrochemical evidence suggests, while indicative sputter-etch Auger Electron Spectroscopy points to the coexistence of the two metals in the particle core. SEM/EDS characterisation of the deposits revealed the existence of Pt(M) and Au(M) extensively agglomerated nanoparticles (M: Cu, Fe, Co, Ni). The surface electrochemistry of the deposits (hydrogen adsorption/desorption on Pt and oxide formation/stripping on Au) proved the complete coverage of the bimetallic particles by Pt or Au and allowed an estimate of their electroactive surface area. The study of hydrogen evolution at these deposits points to a modification of the electronic properties of the Pt and Au surface layers by the core metal (due to strain effects and/or ligand-electronic interactions) and further confirmed that these layers form a very thin outer shell

  1. Amperometric detection of carbohydrates based on the glassy carbon electrode modified with gold nano-flake layer

    Directory of Open Access Journals (Sweden)

    Huy Du Nguyen

    2015-09-01

    Full Text Available An electro-deposition approach was established to incorporate the gold nano-flakes onto the glassy carbon electrode in electrochemical cells (nano-Au/GC/ECCs. Using pulsed amperometric detection (PAD without any gold oxidation for cleaning (non-oxidative PAD, the nano-Au/GC/ECCs were able to maintain their activity for oxidizing of carbohydrates in a normal alkaline medium. The reproducibility of peak area was about 2 relative standard deviation (RSD,% for 6 consecutive injections. A dynamic range of carbohydrates was obtained over a concentration range of 5–80 mg L−1 and the limits of detection (LOD were of 2 mg L−1 for fructose and lactose and 1 mg L−1 for glucose and galactose. Moreover, the nano-Au/GC/ECC using the non-oxidative PAD was able to combine with the internal standard method for determination of lactose in fresh cow milk sample.

  2. Stripping voltammetry glassy carbon on the study of Cd and Pb heavy metals pollution using anadara antiquata linn bioindicator

    International Nuclear Information System (INIS)

    Iswani, G.S.; Hidayat, F.; Zulkarnaen, A.

    1996-01-01

    The presence of cadmium and lead in sea water and shell fish (anadara antiquata linn) bioindicator in Gresik waters by glassy carbon stripping voltammetry was studied at menu 2 parameters as follows: time and potential plating-1000V and 90 second, sweep rate: 375 mV/second, strip time 2 second, electrolyte: aquatrides, pH = 0.4 (for shell fish) and -1000 V and 120 second, 999 mV/se con, 2 second, chloracetic, pH = 5.0. It was found that the mean of Cd and Pb contents in sea water at pH = 7.0, salinity = 28-29 ppm, oxygen content = 7.1-8.1 and temperature = 27-30 o C which was monitoring at location 1.2 and location 3.4 were 0.01 and 0.17 ppm, 1.44 and 1.35 ppm respectively. Furthermore the mean of Cd and Pb contents in shell fish at location 1.2 and 3.4 (snail range and shell fish dry weight were reported) were 5.94 and 3.05 ppm, 0,03 and 0,03 ppm. The t-tes for Cd and Pb contents in sea waters and shell fish at location 1,2 compared with location 3.4 were significant and no significant. The accuracy of the method was tested with SRM coppepoda MA-A-1-A-a and W-4. (author)

  3. Voltammetric behavior of Mammeisin (MA) at a glassy carbon electrode and its interaction with Bovine Serum Albumin (BSA).

    Science.gov (United States)

    Leuna, Jules-Blaise Mabou; Sop, Sergeot Kungo; Makota, Suzanne; Njanja, Evangeline; Ebelle, Thiery Christophe; Azebaze, Anatole Guy; Ngameni, Emmanuel; Nassi, Achille

    2018-02-01

    The electrochemical oxidation of Mammeisin (MA) was studied in a solution containing acetone and 0.1M phosphate buffer +0.1M KCl (pH=5.3) at a glassy carbon electrode (GCE), using cyclic (CV) and square wave voltammetry (SWV). MA showed a quasi-reversible process, which is pH dependent and that involves the exchange of two electrons and two protons. The oxidation product was adsorbed by the electrode surface to form a film that blocks active sites over repetitive cyclic. Moreover, the interaction of MA and bovine serum albumin (BSA) was studied by CV and SWV at different pHs (5.4, 7.2, 9.5). As a result of the affinity binding with BSA, electrochemically inactive complex was formed. In addition, the oxidation potential of MA in the presence of BSA depends on the pH. The diffusion coefficients of both free and bound MA were estimated from the cyclic voltammetry data using the method developed by Randles-Sevich (D f =9.85×10 -5 cm 2 s -1 and D b =1.27×10 -9 cm 2 s -1 ) and the binding constant of MA-BSA complex, K=3.47×10 2 Lmol -1 , was obtained. Copyright © 2017. Published by Elsevier B.V.

  4. Non-enzymatic detection of glucose using poly(azure A)-nickel modified glassy carbon electrode.

    Science.gov (United States)

    Liu, Tong; Luo, Yiqun; Zhu, Jiaming; Kong, Liyan; Wang, Wen; Tan, Liang

    2016-08-15

    A simple, sensitive and selective non-enzymatic glucose sensor was constructed in this paper. The poly(azure A)-nickel modified glassy carbon electrode was successfully fabricated by the electropolymerization of azure A and the adsorption of Ni(2+). The Ni modified electrode, which was characterized by scanning electron microscope, cyclic voltammetry, electrochemical impedance spectra and X-ray photoelectron spectroscopy measurements, respectively, displayed well-defined current responses of the Ni(III)/Ni(II) couple and showed a good activity for electrocatalytic oxidation of glucose in alkaline medium. Under the optimized conditions, the developed sensor exhibited a broad linear calibration range of 5 μM-12mM for quantification of glucose and a low detection limit of 0.64μM (3σ). The excellent analytical performance including simple structure, fast response time, good anti-interference ability, satisfying stability and reliable reproducibility were also found from the proposed amperometric sensor. The results were satisfactory for the determination of glucose in human serum samples as comparison to those from a local hospital. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. Voltammetric behavior of ketoconazole and its determination in cosmetic preparation using a β-cyclodextrin modified glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    M.A. El Ries

    2013-06-01

    Full Text Available A voltammetric determination of ketoconazole (KCZ at a beta-cyclo-dextrin modified glassy carbon (CDMGC is described. A large increase in the peak currents was observed in cyclic voltammetry (CV and differential pulse voltammetry (DPV of KCZ. This increase in the big current were attributed to the complex formation of the KCZ with β-cyclodextrin. CV studies indicate that the process is irreversible and adsorption-controlled. The effect of pH, scan rate, cyclodextrin concentration and stability of electrodes on the current responses of KCZ was studied. The linearity was obeyed over the concentration range (1–8 × 10−5 mole/l with a common correlation coefficient and limit of detection of 0.9996 and 10.54 × 10−8, respectively, in pH 9 Britton–Robinson (BR buffer. The modified electrode exhibited good sensitivity, and stability. The voltammetric method was successfully applied for the determination of KCZ in pure solution and in cosmetic preparation under batch condition.

  6. Amperometric detection of Sudan I in red chili powder samples using Ag nanoparticles decorated graphene oxide modified glassy carbon electrode.

    Science.gov (United States)

    Prabakaran, E; Pandian, K

    2015-01-01

    A simple and sensitive electrochemical method was developed to determine the concentration of Sudan I in chili powder based on silver nanoparticles decorated graphene oxide modified glassy carbon electrode (AgNPs@GO/GCE). The voltammetry behaviour of Sudan I on modified GCE was investigated in phosphate buffer medium (PBS) with various pH ranges and the electron transfer properties were studied. It is found that the AgNPs@GO/GCE can catalyse the reduction of azo group, -N=N- followed by electrochemical oxidation of (-)OH group present in Sudan I dye molecule. Quantitative detection of Sudan I present in food products was carried out by amperometry method in which reduction potential was fixed at -0.77 V vs. Ag/AgCl. The amperometry method showed an excellent performance with a sensitivity of 6.83 μA mM(-1) and a detection limit of 11.4 × 10(-7)ML(-1). A linear calibration graph was constructed in the ranging 3.90 × 10(-6) to 3.19 × 10(-5)ML(-1). The method was successfully applied for the determination of Sudan I in red chili powder samples. Copyright © 2014 Elsevier Ltd. All rights reserved.

  7. Electrochemical oxidation behavior of hydrochlorothiazide on a glassy carbon electrode and its voltammetric determination in pharmaceutical formulations and biological fluids

    Directory of Open Access Journals (Sweden)

    Ali F. Alghamdi

    2014-09-01

    Full Text Available The electrochemical oxidation behavior of hydrochlorothiazide (HCT on a glassy carbon as a working electrode was investigated in Britton–Robinson (B–R buffer pH 3, by using anodic stripping voltammetry (ASV and cyclic voltammetry (CV. This drug gave a well-defined voltammetric oxidation peak at + 1200 mV versus an Ag/AgCl reference electrode. The electrochemical oxidation process was shown to be irreversible and diffusion controlled, with adsorption characterized over the entire pH range. The optimized conditions, such as accumulation time and potential, scan rate, frequency, pulse amplitude, varying of working electrodes, and instrumental parameters were studied. The calibration graph for HCT was obtained from 4 × 10−6 to 4 × 10−5 M (correlation coefficient = 0.997 using the developed electroanalytical method (ASV. The detection limit of this drug was 4.3 × 10−9 M. ASV and CV techniques with adequate precision and accuracy have been developed and applied for direct determination of HCT in commercial tablets without separation or extraction procedures and biological fluids such as urine and plasma.

  8. Electro-oxidation nitrite based on copper calcined layered double hydroxide and gold nanoparticles modified glassy carbon electrode

    International Nuclear Information System (INIS)

    Cui Lin; Meng Xiaomeng; Xu Minrong; Shang Kun; Ai Shiyun; Liu Yinping

    2011-01-01

    Highlights: → A nitrite sensor fabricated based on copper calcined layered double hydroxides and gold nanoparticles modified electrode. → This sensor exhibited excellent electrocatalytic oxidation to nitrite. → This nitrite sensor exhibited very good analytical performance with low cost, convenient preparation and rapid detection. - Abstract: In this paper, a novel nitrite sensor was constructed based on electrodeposition of gold nanoparticles (AuNPs) on a copper calcined layered double hydroxide (Cu-CLDH) modified glassy carbon electrode. Electrochemical experiments showed that AuNPs/CLDH composite film exhibited excellent electrocatalytic oxidation activity with nitrite due to the synergistic effect of the Cu-CLDH with AuNPs. The fabricated sensor exhibited excellent performance for nitrite detection within a wide concentration interval of 1-191 μM and with a detection limit of 0.5 μM. The superior electrocatalytic response to nitrite was mainly attributed to the large surface area, minimized diffusion resistance, and enhanced electron transfer of the Cu-CLDH and AuNPs composition film. This platform offers a novel route for nitrite sensing with wide analytical applications and will supply the practical applications for a variety of simple, robust, and easy-to-manufacture analytical approaches in the future.

  9. Potential of Glassy Carbon and Silicon Carbide Photonic Structures as Electromagnetic Radiation Shields for Atmospheric Re-entry

    Science.gov (United States)

    Komarevskiy,Nikolay; Shklover, Valery; Braginsky, Leonid; Hafner, Christian; Lawson, John W.

    2012-01-01

    During high-velocity atmospheric entries, space vehicles can be exposed to strong electromagnetic radiation from ionized gas in the shock layer. Glassy carbon (GC) and silicon carbide (SiC) are candidate thermal protection materials due to their high melting point and also their good thermal and mechanical properties. Based on data from shock tube experiments, a significant fraction of radiation at hypersonic entry conditions is in the frequency range from 215 to 415 THz. We propose and analyze SiC and GC photonic structures to increase the reflection of radiation in that range. For this purpose, we performed numerical optimizations of various structures using an evolutionary strategy. Among the considered structures are layered, porous, woodpile, inverse opal and guided-mode resonance structures. In order to estimate the impact of fabrication inaccuracies, the sensitivity of the reflectivity to structural imperfections is analyzed. We estimate that the reflectivity of GC photonic structures is limited to 38% in the aforementioned range, due to material absorption. However, GC material can be effective for photonic reflection of individual, strong spectral line. SiC on the other hand can be used to design a good reflector for the entire frequency range.

  10. Structure and Electromagnetic Properties of Cellular Glassy Carbon Monoliths with Controlled Cell Size

    Directory of Open Access Journals (Sweden)

    Andrzej Szczurek

    2018-05-01

    Full Text Available Electromagnetic shielding is a topic of high importance for which lightweight materials are highly sought. Porous carbon materials can meet this goal, but their structure needs to be controlled as much as possible. In this work, cellular carbon monoliths of well-defined porosity and cell size were prepared by a template method, using sacrificial paraffin spheres as the porogen and resorcinol-formaldehyde (RF resin as the carbon precursor. Physicochemical studies were carried out for investigating the conversion of RF resin into carbon, and the final cellular monoliths were investigated in terms of elemental composition, total porosity, surface area, micropore volumes, and micro/macropore size distributions. Electrical and electromagnetic (EM properties were investigated in the static regime and in the Ka-band, respectively. Due to the phenolic nature of the resin, the resultant carbon was glasslike, and the special preparation protocol that was used led to cellular materials whose cell size increased with density. The materials were shown to be relevant for EM shielding, and the relationships between those properties and the density/cell size of those cellular monoliths were elucidated.

  11. Imprinted sol-gel electrochemical sensor for the determination of benzylpenicillin based on Fe{sub 3}O{sub 4}/SiO{sub 2} multi-walled carbon nanotubes-chitosans nanocomposite film modified carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Hu Yufang [College of Chemistry and Chemical Engineering, Jishou University, Hunan 416000 (China); Li Jiaxing [College of Chemistry and Chemical Engineering, Jishou University, Hunan 416000 (China); Central South University of Forestry and Technology, Hunan 410004 (China); Zhang Zhaohui, E-mail: zhaohuizhang77@163.com [College of Chemistry and Chemical Engineering, Jishou University, Hunan 416000 (China) and State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan 410082 (China); Zhang Huabin; Luo Lijuan [College of Chemistry and Chemical Engineering, Jishou University, Hunan 416000 (China); Yao Shouzhuo [State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan 410082 (China)

    2011-07-18

    Graphical abstract: A novel imprinted sol-gel electrochemical sensor based on Fe{sub 3}O{sub 4}/SiO{sub 2}-MWNTs-CTS nanocomposite film and a thin MIP film has been developed on a carbon electrode. Highlights: {yields} A novel imprinted sol-gel electrochemical sensor based on Fe{sub 3}O{sub 4}/SiO{sub 2}-MWNTs-CTS nanocomposites has been developed. {yields} Fe{sub 3}O{sub 4}/SiO{sub 2}-MWNTs-CTS nanocomposites act as 'electronic wires' to enhance the electron transfer. {yields} The inherent specificity of the MIPs brings about highly selectivity. The imprinted sensor detects benzylpenicillin in real samples successfully. - Abstract: Herein, a novel imprinted sol-gel electrochemical sensor based on multi-walled carbon nanotubes (MWNTs) doped with chitosan film on a carbon electrode has been developed. Prior to doped, the MWNTs have been decorated with Fe{sub 3}O{sub 4} nanoparticles which have been coated uniformly with SiO{sub 2} layer. The characterization of imprinted sensor has been carried out by X-ray diffraction and scanning electron microscopy. The performance of the proposed imprinted sensor has been investigated using cyclic voltammetry and differential pulse voltammetry. The imprinted sensor offers a fast response and sensitive benzylpenicillin quantification. The fabricated benzylpenicillin imprinted sensor exhibits a linear response from 5.0 x 10{sup -8} to 1.0 x 10{sup -3} mol L{sup -1} with a detection limit of 1.5 x 10{sup -9} mol L{sup -1}. For samples analysis, perfect recoveries of the imprinted sensor for benzylpenicillin indicated that the imprinted sensor was able to detect benzylpenicillin in real samples successfully.

  12. Pulsed amperometric detection at glassy carbon electrodes: A new waveform for sensitive and reproducible determination of electroactive compounds.

    Science.gov (United States)

    Nardiello, Donatella; Palermo, Carmen; Natale, Anna; Quinto, Maurizio; Centonze, Diego

    2015-09-24

    In this work, the application of a new pulsed amperometric detection (PAD) waveform at a glassy carbon electrode, operating in typical chromatographic mobile phases, is proposed for the sensitive and reproducible determination of arylethanolaminic and phenolic moiety based compounds (e.g. beta-agonists and polyphenols). Preliminary experiments by cyclic voltammetry were carried out to investigate the electrochemical behaviour and to select the detection and cleaning electrode potentials. The proposed potential-time profile was designed to prevent the carbon electrode fouling under repeated analyses, thus ensuring a reproducible and sensitive quantitative determination, without the need of any mechanical or chemical electrode cleaning procedure. The waveform electrochemical parameters, including detection and delay times, were optimized in terms of sensitivity, limit of detection and response stability. The optimized waveform allowed the sensitive and stable detection of model compounds, such as clenbuterol and caffeic acid, that showed detection limits of 0.1 μg L(-1) and 14 μg L(-1), quantification limits of 0.4 μg L(-1) and 46 μg L(-1), and linearity up to 100 μg L(-1) (r = 0.9993) and 10 mg L(-1) (r = 0.9998), respectively. Similar results were obtained for other compounds of the same classes, with precision values under repeatability conditions ranging from 3.0 to 5.9%. The proposed method can be then considered as an excellent alternative to the post-column detection of beta-agonists, phenols and polyphenols. Copyright © 2015 Elsevier B.V. All rights reserved.

  13. Electrokinetic and impedimetric dynamics of FeCo-nanoparticles on glassy carbon electrode

    CSIR Research Space (South Africa)

    Ikpo, CO

    2013-01-01

    Full Text Available voltammetric experiments revealed a diffusion-controlled electron transfer process on the GCE/FeCo electrode surface. Further interrogation on the electrochemical properties of the FeCo nanoelectrode in an oxygen saturated 1 M LiClO4 containing 1:1 v/v ethylene-carbonate...

  14. Glassy Dynamics

    DEFF Research Database (Denmark)

    Jensen, Henrik J.; Sibani, Paolo

    2007-01-01

    The term glassy dynamics is often used to refer to the extremely slow relaxation observed in several types of many component systems. The time span needed to reach a steady, time independent, state will typically be far beyond experimentally accessible time scales. When melted alloys are cooled...... down they typically do not enter a crystalline ordered state. Instead the atoms retain the amorphous arrangement characteristic of the liquid high temperature phase while the mobility of the molecules decreases very many orders of magnitude. This colossal change in the characteristic dynamical time...

  15. Glassy carbon electrode modified with gold nanoparticles for ractopamine and metaproterenol sensing

    Science.gov (United States)

    Duan, Jiahua; He, Dawei; Wang, Wenshuo; Liu, Yongchuan; Wu, Hongpeng; Wang, Yongsheng; Fu, Ming

    2013-06-01

    In this Letter, the gold nanoparticles (AuNPs) were used as an enhanced material for selective detection of ractopamine and metaproterenol with electrochemical methods. The morphology and size of gold nanoparticles were characterized by scanning electron microscopy and absorption spectrum. Meanwhile, the electrical properties of modified glass carbon electrode (GCE) were studied by electrochemical impedance spectroscopy. The electrochemical behaviors of ractopamine and metaproterenol were well explained by PM3 calculated method and cyclic voltammetry. Importantly, the ractopamine and metaproterenol were effectively detected. The detection range has been broadened to (10-9-10-5 M) and the detection time has been shortened to a few minutes.

  16. A glassy carbon electrode modified with β-cyclodextin, multiwalled carbon nanotubes and graphene oxide for sensitive determination of 1,3-dinitrobenzene

    International Nuclear Information System (INIS)

    Li, Junhua; Feng, Haibo; Liu, Jinlong; Liu, Youcai; Jiang, Jianbo; Feng, Yonglan; Qian, Dong

    2014-01-01

    We are presenting a host-guest electrochemical platform for sensing the pollutant 1,3-dinitrobenzene. The method is based on the use of a glassy carbon electrode (GCE) covered with a composite made from multiwalled carbon nanotubes and graphene oxide, and functionalized with β-cyclodextrin (β-CD). The resultant composite was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and electrochemical techniques. The modified GCE was used for the sensitive detection of 1,3-dinitrobenzene (DNB) at working voltages of −355 mV and −483 mV. Due to the specific recognition property of β-CD and the excellent electronic properties of the carbon nanomaterials, the electrode exhibits outstanding supramolecular recognition and enhanced electrochemical response to DNB compared to more conventional electrodes. Under optimum conditions, the peak currents vary linearly with the DNB concentrations in the range from 0.02 to 30.0 μM, and the detection limit is 5.0 nM (at an S/N of 3). The electrode exhibits long-term stability and has been successfully applied to the determination of DNB in spiked soil and water samples. (author)

  17. Electrosorption of Os(III)-complex at single-wall carbon nanotubes immobilized on a glassy carbon electrode: Application to nanomolar detection of bromate, periodate and iodate

    International Nuclear Information System (INIS)

    Salimi, Abdollah; Kavosi, Begard; Babaei, Ali; Hallaj, Rahman

    2008-01-01

    A simple procedure was developed to prepare a glassy carbon electrode modified with single-wall carbon nanotubes (SWCNTs) and Os(III)-complex. The glassy carbon (GC) electrode modified with CNTs was immersed into Os(III)-complex solution (direct deposition) for a short period of time (60 s). 1,4,8,12-Tetraazacyclotetradecane osmium(III) chloride, (Os(III)LCl 2 ).ClO 4 , irreversibly and strongly adsorbed on SWCNTs immobilized on the surface of GC electrode. Cyclic voltammograms of the Os(III)-complex-incorporated-SWCNTs indicate a pair of well defined and nearly reversible redox couple with surface confined characteristic at wide pH range (1-8). The surface coverage (Γ) and charge transfer rate constant (k s ) of the immobilized Os-complex on SWCNTs were 3.07 x 10 -9 mol cm -2 , 5.5 (±0.2) s -1 , 2.94 x 10 -9 mol cm -2 , 7.3 (±0.3) s -1 at buffer solution with pH 2 and 7, respectively, indicate high loading ability of SWCNTs for Os(III) complex and great facilitation of the electron transfer between electroactive redox center and carbon nanotubes immobilized on the electrode surface. Modified electrodes showed higher electrocatalytic activity toward reduction of BrO 3 - , IO 3 - and IO 4 - in acidic solutions. The catalytic rate constants for catalytic reduction bromate, periodate and iodate were 3.79 (±0.2) x 10 3 , 7.32 (±0.2) x 10 3 and 1.75 (±0.2) x 10 3 M -1 s -1 , respectively. The hydrodynamic amperometry of rotating modified electrode at constant potential (0.3 V) was used for nanomolar detection of selected analytes. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantage of this sensor

  18. Laccase on Black Pearl 2000 modified glassy carbon electrode: Characterization of direct electron transfer and biological sensing properties for pyrocatechol

    International Nuclear Information System (INIS)

    Wang Kunqi; Tang Juan; Zhang Zuoming; Gao Ying; Chen Gang

    2012-01-01

    Highlights: ► Laccase can complete direct electron transfer process on BP2000 matrices. ► Laccase immobilized on BP2000 matrices has catalytic oxidation effect to pyrocatechol. ► A pyrocatechol biosensor has constructed been using Nafion/Lac-BP2000/GC electrode. ► Detection limit and linear range of the biosensor are 0.003 mM and 0.003–5.555 mM. - Abstract: In this paper, it was found that Laccase (Lac) could be stably immobilized on the glassy carbon electrode modified with Black Pearl 2000 (BP2000) and Nafion by a simple technique. The adsorption behavior of Lac immobilized on BP2000 matrix was characterized by environment scanning electron microscope (ESEM), ultraviolet–visible (UV–vis) and Fourier transform infrared (FTIR), which demonstrated that BP2000 could facilitate the electron exchange between the active center of Lac and modified electrode. The direct electrochemistry and electrocatalysis behavior of Lac on the modified electrode were characterized by cyclic voltammogram (CV) which indicated that Lac immobilized on the modified electrode displayed a direct, nearly reversible and surface-controlled redox reaction with an enhanced electron-transfer rate constant of 1.940 s −1 at the scan rate of 100 mV s −1 in 0.1 M phosphate buffer solution (PBS) (pH 7.0). Furthermore, it was also discovered that, in the presence of O 2 , Lac immobilized on the modified electrode exhibited the electrocatalytic response to pyrocatechol, and the kinetic apparent Michaelis-constant (K M app ) obtained from the Lineweaver–Burk equation was 1.79 mM. The detection limit, linear range and sensitivity of the Lac biosensor were 0.003 mM, 0.003–5.555 mM and 99.84 μA mM −1 cm −2 , respectively.

  19. Fabrication of electrochemical theophylline sensor based on manganese oxide nanoparticles/ionic liquid/chitosan nanocomposite modified glassy carbon electrode

    International Nuclear Information System (INIS)

    MansouriMajd, Samira; Teymourian, Hazhir; Salimi, Abdollah; Hallaj, Rahman

    2013-01-01

    In this study, the preparation of a glassy carbon (GC) electrode modified with chitosan/NH 2 -ionic liquid/manganese oxide nanoparticles (Chit/NH 2 -IL/MnO x ) was described for electrocatalytic detection of theophylline (TP). First, chitosan hydrogel (Chit) was electrodeposited on the GC electrode surface at a constant potential (−1.5 V) in acidic solution. Then, the previously synthesized amine-terminated 1-(3-Aminopropyl)-3-methylimidazolium bromide ionic liquid (NH 2 -IL) was covalently attached to the modified electrode via glutaraldehyde (GA) as linking agent. Finally, manganese oxide (MnO x ) nanoparticles were electrodeposited onto the Chit/NH 2 -IL film by potential cycling between −1.0 and 1.7 V in Mn(CH 3 COO) 2 ·4H 2 O neutral aqueous solution. Electrochemical behavior of the modified electrode was evaluated by cyclic voltammetry (CV) technique. The charge transfer coefficient (α) and electron transfer rate constant (k s ) for MnOOH/MnO 2 redox couple were calculated to be 0.35 and 1.62 s −1 , respectively. The resulting system brings new capabilities for electrochemical sensing through combining the advantages of IL and MnO x nanoparticles. The differential pulse voltammetric (DPV) results indicated the high ability of GC/Chit/NH 2 -IL/MnO x modified electrode to catalyze the oxidation of TP. DPV determination of TP in acetate buffer solution (pH 5) gave linear responses over the concentration range up to 120 μM with the detection limit of 50 nM and sensitivity of 804 nA μM −1 . Furthermore, the applicability of the sensor for TP analysis in pharmaceutical samples has been successfully demonstrated

  20. Simultaneous Electrochemical Detection of Dopamine and Ascorbic Acid Using an Iron Oxide/Reduced Graphene Oxide Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Teo Peik-See

    2014-08-01

    Full Text Available The fabrication of an electrochemical sensor based on an iron oxide/graphene modified glassy carbon electrode (Fe3O4/rGO/GCE and its simultaneous detection of dopamine (DA and ascorbic acid (AA is described here. The Fe3O4/rGO nanocomposite was synthesized via a simple, one step in-situ wet chemical method and characterized by different techniques. The presence of Fe3O4 nanoparticles on the surface of rGO sheets was confirmed by FESEM and TEM images. The electrochemical behavior of Fe3O4/rGO/GCE towards electrocatalytic oxidation of DA was investigated by cyclic voltammetry (CV and differential pulse voltammetry (DPV analysis. The electrochemical studies revealed that the Fe3O4/rGO/GCE dramatically increased the current response against the DA, due to the synergistic effect emerged between Fe3O4 and rGO. This implies that Fe3O4/rGO/GCE could exhibit excellent electrocatalytic activity and remarkable electron transfer kinetics towards the oxidation of DA. Moreover, the modified sensor electrode portrayed sensitivity and selectivity for simultaneous determination of AA and DA. The observed DPVs response linearly depends on AA and DA concentration in the range of 1–9 mM and 0.5–100 µM, with correlation coefficients of 0.995 and 0.996, respectively. The detection limit of (S/N = 3 was found to be 0.42 and 0.12 µM for AA and DA, respectively.

  1. Electrochemical surface derivation of glassy carbon by the reduction of triaryl- and alkyldiphenylsulfonium salts

    DEFF Research Database (Denmark)

    Vase, K.H.; Holm, A.H.; Norrman, Kion

    2008-01-01

    The range of materials susceptible to electrochemically assisted grafting onto carbon materials has been expanded to include a new group of compounds. This new approach is based on the reduction of symmetrical or unsymmetrical triarylsulfonium salts and alkyldiphenylsulfonium salts. Our findings......, the alkyldiphenylsulfonium salts are found to cleave almost exclusively to an alkyl radical and diphenyl sulfide. As judged from the electrochemical blocking properties of the films made from such species, either relatively thick or compact films are formed. The mass spectrometric analysis indicates that the films are made...... of a combination of alkyl and aryl groups and possibly related structural derivatives. Importantly, our findings provide evidence that it is possible to graft electrode surfaces with reactive aryl radicals even using precursors reduced at potentials that are substantially more negative than the estimated reduction...

  2. Improved immobilization of laccase on a glassy carbon electrode by oriented covalent attachment

    Directory of Open Access Journals (Sweden)

    Liu Xin

    2014-01-01

    Full Text Available A laccase from Thermus thermophilus HB27 was reported to be potentially useful in the design of a temperature controlled biofuel cell. For enhancing its application in different thermal conditions, we engineered a laccase-oriented immobilized electrode. A site-directed mutant N323C of the laccase was constructed. A photometric assay was employed in order to compare the catalytic properties of wild-type laccase and mutant. The mutant was attached to a glass carbon electrode by covalent cross-linking. The electrochemical properties of the immobilized laccase were investigated by cyclic voltammetry. This immobilization allowed the active electrode to function at temperatures up to 95°C. The thermal and pH dependence profiles were similar to those of the soluble enzyme investigated by spectrophotometry.

  3. A novel non-enzymatic hydrogen peroxide sensor based on single walled carbon nanotubes-manganese complex modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Salimi, Abdollah, E-mail: absalimi@uok.ac.i [Department of Chemistry, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Research Center for Nanotechnology, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Mahdioun, Monierosadat; Noorbakhsh, Abdollah [Department of Chemistry, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Abdolmaleki, Amir [Department of Chemistry, Isfahan University of Technology, Isfahan, 84156/83111 (Iran, Islamic Republic of); Ghavami, Raoof [Department of Chemistry, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of)

    2011-03-30

    A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWCNTs) and phenazine derivative of Mn-complex. With immersing the GC/CNTs modified electrode into Mn-complex solution for a short period of time 20-100 s, a stable thin layer of the complex was immobilized onto electrode surface. Modified electrode showed a well defined redox couples at wide pH range (1-12). The surface coverages and heterogeneous electron transfer rate constants (k{sub s}) of immobilized Mn-complex were approximately 1.58 x 10{sup -10} mole cm{sup -2} and 48.84 s{sup -1}. The modified electrode showed excellent electrocatalytic activity toward H{sub 2}O{sub 2} reduction. Detection limit, sensitivity, linear concentration range and k{sub cat} for H{sub 2}O{sub 2} were, 0.2 {mu}M and 692 nA {mu}M{sup -1} cm{sup -2}, 1 {mu}M to 1.5 mM and 7.96({+-}0.2) x 10{sup 3} M{sup -1} s{sup -1}, respectively. Compared to other modified electrodes, this electrode has many advantageous such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability.

  4. A novel non-enzymatic hydrogen peroxide sensor based on single walled carbon nanotubes-manganese complex modified glassy carbon electrode

    International Nuclear Information System (INIS)

    Salimi, Abdollah; Mahdioun, Monierosadat; Noorbakhsh, Abdollah; Abdolmaleki, Amir; Ghavami, Raoof

    2011-01-01

    A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWCNTs) and phenazine derivative of Mn-complex. With immersing the GC/CNTs modified electrode into Mn-complex solution for a short period of time 20-100 s, a stable thin layer of the complex was immobilized onto electrode surface. Modified electrode showed a well defined redox couples at wide pH range (1-12). The surface coverages and heterogeneous electron transfer rate constants (k s ) of immobilized Mn-complex were approximately 1.58 x 10 -10 mole cm -2 and 48.84 s -1 . The modified electrode showed excellent electrocatalytic activity toward H 2 O 2 reduction. Detection limit, sensitivity, linear concentration range and k cat for H 2 O 2 were, 0.2 μM and 692 nA μM -1 cm -2 , 1 μM to 1.5 mM and 7.96(±0.2) x 10 3 M -1 s -1 , respectively. Compared to other modified electrodes, this electrode has many advantageous such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability.

  5. Selective Determination of Serotonin on Poly(3,4-ethylenedioxy pyrrole)-single-walled Carbon Nanotube-Modified Glassy Carbon Electrodes

    International Nuclear Information System (INIS)

    Kim, Seul Ki; Bae, Si Ra; Ahmed, Mohammad Shamsuddin; You, Jung Min; Jeon, Seung Won

    2011-01-01

    An electrochemically-modified electrode [P(EDOP-SWNTs)/GCE] was prepared by electropolymerization of 3,4-ethylenedioxy pyrrole (EDOP) single-walled carbon nanotubes (SWNTs) on the surface of a glassy carbon electrode (GCE) and characterized by SEM, CV, and DPV. This modified electrode was employed as an electrochemical biosensor for the selective determination of serotonin concentrations at pH 7.4 and exhibited a typical enhanced effect on the current response of serotonin with a lower oxidation overpotential. The linear response was in the range of 1.0 x 10 -7 to 1.0 x 10 -5 M, with a correlation coefficient of 0.998 on the anodic current. The lower detection limit was calculated as 5.0 nM. Due to the relatively low currents and difference of potentials in the electrochemical responses of uric acid (UA), ascorbic acid (AA), and dopamine (DA), the modified electrode was a useful and effective sensing device for the selective and sensitive serotonin determination in the presence of UA, AA, and DA

  6. An electrochemical sensor for rizatriptan benzoate determination using Fe3O4 nanoparticle/multiwall carbon nanotube-modified glassy carbon electrode in real samples.

    Science.gov (United States)

    Madrakian, Tayyebeh; Maleki, Somayeh; Heidari, Mozhgan; Afkhami, Abbas

    2016-06-01

    In this paper a sensitive and selective electrochemical sensor for determination of rizatriptan benzoate (RZB) was proposed. A glassy carbon electrode was modified with nanocomposite of multiwalled carbon nanotubes (MWCNTs) and Fe3O4 nanoparticles (Fe3O4/MWCNTs/GCE). The results obtained clearly show that the combination of MWCNTs and Fe3O4 nanoparticles definitely improves the sensitivity of modified electrode to RZB determination. The morphology and electroanalytical performance of the fabricated sensor were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), square wave voltammetry (SWV) and cyclic voltammetry (CV). Also, the effect of experimental and instrumental parameters on the sensor response was evaluated. The square wave voltammetric response of the electrode to RZB was linear in the range 0.5-100.0 μmol L(-1) with a detection limit of 0.09 μmol L(-1) under the optimum conditions. The investigated method showed good stability, reproducibility and repeatability. The proposed sensor was successfully applied for real life samples of blood serum and RZB determination in pharmaceutical. Copyright © 2016 Elsevier B.V. All rights reserved.

  7. Direct electron transfer and electrocatalysis of glucose oxidase immobilized on glassy carbon electrode modified with Nafion and mesoporous carbon FDU-15

    International Nuclear Information System (INIS)

    Wang Kunqi; Yang Hua; Zhu Lin; Ma Zhongsu; Xing Shenyang; Lv Qiang; Liao Jianhui; Liu Changpeng; Xing Wei

    2009-01-01

    In this paper, it was found that glucose oxidase (GOD) has been stably immobilized on glassy carbon electrode modified with mesoporous carbon FDU-15 (MC-FDU-15) and Nafion by simple technique. The sorption behavior of GOD immobilized on MC-FDU-15 matrix was characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis), FTIR, respectively, which demonstrated that MC-FDU-15 could facilitate the electron exchange between the active center of GOD and electrode. The direct electrochemistry and electrocatalysis behavior of GOD on the modified electrode were characterized by cyclic voltammogram (CV) which indicated that GOD immobilized on Nafion and MC-FDU-15 matrices display direct, reversible and surface-controlled redox reaction with an enhanced electron transfer rate constant of 4.095 s -1 in 0.1 M phosphate buffer solution (PBS) (pH 7.12). Furthermore, it was also discovered that, in the presence of O 2 , GOD immobilized on Nafion and MC-FDU-15 matrices could produce a linear response to glucose. Thus, Nafion/GOD-MC-FDU-15/GC electrode is hopeful to be used in glucose biosensor. In addition, GOD immobilized on MC-FDU-15 and Nafion matrices possesses an excellent bioelectrocatalytic activity for the reduction of O 2 . So, the Nafion/GOD-MC-FDU-15/GC electrode can be utilized as the cathode in biofuel cell.

  8. Selective Determination of Serotonin on Poly(3,4-ethylenedioxy pyrrole)-single-walled Carbon Nanotube-Modified Glassy Carbon Electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seul Ki; Bae, Si Ra; Ahmed, Mohammad Shamsuddin; You, Jung Min; Jeon, Seung Won [Chonnam National University, Gwangju (Korea, Republic of)

    2011-04-15

    An electrochemically-modified electrode [P(EDOP-SWNTs)/GCE] was prepared by electropolymerization of 3,4-ethylenedioxy pyrrole (EDOP) single-walled carbon nanotubes (SWNTs) on the surface of a glassy carbon electrode (GCE) and characterized by SEM, CV, and DPV. This modified electrode was employed as an electrochemical biosensor for the selective determination of serotonin concentrations at pH 7.4 and exhibited a typical enhanced effect on the current response of serotonin with a lower oxidation overpotential. The linear response was in the range of 1.0 x 10{sup -7} to 1.0 x 10{sup -5} M, with a correlation coefficient of 0.998 on the anodic current. The lower detection limit was calculated as 5.0 nM. Due to the relatively low currents and difference of potentials in the electrochemical responses of uric acid (UA), ascorbic acid (AA), and dopamine (DA), the modified electrode was a useful and effective sensing device for the selective and sensitive serotonin determination in the presence of UA, AA, and DA.

  9. Impedimetric Salmonella aptasensor using a glassy carbon electrode modified with an electrodeposited composite consisting of reduced graphene oxide and carbon nanotubes

    International Nuclear Information System (INIS)

    Jia, Fei; Dai, Ruitong; Duan, Nuo; Wu, Shijia; Wang, Zhouping; Li, Xingmin

    2016-01-01

    We describe a Salmonella biosensor that was obtained by electrochemical immobilization of a nanocomposite consisting of reduced graphene oxide (rGO) and carboxy-modified multi-walled carbon nanotubes (MWCNTs) directly on the surface of a glassy carbon electrode (GCE). An amino-modified aptamer specific for Salmonella was covalently bound to the rGO-MWCNT composite via amide bonds. The morphology of the rGO-MWCNT nanocomposite was characterized by transmission electron microscopy and scanning electron microscopy. Cyclic voltammetry and electrochemical impedance spectroscopy were used to monitor all steps during assembly. When exposed to samples containing Salmonella, the anti-Salmonella aptamer on the electrode captures its target. Hence, electron transfer is blocked, and this results in a large increase in impedance. Salmonella can be quantified by this aptasensor, typically operated at a working voltage of 0.2 V (vs. Ag/AgCl), in the range from 75 to 7.5 × 10 5 cfu⋅mL −1 and detection limit of 25 cfu⋅mL −1 (at an S/N of 3). The method is perceived to have a wide scope in that other bacteria may be detected by analogy to this approach and with very low limits of detection by applying respective analyte-specific aptamers. (author)

  10. An amperometric penicillin biosensor with enhanced sensitivity based on co-immobilization of carbon nanotubes, hematein, and {beta}-lactamase on glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Chen Bi; Ma Ming [Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China), College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081 (China); Su Xiaoli, E-mail: xsu@hunnu.edu.cn [Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China), College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081 (China)

    2010-07-26

    An amperometric penicillin biosensor with enhanced sensitivity was successfully developed by co-immobilization of multi-walled carbon nanotubes (MWCNTs), hematein, and {beta}-lactamase on glassy carbon electrode using a layer-by-layer assembly technique. Under catalysis of the immobilized enzyme, penicillin was hydrolyzed, decreasing the local pH. The pH change was monitored amperometrically with hematein as a pH-sensitive redox probe. MWCNTs were used as an electron transfer enhancer as well as an efficient immobilization matrix for the sensitivity enhancement. The effects of immobilization procedure, working potential, enzyme quantity, buffer concentration, and sample matrix were investigated. The biosensor offered a minimum detection limit of 50 nM (19 {mu}g L{sup -1}) for penicillin V, lower than those of the conventional pH change-based biosensors by more than two orders of magnitude. The electrode-to-electrode variation of the response sensitivity was 7.0% RSD.

  11. A very low potential electrochemical detection of L-cysteine based on a glassy carbon electrode modified with multi-walled carbon nanotubes/gold nanorods.

    Science.gov (United States)

    Silva, Francisco de Assis dos Santos; da Silva, Monique Gabriella Angelo; Lima, Phabyanno Rodrigues; Meneghetti, Mario Roberto; Kubota, Lauro Tatsuo; Goulart, Marilia Oliveira Fonseca

    2013-12-15

    A nanohybrid platform built with multi-walled carbon nanotubes and gold nanorods, prepared via a cationic surfactant-containing seed-mediated sequential growth process, in aqueous solution, on a glassy carbon substrate has been successfully developed to be used in the electrocatalytic oxidation of L-cysteine (Cys). The nanohybrid was characterized by transmission electron microscopy, Raman spectroscopy and electrochemical measurements. Cyclic voltammetry results had shown that the modified electrode allows the oxidation of Cys at a very low anodic potential (0.00 V vs. Ag/AgCl). The kinetic constant kcat for the catalytic oxidation of Cys was evaluated by chronoamperometry and provided a value of 5.6×10(4) L mol(-1) s(-1). The sensor presents a linear response range from 5.0 up to 200.0 µmol L(-1), detection limit of 8.25 nmol L(-1) and a sensitivity of 120 nA L µmol(-1). Copyright © 2013 Elsevier B.V. All rights reserved.

  12. Electrocatalytic Oxidation of Venlafaxine at a Multiwall Carbon Nanotubes-Ionic Liquid Gel Modified Glassy Carbon Electrode and Its Electrochemical Determination

    Directory of Open Access Journals (Sweden)

    Ling Ding

    2015-03-01

    Full Text Available The electrocatalytic oxidation of venlafaxine (VEN was investigated at a glassy carbon electrode (GCE, the modified electrode by a gel containing multiwall carbon nanotubes (MWCNTs and a room-temperature ionic liquid (RTIL, 1-butyl-3-methylimidazolium hexafluorophate (BMIMPF6 in 0.10 mol L−1 phosphate buffer solution (PBS, pH 6.8. It was found that an irreversible anodic oxidation peak of VEN with the peak potential (Epa as 0.780 V appeared at MWCNTs-RTIL/GCE. The electrode reaction process was a diffusion-controlled one and the electrochemical oxidation involved two electrons transferring and two protons participation. Furthermore, the charge-transfer coefficient (α, and the electrode reaction rate constant (kf of VEN were found to be 0.91 and 3.04×10−2 s−1, respectively. Under the optimized conditions, the electrocatalytic oxidation peak currents were linearly dependent on the concentration of VEN in the concentration range from 2.0×10−6 mol L−1 ~ 2.0×10−3 mol L−1 with the limit of detection (S / N = 3 as 1.69×10−6 mol L−1. The proposed method has been successfully applied in the electrochemical quantitative determination of VEN content in commercial venlafaxine hydrochloride capsules and the determination results could meet the requirement of the quantitative determination.

  13. A sensitive electrochemical sensor for paracetamole based on a glassy carbon electrode modified with multiwalled carbon nanotubes and dopamine nanospheres functionalized with gold nanoparticles

    International Nuclear Information System (INIS)

    Liu, Xue; Wang, Ling-Ling; Wang, Ya-Ya; Zhang, Xiao-Yan

    2014-01-01

    We describe an electrochemical sensor for paracetamole that is based on a glassy carbon electrode modified with multiwalled carbon nanotubes and dopamine nanospheres functionalized with gold nanoparticles. The functionalized nanospheres were prepared by a chemical route and characterized by scanning electron microscopy. The well-dispersed gold nanoparticles were anchored on the dopamine nanosphere via a chemical reduction of the gold precursor. The stepwise fabrication of the modified electrode and its electrochemical response to paracetamole were evaluated using electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrode displayed improved electrocatalytic activity towards paracetamole, a lower oxidation potential (371 mV), and a larger peak current when compared to a bare electrode or other modified electrodes. The kinetic parameters governing the electro-oxidation of paracetamole were studied, and the analytical conditions were optimized. The peak current was linearly related to the concentration of paracetamole in 0.8–400 μM range, and the detection limit was 50 nM (at an SNR of 3). The method was successfully applied to the determination of paracetamole in spiked human urine samples and gave recoveries between 95.3 and 105.2 %. (author)

  14. Simple flow injection for determination of sulfite by amperometric detection using glassy carbon electrode modified with carbon nanotubes-PDDA-gold nanoparticles.

    Science.gov (United States)

    Amatatongchai, Maliwan; Sroysee, Wongduan; Chairam, Sanoe; Nacapricha, Duangjai

    2015-02-01

    A new approach is presented for sensitive and selective measurement of sulfite (SO3(2-)) in beverages based on a simple flow injection system with amperometric detection. In this work, the sulfite sensor was a glassy carbon electrode modified with multiwall carbon nanotubes-poly(diallyldimethylammonium chloride)-gold nanoparticles composites (CNTs-PDDA-AuNPs/GC). Electrochemical oxidation of sulfite with this electrode was first studied in 0.1M phosphate buffer (pH 7.0) using cyclic voltammetry. The results indicated that the CNTs-PDDA-AuNPs/GC electrode possesses electrocatalytic activity for the oxidation of sulfite with high sensitivity and selectivity. Sulfite was quantified using amperometric measurement with the new sensor at +0.4V vs Ag/AgCl in conjunction with flow injection. The linear working range for the quantitation of sulfite was 2-200 mg L(-1) (r(2)=0.998) with a detection limit of 0.03 mg L(-1) (3σ of blank) and an estimated precision of 1.5%.The proposed method was successfully applied to the determination of sulfite in fruit juices and wines with a sample throughput of 23 samples per hour. Copyright © 2014 Elsevier B.V. All rights reserved.

  15. A novel highly selective and sensitive detection of serotonin based on Ag/polypyrrole/Cu2O nanocomposite modified glassy carbon electrode.

    Science.gov (United States)

    Selvarajan, S; Suganthi, A; Rajarajan, M

    2018-06-01

    A silver/polypyrrole/copper oxide (Ag/PPy/Cu 2 O) ternary nanocomposite was prepared by sonochemical and oxidative polymerization simple way, in which Cu 2 O was decorated with Ag nanoparticles, and covered by polyprrole (PPy) layer. The as prepared materials was characterized by UV-vis-spectroscopy (UV-vis), FT-IR, X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) with EDX, high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Sensing of serotonin (5HT) was evaluated electrocatalyst using polypyrrole/glassy carbon electrode (PPy/GCE), polypyrrole/copper oxide/glassy carbon electrode (PPy/Cu 2 O/GCE) and silver/polypyrrole/copper oxide/glassy carbon electrode (Ag/PPy/Cu 2 O/GCE). The Ag/PPy/Cu 2 O/GCE was electrochemically treated in 0.1MPBS solution through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The peak current response increases linearly with 5-HT concentration from 0.01 to 250 µmol L -1 and the detection limit was found to be 0.0124 μmol L -1 . It exhibits high electrocatalytic activity, satisfactory repeatability, stability, fast response and good selectivity against potentially interfering species, which suggests its potential in the development of sensitive, selective, easy-operation and low-cost serotonin sensor for practical routine analyses. The proposed method is potential to expand the possible applied range of the nanocomposite material for detection of various concerned electro active substances. Copyright © 2018 Elsevier B.V. All rights reserved.

  16. Synthesis and Characterization of Ferrocene Derivatives and Preliminarily Electrocatalytic Oxidation of L-Cysteine at Nafion-Ferrocene Derivatives Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Jianping Yong

    2014-01-01

    Full Text Available Five new structural ferrocene derivatives (2a~2e were firstly synthesized and characterized by 1H NMR, 13C NMR, ESI-MS, and XRD. Subsequently, the preliminarily electrocatalytic oxidation of L-cysteine (L-Cys at nafion-ferrocene derivatives modified glassy carbon electrode (GCE has also been investigated by cyclic voltammetry. The results showed that 2e can dramatically electrocatalyze the oxidation of L-cysteine at its modified GCE in 0.1 mol L−1 NaNO3 aqueous solution with a quasireversible process with ΔEp≈55 mV.

  17. Electrocatalytic oxidation and selective determination of an opioid analgesic methadone in the presence of acetaminophen at a glassy carbon electrode modified with functionalized multi-walled carbon nanotubes: application for human urine, saliva and pharmaceutical samples analysis.

    Science.gov (United States)

    Amiri-Aref, Mohaddeseh; Raoof, Jahan Bakhsh; Ojani, Reza

    2013-09-01

    For the first time, electrocatalytic oxidation and selective determination of methadone (Mtd), as a long-acting opioid, in the presence of acetaminophen (Ac) has been investigated at a glassy carbon electrode modified with functionalized multi-walled carbon nanotubes. This simple and sensitive electrochemical sensor was fabricated through the drop-casting of functionalized multi-walled carbon nanotubes (fMWCNT) on the surface of a glassy carbon electrode (GCE). The electrocatalytic oxidations of Ac and Mtd are both individually and simultaneously investigated at the surface of the fMWCNT modified glassy carbon electrode (fMWCNT/MGCE) through using cyclic and differential pulse voltammetric studies. The fMWCNT/MGCE offered a considerable enhancement in the anodic peak current of Ac and Mtd associated with separating their overlapping voltammetric responses with potential difference of 290 mV. The catalytic peak currents obtained from differential pulse voltammetry of Ac and Mtd increased linearly with their concentration at the ranges of 0.45-90.0 μM and 0.5-100.0 μM, respectively, and the detection limits for Ac and Mtd were sequentially 0.35 μM and 0.28 μM. Furthermore, this electrochemical sensor was successfully implemented for the quantitative determination of Ac and Mtd in human urine, saliva and pharmaceutical samples using standard addition method and the obtained results were found to be satisfactory. Copyright © 2013 Elsevier B.V. All rights reserved.

  18. Highly Sensitive Detection of Arsenite Based on Its Affinity toward Ruthenium Nanoparticles Decorated on Glassy Carbon Electrode.

    Science.gov (United States)

    Gupta, Ruma; Gamare, Jayashree S; Pandey, Ashok K; Tyagi, Deepak; Kamat, Jayshree V

    2016-02-16

    Metallic ruthenium nanoparticles (Ru NPs) are formed on the glassy carbon electrode (GC) at electrodeposition potential of -0.75 V, as observed from X-ray photoelectron spectroscopy. Thus formed Ru NPs have the arsenite selective surface and conducting core that is ideally suited for designing a highly sensitive and reproducible response generating matrix for the arsenite detection at an ultratrace concentration in aqueous matrices. Contrary to this, arsenate ions sorb via chemical interactions on the ruthenium oxide (RuO2 and RuO3) NPs formed at -0.25 V, but not on the Ru NPs. For exploring a possibility of the quantification of arsenite in the ultratrace concentration range, the Ru NPs have been deposited on the GC by a potentiostatic pulse method of electrodeposition at optimized -0.75 V for 1000 s. Arsenite preconcentrates onto the Ru surface just by dipping the RuNPs/GC into the arsenite solution as it interacts chemically with Ru NPs. Electrochemical impedance spectroscopy of As(III) loaded RuNPs/GC shows a linear increase in the charge transfer resistance with an increase in As(III) conc. Using a differential pulse voltammetric technique, arsenite is oxidized to arsenate leading to its quantitative determination without any interference of Cu(2+) ions that are normally encountered in the water systems. Thus, the use of RuNPs/GC eliminates the need for a preconcentration step in stripping voltammetry, which requires optimization of the parameters like preconcentration potential, time, stirring, inferences, and so on. The RuNPs/GC based differential pulse voltammetric (DPV) technique can determine the concentration of arsenite in a few min with a detection limit of 0.1 ppb and 5.4% reproducibility. The sensitivity of 2.38 nA ppb(-1) obtained in the present work for As(III) quantification is considerably better than that reported in the literature, with a similar detection limit and mild conditions (pH = 2). The RuNPs/GC based DPV has been evaluated for its

  19. Platinum nanoparticles decorated dendrite-like gold nanostructure on glassy carbon electrodes for enhancing electrocatalysis performance to glucose oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Hongmei [Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, School of Materials Science and Engineering, Hubei University, No. 368 Youyi Avenue, Wuchang, Wuhan 430062 (China); Chang, Gang, E-mail: changgang@hubu.edu.cn [Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, School of Materials Science and Engineering, Hubei University, No. 368 Youyi Avenue, Wuchang, Wuhan 430062 (China); Lei, Ming [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); He, Hanping [College of Chemistry and Chemical Engineer, Hubei University, Youyi Road 368, Wuchang, Wuhan, Hubei 430062 (China); Liu, Xiong; Shu, Honghui; Xia, Tiantian; Su, Jie [Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, School of Materials Science and Engineering, Hubei University, No. 368 Youyi Avenue, Wuchang, Wuhan 430062 (China); He, Yunbin, E-mail: ybhe@hubu.edu.cn [Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, School of Materials Science and Engineering, Hubei University, No. 368 Youyi Avenue, Wuchang, Wuhan 430062 (China)

    2016-10-30

    Highlights: • Pt/DGNs/GC composites were obtained via a clean and facile method without any templates, surfactants, or stabilizers. • Controlling chemical reduction deposition time, the amount of platinum nanoparticles on Au surface could be regulated, which further tuned electrocatalytic properties toward glucose oxidation. • The obtained Pt/DGNs/GC composites with high electrochemical active surface area (ECSA) show superior electrocatalytic activity to glucose. • The sensor based on Pt/DGNs/GC exhibited excellent sensitivity, selectivity and stability for nonenzymatic glucose detection. - Abstract: Platinum nanoparticles decorated dendrite-like gold nanostructure, bimetal composite materials on glassy carbon electrode (Pt/DGNs/GC) for enhancing electrocatalysis to glucose oxidation was designed and successfully fabricated by a facile two-step deposition method without any templates, surfactants, or stabilizers. Dendrite-like gold nanostructure was firstly deposited on the GC electrode via the potentiostatic method, and then platinum nanoparticles were decorated on the surface of gold substrate through chemical reduction deposition. X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) were applied to characterize the evolution of morphology and structure of the as-prepared Pt/DGNs/GC. Based on electrochemical measurements such as cyclic voltammetry, linear voltammetry and chronoamperometry, Pt/DGNs/GC exhibited significantly enhanced electrocatalytic performance to glucose oxidation compared those of pure dendrite-like Au nanoparticles in our previous report. Controlling chemical reduction deposition time, the amount of platinum nanoparticles on Au surface could be regulated, which further tuned electrocatalytic properties toward glucose oxidation. The dendrite-like gold surface partially covered by platinum nanoparticles dramatically enhanced the electrocatalytic performance for the

  20. modified glassy carbon elect

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  1. Electrochemical characterization of glassy carbon electrode modified with 1,10-phenanthroline groups by two pathways: reduction of the corresponding diazonium ions and reduction of phenanthroline

    International Nuclear Information System (INIS)

    Shul, Galyna; Weissmann, Martin; Bélanger, Daniel

    2015-01-01

    The electrochemical behaviour of 1,10-phenanthroline molecules immobilized on a glassy carbon electrode surface by electrochemical reduction of the corresponding in-situ generated diazonium ions in an aqueous solution was investigated. Firstly, the derivatization of glassy carbon electrode was confirmed by the presence of the barrier effect in the solution of a redox probe. Secondly, atomic force microscopy measurements revealed the deposition of thin (< 2 nm) uniform 1,10-phenanthroline film on the surface of pyrolyzed photoresist film electrode. Thirdly, the initially electrochemically inactive grafted organic film became electroactive after being subjected to electrochemical reduction and oxidation. Fourthly, the electrochemical behaviour of phenanthroline modified electrode by electrochemical reduction of the corresponding diazonium cations was found to be similar to that of electrode modified by electrochemical reduction of only phenanthroline dissolved in an aqueous acid solution. Finally, cyclic voltammetry experiments using various methyl substituted phenanthroline derivatives provided direct evidence that functional groups responsible for the film electroactivity are formed at 5 or/and 6 positions of grafted phenanthroline molecules. On the other hand, a phenanthroline derivative having these positions blocked by methyl groups can also display electroactivity with position 7 being most likely involved in the observed redox process

  2. A process of glassy carbon etching without the micro masking effect for the fabrication of a mold with a high-quality surface

    Science.gov (United States)

    Youn, Sung-Won; Ueno, Akihisa; Takahashi, Masaharu; Maeda, Ryutaro

    2009-12-01

    The surface quality of a mold is one of the major factors in imprint lithography as it determines the final surface quality and the minimum size of the replicated patterns. This paper describes a process for O2-based reactive ion etching (RIE) of glassy carbon (GC) without encountering any micro masking effect. Glassy carbon, because of its attractive properties such as its surface inertness, thermal stability and extraordinary hardness, has drawn much interest as a mold material for high-temperature imprinting on glasses and metals. Etch profiles with highly smooth surfaces free of micro masking effects were achieved by adding SF6 to the etching gas. The fraction of SF6 in the gas mixture (ranging from 0.1 to 0.6) showed little change in the quality of the etched surface, but it did lead to a proportional decrease in the etch rate of GC. A reasonable GC etch rate (115-120 nm min-1) and a smooth etch surface were obtained using SF6 at a fraction 0.2 or below. Using electron beam lithography (EBL), and processing under the established SF6/O2 RIE conditions, GC molds were fabricated and successfully applied to thermal imprinting onto glass and metals.

  3. Impedimetric PSA aptasensor based on the use of a glassy carbon electrode modified with titanium oxide nanoparticles and silk fibroin nanofibers.

    Science.gov (United States)

    Benvidi, Ali; Banaei, Maryam; Tezerjani, Marzieh Dehghan; Molahosseini, Hosein; Jahanbani, Shahriar

    2017-12-14

    This article describes an impedimetric aptasensor for the prostate specific antigen (PSA), a widely accepted prostate cancer biomarker. A glassy carbon electrode (GCE) was modified with titanium oxide nanoparticles (TiO 2 ) and silk fibroin nanofiber (SF) composite. The aptasensor was obtained by immobilizing a PSA-binding aptamer on the AuNP-modified with 6-mercapto-1-hexanol. The single fabrication steps were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The assay has two linear response ranges (from 2.5 fg.mL -1 to 25 pg.mL -1 , and from 25 pg.mL -1 to 25 ng.mL -1 ) and a 0.8 fg.mL -1 detection limit. After optimization of experimental conditions, the sensor is highly selective for PSA over bovine serum albumin and lysozyme. It was successfully applied to the detection of PSA in spiked serum samples. Graphical abstract Schematic of the fabrication of an aptasensor for the prostate specific antigen (PSA). It is based on the use of a glassy carbon electrode modified with gold nanoparticles and titanium oxide-silk fibroin. The immobilization process of aptamer and interaction with PSA were followed by electrochemical impedance spectroscopy technique.

  4. Highly sensitive amperometric sensor for micromolar detection of trichloroacetic acid based on multiwalled carbon nanotubes and Fe(II)–phtalocyanine modified glassy carbon electrode

    International Nuclear Information System (INIS)

    Kurd, Masoumeh; Salimi, Abdollah; Hallaj, Rahman

    2013-01-01

    A highly sensitive electrochemical sensor for the detection of trichloroacetic acid (TCA) is developed by subsequent immobilization of phthalocyanine (Pc) and Fe(II) onto multiwalled carbon nanotubes (MWCNTs) modified glassy carbon (GC) electrode. The GC/MWCNTs/Pc/Fe(II) electrode showed a pair of well-defined and nearly reversible redox couple correspondent to (Fe(III)Pc/Fe(II)Pc) with surface-confined characteristics. The surface coverage (Γ) and heterogeneous electron transfer rate constant (k s ) of immobilized Fe(II)–Pc were calculated as 1.26 × 10 −10 mol cm −2 and 28.13 s −1 , respectively. Excellent electrocatalytic activity of the proposed GC/MWCNTs/Pc/Fe(II) system toward TCA reduction has been indicated and the three consequent irreversible peaks for electroreduction of CCl 3 COOH to CH 3 COOH have been clearly seen. The observed chronoamperometric currents are linearly increased with the concentration of TCA at concentration range up to 20 mM. Detection limit and sensitivity of the modified electrode were 2.0 μM and 0.10 μA μM −1 cm −2 , respectively. The applicability of the sensor for TCA detection in real samples was tested. The obtained results suggest that the proposed system can serve as a promising electrochemical platform for TCA detection. Highlights: ► Phthalocyanine (PC) and Fe(II) immobilized onto MWCNTs modified GC electrode. ► A pair of well-defined redox couple correspondent to (Fe(III)Pc/Fe(II)Pc) observed. ► Modified electrode shows excellent catalytic activity to electroreduction of CCl 3 COOH. ► Amperometry and cyclic voltammetry techniques were used for detection of CCl 3 COOH. ► Detection limit and sensitivity were 2.0 μM and 0.10 μA μM −1 cm −2 , respectively

  5. Analytical application of polymethylene blue-multiwalled carbon nanotubes modified glassy carbon electrode on anticancer drug irinotecan and determination of its ionization constant value.

    Science.gov (United States)

    Karadas, Nurgul; Sanli, Senem; Akmese, Bediha; Dogan-Topal, Burcu; Can, Alp; Ozkan, Sibel A

    2013-10-15

    The voltammetric behavior of anticancer drug irinotecan (IRT) was investigated at poly (methylene blue)/multi-walled carbon nanotube (PMB/MWCNT) modified glassy carbon electrode (GCE). The modified electrode surface was characterized by a scanning electron microscope (SEM). The PMB/MWCNT modified GCE exhibits a distinct shift of the oxidation potential of IRT on the cathodic direction and a considerable enhancement of the peak current compared with bare electrode. The calibration curve was linear between the concentration range 8.0 × 10(-6) and 8.0 × 10(-5)M with the detection limit of 2.14 × 10(-7)M by differential pulse voltammetry in pH 10.0 Britton-Robinson buffer solution. Controlled potential coulometry was applied to find transferred electron numbers due to the oxidation of IRT. In this study, the pKa value of IRT was also determined by the dependence of the retention factor on the pH of the mobile phase. The effect of the mobile phase composition on the ionization constant was studied by measuring the pKa at different acetonitrile-water mixtures, ranging between 35 and 50% (v/v) using the reversed-phase liquid chromatography (RP-LC) method with UV detector. IRT was exposed to thermal, photolytic, hydrolytic and oxidative stress conditions, and the stressed samples were detected by the proposed method. Sensitive, rapid, and fully validated electrochemical and RP-LC methods for the determination of IRT in its dosage form were presented in details. Copyright © 2013 Elsevier B.V. All rights reserved.

  6. Voltammetric Determination of Acetaminophen in the Presence of Codeine and Ascorbic Acid at Layer-by-Layer MWCNT/Hydroquinone Sulfonic Acid-Overoxidized Polypyrrole Modified Glassy Carbon Electrode

    OpenAIRE

    Shahrokhian, Saeed; Saberi, Reyhaneh-Sadat

    2011-01-01

    A very sensitive electrochemical sensor constructed of a glassy carbon electrode modified with a layer-by-layer MWCNT/doped-overoxidized polypyrrole (oppy/MWCNT /GCE) was used for the determination of acetaminophen (AC) in the presence of codeine and ascorbic acid (AA). In comparison to the bare glassy carbon electrode, a considerable shift in the peak potential together with an increase in the peak current was observed for AC on the surface of oppy/MWCNT/GCE, which can be related to the enla...

  7. Comparison of impedimetric detection of DNA hybridization on the various biosensors based on modified glassy carbon electrodes with PANHS and nanomaterials of RGO and MWCNTs.

    Science.gov (United States)

    Benvidi, Ali; Tezerjani, Marzieh Dehghan; Jahanbani, Shahriar; Mazloum Ardakani, Mohammad; Moshtaghioun, Seyed Mohammad

    2016-01-15

    In this research, we have developed lable free DNA biosensors based on modified glassy carbon electrodes (GCE) with reduced graphene oxide (RGO) and carbon nanotubes (MWCNTs) for detection of DNA sequences. This paper compares the detection of BRCA1 5382insC mutation using independent glassy carbon electrodes (GCE) modified with RGO and MWCNTs. A probe (BRCA1 5382insC mutation detection (ssDNA)) was then immobilized on the modified electrodes for a specific time. The immobilization of the probe and its hybridization with the target DNA (Complementary DNA) were performed under optimum conditions using different electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The proposed biosensors were used for determination of complementary DNA sequences. The non-modified DNA biosensor (1-pyrenebutyric acid-N- hydroxysuccinimide ester (PANHS)/GCE), revealed a linear relationship between ∆Rct and logarithm of the complementary target DNA concentration ranging from 1.0×10(-16)molL(-1) to 1.0×10(-10)mol L(-1) with a correlation coefficient of 0.992, for DNA biosensors modified with multi-wall carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) wider linear range and lower detection limit were obtained. For ssDNA/PANHS/MWCNTs/GCE a linear range 1.0×10(-17)mol L(-1)-1.0×10(-10)mol L(-1) with a correlation coefficient of 0.993 and for ssDNA/PANHS/RGO/GCE a linear range from 1.0×10(-18)mol L(-1) to 1.0×10(-10)mol L(-1) with a correlation coefficient of 0.985 were obtained. In addition, the mentioned biosensors were satisfactorily applied for discriminating of complementary sequences from noncomplementary sequences, so the mentioned biosensors can be used for the detection of BRCA1-associated breast cancer. Copyright © 2015. Published by Elsevier B.V.

  8. Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

    International Nuclear Information System (INIS)

    Salimi, Abdollah; MamKhezri, Hussein; Hallaj, Rahman; Zandi, Shiva

    2007-01-01

    In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k s ) of Fe(III)P immobilized on MWCNTs were 7.68 x 10 -9 mol cm -2 and 1.8 s -1 , respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO 3 - , IO 3 - and BrO 3 - in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 x 10 3 , 7.4 x 10 3 and 4.8 x 10 2 M -1 s -1 , respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and

  9. Highly sensitive amperometric sensor for micromolar detection of trichloroacetic acid based on multiwalled carbon nanotubes and Fe(II)–phtalocyanine modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Kurd, Masoumeh [Department of Chemistry, University of Kurdistan, P. O. Box 416, Sanandaj (Iran, Islamic Republic of); Salimi, Abdollah, E-mail: absalimi@uok.ac.ir [Department of Chemistry, University of Kurdistan, P. O. Box 416, Sanandaj (Iran, Islamic Republic of); Research Center for Nanotechnology, University of Kurdistan, P. O. Box 416, Sanandaj (Iran, Islamic Republic of); Hallaj, Rahman [Department of Chemistry, University of Kurdistan, P. O. Box 416, Sanandaj (Iran, Islamic Republic of)

    2013-04-01

    A highly sensitive electrochemical sensor for the detection of trichloroacetic acid (TCA) is developed by subsequent immobilization of phthalocyanine (Pc) and Fe(II) onto multiwalled carbon nanotubes (MWCNTs) modified glassy carbon (GC) electrode. The GC/MWCNTs/Pc/Fe(II) electrode showed a pair of well-defined and nearly reversible redox couple correspondent to (Fe(III)Pc/Fe(II)Pc) with surface-confined characteristics. The surface coverage (Γ) and heterogeneous electron transfer rate constant (k{sub s}) of immobilized Fe(II)–Pc were calculated as 1.26 × 10{sup −10} mol cm{sup −2} and 28.13 s{sup −1}, respectively. Excellent electrocatalytic activity of the proposed GC/MWCNTs/Pc/Fe(II) system toward TCA reduction has been indicated and the three consequent irreversible peaks for electroreduction of CCl{sub 3}COOH to CH{sub 3}COOH have been clearly seen. The observed chronoamperometric currents are linearly increased with the concentration of TCA at concentration range up to 20 mM. Detection limit and sensitivity of the modified electrode were 2.0 μM and 0.10 μA μM{sup −1} cm{sup −2}, respectively. The applicability of the sensor for TCA detection in real samples was tested. The obtained results suggest that the proposed system can serve as a promising electrochemical platform for TCA detection. Highlights: ► Phthalocyanine (PC) and Fe(II) immobilized onto MWCNTs modified GC electrode. ► A pair of well-defined redox couple correspondent to (Fe(III)Pc/Fe(II)Pc) observed. ► Modified electrode shows excellent catalytic activity to electroreduction of CCl{sub 3}COOH. ► Amperometry and cyclic voltammetry techniques were used for detection of CCl{sub 3}COOH. ► Detection limit and sensitivity were 2.0 μM and 0.10 μA μM{sup −1} cm{sup −2}, respectively.

  10. Manganese oxide nanoflakes/multi-walled carbon nanotubes/chitosan nanocomposite modified glassy carbon electrode as a novel electrochemical sensor for chromium (III) detection

    International Nuclear Information System (INIS)

    Salimi, Abdollah; Pourbahram, Bahareh; Mansouri-Majd, Samira; Hallaj, Rahman

    2015-01-01

    Highlights: • CNTs/chitosan/GC electrode used as platform for electrodeposition of MnO x -nanoflakes. • Modified electrode has excellent catalytic activity for oxidation of Cr 3+ at pH 3–7. • Detection limit and sensitivity of sensor for Cr 3+ detection were 0.3 μM and 18.7 nA/μM. • Sensor has good stability and high selectivity in the presence of common interferences. • Sensor applied for the detection of Cr 3+ in real samples with satisfactory results. - Abstract: In this research a nanocomposite containing chitosan (Chit) and maltiwalled carbon nanotubes (MWCNTs) was applied as platform for immobilization of electrodeposited manganese oxide (MnOx) nanostructures. First, glassy carbon (GC) electrode modified with thin film of Chitosan/MWCNTs nanocomposite. Then MnO x nanostructures was electrodeposited onto Chitosan/MWCNTs modified GC electrode using combination of constant potential step (0.6 V) and cyclic voltammetry(0.3–0.6 V) techniques. The XRD patterns and scanning electron microscope images indicated immobilization of uniformly MnOx nanoflakes with high crystallite onto MWCNTs/Chit film. The modified electrode shows a well-defined redox couple for Mn 2+ /MnO 2 system. Charge transfer coefficient (α), electron transfer rate constant (k s ) and surface concentration (Γ) were 0.394, 3.44 s −1 and 3.3 × 10 −11 mol cm −2 , respectively. The modified electrode showed excellent electrocatalytic activity toward oxidation of chromium (III) at natural pH solutions. Cyclic voltammetry and hydrodynamic amperometery were applied as measuring techniques for chromium detection. Detection limit, sensitivity and linear concentration range of the sensor were, 0.3 (μM), 18.7 nAμ M −1 and 3 μM to 200 μM, respectively. Moreover, the sensor retained about 90% of its original response toward Cr(III) after storage three months in ambient condition. Furthermore, the sensor response toward different common interferences was negligible. Finally, the

  11. Methanol oxidation at platinized lead coatings prepared by a two-step electrodeposition-electroless deposition process on glassy carbon and platinum substrates

    International Nuclear Information System (INIS)

    Papadimitriou, S.; Tegou, A.; Pavlidou, E.; Kokkinidis, G.; Sotiropoulos, S.

    2007-01-01

    Platinized lead deposits, Pt(Pb), have been formed on glassy carbon (GC) and platinum electrodes by a two-step process, whereby a controlled amount of Pb was electrodeposited onto the substrates and was subsequently coated with a thin Pt layer upon immersion of the Pb/GC or Pb/Pt electrodes into a chloroplatinic acid solution. The spontaneous surface replacement of Pb by Pt resulted in Pt(Pb)/GC or Pt(Pb)/Pt electrodes which consisted of dispersed Pt(Pb) particles and displayed typical Pt surface electrochemistry in deaerated acid solutions. When tested as methanol oxidation anodes, these electrodes exhibited enhanced electrocatalytic activity both during voltammetric and constant potential experiments. This behaviour is attributed to an electronic effect of the underlying Pb onto the Pt surface layer

  12. Glassy carbon electrodes modified with composites of starburst-PAMAM dendrimers containing metal nanoparticles for amperometric detection of dopamine in urine.

    Science.gov (United States)

    Bustos, Erika Bustos; Jiménez, Ma Guadalupe García; Díaz-Sánchez, Blanca R; Juaristi, Eusebio; Chapman, Thomas W; Godínez, Luis A

    2007-06-15

    Composites of hydroxyl-terminated PAMAM dendrimers, generation 4.0 (64 peripheral OH groups) containing either Ir, Pt or Rh nanoparticles were synthesized and characterized in solution. Each one of these composites was then immobilized on a glassy carbon electrode (GC) and incorporated as an amperometric detector for dopamine in a high-performance liquid chromatograph (HPLC). Comparison of the analytical performance of the novel electrochemical detectors with a typical UV-vis optical detector for dopamine revealed that the sensitivity of the GC electrode modified with dendrimer-Rh composite is comparable to that of the spectroscopic detector, with a detection limit of 0.15muM, and is linear up to at least 1.0mM (R(2)=0.998). Furthermore, it was found that the electroanalytical approach suffers minimal matrix effects that arise in the analysis of dopamine in samples of urine.

  13. A novel electrochemical sensor for the analysis of β-agonists: The poly(acid chrome blue K)/graphene oxide-nafion/glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Xiaoyun [State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047 (China); Ni, Yongnian, E-mail: ynni@ncu.edu.cn [State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047 (China); Department of Chemistry, Nanchang University, Nanchang 330031 (China); Kokot, Serge, E-mail: s.kokot@qut.edu.au [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane 4001 (Australia)

    2013-09-15

    Graphical abstract: A new modified electrode was constructed by the electro-polymerization of acid chrome blue K (ACBK) at a graphene-nafion modified glassy carbon electrode (GCE). The novel electrode was successfully employed for the analysis of eight β-agonist analytes with high sensitivity. -- Highlights: • Construction of the poly-ACBK/graphene-nafion/GCE. •The modified electrode showed high sensitivity for the analysis of the β-agonists. • A novel method was successfully developed for the analysis of clenbuterol in pork. • Research provided a new method of constructing electrodes for biological analysis. -- Abstract: A novel modified electrode was constructed by the electro-polymerization of 4,5-dihydroxy-3-[(2-hydroxy-5-sulfophenyl)azo]-2,7-naphthalenedisulfonic acid trisodium salt (acid chrome blue K (ACBK)) at a graphene oxide (GO)-nafion modified glassy carbon electrode (GCE). The characterization of an electrochemically synthesized poly-ACBK/GO-nafion film was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques, and the results were interpreted and compared at each stage of the electrode construction. Electrochemical oxidation of eight β-agonists – clenbuterol, salbutamol, terbutaline, ractopamine, dopamine, dobutamine, adrenaline, and isoprenaline, was investigated by CV at the different electrodes. At the poly-ACBK/GO-nafion/GCE, the linear sweep voltammetry peak currents of the eight β-agonists increased linearly with their concentrations in the range of 1.0–36.0 ng mL{sup −1}, respectively, and their corresponding limits of detection (LODs) were within the 0.58–1.46 ng mL{sup −1} range. This electrode showed satisfactory reproducibility and stability, and was used successfully for the quantitative analysis of clenbuterol in pork samples.

  14. Electrochemical mechanism of eugenol at a Cu doped gold nanoparticles modified glassy carbon electrode and its analytical application in food samples

    International Nuclear Information System (INIS)

    Lin, Xiaoyun; Ni, Yongnian; Kokot, Serge

    2014-01-01

    Graphical abstract: A simple one-step electrodeposition method was used to fabricate a Cu doped gold nanoparticles modified glassy carbon electrode. An electrochemical reaction mechanism for o-methoxy phenols was suggested. In addition, the above Cu@AuNPs/GCE was successfully employed for the analysis of eugenol in food samples. - Highlights: • One-step construction of the Cu@AuNPs/GCE electrode. • The modified electrode showed high sensitivity for the analysis of eugenol. • Electrochemical mechanism of eugenol by use of Cu@AuNPs/GCE was inferred. • The novel method was successfully employed for analysis of eugenol in food samples. - Abstract: A simple one-step electrodeposition method was used to construct a glassy carbon electrode (GCE), which has been modified with Cu doped gold nanoparticles (GNPs), i.e. a Cu@AuNPs/GCE. This electrode was characterized with the use of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The eugenol was electrocatalytically oxidized at the Cu@AuNPs/GCE. At this electrode, in comparison with the behavior at the GCE alone, the corresponding oxidation peak current was enhanced and the shift of the oxidation potentials to lower values was observed. Electrochemical behavior of eugenol at the Cu@AuNPs/GCE was investigated with the use of the cyclic voltammetry (CV) technique, and additionally, in order to confirm the electrochemical reaction mechanism for o-methoxy phenols, CVs for catechol, guaiacol and vanillin were investigated consecutively. Based on this work, an electrochemical reaction mechanism for o-methoxy phenols was suggested, and in addition, the above Cu@AuNPs/GCE was successfully employed for the analysis of eugenol in food samples

  15. Electrocatalytic reduction of oxygen at glassy carbon electrode modified by polypyrrole/anthraquinones composite film in various pH media

    International Nuclear Information System (INIS)

    Valarselvan, S.; Manisankar, P.

    2011-01-01

    Graphical abstract: The electrocatalytic reduction of dioxygen by one mono and four dihydroxy derivatives of 9,10-anthraquinone (AQ) incorporated in polypyrrole (PPy) matrix on glassy carbon electrode has been investigated. AQ and PPy composite film showed excellent electrocatalytic performance for the reduction of O 2 to H 2 O 2 . Highlights: → Hydroxyl derivatives of anthraquinones as electrocatalysts for dioxygen reduction. → AQ/PPy composite film on GC electrode exhibits potent electrocatalytic activity. → Substituent groups influence electrocatalytic dioxygen reduction. → Surface coverage varies the rate of electrocatalytic dioxygen reduction. - Abstract: The electrocatalytic reduction of dioxygen by one mono and four dihydroxy derivatives of 9,10-anthraquinone (AQ) incorporated in polypyrrole (PPy) matrix on glassy carbon electrode has been investigated. The electrochemical behaviour of the modified electrodes was examined in various pH media and both the formal potential of anthraquinones and reduction potential of dioxygen exhibited pH dependence. AQ and PPy composite film showed excellent electrocatalytic performance for the reduction of O 2 to H 2 O 2 . pH 6.0 was chosen as the most suitable medium to study the electrocatalysis by comparing the peak potential of oxygen reduction and enhancement in peak current for oxygen reduction. The diffusion coefficient values of AQ at the modified electrodes and the number of electrons involved in AQ reduction were evaluated by chronoamperometric and chronocoulometric techniques, respectively. In addition, hydrodynamic voltammetric studies showed the involvement of two electrons in O 2 reduction. The mass specific activity of AQ used, the diffusion coefficient of oxygen and the heterogeneous rate constants for the oxygen reduction at the surface of modified electrodes were also determined by rotating disk voltammetry.

  16. An aptasensor for voltammetric and impedimetric determination of cocaine based on a glassy carbon electrode modified with platinum nanoparticles and using rutin as a redox probe

    International Nuclear Information System (INIS)

    Roushani, Mahmoud; Shahdost-fard, Faezeh

    2016-01-01

    We describe a method for the determination of cocaine that is based on a glassy carbon electrode modified with a nanocomposite consisting of multiwalled carbon nanotubes, an ionic liquid, and chitosan. The electrode was made cocaine-responsive by immobilizing a cocaine-specific aptamer and platinum nanoparticles (PtNPs) on the modified electrode. The use of PtNPs resulted in the acceleration of the electron transfer kinetics of the reduction of the redox probe rutin and enhances sensitivity. The sensor, best operated at a working voltage of 260 mV vs. Ag/AgCl, has a linear response to cocaine in the 1 nM to 11 μM concentration range, and the detection limit is 100 pM (at an S/N ratio of 3). We think this strategy to represent a promising platform for the sensitive and selective determination of cocaine. The sensor is adequately stable and was successfully applied to the determination of cocaine in spiked serum. (author)

  17. Electrochemical determination of theophylline in foodstuff, tea and soft drinks based on urchin-like CdSe microparticles modified glassy carbon electrode.

    Science.gov (United States)

    Yin, Huanshun; Meng, Xiaomeng; Su, Haichao; Xu, Minrong; Ai, Shiyun

    2012-09-15

    A simply electrochemical method based on CdSe microparticles modified glassy carbon electrode (GCE) was developed to determine theophylline using cyclic voltammetry and differential pulse voltammetry. Theophylline showed a well-defined oxidation peak at the fabricated electrode in phosphate buffer solution and the oxidation peak current is much higher than that at the bare GCE, indicating that CdSe can effectively improve the oxidation of theophylline. Several effect factors on theophylline determination were optimised, such as CdSe amount, solution pH, scan rate and accumulation time. Under the optimal conditions, the oxidation peak current of theophylline was proportional to its concentration in the range of 1.0-40 and 40-700 μM with a correlation coefficient of 0.9974 and 0.9956, respectively. The limit of detection was estimated to be 0.4 μM (S/N=3). The developed method showed good reproducibility and excellent selectivity. The fabricated electrode was successfully used to determine theophylline in tea, carbonated cola drink, fruit juice drink, fermented milk drink and preserved fruit with acceptable recovery. Copyright © 2012 Elsevier Ltd. All rights reserved.

  18. A new sensor based on glassy carbon electrode modified with nanocomposite for simultaneous determination of acetaminophen, ascorbic acid and uric acid

    Directory of Open Access Journals (Sweden)

    Mohammad Afrasiabi

    2016-09-01

    Full Text Available A chemically-modified electrode has been constructed based on a single walled carbon nanotube/chitosan/room temperature ionic liquid nanocomposite modified glassy carbon electrode (SWCNTs–CHIT–RTIL/GCE. It was demonstrated that this sensor could be used for simultaneous determination of acetaminophen (ACT, uric acid (URI and ascorbic acid (ASC. The measurements were carried out by application of differential pulse voltammetry (DPV, cyclic voltammetry (CV and chronoamperometry (CA methods. Electrochemical studies suggested that the RTIL and SWCNTs provided a synergistic augmentation that can increase current responses by improvement of electron transfers of these compounds on the electrode surface. The presence of the CHIT in the modified electrode can enhance the repeatability of the sensor by its antifouling effect. The modified electrode showed electrochemical responses with high sensitivity for ACT, URI and ASC determination, which makes it a suitable sensor for simultaneous sub-μmol L−1 detection of ACT, URI and ASC in aqueous solutions. The analytical performance of this sensor has been evaluated for detection of ACT, URI and ASC in human serum and urine with satisfactory results.

  19. PdCo porous nanostructures decorated on polypyrrole @ MWCNTs conductive nanocomposite—Modified glassy carbon electrode as a powerful catalyst for ethanol electrooxidation

    Energy Technology Data Exchange (ETDEWEB)

    Fard, Leyla Abolghasemi [Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, University of Mazandaran, 3rd Kilometer of Air Force Road, 47416-95447, Babolsar (Iran, Islamic Republic of); Ojani, Reza, E-mail: fer-o@umz.ac.ir [Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, University of Mazandaran, 3rd Kilometer of Air Force Road, 47416-95447, Babolsar (Iran, Islamic Republic of); Raoof, Jahan Bakhsh [Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, University of Mazandaran, 3rd Kilometer of Air Force Road, 47416-95447, Babolsar (Iran, Islamic Republic of); Zare, Ehsan Nazarzadeh; Lakouraj, Moslem Mansour [Polymer Research Laboratory Department of Organic-Polymer Chemistry, Faculty of Chemistry, University of Mazandaran, 3rd Kilometer of Air Force Road, 47416-95447, Babolsar (Iran, Islamic Republic of)

    2017-04-15

    Highlights: • The PdCo PNS/PPy@MWCNT electrocatalyst was easily prepared. • The electrocatalyst exhibits high electrocatalytic activity and stability toward the EOR. • The specific activity of PdCo PNS/PPy@MWCNTs for ethanol electrooxidation (1.65 mA cm{sup −2}) is higher than those of other compared electrocatalysts. • The high electrocatalytic performance is attributed to concerted effects of Porous nature, Co and PPy@MWCNT. • The PdCo PNS/PPy@MWCNT electrocatalyst has never been reported. - Abstract: In the current study, well-defined PdCo porous nanostructure (PdCo PNS) is prepared by a simple one-pot wet-chemical method and polypyrrole@multi-walled carbon nanotubes (PPy@MWCNTs) nanocomposite is used as a catalyst support. The morphology and the structural properties of the prepared catalyst were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrocatalytic performance of PdCo PNS/PPy@MWCNTs on glassy carbon electrode has been evaluated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques. The specific activity of PdCo PNS/PPy@MWCNTs for ethanol electrooxidation (1.65 mA cm{sup −2}) is higher than those of other compared electrocatalysts. Also, PdCo PNS/PPy@MWCNTs catalyst represented higher electrocatalytic activity, better long-term stability and high level of poisoning tolerance to the carbonaceous oxidative intermediates for ethanol electrooxidation reaction in alkaline media. Furthermore, the presence of PPY@MWCNTs on the surface of GCE produce a high activity to electrocatalyst, which might be due to the easier charge transfer at polymer/carbon nanotubes interfaces, higher electrochemically accessible surface areas and electronic conductivity. The superior catalytic activity of PdCo PNS/PPy@MWCNTs suggests it to be as a promising electrocatalyst for future direct ethanol fuel cells.

  20. Modification of glassy carbon electrode with poly(hydroxynaphthol blue)/multi-walled carbon nanotubes composite and construction a new voltammetric sensor for the simultaneous determination of hydroquinone, catechol, and resorcinol

    Science.gov (United States)

    Daneshinejad, Hassan; Arab Chamjangali, Mansour; Goudarzi, Nasser; Hossain Amin, Amir

    2018-03-01

    A novel voltammetric sensor is developed based on a poly(hydroxynaphthol blue)/multi-walled carbon nanotubes-modified glassy carbon electrode for the simultaneous determination of the dihydroxybenzene isomers hydroquinone (HQ), catechol (CC), and resorcinol (RS). The preparation and basic electrochemical performance of the sensor are investigated in details. The electrochemical behavior of the dihydroxybenzene isomers at the sensor is studied by the cyclic and differential pulse voltammetric techniques. The results obtained show that this new electrochemical sensor exhibits an excellent electro-catalytic activity towards oxidation of the three isomers. The mechanism of this electro-catalytic activity is discussed. Using the optimum parameters, limit of detection obtained 0.24, 0.24, and 0.26 μmol L-1 for HQ, CC, and RS, respectively. The modified electrode is also successfully applied to the simultaneous determination of dihydroxybenzene in water samples.

  1. Immobilization of [Cu(bpy)2]Br2 complex onto a glassy carbon electrode modified with alpha-SiMo12O40(4-) and single walled carbon nanotubes: application to nanomolar detection of hydrogen peroxide and bromate.

    Science.gov (United States)

    Salimi, Abdollah; Korani, Aazam; Hallaj, Rahman; Khoshnavazi, Roshan; Hadadzadeh, Hasan

    2009-03-02

    A simple procedure has been used for preparation of modified glassy carbon electrode with carbon nanotubes and copper complex. Copper complex [Cu(bpy)(2)]Br(2) was immobilized onto glassy carbon (GC) electrode modified with silicomolybdate, alpha-SiMo(12)O(40)(4-) and single walled carbon nanotubes (SWCNTs). Copper complex and silicomolybdate irreversibly and strongly adsorbed onto GC electrode modified with CNTs. Electrostatic interactions between polyoxometalates (POMs) anions and Cu-complex, cations mentioned as an effective method for fabrication of three-dimensional structures. The modified electrode shows three reversible redox couples for polyoxometalate and one redox couple for Cu-complex at wide range of pH values. The electrochemical behavior, stability and electron transfer kinetics of the adsorbed redox couples were investigated using cyclic voltammetry. Due to electrostatic interaction, copper complex immobilized onto GC/CNTs/alpha-SiMo(12)O(40)(4-) electrode shows more stable voltammetric response compared to GC/CNTs/Cu-complex modified electrode. In comparison to GC/CNTs/Cu-complex the GC/CNTs/alpha-SiMo(12)O(40)(4-) modified electrodes shows excellent electrocatalytic activity toward reduction H(2)O(2) and BrO(3)(-) at more reduced overpotential. The catalytic rate constants for catalytic reduction hydrogen peroxide and bromate were 4.5(+/-0.2)x10(3) M(-1) s(-1) and 3.0(+/-0.10)x10(3) M(-1) s(-1), respectively. The hydrodynamic amperommetry technique at 0.08 V was used for detection of nanomolar concentration of hydrogen peroxide and bromate. Detection limit, sensitivity and linear concentration range proposed sensor for bromate and hydrogen peroxide detection were 1.1 nM and 6.7 nA nM(-1), 10 nM-20 microM, 1 nM, 5.5 nA nM(-1) and 10 nM-18 microM, respectively.

  2. Development of a voltammetric procedure for assay of the antihistamine drug hydroxyzine at a glassy carbon electrode: Quantification and pharmacokinetic studies.

    Science.gov (United States)

    Beltagi, A M; Abdallah, O M; Ghoneim, M M

    2008-01-15

    An electrochemical study of hydroxyzine at a glassy carbon electrode was carried out in the Britton-Robinson universal buffer of pH 2-11. Hydroxyzine was oxidized in a single two-electron irreversible process controlled mainly by adsorption. A simple, sensitive and time-saving square-wave adsorptive anodic stripping voltammetric procedure has been developed for determination of hydroxyzine in its commercial tablets and human serum without prior extraction. The optimized procedural conditions were: frequency=120Hz, scan increment=10mV, pulse-amplitude=25mV, accumulation potential=-0.3V, accumulation time=90-300s and a Britton-Robinson universal buffer of pH 4 as a supporting electrolyte. Mean recoveries of 100.5+/-0.71 and 98.6+/-1.12% (n=5) were achieved for assay of hydroxyzine in Atarax 10 and 25mg dosage forms, respectively. Limit of detection of 1.5x10(-8)molL(-1) (5.624ngmL(-1)) and limit of quantitation of 5.0x10(-8)molL(-1) (18.746ngmL(-1)) were achieved in human serum with a mean recovery of 98.4+/-1.22%, without prior extraction of the drug. Moreover, the described procedure was applied for evaluating the pharmacokinetic parameters of hydroxyzine in plasma of two healthy volunteers after administration of a single oral dose (Atarax)-25mg).

  3. Electrocatalytic oxidation behavior of NADH at Pt/Fe{sub 3}O{sub 4}/reduced-graphene oxide nanohybrids modified glassy carbon electrode and its determination

    Energy Technology Data Exchange (ETDEWEB)

    Roushani, Mahmoud, E-mail: mahmoudroushani@yahoo.com [Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, 69315516 (Iran, Islamic Republic of); Hoseini, S. Jafar [Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj, 7591874831 (Iran, Islamic Republic of); Azadpour, Mitra [Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, 69315516 (Iran, Islamic Republic of); Heidari, Vahid; Bahrami, Mehrangiz; Maddahfar, Mahnaz [Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj, 7591874831 (Iran, Islamic Republic of)

    2016-10-01

    We have developed Pt/Fe{sub 3}O{sub 4}/reduced-graphene oxide nanohybrids modified glassy carbon (Pt/Fe{sub 3}O{sub 4}/RGO/GC) electrode as a novel system for the preparation of electrochemical sensing platform. Characterization of as-made composite was determined using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and energy-dispersive analysis of X-ray (EDAX) where the Pt, Fe, Si, O and C elements were observed. The Pt/Fe{sub 3}O{sub 4}/RGO/GC electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effect between Pt, Fe{sub 3}O{sub 4} and RGO, the nanohybrid exhibited excellent performance toward dihydronicotinamide adenine dinucleotide (NADH) oxidation in 0.1 M phosphate buffer solution, pH 7.0, with a low detection limit of 5 nM. - Highlights: • Preparation of a novel electrochemical sensing platform system • Excellent performance of Pt/Fe{sub 3}O{sub 4}/reduced-graphene oxide nanohybrids • Dihydronicotinamide adenine dinucleotide oxidation with a low detection limit of 5 nM.

  4. Electrochemical sensing of nitrite using a glassy carbon electrode modified with reduced functionalized graphene oxide decorated with flower-like zinc oxide

    International Nuclear Information System (INIS)

    Marlinda, Ab Rahman; Pandikumar, Alagarsamy; Yusoff, Norazriena; Huang, Nay Ming; Lim, Hong Ngee

    2015-01-01

    A nanocomposite consisting of flower-like zinc oxide (ZnO) and reduced functionalized graphene oxide (rFGO) was prepared via a hydrothermal route, and characterized by spectrophotometry, photoluminescence, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The nanocomposite was deposited on the surface of a glassy carbon electrode and studied using impedance spectroscopy. It exhibits excellent electrocatalytic activity toward the oxidation of nitrite. At a working potential of 0.9 V (vs. Ag/AgCl), it displayed a higher current and lower over potential (reduced by up to ∼200 mV) than controlled electrodes. This is attributed to the synergistic catalytic effects of the ZnO and rfGO. The oxidation current is linearly related to the concentration of nitrite in the 10 μM to 8 mM range, and the detection limit is 33 μM. Its excellent electrocatalytic activity, wide linear range, low detection limit, high sensitivity, and rapid response time make this nanocomposite-based electrode a potential candidate for practical applications. (author)

  5. Differential pulse voltammetric determination of salbutamol sulfate in syrup pharmaceutical formulation using poly(4-amino-3-hydroxynaphthalene sulfonic acid modified glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    Meareg Amare

    2017-10-01

    Full Text Available A new method for determination of salbutamol sulfate has been developed using poly(4-amino-3-hydroxynaphthalene sulfonic acid/GCE. Cyclic voltammetric investigation of the electrochemical behavior of salbutamol sulfate at the polymer modified glassy carbon unveiled electrocatalytic activity of the modifier towards irreversible oxidation of salbutamol sulfate. Dependence of peak current predominantly on scan rate than on square root of scan rate, and peak potential shift with pH demonstrated that oxidation of salbutamol sulfate at the polymer modified electrode follows adsorption reaction kinetics with proton participation.Under optimized solution and differential pulse voltammetric parameters, the oxidative peak current showed linear dependence on salbutamol sulfate concentration in the range 0.2 to 8 μM with method detection limit (3s/m and determination coefficient (R2 of 6.8 × 10−8 M and 0.99786, respectively. Low method detection limit, relatively wide linear range, and recovery results of spiked standard salbutamol sulfate in syrup samples in the range 96.7–98.9% validated the method for determination of salbutamol sulfate in pharmaceutical formulations.Differential pulse voltammetric analysis of salbutamol sulfate syrup formulation for its salbutamol sulfate content revealed 98.8 to 99.3% of the labeled value confirming the applicability of the developed method for determination of salbutamol sulfate in real samples. Keywords: Electrochemistry, Analytical chemistry

  6. A study on enhancement of Np extraction by TBP through the electrochemical adjustment of Np valance by using a glassy carbon fiber column electrode system

    International Nuclear Information System (INIS)

    Kim, K. W.; Song, K. C.; Lee, I. H.; Choi, I. K.; Yoo, J. H.

    1999-01-01

    The Np valance state in nitric acid and the effect of nitrous acid on the Np valance composition were studied through ways of absorbance by spectrophotometer, extraction by TBP, and electrochemistry. Enhancement of Np extraction to 30 vol.% TBP was carried out through adjustment of Np valance state by using a glassy carbon fiber column electrode system. The Np solution used in this work consisted of only Np(V) and Np(VI) without Np(IV). The composition of Np(V) in the range of 0.5M ∼ 5.5 M nitric acid was 32% ∼ 19%. The electrolytic oxidation of Np(V) coexisting with Np(VI) in the solution enhanced Np extraction by 30 vol.% TBP about five times more than the one without the electrolytic oxidation. The facts were confirmed that the nitrous acid of less than about 10 -5 M acted as a catalyst to accelerate the chemical oxidation reaction of Np(V) to Np(VI) and the nitrous acid of more than 10 -3 M reduced Np(VI) to Np(V) reversely

  7. Very sensitive electrochemical determination of diuron on glassy carbon electrode modified with reduced graphene oxide-gold nanoparticle-Nafion composite film.

    Science.gov (United States)

    Zarei, K; Khodadadi, A

    2017-10-01

    In this work, a very sensitive electrochemical sensor based on glassy carbon electrode (GCE) modified with reduced graphene oxide-gold nanoparticles/Nafion (rGO-AuNPs/Nafion) composite film was applied to determine diuron. Synthesized GO was characterized using X-ray diffraction (XRD) and UV-visible spectroscopy. The surface morphology of the rGO-AuNPs/Nafion film was also characterized using scanning electron microscopy and electrochemical impedance spectroscopy. Cyclic voltammetry (CV) and adsorptive differential pulse voltammetry (AdDPV) were applied to investigate the electrochemical response of the diuron on the modified electrode. The electrode showed a linear response at 1.0×10 -9 -1.0×10 -7 M and a detection limit of 0.3nM under the optimized conditions. The effect of some other species on the determination of diuron was investigated and the sensor showed good selectivity for determination of diuron. The constructed sensor was applied to determine diuron in enriched samples of orange juice, mineral and tap water which statistical t-test showed accuracy of method. Also the sensor was applied to obtain diuron content in the tea sample. The reliability of the proposed sensor was confirmed after comparing the results with those obtained using high performance liquid chromatography (HPLC) as a comparative method. Copyright © 2017 Elsevier Inc. All rights reserved.

  8. Dopamine and uric acid electrochemical sensor based on a glassy carbon electrode modified with cubic Pd and reduced graphene oxide nanocomposite.

    Science.gov (United States)

    Wang, Jin; Yang, Beibei; Zhong, Jiatai; Yan, Bo; Zhang, Ke; Zhai, Chunyang; Shiraishi, Yukihide; Du, Yukou; Yang, Ping

    2017-07-01

    A cubic Pd and reduced graphene oxide modified glassy carbon electrode (Pd/RGO/GCE) was fabricated to simultaneously detect dopamine (DA) and uric acid (UA) by cyclic voltammetry (CV) and different pulse voltammetry (DPV) methods. Compared with Pd/GCE and RGO/GCE, the Pd/RGO/GCE exhibited excellent electrochemical activity in electrocatalytic behaviors. Performing the Pd/RGO/GCE in CV measurement, the well-defined oxidation peak potentials separation between DA and UA reached to 145mV. By using the differential pulse voltammetry (DPV) technique, the calibration curves for DA and UA were found linear with the concentration range of 0.45-421μM and 6-469.5μM and the detection limit (S/N =3) were calculated to be 0.18μM and 1.6μM, respectively. Furthermore, the Pd/RGO/GCE displayed high selectivity when it was applied into the determination of DA and UA even though in presence of high concentration of interferents. Additionally, the prepared electrochemical sensor of Pd/RGO/GCE demonstrated a practical feasibility in rat urine and serum samples determination. Copyright © 2017 Elsevier Inc. All rights reserved.

  9. Glassy carbon electrode modified with 7,7,8,8-tetracyanoquinodimethane and graphene oxide triggered a synergistic effect: Low-potential amperometric detection of reduced glutathione.

    Science.gov (United States)

    Yuan, Baiqing; Xu, Chunying; Zhang, Renchun; Lv, Donghui; Li, Sujuan; Zhang, Daojun; Liu, Lin; Fernandez, Carlos

    2017-10-15

    A sensitive electrochemical sensor based on the synergistic effect of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and graphene oxide (GO) for low-potential amperometric detection of reduced glutathione (GSH) in pH 7.2 phosphate buffer solution (PBS) has been reported. This is the first time that the combination of GO and TCNQ have been successfully employed to construct an electrochemical sensor for the detection of glutathione. The surface of the glassy carbon electrode (GCE) was modified by a drop casting using TCNQ and GO. Cyclic voltammetric measurements showed that TCNQ and GO triggered a synergistic effect and exhibited an unexpected electrocatalytic activity towards GSH oxidation, compared to GCE modified with only GO, TCNQ or TCNQ/electrochemically reduced GO. Three oxidation waves for GSH were found at -0.05, 0.1 and 0.5V, respectively. Amperometric techniques were employed to detect GSH sensitively using a GCE modified with TCNQ/GO at -0.05V. The electrochemical sensor showed a wide linear range from 0.25 to 124.3μM and 124.3μM to 1.67mM with a limit of detection of 0.15μM. The electroanalytical sensor was successfully applied towards the detection of GSH in an eye drop solution. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. Simultaneous determination of caffeine and paracetamol by square wave voltammetry at poly(4-amino-3-hydroxynaphthalene sulfonic acid)-modified glassy carbon electrode.

    Science.gov (United States)

    Tefera, Molla; Geto, Alemnew; Tessema, Merid; Admassie, Shimelis

    2016-11-01

    Poly(4-amino-3-hydroxynaphthalene sulfonic acid)-modified glassy carbon electrode (poly(AHNSA)/GCE) was prepared for simultaneous determination of caffeine and paracetamol using square-wave voltammetry. The method was used to study the effects of pH and scan rate on the voltammetric response of caffeine and paracetamol. Linear calibration curves in the range of 10-125μM were obtained for both caffeine and paracetamol in acetate buffer solution of pH 4.5 with a correlation coefficient of 0.9989 and 0.9986, respectively. The calculated detection limits (S/N=3) were 0.79μM for caffeine and 0.45μM for paracetamol. The effects of some interfering substances in the determination of caffeine and paracetamol were also studied and their interferences were found to be negligible which proved the selectivity of the modified electrode. The method was successfully applied for the quantitative determination of caffeine and paracetamol in Coca-Cola, Pepsi-Cola and tea samples. Copyright © 2016 Elsevier Ltd. All rights reserved.

  11. Electrocatalytic Reduction of Hydrogen Peroxide on Palladium-Gold Codeposits on Glassy Carbon: Applications to the Design of Interference-Free Glucose Biosensor

    Directory of Open Access Journals (Sweden)

    Elena Horozova

    2011-01-01

    Full Text Available Following our previous studies on the catalytic activity electrochemically codeposited on graphite Pd-Pt electrocatalysts for hydrogen peroxide electroreduction, a series of glassy carbon electrodes were modified with Pd or (Pd+Au deposits aiming at the development of even more efficient electrocatalysts for the same process. The resulting electrodes were found to be very effective at low applied potentials (−100 and −50 mV versus Ag/AgCl, 1 M KCl. The surface topography of the electrode modified with Pd+Au mixed in proportions 90% : 10%, exhibiting optimal combination of sensitivity and linear dynamic range towards hydrogen peroxide electrochemical reduction, was studied with SEM and AFM. The applicability of the same electrode as transducer in an amperometric biosensor for glucose assay was demonstrated. At an applied potential of −50 mV, the following were determined: detection limit (S/N=3 of 6×10−6 M glucose, electrode sensitivity of 0.15 μA μM−1, and strict linearity up to concentration of 3×10−4 M.

  12. A novel electrochemical sensor for the analysis of β-agonists: the poly(acid chrome blue K)/graphene oxide-nafion/glassy carbon electrode.

    Science.gov (United States)

    Lin, Xiaoyun; Ni, Yongnian; Kokot, Serge

    2013-09-15

    A novel modified electrode was constructed by the electro-polymerization of 4,5-dihydroxy-3-[(2-hydroxy-5-sulfophenyl)azo]-2,7-naphthalenedisulfonic acid trisodium salt (acid chrome blue K (ACBK)) at a graphene oxide (GO)-nafion modified glassy carbon electrode (GCE). The characterization of an electrochemically synthesized poly-ACBK/GO-nafion film was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques, and the results were interpreted and compared at each stage of the electrode construction. Electrochemical oxidation of eight β-agonists - clenbuterol, salbutamol, terbutaline, ractopamine, dopamine, dobutamine, adrenaline, and isoprenaline, was investigated by CV at the different electrodes. At the poly-ACBK/GO-nafion/GCE, the linear sweep voltammetry peak currents of the eight β-agonists increased linearly with their concentrations in the range of 1.0-36.0 ng mL(-1), respectively, and their corresponding limits of detection (LODs) were within the 0.58-1.46 ng mL(-1) range. This electrode showed satisfactory reproducibility and stability, and was used successfully for the quantitative analysis of clenbuterol in pork samples. Copyright © 2013 Elsevier B.V. All rights reserved.

  13. Electrocatalytic simultaneous determination of ascorbic acid, uric acid and L-Cysteine in real samples using quercetin silver nanoparticles-graphene nanosheets modified glassy carbon electrode

    Science.gov (United States)

    Zare, Hamid R.; Jahangiri-Dehaghani, Fahime; Shekari, Zahra; Benvidi, Ali

    2016-07-01

    By immobilizing of quercetin at the surface of a glassy carbon electrode modified with silver nanoparticles and graphene nanosheets (Q-AgNPs-GNs-GCE) a new sensor has been fabricated. The cyclic voltammogram of Q-AgNPs-GNs-GCE shows a stable redox couple with surface confined characteristics. Q-AgNPs-GNs-GCE demonstrated a high catalytic activity for L-Cysteine (L-Cys) oxidation. Results indicated that L-Cys peak potential at Q-AgNPs-GNs-GCE shifted to less positive values compared to GNs-GCE or AgNPs-GCE. Also, the kinetic parameters such as the electron transfer coefficient,, and the heterogeneous electron transfer rate constant, k‧, for the oxidation of L-Cys at the Q-AgNPs-GNs-GCE surface were estimated. In differential pulse voltammetric determination, the detection limit of L-Cys was obtained 0.28 μM, and the calibration plots were linear within two ranges of 0.9-12.4 μM and 12.4-538.5 μM of L-Cys. Also, the proposed modified electrode is used for the simultaneous determinations of ascorbic acid (AA), uric acid (UA), and L-Cys. Finally, this study has demonstrated the practical analytical utility of the sensor for determination of AA in vitamin C tablet, L-Cys in a milk sample and UA in a human urine sample.

  14. Electrochemical hydrogen peroxide sensor based on a glassy carbon electrode modified with nanosheets of copper-doped copper(II) oxide

    International Nuclear Information System (INIS)

    Song, Haiyan; Ma, Chaohong; You, Liyan; Cheng, Zhenyu; Zhang, Xinhui; Yin, Baishuang; Zhang, Keqin; Ni, Yongnian

    2015-01-01

    A new electrochemical sensor for H 2 O 2 was constructed by depositing copper doped CuO nanosheets on a glassy carbon electrode (GCE). The morphology and composition of the modified electrode were characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The electrochemical properties of the electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The catalytic performance of the sensor was studied in 100 mM NaOH solution via differential pulse voltammetry and revealed the sensor to display significantly improved electrocatalytic activity with respect to the analysis of the H 2 O 2 in comparison to a plain GCE or a GCE modified with copper only. The response to H 2 O 2 at a working voltage of −0.46 V (vs. Ag/AgCl) is linear in the 0.003 – 8 mM concentration range, and the detection limit is 0.21 mM (at an S/N ratio of 3). Satisfactory results were obtained in the analysis of tap, rain and river waters spiked with H 2 O 2 . The analytical performance of this electrode compares favorably to the results obtained with other commonly used techniques for analysis of H 2 O 2 . (author)

  15. Determination of vitamin E in margarines and edible oils using square wave anodic stripping voltammetry with a glassy carbon paste electrode.

    Science.gov (United States)

    Sýs, Milan; Švecová, Blanka; Švancara, Ivan; Metelka, Radovan

    2017-08-15

    A new electroanalytical method for determination of vitamin E in the form of the total content of tocopherols present in margarines and edible oils has been developed. The method is based on extraction of these biologically active compounds into silicone oil, acting as lipophilic binder of glassy carbon paste electrode, with subsequent electrochemical detection by square wave anodic stripping voltammetry (SWASV) in 0.1M HNO 3 . The values of vitamin E contents were expressed as mass equivalent of α-tocopherol known as the most active form of this lipophilic vitamin. The linear ranges for α-tocopherol determination were 5×10 -7 -4×10 -5 and 5×10 -8 -1×10 -5 molL -1 with the detection limits of 1×10 -7 and 3.3×10 -9 molL -1 for 5 and 15min accumulation, respectively. The results have shown that SWASV with extraction step is very sensitive method for the determination of vitamin E, being comparable to reversed-phase high performance liquid chromatography chosen as reference method. Copyright © 2017 Elsevier Ltd. All rights reserved.

  16. Synergy of Cobalt and Silver Microparticles Electrodeposited on Glassy Carbon for the Electrocatalysis of the Oxygen Reduction Reaction: An Electrochemical Investigation

    Directory of Open Access Journals (Sweden)

    Claudio Zafferoni

    2015-08-01

    Full Text Available The combination of two different metals, each of them acting on different steps of the oxygen reduction reaction (ORR, yields synergic catalytic effects. In this respect, the electrocatalytic effect of silver is enhanced by the addition of cobalt, which is able to break the O–O bond of molecular oxygen, thus accelerating the first step of the reduction mechanism. At the same time, research is to further reduce the catalyst’s cost, reducing the amount of Ag, which, even though being much less expensive than Pt, is still a noble metal. From this point of view, using a small amount of Ag together with an inexpensive material, such as graphite, represents a good compromise. The aim of this work was to verify if the synergic effects are still operating when very small amounts of cobalt (2–10 μg·cm−2 are added to the microparticles of silver electrodeposited on glassy carbon, described in a preceding paper from us. To better stress the different behaviour observed when cobalt and silver are contemporarily present in the deposit, the catalytic properties of cobalt alone were investigated. The analysis was completed by the Levich plots to evaluate the number of electrons involved and by Tafel plots to show the effects on the reaction mechanism.

  17. Voltammetric determination of sudan ii in food samples at graphene modified glassy carbon electrode based on the enhancement effect of sodium dodecyl sulfate

    International Nuclear Information System (INIS)

    Ma, X.; Chen, M.; Chao, M.

    2013-01-01

    Summary: Herein, a novel electrochemical method was de veloped for the determination of Sudan II based on the electrochemical catalytic activity of graphene modified glassy carbon electrode (GME) and the enhancement effect of sodium dodecyl sulfate (SDS). In a pH 6.0 phosphate buffer solution, Sudan II exhibited a pair of well-defined quasi reversible redox peaks at the GME in the presence of 5.0x10/sup -5/ mol L/sup 1/ SDS. The oxidation peak current of Sudan II was linearly proportional to its concentration in a range from 4.0x10/sup -8/ to 4.0x10/sup -6/ mol L/sup 1/, with a linear regression equation of ipa (A) = 3.35 c + 5.96 x 10/sup -6/, r = 0.9988 and a detection limit of 8.0x10/sup -9/ mol L/sup 1/. The recoveries from the standards fortified blank samples were in the range of 94.7% to 97.5% with RSD lower than 4.0%. The novel method has been successfully used to determine Sudan II in food products with satisfactory results. (author)

  18. Removal of a mixture tetracycline-tylosin from water based on anodic oxidation on a glassy carbon electrode coupled to activated sludge.

    Science.gov (United States)

    Yahiaoui, Idris; Aissani-Benissad, Farida; Fourcade, Florence; Amrane, Abdeltif

    2015-01-01

    The purpose of this study was first to examine the electrochemical oxidation of two antibiotics, tetracycline (TC) and tylosin (Tylo), considered separately or in mixture, on a glassy carbon electrode in aqueous solutions; and then to assess the relevance of such electrochemical process as a pre-treatment prior to a biological treatment (activated sludge) for the removal of these antibiotics. The influence of the working potential and the initial concentration of TC and Tylo on the electrochemical pre-treatment process was also investigated. It was noticed that antibiotics degradation was favoured at high potential (2.4 V/ saturated calomel electrode (SCE)), achieving total degradation after 50 min for TC and 40 min for Tylo for 50 mg L(-1) initial concentration, with a higher mineralization efficiency in the case of TC. The biological oxygen demand in 5 days (BOD5)/Chemical oxygen demand (COD) ratio increased substantially, from 0.033 to 0.39 and from 0.038 to 0.50 for TC and Tylo, respectively. Regarding the mixture (TC and Tylo), the mineralization yield increased from 10.6% to 30.0% within 60 min of reaction time when the potential increased from 1.5 to 2.4 V/SCE and the BOD5/COD ratio increased substantially from 0.010 initially to 0.29 after 6 h of electrochemical pre-treatment. A biological treatment was, therefore, performed aerobically during 30 days, leading to an overall decrease of 72% of the dissolved organic carbon by means of the combined process.

  19. Development of sensitive amperometric hydrogen peroxide sensor using a CuNPs/MB/MWCNT-C{sub 60}-Cs-IL nanocomposite modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Roushani, Mahmoud, E-mail: mahmoudroushani@yahoo.com; Bakyas, Kobra; Zare Dizajdizi, Behruz

    2016-07-01

    A sensitive hydrogen peroxide (H{sub 2}O{sub 2}) sensor was constructed based on copper nanoparticles/methylene blue/multiwall carbon nanotubes–fullerene–chitosan–ionic liquid (CuNPs/MB/MWCNTs–C{sub 60}–Cs–IL) nanocomposites. The MB/MWCNTs–C{sub 60}–Cs–IL and CuNPs were modified glassy carbon electrode (GCE) by the physical adsorption and electrodeposition of copper nitrate solution, respectively. The physical morphology and chemical composition of the surface of modified electrode was investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. The electrochemical properties of CuNPs/MB/MWCNTs–C{sub 60}–Cs–IL/GCE were investigated by cyclic voltammetry (CV) and amperometry techniques and the sensor exhibited remarkably strong electrocatalytic activities toward the reduction of hydrogen peroxide. The peak currents possess a linear relationship with the concentration of H{sub 2}O{sub 2} in the range of 0.2 μM to 2.0 mM, and the detection limit is 55.0 nM (S/N = 3). In addition, the modified electrode was used to determine H{sub 2}O{sub 2} concentration in human blood serum sample with satisfactory results. - Highlights: • CuNPs/MB/MWCNT-C{sub 60}-Cs-IL/GC electrode was constructed by layer-by-layer method. • The catalytic performance of the sensor was studied with the use of amperometric technique. • The constructed sensor showed enhanced electrocatalytic activity toward the reduction of H{sub 2}O{sub 2}. • The CuNPs/MB/MWCNT-C{sub 60}-Cs-IL/GC electrode demonstrated high stability for the detection of H{sub 2}O{sub 2}.

  20. Simultaneous Electrochemical Determination of Hydroquinone, Catechol and Resorcinol at Nitrogen Doped Porous Carbon Nanopolyhedrons-multiwall Carbon Nanotubes Hybrid Materials Modified Glassy Carbon Electrode

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wei; Wu, Liang; Zhang, Xiaohua; Chen, Jinhua [Hunan Univ., Changsha (China)

    2014-01-15

    The nitrogen doped porous carbon nanopolyhedrons (N-PCNPs)-multi-walled carbon nanotubes (MWCNTs) hybrid materials were prepared for the first time. Combining the excellent catalytic activities, good electrical conductivities and high surface areas of N-PCNPs and MWCNTs, the simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RE) with good analytical performance was achieved at the N-PCNPs-MWCNTs modified electrode. The linear response ranges for HQ, CC and RE are 0.2-455 μM, 0.7-440 μM and 3.0-365 μM, respectively, and the detection limits (S/N = 3) are 0.03 μM, 0.11 μM and 0.38 μM, respectively. These results are much better than that obtained on some graphene or CNTs-based materials modified electrodes. Furthermore, the developed sensor was successfully applied to simultaneously detect HQ, CC and RE in the local river water samples.

  1. Enhanced Electrochemical Performance of Electrospun Ag/Hollow Glassy Carbon Nanofibers as Free-standing Li-ion Battery Anode

    International Nuclear Information System (INIS)

    Shilpa; Sharma, Ashutosh

    2015-01-01

    Silver with a high theoretical capacity for lithium storage is an attractive alloy based anode for Li-ion batteries, but large volume changes associated with AgLi x alloy formation leads to electrode cracking, pulverization and rapid capacity fading. A buffer matrix, like the electrospun hollow carbon nanofibers, can reduce this problem to a great extent. Herein, we demonstrate the facile synthesis of a free-standing, binder free Ag-C hybrid electrode through co-axial electrospinning, where well dispersed Ag nanoparticles are embedded in hollow carbon nanofibers. Using this approach, the long cycle life of carbon is complemented with the high lithium storage capacity of Ag, resulting in a high performance anode. The Ag-C composite electrode delivers a capacity of 739 mAh g −1 (>conventional graphite anodes) at 50 mA g −1 , with ∼85% capacity retention after 100 cycles. In addition, the Ag-C composite nanofibers are highly porous and exhibit a large accessible surface area (∼726.9 m 2 g −1 ) with an average pore diameter of ∼6.07 nm. The encapsulation of Ag in the hollow interiors not only provides additional lithium storage sites but also enhances the electronic conductivity, which combined with the reduced lithium diffusion path lengths in the nanofibers result in faster charge-discharge kinetics and hence a high rate performance

  2. Molecularly imprinted poly(4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid) modified glassy carbon electrode as an electrochemical theophylline sensor

    International Nuclear Information System (INIS)

    Aswini, K.K.; Vinu Mohan, A.M.; Biju, V.M.

    2016-01-01

    Theophylline is an inexpensive drug employed in asthma and chronic obstructive pulmonary disorder medications and is toxic at higher concentration. The development of a molecularly imprinted polymer based theophylline electrochemical sensor on glassy carbon electrode by the electropolymerization of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid is being discussed in this work. The MIP modification enhances the theophylline recognition ability and the electron transfer kinetics of the bare electrode. The parameters, controlling the performance of the imprinted polymer based sensor, like number of electropolymerization cycles, composition of the pre-polymerization mixture, pH and immersion time were investigated and optimized. The interaction energy and the most stable conformation of the template–monomer complex in the pre-polymerization mixture were determined computationally using ab initio calculations based on density functional theory. The amperometric measurements showed that the developed sensor has a method detection limit of 0.32 μM for the dynamic range of 0.4 to 17 μM, at optimized conditions. The transducer possesses appreciable selectivity in the presence of structurally similar interferents such as theobromine, caffeine and doxofylline. The developed sensor showed remarkable stability and reproducibility and was also successfully employed in theophylline detection from commercially available tablets. - Highlights: • Molecularly imprinted polymer based theophylline sensor was developed. • Imprinted poly(4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid) was electrodeposited. • Most stable template-monomer complex was assigned by computational analysis. • Possessed remarkable selectivity in the presence of structurally similar interferents • Employed for theophylline detection from commercially available tablets

  3. Molecularly imprinted poly(4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid) modified glassy carbon electrode as an electrochemical theophylline sensor

    Energy Technology Data Exchange (ETDEWEB)

    Aswini, K.K., E-mail: aswinikk@ymail.com; Vinu Mohan, A.M.; Biju, V.M., E-mail: vmbiju@ymail.com

    2016-08-01

    Theophylline is an inexpensive drug employed in asthma and chronic obstructive pulmonary disorder medications and is toxic at higher concentration. The development of a molecularly imprinted polymer based theophylline electrochemical sensor on glassy carbon electrode by the electropolymerization of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid is being discussed in this work. The MIP modification enhances the theophylline recognition ability and the electron transfer kinetics of the bare electrode. The parameters, controlling the performance of the imprinted polymer based sensor, like number of electropolymerization cycles, composition of the pre-polymerization mixture, pH and immersion time were investigated and optimized. The interaction energy and the most stable conformation of the template–monomer complex in the pre-polymerization mixture were determined computationally using ab initio calculations based on density functional theory. The amperometric measurements showed that the developed sensor has a method detection limit of 0.32 μM for the dynamic range of 0.4 to 17 μM, at optimized conditions. The transducer possesses appreciable selectivity in the presence of structurally similar interferents such as theobromine, caffeine and doxofylline. The developed sensor showed remarkable stability and reproducibility and was also successfully employed in theophylline detection from commercially available tablets. - Highlights: • Molecularly imprinted polymer based theophylline sensor was developed. • Imprinted poly(4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid) was electrodeposited. • Most stable template-monomer complex was assigned by computational analysis. • Possessed remarkable selectivity in the presence of structurally similar interferents • Employed for theophylline detection from commercially available tablets.

  4. Layer by layer assembly of catalase and amine-terminated ionic liquid onto titanium nitride nanoparticles modified glassy carbon electrode: Study of direct voltammetry and bioelectrocatalytic activity

    International Nuclear Information System (INIS)

    Saadati, Shagayegh; Salimi, Abdollah; Hallaj, Rahman; Rostami, Amin

    2012-01-01

    Highlights: ► Catalase and amine-terminated ionic liquid were immobilized to GC/TiNnp with LBL assembly method. ► First a thin layer of NH 2 -IL is covalently attached to GC/TiNnp electrode using electro-oxidation. ► With alternative assemble of IL and catalase with positive and negative charged, multilayer was formed. ► Immobilized catalase shows excellent electrocatalytic activity toward H 2 O 2 reduction. ► Biosensor response is directly correlated to the number of bilayers. - Abstract: A novel, simple and facile layer by layer (LBL) approach is used for modification of glassy carbon (GC) electrode with multilayer of catalase and nanocomposite containing 1-(3-Aminopropyl)-3-methylimidazolium bromide (amine terminated ionic liquid (NH 2 -IL)) and titanium nitride nanoparticles (TiNnp). First a thin layer of NH 2 -IL is covalently attached to GC/TiNnp electrode using electro-oxidation method. Then, with alternative self assemble positively charged NH 2 -IL and negatively charged catalase a sensitive H 2 O 2 biosensor is constructed, whose response is directly correlated to the number of bilayers. The surface coverage of active catalase per bilayer, heterogeneous electron transfer rate constant (k s ) and Michaelis–Menten constant (K M ) of immobilized catalase were 3.32 × 10 −12 mol cm −2 , 5.28 s −1 and 1.1 mM, respectively. The biosensor shows good stability, high reproducibility, long life-time, and fast amperometric response with the high sensitivity of 380 μA mM −1 cm −2 and low detection limit of 100 nM at concentration range up to 2.1 mM.

  5. Layer by layer assembly of catalase and amine-terminated ionic liquid onto titanium nitride nanoparticles modified glassy carbon electrode: Study of direct voltammetry and bioelectrocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Saadati, Shagayegh [Department of Chemistry, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Salimi, Abdollah, E-mail: absalimi@uok.ac.ir [Department of Chemistry, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Research Center for Nanotechnology, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of); Hallaj, Rahman; Rostami, Amin [Department of Chemistry, University of Kurdistan, P.O. Box 416, Sanandaj (Iran, Islamic Republic of)

    2012-11-13

    Highlights: Black-Right-Pointing-Pointer Catalase and amine-terminated ionic liquid were immobilized to GC/TiNnp with LBL assembly method. Black-Right-Pointing-Pointer First a thin layer of NH{sub 2}-IL is covalently attached to GC/TiNnp electrode using electro-oxidation. Black-Right-Pointing-Pointer With alternative assemble of IL and catalase with positive and negative charged, multilayer was formed. Black-Right-Pointing-Pointer Immobilized catalase shows excellent electrocatalytic activity toward H{sub 2}O{sub 2} reduction. Black-Right-Pointing-Pointer Biosensor response is directly correlated to the number of bilayers. - Abstract: A novel, simple and facile layer by layer (LBL) approach is used for modification of glassy carbon (GC) electrode with multilayer of catalase and nanocomposite containing 1-(3-Aminopropyl)-3-methylimidazolium bromide (amine terminated ionic liquid (NH{sub 2}-IL)) and titanium nitride nanoparticles (TiNnp). First a thin layer of NH{sub 2}-IL is covalently attached to GC/TiNnp electrode using electro-oxidation method. Then, with alternative self assemble positively charged NH{sub 2}-IL and negatively charged catalase a sensitive H{sub 2}O{sub 2} biosensor is constructed, whose response is directly correlated to the number of bilayers. The surface coverage of active catalase per bilayer, heterogeneous electron transfer rate constant (k{sub s}) and Michaelis-Menten constant (K{sub M}) of immobilized catalase were 3.32 Multiplication-Sign 10{sup -12} mol cm{sup -2}, 5.28 s{sup -1} and 1.1 mM, respectively. The biosensor shows good stability, high reproducibility, long life-time, and fast amperometric response with the high sensitivity of 380 {mu}A mM{sup -1} cm{sup -2} and low detection limit of 100 nM at concentration range up to 2.1 mM.

  6. A new kinetic–mechanistic approach to elucidate electrooxidation of doxorubicin hydrochloride in unprocessed human fluids using magnetic graphene based nanocomposite modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Soleymani, Jafar [Hematology–Oncology Research Center, Tabriz University of Medical Sciences, Tabriz 51664 (Iran, Islamic Republic of); Hasanzadeh, Mohammad, E-mail: Mhmmd_hasanzadeh@yahoo.com [Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz (Iran, Islamic Republic of); Shadjou, Nasrin [Department of Nanochemistry, Nano Technology Center, and Faculty of Chemistry, Urmia University, Urmia (Iran, Islamic Republic of); Khoubnasab Jafari, Maryam [Tuberculosis and Lung Disease Research Center, Tabriz University of Medical Sciences, Tabriz (Iran, Islamic Republic of); Gharamaleki, Jalil Vaez [Hematology–Oncology Research Center, Tabriz University of Medical Sciences, Tabriz 51664 (Iran, Islamic Republic of); Yadollahi, Mehdi [Department of Organic Chemistry, Faculty of Chemistry, Tabriz University, Tabriz (Iran, Islamic Republic of); Jouyban, Abolghasem [Pharmaceutical Analysis Research Center and Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz (Iran, Islamic Republic of)

    2016-04-01

    A novel magnetic nanocomposite was synthesized in one step using polymerization of magnetic graph oxide grafted with chlorosulfonic acid (Fe{sub 3}O{sub 4}–GO–SO{sub 3}H) in the presence of polystyrene. The prepared magnetic nanocomposite was characterized using transmission electron microscopy (TEM), dynamic differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), (Thermo-gravimetric/differential thermal analysis (DTA)), Fourier transform infrared (FTIR), and UV–Vis techniques. Magnetic nanocomposite was casted on the surface of the glassy carbon electrode (PS/Fe{sub 3}O{sub 4}–GO–SO{sub 3}H/GCE) and used for the detection and determination of doxorubicin hydrochloride (DOX) in human biological fluids. The cyclic voltammograms (CVs) of the modified electrode in aqueous solution displayed a pair of well-defined, stable and irreversible reductive/oxidation redox systems. CV study indicated that the oxidation process is irreversible and adsorption controlled. In addition, CV results indicated that DOX is oxidized via two electrons and three protons which is an unusual approach for the oxidation of DOX. A sensitive and time-saving procedure was developed for the analysis of DOX in plasma, cerebrospinal fluid, and urine with detection limit of 4.9 nM, 14 nM and 4.3 nM, respectively. - Highlights: • A novel magneto-polymeric nanocomposite (PS/Fe{sub 3}O{sub 4}–GO–SO{sub 3}H) was synthesized. • Application of PS/Fe{sub 3}O{sub 4}–GO–SO{sub 3}H toward detection of DOX was investigated by electrochemistry. • A new kinetic–mechanistic approach to elucidate electrooxidation of DOX was obtained. • DOX was detected in plasma, cerebrospinal fluid, and urine.

  7. Immobilization of Ni–Pd/core–shell nanoparticles through thermal polymerization of acrylamide on glassy carbon electrode for highly stable and sensitive glutamate detection

    International Nuclear Information System (INIS)

    Yu, Huicheng; Ma, Zhenzhen; Wu, Zhaoyang

    2015-01-01

    The preparation of a persistently stable and sensitive biosensor is highly important for practical applications. To improve the stability and sensitivity of glutamate sensors, an electrode modified with glutamate dehydrogenase (GDH)/Ni–Pd/core–shell nanoparticles was developed using the thermal polymerization of acrylamide (AM) to immobilize the synthesized Ni–Pd/core–shell nanoparticles onto a glassy carbon electrode (GCE). The modified electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Electrochemical data showed that the prepared biosensor had remarkably enhanced electrocatalytic activity toward glutamate. Moreover, superior reproducibility and excellent stability were observed (relative average deviation was 2.96% after continuous use of the same sensor for 60 times, and current responses remained at 94.85% of the initial value after 60 d). The sensor also demonstrated highly sensitive amperometric detection of glutamate with a low limit of detection (0.052 μM, S/N = 3), high sensitivity (4.768 μA μM −1  cm −2 ), and a wide, useful linear range (0.1–500 μM). No interference from potential interfering species such as L-cysteine, ascorbic acid, and L-aspartate were noted. The determination of glutamate levels in actual samples achieved good recovery percentages. - Highlights: • Ni–Pd/core–shell nanoparticles were synthesized. • Nanoparticles were immobilized onto electrodes through thermal polymerization. • The modified sensor exhibited excellent stability and sensitivity for glutamate detection. • The biosensor exhibited remarkable electrocatalytic activity toward glutamate. • The sensor successfully detected glutamate in tomato soup samples.

  8. A novel voltammetric sensor for sensitive detection of mercury(II) ions using glassy carbon electrode modified with graphene-based ion imprinted polymer

    Energy Technology Data Exchange (ETDEWEB)

    Ghanei-Motlagh, Masoud, E-mail: m.ghaneimotlagh@yahoo.com [Young Researchers and Elite Club, Kerman Branch, Islamic Azad University, Kerman (Iran, Islamic Republic of); Taher, Mohammad Ali; Heydari, Abolfazl [Department of Chemistry, Faculty of Sciences, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Ghanei-Motlagh, Reza [Department of Pathobiology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of); Gupta, Vinod K. [Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Department of Applied Chemistry, University of Johannesburg, Johannesburg (South Africa)

    2016-06-01

    In this paper, a novel strategy was proposed to prepare ion-imprinted polymer (IIP) on the surface of reduced graphene oxide (RGO). Polymerization was performed using methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, 2,2′–((9E,10E)–1,4–dihydroxyanthracene–9,10–diylidene) bis(hydrazine–1–carbothioamide) (DDBHCT) as the chelating agent and ammonium persulfate (APS) as initiator, via surface imprinted technique. The RGO–IIP was characterized by means of Fourier transform infrared spectroscopy (FT–IR), field emission scanning electron microscopy (FE–SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The electrochemical procedure was based on the accumulation of Hg(II) ions at the surface of a modified glassy carbon electrode (GCE) with RGO–IIP. The prepared RGO–IIP sensor has higher voltammetric response compared to the non-imprinted polymer (NIP), traditional IIP and RGO. The RGO–IIP modified electrode exhibited a linear relationship toward Hg(II) concentrations ranging from 0.07 to 80 μg L{sup −1}. The limit of detection (LOD) was found to be 0.02 μg L{sup −1} (S/N = 3), below the guideline value from the World Health Organization (WHO). The applicability of the proposed electrochemical sensor to determination of mercury(II) ions in different water samples was reported. - Highlights: • The novel Hg(II)-imprinted polymer was synthesized and characterized. • The resulting RGO–IIP was applied for electrochemical monitoring of Hg(II) ions. • The proposed sensor was successfully applied for determination of Hg(II) in real water samples.

  9. Immobilization of Ni–Pd/core–shell nanoparticles through thermal polymerization of acrylamide on glassy carbon electrode for highly stable and sensitive glutamate detection

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Huicheng, E-mail: doyhc@126.com [State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (China); School of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Nanning, 530008 (China); School of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Nanning, 530008 (China); Key Laboratory of Chemistry and Engineering of Forest Products, Guangxi University for Nationalities, Nanning, 530008 (China); Key Laboratory of Guangxi Colleges and Universities for Food Safety and Pharmaceutical Analytical Chemistry, Guangxi University for Nationalities, Nanning, 530008 (China); Ma, Zhenzhen [State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (China); Wu, Zhaoyang, E-mail: zywu@hnu.edu.cn [State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 (China)

    2015-10-08

    The preparation of a persistently stable and sensitive biosensor is highly important for practical applications. To improve the stability and sensitivity of glutamate sensors, an electrode modified with glutamate dehydrogenase (GDH)/Ni–Pd/core–shell nanoparticles was developed using the thermal polymerization of acrylamide (AM) to immobilize the synthesized Ni–Pd/core–shell nanoparticles onto a glassy carbon electrode (GCE). The modified electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Electrochemical data showed that the prepared biosensor had remarkably enhanced electrocatalytic activity toward glutamate. Moreover, superior reproducibility and excellent stability were observed (relative average deviation was 2.96% after continuous use of the same sensor for 60 times, and current responses remained at 94.85% of the initial value after 60 d). The sensor also demonstrated highly sensitive amperometric detection of glutamate with a low limit of detection (0.052 μM, S/N = 3), high sensitivity (4.768 μA μM{sup −1} cm{sup −2}), and a wide, useful linear range (0.1–500 μM). No interference from potential interfering species such as L-cysteine, ascorbic acid, and L-aspartate were noted. The determination of glutamate levels in actual samples achieved good recovery percentages. - Highlights: • Ni–Pd/core–shell nanoparticles were synthesized. • Nanoparticles were immobilized onto electrodes through thermal polymerization. • The modified sensor exhibited excellent stability and sensitivity for glutamate detection. • The biosensor exhibited remarkable electrocatalytic activity toward glutamate. • The sensor successfully detected glutamate in tomato soup samples.

  10. A Nitrite Biosensor Based on Co-immobilization of Nitrite Reductase and Viologen-modified Chitosan on a Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    De Quan

    2010-06-01

    Full Text Available An electrochemical nitrite biosensor based on co-immobilization of copper- containing nitrite reductase (Cu-NiR, from Rhodopseudomonas sphaeroides forma sp. denitrificans and viologen-modified chitosan (CHIT-V on a glassy carbon electrode (GCE is presented. Electron transfer (ET between a conventional GCE and immobilized Cu-NiR was mediated by the co-immobilized CHIT-V. Redox-active viologen was covalently linked to a chitosan backbone, and the thus produced CHIT-V was co-immobilized with Cu-NiR on the GCE surface by drop-coating of hydrophilic polyurethane (HPU. The electrode responded to nitrite with a limit of detection (LOD of 40 nM (S/N = 3. The sensitivity, linear response range, and response time (t90% were 14.9 nA/mM, 0.04−11 mM (r2 = 0.999 and 15 s, respectively. The corresponding Lineweaver-Burk plot showed that the apparent Michaelis-Menten constant (KMapp was 65 mM. Storage stability of the biosensor (retaining 80% of initial activity was 65 days under ambient air and room temperature storage conditions. Reproducibility of the sensor showed a relative standard deviation (RSD of 2.8% (n = 5 for detection of 1 mM of nitrite. An interference study showed that anions commonlyfound in water samples such as chlorate, chloride, sulfate and sulfite did not interfere with the nitrite detection. However, nitrate interfered with a relative sensitivity of 64% and this interference effect was due to the intrinsic character of the NiR employed in this study.

  11. Surface characterization of silver and palladium modified glassy ...

    Indian Academy of Sciences (India)

    WINTEC

    formaldehyde resin. Three types of precursor resin samples were prepared: (i) phenol-formal- dehyde resin without any additions in order to obtain pure glassy carbon precursor before polymerization, (ii) phenol- formaldehyde resin mixed with boric ...

  12. Glassy metallic plastics

    Science.gov (United States)

    Li, Jianfu; Wang, Junqiang; Liu, Xiaofeng; Zhao, Kun; Zhang, Bo; Bai, Haiyang; Pan, Mingxiang; Wang, Weihua

    2010-03-01

    This paper reports a class of bulk metallic glass including Ce-, LaCe-, CaLi-, Yb-, and Sr-based metallic glasses, which are regarded as glassy metallic plastics because they combine some unique properties of both plastics and metallic alloys. These glassy metallic plastics have very low glass transition temperature ( T g ˜25°C to 150°C) and low Young’s modulus (˜20 GPa to 35 GPa). Similar to glassy plastics, these metallic plastics show excellent plastic-like deformability on macro-, micro- and even nano-scale in their supercooled liquid range and can be processed, such as elongated, compressed, bent, and imprinted at low temperatures, in hot water for instance. Under ambient conditions, they display such metallic properties as high thermal and electric conductivities and excellent mechanical properties and other unique properties. The metallic plastics have potential applications and are also a model system for studying issues in glass physics.

  13. Probing the electrochemical double layer of an ionic liquid using voltammetry and impedance spectroscopy: a comparative study of carbon nanotube and glassy carbon electrodes in [EMIM](+)[EtSO(4)](-).

    Science.gov (United States)

    Zheng, J P; Goonetilleke, P C; Pettit, C M; Roy, D

    2010-05-15

    Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are compared as techniques for analyzing double layer capacitances of ionic liquids (ILs) at the surfaces of two carbon-based electrodes. These systems are relevant for energy storage supercapacitors and often are associated with unconventional electrochemical properties. Certain theoretical and experimental aspects of CV and EIS necessary for quantitative evaluation of the capacitance characteristics of such systems are explored. The experiments use 1-ethyl-3-methyl imidazolium ethylsulfate as a model IL electrolyte in combination with a porous electrode of carbon nanotubes (CNTs). The results are compared with those obtained with a nonporous glassy carbon (GC) electrode. The time is constant, and hence the power delivery characteristics of the experimental cell are affected by the electrolyte resistance and residual faradaic reactions of the IL, as well as by the spatially inhomogeneous electrode surfaces. It is shown that adequate characterization of these IL-electrode systems can be achieved by combining CV with EIS. A phenomenological framework for utilizing this combination is discussed.

  14. Catalytic EC′ reaction at a thin film modified electrode

    International Nuclear Information System (INIS)

    Gerbino, Leandro; Baruzzi, Ana M.; Iglesias, Rodrigo A.

    2013-01-01

    Numerical simulations of cyclic voltammograms corresponding to a catalytic EC′ reaction taking place at a thin film modified electrode are performed by way of finite difference method. Besides considering the chemical kinetic occurring inside the thin film, the model takes into account the different diffusion coefficients for each species at each of the involved phases, i.e. the thin film layer and bulk solution. The theoretical formulation is given in terms of dimensionless model parameters but a brief discussion of each of these parameters and their relationship to experimental variables is presented. Special emphasis is given to the use of working curve characteristics to quantify diffusion coefficient, homogeneous kinetic constant and thickness of the thin layer in a real system. Validation of the model is made by comparison of experimental results corresponding to the electron charge transfer of Ru(NH 3 ) 6 3+ /Ru(NH 3 ) 6 2+ hemi-couple at a thin film of a cross-linked chitosan film containing an immobilized redox dye

  15. Enzymatic biosensor based on entrapment of d-amino acid oxidase on gold nanofilm/MWCNTs nanocomposite modified glassy carbon electrode by sol-gel network: Analytical applications for d-alanine in human serum.

    Science.gov (United States)

    Shoja, Yalda; Rafati, Amir Abbas; Ghodsi, Javad

    2017-05-01

    Sensing and determination of d-alanine is studied by using an enzymatic biosensor which was constructed on the basis of d-amino acid oxidase (DAAO) immobilization by sol-gel film onto glassy carbon electrode surface modified with nanocomposite of gold nanofilm (Au-NF) and multiwalled carbon nanotubes (MWCNTs). The Au-NF/MWCNT nanocomposite was prepared by applying the potentiostatic technique for electrodeposition of Au-NF on the MWCNT immobilized on glassy carbon electrode surface. The modified electrode is investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), linear sweep voltammetry (LSV) and cyclic voltammetry(CV) techniques. The linear sweep voltammetry was used for determination of d-alanine and the results showed an excellent linear relationship between biosensor response and d-alanine concentration ranging from 0.25μM to 4.5μM with correction coefficient of 0.999 (n=20). Detection limit for the fabricated sensor was calculated about 20nM (for S/N=3) and sensitivity was about 56.1μAμM -1 cm -2 . The developed biosensor exhibited rapid and accurate response to d-alanine, a good stability (4 weeks) and an average recovery of 98.9% in human serum samples. Copyright © 2017 Elsevier Inc. All rights reserved.

  16. Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

    International Nuclear Information System (INIS)

    Noorbakhsh, Abdollah; Salimi, Abdollah

    2009-01-01

    A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5-120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2-12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k s ) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 x 10 -10 mol cm -2 , 6.12 s -1 , 5.9 x 10 -10 mol cm -2 and 6.58 s -1 , respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) x 10 3 M -1 s -1 and 5.5 (±0.2) x 10 3 M -1 s -1 , respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM -1 nA μM -1 and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM -1 , and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during

  17. Molecular modeling of the voltammetric oxidation at a glassy carbon electrode of the antimalarial drug primaquine and its prodrugs succinylprimaquine and maleylprimaquine

    Energy Technology Data Exchange (ETDEWEB)

    La-Scalea, Mauro A. [Lapen, Laboratorio de Planejamento e Sintese de Quimioterapicos Potencialmente Ativos Contra Endemias Tropicais, Departamento de Farmacia, Faculdade de Ciencias Farmaceuticas, Universidade de Sao Paulo, Av. Prof. Lineu Prestes, 580 Bl. 13 sup., 05508-900 Sao Paulo (Brazil)]. E-mail: scalea@usp.br; Menezes, Carla M.S. [Lapen, Laboratorio de Planejamento e Sintese de Quimioterapicos Potencialmente Ativos Contra Endemias Tropicais, Departamento de Farmacia, Faculdade de Ciencias Farmaceuticas, Universidade de Sao Paulo, Av. Prof. Lineu Prestes, 580 Bl. 13 sup., 05508-900 Sao Paulo (Brazil)]. E-mail: casmenezes@yahoo.com; Matsutami, Guilherme C. [Lapen, Laboratorio de Planejamento e Sintese de Quimioterapicos Potencialmente Ativos Contra Endemias Tropicais, Departamento de Farmacia, Faculdade de Ciencias Farmaceuticas, Universidade de Sao Paulo, Av. Prof. Lineu Prestes, 580 Bl. 13 sup., 05508-900 Sao Paulo (Brazil); Polli, Michelle C. [Lapen, Laboratorio de Planejamento e Sintese de Quimioterapicos Potencialmente Ativos Contra Endemias Tropicais, Departamento de Farmacia, Faculdade de Ciencias Farmaceuticas, Universidade de Sao Paulo, Av. Prof. Lineu Prestes, 580 Bl. 13 sup., 05508-900 Sao Paulo (Brazil); Serrano, Silvia H.P. [Departamento de Quimica Fundamental, Instituto de Quimica, Universidade de Sao Paulo, Av. Prof. Lineu Prestes, 748 Bl. 2 sup., 05508-90 Sao Paulo (Brazil); Ferreira, Elizabeth I. [Lapen, Laboratorio de Planejamento e Sintese de Quimioterapicos Potencialmente Ativos Contra Endemias Tropicais, Departamento de Farmacia, Faculdade de Ciencias Farmaceuticas, Universidade de Sao Paulo, Av. Prof. Lineu Prestes, 580 Bl. 13 sup., 05508-900 Sao Paulo (Brazil)

    2006-07-15

    The 8-aminoquinoline primaquine (PQ) is the only antimalarial drug used as tissue schizonticide and relapsing malaria. Antichagasic activity was also reported. Nevertheless, as it also shows serious side effects, prodrugs such as succinyl and maleyl derivatives have been proposed to decrease its toxicity. Although PQ mechanism of action has not been completely elucidated, the promotion of oxidative stress is an advanced hypothesis that could explain its activity in both plasmodia and trypanosome parasites. The oxidation of PQ and its prodrugs, maleylprimaquine (MPQ) and succinylprimaquine (SPQ), was studied by cyclic voltammetry using glassy carbon electrode. All compounds were oxidized in aqueous medium, with the charge transfer process being pH-dependent in acidic medium and pH-independent in a weak basic medium, being the neutral form more easily oxidized. This indicated that the protonation of the nitrogen atoms displays a determinant role in the voltammetric oxidation, being both prodrugs more easily oxidized than PQ protonated forms, in the order: SPQ < MPQ < PQ. For a better understanding of this behavior, a molecular modeling study was performed using the AM1 semi-empirical method from Spartan 04 for Linux (v.119, Wavefunction Inc.). The medium pH showed to be fundamental not only to the electronic density of the quinoline ring but also to the rearrangement of the nitrogen side chain. The electronic density of primaquine non-protonated quinoline ring is higher than that in its protonated and diprotonated species. Also, the use of prodrugs and the degree of saturation of the carriers (maleic or succinic acid) interfere with this feature. SPQ and MPQ have a slight increase in the quinoline electronic density in comparison to PQ. Nevertheless, the carrier in the side chain of SPQ is closer to the quinoline ring than it is in MPQ, which accounts for the higher electronic density in the former. The most significant effect occurs in the correspondent protonated

  18. Protein/ionic liquid/glassy carbon sensors following analyte focusing by ionic liquid micelle collapse for simultaneous determination of water soluble vitamins in plasma matrices.

    Science.gov (United States)

    Abd El-Hady, D; Albishri, H M

    2015-07-01

    Two novel sensors based on human serum albumin (HSA)-ionic liquid (IL) and bovine serum albumin (BSA)-ionic liquid (IL) composites modified glassy carbon electrode (GCE) were produced for simultaneous determination of water soluble vitamins B2, B6 and C in human plasma following analytes focusing by IL micelles collapse (AFILMC). For selective and efficient extraction, vitamins were dissolved in 3.0molL(-1) micellar solution of 1-octyl-3-methyl imidazolium bromide IL. The extracted vitamins were hydrodynamically injected by 25mbar for 20s into a running buffer of 12.5mmolL(-1) phosphate at pH 6.0 followed by electrochemical detection (ECD) on protein/1-octyl-3-methyl imidazolium hexafluorophosphate IL/GC sensors. The chemical stability of proposed sensors was achieved up to 7 days without any decomposition of PF6-based IL/protein and adsorption of interfering ions. In the current work, the sensitivity enhancement factor (SEF) up to 5000-fold was achieved using the AFILMC/ECD setup compared to conventional CE/UV. Under optimal conditions, linear calibration graphs were obtained from 0.5, 0.5 and 1.0 to 1500.0µgmL(-1) of vitamins B2, B6 and C, respectively. Detection limits of analytes were ranged from 180.0 to 520.0ngmL(-1). The proposed AFILMC/ECD setup was successfully applied to the assay of trace level quantification of vitamins in human plasma samples and also their binding constants with HSA and BSA were determined. The concurrent use of IL micelles for the proposed separation and detection processes exhibited some advantages, such as, a reduction of use toxic solvents, an efficient extraction and a direct injection of samples with a short-single run. Furthermore, IL micelles, having variable possibility of interactions, facilitated the successful achievements of AFILMC/ECD setup for the quantification of vitamins in plasma matrices. Copyright © 2015 Elsevier B.V. All rights reserved.

  19. Electrocatalytic simultaneous determination of ascorbic acid, uric acid and L–Cysteine in real samples using quercetin silver nanoparticles–graphene nanosheets modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Zare, Hamid R., E-mail: hrzare@yazd.ac.ir; Jahangiri-Dehaghani, Fahime; Shekari, Zahra; Benvidi, Ali

    2016-07-01

    Highlights: • Quercetin AgNPs graphene nanosheets modified GCE (Q–AgNPs–GNs–GCE) was prepared as a new sensor. • Q–AgNPs–GNs–GCE shows a high catalytic activity for L–Cysteine (L–Cys) oxidation. • In DPV, the calibration plots were linear within two ranges of 0.9–12.4 μM and 12.4–538.5 μM of L–Cys. • The proposed modified electrode is used for the simultaneous determinations of AA, UA and L–Cys. • Q–AgNPs–GNs–GCE was satisfactorily used for the determination of AA, UA and L–Cys in real samples. - Abstract: By immobilizing of quercetin at the surface of a glassy carbon electrode modified with silver nanoparticles and graphene nanosheets (Q–AgNPs–GNs–GCE) a new sensor has been fabricated. The cyclic voltammogram of Q–AgNPs–GNs–GCE shows a stable redox couple with surface confined characteristics. Q–AgNPs–GNs–GCE demonstrated a high catalytic activity for L–Cysteine (L–Cys) oxidation. Results indicated that L–Cys peak potential at Q–AgNPs–GNs–GCE shifted to less positive values compared to GNs–GCE or AgNPs–GCE. Also, the kinetic parameters such as the electron transfer coefficient,, and the heterogeneous electron transfer rate constant, k′, for the oxidation of L–Cys at the Q–AgNPs–GNs–GCE surface were estimated. In differential pulse voltammetric determination, the detection limit of L–Cys was obtained 0.28 μM, and the calibration plots were linear within two ranges of 0.9–12.4 μM and 12.4–538.5 μM of L–Cys. Also, the proposed modified electrode is used for the simultaneous determinations of ascorbic acid (AA), uric acid (UA), and L–Cys. Finally, this study has demonstrated the practical analytical utility of the sensor for determination of AA in vitamin C tablet, L–Cys in a milk sample and UA in a human urine sample.

  20. Ellipsometric and Electrochemical Characterization of Charge Transport in Electroactive Polymers and of the Surface Phase Produced by Electrochemical Activation of Glassy Carbon Electrodes

    Science.gov (United States)

    Kepley, Larry Joe

    1990-01-01

    In situ ellipsometry was used to study the electrodeposition of polymer films formed by oxidation of bipyrazine, polyvinylferrocene (PVF), and aniline; the deposition of a viologen-containing siloxane polymer (PQ^{2+/+}) formed by electroreduction of N,N^' -bis (-3-(trimethoxysilyl)propyl) -4,4^ '-bipyridinium dichloride (I) solutions and by spin-casting solutions of I; and the oxidation-dependent swelling of spin-cast films of two structurally similar, ferrocene-containing polyamides. Electrodeposited films displayed good optical characteristics (i.e., high reflectivity, uniform coverage, and homogeneity) for thicknesses up to 400 nm in some cases. Nonideal illipsometric behavior was observed when film morphology varied with film growth. The complex refractive index, film thickness, and the viologen and ferrocene concentrations in the films were measured as a function of oxidation state, both during depositions and after transferring coated-electrodes into blank electrolyte solutions. The voltammetry of the redox polymers was studied and charge-transport modeled by finite -difference simulations of charge diffusion and diffusion coupled to dimerization/monomerization reactions. Equations were derived for linear-sweep voltammetry of a reversible couple in equilibrium with its dimer in a thin-layer cell. Ellipsometric data during electrolysis of the redox films by potential sweeps and steps were compared to theoretical curves for diffusional transport to determine the mechanism of charge transport and to optically measure its rate. The influence of redox-induced thickness changes and solvent sorption on charge transport and voltammetric behavior is described. The electrochemical activation of glassy carbon electrodes for electrolysis of aromatic molecules, such as catechol and hydroquinone, was studied by combined ellipsometric and voltammetric measurements. Ellipsometry was used to detect the anodic growth of nearly transparent layer which activated the surface. X

  1. A novel sensor made of Antimony Doped Tin Oxide-silica composite sol on a glassy carbon electrode modified by single-walled carbon nanotubes for detection of norepinephrine.

    Science.gov (United States)

    Wang, Zhao; Wang, Kai; Zhao, Lu; Chai, Shigan; Zhang, Jinzhi; Zhang, Xiuhua; Zou, Qichao

    2017-11-01

    In this study, we designed a novel molecularly imprinted polymer (MIP), Antimony Doped Tin Oxide (ATO)-silica composite sol, which was made using a sol-gel method. Then a sensitive and selective imprinted electrochemical sensor was constructed with the ATO-silica composite sol on a glassy carbon electrode modified by single-walled carbon nanotubes (SWNTs). The introduction of SWNTs increased the sensitivity of the MIP sensor. The surface morphology of the MIP and MIP/SWNTs were characterized by scanning electron microscopy (SEM), and the optimal conditions for detection were determined. The oxidative peak current increased linearly with the concentration of norepinephrine in the range of 9.99×10 -8 M to 1.50×10 -5 M, as detected by cyclic voltammetry (CV), the detection limit was 3.33×10 -8 M (S/N=3). In addition, the proposed electrochemical sensors were successfully applied to detect the norepinephrine concentration in human blood serum samples. The recoveries of the sensors varied from 99.67% to 104.17%, indicating that the sensor has potential for the determination of norepinephrine in clinical tests. Moreover, the imprinted electrochemical sensor was used to selectively detect norepinephrine. The analytical application was conducted successfully and yielded accurate and precise results. Copyright © 2017. Published by Elsevier B.V.

  2. Determination of uric acid in the presence of ascorbic acid with hexacyanoferrate lanthanum film modified electrode

    International Nuclear Information System (INIS)

    Wang Guangfeng; Meng Jian; Liu Hongying; Jiao Shoufeng; Zhang Wei; Chen Daolei; Fang Bin

    2008-01-01

    A glassy carbon electrode modified with LaHCF was constructed and was characterized by cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS). The resulting LaHCF modified glassy carbon electrode had a good catalytic character on uric acid (UA) and was used to detect uric acid and ascorbic acid (AA) simultaneously. This modified electrode exhibits potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards UA and AA with activation overpotential. For UA and AA in mixture, one can well separate from the other with a potential large enough to allow the determination of one in presence of the other. The DPV peak currents obtained increased linearly on the UA in the range of 2.0 x 10 -7 to 1.0 x 10 -4 mol/L with the detection limit (signal-to-noise ratio was 3) for UA 1.0 x 10 -7 mol/L. The proposed method showed excellent selectivity and stability, and the determination of UA and AA simultaneously in urine was satisfactory

  3. Electrochemical immunoassay for the carcinoembryonic antigen based on the use of a glassy carbon electrode modified with an octahedral Cu2O-gold nanocomposite and staphylococcal protein for signal amplification.

    Science.gov (United States)

    Qin, Zhen; Xu, Wei; Chen, Shuai; Chen, Jun; Qiu, Jing Fu; Li, Chao Rui

    2018-04-24

    The authors describe an electrochemical immunoassay for ultrasensitive direct determination of the carcinoembryonic antigen (CEA). A nanocomposite consisting of octahedral Cu2O nanocrystals covered with gold nanoparticles was utilized to modify a glassy carbon electrode which gives a strongly enhanced chronoamperometric signal for H 2 O 2 which is used as an electrochemical probe. The morphology and elemental composition of the the nanocomposite was studied by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. In addition, staphylococcal protein A was placed on the electrode for efficient capture of antibody to further enhance the sensitivity of the assay. Under optimal conditions and at a typical working voltage of -0.4 V (vs. Ag/AgCl), the response covers the 2 pg·mL -1 to 20 ng·mL -1 CEA concentration range with a 200 fg·mL -1 lower detection limit. The method was successfully applied to the determination of CEA in (spiked) human serum. Graphical abstract Schematic of the fabrication of an electrochemical immunosensor for ultrasensitive detection the carcinoembryonic antigen. The sensor is based on the use of a glassy carbon electrode modified with an octahedral Cu 2 O-gold nanocomposite and staphylococcal protein A for signal amplification.

  4. Investigation of electrochemical behavior of lipid lowering agent atorvastatin calcium in aqueous media and its determination from pharmaceutical dosage forms and biological fluids using boron-doped diamond and glassy carbon electrodes.

    Science.gov (United States)

    Dogan-Topal, Burcu; Uslu, Bengi; Ozkan, Sibel A

    2007-08-01

    The electrochemical behavior of atorvastatin calcium at glassy carbon and boron-doped diamond electrodes has been studied using voltammetric techniques. The possible mechanism of oxidation was discussed with model compounds. The dependence of the peak current and potentials on pH, concentration, scan rate and nature of the buffer were investigated for both electrodes. The oxidation of atorvastatin was irreversible and exhibited a diffusion-controlled fashion on the diamond electrode. A linear response was obtained within the range of 9.65 x 10(-7) - 3.86 x 10(-5) M in 0.1 M H(2)SO(4) solution for both electrodes. The detection limits of a standard solution are estimated to be 2.11 x 10(-7) M with differential pulse voltammetry (DPV) and 2.05 x 10(-7)M with square wave voltammetry (SWV) for glassy carbon electrode, and 2.27 x 10(-7) M with DPV and 1.31 x 10(-7)M with SWV for diamond electrodes in 0.1 M H(2)SO(4) solution. The repeatability of the methods was found good for both electrodes. The methods were fully validated and successfully applied to the high-throughput determination of the drug in tablets, human serum and human urine with good recoveries.

  5. Voltammetric Determination of Acetaminophen in the Presence of Codeine and Ascorbic Acid at Layer-by-Layer MWCNT/Hydroquinone Sulfonic Acid-Overoxidized Polypyrrole Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Saeed Shahrokhian

    2011-01-01

    Full Text Available A very sensitive electrochemical sensor constructed of a glassy carbon electrode modified with a layer-by-layer MWCNT/doped-overoxidized polypyrrole (oppy/MWCNT /GCE was used for the determination of acetaminophen (AC in the presence of codeine and ascorbic acid (AA. In comparison to the bare glassy carbon electrode, a considerable shift in the peak potential together with an increase in the peak current was observed for AC on the surface of oppy/MWCNT/GCE, which can be related to the enlarged microscopic surface area of the electrode. The effect of the experimental conditions on the electrode response, such as types of counter ion, pyrrole and counter ion concentration, potential and number of cycles in the polymerization procedure, amount of MWCNT, and the pH, were investigated. Under the optimized conditions, the calibration curve was obtained over two concentration ranges of 2 × 10−7–6 × 10−6 M and 4 × 10−5–1 × 10−4 M of AC with a linear correlation coefficient (R2 of 0.9959 and 0.9947, respectively. The estimated detection limit (3σ for AC was obtained as 5 × 10−8 M. The developed method was successfully applied to analyze the pharmaceutical preparations of AC, and a recovery of 95% with a relative standard deviation of 0.98% was obtained for AC.

  6. The glassy wormlike chain

    International Nuclear Information System (INIS)

    Kroy, Klaus; Glaser, Jens

    2007-01-01

    We introduce a new model for the dynamics of a wormlike chain (WLC) in an environment that gives rise to a rough free energy landscape, which we name the glassy WLC. It is obtained from the common WLC by an exponential stretching of the relaxation spectrum of its long-wavelength eigenmodes, controlled by a single parameter E. Predictions for pertinent observables such as the dynamic structure factor and the microrheological susceptibility exhibit the characteristics of soft glassy rheology and compare favourably with experimental data for reconstituted cytoskeletal networks and live cells. We speculate about the possible microscopic origin of the stretching, implications for the nonlinear rheology, and the potential physiological significance of our results

  7. An electrochemical sensor for rizatriptan benzoate determination using Fe{sub 3}O{sub 4} nanoparticle/multiwall carbon nanotube-modified glassy carbon electrode in real samples

    Energy Technology Data Exchange (ETDEWEB)

    Madrakian, Tayyebeh, E-mail: madrakian@basu.ac.ir; Maleki, Somayeh; Heidari, Mozhgan; Afkhami, Abbas

    2016-06-01

    In this paper a sensitive and selective electrochemical sensor for determination of rizatriptan benzoate (RZB) was proposed. A glassy carbon electrode was modified with nanocomposite of multiwalled carbon nanotubes (MWCNTs) and Fe{sub 3}O{sub 4} nanoparticles (Fe{sub 3}O{sub 4}/MWCNTs/GCE). The results obtained clearly show that the combination of MWCNTs and Fe{sub 3}O{sub 4} nanoparticles definitely improves the sensitivity of modified electrode to RZB determination. The morphology and electroanalytical performance of the fabricated sensor were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), square wave voltammetry (SWV) and cyclic voltammetry (CV). Also, the effect of experimental and instrumental parameters on the sensor response was evaluated. The square wave voltammetric response of the electrode to RZB was linear in the range 0.5–100.0 μmol L{sup −1} with a detection limit of 0.09 μmol L{sup −1} under the optimum conditions. The investigated method showed good stability, reproducibility and repeatability. The proposed sensor was successfully applied for real life samples of blood serum and RZB determination in pharmaceutical. - Highlights: • Simple and sensitive Fe{sub 3}O{sub 4}/MWCNTs/GCE for rizatriptan benzoate determination • The surface morphology of nanocomposite was characterized by SEM and EDS. • Rizatriptan benzoate was measured at 0.09 μmol L{sup −1} with good sensitivity and selectivity. • The electrode has been successfully applied in serum and pharmaceutical samples. • The nanocomposite had excellent electrocatalytic activity and biocompatibility.

  8. Poly-Alizarin red S/multiwalled carbon nanotube modified glassy carbon electrode for the boost up of electrocatalytic activity towards the investigation of dopamine and simultaneous resolution in the presence of 5-HT: A voltammetric study

    Energy Technology Data Exchange (ETDEWEB)

    Reddaiah, K. [Electrochemical Research Laboratory, Department of Chemistry, S.V.U. College of Sciences, Sri Venkateswara University, Tirupati 517 502, Andhra Pradesh (India); Madhusudana Reddy, T., E-mail: tmsreddysvu@gmail.com [Electrochemical Research Laboratory, Department of Chemistry, S.V.U. College of Sciences, Sri Venkateswara University, Tirupati 517 502, Andhra Pradesh (India); Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455 (United States); Venkata Ramana, D.K. [Department of Safety Engineering, Dongguk University, 123 Dongdae-ro, Gyeongju, Gyeongbuk 780 714 (Korea, Republic of); Subba Rao, Y. [DST-PURSE Centre, Sri Venkateswara University, Tirupati 517502, Andhra Pradesh (India)

    2016-05-01

    Poly-Alizarin red S/multiwalled carbon nanotube film on the surface of glassy carbon electrode (poly-AzrS/MWCNT/GCE) was synthesized by electrochemical process and was used for the sensitive and selective determination of dopamine (DA) by employing voltammetric techniques. The electrocatalytic response of the modified electrode was found to exhibit admirable activity. The simultaneous determination of dopamine in the presence of serotonin (5-HT) was found to exhibit very good response at poly-AzrS/MWCNTs/GCE. The effect of pH, scan rate, accumulation time and concentration of dopamine was studied at the developed poly-AzrS/MWCNTs/GCE. The poly-AzrS/MWCNTs/GCE exhibited an efficient electron mediating behavior together with well resolved peaks for dopamine, in 0.1 mol/dm{sup 3} phosphate buffer (PBS) solution of pH 7.0. The limit of detection (LOD) and limit of quantification (LOQ) were found to be as 1.89 × 10{sup −7} mol/dm{sup 3} and 6.312 × 10{sup −7} mol/dm{sup 3} respectively with a dynamic range from 1 × 10{sup −6} to 1.8 × 10{sup −5} mol/dm{sup 3}. The interfacial electron transfer behavior of DA was studied by electrochemical impedance spectroscopy (EIS); the studies showed that the charge transfer rate was enhanced at poly-AzrS/MWCNTs/GCE when compared with bare GCE and poly-AzrS/GCE. - Highlights: • The poly-AzrS/MWCNTs/GCE showed good sensitivity towards DA sensing. • The sensor reduced the overoxidation potentials for DA. • This electrode was successfully used for simultaneous sensing of DA and 5-HT. • The electrode was effectively used for the determination of DA in pharmaceutical formulations.

  9. Electrochemical and Electron Paramagnetic Resonance Study of the Mechanism of Oxidation of Phenazine-di-N-oxide in the Presence of Isopropyl alcohol at Glassy Carbon and Single-Walled Carbon Nanotube Electrodes

    International Nuclear Information System (INIS)

    Kulakovskaya, S.I.; Kulikov, A.V.; Sviridova, L.N.; Stenina, E.V.

    2014-01-01

    Graphical abstract: - Highlights: • The mechanism of oxidation of phenazine-di-N-oxide in the presence of isopropyl alcohol was studied. • The results are explained in terms of the E 1 C 1 E 2 C 2 mechanism of the two-stage electrode process. • The total two-electron catalytic oxidation of i-PrOH in the complex with the phenazine-di-N-oxide radical cation was assumed to occur. - Abstract: The mechanism of oxidation of phenazine-di-N-oxide in the presence of isopropyl alcohol was studied by cyclic voltammetry at glassy carbon (GC) and single-walled carbon nanotubes (SWCNT) electrodes in 0.1 M LiClO 4 solutions in acetonitrile. The adsorption of phenazine-di-N-oxide at SWCNT electrode in 0.1 M LiClO 4 solution in acetonitrile was investigated by measurement of the dependence of the differential double layer capacitance of the electrode C on potential E. The effect of isopropyl alcohol on the shape of cyclic voltammograms (CVs) of phenazine-di-N-oxide and the intensity of Electron Paramagnetic Resonance (EPR) signal of its radical cation was investigated. The catalytic currents were recorded at the oxidation of phenazine-di-N-oxide at SWCNT and GC electrodes in the presence of isopropyl alcohol. The results were explained in terms of the E 1 C 1 E 2 C 2 mechanism of two-stage electrode process characterized by catalytic current recorded at the second electrode stage. The overall two-electron catalytic oxidation of isopropyl alcohol in complex with the phenazine-di-N-oxide radical cation was assumed to occur. It was shown that SWCNT electrodes can be used in the electrocatalytic oxidation of organic compounds in the presence of electrochemically generated phenazine-di-N-oxide radical cation

  10. Electrochemical behaviour of platinum at polymer-modified glassy ...

    Indian Academy of Sciences (India)

    TECS

    Abstract. In this paper, the preparations and voltammetric characteristics of chitosan-modified glassy carbon (Ct-MGC) and platinum electrodes are studied. Ct-MGC can be used for pre-concentration and quantification of trace amounts of platinum in solution. At low pH medium, the complex of Pt with pro- tonated group –NH.

  11. Electrochemical behaviour of platinum at polymer-modified glassy ...

    Indian Academy of Sciences (India)

    modified glassy carbon (Ct-MGC) and platinum electrodes are studied. Ct-MGC can be used for pre-concentration and quantification of trace amounts of platinum in solution. At low pH medium, the complex of Pt with protonated group -NH3+ in the ...

  12. Surface characterization of silver and palladium modified glassy ...

    Indian Academy of Sciences (India)

    WINTEC

    Abstract. In this work, the influence of silver and palladium on the surface of undoped, boron doped and phosphorus doped glassy carbon has been studied. The silver and palladium concentrations in solution, after metal deposition, were measured by atomic absorption spectrophotometer. The morphology of metal coatings.

  13. MWCNTs/Cu(OH)2 nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac

    International Nuclear Information System (INIS)

    Arvand, Majid; Gholizadeh, Tahereh M.; Zanjanchi, Mohammad Ali

    2012-01-01

    This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH) 2 nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF 6 ) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 μM, with a detection limit of 0.04 μM. Electrochemical studies suggested that the MWCNTs/Cu(OH) 2 nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current. Highlights: ► This work examines oxidation of diclofenac at a nanocomposite modified electrode. ► The salient feature of this electrode is large diffusion coefficient. ► The proposed electrode decreased overpotential of diclofenac electrooxidation. ► The modified electrode has good stability and reproducibility.

  14. MWCNTs/Cu(OH){sub 2} nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac

    Energy Technology Data Exchange (ETDEWEB)

    Arvand, Majid, E-mail: arvand@guilan.ac.ir; Gholizadeh, Tahereh M.; Zanjanchi, Mohammad Ali

    2012-08-01

    This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH){sub 2} nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF{sub 6}) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 {mu}M, with a detection limit of 0.04 {mu}M. Electrochemical studies suggested that the MWCNTs/Cu(OH){sub 2} nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current. Highlights: Black-Right-Pointing-Pointer This work examines oxidation of diclofenac at a nanocomposite modified electrode. Black-Right-Pointing-Pointer The salient feature of this electrode is large diffusion coefficient. Black-Right-Pointing-Pointer The proposed electrode decreased overpotential of diclofenac electrooxidation. Black-Right-Pointing-Pointer The modified electrode has good stability and reproducibility.

  15. Electrochemical preparation and electrocatalytic properties of PEDOT/ferricyanide film-modified electrodes

    International Nuclear Information System (INIS)

    Vasantha, V.S.; Chen, S.-M.

    2005-01-01

    The poly(3,4-ethylenedioxy thiophene) (PEDOT)/ferricyanide (FCN) film was synthesized by a potentiostatic and also using potentiodynamic methods namely cyclic voltammetric and chronoamperometric techniques. The EQCM technique was used to study the mechanism of the incorporation of ferricyanide ions on the PEDOT film. The UV-vis absorption results too confirmed the presence of ferricyanide with the PEDOT film. The electrocatalytic oxidation of ascorbic acid was carried out on a glassy carbon electrode modified with the PEDOT/FCN film through cyclic voltammetry, chronoamperometry and rotating disk electrode (RDE) voltammetry as diagnostic techniques. It was found that the catalytic current depended on the concentration of ascorbic acid. The number of electron transfer involved in the rate-determining step was found to be 1 and transfer coefficient (α) equal to 0.476. The diffusion coefficient of ascorbic acid was also estimated through the chrono amperometric and rotating disk electrode methods. The D values of ascorbic acid obtained by through the cyclic and chronoamperometric methods were found to be 4.4103 x 10 -6 and 4.9595 x 10 -6 cm 2 s -1 , respectively. This modified electrode was also used for the simultaneous determination of ascorbic acid and dopamine

  16. A hydrogen-evolving Ni(P2N2)2 electrocatalyst covalently attached to a glassy carbon electrode: preparation, characterization, and catalysis. comparisons with the homogeneous analogue.

    Science.gov (United States)

    Das, Atanu K; Engelhard, Mark H; Bullock, R Morris; Roberts, John A S

    2014-07-07

    A hydrogen-evolving homogeneous Ni(P2N2)2 electrocatalyst with peripheral ester groups has been covalently attached to a 1,2,3-triazolyllithium-terminated planar glassy carbon electrode surface. Coupling proceeds with both the Ni(0) and the Ni(II) complexes. X-ray photoemission spectra show excellent agreement between the Ni(0) coupling product and its parent complex, and voltammetry of the surface-confined system shows that a single species predominates with a surface density of 1.3 × 10(-10) mol cm(-2), approaching the value estimated for a densely packed monolayer. With the Ni(II) system, both photoemission and voltammetric data show speciation to unidentified products on coupling, and the surface density is 6.7 × 10(-11) mol cm(-2). The surface-confined Ni(0) complex is an electroctalyst for hydrogen evolution, showing the onset of catalytic current at the same potential as the soluble parent complex. Decomposition of the surface-confined species is observed in acidic acetonitrile. This is interpreted to reflect the lability of the Ni(II)-phosphine interaction and the basicity of the free phosphine and bears on concurrent efforts to implement surface-confined Ni(P2N2)2 complexes in electrochemical or photoelectrochemical devices.

  17. A Sensor for the Determination of Lindane Using PANI/Zn, Fe(III Oxides and Nylon 6,6/MWCNT/Zn, Fe(III Oxides Nanofibers Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Omolola E. Fayemi

    2016-01-01

    Full Text Available A simple reproducible and environmentally friendly PANI/Zn, Fe(III and Nylon 6,6/MWCNT/Zn, Fe(III oxides nanofibers modified glassy carbon electrode was prepared and used for the electrochemical reduction of lindane. The modified electrodes offer a high sensing current for lindane. The modified electrodes were highly stable with respect to time, so that the single electrode can be used for the multiple analysis of the lindane sample. Cyclic voltammetry and square wave voltammetry were used as the sensing techniques. The dynamic range for the lindane determination was between 9.9 × 10−12 mol/L and 5 × 10−6 mol/L with detection limits of 51 and 32 nM for Nylon 6,6/MWCNT/ZnO and Nylon 6,6/MWCNT/Fe3O4 sensors, respectively. The LoD value reveals that the best electrode is Nylon 6,6/MWCNT/Fe3O4. The analytical utility of the proposed method was checked with drinking water samples.

  18. Investigation of thermal oxidative break-down of polyethylene films modified with grafted polyacrylonitrile

    International Nuclear Information System (INIS)

    Krul', L.P.; Gert, E.V.

    1981-01-01

    Thermal oxidative destruction of polyethylene (PE) films modified by radiation (#betta#-radiation, dose rate is 0.56 Mrad/hr) liquid-phase graft polymerization of acrylonitrile (AN) has been studied. Comparative stability of grafted copolymers, homopolymers and mechanical mixtures of PE and PAN (polyacrylonitrile) to thermal oxidative destruction is studied using the derivatographic method. It is shown that graft of PAN considerably decelerates the development of oxidative and destructive processes in PE, at that, the efficiency of PE chain stabilization increases with the increase of grafted PAN amount. The sample with PAN content x=0.367 (in parts of the mass of grafted film) possesses the highest stability

  19. Simultaneous electrochemical immunosensing of alpha-fetoprotein and prostate specific antigen using a glassy carbon electrode modified with gold nanoparticle-coated silica nanospheres and decorated with Azure A or ferrocene carboxylic acid

    International Nuclear Information System (INIS)

    Zhao, Junqing; Guo, Zilin; Guo, Jinjin; Wang, Junchun; Zhang, Yuzhong; Feng, Dexiang

    2015-01-01

    We describe an electrochemical immunosensor for the simultaneous determination of alpha-fetoprotein (AFP) and prostate specific antigen (PSA) via a modified glassy carbon electrode. Silica nanoparticles (200–300 nm i.d.) with good monodispersity and uniform shape were synthesized, and the following species were then consecutively immobilized on their surface: gold nanoparticles (AuNPs; 5–15 nm i.d.), secondary antibody (Ab 2 ) and the redox-probes Azure A or ferrocenecarboxy acid (Fc). In parallel, two types of primary antibodies (Ab 1 ) were co-immobilized on the surface of the dissolved reduced graphene oxide sheets (rGO) that were also decorated with AuNPs. In the presence of antigens (AFP or PSA), the Ab 2 /Si-AuNPs carrying Azure A and Fc are attached to the AuNP/rGO conjugate via a sandwich type immunoreaction. Differential pulse voltammetry (DPV) was employed to measure the resulting changes in the signal of Fc or Azure A. Two well-resolved oxidation peaks, one at −0.48 V (corresponding to Azure A) and other at + 0.12 V (corresponding to Fc; both vs. SCE) can be observed in the DPV curves. Under optimal conditions, AFP and PSA can be simultaneously determined in the range from 0.01 to 25 ng mL -1 for AFP, and from 0.012 to 25 ng mL -1 for PSA. The detection limits are 3.3 pg mL -1 for AFP and 4.0 pg mL -1 for PSA (at a signal-to-noise ratio of 3). The method was applied to (spiked) real sample analysis, and the recoveries are within 96.0 and 107.2 % for PSA, and within 100.9 and 105.8 % for AFP, indicating that this dual immunosensor matches the requirements of clinical analysis. (author)

  20. Water clustering in glassy polymers.

    Science.gov (United States)

    Davis, Eric M; Elabd, Yossef A

    2013-09-12

    In this study, water solubility and water clustering in several glassy polymers, including poly(methyl methacrylate) (PMMA), poly(styrene) (PS), and poly(vinylpyrrolidone) (PVP), were measured using both quartz spring microbalance (QSM) and Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Specifically, QSM was used to determine water solubility, while FTIR-ATR spectroscopy provided a direct, molecular-level measurement of water clustering. The Flory-Huggins theory was employed to obtain a measure of water-polymer interaction and water solubility, through both prediction and regression, where the theory failed to predict water solubility in both PMMA and PVP. Furthermore, a comparison of water clustering between direct FTIR-ATR spectroscopy measurements and predictions from the Zimm-Lundberg clustering analysis produced contradictory results. The failure of the Flory-Huggins theory and Zimm-Lundberg clustering analysis to describe water solubility and water clustering, respectively, in these glassy polymers is in part due to the equilibrium constraints under which these models are derived in contrast to the nonequilibrium state of glassy polymers. Additionally, FTIR-ATR spectroscopy results were compared to temperature-dependent diffusivity data, where a correlation between the activation energy for diffusion and the measured water clustering was observed.

  1. Physicochemical and Mechanical Properties of Bambara Groundnut Starch Films Modified with Stearic Acid.

    Science.gov (United States)

    Oyeyinka, Samson A; Singh, Suren; Amonsou, Eric O

    2017-01-01

    The physicochemical and mechanical properties of biofilm prepared from bambara starch modified with varying concentrations of stearic acid (0%, 2.5%, 3.5%, 5%, 7%, and 10%) were studied. By scanning electron microscopy, bambara starch films modified with stearic acid (≥3.5%) showed a progressively rough surface compared to those with 2.5% stearic acid and the control. Fourier transform infrared spectroscopy spectra revealed a peak shift of approximately 31 cm -1 , suggesting the promotion of hydrogen bond formation between hydroxyl groups of starch and stearic acid. The addition of 2.5% stearic acid to bambara starch film reduced water vapor permeability by approximately 17%. Bambara starch films modified with higher concentration of stearic acid were more opaque and showed significantly high melting temperatures. However, mechanical properties of starch films were generally negatively affected by stearic acid. Bambara starch film may be modified with 2.5% stearic acid for improved water vapor permeability and thermal stability with minimal effect on tensile strength. © 2016 Institute of Food Technologists®.

  2. Glassy carbon electrodes modified with gelatin functionalized ...

    Indian Academy of Sciences (India)

    . Zhou Y, Bao Q L, Tang L A L, Zhong Y L and Loh K P 2009. Chem. Mater. 21 2950. 29. Sun Z Y, Liu Z M, Wang Y, Han B X, Du J M and Zhang J L. 2005 J. Mater. Chem. 15 4497. 30. Gunckel S, Santander P, Cordano G, Ferreira J, Munoz S,.

  3. Glassy carbon electrodes modified with gelatin functionalized ...

    Indian Academy of Sciences (India)

    also potential health effects which have been found in recent times.16 GA has a ... provide a fast model for analysis of GA in real samples. ..... Souza L P, Calegari F, Zarbin A J G, Junior L H M and. Bergamini M F 2011 J. Agric. Food Chem. 59 7620. 23. Abdel-Hamid R and Newair E F 2011 J. Electroanal. Chem. 657 107.

  4. Cooperative strings and glassy interfaces.

    Science.gov (United States)

    Salez, Thomas; Salez, Justin; Dalnoki-Veress, Kari; Raphaël, Elie; Forrest, James A

    2015-07-07

    We introduce a minimal theory of glass formation based on the ideas of molecular crowding and resultant string-like cooperative rearrangement, and address the effects of free interfaces. In the bulk case, we obtain a scaling expression for the number of particles taking part in cooperative strings, and we recover the Adam-Gibbs description of glassy dynamics. Then, by including thermal dilatation, the Vogel-Fulcher-Tammann relation is derived. Moreover, the random and string-like characters of the cooperative rearrangement allow us to predict a temperature-dependent expression for the cooperative length ξ of bulk relaxation. Finally, we explore the influence of sample boundaries when the system size becomes comparable to ξ. The theory is in agreement with measurements of the glass-transition temperature of thin polymer films, and allows quantification of the temperature-dependent thickness hm of the interfacial mobile layer.

  5. Preparation and antifouling property of polyurethane film modified by chondroitin sulfate

    Science.gov (United States)

    Yuan, Huihui; Xue, Jing; Qian, Bin; Chen, Huaying; Zhu, Yonggang; Lan, Minbo

    2017-02-01

    An antifouling polyurethane film modified by chondroitin sulfate (PU-CS) was prepared by chemical grafting with N-Boc-1,3-propanediamine as a spacer. The different mass fraction of N-Boc-1,3-propanediamine was investigated to obtain PU-CS films with different CS grafting density. The surface properties of PU-CS films were comprehensively characterized. Proteins adsorption and glycosaminoglycans adhesion on films were evaluated. Moreover, inorganic salt deposition on film with highest CS grafting density (3.70 μg/cm2) was briefly investigated. The results showed that the increase of CS grafting density improved not only the hydrophilicity but the antifouling performance of films. The best antifouling film reduced the adsorption of fibrinogen (BFG), human serum albumin (HSA) and lysozyme (LYS) by 81.4%, 95.0% and 76.5%, respectively, and the adhesion of chondroitin (CS), heparin (HP) and hyaluronic acid (HA) by 70.6%, 87.4% and 81.3%, respectively. In addition, the co-adsorption of proteins and glycosaminoglycans reduced up to 86.9% and 75.5%, respectively. Changes in inorganic salt deposition after co-adsorption of proteins and glycosaminoglycans on PU-CS(3) suggested that the proteins promoted the inorganic salt deposition, while glycosaminoglycans inhibited the crystal growth. The negatively charged polysaccharides might promote the generation of smaller crystals which could be conducive to provide theoretical and practical guide to develop novel urinary stents with significant anti-encrustation properties.

  6. Gas-sensing properties of In2O3 films modified with gold nanoparticles

    International Nuclear Information System (INIS)

    Korotcenkov, G.; Brinzari, V.; Han, S.H.; Cho, B.K.

    2016-01-01

    A study of the surface and gas–sensitive properties of In 2 O 3 films modified with gold nanoparticles and synthesized by the successive ionic layer deposition (SILD) method was conducted. In 2 O 3 films were prepared using the spray pyrolysis method. The gas-sensing characteristics were tested using CO, H 2 , and O 3 as target gases. It has been shown that the surface modification with gold nanoparticles gives the opportunity to optimize the response of In 2 O 3 -based gas sensors to both reducing (CO, H 2 ) and oxidizing (O 3 ) gases. It has been found that the sensitizing effect during ozone detection was significantly higher than the effect during CO and H 2 detection. It has been demonstrated that the sensitizing effect depended on the number of SILD cycles used for gold nanoparticle deposition and was maximal for the In 2 O 3 surface decorated with gold nanoparticles with the smallest size. The mechanism of the gold nanoparticles' influence on the gas-sensing properties of the In 2 O 3 films is also discussed. It is suggested that to explain the observed effects, we have to consider both the “electronic” and “chemical” mechanisms of sensitization. Suggestions for studies to be carried out to further improve both the understanding of the nature of the gas-sensitive effects and the parameters of In 2 O 3 :Au-based gas sensors are also formulated. - Highlights: • In 2 O 3 gas sensors modified with gold nanoparticles using SILD method are studied. • AuNPs exhibit activity during interaction with either reducing or oxidizing gases. • Maximal effect of optimization is observed during ozone detection. • Sensitizing effect depends on the number of SILD cycles. • Proposed mechanisms explain effects observed in the In 2 O 3 :Au based gas sensors.

  7. Glassy slags for minimum additive waste stabilization

    International Nuclear Information System (INIS)

    Feng, X.; Wronkiewicz, D.J.; Bates, J.K.; Brown, N.R.; Buck, E.C.; Dietz, N.L.; Gong, M.; Emery, J.W.

    1994-05-01

    Glassy slag waste forms are being developed to complement glass waste forms in implementing Minimum Additive Waste Stabilization (MAWS) for supporting DOE's environmental restoration efforts. The glassy slag waste form is composed of various crystalline and metal oxide phases embedded in a silicate glass phase. The MAWS approach was adopted by blending multiple waste streams to achieve up to 100% waste loadings. The crystalline phases, such as spinels, are very durable and contain hazardous and radioactive elements in their lattice structures. These crystalline phases may account for up to 80% of the total volume of slags having over 80% metal loading. The structural bond strength model was used to quantify the correlation between glassy slag composition and chemical durability so that optimized slag compositions were obtained with limited crucible melting and testing. Slag compositions developed through crucible melts were also successfully generated in a pilot-scale Retech plasma centrifugal furnace at Ukiah, California. Utilization of glassy slag waste forms allows the MAWS approach to be applied to a much wider range of waste streams than glass waste forms. The initial work at ANL has indicated that glassy slags are good final waste forms because of (1) their high chemical durability; (2) their ability to incorporate large amounts of metal oxides; (3) their ability to incorporate waste streams having low contents of flux components; (4) their less stringent requirements on processing parameters, compared to glass waste forms; and (5) their low requirements for purchased additives, which means greater waste volume reduction and treatment cost savings

  8. Bismuth Modified Carbon-Based Electrodes for the Determination of Selected Neonicotinoid Insecticides

    Directory of Open Access Journals (Sweden)

    Marko Rodić

    2011-05-01

    Full Text Available Two types of bismuth modified electrodes, a bismuth-film modified glassy carbon (BiF-GCE and a bismuth bulk modified carbon paste, were applied for the determination of selected nitroguanidine neonicotinoid insecticides. The method based on an ex situ prepared BiF-GCE operated in the differential pulse voltammetric (DPV mode was applied to determine clothianidin in the concentration range from 2.5 to 23 μg cm−3 with a relative standard deviation (RSD not exceeding 1.5%. The tricresyl phosphate-based carbon paste electrodes (TCP-CPEs, bulk modified with 5 and 20 w/w% of bismuth, showed a different analytical performance in the determination of imidacloprid, regarding the peak shape, potential window, and noise level. The TCP-CPE with 5% Bi was advantageous, and the developed DPV method based on it allowed the determination in the concentration range from 1.7 to 60 μg cm−3 with an RSD of 2.4%. To get a deeper insight into the morphology of the bismuth-based sensor surfaces, scanning electron microscopic measurements were performed of both the surface film and the bulk modified electrodes.

  9. Composite system based on biomolecules-functionalized multiwalled carbon nanotube and ionic liquid: Electrochemistry and electrocatalysis of tryptophane

    International Nuclear Information System (INIS)

    Li Li; Bu Caihong; Zhang Yijun; Du Jie; Lu Xiaoquan; Liu Xiuhui

    2011-01-01

    The combination of biomolecules-functionalized multiwalled carbon nanotube (MWNTs) and ionic liquid (IL) yields nanostructured biointerfaces, formed a novel kind of structurally uniform and bioelectrocatalytic activity material. Rutin was chosen as a model biomolecules to investigate the composite system. The MWNTs–Rutin–IL composite film was characterized by different methods including thermogravimetric analysis (TGA), UV–vis spectra, electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscope (SECM). A pair of well-defined quasi reversible redox peaks of rutin was obtained at the MWNTs–Rutin–IL composite film modified glassy carbon electrode (GCE) by direct electron transfer between the rutin and the GCE electrode. Dramatically enhanced biocatalytic and electrocatalytic activity was exemplified at the MWNTs–Rutin–IL/GCE electrode by the oxidized of tryptophane. The oxidation peak currents of tryptophane in such modified electrode increased linearly with the concentrations of tryptophane in the range from 8 × 10 −8 to 2 × 10 −5 mol L −1 with a detection limit of 3.0 × 10 −8 mol L −1 . The unique composite material based on biomolecules-functionalized carbon nanotube and ionic liquid have wide potential applications in direct electrochemistry, biosensors, and biocatalysis.

  10. Solvated electron structure in glassy matrices

    International Nuclear Information System (INIS)

    Kevan, L.

    1981-01-01

    Current knowledge of the detailed geometrical structure of solvated electrons in aqueous and organic media is summarized. The geometry of solvated electrons in glassy methanol, ethanol, and 2-methyltetrahydrofuran is discussed. Advanced electron magnetic resonance methods and development of new methods of analysis of electron spin echo modulation patterns, second moment line shapes, and forbidden photon spin-flip transitions for paramagnetic species in these disordered systems are discussed. 66 references are cited

  11. Improving the cell affinity of a poly(D,L-lactide) film modified by grafting collagen via a plasma technique

    International Nuclear Information System (INIS)

    Zhao Jianhao; Wang Jue; Tu Mei; Luo Binghong; Zhou Changren

    2006-01-01

    Poly(D,L-lactide) films were surface-modified by grafting collagen via NH 3 plasma to improve cell affinity. The modified films were characterized by IR analysis, contact angle measurement, SEM analysis and collagen quantity determination. It was demonstrated that -NH 2 and collagen were incorporated into the surface of PDLLA films. The hydrophilicity of the PDLLA film increased after NH 3 plasma treatment, but decreased with further collagen modification. More collagen was incorporated into the PDLLA films by a grating method as compared to that with an anchorage treatment. L929 fibroblast cells were used to evaluate the cell affinity of the modified films and control. It was shown that PDLLA films surface-modified by grafting collagen via NH 3 plasma more efficiently enhanced the cells attachment and proliferation than those films modified by collagen anchorage or only NH 3 plasma treatment

  12. Spatially heterogeneous ages in glassy dynamics

    International Nuclear Information System (INIS)

    Castillo, Horacio E.; Chamon, Claudio Chamon; Cugliandolo, Leticia F.; Iguain, Jose Luis; Kennett, Malcolm P.

    2003-09-01

    We construct a framework for the study of fluctuations in the nonequilibrium relaxation of glassy systems with and without quenched disorder. We study two types of two-time local correlators with the aim of characterizing the heterogeneous evolution in these systems: in one case we average the local correlators over histories of the thermal noise, in the other case we simply coarse-grain the local correlators obtained for a given noise realization. We explain why the noise-averaged correlators describe the fingerprint of quenched disorder when it exists, while the coarse-grained correlators are linked to noise-induced mesoscopic fluctuations. We predict constraints on the distribution of the fluctuations of the coarse-grained quantities. In particular, we show that locally defined correlations and responses are connected by a generalized local out-of-equilibrium fluctuation-dissipation relation. We argue that large size heterogeneities in the age of the system survive in the long-time limit. A symmetry of the underlying theory, namely invariance under reparametrizations of the time coordinates, underlies these results. We establish a connection between the probabilities of spatial distributions of local coarse-grained quantities and the theory of dynamic random manifolds. We define, and discuss the behavior of, a two-time dependent correlation length from the spatial decay of the fluctuations in the two-time local functions. We characterize the fluctuations in the system in terms of their fractal properties. For concreteness, we present numerical tests performed on disordered spin models in finite and infinite dimensions. Finally, we explain how these ideas can be applied to the analysis of the dynamics of other glassy systems that can be either spin models without disorder or atomic and molecular glassy systems. (author)

  13. A highly sensitive non-enzymatic glucose sensor based on nickel and multi-walled carbon nanotubes nanohybrid films fabricated by one-step co-electrodeposition in ionic liquids

    International Nuclear Information System (INIS)

    Sun Aili; Zheng Jianbin; Sheng Qinglin

    2012-01-01

    Graphical abstract: Cyclic voltammograms of Ni–MWNTs/GCE at different concentrations of glucose. Highlights: ► Ni –MWNT nanohybrid film was successfully synthesized and characterized by SEM and EDS. ► The mechanism of glucose at Ni –MWNT nanohybrid film was evaluated and the upper glucose concentration limit produced a linear response of 17.5 mM. ► Simple of preparation and good analytical response made nanohybrid films a promising sensor material for non-enzymatic glucose sensing in routine analysis. - Abstract: In this paper, nickel was combined with multi-walled carbon nanotubes (Ni–MWNTs) to fabricate nanohybrid films on a conventional glassy carbon electrode using simultaneous electrodeposition of NiCl 2 and the MWNTs in ionic liquids (ILs). The morphologies and elemental compositions of the nanohybrid films were investigated with scanning electron microscopy and energy dispersive spectroscopy. A novel non-enzymatic glucose sensor based on the Ni–MWNT nanohybrid film-modified glassy carbon electrode was described, and its electrochemical behaviors were investigated. The proposed sensor exhibited high electrocatalytic activity and good response to glucose. Under optimal conditions, the sensor showed high sensitivity (67.2 μA mM −1 cm −2 ), rapid response time (<2 s) and a low detection limit (0.89 μM; signal/noise ratio of 3). In particular, the upper glucose concentration limit produced a linear response of 17.5 mM. Thus, the Ni–MWNT nanohybrid films represent promising sensor materials for non-enzymatic glucose sensing in routine analyses.

  14. The sorption induced glass transition in amorphous glassy polymers

    NARCIS (Netherlands)

    van der Vegt, N.F.A.; Wessling, Matthias; Strathmann, H.; Briels, Willem J.

    1999-01-01

    Sorption of CO2 in both the glassy and the rubbery state of an amorphous polyethylenelike polymer was investigated using molecular dynamics simulations. The temperature was chosen such that the system was in its glassy state at low solute concentrations and its rubbery state at large solute

  15. Characterization of n-TiO2 thin films modified with silver nanoparticles

    International Nuclear Information System (INIS)

    Cueto, L.F.; Sanchez-Cervantes, E.M.

    2010-01-01

    Carbon dioxide accumulation in the atmosphere has gained much attention and has reopened many research lines that initiated two or three decades ago. Electrochemical reduction represents one of the most discussed methods, especially where semiconductor and metal-semiconductor cathodes are used to achieve CO 2 transformation into higher-energy products. In the present work, the influence of silver nanoparticles upon CO 2 reduction on n-TiO 2 cathodes in aqueous media is presented. Silver nanoparticles with an average diameter of 250nm were deposited on n-TiO 2 surfaces by the electrochemical Double-Pulse Potential method. A Grazing-Incidence X-Ray Diffraction structural analysis is presented showing the presence of metallic silver, while Atomic Force Microscopy shows surface roughness and particle size before and after surface modification. These measurements were confirmed by Scanning-Electron Microscopy acquainting for the formation of metal particles on the n-TiO 2 surface. Enhancement of CO 2 reduction by the presence of silver on cathodes is shown by cyclic voltammetry. (author)

  16. STRUCTURAL, OPTICAL AND ELECTRICAL PROPERTIES OF PET POLYMER FILMS MODIFIED BY LOW ENERGY Ar+ ION BEAMS

    Science.gov (United States)

    Fawzy, Y. H. A.; Abdel-Hamid, H. M.; El-Okr, M. M.; Atta, A.

    Polyethylene terephthalate (PET) films with thickness 40μm are irradiated with 3keV argon ion beams with different fluence ranging from 0.5×1018ions.cm-2 to 2×1018ions.cm-2 using locally designed broad ion source. The changes in the PET structure are characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscope (SEM) techniques. The XRD patterns show that the peak intensity decreases with irradiation and the particle size decreases from 65.75 Å for the un-irradiated to 52.80 Å after irradiation. The FTIR indicates partial decrease and reduction in the intensity of the bands due to the degradation of the polymer after ion irradiation. The optical energy band gap decreases from 3.14eV to 3.05eV and the number of carbon cluster increases from 119 to 126 after ion irradiation. The results show a slight increase in the electrical conductivities and the dielectric constant (ɛ). The results indicate the effectiveness of using PET films as capacitors and resistors in industrial applications.

  17. The Anisotropic Glassy Properties of Decagonal Quasicrystals

    Directory of Open Access Journals (Sweden)

    Dragoş-Victor Anghel

    2013-01-01

    Full Text Available We use an extended version of the standard tunneling model to explain the anisotropic sound absorption in decagonal quasicrystals. The glassy properties are determined by an ensemble of two level systems (TLSs, arbitrarily oriented. The TLS is characterized by a 3 × 3 symmetric tensor, [T], which couples to the strain field, [S], through a 3 × 3 × 3 × 3 tensor of coupling constants, [R]. The structure of [R] reflects the symmetry of the quasicrystal. We also analyze the probability distributions of the elements of [T] in this particular model for a better understanding of the characteristics of “isotropic” and “anisotropic” distributions of the ensemble of TLSs. We observe that the distribution of the elements is neither simple nor intuitive and therefore it is difficult to guess it a priory, using qualitative arguments based on the symmetry properties.

  18. Formation of a glassy phase in ceramic-like coatings

    International Nuclear Information System (INIS)

    Sazonova, M.V.; Gorbatova, G.N.

    1986-01-01

    The authors investigate the synthesis directly in coatings of a borosilicate melt that could fill the role of glassy matrix, thereby avoiding fusion and processing of the glassy material. The effect of added boron on the formation of coatings based on molybdenum disilicide and tungsten disilicide in air at 900 degrees C is presented. Without an additive no coating forms; there is no adhesion to the graphite and a continuous film does not form. As a result of boron oxidation an easily fused glassy matrix forms, which bonds the molybdenum disilicide or tungsten disilicide particles together and ensures adhesion to the graphite

  19. Characterization of polypropylene films modified for using as ion exchange membrane; Caracterizacao de filmes de polipropileno modificados para uso como membrana trocadora de protons

    Energy Technology Data Exchange (ETDEWEB)

    Zen, H.A.; Geraldes, A.N.; Parra, D.F.; Geraldo, A.B.C.; Araujo, S.G.; Lugao, A.B.; Linardi, M. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2006-07-01

    This paper presents previous results of polypropylene films modified by graft process via ionising radiation. The styrene monomer was used in the graft process in presence of toluene as 100%, 80% and 20% proportions of styrene. The samples were irradiated in a cobalt-60 source at 40 and 80 doses. The TGA, DSC, FTIR characterizations were made and degree of grafting (DOG) was determinate. The results of DOG were confirmed by the FTIR analysis although the most samples were less thermal stable. (author)

  20. Adhesion in hydrogels and model glassy polymers

    Science.gov (United States)

    Guvendiren, Murat

    Two main topics are addressed in this dissertation: (1) adhesion in hydrogels; (2) interfacial interactions between model glassy polymers. A self-assembly technique for the formation of hydrogels from acrylic triblock copolymer solutions was developed, based on vapor phase solvent exchange. Structure formation in the gels was characterized by small angle X-ray scattering, and swelling was measured in controlled pH buffer solutions. Strong gels are formed with polymer weight fractions between 0.01 and 0.15, and with shear moduli between 0.6 kPa and 3.5 kPa. Adhesive functionality, based on 3,4-dihydroxy-L-phenylalanine (DOPA) was also incorporated into the triblock copolymers. The effect of DOPA concentration on gel formation and swelling was investigated in detail. The adhesive properties of DOPA-functionalized hydrogels on TiO2 were investigated with an axisymmetric adhesion method. It was shown that the presence of DOPA enhances the adhesive properties of the hydrogels, but that the effect is minimized at pH values below 10, where the DOPA groups are hydrophobic. Thin film membranes were produced in order to study the specific interactions between DOPA and TiO2 and DOPA and tissue, using a membrane inflation method. The presence of DOPA in the membranes enhances the adhesion on TiO 2 and tissue, although adhesion to tissue requires that the DOPA groups be oxidized while in contact with the tissue of interest. Porous hydrogel scaffolds for tissue engineering applications were formed by adding salt crystals to the triblock copolymer solution prior to solvent exchange. Salt was then leached out by immersing the gel into water. Structures of the porous hydrogels were characterized by confocal laser scanning microscopy. These hydrogels were shown to be suitable for tissue regeneration and drug delivery applications. Diffusion-mediated adhesion between two component miscible polymer systems having very different glassy temperatures was also investigated. Axisymmetric

  1. Glassy state of native collagen fibril?

    Science.gov (United States)

    Gevorkian, S. G.; Allahverdyan, A. E.; Gevorgyan, D. S.; Hu, C.-K.

    2011-07-01

    Our micromechanical experiments show that viscoelastic features of type-I collagen fibril at physiological temperatures display essential dependence on the frequency and speed of heating. For temperatures of 20-30 °C the internal friction has a sharp maximum for a frequency less than 2 kHz. Upon heating the internal friction displays a peak at a temperature Tsoft(v) that essentially depends on the speed of heating v: Tsoft≈70°C for v=1°C/min, and Tsoft≈25°C for v=0.1°C/min. At the same temperature Tsoft(v) Young's modulus passes through a minimum. All these effects are specific for the native state of the fibril and disappear after heat-denaturation. Taken together with the known facts that the fibril is axially ordered as quasicrystal, but disordered laterally, we interpret our findings as indications of a glassy state, where Tsoft is the softening transition.

  2. Glassy dynamics in randomly pinned particle systems

    Science.gov (United States)

    Phan, Anh; Schweizer, Kenneth

    We generalize the force-level, microscopic Elastically Collective Nonlinear Langevin Equation theory of activated relaxation in bulk hard sphere and thermal liquids to address the role of internal quenched disorder. So-called neutral confinement is considered where a subset of particles are randomly pinned and there is no change of equilibrium pair structure. As the pinned fraction grows, the cage scale dynamical constraints are intensified, resulting in the mobile particles becoming more localized, a larger glassy shear modulus, and an enhanced cage scale barrier. However, based on an approximate analysis of how quenched disorder modifies collective elastic field fluctuations, random pinning is predicted to effectively screen or localize the strain field associated with the longer range elastic component of the activation barrier, leading to an overall reduction of it with pinning fraction. The different response of the cage and elastic barriers to quenched disorder results in subtle predictions for how the alpha relaxation time varies with pinning fraction and system volume fraction. A semi-quantitative comparison with recent simulations of a pinned-mobile water model are consistent with the theory. Predictions are made for thermal molecular liquids.

  3. ELECTROCHEMICAL DETERMINATION OF HYDROGEN SULFIDE AT CARBON NANOTUBE MODIFIED ELECTRODES. (R830900)

    Science.gov (United States)

    Carbon nanotube (CNT) modified glassy carbon electrodes exhibiting a strong and stable electrocatalytic response towards sulfide are described. A substantial (400 mV) decrease in the overvoltage of the sulfide oxidation reaction (compared to ordinary carbon electrodes) is...

  4. Gas-sensing properties of In{sub 2}O{sub 3} films modified with gold nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Korotcenkov, G., E-mail: ghkoro@yahoo.com [School of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of); Brinzari, V. [Department of Theoretical Physics, State University of Moldova, Chisinau, Republic of Moldova (Moldova, Republic of); Han, S.H. [Division of Maritime Transportation System, Mokpo National Maritime University, Mokpo (Korea, Republic of); Cho, B.K., E-mail: chobk@gist.ac.kr [School of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of)

    2016-06-01

    A study of the surface and gas–sensitive properties of In{sub 2}O{sub 3} films modified with gold nanoparticles and synthesized by the successive ionic layer deposition (SILD) method was conducted. In{sub 2}O{sub 3} films were prepared using the spray pyrolysis method. The gas-sensing characteristics were tested using CO, H{sub 2}, and O{sub 3} as target gases. It has been shown that the surface modification with gold nanoparticles gives the opportunity to optimize the response of In{sub 2}O{sub 3}-based gas sensors to both reducing (CO, H{sub 2}) and oxidizing (O{sub 3}) gases. It has been found that the sensitizing effect during ozone detection was significantly higher than the effect during CO and H{sub 2} detection. It has been demonstrated that the sensitizing effect depended on the number of SILD cycles used for gold nanoparticle deposition and was maximal for the In{sub 2}O{sub 3} surface decorated with gold nanoparticles with the smallest size. The mechanism of the gold nanoparticles' influence on the gas-sensing properties of the In{sub 2}O{sub 3} films is also discussed. It is suggested that to explain the observed effects, we have to consider both the “electronic” and “chemical” mechanisms of sensitization. Suggestions for studies to be carried out to further improve both the understanding of the nature of the gas-sensitive effects and the parameters of In{sub 2}O{sub 3}:Au-based gas sensors are also formulated. - Highlights: • In{sub 2}O{sub 3} gas sensors modified with gold nanoparticles using SILD method are studied. • AuNPs exhibit activity during interaction with either reducing or oxidizing gases. • Maximal effect of optimization is observed during ozone detection. • Sensitizing effect depends on the number of SILD cycles. • Proposed mechanisms explain effects observed in the In{sub 2}O{sub 3}:Au based gas sensors.

  5. Fe2O3/MWCNTs nanocomposite decorated glassy carbon electrode ...

    Indian Academy of Sciences (India)

    35

    preparation of Fe2O3/MWCNTs, 197.6mg K3[Fe(CN)6] was dissolved in 40 mL of distilled water with PH to 12, and then the .... difficult may be attributed to the shortage of proton [34-37]. So with the increase in ... Fe2O3/MWCNTs/GCE modified electrode showed excellent determination of nitrites in tap water. 4. Conclusion.

  6. A study of nanostructured gold modified glassy carbon electrode for ...

    Indian Academy of Sciences (India)

    The results show that this method allows for Cr(VI) determinations with a much lower detection limit (0.01 g L-1) in the presence of excess of Cr(III) than the commonly used diethylenetriammine pentaacetic acid (DTPA) method. The method was applied to determine levels of chromium(VI) in tap water and sewage water.

  7. Fe2O3/MWCNTs nanocomposite decorated glassy carbon electrode ...

    Indian Academy of Sciences (India)

    35

    Keywords: Fe2O3; MWCNTs; electrochemical determination; nitrite. 1. Introduction. As is known to all that nitrite is universally found within the live process and environment and is generally used as a corrosion inhibitor or additive in some foods [1,2]. However, carcinogenic nitrosamines can be formed by nitrite interact with ...

  8. A study of nanostructured gold modified glassy carbon electrode for ...

    Indian Academy of Sciences (India)

    Wintec

    strument, and also atomic absorption spectrometry. (AAS) and inductively coupled plasma atomic emis- sion spectrometry can only yield information on total. Cr concentration. 9. Therefore, electrochemical methods have been applied for the determination of chromium, which have shown numerous advantages including.

  9. Fe2O3/MWCNTs nanocomposite decorated glassy carbon electrode ...

    Indian Academy of Sciences (India)

    2018-03-23

    Mar 23, 2018 ... result shows that the Fe2O3/MWCNTs-modified GCE can be used to detect nitrite concentration in a wide linear range of. 10–1000 μM with a detection limit of .... drous ethanol and sonicated in ultrapure water bath for 5 min before use. .... nitrites were not stable and could undergo the following conversion:.

  10. Treatment of early glassy cell carcinoma of uterine cervix

    International Nuclear Information System (INIS)

    Kim, Ok Bae; Kim, Jin Hee; Choi, Tae Jin

    2006-01-01

    The purpose of this study was to investigate the clinical findings, treatment, and outcome of patients with glassy cell carcinoma of cervix. We reviewed all cases of glassy cell carcinoma of the uterine cervix confirmed and treated at the Dongsan Medical Center, Keimyung University, between January 1993 and December 2005. There were 7 cases with histopathologically confirmed gassy cell carcinoma. A tumor was diagnosed as glassy cell carcinoma if over 50% of the tumor cell type displayed glassy cell features. Six patients with stage IB had radical hysterectomy and bilateral pelvic node dissection, and 2 of them received adjuvant external pelvic irradiation with concurrent chemotherapy. Remaining one patient with stage IIA had curative concurrent chemoradiotherapy with external pelvic irradiation and brachytherapy. There were 7 patients diagnosed as glassy cell carcinoma among the 3,745 (0.2%) patients of carcinoma of uterine cervix. The mean age of 7 patients was 44 years with range of 35 to 53 years of age. The most frequent symptom was vaginal bleeding (86%). By the punch biopsy undertaken before treatment of 7 cases, 2 only cases could diagnose as glassy cell carcinoma of uterine cervix, but remaining of them confirmed by surgical pathological examination. The mean follow up duration was 73 months with range of 13 to 150 months. All 7 patients were alive without disease after treatment. Glassy cell carcinoma of the uterine cervix is a distinct clinicopathologic entity that demonstrates an aggressive biologic behavior. However for early-stage disease, we may have more favorable clinical outcome with radical surgery followed by chemoradiotherapy

  11. Gold nanoparticles/water-soluble carbon nanotubes/aromatic diamine polymer composite films for highly sensitive detection of cellobiose dehydrogenase gene

    Energy Technology Data Exchange (ETDEWEB)

    Zeng Guangming, E-mail: zgming@hnu.cn [College of Environmental Science and Engineering, Hunan University, Changsha 410082 (China); Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082 (China); Li Zhen, E-mail: happylizhen@yeah.ne [College of Environmental Science and Engineering, Hunan University, Changsha 410082 (China); Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082 (China); Tang Lin; Wu Mengshi; Lei Xiaoxia; Liu Yuanyuan; Liu Can; Pang Ya; Zhang Yi [College of Environmental Science and Engineering, Hunan University, Changsha 410082 (China); Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082 (China)

    2011-05-01

    Highlights: > Gold nanoparticles/multiwalled carbon nanotubes/poly (1,5-naphthalenediamine) modified electrode was fabricated. > The sensor was applied for the detection of cellobiose dehydrogenase genes. > An effective method to distribute MWCNTs and attach to the electrode was proposed. > The composite films greatly improved the sensitivity and enhanced the DNA immobilization. > The DNA biosensor exhibited fairly high sensitivity and quite low detection limit. - Abstract: An electrochemical sensor based on gold nanoparticles (GNPs)/multiwalled carbon nanotubes (MWCNTs)/poly (1,5-naphthalenediamine) films modified glassy carbon electrode (GCE) was fabricated. The effectiveness of the sensor was confirmed by sensitive detection of cellobiose dehydrogenase (CDH) gene which was extracted from Phanerochaete chrysosporium using polymerase chain reaction (PCR). The monomer of 1,5-naphthalenediamine was electropolymerized on the GCE surface with abundant free amino groups which enhanced the stability of MWCNTs modified electrode. Congo red (CR)-functionalized MWCNTs possess excellent conductivity as well as high solubility in water which enabled to form the uniform and stable network nanostructures easily and created a large number of binding sites for electrodeposition of GNPs. The continuous GNPs together with MWCNTs greatly increased the surface area, conductivity and electrocatalytic activity. This electrode structure significantly improved the sensitivity of sensor and enhanced the DNA immobilization and hybridization. The thiol modified capture probes were immobilized onto the composite films-modified GCE by a direct formation of thiol-Au bond and horseradish peroxidase-streptavidin (HRP-SA) conjugates were labeled to the biotinylated detection probes through biotin-streptavidin bond. Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the film assembly and DNA hybridization processes

  12. Thermal Barrier Coatings Resistant to Glassy Deposits

    Science.gov (United States)

    Drexler, Julie Marie

    Engineering of alloys has for years allowed aircraft turbine engines to become more efficient and operate at higher temperatures. As advancements in these alloy systems have become more difficult, ceramic thermal barrier coatings (TBCs), often yttria (7 wt %) stabilized zirconia (7YSZ), have been utilized for thermal protection. TBCs have allowed for higher engine operating temperatures and better fuel efficiency but have also created new engineering problems. Specifically, silica based particles such as sand and volcanic ash that enter the engine during operation form glassy deposits on the TBCs. These deposits can cause the current industrial 7YSZ thermal barrier coatings to fail since the glass formed penetrates and chemically interacts with the TBC. When this occurs, coating failure may occur due to a loss of strain tolerance, which can lead to fracture, and phase changes of the TBC material. There have been several approaches used to stop calcium-magnesium aluminio-silcate (CMAS) glasses (molten sand) from destroying the entire TBC, but overall there is still limited knowledge. In this thesis, 7YSZ and new TBC materials will be examined for thermochemical and thermomechanical performance in the presence of molten CMAS and volcanic ash. Two air plasma sprayed TBCs will be shown to be resistant to volcanic ash and CMAS. The first type of coating is a modified 7YSZ coating with 20 mol% Al2O3 and 5 mol% TiO2 in solid solution (YSZ+20Al+5Ti). The second TBC is made of gadolinium zirconate. These novel TBCs impede CMAS and ash penetration by interacting with the molten CMAS or ash and drastically changing the chemistry. The chemically modified CMAS or ash will crystallize into an apatite or anorthite phase, blocking the CMAS or ash from further destroying the coating. A presented mechanism study will show these coatings are effective due to the large amount of solute (Gd, Al) in the zirconia structure, which is the key to creating the crystalline apatite or

  13. Dielectric Relaxation in Glassy Se100 - x Sbx

    OpenAIRE

    CHOUDHARY, N.; KUMAR, A.

    2014-01-01

    Frequency and temperature dependence of dielectric constant \\varepsilon' and dielectric loss \\varepsilon'' are studied in glassy Se1-x Sbx (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10) in the frequency range from 1--10 kHz and in the temperature range 290 K to 360 K. The experimental results indicate that no dielectric dispersion exist in glassy Se in the operating range of frequencies. However, when Sb concentration increases in Se1-x Sbx (x = 0.02, 0.04, 0.06, ...

  14. Relook on fitting of viscosity with undercooling of glassy liquids

    Indian Academy of Sciences (India)

    The method so far used is to get experimental visco- sity data of a liquid alloy at various temperatures and then fit a curve according to (1) to achieve values of the three VFT parameters (η0, D and T0). Glassy alloys enable to deter- mine viscosity of liquid in the temperature range between Tl and Tg because of its inherent ...

  15. Broadband nanoindentation of glassy polymers: Part II. Viscoplasticity

    Science.gov (United States)

    Joseph E. Jakes; Rod S. Lakes; Don S. Stone

    2012-01-01

    The relationship between hardness and flow stress in glassy polymers is examined. Materials studied include poly(methylmethacrylate), polystyrene, and polycarbonate. Properties are strongly rate dependent, so broadband nanoindentation creep (BNC) is used to measure hardness across a broad range of indentation strain rates (10-4 to 10 s

  16. Broadband nanoindentation of glassy polymers: Part I Viscoelasticity

    Science.gov (United States)

    Joesph E. Jakes; Rod S. Lakes; Don S. Stone

    2012-01-01

    Protocols are developed to assess viscoelastic moduli from unloading slopes in Berkovich nanoindentation across four orders of magnitude in time scale (0.01-100 s unloading time). Measured viscoelastic moduli of glassy polymers poly(methyl methacrylate), polystyrene, and polycarbonate follow the same trends with frequency (1/unloading time) as viscoelastic moduli...

  17. Study of lithium glassy solid electrolyte/electrode interface by ...

    Indian Academy of Sciences (India)

    Cells of lithium ion conducting glassy electrolyte Li2SO4–Li2O–B2O3 with different combinations of electrodes (stainless steel blocking electrode, lithium non-blocking electrode and TiS2 electrode) have been prepared. The a.c. impedance measurements of the cells have been studied at elevated temperature as a function ...

  18. Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors

    Directory of Open Access Journals (Sweden)

    Wei Zheng

    2016-03-01

    Full Text Available Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors.

  19. Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors

    Science.gov (United States)

    Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T.; Evoy, Stephane

    2016-01-01

    Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors. PMID:26985910

  20. Small angle neutron scattering from glassy SiO2

    International Nuclear Information System (INIS)

    Spooner, S.; Hastings, J.B.

    1976-01-01

    The present investigation of neutron scattering from glassy silica was undertaken to resolve whether the small angle scattering observed by Renninger and Uhlmann could also be seen in the bulk samples typically used in neutron-scattering experiments. Within the rather large error bars of this experiment no small angle scattering increase at small angles could be seen. (Auth.)

  1. Microscopic model of the glass transition and the glassy state

    International Nuclear Information System (INIS)

    Shukla, P.

    1982-07-01

    A microscopic model of the glass transition and the glassy state is presented. It is exactly solvable, and offers a unified view of the equilibrium and non-equilibrium aspects of the glass transition. It also provides a statistical-mechanical justification of the irreversible thermodynamic models of the glass transition proposed earlier. (author)

  2. Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors.

    Science.gov (United States)

    Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T; Evoy, Stephane

    2016-03-14

    Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors.

  3. Playback interference of glassy-winged sharp shooter communication

    Science.gov (United States)

    Animal communication is vital to reproduction, particularly for securing a mate. Insects commonly communicate by exchanging vibrational signals that are transmitted through host plants. The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is an important vector of Xylella fastidiosa, a pl...

  4. Disconnecting structure and dynamics in glassy thin films

    Science.gov (United States)

    Sussman, Daniel; Schoenholz, Samuel; Cubuk, Ekin; Liu, Andrea

    The dynamics near the surface of a glassy film are markedly different from those in the bulk. We investigate whether the differences between surface and bulk dynamics can be explained by differences in local microscopic structure. We show that machine learning methods that successfully identify strong correlations between local structure and particle rearrangement dynamics in the bulk completely fail to detect key aspects of thin-film glassy dynamics. Furthermore, we show that no combination of local structural features drawn from a very general set of two- and multi-point functions is able to distinguish between particles at the center of film and those in near the surface where the dynamics are strongly perturbed. We note that the behavior of glassy films has often been interpreted via a model with a glassy, immobile layer near the center of the film and liquid-like mobile layers near free interfaces. Our results suggest that the two populations are indistinguishable in structure, necessitating a purely dynamical theory for additional relaxation processes in the film.

  5. Synthesis of One-Dimensional SiC Nanostructures from a Glassy Buckypaper

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Mengning; Star, Alexander

    2013-02-21

    A simple and scalable synthetic strategy was developed for the fabrication of one-dimensional SiC nanostructures - nanorods and nanowires. Thin sheets of single-walled carbon nanotubes (SWNTs) were prepared by vacuum filtration and were washed repeatedly with sodium silicate (Na₂SiO₃) solution. The resulting “glassy buckypaper” was heated at 1300 - 1500 °C under Ar/H₂ to allow a solid state reaction between C and Si precursors to form a variety of SiC nanostructures. The morphology and crystal structures of SiC nanorods and nanowires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive xray spectroscopy (EDX), electron diffraction (ED) and x-ray diffraction (XRD) techniques. Furthermore, electrical conductance measurements were performed on SiC nanorods, demonstrating their potential applications in high-temperature sensors and control systems.

  6. Nanostructured morphologies in glassy polymer networks

    Science.gov (United States)

    Greenhoe, Brian Merle

    The body of this work describes a novel approach for the dispersion of multi-walled carbon nanotubes in a high Tg epoxy prepolymer matrix using a twin screw high-shear continuous reactor. The method demonstrated improves on previous dispersion methods in several ways. It offers increased efficiency through excellent heat transfer, while being solvent-less, scale-able, and tailorable to drive dispersion states to judiciously chosen dispersion states. Furthermore, it was shown that dispersion state and agglomerate morphology can be directed, in several ways, through processing conditions and also by controlling the matrix viscosity profile through cure. Broadband dielectric spectroscopy, optical hot-stage microscopy, transmission electron microscopy, and atomic force microscopy were used to both directly and indirectly monitor agglomerate dispersion state and track secondary agglomeration through to a cured and vitrified material.

  7. Glassy states in fermionic systems with strong disorder and interactions

    Science.gov (United States)

    Schwab, David J.; Chakravarty, Sudip

    2009-03-01

    We study the competition between interactions and disorder in two dimensions. Whereas a noninteracting system is always Anderson localized by disorder in two dimensions, a pure system can develop a Mott gap for sufficiently strong interactions. Within a simple model, with short-ranged repulsive interactions, we show that, even in the limit of strong interaction, the Mott gap is completely washed out by disorder for an infinite system for dimensions D≤2 , leading to a glassy state. Moreover, the Mott insulator cannot maintain a broken symmetry in the presence of disorder. We then show that the probability of a nonzero gap as a function of system size falls onto a universal curve, reflecting the glassy dynamics. An analytic calculation is also presented in one dimension that provides further insight into the nature of slow dynamics.

  8. Study of lithium glassy solid electrolyte/electrode interface by ...

    Indian Academy of Sciences (India)

    Unknown

    Cells of lithium ion conducting glassy electrolyte Li2SO4–Li2O–B2O3 with different combinations of electrodes (stainless steel blocking electrode, lithium non-blocking electrode and TiS2 electrode) have been pre- pared. The a.c. impedance ... tant requirements for the solid state battery to achieve high current density, more ...

  9. Insecticides sought to control adult glassy-winged sharpshooter

    OpenAIRE

    Akey, David H.; Henneberry, Thomas J.; Toscano, Nick

    2001-01-01

    The bacterium that causes Pierce's disease (Xylella fastidiosa) is transmitted to grapevines by the glassy-winged sharpshooter (GWSS). Insecticides were evaluated for efficacy and residual activity against adult GWSS on grapevines. Ten insecticides were tested in the cyclo-chlorinated, carbamate, organic phosphate, pyrethroid and neonicotinoid chemical classes. Results from field trials indicate that the pyrethroids and neonicotinoids are promising control agents. Information on efficacious a...

  10. Glassy selenium at high pressure: Le Chatelier's principle still works

    Science.gov (United States)

    Brazhkin, V. V.; Tsiok, O. B.

    2017-10-01

    Selenium is the only easily vitrified elementary substance. Numerous experimental studies of glassy Se (g -Se) at high pressures show a large spread in the data on the compressibility and electrical resistivity of g -Se. Furthermore, H. Liu et al. [Proc. Natl. Acad. Sci. USA 105, 13229 (2008), 10.1073/pnas.0806857105] have arrived at the surprising conclusion that the volume of glass increases during pressure-induced crystallization. We have performed high-precision measurements of the specific volume and electrical resistivity of glassy selenium (g -Se) at high hydrostatic pressures up to 9 GPa. The measured bulk modulus at normal pressure is B =(9.0 5 ±0.15 ) GPa and its pressure derivative is BP'=6.4 ±0.2 . In the pressure range P <3 GPa, glassy selenium has an anomalously large negative second derivative of the bulk modulus. The electrical resistivity of g -Se decreases almost exponentially with increasing pressure and reaches 20 Ω cm at a pressure of 8.75 GPa. The inelastic behavior and weak relaxation of the volume for g -Se begin at pressures above 3.5 GPa; the volume and logarithm of the electrical resistivity relax significantly (logarithmically with the time) at pressures above 8 GPa. Bulk measurements certainly indicate that the volume of g -Se glass in the crystallization pressure range is larger than the volumes of both appearing crystalline phases (by 2% and 4%). Therefore, the "volume expansion phenomenon" suggested in [H. Liu et al., Proc. Natl. Acad. Sci. USA 105, 13229 (2008), 10.1073/pnas.0806857105] is not observed, and the pressure-induced crystallization of glassy selenium is consistent with the laws of thermodynamics.

  11. States of Water in Non-Equilibrium Glassy Polymers

    Science.gov (United States)

    Davis, Eric; Elabd, Yossef

    2013-03-01

    For many applications (e.g., packaging, medical devices) a deeper fundamental understanding of the molecular nature of water in glassy polymer coatings is of significant interest. In this study, the sorption and diffusion of water in two glassy polymers, poly(methyl methacrylate) (PMMA) and poly(styrene) (PS), were measured with both quartz crystal microbalance (QSM) and time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Non-Fickian diffusion was observed in both PMMA and PS using both experimental techniques due to the non-equilibrium state of the polymers. The specific states of water were observed with FTIR-ATR spectroscopy, where dimers exist in PMMA below a critical concentration and larger clusters were observed above this concentration. Contrastingly, water only exists in PS as larger clusters over the entire sorption isotherm. A correlation between the states of water and the diffusive activation energy of water was observed. Additionally, the pseudo-equilibrium water sorption isotherms in PMMA and PS were accurately predicted with the non-equilibrium statistical associating fluid theory (NE-SAFT). We predict that the combination of time-resolved FTIR-ATR spectroscopy and NE-SAFT can be used on other water-glassy polymer systems to provide a molecular understanding of non-equilibrium sorption and diffusion.

  12. Non-Equilibrium Water-Glassy Polymer Dynamics

    Science.gov (United States)

    Davis, Eric; Minelli, Matteo; Baschetti, Marco; Sarti, Giulio; Elabd, Yossef

    2012-02-01

    For many applications (e.g., medical implants, packaging), an accurate assessment and fundamental understanding of the dynamics of water-glassy polymer interactions is of great interest. In this study, sorption and diffusion of pure water in several glassy polymers films, such as poly(styrene) (PS), poly(methyl methacrylate) (PMMA), poly(lactide) (PLA), were measured over a wide range of vapor activities and temperatures using several experimental techniques, including quartz spring microbalance (QSM), quartz crystal microbalance (QCM), and time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Non-Fickian behavior (diffusion-relaxation phenomena) was observed by all three techniques, while FTIR-ATR spectroscopy also provides information about the distribution of the states of water and water transport mechanisms on a molecular-level. Specifically, the states of water are significantly different in PS compared to PMMA and PLA. Additionally, a purely predictive non-equilibrium lattice fluid (NELF) model was applied to predict the sorption isotherms of water in these glassy polymers.

  13. Hansen solubility parameters for a carbon fiber/epoxy composite

    DEFF Research Database (Denmark)

    Launay, Helene; Hansen, Charles M.; Almdal, Kristoffer

    2007-01-01

    In this study, the physical affinity between an epoxy matrix and oxidized, unsized carbon fibers has been evaluated using Hansen solubility (cohesion) parameters (HSP). A strong physical compatibility has been shown, since their respective HSP are close. The use of a glassy carbon substrate...... as a model for unsized carbon fiber has been demonstrated as appropriate for the study of interactions between the materials in composite carbon fiber-epoxy systems. The HSP of glassy carbon are similar to those of carbon fibers and epoxy matrix. (C) 2007 Elsevier Ltd. All rights reserved....

  14. Investigation of glassy state molecular motions in thermoset polymers

    Science.gov (United States)

    Tu, Jianwei

    This dissertation presents the investigation of the glassy state molecular motions in isomeric thermoset epoxies by means of solid-state deuterium (2H) NMR spectroscopy technique. The network structure of crosslinked epoxies was altered through monomer isomerism; specifically, diglycidyl ether of bisphenol A (DGEBA) was cured with isomeric amine curatives, i.e., the meta-substituted diaminodiphenylsulfone (33DDS) and para-substituted diaminodiphenylsulfone (44DDS). The use of structural isomerism provided a path way for altering macroscopic material properties while maintaining identical chemical composition within the crosslinked networks. The effects of structural isomerism on the glassy state molecular motions were studied using solid-state 2H NMR spectroscopy, which offers unrivaled power to monitor site-specific molecular motions. Three distinctive molecular groups on each isomeric network, i.e., the phenylene rings in the bisphenol A structure (BPA), the phenylene rings in the diaminodiphenylsulfone structure (DDS), and the hydroxypropoyl ether group (HPE) have been selectively deuterated for a comprehensive study of the structure-dynamics- property relationships in thermoset epoxies. Quadrupolar echo experiments and line shape simulations were employed as the main research approach to gain both qualitative and quantitative motional information of the epoxy networks in the glassy state. Quantitative information on the geometry and rate of the molecular motions allows the elucidation of the relationship between molecular motions and macro physical properties and the role of these motions in the mechanical relaxation. Specifically, it is revealed that both the BPA and HPE moieties in the isomeric networks have almost identical behaviors in the deep glassy state, which indicates that the molecular motions in the glassy state are localized, and the correlation length of the motions does not exceed the length of the DGEBA repeat unit. BPA ring motions contribute

  15. Some Recent Developments in Structure and Glassy Behavior of Proteins

    Science.gov (United States)

    Hu, Chin-Kun

    2012-02-01

    We have used ARVO developed by us to find that the ratio of volume and surface area of proteins in Protein Data Bank distributed in a very narrow region [1]. Such result is useful for the determination of protein 3D structures. It has been widely known that a spin glass model can be used to understand the slow relaxation behavior of a glass at low temperatures [2]. We have used molecular dynamics and simple models of polymer chains to study relaxation and aggregation of proteins under various conditions and found that polymer chains with neighboring monomers connected by rigid bonds can relax very slowly and show glassy behavior [3]. We have also found that native collagen fibrils show glassy behavior at room temperatures [4]. The results of [3] and [4] about the glassy behavior of polymers or proteins are useful for understanding the mechanism for a biological system to maintain in a non-equilibrium state, including the ancient seed [5], which can maintain in a non-equilibrium state for a very long time. (1) M.-C. Wu, M. S. Li, W.-J. Ma, M. Kouza, and C.-K. Hu, EPL, in press (2011); (2) C. Dasgupta, S.-K. Ma, and C.-K. Hu. Phys. Rev. B 20, 3837-3849 (1979); (3) W.-J. Ma and C.-K. Hu, J. Phys. Soc. Japan 79, 024005, 024006, 054001, and 104002 (2010), C.-K. Hu and W.-J. Ma, Prog. Theor. Phys. Supp. 184, 369 (2010); S. G. Gevorkian, A. E. Allahverdyan, D. S. Gevorgyan and C.-K. Hu, EPL 95, 23001 (2011); S. Sallon, et al. Science 320, 1464 (2008).

  16. Gas Transport in Glassy Polymers: Prediction of Diffusional Time Lag

    Directory of Open Access Journals (Sweden)

    Matteo Minelli

    2018-02-01

    Full Text Available The transport of gases in glassy polymeric membranes has been analyzed by means of a fundamental approach based on the nonequilibrium thermodynamic model for glassy polymers (NET-GP that considers the penetrant chemical potential gradient as the actual driving force of the diffusional process. The diffusivity of a penetrant is thus described as the product of a purely kinetic quantity, the penetrant mobility, and a thermodynamic factor, accounting for the chemical potential dependence on its concentration in the polymer. The NET-GP approach, and the nonequilibrium lattice fluid (NELF model in particular, describes the thermodynamic behavior of penetrant/polymer mixtures in the glassy state, at each pressure or composition. Moreover, the mobility is considered to follow a simple exponential dependence on penetrant concentration, as typically observed experimentally, using only two adjustable parameters, the infinite dilution penetrant mobility L10 and the plasticization factor β, both determined from the analysis of the dependence of steady state permeability on upstream pressure. The available literature data of diffusional time lag as a function of penetrant upstream pressure has been reviewed and compared with model predictions, obtained after the values of the two model parameters (L10 and β, have been conveniently determined from steady state permeability data. The model is shown to be able to describe very accurately the experimental time lag behaviors for all penetrant/polymer pairs inspected, including those presenting an increasing permeability with increasing upstream pressure. The model is thus more appropriate than the one based on Dual Mode Sorption, which usually provides an unsatisfactory description of time lag and required an ad hoc modification.

  17. Microscale rheology of a soft glassy material close to yielding.

    Science.gov (United States)

    Jop, Pierre; Mansard, Vincent; Chaudhuri, Pinaki; Bocquet, Lydéric; Colin, Annie

    2012-04-06

    Using confocal microscopy, we study the flow of a model soft glassy material: a concentrated emulsion. We demonstrate the micro-macro link between in situ measured movements of droplets during the flow and the macroscopic rheological response of a concentrated emulsion, in the form of scaling relationships connecting the rheological "fluidity" with local standard deviation of the strain-rate tensor. Furthermore, we measure correlations between these local fluctuations, thereby extracting a correlation length which increases while approaching the yielding transition, in accordance with recent theoretical predictions. © 2012 American Physical Society

  18. A Stress Update Algorithm for Constitutive Models of Glassy Polymers

    Science.gov (United States)

    Danielsson, Mats

    2013-06-01

    A semi-implicit stress update algorithm is developed for the elastic-viscoplastic behavior of glassy polymers. The case of near rate-insensitivity is addressed, and the stress update algorithm is designed to handle this case robustly. A consistent tangent stiffness matrix is derived based on a full linearization of the internal virtual work. The stress update algorithm and (a slightly modified) tangent stiffness matrix are implemented in a commercial finite element program. The stress update algorithm is tested on a large boundary value problem for illustrative purposes.

  19. Crystal-like nature of acoustic excitations in glassy ethanol

    International Nuclear Information System (INIS)

    Matic, A.; Engberg, D.; Boerjesson, L.; Masciovecchio, C.; Santucci, S.C.; Monaco, G.; Verbeni, R.

    2004-01-01

    We report on inelastic x-ray scattering experiments on crystalline and glassy phases of ethanol in order to directly compare the influence of disorder on high frequency acoustic excitations. We find that both the dispersion and the line-width of the longitudinal acoustic excitations in the glass are the same as in the polycrystal in the reciprocal space portion covering the 1st and 2nd Brillouin zones. The structural disorder is found to play little role apart from an intrinsic angular averaging, and the nature of these excitations must essentially be the same in both glass and poly crystal

  20. Preparation of electrochemically reduced graphene oxide/multi-wall ...

    Indian Academy of Sciences (India)

    Through a facile electrochemical method, we prepared an electrochemically reduced graphene oxide (ERGO)/multi-wall carbon nanotubes (MWNTs) hybrid film modified glassy carbon electrode (GCE), and characterized it by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and x-ray ...

  1. Journal of Chemical Sciences | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Through a facile electrochemical method, we prepared an electrochemically reduced graphene oxide (ERGO)/multi-wall carbon nanotubes (MWNTs) hybrid film modified glassy carbon electrode (GCE), and characterized it by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and x-ray ...

  2. Hairy carbon electrodes studied by cyclic voltammetry and battery discharge testing

    Science.gov (United States)

    Chung, Deborah D. L.; Shui, Xiaoping; Frysz, Christine A.

    1993-01-01

    Hairy carbon is a new material developed by growing submicron carbon filaments on conventional carbon substrates. Typical substrate materials include carbon black, graphite powder, carbon fibers, and glassy carbon. A catalyst is used to initiate hair growth with carbonaceous gases serving as the carbon source. To study the electrochemical behavior of hairy carbons, cyclic voltammetry (CV) and discharge testing were conducted. In both cases, hairy carbon results surpassed those of the substrate material alone.

  3. Electrical studies on silver based fast ion conducting glassy materials

    International Nuclear Information System (INIS)

    Rao, B. Appa; Kumar, E. Ramesh; Kumari, K. Rajani; Bhikshamaiah, G.

    2014-01-01

    Among all the available fast ion conductors, silver based glasses exhibit high conductivity. Further, glasses containing silver iodide enhances fast ion conducting behavior at room temperature. Glasses of various compositions of silver based fast ion conductors in the AgI−Ag 2 O−[(1−x)B 2 O 3 −xTeO 2 ] (x=0 to1 mol% in steps of 0.2) glassy system have been prepared by melt quenching method. The glassy nature of the compounds has been confirmed by X-ray diffraction. The electrical conductivity (AC) measurements have been carried out in the frequency range of 1 KHz–3MHz by Impedance Analyzer in the temperature range 303–423K. The DC conductivity measurements were also carried out in the temperature range 300–523K. From both AC and DC conductivity studies, it is found that the conductivity increases and activation energy decreases with increasing the concentration of TeO 2 as well as with temperature. The conductivity of the present glass system is found to be of the order of 10 −2 S/cm at room temperature. The ionic transport number of these glasses is found to be 0.999 indicating that these glasses can be used as electrolyte in batteries

  4. Silicon-tin oxynitride glassy composition and use as anode for lithium-ion battery

    Science.gov (United States)

    Neudecker, Bernd J.; Bates, John B.

    2001-01-01

    Disclosed are silicon-tin oxynitride glassy compositions which are especially useful in the construction of anode material for thin-film electrochemical devices including rechargeable lithium-ion batteries, electrochromic mirrors, electrochromic windows, and actuators. Additional applications of silicon-tin oxynitride glassy compositions include optical fibers and optical waveguides.

  5. Evaluation of grapevine as a host for the glassy-winged sharpshooter

    Science.gov (United States)

    Grapevine was evaluated as a feeding and oviposition host for the glassy-winged sharpshooter. Two sets of experiments were conducted. The first set compared performance and preference of glassy-winged sharpshooter females for grapevine (cv. Chardonnay) versus cowpea (Vigna unguiculata cultivar black...

  6. Effect of chain rigidity on network architecture and deformation behavior of glassy polymer networks

    Science.gov (United States)

    Knowles, Kyler Reser

    Processing carbon fiber composite laminates creates molecular-level strains in the thermoset matrix upon curing and cooling which can lead to failures such as geometry deformations, micro-cracking, and other issues. It is known strain creation is attributed to the significant volume and physical state changes undergone by the polymer matrix throughout the curing process, though storage and relaxation of cure-induced strains remain poorly understood. This dissertation establishes two approaches to address the issue. The first establishes testing methods to simultaneously measure key volumetric properties of a carbon fiber composite laminate and its polymer matrix. The second approach considers the rigidity of the polymer matrix in regards to strain storage and relaxation mechanisms which ultimately control composite performance throughout manufacturing and use. Through the use of a non-contact, full-field strain measurement technique known as digital image correlation (DIC), we describe and implement useful experiments which quantify matrix and composite parameters necessary for simulation efforts and failure models. The methods are compared to more traditional techniques and show excellent correlation. Further, we established relationships which represent matrix-fiber compatibility in regards to critical processing constraints. The second approach involves a systematic study of epoxy-amine networks which are chemically-similar but differ in chain segment rigidity. Prior research has investigated the isomer effect of glassy polymers, showing sizeable differences in thermal, volumetric, physical, and mechanical properties. This work builds on these themes and shows the apparent isomer effect is rather an effect of chain rigidity. Indeed, it was found that structurally-dissimilar polymer networks exhibit very similar properties as a consequence of their shared average network rigidity. Differences in chain packing, as a consequence of chain rigidity, were shown to

  7. Corrosion resistance of siloxane–poly(methyl methacrylate) hybrid films modified with acetic acid on tin plate substrates: Influence of tetraethoxysilane addition

    Energy Technology Data Exchange (ETDEWEB)

    Kunst, S.R.; Cardoso, H.R.P. [LAPEC, Federal University of Rio Grande do Sul – UFRGS, Avenida Bento Gonçalves, 9500 Porto Alegre, RS (Brazil); Oliveira, C.T. [ICET, University Feevale, RS-239, 2755 Novo Hamburgo, RS (Brazil); Santana, J.A.; Sarmento, V.H.V. [Department of Chemistry, Federal University of Sergipe – UFS, Av. Vereador Olímpio Grande s/n, Centro, Itabaiana, SE (Brazil); Muller, I.L. [LAPEC, Federal University of Rio Grande do Sul – UFRGS, Avenida Bento Gonçalves, 9500 Porto Alegre, RS (Brazil); Malfatti, C.F., E-mail: celia.malfatti@ufrgs.br [LAPEC, Federal University of Rio Grande do Sul – UFRGS, Avenida Bento Gonçalves, 9500 Porto Alegre, RS (Brazil)

    2014-04-01

    Highlights: • Siloxane–PMMA film was produced by dip-coating on tin plate substrate. • It was evaluated the influence of (TEOS) addition on siloxane–PMMA hybrid films. • Siloxane–PMMA films without TEOS presented a regular coverage and lowest roughness. • The TEOS addition decrease the corrosion resistance of siloxane–PMMA films. • Siloxane–PMMA without TEOS presented is higher durability in the film wear test. - Abstract: The aim of this paper is to study the corrosion resistance of hybrid films. Tin plate was coated with a siloxane–poly (methyl methacrylate) (PMMA) hybrid film prepared by sol–gel route with covalent bonds between the organic (PMMA) and inorganic (siloxane) phases obtained by hydrolysis and polycondensation of 3-(trimethoxysilylpropyl) methacrylate (TMSM) and polymerization of methyl methacrylate (MMA) using benzoyl peroxide (BPO) as a thermic initiator. Hydrolysis reactions were catalyzed by acetic acid solution avoiding the use of chlorine or stronger acids in the film preparation. The effect of the addition of tetraethoxysilane (TEOS) on the protective properties of the film was evaluated. The hydrophobicity of the film was determined by contact angle measurements, and the morphology was evaluated by scanning electron microscopy (SEM) and profilometry. The local nanostructure was investigated by Fourier transform infrared spectroscopy (FT-IR). The electrochemical behavior of the films was assessed by open circuit potential monitoring, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements in a 0.05 M NaCl solution. The mechanical behavior was evaluated by tribology. The results highlighted that the siloxane–PMMA hybrid films modified with acetic acid are promising anti-corrosive coatings that acts as an efficient diffusion barrier, protecting tin plates against corrosion. However, the coating properties were affected by the TEOS addition, which contributed for the thickness increase

  8. Electrochemical Investigation of Catechol at Poly(niacinamide) Modified Carbon Paste Electrode: A Voltammetric Study

    OpenAIRE

    Teradale, A. B.; Lamani, S. D.; Swamy, B. E. Kumara; Ganesh, P. S.; Das, S. N.

    2016-01-01

    A polymeric thin film modified electrode, that is, poly(niacinamide) modified carbon paste electrode (MCPE), was developed for the electrochemical determination of catechol (CC) by using cyclic voltammetric technique. Compared to bare carbon paste electrode (BCPE), the poly(niacinamide) MCPE shows good electrocatalytic activity towards the oxidation of catechol in phosphate buffer solution (PBS) of physiological pH 7.4. All experimental parameters were optimized. Poly(niacinamide) modified ca...

  9. Glassy behavior and dynamic tweed in defect-free multiferroics

    Science.gov (United States)

    Wang, Xiaofei; Salje, Ekhard K. H.; Sun, Jun; Ding, Xiangdong

    2018-01-01

    Multiferroics often show significant elastic fluctuations even when the transition is strongly stepwise. Molecular dynamics simulations of a generic toy model show the appearance of tweed nanostructures (cross hatched patterns) in the paraelastic phase just above the transition point. This tweed lowers the elastic modulus C12 when approaching the transition temperature. The spatial and temporal correlations of the tweed structure follow the Vogel-Fulcher relationship, and the Vogel-Fulcher temperature is slightly below the transition temperature Ttrans, preventing this glassy state to freeze completely. Spatial correlations of shear strain show that the size of tweed patches reaches about eight lattice spacings near Ttrans. Cross- and rod-shaped diffuse scattering, similar to that in relaxors, emerges around {hh0}* and {h00}* Bragg reflections. The viscosity of the sample increases dramatically at the transition point with a significant precursor increase in the tweed regime.

  10. Glassy dynamics and heterogeneity of polymer thin films

    International Nuclear Information System (INIS)

    Kanaya, Toshiji; Inoue, Rintaro; Kawashima, Kazuko; Miyazaki, Tsukasa; Matsuba, Go; Nishida, Koji; Tsukushi, Itaru; Shibata, Kaoru; Hino, Masahiro

    2009-01-01

    We review our recent studies on glassy dynamics and glass transition of polymer thin films using neutron and X-ray reflectivity and inelastic neutron techniques. In the last decade extensive studies have been performed on polymer thin films to reveal very interesting but unusual properties such as reduction in the glass transition temperature T g with film thickness and negative thermal expansivity for thin films below about 25 nm, and often some contradictory experimental results have been reported. It is believed that a key to solve the controversial situation is to disclose heterogeneous structure or multi-layer structure in polymer thin films. In the review, therefore, we summarize our recent experimental results by neutron and X-ray reflectivity and inelastic neutron scattering, focusing on the dynamic heterogeneity in polymer thin films. (author)

  11. The Glassy Phase of Complex Branching Brownian Motion

    Science.gov (United States)

    Madaule, Thomas; Rhodes, Rémi; Vargas, Vincent

    2015-03-01

    In this paper, we study complex valued branching Brownian motion in the so-called glassy phase, also called phase II. In this context, we prove a limit theorem for the complex partition function hence confirming a conjecture formulated by Lacoin and the last two authors in a previous paper on complex Gaussian multiplicative chaos. We will show that the limiting partition function can be expressed as a product of a Gaussian random variable, mainly due to the windings of the phase, and a stable transform of the so-called derivative martingale, mainly due to the clustering of the modulus. The proof relies on the fine description of the extremal process available in the branching Brownian motion context.

  12. In situ nanocalorimetry of thin glassy organic films

    Science.gov (United States)

    León-Gutierrez, E.; Garcia, G.; Lopeandía, A. F.; Fraxedas, J.; Clavaguera-Mora, M. T.; Rodríguez-Viejo, J.

    2008-11-01

    In this work, we describe the design and first experimental results of a new setup that combines evaporation of liquids in ultrahigh vacuum conditions with in situ high sensitivity thermal characterization of thin films. Organic compounds are deposited from the vapor directly onto a liquid nitrogen cooled substrate, permitting the preparation and characterization of glassy films. The substrate consists of a microfabricated, membrane-based nanocalorimeter that permits in situ measurements of heat capacity under ultrafast heating rates (up to 105 K/s) in the temperature range of 100-300 K. Three glass forming liquids—toluene, methanol, and acetic acid—are characterized. The spikes in heat capacity related to the glass-transition temperature, the fictive temperature and, in some cases, the onset temperature of crystallization are determined for several heating rates.

  13. Pyrolytic carbon black composite and method of making the same

    Energy Technology Data Exchange (ETDEWEB)

    Naskar, Amit K.; Paranthaman, Mariappan Parans; Bi, Zhonghe

    2016-09-13

    A method of recovering carbon black includes the step of providing a carbonaceous source material containing carbon black. The carbonaceous source material is contacted with a sulfonation bath to produce a sulfonated material. The sulfonated material is pyrolyzed to produce a carbon black containing product comprising a glassy carbon matrix phase having carbon black dispersed therein. A method of making a battery electrode is also disclosed.

  14. Electrocatalytic Activity of Electropolymerized Cobalt ...

    African Journals Online (AJOL)

    NICO

    2010-09-20

    Sep 20, 2010 ... The electrocatalytic activity of electropolymerized cobalt tetraaminophthalocyanine (poly-CoTAPc) film modified on the glassy carbon electrode ... nation of these sulphhydryl compounds in human metabolism is essential for .... adduct product was formed by the coordination axially between. Co(II)TAPc and ...

  15. Determination of Volatility and Element Fractionation in Glassy Fallout Debris by SIMS

    Energy Technology Data Exchange (ETDEWEB)

    Williamson, Todd L. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tenner, Travis Jay [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Bonamici, Chloe Elizabeth [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Kinman, William Scott [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Pollington, Anthony Douglas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Steiner, Robert Ernest [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-05-10

    The purpose of this report is to characterize glassy fallout debris using the Trinity Test and then characterize the U-isotopes of U3O8 reference materials that contain weaponized debris.

  16. Sub-nanoscale nanoimprint fabrication of atomically stepped glassy substrates of silicate glass and acryl polymer

    Science.gov (United States)

    Yoshimoto, Mamoru

    2015-11-01

    In the nanoimprint process, the resolution limit of patterning has attracted much attention from both scientific and industrial aspects. In this article, we briefly review the main achievements of our research group on sub-nanoscale nanoimprint fabrication of atomically patterned glassy substrates of oxide glass and polymer. By applying the sapphire (α-Al2O3 single crystal) wafers with self-organized nanopatterns of atomic steps as thermal nanoimprinting molds, we successfully transferred their nanoscale patterns onto the surfaces of glassy substrates such as soda-lime silicate glasses and poly(methyl methacrylate) polymers. The surfaces of nanoimprinted glassy materials exhibited regularly arrayed atomic stairs with 0.2-0.3 nm step height, which were in good agreement with the sub-nanopatterns of sapphire molds. These atomically stepped morphologies on the glassy substrates were found to be stable for about 1 year.

  17. Dielectric relaxation in glassy Se75In25− xPbx alloys

    Indian Academy of Sciences (India)

    In this paper we report the effect of Pb incorporation in the dielectric properties of a-Se75In25 glassy alloy. The temperature and frequency dependence of the dielectric constants and the dielectric losses in glassy Se75In25−Pb ( = 0, 5, 10 and 15) alloys in the frequency range (1 kHz–5 MHz) and temperature range ...

  18. Effects of Carbonization Temperature and Component Ratio on Electromagnetic Interference Shielding Effectiveness of Woodceramics

    Directory of Open Access Journals (Sweden)

    Yubo Tao

    2016-07-01

    Full Text Available Woodceramics were fabricated in a vacuum through carbonization of wood powder impregnated with phenol formaldehyde (PF resin. The effects of carbonization temperature and mass ratio of wood/resin on electromagnetic interference (EMI shielding effectiveness (SE and morphology of woodceramics were explored. The PF resin made wood cell walls have the characteristics of glassy carbon. Wood axial tracheid and ray cells were filled with more glassy carbon by increasing addition of PF resin. Moreover, the increase of carbonization temperature was beneficial to improving SE. Woodceramics (mass ratio 1:1 obtained at 1000 °C presented a medium SE level between 30 MHz and 1.5 GHz.

  19. Delocalized glassy dynamics and many-body localization

    Science.gov (United States)

    Biroli, G.; Tarzia, M.

    2017-11-01

    We analyze the unusual slow dynamics that emerges in the bad metal delocalized phase preceding the many-body localization transition by using single-particle Anderson localization on the Bethe lattice as a toy model of many-body dynamics in Fock space. We probe the dynamical evolution by measuring observables such as the imbalance and equilibrium correlation functions, which display slow dynamics and power laws strikingly similar to those observed in recent simulations and experiments. We relate this unusual behavior to the nonergodic spectral statistics found on Bethe lattices. We discuss different scenarios, such as a true intermediate phase which persists in the thermodynamic limit versus a glassy regime established on finite but very large time and length scales only, and their implications for real-space dynamical properties. In the latter, slow dynamics and power laws extend on a very large time window but are eventually cut off on a time scale that diverges at the many-body localization transition.

  20. Morphological and compositional engineering of Ni/carbon ...

    Indian Academy of Sciences (India)

    Ni/multi-walled carbon nanotubes (MWCNTs) composite films were deposited on the glassy carbon electrode (GCE) by a Ni plating bath containing homogeneously dispersed MWCNTs using polyvinylpyrrolidone (PVP) as dispersion additive. Incorporation of MWCNTs into Ni matrix was greatly enhanced by the application ...

  1. Bicontinuous nanoporous polymers by carbon dioxide foaming

    NARCIS (Netherlands)

    Krause, B.; Münüklü, P.; van der Vegt, N.F.A.; Wessling, Matthias; Sijbesma, H.P.

    2001-01-01

    We investigate the physical foaming process of glassy poly(ether imide) and poly(ether sulfone) using carbon dioxide and report temperature-concentration diagrams ("foam diagrams") marking out the foaming envelope in which dense CO2-saturated films expand and microvoids are introduced. Two types of

  2. Diffusion coefficients of tracers in glassy polymer systems prepared by gamma radiolysis

    International Nuclear Information System (INIS)

    Tonge, M.P.; Gilbert, R.G.

    1996-01-01

    Diffusion-controlled reactions are common in free radical polymerisation reactions, especially in glassy polymer matrices. Such reactions commonly have an important influence on the polymerisation process and final polymer properties. For example, the dominant growth-stopping event (bimolecular termination) is generally diffusion-controlled. In glassy polymer systems, where molecular mobility is very low, the chain growth mechanism (propagation) may become diffusion-controlled. At present, the mechanism for propagation in glassy polymers is poorly understood, but it is expected by the Smoluchowski expression applied to propagation to depend strongly on the diffusion coefficient of monomer. The objective of this study is to measure reliable diffusion coefficients of small tracer molecules in glassy polymers, and compare these with propagation rate coefficients in similar systems, by the prediction above. Samples were initially prepared in a sealed sampled cell containing monomer, inert diluent, and tracer dye. After irradiation for several days, complete conversion of monomer to polymer can be obtained. The diffusion coefficients for two tracer dyes have been measured as a function of weight fraction polymer glassy poly(methyl methacrylate) samples

  3. A Thermodynamic Theory of Solid Viscoelasticity. Part 3: Nonlinear Glassy Viscoelasticity, Stability Constraints, Specifications

    Science.gov (United States)

    Freed, Alan; Leonov, Arkady I.

    2002-01-01

    This paper, the last in the series, continues developing the nonlinear constitutive relations for non-isothermal, compressible, solid viscoelasticity. We initially discuss a single integral approach, more suitable for the glassy state of rubber-like materials, with basic functionals involved in the thermodynamic description for this type of viscoelasticity. Then we switch our attention to analyzing stability constraints, imposed on the general formulation of the nonlinear theory of solid viscoelasticity. Finally, we discuss specific (known from the literature or new) expressions for material functions that are involved in the constitutive formulations of both the rubber-like and glassy-like, complementary parts of the theory.

  4. Elastic properties of aspirin in its crystalline and glassy phases studied by micro-Brillouin scattering

    Science.gov (United States)

    Ko, Jae-Hyeon; Lee, Kwang-Sei; Ike, Yuji; Kojima, Seiji

    2008-11-01

    The acoustic waves propagating along the direction perpendicular to the (1 0 0) cleavage plane of aspirin crystal were investigated using micro-Brillouin spectroscopy from which C11, C55 and C66 were obtained. The temperature dependence of the longitudinal acoustic waves could be explained by normal anharmonic lattice models, while the transverse acoustic waves showed an abnormal increase in the hypersonic attenuation at low temperatures indicating their coupling to local remnant dynamics. The sound velocity as well as the attenuation of the longitudinal acoustic waves of glassy aspirin showed a substantial change at ˜235 K confirming a transition from glassy to supercooled liquid state in vitreous aspirin.

  5. Fabrication and electrochemical behavior of single-walled carbon nanotube/graphite-based electrode

    International Nuclear Information System (INIS)

    Moghaddam, Abdolmajid Bayandori; Ganjali, Mohammad Reza; Dinarvand, Rassoul; Razavi, Taherehsadat; Riahi, Siavash; Rezaei-Zarchi, Saeed; Norouzi, Parviz

    2009-01-01

    An electrochemical method for determining the dihydroxybenzene derivatives on glassy carbon (GC) has been developed. In this method, the performance of a single-walled carbon nanotube (SWCNT)/graphite-based electrode, prepared by mixing SWCNTs and graphite powder, was described. The resulting electrode shows an excellent behavior for redox of 3,4-dihydroxybenzoic acid (DBA). SWCNT/graphite-based electrode presents a significant decrease in the overvoltage for DBA oxidation as well as a dramatic improvement in the reversibility of DBA redox behavior in comparison with graphite-based and glassy carbon (GC) electrodes. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) procedures performed for used SWCNTs

  6. Dielectric relaxation in glassy Se75In25−xPbx alloys

    Indian Academy of Sciences (India)

    to their atomic percentages and were sealed in quartz ampoules (length ~5 cm and internal dia. ~8 mm) in vacuum ... samples were taken out by breaking the quartz ampoules. The glassy nature of the ... measured with the help of a calibrated copper–constantan thermocouple mounted very near to the sample, which could ...

  7. Glassy-winged sharpshooter oviposition effects on foliar grapevine and red-tipped photinia terpenoid levels

    Science.gov (United States)

    The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is an important vector of Xylella fastidiosa, the bacterium that causes Pierce's disease of grapevine and is a threat to grape production throughout the United States. Female GWSS deposit egg masses be...

  8. Absorption of molten fluoride salts in glassy carbon, pyrographite and Hastelloy B

    Czech Academy of Sciences Publication Activity Database

    Vacík, Jiří; Naramoto, H.; Červená, Jarmila; Hnatowicz, Vladimír; Peka, I.; Fink, D.

    2001-01-01

    Roč. 289, č. 3 (2001), s. 308-314 ISSN 0022-3115 R&D Projects: GA ČR GA202/96/0077; GA ČR GV202/97/K038; GA AV ČR KSK1010104 Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.366, year: 2001

  9. Micro volume voltammetric determination of 4-nitrophenol in dimethyl sulfoxide at a glassy carbon electrode

    Czech Academy of Sciences Publication Activity Database

    Gajdar, J.; Barek, J.; Fojta, Miroslav; Fischer, J.

    2017-01-01

    Roč. 148, č. 9 (2017), s. 1639-1644 ISSN 0026-9247 Institutional support: RVO:68081707 Keywords : square-wave voltammetry * nitrobenzene Subject RIV: CE - Biochemistry OBOR OECD: Biochemistry and molecular biology Impact factor: 1.282, year: 2016

  10. Investigation of the porous structure of glassy carbon by SAXS - an application of synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Braun, A.; Baertsch, M.; Schnyder, B.; Koetz, R.; Haas, O. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1999-08-01

    The porous structure of Electrochemical Double Layer Capacitor (EDC) Electrodes was investigated using Small Angle X-ray Scattering (SAXS), assuming logarithmically normal distributed micropores. (author) 2 figs., 1 ref.

  11. Copper nanoparticle modified carbon electrode for determination of dopamine

    International Nuclear Information System (INIS)

    Oztekin, Yasemin; Tok, Mutahire; Bilici, Esra; Mikoliunaite, Lina; Yazicigil, Zafer; Ramanaviciene, Almira; Ramanavicius, Arunas

    2012-01-01

    This paper reports the synthesis and characterization of copper nanoparticles (CuNPs) and application of copper nanoparticle-modified glassy carbon electrode for the electrochemical determination of dopamine. Electrochemical measurements were performed using differently modified glassy carbon (GC) electrodes. Bare, oxidized before modification and copper nanoparticle-modified glassy carbon electrodes (bare-GC, ox-GC and CuNP/GC electrodes, respectively) were characterized by cyclic voltammetry and electrochemical impedance spectroscopy in the presence of redox probes. Atomic force microscopy was used for the visualization of electrode surfaces. The CuNP/GC electrode was found to be suitable for the selective determination of dopamine even in the presence of ascorbic acid, uric acid, and p-acetamidophenol. The observed linear range of CuNP/GC for dopamine was from 0.1 nM to 1.0 μM while the detection limit was estimated to be 50 pM. It was demonstrated that here reported glassy carbon electrode modified by copper nanoparticles is suitable for the determination of dopamine in real samples such as human blood serum.

  12. Rheological analysis of the phenolic and furfuryl resins used in the carbon materials processing

    Directory of Open Access Journals (Sweden)

    Edson Cocchieri Botelho

    2000-04-01

    Full Text Available Carbon materials processing is an advanced technology due to its aerospace and medical applications. In the aerospace area one can mention the carbon/carbon composites used in rockets and aeronautical brakes; in the medical area one can mention the intrabody implant tools such as heart and hydrocephalic valves and pacemaker electrode tips. The highly sophisticated purpose of its application requires a very tight processing control, which defines the microstructure the mechanical, thermal and electrical characteristics of the final material. The objective of this study is to correlate rheological, chromatographic and thermal analysis of phenolic and furfuryl resins, aiming their use as raw materials in carbon/carbon composite and glassy carbon processing. The obtained results are correlated and used directly in the establishment of the adequate parameters for carbon reinforcement impregnation and to prepare glassy carbon samples with controlled porosity.

  13. Thermoanalytical characterization of carbon/carbon hybrid material, Apple Woodceramics

    International Nuclear Information System (INIS)

    Ozao, Riko; Nishimoto, Yuko; Pan, Wei-Ping; Okabe, Toshihiro

    2006-01-01

    Woodceramics, a carbon/carbon composite of plant-originated carbon reinforced by glassy carbon from phenolic resin, was prepared from apple pomace at carbonizing temperatures of 1073 K (AWC800) and 1473 K (AWC1200), and characterized by thermoanalytical methods and X-ray diffraction (XRD). Simultaneous differential scanning calorimetry (DSC) and thermogravimetric (TG) showed complicated overlapping reactions similar to those of coal. The initial temperature of pyrolysis was obtained by fitting logistic functions to observed TG data. The results suggested that AWC1200 contained more volatile matter than AWC800. In an inert atmosphere, complicated devolatilization takes place. In an oxidizing atmosphere, thermal change occurs roughly in four steps: desorption of physically adsorbed matter; pyrolysis into aliphatic and aromatic fragments; ignition; combustion of char. The oxidation resistance of AWC1200 was superior to AWC800

  14. Horseradish peroxidase-labeled silver/reduced graphene oxide thin film-modified screen-printed electrode for detection of carcinoembryonic antigen.

    Science.gov (United States)

    Lee, S X; Lim, H N; Ibrahim, I; Jamil, A; Pandikumar, A; Huang, N M

    2017-03-15

    In this study, a disposable and simple electrochemical immunosensor was fabricated for the detection of carcinoembryonic antigen. In this method, silver nanoparticles (AgNPs) were mixed with reduced graphene oxide (rGO) to modify the surface of screen-printed carbon electrode (SPE). Initially, AgNPs-rGO modified-SPEs were fabricated by using simple electrochemical deposition method. Then the carcinoembryonic antigen (CEA) was immobilized between the primary antibody and horseradish peroxidase (HRP)-conjugated secondary antibody onto AgNPs-rGO modified-SPEs to fabricate a sandwich-type electrochemical immunosensor. The proposed method could detect the CEA with a linear range of 0.05-0.50µgmL -1 and a detection limit down to 0.035µgmL -1 as compared to its non-sandwich counterpart, which yielded a linear range of 0.05-0.40µgmL -1 , with a detection limit of 0.042µgmL -1 . The immunosensor showed good performance in the detection of carcinoembryonic antigen, exhibiting a simple, rapid and low-cost. The immunosensor showed a higher sensitivity than an enzymeless sensor. Copyright © 2015 Elsevier B.V. All rights reserved.

  15. A Comparative Study of Poly(Azure A Film-Modified Disposable Electrodes for Electrocatalytic Oxidation of H2O2: Effect of Doping Anion

    Directory of Open Access Journals (Sweden)

    Jerónimo Agrisuelas

    2018-01-01

    Full Text Available In the present paper, poly(azure A (PAA films were electrosynthetized in the presence of different doping anions on disposable screen-printed carbon electrodes (SPCEs. The anions used included inorganic monoatomic (chloride and fluoride, inorganic polyatomic (nitrate and sulfate and organic polyatomic (dodecyl sulfate, DS species. The coated electrodes thus obtained were characterized by electrochemical techniques and SEM. They showed improved electrocatalytic activities towards hydrogen peroxide oxidation compared to that of a bare SPCE. In particular, the insertion of DS anions inside PAA films provided a special sensitivity to the electrocatalysis of H2O2, which endowed these electrodes with promising analytical features for H2O2 quantification. We obtained a wide linear response for H2O2 within a range of 5 µM to 3 mM and a limit of detection of 1.43 ± 0.10 µM (signal-to-noise ratio of 3. Furthermore, sensitivity was 72.4 ± 0.49 nA·µM−1∙cm−2 at a relatively low electrocatalytic oxidation overpotential of 0.5 V vs. Ag. The applicability of this boosted system was tested by the analysis of H2O2 in commercial samples of a hair lightener and an antiseptic and was corroborated by spectrophotometric methods.

  16. Comparison of the enthalpy recovery and free volume of polyvinylpyrrolidone during anomalous glassy to rubbery transition.

    Science.gov (United States)

    Zelkó, Romána; Süvegh, Károly

    2004-03-01

    Previous studies confirmed that along with the structural changes of the amorphous binder, that of the polyvinylpyrrolidone, the tensile strength and consequently, the dissolution behaviour of its tablets changed significantly during the storage period. Structural formation during the glassy to rubbery transition of polyvinylpyrrolidone was followed by the changes in the free volume and enthalpy recovery values of the polymer. The results suggest that the apparent structure formation of water and polymer under glassy to rubbery transition is interrelated in a dynamic and complex manner which can be tracked by the combination of enthalpy recovery studies and positron lifetime measurements. Positron lifetime measurements more sensitively react to the structural rearrangements than enthalpy recovery, thus it can be recommended as a sensitive tool for stability tests during the formulation phase of drug development.

  17. Relaxation of enthalpy fluctuations during sub-T(g) annealing of glassy selenium.

    Science.gov (United States)

    Gulbiten, Ozgur; Mauro, John C; Lucas, Pierre

    2013-06-28

    The relaxation behavior of glass is influenced by the presence of dynamical heterogeneities, which lead to an intrinsically non-monotonic decay of fluctuations in density and enthalpy during isothermal annealing. This is apparently a universal feature of fragile glass forming systems associated with localized spatial variations in relaxation time. Here we present direct experimental observation of the nonmonotonic evolution of enthalpy fluctuations in glassy selenium annealed near room temperature. The nonmonotonic change in the distribution of enthalpy fluctuations measured by heat capacity spectroscopy offers direct evidence for the presence of dynamical heterogeneity in this glass. An enthalpy landscape model of selenium is then used to simulate annealing under identical conditions. The simulation results closely follow the evolution of enthalpy fluctuations observed experimentally. The close match between model and experiment demonstrate that enthalpy and density fluctuations are sources of dynamical heterogeneities in glassy materials.

  18. Orbital physics in sulfur spinels: ordered, liquid and glassy ground states

    International Nuclear Information System (INIS)

    Buettgen, N; Hemberger, J; Fritsch, V; Krimmel, A; Muecksch, M; Nidda, H-A Krug von; Lunkenheimer, P; Fichtl, R; Tsurkan, V; Loidl, A

    2004-01-01

    Measurements of magnetization M(T, H), heat capacity C(T), NMR lineshift K(T) and linewidth Δ(T), neutron scattering S(Q, ω, T) and broadband dielectric spectroscopy ε(ω, T) provide experimental evidence of the different orbital ground states in the cubic sulfur spinels under investigation. In all compounds, the tetrahedrally coordinated Jahn-Teller ions Fe 2+ are characterized by a degeneracy of the orbital degrees of freedom. Particularly, we found a long-range orbital ordering in polycrystalline (PC) FeCr 2 S 4 , and a glassy freezing of the orbital degrees of freedom in FeCr 2 S 4 (single crystals) (SCs). In contrast, FeSc 2 S 4 belongs to the rare class of spin-orbital liquids, where quantum fluctuations accompanying the glassy freezing of the orbitals suppress long-range magnetic order

  19. Connection between NMR and electrical conductivity in glassy chalcogenide fast ionic conductors

    International Nuclear Information System (INIS)

    Kim, K.H.

    1995-01-01

    The work documented in this thesis follows the traditional order. In this chapter a general discussion of ionic conduction and of glassy materials are followed by a brief outline of the experimental techniques for the investigation of fast ionic conduction in glassy materials, including NMR and impedance spectroscopy techniques. A summary of the previous and present studies is presented in the last section of this introductory chapter. The details of the background theory and models are found in the Chapter II, followed by the description of the experimental details in Chapter III. Chapter IV of the thesis describes the experimental results and the analysis of the experimental observations followed by the conclusions in chapter V

  20. Connection between NMR and electrical conductivity in glassy chalcogenide fast ionic conductors

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kyung -Han [Iowa State Univ., Ames, IA (United States)

    1995-07-07

    The work documented in this thesis follows the traditional order. In this chapter a general discussion of ionic conduction and of glassy materials are followed by a brief outline of the experimental techniques for the investigation of fast ionic conduction in glassy materials, including NMR and impedance spectroscopy techniques. A summary of the previous and present studies is presented in the last section of this introductory chapter. The details of the background theory and models are found in the Chapter II, followed by the description of the experimental details in Chapter III. Chapter IV of the thesis describes the experimental results and the analysis of the experimental observations followed by the conclusions in chapter V.

  1. The electronic fine structure of 4-nitrophenyl functionalized single-walled carbon nanotubes

    International Nuclear Information System (INIS)

    Chakraborty, Amit K; Coleman, Karl S; Dhanak, Vinod R

    2009-01-01

    Controlling the electronic structure of carbon nanotubes (CNTs) is of great importance to various CNT based applications. Herein the electronic fine structure of single-walled carbon nanotube films modified with 4-nitrophenyl groups, produced following reaction with 4-nitrobenzenediazonium tetrafluoroborate, was investigated for the first time. Various techniques such as x-ray and ultra-violet photoelectron spectroscopy, and near edge x-ray absorption fine structure studies were used to explore the electronic structure, and the results were compared with the measured electrical resistances. A reduction in number of the π electronic states in the valence band consistent with the increased resistance of the functionalized nanotube films was observed.

  2. Diffuse X-ray scattering by glassy crystalline cyclohexanol : preliminary results

    OpenAIRE

    Ceccaldi , D.; Denoyer , F.; Lambert , M.; Szwarc , H.

    1980-01-01

    Diffuse X-ray scattering experiments have been performed to define structural criteria for the glassy crystalline state. When quenching single crystals of the plastic phase of cyclohexanol, the low temperature photographs disclose a structuration of the diffusion patterns that can be assigned to strongly anisotropic short range intermolecular correlations within an orientational disorder. When quenching liquid samples, an amorphous cyclohexanol phase has been discovered.

  3. Co-based soft magnetic bulk glassy alloys optimized for glass ...

    Indian Academy of Sciences (India)

    testing machine at a strain rate of 5 × 10. −4 s. −1 at room tem- perature using the glassy rods with a dimension of 2 mm in diameter and 4 mm in length. Is was measured with a vibrat- ing sample magnetometer (VSM) under an applied field of. 400 kA m. −1 . Hc was measured with a B–H loop tracer under a field of 800 A m.

  4. Effect of thermodynamic history on secondary relaxation in glassy phenolphthalein-dimethyl-ether

    Science.gov (United States)

    Prevosto, D.; Capaccioli, S.; Lucchesi, M.; Rolla, P. A.; Paluch, M.; Pawlus, S.

    2006-03-01

    We present a study of the intermediate secondary relaxation process of phenolphthalein-dimethyl-ether. Though this process is intramolecular in nature, it reveals pronounced pressure dependence. Moreover, its relaxation frequency and intensity exhibit pronounced dependence on the thermal history followed during vitrification. These results suggest that the nonequilibrium nature of the glassy state influences this secondary relaxation principally through the dependence on the specific volume.

  5. Dynamics and Geometry of Icosahedral Order in Liquid and Glassy Phases of Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Masato Shimono

    2015-07-01

    Full Text Available The geometrical properties of the icosahedral ordered structure formed in liquid and glassy phases of metallic glasses are investigated by using molecular dynamics simulations. We investigate the Zr-Cu alloy system as well as a simple model for binary alloys, in which we can change the atomic size ratio between alloying components. In both cases, we found the same nature of icosahedral order in liquid and glassy phases. The icosahedral clusters are observed in liquid phases as well as in glassy phases. As the temperature approaches to the glass transition point Tg, the density of the clusters rapidly grows and the icosahedral clusters begin to connect to each other and form a medium-range network structure. By investigating the geometry of connection between clusters in the icosahedral network, we found that the dominant connecting pattern is the one sharing seven atoms which forms a pentagonal bicap with five-fold symmetry. From a geometrical point of view, we can understand the mechanism of the formation and growth of the icosahedral order by using the Regge calculus, which is originally employed to formulate a theory of gravity. The Regge calculus tells us that the distortion energy of the pentagonal bicap could be decreased by introducing an atomic size difference between alloying elements and that the icosahedral network would be stabilized by a considerably large atomic size difference.

  6. A thermodynamic model for growth mechanisms of multiwall carbon nanotubes.

    Energy Technology Data Exchange (ETDEWEB)

    Kaatz, Forrest H.; Overmyer, Donald L.; Siegal, Michael P.

    2006-02-01

    Multiwall carbon nanotubes are grown via thermal chemical vapor deposition between temperatures of 630 and 830 C using acetylene in nitrogen as the carbon source. This process is modeled using classical thermodynamics to explain the total carbon deposition as a function of time and temperature. An activation energy of 1.60 eV is inferred for nanotube growth after considering the carbon solubility term. Scanning electron microscopy shows growth with diameters increasing linearly with time. Transmission electron microscopy and Raman spectroscopy show multiwall nanotubes surrounded by a glassy-carbon sheath, which grows with increasing wall thickness as growth temperatures and times rise.

  7. Thermodynamic model for growth mechanisms of multiwall carbon nanotubes

    Science.gov (United States)

    Kaatz, F. H.; Siegal, M. P.; Overmyer, D. L.; Provencio, P. P.; Tallant, D. R.

    2006-12-01

    Multiwall carbon nanotubes are grown via thermal chemical vapor deposition between temperatures of 630 and 830°C using acetylene in nitrogen as the carbon source. This process is modeled using classical thermodynamics to explain the total carbon deposition as a function of time and temperature. An activation energy of 1.60eV is inferred for nanotube growth after considering the carbon solubility term. Scanning electron microscopy shows growth with diameters increasing linearly with time. Transmission electron microscopy and Raman spectroscopy show multiwall nanotubes surrounded by a glassy-carbon sheath, which grows with increasing wall thickness as growth temperatures and times rise.

  8. Plasma Polymerized Thin Films of Maleic Anhydride and 1,2-methylenedioxybenzene for Improving Adhesion to Carbon Surfaces

    DEFF Research Database (Denmark)

    Drews, Joanna Maria; Goutianos, Stergios; Kingshott, Peter

    2007-01-01

    Low power 2-phase AC plasma polymerization has been used to surface modify glassy carbon substrates that are used as an experimental model for carbon fibers in reinforced composites. In order to probe the role of carboxylic acid density on the interfacial adhesion strength a combination...

  9. First-principles molecular dynamics study of glassy GeS2: Atomic structure and bonding properties

    Science.gov (United States)

    Celino, M.; Le Roux, S.; Ori, G.; Coasne, B.; Bouzid, A.; Boero, M.; Massobrio, C.

    2013-11-01

    The structure of glassy GeS2 is studied in the framework of density functional theory, by using a fully self-consistent first-principles molecular dynamics (FPMD) scheme. A comparative analysis is performed with previous molecular dynamics data obtained within the Harris functional (HFMD) total energy approach. The calculated total neutron structure factor exhibits an unprecedented agreement with the experimental counterpart. In particular, the height of the first sharp diffraction peak (FSDP) improves considerably upon the HFMD results. Both the Ge and the S subnetworks are affected by a consistent number of miscoordinations, coexisting with the main tetrahedral structural motif. Glassy GeS2 features a short-range order quite similar to the one found in glassy GeSe2, a notable exception being the larger number of edge-sharing connections. An electronic structure localization analysis, based on the Wannier functions formalism, provides evidence of a more enhanced ionic character in glassy GeS2 when compared to glassy GeSe2.

  10. Polymorphic ethyl alcohol as a model system for the quantitative study of glassy behaviour

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, H.E.; Schober, H.; Gonzalez, M.A. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France); Bermejo, F.J.; Fayos, R.; Dawidowski, J. [Consejo Superior de Investigaciones Cientificas, Madrid (Spain); Ramos, M.A.; Vieira, S. [Universidad Autonoma de Madrid (Spain)

    1997-04-01

    The nearly universal transport and dynamical properties of amorphous materials or glasses are investigated. Reasonably successful phenomenological models have been developed to account for these properties as well as the behaviour near the glass-transition, but quantitative microscopic models have had limited success. One hindrance to these investigations has been the lack of a material which exhibits glass-like properties in more than one phase at a given temperature. This report presents results of neutron-scattering experiments for one such material ordinary ethyl alcohol, which promises to be a model system for future investigations of glassy behaviour. (author). 8 refs.

  11. Glassy metals

    CERN Document Server

    Russew, Krassimir

    2016-01-01

    The topics discussed in this book focus on fundamental problems concerning the structural relaxation of amorphous metallic alloys, above all the possibility of studying it on the basis of viscous flow behavior and its relation to rheological anomalies, such as bend stress relaxation, thermal expansion, specific heat, density changes, and crystallization. Most relaxation studies deal with the relaxation changes of a single definite material property, and not with a wider spectrum of physical properties integrated into a common framework. This book shows that it is possible to describe these property changes on the basis of a more comprehensive theoretical understanding of their mechanism.

  12. Structural characterization and aging of glassy pharmaceuticals made using acoustic levitation.

    Science.gov (United States)

    Benmore, Chris J; Weber, J K R; Tailor, Amit N; Cherry, Brian R; Yarger, Jeffery L; Mou, Qiushi; Weber, Warner; Neuefeind, Joerg; Byrn, Stephen R

    2013-04-01

    Here, we report the structural characterization of several amorphous drugs made using the method of quenching molten droplets suspended in an acoustic levitator. (13) C NMR, X-ray, and neutron diffraction results are discussed for glassy cinnarizine, carbamazepine, miconazole nitrate, probucol, and clotrimazole. The (13) C NMR results did not find any change in chemical bonding induced by the amorphization process. High-energy X-ray diffraction results were used to characterize the ratio of crystalline to amorphous material present in the glasses over a period of 8 months. All the glasses were stable for at least 6 months except carbamazepine, which has a strong tendency to crystallize within a few months. Neutron and X-ray pair distribution function analyses were applied to the glassy materials, and the results were compared with their crystalline counterparts. The two diffraction techniques yielded similar results in most cases and identified distinct intramolecular and intermolecular correlations. The intramolecular scattering was calculated based on the crystal structure and fit to the measured X-ray structure factor. The resulting intermolecular pair distribution functions revealed broad-nearest and next-nearest neighbor molecule-molecule correlations. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:1290-1300, 2013. Copyright © 2013 Wiley Periodicals, Inc.

  13. Comparing the mechanism of water condensation and evaporation in glassy aerosol.

    Science.gov (United States)

    Bones, David L; Reid, Jonathan P; Lienhard, Daniel M; Krieger, Ulrich K

    2012-07-17

    Atmospheric models generally assume that aerosol particles are in equilibrium with the surrounding gas phase. However, recent observations that secondary organic aerosols can exist in a glassy state have highlighted the need to more fully understand the kinetic limitations that may control water partitioning in ambient particles. Here, we explore the influence of slow water diffusion in the condensed aerosol phase on the rates of both condensation and evaporation, demonstrating that significant inhibition in mass transfer occurs for ultraviscous aerosol, not just for glassy aerosol. Using coarse mode (3-4 um radius) ternary sucrose/sodium chloride/aqueous droplets as a proxy for multicomponent ambient aerosol, we demonstrate that the timescale for particle equilibration correlates with bulk viscosity and can be ≫10(3) s. Extrapolation of these timescales to particle sizes in the accumulation mode (e.g., approximately 100 nm) by applying the Stokes-Einstein equation suggests that the kinetic limitations imposed on mass transfer of water by slow bulk phase diffusion must be more fully investigated for atmospheric aerosol. Measurements have been made on particles covering a range in dynamic viscosity from  10(13) Pa s. We also retrieve the radial inhomogeneities apparent in particle composition during condensation and evaporation and contrast the dynamics of slow dissolution of a viscous core into a labile shell during condensation with the slow percolation of water during evaporation through a more homogeneous viscous particle bulk.

  14. In situ AFM investigation of slow crack propagation mechanisms in a glassy polymer

    Science.gov (United States)

    George, M.; Nziakou, Y.; Goerke, S.; Genix, A.-C.; Bresson, B.; Roux, S.; Delacroix, H.; Halary, J.-L.; Ciccotti, M.

    2018-03-01

    A novel experimental technique based on in situ AFM monitoring of the mechanisms of damage and the strain fields associated to the slow steady-state propagation of a fracture in glassy polymers is presented. This micron-scale investigation is complemented by optical measurements of the sample deformation up to the millimetric macroscopic scale of the sample in order to assess the proper crack driving conditions. These multi-scale observations provide important insights towards the modeling of the fracture toughness of glassy polymers and its relationship with the macromolecular structure and non-linear rheological properties. This novel technique is first tested on a standard PMMA thermoplastic in order to both evaluate its performance and the richness of this new kind of observations. Although the fracture propagation in PMMA is well known to proceed through crazing in the bulk of the samples, our observations provide a clear description and quantitative evaluation of a change of fracture mechanism towards shear yielding fracture accompanied by local necking close to the free surface of the sample, which can be explained by the local change of stress triaxiality. Moreover, this primary surface necking mechanism is shown to be accompanied by a network of secondary grooves that can be related to surface crazes propagating towards the interior of the sample. This overall scenario is validated by post-mortem fractographic investigations by scanning electron microscopy.

  15. Room-temperature nonlinear transport phenomena in low-dimensional Ni-Nb-Zr-H glassy alloys and its device

    Energy Technology Data Exchange (ETDEWEB)

    Fukuhara, Mikio; Yoshida, Hajime [Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba, Sendai, 980-8577 (Japan)

    2014-05-15

    We report the room-temperature switching and Coulomb blockade effects in three–terminal glassy alloy field effect transistor (GAFET), using the millimeter sized glassy alloy. By applying dc and ac voltages to a gate electrode, GAFET can be switched from a metallic conducting state to an insulating state with Coulomb oscillation at a period of 14 μV at room temperature. The transistor showed the three-dimensional Coulomb diamond structure. The fabrication of a low-energy controllable device throws a new light on cluster electronics without wiring.

  16. Enhanced polystyrene surface mobility under carbon dioxide at low temperature for nanoparticle embedding control

    NARCIS (Netherlands)

    Yang, Qiuyan; Xu, Qun; Loos, Katja

    2015-01-01

    The surface properties of polystyrene (PS) films under carbon dioxide (CO2) were studied via a particle embedding technique at quite a low temperature range (308 to 323 K) in which polystyrene is typically considered to be in a glassy state without CO2. Atomic force microscope (AFM) technique with a

  17. Chemically modified carbon-based electrodes for the detection of some substances of environmental and biomedical significance

    OpenAIRE

    Hutton, Emily Anne

    2003-01-01

    The thesis opens with an introduction to some basic electroanalytical principles, and a brief description of carbon-based electrodes, with a particular focus on glassy carbon and carbon fibre microelectrodes. Also included is a review of the most commonly employed electrode modification procedures, with some examples of the analytical applications of modified electrodes. The second chapter describes the use of the bismuth film electrode (BiFE), which consists of a bismuth film electrochem...

  18. Detection and typing of Xylella fastidiosa from glassy-winged sharpshooter for Pierce’s disease epidemiology

    Science.gov (United States)

    Epidemiology of Pierce’s disease of grape, caused by the bacterial pathogen Xylella fastidiosa (Xf), is largely dependent on populations of insect vectors such as the invasive glassy-winged sharpshooter (GWSS) (Homalodisca vitripennis). In the grape-growing regions of the southern San Joaquin Valley...

  19. Design of a candidate vibrational signal for mating disruption against the glassy-winged sharpshooter, Homalodisca Vitripennis

    Science.gov (United States)

    The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is an important pest of grapevines due to its ability to transmit Xylella fastidiosa, the causal agent of Pierce’s disease. GWSS mating communication is based on vibrational signals; therefore, vibrational mating disruption could be an ...

  20. Geographic distribution and relative abundance of the invasive glassy-winged sharpshooter: effects of temperature and egg parasitoids.

    Science.gov (United States)

    Gutierrez, Andrew Paul; Ponti, Luigi; Hoddle, Mark; Almeida, Rodrigo P P; Irvin, Nicola A

    2011-08-01

    The capacity to predict the geographic distribution and relative abundance of invasive species is pivotal to developing policy for eradication or control and management. Commonly used methods fall under the ambit of ecological niche models (ENMs). These methods were reviewed and shortcomings identified. Weather-driven physiologically based demographic models (PBDMs) are proposed that resolve many of the deficiencies of ENMs. The PBDM approach is used to analyze the invasiveness of the polyphagous glassy-winged sharpshooter (Homalodisca vitripennis [Germar]), a pest native to the southeastern United States and northeastern Mexico that extended its range into California in 1989. Glassy-winged sharpshooter vectors the pathogenic bacterium, Xylella fastidiosa (Wells) that causes Pierce's disease in grape and scorch-like diseases in other plants. PBDMs for glassy-winged sharpshooter and its egg parasitoids (Gonatocerus ashmeadi Girault and G. triguttatus Girault) were developed and linked to a PBDM for grape published by Wermelinger et al. (1991). Daily weather data from 108 locations across California for the period 1995-2006 were used to drive the PBDM system, and GRASS GIS was used to map the simulation results. The geographic distribution of glassy-winged sharpshooter, as observed, is predicted to be largely restricted to the warm areas of southern California, with the action of the two egg parasitoids reducing its abundance >90%. The average indispensable mortality contributed by G. triguttatus is central valley of California. The utility of holistic analyses for formulating control policy and tactics for invasive species is discussed.

  1. Following Gibbs states adiabatically: the energy landscape of mean field glassy systems

    Energy Technology Data Exchange (ETDEWEB)

    Zdeborova, Lenka [Los Alamos National Laboratory; Krzakala, Florent [ESPCI

    2009-01-01

    We introduce a generalization of the cavity, or Bethe-Peierls, method that allows to follow Gibbs states when an external parameter, e.g. the temperature, is adiabatically changed. This allows to obtain new quantitative results on the static and dynamic behavior of mean field disordered systems such as models of glassy and amorphous materials or random constraint satisfaction problems. As a first application, we discuss the residual energy after a very slow annealing, the behavior of out-of-equilibrium states, and demonstrate the presence of temperature chaos in equilibrium. We also explore the energy landscape, and identify a new transition from an computationally easier canyons-dominated region to a harder valleys-dominated one.

  2. Plutonium segregation in glassy aerodynamic fallout from a nuclear weapon test.

    Science.gov (United States)

    Holliday, K S; Dierken, J M; Monroe, M L; Fitzgerald, M A; Marks, N E; Gostic, R C; Knight, K B; Czerwinski, K R; Hutcheon, I D; McClory, J W

    2017-02-14

    This study combines electron microscopy equipped with energy dispersive spectroscopy to probe major element composition and autoradiography to map plutonium in order to examine the spatial relationships between plutonium and fallout composition in aerodynamic glassy fallout from a nuclear weapon test. A sample set of 48 individual fallout specimens were interrogated to reveal that the significant chemical heterogeneity of this sample set could be described compositionally with a relatively small number of compositional endmembers. Furthermore, high concentrations of plutonium were never associated with several endmember compositions and concentrated with the so-called mafic glass endmember. This result suggests that it is the physical characteristics of the compositional endmembers and not the chemical characteristics of the individual component elements that govern the un-burnt plutonium distribution with respect to major element composition in fallout.

  3. On melting dynamics and the glass transition. II. Glassy dynamics as a melting process.

    Science.gov (United States)

    Krzakala, Florent; Zdeborová, Lenka

    2011-01-21

    There are deep analogies between the melting dynamics in systems with a first-order phase transition and the dynamics from equilibrium in super-cooled liquids. For a class of Ising spin models undergoing a first-order transition--namely p-spin models on the so-called Nishimori line--it can be shown that the melting dynamics can be exactly mapped to the equilibrium dynamics. In this mapping the dynamical--or mode-coupling--glass transition corresponds to the spinodal point, while the Kauzmann transition corresponds to the first-order phase transition itself. Both in mean field and finite dimensional models this mapping provides an exact realization of the random first-order theory scenario for the glass transition. The corresponding glassy phenomenology can then be understood in the framework of a standard first-order phase transition.

  4. A random walk description of the heterogeneous glassy dynamics of attracting colloids

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhuri, Pinaki; Berthier, Ludovic; Kob, Walter [Laboratoire des Colloides, Verres et Nanomateriaux, UMR 5587, Universite Montpellier II and CNRS, 34095 Montpellier (France); Gao Yongxiang; Kilfoil, Maria [Department of Physics, McGill University, Montreal, H3A 2T8 (Canada)], E-mail: berthier@lcvn.univ-montp2.fr

    2008-06-18

    We study the heterogeneous dynamics of attractive colloidal particles close to the gel transition using confocal microscopy experiments combined with a theoretical statistical analysis. We focus on single particle dynamics and show that the self-part of the van Hove distribution function is not the Gaussian expected for a Fickian process, but that it reflects instead the existence, at any given time, of colloids with widely different mobilities. Our confocal microscopy measurements can be described well by a simple analytical model based on a conventional continuous time random walk picture, as already found for several other glassy materials. In particular, the theory successfully accounts for the presence of broad tails in the van Hove distributions that exhibit exponential, rather than Gaussian, decay at large distance.

  5. Glassy and Metastable Crystalline BaTi2O5 by Containerless Processing

    Science.gov (United States)

    Yoda, Shinichi; Kentei Yu, Yu; Kumar, Vijaya; Kameko, Masashi

    Many efforts have been devoted to forming bulk glass from the melt of ferroelectric crystalline materials without adding any network-forming oxides such as SiO2 due to the potential for producing transparent glass ceramics with high dielectric constant and enhanced piezoelectric, pyroelectric and electro-optic use. The containerless processing is an attractive synthesis tech-nique as it can prevent melt contamination, minimize heterogeneous nucleation, and allow melt to achieve deep undercooling for forming metastable and glassy materials. We have fabricated a new ferroelectric materiel BaTi2 O5 [1] as bulk glass from melt by us-ing containerless processing and studied the phase relationship between microstructure and ferroelectric properties of BaTi2 O5 [2]. The structures of glassy and metastable crystalline BaTi2 O5 fabricated by the containerless pro-cessing were comprehensively investigated by combined X-ray and neutron diffractions, XANES analyses and computer simulations [3]. The 3-dimensional atomic structure of glassy BaTi2 O5 (g-BaTi2 O5 ), simulated by Reverse Monte Carlo (RMC) modelling on diffraction data, shows that extremely distorted TiO5 polyhedra interconnected with both corner-and edge-shared oxy-gen, formed a higher packing density structure than that of conventional silicate glass linked with only corner-sharing of SiO4 polyhedra. In addition, XANES measurement reveales that five-coordinated TiO5 polyhedra were formable in the crystallized metastable a-and b-BaTi2 O5 phases. The structure of metastable b-BaTi2 O5 was solved by ab initio calculation, and refined by Rietveld refinement as group Pnma with unit lattices a = 10.23784 ˚, b = 3.92715 ˚, c A A = 10.92757 A ˚. Our results show that the glass-forming ability enhanced by containerless pro-cessing, not by `strong glass former', fabricated new bulk oxide glasses with peculiar structures and properties. The intermediate-range structure of g-BaTi2 O5 and the crystalline structure of

  6. Polymer thin films as a route to access low energy glassy states

    Science.gov (United States)

    Cangialosi, Daniele; Boucher, Virginie M.; Alegria, Angel; Colmenero, Juan

    We investigate the enthalpy recovery in the glassy state of stacked polystyrene films with thickness 30 nm. We first show how the equilibrium dynamics and thermodynamics of such films is mainly bulk-like. When studying enthalpy recovery, we find two mechanisms of equilibration: one showing up below 348 K, that is, the films Tg; and the second active below 308 K. The latter mechanism appear to have low activation energy and, as a result, gives rise to dramatic decrease of the fictive temperature Tf within relatively short aging times. This allows to achieve low energy glasses, in particular approaching the Kauzmann temperature (Tk), that is, the temperature at which the entropy of the glass equals that of the crystal. The implications of our results are discussed.

  7. Design of a Well-Defined Polyrotaxane Structure on a Glassy Polymer Surface.

    Science.gov (United States)

    Taneda, Hidenobu; Shundo, Atsuomi; Matsuno, Hisao; Tanaka, Keiji

    2018-01-16

    The polymer dynamics at the water interface play a crucial role in the manifestation of biorelated functions. One of the strategies for this is to form inclusion complexes of polymer chains with cyclic compounds. However, such an idea has been limited to bulk materials so far. Here we propose a preparation pathway for a polyrotaxane structure composed of poly(ethylene oxide) (PEO) and α-cyclodextrin (CD) at the outermost surface of a glassy poly(methyl methacrylate) film on the basis of the combination of a click reaction and the Langmuir-Blodgett method. The chain motion of PEO at the water interface could be regulated by threading of CD molecules on PEO and thereby the biological responses such as protein adsorption and platelet adhesion altered depending on the extent of complexation.

  8. Linear response in aging glassy systems, intermittency and the Poisson statistics of record fluctuations

    DEFF Research Database (Denmark)

    Sibani, Paolo

    2007-01-01

    in a correlated fashion and through irreversible bursts, `quakes', which punctuate reversible and equilibrium-like fluctuations of zero average. The temporal distribution of the quakes is a Poisson distribution with an average growing logarithmically on time, indicating that the quakes are triggered by record...... to capture the time dependencies of the EA simulation results. Finally, we argue that whenever the changes of the linear response function and of its conjugate autocorrelation function follow from the same intermittent events a fluctuation-dissipation-like relation can arise between the two in off......We study the intermittent behavior of the energy decay and the linear magnetic response of a glassy system during isothermal aging after a deep thermal quench, using the Edward-Anderson spin glass model as a paradigmatic example. The large intermittent changes in the two observables occur...

  9. "Non-equilibrium" block copolymer micelles with glassy cores: a predictive approach based on theory of equilibrium micelles.

    Science.gov (United States)

    Nagarajan, Ramanathan

    2015-07-01

    Micelles generated in water from most amphiphilic block copolymers are widely recognized to be non-equilibrium structures. Typically, the micelles are prepared by a kinetic process, first allowing molecular scale dissolution of the block copolymer in a common solvent that likes both the blocks and then gradually replacing the common solvent by water to promote the hydrophobic blocks to aggregate and create the micelles. The non-equilibrium nature of the micelle originates from the fact that dynamic exchange between the block copolymer molecules in the micelle and the singly dispersed block copolymer molecules in water is suppressed, because of the glassy nature of the core forming polymer block and/or its very large hydrophobicity. Although most amphiphilic block copolymers generate such non-equilibrium micelles, no theoretical approach to a priori predict the micelle characteristics currently exists. In this work, we propose a predictive approach for non-equilibrium micelles with glassy cores by applying the equilibrium theory of micelles in two steps. In the first, we calculate the properties of micelles formed in the mixed solvent while true equilibrium prevails, until the micelle core becomes glassy. In the second step, we freeze the micelle aggregation number at this glassy state and calculate the corona dimension from the equilibrium theory of micelles. The condition when the micelle core becomes glassy is independently determined from a statistical thermodynamic treatment of diluent effect on polymer glass transition temperature. The predictions based on this "non-equilibrium" model compare reasonably well with experimental data for polystyrene-polyethylene oxide diblock copolymer, which is the most extensively studied system in the literature. In contrast, the application of the equilibrium model to describe such a system significantly overpredicts the micelle core and corona dimensions and the aggregation number. The non-equilibrium model suggests ways to

  10. Probing Properties of Glassy Water and Other Liquids with Site Selective Spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    Dang, Nhan Chuong [Iowa State Univ., Ames, IA (United States)

    2005-01-01

    The standard non-photochemical hole burning (NPHB) mechanism, which involves phonon-assisted tunneling in the electronically excited state, was originally proposed to explain the light-induced frequency change of chemically stable molecules in glassy solids at liquid helium temperatures by this research group more than two decades ago. The NPHB mechanism was then further elucidated and the concept of intrinsic to glass configurational relaxation processes as pre-mediating step to the hole burning process was introduced. The latter provided the theoretical basis for NPHB to evolve into a powerful tool probing the dynamics and nature of amorphous media, which aside from ''simple'' inorganic glasses may include also ''complex'' biological systems such as living cells and cancerous/normal tissues. Presented in this dissertation are the experimental and theoretical results of hole burning properties of aluminum phthalocyanine tetrasulphonate (APT) in several different matrices: (1) hyperquenched glassy water (HGW); (2) cubic ice (Ic); and (3) water confined into poly(2-hydroxyethylmethacrylate) (poly-HEMA). In addition, results of photochemical hole burning (PHB) studies obtained for phthalocyanine tetrasulphonate (PcT) in HGW and free base phthalocyanine (Pc) in ortho-dichlorobenzene (DCB) glass are reported. The goal of this dissertation was to provide further evidence supporting the NPHB mechanism and to provide more insight that leads to a better understanding of the kinetic events (dynamics) in glasses, and various dynamical processes of different fluorescent chromorphores in various amorphous solids and the liquid that exist above the glass transition temperature (Tg). The following issues are addressed in detail: (1) time evolution of hole being burned under different conditions and in different hole burning systems; (2) temperature dependent hole profile; and (3) the structure

  11. Effect of solute nature on the polyamorphic transition in glassy polyol aqueous solutions.

    Science.gov (United States)

    Suzuki, Yoshiharu

    2017-08-14

    I examined the polyamorphic behavior of glassy dilute aqueous solutions of polyols (ethylene glycol, glycerol, meso-erythritol, xylitol, and D-sorbitol) under pressure at low temperatures. Although the volume change of the glassy aqueous solution varied continuously against pressure, the rate of the volume change appeared to vary discontinuously at the onset pressure of the gradual polyamorphic transition. It is thought that low-density liquid-like solvent water and high-density liquid-like solvent water coexist during the transition. Moreover, the existence of a solute induces the shift of polyamorphic transition to the lower-pressure side. The effect of a solute on the polyamorphic transition becomes larger in the order ethylene glycol, glycerol, meso-erythritol, xylitol, and D-sorbitol. Therefore, the solute can become a variable controlling the polyamorphic state of liquid water. This experimental result suggests that the metastable-equilibrium phase boundary between the low-density and the high-density amorphs for pure water is likely to be located at 0.22-0.23 GPa at about 150 K, which is slightly larger than the previously estimated pressure. Moreover, the solute-nature dependence on the polyamorphic transition seems to connect to that on the homogeneous nucleation temperature of polyol aqueous solution at ambient pressure. The region in which a low-density liquid appears coincides with the region in which the nucleus of ice Ih appears, suggesting that the formation of a low-density liquid is a precursory phenomenon of the nucleation of ice Ih.

  12. Effect of solute nature on the polyamorphic transition in glassy polyol aqueous solutions

    Science.gov (United States)

    Suzuki, Yoshiharu

    2017-08-01

    I examined the polyamorphic behavior of glassy dilute aqueous solutions of polyols (ethylene glycol, glycerol, meso-erythritol, xylitol, and D-sorbitol) under pressure at low temperatures. Although the volume change of the glassy aqueous solution varied continuously against pressure, the rate of the volume change appeared to vary discontinuously at the onset pressure of the gradual polyamorphic transition. It is thought that low-density liquid-like solvent water and high-density liquid-like solvent water coexist during the transition. Moreover, the existence of a solute induces the shift of polyamorphic transition to the lower-pressure side. The effect of a solute on the polyamorphic transition becomes larger in the order ethylene glycol, glycerol, meso-erythritol, xylitol, and D-sorbitol. Therefore, the solute can become a variable controlling the polyamorphic state of liquid water. This experimental result suggests that the metastable-equilibrium phase boundary between the low-density and the high-density amorphs for pure water is likely to be located at 0.22-0.23 GPa at about 150 K, which is slightly larger than the previously estimated pressure. Moreover, the solute-nature dependence on the polyamorphic transition seems to connect to that on the homogeneous nucleation temperature of polyol aqueous solution at ambient pressure. The region in which a low-density liquid appears coincides with the region in which the nucleus of ice Ih appears, suggesting that the formation of a low-density liquid is a precursory phenomenon of the nucleation of ice Ih.

  13. Electroanalytical performance of carbon films with near-atomic flatness.

    Science.gov (United States)

    Ranganathan, S; McCreery, R L

    2001-03-01

    Physicochemical and electrochemical characterization of carbon films obtained by pyrolyzing a commercially available photoresist has been performed. Photoresist spin-coated on to a silicon wafer was pyrolyzed at 1,000 degrees C in a reducing atmosphere (95% nitrogen and 5% hydrogen) to produce conducting carbon films. The pyrolyzed photoresist films (PPF) show unusual surface properties compared to other carbon electrodes. The surfaces are nearly atomically smooth with a root-mean-square roughness of carbon atomic ratio compared to conventional glassy carbon and show relatively weak adsorption of methylene blue and anthraquinone-2,6-disulfonate. The low oxygen/carbon ratio and the relative stability of PPF indicate that surfaces may be partially hydrogen terminated. The pyrolyzed films were compared to glassy carbon (GC) heat treated under the same conditions as pyrolysis to evaluate the electroanalytical utility of PPF. Heterogeneous electron-transfer kinetics of various redox systems were evaluated. For Ru(NH3)6(3+/2+), Fe(CN)6(3-/4-), and chlorpromazine, fresh PPF surfaces show electron-transfer rates similar to those on GC, but for redox systems such as Fe3+/2+, ascorbic acid, dopamine, and oxygen, the kinetics on PPF are slower. Very weak interactions between the PPF surface and these redox systems lead to their slow electron-transfer kinetics. Electrochemical anodization results in a simultaneous increase in background current, adsorption, and electron-transfer kinetics. The PPF surfaces can be chemically modified via diazonium ion reduction to yield a covalently attached monolayer. Such a modification could help in the preparation of low-cost, high-volume analyte-specific electrodes for diverse electroanalytical applications. Overall, pyrolysis of the photoresist yields an electrode surface with properties similar to a very smooth version of glassy carbon, with some important differences in surface chemistry.

  14. Dynamic Raman Spectroelectrochemistry of Single Walled Carbon Nanotubes modified electrodes using a Langmuir-Schaefer method

    OpenAIRE

    Ibáñez, David; Romero, Edna Cecilia; Colina, Álvaro; Heras, Aránzazu

    2014-01-01

    Raman spectroelectrochemistry is a fundamental technique to characterize single walled carbon nanotube (SWCNT) films. In this work, we have performed the study of SWCNT films transferred to a glassy carbon electrode using a Langmuir-Schaefer method. Langmuir balance has allowed us to control the characteristics of the film that can be easily transferred to the electrode support. Time-resolved Raman spectroelectrochemistry experiments at scan rates between 20 and 400 mV s−1 were done in two di...

  15. The selective electrochemical detection of homocysteine in the presence of glutathione, cysteine, and ascorbic acid using carbon electrodes.

    Science.gov (United States)

    Lee, P T; Lowinsohn, D; Compton, R G

    2014-08-07

    The detection of homocysteine, HCys, was achieved with the use of catechol via 1,4-Michael addition reaction using carbon electrodes: a glassy carbon electrode and a carbon nanotube modified glassy carbon electrode. The selective detection of homocysteine was investigated and achieved in the absence and presence of glutathione, cysteine and ascorbic acid using cyclic voltammetry and square wave voltammetry. A calibration curve of homocysteine detection was determined and the sensitivity is (0.20 ± 0.02) μA μM(-1) and the limit of detection is 660 nM within the linear range. Lastly, commercially available multi walled carbon nanotube screen printed electrodes were applied to the system for selective homocysteine detection. This work presents a potential practical application towards medical applications as it can be highly beneficial towards quality healthcare management.

  16. Iridium and ruthenium complexes covalently bonded to carbon surfaces by means of electrochemical oxidation of aromatic amines

    Czech Academy of Sciences Publication Activity Database

    Sandroni, M.; Volpi, G.; Fiedler, Jan; Buscaino, R.; Viscardi, G.; Milone, L.; Gobetto, R.; Nervi, C.

    2010-01-01

    Roč. 158, 1-2 (2010), s. 22-28 ISSN 0920-5861 R&D Projects: GA ČR GA203/09/0705 Institutional research plan: CEZ:AV0Z40400503 Keywords : functionalization * glassy carbon electrode * metallorganic complexes * cyclic voltammetry Subject RIV: CG - Electrochemistry Impact factor: 2.993, year: 2010

  17. SU-8 Photolithography as a Toolbox for Carbon MEMS

    Directory of Open Access Journals (Sweden)

    Rodrigo Martinez-Duarte

    2014-09-01

    Full Text Available The use of SU-8 as precursor for glass-like carbon, or glassy carbon, is presented here. SU-8 carbonizes when subject to high temperature under inert atmosphere. Although epoxy-based precursors can be patterned in a variety of ways, photolithography is chosen due to its resolution and reproducibility. Here, a number of improvements to traditional photolithography are introduced to increase the versatility of the process. The shrinkage of SU-8 during carbonization is then detailed as one of the guidelines necessary to design carbon patterns. A couple of applications—(1 carbon-electrode dielectrophoresis for bioparticle manipulation; and (2 the use of carbon structures as micro-molds are also presented.

  18. Glass-like carbon, pyrolytic graphite or nanostructured carbon for electrochemical sensing of bismuth ion?

    Directory of Open Access Journals (Sweden)

    Jadranka Milikić

    2016-06-01

    Full Text Available Different carbon electrodes were explored for application in electroanalysis, namely for sensing of bismuth ion as model analyte. Carbon materials tested included glassy carbon, basal and edge plane pyrolytic graphite, as well as nanostructured carbonized polyaniline prepared in the presence of 3,5-dinitrosalicylic acid. Bismuth ion was chosen as model analyte as protocol for its detection and quantifications is still to be determined. Herein, anodic stripping voltammetry was used with study of effect of several parameters such as scan rate and deposition time. Electrode based on carbonized polyaniline showed the highest activity for bismuth ion sensing in terms of the highest current densities recorded both in a laboratory and in real sample, while basal plane pyrolytic graphite electrode gave the lowest limit of detection.

  19. VNIR reflectance spectroscopy of glassy igneous material with variable oxidation states

    Science.gov (United States)

    Carli, Cristian; Di Genova, Danilo; Roush, Ted L.; Ertel-Ingrisch, Werner; Capaccioni, Fabrizio; Dingwell, Donald B.

    2017-04-01

    Silicate glasses with igneous compositions may represent an abundant component of planetary surface material via effusive volcanism or impact cratering processes. Several planetary surfaces are mapped with hyper-spectrometers in the visible and near-infrared (VNIR). In this spectral range, crystal field (C.F.) absorptions are useful to discriminate iron-bearing silicate components. At the same time, in the VNIR reflectance spectroscopy iron bearing glasses may exhibit a C.F. absorption at ˜1.1 μm. A weak C.F. absorption is also present at ˜1.9 μm. These absorptions can be therefore diagnostic for glassy component and can also affect the C.F. absorptions of mafic minerals when mixed in the regolith. So far, few studies investigated the spectral properties of systematic glasses compositions and at different oxygen fucacity. For these reasons studying glassy materials, and their optical constants, represents an important effort to document and to interpret, spectral features of Solar System silicate crusts where glasses are present, but may be difficult to map. In previous work Carli et al. (2016) considered the composition of glassy igneous materials produced in Earth-like atmospheric conditions (i.e. oxidized conditions). Here, we expand on that effort by including glasses formed under more reducing condition. In this study, glasses were produced at -9.3 log fO2 and 1400 ˚ C for a duration of 4 h at the Department of Earth and Environmental Sciences at the University of Munich using a gas-mixing furnace. The major element composition, sample homogeneity, and the Fe3+/Fetot. ratio of run products were analytically determined. Moreover, Raman spectra of the same samples were also acquired. Afterwards, powders were produced with nine-grain size from 250-224 μm to 50-20 μm and measured in bidirectional reflectance at Spectroscopy LABoratory (IAPS-INAF, Rome). Reflectance spectra were acquired from 0.35 to 2.5 μm with a Field-Pro Spectrometer mounted on a

  20. Mode coupling theory for nonequilibrium glassy dynamics of thermal self-propelled particles.

    Science.gov (United States)

    Feng, Mengkai; Hou, Zhonghuai

    2017-06-28

    We present a mode coupling theory study for the relaxation and glassy dynamics of a system of strongly interacting self-propelled particles, wherein the self-propulsion force is described by Ornstein-Uhlenbeck colored noise and thermal noises are included. Our starting point is an effective Smoluchowski equation governing the distribution function of particle positions, from which we derive a memory function equation for the time dependence of density fluctuations in nonequilibrium steady states. With the basic assumption of the absence of macroscopic currents and standard mode coupling approximation, we can obtain expressions for the irreducible memory function and other relevant dynamic terms, wherein the nonequilibrium character of the active system is manifested through an averaged diffusion coefficient D[combining macron] and a nontrivial structural function S 2 (q) with q being the magnitude of wave vector q. D[combining macron] and S 2 (q) enter the frequency term and the vertex term for the memory function, and thus influence both the short time and the long time dynamics of the system. With these equations obtained, we study the glassy dynamics of this thermal self-propelled particle system by investigating the Debye-Waller factor f q and relaxation time τ α as functions of the persistence time τ p of self-propulsion, the single particle effective temperature T eff as well as the number density ρ. Consequently, we find the critical density ρ c for given τ p shifts to larger values with increasing magnitude of propulsion force or effective temperature, in good accordance with previously reported simulation work. In addition, the theory facilitates us to study the critical effective temperature T for fixed ρ as well as its dependence on τ p . We find that T increases with τ p and in the limit τ p → 0, it approaches the value for a simple passive Brownian system as expected. Our theory also well recovers the results for passive systems and can be

  1. Determining the structural relaxation times deep in the glassy state of the pharmaceutical Telmisartan

    Energy Technology Data Exchange (ETDEWEB)

    Adrjanowicz, K; Paluch, M [Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland); Ngai, K L [Naval Research Laboratory, Washington, DC 20375-5320 (United States)

    2010-03-31

    By using the dielectric relaxation method proposed recently by Casalini and Roland (2009 Phys. Rev. Lett. 102 035701), we were able to determine the structural alpha-relaxation times deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy state tau{sub a}lpha is so long that it cannot be measured but tau{sub b}eta, which is usually much shorter, can be directly determined. The method basically takes advantage of the connection between the alpha-relaxation and the secondary beta-relaxation of the Johari-Goldstein kind, including a relation between their relaxation times tau{sub a}lpha and tau{sub b}eta, respectively. Thus, tau{sub a}lpha of Telmisartan were determined by monitoring the change of the dielectric beta-loss, epsilon'', with physical aging time at temperatures well below the vitrification temperature. The values of tau{sub a}lpha were compared with those expected by the coupling model (CM). Unequivocal comparison cannot be made in the case of Telmisartan because its beta-loss peak is extremely broad, and the CM predicts only an order of magnitude agreement between the primitive relaxation frequency and the beta-peak frequency. We also made an attempt to analyze all isothermal and aging susceptibility data after transformation into the electric modulus representation. The tau{sub a}lpha found in the glass state by using the method of Casalini and Roland in the modulus representation are similar to those obtained in the susceptibility representation. However, it is remarkable that the stretching parameter beta{sub KWWM} = 0.51 in the electric modulus representation gives more precise fits to the aging data than in the susceptibility representation with beta{sub KWW} = 0.61. Our results suggest that the electric modulus representation may be useful as an alternative to analyze aging data, especially in the case of highly polar glassformers having a large ratio of low frequency and high frequency dielectric

  2. Glassy behavior of the Nd sublattice induced by Fe doping in NdFexGa1-xO3

    International Nuclear Information System (INIS)

    Bartolome, F.; Parra-Borderias, M.; Blasco, J.; Bartolome, J.

    2007-01-01

    The evolution of the magnetic ordering of Nd with the Fe content in NdFe x Ga 1-x O 3 is studied by low-temperature specific-heat measurements for x= =0.2. Fe doping creates a distribution of internal fields on Nd, originating a Schottky contribution to the specific heat which is present for x>0. The power law followed by the low-temperature specific heat suggests a glassy behavior for x>=0.1

  3. Dielectric relaxation studies in super-cooled liquid and glassy phases of anti-cancerous alkaloid: Brucine

    Science.gov (United States)

    Afzal, Aboothahir; Shahin Thayyil, M.; Sulaiman, M. K.; Kulkarni, A. R.

    2018-05-01

    Brucine has good anti-tumor effects, on both liver cancer and breast cancer. It has bioavailability of 40.83%. Since the bioavailability of the drug is low, an alternative method to increase its bioavailability and solubility is by changing the drug into glassy form. We used Differential Scanning Calorimetry (DSC) for studying the glass forming ability of the drug. Brucine was found to be a very good glass former glass transition temperature 365 K. Based on the DSC analysis we have used broadband dielectric spectroscopy (BDS) for studying the drug in the super cooled and glassy state. BDS is an effective tool to probe the molecular dynamics in the super cooled and glassy state. Molecular mobility is found to be present even in the glassy state of this active pharmaceutical ingredient (API) which is responsible for the instability. Our aim is to study the factors responsible for instability of this API in amorphous form. Cooling curves for dielectric permittivity and dielectric loss revealed the presence of structural (α) and secondary relaxations (β and γ). Temperature dependence of relaxation time is fitted by Vogel-Fulcher-Tammann equation and found the values of activation energy of the α relaxation, fragility and glass transition temperature. Paluch's anti correlation is also verified, that the width of the α-loss peak at or near the glass transition temperature Tg is strongly anticorrelated with the polarity of the molecule. The larger the dielectric relaxation strength Δɛ (Tg) of the system, the narrower is the α-loss peak (higher value of βKWW).

  4. Dielectric relaxation studies in super-cooled liquid and glassy phases of anti-cancerous alkaloid: Brucine

    Science.gov (United States)

    Afzal, Aboothahir; Shahin Thayyil, M.; Sulaiman, M. K.; Kulkarni, A. R.

    2017-12-01

    Brucine has good anti-tumor effects, on both liver cancer and breast cancer. It has bioavailability of 40.83%. Since the bioavailability of the drug is low, an alternative method to increase its bioavailability and solubility is by changing the drug into glassy form. We used Differential Scanning Calorimetry (DSC) for studying the glass forming ability of the drug. Brucine was found to be a very good glass former glass transition temperature 365 K. Based on the DSC analysis we have used broadband dielectric spectroscopy (BDS) for studying the drug in the super cooled and glassy state. BDS is an effective tool to probe the molecular dynamics in the super cooled and glassy state. Molecular mobility is found to be present even in the glassy state of this active pharmaceutical ingredient (API) which is responsible for the instability. Our aim is to study the factors responsible for instability of this API in amorphous form. Cooling curves for dielectric permittivity and dielectric loss revealed the presence of structural (α) and secondary relaxations (β and γ). Temperature dependence of relaxation time is fitted by Vogel-Fulcher-Tammann equation and found the values of activation energy of the α relaxation, fragility and glass transition temperature. Paluch's anti correlation is also verified, that the width of the α-loss peak at or near the glass transition temperature Tg is strongly anticorrelated with the polarity of the molecule. The larger the dielectric relaxation strength Δɛ (Tg) of the system, the narrower is the α-loss peak (higher value of βKWW).

  5. Changes in the thermoelectric response of vitreous carbon due to the irradiation by γ-rays

    Science.gov (United States)

    Culebras, M.; Madroñero, A.; Mota, C.; Gómez, C. M.; Amo, Jose M.; Cantarero, A.

    2014-07-01

    In order to study variations in the thermoelectric properties, some commercial glassy carbon samples were subjected to a sequence of steps consisting of a combination of irradiation with γ-rays produced by radioisotopes 60Co, and hydrogen adsorption when the samples were put in an over pressured atmosphere of this gas. With this procedure it was possible to observe that the irradiation decreases the electrical conductivity of glassy carbon samples and the hydrogenation changes the sign of Seebeck coefficient. The material initially is an n-type semiconductor, but with hydrogenation changes to p-type semiconductor. X-ray diffraction analysis showed that the hydrogenated vitreous carbon is more amorphous than the pristine material and the γ-rays irradiation produces changes in the crystallite size and shape.

  6. FTIR and Mössbauer spectroscopic study of sodium-aluminum-iron phosphate glassy materials for high level waste immobilization

    Science.gov (United States)

    Stefanovsky, S. V.; Stefanovsky, O. I.; Remizov, M. B.; Belanova, E. A.; Kozlov, P. V.; Glazkova, Ya. S.; Sobolev, A. V.; Presniakov, I. A.; Kalmykov, S. N.; Myasoedov, B. F.

    2015-11-01

    Complex sodium-aluminum-iron phosphate glassy materials with various Al2O3 to Fe2O3 ratio containing high level waste (HLW) surrogate were characterized by X-ray diffraction and scanning electron microscopy and studied in details by Fourier transform infrared (FTIR) spectroscopy. The samples with high Al2O3 content and not containing Fe2O3 were predominantly amorphous but subjected to devitrification under annealing. Addition of B2O3 and partial Fe2O3 substitution for Al2O3 in the materials increases their resistance to devitrification whereas further substitution and NiO incorporation significantly increase the tendency to devitrification. FTIR spectra demonstrate changes in the structure of glassy materials caused by both structural variations in the anionic motif and occurrence of crystalline phases in the materials. According to Mössbauer spectroscopy data, iron in the glassy samples is present as octahedrally coordinated Fe3+ ions while in the partly devitrified samples iron is partitioned among vitreous and crystalline phases entering the vitreous phase mainly as Fe3+O6 units and crystalline phases as major Fe3+ and minor Fe2+ ions in a magnetically ordered state and participating in a "fast" electronic exchange.

  7. Investigations into crazing in glassy amorphous polymers through molecular dynamics simulations

    Science.gov (United States)

    Venkatesan, Sudarkodi; Basu, Sumit

    2015-04-01

    In many glassy amorphous polymers, localisation of deformation during loading leads to crazes. Crazes are crack like features whose faces are bridged either by fibrils or a cellular network of voids and fibrils. While formation of crazes is aided by the presence of surface imperfections and embedded dust particles, in this work, we focus on intrinsic crazes that form spontaneously in the volume of the material. We perform carefully designed molecular dynamics simulations on well equilibrated samples of a model polymer with a view to gaining insights into certain incompletely understood aspects of the crazing process. These include genesis of the early nanovoids leading to craze nucleation, mechanisms of stabilising the cellular or fibrillar structure and the competition between chain scission and chain disentanglement in causing the final breakdown of the craze. Additionally, we identify and enumerate clusters of entanglement points with high functionality as effective topological constraints on macromolecular chains. We show that regions with low density of entanglement clusters serve as sites for nanovoid nucleation under high mean stress. Growth occurs by the repeated triggering of cavitation instabilities above a growing void. The growth of the void is aided by disentanglement in and flow of entanglements away from the cavitating region. Finally, for the chain lengths chosen, scission serves to supply short chains to the growing craze but breakdown occurs by complete disentanglement of the chains. In fact, most of the energy supplied to the material seems to be used in causing disentanglements and very little energy is required to create a stable fibril.

  8. Onset of shear thinning in glassy liquids: Shear-induced small reduction of effective density.

    Science.gov (United States)

    Furukawa, Akira

    2017-01-01

    We propose a simple mechanism for describing the onset of shear thinning in a high-density glassy liquid. In a shear flow, along the compression axis, the overlap between neighboring particles is more enhanced than that at equilibrium, meaning that the "effective" size is reduced along this axis. On the other hand, along the extension axis perpendicular to the compression axis, the average structural configurations are stretched, but it does not indicate the expansion of the "effective" size itself. This asymmetric shear flow effect for particles results in a small reduction of the "effective" density. Because, in glass-forming liquids, the structural relaxation time τ_{α} strongly depends on the density ρ, even a very small reduction of the effective density should lead to a significant decrease of the relaxation time under shear flow. We predict that the crossover shear rate from Newtonian to non-Newtonian flow behaviors is given by γ[over ̇]_{c}=[ρ(∂τ_{α}/∂ρ)]^{-1}, which can be much smaller than 1/τ_{α} near the glass transition point. It is shown that this prediction is consistent with the results of molecular dynamics simulations.

  9. NQR of 35Cl nuclei in glassy solution of chlorobenzene in pyridine

    International Nuclear Information System (INIS)

    Wolfeson, A.E.; Brunetti, A.H.; Pusiol, D.J.; Pontuschka, W.M.

    1989-06-01

    Pulsed nuclear quadrupole resonance (NQR) measurements of 35 Cl nuclei were performed on 43.5 mol% chlorobenzene solution in pyridine a) in glassy state (T g =131K) after quenching in liquid nitrogen and b) in crystalline precipitate under slow cooling starting from liquid phase. In both cases the NQR lineshape (obtained with FFT method) consisted of a structure of two peaks, interpreted as contributions of two non-equivalent 35 Cl nuclei sites. A theoretical model is proposed for the lineshape analysis and the best fit parameters yield excellent agreement with experimental spectra. It is suggested that the non-equivalent sites consist of nearly parallel and anti-parallel alignement of chlorobenzene and pyridine molecules and that the line broadening mechanism is due to a random distribution of angular displacements from these positions. Our data are in agreement with Goldstein studies of molecular relaxation processes related to the changes observed on physical properties of amorphous materials at T g . (author) [pt

  10. Spinodals with Disorder: From Avalanches in Random Magnets to Glassy Dynamics

    Science.gov (United States)

    Nandi, Saroj Kumar; Biroli, Giulio; Tarjus, Gilles

    2016-04-01

    We revisit the phenomenon of spinodals in the presence of quenched disorder and develop a complete theory for it. We focus on the spinodal of an Ising model in a quenched random field (RFIM), which has applications in many areas from materials to social science. By working at zero temperature in the quasistatically driven RFIM, thermal fluctuations are eliminated and one can give a rigorous content to the notion of spinodal. We show that the latter is due to the depinning and the subsequent expansion of rare droplets. We work out the associated critical behavior, which, in any finite dimension, is very different from the mean-field one: the characteristic length diverges exponentially and the thermodynamic quantities display very mild nonanalyticities much like in a Griffith phenomenon. From the recently established connection between the spinodal of the RFIM and glassy dynamics, our results also allow us to conclusively assess the physical content and the status of the dynamical transition predicted by the mean-field theory of glass-forming liquids.

  11. Generation and extinction of crystal nuclei in an extremely non-equilibrium glassy state of salol

    CERN Document Server

    Paladi, F

    2003-01-01

    Strange generation and subsequent extinction of crystal nuclei were observed in the glassy state of salol (phenyl salicylate) during the course of ageing at very low constant-temperatures. The presence/absence of crystal nuclei within the glass were judged, by using a differential scanning calorimeter (DSC), from whether the crystal growth and fusion phenomena were observed in the following heating process or not. The liquid sample was cooled rapidly at 200 K min sup - sup 1 from 333 K above the fusion temperature down to a desired ageing temperature (T sub a) below the glass transition temperature (T sub g = 220 K), aged there for different periods (t sub a), and then heated up to 213 K at 200 K min sup - sup 1. The DSC measurement was carried out at 10 K min sup - sup 1 from 213 to 333 K. The ageing periods were taken in a range between 30 s and 316 min. At T sub a = 213 K, crystal nucleation was found to proceed for ageing longer than 100 min. No crystal nucleation was found at T sub a in between 123 and 1...

  12. Au55, a stable glassy cluster: results of ab initio calculations

    Directory of Open Access Journals (Sweden)

    Dieter Vollath

    2017-10-01

    Full Text Available Structure and properties of small nanoparticles are still under discussion. Moreover, some thermodynamic properties and the structural behavior still remain partially unknown. One of the best investigated nanoparticles is the Au55 cluster, which has been analyzed experimentally and theoretically. However, up to now, the results of these studies are still inconsistent. Consequently, we have carried out the present ab initio study of the Au55 cluster, using up-to-date computational concepts, in order to clarify these issues. Our calculations have confirmed the experimental result that the thermodynamically most stable structure is not crystalline, but it is glassy. The non-crystalline structure of this cluster was validated by comparison of the coordination numbers with those of a crystalline cluster. It was found that, in contrast to bulk materials, glass formation is connected to an energy release that is close to the melting enthalpy of bulk gold. Additionally, the surface energy of this cluster was calculated using two different theoretical approaches resulting in values close to the surface energy for bulk gold. It shall be emphasized that it is now possible to give a confidence interval for the value of the surface energy.

  13. Complex nonequilibrium dynamics of stacked polystyrene films deep in the glassy state

    Science.gov (United States)

    Boucher, Virginie M.; Cangialosi, Daniele; Alegría, Angel; Colmenero, Juan

    2017-05-01

    We investigate the kinetics of enthalpy recovery in stacked glassy polystyrene (PS) films with thickness from 30 to 95 nm over a wide temperature range below the glass transition temperature (Tg). We show that the time evolution toward equilibrium exhibits two mechanisms of recovery, in ways analogous to bulk PS. The fast mechanism, allowing partial enthalpy recovery toward equilibrium, displays Arrhenius temperature dependence with low activation energy, whereas the slow mechanism follows pronounced super-Arrhenius temperature dependence. In comparison to bulk PS, the time scales of the two mechanisms of recovery are considerably shorter and decreasing with the film thickness. Scaling of the equilibration times at various thicknesses indicates that the fast mechanism of recovery is compatible with the free volume holes diffusion model. Conversely, the slow mechanism of recovery appears to be accelerated with decreasing thickness more than predicted by the model and, therefore, its description requires additional ingredients. The implications, from both a fundamental and technological viewpoint, of the ability of thin polymer films to densify in relatively short time scales are discussed.

  14. Thermodynamic parameters of bonds in glassy materials from viscosity-temperature relationships

    International Nuclear Information System (INIS)

    Ojovan, Michael I; Travis, Karl P; Hand, Russell J

    2007-01-01

    Doremus's model of viscosity assumes that viscous flow in amorphous materials is mediated by broken bonds (configurons). The resulting equation contains four coefficients, which are directly related to the entropies and enthalpies of formation and motion of the configurons. Thus by fitting this viscosity equation to experimental viscosity data these enthalpy and entropy terms can be obtained. The non-linear nature of the equation obtained means that the fitting process is non-trivial. A genetic algorithm based approach has been developed to fit the equation to experimental viscosity data for a number of glassy materials, including SiO 2 , GeO 2 , B 2 O 3 , anorthite, diopside, xNa 2 O-(1-x)SiO 2 , xPbO-(1-x)SiO 2 , soda-lime-silica glasses, salol, and α-phenyl-o-cresol. Excellent fits of the equation to the viscosity data were obtained over the entire temperature range. The fitting parameters were used to quantitatively determine the enthalpies and entropies of formation and motion of configurons in the analysed systems and the activation energies for flow at high and low temperatures as well as fragility ratios using the Doremus criterion for fragility. A direct anti-correlation between fragility ratio and configuron percolation threshold, which determines the glass transition temperature in the analysed materials, was found

  15. Comparative classical and 'ab initio' molecular dynamics study of molten and glassy germanium dioxide

    International Nuclear Information System (INIS)

    Hawlitzky, M; Horbach, J; Binder, K; Ispas, S; Krack, M

    2008-01-01

    A molecular dynamics (MD) study of the static and dynamic properties of molten and glassy germanium dioxide is presented. The interactions between the atoms are modeled by the classical pair potential proposed by Oeffner and Elliott (OE) (1998 Phys. Rev. B 58 14791). We compare our results to experiments and previous simulations. In addition, an 'ab initio' method, the so-called Car-Parrinello molecular dynamics (CPMD), is applied to check the accuracy of the structural properties, as obtained by the classical MD simulations with the OE potential. As in a similar study for SiO 2 , the structure predicted by CPMD is only slightly softer than that resulting from the classical MD. In contrast to earlier simulations, both the static structure and dynamic properties are in very good agreement with pertinent experimental data. MD simulations with the OE potential are also used to study the relaxation dynamics. As previously found for SiO 2 , for high temperatures the dynamics of molten GeO 2 is compatible with a description in terms of mode coupling theory

  16. Quasi-elastic neutron scattering studies of the slow dynamics of supercooled and glassy aspirin.

    Science.gov (United States)

    Zhang, Yang; Tyagi, Madhusudan; Mamontov, Eugene; Chen, Sow-Hsin

    2012-02-15

    Aspirin, also known as acetylsalicylic acid (ASA), is not only a wonderful drug, but also a good glass former. Therefore, it serves as an important molecular system to study the near-arrest and arrested phenomena. In this paper, a high-resolution quasi-elastic neutron scattering (QENS) technique is used to investigate the slow dynamics of supercooled liquid and glassy aspirin from 410 down to 350 K. The measured QENS spectra can be analyzed with a stretched exponential model. We find that (i) the stretched exponent β(Q) is independent of the wavevector transfer Q in the measured Q range and (ii) the structural relaxation time τ(Q) follows a power-law dependence on Q. Consequently, the Q-independent structural relaxation time τ(0) can be extracted for each temperature to characterize the slow dynamics of aspirin. The temperature dependence of τ(0) can be fitted with the mode-coupling power law, the Vogel-Fulcher-Tammann equation and a universal equation for fragile glass forming liquids recently proposed by Tokuyama in the measured temperature range. The calculated dynamic response function χ(T)(Q, t) using the experimentally determined self-intermediate scattering function of the hydrogen atoms of aspirin shows direct evidence of the enhanced dynamic fluctuations as the aspirin is increasingly supercooled, in agreement with the fixed-time mean squared displacement ⟨x(2)⟩ and the non-Gaussian parameter α(2) extracted from the elastic scattering.

  17. Probing Stress-Induced Optical Birefringence of Glassy Polymers by Whispering Gallery Modes Light Localization.

    Science.gov (United States)

    Milenko, Karolina; Pissadakis, Stavros; Gkantzounis, Georgios; Aluculesei, Alina; Fytas, George

    2017-12-31

    An optical resonance method for the determination of the strain- and stress-optical coefficients of optically transparent polymers is presented and exemplified for monodisperse and bidisperse molecular weight polystyrene (PS). This method employs whispering gallery modes (WGMs) resonation inside a spheroid polymeric cavity, suspended on an optical fiber taper waist, which, in turn, is used for subjecting the polymeric resonator to controlled strain conditions. The wavelength shifts of equal order transverse electric and transverse magnetic polarization WGMs are measured, as well as their relative birefringence versus applied strain. For monodisperse PS microspheroids (2 and 50 kDa) the stress-optical coefficient is negative, contrary to the results for bulk PS in the glassy state indicating different phenyl group orientation of the PS monomer with respect to the strain direction. In the bidisperse (2 and 50 kDa) spheroid with a symmetric monomer composition, local structural irregularities are probably responsible for the observed coupling between WGMs. The method possesses metrological capabilities for probing the molecular orientation of polymer-based resonators.

  18. Glassy dynamics of model colloidal polymers: The effect of "monomer" size

    Science.gov (United States)

    Li, Jian; Zhang, Bo-kai; Li, Hui-shu; Chen, Kang; Tian, Wen-de; Tong, Pei-qing

    2016-05-01

    In recent years, attempts have been made to assemble colloidal particles into chains, which are termed "colloidal polymers." An apparent difference between molecular and colloidal polymers is the "monomer" size. Here, we propose a model to represent the variation from molecular polymer to colloidal polymer and study the quantitative differences in their glassy dynamics. For chains, two incompatible local length scales, i.e., monomer size and bond length, are manifested in the radial distribution function and intramolecular correlation function. The mean square displacement of monomers exhibits Rouse-like sub-diffusion at intermediate time/length scale and the corresponding exponent depends on the volume fraction and the monomer size. We find that the threshold volume fraction at which the caging regime emerges can be used as a rescaling unit so that the data of localization length versus volume fraction for different monomer sizes can gather close to an exponential curve. The increase of monomer size effectively increases the hardness of monomers and thus makes the colloidal polymers vitrify at lower volume fraction. Static and dynamic equivalences between colloidal polymers of different monomer sizes have been discussed. In the case of having the same peak time of the non-Gaussian parameter, the motion of monomers of larger size is much less non-Gaussian. The mode-coupling critical exponents for colloidal polymers are in agreement with that of flexible bead-spring chains.

  19. Hysteresis, reentrance, and glassy dynamics in systems of self-propelled rods.

    Science.gov (United States)

    Kuan, Hui-Shun; Blackwell, Robert; Hough, Loren E; Glaser, Matthew A; Betterton, M D

    2015-01-01

    Nonequilibrium active matter made up of self-driven particles with short-range repulsive interactions is a useful minimal system to study active matter as the system exhibits collective motion and nonequilibrium order-disorder transitions. We studied high-aspect-ratio self-propelled rods over a wide range of packing fractions and driving to determine the nonequilibrium state diagram and dynamic properties. Flocking and nematic-laning states occupy much of the parameter space. In the flocking state, the average internal pressure is high and structural and mechanical relaxation times are long, suggesting that rods in flocks are in a translating glassy state despite overall flock motion. In contrast, the nematic-laning state shows fluidlike behavior. The flocking state occupies regions of the state diagram at both low and high packing fraction separated by nematic-laning at low driving and a history-dependent region at higher driving; the nematic-laning state transitions to the flocking state for both compression and expansion. We propose that the laning-flocking transitions are a type of glass transition that, in contrast to other glass-forming systems, can show fluidization as density increases. The fluid internal dynamics and ballistic transport of the nematic-laning state may promote collective dynamics of rod-shaped micro-organisms.

  20. Effect of holographic grating period on its relaxation in a molecular glassy film

    International Nuclear Information System (INIS)

    Ozols, A; Augustovs, P; Kokars, V; Traskovskis, K; Saharov, D

    2013-01-01

    Holographic grating (HG) relaxation has been experimentally studied in 5,5,5-triphenylpentyl 4-((4-(bis(5,5,5-triphenylpentyl)amino) phenyl) diazenyl) benzoate molecular glassy film for HG periods (Λ) of 0.50, 2.0 and 8.6 μm. A strong effect of HG period on its relaxation is found manifesting itself differently in the volume and on the surface. The volume part of HG is fairly stable during 40 days if Λ > 0.50μm whereas the surface part of HG (most probably, surface relief grating) exhibits relaxational self-enhancement which is maximal at Λ = 8.6μm. It is proposed that thermostimulated directional mass transfer in the process of relaxation can be responsible for this relaxational self-enhancement. Weak HG recording and relatively fast HG decay takes place at Λ=0.50 μm. Therefore, effective chromophore photoorientation domain of about 0.2 μm is supposed

  1. Mechanical properties of Fe-Ni-Cr-Si-B bulk glassy alloy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kee Ahn [School of Advanced Materials Engineering, Andong National University, Andong 760-749 (Korea, Republic of)]. E-mail: keeahn@andong.ac.kr; Kim, Yong Chan [New Metals Research Team, RIST, Pohang 790-330 (Korea, Republic of); Kim, Jung Han [Center for Advanced Aerospace materials, POSTECH, Pohang 790-784 (Korea, Republic of); Lee, Chong Soo [Center for Advanced Aerospace materials, POSTECH, Pohang 790-784 (Korea, Republic of); Namkung, Jung [New Metals Research Team, RIST, Pohang 790-330 (Korea, Republic of); Kim, Moon Chul [New Metals Research Team, RIST, Pohang 790-330 (Korea, Republic of)

    2007-03-25

    The mechanical properties and crystallization behavior of new Fe-Ni-Cr-Si-B-based bulk glassy alloys were investigated. The suitability of the continuous roll casting method for the production of bulk metallic glass (BMG) sheets in such alloy systems was also examined. BMG samples (Fe-Ni-Cr-Si-B, Fe-Ni-Zr-Cr-Si-B, Fe-Ni-Zr-Cr-W-Si-B) in amorphous strip, cylindrical, and sheet forms were prepared through melt spinning, copper mold casting, and twin roll strip casting, respectively. Fe-Ni-Cr-Si-B alloy exhibited compressive strength of up to 2.93 GPa and plastic strain of about 1.51%. On the other hand, the Fe-Ni-Zr-Cr-Si-B, composite-type bulk sample with diameter of 2.0 mm showed remarkable compressive plastic strain of about 4.03%. The addition of zirconium was found to enhance the homogeneous precipitation of nanocrystalline less than 7 nm and to develop a hybrid-composite microstructure with increasing sample thickness. Twin roll strip casting was successfully applied to the fabrication of sheets in Fe-Ni-Cr-Si-B-based BMGs. The combined characteristics of high mechanical properties and ease of microstructure control proved to be promising in terms of the future progress of structural bulk amorphous alloys.

  2. Quasi-elastic neutron scattering studies of the slow dynamics of supercooled and glassy aspirin

    Science.gov (United States)

    Zhang, Yang; Tyagi, Madhusudan; Mamontov, Eugene; Chen, Sow-Hsin

    2012-02-01

    Aspirin, also known as acetylsalicylic acid (ASA), is not only a wonderful drug, but also a good glass former. Therefore, it serves as an important molecular system to study the near-arrest and arrested phenomena. In this paper, a high-resolution quasi-elastic neutron scattering (QENS) technique is used to investigate the slow dynamics of supercooled liquid and glassy aspirin from 410 down to 350 K. The measured QENS spectra can be analyzed with a stretched exponential model. We find that (i) the stretched exponent β(Q) is independent of the wavevector transfer Q in the measured Q range and (ii) the structural relaxation time τ(Q) follows a power-law dependence on Q. Consequently, the Q-independent structural relaxation time τ0 can be extracted for each temperature to characterize the slow dynamics of aspirin. The temperature dependence of τ0 can be fitted with the mode-coupling power law, the Vogel-Fulcher-Tammann equation and a universal equation for fragile glass forming liquids recently proposed by Tokuyama in the measured temperature range. The calculated dynamic response function χT(Q, t) using the experimentally determined self-intermediate scattering function of the hydrogen atoms of aspirin shows direct evidence of the enhanced dynamic fluctuations as the aspirin is increasingly supercooled, in agreement with the fixed-time mean squared displacement langx2rang and the non-Gaussian parameter α2 extracted from the elastic scattering.

  3. Quasi-Elastic Neutron Scattering Studies of the Slow Dynamics of Supercooled and Glassy Aspirin

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yang [ORNL; Tyagi, M. [NCNR and University of Maryland; Mamontov, Eugene [ORNL; Chen, Sow-hsin H [ORNL

    2011-01-01

    Aspirin, also known as acetylsalicylic acid (ASA), is not only a wonderful drug, but also a good glass former. Therefore, it serves as an important molecular system to study the near-arrest and arrested phenomena. In this paper, a high-resolution quasi-elastic neutron scattering (QENS) technique is used to investigate the slow dynamics of supercooled liquid and glassy aspirin from 410 K down to 350 K. The measured QENS spectra can be analyzed with a stretched exponential model. We find that (i) the stretched exponent (Q) is independent of the wave vector transfer Q in the measured Q-range, and (ii) the structural relaxation time (Q) follows a power law dependence on Q. Consequently, the Q-independent structural relaxation time 0 can be extracted for each temperature to characterize the slow dynamics of aspirin. The temperature dependence of 0 can be fitted with the mode coupling power law, the Vogel-Fulcher-Tammann equation and a universal equation for fragile glass forming liquids recently proposed by M. Tokuyama in the measured temperature range. The calculated dynamic response function T(Q,t) using the experimentally determined self-intermediate scattering function of the hydrogen atoms of aspirin shows a direct evidence of the enhanced dynamic fluctuations as the aspirin is increasingly supercooled, in agreement with the fixed-time mean squared displacement x2 and non-Gaussian parameter 2 extracted from the elastic scattering.

  4. New design strategy for reversible plasticity shape memory polymers with deformable glassy aggregates.

    Science.gov (United States)

    Lin, Tengfei; Tang, Zhenghai; Guo, Baochun

    2014-12-10

    Reversible plasticity shape memory (RPSM) is a new concept in the study of shape memory performance behavior and describes a phenomenon in which shape memory polymers (SMPs) can undergo a large plastic deformation at room temperature and subsequently recover their original shape upon heating. To date, RPSM behavior has been demonstrated in only a few polymers. In the present study, we implement a new design strategy, in which deformable glassy hindered phenol (AO-80) aggregates are incorporated into an amorphous network of epoxidized natural rubber (ENR) cured with zinc diacrylate (ZDA), in order to achieve RPSM properties. We propose that AO-80 continuously tunes the glass transition temperature (Tg) and improves the chain mobility of the SMP, providing traction and anchoring the ENR chains by intermolecular hydrogen bonding interactions. The RPSM behavior of the amorphous SMPs is characterized, and the results demonstrate good fixity at large deformations (up to 300%) and excellent recovery upon heating. Large energy storage capacities at Td in these RPSM materials are demonstrated compared with those achieved at elevated temperature in traditional SMPs. Interestingly, the further revealed self-healing properties of these materials are closely related to their RPSM behavior.

  5. Effect of a glassy gellan/polydextrose matrix on the activity of α-D-glucosidase.

    Science.gov (United States)

    Chaudhary, Vinita; Small, Darryl M; Kasapis, Stefan

    2013-06-05

    An investigation of the ability of the enzyme α-D-glucosidase to act on the substrate 4-nitrophenyl α-D-glucopyranoside (pNPG) while embedded in glassy carbohydrate matrices (deacylated gellan with polydextrose and polydextrose alone) is presented. Physicochemical characterisation of the matrices was achieved using the techniques of modulated differential scanning calorimetry, small deformation dynamic oscillation on shear, Fourier transform infra-red spectroscopy, wide angle X-ray diffraction and scanning electron microscopy. A UV-vis spectrophotometric procedure was adapted for the analysis of the activity of α-D-glucosidase in hydrolysing pNPG in the condensed carbohydrate systems. In order to derive a relationship between the structural properties of the matrix and the enzymatic activity, mechanical spectra were recorded using the combined framework of the Williams, Landel and Ferry equation with the time-temperature superposition principle. Theoretical modelling and experimental observations strongly argue for a pronounced effect of the gelling polysaccharide/co-solute mixture on enzymatic activity near the mechanical Tg of the matrix. Copyright © 2013. Published by Elsevier Ltd.

  6. Enhanced host–guest electrochemical recognition of herbicide MCPA using a b-cyclodextrin carbon nanotube sensor

    OpenAIRE

    Rahemi, V.; Vandamme, J.J.; Garrido, J.M.P.J.; Borges, F.; Brett, C.M.A.; Garrido, E.M.P.J.

    2012-01-01

    An electrochemical sensor for the determination of the chlorophenoxy herbicide MCPA has been developed, based on a combination of multi-walled carbon nanotubes with incorporated b-cyclodextrin and a polyaniline film modified glassy carbon electrode. The proposed molecular host–guest recogni-tion based sensor has a high electrochemical sensitivity for the determination of MCPA. The electrochemical behaviour of MCPA at the chemically modified electrode was investigated in detail by cyclic volta...

  7. Electrochemistry of parent and exo-skeletally substituted icosahedral monocarba and dicarbaboranes and their derivatives at the graphite carbon electrode in aqueous phosphate buffers

    Czech Academy of Sciences Publication Activity Database

    Fojt, Lukáš; Fojta, Miroslav; Grüner, Bohumír; Vespalec, Radim

    Roč. 730, SEP15 ( 2014 ), s. 16-19 ISSN 1572-6657 R&D Projects: GA ČR(CZ) GBP206/12/G151 Institutional support: RVO:68081707 ; RVO:61388980 Keywords : Boranes * Carboranes * Glassy carbon electrode Subject RIV: BO - Biophysics; CA - Inorganic Chemistry (UACH-T) Impact factor: 2.729, year: 2014

  8. High performance supercapacitor based on graphene-silver nanoparticles-polypyrrole nanocomposite coated on glassy carbon electrode

    Science.gov (United States)

    Kalambate, Pramod K.; Dar, Riyaz A.; Karna, Shashi P.; Srivastava, Ashwini K.

    2015-02-01

    In the current study, we present a new hybrid material of double layer capacitive material graphene (GNS), pseudo capacitive polypyrrole (PPY) and highly conducting silver nanoparticles (AgNPs). Graphene/Silver nanoparticles/polypyrrole (GNS/AgNPs/PPY) composite has been synthesized by in situ oxidative polymerization of pyrrole in the presence of GNS and AgNPs. The different mass concentrations of AgNPs were utilized to improve the capacitive performance of supercapacitor. Characterization of the electrode material has been carried out by X-ray diffraction, Raman spectroscopy, Thermal methods, Scanning electron microscopy (SEM) and Transmission electron microscopy. SEM images showed that PPY nanoparticles uniformly coated on graphene sheets along with AgNPs. Electrochemical characterization of the electrode surface has been carried out by means of cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. Remarkably, GNS/AgNPs/PPY exhibits specific capacitance of 450 F g-1 at current density of 0.9 mA g-1, which is far better than GNS/PPY (288 F g-1), AgNPs/PPY (216 F g-1) and PPY (153 F g-1). Furthermore, GNS/AgNPs/PPY shows high charge-discharge reversibility and retaining over 92.0% of its initial value after 1000 cycles. The cyclic stability of the composite is improved due to the synergistic effect of GNS, AgNPs and PPY.

  9. Study of Ag-Pd bimetallic nanoparticles modified glassy carbon electrode for detection of L-cysteine

    Science.gov (United States)

    Murugavelu, M.; Karthikeyan, B.

    2014-11-01

    Ag-Pd bimetallic nanoparticles (Ag-Pd BNPs) as an enhanced sensing material with improved electronic transmission rates in the electrochemical sensing of L-cysteine (L-cys) has been reported. The morphology of Ag-Pd BNPs was characterized with X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and cyclic voltammetry (CV). Oxidation of L-cys on Ag-Pd BNPs is investigated in detail by discussing the effect of the structure and from the electrocatalytic oxidation of L-cys. We found that the Ag-Pd BNPs exhibited high electrocatalytic activity towards L-cys oxidation in neutral condition and could be used for the development of nonenzymatic L-cys sensor. Based on the efficient catalytic ability of Ag-Pd BNPs, the fabricated biosensor exhibited a wide linear range of responses to the L-cys with the concentration detection limit of nearly down to 2 mM with fast response time.

  10. Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS).

    Science.gov (United States)

    Pramanick, Bidhan; Martinez-Chapa, Sergio O; Madou, Marc; Hwang, Hyundoo

    2017-06-17

    A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long and hollow glassy carbon microfibers derived from human hairs is introduced. The long and hollow carbon structures were made by the pyrolysis of human hair at 900 °C in a N2 atmosphere. The morphology and chemical composition of natural and pyrolyzed human hairs were investigated using scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX), respectively, to estimate the physical and chemical changes due to pyrolysis. Raman spectroscopy was used to confirm the glassy nature of the carbon microstructures. Pyrolyzed hair carbon was introduced to modify screen-printed carbon electrodes ; the modified electrodes were then applied to the electrochemical sensing of dopamine and ascorbic acid. Sensing performance of the modified sensors was improved as compared to the unmodified sensors. To obtain the desired carbon structure design, carbon micro-/nanoelectromechanical system (C-MEMS/C-NEMS) technology was developed. The most common C-MEMS/C-NEMS fabrication process consists of two steps: (i) the patterning of a carbon-rich base material, such as a photosensitive polymer, using photolithography; and (ii) carbonization through the pyrolysis of the patterned polymer in an oxygen-free environment. The C-MEMS/NEMS process has been widely used to develop microelectronic devices for various applications, including in micro-batteries, supercapacitors, glucose sensors, gas sensors, fuel cells, and triboelectric nanogenerators. Here, recent developments of a high-aspect ratio solid and hollow carbon microstructures with SU8 photoresists are discussed. The structural shrinkage during pyrolysis was investigated using confocal microscopy and SEM. Raman spectroscopy was used to confirm the crystallinity of the structure, and the atomic percentage of the elements present in the material before and after

  11. Dispersion of multi-wall carbon nanotubes in polyhistidine: Characterization and analytical applications

    International Nuclear Information System (INIS)

    Dalmasso, Pablo R.; Pedano, María L.; Rivas, Gustavo A.

    2012-01-01

    Highlights: ► Polyhistidine (Polyhis) is an efficient dispersing agent of MWCNT. ► MWCNT/Polyhis ratio and sonication time are critical variables when dispersing MWCNT. ► MWCNT–Polyhis deposited at GCE largely catalyzes the oxidation of ascorbic acid. ► GCE/MWCNT–Polyhis allows the selective and sensitive quantification of UA and Do. - Abstract: We report for the first time the use of polyhistidine (Polyhis) to efficiently disperse multiwall carbon nanotubes (MWCNTs). The optimum dispersion MWCNT–Polyhis was obtained by sonicating for 30 min 1.0 mg mL −1 MWCNTs in 0.25 mg mL −1 Polyhis solution prepared in 75:25 (v/v) ethanol/0.200 M acetate buffer solution pH 5.00. The dispersion was characterized by scanning electron microscopy, and by cyclic voltammetry and amperometry using ascorbic acid as redox marker. The modification of glassy carbon electrodes with MWCNT–Polyhis produces a drastic decrease in the overvoltage for the oxidation of ascorbic acid (580 mV) at variance with the response observed at glassy carbon electrodes modified just with Polyhis, where the charge transfer is more difficult due to the blocking effect of the polymer. The reproducibility for the sensitivities obtained after 10 successive calibration plots using the same surface was 6.3%. The MWCNT-modified glassy carbon electrode demonstrated to be highly stable since after 45 days storage at room temperature the response was 94.0% of the original. The glassy carbon electrode modified with MWCNT–Polyhis dispersion was successfully used to quantify dopamine or uric acid at nanomolar levels, even in the presence of large excess of ascorbic acid. Determinations of uric acid in human blood serum samples demonstrated a very good correlation with the value reported by Wienner laboratory.

  12. Diffusive mass transport in agglomerated glassy fallout from a near-surface nuclear test

    Science.gov (United States)

    Weisz, David G.; Jacobsen, Benjamin; Marks, Naomi E.; Knight, Kim B.; Isselhardt, Brett H.; Matzel, Jennifer E.

    2018-02-01

    Aerodynamically-shaped glassy fallout is formed when vapor phase constituents from the nuclear device are incorporated into molten carriers (i.e. fallout precursor materials derived from soil or other near-field environmental debris). The effects of speciation and diffusive transport of condensing constituents are not well defined in models of fallout formation. Previously we reported observations of diffuse micrometer scale layers enriched in Na, Fe, Ca, and 235U, and depleted in Al and Ti, at the interfaces of agglomerated fallout objects. Here, we derive the timescales of uranium mass transport in such fallout as it cools from 2500 K to 1500 K by applying a 1-dimensional planar diffusion model to the observed 235U/30Si variation at the interfaces. By modeling the thermal transport between the fireball and the carrier materials, the time of mass transport is calculated to be <0.6 s, <1 s, <2 s, and <3.5 s for fireball yields of 0.1 kt, 1 kt, 10 kt, and 100 kt respectively. Based on the calculated times of mass transport, a maximum temperature of deposition of uranium onto the carrier material of ∼2200 K is inferred (1σ uncertainty of ∼200 K). We also determine that the occurrence of micrometer scale layers of material enriched in relatively volatile Na-species as well as more refractory Ca-species provides evidence for an oxygen-rich fireball based on the vapor pressure of the two species under oxidizing conditions. These results represent the first application of diffusion-based modeling to derive material transport, thermal environments, and oxidation-speciation in near-surface nuclear detonation environments.

  13. The glassy and supercooled state of elemental sulfur: Vibrational modes, structure metastability, and polymer content

    Science.gov (United States)

    Andrikopoulos, K. S.; Kalampounias, A. G.; Falagara, O.; Yannopoulos, S. N.

    2013-09-01

    We report a detailed investigation of vibrational modes, structure, and dynamics of elemental sulfur in the glassy and the supercooled state, using Raman scattering and ab initio calculations. Polarized Raman spectra are recorded - for sulfur quenched from 473 K - over a broad temperature range from 93 K to 273 K where the supercooled liquid crystallized. The temperature induced shifts of the majority of the vibrational modes are determined and compared with the corresponding ones of crystalline sulfur. Analysis of the reduced isotropic spectra showed that the structure of the quenched product is composed of eight member rings (S8) and polymeric chains (Sμ) with a relative fraction comparable to that of the parent liquid at 473 K. Low temperature spectra, where spectral line broadening due to thermal effects is limited, revealed that two different polymeric species are present in the glass with distinct vibrational frequencies. Their interpretation was assisted by ab initio calculations used to simulate the vibrational frequencies of polymeric chains S8k (k = 1, …, 7). Theoretical results exhibit an increasing breathing mode frequency for sulfur chains up to k = 2, although it remains constant beyond the above value. The polymeric content is metastable; heating the glass above its glass transition temperature, Tg, destabilizes the chains and drives them back to the more thermodynamically stable rings. This bond interchange mechanism provides the structural origin of a secondary relaxation process in supercooled sulfur reported long ago, which has been also considered as a complication in the correct fragility estimation of this material. Finally, the Boson peak of the glass was found to exhibit strong temperature dependence even at temperatures below Tg.

  14. Sequencing and de novo assembly of the transcriptome of the glassy-winged sharpshooter (Homalodisca vitripennis.

    Directory of Open Access Journals (Sweden)

    Raja Sekhar Nandety

    Full Text Available BACKGROUND: The glassy-winged sharpshooter Homalodisca vitripennis (Hemiptera: Cicadellidae, is a xylem-feeding leafhopper and important vector of the bacterium Xylella fastidiosa; the causal agent of Pierce's disease of grapevines. The functional complexity of the transcriptome of H. vitripennis has not been elucidated thus far. It is a necessary blueprint for an understanding of the development of H. vitripennis and for designing efficient biorational control strategies including those based on RNA interference. RESULTS: Here we elucidate and explore the transcriptome of adult H. vitripennis using high-throughput paired end deep sequencing and de novo assembly. A total of 32,803,656 paired-end reads were obtained with an average transcript length of 624 nucleotides. We assembled 32.9 Mb of the transcriptome of H. vitripennis that spanned across 47,265 loci and 52,708 transcripts. Comparison of our non-redundant database showed that 45% of the deduced proteins of H. vitripennis exhibit identity (e-value ≤1(-5 with known proteins. We assigned Gene Ontology (GO terms, Kyoto Encyclopedia of Genes and Genomes (KEGG annotations, and potential Pfam domains to each transcript isoform. In order to gain insight into the molecular basis of key regulatory genes of H. vitripennis, we characterized predicted proteins involved in the metabolism of juvenile hormone, and biogenesis of small RNAs (Dicer and Piwi sequences from the transcriptomic sequences. Analysis of transposable element sequences of H. vitripennis indicated that the genome is less expanded in comparison to many other insects with approximately 1% of the transcriptome carrying transposable elements. CONCLUSIONS: Our data significantly enhance the molecular resources available for future study and control of this economically important hemipteran. This transcriptional information not only provides a more nuanced understanding of the underlying biological and physiological mechanisms that

  15. A new Phytoreovirus infecting the glassy-winged sharpshooter (Homalodisca vitripennis)

    International Nuclear Information System (INIS)

    Stenger, Drake C.; Sisterson, Mark S.; Krugner, Rodrigo; Backus, Elaine A.; Hunter, Wayne B.

    2009-01-01

    A new virus species of the genus Phytoreovirus was isolated from glassy-winged sharpshooter (GWSS), Homalodisca vitripennis Germar (Hemiptera: Cicadellidae), in California and designated here as Homalodisca vitripennis reovirus (HoVRV). Extraction of nucleic acid from GWSS adults collected from three Californian populations revealed an array of double-stranded (ds) RNA species that was soluble in 2 M LiCl and resistant to degradation upon exposure to S1 nuclease and DNase. Analysis of nucleic acid samples from single GWSS adults indicated that HoVRV dsRNA accumulated to high titer in individual insects. Double-shelled isometric virus particles purified from GWSS adults resembled those observed in thin sections of GWSS salivary glands by transmission electron microscopy. Purified HoVRV virions contained 12 dsRNA segments that, based on complete nucleotide sequences, ranged in size from 4475 to 1040 bp. Sequence comparisons indicated that the HoVRV dsRNA segments were most closely related (58.5 to 43.7% nt sequence identity) to the corresponding genome segments of Rice dwarf virus (RDV). Each HoVRV dsRNA segment encoded a single open reading frame (> 300 nts) except for segment 11, which appears to be dicistronic. Terminal nucleotide sequences of HoVRV positive-sense RNAs were similar to other phytoreoviruses (GGCG or GGCA at the 5'-end and UGAU or CGAU at the 3'-end) with adjacent imperfect inverted repeats potentially able to base pair. Phylogenetic analyses of the RNA-directed RNA polymerase (encoded by segment 1) and the outer capsid protein (encoded by segment 8) confirmed placement of HoVRV as a species of the genus Phytoreovirus sharing a most recent common ancestor with RDV. Reverse transcription-polymerase chain reaction assays revealed that HoVRV infection of GWSS in California was common and that the virus also occurred in GWSS populations from the Carolinas and Texas.

  16. Understanding the processes involved in weathering and experimental alteration of glassy materials. The case of some volcanic glasses from eastern Sicily (Italy)

    International Nuclear Information System (INIS)

    Liotta, Angelo

    2014-01-01

    The objective of this thesis is to study the effects of weathering and experimental alteration in order to understand the geochemical processes involved and the variation of mineral phases in altered natural glasses. For the first time, five samples of natural volcanic glasses having different composition were collected in eastern Sicily (Italy) in order to be artificially altered and analyzed. The study of naturally altered samples has allowed to observe the effects of weathering after a period of time corresponding to the age of the sample. Moreover, the use of samples of natural glass of volcanic origin has allowed to obtain some powder or thin plates of fresh silicate glass that have been subjected to artificial alteration in the laboratory, in order to model the geochemical processes that have occurred. Alteration experiments were conducted in pure water at 90 C; samples have been altered from 1 to 1000 days of experiment. The characterization of the samples was obtained by Raman spectroscopy, which showed the effects of the devitrification and the presence of some secondary minerals such as carbonates and anatase on the obsidian thin plates, but also phillipsite and chabazite, two varieties of zeolite usually found in the cavities of oldest basalts. Solid modifications were observed by SEM. The analysis showed the formation of several secondary minerals having a composition compatible with smectites, determined by EDS spectroscopy. All these results allow to test the geochemical modeling in the long term. Further analysis will be needed to reach a full understanding of the weathering of glassy materials. (author)

  17. Electrochemical characterisation of novel screen-printed carbon paste electrodes for voltammetric measurements

    Directory of Open Access Journals (Sweden)

    Sýs Milan

    2017-01-01

    Full Text Available This work is focused on the homemade screen-printed carbon paste electrode containing basically graphite powder (or glassy carbon powder, poly(vinylbchloride (PVC and paraffin oil. It compares the electrochemical properties of conventional carbon-based electrodes and prepared screen-printed carbon paste electrodes towards [Fe(CN6]3-/[Fe(CN6]4- and quinone/hydroquinone redox couples. Significant attention is paid to the development of the corresponding carbon inks, printing and the surface characterisation of the resulting electrodes by the scanning electron microscopy. An optimization consisted of the selection of the organic solvent, the optimal content of the used polymer with the chosen paste binder, appropriate isolation of electric contact, etc. Very similar properties of the prepared screen-printed electrodes, containing only corresponding carbon powder and 3 % PVC, with their conventional carbon paste electrode and glassy carbon-based electrodes, were observed during their characterisation. Screen-printed electrodes, with the pasting liquid usually provided satisfactory analytical data. Moreover, they can be used in the flow injection analysis and could undoubtedly replace the carbon paste grooved electrodes. It can be assumed that certain progress in the development of electrode materials was achieved by this research.

  18. NUCLEATION STUDIES OF GOLD ON CARBON ELECTRODES

    Directory of Open Access Journals (Sweden)

    S. SOBRI

    2008-04-01

    Full Text Available Interest has grown in developing non-toxic electrolytes for gold electrodeposition to replace the conventional cyanide-based bath for long term sustainability of gold electroplating. A solution containing thiosulphate and sulphite has been developed specially for microelectronics applications. However, at the end of the electrodeposition process, the spent electrolyte can contain a significant amount of gold in solution. This study has been initiated to investigate the feasibility of gold recovery from a spent thiosulphate-sulphite electrolyte. We have used flat-plate glassy carbon and graphite electrodes to study the mechanism of nucleation and crystal growth of gold deposition from the spent electrolyte. It was found that at the early stages of reduction process, the deposition of gold on glassy carbon exhibits an instantaneous nucleation of non-overlapping particles. At longer times, the particles begin to overlap and the deposition follows a classic progressive nucleation phenomenon. On the other hand, deposition of gold on graphite does not follow the classical nucleation phenomena.

  19. A wrinkling-based method for investigating glassy polymer film relaxation as a function of film thickness and temperature

    Science.gov (United States)

    Chung, Jun Young; Douglas, Jack F.; Stafford, Christopher M.

    2017-10-01

    We investigate the relaxation dynamics of thin polymer films at temperatures below the bulk glass transition Tg by first compressing polystyrene films supported on a polydimethylsiloxane substrate to create wrinkling patterns and then observing the slow relaxation of the wrinkled films back to their final equilibrium flat state by small angle light scattering. As with recent relaxation measurements on thin glassy films reported by Fakhraai and co-workers, we find the relaxation time of our wrinkled films to be strongly dependent on film thickness below an onset thickness on the order of 100 nm. By varying the temperature between room temperature and Tg (≈100 °C), we find that the relaxation time follows an Arrhenius-type temperature dependence to a good approximation at all film thicknesses investigated, where both the activation energy and the relaxation time pre-factor depend appreciably on film thickness. The wrinkling relaxation curves tend to cross at a common temperature somewhat below Tg, indicating an entropy-enthalpy compensation relation between the activation free energy parameters. This compensation effect has also been observed recently in simulated supported polymer films in the high temperature Arrhenius relaxation regime rather than the glassy state. In addition, we find that the film stress relaxation function, as well as the height of the wrinkle ridges, follows a stretched exponential time dependence and the short-time effective Young's modulus derived from our modeling decreases sigmoidally with increasing temperature—both characteristic features of glassy materials. The relatively facile nature of the wrinkling-based measurements in comparison to other film relaxation measurements makes our method attractive for practical materials development, as well as fundamental studies of glass formation.

  20. Improvement of glassy sol-gel sensors for preventive conservation of historical materials against acidity

    Directory of Open Access Journals (Sweden)

    Carmona, N.

    2007-08-01

    Full Text Available Sensors based on sol-gel glassy coatings doped with 2[4-(dimethyl-amino phenylazo] benzoic acid are able to change their optical absorption when they are submitted to different concentration of H3O+ and OH-. The sensors behaviour in field tests was studied in Cracow (Poland, varying the normal procedure of operation to improve their response. Both the sensors optical parameters and the environmental conditions (temperature, humidity, pressure, SO2 and NOx concentrations were measured. The sensors response was analysed in terms of their visible absorbance changes, which are due to local neutralisation reactions in the sensors surface by the join effect of acid pollutants and humidity. Correlations between the main acid pollutant (SO2 concentration and the sensors response are established to provide a relation between the optical absorption and the environmental pH. The sensors are able to detect and monitorise environmental acidity, as well as to alert on the pollutant concentration that may damage most of the historical materials.

    Los sensores a base de recubrimientos vítreos sol-gel dopados con ácido 2[4-(dimetil-amino fenilazo] benzoico son capaces de cambiar su absorción óptica cuando se someten a distintas concentraciones de iones H3O+ y OH-. La respuesta de los sensores en ensayos de campo se estudió en Cracovia (Polonia variando el procedimiento normal de uso, con el fin de mejorar su respuesta. Se midieron tanto los parámetros ópticos de los sensores como las condiciones ambientales (temperatura, humedad, presión y concentraciones de SO2 y de NOx. La respuesta de los sensores se analizó en términos de los cambios de su absorción visible. Dichos cambios se deben a reacciones locales de neutralización que tienen lugar en la superficie de los sensores, debido al efecto conjunto de los contaminantes de carácter ácido y a la humedad ambiental. Se establecieron correlaciones entre la concentración del contaminante