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1

Effect of carbon nano-fibers (CNFs) content on thermal and mechanical properties of CNFs/SiC nano-composites  

International Nuclear Information System (INIS)

Carbon nano-fibers dispersed ?-SiC (CNFs/SiC) nano-composites were prepared by hot-pressing via a transient eutectic phase route at 1900 C for 1 h under 20 MPa in Ar. The effects of additional CNFs content between 1 and 10 wt.% were investigated, based on densification, microstructure, thermal and mechanical properties. The CNFs/SiC nano-composites by the CNFs contents below 5 wt.% exhibited excellent relative densities over 98% with well dispersed CNFs. However, the CNFs/SiC nano-composites containing the CNFs of 10 wt.% possessed a relative density of 92%, accompanying CNFs agglomerates and many pores located inside the agglomerates. The three point bending strength gradually decreased with the increase of CNFs content, but the indentation fracture toughness increased to 5.7 MPa m1/2 by the CNFs content of 5 wt.% The thermal conductivity was enhanced with the increase of CNFs content and represented a maximum value of 80 W/mK at the CNFs content of 5 wt.%. (authors)

2

Synthesis of Carbon Nanofibers and Carbon Nanotubes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) have attracted intense research efforts with the expectation that these materials may have many unique properties and potential applications. The most promising way for large-scale synthesis of CNFs and CNTs is chemical vapor deposition (CVD). CNFs were synthesized on a series of hydrotalcite (HT) derived 77 wt.% Ni-Fe/Al2O3 catalysts in order to achieve the optimization of productivity and quality. It was found that only the Fe catalyst w...

Yu, Zhixin

2005-01-01

3

Optical properties of carbon nanofiber photonic crystals  

International Nuclear Information System (INIS)

Carbon nanofibers (CNFs) are used as components of planar photonic crystals. Square and rectangular lattices and random patterns of vertically aligned CNFs were fabricated and their properties studied using ellipsometry. We show that detailed information such as symmetry directions and the band structure of these novel materials can be extracted from considerations of the polarization state in the specular beam. The refractive index of the individual nanofibers was found to be nCNF = 4.1.

4

Optical properties of carbon nanofiber photonic crystals  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (CNFs) are used as components of planar photonic crystals. Square and rectangular lattices and random patterns of vertically aligned CNFs were fabricated and their properties studied using ellipsometry. We show that detailed information such as symmetry directions and the band structure of these novel materials can be extracted from considerations of the polarization state in the specular beam. The refractive index of the individual nanofibers was found to be n{sub CNF} = 4.1.

Rehammar, R; Kinaret, J M [Department of Applied Physics, Chalmers University of Technology, Gothenburg SE-412 96 (Sweden); Magnusson, R; Arwin, H [Department of Physics, Chemistry and Biology, Linkoeping University, Linkoeping SE-581 83 (Sweden); Fernandez-Dominguez, A I; Maier, S A [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom); Campbell, E E B, E-mail: robert.rehammar@chalmers.se [EaStCHEM, School of Chemistry, Edinburgh University, Edinburgh EH9 3JJ (United Kingdom)

2010-11-19

5

Effect of CNFs surface modification using noncovalent functionalization on electrochemical carbon corrosion in polymer electrolyte membrane fuel cells  

Energy Technology Data Exchange (ETDEWEB)

This presentation reported on a study that explored the effects of chemical oxidation of carbon nanofiber (CNF) supports on electrochemical carbon corrosion. Electrochemical carbon corrosion is known to weaken the performance of polymer electrolyte membrane (PEM) fuel cells, particularly during repeated start up/shut down procedures. The conversion of carbon to carbon dioxide (CO{sub 2}) results in a decrease of the carbon surface available for platinum (Pt) catalyst loading. As such, corrosion forces Pt particles to aggregate and reduces the electrochemically active surface area of Pt. Studies on alleviating carbon corrosion to increase the durability of PEM fuel cells have concentrated on graphitized carbon types such as CNFs and carbon nanotubes (CNTs). Due to the hydrophobic nature of the CNF and CNT supports, it is difficult to load Pt particles when preparing carbon supported Pt catalysts. The surface of CNFs and CNTs must be functionalized prior to their use as catalyst supports to control their hydrophobic properties. The hydrophobic-to-hydrophilic conversion can be made via chemical oxidation by refluxing concentrated acidic solutions which introduces oxygen-containing surface groups. Surface oxidization of CNFs and CNTs results in better deposition of metal nanoparticles. In contrast to the advantages of good dispersion, electrochemical corrosion of CNFs and CNTs after the oxidative treatment may be detrimental, particularly since water is the most critical factor for carbon corrosion. Increasing the chemical oxidation time of CNFs increases the number of surface oxygen functional groups on CNFs and, therefore, increases the hydrophilicity of the surfaces. In this study, chemical oxidation treatment promoted a homogeneous dispersion of small Pt particles and enhanced Pt content. However, the chemical oxidation of CNF accelerated the electrochemical carbon corrosion and decreased the performance of the membrane electrode assembly (MEA). It was concluded that chemical oxidation pre-treatment should be avoided when preparing CNF supported Pt catalysts because of the damaging effects on electrochemical carbon corrosion. The carbon surface was converted to hydrophilic using a non-destructive method in which an organic material was used to modify the surface. 2 refs.

Oh, H.S.; Kim, H. [Yonsei Univ., Seoul (Korea, Republic of). Dept. of Chemical and Biomolecular Engineering

2010-07-01

6

Controllable synthesis of helical, straight, hollow and nitrogen-doped carbon nanofibers and their magnetic properties  

International Nuclear Information System (INIS)

Graphical abstract: The helical, straight and hollow carbon nanofibers can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. Display Omitted Highlights: ? CNFs were synthesized via pyrolysis of acetylene on copper NPs. ? The helical, straight, hollow and N-doped CNFs can be selectively synthesized. ? The growth mechanism of different types of CNFs was proposed. -- Abstract: Carbon nanofibers (CNFs) with various morphologies were synthesized by catalytic pyrolysis of acetylene on copper nanoparticles which were generated from the in situ decomposition of copper acetylacetonate. The morphology of the pristine and acid-washed CNFs was investigated by field emission scanning electron microscope and high-resolution transmission electron microscope. Helical, straight and hollow CNFs can be selectively synthesized by adjusting either the reaction temperature or feed gas composition. The growth mechanism for these three types of CNFs was proposed.

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Strong Metal-Support Interaction: Growth of Individual Carbon Nanofibers from Amorphous Carbon Interacting with an Electron Beam.  

DEFF Research Database (Denmark)

The article discusses the growth behavior of carbon nanofibers (CNFs). It mentions that CNFs can be synthesized using methods such as arc-discharge, laser ablation and chemical vapor deposition. It further states that CNFs can be grown from a physical mixing of amorphous carbon and CGO/Ni nanoparticles, devoid of any gaseous carbon source and external heating and stimulated by an electron beam in a 300 kilo volt transmission electron microscope.

Zhang, Wei; Kuhn, Luise Theil

2013-01-01

8

Laccase biosensor based on electrospun copper/carbon composite nanofibers for catechol detection.  

Science.gov (United States)

The study compared the biosensing properties of laccase biosensors based on carbon nanofibers (CNFs) and copper/carbon composite nanofibers (Cu/CNFs). The two kinds of nanofibers were prepared by electrospinning and carbonization under the same conditions. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were employed to investigate the morphologies and structures of CNFs and Cu/CNFs. The amperometric results indicated that the Cu/CNFs/laccase(Lac)/Nafion/glass carbon electrode (GCE) possessed reliable analytical performance for the detection of catechol. The sensitivity of the Cu/CNFs/Lac/Nafion/GCE reached 33.1 ?A/mM, larger than that of CNFs/Lac/Nafion/GCE. Meanwhile, Cu/CNFs/Lac/Nafion/GCE had a wider linear range from 9.95 × 10(-6) to 9.76 × 10(-3) M and a lower detection limit of 1.18 ?M than CNFs/Lac/Nafion/GCE. Moreover, it exhibited a good repeatability, reproducibility, selectivity and long-term stability, revealing that electrospun Cu/CNFs have great potential in biosensing. PMID:24561403

Fu, Jiapeng; Qiao, Hui; Li, Dawei; Luo, Lei; Chen, Ke; Wei, Qufu

2014-01-01

9

Laccase Biosensor Based on Electrospun Copper/Carbon Composite Nanofibers for Catechol Detection  

Science.gov (United States)

The study compared the biosensing properties of laccase biosensors based on carbon nanofibers (CNFs) and copper/carbon composite nanofibers (Cu/CNFs). The two kinds of nanofibers were prepared by electrospinning and carbonization under the same conditions. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were employed to investigate the morphologies and structures of CNFs and Cu/CNFs. The amperometric results indicated that the Cu/CNFs/laccase(Lac)/Nafion/glass carbon electrode (GCE) possessed reliable analytical performance for the detection of catechol. The sensitivity of the Cu/CNFs/Lac/Nafion/GCE reached 33.1 ?A/mM, larger than that of CNFs/Lac/Nafion/GCE. Meanwhile, Cu/CNFs/Lac/Nafion/GCE had a wider linear range from 9.95 × 10?6 to 9.76 × 10?3 M and a lower detection limit of 1.18 ?M than CNFs/Lac/Nafion/GCE. Moreover, it exhibited a good repeatability, reproducibility, selectivity and long-term stability, revealing that electrospun Cu/CNFs have great potential in biosensing. PMID:24561403

Fu, Jiapeng; Qiao, Hui; Li, Dawei; Luo, Lei; Chen, Ke; Wei, Qufu

2014-01-01

10

Laccase Biosensor Based on Electrospun Copper/Carbon Composite Nanofibers for Catechol Detection  

Directory of Open Access Journals (Sweden)

Full Text Available The study compared the biosensing properties of laccase biosensors based on carbon nanofibers (CNFs and copper/carbon composite nanofibers (Cu/CNFs. The two kinds of nanofibers were prepared by electrospinning and carbonization under the same conditions. Scanning electron microscopy (SEM, X-ray diffraction (XRD and Raman spectroscopy were employed to investigate the morphologies and structures of CNFs and Cu/CNFs. The amperometric results indicated that the Cu/CNFs/laccase(Lac/Nafion/glass carbon electrode (GCE possessed reliable analytical performance for the detection of catechol. The sensitivity of the Cu/CNFs/Lac/Nafion/GCE reached 33.1 ?A/mM, larger than that of CNFs/Lac/Nafion/GCE. Meanwhile, Cu/CNFs/Lac/Nafion/GCE had a wider linear range from 9.95 × 10?6 to 9.76 × 10?3 M and a lower detection limit of 1.18 ?M than CNFs/Lac/Nafion/GCE. Moreover, it exhibited a good repeatability, reproducibility, selectivity and long-term stability, revealing that electrospun Cu/CNFs have great potential in biosensing.

Jiapeng Fu

2014-02-01

11

Change in carbon nanofiber resistance from ambient to vacuum  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electrical properties of carbon nanofibers (CNFs) can be affected by adsorbed gas species. In this study, we compare the resistance values of CNF devices in a horizontal configuration in air and under vacuum. CNFs in air are observed to possess lower current capacities compared to those in vacuum. Further, Joule heating due to current stressing can result in desorption of gas molecules responsible for carrier trapping, leading to lower resistances and higher breakdown currents in vacuum, ...

Shusaku Maeda; Patrick Wilhite; Nobuhiko Kanzaki; Toshishige Yamada; Yang, Cary Y.

2011-01-01

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Selective adhesion and mineral deposition by osteoblasts on carbon nanofiber patterns  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In an effort to develop better orthopedic implants, osteoblast (bone-forming cells) adhesion was determined on microscale patterns (30 ?m lines) of carbon nanofibers placed on polymer substrates. Patterns of carbon nanofibers (CNFs) on a model polymer (polycarbonate urethane [PCU]) were developed using an imprinting method that placed CNFs in selected regions. Results showed the selective adhesion and alignment of osteoblasts on CNF patterns placed on PCU. Results also showed greater attract...

Khang, Dongwoo; Sato, Michiko; Price, Rachel L.; Ribbe, Alexander E.; Webster, Thomas J.

2006-01-01

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Growth of bridging carbon nanofibers in cracks formed by heat-treating iron oxide thin sheets in acetylene gas  

Directory of Open Access Journals (Sweden)

Full Text Available We produced novel carbon nanofibers (CNFs by oxidizing high-purity iron foil and then carburizing it in acetylene gas flow. This formed cracks in the heat-treated iron foil with CNFs bridging the two walls of each crack. The CNFs were drawn out from the walls as the crack opened during heat treatment. This will be a new method to grow and arrange carbon nanotubes and nanosheets without using metal nanoparticles or template substrates.

Takeshi Hikata

2013-04-01

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Growth of bridging carbon nanofibers in cracks formed by heat-treating iron oxide thin sheets in acetylene gas  

Science.gov (United States)

We produced novel carbon nanofibers (CNFs) by oxidizing high-purity iron foil and then carburizing it in acetylene gas flow. This formed cracks in the heat-treated iron foil with CNFs bridging the two walls of each crack. The CNFs were drawn out from the walls as the crack opened during heat treatment. This will be a new method to grow and arrange carbon nanotubes and nanosheets without using metal nanoparticles or template substrates.

Hikata, Takeshi; Okubo, Soichiro; Higashi, Yugo; Matsuba, Teruaki; Utsunomiya, Risa; Tsurekawa, Sadahiro; Murakami, Katsuhisa; Fujita, Jun-ichi

2013-04-01

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Fabrication of Uniform Au–Carbon Nanofiber by Two-Step Low Temperature Decomposition  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper presents a facile and efficient way to prepare carbon nanofibers ornamented with Au nanoparticles (Au/CNFs). Gold nanoparticles were first deposited in the channels of an anodized aluminum oxide (AAO) membrane by thermal decomposition of HAuCl4and then carbon nanofibers were produced in the same channels loaded with the Au nanoparticles by decomposition of sucrose at 230 °C. An electron microscopy study revealed that the carbon nanofibers, ~10 nm thick and 6 ?m long, were decorat...

Lee, Myeongsoon; Hong, Seong-cheol; Kim, Don

2009-01-01

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Synthetic hierarchical nanostructures: growth of carbon nanofibers on microfibers by chemical vapor deposition  

International Nuclear Information System (INIS)

In this paper the synthesis of three-dimensional hierarchical nanostructures by pyrolysis of acetylene to grow carbon nanofibers (CNFs) on carbon microfibers (CMFs) and glass microfibers (GMFs) is reported. The morphology and structure of the as-prepared CNFs were studied by scanning electron microscopy and high-resolution transmission electron microscopy. CNFs grown on both substrates typically exhibited two types of morphology: the coil-like CNFs with frequent change in orientation and the relatively straight and long CNFs with parallel graphene sheets. The ethanol pretreatment was effective at improving the yield and distribution of the as-grown CNFs on CMFs, but showed an adverse effect to the CNF growth on GMFs. The influence of different substrates and growth temperatures on CNF morphology and the possible growth mechanism for the observed microstructures was discussed.

17

Synthesis and hydrogen storage capacity of exfoliated turbostratic carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Turbostratic carbon nanofibers (CNFs) with a rough surface, open pore walls, and a defect structure were continuously produced by the thermal decomposition of alcohol in the presence of an iron catalyst and a sulfur promoter at 1100 C under a nitrogen atmosphere in a vertical chemical vapor deposition reactor. A graphite exfoliation technique using intercalation and thermal shock was employed to expand the graphene layers of the as-produced turbostratic CNFs. The hydrogen storage capacity of the turbostratic CNF samples was measured using the volumetric method with a pressure of up to 1 MPa at 77 K. The hydrogen storage capacities of the as-produced and exfoliated turbostratic CNFs were 1.5 and 5 wt%, respectively. The defects on the surface and expandable graphitic structure are considered important keys to increasing the hydrogen uptake in turbostratic CNFs. (author)

Wu, Hung-Chih; Li, Yuan-Yao [Department of Chemical Engineering, National Chung Cheng University, Chia-Yi, 621 Taiwan (China); Sakoda, Akiyoshi [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

2010-05-15

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Boric oxide deposition on carbon nanofibers for oxidation resistance.  

Science.gov (United States)

The boric oxide deposition was performed to improve the oxidation resistivity of carbon nanofiber (CNF) from electrospinning at elevated temperatures. The stabilized electrospun polyacrylonitrile (PAN) nanofibers were coated with boric oxide, followed by heat treatment up to 1000, 1200, and 1400 degrees C in an inert nitrogen atmosphere. The relative oxidation resistance of boric oxide-coated CNFs showed oxidation resistive property, which was determined by weight loss after running a thermogravimetric analyzer (TGA) under air flow. The data were used for the calculations of activation energies through Arrhenius plot. The oxidation resistance of the boric oxide-coated CNFs was depended on the heat treatment temperature, the higher the temperature more resistive to oxidation. The boric oxide-coated CNFs showed extended oxidation resistivity as remaining 40-83% (w) of the original weight at the high temperature 1000 degrees C under air. PMID:23882810

Chae, Hyang Hoon; Kim, Bo-Hye; Yang, Kap Seung; Woo, Hee-Gweon

2013-08-01

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Electrical properties measurements on individual carbon nanofibers by scanning spreading resistance microscopy  

Science.gov (United States)

Vertically aligned 850-nm-long carbon nanofibers (CNFs) are grown on a titanium nitride (TiN) layer by a radio-frequency plasma system at 560 °C. Electrical properties of individual CNFs are statistically determined by a current sensing atomic force microscopy mode. An interpretation based on electrical contact resistance model classically used to describe macroscopic observations, combined with a semiclassical approach commonly used for such nano-objects, is proposed here to explain dispersion in obtained values. Roughness of the TiN layer is responsible for this dispersion by varying contact surface between CNF and the TiN layer, while interface oxidation equally affects the transport by adding a barrier at the interface. Some CNFs exhibit very low resistances (few kilohms), implying that good contact is obtained between the nanofiber and the substrate, while others CNFs exhibit high resistance, attributed to local poor electrical contacts between CNFs and TiN layer.

Fourdrinier, L.; Le Poche, H.; Chevalier, N.; Mariolle, D.; Rouviere, E.

2008-12-01

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Control of carbon nanostructure: From nanofiber toward nanotube and back  

International Nuclear Information System (INIS)

The unique properties of carbon nanofibers (CNFs) make them attractive for numerous applications ranging from field emitters to biological probes. In particular, it is the deterministic synthesis of CNFs, which requires precise control over geometrical characteristics such as location, length, diameter, and alignment, that enables the diverse applications. Catalytic plasma enhanced chemical vapor deposition of vertically aligned CNFs is a growth method that offers substantial control over the nanofiber geometry. However, deterministic synthesis also implies control over the nanofiber's physical and chemical properties that are defined by internal structure. Until now, true deterministic synthesis has remained elusive due to the lack of control over internal graphitic structure. Here we demonstrate that the internal structure of CNFs can be influenced by catalyst preparation and ultimately defined by growth conditions. We have found that when the growth rate is increased by 100-fold, obtained through maximized pressure, plasma power, and temperature, the resulting nanofibers have an internal structure approaching that of multiwalled nanotubes. We further show that the deliberate modulation of growth parameters results in modulation of CNF internal structure, and this property has been used to control the CNF surface along its length for site specific chemistry and electrochemistry

 
 
 
 
21

Control of carbon nanostructure: from nanofiber toward nanotube and back  

Energy Technology Data Exchange (ETDEWEB)

The unique properties of carbon nanofibers (CNFs) make them attractive for numerous applications ranging from field emitters to biological probes. In particular, it is the deterministic synthesis of CNFs, which requires precise control over geometrical characteristics such as location, length, diameter and alignment, that enables the diverse applications. Catalytic plasma enhanced chemical vapor deposition of vertically aligned carbon nanofibers is a growth method that offers substantial control over the nanofiber geometry. However, deterministic synthesis also implies control over the nanofiber's physical and chemical properties that are defined by internal structure. Until now, true deterministic synthesis has remained elusive due to the lack of control over internal graphitic structure. Here we demonstrate that the internal structure of CNFs can be influenced by catalyst preparation and ultimately defined by growth conditions. We have found that when the growth rate is increased by 100-fold, obtained through maximized pressure, plasma power and temperature, the resulting nanofibers have an internal structure approaching that of multi-walled nanotubes. We further show that the deliberate modulation of growth parameters results in modulation of CNF internal structure, and this property has been used to control the CNF surface along its length for site specific chemistry and electrochemistry.

Melechko, Anatoli Vasilievich [ORNL; Klein, Kate L [ORNL; Fowlkes, Jason Davidson [ORNL; Hensley, Dale K [ORNL; Rack, P. D. [University of Tennessee, Knoxville (UTK); Merkulov, Igor A [ORNL; Horton Jr, Joe A [ORNL; Simpson, Michael L [ORNL

2007-01-01

22

Catalytic growth of carbon nanofibers on Cr nanoparticles on a carbon substrate: adsorbents for organic dyes in water  

Energy Technology Data Exchange (ETDEWEB)

We have produced carbon nanofibers (CNFs) using leather waste that had been tanned with a chromium bath, and when dried contained Cr{sub 2}O{sub 3}. Suitable reduction processing produced a carbon substrate with supported nanoparticles of chromium metal. Powder X-ray diffraction showed that the Cr{sub 2}O{sub 3} is reduced on the carbon surface to produce CrC and metal Cr, which is the effective catalyst for the CNFs growth. The CNF arrays were confirmed by TEM images. Raman data revealed that the synthesized CNFs have a poor-quality graphite structure which favors their use in adsorption processes. These CNFs presented higher affinity to adsorb anionic dyes, whereas the cationic dyes are better adsorbed on the carbon substrate. The low-cost and availability of the carbon precursor makes their potential use to produce CNFs of interest.

Alves de Oliveira, Luiz Carlos, E-mail: luizoliveira@qui.ufmg.br; Candido da Silva, Adilson; Rodrigues Teixeira Machado, Alan [ICEx, Universidade Federal de Minas Gerais, Departamento de Quimica (Brazil); Diniz, Renata [Universidade Federal de Juiz de Fora, Departamento de Quimica (Brazil); Cesar Pereira, Marcio [Universidade Federal dos Vales do Jequitinhonha e Mucuri, Instituto de Ciencia, Engenharia e Tecnologia (Brazil)

2013-05-15

23

Catalytic growth of carbon nanofibers on Cr nanoparticles on a carbon substrate: adsorbents for organic dyes in water  

International Nuclear Information System (INIS)

We have produced carbon nanofibers (CNFs) using leather waste that had been tanned with a chromium bath, and when dried contained Cr2O3. Suitable reduction processing produced a carbon substrate with supported nanoparticles of chromium metal. Powder X-ray diffraction showed that the Cr2O3 is reduced on the carbon surface to produce CrC and metal Cr, which is the effective catalyst for the CNFs growth. The CNF arrays were confirmed by TEM images. Raman data revealed that the synthesized CNFs have a poor-quality graphite structure which favors their use in adsorption processes. These CNFs presented higher affinity to adsorb anionic dyes, whereas the cationic dyes are better adsorbed on the carbon substrate. The low-cost and availability of the carbon precursor makes their potential use to produce CNFs of interest.

24

Production of Carbon Nanofibers Using a CVD Method with Lithium Fluoride as a Supported Cobalt Catalyst  

Directory of Open Access Journals (Sweden)

Full Text Available Carbon nanofibers (CNFs have been synthesized in high yield (>70% by catalytic chemical vapor deposition (CCVD on Co/LiF catalyst using acetylene as carbon source. A novel catalyst support (LiF is reported for the first time as an alternative for large-scale production of carbon nanofibers while purification process of nanofibers is easier. In our experiment, the sealed furnace was heated at 700∘C for 0.5 hour (the heating rate was 10∘C/min and then cooled to room temperature in the furnace naturally. Catalytic chemical vapor deposition is of interest for fundamental understanding and improvement of commercial synthesis of carbon nanofibers (CNFs. The obtained sample was sequentially washed with ethanol, dilutes acid, and distilled water to remove residual impurities, amorphous carbon materials, and remaining of catalyst, and then dried at 110∘C for 24 hours. The combined physical characterization through several techniques, such as high-resolution transmission electron microscope (TEM, scanning electron microscope (SEM, thermogarvimetric analysis (TGA, and zeta-sizer and Raman spectroscopy, allows determining the geometric characteristic and the microstructure of individual carbon nanofibers. Catalytic chemical vapor deposition is of interest for fundamental understanding and improvement of commercial synthesis of carbon nanofibers (CNFs. As a matter of fact, the method of CCVD guarantees the production of CNFs for different applications.

S. A. Manafi

2008-02-01

25

Fabrication of double-tubular carbon nanofibers using quadruple coaxial electrospinning.  

Science.gov (United States)

This work reports the fabrication of double-tubular (or tube-in-tube) carbon nanofibers (CNFs). Tetra-layered nanofibers were manufactured using coaxial electrospinning with a concentric quadruple cylindrical nozzle system. Subsequent heat treatment eroded the first and third layers and converted the second and fourth layers into the carbonized structure, resulting in double-tubular CNFs. The morphologies and microstructures of the two tubes in the CNFs were investigated, revealing that the outer layer possessed denser and higher quality carbon crystals due to the coaxial electrospinning mechanism. Nanoparticles were readily incorporated between the two tubes in the double-tubular CNFs, providing a method for developing new multi-functional one dimensional materials. PMID:25361215

Lee, Byoung-Sun; Yang, Ho-Sung; Yu, Woong-Ryeol

2014-11-21

26

One-step catalytic growth of carbon nanofiber arrays vertically aligned on carbon substrate  

International Nuclear Information System (INIS)

Highlights: ? Acetylene as carbon resource and copper foil as catalyst. ? Three carbon nanostructures are synthesized by modulating feeding gas compositions. ? NH3 is a key factor in the growth of VA-CNF arrays. -- Abstract: Vertically aligned carbon nanofiber (VA-CNF) arrays on carbon substrate have been synthesized via one-step chemical vapor deposition process on copper foil, by using acetylene as carbon resource. Three types of carbon nanostructures, viz. bare carbon films, CNFs and VA-CNFs grown on carbon substrate, could be selectively synthesized by only modulating the concentration of C2H2 and NH3 in the feeding gases. It was found that NH3 was a key factor in the growth of VA-CNF arrays, which could increase the diffusion capability of copper atoms in carbon materials, therefore promote forming larger spherical Cu NPs catalysts for the growth of VA-CNFs. Furthermore, a growth mechanism in different feeding gas compositions was proposed.

27

A catechol biosensor based on electrospun carbon nanofibers.  

Science.gov (United States)

Carbon nanofibers (CNFs) were prepared by combining electrospinning with a high-temperature carbonization technique. And a polyphenol biosensor was fabricated by blending the obtained CNFs with laccase and Nafion. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscope (FE-SEM) were, respectively, employed to investigate the structures and morphologies of the CNFs and of the mixtures. Cyclic voltammetry and chronoamperometry were employed to study the electrocatalysis of the catechol biosensor. The results indicated that the sensitivity of the biosensor was 41 µA·mM(-1), the detection limit was 0.63 µM, the linear range was 1-1310 µM and the response time was within 2 seconds, which excelled most other laccase-based biosensor reported. Furthermore, the biosensor showed good repeatability, reproducibility, stability and tolerance to interferences. This novel biosensor also demonstrated its promising application in detecting catechol in real water samples. PMID:24778958

Li, Dawei; Pang, Zengyuan; Chen, Xiaodong; Luo, Lei; Cai, Yibing; Wei, Qufu

2014-01-01

28

Electron gun using carbon-nanofiber field emitter  

Science.gov (United States)

An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10CNFs was estimated to be D <50?m in diameter. Superior performance was realized by using CNFs with larger fiber radii (100-500nm) grown sparsely on the metal tips, which were installed in a holder at the short length L =0.5mm.

Sakai, Y.; Haga, A.; Sugita, S.; Kita, S.; Tanaka, S.-I.; Okuyama, F.; Kobayashi, N.

2007-01-01

29

Bulk scale production of carbon nanofibers in an economical way  

Science.gov (United States)

An economical route for the scalable production of carbon nanofibers (CNFs) on a sodium chloride support has been developed. CNFs have been synthesized by chemical vapor deposition (CVD) method by using metal formate as catalyst precursors at 680°C. Products were characterized by SEM, TEM, Raman spectroscopy and XRD method. By thermal analysis, the purity of the as grown products and purified products were determined. This method avoids calcination and reduction process which was employed in commercial catalysts such as metal oxide or nitrate. The problems such as detrimental effect, environmental and even cost have been overcome by using sodium chloride as support. The yield of CNFs up to 7800 wt.% relative to the nickel catalyst has been achieved in the growth time of 15 min. The advantage of this synthesis technique is the simplicity and use of easily available low cost precursors.

Rajarao, Ravindra; Bhat, Badekai Ramachandra

2012-12-01

30

Electron gun using carbon-nanofiber field emitter  

International Nuclear Information System (INIS)

An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10< E<20 keV were focused by the electrostatic lens and impinged on a W target for x-ray radiography. Analyzing the recorded x-ray radiographs, the focal spot size of the electron beam extracted from the CNFs was estimated to be D<50 ?m in diameter. Superior performance was realized by using CNFs with larger fiber radii (100-500 nm) grown sparsely on the metal tips, which were installed in a holder at the short length L=0.5 mm

31

Characterization of field-electron emission from carbon nanofibers grown on Pd wire  

Science.gov (United States)

Field-electron emission from carbon nanofibers (CNFs) on Pd wires of 50?m in diameter was extensively studied in ultrahigh vacuum ambience by measuring current-voltage curves and stability over time. The CNFs, grown by plasma-enhanced chemical vapor deposition, were aligned perpendicular to the wire and were topped with a faceted single crystal of Pd. The emission from the CNFs was characterized by remarkable stability over a long time (600 h), and exhibited a maximum current of I=1.3mA. The maximum current corresponds to a current density of J?0.6A/cm2 when estimated considering only the geometrical emitting area.

Kita, S.; Sakai, Y.; Fukushima, T.; Mizuta, Y.; Ogawa, A.; Senda, S.; Okuyama, F.

2004-11-01

32

Graphene nanoribbons hybridized carbon nanofibers: remarkably enhanced graphitization and conductivity, and excellent performance as support material for fuel cell catalysts  

Science.gov (United States)

High electronic conductivity of the support material and uniform distribution of the catalyst nanoparticles (NPs) are extremely desirable for electrocatalysts. In this paper, we present our recent progress on electrocatalysts for fuel cells with simultaneously improved conductivity of the supporting carbon nanofibers (CNFs) and distribution of platinum (Pt) NPs through facile incorporation of graphene nanoribbons (GNRs). Briefly, GNRs were obtained by the cutting and unzipping of multiwalled carbon nanotubes (MWCNTs) and subsequent thermal reduction and were first used as novel nanofillers in CNFs towards high performance support material for electrocatalysis. Through electrospinning and carbonization processes, GNR embedded carbon nanofibers (G-CNFs) with greatly enhanced graphitization and electronic conductivity were synthesized. Chemical deposition of Pt NPs onto G-CNFs generated a new Pt-G-CNF hybrid catalyst, with homogeneously distributed Pt NPs of ~3 nm. Compared to Pt-CNF (Pt on pristine CNFs) and Pt-M-CNF (Pt on MWCNT embedded CNFs), Pt-G-CNF hybrids exhibit significantly improved electrochemically active surface area (ECSA), better CO tolerance for electro-oxidation of methanol and higher electrochemical stability, testifying G-CNFs are promising support materials for high performance electrocatalysts for fuel cells.High electronic conductivity of the support material and uniform distribution of the catalyst nanoparticles (NPs) are extremely desirable for electrocatalysts. In this paper, we present our recent progress on electrocatalysts for fuel cells with simultaneously improved conductivity of the supporting carbon nanofibers (CNFs) and distribution of platinum (Pt) NPs through facile incorporation of graphene nanoribbons (GNRs). Briefly, GNRs were obtained by the cutting and unzipping of multiwalled carbon nanotubes (MWCNTs) and subsequent thermal reduction and were first used as novel nanofillers in CNFs towards high performance support material for electrocatalysis. Through electrospinning and carbonization processes, GNR embedded carbon nanofibers (G-CNFs) with greatly enhanced graphitization and electronic conductivity were synthesized. Chemical deposition of Pt NPs onto G-CNFs generated a new Pt-G-CNF hybrid catalyst, with homogeneously distributed Pt NPs of ~3 nm. Compared to Pt-CNF (Pt on pristine CNFs) and Pt-M-CNF (Pt on MWCNT embedded CNFs), Pt-G-CNF hybrids exhibit significantly improved electrochemically active surface area (ECSA), better CO tolerance for electro-oxidation of methanol and higher electrochemical stability, testifying G-CNFs are promising support materials for high performance electrocatalysts for fuel cells. Electronic supplementary information (ESI) available: Experimental Section; IR; Raman spectra. See DOI: 10.1039/c3nr04663j

Wang, Chaonan; Gao, Hongrong; Li, Hong; Zhang, Yiren; Huang, Bowen; Zhao, Junhong; Zhu, Yan; Yuan, Wang Zhang; Zhang, Yongming

2014-01-01

33

Fabrication of a carbon nanofiber sheet as a micro-porous layer for proton exchange membrane fuel cells  

Energy Technology Data Exchange (ETDEWEB)

A carbon nanofiber sheet (CNFS) has been prepared by electrospinning, stabilisation and subsequent carbonisation processes. Imaging with scanning electron microscope (SEM) indicates that the CNFS is formed by nonwoven nanofibers with diameters between 400 and 700 nm. The CNFS, with its three-dimensional pores, shows excellent electrical conductivity and hydrophobicity. In addition, it is found that the CNFS can be successfully applied as a micro-porous layer (MPL) in the cathode gas diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC). The GDL with the CNFS as a MPL has higher gas permeability than a conventional GDL. Moreover, the resultant cathode GDL exhibits excellent fuel cell performance with a higher peak power density than that of a cathode GDL fabricated with a conventional MPL under the same test condition. (author)

Duan, Qiongjuan; Wang, Jiong; Lu, Yonggen [College of Material Science and Engineering, Donghua University, Shanghai 201620 (China); Wang, Biao; Wang, Huaping [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University, Shanghai 201620 (China); College of Material Science and Engineering, Donghua University, Shanghai 201620 (China)

2010-12-15

34

Chlorine effect on the formation of carbon nanofibers.  

Science.gov (United States)

Platelet graphite nanofibers (GNFs) and turbostratic carbon nanofibers (CNFs) are synthesized by the thermal evaporation and decomposition of a polymer-based mixture at 700 degrees C using Ni as a catalyst. The mixture consists of poly(ethylene glycol) (PEG), serving as the carbon source, and hydrochloric acid solution (HCl(aq)), serving as the promoter/additive for the growth of CNFs. High-purity zigzag-shaped platelet GNFs form with 10 wt% HCl(aq) as an additive in the PEG. The diameters of the platelet GNFs are in the range of 40-60 nm, with lengths of a few micrometers. High-resolution transmission electron microscopy images indicate a high degree of graphitization and well ordered graphene layers along the fiber axis. In contrast, high-purity turbostratic CNFs form with 20 wt% HCl(aq) in the PEG. The diameter and length of the turbostratic CNFs are 20-40 nm and a few micrometers, respectively. The participation of HCl in the thermal process leads to the formation of Ni-Cl compounds. The amount of chlorine affects the shape of the Ni catalyst, which determines the type of CNF formed. PMID:23447943

Lin, Wang-Hua; Takahashi, Yusuke; Li, Yuan-Yao; Sakoda, Akiyoshi

2012-12-01

35

Electrochemical catalytic activity for oxygen reduction reaction of nitrogen-doped carbon nanofibers.  

Science.gov (United States)

The electrocatalytic activity of nitrogen-doped carbon nanofibers (N-CNFs), which are synthesized directly from vaporized acetonitrile over nickel-iron based catalysts, for oxygen reduction reaction (ORR), was investigated. The nitrogen content and specific surface area of N-CNFs can be controlled through the synthesis temperature (300-680 degrees C). The graphitization degree of N-CNFs also are significantly affected by the temperature, whereas the chemical compositions of nitrogen species are similar irrespective of the synthesis conditions. From measurement of the electrochemical double layer capacitance, the surface of N-CNFs is found to have stronger interaction with ions than undoped-carbon surfaces. Although N-CNFs show higher over-potential than Pt catalysts do, N-CNFs were observed to have a noticeable ORR activity, as opposed to the carbon samples without nitrogen doping. The activity dependency of N-CNFs on the content of the nitrogen with which they were doped is discussed, based on the experiment results. The single cell of the direct methanol fuel cell (DMFC) was tested to investigate the performance of a membrane-electrode assembly that includes N-CNFs as the cathode catalyst layer. PMID:22121714

Kim, Jiyoung; Lim, Seongyop; Kim, Sang-Kyung; Peck, Dong-Hyun; Lee, Byungrok; Yoon, Seong-Ho; Jung, Doohwan

2011-07-01

36

Use of facile mechanochemical method to functionalize carbon nanofibers with nanostructured polyaniline and their electrochemical capacitance  

Science.gov (United States)

A facile approach to functionalize carbon nanofibers [CNFs] with nanostructured polyaniline was developed via in situ mechanochemical polymerization of polyaniline in the presence of chemically treated CNFs. The nanostructured polyaniline grafting on the CNF was mainly in a form of branched nanofibers as well as rough nanolayers. The good dispersibility and processability of the hybrid nanocomposite could be attributed to its overall nanostructure which enhanced its accessibility to the electrolyte. The mechanochemical oxidation polymerization was believed to be related to the strong Lewis acid characteristic of FeCl3 and the Lewis base characteristic of aniline. The growth mechanism of the hierarchical structured nanofibers was also discussed. After functionalization with the nanostructured polyaniline, the hybrid polyaniline/CNF composite showed an enhanced specific capacitance, which might be related to its hierarchical nanostructure and the interaction between the aromatic polyaniline molecules and the CNFs.

Du, Xusheng; Liu, Hong-Yuan; Cai, Guipeng; Mai, Yiu-Wing; Baji, Avinash

2012-02-01

37

Synthesis of nitrogen-doped porous carbon nanofibers as an efficient electrode material for supercapacitors.  

Science.gov (United States)

Supercapacitors (also known as ultracapacitors) are considered to be the most promising approach to meet the pressing requirements of energy storage. Supercapacitive electrode materials, which are closely related to the high-efficiency storage of energy, have provoked more interest. Herein, we present a high-capacity supercapacitor material based on the nitrogen-doped porous carbon nanofibers synthesized by carbonization of macroscopic-scale carbonaceous nanofibers (CNFs) coated with polypyrrole (CNFs@polypyrrole) at an appropriate temperature. The composite nanofibers exhibit a reversible specific capacitance of 202.0 F g(-1) at the current density of 1.0 A g(-1) in 6.0 mol L(-1) aqueous KOH electrolyte, meanwhile maintaining a high-class capacitance retention capability and a maximum power density of 89.57 kW kg(-1). This kind of nitrogen-doped carbon nanofiber represents an alternative promising candidate for an efficient electrode material for supercapacitors. PMID:22769051

Chen, Li-Feng; Zhang, Xu-Dong; Liang, Hai-Wei; Kong, Mingguang; Guan, Qing-Fang; Chen, Ping; Wu, Zhen-Yu; Yu, Shu-Hong

2012-08-28

38

Study on mechanical, morphological and electrical properties of carbon nanofiber/polyetherimide composites  

International Nuclear Information System (INIS)

Polyetherimide (PEI) and carbon nanofiber (CNF) composites have been developed successfully by using a Sigma high temperature internal mixer and then compression molded. The amount of carbon nanofibers used was 1-3 phr (parts per hundred of polymer), respectively. Thermal properties were characterized by using thermogravimetric analysis (TGA). Thermal conductivity was measured at temperatures between 50 and 180 oC. Thermal conductivity increased with the incorporation of CNFs. Scanning electron microscopy (SEM) showed the state of dispersion of CNFs, in the entire volume of matrix. Dynamic mechanical analysis (DMA) demonstrates that both the storage modulus (E') and glass transition temperature (Tg) of the PEI/CNF composites is increased. The storage modulus of the polymer is significantly increased by the incorporation of acid treated CNFs particularly at high temperatures, indicating there is some chemical bonding between PEI and CNFCOOH (acid treated CNFs). The study showed that acid treatment of carbon nanofibers enhanced the dispersion and interfacial bonding between fibers and the matrix, and hence improved the electrical conductivity properties. Modification results in a significant decrease in resistivity compared to as received CNFs composites. The electrical conductivity of the composites was measured as a function of temperature

39

Study on mechanical, morphological and electrical properties of carbon nanofiber/polyetherimide composites  

Energy Technology Data Exchange (ETDEWEB)

Polyetherimide (PEI) and carbon nanofiber (CNF) composites have been developed successfully by using a Sigma high temperature internal mixer and then compression molded. The amount of carbon nanofibers used was 1-3 phr (parts per hundred of polymer), respectively. Thermal properties were characterized by using thermogravimetric analysis (TGA). Thermal conductivity was measured at temperatures between 50 and 180 {sup o}C. Thermal conductivity increased with the incorporation of CNFs. Scanning electron microscopy (SEM) showed the state of dispersion of CNFs, in the entire volume of matrix. Dynamic mechanical analysis (DMA) demonstrates that both the storage modulus (E') and glass transition temperature (T{sub g}) of the PEI/CNF composites is increased. The storage modulus of the polymer is significantly increased by the incorporation of acid treated CNFs particularly at high temperatures, indicating there is some chemical bonding between PEI and CNFCOOH (acid treated CNFs). The study showed that acid treatment of carbon nanofibers enhanced the dispersion and interfacial bonding between fibers and the matrix, and hence improved the electrical conductivity properties. Modification results in a significant decrease in resistivity compared to as received CNFs composites. The electrical conductivity of the composites was measured as a function of temperature.

Kumar, S. [Materials Science Centre, Indian Institute of Technology, Kharagpur 721302 (India)], E-mail: s.kumar_iitkgp@yahoo.co.in; Rath, T.; Mahaling, R.N.; Reddy, C.S. [Materials Science Centre, Indian Institute of Technology, Kharagpur 721302 (India); Das, C.K. [Materials Science Centre, Indian Institute of Technology, Kharagpur 721302 (India)], E-mail: ckd@matse.iitkgp.ernet.in; Pandey, K.N.; Srivastava, R.B.; Yadaw, S.B. [Defense Materials and Stores, Research Development and Establishment, Kanpur 208013 (India)

2007-06-25

40

Preparation of a new adsorbent from activated carbon and carbon nanofiber (AC/CNF) for manufacturing organic-vacbpour respirator cartridge  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract In this study a composite of activated carbon and carbon nanofiber (AC/CNF) was prepared to improve the performance of activated carbon (AC) for adsorption of volatile organic compounds (VOCs) and its utilization for respirator cartridges. Activated carbon was impregnated with a nickel nitrate catalyst precursor and carbon nanofibers (CNF) were deposited directly on the AC surface using catalytic chemical vapor deposition. Deposited CNFs on catalyst particles in AC micropor...

Mehdi Jahangiri; Javad Adl; Seyyed Jamaleddin Shahtaheri; Alimorad Rashidi; Amir Ghorbanali; Hossein Kakooe; Abbas Rahimi Forushani; Mohammad Reza Ganjali

2013-01-01

 
 
 
 
41

In situ encapsulation of germanium clusters in carbon nanofibers: high-performance anodes for lithium-ion batteries.  

Science.gov (United States)

Alloyed anode materials for lithium-ion batteries (LIBs) usually suffer from considerable capacity losses during charge-discharge process. Herein, in?situ-grown germanium clusters are homogeneously encapsulated into porous nitrogen-doped carbon nanofibers (N-CNFs) to form Ge/N-CNFs hybrids, using a facile electrospinning method followed by thermal treatment. When used as anode in LIBs, the Ge/N-CNFs hybrids exhibit excellent lithium storage performance in terms of specific capacity, cycling stability, and rate capability. The excellent electrochemical properties can be attributed to the unique structural features: the distribution of the germanium clusters, porous carbon nanofibers, and Ge?N chemical bonds all contribute to alleviating the large volume changes of germanium during the discharge-charge process, while at same time the unique porous N-CNFs not only increase the contact area between the electrode and the electrolyte, but also the conductivity of the hybrid. PMID:25154731

Wang, Wei; Xiao, Ying; Wang, Xia; Liu, Bing; Cao, Minhua

2014-10-01

42

Carbon nanofiber supercapacitors with large areal capacitances  

Science.gov (United States)

We develop supercapacitor (SC) devices with large per-area capacitances by utilizing three-dimensional (3D) porous substrates. Carbon nanofibers (CNFs) functioning as active SC electrodes are grown on 3D nickel foam. The 3D porous substrates facilitate a mass loading of active electrodes and per-area capacitance as large as 60 mg/cm2 and 1.2 F/cm2, respectively. We optimize SC performance by developing an annealing-free CNF growth process that minimizes undesirable nickel carbide formation. Superior per-area capacitances described here suggest that 3D porous substrates are useful in various energy storage devices in which per-area performance is critical.

McDonough, James R.; Choi, Jang Wook; Yang, Yuan; La Mantia, Fabio; Zhang, Yuegang; Cui, Yi

2009-12-01

43

Synthesis and characterization of carbon nanofibers by catalytic chemical vapor deposition using non-ferromagnetic metal complexes.  

Science.gov (United States)

Carbon nanofibers (CNFs) have wide applications in energy storage devices, electrically conducting composites, selective adsorbents, and catalyst supports. Catalytic chemical vapor deposition was carried out in this work to synthesize CNFs at mild temperatures of 700 and 800 degrees C. Non-ferromagnetic metal complexes of La, Nb, and Ti, spread on porous NaX-type zeolite support, were tested as new catalyst. CNFs ranging from 30 to 200 nm in diameter were obtained. Images of transmission electron microscopy showed encapsulated transition-metal nanoparticles by CNFs. X-ray diffraction patterns revealed the crystalline structures of La (FCC), Nb (BCC), and Ti (HCP) formed over zeolite. Magnetic hysteresis loops showed superconductivity from the CNF-encapsulated Nb at 2 K. Raman spectra showed that all the samples possessed graphitic and amorphous carbon structures. Based on the SEM images and Raman spectra, the three metals all catalyzed the synthesis of CNFs. PMID:24738371

Su, Chi-Jung; Yuan, Wei-Li; Lai, Tzu-Wei; Lei, Chien-Ming

2014-06-01

44

Graphene nanoribbons hybridized carbon nanofibers: remarkably enhanced graphitization and conductivity, and excellent performance as support material for fuel cell catalysts.  

Science.gov (United States)

High electronic conductivity of the support material and uniform distribution of the catalyst nanoparticles (NPs) are extremely desirable for electrocatalysts. In this paper, we present our recent progress on electrocatalysts for fuel cells with simultaneously improved conductivity of the supporting carbon nanofibers (CNFs) and distribution of platinum (Pt) NPs through facile incorporation of graphene nanoribbons (GNRs). Briefly, GNRs were obtained by the cutting and unzipping of multiwalled carbon nanotubes (MWCNTs) and subsequent thermal reduction and were first used as novel nanofillers in CNFs towards high performance support material for electrocatalysis. Through electrospinning and carbonization processes, GNR embedded carbon nanofibers (G-CNFs) with greatly enhanced graphitization and electronic conductivity were synthesized. Chemical deposition of Pt NPs onto G-CNFs generated a new Pt-G-CNF hybrid catalyst, with homogeneously distributed Pt NPs of ?3 nm. Compared to Pt-CNF (Pt on pristine CNFs) and Pt-M-CNF (Pt on MWCNT embedded CNFs), Pt-G-CNF hybrids exhibit significantly improved electrochemically active surface area (ECSA), better CO tolerance for electro-oxidation of methanol and higher electrochemical stability, testifying G-CNFs are promising support materials for high performance electrocatalysts for fuel cells. PMID:24305657

Wang, Chaonan; Gao, Hongrong; Li, Hong; Zhang, Yiren; Huang, Bowen; Zhao, Junhong; Zhu, Yan; Yuan, Wang Zhang; Zhang, Yongming

2014-01-01

45

Formation of positronium in cup-stacked carbon nanofibers  

International Nuclear Information System (INIS)

The positron-lifetime spectrum for cup-stacked carbon nanofibers (CNFs) is composed of three components: 0.125 ns (fixed) (6%), 0.345 ns (75%), 1.21 ns (19%). The longest-lived component assigned to ortho-positronium (o-Ps) verifies a prominent yield of o-Ps, which is in contrast with the fact that no o-Ps is detected for uncapped cylindrical multi-walled carbon nanotubes. CNFs heat-treated to 1073 K in vacuo showed a positron-lifetime spectrum the same as that of untreated CNFs, which demonstrates that the thermal detachment of some functional groups from the surface of the CNFs does not change the Ps yield. The yield is found almost independent of temperature between 10 and 280 K. A single CNF, ca. 50 nm in outer diameter, observed by transmission electron-microscopy, comprises stacked cups of 9?12 truncated conical graphene sheets at ca. 20 with respect to the fiber axis, so that all edges of graphene sheets are found on the zigzag outer- as well as inner-surfaces of the fiber. The Raman spectrum for CNFs exhibits a band of a disorder-induced mode at 1349 cm-1 (D-band) and a band of the E2g2 in-plane mode at 1577 cm-1 (G-band). The intensity-ratios of a D-band to a G-band are 0.17, 0.25 and 0 for a mat of CNFs, the edge plane and the basal plane of a highly oriented pyrolitic graphite block, respectively. For graphite materials, Ps is formed from the positrons trapped in the defects originating from edges of graphene sheets. (orig.)

46

Carbon Nanofiber Nanoelectrodes for Biosensing Applications  

Science.gov (United States)

A sensor platform based on vertically aligned carbon nanofibers (CNFs) has been developed. Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. Here, we report two studies using vertically aligned CNF nanoelectrodes for biomedical applications. CNF arrays are investigated as neural stimulation and neurotransmitter recording electrodes for application in deep brain stimulation (DBS). Polypyrrole coated CNF nanoelectrodes have shown great promise as stimulating electrodes due to their large surface area, low impedance, biocompatibility and capacity for highly localized stimulation. CNFs embedded in SiO2 have been used as sensing electrodes for neurotransmitter detection. Our approach combines a multiplexed CNF electrode chip, developed at NASA Ames Research Center, with the Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS) system, developed at the Mayo Clinic. Preliminary results indicate that the CNF nanoelectrode arrays are easily integrated with WINCS for neurotransmitter detection in a multiplexed array format. In the future, combining CNF based stimulating and recording electrodes with WINCS may lay the foundation for an implantable smart therapeutic system that utilizes neurochemical feedback control while likely resulting in increased DBS application in various neuropsychiatric disorders. In total, our goal is to take advantage of the nanostructure of CNF arrays for biosensing studies requiring ultrahigh sensitivity, high-degree of miniaturization, and selective biofunctionalization.

Koehne, Jessica Erin

2014-01-01

47

Carbon nanofiber–sulfur composite cathode materials with different binders for secondary Li/S cells  

International Nuclear Information System (INIS)

A sulfur-coated carbon nanofiber (CNF–S) composite cathode material was prepared by a chemical deposition method in an aqueous solution. This CNF–S material was evaluated as the cathode material in lithium/sulfur cells with three different binders. The results of the SEM and TGA measurements reveal that CNF–S has a typical core–shell structure, containing 75.7 w/o sulfur coated uniformly on the surface of the CNFs. The effects of different binders on the potential profiles, electrode capacity and capacity retention with cycling were investigated. The electrode prepared with CMC + SBR binder has the best performance compared with PVdF and PEO binders, exhibiting a specific capacity of up to 1313 mAh g?1 S at the initial discharge and a specific capacity of 586 mAh g?1 S after 60 cycles.

48

Carbon nanofiber interconnect RF characteristics improvement with deposited tungsten contacts.  

Science.gov (United States)

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are potential materials for high-performance electronic devices and circuits due to their light weight and excellent electrical properties such as high current capacity and tolerance to electromigration. In addition, at high frequencies, these materials exhibit transport behavior which holds special promise for applications as on-chip interconnects. Contact resistance at CNF-metal interface is a major factor in limiting the electrical performance of CNF interconnects at all frequencies. In this paper, it is demonstrated that the contact resistance can be minimized and the high-frequency characteristics much enhanced by depositing tungsten on CNF-metal electrode contacts. PMID:24745286

Vyas, Anshul A; Madriz, Francisco; Kanzaki, Nobuhiko; Wilhite, Patrick; Sun, Xuhui; Yamada, Toshishige; Yang, Cary Y

2014-03-01

49

Occupational nanosafety considerations for carbon nanotubes and carbon nanofibers.  

Science.gov (United States)

Carbon nanotubes (CNTs) are carbon atoms arranged in a crystalline graphene lattice with a tubular morphology. CNTs exhibit high tensile strength, possess unique electrical properties, are durable, and can be functionalized. These properties allow applications as structural materials, in electronics, as heating elements, in batteries, in the production of stain-resistant fabric, for bone grafting and dental implants, and for targeted drug delivery. Carbon nanofibers (CNFs) are strong, flexible fibers that are currently used to produce composite materials. Agitation can lead to aerosolized CNTs and CNFs, and peak airborne particulate concentrations are associated with workplace activities such as weighing, transferring, mixing, blending, or sonication. Most airborne CNTs or CNFs found in workplaces are loose agglomerates of micrometer diameter. However, due to their low density, they linger in workplace air for a considerable time, and a large fraction of these structures are respirable. In rat and mouse models, pulmonary exposure to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or CNFs causes the following pulmonary reactions: acute pulmonary inflammation and injury, rapid and persistent formation of granulomatous lesions at deposition sites of large CNT agglomerates, and rapid and progressive alveolar interstitial fibrosis at deposition sites of more dispersed CNT or CNF structures. Pulmonary exposure to SWCNTs can induce oxidant stress in aortic tissue and increases plaque formation in an atherosclerotic mouse model. Pulmonary exposure to MWCNTs depresses the ability of coronary arterioles to respond to dilators. These cardiovascular effects may result from neurogenic signals from sensory irritant receptors in the lung. Pulmonary exposure to MWCNTs also upregulates mRNA for inflammatory mediators in selected brain regions, and pulmonary exposure to SWCNTs upregulates the baroreceptor reflex. In addition, pulmonary exposure to MWCNTs may induce levels of inflammatory mediators in the blood, which may affect the cardiovascular system. Intraperitoneal instillation of MWCNTs in mice has been associated with abdominal mesothelioma. MWCNTs deposited in the distal alveoli can migrate to the intrapleural space, and MWCNTs injected in the intrapleural space can cause lesions at the parietal pleura. However, further studies are required to determine whether pulmonary exposure to MWCNTs can induce pleural lesions or mesothelioma. In light of the anticipated growth in the production and use of CNTs and CNFs, worker exposure is possible. Because pulmonary exposure to CNTs and CNFs causes inflammatory and fibrotic reactions in the rodent lung, adverse health effects in workers represent a concern. NIOSH has conducted a risk assessment using available animal exposure-response data and is developing a recommended exposure limit for CNTs and CNFs. Evidence indicates that engineering controls and personal protective equipment can significantly decrease workplace exposure to CNTs and CNFs. Considering the available data on health risks, it appears prudent to develop prevention strategies to minimize workplace exposure. These strategies would include engineering controls (enclosure, exhaust ventilation), worker training, administrative controls, implementation of good handling practices, and the use of personal protective equipment (such as respirators) when necessary. NIOSH has published a document containing recommendations for the safe handling of nanomaterials. PMID:23210709

Castranova, Vincent; Schulte, Paul A; Zumwalde, Ralph D

2013-03-19

50

Structure, mechanical properties and friction behavior of UHMWPE/HDPE/carbon nanofibers  

International Nuclear Information System (INIS)

Effects of untreated and pretreated carbon nanofibers (CNFs) on the crystallization behavior, friction behavior, and mechanical properties of ultra high molecular weight polyethylene (UHMWPE)/high density polyethylene (HDPE) nanocomposites prepared by a twin-screw extrusion were studied. The differential scanning calorimetry and wide angle X-ray diffraction measurements indicated that the addition of CNFs impacted the temperature of crystallization, but had no significant effects on the crystalline structure of the UHMWPE/HDPE blend. The degree of crystallinity, and the tensile strength and modulus of the UHMWPE/HDPE systems exhibited an increasing trend initially with addition of CNFs, followed by a decrease at higher contents. With the increase of untreated CNF content, the friction coefficient of UHMWPE/HDPE was decreasing and displayed less change in the process of friction. The microstructure features on the fracture surfaces and friction surfaces of the polymer blend and the nanocomposites were analyzed in detail by scanning electron microscope observations. The degree of crystallinity of the nanocomposites with the pretreated CNFs exhibited a decrease due to the better interface adhesion compared to that in the nanocomposites with the same loading untreated CNFs. The enhancement in tensile strength of nanocomposites containing 0.5 wt% treated CNFs was four times higher (32%) than that of the nanocomposites containing untreated CNFs (8%) over that of the pure polymer

51

Structure, mechanical properties and friction behavior of UHMWPE/HDPE/carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Effects of untreated and pretreated carbon nanofibers (CNFs) on the crystallization behavior, friction behavior, and mechanical properties of ultra high molecular weight polyethylene (UHMWPE)/high density polyethylene (HDPE) nanocomposites prepared by a twin-screw extrusion were studied. The differential scanning calorimetry and wide angle X-ray diffraction measurements indicated that the addition of CNFs impacted the temperature of crystallization, but had no significant effects on the crystalline structure of the UHMWPE/HDPE blend. The degree of crystallinity, and the tensile strength and modulus of the UHMWPE/HDPE systems exhibited an increasing trend initially with addition of CNFs, followed by a decrease at higher contents. With the increase of untreated CNF content, the friction coefficient of UHMWPE/HDPE was decreasing and displayed less change in the process of friction. The microstructure features on the fracture surfaces and friction surfaces of the polymer blend and the nanocomposites were analyzed in detail by scanning electron microscope observations. The degree of crystallinity of the nanocomposites with the pretreated CNFs exhibited a decrease due to the better interface adhesion compared to that in the nanocomposites with the same loading untreated CNFs. The enhancement in tensile strength of nanocomposites containing 0.5 wt% treated CNFs was four times higher (32%) than that of the nanocomposites containing untreated CNFs (8%) over that of the pure polymer.

Sui, G. [School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164 (United States); Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer, Beijing University of Chemical Technology, Beijing 100029 (China); Zhong, W.H. [School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164 (United States)], E-mail: katie_zhong@wsu.edu; Ren, X.; Wang, X.Q. [School of Material Science and Engineering, Beihang University, Beijing 100083 (China); Yang, X.P. [Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer, Beijing University of Chemical Technology, Beijing 100029 (China)

2009-05-15

52

Processing and Structure of Carbon Nanofiber Paper  

Directory of Open Access Journals (Sweden)

Full Text Available A unique concept of making nanocomposites from carbon nanofiber paper was explored in this study. The essential element of this method was to design and manufacture carbon nanofiber paper with well-controlled and optimized network structure of carbon nanofibers. In this study, carbon nanofiber paper was prepared under various processing conditions, including different types of carbon nanofibers, solvents, dispersants, and acid treatment. The morphologies of carbon nanofibers within the nanofiber paper were characterized with scanning electron microscopy (SEM. In addition, the bulk densities of carbon nanofiber papers were measured. It was found that the densities and network structures of carbon nanofiber paper correlated to the dispersion quality of carbon nanofibers within the paper, which was significantly affected by papermaking process conditions.

Zhongfu Zhao

2009-01-01

53

Growth of carbon nanofibers on carbon fabric with Ni nanocatalyst prepared using pulse electrodeposition  

International Nuclear Information System (INIS)

The pulse electrodeposition (PED) technique was utilized to deposit nanosized (?10 nm) Ni catalysts on carbon fabric (CF). Via an in situ potential profile, the PED technique can control the Ni catalyst loading, which is an important parameter for the growth of carbon nanofibers (CNFs) on CF. The preparation of CNF-coated CF (carpet-like CF) was carried out in a thermal chemical vapor deposition system with an optimum loading of Ni catalysts deposited in the PED pulse range from 20 to 320 cycles. CNFs grown at 813 K using different pulse cycles had a narrow diameter distribution, around 15 ± 5 nm to 29 ± 7 nm; they have a hydrophobic surface, like lotus leaves. Transmission electron microscopy images confirmed the graphene structural transformation of CNFs with the growth temperature. Solid wire CNFs were initially grown at 813 K with graphene edges exposed on the external surface. At elevated growth temperatures (1073 and 1173 K), bamboo-like CNFs were obtained, with herringbone structures and intersectional hollow cores

54

Change in carbon nanofiber resistance from ambient to vacuum  

Directory of Open Access Journals (Sweden)

Full Text Available The electrical properties of carbon nanofibers (CNFs can be affected by adsorbed gas species. In this study, we compare the resistance values of CNF devices in a horizontal configuration in air and under vacuum. CNFs in air are observed to possess lower current capacities compared to those in vacuum. Further, Joule heating due to current stressing can result in desorption of gas molecules responsible for carrier trapping, leading to lower resistances and higher breakdown currents in vacuum, where most adsorbed gaseous species are evacuated before any significant re-adsorption can occur. A model is proposed to describe these observations, and is used to estimate the number of adsorbed molecules on a CNF device.

Shusaku Maeda

2011-04-01

55

Change in carbon nanofiber resistance from ambient to vacuum  

Science.gov (United States)

The electrical properties of carbon nanofibers (CNFs) can be affected by adsorbed gas species. In this study, we compare the resistance values of CNF devices in a horizontal configuration in air and under vacuum. CNFs in air are observed to possess lower current capacities compared to those in vacuum. Further, Joule heating due to current stressing can result in desorption of gas molecules responsible for carrier trapping, leading to lower resistances and higher breakdown currents in vacuum, where most adsorbed gaseous species are evacuated before any significant re-adsorption can occur. A model is proposed to describe these observations, and is used to estimate the number of adsorbed molecules on a CNF device.

Maeda, Shusaku; Wilhite, Patrick; Kanzaki, Nobuhiko; Yamada, Toshishige; Yang, Cary Y.

2011-06-01

56

Size Control of Carbon Nanofiber Probes Fabricated by Ion Irradiation  

Science.gov (United States)

The effect of ion species and fabrication temperature on the size of ion-induced carbon nanofibers (CNFs) grown on tips of scanning probe microscope cantilevers was investigated in detail. Similarly to that using Ar+ ions, the fabrication of CNF probes using Ne+ and Xe+ ions was possible. Xe+ sputtering yielded the shortest CNF probes owing to its large sputtering effect; however, a significant difference in the size of the CNF probes between Ne+ and Ar+ ion irradiation was not observed. The CNFs increased in length with fabrication temperature owing to the enhanced diffusion of C atoms at elevated temperatures; however, the CNF diameter remained almost constant independent of fabrication temperature. Therefore, the fabrication at elevated temperatures was effective for the rapid fabrication of practical CNF probes. Thus, the CNF probe size was controllable by adjusting the fabrication temperature and ion species.

Inaba, Kazuhisa; Sugita, Yoshitaka; Suzuki, Takahito; Tanemura, Masaki; Hayashi, Akari; Hayashi, Yasuhiko; Kitazawa, Masashi; Ohta, Ryo

2010-08-01

57

Carbon nanofibers and carbon nanotubes sensitize prostate and bladder cancer cells to platinum-based chemotherapeutics.  

Science.gov (United States)

Recent data suggest that carbon nanomaterials can act as antitumor agents themselves by increasing the efficiency of cytotoxic agents when applied in combination. Here, carbon nanofibers (CNFs) and multi-walled carbon nanotubes (CNTs) were investigated regarding their impact on cellular function, cellular uptake and ability to sensitize cancer cells of urological origin to the conventional chemotherapeutics cisplatin and carboplatin. CNFs and CNTs (1-200 microg/ml) showed a low to moderate impairment of cellular function with CNFs being more deleterious than CNTs. Inhibition of cellular viability by the nanomaterials was about 20% at most. In combinatory treatments, CNFs and CNTs markedly enhanced the effects of cisplatin and carboplatin on cellular viability by 1.2- to 2.8-fold in prostate, bladder and cisplatin-resistant prostate cancer cells in comparison to the individual effects of the chemotherapeutics. Particularly the cell viability-diminishing effect of CNFs alone and in combination with the chemotherapeutics was more pronounced with dispersions prepared with human serum albumin than with phospholipid-polyethylene glycol. Albumin might mediate the cellular uptake of carbon nanomaterials which was underlined by the co-localization of albumin and carbon nanomaterials along the cellular surface as evidenced by fluorescence microscopy. Transmission electron microscopy revealed that both carbon nanomaterials were internalized by cancer cells, thereby possibly leading to an enhanced accumulation of the chemotherapeutic drugs. In fact, CNFs enhanced the cellular accumulation of carboplatin by 28% as compared to the single treatment with carboplatin. In conclusion, carbon nanomaterial-based applications could present a new strategy to overcome chemoresistance by sensitizing cancer cells to conventional chemotherapeutics. PMID:24730242

Ringel, Jessica; Erdmann, Kati; Hampel, Silke; Kraemer, Kai; Maier, Diana; Arlt, Marcus; Kunze, Doreen; Wirth, Manfred P; Fuessel, Susanne

2014-03-01

58

Catalytic Growth of Macroscopic Carbon Nanofibers Bodies with Activated Carbon  

Science.gov (United States)

Carbon-carbon composite of activated carbon and carbon nanofibers have been synthesized by growing Carbon nanofiber (CNF) on Palm shell-based Activated carbon (AC) with Ni catalyst. The composites are in an agglomerated shape due to the entanglement of the defective CNF between the AC particles forming a macroscopic body. The macroscopic size will allow the composite to be used as a stabile catalyst support and liquid adsorbent. The preparation of CNT/AC nanocarbon was initiated by pre-treating the activated carbon with nitric acid, followed by impregnation of 1 wt% loading of nickel (II) nitrate solutions in acetone. The catalyst precursor was calcined and reduced at 300° C for an hour in each step. The catalytic growth of nanocarbon in C2H4/H2 was carried out at temperature of 550° C for 2 hrs with different rotating angle in the fluidization system. SEM and N2 isotherms show the level of agglomeration which is a function of growth density and fluidization of the system. The effect of fluidization by rotating the reactor during growth with different speed give a significant impact on the agglomeration of the final CNF/AC composite and thus the amount of CNFs produced. The macrostructure body produced in this work of CNF/AC composite will have advantages in the adsorbent and catalyst support application, due to the mechanical and chemical properties of the material.

Abdullah, N.; Rinaldi, A.; Muhammad, I. S.; Hamid, S. B. Abd.; Su, D. S.; Schlogl, R.

2009-06-01

59

Catalytic Growth of Macroscopic Carbon Nanofibers Bodies with Activated Carbon  

International Nuclear Information System (INIS)

Carbon-carbon composite of activated carbon and carbon nanofibers have been synthesized by growing Carbon nanofiber (CNF) on Palm shell-based Activated carbon (AC) with Ni catalyst. The composites are in an agglomerated shape due to the entanglement of the defective CNF between the AC particles forming a macroscopic body. The macroscopic size will allow the composite to be used as a stabile catalyst support and liquid adsorbent. The preparation of CNT/AC nanocarbon was initiated by pre-treating the activated carbon with nitric acid, followed by impregnation of 1 wt% loading of nickel (II) nitrate solutions in acetone. The catalyst precursor was calcined and reduced at 300 deg. C for an hour in each step. The catalytic growth of nanocarbon in C2H4/H2 was carried out at temperature of 550 deg. C for 2 hrs with different rotating angle in the fluidization system. SEM and N2 isotherms show the level of agglomeration which is a function of growth density and fluidization of the system. The effect of fluidization by rotating the reactor during growth with different speed give a significant impact on the agglomeration of the final CNF/AC composite and thus the amount of CNFs produced. The macrostructure body produced in this work of CNF/AC composite will have advantages in the adsorbent and catalyst support application, due to the mechanical and chemical properties of the material.

60

Carbon nanofiber growth in plasma-enhanced chemical vapor deposition  

Science.gov (United States)

A theoretical model to describe the plasma-assisted growth of carbon nanofibers (CNFs) is proposed. Using the model, the plasma-related effects on the nanofiber growth parameters, such as the growth rate due to surface and bulk diffusion, the effective carbon flux to the catalyst surface, the characteristic residence time and diffusion length of carbon atoms on the catalyst surface, and the surface coverages, have been studied. The dependence of these parameters on the catalyst surface temperature and ion and etching gas fluxes to the catalyst surface is quantified. The optimum conditions under which a low-temperature plasma environment can benefit the CNF growth are formulated. These results are in good agreement with the available experimental data on CNF growth and can be used for optimizing synthesis of related nanoassemblies in low-temperature plasma-assisted nanofabrication.

Denysenko, I.; Ostrikov, K.; Cvelbar, U.; Mozetic, M.; Azarenkov, N. A.

2008-10-01

 
 
 
 
61

Carbon nanofiber growth in plasma-enhanced chemical vapor deposition  

International Nuclear Information System (INIS)

A theoretical model to describe the plasma-assisted growth of carbon nanofibers (CNFs) is proposed. Using the model, the plasma-related effects on the nanofiber growth parameters, such as the growth rate due to surface and bulk diffusion, the effective carbon flux to the catalyst surface, the characteristic residence time and diffusion length of carbon atoms on the catalyst surface, and the surface coverages, have been studied. The dependence of these parameters on the catalyst surface temperature and ion and etching gas fluxes to the catalyst surface is quantified. The optimum conditions under which a low-temperature plasma environment can benefit the CNF growth are formulated. These results are in good agreement with the available experimental data on CNF growth and can be used for optimizing synthesis of related nanoassemblies in low-temperature plasma-assisted nanofabrication

62

Direct production of carbon nanofibers decorated with Cu2O by thermal chemical vapor deposition on Ni catalyst electroplated on a copper substrate  

Directory of Open Access Journals (Sweden)

Full Text Available  Carbon nanofibers (CNFs decorated with Cu2O particles were grown on a Ni catalyst layer deposited on a Cu substrate by thermal. chemical vapor deposition from liquid petroleum gas. Ni catalyst nanoparticles with different sizes were produced in an electroplating system at 35?C. These nanoparticles provide the nucleation sites for CNF growth, removing the need for a buffer layer. High temperature surface segregation of the Cu substrate into the Ni catalyst layer and its exposition to O2 at atmospheric environment, during the CNFs growth, lead to the production of CNFs decorated with Cu2O particles. The surface morphology of the Ni catalyst films and grown CNFs over it was studied by scanning electron microscopy. Transmission electron microscopy and Raman spectroscopy revealed the formation of CNFs. The selected area electron diffraction pattern and electron diffraction studies show that these CNFs were decorated with Cu2O nanoparticles.

MA Vesaghi

2012-12-01

63

Novel phenolic biosensor based on a magnetic polydopamine-laccase-nickel nanoparticle loaded carbon nanofiber composite.  

Science.gov (United States)

A novel phenolic biosensor was prepared on the basis of a composite of polydopamine (PDA)-laccase (Lac)-nickel nanoparticle loaded carbon nanofibers (NiCNFs). First, NiCNFs were fabricated by a combination of electrospinning and a high temperature carbonization technique. Subsequently, the magnetic composite was obtained through one-pot Lac-catalyzed oxidation of dopamine (DA) in an aqueous suspension containing Lac, NiCNFs, and DA. Finally, a magnetic glass carbon electrode (MGCE) was employed to separate and immobilize the composite; the modified electrode was then denoted as PDA-Lac-NiCNFs/MGCE. Fourier transform infrared (FT-IR) spectra and cyclic voltammetry (CV) analyses revealed the NiCNFs had good biocompatibility for Lac immobilization and greatly facilitated the direct electron transfer between Lac and electrode surface. The immobilized Lac showed a pair of stable and well-defined redox peaks, and the electrochemical behavior of Lac was a surface-controlled process in pH 5.5 acetate buffer solution. The PDA-Lac-NiCNFs/MGCE for biosensing of catechol exhibited a sensitivity of 25 ?A mM(-1) cm(-2), a detection limit of 0.69 ?M (S/N = 3), and a linear range from 1 ?M to 9.1 mM, as well as good selectivity and stability. Meanwhile, this novel biosensor demonstrated its promising application in detecting catechol in real water samples. PMID:24606719

Li, Dawei; Luo, Lei; Pang, Zengyuan; Ding, Lei; Wang, Qingqing; Ke, Huizhen; Huang, Fenglin; Wei, Qufu

2014-04-01

64

Melt shear rheology of carbon nanofiber/polystyrene composites  

Energy Technology Data Exchange (ETDEWEB)

The rheological behavior and morphology of carbon nanofiber/polystyrene (CNF/PS) composites in their melt phase have been characterized both through experimental measurements and modeling. Composites prepared in the two different processes of solvent casting and melt blending are contrasted; melt-blended and solvent-cast composites were each prepared with CNF loadings of 2, 5, and 10 wt%. A morphological study revealed that the melt blending process results in composites with shorter CNFs than in the solvent-cast composites, due to damage caused by the higher stresses the CNFs encounter in melt blending, and that both processes retain the diameter of the as-received CNFs. The addition of carbon nanofiber to the polystyrene through either melt blending or solvent casting increases the linear viscoelastic moduli, G' and G{sup ''}, and steady-state viscosity, {eta}, in the melt phase monotonically with CNF concentration, more so in solvent cast composites with their longer CNFs. The melt phase of solvent-cast composites with higher CNF concentrations exhibit a plateau of the elastic modulus, G', at low frequencies, an apparent yield stress, and large first normal stress difference, N{sub 1}, at low strain rates, which can be attributed to contact-based network nanostructure formed by the long CNFs. A nanostructurally-based model for CNF/PS composites in their melt phase is presented which considers the composite system as rigid rods in a viscoelastic fluid matrix. Except for two coupling parameters, all material constants in the model for the composite systems are deduced from morphological and shear flow measurements of its separate nanofiber and polymer melt constituents of the composite. These two coupling parameters are polymer-fiber interaction parameter, {sigma}, and interfiber interaction parameter, C{sub I}. Through comparison with our experimental measurements of the composite systems, we deduce that {sigma} is effectively 1 (corresponding to no polymer-fiber interaction) for all CNF/PS nanocomposites studied. The dependence of CNF orientation on strain rate which we observe in our experiments is captured in the model by considering the interfiber interaction parameter, C{sub I}, as a function of strain rate. Applied to shear flows, the model predicts the melt-phase, steady-state viscosities, and normal stress differences of the CNF/PS composites as functions of shear rate, polymer matrix properties, fiber length, and mass concentration consistent with our experimental measurements. (orig.)

Wang, Yingru; Bechtel, Stephen E. [Ohio State University, Department of Mechanical Engineering, Columbus, OH (United States); Xu, Jianhua; Koelling, Kurt W. [Ohio State University, Department of Chemical and Biomolecular Engineering, Columbus, OH (United States)

2006-08-15

65

Characterization of interfaces in ZrO2-carbon nanofiber composite  

International Nuclear Information System (INIS)

Zirconia-carbon nanofiber (CNF) composite was prepared with the aim of improving the electrical conductivity of the zirconia. Transmission electron microscopy was used to characterize the interfaces in the composite and to explain the significantly improved conductivity compared with monolithic zirconia. Three different interfaces have been found: clear ZrO2/ZrO2 boundaries, ZrO2/ZrO2 boundaries with CNF and ZrO2/ZrO2 boundaries with disordered graphite (which results from the destruction of CNFs during processing). The modified grain boundaries together with the presence of CNFs are the reason for the improved conductivity.

66

Extraction of contact resistance in carbon nanofiber via interconnects with varying lengths  

Science.gov (United States)

A method to extract the contact resistance and bulk resistivity of vertically grown carbon nanofibers (CNFs) or similar one-dimensional nanostructures is described. Using a silicon-compatible process to fabricate a terrace test structure needed for the CNF length variation, the contact resistance is extracted by measuring in situ the resistances of individual CNFs with different lengths and within a small range of diameters using a nanoprober inside a scanning electron microscope. Accurate determination of contact resistances for various combinations of catalysts and underlayer metals can lead to eventual optimization of materials' growth and device fabrication processes for CNF via interconnects.

Li, Ke; Wu, Raymond; Wilhite, Patrick; Khera, Vinit; Krishnan, Shoba; Sun, Xuhui; Yang, Cary Y.

2010-12-01

67

Synergistic effect of carbon nanofiber and carbon nanopaper on shape memory polymer composite  

Science.gov (United States)

The present work studies the synergistic effect of carbon nanofiber (CNF) and carbon nanopaper on the shape recovery of shape memory polymer (SMP) composite. The combination of CNF and carbon nanopaper was used to improve the thermal and electrical conductivities of the SMP composite. The carbon nanopaper was coated on the surface of the SMP composite in order to achieve the actuation by electrical resistive heating. CNFs were blended with the SMP resin to improve the thermal conductivity to facilitate the heat transfer from the nanopaper to the underlying SMP composite to accelerate the electroactive responses.

Lu, Haibao; Liu, Yanju; Gou, Jihua; Leng, Jinsong; Du, Shanyi

2010-02-01

68

Occupational Exposure to Carbon Nanotubes and Nanofibers  

Science.gov (United States)

... CNTs and CNFs are tiny, cylindrical, large aspect ratio, manufactured forms of carbon. There is no single ... of research studies with rodents have shown adverse lung effects at relatively low-mass doses of CNT ...

69

Encapsulation of MnO Nanocrystals in Electrospun Carbon Nanofibers as High-Performance Anode Materials for Lithium-Ion Batteries  

Science.gov (United States)

A novel and controllable approach is developed for the synthesis of MnO nanocrystals embedded in carbon nanofibers (MnO/CNFs) through an electrospinning process. The as-formed MnO/CNFs have a porous structure with diameters of 100-200 nm and lengths up to several millimeters. When used as an anode material for lithium-ion batteries, the resulting MnO/CNFs exhibit superior electrochemical performances with high specific capacity, good cyclability, and excellent rate capability. The unique porous carbon nanofibers (PCNFs) can not only improve the contact area between the electrode and the electrolyte, but also alleviate the impact of the large volume effect of MnO during the electrochemical cycling. It is expected that the present synthetic strategy can be extended to synthesize other nanostructured oxides encapsulated in carbon nanofibers for extensive energy transfer and storage applications.

Liu, Bin; Hu, Xianluo; Xu, Henghui; Luo, Wei; Sun, Yongming; Huang, Yunhui

2014-03-01

70

Structure Control of V2O5/CNFs/Cordierite Monolith Catalyst and Its Catalytic Performance on NO Removal from Flue Gas  

Directory of Open Access Journals (Sweden)

Full Text Available Carbon nanofibers (CNFs were grown on Al2O3-coated cordierite monolith by chemical vapor deposition. The microstructure of V2O5 catalyst supported on cordierite monolith with CNFs layer was investigated by using scanning electron microscope (SEM, transmission electron microscope (TEM, X-ray powder diffraction (XRD and X-ray photoelectron spectroscope (XPS techniques, as well as its activity for the selective catalytic reduction (SCR of NO by NH3. The compressive strength of prepared CNFs/cordierite monolith composite was 34.46 MPa and the thickness of CNFs layer was 0.74 ?m. The V2O5/CNFs/cordierite monolith catalysts had high NO removal activity in the temperature range of 150-250¡?When the CNFs yield and V2O5 loading were 12.5% and 1%, respectively, the NO conversion of the catalyst could reach 95% at 250¡?

WANG Yan-Li, WANG Xu-Jian, ZHAN Liang, QIAO Wen-Ming, LIANG Xiao-Yi, LING Li-Cheng

2012-08-01

71

One-step catalytic growth of carbon nanofiber arrays vertically aligned on carbon substrate  

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? Acetylene as carbon resource and copper foil as catalyst. ? Three carbon nanostructures are synthesized by modulating feeding gas compositions. ? NH{sub 3} is a key factor in the growth of VA-CNF arrays. -- Abstract: Vertically aligned carbon nanofiber (VA-CNF) arrays on carbon substrate have been synthesized via one-step chemical vapor deposition process on copper foil, by using acetylene as carbon resource. Three types of carbon nanostructures, viz. bare carbon films, CNFs and VA-CNFs grown on carbon substrate, could be selectively synthesized by only modulating the concentration of C{sub 2}H{sub 2} and NH{sub 3} in the feeding gases. It was found that NH{sub 3} was a key factor in the growth of VA-CNF arrays, which could increase the diffusion capability of copper atoms in carbon materials, therefore promote forming larger spherical Cu NPs catalysts for the growth of VA-CNFs. Furthermore, a growth mechanism in different feeding gas compositions was proposed.

Li, Xun [State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructure, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China); State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China); Xu, Zheng, E-mail: zhengxu@nju.edu.cn [State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructure, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China)

2012-06-15

72

Multi-scale carbon micro/nanofibers-based adsorbents for protein immobilization.  

Science.gov (United States)

In the present study, different proteins, namely, bovine serum albumin (BSA), glucose oxidase (GOx) and the laboratory purified YqeH were immobilized in the phenolic resin precursor-based multi-scale web of activated carbon microfibers (ACFs) and carbon nanofibers (CNFs). These biomolecules are characteristically different from each other, having different structure, number of parent amino acid molecules and isoelectric point. CNF was grown on ACF substrate by chemical vapor deposition, using Ni nanoparticles (Nps) as the catalyst. The ultra-sonication of the CNFs was carried out in acidic medium to remove Ni Nps from the tip of the CNFs to provide additional active sites for adsorption. The prepared material was directly used as an adsorbent for proteins, without requiring any additional treatment. Several analytical techniques were used to characterize the prepared materials, including scanning electron microscopy, Fourier transform infrared spectroscopy, BET surface area, pore-size distribution, and UV-vis spectroscopy. The adsorption capacities of prepared ACFs/CNFs in this study were determined to be approximately 191, 39 and 70 mg/g for BSA, GOx and YqeH, respectively, revealing that the carbon micro-nanofibers forming synthesized multi-scale web are efficient materials for the immobilization of protein molecules. PMID:24656351

Singh, Shiv; Singh, Abhinav; Bais, Vaibhav Sushil Singh; Prakash, Balaji; Verma, Nishith

2014-05-01

73

Adsorption behavior of perfluorinated sulfonic acid ionomer on highly graphitized carbon nanofibers and their thermal stabilities  

DEFF Research Database (Denmark)

A systematic adsorption study of perfluorinated sulfonic acid Nafion® ionomer on ribbon type highly graphitized carbon nanofibers (CNFs) was carried out using 19 fluorine nuclear magnetic resonance spectroscopy. Based on the values obtained for the equilibrium constant (Keq., derived from Langmuir isotherm), the ionomer has varying affinities for CNFs (Keq. = between 5 and 22) as compared to Vulcan (Keq. = 18), depending on surface treatments. However, the interactions are most likely governed by different adsorption mechanisms depending on hydrophilicity / hydrophobicity of the adsorbent carbon. The ionomer is probably adsorbed via the polar sulfonic group on hydrophilic Vulcan, whereas, it is adsorbed primarily via hydrophobic -CF2- backbone on the highly hydrophobic pristine CNFs. Ionomer adsorption behavior is gradually altered from apolar to polar group adsorption for the acid modified CNFs of decreasing hydrophobicity. This is indicated by the initial decrease and then increase in the value of Keq. withthe increasing strength of the acid treatment. The corresponding carbon - ionomer composite also showed varying thermal stability depending on Nafion orientation. The specific maximum surface coverage (?Smax) of the CNFs is one order of magnitude higher than the one of Vulcan. The large discrepancy is due to the fact that the ionomers are inaccessible to the internal surface area of Vulcan with high micro porosity.

Andersen, Shuang Ma; Borghei, Maryam

2014-01-01

74

Characterization of field emission from carbon nanofibers on a metal tip  

Science.gov (United States)

Field electron emission from carbon nanofibers (CNFs) grown on a tungsten tip has been characterized by measuring emission current-voltage (I-V) curves and observing emission patterns on a phosphor screen. CNFs were vertically grown on the tip by plasma-enhanced chemical vapor deposition. Field emission from the CNFs over 100 ?A was strongly dependent on emitter-anode distance, and the dominant field electrons were emitted within an angular spread of ?? ˜25°, indicating the electron emission took place mainly from the emitter's apex area. By analyzing the I-V curves with the aid of the Fowler-Nordheim theory, the maximum current density was estimated to be about J =2×109 A/m2.

Sakai, Y.; Tone, D.; Nagatsu, S.; Endo, T.; Kita, S.; Okuyama, F.

2009-08-01

75

High yield synthesis of carbon nanofibers in an environmental friendly route  

Science.gov (United States)

An environmental friendly route for the high yield synthesis of carbon nanofibers (CNFs) has been developed. CNFs have been synthesized using nickel formate as catalyst precursor at 680°C using chemical vapor deposition method. Upon pyrolysis this catalyst precursor yields metal catalyst nanoparticles directly. The sodium chloride and potassium chloride was used as catalyst support, it was chosen because of its non-toxic and water soluble nature. The problems such as detrimental effect, environment and even cost has been avoided by using water soluble supports. The structure of the products was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction method. The purity of as grown products and purified products was determined by thermal analysis. Here, we report the 7,800 and 7,200 wt% yield of CNFs synthesized over NaCl and KCl support. This synthetic route can be used for the large scale synthesis in industries.

Ravindra, R.; Badekai Ramachandra, Bhat

2011-07-01

76

Chemoselective hydrogenation of functionalized nitroarenes and imines by using carbon nanofiber-supported iridium nanoparticles.  

Science.gov (United States)

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF-P, tubular: CNF-T, herringbone: CNF-H) with Ir4(CO)12 in mesitylene at 165 °C provided the corresponding CNF-supported iridium nanoparticles, Ir/CNFs (Ir content=2.3-2.6 wt.%). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size-controlled Ir nanoparticles (average particle size of 1.1-1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF-T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 tm of H2 , and the catalyst is reusable. Ir/CNF-T was also effective for the reductive N-alkylation of anilines with carbonyl compounds. PMID:24347068

Motoyama, Yukihiro; Taguchi, Masahiro; Desmira, Nelfa; Yoon, Seong-Ho; Mochida, Isao; Nagashima, Hideo

2014-01-01

77

Processing and properties of carbon nanofibers reinforced epoxy powder composites  

International Nuclear Information System (INIS)

Commercially available CNFs (diameter 30–300 nm) have been used to develop both bulk and coating epoxy nanocomposites by using a solvent-free epoxy matrix powder. Processing of both types of materials has been carried out by a double-step process consisting in an initial physical premix of all components followed by three consecutive extrusions. The extruded pellets were grinded into powder and sieved. Carbon nanofibers powder coatings were obtained by electrostatic painting of the extruded powder followed by a curing process based in a thermal treatment at 200 °C for 25 min. On the other hand, for obtaining bulk carbon nanofibers epoxy composites, a thermal curing process involving several steps was needed. Gloss and mechanical properties of both nanocomposite coatings and bulk nanocomposites were improved as a result of the processing process. FE-SEM fracture surface microphotographs corroborate these results. It has been assessed the key role played by the dispersion of CNFs in the matrix, and the highly important step that is the processing and curing of the nanocomposites. A processing stage consisted in three consecutive extrusions has reached to nanocomposites free of entanglements neither agglomerates. This process leads to nanocomposite coatings of enhanced properties, as it has been evidenced through gloss and mechanical properties. A dispersion limit of 1% has been determined for the studied system in which a given dispersion has been achieved, as the bedispersion has been achieved, as the bending mechanical properties have been increased around 25% compared with the pristine epoxy resin. It has been also demonstrated the importance of the thickness in the nanocomposite, as it involves the curing stage. The complex curing treatment carried out in the case of bulk nanocomposites has reached to reagglomeration of CNFs.

78

Sensitivity of Dielectric Properties to Wear Process on Carbon Nanofiber/High-Density Polyethylene Composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract We examined the correlation of wear effects with dielectric properties of carbon nanofibers (CNFs; untreated and organosilane-treated)-reinforced high-density polyethylene (HDPE) composites. Wear testing for the nanocomposites over up to 120 h was carried out, and then, dielectric permittivity and dielectric loss factor of the polymer composites with the increased wear time were studied. Scanning electron microscope and optical microscope observations were made to analyze t...

Liu Tian; Wood Weston; Zhong Wei-Hong

2011-01-01

79

Performance of carbon nanofiber-cement composites subjected to accelerated decalcification  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of decalcification on the chemo-mechanical behavior of carbon nanofiber (CNF)-cement composites was studied. Portland cement pastes with and without 0.2% CNFs were subjected to accelerated decalcification by exposure to ammonium nitrate solutions. The influence of microstructural alterations during decalcification on the physical and mechanical properties of the composites was examined. The presence of CNF agglomerates influenced the chemo-mechanical behavior of the composite durin...

Arnold J; Kosson D.; Sanchez F.; Brown L.

2013-01-01

80

Aerosol Monitoring during Carbon Nanofiber Production: Mobile Direct-Reading Sampling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Detailed investigations were conducted at a facility that manufactures and processes carbon nanofibers (CNFs). Presented research summarizes the direct-reading monitoring aspects of the study. A mobile aerosol sampling platform, equipped with an aerosol instrument array, was used to characterize emissions at different locations within the facility. Particle number, respirable mass, active surface area, and photoelectric response were monitored with a condensation particle counter (CPC), a pho...

Evans, Douglas E.; Ku, Bon Ki; Birch, M. Eileen; Dunn, Kevin H.

2010-01-01

 
 
 
 
81

Thermal Expansion of Carbon Nanofiber-Reinforced Multiscale Polymer Composites  

Science.gov (United States)

Improved dimensional stability of composites is desired in applications where they are exposed to varying temperature conditions. The current study aims at analyzing the effect of vapor-grown carbon nanofibers (CNFs) on the thermal expansion behavior of epoxy matrix composites and hollow particle-filled composites (syntactic foams). CNFs have a lower coefficient of thermal expansion (CTE) than epoxy resin, which results in composites with increased dimensional stability as the CNF content is increased. The experimental measurements show that with 10 wt.% CNF, the composite has about 11.6% lower CTE than the matrix resin. In CNF-reinforced syntactic foams, the CTE of the composite decreases with increasing wall thickness and volume fraction of hollow particle inclusions. With respect to neat epoxy resin, a maximum decrease of 38.4% is also observed in the CNF/syntactic foams with microballoon inclusions that range from 15 vol.% to 50 vol.% in all composite mixtures. The experimental results for CNF/syntactic foam are in agreement with a modified version of Kerner's model. A combination of hollow microparticles and nanofibers has resulted in the ability to tailor the thermal expansion of the composite over a wide range.

Poveda, Ronald L.; Achar, Sriniket; Gupta, Nikhil

2012-10-01

82

Nanofiber-crack interaction in a carbon nanofiber reinforced composite  

Science.gov (United States)

The fracture behavior of a nanocomposite reinforced with carbon nanofibers is characterized by considering the interactions between a propagating matrix crack and nanofibers. The nanofibers considered in the study have a hollow structure and transversely isotropic elastic properties. The nanoscale dimensions of these fibers render the experimental measurement of elastic properties very difficult. At the same time, the elastic properties are likely to show a significant variation with a lack of controllability. The nanofiber wall thickness is not constant and instead shows a range of values. The fracture characterization of nanofiber-reinforced composites needs to account for the influence of nanofiber hollow geometry and the interphase between the nanofiber and matrix. However, research work reported to date has been mostly empirical. Analytical studies that consider nanofiber hollow geometry in conjunction with fracture behavior have not been reported. In the present work, an insight is gained into the energetics of a matrix crack propagating towards a nanofiber using an analytical approach. Two-dimensional and three-dimensional studies are performed to compute energy release rates. Mixed mode configurations are also incorporated to evaluate mode II behavior. Additionally, secondary failure mechanisms are investigated by computing the maximum values of interface tractions and their locations. The results of the investigation indicate that the nanofiber wall thickness can have a significant influence on crack energetics. Also, the presence of an interphase between a nanofiber and matrix alters the crack energetics considerably.

Gawandi, Anis A.

83

Direct growth of carbon nanofibers to generate a 3D porous platform on a metal contact to enable an oxygen reduction reaction.  

Science.gov (United States)

For carbon nanotube-based electronics to achieve their full performance potential, it is imperative to minimize the contact resistance between macroscale metal contacts and the carbon nanotube (CNT) nanoelectrodes. We have developed a three-dimensional electrode platform that consists of carbon nanofibers (CNFs) that are directly grown on a metal contact, such as copper (Cu). Carbon nanofiber morphology can be tailored by adjusting the annealing time of a thin electrochemically deposited nickel catalyst layer on copper. We demonstrate that increasing the annealing time increases the amount of copper infused into the nickel catalyst layer. This reduces the carbon deposition rate, and consequently a more well-defined CNF 3D architecture can be fabricated. This direct growth of CNFs on a Cu substrate yields an excellent electron transfer pathway, with contact resistance between CNFs and Cu being comparable to that of a Cu-Cu interface. Furthermore, the excellent bonding strength between CNFs and Cu can be maintained over prolonged periods of ultrasonication. The porous 3D platform affixed with intertwined CNFs allows facile surface functionalization. Using a simple solution soaking procedure, the CNF surface has been successfully functionalized with iron(II) phthalocyanine (FePc). FePc functionalized CNFs exhibit excellent oxygen reduction capability, equivalent to platinum-carbon electrodes. This result demonstrates the technological promise of this new 3D electrode platform that can be exploited in other applications that include sensing, battery, and supercapacitors. PMID:23171171

Pan, David; Ombaba, Matthew; Zhou, Zhi-You; Liu, Yang; Chen, Shaowei; Lu, Jennifer

2012-12-21

84

Nondestructive evaluation of ±45° flat-braided carbon-fiber-reinforced polymers with carbon nanofibers using HTS-SQUID gradiometer  

International Nuclear Information System (INIS)

Highlights: ? Tensile load was applied to braided CFRPs with and without CNFs and cutting edges. ? Visualization method using SQUID gradiometer was also applied to the braided CFRPs. ? Different destructive mechanisms and current distributions were obtained. ? Dispersed CNFs enhanced mechanical and electrical properties of the braided CFRPs. -- Abstract: Step-by-step tensile tests were applied to flat-braided carbon-fiber-reinforced polymers with and without added dispersions of carbon nanofibers (CNFs) and with and without sample sides cut off to study their mechanical properties and destructive mechanisms by means of in situ observation and stress–strain measurements. An ex situ nondestructive evaluation technique, using a high-temperature superconductor superconducting quantum interference device gradiometer, was also applied to the samples to study their electrical properties; the relationships between the mechanical and electrical properties by visualizing current maps in the samples during ac current injection was also studied. Clear differences were observed in the mechanical and electrical properties and the destructive mechanisms between the samples with and without CNFs and with and without cut off sides. These differences were mainly attributed to the addition of CNFs, which enhanced the mechanical and electrical connections between the carbon fiber bundles

85

Classical molecular dynamics simulations of carbon nanofiber nucleation: the effect of carbon concentration in Ni carbide.  

Science.gov (United States)

The atomic-scale nucleation mechanism of vapor-grown carbon nanofibers (CNFs) is investigated using classical molecular dynamics simulations with a developed parameterization. Carbon precipitation and graphene plane formation are simulated, taking into account the carbon concentration (CC) in Ni carbide. The simulated results show that the carbon atoms formed sp(2) networks or sp chains in the Ni nanocrystals and then precipitated onto the Ni surface with distinct precipitation dynamics and time intervals that are dependent on the CC. The lowest-energy configurations of the precipitated carbon atoms exhibit an irregular corrugated network, a defective graphene plane, and separate defective graphene planes under high, medium, and low CC, respectively. These observations are in good agreement with the microstructural characteristics of different types of CNFs from experiments. Pair correlation function calculations show that the precipitated carbon structures exhibit different graphite orderings. The study reveals the atomistic CNF nucleation mechanism and emphasizes the critical role of metal carbide CC in the microstructure formation of CNFs during synthesis. PMID:23999539

Tang, Xian; Xie, Zhiyong; Yin, Teng; Wang, Ji-Wei; Yang, Piaopiao; Huang, Qizhong

2013-10-14

86

A nonlinear effective thermal conductivity model for carbon nanotube and nanofiber suspensions  

International Nuclear Information System (INIS)

It has been experimentally demonstrated that suspensions of carbon nanotubes (CNTs) and nanofibers (CNFs) significantly increase the thermal conductivity of nanofluids; however, a physically sound theory of the underlying phenomenon is still missing. In this study, the nonlinear nature of the effective thermal conductivity enhancement with the particle concentration of CNT and CNF nanofluids is explained physically using the excluded volume concept. Specifically, the number of contacting CNTs and CNFs could be calculated by using the excluded volume concept, where the distance for heat to travel in a cylinder between the contacting cylinders in the thermal network of percolating CNTs and CNFs increased with the excluded volume. In contrast to the effective thermal conductivity model of Sastry et al (2008 Nanotechnology 19 055704) the present revised model could reproduce the nonlinear increase of the thermal conductivity with particle concentration, as well as the dependence on the diameter and aspect ratio of the CNTs and CNFs. It was found that the alignment of CNTs and CNFs due to the long range repulsion force decreases the excluded volume, leading to both the convex and concave nonlinear as well as linear increase of the thermal conductivity with particle concentration. The difference between various carrier fluids of the suspensions could be explained as the result of the change in the excluded volume in different base fluidsluids

87

A nonlinear effective thermal conductivity model for carbon nanotube and nanofiber suspensions  

Energy Technology Data Exchange (ETDEWEB)

It has been experimentally demonstrated that suspensions of carbon nanotubes (CNTs) and nanofibers (CNFs) significantly increase the thermal conductivity of nanofluids; however, a physically sound theory of the underlying phenomenon is still missing. In this study, the nonlinear nature of the effective thermal conductivity enhancement with the particle concentration of CNT and CNF nanofluids is explained physically using the excluded volume concept. Specifically, the number of contacting CNTs and CNFs could be calculated by using the excluded volume concept, where the distance for heat to travel in a cylinder between the contacting cylinders in the thermal network of percolating CNTs and CNFs increased with the excluded volume. In contrast to the effective thermal conductivity model of Sastry et al (2008 Nanotechnology 19 055704) the present revised model could reproduce the nonlinear increase of the thermal conductivity with particle concentration, as well as the dependence on the diameter and aspect ratio of the CNTs and CNFs. It was found that the alignment of CNTs and CNFs due to the long range repulsion force decreases the excluded volume, leading to both the convex and concave nonlinear as well as linear increase of the thermal conductivity with particle concentration. The difference between various carrier fluids of the suspensions could be explained as the result of the change in the excluded volume in different base fluids.

Koo, J; Kang, Y [Department of Mechanical Engineering Kyung Hee University, 1, Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701 (Korea, Republic of); Kleinstreuer, C [Department of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, 3211 Broughton Hall, Raleigh, NC 27695-7910 (United States)], E-mail: jmkoo@khu.ac.kr

2008-09-17

88

A nonlinear effective thermal conductivity model for carbon nanotube and nanofiber suspensions  

Science.gov (United States)

It has been experimentally demonstrated that suspensions of carbon nanotubes (CNTs) and nanofibers (CNFs) significantly increase the thermal conductivity of nanofluids; however, a physically sound theory of the underlying phenomenon is still missing. In this study, the nonlinear nature of the effective thermal conductivity enhancement with the particle concentration of CNT and CNF nanofluids is explained physically using the excluded volume concept. Specifically, the number of contacting CNTs and CNFs could be calculated by using the excluded volume concept, where the distance for heat to travel in a cylinder between the contacting cylinders in the thermal network of percolating CNTs and CNFs increased with the excluded volume. In contrast to the effective thermal conductivity model of Sastry et al (2008 Nanotechnology 19 055704) the present revised model could reproduce the nonlinear increase of the thermal conductivity with particle concentration, as well as the dependence on the diameter and aspect ratio of the CNTs and CNFs. It was found that the alignment of CNTs and CNFs due to the long range repulsion force decreases the excluded volume, leading to both the convex and concave nonlinear as well as linear increase of the thermal conductivity with particle concentration. The difference between various carrier fluids of the suspensions could be explained as the result of the change in the excluded volume in different base fluids.

Koo, J.; Kang, Y.; Kleinstreuer, C.

2008-09-01

89

Fabrication of Uniform Au–Carbon Nanofiber by Two-Step Low Temperature Decomposition  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract This paper presents a facile and efficient way to prepare carbon nanofibers ornamented with Au nanoparticles (Au/CNFs. Gold nanoparticles were first deposited in the channels of an anodized aluminum oxide (AAO membrane by thermal decomposition of HAuCl4and then carbon nanofibers were produced in the same channels loaded with the Au nanoparticles by decomposition of sucrose at 230 °C. An electron microscopy study revealed that the carbon nanofibers, ~10 nm thick and 6 ?m long, were decorated with Au nanoparticles with a diameter of 10 nm. This synthetic route can produce uniform Au nanoparticles on CNF surfaces without using any additional chemicals to modify the AAO channels or the CNF surfaces.

Lee Myeongsoon

2009-01-01

90

Fabrication of Uniform Au-Carbon Nanofiber by Two-Step Low Temperature Decomposition  

Science.gov (United States)

This paper presents a facile and efficient way to prepare carbon nanofibers ornamented with Au nanoparticles (Au/CNFs). Gold nanoparticles were first deposited in the channels of an anodized aluminum oxide (AAO) membrane by thermal decomposition of HAuCl4 and then carbon nanofibers were produced in the same channels loaded with the Au nanoparticles by decomposition of sucrose at 230 °C. An electron microscopy study revealed that the carbon nanofibers, ~10 nm thick and 6 ?m long, were decorated with Au nanoparticles with a diameter of 10 nm. This synthetic route can produce uniform Au nanoparticles on CNF surfaces without using any additional chemicals to modify the AAO channels or the CNF surfaces.

Lee, Myeongsoon; Hong, Seong-Cheol; Kim, Don

2009-08-01

91

Fabrication of Uniform Au–Carbon Nanofiber by Two-Step Low Temperature Decomposition  

Science.gov (United States)

This paper presents a facile and efficient way to prepare carbon nanofibers ornamented with Au nanoparticles (Au/CNFs). Gold nanoparticles were first deposited in the channels of an anodized aluminum oxide (AAO) membrane by thermal decomposition of HAuCl4and then carbon nanofibers were produced in the same channels loaded with the Au nanoparticles by decomposition of sucrose at 230 °C. An electron microscopy study revealed that the carbon nanofibers, ~10 nm thick and 6 ?m long, were decorated with Au nanoparticles with a diameter of 10 nm. This synthetic route can produce uniform Au nanoparticles on CNF surfaces without using any additional chemicals to modify the AAO channels or the CNF surfaces. PMID:20596484

2009-01-01

92

Morphological Control of Ion-Induced Carbon Nanofibers and Their Field Emission Properties  

Science.gov (United States)

Carbon nanofibers (CNFs) were fabricated on graphite plates using “Ar+ ion sputtering method” in large amount at room temperature. The morphology of CNFs was controlled by a simultaneous carbon supply during ion sputtering. CNF-tipped cones were formed on graphite plate surfaces without carbon supply whereas those with a simultaneous carbon supply featured mainly needle-like protrusions of large size. The field electron emission (FE) properties, measured using parallel plate configurations in 10-4 Pa range, showed the threshold fields of 4.4 and 5.2V/µm with a current density of 1 µA/cm2 for CNF-tipped cones and needle-like protrusion, respectively. Reliability test results indicated that CNF-tipped cones were more stable than needle-like protrusion. The morphological change after reliability test showed a so-called “self-regenerative” process and structure damage for CNF-tipped cones and needle-like protrusions, respectively.

Yusop, Mohd Zamri Bin Mohd; Ghosh, Pradip; Wang, Zhipeng; Tanemura, Masaki; Hayashi, Yasuhiko; Soga, Tetsuo

93

Control of nitrogen insertion during the growth of nitrogen-containing carbon nanofibers on cordierite monolith walls.  

Science.gov (United States)

A well attached coating of nitrogen-functionalised carbon nanofibers (N-CNFs) has been prepared on the walls of cordierite monolith channels. It is formed via concurrent decomposition of ethane and ammonia catalysed by nickel nanoparticles dispersed on alumina coated cordierite monolith. N-CNF/monoliths synthesis employing several growth temperatures and NH(3) compositions was exhaustively characterised by Raman, XPS, elemental analysis and TEM. Synthesis conditions affected profoundly content and type of nitrogen functionality, enabling its fine tuning. N-CNFs surface chemistry and microstructure differed remarkably from its N-free counterparts. PMID:22307412

Roldán, Laura; Armenise, Sabino; Marco, Yanila; García-Bordejé, Enrique

2012-03-14

94

Preparations of carbon nanofiber emitters for diode type field emission display with organic luminescence thin films  

International Nuclear Information System (INIS)

Carbon nanofiber (CNF), which was massively synthesized by thermal vapor deposition, emitters were fabricated by following easy processes: screen printing (SP), spin coating (SC) and spray spreading (SS) methods. Emission current density of 23 ?A/cm2 at 300 V was obtained after treatment by nitric acid to CNF paste in the SP method. Specimen prepared by the SC method with nanofibers of which length is approximately 1.5 ?m showed 85.2 ?A/cm2 at 350 V. The surface was sufficiently smooth and CNFs were dispersive with the density of 1.0 * 107 cm-2. Such the surface structure is suitable for electric field being applied to CNFs uniformly. The result of the SS method insisted that the existence of the nanofibers with the length less than 1 ?m on the substrate was important to obtain a high performance of emitter. In the SS method sparse CNFs were obtained, that is suitable surface structure for emission, with the decanted suspension from tetrahydrofuran (THF) rather than that of dimethylformamide (DMF). The boiling temperature of solution for suspension and substrate temperature during spray were significant parameters in the SS method. The electric field enhancement factor was 2560 in the specimen with DMF

95

Preparations of carbon nanofiber emitters for diode type field emission display with organic luminescence thin films  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofiber (CNF), which was massively synthesized by thermal vapor deposition, emitters were fabricated by following easy processes: screen printing (SP), spin coating (SC) and spray spreading (SS) methods. Emission current density of 23 {mu}A/cm{sup 2} at 300 V was obtained after treatment by nitric acid to CNF paste in the SP method. Specimen prepared by the SC method with nanofibers of which length is approximately 1.5 {mu}m showed 85.2 {mu}A/cm{sup 2} at 350 V. The surface was sufficiently smooth and CNFs were dispersive with the density of 1.0 * 10{sup 7} cm{sup -2}. Such the surface structure is suitable for electric field being applied to CNFs uniformly. The result of the SS method insisted that the existence of the nanofibers with the length less than 1 {mu}m on the substrate was important to obtain a high performance of emitter. In the SS method sparse CNFs were obtained, that is suitable surface structure for emission, with the decanted suspension from tetrahydrofuran (THF) rather than that of dimethylformamide (DMF). The boiling temperature of solution for suspension and substrate temperature during spray were significant parameters in the SS method. The electric field enhancement factor was 2560 in the specimen with DMF.

Iwata, Nobuyuki [Department of Electronics and Computer Science, CST Nihon University, 7-24-1 Narashinodai, Funabashi-shi, Chiba, 274-8501 (Japan)], E-mail: iwata@ecs.cst.nihon-u.ac.jp; Hata, Yasunori; Yoshikuni, Masato; Yamamoto, Hiroshi [Department of Electronics and Computer Science, CST Nihon University, 7-24-1 Narashinodai, Funabashi-shi, Chiba, 274-8501 (Japan)

2007-09-15

96

Effect of carbon nanofibers on the infiltration and thermal conductivity of carbon/carbon composites  

International Nuclear Information System (INIS)

Highlights: ? The CNFs improve the infiltration rate and thermal properties of carbon/carbon composites. ? The densification rate increases with the CNF content increasing at the beginning of infiltration. ? The values of the thermal conductivity of the composite obtain their maximum values at 5 wt.%. -- Abstract: Preforms containing 0, 5, 10, 15 and 20 wt.% carbon nanofibers (CNFs) were fabricated by spreading layers of carbon cloth, and infiltrated using the electrified preform heating chemical vapor infiltration method (ECVI) under atmospheric pressure. Initial thermal gradients were determined. Resistivity and density evolutions with infiltration time have been recorded. Scanning electron microscopy, polarized light micrograph and X-ray diffraction technique were used to analyze the experiment results. The results showed that the infiltration rate increased with the rising of CNF content, and after 120 h of infiltration, the density was the highest when the CNF content was 5 wt.%, but the composite could not be densified efficiently as the CNF content ranged from 10 wt.% to 20 wt.%. CNF-reinforced C/C composites have enhanced thermal conductivity, the values at 5 wt.% were increased by nearly 5.5-24.1% in the X-Y direction and 153.8-251.3% in the Z direction compared to those with no CNFs. When the additive content was increased to 20 wt.%, due to the holes and cavities in the CNF web and between carbon cloth and matrix, the thermal conductivities in the X-Y and Z directions decreased from their maximum values at 5 wt.%.

97

Deposition of vertically oriented carbon nanofibers in atmospheric pressure radio frequency discharge  

International Nuclear Information System (INIS)

Deposition of vertically oriented carbon nanofibers (CNFs) has been studied in an atmospheric pressure radio frequency discharge without dielectric barrier covering the metallic electrodes. When the frequency is sufficiently high so that ions reside in the gap for more than one rf cycle ('trapped ions'), the operating voltage decreases remarkably and the transition from a uniform glow discharge to an arc discharge is suppressed even without dielectric barriers. More importantly, the trapped ions are able to build up a cathodic ion sheath. A large potential drop is created in the sheath between the bulk plasma and the electrode, which is essential for aligning growing CNFs. At the same time, the damage to CNFs due to ion bombardment can be minimized at atmospheric pressure. The primary interest of the present work is in identifying the cathodic ion sheath and investigating how it influences the alignment of growing CNFs in atmospheric pressure plasma-enhanced chemical-vapor deposition. Spectral emission profiles of He (706 nm), H? (656 nm), and CH (432 nm) clearly showed that a dark space is formed between the cathode layer and the heated bottom electrode. However, increasing the rf power induced the transition to a nonuniform ?-mode discharge which creates intense plasma spots in the dark space. Aligned CNFs can be grown at moderate input power during the initial stage of the deposition process. Catalyst particles were heavily contaminated by precipitated carbon in contaminated by precipitated carbon in less than 5 min. Alignment deteriorates as CNFs grow and deposition was virtually terminated by the deactivation of catalyst particles

98

Maghemite nanoparticles on electrospun CNFs template as prospective lithium-ion battery anode.  

Science.gov (United States)

In this work, maghemite (?-Fe2O3) nanoparticles were uniformly coated on carbon nanofibers (CNFs) by a hybrid synthesis procedure combining an electrospinning technique and hydrothermal method. Polyacrylonitrile nanofibers fabricated by the electrospinning technique serve as a robust support for iron oxide precursors during the hydrothermal process and successfully limit the aggregation of nanoparticles at the following carbonization step. The best materials were optimized under a carbonization condition of 600 °C for 12 h. X-ray diffraction and electron microscopy studies confirm the formation of a maghemite structure standing on the surface of CNFs. The average size of ?-Fe2O3 nanoparticles is below 100 nm, whereas CNFs are ?150 nm in diameter. In comparison with aggregated bare iron oxide nanoparticles, the as-prepared carbon-maghemite nanofibers exhibit a higher surface area and greatly improved electrochemical performance (>830 mAh g(-1) at 50 mA g(-1) for 40 cycles and high rate capacity up to 5 A g(-1) in the voltage range of 0.005-3 V vs Li). The greatly enhanced electrochemical performance is attributed to the unique one-dimensional nanostructure and the limited aggregation of nanoparticles. PMID:24383672

Wu, Yongzhi; Zhu, Peining; Reddy, M V; Chowdari, B V R; Ramakrishna, S

2014-02-12

99

Synthesis of Carbon Nanofibers Based on Resol Type Phenol Resin and Fe(III) Catalysts  

International Nuclear Information System (INIS)

The carbon nanofibers (CNFs) used in this study were synthesized with an iron catalyst and ethylene as a carbon source. A concentration of 30 wt % iron(III) acetylacetonate was dissolved in resol type phenol resin and polyurethane foam was put into the solution. The sample was calendered after being cured at 80 .deg. C in air for 24 h. Stabilization and carbonization of the resol type phenol resin and reduction of the Fe3+ were completed in a high-temperature furnace by the following steps: heating to 600 .deg. C at a rate of 10 .deg. C/min with a mixture of H2/N2 for 4 h to reduce the Fe3+ to Fe; heating to 1000 .deg. C in N2 at a rate 10 .deg. C/min for 30 minutes for pyrolysis; synthesizing CNFs in a mixture of 20.1% ethylene and H2/N2 at 700 .deg. C for 2 h using a CVD process. Finally, the structural characterization of the CNFs was performed by scanning electron microscopy and a synthesis analysis was carried out using energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Specific surface area analysis of the CNFs was also performed by N2-sorption

100

Efficient synthesis of Pt nanoparticles supported on hydrophobic graphitized carbon nanofibers for electrocatalysts using noncovalent functionalization  

Energy Technology Data Exchange (ETDEWEB)

As an alternative to the oxidative acid treatment, a noncovalent {pi}-{pi} interaction method is employed to deposit Pt electrocatalysts on highly hydrophobic carbon nanofibers (CNFs) for the application of polymer electrolyte membrane (PEM) fuel cells. Three different functionalization agents, namely benzyl mercaptan (BM), 1-aminopyrene (AP), and 1-pyrenecarboxylic acid (PCA), are used to functionalize CNFs and the effect of these groups on the electrochemical properties is examined. While the BM and AP act as a poison to Pt catalyst, the functionalization of CNF with PCA improves the distribution and loading of Pt as well as reducing the sintering of Pt particles. From the carbon corrosion test, unlike the oxidative acid treatment, the PCA treatment sustains the corrosion resistance of CNFs because it preserves the intrinsic properties of CNFs without damaging their surface structure. Therefore, the PCA treatment is a very effective way to prepare catalysts for PEM fuel cells and also extended to the fabrication of graphitized-carbon-supported catalysts of other precious metal for various applications. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Oh, Hyung-Suk; Kim, Hansung [Department of Chemical and Biomolecular Engineering, Yonsei University, 134 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749 (Korea, Republic of)

2011-10-21

 
 
 
 
101

In situ growth cupric oxide nanoparticles on carbon nanofibers for sensitive nonenzymatic sensing of glucose  

International Nuclear Information System (INIS)

Highlights: • CuO nanoparticles were directly and homogeneously grown on carbon nanofibers. • The obtained nanocomposite showed high electrooxidize activity to glucose. • A nonenzymatic glucose sensor was constructed based on the functional nanocomposite. • This sensor showed good performance to glucose. • The proposed sensor was successfully applied in detection of glucose in blood serum. -- Abstract: A novel method was employed to directly and homogeneously attaching cupric oxide nanoparticles (CuONPs) on carbon nanofibers (CNFs) for sensitive amperometric nonenzymatic sensing of glucose. The obtained CuONPs-CNFs nanocomposite was characterized by transmission electron microscopy and X-ray diffraction. The CuONPs-CNFs nanocomposite modified glassy carbon electrode showed high electrocatalytic activity toward the oxidation of glucose in alkaline media and a nonenzymatic glucose sensor was constructed based on the functional nanocomposite modified electrode. Under optimal experimental conditions, the designed sensor exhibited a wide linear response to glucose ranging from 5.0 × 10?7 to 1.1 × 10?2 M with a high sensitivity of 2739 ?A mM?1 cm?2 and a low detection limit down to 0.2 ?M at the signal to noise ratio of 3. This sensor showed good accuracy, acceptable precision and reproducibility. Moreover, the proposed sensor was successfully applied in the detection of glucose in human blood serum indicating its possibility in practical application

102

Chemical vapor-deposited carbon nanofibers on carbon fabric for supercapacitor electrode applications.  

Science.gov (United States)

Entangled carbon nanofibers (CNFs) were synthesized on a flexible carbon fabric (CF) via water-assisted chemical vapor deposition at 800°C at atmospheric pressure utilizing iron (Fe) nanoparticles as catalysts, ethylene (C2H4) as the precursor gas, and argon (Ar) and hydrogen (H2) as the carrier gases. Scanning electron microscopy, transmission electron microscopy, and electron dispersive spectroscopy were employed to characterize the morphology and structure of the CNFs. It has been found that the catalyst (Fe) thickness affected the morphology of the CNFs on the CF, resulting in different capacitive behaviors of the CNF/CF electrodes. Two different Fe thicknesses (5 and 10 nm) were studied. The capacitance behaviors of the CNF/CF electrodes were evaluated by cyclic voltammetry measurements. The highest specific capacitance, approximately 140 F g-1, has been obtained in the electrode grown with the 5-nm thickness of Fe. Samples with both Fe thicknesses showed good cycling performance over 2,000 cycles. PMID:23181897

Gao, Yang; Pandey, Gaind P; Turner, James; Westgate, Charles R; Sammakia, Bahgat

2012-01-01

103

Gas-induced formation of Cu nanoparticle as catalyst for high-purity straight and helical carbon nanofibers.  

Science.gov (United States)

The facile preparation of high-purity carbon nanofibers (CNFs) remains challenging due to the high complexity and low controllability in reaction. A novel approach using gas-induced formation of Cu crystals to control the growth of CNFs is developed in this study. By adjusting the atmospheric composition, controllable preparation of Cu nanoparticles (NPs) with specific size and shape is achieved, and they are further used as a catalyst for the growth of straight or helical CNFs with good selectivity and high yield. The preparation of Cu NPs and the formation of CNFs are completed by a one-step process. The inducing effect of N(2), Ar, H(2), and C(2)H(2) on the formation of Cu NPs is systematically investigated through a combined experimental and computational approach. The morphology of CNFs obtained under different conditions is rationalized in terms of Cu NP and CNF growth models. The results suggest that the shapes of CNFs, namely, straight or helical, depend closely on the size, shape, and facet activity of Cu NPs, while such a gas-inducing method offers a simple way to control the formation of Cu NPs. PMID:22963353

Jian, Xian; Jiang, Man; Zhou, Zuowan; Zeng, Qun; Lu, Jun; Wang, Dingchuan; Zhu, Junting; Gou, Jihua; Wang, Yong; Hui, David; Yang, Mingli

2012-10-23

104

Improved of the wear resistance of carbon nanofiber/epoxy nanocomposite by a surface functionalization of the reinforcement  

Science.gov (United States)

A functionalization process with HNO3 acid on carbon nanofibers has been carried out in order to improve the wear resistance of a carbon nanofiber (CNF)/epoxi resin nanocomposite materials. Friction and wear tests were carried out using ball-on-disk equipment. Results show that the wear volume loss is reduced with CNF content. Therefore, the use of functionalized CNFs in the manufacturing of epoxy matrix nanocomposites achieves to improve both the contact reinforcement/matrix and the filler distribution in the nanocomposite. The wear resistance increases 30% to 40% over the untreated CNF.

Barrena, M. I.; Gómez de Salazar, J. M.; Soria, A.; Cañas, R.

2014-01-01

105

Carbon-Nanofiber-Reinforced Syntactic Foams: Compressive Properties and Strain Rate Sensitivity  

Science.gov (United States)

The current study is focused on exploring the possibility of reinforcing syntactic foams with carbon nanofibers (CNFs). Syntactic foams are hollow, particle-filled composites that are widely used in marine structures and are now finding applications in other modes of transportation due to their high stiffness-to-weight ratio. The compressive properties of syntactic foams reinforced with CNFs are characterized over the strain rate range of 10-4 to 3,000 s-1, which covers seven orders of magnitude. The results show that despite lower density with respect to neat epoxy, CNF/syntactic foams can have up to 7.3% and 15.5% higher quasi-static compressive strength and modulus, respectively, for the compositions that were characterized in the current study. In addition, these properties can be tailored over a wide range by means of hollow particle wall thickness and volume fraction, and CNF volume fraction. The compressive strength of CNF/syntactic foams is also shown to generally increase by up to a factor of 3.41 with increasing strain rate when quasi-static and high-strain-rate testing data are compared. Extensive microscopy of the CNF/syntactic foams is conducted to understand the failure and energy absorption mechanisms. Crack bridging by CNFs is observed in the specimens, which can delay final failure and increase the energy absorption capacity of the specimens. Deformation of CNFs is also noticed in the material microstructure. The deformation and failure mechanisms of nanofibers are related to the test strain rate and the structure of CNFs.

Poveda, Ronald L.; Gupta, Nikhil

2014-01-01

106

Direct synthesis of carbon nanofibers from South African coal fly ash  

Science.gov (United States)

Carbon nanofibers (CNFs), cylindrical nanostructures containing graphene, were synthesized directly from South African fly ash (a waste product formed during the combustion of coal). The CNFs (as well as other carbonaceous materials like carbon nanotubes (CNTs)) were produced by the catalytic chemical vapour deposition method (CCVD) in the presence of acetylene gas at temperatures ranging from 400°C to 700°C. The fly ash and its carbonaceous products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), laser Raman spectroscopy and Brunauer-Emmett-Teller (BET) surface area measurements. It was observed that as-received fly ash was capable of producing CNFs in high yield by CCVD, starting at a relatively low temperature of 400°C. Laser Raman spectra and TGA thermograms showed that the carbonaceous products which formed were mostly disordered. Small bundles of CNTs and CNFs observed by TEM and energy-dispersive spectroscopy (EDS) showed that the catalyst most likely responsible for CNF formation was iron in the form of cementite; X-ray diffraction (XRD) and Mössbauer spectroscopy confirmed these findings.

Hintsho, Nomso; Shaikjee, Ahmed; Masenda, Hilary; Naidoo, Deena; Billing, Dave; Franklyn, Paul; Durbach, Shane

2014-08-01

107

Effect of Sulfur Concentration on the Morphology of Carbon Nanofibers Produced from a Botanical Hydrocarbon  

Directory of Open Access Journals (Sweden)

Full Text Available AbstractCarbon nanofibers (CNF with diameters of 20–130 nm with different morphologies were obtained from a botanical hydrocarbon: Turpentine oil, using ferrocene as catalyst source and sulfur as a promoter by simple spray pyrolysis method at 1,000 °C. The influence of sulfur concentration on the morphology of the carbon nanofibers was investigated. SEM, TEM, Raman, TGA/DTA, and BET surface area were employed to characterize the as-prepared samples. TEM analysis confirms that as-prepared CNFs have a very sharp tip, bamboo shape, open end, hemispherical cap, pipe like morphology, and metal particle trapped inside the wide hollow core. It is observed that sulfur plays an important role to promote or inhibit the CNF growth. Addition of sulfur to the solution of ferrocene and turpentine oil mixture was found to be very effective in promoting the growth of CNF. Without addition of sulfur, carbonaceous product was very less and mainly soot was formed. At high concentration of sulfur inhibit the growth of CNFs. Hence the yield of CNFs was optimized for a given sulfur concentration.

Ghosh Kaushik

2008-01-01

108

Effect of Sulfur Concentration on the Morphology of Carbon Nanofibers Produced from a Botanical Hydrocarbon  

Science.gov (United States)

Carbon nanofibers (CNF) with diameters of 20 130 nm with different morphologies were obtained from a botanical hydrocarbon: Turpentine oil, using ferrocene as catalyst source and sulfur as a promoter by simple spray pyrolysis method at 1,000 °C. The influence of sulfur concentration on the morphology of the carbon nanofibers was investigated. SEM, TEM, Raman, TGA/DTA, and BET surface area were employed to characterize the as-prepared samples. TEM analysis confirms that as-prepared CNFs have a very sharp tip, bamboo shape, open end, hemispherical cap, pipe like morphology, and metal particle trapped inside the wide hollow core. It is observed that sulfur plays an important role to promote or inhibit the CNF growth. Addition of sulfur to the solution of ferrocene and turpentine oil mixture was found to be very effective in promoting the growth of CNF. Without addition of sulfur, carbonaceous product was very less and mainly soot was formed. At high concentration of sulfur inhibit the growth of CNFs. Hence the yield of CNFs was optimized for a given sulfur concentration.

Ghosh, Pradip; Soga, Tetsuo; Ghosh, Kaushik; Jimbo, Takashi; Katoh, Ryoji; Sumiyama, Kenji; Ando, Yoshinori

2008-07-01

109

Fabrication and Characterization of High Temperature Resin/Carbon Nanofiber Composites  

Science.gov (United States)

Multifunctional composites present a route to structural weight reduction. Nanoparticles such as carbon nanofibers (CNF) provide a compromise as a lower cost nanosize reinforcement that yields a desirable combination of properties. Blends of PETI-330 and CNFs were prepared and characterized to investigate the potential of CNF composites as a high performance structural medium. Dry mixing techniques were employed and the effect of CNF loading level on melt viscosity was determined. The resulting powders were characterized for degree of mixing, thermal and rheological properties. Based on the characterization results, samples containing 30 and 40 wt% CNF were scaled up to approx.300 g and used to fabricate moldings 10.2 cm x 15.2 cm x 0.32 cm thick. The moldings were fabricated by injecting the mixtures at 260-280 C into a stainless steel tool followed by curing for 1 h at 371 C. The tool was designed to impart high shear during the process in an attempt to achieve some alignment of CNFs in the flow direction. Moldings were obtained that were subsequently characterized for thermal, mechanical and electrical properties. The degree of dispersion and alignment of CNFs were investigated using high-resolution scanning electron microscopy. The preparation and preliminary characterization of PETI-330/CNF composites are discussed. Keywords: resins, carbon nanofibers, scanning electron microscopy, electrical properties, thermal conductivity,injection

Ghose, Sayata; Watson, Kent A.; Working, Dennis C.; Criss, Jim M.; Siochi, Emilie J.; Connell, John W.

2005-01-01

110

Adsorbents based on carbon microfibers and carbon nanofibers for the removal of phenol and lead from water.  

Science.gov (United States)

This paper describes the production, characteristics, and efficacy of carbon microfibers and carbon nanofibers for the removal of phenol and Pb(2+) from water by adsorption. The first adsorbent produced in the current investigation contained the ammonia (NH(3)) functionalized micron-sized activated carbon fibers (ACF). Alternatively, the second adsorbent consisted of a multiscale web of ACF/CNF, which was prepared by growing carbon nanofibers (CNFs) on activated ACFs via catalytic chemical vapor deposition (CVD) and sonication, which was conducted to remove catalytic particles from the CNF tips and open the pores of the CNFs. The two adsorbents prepared in the present study, ACF and ACF/CNF, were characterized by several analytical techniques, including SEM-EDX and FT-IR. Moreover, the chemical composition, BET surface area, and pore-size distribution of the materials were determined. The hierarchal web of carbon microfibers and nanofibers displayed a greater adsorption capacity for Pb(2+) than ACF. Interestingly, the adsorption capacity of ammonia (NH(3)) functionalized ACFs for phenol was somewhat larger than that of the multiscale ACF/CNF web. Difference in the adsorption capacity of the adsorbents was attributed to differences in the size of the solutes and their reactivity towards ACF and ACF/CNF. The results indicated that ACF-based materials were efficient adsorbents for the removal of inorganic and organic solutes from wastewater. PMID:21507421

Chakraborty, Anindita; Deva, Dinesh; Sharma, Ashutosh; Verma, Nishith

2011-07-01

111

Factors affecting the growth of carbon nanofibers on titanium substrates and their electrical properties.  

Science.gov (United States)

The goal of this work is to investigate the growth mechanism of carbon nanofibers (CNFs) on titanium (Ti) substrates and the factors that affect the growth the CNFs. Ti substrates were chosen because they are a biocompatible material and the results of this work have potential application for electrochemical biosensors and/or supercapacitors. CNFs were synthesized via water-assisted chemical vapor deposition at 800 degrees C and at atmospheric pressure utilizing iron (Fe) nanoparticles as catalysts, ethylene (C2H4) as the precursor gas, and argon (Ar) and hydrogen (H2) as the carrier gases. The introduction of an Al2O3 buffer layer and the thickness as well as the roughness of the Ti substrates was found to affect the morphology and distribution of the Fe nanoparticles, and thus the morphology of the CNFs. The sputtered buffer layer leads to fewer catalyst nanoparticles that diffuse into the underlying Ti layer which results in a more uniform and denser distribution of the Fe nanoparticles. Stronger catalyst-substrate interaction results in a larger and sparser distribution of the Fe nanoparticles. On the other hand, when the roughness of the substrate exceeds the thickness of the Fe catalyst layer, the nanoparticles tend to form into large sized particles. The longest and densest CNFs (10.7 microm in length) were grown on a Ti layer of 10 nm in thickness with the introduction of the buffer layer. The characterization of CNFs was carried out using scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), atomic force microscopy (AFM), transmission electron microscopy (TEM). The electrical properties of the CNF films were investigated via the four-point probe method that showed an ohmic behavior. The sheet resistances of the CNF films on Ti substrates of different thickness were also reported. PMID:23421139

Gao, Yang; Adusumilli, Siva P; Turner, James; Lesperance, Leann; Westgate, Charles; Sammakia, Baghat

2012-10-01

112

Gas phase oxidation as a tool to introduce oxygen containing groups on metal-loaded carbon nanofibers  

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Oxygen containing groups were introduced, onto carbon nanofibers (CNFs) that were previously loaded with palladium, using HNO3 vapor. Using traditional liquid-phase oxidations this is not possible due to severe metal leaching. For the samples oxidized using HNO3 vapor temperature programmed desorption and X-ray photoelectron spectroscopy revealed the presence of two major classes of oxygen containing groups, i.e. carboxylic acid groups which are thermally stable up to 300 °C and less acidic ...

Gosselink, R. W.; Berg, R. Den; Xia, B.; Muhler, M.; Jong, K. P.; Bitter, J. H.

2012-01-01

113

Electromechanically tunable carbon nanofiber photonic crystal.  

Science.gov (United States)

We demonstrate an electrically tunable 2D photonic crystal array constructed from vertically aligned carbon nanofibers. The nanofibers are actuated by applying a voltage between adjacent carbon nanofiber pairs grown directly on metal electrodes, thus dynamically changing the form factor of the photonic crystal lattice. The change in optical properties is characterized using optical diffraction and ellipsometry. The experimental results are shown to be in agreement with theoretical predictions and provide a proof-of-principle for rapidly switchable photonic crystals operating in the visible that can be fabricated using standard nanolithography techniques combined with plasma CVD growth of the nanofibers. PMID:23272804

Rehammar, Robert; Ghavanini, Farzan Alavian; Magnusson, Roger; Kinaret, Jari M; Enoksson, Peter; Arwin, Hans; Campbell, Eleanor E B

2013-02-13

114

Growth of Y-shaped Carbon Nanofibers from Ethanol Flames  

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Full Text Available Abstract Y-shaped carbon nanofibers as a multi-branched carbon nanostructure have potential applications in electronic devices. In this article, we report that several types of Y-shaped carbon nanofibers are obtained from ethanol flames. These Y-shaped carbon nanofibers have different morphologies. According to our experimental results, the growth mechanism of Y-shaped carbon nanofibers has been discussed and a possible growth model of Y-shaped carbon nanofibers has been proposed.

Cheng Jin

2008-01-01

115

Structure and electrochemical applications of boron-doped graphitized carbon nanofibers  

International Nuclear Information System (INIS)

Boron-doped graphitized carbon nanofibers (CNFs) were prepared by optimizing CNFs preparation, surface treatment, graphitization and boron-added graphitization. The interlayer spacing (d002) of the boron-doped graphitized CNFs reached 3.356 ?, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d002 is less than 3.400 ?, were selected for further heat treatment. The first heat treatment of PCNFs at 2800?°C yielded a d002 between 3.357 and 3.365 ?. Successive nitric acid treatment and a second heat treatment with boric acid reduced d002 to 3.356 ?. The resulting boron-doped PCNFs exhibited a high discharge capacity of 338 mAh g?1 between 0 and 0.5 V versus Li/Li+ and 368 mAh g?1 between 0 and 1.5 V versus Li/Li+. The first-cycle Coulombic efficiency was also enhanced to 71–80%. Such capacity is comparable to that of natural graphite under the same charge/discharge conditions. The boron-doped PCNFs also exhibited improved rate performance with twice the capacity of boron-doped natural graphite at a discharge rate of 5 C. (paper)

116

Effect of thermal interface on heat flow in carbon nanofiber composites.  

Science.gov (United States)

The thermal transport process in carbon nanofiber (CNF)/epoxy composites is addressed through combined micromechanics and finite element modeling, guided by experiments. The heat exchange between CNF constituents and matrix is studied by explicitly accounting for interface thermal resistance between the CNFs and the epoxy matrix. The effects of nanofiber orientation and discontinuity on heat flow and thermal conductivity of nanocomposites are investigated through simulation of the laser flash experiment technique and Fourier's model of heat conduction. Our results indicate that when continuous CNFs are misoriented with respect to the average temperature gradient, the presence of interfacial resistance does not affect the thermal conductivity of the nanocomposites, as most of the heat flow will be through CNFs; however, interface thermal resistance can significantly alter the patterns of heat flow within the nanocomposite. It was found that very high interface resistance leads to heat entrapment at the interface near to the heat source, which can promote interface thermal degradation. The magnitude of heat entrapment, quantified via the peak transient temperature rise at the interface, in the case of high thermal resistance interfaces becomes an order of magnitude more intense as compared to the case of low thermal resistance interfaces. Moreover, high interface thermal resistance in the case of discontinuous fibers leads to a nearly complete thermal isolation of the fibers from the matrix, which will marginalize the contribution of the CNF thermal conductivity to the heat transfer in the composite. PMID:24344861

Gardea, F; Naraghi, M; Lagoudas, D

2014-01-22

117

Carbon nanofibers as electrocatalyst support for fuel cells: Effect of hydrogen on their properties in CH{sub 4} decomposition  

Energy Technology Data Exchange (ETDEWEB)

The influence of low partial pressure of hydrogen on carbon nanofibers (CNFs) properties has been studied in the synthesis by methane catalytic decomposition, with the purpose of using them in polymer electrolyte fuel cells as electrocatalyst support. Using CNFs in this kind of application presents a good perspective to improve the fuel cell overall performance. CNF growth in the catalytic decomposition of methane and the characteristics which are typically required in a carbonaceous support, are influenced by hydrogen concentration, which has been studied at different temperatures. The textural, morphological and structural characteristics of the obtained CNFs have been determined by nitrogen physisorption, X-ray diffraction, electron microscopy and thermogravimetry. Electrical conductivity of CNFs has been measured compressing the powder and using a two-probe method. It was observed that low values of partial pressure of hydrogen in methane influence positively structural ordering of CNFs, and in turn improve electrical conductivity, with a slight influence on textural properties leading to highly mesoporous carbon. (author)

Sebastian, D.; Suelves, I.; Lazaro, M.J.; Moliner, R. [Instituto de Carboquimica (CSIC), Miguel Luesma Castan 4, 50018 Zaragoza (Spain)

2009-07-01

118

Sensitivity of Dielectric Properties to Wear Process on Carbon Nanofiber/High-Density Polyethylene Composites  

Science.gov (United States)

We examined the correlation of wear effects with dielectric properties of carbon nanofibers (CNFs; untreated and organosilane-treated)-reinforced high-density polyethylene (HDPE) composites. Wear testing for the nanocomposites over up to 120 h was carried out, and then, dielectric permittivity and dielectric loss factor of the polymer composites with the increased wear time were studied. Scanning electron microscope and optical microscope observations were made to analyze the microstructure features of the nanocomposites. The results reveal that there exist approximate linear relationships of permittivity with wear coefficient for the nanocomposites. Composites containing silanized CNFs with the sufficiently thick coating exhibited high wear resistance. The change in permittivity was more sensitive to the increased wear coefficient for the nanocomposites with lower wear resistance. This work provides potential for further research on the application of dielectric signals to detect the effects of wear process on lifetime of polymeric materials.

Liu, Tian; Wood, Weston; Zhong, Wei-Hong

2011-12-01

119

Optical limiting of high-repetition-rate laser pulses by carbon nanofibers suspended in polydimethylsiloxane  

Science.gov (United States)

The optical limiting (OL) behavior of carbon nanofibers (CNFs) in polydimethylsiloxane (PDMS) was studied and compared with that of CNFs in water, and polyhedral multi-shell fullerene-like nanostructures (PMFNs) also in water. It was shown that when switching from single-shot to pulse-periodic regime of laser pulses (10 Hz), the CNF in PDMS suspension retains its OL characteristics, while in the aqueous suspensions, considerable degradation of OL characteristics is observed. It was also observed that a powerful laser pulse causes the CNF in PDMS suspension to become opaque for at least three seconds, while such a pulse brings out a bleaching effect in aqueous PMFN and CNF suspensions. The processes of OL degradation in aqueous suspensions, bleaching and darkening of the studied materials are discussed herein.

Videnichev, Dmitry A.; Belousova, Inna M.

2014-06-01

120

Sensitivity of Dielectric Properties to Wear Process on Carbon Nanofiber/High-Density Polyethylene Composites  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract We examined the correlation of wear effects with dielectric properties of carbon nanofibers (CNFs; untreated and organosilane-treated-reinforced high-density polyethylene (HDPE composites. Wear testing for the nanocomposites over up to 120 h was carried out, and then, dielectric permittivity and dielectric loss factor of the polymer composites with the increased wear time were studied. Scanning electron microscope and optical microscope observations were made to analyze the microstructure features of the nanocomposites. The results reveal that there exist approximate linear relationships of permittivity with wear coefficient for the nanocomposites. Composites containing silanized CNFs with the sufficiently thick coating exhibited high wear resistance. The change in permittivity was more sensitive to the increased wear coefficient for the nanocomposites with lower wear resistance. This work provides potential for further research on the application of dielectric signals to detect the effects of wear process on lifetime of polymeric materials.

Liu Tian

2011-01-01

 
 
 
 
121

A fine-focusing x-ray source using carbon-nanofiber field emitter  

Science.gov (United States)

A fine-focusing x-ray source has been constructed employing a field electron emitter prepared by growing carbon-nanofibers (CNFs) on a metal tip. The x-ray source is composed of a CNF field electron emitter, an electrostatic lens, two magnetic lenses, and a W-target for generating x-rays by electron impact. The CNFs provided field electrons with a current density of J ˜5×109 A/m2, which was evaluated with the aid of Fowler-Nordheim theory. The electron beam extracted from the CNF emitter was accelerated to the energies of E =10-25 keV, and then focused by the lenses. By recording the x-ray images of test charts, the optimum resolution of the x-ray source was estimated to be approximately Dx=0.5 ?m.

Sugimoto, W.; Sugita, S.; Sakai, Y.; Goto, H.; Watanabe, Y.; Ohga, Y.; Kita, S.; Ohara, T.

2010-08-01

122

Side electron emission device using a composite of carbon nanofibers and aluminum  

Energy Technology Data Exchange (ETDEWEB)

A new side electron emission device (SEED) was fabricated with carbon nanofiber/aluminum (CNF/Al) composites prepared by the elastomer precursor method. In the SEED, a cross-sectional side face of the CNF/Al composite plate was perpendicularly placed onto an anode surface by inserting an insulating spacer. Above a certain threshold voltage in a vacuum, field electrons were obtained from the side face of the composite emitter. With increasing content of CNFs in the composite, the threshold voltage decreased and emission currents increased. The current of {approx} 8 {mu}A was kept stable up to 93 h under a continuous application of 1 kV. This improved stability as compared to a conventional field emission device was attributed to a reduced damage of CNFs in the SEED structure.

Tanaka, Hirotaka; Nakamura, Hironao [Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192 (Japan); Yanagi, Hisao, E-mail: yanagi@ms.naist.j [Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192 (Japan); Kita, Takashi [Graduate School of Science and Technology, Kobe University, Rokkodai, Nada-ku, Kobe 657-8501 (Japan); Yokoyama, Kazuyuki; Magario, Akira; Noguchi, Toru [Research and Development Division, Nisshin Kogyo Co., Ltd., 840 Kokubu, Ueda, Nagano 836-8505 (Japan)

2009-11-30

123

Fabrication and Properties of Ethylene Vinyl Acetate-Carbon Nanofiber Nanocomposites  

Science.gov (United States)

Carbon nanofiber (CNF) is one of the stiffest materials produced commercially, having excellent mechanical, electrical, and thermal properties. The reinforcement of rubbery matrices by CNFs was studied in the case of ethylene vinyl acetate (EVA). The tensile strength was greatly (61%) increased, even for very low fiber content (i.e., 1.0 wt.%). The surface modification of the fiber by high energy electron beam and gamma irradiation led to better dispersion in the rubber matrix. This in turn gave rise to further improvements in mechanical and dynamic mechanical properties of EVA. The thermal conductivity also exhibited improvements from that of the neat elastomer, although thermal stability of the nanocomposites was not significantly altered by the functionalization of CNFs. Various results were well supported by the morphological analysis of the nanocomposites.

George, Jinu Jacob; Bhowmick, Anil K.

2008-12-01

124

Fabrication and Properties of Ethylene Vinyl Acetate-Carbon Nanofiber Nanocomposites  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Carbon nanofiber (CNF is one of the stiffest materials produced commercially, having excellent mechanical, electrical, and thermal properties. The reinforcement of rubbery matrices by CNFs was studied in the case of ethylene vinyl acetate (EVA. The tensile strength was greatly (61% increased, even for very low fiber content (i.e., 1.0 wt.%. The surface modification of the fiber by high energy electron beam and gamma irradiation led to better dispersion in the rubber matrix. This in turn gave rise to further improvements in mechanical and dynamic mechanical properties of EVA. The thermal conductivity also exhibited improvements from that of the neat elastomer, although thermal stability of the nanocomposites was not significantly altered by the functionalization of CNFs. Various results were well supported by the morphological analysis of the nanocomposites.

George JinuJacob

2008-01-01

125

A fine-focusing x-ray source using carbon-nanofiber field emitter  

International Nuclear Information System (INIS)

A fine-focusing x-ray source has been constructed employing a field electron emitter prepared by growing carbon-nanofibers (CNFs) on a metal tip. The x-ray source is composed of a CNF field electron emitter, an electrostatic lens, two magnetic lenses, and a W-target for generating x-rays by electron impact. The CNFs provided field electrons with a current density of J?5x109 A/m2, which was evaluated with the aid of Fowler-Nordheim theory. The electron beam extracted from the CNF emitter was accelerated to the energies of E=10-25 keV, and then focused by the lenses. By recording the x-ray images of test charts, the optimum resolution of the x-ray source was estimated to be approximately Dx=0.5 ?m.

126

In situ transmission electron microscopy study of electrochemical sodiation and potassiation of carbon nanofibers.  

Science.gov (United States)

Carbonaceous materials have great potential for applications as anodes of alkali-metal ion batteries, such as Na-ion batteries and K-ion batteries (NIB and KIBs). We conduct an in situ study of the electrochemically driven sodiation and potassiation of individual carbon nanofibers (CNFs) by transmission electron microscopy (TEM). The CNFs are hollow and consist of a bilayer wall with an outer layer of disordered-carbon (d-C) enclosing an inner layer of crystalline-carbon (c-C). The d-C exhibits about three times volume expansion of the c-C after full sodiation or potassiation, thus suggesting a much higher storage capacity of Na or K ions in d-C than c-C. For the bilayer CNF-based electrode, a steady sodium capacity of 245 mAh/g is measured with a Coulombic efficiency approaching 98% after a few initial cycles. The in situ TEM experiments also reveal the mechanical degradation of CNFs through formation of longitudinal cracks near the c-C/d-C interface during sodiation and potassiation. Geometrical changes of the tube are explained by a chemomechanical model using the anisotropic sodiation/potassiation strains in c-C and d-C. Our results provide mechanistic insights into the electrochemical reaction, microstructure evolution and mechanical degradation of carbon-based anodes during sodiation and potassiation, shedding light onto the development of carbon-based electrodes for NIBs and KIBs. PMID:24823874

Liu, Ying; Fan, Feifei; Wang, Jiangwei; Liu, Yang; Chen, Hailong; Jungjohann, Katherine L; Xu, Yunhua; Zhu, Yujie; Bigio, David; Zhu, Ting; Wang, Chunsheng

2014-06-11

127

Synthesis of carbon nano-fibers on p-Si having improved temperature sensing capability  

International Nuclear Information System (INIS)

Highlights: ? Synthesis of carbon nanofibers on p-Si. ? RBM in Raman spectra. ? Superior temperature sensing capability. - Abstract: Synthesis of an innovative material for temperature sensor based on carbon nano-fibers (CNFs) on p-Si substrates has been demonstrated. The CNF films were characterized by SEM, Raman and FTIR studies. First order Raman spectra indicated a G band at ?1597 cm?1 corresponding to the E2g tangential stretching mode of an ordered graphitic structure with sp2 hybridization and a D band located ?1350 cm?1 originated from disordered carbon. Gold fingers were deposited on the p-Si/CNF surface for resistance measurement. Temperature sensing properties were also investigated critically. Resistance changes with temperature (?R/R) in p-Si/CNF films are found to be significantly large 30–60% Very stable, reproducible and improved temperature sensing properties would make this material superior to commonly available temperature sensors.

128

SiC/SiO 2 coating for improving the oxidation resistive property of carbon nanofiber  

Science.gov (United States)

The SiC/SiO 2 deposition was performed to improve the oxidation resistive properties of carbon nanofiber (CNF) from electrospinning at elevated temperatures through sol-gel process. The stabilized polyacrylonitrile (PAN) fibers were coated with SiO 2 followed by heat treatment up to 1000 and 1400 °C in an inert argon atmosphere. The chemical compositions of the CNFs surface heat-treated were characterized as C, Si and O existing as SiC and SiO 2 compounds on the surface. The uniform and continuous coating improved the oxidation resistance of the carbon nanofibers. The residual weight of the composite was 70-80% and mixture of SiC, SiO 2 and some residual carbon after exposure to air at 1000 °C.

Kim, Bo-Hye; Kim, Chang Hyo; Yang, Kap Seung; Kim, Ki-Young; Lee, Young-Jun

2010-12-01

129

Polycarboxylation of carbon nanofibers under Friedel-Crafts condition: A simple route to direct binding of carboxylic functionalities to graphitic ?-system  

Science.gov (United States)

The functionalization of carbon nanofibers (CNFs) with oxalyl chloride, via Friedel-Crafts reaction in the presence of aluminum chloride, was first demonstrated as an efficient way to introduce carboxyl groups onto the nanofiber sidewalls. Octa-aminophenylsilsesquioxane (OASQ) was then covalently attached to the carboxylated nanocarbon CNF-(COOH)n through amide linkage. Taking into account the nature of the electrophilic aromatic substitution, this chemical functionalization may involve formation of conjugated carboxylic acid moiety. Structural analysis combined with electron microscopy observation of the robust octasilsesquioxane species show that carboxyl groups are uniformly distributed on the nanofibers surface.

Wu, Jiancheng; Cai, Hualun; Xu, Kai; Fu, Zien; Liu, Xin; Chen, Mingcai; Zhang, Xiuju

2012-11-01

130

Interweaved Si@C/CNTs and CNFs composites as anode materials for Li-ion batteries  

International Nuclear Information System (INIS)

Graphical abstract: In summary, a serious of high-energy wet ball milling, closed spray drying and subsequent chemical vapor deposition methods were introduced successfully to fabricated novel Si@C/CNTs and CNFs composites with carbon nanotubes and carbon nanofibres interweaved with carbon coated silicon spherical composites as superior anodes in lithium-ion batteries. The core-shell structure of Si@C composites can accommodate the volume change of electrode during charge and discharge. Meanwhile, the citric acid pyrolyzed carbon was coated on the surface of the silicon perfectly and constructs the connection network of nano silicon particles. Moreover, the carbon nanotubes and carbon nanofibres, which is interweaved with nano-silicon, also allows high electrical conductivity, improved solid–electrolyte interface formation and structural integrity. Compared with pure silicon and Si@C composites, the novel Si@C/CNTs and CNFs composites had the best combination of reversible capacity and cycleablity, and this anode materials exhibited excellent electrochemical performance. The Si/C composite had a fairly high initial discharge capacity of 2168.7 mA h g?1 with an efficiency of 73%, and the discharge capacity of the 50th cycle maintained surprisingly of 1194.9 mA h g?1. Meanwhile, spray drying and chemical vapor deposition are environmentally friendly, economical, and relatively high-yield method for the production of the Si@C/CNTs and CNFs composites in large quantities. Consequently, the novel Si@C/CNTs and CNFs composite electrodes may be a potential alternative to graphite for high energy density lithium ion batteries. Highlights: • The core/shell structured silicon/carbon composites were prepared by a facile way. • The as-prepared Si@C/CNTs and CNFs composites shows excellent electrochemical performance. • The preparation method has mild experiment conditions and high production rate. • The structure benefited electronic transfer and accommodated volume expansion. -- Abstract: Novel silicon@ carbon/carbon nanotubes and carbon nanofibres (Si@C/CNTs and CNFs) composites have been successfully synthesized by a serious of high-energy wet ball milling, closed spray drying and subsequently chemical vapor deposition methods, in which carbon nanotubes and carbon nanofibers are interweaved with carbon coated silicon (Si@C) spherical composites. As anode materials for lithium-ion batteries, the Si@C/CNTs and CNFs composites demonstrate a high first discharge capacity and excellent cycle ability. The high initial specific discharge capacity is approximately 2169 mA h g?1 and a reversible specific capacity approached 1195 mA h g?1 after 50 cycles at a high current density of 300 mA g?1

131

Performance of carbon nanofiber-cement composites subjected to accelerated decalcification  

Directory of Open Access Journals (Sweden)

Full Text Available The effect of decalcification on the chemo-mechanical behavior of carbon nanofiber (CNF-cement composites was studied. Portland cement pastes with and without 0.2% CNFs were subjected to accelerated decalcification by exposure to ammonium nitrate solutions. The influence of microstructural alterations during decalcification on the physical and mechanical properties of the composites was examined. The presence of CNF agglomerates influenced the chemo-mechanical behavior of the composite during decalcification. Precipitation of secondary hydrates within the agglomerates during decalcification resulted in a decrease in local porosity, which strengthened the composite and slowed the loss of flexural strength.

Arnold J.

2013-07-01

132

Plum-branch-like carbon nanofibers decorated with SnO2 nanocrystals  

Science.gov (United States)

Novel plum-branch-like carbon nanofibers (CNFs) decorated with SnO2 nanocrystals have been synthesized by electrospinning and subsequent thermal treatment in an Ar/H2O atmosphere. The morphologies of the as-synthesized SnO2/CNF composites and the contents of carbon and SnO2 can be controlled by adjusting the heat treatment temperature. It is proposed that the growth of SnO2/CNF composites follows the outward diffusion of tin composites from the as-spun tin composite/polyacrylonitrile (PAN) nanofibers, pyrolysis of PAN and oxidation of tin composites, and then formation of SnO2 nanocrystals around the CNFs. This novel 1D SnO2/CNF composite may have potential application in nanobatteries, nano fuel cells, and nanosensors. A preliminary result has revealed that the SnO2/CNF composite presents favourable electrochemical performance in lithium-ion batteries.Novel plum-branch-like carbon nanofibers (CNFs) decorated with SnO2 nanocrystals have been synthesized by electrospinning and subsequent thermal treatment in an Ar/H2O atmosphere. The morphologies of the as-synthesized SnO2/CNF composites and the contents of carbon and SnO2 can be controlled by adjusting the heat treatment temperature. It is proposed that the growth of SnO2/CNF composites follows the outward diffusion of tin composites from the as-spun tin composite/polyacrylonitrile (PAN) nanofibers, pyrolysis of PAN and oxidation of tin composites, and then formation of SnO2 nanocrystals around the CNFs. This novel 1D SnO2/CNF composite may have potential application in nanobatteries, nano fuel cells, and nanosensors. A preliminary result has revealed that the SnO2/CNF composite presents favourable electrochemical performance in lithium-ion batteries. Electronic supplementary information (ESI) available: Figures S1-S6. See DOI: 10.1039/c0nr00009d

Yang, Zunxian; Du, Guodong; Guo, Zaiping; Yu, Xuebin; Li, Sean; Chen, Zhixin; Zhang, Peng; Liu, Huakun

2010-06-01

133

Performance of carbon nanofiber-cement composites subjected to accelerated decalcification  

International Nuclear Information System (INIS)

The effect of decalcification on the chemo-mechanical behavior of carbon nanofiber (CNF)-cement composites was studied. Portland cement pastes with and without 0.2% CNFs were subjected to accelerated decalcification by exposure to ammonium nitrate solutions. The influence of microstructural alterations during decalcification on the physical and mechanical properties of the composites was examined. The presence of CNF agglomerates influenced the chemo-mechanical behavior of the composite during decalcification. Precipitation of secondary hydrates within the agglomerates during decalcification resulted in a decrease in local porosity, which strengthened the composite and slowed the loss of flexural strength. (authors)

134

Performance of carbon nanofiber-cement composites subjected to accelerated decalcification  

Science.gov (United States)

The effect of decalcification on the chemo-mechanical behavior of carbon nanofiber (CNF)-cement composites was studied. Portland cement pastes with and without 0.2% CNFs were subjected to accelerated decalcification by exposure to ammonium nitrate solutions. The influence of microstructural alterations during decalcification on the physical and mechanical properties of the composites was examined. The presence of CNF agglomerates influenced the chemo-mechanical behavior of the composite during decalcification. Precipitation of secondary hydrates within the agglomerates during decalcification resulted in a decrease in local porosity, which strengthened the composite and slowed the loss of flexural strength.

Brown, L.; Sanchez, F.; Kosson, D.; Arnold, J.

2013-07-01

135

Phosphorus-doped tin oxides/carbon nanofibers webs as lithium-ion battery anodes with enhanced reversible capacity  

Science.gov (United States)

Phosphorus-doped tin oxides/carbon nanofibers (P-SnOx/CNFs) composite materials are prepared via electrospinning of a mixed solution composed of polyacrylonitrile (PAN), N,N-dimethyl formamide (DMF), tin tetrachloride, ethylene glycol and phosphoric acid as well as subsequent thermal treatments. The P-SnOx/CNFs samples with tunable P-doping contents are directly used as anodes for lithium-ion batteries without any binders and conductors, exhibiting enhanced reversible capacities and cycling stabilities in comparison with pristine undoped SnOx/CNFs (0P-SnOx/CNFs). In a controlled experiment, the 0.25P-SnOx/CNFs anode with the atomic ratio of P:Sn = 0.25:1 shows the highest specific reversible capacity of 676 mA h g-1 at 200 mA g-1 after 100 cycles. Even at a higher current density of 2000 mA g-1, it still maintains a superior specific reversible capacity of 288 mA h g-1. The improved electrochemical performances are attributed to the P-doping effects such as inducement of a stable structural protection for tin particles, and enhancement of lithium ion diffusion coefficient and electron kinetics of electrode materials.

Liu, Xiaowei; Teng, Donghua; Li, Ting; Yu, Yunhua; Shao, Xiaohong; Yang, Xiaoping

2014-12-01

136

In situ characterization of vertically oriented carbon nanofibers for three-dimensional nano-electro-mechanical device applications  

International Nuclear Information System (INIS)

We have performed mechanical and electrical characterization of individual as-grown, vertically oriented carbon nanofibers (CNFs) using in situ techniques, where such high-aspect-ratio, nanoscale structures are of interest for three-dimensional (3D) electronics, in particular 3D nano-electro-mechanical-systems (NEMS). Nanoindentation and uniaxial compression tests conducted in an in situ nanomechanical instrument, SEMentor, suggest that the CNFs undergo severe bending prior to fracture, which always occurs close to the bottom rather than at the substrate-tube interface, suggesting that the CNFs are well adhered to the substrate. This is also consistent with bending tests on individual tubes which indicated that bending angles as large as ? 700 could be accommodated elastically. In situ electrical transport measurements revealed that the CNFs grown on refractory metallic nitride buffer layers were conducting via the sidewalls, whereas those synthesized directly on Si were electrically unsuitable for low-voltage dc NEMS applications. Electrostatic actuation was also demonstrated with a nanoprobe in close proximity to a single CNF and suggests that such structures are attractive for nonvolatile memory applications. Since the magnitude of the actuation voltage is intimately dictated by the physical characteristics of the CNFs, such as diameter and length, we also addressed the ability to tune these parameters, to some extent, by adjusting the plasma-enhanced xtent, by adjusting the plasma-enhanced chemical vapor deposition growth parameters with this bottom-up synthesis approach.

137

Optimization of nafion ionomer content using synthesized Pt/carbon nanofibers catalyst in polymer electrolyte membrane fuel cell.  

Science.gov (United States)

In this study, carbon nanofiber (CNF) was used as a support in which 47.5 wt% Pt/CNFs catalyst was prepared by a modified polyol method. The platinum particle size and dispersion on the CNFs are approximately 2-4 nm as determined by X-ray diffractometry and transmission electron microscopy. The specific surface area was approximated as 55.90 m2/g by BET analysis. Electrodes were prepared by the spray method and have a size of 5 cm2. A commercial catalyst (TKK, 46 wt% Pt/C) was used as the anode and the cathode was Pt/CNFs. Different amounts of Nafion ionomer (Aldrich, 5 wt% solution, in the range of 0-20 wt%) were coated on a membrane (Dupont, Nafion 212) with 0.4 mg/cm2 of Pt catalyst at the cathode side. The resulting polarization, ohmic and mass transfer resistances changed significantly based on the Nafion ionomer content. Optimum Nafion ionomer content in the 47.5 wt% Pt/CNFs was 5 wt%. The well-dispersed Nafion ionomer was observed on the catalyst surface area using SEM-EDAX analysis. A sufficient triple-phase boundary was formed by a small amount of Nation ionomer due to the BET surface area of the Pt/CNFs. PMID:22966581

Jung, Ju-Hae; Cha, Moon-Soon; Kim, Jun-Bom

2012-07-01

138

Dynamic Mechanical Properties of PMN/CNFs/EP Composites  

International Nuclear Information System (INIS)

In this research, piezoelectric ceramic PMN(lead magnesium niobate-lead zirconate-lead titanate)/carbon nano-fibers(CNFs)/epoxy resin(EP) ccomposites were prepared and the dynamic mechanical properties and damping mechanism of PMN/CNFs/EP composites were investigated. The addition of CNFs into PMN/EP composite results in decrease of volume resistivity of the composite. When the concentration of CNFs is 0.6% weight of epoxy resin the volume resistivity of PMN/CNFs/EP composite is about 108 ?·m. Dynamic mechanical analysis indicates that the loss factor, loss area, and damping temperature range of PMN/CNFs/EP composites increase with the CNFs content increasing till to 0.6% of weight of epoxy resin. When the CNFs content is more than 0.6% the damping properties of composites decrease oppositely. In PMN/CNFs/EP composites, the CNFs content 0.6% and the volume resistivity of PMN/CNFs/EP composites about 108 ?·m just satisfy the practicing condition of piezo-damping, so the composites show optimal damping property.

139

Dynamic Mechanical Properties of PMN/CNFs/EP Composites  

Energy Technology Data Exchange (ETDEWEB)

In this research, piezoelectric ceramic PMN(lead magnesium niobate-lead zirconate-lead titanate)/carbon nano-fibers(CNFs)/epoxy resin(EP) ccomposites were prepared and the dynamic mechanical properties and damping mechanism of PMN/CNFs/EP composites were investigated. The addition of CNFs into PMN/EP composite results in decrease of volume resistivity of the composite. When the concentration of CNFs is 0.6% weight of epoxy resin the volume resistivity of PMN/CNFs/EP composite is about 10{sup 8} {Omega}{center_dot}m. Dynamic mechanical analysis indicates that the loss factor, loss area, and damping temperature range of PMN/CNFs/EP composites increase with the CNFs content increasing till to 0.6% of weight of epoxy resin. When the CNFs content is more than 0.6% the damping properties of composites decrease oppositely. In PMN/CNFs/EP composites, the CNFs content 0.6% and the volume resistivity of PMN/CNFs/EP composites about 10{sup 8} {Omega}{center_dot}m just satisfy the practicing condition of piezo-damping, so the composites show optimal damping property.

Shi Minxian; Huang Zhixiong; Qin Yan, E-mail: minxianshi@whut.edu.cn [School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 (China)

2011-10-29

140

Dynamic Mechanical Properties of PMN/CNFs/EP Composites  

Science.gov (United States)

In this research, piezoelectric ceramic PMN(lead magnesium niobate-lead zirconate-lead titanate)/carbon nano-fibers(CNFs)/epoxy resin(EP) ccomposites were prepared and the dynamic mechanical properties and damping mechanism of PMN/CNFs/EP composites were investigated. The addition of CNFs into PMN/EP composite results in decrease of volume resistivity of the composite. When the concentration of CNFs is 0.6% weight of epoxy resin the volume resistivity of PMN/CNFs/EP composite is about 108 ?·m. Dynamic mechanical analysis indicates that the loss factor, loss area, and damping temperature range of PMN/CNFs/EP composites increase with the CNFs content increasing till to 0.6% of weight of epoxy resin. When the CNFs content is more than 0.6% the damping properties of composites decrease oppositely. In PMN/CNFs/EP composites, the CNFs content 0.6% and the volume resistivity of PMN/CNFs/EP composites about 108 ?·m just satisfy the practicing condition of piezo-damping, so the composites show optimal damping property.

Shi, Minxian; Huang, Zhixiong; Qin, Yan

2011-10-01

 
 
 
 
141

In situ synthesis of Pt/carbon nanofiber nanocomposites with enhanced electrocatalytic activity toward methanol oxidation.  

Science.gov (United States)

Pt/carbon nanofiber (Pt/CNF) nanocomposites were facilely synthesized by the reduction of hexachloroplatinic acid (H(2)PtCl(6)) using formic acid (HCOOH) in aqueous solution containing electrospun carbon nanofibers at room temperature. The obtained Pt/CNF nanocomposites were characterized by TEM and EDX. The Pt nanoparticles could in situ grow on the surface of CNFs with small particle size, high loading density, and uniform dispersion by adjusting the concentration of H(2)PtCl(6) precursor. The electrocatalytic activities of the Pt/CNF nanocomposites were also studied. These Pt/CNF nanocomposites exhibited higher electrocatalytic activity toward methanol oxidation reaction compared with commercial E-TEK Pt/C catalyst. The results presented may offer a new approach to facilely synthesize direct methanol fuel cells (DMFCs) catalyst with enhanced electrocatalytic activity and low cost. PMID:22082800

Wang, Dawei; Liu, Yang; Huang, Jianshe; You, Tianyan

2012-02-01

142

Revealing the Role of Catalysts in Carbon Nanotubes and Nanofibers by Scanning Transmission X-ray Microscopy  

Science.gov (United States)

The identification of effective components on the atomic scale in carbon nanomaterials which improve the performance in various applications remains outstanding challenges. Here the catalyst residues in individual carbon nanotube (CNT) and carbon nanofiber (CNF) were clearly imaged with a concurrent characterization of their electronic structure by nanoscale scanning transmission X-ray microscopy. Except for prominent catalyst nanoparticle at the tip, tiny catalyst clusters along the tube (fiber) were detected, indicating a migration of the catalysts with the growth of CNTs (CNFs). The observation provides the direct evidence on the atomic metal in CNT for oxygen reduction reported in the literature. Interaction between catalysts (Fe, Ni) and CNTs (CNFs) at the tip was also identified by comparing the X-ray absorption spectra. A deep understanding of catalyst residues such as Fe or Ni in carbon nanomaterials is very vital to growth mechanism development and practical applications.

Gao, Jing; Zhong, Jun; Bai, Lili; Liu, Jinyin; Zhao, Guanqi; Sun, Xuhui

2014-01-01

143

Aerosol Monitoring during Carbon Nanofiber Production: Mobile Direct-Reading Sampling  

Science.gov (United States)

Detailed investigations were conducted at a facility that manufactures and processes carbon nanofibers (CNFs). Presented research summarizes the direct-reading monitoring aspects of the study. A mobile aerosol sampling platform, equipped with an aerosol instrument array, was used to characterize emissions at different locations within the facility. Particle number, respirable mass, active surface area, and photoelectric response were monitored with a condensation particle counter (CPC), a photometer, a diffusion charger, and a photoelectric aerosol sensor, respectively. CO and CO2 were additionally monitored. Combined simultaneous monitoring of these metrics can be utilized to determine source and relative contribution of airborne particles (CNFs and others) within a workplace. Elevated particle number concentrations, up to 1.15 × 106 cm?3, were found within the facility but were not due to CNFs. Ultrafine particle emissions, released during thermal treatment of CNFs, were primarily responsible. In contrast, transient increases in respirable particle mass concentration, with a maximum of 1.1 mg m?3, were due to CNF release through uncontrolled transfer and bagging. Of the applied metrics, our findings suggest that particle mass was probably the most useful and practical metric for monitoring CNF emissions in this facility. Through chemical means, CNFs may be selectively distinguished from other workplace contaminants (Birch et al., in preparation), and for direct-reading monitoring applications, the photometer was found to provide a reasonable estimate of respirable CNF mass concentration. Particle size distribution measurements were conducted with an electrical low-pressure impactor and a fast particle size spectrometer. Results suggest that the dominant CNF mode by particle number lies between 200 and 250 nm for both aerodynamic and mobility equivalent diameters. Significant emissions of CO were also evident in this facility. Exposure control recommendations were described for processes as required. PMID:20447936

Evans, Douglas E.; Ku, Bon Ki; Birch, M. Eileen; Dunn, Kevin H.

2010-01-01

144

Comparative Study of the Rheological Behavior of Multiwalled Carbon Nanotubes and Nanofiber Composites Prepared by the Dilution of a Masterbatch of Polypropylene  

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In this investigation, the characteristics and the rheological properties of two different nanocomposite systems were investigated. These systems consisted of a dispersion of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) in a polypropylene (PP) matrix. The mixing process was carried out by melt compounding with a twin-screw corotating extruder with different reinforcement amounts (0.2-20 wt %) from concentrated masterbatches (20 wt %) of PP/CNT and PP/CNF. The results show a remarkable...

Boronat Vitoria, Teodomiro; Garci?a Sanoguera, David; Pascual, J.; Peris, F.; Sa?nchez Nacher, Lourdes

2012-01-01

145

Graphene wrapping as a protective clamping layer anchored to carbon nanofibers encapsulating Si nanoparticles for a Li-ion battery anode  

Science.gov (United States)

Carbon nanofibers encapsulating Si nanoparticles (CNFs/SiNPs) were prepared via an electrospinning method and chemically functionalized with 3-aminopropyltriethoxysilane (APS) to be grafted onto graphene oxide (GO). As a result, the thin and flexible GO, which exhibits a negative charge in aqueous solution, fully wrapped around the APS-functionalized CNFs with a positive surface charge via electrostatic self-assembly. After the formation of chemical bonds between the epoxy groups on GO and the amine groups in APS via an epoxy ring opening reaction, the GO was chemically reduced to a reduced graphene oxide (rGO). Electrochemical and morphological characterizations showed that capacity loss by structural degradation and electrolyte decomposition on Si surface were significantly suppressed in the rGO-wrapped CNFs/SiNPs (CNFs/SiNPs@rGO). Superior capacities were consequently maintained for up to 200 cycles at a high current density (1048 mA h g-1 at 890 mA g-1) compared to CNFs/SiNPs without the rGO wrapping (304 mA h g-1 at 890 mA g-1). Moreover, the resistance of the SEI layer and charge transfer resistance were also considerably reduced by 24% and 88%, respectively. The described graphene wrapping offers a versatile way to enhance the mechanical integrity and electrochemical stability of Si composite anode materials.Carbon nanofibers encapsulating Si nanoparticles (CNFs/SiNPs) were prepared via an electrospinning method and chemically functionalized with 3-aminopropyltriethoxysilane (APS) to be grafted onto graphene oxide (GO). As a result, the thin and flexible GO, which exhibits a negative charge in aqueous solution, fully wrapped around the APS-functionalized CNFs with a positive surface charge via electrostatic self-assembly. After the formation of chemical bonds between the epoxy groups on GO and the amine groups in APS via an epoxy ring opening reaction, the GO was chemically reduced to a reduced graphene oxide (rGO). Electrochemical and morphological characterizations showed that capacity loss by structural degradation and electrolyte decomposition on Si surface were significantly suppressed in the rGO-wrapped CNFs/SiNPs (CNFs/SiNPs@rGO). Superior capacities were consequently maintained for up to 200 cycles at a high current density (1048 mA h g-1 at 890 mA g-1) compared to CNFs/SiNPs without the rGO wrapping (304 mA h g-1 at 890 mA g-1). Moreover, the resistance of the SEI layer and charge transfer resistance were also considerably reduced by 24% and 88%, respectively. The described graphene wrapping offers a versatile way to enhance the mechanical integrity and electrochemical stability of Si composite anode materials. Electronic supplementary information (ESI) available: SEM images and XRD pattern of CNFs/SiNPs; photographs of CNFs/SiNPs@rGO solutions; SEM images of CNFs/SiNPs@rGO at different graphene concentrations; SEM images of CNFs@SiNPs@rGO without APS functionalization; Electrochemical cell performance of CNFs@SiNPs@rGO with different wrapping concentrations; and electrochemical impendence spectroscopy data for CNFs@SiNPs and CNFs@SiNPs@rGO after the first discharge. See DOI: 10.1039/c4nr03173c

Shin, Jungwoo; Park, Kyusung; Ryu, Won-Hee; Jung, Ji-Won; Kim, Il-Doo

2014-10-01

146

Enhanced activity and selectivity of carbon nanofiber supported Pd catalysts for nitrite reduction.  

Science.gov (United States)

Pd-based catalyst treatment represents an emerging technology that shows promise to remove nitrate and nitrite from drinking water. In this work we use vapor-grown carbon nanofiber (CNF) supports in order to explore the effects of Pd nanoparticle size and interior versus exterior loading on nitrite reduction activity and selectivity (i.e., dinitrogen over ammonia production). Results show that nitrite reduction activity increases by 3.1-fold and selectivity decreases by 8.0-fold, with decreasing Pd nanoparticle size from 1.4 to 9.6 nm. Both activity and selectivity are not significantly influenced by Pd interior versus exterior CNF loading. Consequently, turnover frequencies (TOFs) among all CNF catalysts are similar, suggesting nitrite reduction is not sensitive to Pd location on CNFs nor Pd structure. CNF-based catalysts compare favorably to conventional Pd catalysts (i.e., Pd on activated carbon or alumina) with respect to nitrite reduction activity and selectivity, and they maintain activity over multiple reduction cycles. Hence, our results suggest new insights that an optimum Pd nanoparticle size on CNFs balances faster kinetics with lower ammonia production, that catalysts can be tailored at the nanoscale to improve catalytic performance for nitrite, and that CNFs hold promise as highly effective catalyst supports in drinking water treatment. PMID:22295991

Shuai, Danmeng; Choe, Jong Kwon; Shapley, John R; Werth, Charles J

2012-03-01

147

Carbon Nanofibers and Their Composites: A Review of Synthesizing, Properties and Applications  

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Full Text Available Carbon nanofiber (CNF, as one of the most important members of carbon fibers, has been investigated in both fundamental scientific research and practical applications. CNF composites are able to be applied as promising materials in many fields, such as electrical devices, electrode materials for batteries and supercapacitors and as sensors. In these applications, the electrical conductivity is always the first priority need to be considered. In fact, the electrical property of CNF composites largely counts on the dispersion and percolation status of CNFs in matrix materials. In this review, the electrical transport phenomenon of CNF composites is systematically summarized based on percolation theory. The effects of the aspect ratio, percolation backbone structure and fractal characteristics of CNFs and the non-universality of the percolation critical exponents on the electrical properties are systematically reviewed. Apart from the electrical property, the thermal conductivity and mechanical properties of CNF composites are briefly reviewed, as well. In addition, the preparation methods of CNFs, including catalytic chemical vapor deposition growth and electrospinning, and the preparation methods of CNF composites, including the melt mixing and solution process, are briefly introduced. Finally, their applications as sensors and electrode materials are described in this review article.

Lichao Feng

2014-05-01

148

Field emission from combined structures of carbon nanotubes and carbon nanofibers  

International Nuclear Information System (INIS)

A convenient and inexpensive approach to producing carbonaceous field emitters has been developed. Combined structures of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were grown on graphitic substrates with an improved chemical vapor deposition (CVD) method. The fabrication featured a high reaction temperature and a rapid temperature rising. In each combined structure, a CNT with good crystallinity was surrounded by a cone-shaped CNF. The CNTs and the bases of the CNFs were less than 0.1 and 10 ?m in diameter, respectively. These combined CNT/CNF structures, several ten microns in length, had an upward orientation from the substrate and an appropriate separation between each other, which are believed to be two favorable factors to the field emission. Electron current was readily extracted from them. Current densities of 10 ?A/cm2 and 1 mA/cm2 were obtained when the average fields between the anode and the cathode were 2.3 and 3.9 V/?m, respectively.

149

Novel hybrid carbon nanofiber/highly branched graphene nanosheet for anode materials in lithium-ion batteries.  

Science.gov (United States)

The novel hybrid carbon nanofiber (CNF)/highly branched graphene nanosheet (HBGN) is synthesized via a simple two-step CVD method and its application as the anode material in a lithium-ion battery (LIB) is demonstrated. The CNFs offer a good electrical conductivity and a robust supporting structure, while the HBGNs provide increased Li storage sites including nanoporous cavities, large surface area, and edges of exposed graphene platelets. The hybrid material showed a reversible capacity of 300 mAh g(-1) with excellent cycling stability. Our study provides a new avenue for design and synthesis of carbon-carbon hybrid materials for versatile applications. PMID:25310206

Kim, Haejune; Huang, Xingkang; Guo, Xiaoru; Wen, Zhenhai; Cui, Shumao; Chen, Junhong

2014-11-12

150

Carbon nanofibers decorated with molybdenum disulfide nanosheets: synergistic lithium storage and enhanced electrochemical performance.  

Science.gov (United States)

Traditional lithium-ion batteries that are based on layered Li intercalation electrode materials are limited by the intrinsically low theoretical capacities of both electrodes and cannot meet the increasing demand for energy. A facile route for the synthesis of a new type of composite nanofibers, namely carbon nanofibers decorated with molybdenum disulfide sheets (CNFs@MoS2 ), is now reported. A synergistic effect was observed for the two-component anode, triggering new electrochemical processes for lithium storage, with a persistent oxidation from Mo (or MoS2 ) to MoS3 in the repeated charge processes, leading to an ascending capacity upon cycling. The composite exhibits unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior high-rate capability, suggesting its potential application in high-energy lithium-ion batteries. PMID:25213751

Zhou, Fei; Xin, Sen; Liang, Hai-Wei; Song, Lu-Ting; Yu, Shu-Hong

2014-10-20

151

Thermal?Electrical Character of in Situ Synthesized Polyimide-Grafted Carbon Nanofiber Composites  

Energy Technology Data Exchange (ETDEWEB)

Notwithstanding the success of polymer-carbon nanotube (CNT) nanocomposites, a solid understanding of the impact of external perturbations, including temperature and stress, on the electrical response, its reproducibility, and the subsequent relationship to the topology of the percolative morphology and molecular details of the CNT-CNT contact junction is not complete. Using an in situ synthesis approach, two series of polymide (CP2)-carbon nanofiber (CNF) composites are prepared with quantitatively (small-angle X-ray scattering) comparable CNF dispersions, but differing in the structure of the CNF-polymer interface. Amino-functionalized CNFs (FCNFs) enable direct formation of CP2 grafts onto the CNFs, whereas pristine CNFs (PCNFs) result in a relatively weak interface between the carbon nanofiber and CP2 matrix. In general, low-frequency ac impedance measurements are well described by the percolation bond model, yielding a percolation threshold below 1 vol % (0.24 and 0.68 vol % for PCNF-CP2 and FCNF-CP2, respectively). However, the design of the interface is determined to be crucial for controlling the electrical behavior in four substantial ways: magnitude of the limiting conductivity, linearity of the I-V response, magnitude and direction of temperature-dependent resistivity, and reproducibility of the absolute value of the resistivity with thermal cycling. These observations are consistent with a direct CNF-CNF contact limiting transport in the PCNF-CP2 system, where the CP2 grafts onto the FCNF from a dielectric layer, limiting transport within the FCNF-CP2 system. Furthermore, the grafted CP2 chains on the FCNF reduce local polymer dewetting at the CNF surfaces when the temperature exceeds the CP2 glass transition. This appears to stabilize the structure of the percolation network and associated conductivity. The general behavior of these interfacial extremes (pristine and fully functionalized CNFs) set important bounds on the design of interface modification for CNFs when the intended use is for electrical performance at elevated temperatures or under extreme current loads.

Arlen, Michael J.; Wang, David; Jacobs, J. David; Justice, Ryan; Trionfi, Aaron; Hsu, Julia W.P.; Schaffer, Dale; Tan, Loon-Seng; Vaia, Richard A. (Sandia); (UCIN); (AFRL)

2008-12-09

152

In situ formation of hollow graphitic carbon nanospheres in electrospun amorphous carbon nanofibers for high-performance Li-based batteries  

Science.gov (United States)

We report on in situ formation of hollow graphitic carbon nanospheres (HGCNs) in amorphous carbon nanofibers (ACNFs) by a combination of electrospinning, calcination and acid treatment. The prepared carbon nanofibers contain many HGCNs on which defects such as discontinuous graphene sheets with a large d-spacing in their wall exist and provide extra sites for Li+ storage and serve as buffers for withstanding large volume expansion and shrinkage during the Li insertion and extraction procedure. Furthermore, some exposed HGCNs on the surface of the ACNFs as well as hollow structures are favorable for lithium ion diffusion from different orientations and sufficient contact between active material and electrolyte. In addition, the high conductivity architectures facilitate collection and transport of electrons during the cycling process. As a result, the ACNFs/HGCNs display a high reversible specific gravimetric capacity of ~750 mA h g-1 and volumetric capacity of ~1.1 A h cm-3 with outstanding rate capability and good cycling stability, which is superior to those of carbon nanofibers (CNFs), carbon nanotubes (CNTs), porous ACNFs, graphene nanosheets (GNSs), GNSs/CNFs, hollow carbon nanospheres and graphite. The synthesis process is simple, low-cost and environmentally friendly, providing new avenues for the rational engineering of high-energy carbon-based anode materials.

Chen, Yuming; Lu, Zhouguang; Zhou, Limin; Mai, Yiu-Wing; Huang, Haitao

2012-10-01

153

Activated carbon nanofibers (ACNF) as cathode for single chamber microbial fuel cells (SCMFCs)  

Science.gov (United States)

The suitability of carbon nanofibers (CNF) based cathodes as alternative to the platinum (Pt)-based cathode in single chamber microbial fuel cells (SCMFCs) were extensively studied over 3-month operational period. MFCs were fed with two solutions: synthetic wastewater (phosphate buffer (PBS) plus sodium acetate) and real wastewater (mixed liquor suspendedsolid (MLSS) solution). CNFs were chemically activated using HNO3 and then hot pressed on a carbon cloth support to increase surface area. The cathode polarization showed a better behavior of the clean Pt-based cathode in abiotic conditions. The activation of the nanofibers (ACNFs) gave an advantage to the cathode performances compared to the raw CNFs. The SCMFCs fed with PBS showed four times higher power generation compared to MLSS solution. All the cathodes showed a decrease in performances over time, and the advantage of the Pt over CNF/ACNF disappeared. CNF/ACNF cathodes showed more stability in performances in long time operations. Biofilm formation, salt precipitations on the cathode, and the presence of hydrogen sulfide decreased the activity of Pt cathodes. A degradation and Pt detachment were noticed on Pt cathodes over time. In contrast, CNF/ACNF cathodes exhibited less deterioration throughout the operational period, which demonstrated a great potential as cost-effective cathodes for long-term operation.

Santoro, Carlo; Stadlhofer, Astrid; Hacker, Viktor; Squadrito, Gaetano; Schröder, Uwe; Li, Baikun

2013-12-01

154

Effect of carbon nanofiber surface functional groups on oxygen reduction in alkaline solution  

Science.gov (United States)

Carbon nanofibers (CNFs) with different content of surface functional groups which are carboxyl groups (CNF-OX), carbonyl groups (CNF-CO) and hydroxyl groups (CNF-OH) and nitrogen-containing groups (CNF-ON) are synthesized, and their electrocatalytic activities toward oxygen reduction reaction (ORR) in alkaline solution are investigated. The result of X-ray photoelectron spectroscopy (XPS) characterization indicates that a higher concentration of carboxyl groups, carbonyl groups and hydroxyl groups are imported onto the CNF-OX, CNF-CO and CNF-OH, respectively. Cyclic voltammetry shows that both the oxygen- and nitrogen-containing groups can improve the electrocatalytic activity of CNFs for ORR. The CNF-ON/GC electrode, which has nitrogen-containing groups, exhibits the highest current density of ORR. Rotating disk electrode (RDE) characterization shows that the oxygen reduction on CNF-ON/GC electrode proceeds almost entirely through the four-electron reduction pathway, the CNF-OX/GC, CNF-CO/GC and CNF-OH/GC electrodes proceed a two-electron reduction pathway at low potentials (-0.2 V to -0.6 V) followed by a gradual four-electron reduction pathway at more negative potentials, while the untreated carbon nanofiber (CNF-P/GC) electrode proceeds predominantly by a two-electron reduction pathway within the whole range of potential studied.

Zhong, Ren-Sheng; Qin, Yuan-Hang; Niu, Dong-Fang; Tian, Jing-Wei; Zhang, Xin-Sheng; Zhou, Xin-Gui; Sun, Shi-Gang; Yuan, Wei-Kang

2013-03-01

155

Lithium aluminosilicate reinforced with carbon nanofiber and alumina for controlled-thermal-expansion materials  

International Nuclear Information System (INIS)

Materials with a very low or tailored thermal expansion have many applications ranging from cookware to the aerospace industry. Among others, lithium aluminosilicates (LAS) are the most studied family with low and negative thermal expansion coefficients. However, LAS materials are electrical insulators and have poor mechanical properties. Nanocomposites using LAS as a matrix are promising in many applications where special properties are achieved by the addition of one or two more phases. The main scope of this work is to study the sinterability of carbon nanofiber (CNFs)/LAS and CNFs/alumina/LAS nanocomposites, and to adjust the ratio among components for obtaining a near-zero or tailored thermal expansion. Spark plasma sintering of nanocomposites, consisting of commercial CNFs and alumina powders and an ad hoc synthesized ?-eucryptite phase, is proposed as a solution to improving mechanical and electrical properties compared with the LAS ceramics obtained under the same conditions. X-ray diffraction results on phase compositions and microstructure are discussed together with dilatometry data obtained in a wide temperature range (?150 to 450 °C). The use of a ceramic LAS phase makes it possible to design a nanocomposite with a very low or tailored thermal expansion coefficient and exceptional electrical and mechanical properties.

156

Electrochemical characterization of a carbon nanofiber electrode system hybridized with PEDOT-PSS.  

Science.gov (United States)

In this work, electrochemical properties of a bilayer electrode system prepared from an electrically conducting polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), PEDOT-PSS coated carbon nanofibers (CNFs), have been investigated. The CNFs were used as supports for the deposition of PEDOT-PSS by a dip-coating technique to yield a bilayer electrode system. Electrodes prepared by such a method were used in supercapacitors operating in acidic (1 M H2SO4) electrolytes. The capacitance values were estimated by voltammetry and galvanostatic techniques with a three-electrode cell configuration. Due to the CNF's graphitic structure and the presence of exterior walls with numerous edges, a high specific surface area and easily accessible electrode/electrolyte interface were obtained, thus yielding good capacitance in the bilayer active materials. The capacitance for PEDOT-PSS coated CNF bilayer electrodes ranged from 80 to 180 F/g and the fabricated materials showed good cycling performance with high stability in aqueous electrolytes. This was probably due to enhanced access to the CNFs, leading to the generation of a double layer and, ultimately, higher values of the capacitance. PMID:24266165

Seo, Min-Kang; Kuk, Yun-Su; Park, Soo-Jin

2013-12-01

157

Study of Pb Adsorption by Carbon Nanofibers Grown on Powdered Activated Carbon  

Directory of Open Access Journals (Sweden)

Full Text Available The sorption of lead (Pb from aqueous solutions by using carbon nanofibers (CNFs grown on nickel impregnated Powdered Activated Carbon (PAC was studied. In this study, we investigated the affection of the lead initial concentration on the sorption of the heavy metal from water. The isotherm of the sorption of the heavy metal onto the nanocomposite was also studied. Firstly, the optimum pH for the sorption of the lead ions was determined. The maximum sorption capacity of the heavy metal onto the adsorbent was achieved at initial pH of 5.5. The effects of initial lead ions concentration were examined and the results showed that the adsorption capacities of the carbon nanofibers to uptake the heavy metal increased from about 16 to 89 mg g-1 with increasing the initial lead concentration from 5 to 70 mg L-1. The process sorption could be best fitted by the Langmuir isotherm. The equilibrium sorption capacities of lead ion were determined and found to be 100 mg g-1.

Ma`an Fahmi R. Al-Khatib

2010-01-01

158

Immobilization of nanofibrous A- or B-site substituted LaMnO{sub 3} perovskite-type oxides on macroscopic fiber with carbon nanofibers templates  

Energy Technology Data Exchange (ETDEWEB)

The immobilization of nanofibrous A- or B-site substituted LaMnO{sub 3} perovskite-type oxides on macroscopic silica fiber via a unique and facile carbon nanofibers (CNFs) template-based method was reported. Field emission scanning electron microscopy (FE-SEM), coupled with X-ray diffraction (XRD) analysis confirmed the template effect and the existence of nanofibrous materials immobilized on silica fiber.

Wu, Qiang; Sadakane, Masahiro; Ogihara, Hitoshi [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-0021 (Japan); Ueda, Wataru, E-mail: Ueda@cat.hokudai.ac.jp [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-0021 (Japan)

2010-09-15

159

Immobilization of nanofibrous A- or B-site substituted LaMnO3 perovskite-type oxides on macroscopic fiber with carbon nanofibers templates  

International Nuclear Information System (INIS)

The immobilization of nanofibrous A- or B-site substituted LaMnO3 perovskite-type oxides on macroscopic silica fiber via a unique and facile carbon nanofibers (CNFs) template-based method was reported. Field emission scanning electron microscopy (FE-SEM), coupled with X-ray diffraction (XRD) analysis confirmed the template effect and the existence of nanofibrous materials immobilized on silica fiber.

160

Controlled Growth of NiCo2O4 Nanorods and Ultrathin Nanosheets on Carbon Nanofibers for High-performance Supercapacitors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two one-dimensional hierarchical hybrid nanostructures composed of NiCo2O4 nanorods and ultrathin nanosheets on carbon nanofibers (CNFs) are controllably synthesized through facile solution methods combined with a simple thermal treatment. The structure of NiCo2O4 can be easily controlled to be nanorods or nanosheets by using different additives in the synthesis. These two different nanostructures are evaluated as electrodes for high performance supercapacitors, in view of their apparent adva...

Zhang, Genqiang; Lou, Xiong Wen

2013-01-01

 
 
 
 
161

Carbon nanofibers modified with heteroatoms as metal-free catalysts for the oxidative dehydrogenation of propane.  

Science.gov (United States)

Carbon nanofibres (CNFs) were modified with B and P by an ex?situ approach. In addition, CNFs doped with N were prepared in?situ using ethylenediamine as the N and C source. After calcination, the doped CNFs were used as catalysts for the oxidative dehydrogenation of propane. For B-CNFs, the effects of boron loading and calcination temperature on B speciation and catalytic conversion were studied. For the same reaction temperatures and conversions, B- and P-doped CNFs exhibited higher selectivities to propene than pristine CNFs. The N-CNFs were the most active but the least selective of the catalysts tested here. Our results also show that the type of P precursor affects the selectivity to propene and that CNFs modified using triphenylphosphine as the precursor provided the highest selectivity at isoconversion. PMID:25138580

Marco, Yanila; Roldán, Laura; Muñoz, Edgar; García-Bordejé, Enrique

2014-09-01

162

Tuning the acid/metal balance of carbon nanofiber-supported nickel catalysts for hydrolytic hydrogenation of cellulose.  

Science.gov (United States)

Carbon nanofibers (CNFs) are a class of graphitic support materials with considerable potential for catalytic conversion of biomass. Earlier, we demonstrated the hydrolytic hydrogenation of cellulose over reshaped nickel particles attached at the tip of CNFs. The aim of this follow-up study was to find a relationship between the acid/metal balance of the Ni/CNFs and their performance in the catalytic conversion of cellulose. After oxidation and incipient wetness impregnation with Ni, the Ni/CNFs were characterized by various analytical methods. To prepare a selective Ni/CNF catalyst, the influences of the nature of oxidation agent, Ni activation, and Ni loading were investigated. Under the applied reaction conditions, the best result, that is, 76 % yield in hexitols with 69 % sorbitol selectivity at 93 % conversion of cellulose, was obtained on a 7.5 wt % Ni/CNF catalyst prepared by chemical vapor deposition of CH(4) on a Ni/?-Al(2)O(3) catalyst, followed by oxidation in HNO(3) (twice for 1 h at 383 K), incipient wetness impregnation, and reduction at 773 K under H(2). This preparation method leads to a properly balanced Ni/CNF catalyst in terms of Ni dispersion and hydrogenation capacity on the one hand, and the number of acidic surface-oxygen groups responsible for the acid-catalyzed hydrolysis on the other. PMID:22730195

Van de Vyver, Stijn; Geboers, Jan; Schutyser, Wouter; Dusselier, Michiel; Eloy, Pierre; Dornez, Emmie; Seo, Jin Won; Courtin, Christophe M; Gaigneaux, Eric M; Jacobs, Pierre A; Sels, Bert F

2012-08-01

163

Electrical resistance of carbon-nanofiber concrete  

International Nuclear Information System (INIS)

Concrete is the most widely used construction material, and carbon nanofibers have many advantages in both mechanical and electrical properties such as high strength, high Young's modulus and high conductivity. In this paper, the mechanical and electrical properties of concrete containing carbon nanofibers (CNF) are experimentally studied. The test results indicate that the compressive strength and per cent reduction in electrical resistance while loading concrete containing CNF are much greater than those of plain concrete. Finally, a reasonable concentration of CNF is obtained for use in concrete which not only enhances compressive strength, but also improves the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete

164

Electrical resistance of carbon-nanofiber concrete  

Science.gov (United States)

Concrete is the most widely used construction material, and carbon nanofibers have many advantages in both mechanical and electrical properties such as high strength, high Young's modulus and high conductivity. In this paper, the mechanical and electrical properties of concrete containing carbon nanofibers (CNF) are experimentally studied. The test results indicate that the compressive strength and per cent reduction in electrical resistance while loading concrete containing CNF are much greater than those of plain concrete. Finally, a reasonable concentration of CNF is obtained for use in concrete which not only enhances compressive strength, but also improves the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete.

Gao, Di; Sturm, Mariel; Mo, Y. L.

2009-09-01

165

Surface morphology and field emission characteristics of carbon nanofiber films grown by chemical vapor deposition on alloy catalyst  

International Nuclear Information System (INIS)

Carbon nanofiber (CNF) films have been successfully grown on Pd-Se, Fe-Ni, and Ni-Cu alloy catalysts at low temperatures by a thermal chemical vapor deposition method. Among these alloy catalysts, Ni-Cu alloy catalyst was found to be most suitable for low temperature growth of CNF (400 deg. C). Using Pd-Se and Fe-Ni alloy catalysts, CNFs were grown at the lowest temperature of 500 deg. C. The CNFs grown using Pd-Se catalyst were found to have more defective structure than that obtained with the other catalysts, and exhibited excellent field emission property (threshold field is estimated about 1.1 V/mm). It is likely that defects play a role as electron emission sites

166

Surface morphology and field emission characteristics of carbon nanofiber films grown by chemical vapor deposition on alloy catalyst  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofiber (CNF) films have been successfully grown on Pd-Se, Fe-Ni, and Ni-Cu alloy catalysts at low temperatures by a thermal chemical vapor deposition method. Among these alloy catalysts, Ni-Cu alloy catalyst was found to be most suitable for low temperature growth of CNF (400 deg. C). Using Pd-Se and Fe-Ni alloy catalysts, CNFs were grown at the lowest temperature of 500 deg. C. The CNFs grown using Pd-Se catalyst were found to have more defective structure than that obtained with the other catalysts, and exhibited excellent field emission property (threshold field is estimated about 1.1 V/mm). It is likely that defects play a role as electron emission sites.

Kamada, K.; Ikuno, T.; Takahashi, S.; Oyama, T.; Yamamoto, T.; Kamizono, M.; Ohkura, S.; Honda, S.; Katayama, M.; Hirao, T.; Oura, K

2003-05-15

167

Evaluation of carbon fiber composites modified by in situ incorporation of carbon nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon fiber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/e...

André Navarro de Miranda; Luiz Claudio Pardini; Carlos Alberto Moreira dos Santos; Ricardo Vieira

2011-01-01

168

Atomic Force and Optical Microscopy Characterization of the Deformation of Individual Carbon Nanotubes and Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available A popular technique for characterizing the mechanical properties of carbon nanotubes is to apply a one-dimension axial compression and measure its response to the compressive force. At some critical compression, a dramatic decrease in the force is observed. This has previously been attributed to Euler buckling, allowing the elastic modulus to be calculated from the Euler buckling force. We have attached individual plasma enhanced chemical vapor deposition (PECVD grown carbon nanofibers (CNFs and thermal chemical vapor deposition (CVD grown carbon nanotubes (CNTs to the apex of an atomic force microscope (AFM cantilever to examine this mechanical response. By combining the force measurements and simultaneous video microscopy, we are able to observe the mechanical deformation and correlate points in the force curve with phenomena such as slipping and bending. Analysis of the mechanical response must therefore be interpreted in terms of bending and/or slipping of a tube compressed by an off-normal force.

Brett A. Cruden

2008-03-01

169

Label-Free Detection of Cardiac Troponin-I Using Carbon Nanofiber Based Nanoelectrode Arrays  

Science.gov (United States)

A sensor platform based on vertically aligned carbon nanofibers (CNFs) has been developed. Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. A carbon nanofiber (CNF) multiplexed array has been fabricated with 9 sensing pads, each containing 40,000 carbon nanofibers as nanoelectrodes. Here, we report the use of vertically aligned CNF nanoelectrodes for the detection of cardiac Troponin-I for the early diagnosis of myocardial infarction. Antibody, antitroponin, probe immobilization and subsequent binding to human cardiac troponin-I were characterized using electrochemical impedance spectroscopy and cyclic voltammetry techniques. Each step of the modification process resulted in changes in electrical capacitance or resistance to charge transfer due to the changes at the electrode surface upon antibody immobilization and binding to the specific antigen. This sensor demonstrates high sensitivity, down to 0.2 ng/mL, and good selectivity making this platform a good candidate for early stage diagnosis of myocardial infarction.

Periyakaruppan, Adaikkappan; Koehne, Jessica Erin; Gandhiraman, Ram P.; Meyyappan, M.

2013-01-01

170

Graphene wrapping as a protective clamping layer anchored to carbon nanofibers encapsulating Si nanoparticles for a Li-ion battery anode.  

Science.gov (United States)

Carbon nanofibers encapsulating Si nanoparticles (CNFs/SiNPs) were prepared via an electrospinning method and chemically functionalized with 3-aminopropyltriethoxysilane (APS) to be grafted onto graphene oxide (GO). As a result, the thin and flexible GO, which exhibits a negative charge in aqueous solution, fully wrapped around the APS-functionalized CNFs with a positive surface charge via electrostatic self-assembly. After the formation of chemical bonds between the epoxy groups on GO and the amine groups in APS via an epoxy ring opening reaction, the GO was chemically reduced to a reduced graphene oxide (rGO). Electrochemical and morphological characterizations showed that capacity loss by structural degradation and electrolyte decomposition on Si surface were significantly suppressed in the rGO-wrapped CNFs/SiNPs (CNFs/SiNPs@rGO). Superior capacities were consequently maintained for up to 200 cycles at a high current density (1048 mA h g(-1) at 890 mA g(-1)) compared to CNFs/SiNPs without the rGO wrapping (304 mA h g(-1) at 890 mA g(-1)). Moreover, the resistance of the SEI layer and charge transfer resistance were also considerably reduced by 24% and 88%, respectively. The described graphene wrapping offers a versatile way to enhance the mechanical integrity and electrochemical stability of Si composite anode materials. PMID:25219404

Shin, Jungwoo; Park, Kyusung; Ryu, Won-Hee; Jung, Ji-Won; Kim, Il-Doo

2014-10-01

171

Dielectric transition of polyacrylonitrile derived carbon nanofibers  

Science.gov (United States)

The dielectric behavior of polyacrylonitrile derived carbon nanofibers formed at different carbonization temperatures was investigated using impedance spectroscopy. The impedance data are presented in the form of Cole-Cole plots and four equivalent electrical circuits are derived. It is found that by increasing carbonization temperature from 500 to 800 °C, a strong capacitive element in the parallel equivalent circuit is transformed into an inductive element, while the contact resistance and parallel resistance are significantly decreased. Along with the morphological and chemical structural evolution, respectively witnessed by scanning electron microscopy and Raman spectroscopy, the dielectric transition deduced from the transformation of electrical circuits can be correlated to the proposed microstructural changes of polyacrylonitrile derived carbon nanofibers and the interaction/interference among them.

Li, Jiangling; Su, Shi; Zhou, Lei; Abbot, Andrew M.; Ye, Haitao

2014-09-01

172

Effect of Plasma Environment on Synthesis of Vertically Aligned Carbon Nanofibers in Plasma-Enhanced Chemical Vapor Deposition  

Science.gov (United States)

We present a theoretical model describing a plasma-assisted growth of carbon nanofibers (CNFs), which involves two competing channels of carbon incorporation into stacked graphene sheets: via surface diffusion and through the bulk of the catalyst particle (on the top of the nanofiber), accounting for a range of ion- and radical-assisted processes on the catalyst surface. Using this model, it is found that at low surface temperatures, T s, the CNF growth is indeed controlled by surface diffusion, thus quantifying the semiempirical conclusions of earlier experiments. On the other hand, both the surface and bulk diffusion channels provide a comparable supply of carbon atoms to the stacked graphene sheets at elevated synthesis temperatures. It is also shown that at low T s, insufficient for effective catalytic precursor decomposition, the plasma ions play a key role in the production of carbon atoms on the catalyst surface. The model is used to compute the growth rates for the two extreme cases of thermal and plasma-enhanced chemical vapor deposition of CNFs. More importantly, these results quantify and explain a number of observations and semiempirical conclusions of earlier experiments.

Denysenko, Igor; Ostrikov, Kostya; Azarenkov, Nikolay A.; Yu, Ming Y.

173

Electrocatalytic properties of Pt/carbon composite nanofibers  

International Nuclear Information System (INIS)

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H2SO4 and 5.0 mM K4[Fe(CN)6] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm-2 has the highest activity.

174

Electrocatalytic properties of Pt/carbon composite nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H{sub 2}SO{sub 4} and 5.0 mM K{sub 4}[Fe(CN){sub 6}] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm{sup -2} has the highest activity.

Lin Zhan; Ji Liwen [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, 2401 Research Drive, Raleigh, NC 27695-8301 (United States); Zhang Xiangwu [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, 2401 Research Drive, Raleigh, NC 27695-8301 (United States)], E-mail: xiangwu_zhang@ncsu.edu

2009-11-30

175

Carbon nanofibers: a versatile catalytic support  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The aim of this article is present an overview of the promising results obtained while using carbon nanofibers based composites as catalyst support for different practical applications: hydrazine decomposition, styrene synthesis, direct oxidation of H2S into elementary sulfur and as fuel-cell electr [...] odes. We have also discussed some prospects of the use of these new materials in total combustion of methane and in ammonia decomposition. The macroscopic carbon nanofibers based composites were prepared by the CVD method (Carbon Vapor Deposition) employing a gaseous mixture of hydrogen and ethane. The results showed a high catalytic activity and selectivity in comparison to the traditional catalysts employed in these reactions. The fact was attributed, mainly, to the morphology and the high external surface of the catalyst support.

Nelize Maria de Almeida, Coelho; Jomar Livramento Barros, Furtado; Cuong, Pham-Huu; Ricardo, Vieira.

2008-09-01

176

Carbon nanofibers: a versatile catalytic support  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this article is present an overview of the promising results obtained while using carbon nanofibers based composites as catalyst support for different practical applications: hydrazine decomposition, styrene synthesis, direct oxidation of H2S into elementary sulfur and as fuel-cell electrodes. We have also discussed some prospects of the use of these new materials in total combustion of methane and in ammonia decomposition. The macroscopic carbon nanofibers based composites were prepared by the CVD method (Carbon Vapor Deposition employing a gaseous mixture of hydrogen and ethane. The results showed a high catalytic activity and selectivity in comparison to the traditional catalysts employed in these reactions. The fact was attributed, mainly, to the morphology and the high external surface of the catalyst support.

Nelize Maria de Almeida Coelho

2008-09-01

177

Carbon nanofibers: a versatile catalytic support  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The aim of this article is present an overview of the promising results obtained while using carbon nanofibers based composites as catalyst support for different practical applications: hydrazine decomposition, styrene synthesis, direct oxidation of H2S into elementary sulfur and as fuel-cell electr [...] odes. We have also discussed some prospects of the use of these new materials in total combustion of methane and in ammonia decomposition. The macroscopic carbon nanofibers based composites were prepared by the CVD method (Carbon Vapor Deposition) employing a gaseous mixture of hydrogen and ethane. The results showed a high catalytic activity and selectivity in comparison to the traditional catalysts employed in these reactions. The fact was attributed, mainly, to the morphology and the high external surface of the catalyst support.

Nelize Maria de Almeida, Coelho; Jomar Livramento Barros, Furtado; Cuong, Pham-Huu; Ricardo, Vieira.

178

Enhanced electrical capacitance of porous carbon nanofibers derived from polyacrylonitrile and boron trioxide  

International Nuclear Information System (INIS)

Carbon nanofibers (CNFs) containing boron and nitrogen are prepared from polyacrylonitrile and boron trioxide (B2O3) by using simple electrospinning. The B2O3 introduction into a PAN solution causes a porous structure with stabilized [O]BN functional groups to develop in the processes of stabilization and carbonization. The pore structure and the functional groups such as B atoms and [O]BN introduce synergistic effects by not only increasing the power density but also the energy density, as shown by the results. The energy storage capabilities of the electrode prepared from 20 wt% B2O3 added to the PAN solution are as follows: a capacitance of 184.0 F g?1 and an energy density of 18.7–25.2 Wh kg?1 in the respective power density range of 400–10,000 W kg?1 in 6 M KOH electrolyte. Hence, these CNFs exhibit a very promising potential as electrode materials for electrical double-layer capacitors due to their unique microstructure and proper proportion of heteroatoms

179

Damping Augmentation of Nanocomposites Using Carbon Nanofiber Paper  

Directory of Open Access Journals (Sweden)

Full Text Available Vacuum-assisted resin transfer molding (VARTM process was used to fabricate the nanocomposites through integrating carbon nanofiber paper into traditional glass fiber reinforced composites. The carbon nanofiber paper had a porous structure with highly entangled carbon nanofibers and short glass fibers. In this study, the carbon nanofiber paper was employed as an interlayer and surface layer of composite laminates to enhance the damping properties. Experiments conducted using the nanocomposite beam indicated up to 200–700% increase of the damping ratios at higher frequencies. The scanning electron microscopy (SEM characterization of the carbon nanofiber paper and the nanocomposites was also conducted to investigate the impregnation of carbon nanofiber paper by the resin during the VARTM process and the mechanics of damping augmentation. The study showed a complete penetration of the resin through the carbon nanofiber paper. The connectivities between carbon nanofibers and short glass fibers within the carbon nanofiber paper were responsible for the significant energy dissipation in the nanocomposites during the damping tests.

Gangbing Song

2006-06-01

180

Free-standing nitrogen-doped carbon nanofiber films as highly efficient electrocatalysts for oxygen reduction  

Science.gov (United States)

Free-standing nitrogen-doped carbon nanofiber (NCNF) films based on polyacrylonitrile (PAN) were prepared simply by the combination of electrospinning and thermal treatment. We reused the nitrogen-rich gas generated as the byproduct of PAN at elevated temperature, mainly NH3, for surface etching and nitrogen doping. The as-obtained NCNFs exhibited a rougher surface and smaller diameter than pristine carbon nanofibers. Despite the decreased total N content, a significant increase in the content of pyrrolic-N was observed for the NCNFs. In application to electrochemistry, the free-standing NCNF films showed comparable catalytic activity with a close four-electron pathway to a commercial Pt/C catalyst in alkaline medium toward oxygen reduction reaction (ORR), which can be attributed to the nitrogen doping and high hydrophilicity. More importantly, the ORR current density on the NCNFs only dropped 6.6% after 10 000 s of continuous operation, suggesting an enhanced long-time durability. In addition, the NCNFs also showed better electrocatalytic selectivity than Pt/C. Our work reveals a facile but efficient approach for the synthesis of free-standing NCNF films as a promising alternative to Pt-based electrocatalysts in fuel cells.Free-standing nitrogen-doped carbon nanofiber (NCNF) films based on polyacrylonitrile (PAN) were prepared simply by the combination of electrospinning and thermal treatment. We reused the nitrogen-rich gas generated as the byproduct of PAN at elevated temperature, mainly NH3, for surface etching and nitrogen doping. The as-obtained NCNFs exhibited a rougher surface and smaller diameter than pristine carbon nanofibers. Despite the decreased total N content, a significant increase in the content of pyrrolic-N was observed for the NCNFs. In application to electrochemistry, the free-standing NCNF films showed comparable catalytic activity with a close four-electron pathway to a commercial Pt/C catalyst in alkaline medium toward oxygen reduction reaction (ORR), which can be attributed to the nitrogen doping and high hydrophilicity. More importantly, the ORR current density on the NCNFs only dropped 6.6% after 10 000 s of continuous operation, suggesting an enhanced long-time durability. In addition, the NCNFs also showed better electrocatalytic selectivity than Pt/C. Our work reveals a facile but efficient approach for the synthesis of free-standing NCNF films as a promising alternative to Pt-based electrocatalysts in fuel cells. Electronic supplementary information (ESI) available: Experimental and characterization details; SEM, contact angles of CNFs-A, CNFs-B and NCNFs; rotating disk electrode voltammograms and Koutecky-Levich plots of CNFs-A and CNFs-B; rotating ring-disk electrode voltammograms of NCNFs and Pt/C; and the electrocatalytic selectivity of the NCNFs and Pt/C. See DOI: 10.1039/c3nr03229a

Liu, Dong; Zhang, Xueping; Sun, Zaicheng; You, Tianyan

2013-09-01

 
 
 
 
181

Electron-beam and ion-beam-induced deposited tungsten contacts for carbon nanofiber interconnects  

Science.gov (United States)

Ion-beam-induced deposition (IBID) and electron-beam-induced deposition (EBID) with tungsten (W) are evaluated for engineering electrical contacts with carbon nanofibers (CNFs). While a different tungsten-containing precursor gas is utilized for each technique, the resulting tungsten deposits result in significant contact resistance reduction. The performance of CNF devices with W contacts is examined and conduction across these contacts is analyzed. IBID-W, while yielding lower contact resistance than EBID-W, can be problematic in the presence of on-chip semiconducting devices, whereas EBID-W provides substantial contact resistance reduction that can be further improved by current stressing. Significant differences between IBID-W and EBID-W are observed at the electrode contact interfaces using high-resolution transmission electron microscopy. These differences are consistent with the observed electrical behaviors of their respective test devices.

Wilhite, Patrick; Uh, Hyung Soo; Kanzaki, Nobuhiko; Wang, Phillip; Vyas, Anshul; Maeda, Shusaku; Yamada, Toshishige; Yang, Cary Y.

2014-09-01

182

Temperature dependence of carbon nanofiber resistance  

International Nuclear Information System (INIS)

Transport properties under current stress are examined for a carbon nanofiber (CNF) on an insulating substrate between tungsten-deposited gold electrodes. The temperature dependence of CNF resistance is determined based on our previously reported heat transport model. The measured devices exhibit a thermal activation behavior, suggesting transport in a disordered medium. The extracted activation energies fall within the 22-35 meV range.

183

Temperature dependence of carbon nanofiber resistance  

Science.gov (United States)

Transport properties under current stress are examined for a carbon nanofiber (CNF) on an insulating substrate between tungsten-deposited gold electrodes. The temperature dependence of CNF resistance is determined based on our previously reported heat transport model. The measured devices exhibit a thermal activation behavior, suggesting transport in a disordered medium. The extracted activation energies fall within the 22-35 meV range.

Yamada, Toshishige; Yabutani, Hisashi; Saito, Tsutomu; Yang, Cary Y.

2010-07-01

184

Electrospun Co–Sn alloy/carbon nanofibers composite anode for lithium ion batteries  

International Nuclear Information System (INIS)

Highlights: •Co–Sn/CNF was prepared by electrospinning and thermal process. •CoSn alloy formation influenced on performance of Co–Sn/CNF. •Co–Sn/CNF composites exhibited the fully interconnected structure. •The discharge capacity for Co–Sn/CNF-800 was 560 mA h g?1 at 80th cycle. -- Abstract: Co–Sn alloy embedded carbon nanofiber (Co–Sn/CNF) composites functioning as anode materials were prepared by using electrospinning technique followed with stabilization and carbonization with heat treatments. Co–Sn/CNF carbonized at 800 °C (Co–Sn/CNF-800) was composed of large amounts of CoSn alloy compared to CoSn2 alloy and Sn crystalline phases both embedded in carbon nanofibers (CNF). The 80th discharge capacity of Co–Sn/CNFs were ranked by their preparation temperature: 800 °C (560 mA h g?1) > 900 °C (504 mA h g?1) > 700 °C (501 mA h g?1). The excellent specific discharge capacity and cycle retention of the sample prepared at 800 °C were attributed to the abundant formation of CoSn facilitating the reversible reaction, the presence of Sn, the buffering role of CNF, and the excellent distribution of nanoparticles by electrospinning. The electrochemical performance for Co–Sn/CNF-900 is lower than that of Co–Sn/CNF-800 because of the formation of CoSn2 showing a two-step mechanism involving irreversible reaction

185

Field-emission-type x-ray source using carbon-nanofibers  

Science.gov (United States)

An x-ray irradiation system of field-emission type has been constructed using carbon-nanofibers (CNFs) grown on a palladium wire that is 50?m in diameter. The electron current emitted from the CNFs was approximately 1mA and was stable within 10% for a long time t >5000h. The electrons passing through a slit in the gate electrode were accelerated to the desired energy, and were made to impinge on the metal target (Ti, Cu, Mo, and W) for generating x rays. The x-rays transmitted through Be-window were characterized using energy analyzers and a dosimeter. At an acceleration voltage of Va=50kV, the energy spectra of the x-rays were exclusively composed of characteristic signals except for the Mo-target, and the dose rates of x-rays were D =2.5-14Gy/min, depending on the target metals. This system also provides sharp x-ray images of both biological and nonbiological materials.

Kita, S.; Watanabe, Y.; Ogawa, A.; Ogura, K.; Sakai, Y.; Matsumoto, Y.; Isokane, Y.; Okuyama, F.; Nakazato, T.; Otsuka, T.

2008-03-01

186

A novel carbon nanofibers grown on glass microballoons immunosensor: a tool for early diagnosis of malaria.  

Science.gov (United States)

This paper presents a novel method for direct detection of Plasmodium falciparum histidine rich protein-2 (PfHRP-2) antigen using carbon nanofiber (CNF) forests grown on glass microballoons (NMBs). Secondary antibodies specific to PfHRP-2 densely attached to the CNFs exhibit extraordinary ability for the detection of minute concentrations of Plasmodium species. A sandwich immunoassay protocol was employed, where a glass substrate was used to immobilize primary antibodies at designated capture zones. High signal amplification was obtained in both colorimetric and electrical measurements due to the CNFs through specific binding. As a result, it was possible to detect PfHRP-2 levels as low as 0.025 ng/mL concentration in phosphate buffered saline (PBS) using a visual signal within only 1 min of test duration. Lower limits of 0.01 ng/mL was obtained by measuring the electrical resistivity of the capture zone. This method is also highly selective and specific in identifying PfHRP-2 and other Plasmodium species from the same solution. In addition, the stability of the labeling mechanism eliminates the false signals generated by the use of dyes in current malaria rapid diagnostic test kits (MRDTs). Thus, the rapid, sensitive and high signal amplification capabilities of NMBs is a promising tool for early diagnosis of malaria and other infectious diseases. PMID:25120159

Gikunoo, Emmanuel; Abera, Adeyabeba; Woldesenbet, Eyassu

2014-01-01

187

The synthesis of titanium carbide-reinforced carbon nanofibers  

International Nuclear Information System (INIS)

Tailoring hard materials into nanoscale building blocks can greatly extend the applications of hard materials and, at the same time, also represents a significant challenge in the field of nanoscale science. This work reports a novel process for the preparation of carbon-based one-dimensional hard nanomaterials. The titanium carbide-carbon composite nanofibers with an average diameter of 90 nm are prepared by an electrospinning technique and a high temperature pyrolysis process. A composite solution containing polyacrylonitrile and titanium sources is first electrospun into the composite nanofibers, which are subsequently pyrolyzed to produce the desired products. The x-ray diffraction pattern and transmission electron microscopy results show that the main phase of the as-synthesized nanofibers is titanium carbide. The Raman analyses show that the composite nanofibers have low graphite clusters in comparison with the pure carbon nanofibers originating from the electrospun polyacrylonitrile nanofibers. The mechanical property tests demonstrate that the titanium carbide-carbon nanofiber membranes have four times higher tensile strength than the carbon nanofiber membranes, and the Young's modulus of the titanium carbide-carbon nanofiber membranes increases in direct proportion to the titanium quantity.

188

Silver-incorporated composites of Fe2O3 carbon nanofibers as anodes for high-performance lithium batteries  

Science.gov (United States)

Composites of Ag-incorporated carbon nanofibers (CNFs) confined with Fe2O3 nanoparticles (Ag-Fe2O3/CNFs) have been synthesized through an electrospinning method and evaluated as anodes for lithium batteries (LIBs). The obtained Ag-Fe2O3/CNF anodes show good LIB performance with a capacity of 630 mAh g-1 tested at 800 mA g-1 after 150 cycles with almost no capacity loss and superb rate performance. The obtained properties for Ag-Fe2O3/CNF anodes are much better than Fe2O3/CNF anodes without Ag-incorporating. In addition, the low-temperature LIB performances for Ag-Fe2O3/CNF anodes have been investigated for revealing the enhanced mechanism of Ag-incorporating. The superior electrochemical performances of the Ag-Fe2O3/CNFs are associated with a synergistic effect of the CNF matrix and the highly conducting Ag incorporating. This unique configuration not only facilitates electron conduction especially at a relative temperature, but also maintains the structural integrity of active materials. Meanwhile, the related analysis of the AC impedance spectroscopy and the corresponding hypothesis for DC impedance confirm that such configuration can effectively enhance the charge-transfer efficiency and the lithium diffusion coefficient. Therefore, CNF-supported coupled with Ag incorporating synthesis supplied a promising route to obtain Fe2O3 based anodes with high-performance LIBs especially at low temperature.

Zou, Mingzhong; Li, Jiaxin; Wen, WeiWei; Chen, Luzhuo; Guan, Lunhui; Lai, Heng; Huang, Zhigao

2014-12-01

189

Carbon nanofiber/cobalt oxide nanopyramid core-shell nanowires for high-performance lithium-ion batteries  

Science.gov (United States)

Carbon nanofiber (CNF)/Co3O4 nanopyramid core-shell nanowires (NWs) are synthesized using an electrospinning method followed by reduction and hydrothermal treatment in order to improve the capacity, cycle stability, and high-rate capability of the electrodes in Li ion batteries (LIBs). The morphology, crystal structure, and chemical states of all samples are investigated by means of field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. For comparison, conventional CNFs, octahedral Co3O4, and Co3O4/CNF composite electrodes are prepared. LIB cells fabricate with the CNF/Co3O4 nanopyramid core-shell NWs exhibit superb discharge capacity (1173 mAh g-1 at the 1st cycle), cycle stability (795 mAh g-1 at 50 cycles), high initial Coulombic efficiency (84.8%), and high-rate capability (570 mAh g-1 at a current density of 700 mA g-1) as compared to the conventional CNF, octahedral Co3O4, and Co3O4/CNF composite electrodes. The performance improvement is owing to the introduction of one-dimensional CNFs relative to efficient electron transport in the core region, extensive utilization of Co3O4 nanopyramids with high capacity grown closely on the CNFs in the shell region, and the network structures of the electrode relative to the improvement of Li ion diffusion.

An, Geon-Hyoung; Ahn, Hyo-Jin

2014-12-01

190

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Directory of Open Access Journals (Sweden)

Full Text Available Polycaprolacton (PCL and multiwalled carbon nanotubes/PCL (P-MWNT/PCL were prepared by electrospinning technique. The average diameter of the nanofibers was below 400 nm. The mechanical properties of the P-MWNT/PCL nanofibers were higher than that of neat PCL nanofibers. It was also found that the mechanical properties of the composite nanofibers were decreased as increased the amount of P-MWNTs, which were due to the poor dispersion of the P-MWNTs in the PCL matrix or agglomeration of MWNTs at high concentration. The thermal stability of the P-MWNT/PCL nanofibers was higher than PCL nanofibers. The conductivity of the adsorbed P-MWNT on PCL (

nanofibers was 1.27 x 10-4 S/cm.

KHALID SAEED

2009-12-01

191

Direct imaging of current paths in multiwalled carbon nanofiber polymer nanocomposites using conducting-tip atomic force microscopy  

Science.gov (United States)

Using conducting-tip atomic force microscopy (C-AFM), we study the spatial distribution of current paths and local electrical properties in carbon nanofiber/polymer nanocomposites. Previous studies of similar systems were hindered by a polymer-rich skin layer that exists at the nanocomposite surfaces. We present an experimental technique using oxygen plasma etching to controllably remove this polymer skin layer. After this treatment, we can directly probe the microscopic transport characteristics of the nanocomposite using C-AFM. The C-AFM results show that the electrical transport is solely carried by the carbon nanofiber (CNF) networks in the nanocomposites. In addition, high-resolution C-AFM maps show nonuniform distribution of current along the length of some CNFs, suggesting the presence of a heterogeneously distributed adsorbed polymer layer around nanofibers. Finally, two probe conductivity measurements in which one electrode (the C-AFM tip) is contacting a single constituent conducting particle were performed to study local conductivity. Results indicate that Ohmic pathways exist in the conducting network of the nanocomposite to the lowest measured nanofiber concentrations. However, non-Ohmic behavior indicating tunneling transport may also be present, especially near the percolation threshold.

Trionfi, A.; Scrymgeour, D. A.; Hsu, J. W. P.; Arlen, M. J.; Tomlin, D.; Jacobs, J. D.; Wang, D. H.; Tan, L.-S.; Vaia, R. A.

2008-10-01

192

Improving the cyclability and rate capability of carbon nanofiber anodes through in-site generation of SiOx-rich overlayers  

International Nuclear Information System (INIS)

SiOx-rich overlayed carbon nanofibers (SiOx-CNFs) are facilely fabricated through the electrospinning of tetraethyl orthosilicate (TEOS) and polyacrylonitrile (PAN) solution and subsequent hydrolyzation and heat treatments. The SiOx-rich overlayer is apparently observed by high-resolution transmission electron microscopy (HR-TEM), which is also identified using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). The SiOx-CNF electrode shows greatly improved cycle stability and rate capability, remaining 84.2% of its initial discharge capacity in contrast to only 61.4% for pure CNFs and exhibiting a reversible capacity of 288 mAh g?1 at 2 A g?1 compared with that (218 mAh g?1) of pure CNFs. This result is ascribed to the formation of a dense and stable SEI film and the highly improved ionic conductivity of SiOx-CNFs during the Li+ insertion/extraction processes. These results suggest that the introduction of SiOx-rich overlayer onto electrodes is an effective strategy to enhance the stability of SEI film and facilitate the surface Li-ion transfer of electrodes, and thus to improve their cycle stability and rate capability

193

Copper-doped Li4Ti5O12/carbon nanofiber composites as anode for high-performance sodium-ion batteries  

Science.gov (United States)

Lithium titanium oxide (Li4Ti5O12) is a promising anode material, owing to its superior safety and reliability. However, the main challenge of Li4Ti5O12 is the low material conductivity which restricts its electrochemical performance. In order to use Li4Ti5O12 in practical sodium-ion batteries, copper-doped Li4Ti5O12 (Li4-xCuxTi5O12, x = 0, 0.05, 0.1) nanoparticles were prepared to enhance the electronic conductivity. Copper-doped Li4Ti5O12 nanoparticles were then embedded in continuous carbon nanofibers (CNFs), which gave rise to fast electron transfer along the fiber direction. After copper-doping and CNF embedding, the resultant copper-doped Li4Ti5O12/CNFs achieved excellent reversible capacity (158.1 mAh g-1) at 30 mA g-1, high coulombic efficiency (99.87%), and good capacity retention (91%) after 150 cycles. In addition, copper-doped Li4Ti5O12/CNFs also exhibited good rate capability. It is, therefore, demonstrated that copper-doped Li4Ti5O12/CNFs are promising anode candidate.

Ge, Yeqian; Jiang, Han; Fu, Kun; Zhang, Changhuan; Zhu, Jiadeng; Chen, Chen; Lu, Yao; Qiu, Yiping; Zhang, Xiangwu

2014-12-01

194

Effect of carbon nanofiber surface groups on oxygen reduction reaction of supported Pt electrocatalyst  

International Nuclear Information System (INIS)

Highlights: ? We studied the effect of oxygen-groups on the particle size and deposition of Pt particles. ? Pt/CNF-OH exhibits smaller Pt mean particle size compared with Pt/CNF-OX. ? Pt/CNF-OH/GC electrode exhibits a better ORR activity than Pt/CNF-OX/GC electrode. -- Abstract: Pt nanoparticles supported on the acid-treated carbon nanofiber (CNF-OX) and LiAlH4-treated carbon nanofiber (CNF-OH) are synthesized via ethylene glycol reduction method. The nature of oxygen-containing surface groups on the CNF-OX and CNF-OH is investigated by potentiometric titration and XPS characterization. Titration of the support materials shows that LiAlH4 can effectively convert the carboxylic acid groups (from 0.21 mmol g?1 to 0.06 mmol g?1) to hydroxyl groups (from 0.09 mmol g?1 to 0.17 mmol g?1), which is agreed well with the results of XPS characterization. High resolution transmission electron microscopy (HRTEM) characterization shows that the Pt nanoparticles are highly dispersed on the two modified CNFs, and the Pt nanoparticles supported on the CNF-OH have a smaller particle size and a more uniform particle size distribution. Rotating disk electrode (RDE) analysis reveals that Pt/CNF-OH exhibits a better activity for ORR than Pt/CNF-OX, and this may be associated with the smaller particle size and better dispersion of Pt nanoparticles on the CNF-OH

195

Sandwich-lithiation and longitudinal crack in amorphous silicon coated on carbon nanofibers.  

Science.gov (United States)

Silicon-carbon nanofibers coaxial sponge, with strong mechanical integrity and improved electronic conductivity, is a promising anode structure to apply into commercial high-capacity lithium ion batteries. We characterized the electrochemical and mechanical behaviors of amorphous silicon-coated carbon nanofibers (a-Si/CNFs) with in situ transmission electron microscopy (TEM). It was found that lithiation of the a-Si coating layer occurred from the surface and the a-Si/CNF interface concurrently, and propagated toward the center of the a-Si layer. Such a process leads to a sandwiched Li(x)Si/Si/Li(x)Si structure, indicating fast Li transport through the a-Si/CNF interface. Nanocracks and sponge-like structures developed in the a-Si layer during the lithiation-delithiation cycles. Lithiation of the a-Si layer sealed in the hollow CNF was also observed, but at a much lower speed than the counterpart of the a-Si layer coated on the CNF surface. An analytical solution of the stress field was formulated based on the continuum theory of finite deformation, explaining the experimental observation of longitudinal crack formation and general mechanical degradation mechanism in a-Si/CNF electrode. PMID:22984869

Wang, Jiang Wei; Liu, Xiao Hua; Zhao, Kejie; Palmer, Andrew; Patten, Erin; Burton, David; Mao, Scott X; Suo, Zhigang; Huang, Jian Yu

2012-10-23

196

The role of carbon nanofiber defects on the electrical and mechanical properties of CNF-based resins  

International Nuclear Information System (INIS)

Heat treatment of carbon nanofibers has proven to be an effective method in removing defects from carbon nanofibers, causing a strong increase in their structural perfection and thermal stability. It affects the bonding states of carbon atoms in the nanofiber structure and causes a significant transformation in the hybridization state of the bonded carbon atoms. Nanofilled resins made of heat-treated CNF show significant increases in their electrical conductivity even at low concentrations. This confirms that enhancement in the perfection of the fiber structure with consequent change in the morphological features plays a prominent role in affecting the electrical properties. Indeed heat-treated CNFs display a stiff structure and a smooth surface which tends to lower the thickness of the unavoidable insulating epoxy layer formed around the CNF which, in turn, plays a fundamental role in the electrical transport properties along the conducting clusters. This might be very beneficial in terms of electrical conductivity but might have negligible effect on the mechanical properties. (paper)

197

The role of carbon nanofiber defects on the electrical and mechanical properties of CNF-based resins  

Science.gov (United States)

Heat treatment of carbon nanofibers has proven to be an effective method in removing defects from carbon nanofibers, causing a strong increase in their structural perfection and thermal stability. It affects the bonding states of carbon atoms in the nanofiber structure and causes a significant transformation in the hybridization state of the bonded carbon atoms. Nanofilled resins made of heat-treated CNF show significant increases in their electrical conductivity even at low concentrations. This confirms that enhancement in the perfection of the fiber structure with consequent change in the morphological features plays a prominent role in affecting the electrical properties. Indeed heat-treated CNFs display a stiff structure and a smooth surface which tends to lower the thickness of the unavoidable insulating epoxy layer formed around the CNF which, in turn, plays a fundamental role in the electrical transport properties along the conducting clusters. This might be very beneficial in terms of electrical conductivity but might have negligible effect on the mechanical properties.

Guadagno, Liberata; Raimondo, Marialuigia; Vittoria, Vittoria; Vertuccio, Luigi; Lafdi, Khalid; De Vivo, Biagio; Lamberti, Patrizia; Spinelli, Giovanni; Tucci, Vincenzo

2013-08-01

198

Tunneling between carbon nanofiber and gold electrodes  

Science.gov (United States)

In a carbon nanofiber (CNF)-metal system such as a bridge between two gold electrodes, passing high current (current stressing) reduces the total resistance of the system (CNF resistance RCNF plus contact resistance Rc) by orders of magnitude. The role of current stressing is modeled as a reduction in the interfacial tunneling gap with transport characteristics attributed to tunneling between Au and CNF. The model predicts a reduction in Rc and gradual disappearance of the nonlinearity in the current-voltage (I-V) characteristics as Rc decreases. These results are consistent with measured I-V behavior.

Yamada, Toshishige; Saito, Tsutomu; Suzuki, Makoto; Wilhite, Patrick; Sun, Xuhui; Akhavantafti, Navid; Fabris, Drazen; Yang, Cary Y.

2010-02-01

199

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Polycaprolacton (PCL) and multiwalled carbon nanotubes/PCL (P-MWNT/PCL) were prepared by electrospinning technique. The average diameter of the nanofibers was below 400 nm. The mechanical properties of the P-MWNT/PCL nanofibers were higher than that of neat PCL nanofibers. It was also found that the mechanical properties of the composite nanofibers were decreased as increased the amount of P-MWNTs, which were due to the poor dispersion of the P-MWNTs in the PCL matrix or agglomeration of MWNT...

KHALID SAEED; PARK SOO-YOUNG; MOHAMMAD ISHAQ

2009-01-01

200

Multifunctional carbon nanofiber/nanotube smart materials  

Science.gov (United States)

This paper discusses the development of new multifunctional smart materials based on Carbon Nanofibers (CNF) and Multi-Wall Carbon Nanotubes (MWCNT). The material properties of CNF/MWCNT are a little lower than the properties of Single Wall Carbon Nanotubes (SWCNT). However, the CNF/MWCNT have the potential for more practical applications since their cost is lower. This paper discusses the development of four CNF/MWCNT-based sensors and actuators. These are: (i) an Electrochemical Wet Actuator for use in a liquid electrolyte, (ii) an Electrochemical Dry Actuator for use in a dry environment, (iii) a Bioelectronic sensor; and (iv) a MWCNT neuron for structural health monitoring. These materials are exciting because of their unique properties and many applications.

Yun, Yeo-Heung; Kang, Inpil; Gollapudi, Ramanand; Lee, Jong W.; Hurd, Douglas; Shanov, Vesselin N.; Schulz, Mark J.; Kim, Jay; Shi, Donglu; Boerio, J. F.; Subramaniam, Srinivas

2005-05-01

 
 
 
 
201

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: English Abstract in english Polycaprolacton (PCL) and multiwalled carbon nanotubes/PCL (P-MWNT/PCL) were prepared by electrospinning technique. The average diameter of the nanofibers was below 400 nm. The mechanical properties of the P-MWNT/PCL nanofibers were higher than that of neat PCL nanofibers. It was also found that the [...] mechanical properties of the composite nanofibers were decreased as increased the amount of P-MWNTs, which were due to the poor dispersion of the P-MWNTs in the PCL matrix or agglomeration of MWNTs at high concentration. The thermal stability of the P-MWNT/PCL nanofibers was higher than PCL nanofibers. The conductivity of the adsorbed P-MWNT on PCL (

KHALID, SAEED; PARK, SOO-YOUNG; MOHAMMAD, ISHAQ.

202

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: English Abstract in english Polycaprolacton (PCL) and multiwalled carbon nanotubes/PCL (P-MWNT/PCL) were prepared by electrospinning technique. The average diameter of the nanofibers was below 400 nm. The mechanical properties of the P-MWNT/PCL nanofibers were higher than that of neat PCL nanofibers. It was also found that the [...] mechanical properties of the composite nanofibers were decreased as increased the amount of P-MWNTs, which were due to the poor dispersion of the P-MWNTs in the PCL matrix or agglomeration of MWNTs at high concentration. The thermal stability of the P-MWNT/PCL nanofibers was higher than PCL nanofibers. The conductivity of the adsorbed P-MWNT on PCL (

KHALID, SAEED; PARK, SOO-YOUNG; MOHAMMAD, ISHAQ.

2009-12-01

203

IN-SITU SYNCHROTRON SAXS/WAXD STUDIES DURING MELT SPINNING OF MODIFIED CARBON NANOFIBER AND ISOTACTIC POLYPROPYLENE NANOCOMPOSITE  

International Nuclear Information System (INIS)

The structural development of a nanocomposite, containing 95 wt% isotactic polypropylene (iPP) and 5 wt% modified carbon nanofiber (MCNF), during fiber spinning was investigated by in situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. The modification of carbon nanofibers (CNFs) was accomplished by a chemical surface treatment using in situ polymerization of olefin segments to enhance its compatibility with iPP, where the iPP/MCNF nanocomposite was prepared by twostep blending to ensure the dispersion of MCNF. X-ray results showed that at low spin-draw ratios, the iPP/MCNF nanocomposite fiber exhibited much higher iPP crystalline orientation than the control iPP fiber. At higher spin-draw ratios, the crystalline orientation of the nanocomposite fiber and that of the pure iPP fiber was about the same. The crystallinity of the composite fiber was higher than that of the control iPP fiber, indicating the nucleating effect of the modified carbon nanofibers. The nanocomposite fiber also showed larger long periods at low spin-draw ratios. Measurements of mechanical properties indicated that the nanocomposite fiber with 5 wt% MCNF had much higher tensile strength, modulus and longer elongation to break. The mechanical enhancement can be attributed to the dispersion of MCNF in the matrix, which was confirmed by SEM results

204

Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors  

Science.gov (United States)

This paper presents highly conductive carbon nanofiber/MnO2 coaxial cables in which individual electrospun carbon nanofibers are coated with an ultrathin hierarchical MnO2 layer. In the hierarchical MnO2 structure, an around 4 nm thick sheath surrounds the carbon nanofiber (CNF) in a diameter of 200 nm, and nano-whiskers grow radically outward from the sheath in view of the cross-section of the coaxial cables, giving a high specific surface area of MnO2. The CNFs are synthesized by electrospinning a precursor containing iron acetylacetonate (AAI). The addition of AAI not only enlarges the specific surface area of the CNF but also greatly enhances their electronic conductivity, which leads to a dramatic improvement in the specific capacitance and the rate capability of the CNF/MnO2 electrode. The AAI-CNF/MnO2 electrode shows a specific capacitance of 311 F g-1 for the whole electrode and 900 F g-1 for the MnO2 shell at a scan rate of 2 mV s-1. Good cycling stability, high energy density (80.2 Wh kg-1) and high power density (57.7 kW kg-1) are achieved. This work indicates that high electronic conductivity of the electrode material is crucial to achieving high power and energy density for pseudo-supercapacitors.

Zhi, Mingjia; Manivannan, Ayyakkannu; Meng, Fanke; Wu, Nianqiang

2012-06-01

205

Potential applications of nanofiber textile covered by carbon coatings  

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: Nanospider technology is modified electrospinning method for production nanofiber textile from polymer solutions. This material can be used as wound dressing and filter materials for example. Carbon coatings deposited onto surface of polymer nanofiber textiles are predicted to improve filtration effectivity of filters and bioactivity of wound dressings. Carbon coatings have been produced by Microwave Radio Frequency Plasma Assisted Chemical Vapor Deposition (MW/RF PACVD method.Design/methodology/approach: Carbon coatings were deposited on polymer nanofiber textile by MW/RF PACVD method. Nanocomposite obtained in this way was characterized by the contact angle studies and by scanning electron microscope (SEM.Findings: Carbon coatings can be deposited on the polymer nanofibers by MW/RF PACVD method. Content of diamond phase in produced carbon coatings has been confirmed by wetability test. A SEM microscopic images have shown that the spaces between the nanofibers have not been closed by the material of the film.Research limitations/implications: MW/RF PACVD makes carbon coating synthesis possible in lower temperature, what is essential in case of applying the polymer substrate. Use of any other method than MW/RF PACVD for deposition of carbon coatings onto polymer nanofiber textile is not covered in this paper.Practical implications: Nanofiber textile produced by Nanospider is very good mechanical filter. Carbon onto surface of nanofibers can cause from this material active filter. Since this nanocomposite enables the transport of oxygen and exudate, simultaneously is impenetrable for bacteria or even viruses, it can be used for wound dressing.Originality/value: It is our belief that we are first to have deposited carbon coatings on nanofiber textile. We hope that in this way we have prepared very good material for filtration of air and for wound dressing.

Z. Ro?ek

2008-03-01

206

Evaluation of carbon fiber composites modified by in situ incorporation of carbon nanofibers  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon f [...] iber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/epoxy) composites were molded and electrical conductivity was measured. Also, the CF/CNF/epoxy composites were tested under flexure and interlaminar shear. The results showed an overall reduction in mechanical properties as a function of added nanofiber, although electrical conductivity increased up to 74% with the addition of nanofibers. Thus CF/CNF/epoxy composites can be used as electrical dissipation discharge materials.

André Navarro de, Miranda; Luiz Claudio, Pardini; Carlos Alberto Moreira dos, Santos; Ricardo, Vieira.

207

Evaluation of carbon fiber composites modified by in situ incorporation of carbon nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon fiber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/epoxy composites were molded and electrical conductivity was measured. Also, the CF/CNF/epoxy composites were tested under flexure and interlaminar shear. The results showed an overall reduction in mechanical properties as a function of added nanofiber, although electrical conductivity increased up to 74% with the addition of nanofibers. Thus CF/CNF/epoxy composites can be used as electrical dissipation discharge materials.

André Navarro de Miranda

2011-12-01

208

Evaluation of carbon fiber composites modified by in situ incorporation of carbon nanofibers  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon f [...] iber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/epoxy) composites were molded and electrical conductivity was measured. Also, the CF/CNF/epoxy composites were tested under flexure and interlaminar shear. The results showed an overall reduction in mechanical properties as a function of added nanofiber, although electrical conductivity increased up to 74% with the addition of nanofibers. Thus CF/CNF/epoxy composites can be used as electrical dissipation discharge materials.

André Navarro de, Miranda; Luiz Claudio, Pardini; Carlos Alberto Moreira dos, Santos; Ricardo, Vieira.

2011-12-01

209

Vertically oriented nickel nanorod/carbon nanofiber core/shell structures synthesized by plasma-enhanced chemical vapor deposition  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Plasma-enhanced chemical vapor deposition, without a nickel-containing gaseous precur- sor, was used to synthesize continuous nickel (Ni) nanorods inside the hollow cavity of car- bon nanofibers (CNFs), thus forming vertically aligned Ni/CNF core/shell structures. Scanning and transmission electron microscopic images indicate that the elongated Ni nanorods originate from the catalyst particles at the tips of the CNFs and that their forma- tion is due to the effect of extrusion induced by the ...

He, Zanbing; Lee, Chang Seok; Maurice, Jean Luc; Pribat, Didier; Haghi-ashtiani, Paul; Cojocaru, Costel Sorin

2011-01-01

210

In-situ synthesis and thermal-electrical properties of CP2- polyimide/pristine and amine-functionalized carbon nanofiber composites  

Science.gov (United States)

Vapor-grown carbon nanofibers (VGCNF) functionalized with amine-containing pendants, viz.H2N-VGCNF, reacted with 2,2-bis(phthalic anhydride)-1,1,1,3,3,3-hexafluoroisopropane, which was the dianhydride monomer used in in-situ polymerization with 1,3-bis(3-aminophenoxy)benzene to afford a series of CP2-polyimide nanocomposite films (FCNFCP2), containing 0.18-9.19 wt % of H2N-VGCNF (corresponding to 0.10-5.0 wt % of pristine VGCNF), via conventional poly(amic acid) precursor method. For comparison, another series of in situ nanocomposites containing pristine VGCNF (0.10-5.0 wt %) was also prepared similarly. While H2N-VGCNFs enabled direct formation of CP2 grafts on the nanofibers, pristine VGCNFs would result in a relatively weak interface between nanofibers and the CP2 matrix. Conducting-tip atomic force microscopy (C-AFM) showed that the electrical transport was solely through the nanofiber networks in the PCNF-CP2. In general, low-frequency ac impedance measurements followed well the percolation bond model with low percolation threshold; 0.24 and 0.68 vol % for PCNF-CP2 and FCNF-CP2, respectively. However, the design of interface is determined to be crucial for controlling the electrical behavior in four substantial ways: (i) magnitude of limiting conductivity, (ii) linearity of I-V response, (iii) magnitude and direction of temperature-dependent resistivity, and (iv) reproducibility of the absolute value of resistivity with thermal cycling. These observations are consistent with a direct CNF-CNF contact limiting transport in the PCNF-CP2 system, where the CP2 grafts on FCNF form a dielectric layer between individual CNFs, limiting transport within the FCNF-CP2 system. Furthermore, the CP2 grafts on the FCNF surface reduce local polymer dewetting at the nanofiber surfaces when the temperatures exceed the CP2 glass transition, and stabilize the structure of the percolation network and associated conductivity. The general behavior of these interfacial extremes (pristine and fully functionalized CNFs) set important bounds on the design of interface modification for CNFs when the intended use is for electrical performance at elevated temperatures or under extreme current loads. The influence of processing conditions resulting in the spread of measured conductivity by several orders of magnitude for films containing the same type and same amount of CNFs is also reported.

Wang, David H.; Jacobs, J. David; Trionfi, Aaron; Arlen, Michael J.; Hsu, Julia W. P.; Vaia, Richard A.; Tan, Loon-Seng

2009-07-01

211

A carbon nanofiber based biosensor for simultaneous detection of dopamine and serotonin in the presence of ascorbic acid.  

Science.gov (United States)

A biosensor based on an array of vertically aligned carbon nanofibers (CNFs) grown by plasma enhanced chemical vapor deposition is found to be effective for the simultaneous detection of dopamine (DA) and serotonin (5-HT) in the presence of excess ascorbic acid (AA). The CNF electrode outperforms the conventional glassy carbon electrode (GCE) for both selectivity and sensitivity. Using differential pulse voltammetry (DPV), three distinct peaks are seen for the CNF electrode at 0.13 V, 0.45 V, and 0.70 V for the ternary mixture of AA, DA, and 5-HT. In contrast, the analytes are indistinguishable in a mixture using a GCE. For the CNF electrode, the detection limits are 50 nM for DA and 250 nM for 5-HT. PMID:23228495

Rand, Emily; Periyakaruppan, Adaikkappan; Tanaka, Zuki; Zhang, David A; Marsh, Michael P; Andrews, Russell J; Lee, Kendall H; Chen, Bin; Meyyappan, M; Koehne, Jessica E

2013-04-15

212

Germanium nanoparticles encapsulated in flexible carbon nanofibers as self-supported electrodes for high performance lithium-ion batteries  

Science.gov (United States)

Germanium is a promising high-capacity anode material for lithium ion batteries, but still suffers from poor cyclability due to its huge volume variation during the Li-Ge alloy/dealloy process. Here we rationally designed a flexible and self-supported electrode consisting of Ge nanoparticles encapsulated in carbon nanofibers (Ge-CNFs) by using a facile electrospinning technique as potential anodes for Li-ion batteries. The Ge-CNFs exhibit excellent electrochemical performance with a reversible specific capacity of ~1420 mA h g-1 after 100 cycles at 0.15 C with only 0.1% decay per cycle (the theoretical specific capacity of Ge is 1624 mA h g-1). When cycled at a high current of 1 C, they still deliver a reversible specific capacity of 829 mA h g-1 after 250 cycles. The strategy and design are simple, effective, and versatile. This type of flexible electrodes is a promising solution for the development of flexible lithium-ion batteries with high power and energy densities.Germanium is a promising high-capacity anode material for lithium ion batteries, but still suffers from poor cyclability due to its huge volume variation during the Li-Ge alloy/dealloy process. Here we rationally designed a flexible and self-supported electrode consisting of Ge nanoparticles encapsulated in carbon nanofibers (Ge-CNFs) by using a facile electrospinning technique as potential anodes for Li-ion batteries. The Ge-CNFs exhibit excellent electrochemical performance with a reversible specific capacity of ~1420 mA h g-1 after 100 cycles at 0.15 C with only 0.1% decay per cycle (the theoretical specific capacity of Ge is 1624 mA h g-1). When cycled at a high current of 1 C, they still deliver a reversible specific capacity of 829 mA h g-1 after 250 cycles. The strategy and design are simple, effective, and versatile. This type of flexible electrodes is a promising solution for the development of flexible lithium-ion batteries with high power and energy densities. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00140k

Li, Weihan; Yang, Zhenzhong; Cheng, Jianxiu; Zhong, Xiongwu; Gu, Lin; Yu, Yan

2014-04-01

213

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladium nanoparticles  

International Nuclear Information System (INIS)

This paper studies the mechanism of the formation of carbon nanostructures on carbon nanofibers with Pd nanoparticles by using different carbon sources. The carbon nanofibers with Pd nanoparticles were produced by carbonizing electrospun polyacrylonitrile (PAN) nanofibers including Pd(Ac)2. Such PAN-based carbon nanofibers were then used as substrates to grow hierarchical carbon nanostructures. Toluene, pyridine and chlorobenzine were employed as carbon sources for the carbon nanostructures. With the Pd nanoparticles embedded in the carbonized PAN nanofibers acting as catalysts, molecules of toluene, pyridine or chlorobenzine were decomposed into carbon species which were dissolved into the Pd nanoparticles and consequently grew into straight carbon nanotubes, Y-shaped carbon nanotubes or carbon nano-ribbons on the carbon nanofiber substrates. X-ray diffraction analysis and transmission electron microscopy (TEM) were utilized to capture the mechanism of formation of Pd nanoparticles, regular carbon nanotubes, Y-shaped carbon nanotubes and carbon nano-ribbons. It was observed that the Y-shaped carbon nanotubes and carbon nano-ribbons were formed on carbonized PAN nanofibers containing Pd-nanoparticle catalyst, and the carbon sources played a crucial role in the formation of different hierarchical carbon nanostructures

214

Potential applications of nanofiber textile covered by carbon coatings  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Purpose: Nanospider technology is modified electrospinning method for production nanofiber textile from polymer solutions. This material can be used as wound dressing and filter materials for example. Carbon coatings deposited onto surface of polymer nanofiber textiles are predicted to improve filtration effectivity of filters and bioactivity of wound dressings. Carbon coatings have been produced by Microwave Radio Frequency Plasma Assisted Chemical Vapor Deposition (MW/RF PACVD) method.Desig...

Roz?ek, Z.; Kaczorowski, W.; Luka?s?, D.; Louda, P.; Mitura, S.

2008-01-01

215

Preparation of a new adsorbent from activated carbon and carbon nanofiber (AC/CNF) for manufacturing organic-vacbpour respirator cartridge.  

Science.gov (United States)

In this study a composite of activated carbon and carbon nanofiber (AC/CNF) was prepared to improve the performance of activated carbon (AC) for adsorption of volatile organic compounds (VOCs) and its utilization for respirator cartridges. Activated carbon was impregnated with a nickel nitrate catalyst precursor and carbon nanofibers (CNF) were deposited directly on the AC surface using catalytic chemical vapor deposition. Deposited CNFs on catalyst particles in AC micropores, were activated by CO2 to recover the surface area and micropores. Surface and textural characterizations of the prepared composites were investigated using Brunauer, Emmett and Teller's (BET) technique and electron microscopy respectively. Prepared composite adsorbent was tested for benzene, toluene and xylene (BTX) adsorption and then employed in an organic respirator cartridge in granular form. Adsorption studies were conducted by passing air samples through the adsorbents in a glass column at an adjustable flow rate. Finally, any adsorbed species not retained by the adsorbents in the column were trapped in a charcoal sorbent tube and analyzed by gas chromatography. CNFs with a very thin diameter of about 10-20 nm were formed uniformly on the AC/CNF. The breakthrough time for cartridges prepared with CO2 activated AC/CNF was 117 minutes which are significantly longer than for those cartridges prepared with walnut shell- based activated carbon with the same weight of adsorbents. This study showed that a granular form CO2 activated AC/CNF composite could be a very effective alternate adsorbent for respirator cartridges due to its larger adsorption capacities and lower weight. PMID:23369424

Jahangiri, Mehdi; Adl, Javad; Shahtaheri, Seyyed Jamaleddin; Rashidi, Alimorad; Ghorbanali, Amir; Kakooe, Hossein; Forushani, Abbas Rahimi; Ganjali, Mohammad Reza

2013-01-01

216

Interfacial engineering of carbon nanofiber-graphene-carbon nanofiber heterojunctions in flexible lightweight electromagnetic shielding networks.  

Science.gov (United States)

Lightweight carbon materials of effective electromagnetic interference (EMI) shielding have attracted increasing interest because of rapid development of smart communication devices. To meet the requirement in portable electronic devices, flexible shielding materials with ultrathin characteristic have been pursued for this purpose. In this work, we demonstrated a facile strategy for scalable fabrication of flexible all-carbon networks, where the insulting polymeric frames and interfaces have been well eliminated. Microscopically, a novel carbon nanofiber-graphene nanosheet-carbon nanofiber (CNF-GN-CNF) heterojunction, which plays the dominant role as the interfacial modifier, has been observed in the as-fabricated networks. With the presence of CNF-GN-CNF heterojunctions, the all-carbon networks exhibit much increased electrical properties, resulting in the great enhancement of EMI shielding performance. The related mechanism for engineering the CNF interfaces based on the CNF-GN-CNF heterojunctions has been discussed. Implication of the results suggests that the lightweight all-carbon networks, whose thickness and density are much smaller than other graphene/polymer composites, present more promising potential as thin shielding materials in flexible portable electronics. PMID:24914611

Song, Wei-Li; Wang, Jia; Fan, Li-Zhen; Li, Yong; Wang, Chan-Yuan; Cao, Mao-Sheng

2014-07-01

217

Electrospun Co–Sn alloy/carbon nanofibers composite anode for lithium ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •Co–Sn/CNF was prepared by electrospinning and thermal process. •CoSn alloy formation influenced on performance of Co–Sn/CNF. •Co–Sn/CNF composites exhibited the fully interconnected structure. •The discharge capacity for Co–Sn/CNF-800 was 560 mA h g{sup ?1} at 80th cycle. -- Abstract: Co–Sn alloy embedded carbon nanofiber (Co–Sn/CNF) composites functioning as anode materials were prepared by using electrospinning technique followed with stabilization and carbonization with heat treatments. Co–Sn/CNF carbonized at 800 °C (Co–Sn/CNF-800) was composed of large amounts of CoSn alloy compared to CoSn{sub 2} alloy and Sn crystalline phases both embedded in carbon nanofibers (CNF). The 80th discharge capacity of Co–Sn/CNFs were ranked by their preparation temperature: 800 °C (560 mA h g{sup ?1}) > 900 °C (504 mA h g{sup ?1}) > 700 °C (501 mA h g{sup ?1}). The excellent specific discharge capacity and cycle retention of the sample prepared at 800 °C were attributed to the abundant formation of CoSn facilitating the reversible reaction, the presence of Sn, the buffering role of CNF, and the excellent distribution of nanoparticles by electrospinning. The electrochemical performance for Co–Sn/CNF-900 is lower than that of Co–Sn/CNF-800 because of the formation of CoSn{sub 2} showing a two-step mechanism involving irreversible reaction.

Jang, Bo-Ok; Park, Seok-Hwan; Lee, Wan-Jin, E-mail: wjlee@jnu.ac.kr

2013-10-15

218

Morphology and Size of Ion Induced Carbon Nanofibers: Effect of Ion Incidence Angle, Sputtering Rate, and Temperature  

Science.gov (United States)

Graphite surfaces were bombarded with oblique Ar+ ions at 1 keV to induce the carbon nanofiber (CNF) growth at room temperature and at high temperature (300 °C), and their dependence of length, diameter and number density on ion-incidence angle and sputtering rate was investigated in detail. The sputtered surface ion-irradiated at normal incidence produced huge cones and rod-like structures. It was found that some of the cones possessed the non-aligned thick carbon fibers on the top. By contrast, obliquely ion-irradiation induced the formation of densely distributed CNF-tipped cones. The higher ion-incidence angle produced CNF of smaller diameter and high fabrication temperature favors the formation of longer fiber with higher numerical density. In addition, the number density of the CNF-tipped cones strongly depended upon the ion-incidence angle rather than the sputtering rate. Thus, the diameter, length and number density of CNFs were strongly dependent upon the ion-irradiation parameters. It is believed that myriad of applications is possible with ion-induced CNFs by selecting the suitable ion-irradiation parameters.

Zamri Yusop, Mohd; Yamaguchi, Kohei; Suzuki, Takahito; Ghosh, Pradip; Hayashi, Akari; Hayashi, Yasuhiko; Tanemura, Masaki

2011-01-01

219

Improved fire retardancy of thermoset composites modified with carbon nanofibers  

International Nuclear Information System (INIS)

Multifunctional thermoset composites were made from polyester resin, glass fiber mats and carbon nanofiber sheets (CNS). Their flaming behavior was investigated with cone calorimeter under well-controlled combustion conditions. The heat release rate was lowered by pre-planting carbon nanofiber sheets on the sample surface with the total fiber content of only 0.38 wt.%. Electron microscopy showed that carbon nanofiber sheet was partly burned and charred materials were formed on the combusting surface. Both the nanofibers and charred materials acted as an excellent insulator and/or mass transport barrier, improving the fire retardancy of the composite. This behavior agrees well with the general mechanism of fire retardancy in various nanoparticle-thermoplastic composites.

220

MEMS-based carbon nanotube and carbon nanofiber Cu micro special electric contact  

International Nuclear Information System (INIS)

Two new electrical contact materials, carbon nanotube (CNT) and carbon nanofiber (CNF), Cu-matrix composite films are prepared by composite electroplating. The microstructure, morphology and physical performance of Cu–CNT/CNF composite films were analyzed by a scanning electron microscope, a Vickers hardness tester and a semiconductor parameter analyzer. The scanning electron microscope images showed that the CNTs/CNFs were dispersed uniformly and combined well in the Cu matrix. Furthermore, the Cu–CNT/CNF composite films show relatively good physical properties, for example the hardnesses of Cu/CNT and Cu/CNF composite films are 156 HV and 207 HV, about 13.9% and 51.1% higher than that of the pure copper plating film (137 HV); the resistivities of CNT/CNF composite plating films are 2.656 × 10?6 ? cm and 1.815 × 10?6 ? cm, lower than those of other Cu-matrix composites such as CuW, 4.35 × 10?6 ? cm, and CuMo, 3.571 × 10?6 ? cm. In addition, CNT and CNF Cu micro special electric contacts have been designed and successfully fabricated by MEMS technology. The arc-erosion behavior of Cu/CNT and Cu/CNF contacts has been examined on an electric arc-erosion apparatus. The test result shows that the arc-erosion losses of Cu/CNT and Cu/CNF contacts are 2.7 mg and 3.0 mg, 22.9% and 14.3% lower than that of pure Cu (3.5 mg) under the same condition

 
 
 
 
221

MEMS-based carbon nanotube and carbon nanofiber Cu micro special electric contact  

Science.gov (United States)

Two new electrical contact materials, carbon nanotube (CNT) and carbon nanofiber (CNF), Cu-matrix composite films are prepared by composite electroplating. The microstructure, morphology and physical performance of Cu-CNT/CNF composite films were analyzed by a scanning electron microscope, a Vickers hardness tester and a semiconductor parameter analyzer. The scanning electron microscope images showed that the CNTs/CNFs were dispersed uniformly and combined well in the Cu matrix. Furthermore, the Cu-CNT/CNF composite films show relatively good physical properties, for example the hardnesses of Cu/CNT and Cu/CNF composite films are 156 HV and 207 HV, about 13.9% and 51.1% higher than that of the pure copper plating film (137 HV); the resistivities of CNT/CNF composite plating films are 2.656 × 10-6 ? cm and 1.815 × 10-6 ? cm, lower than those of other Cu-matrix composites such as CuW, 4.35 × 10-6 ? cm, and CuMo, 3.571 × 10-6 ? cm. In addition, CNT and CNF Cu micro special electric contacts have been designed and successfully fabricated by MEMS technology. The arc-erosion behavior of Cu/CNT and Cu/CNF contacts has been examined on an electric arc-erosion apparatus. The test result shows that the arc-erosion losses of Cu/CNT and Cu/CNF contacts are 2.7 mg and 3.0 mg, 22.9% and 14.3% lower than that of pure Cu (3.5 mg) under the same condition.

Deng, Min; Ding, Guifu; Wang, Yan; Wang, Yuchao; Wang, Hong; Fu, Shi

2009-06-01

222

Carbon nanofiber reinforced epoxy matrix composites and syntactic foams - mechanical, thermal, and electrical properties  

Science.gov (United States)

The tailorability of composite materials is crucial for use in a wide array of real-world applications, which range from heat-sensitive computer components to fuselage reinforcement on commercial aircraft. The mechanical, electrical, and thermal properties of composites are highly dependent on their material composition, method of fabrication, inclusion orientation, and constituent percentages. The focus of this work is to explore carbon nanofibers (CNFs) as potential nanoscale reinforcement for hollow particle filled polymer composites referred to as syntactic foams. In the present study, polymer composites with high weight fractions of CNFs, ranging from 1-10 wt.%, are used for quasi-static and high strain rate compression analysis, as well as for evaluation and characterization of thermal and electrical properties. It is shown that during compressive characterization of vapor grown carbon nanofiber (CNF)/epoxy composites in the strain rate range of 10-4-2800 s-1, a difference in the fiber failure mechanism is identified based on the strain rate. Results from compression analyses show that the addition of fractions of CNFs and glass microballoons varies the compressive strength and elastic modulus of epoxy composites by as much as 53.6% and 39.9%. The compressive strength and modulus of the syntactic foams is also shown to generally increase by a factor of 3.41 and 2.96, respectively, with increasing strain rate when quasi-static and high strain rate testing data are compared, proving strain rate sensitivity of these reinforced composites. Exposure to moisture over a 6 month period of time is found to reduce the quasi-static and high strain rate strength and modulus, with a maximum of 7% weight gain with select grades of CNF/syntactic foam. The degradation of glass microballoons due to dealkalization is found to be the primary mechanism for reduced mechanical properties, as well as moisture diffusion and weight gain. In terms of thermal analysis results, the coefficient of thermal expansion (CTE) of CNF/epoxy and CNF/syntactic foam composites reinforced with glass microballoons decrease by as much as 11.6% and 38.4%. The experimental CTE values for all of the composites also fit within the bounds of established analytical models predicting the CTE of fiber and particle-reinforced composites. Further thermal studies through dynamic mechanical analysis demonstrated increased thermal stability and damping capability, where the maximum use and glass transition temperatures increase as much as 27.1% and 25.0%, respectively. The electrical properties of CNF reinforced composites are evaluated as well, where the electrical impedance decreases and the dielectric constant increases with addition of CNFs. Such behavior occurs despite the presence of epoxy and glass microballoons, which serve as insulative phases. Such results are useful in design considerations of lightweight composite materials used in weight saving, compressive strength, and damage tolerance applications, such as lightweight aircraft structure reinforcement, automobile components, and buoyancy control with marine submersibles. The results of the analyses have also evaluated certain factors for environmental exposure and temperature extremes, as well as considerations for electronics packaging, all of which have also played a role in shaping avant-garde composite structure designs for efficient, versatile, and long-life service use.

Poveda, Ronald Leonel

223

Structural transformation of vapor grown carbon nanofibers studied by HRTEM  

International Nuclear Information System (INIS)

Vapor grown carbon nanofibers have been extensively manufactured and investigated in recent years. In this study commercially available vapor grown carbon nanofibers subjected to different processing and post processing conditions were studied employing high resolution TEM images. The analysis showed that the fibers consist primarily of conical nanofibers, but can contain a significant amount of bamboo nanofibers. Most conical nanofibers were found to consist of an ordered inner layer and a disordered outer layer, with the cone angle distribution of the inner layers indicating that these cannot have a stacked cone structure but are compatible with a cone-helix structure. Fibers that have been heat treated to temperatures above 1,500 oC undergo a structural transformation with the ordered inner layers changing from a cone-helix structure to a highly ordered multiwall stacked cone structure. The bamboo nanofibers were found to have a tapered multiwall nanotube structure for the wall and a multishell fullerene structure for the cap of each segment, surrounded by a disordered outer layer. When these fibers are heat treated the disordered outer layers transform to an ordered multiwall nanotube structure and merge with the wall of each segment. The end caps of each segment transform from a smooth multiwall fullerene structure to one consisting of disjointed graphene planes. A reaction-diffusion mechanism is proposed to explain the growth and structure of the bambplain the growth and structure of the bamboo nanofibers.

224

Synergistic effect of carbon nanofiber and sub-micro filamentary nickel nanostrand on the shape memory polymer nanocomposite  

International Nuclear Information System (INIS)

This work studies the synergistic effect of carbon nanofiber (CNF) and sub-micro filamentary nickel nanostrand on the thermal and electrical properties, as well as the electro-active shape memory behavior, of a shape memory polymer (SMP) nanocomposite. The combination of electrical CNF and electromagnetic nickel nanostrand is used to render insulating thermo-responsive SMPs conductive. Subsequently, the shape memory behavior of the SMP can be activated by the electrical resistive heating. It is shown that sub-micro filamentary nickel-coated nanostrands significantly improved the electrical conductivity to facilitate the actuation of the SMP nanocomposite despite the low nanostrand volume content and low electrical voltage. Also the CNFs are blended with the SMP resin to facilitate the dispersion of nanostrands and improve the thermal conductivity to accelerate the electro- and thermo-active responses

225

Scanning Conductance Microscopy of Carbon Nanotubes and Polyethylene Oxide Nanofibers  

Science.gov (United States)

We have developed a quantitative model that explains the phase shifts observed in Scanning Conductance Microscopy, by considering the change in the total capacitance of the tip-sample-substrate system. We show excellent agreement with data on samples of (conducting) single wall carbon nanotubes and insulating polyethylene oxide (PEO) nanofibers. Data for large diameter, conducting doped polyaniline/PEO nanofibers are qualitatively explained. This quantitative approach is used to determine the dielectric constant of PEO nanofiber ?f = 2.88 ± 0.12, a general method that can be extended to other dielectric nanowires.

Staii, Cristian; Pinto, Nicholas J.; Johnson, Alan T.

2004-09-01

226

Improvement of thermal contact resistance by carbon nanotubes and nanofibers  

Science.gov (United States)

Interfacial thermal resistance results of various nanotube and nanofiber coatings, prepared by chemical vapor deposition (CVD) methods, are reported at relatively low clamping pressures. The five types of samples examined include multi-walled and single-walled nanotubes growth by CVD, multi-walled nanotubes grown by plasma enhanced CVD (PECVD) and carbon nanofibers of differing aspect ratio grown by PECVD. Of the samples examined, only high aspect ratio nanofibers and thermally grown multi-walled nanotubes show an improvement in thermal contact resistance. The improvement is approximately a 60% lower thermal resistance than a bare Si-Cu interface and is comparable to that attained by commercially available thermal interface materials.

Chuang, Helen F.; Cooper, Sarah M.; Meyyappan, M.; Cruden, Brett A.

2004-01-01

227

Formation and electrochemical performance of copper/carbon composite nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Copper-loaded carbon nanofibers are fabricated by thermally treating electrospun Cu(CH{sub 3}COO){sub 2}/polyacrylonitrile nanofibers and utilized as an energy-storage material for rechargeable lithium-ion batteries. These composite nanofibers deliver more than 400 mA g{sup -1} reversible capacities at 50 and 100 mA g{sup -1} current densities and also maintain clear fibrous morphology and good structural integrity after 50 charge/discharge cycles. The relatively high capacity and good cycling performance of these composite nanofibers, stemmed from the integrated combination of metallic copper and disordered carbon as well as their unique textures and surface properties, make them a promising electrode candidate for next-generation lithium-ion batteries.

Ji Liwen; Lin Zhan; Zhou Rui; Shi Quan; Toprakci, Ozan; Medford, Andrew J.; Millns, Christopher R. [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, NC 27695-8301 (United States); Zhang Xiangwu, E-mail: xiangwu_zhang@ncsu.ed [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, NC 27695-8301 (United States)

2010-02-01

228

Formation and electrochemical performance of copper/carbon composite nanofibers  

International Nuclear Information System (INIS)

Copper-loaded carbon nanofibers are fabricated by thermally treating electrospun Cu(CH3COO)2/polyacrylonitrile nanofibers and utilized as an energy-storage material for rechargeable lithium-ion batteries. These composite nanofibers deliver more than 400 mA g-1 reversible capacities at 50 and 100 mA g-1 current densities and also maintain clear fibrous morphology and good structural integrity after 50 charge/discharge cycles. The relatively high capacity and good cycling performance of these composite nanofibers, stemmed from the integrated combination of metallic copper and disordered carbon as well as their unique textures and surface properties, make them a promising electrode candidate for next-generation lithium-ion batteries.

229

Functionalized carbon nanotubes and nanofibers for biosensing applications  

Energy Technology Data Exchange (ETDEWEB)

This review summarizes the recent advances of carbon nanotube (CNT) and carbon nanofiber (CNF)-based electrochemical biosensors with an emphasis on the applications of CNTs. Carbon nanotubes and carbon nanofibers have unique electric, electrocatalytic, and mechanical properties which make them efficient materials for the use in electrochemical biosensor development. In this article, the functionalization of CNTs for biosensors is simply discussed. The electrochemical biosensors based on CNT and their various applications, e.g., measurement of small biological molecules and environmental pollutants, detection of DNA, and immunosensing of disease biomarkers, are reviewed. Moreover, the development of carbon nanofiber-based electrochemical biosensors and their applications are outlined. Finally, some challenges are discussed in the conclusion.

Wang, Jun; Lin, Yuehe

2008-07-30

230

Direct synthesis of novel vanadium oxide embedded porous carbon nanofiber decorated with iron nanoparticles as a low-cost and highly efficient visible-light-driven photocatalyst.  

Science.gov (United States)

Template-free porous carbon nanofibers embedded by vanadium oxide and decorated with iron nanoparticles (Fe@V-CNF) were prepared in a time and cost-saving manner by combining electrospinning and heat treatment processes. Cost-saving ammonium metavanadate was used as a semiconductor precursor of vanadium oxide (VOx) as well as porogen. The generated pores in the carbon nanofiber (CNFs) matrix formed pathways between the embedded VOx and the surface of CNFs and Fe NPs, thus, facilitate photo-generated electron transfer. The characterization results revealed that Fe@V-CNF comprised graphitic fibers with well-dispersed distribution of nanosized Fe NPs (~7 nm) along the surface of CNF. Thereby, it enhanced the visible-light harvesting. The prepared Fe@V-CNF had remarkable light absorption in the visible region. It demonstrated much higher photocatalytic efficiency of photodegradation of organic dyes compared with the pure CNF and vanadium oxide embedded CNF (V-CNF). Notably, Fe@V-CNF achieved 99.9% dye degradation within 15-20 min. And, it could be conveniently recycled due to its one-dimensional nanostructural property. PMID:24407677

Taha, Ahmed Aboueloyoun; Hriez, Amir A; Wu, Yi-nan; Wang, Hongtao; Li, Fengting

2014-03-01

231

The use of carbon nanofibers microcolumn preconcentration for inductively coupled plasma mass spectrometry determination of Mn, Co and Ni  

International Nuclear Information System (INIS)

Based on carbon nanofibers (CNFs) as a solid phase extraction adsorbent, a microcolumn preconcentration method coupled to inductively coupled plasma mass spectrometry (ICP-MS) was developed for the determination of trace elements (Mn, Co and Ni). The effect of various experimental parameters such as pH, sample flow rate and volume, elution solution and interfering ions on the retention of the studied ions have been investigated systematically. During all the steps of the experimental process, Mn, Co and Ni could be quantitatively sorbed on the microcolumn containing CNFs in the range of pH 6.0-9.0, and then eluted completely with 0.5 mol ml-1 HNO3. A preconcentration factor of 150-fold was obtained. The detection limits for Mn, Co and Ni were 40, 0.4 and 8.0 pg ml-1, respectively, with relative standard deviations less than 6.0%. In order to validate the proposed method, two certified reference materials of human hair (GBW 07601) and mussel (GBW 08571), and water sample were analyzed with satisfactory results. The recoveries were between 95.0 and 114%

232

The use of carbon nanofibers microcolumn preconcentration for inductively coupled plasma mass spectrometry determination of Mn, Co and Ni  

Energy Technology Data Exchange (ETDEWEB)

Based on carbon nanofibers (CNFs) as a solid phase extraction adsorbent, a microcolumn preconcentration method coupled to inductively coupled plasma mass spectrometry (ICP-MS) was developed for the determination of trace elements (Mn, Co and Ni). The effect of various experimental parameters such as pH, sample flow rate and volume, elution solution and interfering ions on the retention of the studied ions have been investigated systematically. During all the steps of the experimental process, Mn, Co and Ni could be quantitatively sorbed on the microcolumn containing CNFs in the range of pH 6.0-9.0, and then eluted completely with 0.5 mol ml{sup -1} HNO{sub 3}. A preconcentration factor of 150-fold was obtained. The detection limits for Mn, Co and Ni were 40, 0.4 and 8.0 pg ml{sup -1}, respectively, with relative standard deviations less than 6.0%. In order to validate the proposed method, two certified reference materials of human hair (GBW 07601) and mussel (GBW 08571), and water sample were analyzed with satisfactory results. The recoveries were between 95.0 and 114%.

Chen Shizhong [Key Laboratory, Wuhan Polytechnic University, Wuhan 430023 (China)], E-mail: chenshizhong62@163.com; Xiao Mingfa; Lu Dengbo; Wang Zhan [Key Laboratory, Wuhan Polytechnic University, Wuhan 430023 (China)

2007-11-15

233

The use of carbon nanofibers microcolumn preconcentration for inductively coupled plasma mass spectrometry determination of Mn, Co and Ni  

Science.gov (United States)

Based on carbon nanofibers (CNFs) as a solid phase extraction adsorbent, a microcolumn preconcentration method coupled to inductively coupled plasma mass spectrometry (ICP-MS) was developed for the determination of trace elements (Mn, Co and Ni). The effect of various experimental parameters such as pH, sample flow rate and volume, elution solution and interfering ions on the retention of the studied ions have been investigated systematically. During all the steps of the experimental process, Mn, Co and Ni could be quantitatively sorbed on the microcolumn containing CNFs in the range of pH 6.0-9.0, and then eluted completely with 0.5 mol ml - 1 HNO 3. A preconcentration factor of 150-fold was obtained. The detection limits for Mn, Co and Ni were 40, 0.4 and 8.0 pg ml - 1 , respectively, with relative standard deviations less than 6.0%. In order to validate the proposed method, two certified reference materials of human hair (GBW 07601) and mussel (GBW 08571), and water sample were analyzed with satisfactory results. The recoveries were between 95.0 and 114%.

Chen, Shizhong; Xiao, Mingfa; Lu, Dengbo; Wang, Zhan

2007-11-01

234

Alumina-carbon nanofibers nanocomposites obtained by spark plasma sintering for proton exchange membrane fuel cell bipolar plates  

Energy Technology Data Exchange (ETDEWEB)

There is an increasing demand of multifunctional materials for a wide variety of technological developments. Bipolar plates for proton exchange membrane fuel cells are an example of complex functionality components that must show among other properties high mechanical strength, electrical, and thermal conductivity. The present research explored the possibility of using alumina-carbon nanofibers (CNFs) nanocomposites for this purpose. In this study, it was studied for the first time the whole range of powder compositions in this system. Homogeneous powders mixtures were prepared and subsequently sintered by spark plasma sintering. The materials obtained were thoroughly characterized and compared in terms of properties required to be used as bipolar plates. The control on material microstructure and composition allows designing materials where mechanical or electrical performances are enhanced. A 50/50 vol.% alumina-CNFs composite appears to be a very promising material for this kind of application. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Borrell, A.; Torrecillas, R. [Centro de Investigacion en Nanomateriales y Nanotecnologia (CINN) Consejo Superior de Investigaciones Cientificas, Universidad de Oviedo, Principado de Asturias, Parque Tecnologico de Asturias, Llanera Asturias (Spain); Rocha, V.G.; Fernandez, A. [ITMA Materials Technology, Parque Tecnologico de Asturias, Llanera Asturias (Spain)

2012-08-15

235

Optimized Distribution and Morphology of Carbon Nanofibers for a Field Emitter Grown by Nickel and Chromium Cosputtering  

Directory of Open Access Journals (Sweden)

Full Text Available To obtain a high field emission (FE current with a low driving voltage, it is important to control and optimize carbon nanofiber (CNF array patterns for FE. While there have been various means for controlling CNF array patterns reported over the past few decades, array patterning using lithography is the method typically used to control CNF morphology. Because lithography uses many masks and is costly, it is necessary to establish a simpler process. In this study, the grain size and distribution of catalysts with phase separation were controlled. A system which controls the morphology of small bundles of CNFs was constructed with the distance between the bundles kept constant in order to obtain a higher FE current. The Ni catalyst layer for forming the CNF morphology was separated by noncatalytic Cr grains formed by cosputtering. As a result, it was possible to control the Ni content, the grain size and synthesis density of CNFs in the alloy with a varying number of nickel pellets placed on the chromium target. This method is an epochmaking CNF patterning technique very different from lithography.

Norihiro Shimoi

2013-04-01

236

High-Resolution Imaging of Plasmid DNA in Liquids in Dynamic Mode Atomic Force Microscopy Using a Carbon Nanofiber Tip  

Science.gov (United States)

To understand the motion of DNA and DNA complexes, the real-time visualization of living DNA in liquids is quite important. Here, we report the high-resolution imaging of plasmid DNA in water using a rapid-scan atomic force microscopy (AFM) system equipped with a carbon nanofiber (CNF) probe. To achieve a rapid high-resolution scan, small SiN cantilevers with dimensions of 2 (width) × 0.1 (thickness) × 9 µm (length) and a bent end (tip view structure) were employed as base cantilevers onto which single CNFs were grown. The resonant frequencies of the cantilever were 1.5 MHz in air and 500 kHz in water, and the spring constant was calculated to be 0.1 N/m. Single CNFs, typically 88 nm in length, were formed on an array of the cantilevers in a batch process by the ion-irradiation method. An AFM image of a plasmid DNA taken in water at 0.2 fps (5 s/image) using a batch-fabricated CNF-tipped cantilever clearly showed the helix turns of the double strand DNA. The average helical pitch measured 3.4 nm (?: 0.5 nm), which was in good agreement with that determined by the X-ray diffraction method, 3.4 nm. Thus, it is presumed that the combined use of the rapid-scan AFM system with the ion-induced CNF probe is promising for the dynamic analysis of biomolecules.

Kitazawa, Masashi; Ito, Shuichi; Yagi, Akira; Sakai, Nobuaki; Uekusa, Yoshitugu; Ohta, Ryo; Inaba, Kazuhisa; Hayashi, Akari; Hayashi, Yasuhiko; Tanemura, Masaki

2011-08-01

237

Characterization of small-scale batch-fabricated carbon nanofiber probes  

International Nuclear Information System (INIS)

Linear-shaped single carbon nanofibers (CNFs) were batch-grown onto commercially available Si cantilevers for atomic force microscope by the Ar+-ion-irradiation method (9 cantilevers/batch). The force-curve measurements revealed that the long CNF probes (? 1 ?m in length) were as flexible as the carbon nanotubes probes, whereas the short CNF probes (? 400 nm in length) were characterized by the rigid nature similar to the Si probes. Thus, the mechanical properties of CNF probes were controllable by the CNF length. The ion-induced CNF probes were metallic in electrical property, and the higher resolution images in scanning spreading resistance microscopy was attained by the CNF probes than by conventional conductive diamond probes, due to the small tip radius, high aspect ratio and the durability of the CNF probes. Because the small-scale batch-fabricated CNF probes showed good uniformity in the size, mechanical and electrical properties, it was concluded that they are promising as practical conductive SPM probes

238

Characterization of small-scale batch-fabricated carbon nanofiber probes  

Energy Technology Data Exchange (ETDEWEB)

Linear-shaped single carbon nanofibers (CNFs) were batch-grown onto commercially available Si cantilevers for atomic force microscope by the Ar{sup +}-ion-irradiation method (9 cantilevers/batch). The force-curve measurements revealed that the long CNF probes ({approx} 1 {mu}m in length) were as flexible as the carbon nanotubes probes, whereas the short CNF probes ({approx} 400 nm in length) were characterized by the rigid nature similar to the Si probes. Thus, the mechanical properties of CNF probes were controllable by the CNF length. The ion-induced CNF probes were metallic in electrical property, and the higher resolution images in scanning spreading resistance microscopy was attained by the CNF probes than by conventional conductive diamond probes, due to the small tip radius, high aspect ratio and the durability of the CNF probes. Because the small-scale batch-fabricated CNF probes showed good uniformity in the size, mechanical and electrical properties, it was concluded that they are promising as practical conductive SPM probes.

Kitazawa, M; Ohta, R [Olympus Co. Ltd., 6666 Inatomi, Tatsuno, Kami-Ina-Gun, Nagano 399-0495 (Japan); Sugita, Y; Tanaka, J; Tanemura, M [Department of Environmental Technology, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)], E-mail: ma_kitazawa@ot.olympus.co.jp

2008-03-15

239

Mechanical Properties of Individual Composite Poly(methyl-methacrylate) -Multiwalled Carbon Nanotubes Nanofibers  

Science.gov (United States)

Multiwalled carbon nanotubes with their superb mechanical properties are an unique filler material for polymer composites. Here, we present an investigation of mechanical properties of electrospun Poly-(methyl-methacrylate) multiwalled carbon nanotubes composite nanofibers. The method of electrospinning was used to fabricate suspended individual Poly-(methyl-methacrylate) multiwalled carbon nanotubes nanofibers. In order to reinforce the nanofibers, different high concentration of multiwalled carbon nanotubes were used. Transmission electron microscopy measurements reveal a successful filling of the nanofibers. The different types of nanofibers were deposited at SiO2 substrates. Which were previously etched, to create trenches for bend tests. Followed by fixing the nanofiber with a focus ion beam platinum deposition at the trench edges. An atomic force microscopy was used to perform the mechanical nanofiber bending tests over trenches. The results were compared with pristine Poly-(methyl- methacrylate) nanofibers to nanofibers with 15 weight% and 20 weight% multiwalled carbon nanotubes composite fibers. We observed that pristine nanofibers have Young's modulus of 136 MPa, while for composite nanofibers with 15 weight% have 2.65 GPa and with 20 weight% have 6.06 GPa (at room temperature and air ambiance). This corresponds to an increase of Young's modulus of 19 fold between the pristine nanofibers and the 15 weight% of mutliwalled carbon nanotubes filled nanofibers. Therefore the increase of the Young's modulus compared between the pristine and the 20 weight% MWCNT filled nanofibers corresponds to 45 fold.

Grabbert, Niels; Wang, Bei; Avnon, Asaf; Zhuo, Shuyao; Datsyuk, Vitaliy; Trotsenko, Svitlana; Mackowiak, Piotr; Kaletta, Katrin; Lang, Klaus-Dieter; Ngo, Ha-Duong

2014-08-01

240

Development of bimetal-grown multi-scale carbon micro-nanofibers as an immobilizing matrix for enzymes in biosensor applications.  

Science.gov (United States)

This study describes the development of a novel bimetal (Fe and Cu)-grown hierarchical web of carbon micro-nanofiber-based electrode for biosensor applications, in particular to detect glucose in liquids. Carbon nanofibers (CNFs) are grown on activated carbon microfibers (ACFs) by chemical vapor deposition (CVD) using Cu and Fe as the metal catalysts. The transition metal-fiber composite is used as the working electrode of a biosensor applied to detect glucose in liquids. In such a bi-nanometal-grown multi-scale web of ACF/CNF, Cu nanoparticles adhere to the ACF-surface, whereas Fe nanoparticles used to catalyze the growth of nanofibers attach to the CNF tips. By ultrasonication, Fe nanoparticles are dislodged from the tips of the CNFs. Glucose oxidase (GOx) is subsequently immobilized on the tips by adsorption. The dispersion of Cu nanoparticles at the substrate surface results in increased conductivity, facilitating electron transfer from the glucose solution to the ACF surface during the enzymatic reaction with glucose. The prepared Cu-ACF/CNF/GOx electrode is characterized for various surface and physicochemical properties by different analytical techniques, including scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDX), Fourier-transform infrared spectroscopy (FTIR), BET surface area analysis, and transmission electron microscopy (TEM). The electrochemical tests show that the prepared electrode has fast response current, electrochemical stability, and high electron transfer rate, corroborated by CV and calibration curves. The prepared transition metal-based carbon electrode in this study is cost-effective, simple to develop, and has a stable immobilization matrix for enzymes. PMID:23910348

Hood, Amit R; Saurakhiya, Neelam; Deva, Dinesh; Sharma, Ashutosh; Verma, Nishith

2013-10-01

 
 
 
 
241

Preparation of Electrically Conductive Polystyrene/Carbon Nanofiber Nanocomposite Films  

Science.gov (United States)

A simple and effective approach to prepare conductive polystyrene/carbon nanofiber (PS/CNF) nanocomposite films via a solution dispersion method is presented. Inexpensive CNF, which has a structure similar to multi-walled carbon nanotubes, is chosen as a nanofiller in this experiment to achieve conductivity in PS films. A good dispersion is…

Sun, Luyi; O'Reilly, Jonathan Y.; Tien, Chi-Wei; Sue, Hung-Jue

2008-01-01

242

Synthesis of carbon nanofiber films and nanofiber composite coatings by laser-assisted catalytic chemical vapor deposition  

International Nuclear Information System (INIS)

Uniform carbon nanofiber films and nanofiber composite coatings were synthesized from ethylene on nickel coated alumina substrates by laser-assisted catalytic chemical vapor deposition. Laser annealing of a 50 nm thick nickel film produced the catalytic nanoparticles. Thermal decomposition of ethylene over nickel nanoparticles was initiated and maintained by an argon ion laser operated at 488 nm. The films were examined by scanning electron microscopy and by transmission electron microscopy. Overall film uniformity and structure were assessed using micro-Raman spectroscopy. Film quality was related to the experimental parameters such as incident laser power density and irradiation time. For long irradiation times, carbon can be deposited by a thermal process rather than by a catalytic reaction directly over the nanofiber films to form carbon nanocomposite coatings. The process parameters leading to high quality nanofiber films free of amorphous carbon by-products as well as those leading to nanofiber composite coatings are presented

243

Numerical analysis of electron emission site distribution of carbon nanofibers for field emission properties.  

Science.gov (United States)

To obtain optimal field emission (FE) properties, it is important to evaluate FE parameters including the electron emission site ? and the field enhancement factor ?. However, it is difficult to evaluate ? quantitatively because the emitting electrons cannot be observed directly. The authors have aimed to analyze this site using an original architecture with a computation system tool based on the surface charge method, and a three-dimensional model has been employed to calculate FE properties with high accuracy. In this study, to analyze ? for determining FE properties, each carbon nanofiber (CNF) model separated by Cr islands which include the minimum area for calculating electric fields by the surface charge method was constructed on the surface of a Ni catalyst. The FE current was simulated with a Fowler-Nordheim formula using the calculated electric fields, followed by a simulation performed using all CNFs on a field emitter cathode. The electron emission site ? was determined by comparing the simulation and experimental results of the FE current. It was found that ? depends on the morphology of the CNF bundles, and a close quantitative correspondence between the experimental and the computation results of FE properties was obtained. In summary, a method of analyzing FE properties was established using an original architecture, making it possible to predict FE properties with a computational tool based on the surface charge method. PMID:23273149

Shimoi, Norihiro; Tanaka, Shun-ichiro

2013-02-01

244

Numerical analysis of acoustic wave propagation in layered carbon nanofiber reinforced polymer composites  

Science.gov (United States)

Polymer composites reinforced by carbon nanofibers (CNFs) in the form of paper sheet show significant vibration and acoustic damping improvement when compared to pure matrix materials. Without looking into the microscopic energy dissipation mechanisms, this paper analyzes the wave propagation in the composites from a macroscopic point of view. The CNF nanocomposites in this study were treated as stacking of alternating layers of pure polymer and CNF reinforced polymer. Analyses of acoustic wave propagation focused on revealing the effects of acoustic impedance discontinuity at the interfaces of the layered structure. Plane wave transmission coefficient has been calculated as a function of the number of the layer repeats and thickness at different wave frequencies. Oscillations in the transmission coefficient have been observed when the acoustic wavelength is on the same order of the bilayer thickness, indicating the possibility of designing the nanocomposite structure to optimize noise reduction characteristics. The numerical analysis converges with effective media theory when acoustic wavelength is much larger than the layer thickness.

Sun, Li; Yu, Yong; Song, Gangbing; Gou, Jihua

2008-08-01

245

Growth and field emission properties of vertically aligned carbon nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Vertically aligned carbon nanofibers (VACNFs) were synthesized on Ni-coated Si substrates using a dc plasma-enhanced chemical-vapor deposition system. The size of the Ni islands used as catalyst to grow the VACNFs was formed by both thermal annealing and laser processing on thin metal layers. It was observed that the diameter of the carbon nanofibers is strongly dependent on the initial Ni island dimension. By varying the laser power from 228 to 279 mJ/cm(2), the size of these Ni islands c...

Poa, Chp; Henley, Sj; Chen, Gy; Adikaari, Aadt; Giusca, Ce; Silva, Srp

2005-01-01

246

Carbon nanofiber layers on metal and carbon substrates : PEM fuel cell and microreactor applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis describes the preparation of CNF layers on flat and porous substrates and their application as catalyst supports for chemical and electrochemical gas?liquidsolid (G?L?S) catalytic reactions. Metal nanoparticles growing CNFs on flat metal substrates at 600°C are easily formed from NiO, in contrast to Fe and Co oxides, leading to higher carbon deposition rates. However, high activity towards total carbon deposition is generally detrimental for obtaining well?...

Pacheco Benito, Sergio

2011-01-01

247

Human cytochrome P450 3A4 and a carbon nanofiber modified film electrode as a platform for the simple evaluation of drug metabolism and inhibition reactions.  

Science.gov (United States)

Electrochemical biosensors consisting of cytochrome P450 enzyme modified electrodes have been developed to provide a simple method for screening the metabolism of a drug and its inhibitor. Here, we report a very simple electrochemically driven biosensor for detecting drug metabolism and its inhibition based on cytochrome P450 3A4 (CYP3A4) and a carbon nanofiber (CNF) modified film electrode without any other modified layers such as mediator films. Direct electron transfer (DET) between CYP3A4 and CNFs was observed at a formal potential of -0.302 V. The electrocatalytic reduction current increased with the addition of drugs including testosterone and quinidine. In contrast, the reduction current was greatly suppressed in the presence of ketoconazole, which is a CYP3A4 inhibitor. CNFs with high conductivity, a large surface area and sufficient edge planes provide a suitable microenvironment for achieving excellent DET and biocatalysis properties, which could not be observed when we used other carbon materials such as carbon nanotube (CNT) and carbon black (CB) modified electrodes, indicating that our system is promising as a new bioelectronic platform for electrochemical biosensing. PMID:24027778

Xue, Qiang; Kato, Dai; Kamata, Tomoyuki; Guo, Qiaohui; You, Tianyan; Niwa, Osamu

2013-11-01

248

Surface functionalization of carbon nanofibers by sol-gel coating of zinc oxide  

International Nuclear Information System (INIS)

In this paper the functional carbon nanofibers were prepared by the carbonization of ZnO coated PAN nanofibers to expand the potential applications of carbon nanofibers. Polyacrylonitrile (PAN) nanofibers were obtained by electrospinning. The electrospun PAN nanofibers were then used as substrates for depositing the functional layer of zinc oxide (ZnO) on the PAN nanofiber surfaces by sol-gel technique. The effects of coating, pre-oxidation and carbonization on the surface morphology and structures of the nanofibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM), respectively. The results of SEM showed a significant increase of the size of ZnO nanograins on the surface of nanofibers after the treatments of coating, pre-oxidation and carbonization. The observations by SEM also revealed that ZnO nanoclusters were firmly and clearly distributed on the surface of the carbon nanofibers. FTIR examination also confirmed the deposition of ZnO on the surface of carbon nanofibers. The XRD analysis indicated that the crystal structure of ZnO nanograins on the surface of carbon nanofibers

249

High density carbon materials obtained at relatively low temperature by spark plasma sintering of carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Graphitic materials obtained at low temperatures are interesting for a wide range of industrial applications including bipolar plates. In this work, graphite based nanocomposites have been obtained starting from carbon nanofibers and a mixture of carbon nanofibers with 20 vol.% of alumina nanopowders. High density carbon components were obtained by using Spark Plasma Sintering at temperatures as low as 1500-1800 C for this kind of materials. The effect of spark plasma sintering parameters on the final density, and the mechanical and electrical properties of resulting nanocomposites have been investigated. Pure carbon nanofibers with around 90% of theoretical density and fracture strength of 60 MPa have been obtained at temperatures as low as 1500 C applying a pressure of 80 MPa during sintering. It has been proved that attrition milling is a suitable method for preparing homogeneous mixtures of carbon nanofibers and alumina powders. (orig.)

Borrell, Amparo; Torrecillas, Ramon [Nanomaterials and Nanotechnology Research Center (CINN), Principado de Asturias - Consejo Superior de Investigaciones Cientificas (CSIC), Univ. de Oviedo, Parque Tecnologico de Asturias, Llanera (Spain); Fernandez, Adolfo [Fundacion ITMA, Parque Tecnologico de Asturias, Llanera (Spain); Merino, Cesar [Grupo Antolin Ingenieria, Burgos (Spain)

2010-01-15

250

Improved bioactivity of PAN-based carbon nanofibers decorated with bioglass nanoparticles.  

Science.gov (United States)

Composite nanofibers composed of polyacrylonitrile (PAN)-based carbon nanofibers and bioactive glass (BG) nanoparticles have been prepared by electrospinning and in situ sintering. Morphology observation showed that the BG nanoparticles of size 20-50?nm were uniformly distributed on the surface of composite nanofibers with 350?nm average diameter after carbonization. Biological mineralization indicated the formation of apatite-like layer on the surface of composite nanofibers, in which the composition of carbonate hydroxyapatite was proved by FTIR and XRD analysis. Cell growth dynamics according to cellular morphology, CCK-8 assay, and alkaline phosphatase activity assay exhibited better cell adhesion, proliferation, and osteogenic induction of bone marrow-derived mesenchymal stem cells cultured on the composite nanofibers, which suggested the higher bioactivity of composite nanofibers compared to pure PAN-based carbon nanofibers. PMID:24266838

Han, Bing; Zhang, Xuehui; Liu, Haiyang; Deng, Xuliang; Cai, Qing; Jia, Xiaolong; Yang, Xiaoping; Wei, Yan; Li, Gang

2014-01-01

251

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection  

Science.gov (United States)

The aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF) composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy composite electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrode exhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry scheme.

Manea, Florica; Motoc, Sorina; Pop, Aniela; Remes, Adriana; Schoonman, Joop

2012-06-01

252

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection:  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF) composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy composite electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrode exhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry scheme.

Manea, F.; Motoc, S.; Pop, A.; Remes, A.; Schoonman, J.

2012-01-01

253

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF) composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy composite electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrode exhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry scheme.

2012-01-01

254

Effects of increasing carbon nanofiber density in polyurethane composites for inhibiting bladder cancer cell functions.  

Science.gov (United States)

Polyurethane (PU) is a versatile elastomer that is commonly used in biomedical applications. In turn, materials derived from nanotechnology, specifically carbon nanofibers (CNFs), have received increasing attention for their potential use in biomedical applications. Recent studies have shown that the dispersion of CNFs in PU significantly enhances composite nanoscale surface roughness, tensile properties, and thermal stability. Although there have been studies concerning normal primary cell functions on such nanocomposites, there have been few studies detailing cancer cell responses. Since many patients who require bladder transplants have suffered from bladder cancer, the ideal bladder prosthetic material should not only promote normal primary human urothelial cell (HUC) function, but also inhibit the return of bladder cancerous cell activity. This study examined the correlation between transitional (UMUC) and squamous (or SCaBER) urothelial carcinoma cells and HUC on PU:CNF nanocomposites of varying PU and CNF weight ratios (from pure PU to 4:1 [PU:CNF volume ratios], 2:1, 1:1, 1:2, and 1:4 composites to pure CNF). Composites were characterized for mechanical properties, wettability, surface roughness, and chemical composition by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and goniometry. The adhesion and proliferation of UMUC and SCaBER cancer cells were assessed by MTS assays. Cellular responses were further quantified by measuring the amounts of nuclear mitotic protein 22 (NMP-22), vascular endothelial growth factor (VEGF), and tumor necrosis factor alpha. Results demonstrated that both UMUC and SCaBER cell proliferation rates decreased over time on substrates with increased CNF in PU. In addition, with the exception of VEGF from UMUC (which was the same across all materials), composites containing the most CNF activated cancer cells (UMUC and SCaBER) the least, as shown by their decreased expression of NMP-22, tumor necrosis factor alpha, and VEGF. Moreover, the adhesion of HUC increased on composites containing more CNF than PU. Overall levels of NMP-22 were significantly lower in HUC than in cancerous UMUC and SCaBER cells on PU:CNF composites. Thus, this study provided a novel nanocomposite consisting of CNF and PU that should be further studied for inhibiting the return of cancerous bladder tissue and for promoting normal non-cancerous bladder tissue formation. PMID:21417694

Tsang, Melissa; Chun, Young Wook; Im, Yeon Min; Khang, Dongwoo; Webster, Thomas J

2011-07-01

255

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes.  

Science.gov (United States)

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices. PMID:21971265

El Mel, A A; Achour, A; Xu, W; Choi, C H; Gautron, E; Angleraud, B; Granier, A; Le Brizoual, L; Djouadi, M A; Tessier, P Y

2011-10-28

256

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes  

Science.gov (United States)

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600 °C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500 °C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.

El Mel, A. A.; Achour, A.; Xu, W.; Choi, C. H.; Gautron, E.; Angleraud, B.; Granier, A.; Le Brizoual, L.; Djouadi, M. A.; Tessier, P. Y.

2011-10-01

257

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes  

Energy Technology Data Exchange (ETDEWEB)

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600 deg. C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500 deg. C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.

El Mel, A A; Achour, A; Gautron, E; Angleraud, B; Granier, A; Le Brizoual, L; Djouadi, M A; Tessier, P Y [Universite de Nantes, CNRS, Institut des Materiaux Jean Rouxel, UMR 6502, 2 rue de la Houssiniere, BP 32229, 44322 Nantes Cedex 3 (France); Xu, W; Choi, C H [Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030 (United States)

2011-10-28

258

Broad-Band Electrical Conductivity of High Density Polyethylene Nanocomposites with Carbon Nanoadditives: Multiwall Carbon Nanotubes and Carbon Nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A study is presented of the electrical properties of a series of nanocomposites based on high density polyethylene (HDPE) as a matrix and either carbon nanofiber (CNF) or multiwall carbon nanotube (MWCNT) as a nanoadditive. The measurements of the electrical conductivity over a broad-band of frequencies (10-2 > F/Hz > 109)allow improvement of the description of the electrical properties of polymer nanocomposites based on either carbon nanofibers or carbon nanotubes. Despite the lack of ...

Linares, A.; Canalda, J. C.; Cagiao, M. E.; Garci?a-gutie?rrez, M. C.; Nogales, A.; Marti?n-gullo?n, I.; Vera, J.; Ezquerra, T. A.

2008-01-01

259

Highly active carbonaceous nanofibers: a versatile scaffold for constructing multifunctional free-standing membranes.  

Science.gov (United States)

Translating the unique characteristics of individual nanoscale components into macroscopic materials such as membranes or sheets still remains a challenge, as the engineering of these structures often compromises their intrinsic properties. Here, we demonstrate that the highly active carbonaceous nanofibers (CNFs), which are prepared through a template-directed hydrothermal carbonization process, can be used as a versatile nanoscale scaffold for constructing macroscopic multifunctional membranes. In order to demonstrate the broad applicability of the CNF scaffold, we fabricate a variety of CNF-based composite nanofibers, including CNFs-Fe(3)O(4), CNFs-TiO(2), CNFs-Ag, and CNFs-Au through various chemical routes. Importantly, all of them inherit unique dimensionality (high aspect ratio) and mechanical properties (flexibility) of the original CNF scaffolds and thus can be assembled into macroscopic free-standing membranes through a simple casting process. We also demonstrate the wide application potentials of these multifunctional composite membranes in magnetic actuation, antibiofouling filtration, and continuous-flow catalysis. PMID:21932782

Liang, Hai-Wei; Zhang, Wen-Jun; Ma, Yi-Ni; Cao, Xiang; Guan, Qing-Fang; Xu, Wei-Ping; Yu, Shu-Hong

2011-10-25

260

Template Synthesis of Carbon Nanofibers Containing Linear Mesocage Arrays  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Carbon nanofibers containing linear mesocage arrays were prepared via evaporation induced self-assembly method within AAO template with an average channel diameter of about 25 nm. The TEM results show that the mesocages have an elongated shape in the transversal direction. The results of N2 adsorption–desorption analysis indicate that the sample possesses a cage-like mesoporous structure and the average mesopore size of the sample is about 18 nm.

Wang Yongwen

2010-01-01

 
 
 
 
261

Self-heating function of carbon nanofiber cement pastes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The viability of carbon nanofiber (CNF) composites in cement matrices as a self-heating material is reported in this paper. This functional application would allow the use of CNF cement composites as a heating element in buildings, or for deicing pavements of civil engineering transport infrastructures, such as highways or airport runways. Cement pastes with the addition of different CNF dosages (from 0 to 5% by cement mass) have been prepared. Afterwards, tests were run at different fixed vo...

Galao Malo, O?scar; Baeza Los Santos, Francisco Javier; Zornoza Go?mez, Emilio; Garce?s Terradillos, Pedro

2014-01-01

262

Effect of carbon nanofiber dispersion on the properties of PIP-SiC/SiC composites  

Energy Technology Data Exchange (ETDEWEB)

SiC/SiC composites with and without dispersed carbon nanofiber were fabricated by the polymer impregnation and pyrolysis process. The effect of dispersing carbon nanofiber on the mechanical and thermal properties of SiC/SiC composites was investigated. The bending strength and elastic modulus of SiC/SiC composites with carbon nanofiber decreased slightly compared to those of the SiC/SiC composites without the nanofiber. On the other hand, the thermal conductivity of SiC/SiC composites increased with increasing amount of dispersed nanofiber. The dominant reason is considered to be that the pore shape changed from an oblong shape perpendicular to the direction of heat flow to an isotropic. The shape change resulted from the dispersed carbon nanofiber.

Taguchi, T., E-mail: taguchi.tomitsugu@jaea.go.jp [Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195 (Japan); Hasegawa, Y., E-mail: hasegawa@artkagaku.co.jp [Art Kagaku Co., Ltd., 3129-40 Muramatsu, Tokai, Ibaraki 319-1231 (Japan); Shamoto, S., E-mail: shamoto.shinichi@jaea.go.jp [Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195 (Japan)

2011-10-01

263

Effect of carbon nanofiber dispersion on the properties of PIP-SiC/SiC composites  

International Nuclear Information System (INIS)

SiC/SiC composites with and without dispersed carbon nanofiber were fabricated by the polymer impregnation and pyrolysis process. The effect of dispersing carbon nanofiber on the mechanical and thermal properties of SiC/SiC composites was investigated. The bending strength and elastic modulus of SiC/SiC composites with carbon nanofiber decreased slightly compared to those of the SiC/SiC composites without the nanofiber. On the other hand, the thermal conductivity of SiC/SiC composites increased with increasing amount of dispersed nanofiber. The dominant reason is considered to be that the pore shape changed from an oblong shape perpendicular to the direction of heat flow to an isotropic. The shape change resulted from the dispersed carbon nanofiber.

264

Physicochemical investigations of carbon nanofiber supported Cu / ZrO2 catalyst  

Science.gov (United States)

Zirconia-promoted copper/carbon nanofiber catalysts (Cu - ZrO2/ CNF ) were prepared by the sequential deposition precipitation method. The Herringbone type of carbon nanofiber GNF-100 (Graphite nanofiber) was used as a catalyst support. Carbon nanofiber was oxidized to (CNF-O) with 5% and 65 % concentration of nitric acid (HNO3). The CNF activated with 5% HNO3 produced higher surface area which is 155 m2/g. The catalyst was characterized by X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) and N2 adsorption-desorption. The results showed that increase of HNO3 concentration reduced the surface area and porosity of the catalyst.

Din, Israf Ud; Shaharun, Maizatul S.; Subbarao, Duvvuri; Naeem, A.

2014-10-01

265

Influence of carbon nanofiber properties as electrocatalyst support on the electrochemical performance for PEM fuel cells  

Energy Technology Data Exchange (ETDEWEB)

Novel carbonaceous supports for electrocatalysts are being investigated to improve the performance of polymer electrolyte fuel cells. Within several supports, carbon nanofibers blend two properties that rarely coexist in a material: a high mesoporosity and a high electrical conductivity, due to their particular structure. Carbon nanofibers have been obtained by catalytic decomposition of methane, optimizing growth conditions to obtain carbon supports with different properties. Subsequently, the surface chemistry has been modified by an oxidation treatment, in order to create oxygen surface groups of different nature that have been observed to be necessary to obtain a higher performance of the electrocatalyst. Platinum has then been supported on the as-prepared carbon nanofibers by different deposition methods and the obtained catalysts have been studied by different electrochemical techniques. The influence of carbon nanofibers properties and functionalization on the electrochemical behavior of the electrocatalysts has been studied and discussed, obtaining higher performances than commercial electrocatalysts with the highest electrical conductive carbon nanofibers as support. (author)

Sebastian, D.; Suelves, I.; Moliner, R.; Lazaro, M.J. [Instituto de Carboquimica (CSIC), Energy and Environment, C/Miguel Luesma Castan 4, 50018 Zaragoza (Spain); Calderon, J.C.; Gonzalez-Exposito, J.A.; Pastor, E. [Universidad de La Laguna, Dpto de Quimica-Fisica, Avda. Astrofisico Francisco Sanchez s/n, 38071 La Laguna, Tenerife (Spain); Martinez-Huerta, M.V. [Instituto de Catalisis y Petroleoquimica (CSIC), C/Marie Curie 2, 28049 Madrid (Spain)

2010-09-15

266

Relationship between Single Walled Carbon Nanotubes Individual Dispersion Behavior and Properties of Electrospun Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available The dispersion stability behavior of single walled carbon nanotube (SWCNT has important effects on morphological and mechanical properties of SWCNT/polymer composite nanofibers. The relationship of the dispersion conditions with morphological and mechanical characteristics for SWCNT / polyacrylonitrile (PAN / polyvinylpyrrolidone (PVP composite nanofibers have been examined. The SEM and TEM analyses of the nanofibers revealed that the deformation in the nanofiber structures increases with increasing SWCNT concentration. Our data indicate that with increasing the amount of SWCNT (from 0 to 2 wt %, the average nanofiber diameter was increased from 163±19 nm to 307±34 nm. Tensile results showed that only 2 wt % SWCNT loading to the electrospun composite nanofibers gave rise to 10-fold and 3-fold increase in the tensile modulus and tenacity of nanofiber layers, respectively. Essentially, high mechanical properties and uniform morphology of the composite naofibers were found at SWCNT concentration of ~2 wt % due to their stable and individual dispersion.

Haji A.

2013-09-01

267

CoSn/carbon composite nanofibers for applications as anode in lithium-ion batteries  

International Nuclear Information System (INIS)

CoSn/carbon composite nanofibers were prepared by electrospinning followed by heat treatment. Uniform morphologies and microstructures were observed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The results demonstrated that well-dispersed nanoparticles of CoSn intermetallic compound and Sn with diameter of about 30–50 nm embedded in carbon nanofibers were prepared after carbonization at 850 °C. Compared with pure carbon nanofibers without the nanoparticles, CoSn/carbon composite nanofibers showed a high reversible capacity and excellent cycling performance, resulting from the formation of CoSn intermetallic nanoparticles and buffering by the carbon nanofiber matrix. The nanofiber mats with good flexibility were utilized as anodes in lithium-ion batteries, and the CoSn/carbon composite nanofibers exhibited a good fibrous morphology after the discharge/charge processes. Results indicated that electrospinning could be a feasible method to prepare Co–Sn–C composite nanofibers as anodes in lithium-ion batteries

268

CoSn/carbon composite nanofibers for applications as anode in lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

CoSn/carbon composite nanofibers were prepared by electrospinning followed by heat treatment. Uniform morphologies and microstructures were observed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The results demonstrated that well-dispersed nanoparticles of CoSn intermetallic compound and Sn with diameter of about 30-50 nm embedded in carbon nanofibers were prepared after carbonization at 850 Degree-Sign C. Compared with pure carbon nanofibers without the nanoparticles, CoSn/carbon composite nanofibers showed a high reversible capacity and excellent cycling performance, resulting from the formation of CoSn intermetallic nanoparticles and buffering by the carbon nanofiber matrix. The nanofiber mats with good flexibility were utilized as anodes in lithium-ion batteries, and the CoSn/carbon composite nanofibers exhibited a good fibrous morphology after the discharge/charge processes. Results indicated that electrospinning could be a feasible method to prepare Co-Sn-C composite nanofibers as anodes in lithium-ion batteries.

Lu, Weili; Luo, Chenghao; Li, Yu; Feng, Yiyu; Feng, Wei, E-mail: weifeng@tju.edu.cn; Zhao, Yunhui; Yuan, Xiaoyan, E-mail: yuanxy@tju.edu.cn [Tianjin University, School of Materials Science and Engineering, Tianjin Key Laboratory of Composite and Functional Materials (China)

2013-09-15

269

Designing an ultrathin silica layer for highly durable carbon nanofibers as the carbon support in polymer electrolyte fuel cells  

Science.gov (United States)

A critical issue for maintaining long-term applications of polymer electrolyte fuel cells (PEFCs) is the development of an innovative technique for the functionalization of a carbon support that preserves their exceptional electrical conductivity and robustly enriches their durability. Here, we report for the first time how the formation of a partially coated, ultrathin, hydrophobic silica layer around the surfaces of the carbon nanofiber (CNF) helps improve the durability of the CNF without decreasing the significant electrical conductivity of the virgin CNF. The synthesis involved the adsorption of polycarbomethylsilane (PS) on the CNF's sidewalls, followed by high temperature pyrolysis of PS, resulting in a highly durable, conductive carbon support in PEFCs. The Pt nanoparticles are in direct contact with the surface of the carbon in the empty spaces between unevenly coated silica layers, which are not deposited directly onto the silica layer. The presence of a Pt nanoparticle layer that was thicker than the silica layer would be a quite advantageous circumstance that provides contact with other neighboring CNFs without having a significant adverse effect that deeply damages the electrical conductivity of the neighboring CNF composites with the silica layer. Furthermore, the ultrathin, hydrophobic silica layer around the surfaces of the CNF provides great potential to reduce the presence of water molecules in the vicinity of the carbon supports and the &z.rad;OH radicals formed on the surface of the Pt catalyst. As a result, the CNF with a 5 wt% silica layer that we prepared has had extremely high initial performance and durability under severe carbon corrosion conditions, starting up with 974 mA cm-2 at 0.6 V and ending up with more than 58% of the initial performance (i.e., 569 mA cm-2 at 0.6 V) after a 1.6 V holding test for 6 h. The beginning-of-life and end-of-life performances based on the virgin CNF without the silica layer were 981 and 340 mA cm-2 at 0.6 V, respectively. The CNF having a silica layer had long-term durability which was superior to that of the virgin CNF.

Hwang, Sun-Mi; Park, Jae-Hyun; Lim, Seongyop; Jung, Doo-Hwan; Guim, Hwanuk; Yoon, Young-Gi; Yim, Sung-Dae; Kim, Tae-Young

2014-09-01

270

Ninety-day inhalation toxicity study with a vapor grown carbon nanofiber in rats.  

Science.gov (United States)

A subchronic inhalation toxicity study of inhaled vapor grown carbon nanofibers (CNF) (VGCF-H) was conducted in male and female Sprague Dawley rats. The CNF test sample was composed of > 99.5% carbon with virtually no catalyst metals; Brunauer, Emmett, and Teller (BET) surface area measurements of 13.8 m2/g; and mean lengths and diameters of 5.8 µm and 158 nm, respectively.Four groups of rats per sex were exposed nose-only, 6 h/day, for 5 days/week to target concentrations of 0, 0.50, 2.5, or 25 mg/m3 VGCF-H over a 90-day period and evaluated 1 day later. Assessments included conventional clinical and histopathological methods, bronchoalveolar lavage fluid (BALF) analysis, and cell proliferation (CP) studies of the terminal bronchiole (TB), alveolar duct (AD), and subpleural regions of the respiratory tract. In addition, groups of 0 and 25 mg/m3 exposed rats were evaluated at 3 months postexposure (PE). Aerosol exposures of rats to 0.54 (4.9 f/cc), 2.5 (56 f/cc), and 25 (252 f/cc) mg/m(3) of VGCF-H CNFs produced concentration-related small, detectable accumulation of extrapulmonary fibers with no adverse tissue effects. At the two highest concentrations, inflammation of the TB and AD regions of the respiratory tract was noted wherein fiber-laden alveolar macrophages had accumulated. This finding was characterized by minimal infiltrates of inflammatory cells in rats exposed to 2.5mg/m(3) CNF, inflammation along with some thickening of interstitial walls, and hypertrophy/hyperplasia of type II epithelial cells, graded as slight for the 25mg/m(3) concentration. At 3 months PE, the inflammation in the high dose was reduced. No adverse effects were observed at 0.54mg/m(3). BALF and CP endpoint increases versus controls were noted at 25mg/m(3) VGCF-H but not different from control values at 0.54 or 2.5mg/m(3). After 90 days PE, BALF biomarkers were still increased at 25mg/m(3), indicating that the inflammatory response was not fully resolved. Greater than 90% of CNF-exposed, BALF-recovered alveolar macrophages from the 25 and 2.5mg/m(3) exposure groups contained nanofibers (> 60% for 0.5mg/m(3)). A nonspecific inflammatory response was also noted in the nasal passages. The no-observed-adverse-effect level for VGCF-H nanofibers was considered to be 0.54mg/m(3) (4.9 fibers/cc) for male and female rats, based on the minimal inflammation in the terminal bronchiole and alveolar duct areas of the lungs at 2.5mg/m(3) exposures. It is noteworthy that the histopathology observations at the 2.5mg/m(3) exposure level did not correlate with the CP or BALF data at that exposure concentration. In addition, the results with CNF are compared with published findings of 90-day inhalation studies in rats with carbon nanotubes, and hypotheses are presented for potency differences based on CNT physicochemical characteristics. Finally, the (lack of) relevance of CNF for the high aspect ratio nanomaterials/fiber paradigm is discussed. PMID:22581831

Delorme, Michael P; Muro, Yukihiro; Arai, Toshihiro; Banas, Deborah A; Frame, Steven R; Reed, Kenneth L; Warheit, David B

2012-08-01

271

Flow-through dispersed carbon nanofiber-based microsolid-phase extraction coupled to liquid chromatography for automatic determination of trace levels of priority environmental pollutants.  

Science.gov (United States)

Handling of carbon nanoparticles as sorptive materials in a flow-through packed-bed mode has been to date hampered by undue pressure drop and deteriorated retention efficiency because of nanoparticle bundling and entanglement. To surmount this limitation, a dedicated stirred-flow sorptive microchamber integrated in a fully automated sequential injection (SI) assembly is herein proposed for expedient handling and reuse of carbon nanoparticles in microsolid-phase extraction (?SPE) procedures. The assembled setup features automatic uptake, preconcentration, and retrieval of target organic species using dispersed nanoparticles as a front-end to liquid chromatographic (LC) assays. Chlorotriazine residues (atrazine, simazine, and propazine) and dealkylated metabolites thereof (deisopropyltriazine (DIA) and deethylatrazine (DEA)) were selected as model compounds because of their electron-poor aromatic structure and potentially strong ?-? interactions with electron-rich sorptive materials. The effect of several parameters on the analytical performance including the type and amount of nanoparticles (carbon nanofibers (CNFs), multiwalled carbon nanotubes (MWCNTs) and oxidized carbon nanotubes (MWCNT-COOH), the sample volume (breakthrough volume), the nature and volume of eluent, and the interface between the sample processing module and LC was explored in detail. Using dispersed CNFs at-line coupled to LC, absolute recovery percentages for 10 mL sample percolation were >94% for the overall herbicides with enrichment factors of ca. 20, limits of detection (S/N = 3) of 0.004-0.03 ng mL(-1), limits of quantification (S/N = 10) of 0.01-0.09 ng mL(-1) and repeatability within the range 0.5-1.8%. The SI-CNF-LC hyphenated system was harnessed to the analysis of not merely untreated environmental waters at concentration levels below those endorsed by the current EU Water Framework Directives but to crude soil extracts for which CNF reuse with no loss of retention efficiency was proven feasible by resorting to appropriate automatic regeneration procedures and internal standardization. PMID:21553915

Boonjob, Warunya; Miró, Manuel; Segundo, Marcela A; Cerdà, Víctor

2011-07-01

272

Ellipsometric investigations of photonic crystals based on carbon nanofibers  

CERN Document Server

Carbon nanofibers (CNF) are used as components of planar photonic crystals (PC). Square and rectangular lattices as well as random patterns of vertically aligned CNF were fabricated and their properties studied using ellipsometry. Conventional methods of ellipsometric analysis used in thin film ellipsometry are not applicable to these samples due to their nanostructured nature. We show that detailed information such as symmetry directions and the band structure of these novel materials can be extracted from considerations of the polarization state in the specular beam.

Rehammar, R; Arwin, H; Kinaret, J M; Campbell, E E B

2010-01-01

273

A hybrid functional nanomaterial: POSS functionalized carbon nanofiber  

International Nuclear Information System (INIS)

A hybrid functional nanomaterial was synthesized by functionalizing carbon nanofibers (CNF) with polyhedral oligomeric silsesquioxane (POSS). The reaction between CNF and the amine group of ocataminophenyl POSS was achieved using carbodiimide chemistry. The CNF-POSS hybrids were designed to increase the reactivity of CNF without affecting its inherent properties. The reactive amine groups of CNF-POSS were further modified with an oligomer of polyimide polymer to improve the interaction with the polymer matrix, thus forming a nanocomposite with enhanced multifunctional properties. Functionalization was characterized using thermal gravimetric analysis (TGA), x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

274

A hybrid functional nanomaterial: POSS functionalized carbon nanofiber  

Energy Technology Data Exchange (ETDEWEB)

A hybrid functional nanomaterial was synthesized by functionalizing carbon nanofibers (CNF) with polyhedral oligomeric silsesquioxane (POSS). The reaction between CNF and the amine group of ocataminophenyl POSS was achieved using carbodiimide chemistry. The CNF-POSS hybrids were designed to increase the reactivity of CNF without affecting its inherent properties. The reactive amine groups of CNF-POSS were further modified with an oligomer of polyimide polymer to improve the interaction with the polymer matrix, thus forming a nanocomposite with enhanced multifunctional properties. Functionalization was characterized using thermal gravimetric analysis (TGA), x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

Iyer, Pallavi; Mapkar, Javed A; Coleman, Maria R, E-mail: maria.coleman6@utoledo.ed [Department of Chemical and Environmental Engineering, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606 (United States)

2009-08-12

275

A hybrid functional nanomaterial: POSS functionalized carbon nanofiber  

Science.gov (United States)

A hybrid functional nanomaterial was synthesized by functionalizing carbon nanofibers (CNF) with polyhedral oligomeric silsesquioxane (POSS). The reaction between CNF and the amine group of ocataminophenyl POSS was achieved using carbodiimide chemistry. The CNF-POSS hybrids were designed to increase the reactivity of CNF without affecting its inherent properties. The reactive amine groups of CNF-POSS were further modified with an oligomer of polyimide polymer to improve the interaction with the polymer matrix, thus forming a nanocomposite with enhanced multifunctional properties. Functionalization was characterized using thermal gravimetric analysis (TGA), x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

Iyer, Pallavi; Mapkar, Javed A.; Coleman, Maria R.

2009-08-01

276

Small-scale batch fabrication of carbon nanofiber probes  

Energy Technology Data Exchange (ETDEWEB)

The batch-growth of linear-shaped single CNFs onto commercially available Si cantilevers (3-9 chips / batch) using the ion-irradiation method was challenged, and the growth parameters were optimized in terms of the sample temperature (up to 70deg. C) and the ion-irradiation time. In every growth condition tested here, the batch-fabrication of CNF probes was achieved. The length and the growth direction of CNFs were controllable well with the ion-irradiation time and the ion-incidence angle, respectively. Thus, oriented and linear-shaped single CNFs, even longer than 1 {mu}m in length, were attainable. Under the optimized growth condition, CNFs were batch-grown uniformly in length with the standard deviation of less than {approx}10 %. CNFs showed almost no temperature dependence in growth rate, and fine CNFs tended to grow for short irradiation duration. Since AFM images of Si grating were attained repeatedly with a good image resolution using CNF probes thus batch-fabricated, the ion-irradiation method was believed to be quite promising to prepare practical CNF probes.

Tanaka, J [Department of Environmental Technology, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Kitazawa, M [Department of Environmental Technology, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Tanemura, M [Department of Environmental Technology, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Ohta, R [Olympus Co. Ltd., 6666 Inatomi, Tatsuno, Kami-Ina-Gun, Nagano 399-0495 (Japan)

2007-04-15

277

Small-scale batch fabrication of carbon nanofiber probes  

International Nuclear Information System (INIS)

The batch-growth of linear-shaped single CNFs onto commercially available Si cantilevers (3-9 chips / batch) using the ion-irradiation method was challenged, and the growth parameters were optimized in terms of the sample temperature (up to 70deg. C) and the ion-irradiation time. In every growth condition tested here, the batch-fabrication of CNF probes was achieved. The length and the growth direction of CNFs were controllable well with the ion-irradiation time and the ion-incidence angle, respectively. Thus, oriented and linear-shaped single CNFs, even longer than 1 ?m in length, were attainable. Under the optimized growth condition, CNFs were batch-grown uniformly in length with the standard deviation of less than ?10 %. CNFs showed almost no temperature dependence in growth rate, and fine CNFs tended to grow for short irradiation duration. Since AFM images of Si grating were attained repeatedly with a good image resolution using CNF probes thus batch-fabricated, the ion-irradiation method was believed to be quite promising to prepare practical CNF probes

278

Fabrication and characterization of carbon nanofiber@mesoporous carbon core-shell composite for the Li-air battery  

Science.gov (United States)

In this study, we successfully design and synthesize the mesoporous carbon coated carbon nanofibers (CNF@mesoCs) for the Li-air battery. The composites are fabricated via electrospinning technique and nanocasting strategy. After mesoporous carbon coating process, the composites have retained their original one-dimensional structure as pristine carbon nanofibers. Every nanofiber entangles with each other to form a three-dimensional cross-linked web structure. Because of the mesoporous carbon coating on carbon nanofibers, the surface area increases from 708 m2 g-1 to 2194 m2 g-1. We confirm that the mesoporous carbon coated on carbon nanofibers is well-graphitized by analysis of Raman spectra. The graphitized surface of CNF@mesoCs (4.638 S cm-1) is believed to result in their higher electrical conductivity than that of pristine carbon nanofibers (3.0759 S cm-1). Without employment of any binders and metal foams, the cathode of CNF@mesoCs exhibits high discharge capacity of 4000 mA h g-1, which is much higher than that from pristine carbon nanofibers (2750 mA h g-1). This work demonstrates that the fabricated CNF@mesoCs structures have a great potential to be employed as light-weight and efficient electrode for energy storage and conversion devices.

Song, Myeong Jun; Shin, Moo Whan

2014-11-01

279

Experimental study of mechanical and electrical properties of carbon nanofiber/epoxy composites  

International Nuclear Information System (INIS)

Epoxy nanocomposites of different content of carbon nanofibers up to 1 wt.% have been fabricated under room temperature and refrigerated curing conditions. The composites were studied in terms of mechanical and electrical properties. Flexural modulus and hardness were found to increase significantly in refrigerated samples due to prevention of aggregates of nanofibers during cure condition. Increase and shifting in G-band by Raman spectra of these samples confirmed stress transfer and reinforcement between epoxy matrix and carbon nanofiber. Electrical conductivity improved by 3-6 orders after infusing carbon nanofibers in insulating epoxy. Room temperature samples acquired higher conductivity that was attributed to network formation by aggregates of nanofibers along the fiber alignment direction as revealed by electron microscopic studies.

280

Branched carbon nanofiber network synthesis at room temperature using radio frequency supported microwave plasmas  

International Nuclear Information System (INIS)

Carbon nanofibers have been grown at room temperature using a combination of radio frequency and microwave assisted plasma-enhanced chemical vapor deposition. The nanofibers were grown, using Ni powder catalyst, onto substrates kept at room temperature by using a purposely designed water-cooled sample holder. Branched carbon nanofiber growth was obtained without using a template resulting in interconnected carbon nanofiber network formation on substrates held at room temperature. This method would allow room-temperature direct synthesized nanofiber networks over relatively large areas, for a range of temperature sensitive substrates, such as organic materials, plastics, and other polymers of interest for nanoelectronic two-dimensional networks, nanoelectromechanical devices, nanoactuators, and composite materials

 
 
 
 
281

Synthesis and electrocatalysis of 1-aminopyrene-functionalized carbon nanofiber-supported platinum-ruthenium nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Platinum-ruthenium/carbon composite nanofibers were prepared by depositing PtRu nanoparticles directly onto electrospun carbon nanofibers using a polyol processing technique. The morphology and size of PtRu nanoparticles were controlled by 1-aminopyrene functionalization. The noncovalent functionalization of carbon nanofibers by 1-aminopyrene is simple and can be carried out at ambient temperature without damaging the integrity and electronic structure of carbon nanofibers. The resulting PtRu/carbon composite nanofibers were characterized by cyclic voltammogram in 0.5 M H{sub 2}SO{sub 4} and 0.125 M CH{sub 3}OH + 0.2 M H{sub 2}SO{sub 4} solutions, respectively. The PtRu/carbon composite nanofibers with 1-aminopyrene functionalization have smaller nanoparticles and a more uniform distribution, compared with those pretreated with conventional acids. Moreover, PtRu/1-aminopyrene functionalized carbon nanofibers have high active surface area and improved performance towards the electrocatalytic oxidation of methanol. (author)

Lin, Zhan; Ji, Liwen; Krause, Wendy E.; Zhang, Xiangwu [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, NC 27695-8301 (United States)

2010-09-01

282

Activated carbon nanofiber webs made by electrospinning for capacitive deionization  

International Nuclear Information System (INIS)

Activated carbon fiber (ACF) webs with a non-woven multi-scale texture were fabricated from polyacrylonitrile (PAN), and their electrosorption performance in capacitive deionization for desalination was investigated. PAN nanofibers were prepared by electrospinning, followed by oxidative stabilization and activation with carbon dioxide at 750–900 °C, resulting in the ACF webs that were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and nitrogen adsorption. The results show that the as-made ACFs have a specific surface area of 335–712 m2/g and an average nanofiber diameter of 285–800 nm, which can be tuned by varying the activation temperature. With the ACF webs as an electrode, an electrosorption capacity as high as 4.64 mg/g was achieved on a batch-type electrosorptive setup operated at 1.6 V. The ACF webs made by electrospinning are of potential as an excellent electrode material for capacitive deionization for desalination.

283

Method for production of polymer and carbon nanofibers from water-soluble polymers.  

Science.gov (United States)

Nanometer scale carbon fibers (carbon nanofibers) are of great interest to scientists and engineers in fields such as materials science, composite production, and energy storage due to their unique chemical, physical, and mechanical properties. Precursors currently used for production of carbon nanofibers are primarily from nonrenewable resources. Lignin is a renewable natural polymer existing in all high-level plants that is a byproduct of the papermaking process and a potential feedstock for carbon nanofiber production. The work presented here demonstrates a process involving the rapid freezing of an aqueous lignin solution, followed by sublimation of the resultant ice, to form a uniform network comprised of individual interconnected lignin nanofibers. Carbonization of the lignin nanofibers yields a similarly structured carbon nanofiber network. The methodology is not specific to lignin; nanofibers of other water-soluble polymers have been successfully produced. This nanoscale fibrous morphology has not been observed in traditional cryogel processes, due to the relatively slower freezing rates employed compared to those achieved in this study. PMID:22716198

Spender, Jonathan; Demers, Alexander L; Xie, Xinfeng; Cline, Amos E; Earle, M Alden; Ellis, Lucas D; Neivandt, David J

2012-07-11

284

Photoluminescence and electron paramagnetic resonance studies of springlike carbon nanofibers  

Science.gov (United States)

Carbon nanofiber (CNF) with springlike and double-helix structures has been synthesized by catalytic thermal pyrolysis of an acetylene precursor at 850-950 °C using iron nanopowder and thiophene as catalyst and promoter, respectively. High resolution electron microscopy revealed a higher d-spacing (˜3.46 Å) of (002) crystal plane than customary multiwalled carbon nanotube (MWCNT) (3.37 Å) that helps in sustaining mechanical shocks better than MWCNTs. The large surface to volume ratio of springlike CNF does provide many delocalized free electrons to enhance the photoluminescence activity. Electron paramagnetic resonance signal showed a single narrow line having g-value 2.0024±0.0002 and spin contribution 3.4956×10-16 spins/g.

Gupta, Bipin Kumar; Shanker, V.; Arora, Manju; Haranath, D.

2009-08-01

285

A simple method to synthesize carbon nanofibers with a parallel growth mode and their capacitive properties  

Science.gov (United States)

Carbon nanofibers with a parallel growth mode were synthesized by a chemical vapor deposition (CVD) method using a nickel catalyst precursor and acetylene carbon source gas at 550 °C, the growth mechanism and growth model of which were discussed and established, respectively. In the case of no pretreatment, the Brunauer-Emmett-Teller (BET) surface area and total pore volume of the as-synthesized carbon nanofibers were 214 m2·g-1 and 0.36 cm3·g-1, respectively. The maximum specific capacitance of the carbon nanofibers was 205.8 F·g-1, examined at a 0.20 V·s-1 sweep rate. The structure and morphology of the carbon nanofibers were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and x-ray powder diffraction (XRD).

Zhang, Qian; Wang, Qiuxiang; Tian, Meijuan; Yu, Jianhua; Sui, Jing; Dong, Lifeng

2014-09-01

286

Electromagnetic Properties of Novel Carbon Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Carbonized bacterial cellulose (CBC with a three dimensional net-linked framework were synthesized from carbonized bacterial cellulose and investigated by X-ray diffraction, Raman spectrum and Transmission electron microscopy. The complex permittivity and permeability of CBC/paraffin wax composite with certain ratio of the composite were measured by vector network analysis in the frequency range of 0.1–18 GHz. It is found that the composite has high permittivity and dielectric loss, especially at the low frequency. The electromagnetic characteristics of the CBC/Fe3O4 complex absorbers synthesized by mixing a small quantity of CBC with Fe3O4 were also studied, aiming at improving the microwave absorbing properties of Fe3O4/Wax composite. When the sample’s thickness was 1.2 mm, the reflection loss reached a minimal value of –21 dB for CBC - Fe3O4/Wax and of –2 dB for Fe3O4/Wax as well.

WANG Gai-Hua, DAI Bo, MA Yong-Jun, REN Yong

2013-04-01

287

EFFECT OF CELLULOSE NANOFIBERS ISOLATED FROM BAMBOO PULP RESIDUE ON VULCANIZED NATURAL RUBBER  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nanocomposites were prepared using two bioresources, viz., cellulose nanofibers (CNFs) extracted from bamboo paper-pulp waste as the reinforcing phase and natural rubber (NR) as the matrix phase. CNFs with diameters up to 50 nm were isolated from bamboo pulp waste, and nanocomposites with 5 and 10% CNFs were obtained via two-roll mill mixing of solid natural rubber with a master batch containing 20 wt% CNFs. The NR phase was cross-linked using sulphur vulcanization. The morphology studies sho...

P. M. Visakh,; Sabu Thomas,; Kristiina Oksman,; Mathew, Aji P.

2012-01-01

288

Hierarchical core-shell carbon nanofiber@ZnIn?S? composites for enhanced hydrogen evolution performance.  

Science.gov (United States)

Improvement of hydrogen evolution ability is an urgent task for developing advanced catalysts. As one of the promising visible-light photocatalysts, ZnIn2S4 suffers from the ultrafast recombination of photoinduced charges, which limits its practical application for efficient solar water splitting. Herein, we reported a two-step method to prepare hierarchical core-shell carbon nanofiber@ZnIn2S4 composites. One-dimensional carbon nanofibers were first prepared by electrospinning and carbonization in N2. The subsequent solvothermal process led to the in situ growth of ZnIn2S4 nanosheets on the carbon nanofibers to fabricate hierarchical structure composites. The hierarchical core-shell configuration structure can help to form an intimate contact between the ZnIn2S4 nanosheet shell and the carbon nanofiber backbone compared with the equivalent physical mixture and can facilitate the interfacial charge transfer driven by the excitation of ZnIn2S4 under visible-light irradiation. Meanwhile, the ultrathin ZnIn2S4 nanosheets were uniformly grown on the surface of the carbon nanofibers, which can avoid agglomeration of ZnIn2S4. These synergistic effects made this unique hierarchical structure composite exhibit a significantly higher visible-light photocatalytic activity toward hydrogen evolution reaction compared with pure ZnIn2S4 or a physical mixture of ZnIn2S4 and carbon nanofibers in the absence of noble metal cocatalysts. PMID:25057818

Chen, Yajie; Tian, Guohui; Ren, Zhiyu; Pan, Kai; Shi, Yunhan; Wang, Jiaqi; Fu, Honggang

2014-08-27

289

Mechanical Damping Properties of Carbon Nanofiber Reinforced Composites  

Science.gov (United States)

In this research an investigation of the damping enhancement achieved, utilizing carbon nano fibers (CNF) to epoxy resin is presented along with a corresponding model to predict damping performance. The addition of CNF fillers to the matrix allows for localized slip between the filler and the matrix on a nanoscale, wherein the matrix can de-bond from the CNFs, allowing the fillers to slip relative to the matrix; thereby, dissipating energy as frictional heat. Due to the nanoscale size of the filler, the specific surface area, of the CNF's, is very large when compared to traditional fiber reinforcement, this attribute allows small fractions of CNF fillers to have a large impact on the structural damping without any significant weight penalties. Moreover, once the composite returns to its undeformed configuration the interface between nano fillers and matrix will then re-establish the Van der Waals interactions that were broken to allow the slip. Thus, localized yet recoverable, frictional slip at the nano scale can be employed to significantly enhance strain dependent damping in composite structures wherein no permanent structural damage is evidenced. To better understand the damping response in CNF reinforced composites this study utilizes experimental and analytical approaches to develop modeling techniques that account for various fundamental attributes of high aspect ratio fillers, specifically the effect of filler aspect ratio, filler waviness, filler orientation relative to loading direction and the effect of multiple fillers on the damping performance and investigated in detail and corresponding modeling techniques are developed to address each of these factors in order to better predict the viscoelastic response of CNF reinforced composites. These models will be beneficial to address composite design while accounting for makeup, constituent properties, filler geometries, filler orientations, and their effective role in damping performance.

Varischetti, Joshua A.

290

Electrospun vanadium pentoxide/carbon nanofiber composites for supercapacitor electrodes  

International Nuclear Information System (INIS)

The vanadium pentoxide (V2O5)/carbon nanofiber composites (CNFCs) were prepared from polyacrylonitrile/V2O5 in N,N-dimethylformamide by a simple electrospinning method, and their electrochemical properties as supercapacitor electrodes were investigated. Different loadings of V2O5, the microstructures of the CNFCs (e.g., nanometer-size diameters, high specific surface areas, narrow pore size distributions, and tunable porosities) were changed, and the textural parameters significantly affected the electrochemical properties of the composites. The CNFC capacitors delivered the high specific capacitances of 150.0 F g?1 for the CNFCs in an aqueous, with promising energy densities of 18.8 Wh kg?1, over a power density range of 400–20,000 W kg?1. The CNFCs simultaneously exhibited excellent capacity retention.

291

Some properties of solid state fractal structures of carbon nanofibers  

International Nuclear Information System (INIS)

Experimental data on the self-organization of massive fractal granules with a total volume of up to 1.1 cm3 consisting of carbon nanofibers, their transverse dimensions 50-70 nm and length up to 1000 nm, are presented. The fractal granules have a density of 1.3 g/cm3, elasticity modulus is 37.4 MPa, and fractal dimension D = 2.95. The resistivity of this material is about three orders of magnitude greater than the values typical of pyrolytic graphite. The surface layers in the fractal granule are characterized by a Seebeck coefficient of ? 24 ?V/K, whereas for the bulk regions the value is ? 11 ?V/K

292

Fabrication and Characterization of Carbon Nanofiber Reinforced Shape Memory Epoxy (CNFR-SME) Composites  

Science.gov (United States)

Shape memory polymers have a wide range of applications due to their ability to mechanically change shapes upon external stimulus, while their achievable composite counterparts prove even more versatile. An overview of literature on shape memory materials, fillers and composites was provided to pave a foundation for the materials used in the current study and their inherent benefits. This study details carbon nanofiber and composite fabrication and contrasts their material properties. In the first section, the morphology and surface chemistry of electrospun-poly(acrylonitrile)-based carbon nanofiber webs were tailored through various fabrication methods and impregnated with a shape memory epoxy. The morphologies, chemical compositions, thermal stabilities and electrical resistivities of the carbon nanofibers and composites were then characterized. In the second section, an overview of thermal, mechanical and shape memory characterization techniques for shape memory polymers and their composites was provided. Thermal and mechanical properties in addition to the kinetic and dynamic shape memory performances of neat epoxy and carbon nanofiber/epoxy composites were characterized. The various carbon nanofiber web modifications proved to have notable influence on their respective composite performances. The results from these two sections lead to an enhanced understanding of these carbon nanofiber reinforced shape memory epoxy composites and provided insight for future studies to tune these composites at will.

Wang, Jiuyang

293

Plasma coating of carbon nanofibers for enhanced dispersion and interfacial bonding in polymer composites  

International Nuclear Information System (INIS)

Ultrathin films of polystyrene were deposited on the surfaces of carbon nanofibers using a plasma polymerization treatment. A small percent by weight of these surface-coated nanofibers were incorporated into polystyrene to form a polymer nanocomposite. The plasma coating greatly enhanced the dispersion of the nanofibers in the polymer matrix. High-resolution transmission-electron-microscopy (HRTEM) images revealed an extremely thin film of the polymer layer (?3 nm) at the interface between the nanofiber and matrix. Tensile test results showed considerably increased strength in the coated nanofiber composite while an adverse effect was observed in the uncoated composites; the former exhibited shear yielding due to enhanced interfacial bonding while the latter fractured in a brittle fashion

294

Effect of Carbon Nanofiber-Matrix Adhesion on Polymeric Nanocomposite Properties—Part II  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A successful integration of two independent phases with good adhesion is imperative for effective translation of superior carbon nanofiber filler properties into a physically superior carbon nanocomposite. Carbon nanofibers were subjected to electrochemical oxidation in 0.1 M nitric acid for varying times. The strength of adhesion between the nanofiber and an epoxy matrix was characterized by flexural strength and modulus. The surface functional groups formed and their concentrat...

Khalid Lafdi; William Fox; Matthew Matzek; Emel Yildiz

2008-01-01

295

Interactions of gold nanoparticles with the interior of hollow graphitized carbon nanofibers.  

Science.gov (United States)

Interactions of free-standing gold nanoparticles and hollow graphitized nanofibers in colloidal suspension are investigated, revealing the first example of the controlled arrangement of nanoparticles inside nano-containers, as directed by their internal structure. The ordering is highly effective for small gold nanoparticles whose sizes are commensurate with the height of graphitic step-edges in the graphitized carbon nanofibers and is less effective for larger gold nanoparticles. Studies aimed at understanding the role of the organic-solvent surface tension, employed for the filling experiments, demonstrate that gold nanoparticles become preferentially anchored into the hollow graphitized carbon nanofibers under a mixture of pentane/CO(2) in supercritical conditions. It is shown that a three-step cleaning procedure enables effective removal of gold nanoparticles adsorbed on the exterior surface of graphitized carbon nanofibers, while ordered arrays of encapsulated nanoparticles are retained. PMID:22334588

La Torre, Alessandro; Fay, Michael W; Rance, Graham A; Del Carmen Gimenez-Lopez, Maria; Solomonsz, William A; Brown, Paul D; Khlobystov, Andrei N

2012-04-23

296

Ultrasound-assisted preparation of electrospun carbon nanofiber/graphene composite electrode for supercapacitors  

Science.gov (United States)

Electrospun carbon nanofiber/graphene (CNF/G) composites are prepared by in situ electrospinning polymeric nanofibers with simultaneous spraying graphene oxide, followed by heat treatment. The freestanding carbon nanofiber web acts as a framework for sustaining graphene, which helps to prevent the agglomeration of graphene and to provide a high conductivity for the efficient charge transfer to the pores. The as-obtained CNF/G composite exhibits a specific capacitance of 183 F g-1, which is approximately 1.6 times higher than that of the pristine CNF. The results have demonstrated that the high performance of the CNF/G composite is due to the novel structure and the synergic effect of graphene and the carbon nanofibers.

Dong, Qiang; Wang, Gang; Hu, Han; Yang, Juan; Qian, Bingqing; Ling, Zheng; Qiu, Jieshan

2013-12-01

297

Nanocomposite hybrid material based on carbon nanofibers and polyoxometalates  

Directory of Open Access Journals (Sweden)

Full Text Available Sintetizamos y caracterizamos materiales h ? ?bridos nanocompositos a base de nanofibras de carb ? on previamente oxidadas (fCNFs y poliox- ometalatos (POM. Las fCNF se analizaron por TEM y XRD donde detectamos la presencia de nanoespirales de carbono y la eliminaci ? on de carbono amorfo y de las fibras mas delgadas. La microestructura del material h ? ?brido nanocomposito (fCNFs-POM se observ ? o por SEM, y los an ? alisis de EDX mostraron la presencia de Cs, P, Mo, y O del POM y C de fCNFs. Adem ? as, los espectros de FTIR confirmaron la presencia de ambos componentes del h ? ?brido, donde su interacci ? on no ha sido clarificada pero intuimos la quimisorci ? on del POM a las fCNFs mediante grupos carbonilos. Finalmente, ensamblamos celdas sim ? etricas supercapacitivas de estado s ? olido, donde la celda con electrodos h ? ?bridos mostr ? o una capacitancia mucho mayor de 120 mF/g, mostrando tanto la contribuci ? on pseudocapacitiva del POM como la doble capa de las nanofibras de carbono. Descriptores:

A.K. Cuentas-Gallegos

2007-01-01

298

Synthesis, chemistry and structure of boron-doped carbon nanotubes and nanofibers  

Science.gov (United States)

The objective of this project is to synthesize novel boron-rich carbon in the form of nanotubes and nanofibers and to determine the influence of high concentrations of boron on the sp2 carbon structure. Research efforts on the influence of high concentrations of boron on the sp 2 carbon structure have been undertaken through a combination of computational prediction and experimental investigation. A theoretical prediction regarding the boron influence on carbon nanotube structure is carried using molecular and quantum mechanical simulations. The influence of substitutional boron on strain, tube diameter, tube length and tube stability is discussed. A high boron doping (10-17 at.%) introduces disorder into the host sp2 carbon structure. Boron-doped carbon nanotubes and nanofibers have been synthesized by a catalytic CVD at 750-900°C from C6H6 and BCl 3. The deposition temperature and reactant ratio (BCl3/C 6H6) influence the microstructure and compositions of the resulting deposits significantly. The boron concentrations of the boron-doped carbon nanotubes and nanofibers are in the range of 5-18 at.% as measured by AES. The optimum temperature to obtain a high boron content sample is around 800°C. The crystal structures and microstructures of boron-doped carbon nanotubes and nanofibers are inhomogeneous. The boron doping into the carbon nanotubes and nanofibers is structure-related. The platelet stacked structure is always very well-ordered with very low boron concentration ( 8%. A disordered transition area between herringbone and tubular structure in a nanofiber of Sample I-1 is observed where the boron concentration is 16%, i.e., consistent with a composition of C6B. Mechanisms of boron-doped nanofiber growth are proposed that involve both surface diffusion and bulk diffusion process. Temperature is the governing factor that determines the process by which either surface diffusion or bulk diffusion dominates. Boron doping also influences the ordering of the carbon layer plane stacking.

Wang, Ling

299

Electrodeposited MnOx/carbon nanofiber composites for use as anode materials in rechargeable lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofiber-supported MnOx composites were prepared by electrodepositing MnOx nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of MnOx nanoparticles were controlled by the surface treatment of carbon nanofibers and the electrodeposition duration time. SEM, TEM/EDS, elemental analysis, and XRD were used to study the morphology and composition of MnOx on the nanofibers. The resultant MnOx/carbon nanofiber composites were used directly as the anode material in lithium half cells and their electrochemical performance was characterized. Results show that MnOx/carbon nanofiber composites prepared by different deposition durations have high reversible capacity, good capacity retention, and excellent structural integrity during cycling. (author)

Lin, Zhan; Ji, Liwen; Woodroof, Mariah D.; Zhang, Xiangwu [Fiber and Polymer Science Program, Department of Textile Engineering, Chemistry and Science, North Carolina State University, 2401 Research Drive, Raleigh, NC 27695-8301 (United States)

2010-08-01

300

Nickel supported carbon nanofibers as an active and selective catalyst for the gas-phase hydrogenation of 2-tert-butylphenol.  

Science.gov (United States)

Nickel supported fishbone carbon nanofibers (CNFs) have been prepared by vacuum impregnation (VI) and homogeneous deposition-precipitation (HDP) methods with different nickel loadings (ca. 5%, 9% and 12%) with the aim to study the influence of the metal incorporation method and the nickel loading in the catalytic activity of gas-phase hydrogenation of 2-tert-butylphenol (2-TBP). Moreover, the influence of the nature of the support was also studied by preparing nickel catalysts supported on other carbon (active carbon (AC) and graphite (G)) and non-carbonaceous materials (alumina (AL) and yttria-stabilized zirconia (YSZ)). Different techniques were employed to characterize both the supports and the final Ni catalysts: atomic absorption spectrometry, N(2) adsorption-desorption analysis, temperature-programed reduction (TPR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Catalytic results revealed that the nickel particle size and support properties affected directly to both the catalytic activity of hydrogenation of 2-TBP, and the rate of secondary reactions such as cis to trans isomerization and 2-tert-butylcyclohexanone (2-TBCN) hydrogenation. PMID:22682327

Díaz, José Antonio; Díaz-Moreno, Rebeca; Silva, Luz Sánchez; Dorado, Fernando; Romero, Amaya; Valverde, José Luis

2012-08-15

 
 
 
 
301

Orientation of Carbon Nano-fiber in Carbon/Silica Composite Prepared under High Magnetic Field  

Energy Technology Data Exchange (ETDEWEB)

Carbon/silica composite films were prepared from colloidal silica aqueous solution in which vapour grown carbon nano-fibers dispersed. The orientation of nano-fibers was attempted by dip-coating substrates under high magnetic field up to 10 T. The fibers started to align along the direction of magnetic field below 1 T. The degree of orientation was saturated at about 6 T. The anisotropic susceptibility, {Delta}{chi} = {chi}{sub ||}-{chi}{sub perpendicular}, was estimated to be (3.05{+-}1.10)x10{sup -7} cm{sup 3}/mol from the fitting of numerical simulation. It was smaller than that reported in previous studies. It was deduced that perturbation of fiber orientation in the sol during drawing and drying, and the existence of coupled fibers in the starting materials suppressed the orientation of fibers.

Kitamura, N; Fukumi, K [National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Takahashi, K; Mogi, I; Awaji, S; Watanabe, K, E-mail: naoyuki.kitamura@aist.go.jp [Institute for Matererials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577 (Japan)

2011-02-15

302

Platinum nanocluster growth on vertically aligned carbon nanofiber arrays: Sputtering experiments and molecular dynamics simulations  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Molecular dynamics simulation of platinum cluster growth on model carbon nanofibers. Black-Right-Pointing-Pointer We compare modeled and experimental cluster growth. Black-Right-Pointing-Pointer We determine sticking coefficient evolution among deposition time and type of nanofibers. Black-Right-Pointing-Pointer We determine cluster size distribution on various model nanofibers. - Abstract: Sputtered platinum nanocluster growth on previously plasma enhanced chemical vapor deposition - PECVD - grown vertically aligned carbon nanofiber arrays is presented. Experimental cluster size distribution is shown to decrease from the CNF top to bottom, as observed by transmission electron microscopy. Molecular dynamics simulations are carried out for understanding early stages of Pt growth on model CNF arrays. Especially, sticking coefficients, concentration profiles along CNF wall, cluster size distributions are calculated. Simulated cluster size distribution are consistent with experimental finding. Sticking coefficient decreases against deposition time. The shape of the sticking curve reflects the nanocluster growth process.

Brault, Pascal, E-mail: Pascal.Brault@univ-orleans.fr [GREMI, UMR7344 CNRS-Universite d' Orleans BP 6744, 45067 Orleans Cedex 2 (France); Caillard, Amaeel [GREMI, UMR7344 CNRS-Universite d' Orleans BP 6744, 45067 Orleans Cedex 2 (France); Charles, Christine; Boswell, Rod W. [Space Plasma, Power and Propulsion Group, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Graves, David B. [Department of Chemical and Biomolecular Engineering, 201 Gilman Hall 1462, University of California Berkeley, CA 94720-1462 (United States)

2012-12-15

303

Platinum nanocluster growth on vertically aligned carbon nanofiber arrays: Sputtering experiments and molecular dynamics simulations  

International Nuclear Information System (INIS)

Highlights: ? Molecular dynamics simulation of platinum cluster growth on model carbon nanofibers. ? We compare modeled and experimental cluster growth. ? We determine sticking coefficient evolution among deposition time and type of nanofibers. ? We determine cluster size distribution on various model nanofibers. - Abstract: Sputtered platinum nanocluster growth on previously plasma enhanced chemical vapor deposition – PECVD – grown vertically aligned carbon nanofiber arrays is presented. Experimental cluster size distribution is shown to decrease from the CNF top to bottom, as observed by transmission electron microscopy. Molecular dynamics simulations are carried out for understanding early stages of Pt growth on model CNF arrays. Especially, sticking coefficients, concentration profiles along CNF wall, cluster size distributions are calculated. Simulated cluster size distribution are consistent with experimental finding. Sticking coefficient decreases against deposition time. The shape of the sticking curve reflects the nanocluster growth process.

304

Carbon nanofiber electrode array for electrochemical detection of dopamine using fast scan cyclic voltammetry  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A carbon nanofiber (CNF) electrode array was integrated with the Wireless Instantaneous Neurotransmitter Sensor System (WINCS) for detection of dopamine using fast scan cyclic voltammetry (FSCV). Dopamine detection performance by CNF arrays was comparable to that of traditional carbon fiber microelectrodes (CFMs), demonstrating that CNF arrays can be utilized as an alternative carbon electrodes for neurochemical monitoring.

Koehne, Jessica E.; Marsh, Michael; Boakye, Adwoa; Douglas, Brandon; Kim, In Yong; Chang, Su-youne; Jang, Dong-pyo; Bennet, Kevin E.; Kimble, Christopher; Andrews, Russell; Meyyappan, M.; Lee, Kendall H.

2011-01-01

305

Carbon nanofiber electrode array for electrochemical detection of dopamine using fast scan cyclic voltammetry  

Science.gov (United States)

A carbon nanofiber (CNF) electrode array was integrated with the Wireless Instantaneous Neurotransmitter Sensor System (WINCS) for detection of dopamine using fast scan cyclic voltammetry (FSCV). Dopamine detection performance by CNF arrays was comparable to that of traditional carbon fiber microelectrodes (CFMs), demonstrating that CNF arrays can be utilized as an alternative carbon electrodes for neurochemical monitoring. PMID:21387028

Koehne, Jessica E.; Marsh, Michael; Boakye, Adwoa; Douglas, Brandon; Kim, In Yong; Chang, Su-Youne; Jang, Dong-Pyo; Bennet, Kevin E.; Kimble, Christopher; Andrews, Russell; Meyyappan, M.; Lee, Kendall H.

2012-01-01

306

Development of radiation processing to functionalize carbon nanofiber to use in nanocomposite for industrial application  

International Nuclear Information System (INIS)

Radiation can be used to modify and improve the properties of materials. Electron beam and gamma ray irradiation has potential application in modifying the structure of carbon fibers in order to produce useful defects in the graphite structure and create reactive sites. In this study was investigated a methodology for radiation grafting processing to modify carbon nanofiber surfaces by grafting acrylic acid. The samples were submitted to direct radiation process. Several parameters were changed such as acrylic acid concentration, radiation dose and percentage of inhibitor to achieve functionalization with higher percentage of oxygen functional groups on carbon nanofiber surface and better dispersion. The samples were characterized by X-ray Photoelectron Spectroscopy and the dispersion stability upon storage was visually investigated. Carbon nanofiber directed irradiated with electron beam and gamma ray in a solution of acrylic acid with 6% of inhibitor (FeSO4.7H2O) and irradiated at 100 kGy had an increase of 20% of oxygen content onto carbon nanofiber surface. The Auger D-parameter for the samples direct irradiated grafted ranged between 17.0-17.7 compared to 21.1-18.9 of the unirradiated ones. This indicated that these samples had less sp2 and more sp3 bonding characteristics than unirradiated samples. This can be an indication of C=C bond breaking leading to the formation of new sp3 carbon atoms on carbon nanofiber surface with oxygen functional groups grafted. The samples grafted presented a good and stable dispersion. (author)

307

Synthesis of calcium carbonate-polyethylene oxide hybrid nanofibers through in-situ electrospinning.  

Science.gov (United States)

In this work, calcium carbonate nanoparticles-polyethylene oxide nanofibers as organic-inorganic hybrid were prepared via in-situ electrospinning. Thus, electrospinning of polyethylene oxide solution saturated with calcium hydroxide was carried out in gaseous carbon dioxide atmosphere. Transmission electron microscopy (TEM) showed that calcium carbonate (CaCO3) nanoparticles were formed on the produced nanofibers of 200-300 nm in diameter. The existence of the formed CaCO3 was also proved by thermogravimetric analysis (TGA) via loss of gaseous CO2 related to the decomposition of CaCO3 at about 500-840 degrees C. X-ray diffraction (XRD) analysis of the nanofibers showed that the formed CaCO3 nanoparticles have vaterite morphology. DSC analysis was used to determine melting point and to calculate the crystallinity of the produced hybrid nanofibers. The TEM, TGA, XRD and DSC analyses results of the obtained nanofibers were compared with those of the nanofibers produced in electrospinning of pure polyethylene oxide solution and polyethylene oxide solution having calcium hydroxide, both in air. PMID:18572696

Faridi-Majidi, Reza; Sharifi-Sanjani, Naser; Madani, Mohammad

2008-05-01

308

Production, characterization, and mechanical behavior of cementitious materials incorporating carbon nanofibers  

Science.gov (United States)

Carbon nanotubes (CNTs) and carbon nanofirbers (CNFs) have excellent properties (mechanical, electrical, magnetic, etc.), which can make them effective nanoreinforcements for improving the properties of materials. The incorporation of CNT/Fs in a wide variety of materials has been researched extensively in the past decade. However, the past study on the reinforcement of cementitious materials with these nanofilaments has been limited. The findings from those studies indicate that CNT/Fs did not significantly improve the mechanical properties of cementitious materials. Two major parameters influence the effectiveness of any discrete inclusion in composite material: The dispersion quality of the inclusions and the interfacial bond between the inclusions and matrix. The main focus of this dissertation is on the dispersion factor, and consists of three main tasks: First a novel thermodynamic-based method for dispersion quantification was developed. Second, a new method, incorporating the utilization of silica fume, was devised to improve and stabilize the dispersion of CNFs in cement paste. And third, the dispersion quantification method and mechanical testing were employed to measure, compare, and correlate the dispersion and mechanical properties of CNF-incorporated cement paste produced with the conventional and new methods. Finally, the main benefits, including the increase in strength and resistance to shrinkage cracking, obtained from the utilization of CNFs in cement paste will be presented. The investigations and the corresponding results show that the novel dispersion quantification method can be implemented easily to perform a wide variety of tasks ranging from measuring dispersion of nanofilaments in composites using their optical/SEM micrographs as input, to measuring the effect of cement particle/clump size on the dispersion of nano inclusions in cement paste. It was found that cement particles do not affect the dispersion of nano inclusions in cement paste significantly while the dispersion of nano inclusions can notably degenerates if the cement particles are agglomerated. The novel dispersion quantification method shows that, the dispersion of CNFs in cement paste significantly improves by utilizing silica fume. However, it was found that the dispersion of silica fume particles is an important parameter and poorly dispersed silica fume cannot enhance the overall dispersion of nano inclusions in cementitious materials. Finally, the mechanical testing and experimentations showed that CNFs, in absence of moist curing, even if poorly dispersed, can provide important benefits in terms of strength and crack resistance.

Yazdanbakhsh, Ardavan

309

Preparation and Application of Carbon Nanofibers-supported Palladium Nanoparticles Catalysts Based on Electrospinning  

Directory of Open Access Journals (Sweden)

Full Text Available Carbon nanofibers-supported palladium nanoparticle catalysts were prepared by electrospinning, chemical reduction and the subsequent high temperature carbonization methods. The experiments were carried out to investigate the influence of different reducing agents (sodium borohydride, hydrazine hydrate and hydrogen gas on morphology of palladium nanoparticles and carbon nanofibers in detail. Catalysts were characterized by UV-Vis spectra, X-ray diffraction, fourier transform infrared spectrum, scanning electron microscope, field emission transmission electron microscope. Results show that the palladium nanoparticles are distributed uniformly on the carbon nanofibers with dimension of about 7 nm, and the catalyst is relatively flexible by using hydrogen gas as reducing agent. Then it was applied to the Heck coupling reaction to test catalytic properties and recyclability. Results indicate that the catalyst possesses excellent stability and recyclability.

GUO Li-Ping, BAI Jie, LIANG Hai-Ou, LI Chun-Ping, SUN Wei-Yan, MENG Qing-Run

2014-08-01

310

Fluorescent carbon nanowires made by pyrolysis of DNA nanofibers and plasmon-assisted emission enhancement of their fluorescence.  

Science.gov (United States)

We report on a facile method for preparing fluorescent carbon nanowires (CNWs) with pyrolysis of highly aligned DNA nanofibers as carbon sources. Silver nanoparticle (AgNP)-doped CNWs were also produced using pyrolysis of DNA nanofibers with well-attached AgNPs, indicating emission enhancement assisted by localized plasmon resonances. PMID:25155962

Nakao, Hidenobu; Tokonami, Shiho; Yamamoto, Yojiro; Shiigi, Hiroshi; Takeda, Yoshihiko

2014-10-14

311

Electrochemical stability of carbon nanofibers in proton exchange membrane fuel cells  

Energy Technology Data Exchange (ETDEWEB)

This fundamental study deals with the electrochemical stability of several non-conventional carbon based catalyst supports, intended for low temperature proton exchange membrane fuel cell (PEMFC) cathodes. Electrochemical surface oxidation of raw and functionalized carbon nanofibers, and carbon black for comparison, was studied following a potential step treatment at 25.0 deg. C in acid electrolyte, which mimics the operating conditions of low temperature PEMFCs. Surface oxidation was characterized using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Cyclic voltammograms clearly showed the presence of the hydroquinone/quinone couple. Furthermore, identification of carbonyl, ether, hydroxyl and carboxyl surface functional groups were made by deconvolution of the XPS spectra. The relative increase in surface oxides on carbon nanofibers during the electrochemical oxidation treatment is significantly smaller than that on carbon black. This suggests that carbon nanofibers are more resistant to the electrochemical corrosion than carbon black under the experimental conditions used in this work. This behaviour could be attributed to the differences found in the microstructure of both kinds of carbons. According to these results, carbon nanofibers possess a high potential as catalyst support to increase the durability of catalysts used in low temperature PEMFC applications.

Alvarez, Garbine [Energy Department, CIDETEC-IK4, Po Miramon, 196, 20009 San Sebastian (Spain); Alcaide, Francisco, E-mail: falcaide@cidetec.es [Energy Department, CIDETEC-IK4, Po Miramon, 196, 20009 San Sebastian (Spain); Miguel, Oscar [Energy Department, CIDETEC-IK4, Po Miramon, 196, 20009 San Sebastian (Spain); Cabot, Pere L. [Laboratori d' Electroquimica de Materials i del Medi Ambient, Dept. Quimica Fisica, Universitat de Barcelona, Marti i Franques, 1-11, 08028 Barcelona (Spain); Martinez-Huerta, M.V.; Fierro, J.L.G. [Instituto de Catalisis y Petroleoquimica (CSIC), Marie Curie 2, Cantoblanco, 28049 Madrid (Spain)

2011-10-30

312

A novel nano-nonwoven fabric with three-dimensionally dispersed nanofibers: entrapment of carbon nanofibers within nonwovens using the wet-lay process  

Science.gov (United States)

This study demonstrates, for the first time, the manufacturing of novel nano-nonwovens that are comprised of three-dimensionally distributed carbon nanofibers within the matrices of traditional wet-laid nonwovens. The preparation of these nano-nonwovens involves dispersing and flocking carbon nanofibers, and optimizing colloidal chemistry during wet-lay formation. The distribution of nanofibers within the nano-nonwoven was verified using polydispersed aerosol filtration testing, air permeability, low surface tension liquid capillary porometry, SEM and cyclic voltammetry. All these characterization techniques indicated that nanofiber flocks did not behave as large solid clumps, but retained the ‘nanoporous’ structure expected from nanofibers. These nano-nonwovens showed significant enhancements in aerosol filtration performance. The reduction-oxidation reactions of the functional groups on nanofibers and the linear variation of electric double-layer capacitance with nanofiber loading were measured using cyclic voltammetry. More than 65 m2 (700 ft2) of the composite were made during the demonstration of process scalability using a Fourdrinier-type continuous pilot papermaking machine. The scalability of the process with the control over pore size distribution makes these composites very promising for filtration and other nonwoven applications.

Karwa, Amogh N.; Barron, Troy J.; Davis, Virginia A.; Tatarchuk, Bruce J.

2012-05-01

313

A novel nano-nonwoven fabric with three-dimensionally dispersed nanofibers: entrapment of carbon nanofibers within nonwovens using the wet-lay process  

International Nuclear Information System (INIS)

This study demonstrates, for the first time, the manufacturing of novel nano-nonwovens that are comprised of three-dimensionally distributed carbon nanofibers within the matrices of traditional wet-laid nonwovens. The preparation of these nano-nonwovens involves dispersing and flocking carbon nanofibers, and optimizing colloidal chemistry during wet-lay formation. The distribution of nanofibers within the nano-nonwoven was verified using polydispersed aerosol filtration testing, air permeability, low surface tension liquid capillary porometry, SEM and cyclic voltammetry. All these characterization techniques indicated that nanofiber flocks did not behave as large solid clumps, but retained the ‘nanoporous’ structure expected from nanofibers. These nano-nonwovens showed significant enhancements in aerosol filtration performance. The reduction–oxidation reactions of the functional groups on nanofibers and the linear variation of electric double-layer capacitance with nanofiber loading were measured using cyclic voltammetry. More than 65 m2 (700 ft2) of the composite were made during the demonstration of process scalability using a Fourdrinier-type continuous pilot papermaking machine. The scalability of the process with the control over pore size distribution makes these composites very promising for filtration and other nonwoven applications. (paper)

314

Effect of twist and porosity on the electrical conductivity of carbon nanofiber yarns  

International Nuclear Information System (INIS)

This study focuses on the effect of twist and porosity on the electrical conductivity of carbon nanofiber (CNF) yarns. The process of fabrication of CNF yarns included the synthesis of aligned ribbons of polyacrylonitrile (PAN) nanofibers via electrospinning. The PAN ribbons were twisted into yarns with twist levels ranging from zero twist to high twists of 1300 turn per meter (tpm). The twist imposed on the ribbons substantially improved the interactions between nanofibers and reduced the porosity. The PAN yarns were subsequently stabilized in air, and then carbonized in nitrogen at 1100?° C for 1 h. Compressive stresses developed between the PAN nanofibers as a result of twist promoted interfusion between neighboring nanofibers, which was accelerated by heating the yarns during stabilization to temperatures above the glass transition of PAN. The electrical conductivity of the yarns was measured with a four point probe measurement technique. Although increasing the twist promotes electrical conductivity between nanofibers by forming junctions between them, our results indicate that the electrical conductivity does not continuously increase with increasing twist, but reaches a threshold value after which it starts to decrease. The causes for this behavior were studied through experimental techniques and further explored using a yarn-equivalent electrical circuit model. (paper)

315

Effect of twist and porosity on the electrical conductivity of carbon nanofiber yarns  

Science.gov (United States)

This study focuses on the effect of twist and porosity on the electrical conductivity of carbon nanofiber (CNF) yarns. The process of fabrication of CNF yarns included the synthesis of aligned ribbons of polyacrylonitrile (PAN) nanofibers via electrospinning. The PAN ribbons were twisted into yarns with twist levels ranging from zero twist to high twists of 1300 turn per meter (tpm). The twist imposed on the ribbons substantially improved the interactions between nanofibers and reduced the porosity. The PAN yarns were subsequently stabilized in air, and then carbonized in nitrogen at 1100?° C for 1 h. Compressive stresses developed between the PAN nanofibers as a result of twist promoted interfusion between neighboring nanofibers, which was accelerated by heating the yarns during stabilization to temperatures above the glass transition of PAN. The electrical conductivity of the yarns was measured with a four point probe measurement technique. Although increasing the twist promotes electrical conductivity between nanofibers by forming junctions between them, our results indicate that the electrical conductivity does not continuously increase with increasing twist, but reaches a threshold value after which it starts to decrease. The causes for this behavior were studied through experimental techniques and further explored using a yarn-equivalent electrical circuit model.

Chawla, S.; Naraghi, M.; Davoudi, A.

2013-06-01

316

Electrospun Carbon Nanofiber Webs with Controlled Density of States for Sensor Applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electrospun carbon nanofiber (CNF) webs with controlled density of states (DOS) are synthesized through varying the carbonization conditions to manipulate the concentration of nanosized graphite domains. These materials exhibit adjustable electrochemical activity and biosensitivity: both electron transfer kinetics for various redox systems and direct electron transfer efficiencies with enzymes increase with the DOS of the CNF webs.

Mao, Xianwen; Simeon, Fritz; Rutledge, Gregory C.; Hatton, T. Alan

2012-01-01

317

Carbon Nanofiber-based Luminol-biotin Probe for Sensitive Chemiluminescence Detection of Protein.  

Science.gov (United States)

A carbon nanofiber-based luminol-biotin probe was synthesized for the sensitive chemiluminescence (CL) detection of a target protein by grafting luminol and biotin onto an oxidized carbon nanofiber. This carbon nanofiber was prepared by chemical vapor-deposition with methane in the presence of the Ni-Cu-MgO catalyst, which was followed by oxidization with HNO3-H2SO4 to produce a carboxyl group on the surface of the nanofiber. The material was grafted with luminol and biotin by means of a standard carbodiimide activation of COOH groups to produce corresponding amides. The substance was water-soluble and thus could be utilized as a sensitive CL probe for a protein assay. The probe showed highly specific affinity towards the biotin-labeled antibody via a streptavidin-biotin interaction. The detection limit for this model assay was approximately 0.2 pmol of the biotinized IgG spotted on a polyvinylidene fluoride (PVDF) membrane. Nonspecific binding to other proteins was not observed. Therefore, the synthesized carbon nanofiber-based CL probe may be useful for a sensitive and specific analysis of the target protein. PMID:25382040

Baj, Stefan; Krawczyk, Tomasz; Pradel, Natalia; Azam, Md Golam; Shibata, Takayuki; Dragusha, Shpend; Skutil, Krzysztof; Pawlyta, Miroslawa; Kai, Masaaki

2014-01-01

318

Silicotungstic acid stabilized Pt-Ru nanoparticles supported on carbon nanofibers electrodes for methanol oxidation  

Energy Technology Data Exchange (ETDEWEB)

Silicotungstic acid stabilized Pt-Ru nanoparticles supported on Functionalized Carbon Nanofibers have been prepared by a microwave-assisted polyol process. The samples were characterized by XRD, SEM and TEM analysis. The electro-catalytic activities of the prepared composites (20% Pt-Ru/STA-CNF) were examined by using Cyclic Voltammetry (CV) for oxidation of methanol. The electro-catalytic activity of the carbon nanofiber based composite (20% Pt-Ru/STA-CNF) electrode for methanol oxidation showed better performance than that of commercially available Johnson Mathey 20% Pt-Ru/C and 20% Pt-Ru/STA-C catalyst. The results imply that carbon nanofiber based STA composite electrodes are excellent potential candidates for application in direct methanol fuel cells. (author)

Maiyalagan, T. [Department of Chemistry, School of Science and Humanities, VIT University, Vellore 632014 (India)

2009-04-15

319

Carbon Nanotubes/Nanofibers by Plasma Enhanced Chemical Vapour Deposition  

Science.gov (United States)

Plasma enhanced chemical vapour deposition (PECVD) has been recently used for the production of vertically aligned carbon nanotubedfibers (CN) directly on substrates. These structures are potentially important technologically as electron field emitters (e.g. microguns, microwave amplifiers, displays), nanoelectrodes for sensors, filter media, superhydrophobic surfaces and thermal interface materials for microelectronics. A parametric study on the growth of CN grown by glow discharge dc-PECVD is presented. In this technique, a substrate containing thin film Ni catalyst is exposed to C2H2 and NH3 gases at 700 C. Without plasma, this process is essentially thermal CVD which produces curly spaghetti-like CN as seen in Fig. 1 (a). With the plasma generated by biasing the substrate at -6OOV, we observed that the CN align vertically during growth as shown in Fig. l(b), and that the magnitude of the applied substrate bias affects the degree of alignment. The thickness of the thin film Ni catalyst was found to determine the average diameter and inversely the length of the CN. The yield and density of the CN were controlled by the use of different diffusion barrier materials under the Ni catalyst. Patterned CN growth [Fig. l(c)], with la variation in CN diameter of 4.1% and 6.3% respectively, is achieved by lithographically defining the Ni thin film prior to growth. The shape of the structures could be varied from very straight nanotube-like to conical tip-like nanofibers by increasing the ratio of C2H2 in the gas flow. Due to the plasma decomposition of C2H2, amorphous carbon (a-C) is an undesirable byproduct which could coat the substrate during CN growth. Using a combination of depth profiled Auger electron spectroscopy to study the substrate and in-situ mass spectroscopy to examine gas phase neutrals and ions, the optimal conditions for a-C free growth of CN is determined.

Teo, K. B. K.; Hash, D. B.; Bell, M. S.; Chhowalla, M.; Cruden, B. A.; Amaratunga, G. A. J.; Meyyappan, M.; Milne, W. I.

2005-01-01

320

Conductivity of carbon nanofiber/polypyrrole conducting nanocomposites  

International Nuclear Information System (INIS)

Carbon nanofiber (CNF) / Polypyrrole (Ppy) composite materials were fabricated by two newly invented processes - filtering, washing and drying the mixture of CNF dispersion and Ppy-NMP solution (FWP process) and heating an aqueous solution of CNF (SH process). CNF/Ppy composite materials have never been reported before in any other research papers. Conductivities of the composite films were obtained by using a four-probe method. To compare the conductivity of CNF/Ppy with that of a pure single-walled carbon nanotube (SWNT), SWNT films were also fabricated and voltage was measured. SEM images were taken for both a surface and a cross-section of composite samples fabricated by the two processes. The CNF/Ppy by FWP was a little brittle because of the low solubility of Ppy in the NMP, and on the other hand, the same material by SH became flexible enough. The conductivity of the pure SWNT film was as high as double the similar case. The conductivity of the pure SWNT film was 20.11 S/cm and 0.013 cm thick. The CNF/Ppy composite films with the thicknesses of 0.062 cm and 0.085 cm gave a conductivity of 63.32 S/cm and 40.57 S/cm, respectively, which are higher than that of the pure SWNT film or SWNT/Polyaniline (PANi) film. The good conductivity of CNF/Ppy composites shows the improved potential for developing the materials for a small actuator

 
 
 
 
321

Conductivity of carbon nanofiber/polypyrrole conducting nanocomposites  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofiber (CNF) / Polypyrrole (Ppy) composite materials were fabricated by two newly invented processes - filtering, washing and drying the mixture of CNF dispersion and Ppy-NMP solution (FWP process) and heating an aqueous solution of CNF (SH process). CNF/Ppy composite materials have never been reported before in any other research papers. Conductivities of the composite films were obtained by using a four-probe method. To compare the conductivity of CNF/Ppy with that of a pure single-walled carbon nanotube (SWNT), SWNT films were also fabricated and voltage was measured. SEM images were taken for both a surface and a cross-section of composite samples fabricated by the two processes. The CNF/Ppy by FWP was a little brittle because of the low solubility of Ppy in the NMP, and on the other hand, the same material by SH became flexible enough. The conductivity of the pure SWNT film was as high as double the similar case. The conductivity of the pure SWNT film was 20.11 S/cm and 0.013 cm thick. The CNF/Ppy composite films with the thicknesses of 0.062 cm and 0.085 cm gave a conductivity of 63.32 S/cm and 40.57 S/cm, respectively, which are higher than that of the pure SWNT film or SWNT/Polyaniline (PANi) film. The good conductivity of CNF/Ppy composites shows the improved potential for developing the materials for a small actuator

Kim, Cheol; Zhang, Shuai [Kyungpook National University, Daegu (Korea, Republic of)

2009-01-15

322

Genotoxicity of carbon nanofibers: are they potentially more or less dangerous than carbon nanotubes or asbestos?  

Science.gov (United States)

The production of carbon nanofibers and nanotubes (CNF/CNT) and their composite products is increasing globally. CNF are generating great interest in industrial sectors such as energy production and electronics, where alternative materials may have limited performance or are produced at a much higher cost. However, despite the increasing industrial use of carbon nanofibers, information on their potential adverse health effects is limited. In the current study, we examine the cytotoxic and genotoxic potential of carbon-based nanofibers (Pyrograf®-III) and compare this material with the effects of asbestos fibers (crocidolite) or single-walled carbon nanotubes (SWCNT). The genotoxic effects in the lung fibroblast (V79) cell line were examined using two complementary assays: the comet assay and micronucleus (MN) test. In addition, we utilized fluorescence in situ hybridization to detect the chromatin pan-centromeric signals within the MN indicating their origin by aneugenic (chromosomal malsegregation) or clastogenic (chromosome breakage) mechanisms. Cytotoxicity tests revealed a concentration- and time-dependent loss of V79 cell viability after exposure to all tested materials in the following sequence: asbestos>CNF>SWCNT. Additionally, cellular uptake and generation of oxygen radicals was seen in the murine RAW264.7 macrophages following exposure to CNF or asbestos but not after administration of SWCNT. DNA damage and MN induction were found after exposure to all tested materials with the strongest effect seen for CNF. Finally, we demonstrated that CNF induced predominantly centromere-positive MN in primary human small airway epithelial cells (SAEC) indicating aneugenic events. Further investigations are warranted to elucidate the possible mechanisms involved in CNF-induced genotoxicity. PMID:21310169

Kisin, E R; Murray, A R; Sargent, L; Lowry, D; Chirila, M; Siegrist, K J; Schwegler-Berry, D; Leonard, S; Castranova, V; Fadeel, B; Kagan, V E; Shvedova, A A

2011-04-01

323

Genotoxicity of carbon nanofibers: Are they potentially more or less dangerous than carbon nanotubes or asbestos?  

International Nuclear Information System (INIS)

The production of carbon nanofibers and nanotubes (CNF/CNT) and their composite products is increasing globally. CNF are generating great interest in industrial sectors such as energy production and electronics, where alternative materials may have limited performance or are produced at a much higher cost. However, despite the increasing industrial use of carbon nanofibers, information on their potential adverse health effects is limited. In the current study, we examine the cytotoxic and genotoxic potential of carbon-based nanofibers (Pyrograf (registered) -III) and compare this material with the effects of asbestos fibers (crocidolite) or single-walled carbon nanotubes (SWCNT). The genotoxic effects in the lung fibroblast (V79) cell line were examined using two complementary assays: the comet assay and micronucleus (MN) test. In addition, we utilized fluorescence in situ hybridization to detect the chromatin pan-centromeric signals within the MN indicating their origin by aneugenic (chromosomal malsegregation) or clastogenic (chromosome breakage) mechanisms. Cytotoxicity tests revealed a concentration- and time-dependent loss of V79 cell viability after exposure to all tested materials in the following sequence: asbestos > CNF > SWCNT. Additionally, cellular uptake and generation of oxygen radicals was seen in the murine RAW264.7 macrophages following exposure to CNF or asbestos but not after administration of SWCNT. DNA damage and MN induction were found after expoage and MN induction were found after exposure to all tested materials with the strongest effect seen for CNF. Finally, we demonstrated that CNF induced predominately centromere-positive MN in primary human small airway epithelial cells (SAEC) indicating aneugenic events. Further investigations are warranted to elucidate the possible mechanisms involved in CNF-induced genotoxicity.

324

Mechanically tough, electrically conductive polyethylene oxide nanofiber web incorporating DNA-wrapped double-walled carbon nanotubes.  

Science.gov (United States)

Electrospun biopolymer-derived nanofiber webs are promising scaffolds for growing tissue and cells. However, the webs are mechanically weak and electrically insulating. We have synthesized a polyethylene oxide (PEO) nanofiber web that is pliable, tough, and electrically conductive, by incorporating optically active, DNA-wrapped, double-walled carbon nanotubes. The nanotubes were individually trapped along the length of the PEO nanofiber and acted as mechanically reinforcing filler and an electrical conductor. PMID:23597171

Kim, Jin Hee; Kataoka, Masakazu; Jung, Yong Chae; Ko, Yong-Il; Fujisawa, Kazunori; Hayashi, Takuya; Kim, Yoong Ahm; Endo, Morinobu

2013-05-22

325

Carbonized Micro- and Nanostructures: Can Downsizing Really Help?  

Directory of Open Access Journals (Sweden)

Full Text Available In this manuscript, we discuss relationships between morphology and mechanical strength of carbonized structures, obtained via pyrolysis of polymeric precursors, across multiple length scales, from carbon fibers (CFs with diameters of 5–10 µm to submicron thick carbon nanofibers (CNFs. Our research points to radial inhomogeneity, skin–core structure, as a size-dependent feature of polyacrylonitrile-based CFs. This inhomogeneity is a surface effect, caused by suppressed diffusion of oxygen and stabilization byproducts during stabilization through skin. Hence, reducing the precursor diameters from tens of microns to submicron appears as an effective strategy to develop homogeneous carbonized structures. Our research establishes the significance of this downsizing in developing lightweight structural materials by comparing intrinsic strength of radially inhomogeneous CFs with that of radially homogeneous CNF. While experimental studies on the strength of CNFs have targeted randomly oriented turbostratic domains, via continuum modeling, we have estimated that strength of CNFs can reach 14 GPa, when the basal planes of graphitic domains are parallel to nanofiber axis. The CNFs in our model are treated as composites of amorphous carbon (matrix, reinforced with turbostratic domains, and their strength is predicted using Tsai–Hill criterion. The model was calibrated with existing experimental data.

Mohammad Naraghi

2014-05-01

326

Modeling the carbon nanofiber addressed liquid crystal microlens array from experimentally observed optical phenomena  

Science.gov (United States)

This paper presents a novel method of using experimentally observed optical phenomena to reverse-engineer a model of the carbon nanofiber-addressed liquid crystal microlens array (C-MLA) using Zemax. It presents the first images of the optical profile for the C-MLA along the optic axis. The first working optical models of the C-MLA have been developed by matching the simulation results to the experimental results. This approach bypasses the need to know the exact carbon nanofiber-liquid crystal interaction and can be easily adapted to other systems where the nature of an optical device is unknown.

Lu, Jiahui; Cole, Matthew T.; Wilkinson, Timothy D.

2014-04-01

327

Solvent-free acetylation of cellulose nanofibers for improving compatibility and dispersion.  

Science.gov (United States)

Cellulose nanofibers (CNFs), as bio-materials derived from wood or non-wood plants, have the advantages of being biodegradable, renewable, low cost, and having good mechanical properties compared to synthetic nanofibers. CNFs have been used as reinforcement in polymeric matrices, however, due to their polar surface, their dispersibility in non-polar solvents and compatibility with hydrophobic matrices are poor. In this work, the chemical modification of CNFs, using acetic anhydride in the presence of pyridine as a catalyst, was studied with the aim of changing the surface properties. Native and chemically modified CNFs were characterized in terms of dynamic absorption, thermal stability, surface chemistry, morphology, and crystal structure. The reaction of acetylation between the acetyl groups and the hydroxyl groups of the CNFs was examined using Fourier transform infrared (FT-IR) analysis, while its extent was assessed by titration. The ester content of CNFs was higher for the acetylated samples compared to the control samples. It was also shown that the crystallinity decreased moderately as a result of esterification. Thermal stability of the modified nanofibers was slightly increased. Unlike native CNFs, a stable aqueous suspension was obtained with the modified nanofibers in both ethanol and acetone. The contact angle measurements confirmed that the surface characteristics of acetylated CNFs were changed from hydrophilic to more hydrophobic. In addition, the obtained acetylated CNFs showed more hydrophobic surface, which is in favor of enhancing the hydrophobic non-polar mediums. PMID:24507293

Ashori, Alireza; Babaee, Mehran; Jonoobi, Mehdi; Hamzeh, Yahya

2014-02-15

328

Plasma oxidation and stabilization of electrospun polyacrylonitrile nanofiber for carbon nanofiber formation  

Science.gov (United States)

The effect of plasma treatment on the stabilization of copolymer P(AN-MA) containing 6.1 mol% methyl acrylate (MA) prepared by an electrospinning technique has been investigated at various oxygen contents (10 %, 20 % and 30 %) and different exposure times. The morphology and chemical structural evolution of electrospun and oxidized nanofibers were studied using field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). FT-IR analysis indicated that the treated nanofibers were effectively oxidized under different contents of oxygen and prolonged plasma exposure times by increasing the peak intensities of polar groups at 1730 and 3400 cm-1 corresponding to C=O stretching band and OH stretching vibration mode, respectively. Additionally, a reduction in the extent of the cyclization reaction is observed with further increase in exposure times and contents of oxygen, which implies lower conversion of C?N bands into C=N ones in the copolymer chain. According to the FE-SEM studies, the surfaces of the treated nanofibers were completely etched after 15 min of treatment due to the existence of strong ion bombardment and a reduction in the average fiber diameters was observed.

Hamideh Mortazavi, S.; Pilehvar, Soheil; Ghoranneviss, Mahmood; Hosseinnejad, M. T.; Zargham, Shamim; Mirarefi, Ali A.; Mirarefi, Amir Y.

2013-11-01

329

Electrochemical enzymatic biosensors using carbon nanofiber nanoelectrode arrays  

Science.gov (United States)

The reduction of electrode size down to nanometers could dramatically enhance detection sensitivity and temporal resolution. Nanoelectrode arrays (NEAs) are of particular interest for ultrasensitive biosensors. Here we report the study of two types of biosensors for measuring enzyme activities using NEAs fabricated with vertically aligned carbon nanofibers (VACNFs). VACNFs of ~100 nm in average diameter and 3-5 ?m in length were grown on conductive substrates as uniform vertical arrays which were then encapsulated in SiO2 matrix leaving only the tips exposed. We demonstrate that such VACNF NEAs can be used in profiling enzyme activities through monitoring the change in electrochemical signals induced by enzymatic reactions to the peptides attached to the VACNF tip. The cleavage of the tetrapeptide with a ferrocene tag by a cancerrelated protease (legumain) was monitored with AC voltammetry. Real-time electrochemical impedance spectroscopy (REIS) was used for fast label-free detection of two reversible processes, i.e. phosphorylation by c-Src tyrosine kinase and dephosphorylation by protein tyrosine phosphatase 1B (PTP1B). The REIS data of phosphorylation were slow and unreliable, but those of dephosphorylation showed large and fast exponential decay due to much higher activity of phosphatase PTP1B. The kinetic data were analyzed with a heterogeneous Michaelis-Menten model to derive the "specificity constant" kcat/Km, which is 8.2x103 M-1s-1 for legumain and (2.1 ± 0.1) x 107 M-1s-1 for phosphatase (PTP1B), well consistent with literature. It is promising to develop VACNF NEA based electrochemical enzymatic biosensors as portable multiplex electronic techniques for rapid cancer diagnosis and treatment monitoring.

Li, Jun; Li, Yi-fen; Swisher, Luxi Z.; Syed, Lateef U.; Prior, Allan M.; Nguyen, Thu A.; Hua, Duy H.

330

Hollow nitrogen-containing core/shell fibrous carbon nanomaterials as support to platinum nanocatalysts and their TEM tomography study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Core/shell nanostructured carbon materials with carbon nanofiber (CNF) as the core and a nitrogen (N)-doped graphitic layer as the shell were synthesized by pyrolysis of CNF/polyaniline (CNF/PANI) composites prepared by in situ polymerization of aniline on CNFs. High-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared and Raman analyses indicated that the PANI shell was carbonized at 900°C. Platinum (Pt) nanoparticles were reduced by formic ...

Zhou, Cuifeng; Liu, Zongwen; Du, Xusheng; Mitchell, David Richard Graham; Mai, Yiu-wing; Yan, Yushan; Ringer, Simon

2012-01-01

331

Electrochemical behavior of TiO2/carbon dual nanofibers  

International Nuclear Information System (INIS)

The charge transfer processes are favored in dual nanofibers composed by TiO2Rutile-Csemigraphitic/Csemigraphitic over other systems such as TiO2Anatase and Rutile-Camorphous/Camorphous and TiO2Rutile-Camorphous, dual and single nanofibers respectively. The study of electrochemical impedance spectroscopy (EIS) shows that the net of nanofibers presented a charge transfer resistance value (Rct) of 3.15 ?. The increased ability of these materials to favor the diffusion of electroactive species in individual nanofibers is that the junction between the n-type semiconductor TiO2 and the semigraphitic material can be of the ohmic kind. Moreover, this observation was supported by cyclic voltammetry (CV) and electrical conductivity studies by two-probe method. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) confirmed the continuity and duality in the morphology of these materials. The effect of heat treatment on crystallinity was evident in the results obtained from the X-Ray Diffraction (XRD) and Selected Area Electron Diffraction (SAED) studies. Due to the electrochemical performance and morphological features of TiO2Rutile-Csemigraphitic/Csemigraphitic dual nanofibers; this novel nanostructured material can be regarded as an excellent candidate for applications such as a base material for electronic devices, photocatalysis, among other similar technologies

332

Carbon functionalized TiO2 nanofibers for high efficiency photocatalysis  

Science.gov (United States)

TiO2 nanofibers (30-50 nm diameter), fabricated by the electro-spinning process, were modified with organo-silane agents via a coupling reaction and were grafted with carbohydrate molecules. The mixture was carbonized to produce a uniform coating of amorphous carbon on the surface of the TiO2 nanofibers. The TiO2@C nanofibers were characterized by high resolution electron microscopy (HRTEM), x-ray diffraction (XRD), x-ray photoelectron (XPS), Fourier transform infrared (FTIR) and UV-vis spectroscopy. The photocatalytic property of the functional TiO2 and carbon nanocomposite was tested via the decomposition of an organic pollutant. The catalytic activity of the covalently functionalized nanocomposite was found to be significantly enhanced in comparison to unfunctionalized composite and pristine TiO2 due to the synergistic effect of nanostructured TiO2 and amorphous carbon bound via covalent bonds. The improvement in performance is due to bandgap modification in the 1D co-axial nanostructure where the anatase phase is bound by nano-carbon, providing a large surface to volume ratio within a confined space. The superior photocatalytic performance and recyclability of 1D TiO2@C nanofiber composites for water purification were established through dye degradation experiments.

Raghava Reddy, Kakarla; Gomes, Vincent G.; Hassan, Mahbub

2014-03-01

333

High-performance lithium storage in nitrogen-enriched carbon nanofiber webs derived from polypyrrole  

International Nuclear Information System (INIS)

Highlights: • N-enriched carbon nanofiber webs are prepared via direct carbonization route with polyporrole as template. • The pyrolysis time plays an important role in N doping level and existing type. • Effect of N-doping on performance of the carbon anode material is investigated. • High reversible capacity of 238 mAh g?1 at 5 A g?1 is attained. -- Abstract: Nitrogen-doped carbon nanofiber webs (N-CNFWs) are prepared by direct pyrolyzation of polypyrrole (PPy) nanofiber webs at 600 °C. The structure and morphology of N-CNFWs are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Raman spectra and elemental analysis. Both the doped N content and the N existing type in carbon, change with the pyrolysis time. As anode material for lithium-ion battery, the N-CNFWs show high capacity and good rate capability. The reversible capacity is up to 668 mAh g?1 at a current density of 0.1 A g?1 and 238 mAh g?1 at 5 A g?1, which can be ascribed to the nanofiber structure and high nitrogen content

334

Magnetron sputtering of platinum nanoparticles onto vertically aligned carbon nanofibers for electrocatalytic oxidation of methanol  

International Nuclear Information System (INIS)

Highlights: ? ? Vertically aligned carbon nanofibers are directly grown on carbon paper. ? Pt nanoparticles deposited onto the carbon nanofibers ensures an effective three-phase boundary and electron pathway. ? The Pt loading plays an important role in influencing the electrochemical activities and Pt utilization effiency. ? The unique structure of Pt/vertically aligned carbon nanofibers has a significant improvement of the Pt utilizaion and show a potential application in direct alcohol fuel cells. - Abstract: The electrochemical activities of Pt-sputtered electrodes based on vertically aligned carbon nanofibers (Pt/VACNFs) directly grown on the carbon paper are investigated. Different Pt loading (0.01 mg cm-2, 0.025 mg cm-2 and 0.05 mg cm-2) electrodes are developed. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that the Pt nanoparticles are homogeneously dispersed on the surface of vertically aligned carbon nanofibers. TEM and X-ray diffraction (XRD) results reveal the Pt nanoparticles diameter increase with increasing Pt loading. The Pt/VACNFs electrodes show good electrochemical active surface area, methanol oxidation peak current density and CO tolerance. The electrochemical catalyst activities weaken as the diameter grows larger. Compared to common electrodes prepared by commercial catalyst in a conventional ink-process, the performance improvement suggests that unique strucement suggests that unique structure of Pt/VACNFs electrode ensures the electronic pathway and Pt nanoparticles exposed to three-phase boundary, which leads to a significant improvement of the Pt utilization and a potential application in direct alcohol fuel cells.

335

Magnetron sputtering of platinum nanoparticles onto vertically aligned carbon nanofibers for electrocatalytic oxidation of methanol  

Energy Technology Data Exchange (ETDEWEB)

Highlights: > Vertically aligned carbon nanofibers are directly grown on carbon paper. > Pt nanoparticles deposited onto the carbon nanofibers ensures an effective three-phase boundary and electron pathway. > The Pt loading plays an important role in influencing the electrochemical activities and Pt utilization effiency. > The unique structure of Pt/vertically aligned carbon nanofibers has a significant improvement of the Pt utilizaion and show a potential application in direct alcohol fuel cells. - Abstract: The electrochemical activities of Pt-sputtered electrodes based on vertically aligned carbon nanofibers (Pt/VACNFs) directly grown on the carbon paper are investigated. Different Pt loading (0.01 mg cm{sup -2}, 0.025 mg cm{sup -2} and 0.05 mg cm{sup -2}) electrodes are developed. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that the Pt nanoparticles are homogeneously dispersed on the surface of vertically aligned carbon nanofibers. TEM and X-ray diffraction (XRD) results reveal the Pt nanoparticles diameter increase with increasing Pt loading. The Pt/VACNFs electrodes show good electrochemical active surface area, methanol oxidation peak current density and CO tolerance. The electrochemical catalyst activities weaken as the diameter grows larger. Compared to common electrodes prepared by commercial catalyst in a conventional ink-process, the performance improvement suggests that unique structure of Pt/VACNFs electrode ensures the electronic pathway and Pt nanoparticles exposed to three-phase boundary, which leads to a significant improvement of the Pt utilization and a potential application in direct alcohol fuel cells.

Zhang Chengxu [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 (China); Department of Modern Physics, University of Science and Technology of China, 230026 (China); Hu Jue, E-mail: hujue@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 (China); Nagatsu, Masaaki [Nanovision Science Section, Graduate School of Science and Technology, Shizuoka University (Japan); Shu Xingsheng [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 (China); Toyoda, Hirotaka [Department of Electrical Engineering and Computer Science, Nagoya University (Japan); Fang Shidong; Meng Yuedong [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 (China)

2011-07-01

336

The importance of interfacial resistance on the thermal behavior of carbon nanofiber/epoxy composites  

Science.gov (United States)

This research addresses the thermal transport in carbon nanofiber (CNF)/epoxy composites via finite element modeling. The effects of nanofiber orientation on thermal transport are investigated through Fourier's Law of heat conduction and through simulation of a high magnitude, short heat pulse. The effect of interface thermal resistance on the effective composite thermal conductivity is also quantified. In addition, a simplified lightning strike simulation is modeled in order to analyze the effect of interfacial thermal resistance on composite behavior when subjected to multiple short heat pulses.

Gardea, Frank; Naraghi, Mohammad; Lagoudas, Dimitris C.

2014-04-01

337

Transparent liquid-crystal-based microlens array using vertically aligned carbon nanofiber electrodes on quartz substrates  

International Nuclear Information System (INIS)

A novel transparent liquid-crystal-based microlens array has been fabricated using an array of vertically aligned multi-wall carbon nanofibers (MWCNFs) on a quartz substrate and its optical characteristics investigated. Electron beam lithography was used for the catalyst patterning on a quartz substrate to grow the MWCNF array of electrodes. The structure of the electrode array was determined through simulation to achieve the best optical performance. Both the patterned catalyst and growth parameters were optimized for optimal MWCNF properties. We report an in-depth optical characterization of these reconfigurable hybrid liquid crystal and nanofiber microlens arrays.

338

Transparent liquid-crystal-based microlens array using vertically aligned carbon nanofiber electrodes on quartz substrates  

Energy Technology Data Exchange (ETDEWEB)

A novel transparent liquid-crystal-based microlens array has been fabricated using an array of vertically aligned multi-wall carbon nanofibers (MWCNFs) on a quartz substrate and its optical characteristics investigated. Electron beam lithography was used for the catalyst patterning on a quartz substrate to grow the MWCNF array of electrodes. The structure of the electrode array was determined through simulation to achieve the best optical performance. Both the patterned catalyst and growth parameters were optimized for optimal MWCNF properties. We report an in-depth optical characterization of these reconfigurable hybrid liquid crystal and nanofiber microlens arrays.

Dai Qing; Rajasekharan, Ranjith; Butt, Haider; Won, Kanghee; Wang Xiaozhi; Wilkinson, Timothy D; Amaragtunga, Gehan, E-mail: qd205@cam.ac.uk [Department of Engineering (Division B), Cape Building, University of Cambridge, 9 J J Thomson Avenue, Cambridge CB3 0FA (United Kingdom)

2011-03-18

339

The Optical Excitation of Zigzag Carbon Nanotubes with Photons Guided in Nanofibers  

CERN Document Server

We consider the excitation of electrons in semiconducting carbon nanotubes by photons from the evanescent field created by a subwavelength-diameter optical fiber. The strongly changing evanescent field of such nanofibers requires dropping the dipole approximation. We show that this leads to novel effects, especially a high dependence of the photon absorption on the relative orientation and geometry of the nanotube-nanofiber setup in the optical and near infrared domain. In particular, we calculate photon absorption probabilities for a straight nanotube and nanofiber depending on their relative angle. Nanotubes orthogonal to the fiber are found to perform much better than parallel nanotubes when they are short. As the nanotube gets longer the absorption of parallel nanotubes is found to exceed the orthogonal nanotubes and approach 100% for extremely long nanotubes. In addition, we show that if the nanotube is wrapped around the fiber in an appropriate way the absorption is enhanced. We find that optical and ne...

Broadfoot, S; Jaksch, D

2011-01-01

340

Characterisation of hydrophobic carbon nanofiber-silica composite film electrodes for redox liquid immobilisation  

International Nuclear Information System (INIS)

Carbon (50-150 nm diameter) nanofibers were embedded into easy to prepare thin films of a hydrophobic sol-gel material and cast onto tin-doped indium oxide substrate electrodes. They promote electron transport and allow efficient electrochemical reactions at solid|liquid and at liquid|liquid interfaces. In order to prevent aggregation of carbon nanofibers silica nanoparticles of 7 nm diameter were added into the sol-gel mixture as a 'surfactant' and homogeneous high surface area films were obtained. Scanning electron microscopy reveals the presence of carbon nanofibers at the electrode surface. The results of voltammetric experiments performed in redox probe-ferrocenedimethanol solution in aqueous electrolyte solution indicate that in the absence of organic phase, incomplete wetting within the hydrophobic film of carbon nanofibers can cause hemispherical diffusion regime typical for ultramicroelectrode like behaviour. The hydrophobic film electrode was modified with two types of redox liquids: pure tert-butylferrocene or dissolved in 2-nitrophenyloctylether as a water-insoluble solvent and immersed in aqueous electrolyte solution. With a nanomole deposit of pure redox liquid, stable voltammetric responses are obtained. The presence of carbon nanofibers embedded in the mesoporous matrix substantially increases the efficiency of the electrode process and stability under voltammetric conditions. Also well-defined response for diluted redox liquids is obtained. From measuuted redox liquids is obtained. From measurements in a range of different aqueous electrolyte media a gradual transition from anion transfer dominated to cation transfer dominated processes is inferred depending on the hydrophilicity of the transferring anion or cation

 
 
 
 
341

Characterisation of hydrophobic carbon nanofiber-silica composite film electrodes for redox liquid immobilisation  

Energy Technology Data Exchange (ETDEWEB)

Carbon (50-150 nm diameter) nanofibers were embedded into easy to prepare thin films of a hydrophobic sol-gel material and cast onto tin-doped indium oxide substrate electrodes. They promote electron transport and allow efficient electrochemical reactions at solid|liquid and at liquid|liquid interfaces. In order to prevent aggregation of carbon nanofibers silica nanoparticles of 7 nm diameter were added into the sol-gel mixture as a 'surfactant' and homogeneous high surface area films were obtained. Scanning electron microscopy reveals the presence of carbon nanofibers at the electrode surface. The results of voltammetric experiments performed in redox probe-ferrocenedimethanol solution in aqueous electrolyte solution indicate that in the absence of organic phase, incomplete wetting within the hydrophobic film of carbon nanofibers can cause hemispherical diffusion regime typical for ultramicroelectrode like behaviour. The hydrophobic film electrode was modified with two types of redox liquids: pure tert-butylferrocene or dissolved in 2-nitrophenyloctylether as a water-insoluble solvent and immersed in aqueous electrolyte solution. With a nanomole deposit of pure redox liquid, stable voltammetric responses are obtained. The presence of carbon nanofibers embedded in the mesoporous matrix substantially increases the efficiency of the electrode process and stability under voltammetric conditions. Also well-defined response for diluted redox liquids is obtained. From measurements in a range of different aqueous electrolyte media a gradual transition from anion transfer dominated to cation transfer dominated processes is inferred depending on the hydrophilicity of the transferring anion or cation.

Niedziolka, Joanna [Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw (Poland); Murphy, Maria A. [Institute of Polymer Technology and Materials Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom); Marken, Frank [Department of Chemistry, University of Bath, Bath BA2 7AY (United Kingdom); Opallo, Marcin [Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw (Poland)]. E-mail: mopallo@ichf.edu.pl

2006-08-15

342

DC Plasma Synthesis of Vertically Aligned Carbon Nanofibers for Biointerfacing  

Science.gov (United States)

Vertically aligned carbon nanofibers (VACNFs) are a class of materials whose nanoscale dimensions and physical properties makes them uniquely suitable as functional elements in many applications for biodetection and biointerfacing on a cellular level. Control of VACNF synthesis by catalytic plasma enhanced chemical vapor deposition (PECVD) presents many challenges in integration into devices and structures designed for biointerfacing, such as transparent or flexible substrates. This dissertation addresses ways to overcome many of these issues in addition to deepening the fundamental understanding of nano-synthesis in catalytic PECVD. First, a survey of the field of VACNF synthesis and biointerfacing is presented, identifying the present challenges and greatest experimental applications. It is followed by experimental observations that elucidate the underlying mechanism to fiber alignment during synthesis, a critical step for deterministic control of fiber growth. Using a grid of electrodes patterned by photolithography on an insulating substrate, it was found that the alignment of the fibers is controlled by the anisotropic etching provided by ions during dc-PECVD synthesis. The VACNFs that have been utilized for many cellular interfacing experiments have unique mechanical and fluorescent properties due to a SiNx coating. The mechanism for SiNx deposition to VACNF sidewalls during synthesis is explored in addition to a detailed study of the optical properties of the coating. To explain the optical properties of this coating it is proposed that the source of photoluminescence for the SiNx coated VACNFs is quantum confinement effects due to the presence of silicon nanoclusters embedded in a Si3N4 matrix. These luminescent fibers have proven useful as registry markers in cell impalefection studies. To realize VACNF arrays used as an inflatable angioplasty balloon with embedded fibers to deliver drugs across the blood-brain barrier, a method for transferring fibers to flexible polydimethylesiloxane (PDMS) is presented. A process has been developed that involves synthesizing fibers on aluminum, followed by spin coating a thin layer of PDMS and then dissolving the underlying aluminum with KOH. Finally, a method of fiber synthesis using just air and acetone as the process gases is presented, enabling the possibility of inatmosphere, large scale VACNF synthesis. It is envisioned that these advancements should assist the viability of large scale VACNF related technologies and will help to bridge the gap between experimental applications and industrial adoption.

Pearce, Ryan Christopher

343

Durability of Carbon Nanofiber (CNF) & Carbon Nanotube (CNT) as Catalyst Support for Proton Exchange Membrane Fuel Cells  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Durability issues have recently been given much attention in Proton Exchange Membrane Fuel Cell (PEMFC) research. It gives fundamental definition for cell life time, capital cost, system stability and technique reliability. Loss of catalyst surface area due to corrosion of supporting material (normally carbon black) is one of the essential degradation mechanisms during cell operation. In this work, durability of Carbon Nanofibers (CNF) & Carbon Nanotubes (CNT) as alternative platinum catalyst...

Andersen, Shuang Ma; Borghei, Maryam; Lund, Peter; Elina, Yli-rantala; Pasanen, Antti; Kauppinen, Esko; Ruiz, Virginia; Kauranen, Pertti; Skou, Eivind Morten

2013-01-01

344

Microwave absorption properties of helical carbon nanofibers-coated carbon fibers  

Directory of Open Access Journals (Sweden)

Full Text Available Helical carbon nanofibers (HCNFs coated-carbon fibers (CFs were fabricated by catalytic chemical vapor deposition method. TEM and Raman spectroscopy characterizations indicate that the graphitic layers of the HCNFs changed from disorder to order after high temperature annealing. The electromagnetic parameters and microwave absorption properties were measured at 2–18 GHz. The maximum reflection loss is 32 dB at 9 GHz and the widest bandwidth under ?10 dB is 9.8 GHz from 8.2 to 18 GHz for the unannealed HCNFs coated-CFs composite with 2.5 mm in thickness, suggesting that HCNFs coated-CFs should have potential applications in high performance microwave absorption materials.

Lei Liu

2013-08-01

345

High performance PEMFCs using ultra-low platinum loading membrane electrode assembly based on gradient carbon nanotube/nanofiber supported electrodes  

Energy Technology Data Exchange (ETDEWEB)

This paper reported on a study that explored the feasibility of using buckypaper (BP) as a catalyst support for proton exchange membrane fuel cell (PEMFC). BP is a free-standing carbon nanotube (CNT)/carbon nanofiber (CNF) composite paper with high catalyst efficiency because its unique microstructure ensures a pathway for electrons. Rather than being uniformly distributed through the entire buckypaper, platinum (Pt) is electrodeposited on the most accessible sites in the BP and is not covered by either CNT/CNF or binder materials. The open pores can be covered by Nafion electrolytes to maximize the 3-phase boundary where the electrochemical reaction takes place. The BP support was found to be corrosion resistant, resulting in improved catalyst durability. The microstructure of buckypaper, notably its porosity, pore size and thickness, can be tailored by using nanotubes of different diameters and lengths to further improve the cell performance. Double-layered buckypaper was used in this study to achieve a microstructure-optimized catalyst layer with gradient pore size distribution and Pt distribution. In this structure, the top layer containing single-walled carbon nanotubes (SWNTs) and CNFs had small porosity and average pore size compared to the bottom layer. The Pt nanoparticles were distributed primarily in the top layer after electrochemical deposition. The Pt abundant layer contacting the electrolyte membrane in a membrane electrode assembly (MEA) facilitates the proton transfer and gas diffusion in the catalyst layer resulting in improved cell performance. The electrochemical performance of the Pt/BP electrocatalyst as a cathode catalyst layer was determined. It was concluded that the superior performance of double-layered buckypaper based electrodes makes it a promising catalyst support for application in PEMFCs. 3 refs., 2 figs.

Zheng, J.P. [Florida A and M Univ.Florida State Univ. College of Engineering, Tallahassee, FL (United States). Dept. of Electrical and Computer Engineering; Florida State Univ., Tallahassee, FL (United States). Center for Advanced Power Systems; Zhu, W. [Florida A and M Univ.-Florida State Univ. College of Engineering, Tallahassee, FL (United States). Dept. of Electrical and Computer Engineering; Florida A and M Univ.-Florida State Univ. College of Engineering, Tallahassee, FL (United States). Dept. of Industrial and Manufacturing Engineering; Liang, R. [Florida A and M Univ.-Florida State Univ. College of Engineering, Tallahassee, FL (United States). Dept. of Industrial and Manufacturing Engineering; Florida State Univ., Tallahassee, FL (United States). High-Performance Materials Inst.

2010-07-01

346

Controlling the optimum surfactants concentrations for dispersing carbon nanofibers in aqueous solution  

Science.gov (United States)

As a new nano-scale functional material, it is necessary to achieve a uniform distribution in the composites for gaining the CNFs' excellent reinforcing effect. In this paper, CNFs were purified by the method of high temperature annealing treatment. Six surfactants, methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), sodium dodecyl sulfate (SDS), dodecylamine (DDA), N, N-dimethyl formamide (DMF) and cetyltrimethyl ammonium bromide (CTAB) were used individually and combinatorially in a certain concentration to disperse the CNFs in aqueous solution. To achieve a good dispersion of the CNFs, a method utilizing ultrasonic processing was employed. The CNFs treated by the method of high temperature annealing treatment were characterized by differential thermal analysis (DTA) and thermogravimetry analysis (TGA), and the ultrasonication-driven dispersion of CNFs in aqueous solutions were monitored by UVvis spectroscopy and transmission electron microscopy (TEM). The experiments reveal that the method of high temperature annealing treatment purified the CNFs and the maximum achievable dispersion of CNFs corresponds to the maximum UV absorbance of the solution. All results show that the surfactants mixture of MC and SDS in a certain concentration of 0.4 and 2.0 g/L has the maximum dispersion effect on CNFs in aqueous solution, the optimum concentration ratio of MC, SDS, and CNFs was 2: 10: 1.

Wang, Bao-Min; Yuan, Zhang; Guo, Zhi-Qiang; Ma, Hai-Nan; Lai, Chuan Fook

2013-12-01

347

Carbon nanofiber mesoporous films: efficient platforms for bio-hydrogen oxidation in biofuel cells.  

Science.gov (United States)

The discovery of oxygen and carbon monoxide tolerant [NiFe] hydrogenases was the first necessary step toward the definition of a novel generation of hydrogen fed biofuel cells. The next important milestone is now to identify and overcome bottlenecks limiting the current densities, hence the power densities. In the present work we report for the first time a comprehensive study of herringbone carbon nanofiber mesoporous films as platforms for enhanced biooxidation of hydrogen. The 3D network allows mediatorless hydrogen oxidation by the membrane-bound hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus. We investigate the key physico-chemical parameters that enhance the catalytic efficiency, including surface chemistry and hierarchical porosity of the biohybrid film. We also emphasize that the catalytic current is limited by mass transport inside the mesoporous carbon nanofiber film. Provided hydrogen is supplied inside the carbon film, the combination of the hierarchical porosity of the carbon nanofiber film with the hydrophobicity of the treated carbon material results in very high efficiency of the bioelectrode. By optimization of the whole procedure, current densities as high as 4.5 mA cm(-2) are reached with a turnover frequency of 48 s(-1). This current density is almost 100 times higher than when hydrogenase is simply adsorbed at a bare graphite electrode, and more than 5 times higher than the average of the previous reported current densities at carbon nanotube modified electrodes, suggesting that carbon nanofibers can be efficiently used in future sustainable H2/O2 biofuel cells. PMID:24296569

de Poulpiquet, Anne; Marques-Knopf, Helena; Wernert, Véronique; Giudici-Orticoni, Marie Thérèse; Gadiou, Roger; Lojou, Elisabeth

2014-01-28

348

Effect of carbon nanofiber addition in the mechanical properties and durability of cementitious materials  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper reports on recent work that is directed at studying the changes in the mechanical properties of Portland cement based mortars due to the addition of carbon nanofiber (CNF). Both flexural and compression strength has been determined and related to the CNF addition to the mix, to the curing time and to the porosity and density of the matrix. Also, corrosion of embedded steel rebars in CNF cement pastes exposed to carbonation and chloride attacks has been investigated. The increase in...

Galao, O.; Zornoza, E.; Baeza, F. J.; Bernabeu, A.; Garce?s, P.

2012-01-01

349

Development of Electro-Mechanical Spinning for Controlled Deposition of Carbon Nanofibers  

Science.gov (United States)

In the past few decades the fields of nanotechnology and miniaturized devices had an exponentially growth of interest in academic and research environment, leading to breakthroughs discoveries that are envisioned to have a profound impact on our economy and society in the near future. Recently, the focus is moving toward the development of technologies that enable the production of micro- /nano-devices on a larger scale and at lower costs. Among the different micro- /nano-devices manufacturing challenges, in this dissertation the aim is to reliably fabricate suspend carbon micro- /nano-fibers between two carbon electrode walls in a way that can be mass produced at relatively low cost. The first part of this thesis provides an in depth overview of current methods used for the fabrication of carbon based micro devices (C-MEMS) and of electrospinning, a manufacturing technology that emerges as a simple and inexpensive approach to produce nanofibers. Electro-Mechanical Spinning (EMS) has been developed from electrospinning and optimized for the production of suspended carbon nanofibers, aiming to achieve greater deposition control at the single nanofiber level, while maintaining the low cost of electrospinning. After the successful development of EMS, the so fabricated carbon micro- /nano-fibers have been characterized, first from the electrical point of view, then from the mechanical one. The electrical characterization involves conductivity measurements of fibers with respect of different and controllable manufacturing processes steps. Variations of those manufacturing parameters have been proven to be capable of tailoring the carbon structure and, therefore, the conductivity of the fibers within a desired range. Further investigation regarding the electrical properties was also conducted to prevent (or control) current induced fiber breakdown. Finally, the Young's modulus of those fibers was investigated and observed to be dependent on the fibers thickness. Similarly to conductivity, variations in Young's modulus are also related to formation of a different carbon structure when fibers diameter is below certain values. In conclusion, appropriate combinations of EMS and C-MEMS processes were proven to be capable of fabricating controllable suspended carbon nanofibers with tuned conductivity and Young's modulus properties.

Canton, Giulia

350

Photocatalytic Oxidation of Volatile Organic Compounds Over Electrospun Activated TIO2/CARBON Nanofiber Composite  

Science.gov (United States)

In this study, TiO2/PAN-based fibers were prepared by electrospinning a composite solution containing both the desirable contents of TiO2 and a 10 wt. % PAN polymer solution dissolved in N, N-dimethylformamide. The TiO2 loaded electrospun PAN nanofibers were then carbonized at 1000 °C in N2 atmosphere furnace after stabilization at 230 °C in air. Then CNF/TiO2 nanofibers were oxidized at 450 °C in air. The morphology and structure of the TiO2-embeded carbon nanofibers were investigated by SEM and Raman spectroscopy. Specific surface area was determined using BET equation from N2 adsorption analysis. Photocatalytic tests were conducted in a UV illuminated set-up specialized for the filters using ethanol vapor. The results have shown that ethanol vapor was efficiently degraded on TiO2/CNF composite nanofiber mat under UV illumination. The aim of this study was to further investigate the feasibility of TiO2/ACF for practical indoor air purification.

Gholamvand, Zahra; Aboutalebi, Seyed Hamed; Keyanpour-Rad, Mansoor

351

Study on glow discharge effects on catalyst films for growing aligned carbon nanofibers in negative bias-enhanced hot filament chemical vapor deposition system  

Energy Technology Data Exchange (ETDEWEB)

Aligned carbon nanofibers (ACNFs) were grown on silicon substrates coated with NiFe catalyst films by negative bias-enhanced hot filament chemical vapor deposition (CVD). The growth and structure of the aligned carbon nanofibers were investigated by scanning electron microscopy (SEM). The results indicate that the aligned carbon nanofibers could be synthesized after the glow discharge appears when the negative bias is higher than a certain value, while they are bent if the glow discharge does not appear. Furthermore, the diameters of the aligned carbon nanofibers are reduced and their lengths are increased with increasing the negative bias. It is shown that the glow discharge resulting from the negative bias plays an important role in the growth of aligned carbon nanofibers. Here, the effects of the glow discharge on the growth and structure of the aligned carbon nanofibers are discussed.

Wang, B.B. [College of Applied Mathematics and Physics, Beijing University of Technology, No. 100, Pingleyuan, Chaoyang District, Beijing 100022 (China) and Key Laboratory of Advanced Functional Materials of China Education Ministry, Beijing University of Technology, No.100, Pingleyuan, Chaoyang District (China)]. E-mail: bibenw@bjut.edu.cn; Lee, Soonil [Department of Molecular Science and Technology, Ajou University, Suwon 442-749 (Korea, Republic of); Yan, H. [Key Laboratory of Advanced Functional Materials of China Education Ministry, Beijing University of Technology, No.100, Pingleyuan, Chaoyang District (China); Hou, B.H. [College of Applied Mathematics and Physics, Beijing University of Technology, No. 100, Pingleyuan, Chaoyang District, Beijing 100022 (China); Choi, Seungho [Department of Molecular Science and Technology, Ajou University, Suwon 442-749 (Korea, Republic of)

2005-03-01

352

Fe3O4/carbon composite nanofiber absorber with enhanced microwave absorption performance  

International Nuclear Information System (INIS)

Highlights: ? PAN/AAI/DMF solutions for electrospinning. ? Fe3O4/carbon composite nanofibers as microwave absorbers. ? Microwave absorption performance has been much enhanced than pure carbon naonfibers. ? Microwave absorption mechanisms have been discussed as a key point. - Abstract: Fe3O4/carbon composite nanofibers were prepared by electrospinning polyacrylonitrile (PAN)/acetyl acetone iron (AAI)/dimethyl formamide (DMF) solution, followed by stabilization and carbonization. SEM and TEM observations reveal that the fibers are lengthy and uniform, and are loaded with well-distributed Fe3O4 nanoparticles, which are evidenced by XRD. Electrical and magnetic properties of the samples were studied to show the effect of enhancement of electrical conductivity and magnetic hysteresis performance. Finally, the permittivity and permeability parameters were measured by a vector network analyzer, and the reflectivity loss was calculated based on Transmission Line Theory. Results show that Fe3O4/C composite nanofibers exhibit enhanced properties of microwave absorption as compared to those of pure carbon nanofibers by: decreasing reflectivity loss values; widening absorption width and improving performance in low frequency (2–5 GHz) absorption. Absorption properties can be tuned by changing AAI content, carbonization temperature, composite fiber/paraffin ratio and coating thicknessffin ratio and coating thickness. It is shown that with coating thickness of 5 mm and fiber/paraffin ratio of 5 wt.%, the bandwidth for reflection loss under ?5 dB can reach a maximum of 12–13 GHz in the range of 2–18 GHz, accompanying with a minimum reflection loss of ?40 to ?45 dB, and preferred low frequency band absorption can also be obtained. The mechanisms for the enhanced absorption performance were briefly discussed. It is supposed that this kind of composite material is promising for resolving the problems of weak absorption in the low frequency range and narrow bandwidth absorption.

353

Preparation of flexible zinc oxide/carbon nanofiber webs for mid-temperature desulfurization  

Science.gov (United States)

Polyacrylonitrile (PAN) derived carbon nanofiber (CNF) webs loaded with zinc oxide (ZnO) were synthesized using electrospinning and heat treatment at 600 °C. Uniformly dispersed ZnO nanoparticles, clarified by X-ray diffraction and scanning electron microscopy, were observed on the surface of the nanofiber composites containing 13.6-29.5 wt% of ZnO. The further addition of ZnO up to 34.2 wt% caused agglomeration with a size of 50-80 nm. Higher ZnO contents led the concentrated ZnO nanoparticles on the surface of the nanofibers rather than uniform dispersion along the cross-section of the fiber. The flexible composite webs were crushed and tested for hydrogen sulfide (H2S) adsorption at 300 °C. Breakthrough experiments with the ZnO/CNF composite containing 25.7 wt% of ZnO for H2S adsorption showed three times higher ZnO utilization efficiency compared to pure ZnO nano powders, attributed to chemisorption of the larger surface area of well dispersed ZnO particles on nanofibers and physical adsorption of CNF.

Kim, Soojung; Bajaj, Bharat; Byun, Chang Ki; Kwon, Soon-Jin; Joh, Han-Ik; Yi, Kwang Bok; Lee, Sungho

2014-11-01

354

Catalytic growth of macroscopic carbon nanofiber bodies with high bulk density and high mechanical strength  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanofibers (CNF) are non-microporous graphitic materials with a high surface area (100–200 m2/g), high purity and tunable surface chemistry. Therefore the material has a high potential for use as catalyst support. However, in some instances it is claimed that the low density and low mechanical strength of the macroscopic particles hamper their application. In this study we show that the bulk density and mechanical strength of CNF bodies can be tuned to values comparable to t...

Lee, M. K.; Dillen, A. J.; Geus, John W.; Jong, K. P.; Bitter, J. H.

2006-01-01

355

Carbon Nanofibers enhance the Fracture toughness and Fatigue Performance of a Structural Epoxy system  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract This study investigates the monotonic and dynamic fracture characteristics of a discontinuous fiber reinforced polymer matrix. Specifically, small amounts (0-1 wt%) of a helical-ribbon carbon nanofiber (CNF) were added to an amine cured epoxy system. The resulting nanocomposites were tested to failure in two modes of testing; Mode I fracture toughness and constant amplitude of stress tension-tension fatigue. Fracture toughness testing revealed that adding 0.5 and 1.0 wt% C...

2010-01-01

356

A New Strategy to Pretreat Carbon Nanofiber and Its Application in Determination of Dopamine  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A novel sonochemical process, using hydrogen peroxide in a laboratory ultrasonic bath, was employed to pretreat the carbon nanofiber (CNF) for creating oxygen-rich groups on the surface of CNF. After the sonochemical process, the CNF showed good hydrophilicity and high electrochemical activity. Compared to normal pretreatment process, this sonochemical process is timesaving and effective for dispersion and functionalization of CNF. The resulting CNF showed high catalytic activity toward the o...

Dong Liu; Yang Liu; Haoqing Hou; Tianyan You

2010-01-01

357

Control of spatial cell attachment on carbon nanofiber patterns on polycarbonate urethane  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A highly aligned pattern of carbon nanofibers (CNF) on polycarbonate urethane (PCU) for tissue engineering applications was created by placing a CNF–ethanol solution in 30?m width copper grid grooves on top of PCU. In vitro results provided the first evidence that fibroblasts and vascular smooth muscle cells selectively adhered to the PCU regions. However, endothelial cells did not display a preference for adhesion to the CNF compared with PCU regions. Previous studies have shown selective...

Bajaj, Piyush; Khang, Dongwoo; Webster, Thomas J.

2006-01-01

358

Size-selectivity and anomalous subdiffusion of nanoparticles through carbon nanofiber-based membranes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A simulation is presented here that serves the dual functions of generating a nanoporous membrane replica and executing the Brownian motion of nanoparticles through the virtual membrane. Specifically, the concentration profile of a dilute solution of fluorescent particles in a stochastic and SiO2-coated carbon nanofiber (oxCNF), nanoporous membrane was simulated. The quality of the simulated profile was determined by comparing the results with experimental concentration profiles. The experime...

Fowlkes, J. D.; Fletcher, B. L.; Retterer, S. T.; Melechko, A. V.; Simpson, M. L.; Doktycz, M. J.

2008-01-01

359

Electrochemical properties of oxygenated cup-stacked carbon nanofiber-modified electrodes.  

Science.gov (United States)

Oxygenated cup-stacked carbon nanofibers (CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were investigated as electrode materials by using typical redox species in electrochemistry, Fe(2+/3+), [Fe(CN)6](3-/4-), and dopamine. The electron transfer rates for these redox species at oxygenated CSCNF electrodes were higher than those at edge-oriented pyrolytic graphite and glassy carbon electrodes. In addition, the oxygen-containing functional groups also contributed to the electron transfer kinetics at the oxygenated CSCNF surface. The electron transfer rate of Fe(2+/3+) was accelerated and that of [Fe(CN)6](3-/4-) was decelerated by the oxygen-containing groups, mainly due to the electrostatic attraction and repulsion, respectively. The electrochemical reaction selectivities at the oxygenated CSCNF surface were tunable by controlling the amount of nanofibers and the oxygen/carbon atomic ratio at the nanofiber surface. Thus, the oxygenated CSCNFs would be useful electrode materials for energy-conversion, biosensing, and other electrochemical devices. PMID:24817367

Ko, Seongjae; Tatsuma, Tetsu; Sakoda, Akiyoshi; Sakai, Yasuyuki; Komori, Kikuo

2014-06-28

360

Effect of Carbon Nanofiber Heat Treatment on Physical Properties of Polymeric Nanocomposites—Part I  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The definition of a nanocomposite material has broadened significantly to encompass a large variety of systems made of dissimilar components and mixed at the nanometer scale. The properties of nanocomposite materials also depend on the morphology, crystallinity, and interfacial characteristics of the individual constituents. In the current work, vapor-grown carbon nanofibers were subjected to varying heat-treatment temperatures. The strength of adhesion between the nanofiber and an epoxy (the...

Emel Yildiz; Matthew Matzek; William Fox; Khalid Lafdi

2008-01-01

 
 
 
 
361

The influence of the dispersion method on the electrical properties of vapor-grown carbon nanofiber/epoxy composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract The influence of the dispersion of vapor-grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/Epoxy composites has been studied. A homogenous dispersion of the VGCNF does not imply better electrical properties. In fact, it is demonstrated that the most simple of the tested dispersion methods results in higher conductivity, since the presence of well-distributed nanofiber clusters appears to be a key factor for increasing composite conductivity. PACS:...

Covas José; van Hattum Ferrie; Simoes Ricardo; Klosterman Donald; Cardoso Paulo; Silva Jaime; Lanceros-Mendez Senentxu

2011-01-01

362

Simple synthesis of mesoporous carbon nanofibers with hierarchical nanostructure for ultrahigh lithium storage.  

Science.gov (United States)

In this study, a simple and reproducible synthesis strategy was developed to fabricate mesoporous carbon nanofibers (MCNFs) by using dual hard templates, a porous anodic aluminum oxide (AAO) membrane, and colloidal silica (Ludox TM-40). By using commercial templates, and removing AAO and the silica simultaneously, the synthesis procedures for MCNFs are greatly simplified without the need for separate preparation or the removal of templates in sequence. With phenol resin as a carbon precursor, the as-prepared MCNFs material reveals not only high surface area and mesoporous volume but also hierarchical nanostructure composed of hollow macrochannels derived from the AAO template, large mesopores (ca. 22 nm) from the removal of silica particles and micropores from the carbonization of phenol resin. Such unique surface and structural characteristics could provide a large quantity of active sites for Li storage and facilitate fast mass transport. Moreover, a one-dimensional (1D) carbon nanofiber (CNF) nanostructure favors fast electron transfer. The as-prepared MCNF anode demonstrates ultrahigh lithium storage capacity particularly at high rates, which is much higher than that reported for the commercial graphite and also significantly higher than other nanostructured carbon materials, such as ordered mesoporous carbon CMK-3 and ordered multimodal porous carbon (OMPC). PMID:24490802

Xing, Yalan; Wang, Yanjie; Zhou, Chungen; Zhang, Shichao; Fang, Baizeng

2014-02-26

363

Cyclability study of silicon-carbon composite anodes for lithium-ion batteries using electrochemical impedance spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Research highlights: {yields} Silicon-carbon anode materials for Li-ion batteries were synthesized. {yields} Carbonization and annealing processes were used in electrode preparation. {yields} Capacity fading mechanism was investigated by electrochemical impedance spectroscopy. {yields} Impedance evolution revealed better stability of the carbonized anode material. - Abstract: The effects of carbonization process and carbon nanofiber/nanotube additives on the cycling stability of silicon-carbon composite anodes were investigated by monitoring the impedance evolution during charge/discharge cycles with electrochemical impedance spectroscopy (EIS). Three types of Si-C anodes were investigated: the first type consisted of Si nanoparticles incorporated into a network of carbon nanofibers (CNFs) and multi-walled carbon nanotubes (MWNTs), with annealed polymer binder. The second type of Si-C anodes was prepared by further heat treatment of the first Si-C anodes to carbonize the polymer binder. The third Si-C anode was as same as the second one except no CNFs and MWNTs being added. Impedance analysis revealed that the carbonization process stabilized the Si-C anode structure and decreased the charge transfer resistance, thus improving the cycling stability. On the other hand, although the MWNTs/CNFs additives could enhance the electronic conductivity of the Si-C anodes, the induced inhomogeneous structure decreased the integrity of the electrode, resulting in a poor long term cycling stability.

Guo Juchen; Sun, Ann; Chen Xilin [Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742 (United States); Wang Chunsheng, E-mail: cswang@umd.ed [Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742 (United States); Manivannan, Ayyakkannu [US Department of Energy, National Energy Technology Laboratory, Morgantown, WV 26507 (United States)

2011-04-15

364

Electrospun La0.8Sr0.2MnO3 nanofibers for a high-temperature electrochemical carbon monoxide sensor  

International Nuclear Information System (INIS)

Lanthanum strontium manganite (La0.8Sr0.2MnO3, LSM) nanofibers have been synthesized by the electrospinning method. The electrospun nanofibers are intact without morphological and structural changes after annealing at 1050?°C. The LSM nanofibers are employed as the sensing electrode of an electrochemical sensor with yttria-stabilized zirconia (YSZ) electrolyte for carbon monoxide detection at high temperatures over 500?°C. The electrospun nanofibers form a porous network electrode, which provides a continuous pathway for charge transport. In addition, the nanofibers possess a higher specific surface area than conventional micron-sized powders. As a result, the nanofiber electrode exhibits a higher electromotive force and better electro-catalytic activity toward CO oxidation. Therefore, the sensor with the nanofiber electrode shows a higher sensitivity, lower limit of detection and faster response to CO than a sensor with a powder electrode. (paper)

365

Aerosynthesis: Growths of Vertically Aligned Carbon Nanofibers with Air DC Plasma  

Energy Technology Data Exchange (ETDEWEB)

Vertically aligned carbon nanofibers (VACNF) have been synthesized in a mixture of acetone and air using catalytic DC plasma enhanced chemical vapor deposition. Typically, ammonia or hydrogen is used as etchant gas in the mixture to remove carbon that otherwise passivates the catalyst surface and impedes growth. Our demonstration of using air as the etchant gas opens up a possibility that ion etching could be sufficient to maintain the catalytic activity state during synthesis. It also demonstrates the path toward growing VACNFs in open atmosphere.

Kodumagulla, A [North Carolina State University; Varanasi, V [North Carolina State University; Pearce, Ryan [North Carolina State University; Wu, W-C [North Carolina State University; Hensley, Dale K [ORNL; Tracy, Joseph B [North Carolina State University; McKnight, Timothy E [ORNL; Melechko, Anatoli [North Carolina State University

2014-01-01

366

Controlling SEI Formation on SnSb-Porous Carbon Nanofibers for Improved Na Ion Storage  

Energy Technology Data Exchange (ETDEWEB)

Porous carbon nanofiber (CNF)-supported tin-antimony (SnSb) alloys is synthesized and applied as sodium ion battery anode. The chemistry and morphology of the solid electrolyte interphase (SEI) film and its correlation with the electrode performance are studied. The addition of fluoroethylene carbonate (FEC) in electrolyte significantly reduces electrolyte decomposition and creates a very thin and uniform SEI layer on the cycled electrode surface which could promote the kinetics of Na-ion migration/transportation, leading to excellent electrochemical performance.

Ji, Liwen; Gu, Meng; Shao, Yuyan; Li, Xiaolin; Engelhard, Mark H.; Arey, Bruce W.; Wang, Wei; Nie, Zimin; Xiao, Jie; Wang, Chong M.; Zhang, Jiguang; Liu, Jun

2014-05-14

367

Characterization of poly(methyl methacrylate) and thermoplastic polyurethane-carbon nanofiber composites produced by chaotic mixing  

Science.gov (United States)

Chaotic mixing is a novel mixing technique offering high mixing efficiency even under mild shearing conditions. In this work, chaotic mixing was used to prepare composites of carbon nanofibers and two thermoplastic polymers---poly (methyl methacrylate) (PMMA) and thermoplastic polyurethanes (TPU)---and their electrical, mechanical, and thermal properties were evaluated. The TPU systems were based on the reaction products of 4,4'-diphenylmethane diisocyanate, (MDI), soft segment polyol, and 1,4-butanediol as chain extender. Soft segment polyols in the form of poly(propylene glycol) (PPG), and poly(epsilon-caprolactone)diol (PCL) were used to obtain respectively amorphous and crystalline soft segments. Of these, the TPU system based on crystalline soft segment exhibited shape memory effects. Both, as-received untreated carbon nanofibers (CNF) with a very low amount of atomic oxygen on the surface, and oxidized carbon nanofibers (CNFOX) were used. CNFOX was also modified by esterifying with PPG to produce a third type of carbon nanofiber named CNFOL. These carbon nanofibers were examined by X-ray photoelectron spectroscopy to determine the elemental composition of the surface, and by scanning electron microscopy and transmission electron microscopy to determine the surface morphology.

Jiminez, Guillermo A.

368

A high performance silicon/carbon composite anode with carbon nanofiber for lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with carbon nanofiber (CNF) was examined as an anode for lithium-ion batteries. CNF was incorporated into the composite by two methods; direct mixing of CNF with the nano-Si powder coated with carbon produced by pyrolysis of PVC (referred to as Si/C/CNF-1) and mixing of CNF, nano-Si powder, and PVC with subsequent firing (referred to as Si/C/CNF-2). The external Brunauer-Emmett-Teller (BET) surface area of Si/C/CNF-1 was comparable to that of Si/C/CNF-2. The micropore BET surface area of Si/C/CNF-2 (73.86 m{sup 2} g{sup -1}) was extremely higher than that of Si/C/CNF-1 (0.74 m{sup 2} g{sup -1}). The composites prepared by both methods exhibited high capacity and excellent cycling stability for lithium insertion and extraction. A capacity of more than 900 mA h g{sup -1} was maintained after 30 cycles. The coulombic efficiency of the first cycle for Si/C/CNF-1 was as low as 53%, compared with 73% for Si/C/CNF-2. Impedance analysis of cells containing these anode materials suggested that the charge transfer resistance for Si/C/CNF-1 was not changed by cycling, but that Si/C/CNF-2 had high charge transfer resistance after cycling. A composite electrode prepared by mixing Si/C/CNF-2 and CNF exhibited a high reversible capacity at high rate, excellent cycling performance, and a high coulombic efficiency during the first lithium insertion and extraction cycles. (author)

Si, Q.; Hanai, K.; Ichikawa, T.; Hirano, A.; Imanishi, N.; Takeda, Y.; Yamamoto, O. [Department of Chemistry, Faculty of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507 (Japan)

2010-03-15

369

Effect of Carbon Nanofiber-Matrix Adhesion on Polymeric Nanocomposite Properties—Part II  

Directory of Open Access Journals (Sweden)

Full Text Available A successful integration of two independent phases with good adhesion is imperative for effective translation of superior carbon nanofiber filler properties into a physically superior carbon nanocomposite. Carbon nanofibers were subjected to electrochemical oxidation in 0.1 M nitric acid for varying times. The strength of adhesion between the nanofiber and an epoxy matrix was characterized by flexural strength and modulus. The surface functional groups formed and their concentration of nanofibers showed a dependence on the degree of oxidation. The addition of chemical functional groups on the nanofiber surface allows them to physically and chemically adhere to the continuous resin matrix. The chemical interaction with the continuous epoxy matrix results in the creation of an interphase region. The ability to chemically and physically interact with the epoxy region is beneficial to the mechanical properties of a carbon nanocomposite. A tailored degree of surface functionalization was found to increase adhesion to the matrix and increase flexural modulus.

Khalid Lafdi

2008-01-01

370

Optical excitation of zigzag carbon nanotubes with photons guided in nanofibers  

Science.gov (United States)

We consider the excitation of electrons in semiconducting carbon nanotubes by photons from the evanescent field created by a subwavelength-diameter optical fiber. The strongly changing evanescent field of such nanofibers requires dropping the dipole approximation. We show that this leads to novel effects, especially a high dependence of the photon absorption on the relative orientation and geometry of the nanotube-nanofiber setup in the optical and near-infrared domain. In particular, we calculate photon absorption probabilities for a straight nanotube and nanofiber depending on their relative angle. Nanotubes orthogonal to the fiber are found to perform much better than parallel nanotubes when they are short. As the nanotube gets longer the absorption of parallel nanotubes is found to exceed the orthogonal nanotubes and approach 100% for extremely long nanotubes. In addition, we show that if the nanotube is wrapped around the fiber in an appropriate way the absorption is enhanced. We find that optical and near-infrared photons could be converted to excitations with efficiencies that may exceed 90%. This may provide opportunities for future photodetectors and we discuss possible setups.

Broadfoot, S.; Dorner, U.; Jaksch, D.

2012-05-01

371

Immobilization and release strategies for DNA delivery using carbon nanofiber arrays and self-assembled monolayers  

Energy Technology Data Exchange (ETDEWEB)

We report a strategy for immobilizing dsDNA (double-stranded DNA) onto vertically aligned carbon nanofibers and subsequently releasing this dsDNA following penetration and residence of these high aspect ratio structures within cells. Gold-coated nanofiber arrays were modified with self-assembled monolayers (SAM) to which reporter dsDNA was covalently and end-specifically bound with or without a cleavable linker. The DNA-modified nanofiber arrays were then used to impale, and thereby transfect, Chinese hamster lung epithelial cells. This mechanical approach enables the transport of bound ligands directly into the cell nucleus and consequently bypasses extracellular and cytosolic degradation. Statistically significant differences were observed between the expression levels from immobilized and releasable DNA, and these are discussed in relation to the distinct accessibility and mode of action of glutathione, an intracellular reducing agent responsible for releasing the bound dsDNA. These results prove for the first time that an end-specifically and covalently SAM-bound DNA can be expressed in cells. They further demonstrate how the choice of immobilization and release methods can impact expression of nanoparticle delivered DNA.

Peckys, Diana B [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6030 (United States); Melechko, Anatoli V [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 (United States); Simpson, Michael L [University of Tennessee in Knoxville, Knoxville, TN 37996-2200 (United States); McKnight, Timothy E [Measurement Science and Systems Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6006 (United States)], E-mail: peckysdb@ornl.gov

2009-04-08

372

Immobilization and release strategies for DNA delivery using carbon nanofiber arrays and self-assembled monolayers  

Science.gov (United States)

We report a strategy for immobilizing dsDNA (double-stranded DNA) onto vertically aligned carbon nanofibers and subsequently releasing this dsDNA following penetration and residence of these high aspect ratio structures within cells. Gold-coated nanofiber arrays were modified with self-assembled monolayers (SAM) to which reporter dsDNA was covalently and end-specifically bound with or without a cleavable linker. The DNA-modified nanofiber arrays were then used to impale, and thereby transfect, Chinese hamster lung epithelial cells. This mechanical approach enables the transport of bound ligands directly into the cell nucleus and consequently bypasses extracellular and cytosolic degradation. Statistically significant differences were observed between the expression levels from immobilized and releasable DNA, and these are discussed in relation to the distinct accessibility and mode of action of glutathione, an intracellular reducing agent responsible for releasing the bound dsDNA. These results prove for the first time that an end-specifically and covalently SAM-bound DNA can be expressed in cells. They further demonstrate how the choice of immobilization and release methods can impact expression of nanoparticle delivered DNA.

Peckys, Diana B.; Melechko, Anatoli V.; Simpson, Michael L.; McKnight, Timothy E.

2009-04-01