WorldWideScience
 
 
1

Novel Pt electrocatalyst supported on microstructure controllable carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (CNFs) were synthesized in order to modify their catalytic properties and adjust their interaction with supported metal nanoparticles. Platelet CNFs, fish-bone CNFs, and tubular CNFs were synthesized with platinum (Pt) electrocatalysts and activated carbon. Cyclic voltammetry was used to study electrochemical surface areas and ORR performance. The study showed that the electrocatalysts supported on platelet CNFs exhibited a higher electrochemical surface and had a more positive ORR onset reduction potential than electrocatalysts supported on other CNFs. The platelet CNFs had a stronger interaction with the Pt nanoparticles than the tubular CNFs. A rotating disk electrode (RDE) analysis demonstrated that the ORR on the Pt CNFS is a 4-e pathway. It was concluded that electrocatalysts supported on all CNFs have a higher exchange current density than activated carbon-based electrocatalysts.

Zheng, J.; Qiao, J.; Li, B.; Ma, J. [Tongji Univ., Shanghai (China). School of Automotive Studies, Clean Energy Automotive Engineering Center; Li, P. [East China Univ. of Science and Technology, Shanghai (China). State Key Laboratory of Chemical Engineering; Wang, H. [National Research Council of Canada, Vancouver, BC (Canada). Inst. for Fuel Cell Innovation

2009-07-01

2

Ultrasmall microlens array based on vertically aligned carbon nanofibers.  

Science.gov (United States)

An ultrasmall tunable microlens with a diameter of 1.5 ?m is fabricated using nematic liquid crystals (electrically tunable medium) and vertically aligned carbon nanofibers (CNFs, electrodes). Individual CNFs are grown at the center of circular dielectric regions. This allows the CNFs to produce a more Gaussian electric field profile and hence more uniformity in lens array switching. PMID:22696434

Dai, Qing; Rajasekharan, Ranjith; Butt, Haider; Qiu, Xiaohui; Amaragtunga, Gehan; Wilkinson, Timothy D

2012-06-14

3

Ultrasmall microlens array based on vertically aligned carbon nanofibers.  

UK PubMed Central (United Kingdom)

An ultrasmall tunable microlens with a diameter of 1.5 ?m is fabricated using nematic liquid crystals (electrically tunable medium) and vertically aligned carbon nanofibers (CNFs, electrodes). Individual CNFs are grown at the center of circular dielectric regions. This allows the CNFs to produce a more Gaussian electric field profile and hence more uniformity in lens array switching.

Dai Q; Rajasekharan R; Butt H; Qiu X; Amaragtunga G; Wilkinson TD

2012-08-01

4

Optical properties of carbon nanofiber photonic crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 stru...

Rehammar, R; Magnusson, Roger; Fernandez-Dominguez, A I; Arwin, Hans; Kinaret, J M; Maier, S A; Campbell, E E B

5

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.

2010-11-19

6

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

7

Optical properties of carbon nanofiber photonic crystals  

Science.gov (United States)

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.

Rehammar, R.; Magnusson, R.; Fernandez-Dominguez, A. I.; Arwin, H.; Kinaret, J. M.; Maier, S. A.; Campbell, E. E. B.

2010-11-01

8

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

9

A novel catalyst for synthesis of styrene: carbon nanofibers immobilized on activated carbon.  

UK PubMed Central (United Kingdom)

Carbon NanoFibers (CNFs) with hierarchically structure have been immobilized onto Activated Carbon (AC) by impregnation with an aqueous solution of Fe(CH3COO)2, reduction and subsequent chemical vapor decomposition of ethylene. The morphology of the CNFs can be modulated by adjusting the pH of the Fe(CH3COO)2 solution used for impregnating the AC. A stable yield of 35% in the oxidative dehydrogenation of ethylbenzene to styrene was obtained at a temperature of 673 K, around 200 K lower than the current industrial process. The immobilized CNFs on AC catalysts combine the catalytic properties of the carbon nanofibers and the suprastructure of the AC host. The final material is an easy to handle active catalyst, with an open structure of immobilized CNFs avoiding the pressure drop problem, which is typically observed for fine powder forms of CNFs. The immobilized CNFs on AC are attractive for gas-phase fixed-bed industrial applications.

Delgado JJ; Chen XW; Su DS; Hamid SB; Schlögl R

2007-10-01

10

Thermal, Morphological, and Mechanical Characterization of Novel Carbon Nanofiber-Filled Bismaleimide Composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Novel carbon nanofiber (CNF) -filled bismalemide composites were fabricated by a thermokinetic mixing method. The thermal and mechanical properties of composites containing 1 wt % and 2 wt % CNFs were investigated. Thermogravimetric analysis demonstrated that minimal improvement in thermal stability...

Faraz, M. I.; Bhowmik, S.; De Ruijter, C.; Laoutid, Fouad; Benedictus, R.; Dubois, Philippe; Page, J. V. S.; Jeson, S.

11

Pt/Carbon Nanofiber Nanocomposites as Electrocatalysts for Direct Methanol Fuel Cells: Prominent Effects of Carbon Nanofiber Nanostructures  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (CNFs) with different microstructures, including platelet-CNFs (PCNFs), fish-bone-CNFs, and tube-CNFs, were synthesized, characterized and evaluated toward methanol oxidation reaction (MOR). The CNFs studied here showed several structures in which various stacked morphologies as well as the ordering of their size and graphite layers can be well controlled. Platinum nanoparticles have been electrodeposited on CNFs surfaces, and their electrocatalytic activities toward MOR have been studied by using cyclic voltammetry, chronoamperometry, and linear sweep voltammograms. Morphologies, textural properties, and the crystalline structure of the CNFs supports and catalysts have been characterized with transmission electron microscopy and scanning electron microscopy. The comparative tests conclude that Pt/PCNFs have the best electrocatalytic performance and good stability at room temperature. The high electrocatalytic activity and stability can be attributed to the specific microstructure of PCNFs, which have large numbers of edge-active carbon atoms on the surface of the CNFs as well as synergistic effects between CNFs and the platinum nanoparticles. The results suggest that PCNFs are excellent potential candidates as catalyst supports in direct methanol fuel cells.

Li, Zhizhou; Cui, Xiaoli; Zhang, Xinsheng; Wang, Qingfei; Shao, Yuyan; Lin, Yuehe

2009-04-01

12

The effect of embedded carbon nanotubes on the morphological evolution during the carbonization of poly(acrylonitrile) nanofibers  

International Nuclear Information System (INIS)

Hybrid nanofibers with different concentrations of multi-walled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique and subsequently carbonized. The morphology of the fabricated carbon nanofibers (CNFs) at different stages of the carbonization process was characterized by transmission electron microscopy and Raman spectroscopy. The polycrystalline nature of the CNFs was shown, with increasing content of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results indicate that embedded MWCNTs in the PAN nanofibers nucleate the growth of carbon crystals during PAN carbonization

2008-04-23

13

The effect of embedded carbon nanotubes on the morphological evolution during the carbonization of poly(acrylonitrile) nanofibers  

Science.gov (United States)

Hybrid nanofibers with different concentrations of multi-walled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique and subsequently carbonized. The morphology of the fabricated carbon nanofibers (CNFs) at different stages of the carbonization process was characterized by transmission electron microscopy and Raman spectroscopy. The polycrystalline nature of the CNFs was shown, with increasing content of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results indicate that embedded MWCNTs in the PAN nanofibers nucleate the growth of carbon crystals during PAN carbonization.

Prilutsky, Sabina; Zussman, Eyal; Cohen, Yachin

2008-04-01

14

The effect of embedded carbon nanotubes on the morphological evolution during the carbonization of poly(acrylonitrile) nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Hybrid nanofibers with different concentrations of multi-walled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique and subsequently carbonized. The morphology of the fabricated carbon nanofibers (CNFs) at different stages of the carbonization process was characterized by transmission electron microscopy and Raman spectroscopy. The polycrystalline nature of the CNFs was shown, with increasing content of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results indicate that embedded MWCNTs in the PAN nanofibers nucleate the growth of carbon crystals during PAN carbonization.

Prilutsky, Sabina; Cohen, Yachin [Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Zussman, Eyal [Department of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 32000 (Israel)], E-mail: yachinc@techunix.technion.ac.il

2008-04-23

15

Electrospun MgO-loaded carbon nanofibers: Enhanced field electron emission from the fibers in vacuum  

Science.gov (United States)

MgO-loaded electrospun carbon nanofibers (MgO/CNFs) were prepared by electrospinning a magnesium acetate containing polyacrylonitrile composite followed by stabilization under an air atmosphere at 280 °C and carbonization under a nitrogen atmosphere at 800 °C. In addition to investigating the morphological and material features of the nanofibers, the field emission (FE) characteristics of the carbonized NFs (CNFs), performed in an ultra-high vacuum chamber utilizing scanning electron microscopy (SEM), were determined. The results of the investigation show that the MgO/CNFs (195.5% enhancement) display enhanced field electron emission as compared to that of pure CNFs as a result of the existence of a MgO phase. Consequently, it appears that the graphitic structures of CNFs can be tuned, a finding that has significance in studies aimed at developing new field electron emission devices.

Aykut, Yakup

2013-02-01

16

Carbon nanotubes nucleate the growth of graphitic layers during carbonization.of electrospun poly(acrylonitrile) nanofibers.  

Science.gov (United States)

Hybrid nanofibers with varying concentration of multiwalled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique and subsequently carbonized. The morphology of the fabricated carbon nanofibers (CNFs) at different stages of the carbonization process was characterized by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. In-situ morphological changes during heating were followed by HRTEM using a heated stage. The polycrystalline nature of the CNFs was shown, with increasing content of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results indicate that MWCNTs embedded within the PAN nanofibers nucleate the growth of graphitic layers during PAN carbonization.

Prilutsky, Sabina; Cohen, Yachin; Zussman, Eyal

2009-03-01

17

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 us...

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

18

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 t...

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

19

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

2013-01-01

20

Carbon nanofibers grown on metallic filters as novel catalytic materials  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon nanofibers (CNF) were synthesized on sintered metal fibers (SMF) filters of nickel and Ni-containing alloys (Inconel, stainless steel (SS)) by thermal chemical vapor deposition of ethane in the presence of hydrogen at not, vert, similar660 °C. The CNFs were formed directly over the SMF filter...

Tribolet, Pascal; Kiwi-Minsker, Lioubov

 
 
 
 
21

Effect of carbon nanofibers microstructure on electrocatalytic activities of Pd electrocatalysts for ethanol oxidation in alkaline medium  

Energy Technology Data Exchange (ETDEWEB)

Pd electrocatalysts supported on three types of carbon nanofibers (CNFs), viz. platelet CNFs (p-CNFs), fish-bone CNFs (f-CNFs) and tubular CNFs (t-CNFs) are prepared and the effect of CNFs microstructure on the activities of the electrocatalysts for ethanol oxidation reaction (EOR) is investigated. The information on structural characteristics is obtained by high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. Electrochemical techniques are employed to characterize the microstructure effect of CNFs on the catalytic activities of catalysts. HRTEM images indicate the microstructure of CNFs has a powerful influence on the distribution of Pd particles. The results of the electrochemical characterization also indicate that the structure of CNFs significantly influences the catalytic activities of the electrocatalysts and p-CNFs supported Pd electrocatalyst has the best performance for ethanol oxidation in an alkaline medium because p-CNFs has the highest ratio of edge atoms to basal atoms and correspondingly the fastest electrode kinetics and strongest Pd-CNFs interaction. (author)

Qin, Yuan-Hang; Yang, Hou-Hua; Zhang, Xin-Sheng; Li, Ping [State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 (China); Ma, Chun-An [State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, Zhejiang University of Technology, Hangzhou 310014 (China)

2010-08-15

22

Effects of Microstructure of Carbon Nanofibers for Amperometric Detection of Hydrogen Peroxide  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (CNFs) with different microstructures, including platelet-carbon nanofibers (PCNFs), fish-bone-carbon nanofibers (FCNFs), and tube-carbon nanofibers (TCNFs), were synthesized, characterized, and evaluated for electrochemical sensing of hydrogen peroxide. The CNFs studied here can show several microstructures in which various stacked morphologies and their sizes and graphite-layer ordering can be well controlled. Glassy carbon (GC) electrodes modified by CNFs were fabricated and compared for amperometric detection of hydrogen peroxide. Sensors of PCNFs/GC, FCNFs/GC, and TCNFs/GC were used in the amperometric detection of H2O2 in a solution of 0.05 M phosphate buffered saline solution (pH 7.4).

Li, Zhizhou; Cui, Xiaoli; Zheng, Junsheng; Wang, Qingfei; Lin, Yuehe

2007-08-10

23

Enhanced Field Electron Emission from Electrospun Co-Loaded Activated Porous Carbon Nanofibers.  

UK PubMed Central (United Kingdom)

Highly porous, Co-loaded, activated carbon nanofibers (Co/AP-CNFs) were prepared by electrospinning a CoCl(2)-containing polyacrylonitrile composite, followed by thermal treatment processes under air and inert atmospheres. Observations show that carbon nanofibers (CNFs) generated in this fashion have a dramatically large porosity that results in an increase in the specific surface area from 193.5 to 417.3 m(2) g(-1)as a consequence of the presence of CoCl(2) in PAN/CoCl(2) precursor nanofibers. The nanofibers have a larger graphitic structure, which is enhanced by the addition of the cobaltous phase during the carbonization process. Besides evaluating the morphological and material features of the fibers, we have also carried out a field electron emission investigation of the fibers. The results show that an enhancement in the field electron emission of Co/AP-CNFs occurs as a result of the existence of cobalt in the carbon nanofibers, which results in a greater graphitization, increased specific total surface area and porosity of the carbon nanofibers. Overall, the Co/AP-CNFs are prepared in a facile manner and exhibit an enhanced field electron emission (54.79%) compared to that of pure CNFs, a feature that suggests their potential application to field electron emission devices.

Aykut Y

2012-07-01

24

Functionalized carbon nanofibers as solid-Acid catalysts for transesterification.  

UK PubMed Central (United Kingdom)

Carbon nanofibers (CNFs) were functionalized with aryl sulfonic acid groups using in?situ diazonium coupling. The use of diazonium coupling yielded an acidic carbon material, in which the introduced acidic groups are readily accessible to the triglyceride substrate. The material is an efficient catalyst for the transesterification of triolein and methanol, outperforming conventional sulfonated carbons in both stability and activity per acid site. Upon comparing CNFs with varying degrees of functionalization, a linear correlation between sulfonic acid sites and catalytic performance was found.

Stellwagen DR; van der Klis F; van Es DS; de Jong KP; Bitter JH

2013-09-01

25

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

26

Pulsed laser dewetting of nickel catalyst for carbon nanofiber growth  

Energy Technology Data Exchange (ETDEWEB)

We present a pulsed laser dewetting technique that produces single nickel catalyst particles from lithographically patterned disks for subsequent carbon nanofiber growth through plasma enhanced chemical vapor deposition. Unlike the case for standard heat treated Ni catalyst disks, for which multiple nickel particles and consequently multiple carbon nanofibers (CNFs) are observed, single vertically aligned CNFs could be obtained from the laser dewetted catalyst. Different laser dewetting parameters were tested in this study, such as the laser energy density and the laser processing time measured by the total number of laser pulses. Various nickel disk radii and thicknesses were attempted and the resultant number of carbon nanofibers was found to be a function of the initial disk dimension and the number of laser pulses.

Guan, Y F; Pearce, R C; Simpson, M L; Rack, P D [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Melechko, A V; Hensley, D K [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)], E-mail: prack@utk.edu

2008-06-11

27

Boric oxide deposition on carbon nanofibers for oxidation resistance.  

UK PubMed Central (United Kingdom)

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.

Chae HH; Kim BH; Yang KS; Woo HG

2013-08-01

28

High photocatalytic activity of ZnO-carbon nanofiber heteroarchitectures.  

Science.gov (United States)

One-dimensional ZnO-carbon nanofibers (CNFs) heteroarchitectures with high photocatalytic activity have been successfully obtained by a simple combination of electrospinning technique and hydrothermal process. The as-obtained products were characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and IR spectrum. The results revealed that the secondary ZnO nanostructures were successfully grown on the primary CNFs substrates without aggregation. And, the coverage density of ZnO nanoparticles coating on the surface of the CNFs could be controlled by simply adjusting the mass ratio of zinc acetate to CNFs in the precursor during the hydrothermal process for the fabrication of ZnO-CNFs heterostructures. The obtained ZnO-CNFs heteroarchitectures showed high photocatalytic property to degrade rhodamine B (RB) because of the formation of heteroarchitectures, which might improve the separation of photogenerated electrons and holes. Moreover, the ZnO-CNFs heteroarchitectures could be easily recycled without the decrease in photocatalytic activity due to their one-dimensional nanostructural property. PMID:21291208

Mu, Jingbo; Shao, Changlu; Guo, Zengcai; Zhang, Zhenyi; Zhang, Mingyi; Zhang, Peng; Chen, Bin; Liu, Yichun

2011-02-03

29

High photocatalytic activity of ZnO-carbon nanofiber heteroarchitectures.  

UK PubMed Central (United Kingdom)

One-dimensional ZnO-carbon nanofibers (CNFs) heteroarchitectures with high photocatalytic activity have been successfully obtained by a simple combination of electrospinning technique and hydrothermal process. The as-obtained products were characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and IR spectrum. The results revealed that the secondary ZnO nanostructures were successfully grown on the primary CNFs substrates without aggregation. And, the coverage density of ZnO nanoparticles coating on the surface of the CNFs could be controlled by simply adjusting the mass ratio of zinc acetate to CNFs in the precursor during the hydrothermal process for the fabrication of ZnO-CNFs heterostructures. The obtained ZnO-CNFs heteroarchitectures showed high photocatalytic property to degrade rhodamine B (RB) because of the formation of heteroarchitectures, which might improve the separation of photogenerated electrons and holes. Moreover, the ZnO-CNFs heteroarchitectures could be easily recycled without the decrease in photocatalytic activity due to their one-dimensional nanostructural property.

Mu J; Shao C; Guo Z; Zhang Z; Zhang M; Zhang P; Chen B; Liu Y

2011-02-01

30

Growth of carbon nanofibers on metal-catalyzed substrates by pulsed laser ablation of graphite  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (CNFs) were grown on metal-catalyzed Si substrates by pulsed laser ablation of graphite. Metal catalysts, Ni, NiCo, Pd and PdNi, were respectively deposited on Si substrates with a SiO{sub 2} layer of 200-nm thickness by a dip coat method, and the substrates placed in a laser oven apparatus. By pulsed laser ablation of graphite for 2 hours, CNFs were grown at oven temperatures {>=} 1000deg. C. Diameters of grown CNFs were about 20-30 nm by scanning electron microscopy, and increased with oven temperature. The difference of CNF growth by the catalysts was shown. Pd-contained catalysts grew thicker CNFs than the other catalysts; while PdNi and NiCo yielded a higher number density of CNFs than the other catalysts. CNF diameter and length changed according to the substrate position from the target. We also discussed the growth mechanism of CNFs with this method.

Suda, Y; Tanaka, A; Okita, A; Sakai, Y; Sugawara, H [Graduate School of Information Science and Technology, Hokkaido University, North 14, West 9, Sapporo 060-0814 (Japan)

2007-04-15

31

Growth of carbon nanofibers on metal-catalyzed substrates by pulsed laser ablation of graphite  

Science.gov (United States)

Carbon nanofibers (CNFs) were grown on metal-catalyzed Si substrates by pulsed laser ablation of graphite. Metal catalysts, Ni, NiCo, Pd and PdNi, were respectively deposited on Si substrates with a SiO2 layer of 200-nm thickness by a dip coat method, and the substrates placed in a laser oven apparatus. By pulsed laser ablation of graphite for 2 hours, CNFs were grown at oven temperatures >= 1000°C. Diameters of grown CNFs were about 20-30 nm by scanning electron microscopy, and increased with oven temperature. The difference of CNF growth by the catalysts was shown. Pd-contained catalysts grew thicker CNFs than the other catalysts; while PdNi and NiCo yielded a higher number density of CNFs than the other catalysts. CNF diameter and length changed according to the substrate position from the target. We also discussed the growth mechanism of CNFs with this method.

Suda, Y.; Tanaka, A.; Okita, A.; Sakai, Y.; Sugawara, H.

2007-04-01

32

Growth of carbon nanofibers on metal-catalyzed substrates by pulsed laser ablation of graphite  

International Nuclear Information System (INIS)

Carbon nanofibers (CNFs) were grown on metal-catalyzed Si substrates by pulsed laser ablation of graphite. Metal catalysts, Ni, NiCo, Pd and PdNi, were respectively deposited on Si substrates with a SiO2 layer of 200-nm thickness by a dip coat method, and the substrates placed in a laser oven apparatus. By pulsed laser ablation of graphite for 2 hours, CNFs were grown at oven temperatures ? 1000deg. C. Diameters of grown CNFs were about 20-30 nm by scanning electron microscopy, and increased with oven temperature. The difference of CNF growth by the catalysts was shown. Pd-contained catalysts grew thicker CNFs than the other catalysts; while PdNi and NiCo yielded a higher number density of CNFs than the other catalysts. CNF diameter and length changed according to the substrate position from the target. We also discussed the growth mechanism of CNFs with this method.

2007-01-01

33

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

2007-10-01

34

Synthesis of amorphous carbon nanofibers using iron nanoparticles as catalysts  

Science.gov (United States)

Amongst various carbon nanomaterials, carbon nanofibers (CNFs) have lately attracted considerable interest as a promising reinforcement in polymer matrix composites. CNFs are often synthesized using copper nanoparticles as catalysts and by using chemical vapor deposition (CVD). In this work iron (Fe) nanoparticles are used as catalysts to synthesize amorphous carbon nanofibers. This owes significance since Fe nanoparticles often lead to tubes rather than fibers. Fe nanoparticles (size ~30-60nm) are prepared by first mixing an appropriate quantity of potassium sodium tartrate tetrahydrate salt with iron (II) chloride dehydrate to obtain iron tartrate and then dried and heated in vacuum oven at about 250°C to remove tartrate. In a subsequent step, CNFs are obtained by using CVD. Acetylene was used as the carbon source in the CVD process. Scanning and transmission electron microscopy show the formation of nanofibers whose diameter is dependent on the size of Fe catalysts. Raman scattering from the fibers show that they are made up of carbon and are amorphous.

Ali, Mokhtar; Ramana, G. Venkata; Padya, Balaji; Srikanth, V. V. S. S.; Jain, P. K.

2013-06-01

35

Carbon nanofibers grown on activated carbon fiber fabrics as electrode of supercapacitors  

International Nuclear Information System (INIS)

Carbon nanofibers (CNFs) were grown directly on activated carbon fiber fabric (ACFF), which was then used as the electrode of supercapacitors. Cyclic voltammetry and ac impedance were used to characterize the electrochemical properties of ACFF and CNF/ACFF electrodes in both aqueous and organic electrolytes. ACFF electrodes show higher specific capacitance than CNF/ACFF electrodes due to larger specific surface area. However, the spaces formed between the CNFs in the CNF/ACFF electrodes are more easily accessed than the slit-type pores of ACFF, and much higher electrical-double layer capacitance was obtained for CNF/ACFF electrodes.

2007-01-01

36

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

UK PubMed Central (United Kingdom)

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.

Chen LF; Zhang XD; Liang HW; Kong M; Guan QF; Chen P; Wu ZY; Yu SH

2012-08-01

37

Fischer-Tropsch synthesis on hierarchically structured cobalt nanoparticle/carbon nanofiber/carbon felt composites.  

Science.gov (United States)

The hierarchically structured carbon nanofibers (CNFs)/carbon felt composites, in which CNFs were directly grown on the surface of microfibers in carbon felt, forming a CNF layer on a micrometer range that completely covers the microfiber surfaces, were tested as a novel support material for cobalt nanoparticles in the highly exothermic Fischer-Tropsch (F-T) synthesis. A compact, fixed-bed reactor, made of disks of such composite materials, offered the advantages of improved heat and mass transfer, relatively low pressure drop, and safe handling of immobilized CNFs. An efficient 3-D thermal conductive network in the composite provided a relatively uniform temperature profile, whereas the open structure of the CNF layer afforded an almost 100?% effectiveness of Co nanoparticles in the F-T synthesis in the fixed bed. The greatly improved mass and heat transport makes the compact reactor attractive for applications in the conversion of biomass, coal, and natural gas to liquids. PMID:21563315

Zarubova, Sarka; Rane, Shreyas; Yang, Jia; Yu, Yingda; Zhu, Ye; Chen, De; Holmen, Anders

2011-05-11

38

Fischer-Tropsch synthesis on hierarchically structured cobalt nanoparticle/carbon nanofiber/carbon felt composites.  

UK PubMed Central (United Kingdom)

The hierarchically structured carbon nanofibers (CNFs)/carbon felt composites, in which CNFs were directly grown on the surface of microfibers in carbon felt, forming a CNF layer on a micrometer range that completely covers the microfiber surfaces, were tested as a novel support material for cobalt nanoparticles in the highly exothermic Fischer-Tropsch (F-T) synthesis. A compact, fixed-bed reactor, made of disks of such composite materials, offered the advantages of improved heat and mass transfer, relatively low pressure drop, and safe handling of immobilized CNFs. An efficient 3-D thermal conductive network in the composite provided a relatively uniform temperature profile, whereas the open structure of the CNF layer afforded an almost 100?% effectiveness of Co nanoparticles in the F-T synthesis in the fixed bed. The greatly improved mass and heat transport makes the compact reactor attractive for applications in the conversion of biomass, coal, and natural gas to liquids.

Zarubova S; Rane S; Yang J; Yu Y; Zhu Y; Chen D; Holmen A

2011-07-01

39

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.

2080-01-00

40

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

 
 
 
 
41

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 emi...

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

42

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 d...

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

43

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 alterat...

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

44

Fabrication and Properties of Ethylene Vinyl Acetate-Carbon Nanofiber Nanocomposites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, eve...

George, JinuJacob; Bhowmick, Anil K

45

Textural and electrochemical characterization of porous carbon nanofibers as electrodes for supercapacitors  

Energy Technology Data Exchange (ETDEWEB)

Porous carbon nanofibers (CNFs) enriched with the graphitic structure were synthesized by thermal decomposition from a mixture containing polyethylene glycol and nickel chloride (catalyst). The textural and electrochemical properties of porous CNFs were systematically compared with those of commercially available multi-walled carbon nanotubes (MWCNTs). The high ratio of mesopores and large amount of open edges of porous CNFs with a higher specific surface area, very different from that of MWCNTs, are favorable for the penetration of electrolytes meanwhile the graphene layers of porous CNFs serve as a good electronic conductive medium of electrons. The electrochemical properties of porous CNFs and MWCNTs were characterized for the application of supercapacitors using cyclic voltammetry, galvanostatic charge-discharge method, and electrochemical impedance spectroscopic analyses. The porous CNFs show better capacitive performances (C{sub S} = 98.4 F g{sup -1} at 25 mV s{sup -1} and an onset frequency of behaving as a capacitor at 1.31 kHz) than that of MWCNTs (C{sub S} = 17.8 F g{sup -1} and an onset frequency at 1.01 kHz). This work demonstrates the promising capacitive properties of porous CNFs for the application of electrochemical supercapacitors. (author)

Huang, Chao-Wei; Wu, Yung-Tai; Hu, Chi-Chang; Li, Yuan-Yao [Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621 (China)

2007-10-11

46

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

International Nuclear Information System (INIS)

[en] 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.

2012-03-30

47

Extraordinary improvement of the graphitic structure of continuous carbon nanofibers templated with double wall carbon nanotubes.  

UK PubMed Central (United Kingdom)

Carbon nanotubes are being widely studied as a reinforcing element in high-performance composites and fibers at high volume fractions. However, problems with nanotube processing, alignment, and non-optimal stress transfer between the nanotubes and surrounding matrix have so far prevented full utilization of their superb mechanical properties in composites. Here, we present an alternative use of carbon nanotubes, at a very small concentration, as a templating agent for the formation of graphitic structure in fibers. Continuous carbon nanofibers (CNF) were manufactured by electrospinning from polyacrylonitrile (PAN) with 1.2% of double wall nanotubes (DWNT). Nanofibers were oxidized and carbonized at temperatures from 600 °C to 1850 °C. Structural analyses revealed significant improvements in graphitic structure and crystal orientation in the templated CNFs, with the largest improvements observed at lower carbonization temperatures. In situ pull-out experiments showed good interfacial bonding between the DWNT bundles and the surrounding templated carbon matrix. Molecular Dynamics (MD) simulations of templated carbonization confirmed oriented graphitic growth and provided insight into mechanisms of carbonization initiation. The obtained results indicate that global templating of the graphitic structure in fine CNFs can be achieved at very small concentrations of well-dispersed DWNTs. The outcomes reveal a simple and inexpensive route to manufacture continuous CNFs with improved structure and properties for a variety of mechanical and functional applications. The demonstrated improvement of graphitic order at low carbonization temperatures in the absence of stretch shows potential as a promising new manufacturing technology for next generation carbon fibers.

Papkov D; Beese AM; Goponenko A; Zou Y; Naraghi M; Espinosa HD; Saha B; Schatz GC; Moravsky A; Loutfy R; Nguyen ST; Dzenis Y

2013-01-01

48

Extraordinary improvement of the graphitic structure of continuous carbon nanofibers templated with double wall carbon nanotubes.  

Science.gov (United States)

Carbon nanotubes are being widely studied as a reinforcing element in high-performance composites and fibers at high volume fractions. However, problems with nanotube processing, alignment, and non-optimal stress transfer between the nanotubes and surrounding matrix have so far prevented full utilization of their superb mechanical properties in composites. Here, we present an alternative use of carbon nanotubes, at a very small concentration, as a templating agent for the formation of graphitic structure in fibers. Continuous carbon nanofibers (CNF) were manufactured by electrospinning from polyacrylonitrile (PAN) with 1.2% of double wall nanotubes (DWNT). Nanofibers were oxidized and carbonized at temperatures from 600 °C to 1850 °C. Structural analyses revealed significant improvements in graphitic structure and crystal orientation in the templated CNFs, with the largest improvements observed at lower carbonization temperatures. In situ pull-out experiments showed good interfacial bonding between the DWNT bundles and the surrounding templated carbon matrix. Molecular Dynamics (MD) simulations of templated carbonization confirmed oriented graphitic growth and provided insight into mechanisms of carbonization initiation. The obtained results indicate that global templating of the graphitic structure in fine CNFs can be achieved at very small concentrations of well-dispersed DWNTs. The outcomes reveal a simple and inexpensive route to manufacture continuous CNFs with improved structure and properties for a variety of mechanical and functional applications. The demonstrated improvement of graphitic order at low carbonization temperatures in the absence of stretch shows potential as a promising new manufacturing technology for next generation carbon fibers. PMID:23249440

Papkov, Dimitry; Beese, Allison M; Goponenko, Alexander; Zou, Yan; Naraghi, Mohammad; Espinosa, Horacio D; Saha, Biswajit; Schatz, George C; Moravsky, Alexander; Loutfy, Raouf; Nguyen, Sonbinh T; Dzenis, Yuris

2012-12-18

49

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.

2009-05-15

50

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.

S Nayeb Sadeghi; A Shafiekhani; MA Vesaghi

2012-01-01

51

Occupational nanosafety considerations for carbon nanotubes and carbon nanofibers.  

UK PubMed Central (United Kingdom)

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.

Castranova V; Schulte PA; Zumwalde RD

2013-03-01

52

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; Patrick Wilhite; Nobuhiko Kanzaki; Toshishige Yamada; Cary Y. Yang

2011-01-01

53

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

54

Processing and Structure of Carbon Nanofiber Paper  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Zhongfu Zhao; Jihua Gou; Aurangzeb Khan

55

Carbon nanofibers prepared via electrospinning  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers prepared via electrospinning and following carbonization are summarized by focusing on the structure and properties in relation to their applications, after a brief review of electrospinning of some polymers. Carbon precursors, pore structure control, improvement in electrical conductivity,and metal loading into carbon nanofibers via electrospinning are discussed from the viewpoint of structure and texture control of carbon. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Inagaki, Michio [Professor Emeritus of Hokkaido University, Sapporo (Japan); Yang, Ying [Department of Electrical Engineering, Tsinghua University, Beijing (China); Kang, Feiyu [Department of Materials Science and Engineering, Tsinghua University, Beijing (China)

2012-05-15

56

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.

2008-10-01

57

Synthesis of Carbon Nanotubes and Nanofibers on Silica and Cement Matrix Materials  

Directory of Open Access Journals (Sweden)

Full Text Available In order to create strong composite materials, a good dispersion of carbon nanotubes (CNTs) and nanofibers (CNFs) in a matrix material must be obtained. We proposed a simple method of growing the desirable carbon nanomaterial directly on the surface of matrix particles. CNTs and CNFs were synthesised on the surface of model object, silica fume particles impregnated by iron salt, and directly on pristine cement particles, naturally containing iron oxide. Acetylene was successfully utilised as a carbon source in the temperature range from 550 to 750?C. 5–10 walled CNTs with diameters of 10–15?nm at 600?C and 12–20?nm at 750?C were synthesised on silica particles. In case of cement particles, mainly CNFs with a diameter of around 30?nm were grown. It was shown that high temperatures caused chemical and physical transformation of cement particles.

Prasantha R. Mudimela; Larisa I. Nasibulina; Albert G. Nasibulin; Andrzej Cwirzen; Markus Valkeapää; Karin Habermehl-Cwirzen; Jari E. M. Malm; Maarit J. Karppinen; Vesa Penttala; Tatiana S. Koltsova; Oleg V. Tolochko; Esko I. Kauppinen

2009-01-01

58

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

59

Reticular Sn nanoparticle-dispersed PAN-based carbon nanofibers for anode material in rechargeable lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Reticular tin nanoparticle-dispersed carbon (Sn/C) nanofibers (CNFs) were fabricated by stabilization of electrospun SnCl{sub 4}/PAN (PAN stands for nanoceria-polyacrylonitrile) composite fibers and subsequent carbonization at different temperatures. These Sn/C composite nanofibers used as anode materials for rechargeable lithium-ion batteries (LIBs) show that the Sn/C nanofibers at 700 and 850 C present much higher charge (785.8 and 811 mA h g{sup -1}) and discharge (1211.7 and 993 mA h g{sup -1}) capacities than those at 550 and 1000 C and the as-received CNFs at 850 C, corresponding to coulombic efficiencies of 64.9% and 81.7%, respectively. The superior electrochemical properties of the intriguing Sn/C nanofibers indicate a promising application in high performance Li-ion batteries. (author)

Yu, Yunhua; Yang, Qing; Teng, Donghua; Yang, Xiaoping [Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029 (China); Ryu, Seungkon [Department of Chemical Engineering, Chungnam National University, Daejeon 305764 (Korea)

2010-09-15

60

Carbon nanofibers grafted on activated carbon as an electrode in high-power supercapacitors.  

Science.gov (United States)

A hybrid electrode material for high-power supercapacitors was fabricated by grafting carbon nanofibers (CNFs) onto the surface of powdered activated carbon (AC) through catalytic chemical vapor deposition (CCVD). A uniform thin layer of disentangled CNFs with a herringbone structure was deposited on the carbon surface through the decomposition of propane at 450?°C over an AC-supported nickel catalyst. CNF coating was controlled by the reaction time and the nickel content. The superior CNF/AC composite displays excellent electrochemical performance in a 0.5?mol?L(-1) solution of K2 SO4 due to its unique structure. At a high scan rate (100?mV?s(-1) ) and current loading (20?A?g(-1) ), the capacitance values were three- and fourfold higher than those for classical AC/carbon black composites. Owing to this feature, a high energy of 10?Wh?kg(-1) was obtained over a wide power range in neutral medium at a voltage of 0.8?V. The significant enhancement of charge propagation is attributed to the presence of herringbone CNFs, which facilitate the diffusion of ions in the electrode and play the role of electronic bridges between AC particles. An in?situ coating of AC with short CNFs (below 200?nm) is a very attractive method for producing the next generation of carbon composite materials with a high power performance in supercapacitors working in neutral medium. PMID:23794416

Gryglewicz, Gra?yna; Sliwak, Agata; Béguin, François

2013-06-21

 
 
 
 
61

Carbon nanofibers grafted on activated carbon as an electrode in high-power supercapacitors.  

UK PubMed Central (United Kingdom)

A hybrid electrode material for high-power supercapacitors was fabricated by grafting carbon nanofibers (CNFs) onto the surface of powdered activated carbon (AC) through catalytic chemical vapor deposition (CCVD). A uniform thin layer of disentangled CNFs with a herringbone structure was deposited on the carbon surface through the decomposition of propane at 450?°C over an AC-supported nickel catalyst. CNF coating was controlled by the reaction time and the nickel content. The superior CNF/AC composite displays excellent electrochemical performance in a 0.5?mol?L(-1) solution of K2 SO4 due to its unique structure. At a high scan rate (100?mV?s(-1) ) and current loading (20?A?g(-1) ), the capacitance values were three- and fourfold higher than those for classical AC/carbon black composites. Owing to this feature, a high energy of 10?Wh?kg(-1) was obtained over a wide power range in neutral medium at a voltage of 0.8?V. The significant enhancement of charge propagation is attributed to the presence of herringbone CNFs, which facilitate the diffusion of ions in the electrode and play the role of electronic bridges between AC particles. An in?situ coating of AC with short CNFs (below 200?nm) is a very attractive method for producing the next generation of carbon composite materials with a high power performance in supercapacitors working in neutral medium.

Gryglewicz G; Sliwak A; Béguin F

2013-08-01

62

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

63

Exposure and emissions monitoring during carbon nanofiber production--Part II: polycyclic aromatic hydrocarbons.  

UK PubMed Central (United Kingdom)

Production of carbon nanofibers and nanotubes (CNFs/CNTs) and their composite products is increasing globally. High-volume production may increase the exposure risks for workers who handle these materials. Though health effects data for CNFs/CNTs are limited, some studies raise serious health concerns. Given the uncertainty about their potential hazards, there is an immediate need for toxicity data and field studies to assess exposure to CNFs/CNTs. An extensive study was conducted at a facility that manufactures and processes CNFs. Filter, sorbent, cascade impactor, bulk, and microscopy samples, combined with direct-reading instruments, provided complementary information on air contaminants. Samples were analyzed for organic and elemental carbon (OC and EC), metals, and polycyclic aromatic hydrocarbons (PAHs), with EC as a measure of CNFs. Transmission electron microscopy with energy-dispersive X-ray spectroscopy also was applied. Fine/ultrafine iron-rich soot, PAHs, and carbon monoxide were production byproducts. Direct-reading instrument results were reported previously [Evans DE et al. (Aerosol monitoring during carbon nanofiber production: mobile direct-reading sampling. Ann Occup Hyg 2010; 54:514-31)]. Results for time-integrated samples are reported as companion papers in this issue. OC and EC, metals, and microscopy results are reported in Part I [Birch ME et al. (Exposure and emissions monitoring during carbon nanofiber production-Part I: elemental carbon and iron-soot aerosols. Ann Occup Hyg 2011; 55: 1016-36.)] whereas results for PAHs are reported here. Naphthalene and acenaphthylene were the dominant PAHs with average concentrations ranging from 115 to 336 ?g m(-3) and 35 to 84 ?g m(-3), respectively. Concentrations of other PAHs ranged from ?1 to 10 ?g m(-3).

Birch ME

2011-11-01

64

Exposure and emissions monitoring during carbon nanofiber production--Part II: polycyclic aromatic hydrocarbons.  

Science.gov (United States)

Production of carbon nanofibers and nanotubes (CNFs/CNTs) and their composite products is increasing globally. High-volume production may increase the exposure risks for workers who handle these materials. Though health effects data for CNFs/CNTs are limited, some studies raise serious health concerns. Given the uncertainty about their potential hazards, there is an immediate need for toxicity data and field studies to assess exposure to CNFs/CNTs. An extensive study was conducted at a facility that manufactures and processes CNFs. Filter, sorbent, cascade impactor, bulk, and microscopy samples, combined with direct-reading instruments, provided complementary information on air contaminants. Samples were analyzed for organic and elemental carbon (OC and EC), metals, and polycyclic aromatic hydrocarbons (PAHs), with EC as a measure of CNFs. Transmission electron microscopy with energy-dispersive X-ray spectroscopy also was applied. Fine/ultrafine iron-rich soot, PAHs, and carbon monoxide were production byproducts. Direct-reading instrument results were reported previously [Evans DE et al. (Aerosol monitoring during carbon nanofiber production: mobile direct-reading sampling. Ann Occup Hyg 2010; 54:514-31)]. Results for time-integrated samples are reported as companion papers in this issue. OC and EC, metals, and microscopy results are reported in Part I [Birch ME et al. (Exposure and emissions monitoring during carbon nanofiber production-Part I: elemental carbon and iron-soot aerosols. Ann Occup Hyg 2011; 55: 1016-36.)] whereas results for PAHs are reported here. Naphthalene and acenaphthylene were the dominant PAHs with average concentrations ranging from 115 to 336 ?g m(-3) and 35 to 84 ?g m(-3), respectively. Concentrations of other PAHs ranged from ?1 to 10 ?g m(-3). PMID:21976308

Birch, M Eileen

2011-10-05

65

In situ TEM observation of Fe-included carbon nanofiber: evolution of structural and electrical properties in field emission process.  

Science.gov (United States)

In situ transmission electron microscopy (TEM) of single Fe-included carbon nanofibers (CNFs) revealed that the fine polycrystalline structure in the shank region of CNFs transformed to graphitic, hollow structures during a field emission (FE) process. The iron metal platelets agglomerated during the FE process and perceptibly were emitted from the shank, which featured bamboo-like carbon nanotube (CNT) structures. The structural evolution also improved the electrical properties, and the FE current was remarkably increased, that is, 1000 times higher than the initial value (from 10(-9) to 10(-6) A). The structural transformations were effectuated by Joule heating that generated simultaneously during the FE process. The in situ TEM study of room-temperature-synthesized CNFs could provide essential information regarding CNFs' structural transformation for their possible application in future electron emitter sources. PMID:23046404

Yusop, Mohd Zamri Mohd; Ghosh, Pradip; Yaakob, Yazid; Kalita, Golap; Sasase, Masato; Hayashi, Yasuhiko; Tanemura, Masaki

2012-10-16

66

In situ TEM observation of Fe-included carbon nanofiber: evolution of structural and electrical properties in field emission process.  

UK PubMed Central (United Kingdom)

In situ transmission electron microscopy (TEM) of single Fe-included carbon nanofibers (CNFs) revealed that the fine polycrystalline structure in the shank region of CNFs transformed to graphitic, hollow structures during a field emission (FE) process. The iron metal platelets agglomerated during the FE process and perceptibly were emitted from the shank, which featured bamboo-like carbon nanotube (CNT) structures. The structural evolution also improved the electrical properties, and the FE current was remarkably increased, that is, 1000 times higher than the initial value (from 10(-9) to 10(-6) A). The structural transformations were effectuated by Joule heating that generated simultaneously during the FE process. The in situ TEM study of room-temperature-synthesized CNFs could provide essential information regarding CNFs' structural transformation for their possible application in future electron emitter sources.

Yusop MZ; Ghosh P; Yaakob Y; Kalita G; Sasase M; Hayashi Y; Tanemura M

2012-11-01

67

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

Science.gov (United States)

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.

Hatsukade, Y.; Shinyama, Y.; Yoshida, K.; Takai, Y.; Aly-Hassan, M. S.; Nakai, A.; Hamada, H.; Adachi, S.; Tanabe, K.; Tanaka, S.

2013-01-01

68

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

69

Occupational Exposure to Carbon Nanotubes and Nanofibers  

Science.gov (United States)

... Bulletin 65: Occupational Exposure to Carbon Nanotubes and Nanofibers The Occupational Safety and Health Act of 1970 ( ... studies indicate that carbon nanotubes (CNT) and carbon nanofibers (CNF) may pose a respiratory hazard. CNTs and ...

70

Room-temperature growth of a carbon nanofiber on the tip of conical carbon protrusions  

International Nuclear Information System (INIS)

Glassy carbon was Ar+-ion bombarded with a simultaneous Mo supply under ultrahigh vacuum conditions using a microprotrusion fabrication system that consists of a differentially pumped ion gun and a seed-material supply source. Conical protrusions were formed by sputtering with a seed supply, and carbon nanofibers (CNFs) grew on the tips even at room temperature. The length of CNFs reached up to ?10 ?m, and their diameter was almost uniform (50 nm) in the growth direction. The short CNFs aligned in the ion beam direction, whereas the long ones were non-aligned. The CNF growth on a glassy carbon surface was ascribed to the enhanced surface texturing and to the massive redeposition of C atoms onto cones, both of which are specific to the oblique ion bombardment: The former would lead to an increase in the number of possible nucleation sites for the CNF growth, and the C atoms arising from the latter process would migrate toward the conical tips, thus forming CNFs.

2004-05-10

71

Exposure and emissions monitoring during carbon nanofiber production--Part I: elemental carbon and iron-soot aerosols.  

Science.gov (United States)

Production of carbon nanofibers and nanotubes (CNFs/CNTs) and their composite products is increasing globally. High volume production may increase the exposure risks for workers who handle these materials. Though health effects data for CNFs/CNTs are limited, some studies raise serious health concerns. Given the uncertainty about their potential hazards, there is an immediate need for toxicity data and field studies to assess exposure to CNFs/CNTs. An extensive study was conducted at a facility that manufactures and processes CNFs. Filter, sorbent, cascade impactor, bulk, and microscopy samples, combined with direct-reading instruments, provided complementary information on air contaminants. Samples were analyzed for organic carbon (OC) and elemental carbon (EC), metals, and polycyclic aromatic hydrocarbons (PAHs), with EC as a measure of CNFs. Transmission electron microscopy with energy-dispersive X-ray spectroscopy also was applied. Fine/ultrafine iron-rich soot, PAHs, and carbon monoxide were production byproducts. Direct-reading instrument results were reported previously [Evans DE et al. (Aerosol monitoring during carbon nanofiber production: mobile direct-reading sampling. Ann Occup Hyg 2010;54:514-31.)] Results for time-integrated samples are reported as companion papers in this Issue. OC and EC, metals, and microscopy results are reported here, in Part I, while results for PAHs are reported in Part II [Birch ME. (Exposure and Emissions Monitoring during Carbon Nanofiber Production-Part II: Polycyclic Aromatic Hydrocarbons. Ann. Occup. Hyg 2011; 55: 1037-47.)]. Respirable EC area concentrations inside the facility were about 6-68 times higher than outdoors, while personal breathing zone samples were up to 170 times higher. PMID:21965464

Birch, M Eileen; Ku, Bon-Ki; Evans, Douglas E; Ruda-Eberenz, Toni A

2011-09-28

72

Exposure and emissions monitoring during carbon nanofiber production--Part I: elemental carbon and iron-soot aerosols.  

UK PubMed Central (United Kingdom)

Production of carbon nanofibers and nanotubes (CNFs/CNTs) and their composite products is increasing globally. High volume production may increase the exposure risks for workers who handle these materials. Though health effects data for CNFs/CNTs are limited, some studies raise serious health concerns. Given the uncertainty about their potential hazards, there is an immediate need for toxicity data and field studies to assess exposure to CNFs/CNTs. An extensive study was conducted at a facility that manufactures and processes CNFs. Filter, sorbent, cascade impactor, bulk, and microscopy samples, combined with direct-reading instruments, provided complementary information on air contaminants. Samples were analyzed for organic carbon (OC) and elemental carbon (EC), metals, and polycyclic aromatic hydrocarbons (PAHs), with EC as a measure of CNFs. Transmission electron microscopy with energy-dispersive X-ray spectroscopy also was applied. Fine/ultrafine iron-rich soot, PAHs, and carbon monoxide were production byproducts. Direct-reading instrument results were reported previously [Evans DE et al. (Aerosol monitoring during carbon nanofiber production: mobile direct-reading sampling. Ann Occup Hyg 2010;54:514-31.)] Results for time-integrated samples are reported as companion papers in this Issue. OC and EC, metals, and microscopy results are reported here, in Part I, while results for PAHs are reported in Part II [Birch ME. (Exposure and Emissions Monitoring during Carbon Nanofiber Production-Part II: Polycyclic Aromatic Hydrocarbons. Ann. Occup. Hyg 2011; 55: 1037-47.)]. Respirable EC area concentrations inside the facility were about 6-68 times higher than outdoors, while personal breathing zone samples were up to 170 times higher.

Birch ME; Ku BK; Evans DE; Ruda-Eberenz TA

2011-11-01

73

Plum-branch-like carbon nanofibers decorated with SnO2 nanocrystals.  

UK PubMed Central (United Kingdom)

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.

Yang Z; Du G; Guo Z; Yu X; Li S; Chen Z; Zhang P; Liu H

2010-06-01

74

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

UK PubMed Central (United Kingdom)

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.

Pan D; Ombaba M; Zhou ZY; Liu Y; Chen S; Lu J

2012-12-01

75

Morphological Evolution of Carbon Nanofibers Encapsulating SnCo Alloys and Its Effect on Growth of the Solid Electrolyte Interphase Layer.  

Science.gov (United States)

Two distinctive one-dimensional (1-D) carbon nanofibers (CNFs) encapsulating irregularly and homogeneously segregated SnCo nanoparticles were synthesized via electrospinning of polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) polymers containing Sn-Co acetate precursors and subsequent calcination in reducing atmosphere. CNFs synthesized with PVP, which undergoes structural degradation of the polymer during carbonization processes, exhibited irregular segregation of heterogeneous alloy particles composed of SnCo, Co3Sn2, and SnO with a size distribution of 30-100 nm. Large and exposed multiphase SnCo particles in PVP-driven amorphous CNFs (SnCo/PVP-CNFs) kept decomposing liquid electrolyte and were partly detached from CNFs during cycling, leading to a capacity fading at the earlier cycles. The closer study of solid electrolyte interphase (SEI) layers formed on the CNFs reveals that the gradual growth of fiber radius due to continuous increment of SEI layer thickness led to capacity fading. In contrast, SnCo particles in PAN-driven CNFs (SnCo/PAN-CNFs) showed dramatically reduced crystallite sizes (<10 nm) of single phase SnCo nanoparticles which were entirely embedded in dense, semicrystalline, and highly conducting 1-D carbon matrix. The growth of SEI layer was limited and saturated during cycling. As a result, SnCo/PAN-CNFs showed much improved cyclability (97.9% capacity retention) and lower SEI layer thickness (86 nm) after 100 cycles compared to SnCo/PVP-CNFs (capacity retention, 71.9%; SEI layer thickness, 593 nm). This work verifies that the thermal behavior of carbon precursor is highly responsible for the growth mechanism of SEI layer accompanied with particles detachment and cyclability of alloy particle embedded CNFs. PMID:23875909

Shin, Jungwoo; Ryu, Won-Hee; Park, Kyu-Sung; Kim, Il-Doo

2013-07-22

76

Morphological evolution of carbon nanofibers encapsulating SnCo alloys and its effect on growth of the solid electrolyte interphase layer.  

UK PubMed Central (United Kingdom)

Two distinctive one-dimensional (1-D) carbon nanofibers (CNFs) encapsulating irregularly and homogeneously segregated SnCo nanoparticles were synthesized via electrospinning of polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) polymers containing Sn-Co acetate precursors and subsequent calcination in reducing atmosphere. CNFs synthesized with PVP, which undergoes structural degradation of the polymer during carbonization processes, exhibited irregular segregation of heterogeneous alloy particles composed of SnCo, Co3Sn2, and SnO with a size distribution of 30-100 nm. Large and exposed multiphase SnCo particles in PVP-driven amorphous CNFs (SnCo/PVP-CNFs) kept decomposing liquid electrolyte and were partly detached from CNFs during cycling, leading to a capacity fading at the earlier cycles. The closer study of solid electrolyte interphase (SEI) layers formed on the CNFs reveals that the gradual growth of fiber radius due to continuous increment of SEI layer thickness led to capacity fading. In contrast, SnCo particles in PAN-driven CNFs (SnCo/PAN-CNFs) showed dramatically reduced crystallite sizes (<10 nm) of single phase SnCo nanoparticles which were entirely embedded in dense, semicrystalline, and highly conducting 1-D carbon matrix. The growth of SEI layer was limited and saturated during cycling. As a result, SnCo/PAN-CNFs showed much improved cyclability (97.9% capacity retention) and lower SEI layer thickness (86 nm) after 100 cycles compared to SnCo/PVP-CNFs (capacity retention, 71.9%; SEI layer thickness, 593 nm). This work verifies that the thermal behavior of carbon precursor is highly responsible for the growth mechanism of SEI layer accompanied with particles detachment and cyclability of alloy particle embedded CNFs.

Shin J; Ryu WH; Park KS; Kim ID

2013-08-01

77

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

78

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

2013-09-03

79

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

UK PubMed Central (United Kingdom)

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.

Tang X; Xie Z; Yin T; Wang JW; Yang P; Huang Q

2013-10-01

80

Current Capacity of Carbon Nanofiber Interconnects.  

Science.gov (United States)

Carbon nanofibers are promising interconnect materials for future military applications. How they behave in the elevated ambient temperature environment of a battle field is studied by performing series of current- induced nanofiber breakdown experiments....

C. Y. Yang P. Wilhite T. Yamada W. Bet- Sayad

2008-01-01

 
 
 
 
81

Pt immobilization on TiO{sub 2}-embedded carbon nanofibers using photodeposition  

Energy Technology Data Exchange (ETDEWEB)

Currently, the use of fuel cell electrodes containing Pt catalysts has been limited due to technological problems in this system, primarily the system's high cost. The improvement of Pt catalyst use has been achieved by changes in the Pt immobilization method. In this study, we have studied Pt immobilization on carbon nanofiber composites using the photodeposition method. First, we prepared the carbon nanofibers, which were homogeneously embedded TiO{sub 2} using the electrospinning technology. These TiO{sub 2}-embedded carbon nanofiber composites (TiO{sub 2}/CNFs) were then immersed in a Pt precursor solution and irradiated with UV light. The obtained Pt-deposited TiO{sub 2}/CNFs contained Pt that was immobilized on the carbon nanofibers, and the Pt particle size was 2-5 nm. The XPS spectra showed that the amount of Pt increased with an increasing UV irradiation time. The current densities and total charge also increased with an increase in the UV irradiation time, possibly due to an increase of active specific area by finely dispersed Pt nanoparticles. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Choi, S.K.; Park, H. [School of Physics and Energy Science, Kyungpook National University, Daegu (Korea, Republic of); Lim, S.K.; Chang, D. [Division of Nano and Bio Technology, Daegu Gyeongbuk Institute of Science and Technology DGIST, Daegu, 704-230 (Korea, Republic of); Kim, S.

2010-10-15

82

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.

2006-06-02

83

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

84

Synthesis and mechanical properties of interconnected carbon nanofiber network reinforced polydimethylsiloxane composites.  

UK PubMed Central (United Kingdom)

Carbon nanofiber (CNF) reinforced elastomer composites with light weight, sustainability of large deformation, chemical stability, corrosion and fatigue resistance, and vibration and noise reduction capability can have positive impact on a wide range of applications. However, this type of composite is still a under studied research area due to the difficulties in material handling and processing. To improve processing control and reproducibility for large scale engineering applications, cost effective carbon nanofibers (CNFs) in form of interconnected porous network structure were used as nanofillers. Processing, microstructure and mechanical properties of carbon nanofibers reinforced polydimethylsiloxane (PDMS) have been studied. Mechanical measurements on the composites show that the CNF-PDMS interfacial bonding can be until failure, interfacial debonding happens in the CNF-PDMS composites and the resulted permanent deformation stabilizes with increasing load-unload cycles with significant energy dissipation.

Zhao ZY; Khatri ND; Nguyen K; Song SQ; Sun L

2011-02-01

85

Synthesis and mechanical properties of interconnected carbon nanofiber network reinforced polydimethylsiloxane composites.  

Science.gov (United States)

Carbon nanofiber (CNF) reinforced elastomer composites with light weight, sustainability of large deformation, chemical stability, corrosion and fatigue resistance, and vibration and noise reduction capability can have positive impact on a wide range of applications. However, this type of composite is still a under studied research area due to the difficulties in material handling and processing. To improve processing control and reproducibility for large scale engineering applications, cost effective carbon nanofibers (CNFs) in form of interconnected porous network structure were used as nanofillers. Processing, microstructure and mechanical properties of carbon nanofibers reinforced polydimethylsiloxane (PDMS) have been studied. Mechanical measurements on the composites show that the CNF-PDMS interfacial bonding can be until failure, interfacial debonding happens in the CNF-PDMS composites and the resulted permanent deformation stabilizes with increasing load-unload cycles with significant energy dissipation. PMID:21456144

Zhao, Z Y; Khatri, N D; Nguyen, K; Song, S Q; Sun, L

2011-02-01

86

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; Hong Seong-Cheol; Kim Don

2009-01-01

87

Manufacturing of high performance polymer nanocomposites containing carbon nanotubes and carbon nanofibers using ultrasound assisted extrusion process  

Science.gov (United States)

The major objective of this study was to investigate the effect of ultrasonic treatment on the state of dispersion and properties of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) in polymer matrices. In order to achieve this objective, an ultrasonic single screw extruder operating at a frequency of 20 kHz and an amplitude of upto 10 microm and an ultrasonic twin screw extruder operating at a frequency of 40 kHz and an amplitude of upto 6.0 microm, were used to process highly viscous materials and disperse these nanofillers homogeneously in a polymer matrix at residence times of order of seconds. High temperature thermoplastic resins including polyetherimide (PEI), liquid crystalline polymer (LCP) and polyetheretherketone (PEEK) were used. Multiwalled carbon nanotubes (MWNTs) and CNFs were used as reinforcing fillers. The effect of nanofiller loading and ultrasonic amplitudes on rheological, mechanical, electrical, thermal and morphological properties of the nanocomposites was studied. Ultrasonic treatment showed a tremendous decrease in die pressure. Morphological studies showed that ultrasonic treatment improved dispersion of CNFs and CNTs in polymer matrices. PEI/CNFs and PEI/MWNTs nanocomposites were prepared using ultrasound assisted single and twin screw extruder, respectively. A permanent increase in the viscosity, storage and loss modulus and decrease in tan delta was observed with ultrasonic treatment. Ultrasonically treated PEI/CNFs nanocomposites showed a decrease in electrical percolation threshold value as compared to the untreated ones. Breakage of CNFs was observed primarily due to extrusion process alone. In case of PEI/MWNTs nanocomposites, percolation threshold value was found to be between 1 and 2 wt% loading of CNTs for both treated and untreated samples. LCP/CNFs nanocomposites were prepared using ultrasound assisted twin screw extruder with separate feeding of CNFs in the polymer melt. In contrast to behavior of PEI/CNFs and PEI/MWNTs nanocomposites, the rheological behavior of LCP/CNFs nanocomposites practically was not affected with the ultrasonic treatment due to a reduction in fibrillation of LCP matrix in the presence of CNFs. Similar to PEI/CNFs nanocomposites; ultrasonically treated samples showed a decrease in the electrical percolation threshold value as compared to the untreated ones. Due to reduction in fibrillation of LCP no improvement in the mechanical properties was observed on addition of CNFs. After introducing the orientation by fiber spinning of LCP/CNFs nanocomposites, a tremendous increase in the mechanical properties of fibers was observed with increase in the draw down ratio. PEEK/MWNTs nanocomposites were prepared using ultrasonic single screw extruder. In contrast to PEI/CNFs and PEI/MWNTs nanocomposites, ultrasonically treated PEEK/MWNTs nanocomposites showed decrease in the complex viscosity, storage modulus. Loss modulus and increase in tan delta as compared to untreated ones. This could be due to the competition between increased dispersion of CNTs and a possible degradation of the polymeric chains in the presence of CNTs and a possible reduction of CNTs length on application of ultrasound. Due to above effects, ultrasonic treatment reduced the physical contacts between the CNTs and hence increased the volume resistivity near the percolation threshold. No degradation of pure PEEK matrix upon application of ultrasound was observed.

Kumar, Rishi

88

Carbon nanofiber reinforced aluminum matrix composite fabricated by combined process of spark plasma sintering and hot extrusion.  

UK PubMed Central (United Kingdom)

Spark plasma sintering and hot extrusion processes have been employed for fabricating carbon nanofiber (CNF)-aluminum (Al) matrix bulk materials. The Al powder and the CNFs were mixed in a mixing medium of natural rubber. The CNFs were well dispersed onto the Al particles. After removal of the natural rubber, the Al-CNF mixture powders were highly densified. From the microstructural viewpoint, the composite materials were observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. The CNFs were found to be located on every grain boundary and aligned with the extrusion direction of the Al-CNF bulk materials. Some Al carbides (Al4C3) were also observed at the surface of the CNFs. This carbide was created by a reaction between the Al and the disordered CNF. The CNFs and the formation of Al4C3 play an important role in the enhancement of the mechanical properties of the Al-CNF bulk material. The CNFs can also be used for engineering reinforcement of other matrix materials such as ceramics, polymers and more complex matrices.

Kwon H; Kurita H; Leparoux M; Kawasaki A

2011-05-01

89

Carbon nanofiber reinforced aluminum matrix composite fabricated by combined process of spark plasma sintering and hot extrusion.  

Science.gov (United States)

Spark plasma sintering and hot extrusion processes have been employed for fabricating carbon nanofiber (CNF)-aluminum (Al) matrix bulk materials. The Al powder and the CNFs were mixed in a mixing medium of natural rubber. The CNFs were well dispersed onto the Al particles. After removal of the natural rubber, the Al-CNF mixture powders were highly densified. From the microstructural viewpoint, the composite materials were observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. The CNFs were found to be located on every grain boundary and aligned with the extrusion direction of the Al-CNF bulk materials. Some Al carbides (Al4C3) were also observed at the surface of the CNFs. This carbide was created by a reaction between the Al and the disordered CNF. The CNFs and the formation of Al4C3 play an important role in the enhancement of the mechanical properties of the Al-CNF bulk material. The CNFs can also be used for engineering reinforcement of other matrix materials such as ceramics, polymers and more complex matrices. PMID:21780415

Kwon, Hansang; Kurita, Hiroki; Leparoux, Marc; Kawasaki, Akira

2011-05-01

90

A new way to synthesize carbon nanofiber film on bulk titanium via hybrid surface mechanical attrition treatment  

Science.gov (United States)

Carbon nanofiber film was formed on bulk pure titanium via hybrid surface mechanical attrition treatment (SMAT). The microstructure of the sample was investigated by SEM, TEM, and RAMAN characterization. The CNFs are extremely long and uniform, exhibiting a high degree of uniformity of size of about 20 nm. The possible growth mechanism was discussed. SMAT Ti played the role of catalyst and substrate during synthesizing process.

Yang, X. F.; Lu, J.

2013-01-01

91

Structure and electrochemical applications of boron-doped graphitized carbon nanofibers.  

Science.gov (United States)

Boron-doped graphitized carbon nanofibers (CNFs) were prepared by optimizing CNFs preparation, surface treatment, graphitization and boron-added graphitization. The interlayer spacing (d???) of the boron-doped graphitized CNFs reached 3.356 ?, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d??? is less than 3.400 ?, were selected for further heat treatment. The first heat treatment of PCNFs at 2800?°C yielded a d??? between 3.357 and 3.365 ?. Successive nitric acid treatment and a second heat treatment with boric acid reduced d??? 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. PMID:22797214

Yeo, Jae-Seong; Jang, Sang-Min; Miyawaki, Jin; An, Bai; Mochida, Isao; Rhee, Choong Kyun; Yoon, Seong-Ho

2012-07-13

92

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)

2012-08-10

93

Diffraction from carbon nanofiber arrays.  

UK PubMed Central (United Kingdom)

A square planar photonic crystal composed of carbon nanofibers was fabricated using e-beam lithography and chemical vapor deposition. The diffraction properties of the system were characterized experimentally and compared with theory and numerical simulations. The intensities of the (-1,0) and (-1,-1) diffraction beams were measured as functions of the angles of incidence for both s and p-polarization. The obtained radiation patterns can be explained using a simple ray interference model, but finite-difference time-domain (FDTD) calculations are necessary to reproduce the observed dependence of the scattered radiation intensity on incident laser polarization. We explain this in terms of the aspect ratio of the nanofibers and the excitation of surface plasmon polaritons at the substrate interface.

Rehammar R; Francescato Y; Fernández-Domínguez AI; Maier SA; Kinaret JM; Campbell EE

2012-01-01

94

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.

2013-08-01

95

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

International Nuclear Information System (INIS)

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 ? 8 ?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.

2009-11-30

96

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

97

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.

2010-08-15

98

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; Wood Weston; Zhong Wei-Hong

2011-01-01

99

Carbon nanofiber polymer composites: evaluation of life cycle energy use.  

UK PubMed Central (United Kingdom)

Holistic evaluation of emerging nanotechnologies using systems analysis is pivotal for guiding their safe and sustainable development. While toxicity studies of engineered nanomaterials are essential, understanding of the potential large scale impacts of nanotechnology is also critical for developing sustainable nanoproducts. This work evaluates the life cycle energetic impact associated with the production and use of carbon nanofiber (CNF) reinforced polymer nanocomposites (PNC). Specifically, both simple CNF and carbon nanofiber-glass fiber (CNF-GF) hybrid PNCs are evaluated and compared with steel for equal stiffness design. Life cycle inventory is developed based on published literature and best available engineering information. A cradle-to-gate comparison suggests that for equal stiffness design, CNF reinforced PNCs are 1.6-12 times more energy intensive than steel. It is anticipated that the product use phase may strongly influence whether any net savings in life cycle energy consumption can be realized. A case study involving the use of CNF and CNF-GF reinforced PNCs in the body panels of automobiles highlights that the use of PNCs with lower CNF loading ratios has the potential for net life cycle energy savings relative to steel owing to improved fuel economy benefits. Other factors such as cost, toxicity impact of CNF, and end-of-life issues specific to CNFs need to be considered to evaluate the final economic and environmental performance of CNF reinforced PNC materials.

Khanna V; Bakshi BR

2009-03-01

100

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

2013-01-03

 
 
 
 
101

Growth of Y-shaped Carbon Nanofibers from Ethanol Flames  

Directory of Open Access Journals (Sweden)

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; Zou Xiaoping; Zhang Hongdan; Li Fei; Ren Pengfei; Zhu Guang; Su Yi; Wang Maofa

2008-01-01

102

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

UK PubMed Central (United Kingdom)

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.

Jung JH; Cha MS; Kim JB

2012-07-01

103

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

104

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

2011-10-23

105

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

UK PubMed Central (United Kingdom)

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.

Wang D; Liu Y; Huang J; You T

2012-02-01

106

Carbon nanofiber electrode for neurochemical monitoring.  

UK PubMed Central (United Kingdom)

The ability to rapidly detect neurotransmitter release has broad implications in the study of a variety of neurodegenerative diseases. Electrochemical detection methods using carbon nanofiber nanoelectrodes integrated into the Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) offer many important advantages including biocompatibility, selectivity, sensitivity, and rapid adsorption kinetics. Carbon nanofiber nanoelectrodes exhibit greater selectivity and sensitivity in the electrochemical detection of neurotransmitters compared to macroelectrodes and are able to resolve a ternary mixture of dopamine (DA), serotonin (5-HT), and ascorbic acid as well as to detect individual neurotransmitters in concentrations as low as 50 nM for DA and 100 nM for 5-HT using differential pulse voltammetry. Adsorption kinetics studies and isopropyl alcohol treatments modeled on previous studies on carbon fiber microelectrodes were conducted to investigate the analogous properties on carbon nanofiber electrodes using fast-scan cyclic voltammetry with WINCS and showed analogous results in carbon nanofiber electrodes compared with carbon fiber microelectrodes.

Zhang DA; Rand E; Marsh M; Andrews RJ; Lee KH; Meyyappan M; Koehne JE

2013-10-01

107

Carbon Nanofiber Electrode for Neurochemical Monitoring.  

UK PubMed Central (United Kingdom)

The ability to rapidly detect neurotransmitter release has broad implications in the study of a variety of neurodegenerative diseases. Electrochemical detection methods using carbon nanofiber nanoelectrodes integrated into the Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) offer many important advantages including biocompatibility, selectivity, sensitivity, and rapid adsorption kinetics. Carbon nanofiber nanoelectrodes exhibit greater selectivity and sensitivity in the electrochemical detection of neurotransmitters compared to macroelectrodes and are able to resolve a ternary mixture of dopamine (DA), serotonin (5-HT), and ascorbic acid as well as to detect individual neurotransmitters in concentrations as low as 50 nM for DA and 100 nM for 5-HT using differential pulse voltammetry. Adsorption kinetics studies and isopropyl alcohol treatments modeled on previous studies on carbon fiber microelectrodes were conducted to investigate the analogous properties on carbon nanofiber electrodes using fast-scan cyclic voltammetry with WINCS and showed analogous results in carbon nanofiber electrodes compared with carbon fiber microelectrodes.

Zhang DA; Rand E; Marsh M; Andrews RJ; Lee KH; Meyyappan M; Koehne JE

2013-08-01

108

Carbon nanofiber electrode for neurochemical monitoring.  

Science.gov (United States)

The ability to rapidly detect neurotransmitter release has broad implications in the study of a variety of neurodegenerative diseases. Electrochemical detection methods using carbon nanofiber nanoelectrodes integrated into the Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) offer many important advantages including biocompatibility, selectivity, sensitivity, and rapid adsorption kinetics. Carbon nanofiber nanoelectrodes exhibit greater selectivity and sensitivity in the electrochemical detection of neurotransmitters compared to macroelectrodes and are able to resolve a ternary mixture of dopamine (DA), serotonin (5-HT), and ascorbic acid as well as to detect individual neurotransmitters in concentrations as low as 50 nM for DA and 100 nM for 5-HT using differential pulse voltammetry. Adsorption kinetics studies and isopropyl alcohol treatments modeled on previous studies on carbon fiber microelectrodes were conducted to investigate the analogous properties on carbon nanofiber electrodes using fast-scan cyclic voltammetry with WINCS and showed analogous results in carbon nanofiber electrodes compared with carbon fiber microelectrodes. PMID:23975638

Zhang, David A; Rand, Emily; Marsh, Michael; Andrews, Russell J; Lee, Kendall H; Meyyappan, M; Koehne, Jessica E

2013-08-24

109

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.

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

2010-01-01

110

Carbon nanofibers with radially grown graphene sheets derived from electrospinning for aqueous supercapacitors with high working voltage and energy density.  

UK PubMed Central (United Kingdom)

Improvement of energy density is an urgent task for developing advanced supercapacitors. In this paper, aqueous supercapacitors with high voltage of 1.8 V and energy density of 29.1 W h kg(-1) were fabricated based on carbon nanofibers (CNFs) and Na2SO4 electrolyte. The CNFs with radially grown graphene sheets (GSs) and small average diameter down to 11 nm were prepared by electrospinning and carbonization in NH3. The radially grown GSs contain between 1 and a few atomic layers with their edges exposed on the surface. The CNFs are doped with nitrogen and oxygen with different concentrations depending on the carbonizing temperature. The supercapacitors exhibit excellent cycling performance with the capacity retention over 93.7% after 5000 charging-discharging cycles. The unique structure, possessing radially grown GSs, small diameter, and heteroatom doping of the CNFs, and application of neutral electrolyte account for the high voltage and energy density of the present supercapacitors. The present supercapacitors are of high promise for practical application due to the high energy density and the advantages of neutral electrolyte including low cost, safety, low corrosivity, and convenient assembly in air.

Zhao L; Qiu Y; Yu J; Deng X; Dai C; Bai X

2013-06-01

111

Carbon nanofibers with radially grown graphene sheets derived from electrospinning for aqueous supercapacitors with high working voltage and energy density  

Science.gov (United States)

Improvement of energy density is an urgent task for developing advanced supercapacitors. In this paper, aqueous supercapacitors with high voltage of 1.8 V and energy density of 29.1 W h kg-1 were fabricated based on carbon nanofibers (CNFs) and Na2SO4 electrolyte. The CNFs with radially grown graphene sheets (GSs) and small average diameter down to 11 nm were prepared by electrospinning and carbonization in NH3. The radially grown GSs contain between 1 and a few atomic layers with their edges exposed on the surface. The CNFs are doped with nitrogen and oxygen with different concentrations depending on the carbonizing temperature. The supercapacitors exhibit excellent cycling performance with the capacity retention over 93.7% after 5000 charging-discharging cycles. The unique structure, possessing radially grown GSs, small diameter, and heteroatom doping of the CNFs, and application of neutral electrolyte account for the high voltage and energy density of the present supercapacitors. The present supercapacitors are of high promise for practical application due to the high energy density and the advantages of neutral electrolyte including low cost, safety, low corrosivity, and convenient assembly in air.

Zhao, Lei; Qiu, Yejun; Yu, Jie; Deng, Xianyu; Dai, Chenglong; Bai, Xuedong

2013-05-01

112

Electrospun Ni-added SnO2-carbon nanofiber composite anode for high-performance lithium-ion batteries.  

Science.gov (United States)

The SnO(2) anode is a promising anode for next-generation Li ion batteries because of its high theoretical capacity. However, it exhibits inherent capacity fading because of the large volume change and pulverization that occur during the charge/discharge cycles. The buffer matrix, such as electrospun carbon nanofibers (CNFs), can alleviate this problem to some extent, but SnO(2) particles are thermodynamically incompatible with the carbon matrix such that large Sn agglomerates form after carbonization upon melting of the Sn. Herein, we introduce well-dispersed nanosized SnO(2) attached to CNFs for high-performance anodes developed by Ni presence. The addition of Ni increases the stability of the SnO(2) such that the morphologies of the dispersed SnO(2) phase are modified as a function of the Ni composition. The optimal adding composition is determined to be Ni:Sn = 10:90 wt % in terms of the crystallite size and the distribution uniformity. A high capacity retention of 447.6 mA h g(-1) after 100 cycles can be obtained for 10 wt % Ni-added SnO(2)-CNFs, whereas Ni-free Sn/SnO(2)-CNFs have a capacity retention of 304.6 mA h g(-1). PMID:22999049

Kim, Dongha; Lee, Daehee; Kim, Joosun; Moon, Jooho

2012-10-05

113

Electrospun Ni-added SnO2-carbon nanofiber composite anode for high-performance lithium-ion batteries.  

UK PubMed Central (United Kingdom)

The SnO(2) anode is a promising anode for next-generation Li ion batteries because of its high theoretical capacity. However, it exhibits inherent capacity fading because of the large volume change and pulverization that occur during the charge/discharge cycles. The buffer matrix, such as electrospun carbon nanofibers (CNFs), can alleviate this problem to some extent, but SnO(2) particles are thermodynamically incompatible with the carbon matrix such that large Sn agglomerates form after carbonization upon melting of the Sn. Herein, we introduce well-dispersed nanosized SnO(2) attached to CNFs for high-performance anodes developed by Ni presence. The addition of Ni increases the stability of the SnO(2) such that the morphologies of the dispersed SnO(2) phase are modified as a function of the Ni composition. The optimal adding composition is determined to be Ni:Sn = 10:90 wt % in terms of the crystallite size and the distribution uniformity. A high capacity retention of 447.6 mA h g(-1) after 100 cycles can be obtained for 10 wt % Ni-added SnO(2)-CNFs, whereas Ni-free Sn/SnO(2)-CNFs have a capacity retention of 304.6 mA h g(-1).

Kim D; Lee D; Kim J; Moon J

2012-10-01

114

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

UK PubMed Central (United Kingdom)

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.

Shuai D; Choe JK; Shapley JR; Werth CJ

2012-03-01

115

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

Directory of Open Access Journals (Sweden)

Full Text Available 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.

Amparo Borrell, Olga García-Moreno, Ramón Torrecillas, Victoria García-Rocha and Adolfo Fernández

2012-01-01

116

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

Science.gov (United States)

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.

Borrell, Amparo; García-Moreno, Olga; Torrecillas, Ramón; García-Rocha, Victoria; Fernández, Adolfo

2012-02-01

117

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.

2012-01-01

118

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

UK PubMed Central (United Kingdom)

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.

Van de Vyver S; Geboers J; Schutyser W; Dusselier M; Eloy P; Dornez E; Seo JW; Courtin CM; Gaigneaux EM; Jacobs PA; Sels BF

2012-08-01

119

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

2012-06-22

120

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.

Yehya M. Ahmed; Abdullah-Al- Mamun; S.A. Muyibi; Ma`an Fahmi R. Al-Khatib; A.T. Jameel; Mohammed A. AlSaadi

2010-01-01

 
 
 
 
121

Damping Augmentation of Nanocomposites Using Carbon Nanofiber Paper  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 fib...

Jihua Gou; Scott O'Braint; Haichang Gu; Gangbing Song

122

Surface Characterization and Functionalization of Carbon Nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers are high-aspect ratio graphitic materials that have been investigated for numerous applications due to their unique physical properties such as high strength, low density, metallic conductivity, tunable morphology, chemical and environmental stability, as well as compatibility with organochemical modification. Surface studies are extremely important for nanomaterials because not only is the surface structurally and chemically quite different from the bulk, but its properties tend to dominate at the nanoscale due to the drastically increased surface-to-volume ratio. This review surveys recent developments in surface analysis techniques used to characterize the surface structure and chemistry of carbon nanofibers and related carbon materials. These techniques include scanning probe microscopy, infrared and electron spectroscopy, electron microscopy, ion spectrometry, temperature programmed desorption and atom probe analysis. In addition, this article evaluates the methods used to modify the surface of carbon nanofibers in order to enhance their functionality to perform across an exceedingly diverse application space.

Klein, Kate L [ORNL; Melechko, Anatoli Vasilievich [ORNL; McKnight, Timothy E [ORNL; Retterer, Scott T [ORNL; Rack, Philip D [ORNL; Fowlkes, Jason Davidson [ORNL; Joy, David Charles [ORNL; Simpson, Michael L [ORNL

2008-01-01

123

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

124

Using Converter Dust to Produce Low Cost Cementitious Composites by in situ Carbon Nanotube and Nanofiber Synthesis  

Directory of Open Access Journals (Sweden)

Full Text Available Carbon nanotubes (CNTs) and nanofibers (CNFs) were synthesized on clinker and silica fume particles in order to create a low cost cementitious nanostructured material. The synthesis was carried out by an in situ chemical vapor deposition (CVD) process using converter dust, an industrial byproduct, as iron precursor. The use of these materials reduces the cost, with the objective of application in large-scale nanostructured cement production. The resulting products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) and were found to be polydisperse in size and to have defective microstructure. Some enhancement in the mechanical behavior of cement mortars was observed due to the addition of these nano-size materials. The contribution of these CNTs/CNFs to the mechanical strength of mortar specimens is similar to that of high quality CNTs incorporated in mortars by physical mixture.

Péter Ludvig; José M. Calixto; Luiz O. Ladeira; Ivan C.P. Gaspar

2011-01-01

125

Wettability of carbon nanofiber layers on nickel foils.  

Science.gov (United States)

Carbon nanofiber (CNF) layers have been directly synthesized on nickel foils by chemical vapor deposition at 450°C using different H(2) concentrations and reaction times. The addition of 5% H(2) produces thicker, rougher and more porous CNF layers than when 1% H(2) is used. The roughness and porosity increases with reaction time when 5%, 10% or 20% H(2) are used; however, this effect is less pronounced when 1% H(2) is used. CNFs are 50-55 nm in diameter and have a fishbone type structure. We have studied the influence of CNF layer thickness, porosity and surface roughness on the interaction with water by measuring the contact angle. The water wetting properties of the samples are more significantly influenced by the CNF layer thickness than both surface roughness and porosity. When the CNF layer is thicker than ca. 20 ?m, the surface is hydrophobic and the contact angle increases with surface roughness and porosity. When the CNF layer is thinner than ca. 20 ?m, the surface is hydrophilic and the contact angle decreases with increasing surface roughness and porosity. This behavior is attributed to penetration of water, making contact with the hydrophilic C layer between the CNF layer and the foil. PMID:21939980

Pacheco Benito, S; Lefferts, L

2011-08-26

126

Wettability of carbon nanofiber layers on nickel foils.  

UK PubMed Central (United Kingdom)

Carbon nanofiber (CNF) layers have been directly synthesized on nickel foils by chemical vapor deposition at 450°C using different H(2) concentrations and reaction times. The addition of 5% H(2) produces thicker, rougher and more porous CNF layers than when 1% H(2) is used. The roughness and porosity increases with reaction time when 5%, 10% or 20% H(2) are used; however, this effect is less pronounced when 1% H(2) is used. CNFs are 50-55 nm in diameter and have a fishbone type structure. We have studied the influence of CNF layer thickness, porosity and surface roughness on the interaction with water by measuring the contact angle. The water wetting properties of the samples are more significantly influenced by the CNF layer thickness than both surface roughness and porosity. When the CNF layer is thicker than ca. 20 ?m, the surface is hydrophobic and the contact angle increases with surface roughness and porosity. When the CNF layer is thinner than ca. 20 ?m, the surface is hydrophilic and the contact angle decreases with increasing surface roughness and porosity. This behavior is attributed to penetration of water, making contact with the hydrophilic C layer between the CNF layer and the foil.

Pacheco Benito S; Lefferts L

2011-12-01

127

A review of catalytically grown carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers (sometimes known as carbon filaments) can be produced in a relative large scale by the catalytic decomposition of certain hydrocarbons on small metal particles. The diameter of the nanofibers is governed by that of the catalyst particles responsible for their growth. By careful manipulation of various parameters it is possible to generate carbon nanofibers in assorted conformations and at the same time also control the degree of their crystalline order. This paper is a review of the recent advances made in the development of these nanostructures, with emphasis both on the fundamental aspects surrounding the growth of the material and a discussion of the key factors which enable one to control their chemical and physical properties. Attention is also given to some of the possible applications of the nanostructures which center around the unique blend of properties exhibited by the material.

Rodriguez, N.M. (Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States))

1993-12-01

128

Hydrothermal synthesis of ?-nickel hydroxide nanocrystalline thin film and growth of oriented carbon nanofibers  

International Nuclear Information System (INIS)

Novel well-crystallized ?-nickel hydroxide nanocrystalline thin films were successfully synthesized at low temperature on the quartz substrates by hydrothermal method, and the oriented carbon nanofibers (CNFs) were prepared by acetylene cracking at 750 deg. C on thin film as the catalyst precursor. High resolution transmission electron microscopy (HR-TEM) measurement shows that thin films were constructed mainly with hexagonal ?-nickel hydroxide nanosheets. The average diameter of the nanosheets was about 80 nm and thickness about 15 nm. Hydrothermal temperature played an important role in the film growth process, influencing the morphologies and catalytic activity of the Ni catalysts. Ni thin films with high catalytic activity were obtained by reduction of these Ni(OH)2 nanocrystalline thin films synthesized at 170 deg. C for 2 h in hydrothermal condition. The highest carbon yield was 1182%, and was significantly higher than the value of the catalyst precursor which was previously reported as the carbon yield (398%) for Ni catalysts. The morphology and growth mechanism of oriented CNFs were also studied finally.

2009-08-05

129

Hydrothermal synthesis of {beta}-nickel hydroxide nanocrystalline thin film and growth of oriented carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Novel well-crystallized {beta}-nickel hydroxide nanocrystalline thin films were successfully synthesized at low temperature on the quartz substrates by hydrothermal method, and the oriented carbon nanofibers (CNFs) were prepared by acetylene cracking at 750 deg. C on thin film as the catalyst precursor. High resolution transmission electron microscopy (HR-TEM) measurement shows that thin films were constructed mainly with hexagonal {beta}-nickel hydroxide nanosheets. The average diameter of the nanosheets was about 80 nm and thickness about 15 nm. Hydrothermal temperature played an important role in the film growth process, influencing the morphologies and catalytic activity of the Ni catalysts. Ni thin films with high catalytic activity were obtained by reduction of these Ni(OH){sub 2} nanocrystalline thin films synthesized at 170 deg. C for 2 h in hydrothermal condition. The highest carbon yield was 1182%, and was significantly higher than the value of the catalyst precursor which was previously reported as the carbon yield (398%) for Ni catalysts. The morphology and growth mechanism of oriented CNFs were also studied finally.

Zhang Enlei [College of Materials Science and Engineering, Hunan University, Changsha 410082 (China); Tang Yuanhong, E-mail: yhtang2000@163.com [College of Materials Science and Engineering, Hunan University, Changsha 410082 (China) and Powder Metallurgy Research Institute, Central South University, Changsha 410083 (China); Zhang Yong; Guo Chi; Yang Lei [College of Materials Science and Engineering, Hunan University, Changsha 410082 (China)

2009-08-05

130

Zinc Sulfide Tubes Reinforced with Carbon Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Zinc sulfide submicron and nanotubes with outer diameters in the range from 100 to 1000?nm were produced through chemical deposition from vapor under argon pressure. The novel process provides formation of ZnS tubes reinforced with carbon nanofibers. This is the first time that the ZnS tubes are grown with fibers during deposition.

N. N. Kolesnikov; D. N. Borisenko; E. B. Borisenko; A. V. Timonina; V. V. Kveder

2009-01-01

131

75 FR 80819 - Draft Current Intelligence Bulletin “Occupational Exposure to Carbon Nanotubes and Nanofibers  

Science.gov (United States)

...Occupational Exposure to Carbon Nanotubes and Nanofibers'' AGENCY: National Institute for...Occupational Exposure to Carbon Nanotubes and Nanofibers'' has been developed which contains...Occupational Exposure to Carbon Nanotubes and Nanofibers''. Special emphasis will be...

2010-12-23

132

Raman spectroscopy of polystyrene nanofibers—Multiwalled carbon nanotubes composites  

Science.gov (United States)

Raman spectroscopy investigations of nanofibers of polystyrene loaded with various amounts of multiwalled carbon nanotubes are reported. The modifications of the main Raman bands (D and G) of multiwalled carbon nanotubes due to their dispersion in polystyrene demonstrates and quantifies the stress transfer from the polymeric nanofiber matrix (polystyrene) to multiwalled carbon nanotubes. TGA data show an increase of the thermal stability of polystyrene nanofibers upon the loading with multiwalled carbon nanotubes, conforming Raman data.

Chipara, Dorina M.; Macossay, Javier; Ybarra, Ana V. R.; Chipara, A. C.; Eubanks, Thomas M.; Chipara, Mircea

2013-06-01

133

Field emission behavior of aligned carbon nanofiber arrays  

Energy Technology Data Exchange (ETDEWEB)

Aligned carbon nanofiber arrays are synthesized on plain silicon surface by thermal decomposition of propylene with Ni film as the catalyst at 600C. These arrays consist of carbon nanofibers with uniform diameters and heights, standing vertically on the substrate. TEM examinations show that carbon nanofibers have unique layer structure. These arrays also show excellent field emission properties comparable to those of carbon nanotubes during subsequent testing.

Cao, A.Y.; Zhang, X.F.; Xiao, X.; Xu, C.L.; Wei, B.Q.; Liang, J.; Wu, D.H. [Department of Mechanical Engineering, State Key Laboratory of Automotive Safety and Energy, Tsinghua University, 100084 Beijing (China); Ding, M.Q. [Beijing Vacuum Electronic Research Institute, 100016 Beijing (China); Zhuang, D.M. [Surface Science and Engineering Laboratory, Department of Mechanical Engineering, Tsinghua University, 100084 Beijing (China)

2001-12-01

134

Preparation of surfactant-mediated silver and copper nanoparticles dispersed in hierarchical carbon micro-nanofibers for antibacterial applications.  

UK PubMed Central (United Kingdom)

The antibacterial potential of copper (Cu) and silver (Ag) nanoparticles dispersed in a phenolic resin precursor-based multi-scale web of carbon microfibers (ACFs) and nanofibers (CNFs) was assessed in this study. The multi-scale web of ACF/CNF was prepared by growing the CNFs on the ACF substrate by chemical vapor deposition (CVD).The Ag or Cu nanoparticles were used as the catalyst, and acetylene (C2H2) gas was used as the carbon source. An anionic surfactant, sodium dodecyl sulfate (SDS), was used for the preparation of the Cu/Ag-ACF composites to prevent the agglomeration of Cu(II) and Ag(I) ions and achieve a uniform mono-dispersion during the impregnation step. The prepared composites with Cu and Ag dispersed in the ACF and ACF/CNF were characterized using several analytical techniques, including atomic absorption spectroscopy (AAS), Fourier transform infrared (FTIR),X-ray diffraction (XRD), and thermal programming reduction (TPR). The antibacterial properties of the prepared multi-scale or hierarchical structures were evaluated against the gram-negative bacteria Escherichia coli (E.coli) and the gram-positive bacteria Staphylococcus aureus (S. aureus).The results revealed that the prepared Ag-ACF/CNFs were highly effective against these bacteria, achieving a complete inhibition of bacterial growth for over 72hrs.

Singh S; Ashfaq M; Singh RK; Joshi HC; Srivastava A; Sharma A; Verma N

2013-05-01

135

Fabrication of graphene sheets intercalated with manganese oxide/carbon nanofibers: toward high-capacity energy storage.  

UK PubMed Central (United Kingdom)

Herein, 3D nanohybrid architectures consisting of MnO(x) nanocrystals, carbon nanofibers (CNFs), and graphene sheets are fabricated. MnO(x) -decorated CNFs (MCNFs) with diameters of about 50 nm are readily obtained via single-nozzle co-electrospinning, followed by heat treatment. The MCNFs are then intercalated between graphene sheets, yielding the ternary nanohybrid MCNF/reduced graphene oxide (RGO). This straightforward synthesis process readily affords product on a scale of tens of grams. The ultrathin CNFs, which might be a promising alternative to carbon nanotubes (CNTs), overcome the low electrical conductivity of the excellent pseudocapacitive component, MnO(x) . Furthermore, the graphene sheets separated by the MCNFs boost the electrochemical performance of the nanohybrid electrodes. These nanohybrid electrodes exhibit enhanced specific capacitances compared with a sheet electrode fabricated of MCNF-only or RGO-only. Evidently, the RGO sheet acts as a conductive channel inside the nanohybrid, while the intercalated MCNFs increase the efficiency of the ion and charge transfer in the nanohybrid. The proposed nanohybrid architectures are expected to lay the foundation for the design and fabrication of high-performance electrodes.

Kwon OS; Kim T; Lee JS; Park SJ; Park HW; Kang M; Lee JE; Jang J; Yoon H

2013-01-01

136

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.

2009-11-30

137

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

138

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; Jomar Livramento Barros Furtado; Cuong Pham-Huu; Ricardo Vieira

2008-01-01

139

Functionalization of carbon nanofibers with elastomeric block copolymer using carbodiimide chemistry  

International Nuclear Information System (INIS)

Surface functionalization of carbon nanofibers (CNFs) with aminopropyl terminated polydimethylsiloxane [(PDMS-NH2)] and other organic diamines was achieved using carbodiimide chemistry. The carbodiimide chemistry provides faster reaction rate so that the reaction occurs at lower temperature compared to amidation and acylation-amidation chemistry. CNF functionalized with PDMS-NH2 fibers were further functionalized with oligomer of polyimide (6FDA-BisP) using imidization reaction. The formation of block copolymer on the surface of CNF is proposed as an effective method to engineer the interphase between the fiber and the polymer, which is essential to modulate and enhance the properties of the nanocomposite. The efficiency of the carbodiimide chemistry to functionalize amine terminated groups on CNF and the functionalization of block copolymer was characterized using thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy.

2009-02-15

140

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

 
 
 
 
141

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.

2009-06-24

142

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; PARK SOO-YOUNG; MOHAMMAD ISHAQ

2009-01-01

143

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)

2013-08-02

144

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.

2004-01-01

145

Initial growth of vertically aligned carbon nanofibers  

Science.gov (United States)

Samples of vertically aligned carbon nanofibers (VACNFs) were viewed transverse to the growth direction and studied using both scanning and transmission electron microscopy. The VACNFs are composed of graphite layers nearly parallel to the substrate at their bottom end, gradually formed graphite ``cups'' in the main body, and a catalyst particle on the tip. The formation of such structure is due to the corresponding transformation of the shape of the catalyst particle during initial VACNF growth. A model for their initial growth is proposed.

Cui, Hongtao; Yang, Xiaojing; Simpson, Michael L.; Lowndes, Douglas H.; Varela, Maria

2004-05-01

146

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

147

ADSORPTION OF MULTIWALLED CARBON NANOTUBES ON ELECTROSPUN POLYCAPROLACTON NANOFIBERS  

Scientific Electronic Library Online (English)

Full Text Available 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 (more) 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 (

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

2009-12-01

148

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

2012-11-16

149

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; Luiz Claudio Pardini; Carlos Alberto Moreira dos Santos; Ricardo Vieira

2011-01-01

150

Preparation and Application of Fiber Composites made of Carbon nanofibers and Carbide Nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Fabrication of carbon fiber reinforced composites was carried out by hand lay-up method. Carbon nanofibers and SiC nanofibers were used as filler in the composites fabrication. Carbon nanofibers, one of the new carbon materials, have 5{approx}500 nm in diameter and 5-100 nm in length. SiC nanofibers were modified by silicon monoxide vapor with carbon nanofibers. The composites were carbonized at 1000 deg. C in a nitrogen atmosphere, and then densified by molten pitches impregnated in vacuum. Multiple cycles of liquid pitch impregnation and carbonization were carried out to obtain a desired density. The composites were characterized by density, microstructure. The inter-laminar shear strength (ILSS) test was performed for mechanical properties. For the new application, the microwave reflective property of composites was investigated. Dielectric constant and permeability spectrum were measured in 12{approx}18 GHz frequency ranges. On the basis of the wave propagation theory in a lossy media, the reflection loss from the composite inter-layer was predict as a function of frequency. (author). 14 refs., 2 tabs., 5 figs.

Lim, Y.S.; Kim, G.D.; Lee, J.C.; Kim, M.S. [Myongji University, Yongin (Korea); Kim, S.S. [Chungbuk National University, Chongju (Korea)

2000-06-01

151

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

Directory of Open Access Journals (Sweden)

Full Text Available 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 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.

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

2013-01-01

152

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

UK PubMed Central (United Kingdom)

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.

Jahangiri M; Adl J; Shahtaheri SJ; Rashidi A; Ghorbanali A; Kakooe H; Forushani AR; Ganjali MR

2013-01-01

153

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

2013-01-26

154

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladium nanoparticles  

Science.gov (United States)

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.

Lai, Chuilin; Guo, Qiaohui; Wu, Xiang-Fa; Reneker, Darrell H.; Hou, Haoqing

2008-05-01

155

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

2008-05-14

156

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladium nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

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){sub 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.

Lai Chuilin; Guo Qiaohui; Hou Haoqing [Chemistry College of Jiangxi Normal University, Nanchang 330027 (China); Wu Xiangfa [Department of Engineering Mechanics, University of Nebraska-Lincoln, Lincoln, NE 68588-0526 (United States); Reneker, Darrell H [Department of Polymer Science, University of Akron, Akron, OH 44325 (United States)], E-mail: haoqing@jxnu.edu.cn

2008-05-14

157

Controlled growth of NiCo?O? nanorods and ultrathin nanosheets on carbon nanofibers for high-performance supercapacitors.  

UK PubMed Central (United Kingdom)

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 advantages, such as high electroactive surface area, ultrathin and porous features, robust mechanical strength, shorter ion and electron transport path. Their electrochemical performance is systematically studied, and both of these two hierarchical hybrid nanostructures exhibit high capacitance and excellent cycling stability. The remarkable electrochemical performance will undoubtedly make these hybrid structures attractive for high-performance supercapacitors with high power and energy densities.

Zhang G; David Lou XW

2013-01-01

158

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

Science.gov (United States)

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.

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

2011-03-01

159

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.

2009-01-01

160

Functionalization and electrocatalysis on carbon nanofibers  

Science.gov (United States)

Nanoscale hybrid materials such as metal nanoparticles dispersed on nanostructured carbons are promising for use as electrocatalysts due to their chemical and physical properties. Vertically aligned carbon nanofibers (VACNFs) have a unique structure that exposes large amounts of graphitic edge-plane along the sidewalls, suggesting that hybrid VACNF-nanoparticle structures may have particularly good electrochemical response for electrocatalytic reactions. As with other carbon materials, the surface of VACNFs is not highly selective, but the high reactivity of the graphitic edge-plane sites allows for chemical modification with functional organic monolayers, avoiding the need for harsh oxidation techniques. The use of molecular functionalization to interface VACNFs with catalytic metal particles was investigated using two different growth techniques: electroless deposition and pulsed electrochemical deposition. Deposited particles are demonstrated to be catalytically active, despite the presence of the molecular layer. The presence of graphitic edge-plane is found to be important for electrochemical nucleation. Evaluation of the catalytic behavior of this hybrid system using the methanol oxidation reaction as a model system reveals differences in initial catalytic activity and long-term stability of nanoparticles produced by the two growth methods. Development of the electrochemical deposition method demonstrates that nucleation and growth can be controlled by the use of multiple-pulse sequences. This work provides insights into the use of molecular systems for chemical selectivity and the importance of edge-plane sites in catalytic activity of carbon-based hybrid nanostructures.

Hogendoorn, Stephanie Ruth

 
 
 
 
161

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; Shun-Ichiro Tanaka

2013-01-01

162

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 ?m (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

163

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

164

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.

2010-02-01

165

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

166

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.

2008-01-01

167

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

UK PubMed Central (United Kingdom)

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.

Hood AR; Saurakhiya N; Deva D; Sharma A; Verma N

2013-10-01

168

Label-free detection of cardiac troponin-I using carbon nanofiber based nanoelectrode arrays.  

Science.gov (United States)

A label-free biosensor is presented using carbon nanofiber (CNF) nanoelectrode arrays for the detection of cardiac troponin-I in the early diagnosis of myocardial infarction. Immobilization of anti-cTnI Ab on CNFs and the detection of human-cTnI were examined using electrochemical impedance spectroscopy and cyclic voltammetry techniques. Each step of the modification process was monitored, and the results show changes in electrical capacitance or resistance to charge transfer due to the specificity of corresponding adsorption of Ab-Ag interaction. The immunosensor demonstrates a good selectivity and high sensitivity against human-cTnI analytes and is capable of detecting cTnI at concentrations as low as ?0.2 ng/mL, which is 25 times lower than that possible by conventional methods. Analysis of the electrode at various stages using atomic force microscopy and X-ray reflectivity provides information on the surface roughness and orientation of the antibody. PMID:23384128

Periyakaruppan, Adaikkappan; Gandhiraman, Ram P; Meyyappan, M; Koehne, Jessica E

2013-03-25

169

Label-free detection of cardiac troponin-I using carbon nanofiber based nanoelectrode arrays.  

UK PubMed Central (United Kingdom)

A label-free biosensor is presented using carbon nanofiber (CNF) nanoelectrode arrays for the detection of cardiac troponin-I in the early diagnosis of myocardial infarction. Immobilization of anti-cTnI Ab on CNFs and the detection of human-cTnI were examined using electrochemical impedance spectroscopy and cyclic voltammetry techniques. Each step of the modification process was monitored, and the results show changes in electrical capacitance or resistance to charge transfer due to the specificity of corresponding adsorption of Ab-Ag interaction. The immunosensor demonstrates a good selectivity and high sensitivity against human-cTnI analytes and is capable of detecting cTnI at concentrations as low as ?0.2 ng/mL, which is 25 times lower than that possible by conventional methods. Analysis of the electrode at various stages using atomic force microscopy and X-ray reflectivity provides information on the surface roughness and orientation of the antibody.

Periyakaruppan A; Gandhiraman RP; Meyyappan M; Koehne JE

2013-04-01

170

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

UK PubMed Central (United Kingdom)

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.

Shimoi N; Tanaka S

2013-02-01

171

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

172

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 nan...

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

173

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 nan...

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

174

Health effects of exposure to carbon nanofibers: Systematic review, critical appraisal, meta analysis and research to practice perspectives  

International Nuclear Information System (INIS)

[en] Background: Literature reviews examining the relationship between exposure to carbon nanofibers (CNFs) and health consequences are qualitative in nature and do not employ an evidence-based assessment. Objective: This research deals with a systematic review, critical appraisal, and meta-analysis designed to examine the potential health effects associated with exposure to CNFs. The utilization of research findings into practice is also explored. Methods: Published articles were obtained from a search of electronic databases and bibliographies of identified articles. A critical appraisal was conducted using an 'Experimental Appraisal Instrument' developed in this study. The meta-analysis was established using statistical techniques with/without the incorporation of overall study quality. The likelihood of utilizing research findings into practice (i.e., from research to practice) was computed using a four-step algorithm based on the criteria of: strength of association, consistency among studies, temporality, biological gradient, type of experimental unit, type of CNF (single- and multi-wall nanotubes), CNF grade (commercial or altered), exposure dose, exposure duration, and support by analogy from the published literature. Results: Twenty-one experimental studies satisfied the inclusion criteria and were performed on human cells, experimental animal models and animal cells as experimental units. The methodological qualities of published studies ranged from 'very poor' to 'excellent', with 'overall study description' scoring 'good' and 'study execution' equal to 'moderate'. The random-effects model was applied in the meta-analysis calculations as heterogeneity was significant at the 10% for all outcomes reported. The mean standardized meta-estimates for the experimental groups were significantly lower than those for the control groups for cell viability and cell death, respectively. Incorporating the effect of overall study quality score widened the gap between the experimental and control groups. Assessment of research findings on the basis of the four-step algorithm revealed that the likelihood of the results to occur in practice is 'somewhat possible' at this time. That is, if exposure conditions to CNF in the reported studies are similar to those in nano-manufacturing plants, it is somewhat possible that CNFs alter the function of human cells resulting in loss of cell viability and cell death. Conclusions: Our findings suggest that it is 'somewhat possible' for the CNF to penetrate the human cells in the targeted organs and to cause cellular damage. Although the weight of evidence is not sufficient, it is advisable that actions be taken to ensure the protection of workers exposed to CNFs, that is, (a) engineering controls should be established to contain exposure to CNF, and (b) simultaneously rigorous personnel protective equipment should be planned to further minimize the risk of CNF exposure.

2009-06-01

175

Heat treating carbon nanofibers for optimal composite performance  

Energy Technology Data Exchange (ETDEWEB)

Partial graphitization of carbon nanofibers by high-temperature heat treatment can give improved composite properties. The intrinsic electrical conductivity of the bulk carbon nanofibers measured under compression is maximized by giving the fibers an initial heat treatment at 1500 C. Similarly, for carbon nanofiber/polypropylene composites containing up to 12 vol% fiber, initial fiber heat treatments near 1500 C give tensile modulus and strength superior even to composites made from fibers graphitized at 2900 C. However, optimum composite conductivity is obtained with a somewhat lower heat-treatment temperature, near 1300 C. Transmission electron microscopy (TEM) along with x-ray diffraction (XRD) explains these results, showing that heat treating the fibers alters the exterior planes from continuous, coaxial, and poorly crystallized to discontinuous nested conical crystallites inclined at about 25 to the fiber axis.

Howe, Jane Y [ORNL; Tibbetts, Gary G. [Applied Sciences, Inc.; Kwag, C [Applied Sciences, Inc.; Lake, Max L [ORNL

2006-01-01

176

Morphology of PEG-Stabilized Carbon Nanofibers in Water  

Energy Technology Data Exchange (ETDEWEB)

Small-angle light scattering is used to assess the dispersion of poly(ethylene glycol) (PEG)-functionalized carbon nanofibers suspended in water. Analysis of these data elucidates the mechanism by which the functionalized nanofibers are solubilized in water. Linear, tube-like morphology is observed for the PEG-functionalized nanofibers dispersed in water. However, dispersion is not down to the individual tube level as determined by analysis of the light scattering data in conjunction with transmission electron micrographs. Rather, scattering entities are polydisperse side-by-side fiber aggregates (bundles). Because of the presence of water-soluble PEG oligomers on the surfaces of the nanofibers these small-scale aggregates do not agglomerate to form the large-scale clusters that are observed for untreated and acid-treated nanofibers. Acid-treated nanofibers, by contrast, do agglomerate, but in an unusual fashion, showing a 10-h induction period of followed by linear growth of large-scale agglomerates. PEG-functionalization of the acid-treated fibers leads to stabilization by inhibiting formation of the large-scale agglomerates, not by disrupting the side-by-side bundles.

Zhao, Jian; Schaefer, Dale W.; (UCIN); (Qingdao)

2009-09-02

177

Preparation of C/Ni-NiO composite nanofibers for anode materials in lithium-ion batteries  

Science.gov (United States)

Carbon nanofibers (CNFs) embedded with various amounts of Ni and NiO nanoparticles (C/Ni-NiO) were prepared by electrospinning of polyacrylonitrile (PAN), followed by heat treatment. The structure and composition of the obtained C/Ni-NiO composite nanofibers were analyzed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results suggested that the morphology, nanofiber diameter, and the content of the Ni-NiO nanoparticles in the CNFs were controlled by different amounts of nickel acetate added into the PAN. The electrochemical measurements of a charge/discharge experiment and a cyclic voltammetry test indicated that the content and the size of Ni-NiO nanoparticles embedded in the CNFs had a great influence on the electrochemical performance of lithium-ion batteries. CNFs embedded with a certain content of Ni-NiO nanoparticles as binder-free anodes for rechargeable lithium-ion batteries exhibited improved electrochemical performance, including high reversible capacities, good capacity retention, and stable cycling performance. This is mainly ascribed to the formation of a well-distributed Ni-NiO nanoparticle structure and the buffering role of the carbon nanofiber matrix, together with the high theoretical capacity of NiO and the increase in electrode connectivity caused by the formation of electrochemically inactive Ni nanoparticles.

Luo, Chenghao; Lu, Weili; Li, Yu; Feng, Yiyu; Feng, Wei; Zhao, Yunhui; Yuan, Xiaoyan

2013-04-01

178

Flexible sensor based on carbon nanofibers with multifunctional sensing features.  

Science.gov (United States)

Herein, we present the fabrication and characterization of a flexible gas sensor based on carbon nanofibers. The sensing device is composed of interdigitated silver electrodes deposited by inkjet printing on Kapton substrates, subsequently coated with carbon nanofibers as sensing element. Gas sensing response to CO, NH3 and humidity has been characterized in detail. Thermal, mechanical and electromagnetic radiation effects have also been studied and discussed from the point of view of the cross-sensitivity. The obtained results open the door for a new generation of flexible sensors with multifunctional sensing features, which are producible with scalable techniques based on low cost nanomaterials. PMID:23598218

Monereo, O; Claramunt, S; Marigorta, M Martínez de; Boix, M; Leghrib, R; Prades, J D; Cornet, A; Merino, P; Merino, C; Cirera, A

2013-01-21

179

Flexible sensor based on carbon nanofibers with multifunctional sensing features.  

UK PubMed Central (United Kingdom)

Herein, we present the fabrication and characterization of a flexible gas sensor based on carbon nanofibers. The sensing device is composed of interdigitated silver electrodes deposited by inkjet printing on Kapton substrates, subsequently coated with carbon nanofibers as sensing element. Gas sensing response to CO, NH3 and humidity has been characterized in detail. Thermal, mechanical and electromagnetic radiation effects have also been studied and discussed from the point of view of the cross-sensitivity. The obtained results open the door for a new generation of flexible sensors with multifunctional sensing features, which are producible with scalable techniques based on low cost nanomaterials.

Monereo O; Claramunt S; Marigorta MM; Boix M; Leghrib R; Prades JD; Cornet A; Merino P; Merino C; Cirera A

2013-03-01

180

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

UK PubMed Central (United Kingdom)

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.

Xue Q; Kato D; Kamata T; Guo Q; You T; Niwa O

2013-09-01

 
 
 
 
181

Application of catalytically grown carbon nanofiber in double layer capacitor (I) - Preparation and and properties of carbon nanofiber -  

Energy Technology Data Exchange (ETDEWEB)

In order to establish the reaction conditions for producing carbon nanofibers by passing a commercial propane gas over Cu-Ni and Ni catalysts, the experimental conditions such as catalyst composition, reaction temperature and gas flow rate were varied. It was observed by SEM that the obtained carbon deposits were mainly composed of carbon nanofibers with the diameters ranging 50-300 nm. The carbon yield and structure were dependent on the catalyst composition and reaction temperature. The maximum yields of carbon nanofibers from propane decomposition were obtained at temperatures from 650 to 700 {sup o}C and the higher yields were obtained over the alloy catalysts containing 50-90 wt% nickel than the pure nickel catalyst. The specific surface area and electric resistivity were measured as the key properties for the electrode application of a double layer capacitor(DLC). The carbon nanofibers from Cu-Ni catalyst had relatively high surface areas of around 350 m{sup 2}/g, while those from Ni catalyst showed about 150 m{sup 2}/g of surface areas. The electrical resistivity was also dependent on the catalyst composition, raging 0.05-0.25 {Omega}{center_dot} cm and these values were much lower than those for activated carbon which is currently used as the electrode materials.

Kim, M.S.; Kin, D.Y. [Myong Ji University (Korea, Republic of)

1998-02-01

182

Preparation of a New Adsorbent from Activated Carbon and Carbon Nanofiber (AC/CNF) for Manufacturing Organic-Vacbpour Respirator Cartridge  

Directory of Open Access Journals (Sweden)

Full Text Available 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 carbonnanofibers (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 andTeller’s (BET) technique and electron microscopy respectively. Prepared composite adsorbent was tested forbenzene, toluene and xylene (BTX) adsorption and then employed in an organic respirator cartridge in granularform. 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 nmwere 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.

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

2013-01-01

183

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

2008-08-15

184

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

Energy Technology Data Exchange (ETDEWEB)

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.

Shao Dongfeng [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China); Changzhou Textile Garment Institute, Changzhou 213164 (China); Wei Qufu [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China)], E-mail: qfwei@jiangnan.edu.cn; Zhang Liwei; Cai Yibing; Jiang Shudong [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China)

2008-08-15

185

Toward CH4 dissociation and C diffusion during Ni/Fe-catalyzed carbon nanofiber growth: A density functional theory study  

Science.gov (United States)

First-principles calculations have been performed to investigate CH4 dissociation and C diffusion during the Ni/Fe-catalyzed growth of carbon nanofibers (CNFs). Two bulk models with different Ni to Fe molar ratios (1:1 and 2:1) are constructed, and x-ray diffraction (XRD) simulations are conducted to evaluate their reliability. With the comparison between the calculated and experimental XRD patterns, these models are found to be well suited to reproduce the crystalline structures of Ni/Fe bulk alloys. The calculations indicate the binding of the C1 derivatives to the Ni/Fe closest-packed surfaces is strengthened compared to that on Ni(111), arising from the upshift of the weighted d-band centers of catalyst surfaces. Then, the transition states for the four successive dehydrogenation steps in CH4 dissociation are located using the dimer method. It is found that the energy barriers for the first three steps are rather close on the alloyed Ni/Fe and Ni surfaces, while the activation energy for CH dissociation is substantially lowered with the introduction of Fe. The dissolution of the generated C from the surface into the bulk of the Ni/Fe alloys is thermodynamically favorable, and the diffusion of C through catalyst particles is hindered by the Fe component. With the combination of density functional theory calculations and kinetic analysis, the C concentration in catalyst particles is predicted to increase with the Fe content. Meanwhile, other experimental conditions, such as the composition of carbon-containing gases, feedstock partial pressure, and reaction temperature, are also found to play a key role in determining the C concentration in bulk metal, and hence the microstructures of generated CNFs.

Fan, Chen; Zhou, Xing-Gui; Chen, De; Cheng, Hong-Ye; Zhu, Yi-An

2011-04-01

186

Toward CH4 dissociation and C diffusion during Ni/Fe-catalyzed carbon nanofiber growth: a density functional theory study.  

UK PubMed Central (United Kingdom)

First-principles calculations have been performed to investigate CH(4) dissociation and C diffusion during the Ni?Fe-catalyzed growth of carbon nanofibers (CNFs). Two bulk models with different Ni to Fe molar ratios (1:1 and 2:1) are constructed, and x-ray diffraction (XRD) simulations are conducted to evaluate their reliability. With the comparison between the calculated and experimental XRD patterns, these models are found to be well suited to reproduce the crystalline structures of Ni?Fe bulk alloys. The calculations indicate the binding of the C(1) derivatives to the Ni?Fe closest-packed surfaces is strengthened compared to that on Ni(111), arising from the upshift of the weighted d-band centers of catalyst surfaces. Then, the transition states for the four successive dehydrogenation steps in CH(4) dissociation are located using the dimer method. It is found that the energy barriers for the first three steps are rather close on the alloyed Ni?Fe and Ni surfaces, while the activation energy for CH dissociation is substantially lowered with the introduction of Fe. The dissolution of the generated C from the surface into the bulk of the Ni?Fe alloys is thermodynamically favorable, and the diffusion of C through catalyst particles is hindered by the Fe component. With the combination of density functional theory calculations and kinetic analysis, the C concentration in catalyst particles is predicted to increase with the Fe content. Meanwhile, other experimental conditions, such as the composition of carbon-containing gases, feedstock partial pressure, and reaction temperature, are also found to play a key role in determining the C concentration in bulk metal, and hence the microstructures of generated CNFs.

Fan C; Zhou XG; Chen D; Cheng HY; Zhu YA

2011-04-01

187

Electrochemical characteristics of activated carbon nanofiber electrodes for supercapacitors  

International Nuclear Information System (INIS)

In this work, poly(amide imide) solutions in dimethylformamide were electrospun into webs consisting of 350 nm ultrafine nanofibers. These nanofiber webs were used to produce activated carbon nanofibers (ACNFs), through stabilization and carbonisation-activation processes. Experimental results indicated that ACNFs activated at 800 deg. C afforded the highest specific surface area but low mesopore volume. The high specific surface area, mainly due to the micropores, introduced maximum specific capacitance at low current density (150 F g-1 at 10 mA g-1). Elevating the volume fraction of mesopores gave maximum specific capacitance at high current density (100 F g-1 at 1000 mA g-1), which could be explained on the basis of ion mobility in the pores. Thus, the capacitance of the supercapacitors was strongly dependent on the specific surface area and micro- or mesopore volume of the ACNFs.

2009-08-25

188

Electrochemical characteristics of activated carbon nanofiber electrodes for supercapacitors  

Energy Technology Data Exchange (ETDEWEB)

In this work, poly(amide imide) solutions in dimethylformamide were electrospun into webs consisting of 350 nm ultrafine nanofibers. These nanofiber webs were used to produce activated carbon nanofibers (ACNFs), through stabilization and carbonisation-activation processes. Experimental results indicated that ACNFs activated at 800 deg. C afforded the highest specific surface area but low mesopore volume. The high specific surface area, mainly due to the micropores, introduced maximum specific capacitance at low current density (150 F g{sup -1} at 10 mA g{sup -1}). Elevating the volume fraction of mesopores gave maximum specific capacitance at high current density (100 F g{sup -1} at 1000 mA g{sup -1}), which could be explained on the basis of ion mobility in the pores. Thus, the capacitance of the supercapacitors was strongly dependent on the specific surface area and micro- or mesopore volume of the ACNFs.

Seo, Min-Kang [Dept. of Chemistry, Inha University, 253, Nam-gu, Incheon 402-751 (Korea, Republic of); Park, Soo-Jin [Dept. of Chemistry, Inha University, 253, Nam-gu, Incheon 402-751 (Korea, Republic of)], E-mail: sjpark@inha.ac.kr

2009-08-25

189

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

2011-04-25

190

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

191

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

192

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection.  

UK PubMed Central (United Kingdom)

ABSTRACT: 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

193

Occupational exposure assessment in carbon nanotube and nanofiber primary and secondary manufacturers: mobile direct-reading sampling.  

UK PubMed Central (United Kingdom)

UNLABELLED: RESEARCH SIGNIFICANCE: Toxicological evidence suggests the potential for a wide range of health effects from exposure to carbon nanotubes (CNTs) and carbon nanofibers (CNFs). To date, there has been much focus on the use of direct-reading instruments (DRIs) to assess multiple airborne exposure metrics for potential exposures to CNTs and CNFs due to their ease of use and ability to provide instantaneous results. Still, uncertainty exists in the usefulness and interpretation of the data. To address this gap, air-monitoring was conducted at six sites identified as CNT and CNF manufacturers or users and results were compared with filter-based metrics. METHODS: Particle number, respirable mass, and active surface area concentrations were monitored with a condensation particle counter, a photometer, and a diffusion charger, respectively. The instruments were placed on a mobile cart and used as area monitors in parallel with filter-based elemental carbon (EC) and electron microscopy samples. Repeat samples were collected on consecutive days, when possible, during the same processes. All instruments in this study are portable and routinely used for industrial hygiene sampling. RESULTS: Differences were not observed among the various sampled processes compared with concurrent indoor or outdoor background samples while examining the different DRI exposure metrics. Such data were also inconsistent with results for filter-based samples collected concurrently at the same sites [Dahm MM, Evans DE, Schubauer-Berigan MK et al. (2012) Occupational exposure assessment in CNT and nanofiber primary and secondary manufacturers. Ann Occup Hyg; 56: 542-56]. Significant variability was seen between these processes as well as the indoor and outdoor backgrounds. However, no clear pattern emerged linking the DRI results to the EC or the microscopy data (CNT and CNF structure counts). CONCLUSIONS: Overall, no consistent trends were seen among similar processes at the various sites. The DRI instruments employed were limited in their usefulness in assessing and quantifying potential exposures at the sampled sites but were helpful for hypothesis generation, control technology evaluations, and other air quality issues. The DRIs employed are nonspecific, aerosol monitors, and, therefore, subject to interferences. As such, it is necessary to collect samples for analysis by more selective, time-integrated, laboratory-based methods to confirm and quantify exposures.

Dahm MM; Evans DE; Schubauer-Berigan MK; Birch ME; Deddens JA

2013-04-01

194

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

Science.gov (United States)

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 advantages, such as high electroactive surface area, ultrathin and porous features, robust mechanical strength, shorter ion and electron transport path. Their electrochemical performance is systematically studied, and both of these two hierarchical hybrid nanostructures exhibit high capacitance and excellent cycling stability. The remarkable electrochemical performance will undoubtedly make these hybrid structures attractive for high-performance supercapacitors with high power and energy densities.

Zhang, Genqiang; (David) Lou, Xiong Wen

2013-01-01

195

One-step facile construction of high aspect ratio Fe3O4 decorated CNFs with distinctive porous morphology: potential multiuse expectations.  

UK PubMed Central (United Kingdom)

The objective of our study was to develop a new class of Fe3O4 nanocrystals decorated CNFs with characteristic porous morphology by straightforward approach. The utilized CNFs-Fe3O4 hybrid was prepared by sol-gel electrospinning employing polyacrylonitrile and iron (III) nitrate nonahydrate as precursors. Scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy and X-ray diffraction techniques were employed to characterize novel CNFs-Fe3O4 composite. Nanofibers are having porous morphology, diameter size in the range of ~260±20 nm. In order to demonstrate the broad applicability of CNFs-Fe3O4 scaffold, we performed different analysis. The antibacterial activity was tested using Escherichia coli as model organism. With NIH 3T3 mouse fibroblasts, cytotoxicity of prepared high aspect ratio CNFs-Fe3O4 composite was evaluated by thiazoyl blue tetrazolium-bromide (MTT) assay, and fibroblast cell growth behavior with electrospun porous scaffolds was also examined. Interestingly, the prepared nanofibers exhibited enhanced bactericidal performance (minimum inhibition concentrations (MIC) from 5 ?g/mL to 80 ?g/mL) and CNFs-Fe3O4 composite as scaffolds indicated favorable enhancement in cell proliferation. Results from this study suggest that CNFs-Fe3O4 scaffold with small diameters coincidence with unique porous configuration can mimic the natural extracellular matrix (ECM) well and provide potential promises for applications in the fields of tissue engineering and regenerative medicine. Our findings clearly suggest wide application potentials of this (CNFs-Fe3O4) multifunctional composite and the nanofiberous mat can be a very good candidate as a filter for water purification, antibiofouling filtration and ECM for tissue engineering.

Shamshi Hassan M; Amna T; Hwang IH; Khil MS

2013-06-01

196

Vertically aligned carbon nanofibers: interconnecting solid state electronics with biosystems.  

UK PubMed Central (United Kingdom)

Vertically aligned carbon nanofibers (VACNFs) are grown directly on prefabricated electronic circuits with nanoscale precision. Utilizing the free-standing nanofiber array geometry, we have demonstrated the detection of nucleic acids to construct an ultrasensitive electrochemical sensor. Extending this technology towards in vivo applications, we have modified the free-standing VACNF arrays in order to achieve a multifunctional three dimensional (3-D) matrix that interpenetrates the neuronal network of PC12 cells. We found that PC12 cells cultured on the nanofiber arrays can form an extended neural network upon proper chemical and biochemical modification. The soft 3-D nanofiber array architecture provides a novel platform to fine-tune the topographical, mechanical, chemical, and electrical cues at sub-cellular scales. This biomaterial platform can be used for both fundamental studies of nanomaterial-cell interactions and the development of multifunctional, chronically stable implantable devices. The application of these devices and potential utility as a multifunctional platform for neurophysiology and biochemical studies will be discussed.

Cassell AM; Li J; Nguyen-Vu TD; Koehne JE; Chen H; Andrews R; Meyyappan M

2009-08-01

197

Vertically aligned carbon nanofibers: interconnecting solid state electronics with biosystems.  

Science.gov (United States)

Vertically aligned carbon nanofibers (VACNFs) are grown directly on prefabricated electronic circuits with nanoscale precision. Utilizing the free-standing nanofiber array geometry, we have demonstrated the detection of nucleic acids to construct an ultrasensitive electrochemical sensor. Extending this technology towards in vivo applications, we have modified the free-standing VACNF arrays in order to achieve a multifunctional three dimensional (3-D) matrix that interpenetrates the neuronal network of PC12 cells. We found that PC12 cells cultured on the nanofiber arrays can form an extended neural network upon proper chemical and biochemical modification. The soft 3-D nanofiber array architecture provides a novel platform to fine-tune the topographical, mechanical, chemical, and electrical cues at sub-cellular scales. This biomaterial platform can be used for both fundamental studies of nanomaterial-cell interactions and the development of multifunctional, chronically stable implantable devices. The application of these devices and potential utility as a multifunctional platform for neurophysiology and biochemical studies will be discussed. PMID:19928183

Cassell, Alan M; Li, Jun; Nguyen-Vu, Thuy-Duong Barbara; Koehne, Jessica E; Chen, Hua; Andrews, Russell; Meyyappan, M

2009-08-01

198

Carbon nanotube/nanofiber embedded nanoporous anodized aluminium oxide surface and its tribological properties.  

Science.gov (United States)

Nanoporous alumina has been prepared by anodization of pure aluminium using phosphoric acid electrolyte. Carbon nanotubes/nanofibres (CNTs/CNFs) are grown within the pores by chemical vapour deposition technique, using acetylene gas as carbon precursor. Such synthesis of nanostructured carbonaceous materials within the nanoporous oxide template has high potential for many applications (e.g., electronics, magnetic, etc.) in nanotechnology. Possibility of using such material combination for engineering systems where abrasion resistance coupled with self-lubrication (at comparatively higher loads) are the key requirements, has been explored through the present work. Pore structure has been characterized by SEM/FE-SEM in this study and CNTs/CNFs have been examined by TEM, FE-SEM and Raman spectroscopy. While the pore diameters are found to lie in the range of 180-220 nm, the CNTs/CNFs diameter are observed to be in the range of 50 to 220 nm. The CNTs/CNFs growing from bottom of the pores are found to replicate the pore diameter, while those grown above the surface are varying significantly in diameter and probably matching the diameter of the catalyst, which remains adsorbed on the top surface and inner walls of the pores. On comparing friction and wear properties of both materials (viz. anodized alumina and CNTs/CNFs embedded anodized alumina) as determined by pin-on-disc machine using hardened steel disc as counterface, it is found that wear rate and coefficient of friction of CNTs embedded composite surface is significantly lower which is attributed to formation of transfer layer of hard wear resistant alumina mechanically mixed with graphitic CNTs/CNFs. PMID:19049193

Kushwaha, M K; Sil, Anjan; Ray, S

2008-08-01

199

Nanopipe Fabrication Using Vertically Aligned Carbon Nanofiber Templates  

Energy Technology Data Exchange (ETDEWEB)

We report a method to fabricate tubular nanostructures using vertically aligned carbon nanofibers grown by plasma-enhanced chemical vapor deposition as templates. The resulting nanopipes are oriented perpendicular to the substrate and have internal diameters ranging from 30 to 200 nm and can be up to several micrometers in length. These nanopipes can be deterministically positioned on a substrate and arranged into singular devices or arrays.

Melechko, Anatoli Vasilievich [ORNL; McKnight, Timothy E [ORNL; Guillorn, M. A. [Cornell University; Austin, Derek William [ORNL; Illic, B. [Cornell University; Merkulov, Vladimir I [ORNL; Doktycz, Mitchel John [ORNL; Lowndes, Douglas H [ORNL; Simpson, Michael L [ORNL

2002-01-01

200

Nanographene production from platelet carbon nanofiber by supercritical fluid exfoliation  

Science.gov (United States)

Nanographene was synthesized from platelet carbon nanofiber by supercritical fluid (SCF) exfoliation without acid oxidation. During the exfoliation process, a progressive decrease in the number of layers was accompanied by the cutting of the basal plane. Raman spectroscopy was used to identify the quality of the samples, revealing that the defect density in the basal plane of the nanographene can be reduced to less than that of the starting material during SCF exfoliation.

Tomai, Takaaki; Kawaguchi, Yuji; Honma, Itaru

2012-06-01

 
 
 
 
201

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; Zheng Mingbo; Lu Hongling; Feng Shaoqing; Ji Guangbin; Cao Jieming

2010-01-01

202

Supercapacitance from cellulose and carbon nanotube nanocomposite fibers.  

UK PubMed Central (United Kingdom)

Multi-walled carbon nanotube (MWNT)/cellulose composite nanofibers have been prepared by electrospinning a MWNT/cellulose acetate blend solution followed by deacetylation. These composite nanofibers were then used as precursors for carbon nanofibers (CNFs). The effect of nanotubes on the stabilization of the precursor and microstructure of the resultant CNF were investigated using thermogravimetric analysis, transmission electron microscopy and Raman spectroscopy. It is demonstrated that the incorporated MWNTs reduce the activation energy of the oxidative stabilization of cellulose nanofibers from 228 to 203 kJ mol-1. They also increase the crystallite size, structural order and the electrical conductivity of the CNFs. The surface area of the CNFs increased upon addition of nanotubes which protrude the fiber surface leading to a rougher surface. The CNFs were used as the electrodes of supercapacitor. The electrochemical capacitance of the CNF derived from pure cellulose nanofiber is demonstrated to be ~120 F g-1 at a current density of 2 A g-1 which increases to ~150 F g-1 upon the addition of MWNTs.

Deng L; Young RJ; Kinloch IA; Abdelkader AM; Holmes SM; De Haro-Del Rio D; Eichhorn SJ

2013-09-01

203

The use of carbon nanofibers as a novel catalyst support for hydrogenation reactions  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers, grown catalytically by the decomposition of selected hydrocarbons and carbon monoxide, possess unique physical and chemical properties which make them very attractive materials for use as catalyst supports. Three different structures of these carbon nanofibers have been utilised in these hydrogenation studies as a novel catalyst support material. The activity of a metal supported on these different forms of nanofibers were compared against the more traditional catalyst supports, Al{sub 2}O{sub 3}, TiO{sub 2} and active carbon. The different structures and graphitic nature of the carbon nanofibers have been shown to have a profound effect on the activity and selectivity of the hydrogenation reaction. Initial hydrogenation studies have revealed that the catalytic performance of a metal supported on carbon nanofibers was found to be superior when compared to that found fro the same metal supported on traditional catalyst supports or on active carbon.

Park, C.; Rodriguez, N.M.; Baker, R.T.K. [Pennsylvania State Univ., University Park, PA (United States)

1996-10-01

204

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...

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

205

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.; Nasouri K.; Mousavi Shoushtari A.; Kaflou A.

2013-01-01

206

Magnetic Properies of Ni Nanoparticles Used for Carbon Nanofiber Synthesis  

Science.gov (United States)

Magnetic properties of Ni catalyst particles used for vertically-aligned carbon nanofiber (VACNF) synthesis are investigated. Ni thin films are deposited on Si wafers by sputter-depositing to thicknesses of 2--10 nm. The VACNFs are then grown in a Plasma-Enhanced Chemical Vapor Deposition (PECVD) chamber with NH3 and C2H2 at relative flow rates of 80/40 sccm, respectively, a pressure of 3 Torr, and a temperature of 700^oC. The catalyst particles, after nanofiber growth, are 10--150 nm in diameter. Magnetic properties are investigated by SQUID magnetometry in applied magnetic fields of |H| < 10 kOe and temperatures T = 5--300 K. The catalyst particles are ferromagnetic with low coercivity and remanence. The ferromagnetic properties are thermally stable up to room temperature in all but the smallest particle sizes. Saturation magnetization is much less than would be expected from the deposited quantity of Ni metal.

Sorge, K. D.; Malkina, O.; Finkel, C.; Fowlkes, J. D.; Rack, P. D.; Klein, K. L.; Melechko, A. V.; Simpson, M. L.

2007-03-01

207

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

UK PubMed Central (United Kingdom)

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.

Boonjob W; Miró M; Segundo MA; Cerdà V

2011-07-01

208

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

2011-06-06

209

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

2012-05-10

210

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

UK PubMed Central (United Kingdom)

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.

Delorme MP; Muro Y; Arai T; Banas DA; Frame SR; Reed KL; Warheit DB

2012-08-01

211

Synthesis, characterization and formation process of transition metal oxide nanotubes using carbon nanofibers as templates  

International Nuclear Information System (INIS)

[en] Mono and binary transition metal oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air. The transition metal oxide nanotubes were composed of nano-crystallites of metal oxides. The functional groups on the carbon nanofiber templates were essential for the coating of these templates: they acted as adsorption sites for the metal nitrates, ensuring a uniform metal oxide coating. During the removal of the carbon nanofiber templates by calcination in air, the metal oxide coatings promoted the combustion reaction between the carbon nanofibers and oxygen. - Graphical abstract: Mono and binary transition metal-oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air.

2009-01-01

212

Charge transport measurements of vertically aligned carbon nanofibers  

Science.gov (United States)

Vertically aligned carbon nanofibers (VACNFs) have found a variety of electronic applications. To further realize these applications, a good understanding of the charge transport properties is essential. In this work, charge transport properties have been systematically measured for three types of VACNF forests with Ni as catalyst, namely VACNFs grown by direct current PECVD, and inductively coupled PECVD at both normal pressure and low pressure. The structure and composition of these nanofibers have also been investigated in detail prior to the charge transport measurements. Four-probe I-V measurements on individual nanofibers have been enabled by the fabrication of multiple metal ohmic contacts on individual fibers that exhibited resistance of only a few kO. An O2 plasma reactive ion etch method has been used to achieve ohmic contacts between the nanofibers and Ti/Au, Ag/Au, Cd/Au, and Cr/Au electrodes. Direct current VACNFs exhibit linear I-V behavior at room temperature, with a resistivity of approximately 4.2 x 10-3 O·cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the dc VACNFs. The resistivity of these fibers is almost independent of temperature, and the contact resistance decreases as temperature increases. Further studies reveal that the 10--15 nm thick graphitic outer layer dominates the charge transport properties of do VACNFs. This is demonstrated by comparison of charge transport properties of as-grown VACNFs and VACNFs with the outer layer partially removed by oxygen plasma reactive ion etch. The linear I-V behavior of the fibers does not vary as this outer layer becomes thinner, but displays a drastic shift to a rectifying behavior when this layer is completely stripped away from some regions of the nanofiber. This shift may be related with the compositional differences in the outer layer and the inner core of the nanofibers. Two-probe charge transport measurements on inductively coupled PECVD grown VACNFs indicate linear I-V behavior, and the resistivity of both types of inductively coupled PECVD grown VACNFs is on the order of 10-3 to 10-4 O·cm.

Zhang, Lan

213

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.

2006-08-04

214

A hybrid functional nanomaterial: POSS functionalized carbon nanofiber  

International Nuclear Information System (INIS)

[en] 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).

2009-08-12

215

Detection of ricin using a carbon nanofiber based biosensor.  

Science.gov (United States)

We report ricin detection using antibody and aptamer probes immobilized on a nanoelectrode array (NEA) consisting of vertically aligned carbon nanofibers (VACNFs). These biosensor chips are fabricated on a wafer scale using steps common in integrated circuit manufacturing. Electrochemical impedance spectroscopy is used to characterize the detection event and the results indicate that the electron transfer resistance changes significantly after the ricin protein binds to the probe. Further confirmation is obtained from evaluation of the electrode surface by atomic force microscopy which clearly shows a change in height from the bare electrode to the surface bound by the probe-protein. PMID:21852102

Periyakaruppan, Adaikkappan; Arumugam, Prabhu U; Meyyappan, M; Koehne, Jessica E

2011-07-31

216

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

217

Detection of ricin using a carbon nanofiber based biosensor.  

UK PubMed Central (United Kingdom)

We report ricin detection using antibody and aptamer probes immobilized on a nanoelectrode array (NEA) consisting of vertically aligned carbon nanofibers (VACNFs). These biosensor chips are fabricated on a wafer scale using steps common in integrated circuit manufacturing. Electrochemical impedance spectroscopy is used to characterize the detection event and the results indicate that the electron transfer resistance changes significantly after the ricin protein binds to the probe. Further confirmation is obtained from evaluation of the electrode surface by atomic force microscopy which clearly shows a change in height from the bare electrode to the surface bound by the probe-protein.

Periyakaruppan A; Arumugam PU; Meyyappan M; Koehne JE

2011-10-01

218

Electromagnetic Properties of Novel Carbon Nanofibers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 composit...

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

219

Carbon nanofibers decorated with poly(furfuryl alcohol)-derived carbon nanoparticles and tetraethylorthosilicate-derived silica nanoparticles.  

Science.gov (United States)

The present paper introduces a novel method to functionalize nanofiber surfaces with carbon or silica nanoparticles by dip coating. This novel approach holds promise of significant benefits because dip coating of electrospun and carbonized nanofiber mats in poly(furfuryl alcohol) (abbreviated as PFA) is used to increase surface roughness by means of PFA-derived carbon nanoparticles produced at the fiber surface. Also, dip coating in tetraethylorthosilicate (abbreviated as TEOS) is shown to be an effective method for decorating carbon nanofibers with TEOS-derived silica nanoparticles at their surface. Furthermore, dip coating is an inexpensive technique which is easier to implement than the existing methods of nanofiber decoration with silica nanoparticles and results in a higher loading capacity. Carbon nanofiber mats with PFA- or TEOS-decorated surfaces hold promise of becoming the effective electrodes in fuel cells, Li-ion batteries and storage devices. PMID:21981576

Zhang, Y; Yarin, A L

2011-10-25

220

Carbon nanofibers decorated with poly(furfuryl alcohol)-derived carbon nanoparticles and tetraethylorthosilicate-derived silica nanoparticles.  

UK PubMed Central (United Kingdom)

The present paper introduces a novel method to functionalize nanofiber surfaces with carbon or silica nanoparticles by dip coating. This novel approach holds promise of significant benefits because dip coating of electrospun and carbonized nanofiber mats in poly(furfuryl alcohol) (abbreviated as PFA) is used to increase surface roughness by means of PFA-derived carbon nanoparticles produced at the fiber surface. Also, dip coating in tetraethylorthosilicate (abbreviated as TEOS) is shown to be an effective method for decorating carbon nanofibers with TEOS-derived silica nanoparticles at their surface. Furthermore, dip coating is an inexpensive technique which is easier to implement than the existing methods of nanofiber decoration with silica nanoparticles and results in a higher loading capacity. Carbon nanofiber mats with PFA- or TEOS-decorated surfaces hold promise of becoming the effective electrodes in fuel cells, Li-ion batteries and storage devices.

Zhang Y; Yarin AL

2011-12-01

 
 
 
 
221

Soft-templated synthesis of mesoporous carbon nanospheres and hollow carbon nanofibers  

Science.gov (United States)

Using coal tar pitch based amphiphilic carbonaceous materials (ACMs) as the precursor and amphiphilic triblock copolymer Plutonic P123 as the only soft template, carbon nanospheres with partially ordered mesopores and hollow carbon nanofibers were synthesized. The concentration of P123, cp, and the mass ratio of P123 to ACM, r, are the key parameters of controlling the shape of the as-prepared products. Mesoporous carbon nanospheres with diameter of 30-150 nm were prepared under the condition of cp = 13.3 g/L and r = 1.2. When cp = 26.7 g/L and r = 2, hollow carbon nanofibers with diameters of 50-200 nm and mesopores/macropores were obtained. Carbon nanospheres and hollow carbon fibers were amorphous materials. The mesoporous carbon nanospheres show good stability in the cyclic voltammograms and their specific capacitance at 10 mV s-1 is 172.1 F/g.

Cheng, Youliang; Li, Tiehu; Fang, Changqing; Zhang, Maorong; Liu, Xiaolong; Yu, Ruien; Hu, Jingbo

2013-10-01

222

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.

2004-09-15

223

Titanium carbide/carbon composite nanofibers prepared by a plasma process  

International Nuclear Information System (INIS)

The incorporation of metal or metal carbide nanoparticles into carbon nanofibers modifies their properties and enlarges their field of application. The purpose of this work is to report a new non-catalytic and easy method to prepare organized metal carbide-carbon composite nanofibers on nanopatterned silicon substrates prepared by laser interference lithography coupled with deep reactive ion etching. Titanium carbide-carbon composite nanofibers were grown on the top of the silicon lines parallel to the substrate by a hybrid plasma process combining physical vapor deposition and plasma enhanced chemical vapor deposition. The prepared nanofibers were analyzed by scanning electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. We demonstrate that the shape, microstructure and the chemical composition of the as-grown nanofibers can be tuned by changing the plasma conditions.

2010-10-29

224

Characterization of Nanostructure and Electronic Properties of Catalytically Grown Carbon Nanofiber  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers were prepared from the decomposition of various carbon- containing gases over pure Ni, pure Fi and their alloys with Cu. The yields, properties and structure of carbon nanofibers obtained from the various reaction conditions were analyzed. Type of reacting gas, reaction temperature and catalyst composition were changed as the reaction variable. With Ni-Cu catalysts, the maximum yields of carbon nanofibers were obtained at temperatures between 550 and 650 deg. C according to the reacting gas mixtures of C{sub 2}H{sub 2}-H{sub 2}, C{sub 2}H{sub 4}-H{sub 2} and C{sub 3}H{sub 8}-H{sub 2}, and the surface areas of the carbon nanofibers produced were 20{approx}350m{sup 2}/g. In the case of CO-H{sub 2} mixture, the rapid deposition of carbon nanofibers occurred with Fe-Cu catalyst and the maximum yield were obtained around 550 deg. C with the range of surface areas of 140{approx}170m{sup 2}/g. The electrical resistivity of carbon nanofiber regarded as the key property of filler for the application of electromagnetic interference shielding was very sensitive to the type of reactant gas and the catalyst composition ranging 0.07{approx}1.5{omega}cm at a pressure of 10000 psi, and the resistivity of carbon nanofibers produced over pure nickel catalyst were lower than those over allot catalysts. SEM observation showed that the carbon nanofibers produced had the diameters ranging 20{approx}300 nm and the straight structure of carbon nanofibers changed into the twisted or helical conformation by the variation of reacting gas and catalyst composition. (author). 19 refs., 6 tabs., 5 figs.

Kim, M.S.; Woo, W.J.; Song, H.S.; Lee, Y.S.; Lee, J.C. [Myoungji University, Yongin (Korea)

2000-04-01

225

Effect of temperature on the electron field emission from aligned carbon nanofibers and multiwalled carbon nanotubes  

International Nuclear Information System (INIS)

Effect of temperature and aspect ratio on the field emission properties of vertically aligned carbon nanofiber and multiwalled carbon nanotube thin films were studied in detail. Carbon nanofibers and multiwalled carbon nanotube have been synthesized on Si substrates via direct current plasma enhanced chemical vapor deposition technique. Surface morphologies of the films have been studied by a scanning electron microscope, transmission electron microscope and an atomic force microscope. It is found that the threshold field and the emission current density are dependent on the ambient temperature as well as on the aspect ratio of the carbon nanostructure. The threshold field for carbon nanofibers was found to decrease from 5.1 to 2.6 V/?m when the temperature was raised from 300 to 650 K, whereas for MWCNTs it was found to decrease from 4.0 to 1.4 V/?m. This dependence was due to the change in work function of the nanofibers and nanotubes with temperature. The field enhancement factor, current density and the dependence of the effective work function with temperature and with aspect ratio were calculated and we have tried to explain the emission mechanism.

2007-11-15

226

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

227

Temperature and substrate dependence of structure and growth mechanism of carbon nanofiber  

International Nuclear Information System (INIS)

The carbon nanofibers were grown on Ni/Si and Ni/Ti/Si substrates in 1 atm CH4 atmosphere at 640 deg. C and 700 deg. C by thermal chemical vapor deposition method. The carbon nanofibers were characterized by field emission scanning electron microscopy, transmission electron microscopy, and Raman spectrometry for morphology, microstructure, and crystallinity. The electron emission property of carbon nanofibers was also investigated by current-voltage (I-V) measurement. The results showed that the solid amorphous carbon nanofibers could be grown on Ni/Si substrate at 640 deg. C through tip growth mechanism, the carbon nanotubes could be grown on Ni/Si substrate at 700 deg. C through tip growth mechanism, and the carbon nanotubes could be grown on Ni/Ti/Si substrate at 700 deg. C through root growth mechanism.

2008-05-30

228

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.

2012-05-01

229

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

2013-01-01

230

Characterization of polyacrylonitrile based carbon nanofiber mats via electron beam processing.  

UK PubMed Central (United Kingdom)

The aim of this study was to evaluate the ability of electron beam irradiation to drive stabilization reactions within PAN nanofiber mats to obtain carbon nanofiber mats. PAN nanofiber mats with fiber diameters of 300-400 nm were prepared via an electrospinning method. Electrospun PAN nanofiber mats were stabilized by electron beam irradiation with various doses up to 5,000 kGy. Using the irradiation-stabilized PAN nanofiber mats, carbon nanofibers were obtained by pyrolysis in a tube furnace for 1 h at 1,000 degrees C under an N2 atmosphere. FT-IR analysis indicated that the transformation of C[triple bond]N groups to C==N groups was accelerated by electron beam stabilization. The thermal behavior of the PAN nanofiber mats was studied using DSC and TGA. DSC thermograms showed that the peak temperatures of the exothermic reactions were found to decrease with increasing electron beam irradiation doses. Irradiation-stabilized PAN nanofiber mats were not observed to dramatically decrease in weight between 290 degrees C and 320 degrees C, an observation presumed to be related to cyclization. The char yields of PAN were found to increase with increasing irradiation doses.

Kim DY; Shin HK; Jeun JP; Kim HB; Oh SH; Kang PH

2012-07-01

231

Characterization of polyacrylonitrile based carbon nanofiber mats via electron beam processing.  

Science.gov (United States)

The aim of this study was to evaluate the ability of electron beam irradiation to drive stabilization reactions within PAN nanofiber mats to obtain carbon nanofiber mats. PAN nanofiber mats with fiber diameters of 300-400 nm were prepared via an electrospinning method. Electrospun PAN nanofiber mats were stabilized by electron beam irradiation with various doses up to 5,000 kGy. Using the irradiation-stabilized PAN nanofiber mats, carbon nanofibers were obtained by pyrolysis in a tube furnace for 1 h at 1,000 degrees C under an N2 atmosphere. FT-IR analysis indicated that the transformation of C[triple bond]N groups to C==N groups was accelerated by electron beam stabilization. The thermal behavior of the PAN nanofiber mats was studied using DSC and TGA. DSC thermograms showed that the peak temperatures of the exothermic reactions were found to decrease with increasing electron beam irradiation doses. Irradiation-stabilized PAN nanofiber mats were not observed to dramatically decrease in weight between 290 degrees C and 320 degrees C, an observation presumed to be related to cyclization. The char yields of PAN were found to increase with increasing irradiation doses. PMID:22966719

Kim, Du-Yeong; Shin, Hye-Kyoung; Jeun, Joon-Pyo; Kim, Hyun-Bin; Oh, Seung-Hwan; Kang, Phil-Hyun

2012-07-01

232

Review of the Fabrication and Properties of Vapor-Grown Carbon Nanofiber/Polymer Composites (Preprint).  

Science.gov (United States)

Several varieties of vapor-grown carbon nanofibers with diameters under 200 nm and conically shaped grapheme planes canted with respect to the longitudinal fiber axis are available. Because of the strong interfiber bonding, compounding these fibers with p...

B. P. Rice G. G. Tibbetts K. L. Strong M. L. Lake

2006-01-01

233

Pt/carbon nanofibers electrocatalysts for fuel cells. Effect of the support oxidizing treatment  

Energy Technology Data Exchange (ETDEWEB)

Different Pt-based electrocatalysts supported on carbon nanofibers and carbon black (Vulcan XC-72R) have been prepared using a polymer-mediated synthesis. The electrocatalysts have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and cyclic voltammetry. The effect of carbon nanofibers treatment with HNO{sub 3} solution on Pt particle size and electroactive area has been analyzed. Highly dispersed Pt with homogeneous particle size and an electroactive area around of 100 m{sup 2} g{sup -1} is obtained in raw carbon nanofibers. The oxidizing treatment of the carbon nanofibers produces agglomeration of the platinum nanoparticles and an electroactive area of 53 m{sup 2} g{sup -1}. Durability studies indicate a decrease of 14% in the electroactive area after 90 h at 1.2 V in 0.5 M H{sub 2}SO{sub 4} for platinum supported on raw carbon nanofibers and Vulcan XC-72R. The electrocatalyst supported on oxidized carbon nanofibers are stable under similar conditions. (author)

Zaragoza-Martin, F.; de Lecea, C. Salinas-Martinez [Departamento de Quimica Inorganica, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain); Sopena-Escario, D. [Fundacion CIDAUT, Parque tecnologico de Boecillo, E-47151 Boecillo (Valladolid) (Spain); Morallon, E. [Departamento de Quimica Fisica e Instituto Universitario de Materiales, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)

2007-09-27

234

Supercapacitance from cellulose and carbon nanotube nanocomposite fibers.  

UK PubMed Central (United Kingdom)

Multiwalled carbon nanotube (MWNT)/cellulose composite nanofibers have been prepared by electrospinning a MWNT/cellulose acetate blend solution followed by deacetylation. These composite nanofibers were then used as precursors for carbon nanofibers (CNFs). The effect of nanotubes on the stabilization of the precursor and microstructure of the resultant CNFs were investigated using thermogravimetric analysis, transmission electron microscopy and Raman spectroscopy. It is demonstrated that the incorporated MWNTs reduce the activation energy of the oxidative stabilization of cellulose nanofibers from ?230 to ?180 kJ mol(-1). They also increase the crystallite size, structural order, and electrical conductivity of the activated CNFs (ACNFs). The surface area of the ACNFs increased upon addition of nanotubes which protrude from the fiber leading to a rougher surface. The ACNFs were used as the electrodes of a supercapacitor. The electrochemical capacitance of the ACNF derived from pure cellulose nanofibers is demonstrated to be 105 F g(-1) at a current density of 10 A g(-1), which increases to 145 F g(-1) upon the addition of 6% of MWNTs.

Deng L; Young RJ; Kinloch IA; Abdelkader AM; Holmes SM; De Haro-Del Rio DA; Eichhorn SJ

2013-10-01

235

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 va...

Khalid Lafdi; William Fox; Matthew Matzek; Emel Yildiz

236

Hollow carbon nanofiber-encapsulated sulfur cathodes for high specific capacity rechargeable lithium batteries.  

Science.gov (United States)

Sulfur has a high specific capacity of 1673 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a hollow carbon nanofiber-encapsulated sulfur cathode for effective trapping of polysulfides and demonstrate experimentally high specific capacity and excellent electrochemical cycling of the cells. The hollow carbon nanofiber arrays were fabricated using anodic aluminum oxide (AAO) templates, through thermal carbonization of polystyrene. The AAO template also facilitates sulfur infusion into the hollow fibers and prevents sulfur from coating onto the exterior carbon wall. The high aspect ratio of the carbon nanofibers provides an ideal structure for trapping polysulfides, and the thin carbon wall allows rapid transport of lithium ions. The small dimension of these nanofibers provides a large surface area per unit mass for Li(2)S deposition during cycling and reduces pulverization of electrode materials due to volumetric expansion. A high specific capacity of about 730 mAh/g was observed at C/5 rate after 150 cycles of charge/discharge. The introduction of LiNO(3) additive to the electrolyte was shown to improve the Coulombic efficiency to over 99% at C/5. The results show that the hollow carbon nanofiber-encapsulated sulfur structure could be a promising cathode design for rechargeable Li/S batteries with high specific energy. PMID:21916442

Zheng, Guangyuan; Yang, Yuan; Cha, Judy J; Hong, Seung Sae; Cui, Yi

2011-09-20

237

Hollow carbon nanofiber-encapsulated sulfur cathodes for high specific capacity rechargeable lithium batteries.  

UK PubMed Central (United Kingdom)

Sulfur has a high specific capacity of 1673 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a hollow carbon nanofiber-encapsulated sulfur cathode for effective trapping of polysulfides and demonstrate experimentally high specific capacity and excellent electrochemical cycling of the cells. The hollow carbon nanofiber arrays were fabricated using anodic aluminum oxide (AAO) templates, through thermal carbonization of polystyrene. The AAO template also facilitates sulfur infusion into the hollow fibers and prevents sulfur from coating onto the exterior carbon wall. The high aspect ratio of the carbon nanofibers provides an ideal structure for trapping polysulfides, and the thin carbon wall allows rapid transport of lithium ions. The small dimension of these nanofibers provides a large surface area per unit mass for Li(2)S deposition during cycling and reduces pulverization of electrode materials due to volumetric expansion. A high specific capacity of about 730 mAh/g was observed at C/5 rate after 150 cycles of charge/discharge. The introduction of LiNO(3) additive to the electrolyte was shown to improve the Coulombic efficiency to over 99% at C/5. The results show that the hollow carbon nanofiber-encapsulated sulfur structure could be a promising cathode design for rechargeable Li/S batteries with high specific energy.

Zheng G; Yang Y; Cha JJ; Hong SS; Cui Y

2011-10-01

238

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 Concentration Sensor System (WINCS) for the 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 electrode 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

2011-03-08

239

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

UK PubMed Central (United Kingdom)

A carbon nanofiber (CNF) electrode array was integrated with the Wireless Instantaneous Neurotransmitter Concentration Sensor System (WINCS) for the 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 electrode for neurochemical monitoring.

Koehne JE; Marsh M; Boakye A; Douglas B; Kim IY; Chang SY; Jang DP; Bennet KE; Kimble C; Andrews R; Meyyappan M; Lee KH

2011-05-01

240

Study of an alternative process for oxidizing Vapor Grown Carbon Nanofibers using electron beam accelerators  

Science.gov (United States)

The use of a high-energy electron beam was explored in this study as an alternative technique for oxidizing vapor grown carbon nanofiber surfaces. The radiation exposures were carried out at three different electron beam facilities with beam energies of 1.5, 3.0 and 4.5 MeV and radiation doses ranging from 1000 to 3500 kGy. XPS analysis showed that oxygen was readily incorporated on the surface: the ratio O1s/C1s increased approximately by a factor of 4 when the carbon nanofibers were irradiated at 3500 kGy. The oxidized nanofibers exhibited better dispersion in a water/methanol solution (50% v/v) than as-received nanofibers. Raman spectroscopy revealed that the ID/IG ratios for most of the samples were statistically unchanged because the damage on the nanofiber surface was highly localized and did not lead to modifications on the bulk carbon nanofiber structure. The samples irradiated at higher dose rate exhibited significantly higher ID/IG ratios. The radiation process introduced defects on the graphene layers leading to a decrease of the decomposition onset temperatures up to 56 °C lower than the non-irradiated samples. Overall the results were repeatable across all facilities, illustrating the robustness of the process.

Evora, M. C.; Klosterman, D.; Lafdi, K.; Li, L.; Silva, L. G. A.

2013-03-01

 
 
 
 
241

Electrospun single-walled carbon nanotube/polyvinyl alcohol composite nanofibers: structure-property relationships  

International Nuclear Information System (INIS)

Polyvinyl alcohol (PVA) nanofibers and single-walled carbon nanotube (SWNT)/PVA composite nanofibers have been produced by electrospinning. An apparent increase in the PVA crystallinity with a concomitant change in its main crystalline phase and a reduction in the crystalline domain size were observed in the SWNT/PVA composite nanofibers, indicating the occurrence of a SWNT-induced nucleation crystallization of the PVA phase. Both the pure PVA and SWNT/PVA composite nanofibers were subjected to the following post-electrospinning treatments: (i) soaking in methanol to increase the PVA crystallinity, and (ii) cross-linking with glutaric dialdehyde to control the PVA morphology. Effects of the PVA morphology on the tensile properties of the resultant electrospun nanofibers were examined. Dynamic mechanical thermal analyses of both pure PVA and SWNT/PVA composite electrospun nanofibers indicated that SWNT-polymer interaction facilitated the formation of crystalline domains, which can be further enhanced by soaking the nanofiber in methanol and/or cross-linking the polymer with glutaric dialdehyde.

2008-07-30

242

Electrospun carbon-tin oxide composite nanofibers for use as lithium ion battery anodes.  

UK PubMed Central (United Kingdom)

Composite carbon-tin oxide (C-SnO(2)) nanofibers are prepared by two methods and evaluated as anodes in lithium-ion battery half cells. Such an approach complements the long cycle life of carbon with the high lithium storage capacity of tin oxide. In addition, the high surface-to-volume ratio of the nanofibers improves the accessibility for lithium intercalation as compared to graphite-based anodes, while eliminating the need for binders or conductive additives. The composite nanofibrous anodes have first discharge capacities of 788 mAh g(-1) at 50 mA g(-1) current density, which are greater than pure carbon nanofiber anodes, as well as the theoretical capacity of graphite (372 mAh g(-1)), the traditional anode material. In the first protocol to fabricate the C-SnO(2) composites, tin sulfate is directly incorporated within polyacrylonitrile (PAN) nanofibers by electrospinning. During a thermal treatment the tin salt is converted to tin oxide and the polymer is carbonized, yielding carbon-SnO(2) nanofibers. In the second approach, we soak the nanofiber mats in tin sulfate solutions prior to the final thermal treatment, thereby loading the outer surfaces with SnO(2) nanoparticles and raising the tin content from 1.9 to 8.6 wt %. Energy-dispersive spectroscopy and X-ray diffraction analyses confirm the formation of conversion of tin sulfate to tin oxide. Furthermore, analysis with Raman spectroscopy reveals that the additional salt soak treatment from the second fabrication approach increases in the disorder of the carbon structure, as compared to the first approach. We also discuss the performance of our C-SnO(2) compared with its theoretical capacity and other nanofiber electrode composites previously reported in the literature.

Bonino CA; Ji L; Lin Z; Toprakci O; Zhang X; Khan SA

2011-07-01

243

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)

2012-05-11

244

Experimental study and modeling of swelling and bubble growth in carbon nanofiber filled mesophase pitch during carbonization  

Science.gov (United States)

Graphite and all carbon bipolar plates show corrosion resistance in fuel cells and provide good electrical conductivity. These materials typically need to be individually machined, a time consuming and costly process. Mesophase pitch is used to manufacture carbon fibers and carbon-carbon composites. This material provides a good starting point for the production of a moldable, all carbon bipolar plate. However, processing of mesophase pitch to produce all carbon materials requires a time intensive oxidation step to prevent swelling during carbonization. In this work, carbon nanofibers were used to reduce swelling in mesophase pitch. It was found that the increase in viscosity with the addition of carbon nanofibers was responsible for the reduction in swelling. The influence of the filler became apparent above the percolation threshold. At loadings below the percolation threshold, the swelling of the mesophase pitch was not reduced after carbonization. The swelling of the mesophase pitch at a given carbon nanofiber loading was also dependent on the length of the carbon nanofibers. Longer carbon nanofibers led to greater increases in the viscosity of the melt and thus led to greater reduction in swelling. The final carbon product was evaluated for use as a low temperature fuel cell bipolar plate material. Constraining the mesophase pitch during carbonization led to a final product with strength and electrical conductivity comparable to current composite bipolar plate materials. The addition of micron size chopped glass fibers with a softening point near 850°C and carbon nanofibers led to a final product with air permeability less than that of graphite. A spherically symmetric, single bubble growth model was also developed. The model included temperature dependence, liquid to bubble mass transfer and reactions in the system. Results from simulations showed that that the increase in viscosity due to the addition of carbon nanofibers slows the growth of bubbles, but that the time scale of single bubble growth is much shorter than the time over which the foam grows. The single bubble growth model was deemed to be applicable to low loadings of carbon nanofiber, where the bubble size distribution in the final foam is narrow.

Calebrese, Christopher

245

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 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.

2006-08-15

246

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

247

Electrochemical stability of carbon nanofibers in proton exchange membrane fuel cells  

International Nuclear Information System (INIS)

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.

2011-10-30

248

Use of novel carbon-nanofiber-doped carbon liquid crystals as suitable adsorbents for hydrogen storage  

Energy Technology Data Exchange (ETDEWEB)

Over the last few years a number of groups have been exploring the possibilities and limitations associated with using adsorption on newly developed materials for the storage of hydrogen. Here we report the results of hydrogen adsorption investigations on a newly synthesized form of carbon nanofiber-doped carbon liquid crystals. This material shows a marked increase in specific surface area upon activation with water vapor, leading to activated samples that are capable of adsorbing hydrogen upto 3.5% by weight at 77.3 K, at moderate pressures. The possibility of higher adsorption ({proportional_to}6.5 wt. %) in these materials is also discussed. (orig.)

Rawat, D.S.; Talapatra, S.; Migone, A.D. [Department of Physics, Southern Illinois University at Carbondale, 62901, Carbondale, Illinois (United States); Lafdi, K. [University of Dayton Research Institute, 300 College Park, 45469-0168, Dayton, OH (United States); Air Force Research Lab/MLBC, Wright Patterson Air Force Base, 45433, OH (United States)

2004-04-01

249

Patterned growth of individual and multiple vertically aligned carbon nanofibers  

International Nuclear Information System (INIS)

The results of studies of patterned growth of vertically aligned carbon nanofibers (VACNFs) prepared by plasma-enhanced chemical vapor deposition are reported. Nickel (Ni) dots of various diameters and Ni lines with variable widths and shapes were fabricated using electron beam lithography and evaporation, and served for catalytic growth of VACNFs whose structure was determined by high resolution transmission electron microscopy. It is found that upon plasma pre-etching and heating up to 600-700 degree sign C, thin films of Ni break into droplets which initiate the growth of VACNFs. Above a critical dot size multiple droplets are formed, and consequently multiple VACNFs grow from a single evaporated dot. For dot sizes smaller than the critical size only one droplet is formed, resulting in a single VACNF. In the case of a patterned line, the growth mechanism is similar to that from a dot. VACNFs grow along the line, and above a critical linewidth multiple VACNFs are produced across the line. The mechanism of the formation of single and multiple catalyst droplets and subsequently of VACNFs is discussed. (c) 2000 American Institute of Physics

2000-06-12

250

Patterned growth of individual and multiple vertically aligned carbon nanofibers  

Science.gov (United States)

The results of studies of patterned growth of vertically aligned carbon nanofibers (VACNFs) prepared by plasma-enhanced chemical vapor deposition are reported. Nickel (Ni) dots of various diameters and Ni lines with variable widths and shapes were fabricated using electron beam lithography and evaporation, and served for catalytic growth of VACNFs whose structure was determined by high resolution transmission electron microscopy. It is found that upon plasma pre-etching and heating up to 600-700 °C, thin films of Ni break into droplets which initiate the growth of VACNFs. Above a critical dot size multiple droplets are formed, and consequently multiple VACNFs grow from a single evaporated dot. For dot sizes smaller than the critical size only one droplet is formed, resulting in a single VACNF. In the case of a patterned line, the growth mechanism is similar to that from a dot. VACNFs grow along the line, and above a critical linewidth multiple VACNFs are produced across the line. The mechanism of the formation of single and multiple catalyst droplets and subsequently of VACNFs is discussed.

Merkulov, V. I.; Lowndes, D. H.; Wei, Y. Y.; Eres, G.; Voelkl, E.

2000-06-01

251

Patterned growth of individual and multiple vertically aligned carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

The results of studies of patterned growth of vertically aligned carbon nanofibers (VACNFs) prepared by plasma-enhanced chemical vapor deposition are reported. Nickel (Ni) dots of various diameters and Ni lines with variable widths and shapes were fabricated using electron beam lithography and evaporation, and served for catalytic growth of VACNFs whose structure was determined by high resolution transmission electron microscopy. It is found that upon plasma pre-etching and heating up to 600-700 degree sign C, thin films of Ni break into droplets which initiate the growth of VACNFs. Above a critical dot size multiple droplets are formed, and consequently multiple VACNFs grow from a single evaporated dot. For dot sizes smaller than the critical size only one droplet is formed, resulting in a single VACNF. In the case of a patterned line, the growth mechanism is similar to that from a dot. VACNFs grow along the line, and above a critical linewidth multiple VACNFs are produced across the line. The mechanism of the formation of single and multiple catalyst droplets and subsequently of VACNFs is discussed. (c) 2000 American Institute of Physics.

Merkulov, V. I. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Lowndes, D. H. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Wei, Y. Y. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Eres, G. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Voelkl, E. [Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2000-06-12

252

Individually addressable vertically aligned carbon nanofiber-based electrochemical probes  

Science.gov (United States)

In this paper we present the fabrication and initial testing results of high aspect ratio vertically aligned carbon nanofiber (VACNF)-based electrochemical probes. Electron beam lithography was used to define the catalytic growth sites of the VACNFs. Following catalyst deposition, VACNF were grown using a plasma enhanced chemical vapor deposition process. Photolithography was performed to realize interconnect structures. These probes were passivated with a thin layer of SiO2, which was then removed from the tips of the VACNF, rendering them electrochemically active. We have investigated the functionality of completed devices using cyclic voltammetry (CV) of ruthenium hexammine trichloride, a highly reversible, outer sphere redox system. The faradaic current obtained during CV potential sweeps shows clear oxidation and reduction peaks at magnitudes that correspond well with the geometry of these nanoscale electrochemical probes. Due to the size and the site-specific directed synthesis of the VACNFs, these probes are ideally suited for characterizing electrochemical phenomena with an unprecedented degree of spatial resolution.

Guillorn, M. A.; McKnight, T. E.; Melechko, A.; Merkulov, V. I.; Britt, P. F.; Austin, D. W.; Lowndes, D. H.; Simpson, M. L.

2002-03-01

253

Manipulation of bacteriophages with dielectrophoresis on carbon nanofiber nanoelectrode arrays.  

Science.gov (United States)

This work describes efficient manipulation of bacteriophage virus particles using a nanostructured DEP device. The nonuniform electric field for DEP is created by utilizing a nanoelectrode array (NEA) made of vertically aligned carbon nanofibers versus a macroscopic indium tin oxide electrode in a "points-and-lid" configuration integrated in a microfluidic channel. The capture of the virus particles has been systematically investigated versus the flow velocity, sinusoidal AC frequency, peak-to-peak voltage, and virus concentration. The DEP capture at all conditions is reversible and the captured virus particles are released immediately when the voltage is turned off. At the low virus concentration (8.9 × 10(4) pfu/mL), the DEP capture efficiency up to 60% can be obtained. The virus particles are individually captured at isolated nanoelectrode tips and accumulate linearly with time. Due to the comparable size, it is more effective to capture virus particles than larger bacterial cells with such NEA-based DEP devices. This technique can be potentially utilized as a fast sample preparation module in a microfluidic chip to capture, separate, and concentrate viruses and other biological particles in small volumes of dilute solutions in a portable detection system for field applications. PMID:23348683

Madiyar, Foram R; Syed, Lateef U; Culbertson, Christopher T; Li, Jun

2013-03-11

254

Manipulation of bacteriophages with dielectrophoresis on carbon nanofiber nanoelectrode arrays.  

UK PubMed Central (United Kingdom)

This work describes efficient manipulation of bacteriophage virus particles using a nanostructured DEP device. The nonuniform electric field for DEP is created by utilizing a nanoelectrode array (NEA) made of vertically aligned carbon nanofibers versus a macroscopic indium tin oxide electrode in a "points-and-lid" configuration integrated in a microfluidic channel. The capture of the virus particles has been systematically investigated versus the flow velocity, sinusoidal AC frequency, peak-to-peak voltage, and virus concentration. The DEP capture at all conditions is reversible and the captured virus particles are released immediately when the voltage is turned off. At the low virus concentration (8.9 × 10(4) pfu/mL), the DEP capture efficiency up to 60% can be obtained. The virus particles are individually captured at isolated nanoelectrode tips and accumulate linearly with time. Due to the comparable size, it is more effective to capture virus particles than larger bacterial cells with such NEA-based DEP devices. This technique can be potentially utilized as a fast sample preparation module in a microfluidic chip to capture, separate, and concentrate viruses and other biological particles in small volumes of dilute solutions in a portable detection system for field applications.

Madiyar FR; Syed LU; Culbertson CT; Li J

2013-04-01

255

Electrical properties of isotactic polypropylene loaded with carbon nanofibers  

Science.gov (United States)

Nanocomposites have been obtained by dispersing vapor grown carbon nanofibers (VGCNF) within isotactic polypropylene (iPP) via melt mixing. VGCNFs were purified and disentangled before blending with iPP. The mixing was performed by using HAAKE Rheomix, at 180 ^oC and 65 rpm for 9 minutes followed by an additional mixing at 90 rpm for 5 minutes (same temperature). The electrical properties of nanocomposites loaded with various amounts of VGCNFs (0%, 1%, 2.5%, 5%, 7.5%, 10%, 15%, and 20% wt.) have been investigated. DC electrical measurements revealed a percolation threshold at about 12 % wt. VGCNFs. The DC electrical characteristics of the nanocomposites located above the percolation threshold were investigated in detail, in a wide temperature range starting from 20 K up to about 750 K. The investigations revealed small changes of the DC conductivity within the glass and melting transition range of the polymeric matrix. The dominant charge transport mechanism below the glass transition temperature as well as between the glass and melting transition temperature is the variable range hopping. Above the melting temperature an Arrhenius like dependence of the DC conductivity was noticed.

Chipara, Mircea; Ciurea, Magdalena L.; Lozano, Karen; Aldica, Gheorghe V.; Chipara, Dorina M.; Popa, Stelian; Stavarache, Ionel

2013-03-01

256

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

257

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

2013-05-03

258

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

2009-01-01

259

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

260

Nickel nanoparticle chains inside carbonized polymer nanofibers: preparation by electrospinning and ion-beam irradiation  

Science.gov (United States)

Novel organic-inorganic composite 1D nanostructures composed of carbonized conductive nanofibers and nickel nanoparticle chains were prepared by the combination of an electrospinning method from metal complex-containing polymer solutions and an ion-beam irradiation technique. The nickel nanoparticle chains were formed by self-assembly inside the carbonized nanofibers, which were characterized by STEM-HAADF observation and XPS spectroscopy. The existence of nickel complexes and the subsequent formation of nickel nanoparticles enhanced the electrical conductivities of carbonized nanofibers to reach above 0.5 S cm-1 for the 6FDA-6FAP nanofibrous membrane containing 5.0 wt% Ni(acac)2 after ion-beam irradiation at an ion fluence of 1 × 1016 ions per cm2.Novel organic-inorganic composite 1D nanostructures composed of carbonized conductive nanofibers and nickel nanoparticle chains were prepared by the combination of an electrospinning method from metal complex-containing polymer solutions and an ion-beam irradiation technique. The nickel nanoparticle chains were formed by self-assembly inside the carbonized nanofibers, which were characterized by STEM-HAADF observation and XPS spectroscopy. The existence of nickel complexes and the subsequent formation of nickel nanoparticles enhanced the electrical conductivities of carbonized nanofibers to reach above 0.5 S cm-1 for the 6FDA-6FAP nanofibrous membrane containing 5.0 wt% Ni(acac)2 after ion-beam irradiation at an ion fluence of 1 × 1016 ions per cm2. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02421k

Sode, Katsuya; Tanaka, Manabu; Suzuki, Yoshiaki; Kawakami, Hiroyoshi

2013-08-01

 
 
 
 
261

Vertically aligned carbon nanofibers and related structures: Controlled synthesis and directed assembly  

Science.gov (United States)

The controlled synthesis of materials by methods that permit their assembly into functional nanoscale structures lies at the crux of the emerging field of nanotechnology. Although only one of several materials families is of interest, carbon-based nanostructured materials continue to attract a disproportionate share of research effort, in part because of their wide-ranging properties. Additionally, developments of the past decade in the controlled synthesis of carbon nanotubes and nanofibers have opened additional possibilities for their use as functional elements in numerous applications. Vertically aligned carbon nanofibers (VACNFs) are a subclass of carbon nanostructured materials that can be produced with a high degree of control using catalytic plasma-enhanced chemical-vapor deposition (C-PECVD). Using C-PECVD the location, diameter, length, shape, chemical composition, and orientation can be controlled during VACNF synthesis. Here we review the CVD and PECVD systems, growth control mechanisms, catalyst preparation, resultant carbon nanostructures, and VACNF properties. This is followed by a review of many of the application areas for carbon nanotubes and nanofibers including electron field-emission sources, electrochemical probes, functionalized sensor elements, scanning probe microscopy tips, nanoelectromechanical systems (NEMS), hydrogen and charge storage, and catalyst support. We end by noting gaps in the understanding of VACNF growth mechanisms and the challenges remaining in the development of methods for an even more comprehensive control of the carbon nanofiber synthesis process.

Melechko, A. V.; Merkulov, V. I.; McKnight, T. E.; Guillorn, M. A.; Klein, K. L.; Lowndes, D. H.; Simpson, M. L.

2005-02-01

262

Vertically aligned carbon nanofibers and related structures: Controlled synthesis and directed assembly  

International Nuclear Information System (INIS)

The controlled synthesis of materials by methods that permit their assembly into functional nanoscale structures lies at the crux of the emerging field of nanotechnology. Although only one of several materials families is of interest, carbon-based nanostructured materials continue to attract a disproportionate share of research effort, in part because of their wide-ranging properties. Additionally, developments of the past decade in the controlled synthesis of carbon nanotubes and nanofibers have opened additional possibilities for their use as functional elements in numerous applications. Vertically aligned carbon nanofibers (VACNFs) are a subclass of carbon nanostructured materials that can be produced with a high degree of control using catalytic plasma-enhanced chemical-vapor deposition (C-PECVD). Using C-PECVD the location, diameter, length, shape, chemical composition, and orientation can be controlled during VACNF synthesis. Here we review the CVD and PECVD systems, growth control mechanisms, catalyst preparation, resultant carbon nanostructures, and VACNF properties. This is followed by a review of many of the application areas for carbon nanotubes and nanofibers including electron field-emission sources, electrochemical probes, functionalized sensor elements, scanning probe microscopy tips, nanoelectromechanical systems (NEMS), hydrogen and charge storage, and catalyst support. We end by noting gaps in the understanding of VACNF growth mechanisms and the challenges remaining in the development of methods for an even more comprehensive control of the carbon nanofiber synthesis process.

2005-02-15

263

Synthesis of vertically aligned carbon nanofibers for interfacing with live systems  

Energy Technology Data Exchange (ETDEWEB)

The ability to synthesize carbon nanofibers with a high degree of control over their geometry, location, and structure via catalytic plasma-enhanced chemical vapor deposition has expanded the possibility of new applications. The nanoscale dimensions and high aspect ratio of vertically aligned carbon nanofibers (VACNFs), along with favorable physical and chemical characteristics, has provided a nanostructured material with properties that are well-suited for interfacing with live cells and tissues. This review surveys the aspects of synthesis, integration, and functionalization of VACNFs, followed by examples of how VACNFs have been used to interface with live systems for a variety of advanced nanoscale biological applications.

Melechko, Anatoli Vasilievich [ORNL; Desikan, Ramya [ORNL; McKnight, Timothy E [ORNL; Klein, Kate L [ORNL; Rack, P. D. [University of Tennessee, Knoxville (UTK)

2009-01-01

264

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.

2013-05-01

265

Effect of filler dispersion on the electromechanical response of epoxy/vapor-grown carbon nanofiber composites  

Science.gov (United States)

The piezoresistive response of epoxy/vapor-grown carbon nanofiber composites prepared by four different dispersion methods achieving different dispersion levels has been investigated. The composite response was measured as a function of carbon nanofiber loading for the different dispersion methods. Strain sensing by variation of the electrical resistance was tested through four-point bending experiments, and the dependence of the gauge factor as a function of the deformation and velocity of deformation was calculated as well as the stability of the electrical response. The composites demonstrated an appropriate response for being used as a piezoresistive sensor. Specific findings were that the intrinsic piezoresistive response was only effective around the percolation threshold and that good cluster dispersion was more appropriate for a good piezoresistive response than a uniform dispersion of individual nanofibers. The application limits of these materials for sensor applications are also addressed.

Ferreira, A.; Cardoso, P.; Klosterman, D.; Covas, J. A.; van Hattum, F. W. J.; Vaz, F.; Lanceros-Mendez, S.

2012-07-01

266

Direct measurement of bending stiffness and estimation of Young's modulus of vertically aligned carbon nanofibers  

Science.gov (United States)

The bending stiffness of individual, as-grown, vertically aligned carbon nanofibers was measured using a custom-built atomic force microscope placed inside a scanning electron microscope. The internal structure of the nanofiber was best modeled as dual-phase, composed of an inner graphitic core covered with a tapered amorphous carbon shell. It was found that the fibers have a relatively low bending stiffness, with Young's modulus values of about 10 GPa for the inner core and 65 GPa for the outer shell. The low Young's modulus of the inner core is attributed to a non-zero angle between the graphitic sheets and the nanofiber axis. The weak shear modulus between graphitic sheets thereby dominates the mechanical behaviour of the fibers.

Ghavanini, F. A.; Jackman, H.; Lundgren, P.; Svensson, K.; Enoksson, P.

2013-05-01

267

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.

268

Silicon nanoparticles encapsulated in hollow graphitized carbon nanofibers for lithium ion battery anodes.  

UK PubMed Central (United Kingdom)

Silicon (Si) is a promising material for lithium ion battery (LIB) anodes due to its high specific capacity. To overcome its shortcomings such as insulation property and large volume change during the charge-discharge process, a novel hybrid system, Si nanoparticles encapsulated in hollow graphitized carbon nanofibers, is studied. First, electrospun polyacrylonitrile (PAN)-Si hybrid nanofibers were obtained using water as the collector. The loose nanofiber lumps suspended in water have large inter-fiber distance, allowing in situ coating of a thin layer of polydopamine (PDA), the source for graphitized carbon, uniformly throughout the system. The designed morphology and structure were then realized by etching and calcination, and the morphology and structure were subsequently verified by various analytical techniques. Electrochemical measurements show that the resulting hollow hybrid nanofibers (C-PDA-Si NFs) exhibit much better cycling stability and rate capacity than conventional C/Si nanofibers derived by electrospinning of PAN-Si followed by calcination. For instance, the capacity of C-PDA-Si NFs is as high as 72.6% of the theoretical capacity after 50 cycles, and a high capacity of 500 mA h g(-1) can be delivered at a current density of 5 A g(-1). The significantly improved electrochemical properties of C-PDA-Si NFs are due to the excellent electrical conductivity of the carbonized PDA (C-PDA) shell that compensates for the insulation property of Si, the high electrochemical activity of C-PDA, which has a layered structure and is N-doped, the hollow nature of the nanofibers and small size of Si nanoparticles that ensure smooth insertion-extraction of lithium ions and more complete alloying with them, as well as the buffering effect of the remaining PAN-derived carbon around the Si nanoparticles, which stabilizes the structure.

Kong J; Yee WA; Wei Y; Yang L; Ang JM; Phua SL; Wong SY; Zhou R; Dong Y; Li X; Lu X

2013-04-01

269

Nickel/carbon nanofibers composite electrodes as supercapacitors prepared by electrospinning  

International Nuclear Information System (INIS)

Nickel-embedded carbon nanofibers were prepared by the processes of stabilization and carbonation after electrospinning a mixture solution of nickel acetate and polyacrylonitrile in N,N-dimethylformamide. The surface morphology and structure of composites were examined by scanning electron microscope (SEM) and X-ray diffraction (XRD). Compared with performances of composite electrodes with different mass ratios of nickel and carbon by cyclic voltammetry (CV) and chronopotentiogram test, the results show that the introduction of a proper proportion of nickel into carbon could enhance both specific capacitance (SC) and electrochemical stability. The specific capacitance of the carbon nanofiber electrode without the Ni loading was 50 F/g, while that of 22.4 wt.% Ni/carbon electrode increased to 164 F/g. The improved specific capacitance may be attributed to synergic effects from each pristine component, and the electrochemical catalysis effect of nickel.

2009-06-10

270

Low- and high-temperature controls in carbon nanofiber growth in reactive plasmas  

Science.gov (United States)

A numerical growth model is used to describe the catalyzed growth of carbon nanofibers in the sheath of a low-temperature plasma. Using the model, the effects of variation in the plasma sheath parameters and substrate potential on the carbon nanofiber growth characteristics, such as the growth rate, the effective carbon flux to the catalyst surface, and surface coverages, have been investigated. It is shown that variations in the parameters, which change the sheath width, mainly affect the growth parameters at the low catalyst temperatures, whereas the other parameters such as the gas pressure, ion temperature, and percentages of the hydrocarbon and etching gases, strongly affect the carbon nanofiber growth at higher temperatures. The conditions under which the carbon nanofiber growth can still proceed under low nanodevice-friendly process temperatures have been formulated and summarized. These results are consistent with the available experimental results and can also be used for catalyzed growth of other high-aspect-ratio nanostructures in low-temperature plasmas.

Mehdipour, H.; Ostrikov, K.; Rider, A. E.

2010-11-01

271

Manganese oxide nanoparticle-loaded porous carbon nanofibers as anode materials for high-performance lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Mn-based oxide-loaded porous carbon nanofiber anodes, exhibiting large reversible capacity, excellent capacity retention, and good rate capability, are fabricated by carbonizing electrospun polymer/Mn(CH{sub 3}COO){sub 2} composite nanofibers without adding any polymer binder or electronic conductor. The excellent electrochemical performance of these organic/inorganic nanocomposites is a result of the unique combinative effects of nano-sized Mn-based oxides and carbon matrices as well as the highly-developed porous composite nanofiber structure, which make them promising anode candidates for high-performance rechargeable lithium-ion batteries. (author)

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

2009-04-15

272

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...

Galao, O.; Zornoza, E.; Baeza, F. J.; Bernabeu, A.; Garcés, P.

273

Ultracold Thermal Atoms and Bose-Einstein Condensates Interacting with a Single Carbon Nanofiber  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The present thesis investigates the decay of ultracold atoms from a magnetic trap due to the interaction with a single carbon nanofiber. The latter is spatially overlapping with the atomic cloud. For both an ultracold thermal cloud and a Bose-Einstein condensate, the atomic loss has been measured fo...

Schneeweiß, Philipp

274

Nanotextured gold coatings on carbon nanofiber scaffolds as ultrahigh surface-area electrodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

High surface area metal electrodes are desirable for applications in energy storage and energy conversion. Here, the formation and electrochemical characterization of a hybrid material made by electroless deposition of gold onto a scaffolding of vertically aligned carbon nanofibers is described. Ver...

COLAVITA, PAULA

275

Carbon Nanofiber Reinforced and PU-toughened POM Ternary Composites: Friction, Wear and Creep Properties  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Composites composed of polyoxymethylene (POM), polyurethane (PU) and carbon nanofiber (CNF) were produced by water-mediated melt compounding. PU latex and/or aqueous CNF dispersion were introduced into the molten POM in laboratory kneader to prepare toughened and/or nanoreinforced POM compo...

Suchart Siengchin

276

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. Comp...

Dong Liu; Yang Liu; Haoqing Hou; Tianyan You

277

Fracture Toughness of Vapor Grown Carbon Nanofiber-Reinforced Polyethylene Composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The impact fracture behavior of a vapor grown carbon nanofiber (VGCNF) reinforced high-density polyethylene (PE) composite was evaluated. The samples consisting of pure PE and composites with 10?wt% and 20?wt% of VGCNFs were prepared by a combination of hot-pressing and extrusi...

A. R. Adhikari; E. Partida; T. W. Petty; R. Jones; K. Lozano; C. Guerrero

278

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 mus...

Bajaj, Piyush; Khang, Dongwoo; Webster, Thomas J

279

Nanocomposites Based on Vapor-Grown Carbon Nanofibers and an Epoxy: Functionalization, Preparation and Characterization.  

Science.gov (United States)

Vapor-grown carbon nanofibers (VGCNF) were functionalized with amine- containing pendants via a Friedel-Crafts acylation reaction with 4-(3- aminophenoxy)benzoic acid. The resulting H2N-VGCNF was treated with epichlorohydrin, followed by sodium hydroxide ...

A. K. Roy D. H. Wang J. Baek L. Tan S. Sihn

2010-01-01

280

Vertically aligned carbon nanofiber arrays: an electrical and genetic substrate for tissue scaffolding.  

UK PubMed Central (United Kingdom)

We present a discussion of the use of vertically-aligned carbon nanofibers (VACNFs) as nanoscale elements that directly interface to biological whole-cell systems. VACNFs are compatible with a large subset of microfabrication processes, thereby enabling their incorporation into mesoscale hybrid systems that provide addressability of the VACNFs as either bulk electrode material, or as individually addressed nanoelectrodes. These VACNF devices are compatible with cell cultures, and electrochemical addressability of nanofibers can be maintained for extended periods within cell cultures. We present results that demonstrate possible use of VACNF devices as electrical and genetic substrates for tissue scaffolding applications.

McKnight TE; Ericson MN; Jones SW; Melechko AV; Simpson ML

2007-01-01

 
 
 
 
281

Vertically aligned carbon nanofiber arrays: an electrical and genetic substrate for tissue scaffolding.  

Science.gov (United States)

We present a discussion of the use of vertically-aligned carbon nanofibers (VACNFs) as nanoscale elements that directly interface to biological whole-cell systems. VACNFs are compatible with a large subset of microfabrication processes, thereby enabling their incorporation into mesoscale hybrid systems that provide addressability of the VACNFs as either bulk electrode material, or as individually addressed nanoelectrodes. These VACNF devices are compatible with cell cultures, and electrochemical addressability of nanofibers can be maintained for extended periods within cell cultures. We present results that demonstrate possible use of VACNF devices as electrical and genetic substrates for tissue scaffolding applications. PMID:18003224

McKnight, T E; Ericson, M N; Jones, S W; Melechko, A V; Simpson, M L

2007-01-01

282

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

283

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

Science.gov (United States)

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. PMID:21297239

Dai, Qing; Rajasekharan, Ranjith; Butt, Haider; Won, Kanghee; Wang, Xiaozhi; Wilkinson, Timothy D; Amaragtunga, Gehan

2011-02-04

284

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

UK PubMed Central (United Kingdom)

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 Q; Rajasekharan R; Butt H; Won K; Wang X; Wilkinson TD; Amaragtunga G

2011-03-01

285

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

Science.gov (United States)

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

2011-03-01

286

Surface modified PLGA/carbon nanofiber composite enhances articular chondrocyte functions  

Science.gov (United States)

Since articular cartilage has a limited self regeneration capability, alternative methods are needed for repairing cartilage defects. The purpose of the present in vitro study was to explore the effects of material surface properties and external stimulation on chondrocyte (cartilage-synthesizing cell) functions. Based on this information, a goal of this research was to propose a scaffold composite material for enhancing articular chondrocyte function. To improve functions of chondrocytes, material (namely, poly(lactic-co-glycolic acid); PLGA) surfaces were modified via chemical (NaOH) etching techniques. Chondrocytes were cultured on surface-modified 2-D PLGA films and 3-D PLGA tissue engineering scaffolds, which were created by a salt-leaching method. Carbon nanofibers were imprinted on PLGA matrices in an aligned pattern for controlled electrically-active surface features. Electrical stimulation was applied to expedite and enhance chondrocyte functions. Results demonstrated that both NaOH-treated 2-D and 3-D substrates enhanced chondrocyte functions (cell numbers as well as extracellular matrix production) compared to non-treated PLGA substrates. Furthermore, chondrocytes preferred to attach along the carbon nanofiber patterns imprinted on PLGA. Electrical stimulation also enhanced chondrocyte functions on carbon nanofiber/PLGA composites. Underlying material properties that may have enhanced chondrocyte functions include a more hydrophilic surface, surface energy differences due to the presence of carbon nanofibers, increased surface area, altered porosity, and a greater degree of nanometer roughness. Moreover, these altered surface properties positively influenced select protein adsorption that controlled subsequent chondrocyte adhesion. Collectively, this study provided a scaffold model for osteochondral defects that can be synthesized using the above techniques and a layer by layer approach to accommodate the property differences in each layer of natural cartilage. Specifically, these results suggest that the superficial zone, middle zone, and deep zone of cartilage should be composed of carbon nanofibers aligned parallel to the surface in PLGA, randomly oriented carbon nanofibers in PLGA, and carbon nanofibers aligned perpendicular to the surface in PLGA, respectively. Clearly, such scaffolds may ultimately enhance the efficacy of scaffolds used for articular cartilage repair.

Park, Grace Eunseung

287

Improvement of carbon corrosion resistance through heat-treatment in polymer electrolyte membrane fuel cells  

Energy Technology Data Exchange (ETDEWEB)

Electrochemical corrosion of carbon in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) is a critical factor in limiting their durability. The corrosion rate increases during the iterative abnormal operating conditions known as reverse current phenomenon. The corrosion causes a decrease of the active surface of the platinum (Pt) catalyst. The graphitization of carbon increases corrosion resistance, and the hydrophobicity of the carbon surface can also play an important role in decreasing carbon corrosion. This study investigated the effect of heat-treating carbon nanofibers (CNFs) for use in PEMFC applications. The aim of the study was to determine if heat treatments modified the carbon surface by eliminating the oxygen functional group and increasing hydrophobicity. The electrochemical carbon corrosion of CNFs were compared after heat treatments at various temperatures. Mass spectrometry was used to measure electrochemical carbon corrosion by monitoring the amounts of carbon dioxide (CO{sub 2}) produced during the electrochemical oxidation process. 2 refs.

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

2010-07-01

288

Decomposition of Fe5C2 catalyst particles in carbon nanofibers during TEM observation  

International Nuclear Information System (INIS)

The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (?-Fe3C). However, for Haegg carbide nanoparticles (?-Fe5C2), explosive decay is observed after exposure for 5-10 s. This produces small particles of cementite and ?-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Haegg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.

2009-01-01

289

Vertically aligned carbon nanofiber arrays record electrophysiological signals from hippocampal slices.  

UK PubMed Central (United Kingdom)

Vertically aligned carbon nanofiber (VACNF) electrode arrays were tested for their potential application in recording neuro-electrophysiological activity. We report, for the first time, stimulation and extracellular recording of spontaneous and evoked neuroelectrical activity in organotypic hippocampal slice cultures with ultramicroelectrode VACNF arrays. Because the electrodes are carbon-based, these arrays have potential advantages over metal electrodes and could enable a variety of future applications as precise, informative, and biocompatible neural interfaces.

Yu Z; McKnight TE; Ericson MN; Melechko AV; Simpson ML; Morrison B 3rd

2007-08-01

290

Vertically aligned carbon nanofiber arrays record electrophysiological signals from hippocampal slices.  

Science.gov (United States)

Vertically aligned carbon nanofiber (VACNF) electrode arrays were tested for their potential application in recording neuro-electrophysiological activity. We report, for the first time, stimulation and extracellular recording of spontaneous and evoked neuroelectrical activity in organotypic hippocampal slice cultures with ultramicroelectrode VACNF arrays. Because the electrodes are carbon-based, these arrays have potential advantages over metal electrodes and could enable a variety of future applications as precise, informative, and biocompatible neural interfaces. PMID:17604402

Yu, Zhe; McKnight, Timothy E; Ericson, M Nance; Melechko, Anatoli V; Simpson, Michael L; Morrison, Barclay

2007-06-30

291

Fabrication of porous carbon nanofibers and their application as anode materials for rechargeable lithium-ion batteries  

International Nuclear Information System (INIS)

Porous carbon nanofibers were prepared by the electrospinning of a bicomponent polymer solution, followed by thermal treatments under different atmospheres. The surface morphology, thermal properties, and crystalline features of these nanofibers were characterized using various analytic techniques, and it was found that they were formed with turbostratically disordered graphene sheets and had small pores and large surface areas. The unique structure of these porous carbon nanofibers resulted in good electrochemical performance such as high reversible capacity and good cycle stability when they were used as anodes for rechargeable lithium-ion batteries.

2009-04-15

292

Nitrogen-doped porous carbon nanofiber webs as anodes for lithium ion batteries with a superhigh capacity and rate capability.  

UK PubMed Central (United Kingdom)

Nitrogen-doped carbon nanofiber webs (CNFWs) with high surface areas are successfully prepared by carbonization-activation of polypyrrole nanofiber webs with KOH. The as-obtained CNFWs exhibit a superhigh reversible capacity of 943 mAh g(-1) at a current density of 2 A g(-1) even after 600 cycles, which is ascribed to the novel porous nanostructure and high-level nitrogen doping.

Qie L; Chen WM; Wang ZH; Shao QG; Li X; Yuan LX; Hu XL; Zhang WX; Huang YH

2012-04-01

293

Ni K-Edge XANES Analyses of Residual Ni Catalyst in Carbon Nanofiber Using Full Multiple Scattering Theory  

International Nuclear Information System (INIS)

Residual Ni species after Ni removal treatment of carbon nanofibers have been investigated by use of XAFS analyses. Most of the Ni impurities are in Ni monomer which is located on defects in carbon nanofibers. The XAFS analyses combined with the multiple scattering theory give useful information on nano-structures of small amount species. Molecular orbital calculation also support the results from the XAFS analyses.

2007-02-02

294

Nitrogen-doped porous carbon nanofiber webs as anodes for lithium ion batteries with a superhigh capacity and rate capability.  

Science.gov (United States)

Nitrogen-doped carbon nanofiber webs (CNFWs) with high surface areas are successfully prepared by carbonization-activation of polypyrrole nanofiber webs with KOH. The as-obtained CNFWs exhibit a superhigh reversible capacity of 943 mAh g(-1) at a current density of 2 A g(-1) even after 600 cycles, which is ascribed to the novel porous nanostructure and high-level nitrogen doping. PMID:22422374

Qie, Long; Chen, Wei-Min; Wang, Zhao-Hui; Shao, Qing-Guo; Li, Xiang; Yuan, Li-Xia; Hu, Xian-Luo; Zhang, Wu-Xing; Huang, Yun-Hui

2012-03-16

295

Study on glow discharge effects on catalyst films for growing aligned carbon nanofibers in negative bias-enhanced hot filament chemical vapor deposition system  

International Nuclear Information System (INIS)

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.

2005-03-01

296

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

297

Cyclability study of silicon-carbon composite anodes for lithium-ion batteries using electrochemical impedance spectroscopy  

International Nuclear Information System (INIS)

Research highlights: ? Silicon-carbon anode materials for Li-ion batteries were synthesized. ? Carbonization and annealing processes were used in electrode preparation. ? Capacity fading mechanism was investigated by electrochemical impedance spectroscopy. ? 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.

2011-04-15

298

Silicon nanoparticles encapsulated in hollow graphitized carbon nanofibers for lithium ion battery anodes  

Science.gov (United States)

Silicon (Si) is a promising material for lithium ion battery (LIB) anodes due to its high specific capacity. To overcome its shortcomings such as insulation property and large volume change during the charge-discharge process, a novel hybrid system, Si nanoparticles encapsulated in hollow graphitized carbon nanofibers, is studied. First, electrospun polyacrylonitrile (PAN)-Si hybrid nanofibers were obtained using water as the collector. The loose nanofiber lumps suspended in water have large inter-fiber distance, allowing in situ coating of a thin layer of polydopamine (PDA), the source for graphitized carbon, uniformly throughout the system. The designed morphology and structure were then realized by etching and calcination, and the morphology and structure were subsequently verified by various analytical techniques. Electrochemical measurements show that the resulting hollow hybrid nanofibers (C-PDA-Si NFs) exhibit much better cycling stability and rate capacity than conventional C/Si nanofibers derived by electrospinning of PAN-Si followed by calcination. For instance, the capacity of C-PDA-Si NFs is as high as 72.6% of the theoretical capacity after 50 cycles, and a high capacity of 500 mA h g-1 can be delivered at a current density of 5 A g-1. The significantly improved electrochemical properties of C-PDA-Si NFs are due to the excellent electrical conductivity of the carbonized PDA (C-PDA) shell that compensates for the insulation property of Si, the high electrochemical activity of C-PDA, which has a layered structure and is N-doped, the hollow nature of the nanofibers and small size of Si nanoparticles that ensure smooth insertion-extraction of lithium ions and more complete alloying with them, as well as the buffering effect of the remaining PAN-derived carbon around the Si nanoparticles, which stabilizes the structure.Silicon (Si) is a promising material for lithium ion battery (LIB) anodes due to its high specific capacity. To overcome its shortcomings such as insulation property and large volume change during the charge-discharge process, a novel hybrid system, Si nanoparticles encapsulated in hollow graphitized carbon nanofibers, is studied. First, electrospun polyacrylonitrile (PAN)-Si hybrid nanofibers were obtained using water as the collector. The loose nanofiber lumps suspended in water have large inter-fiber distance, allowing in situ coating of a thin layer of polydopamine (PDA), the source for graphitized carbon, uniformly throughout the system. The designed morphology and structure were then realized by etching and calcination, and the morphology and structure were subsequently verified by various analytical techniques. Electrochemical measurements show that the resulting hollow hybrid nanofibers (C-PDA-Si NFs) exhibit much better cycling stability and rate capacity than conventional C/Si nanofibers derived by electrospinning of PAN-Si followed by calcination. For instance, the capacity of C-PDA-Si NFs is as high as 72.6% of the theoretical capacity after 50 cycles, and a high capacity of 500 mA h g-1 can be delivered at a current density of 5 A g-1. The significantly improved electrochemical properties of C-PDA-Si NFs are due to the excellent electrical conductivity of the carbonized PDA (C-PDA) shell that compensates for the insulation property of Si, the high electrochemical activity of C-PDA, which has a layered structure and is N-doped, the hollow nature of the nanofibers and small size of Si nanoparticles that ensure smooth insertion-extraction of lithium ions and more complete alloying with them, as well as the buffering effect of the remaining PAN-derived carbon around the Si nanoparticles, which stabilizes the structure. Electronic supplementary information (ESI) available: The photo of an electrospinning setup with a liquid collector, the photos of a compact electrospun PAN mat and that with PDA coating, the XRD pattern and TGA profile of carbonized PAN-Si hybrid nanofibers, SEM images, FTIR and Raman spectra of hollow PDA nanofibers, the cycling capacity of C-PDA-Si NFs which are prepared

Kong, Junhua; Yee, Wu Aik; Wei, Yuefan; Yang, Liping; Ang, Jia Ming; Phua, Si Lei; Wong, Siew Yee; Zhou, Rui; Dong, Yuliang; Li, Xu; Lu, Xuehong

2013-03-01

299

Experimental and numerical studies on ballistic phonon transport of cup-stacked carbon nanofiber  

International Nuclear Information System (INIS)

A carbon nanofiber material, consisting of a stacked graphene cups, with the potential to conduct heat ballistically has been discovered and tested. Its unexpected high thermal conductivity can be understood by the similarity to a one-dimensional harmonic chain where no phonon is scattered even for an infinite length. A non-equilibrium molecular dynamics simulation for this fiber validated this hypothesis by revealing a uniform temperature distribution between hot and cold reservoirs.

2009-08-01

300

The dominant role of tunneling in the conductivity of carbon nanofiber-epoxy composites  

Energy Technology Data Exchange (ETDEWEB)

In this work, epoxy composites reinforced with vapor-grown carbon nanofibers were prepared by a simple dispersion method and studied in order to identify the main conduction mechanism. The samples show high electrical conductivity values. The results indicate that a good cluster distribution seems to be more important than the fillers dispersion in order to achieve high conductivity values. Interparticle tunneling has been identified as the main mechanism responsible for the observed behavior. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Cardoso, P.; Lanceros-Mendez, S. [Center of Physics, University of Minho, Braga (Portugal); Silva, J. [Center of Physics, University of Minho, Braga (Portugal); IPC - Institute for Polymers and Composites, University of Minho, Guimaraes (Portugal); Paleo, A.J.; van Hattum, F.W.J. [IPC - Institute for Polymers and Composites, University of Minho, Guimaraes (Portugal); Simoes, R. [IPC - Institute for Polymers and Composites, University of Minho, Guimaraes (Portugal); School of Technology, Polytechnic Institute of Cavado and Ave, Barcelos (Portugal)

2010-02-15

 
 
 
 
301

Deposition precipitation for the preparation of carbon nanofiber supported nickel catalysts.  

Science.gov (United States)

Deposition precipitation of nickel hydroxide onto modified carbon nanofibers has been studied and compared to deposition onto silica. The carbon nanofiber support materials consisted of graphite-like material of the fishbone-type with a diameter of 20-50 nm and a specific surface area of 150 m2/g. Modification involved surface oxidation (CNF-O) optionally followed by partial reduction (CNF-OR) or thermal treatment (CNF-OT). Titration of the support materials showed the presence of 0.17 and 0.03 mmol/g carboxylic acid groups for CNF-O and CNF-OR, respectively. For the CNF-OT only basic groups were present. The deposition precipitation of 20 wt % nickel onto these supports has been studied by time dependent pH and nickel loading studies. With silica, nickel ion adsorption did not occur prior to nucleation of the nickel hydroxide phase at pH = 5.6. With CNF-O, nickel ion adsorption took place right from the start of the deposition process at pH = 3.5, and at pH = 5.6 already 4 wt % nickel was adsorbed. Nucleation of nickel hydroxide onto adsorbed nickel ion clusters proceeded subsequently. Characterization of the dried Ni/CNF-O samples with TEM and XRD showed well dispersed and thin (5 nm) platelets of nickel hydroxide adhering to the carbon nanofibers. After reduction at 773 K in hydrogen the Ni/CNF-O contained metallic nickel particles of 8 nm homogeneously distributed over the fibers. With CNF-OR and CNF-OT, precipitation of large platelets (> 500 nm) separate from the support took place. Clearly, the presence of carboxylic acid groups is essential to successfully deposit nickel hydroxide onto modified carbon nanofibers. PMID:16190722

van der Lee, Martijn K; van Dillen, A Jos; Bitter, Johannes H; de Jong, Krijn P

2005-10-01

302

Deposition precipitation for the preparation of carbon nanofiber supported nickel catalysts.  

UK PubMed Central (United Kingdom)

Deposition precipitation of nickel hydroxide onto modified carbon nanofibers has been studied and compared to deposition onto silica. The carbon nanofiber support materials consisted of graphite-like material of the fishbone-type with a diameter of 20-50 nm and a specific surface area of 150 m2/g. Modification involved surface oxidation (CNF-O) optionally followed by partial reduction (CNF-OR) or thermal treatment (CNF-OT). Titration of the support materials showed the presence of 0.17 and 0.03 mmol/g carboxylic acid groups for CNF-O and CNF-OR, respectively. For the CNF-OT only basic groups were present. The deposition precipitation of 20 wt % nickel onto these supports has been studied by time dependent pH and nickel loading studies. With silica, nickel ion adsorption did not occur prior to nucleation of the nickel hydroxide phase at pH = 5.6. With CNF-O, nickel ion adsorption took place right from the start of the deposition process at pH = 3.5, and at pH = 5.6 already 4 wt % nickel was adsorbed. Nucleation of nickel hydroxide onto adsorbed nickel ion clusters proceeded subsequently. Characterization of the dried Ni/CNF-O samples with TEM and XRD showed well dispersed and thin (5 nm) platelets of nickel hydroxide adhering to the carbon nanofibers. After reduction at 773 K in hydrogen the Ni/CNF-O contained metallic nickel particles of 8 nm homogeneously distributed over the fibers. With CNF-OR and CNF-OT, precipitation of large platelets (> 500 nm) separate from the support took place. Clearly, the presence of carboxylic acid groups is essential to successfully deposit nickel hydroxide onto modified carbon nanofibers.

van der Lee MK; van Dillen AJ; Bitter JH; de Jong KP

2005-10-01

303

Vertically aligned carbon nanofiber as nano-neuron interface for monitoring neural function.  

UK PubMed Central (United Kingdom)

UNLABELLED: Neural chips, which are capable of simultaneous multisite neural recording and stimulation, have been used to detect and modulate neural activity for almost thirty years. As neural interfaces, neural chips provide dynamic functional information for neural decoding and neural control. By improving sensitivity and spatial resolution, nano-scale electrodes may revolutionize neural detection and modulation at cellular and molecular levels as nano-neuron interfaces. We developed a carbon-nanofiber neural chip with lithographically defined arrays of vertically aligned carbon nanofiber electrodes and demonstrated its capability of both stimulating and monitoring electrophysiological signals from brain tissues in vitro and monitoring dynamic information of neuroplasticity. This novel nano-neuron interface may potentially serve as a precise, informative, biocompatible, and dual-mode neural interface for monitoring of both neuroelectrical and neurochemical activity at the single-cell level and even inside the cell. FROM THE CLINICAL EDITOR: The authors demonstrate the utility of a neural chip with lithographically defined arrays of vertically aligned carbon nanofiber electrodes. The new device can be used to stimulate and/or monitor signals from brain tissue in vitro and for monitoring dynamic information of neuroplasticity both intracellularly and at the single cell level including neuroelectrical and neurochemical activities.

Yu Z; McKnight TE; Ericson MN; Melechko AV; Simpson ML; Morrison B 3rd

2012-05-01

304

Graphene and carbon nanofiber nanopaper for multifunction composite materials  

Science.gov (United States)

The new structures and multifunctional materials is that it can achieve some other special functions while it has ability to carry, such as wave-transparent, absorbing, anti-lightning, anti-heat, anti-nuclear etc. It represents the direction of future development of structural materials. And graphene is the one of two-dimensional atomic crystal free substance only found in the existence and shows great importance for fundamental studies and technological applications due to its unique structure and a wide range of unusual properties. It exhibits great promise for potential applications in chemistry, materials, and many other technological fields. In this paper, we prepare nanopaper through physical vapor deposition (PVD) with a variety in the weight ratio between graphene and nanofiber. Then prepare composite materials with nanopaper and T300/AG80 prepreg by the meaning of autoclave molding. The morphology of nanopaper was characterized by transmission electron microscopy (TEM) and scanning electron microscope (SEM). And the electrical properties and the EMI shielding performances of these nanocomposites have been investigated experimentally by and four-point probe measurement and vector network analyzer. The experimental results indicate that the composites made from graphene and nanofiber nanopaper have highly electric capability, and the EMI shielding value of composites were all up to -15dB. In the same time the conductivity and the EMI shielding performances were improved with increasing the ratio of graphene in nanopaper. We tested the mechanical properties of composite materials at the same time. The average strength of composite materials is about 2000MPa, the elastic modulus is 130GPa above. We are sure that it can be used as the load-bearing structural material which has a multi-functional performance in the aviation field.

Wu, Chunxia; Lu, Haibao; Liu, Liwu; Liu, Yanju; Leng, Jinsong

2011-03-01

305

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 n...

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

306

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)

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 catal...

Jahangiri, Mehdi; Adl, Javad; Shahtaheri, Seyyed Jamaleddin; Rashidi, Alimorad; Ghorbanali, Amir; Kakooe, Hossein

307

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)

2012-08-03

308

Facile conductive bridges formed between silicon nanoparticles inside hollow carbon nanofibers.  

UK PubMed Central (United Kingdom)

This paper reports on a simple and effective method for improving the electrochemical performance of silicon nanoparticle-core/carbon-shell (Si-core/C-shell) nanofibers. Instead of increasing the encapsulation amount of Si nanoparticles, additional conductive paths between the Si nanoparticles were formed by incorporating a small percentage of multi-walled carbon nanotubes (MWNTs) (e.g., 5 wt% with respect to Si) into the Si nanoparticle core. The electrical conductivity of a single Si-core/C-shell nanofiber was measured by a four-point probe using four nano-manipulators, which showed a more than five times increase according to MWNT addition. A galvanostatic charge-discharge test demonstrated that a small amount of MWNTs greatly improved the electrochemical performance of the Si-core/C-shell nanofibers (e.g., a 25.1% increase in the Li-ion storage capability) due to the enhanced participation of Si through the additional conductive paths formed between the Si nanoparticles.

Lee BS; Son SB; Seo JH; Park KM; Lee G; Lee SH; Oh KH; Ahn JP; Yu WR

2013-06-01

309

Carbon nanotube-incorporated multilayered cellulose acetate nanofibers for tissue engineering applications.  

Science.gov (United States)

We report the fabrication of a novel carbon nanotube-containing nanofibrous polysaccharide scaffolding material via the combination of electrospinning and layer-by-layer (LbL) self-assembly techniques for tissue engineering applications. In this approach, electrospun cellulose acetate (CA) nanofibers were assembled with positively charged chitosan (CS) and negatively charged multiwalled carbon nanotubes (MWCNTs) or sodium alginate (ALG) via a LbL technique. We show that the 3-dimensional fibrous structures of the CA nanofibers do not appreciably change after the multilayered assembly process except that the surface of the fibers became much rougher than that before assembly. The incorporation of MWCNTs in the multilayered CA fibrous scaffolds tends to endow the fibers with improved mechanical property and promote fibroblast attachment, spreading, and proliferation when compared with CS/ALG multilayer-assembled fibrous scaffolds. The approach to engineering the nanofiber surfaces via LbL assembly likely provides many opportunities for new scaffolding materials design in various tissue engineering applications. PMID:23044152

Luo, Yu; Wang, Shige; Shen, Mingwu; Qi, Ruiling; Fang, Yi; Guo, Rui; Cai, Hongdong; Cao, Xueyan; Tomás, Helena; Zhu, Meifang; Shi, Xiangyang

2012-08-25

310

Facile conductive bridges formed between silicon nanoparticles inside hollow carbon nanofibers  

Science.gov (United States)

This paper reports on a simple and effective method for improving the electrochemical performance of silicon nanoparticle-core/carbon-shell (Si-core/C-shell) nanofibers. Instead of increasing the encapsulation amount of Si nanoparticles, additional conductive paths between the Si nanoparticles were formed by incorporating a small percentage of multi-walled carbon nanotubes (MWNTs) (e.g., 5 wt% with respect to Si) into the Si nanoparticle core. The electrical conductivity of a single Si-core/C-shell nanofiber was measured by a four-point probe using four nano-manipulators, which showed a more than five times increase according to MWNT addition. A galvanostatic charge-discharge test demonstrated that a small amount of MWNTs greatly improved the electrochemical performance of the Si-core/C-shell nanofibers (e.g., a 25.1% increase in the Li-ion storage capability) due to the enhanced participation of Si through the additional conductive paths formed between the Si nanoparticles.

Lee, Byoung-Sun; Son, Seoung-Bum; Seo, Jong-Hyun; Park, Kyu-Min; Lee, Geunsung; Lee, Se-Hee; Oh, Kyu Hwan; Ahn, Jae-Pyoung; Yu, Woong-Ryeol

2013-05-01

311

Carbon nanotube-loaded electrospun LiFePO4/carbon composite nanofibers as stable and binder-free cathodes for rechargeable lithium-ion batteries.  

UK PubMed Central (United Kingdom)

LiFePO(4)/CNT/C composite nanofibers were synthesized by using a combination of electrospinning and sol-gel techniques. Polyacrylonitrile (PAN) was used as the electrospinning media and carbon source. Functionalized CNTs were used to increase the conductivity of the composite. LiFePO(4) precursor materials, PAN and functionalized CNTs were dissolved or dispersed in N,N-dimethylformamide separately and they were mixed before electrospinning. LiFePO(4) precursor/CNT/PAN composite nanofibers were then heat-treated to obtain LiFePO(4)/CNT/C composite nanofibers. Fourier transform infrared spectroscopy measurements were done to demonstrate the functionalization of CNTs. The structure of LiFePO(4)/CNT/C composite nanofibers was determined by X-ray diffraction analysis. The surface morphology and microstructure of LiFePO(4)/CNT/C composite nanofibers were characterized using scanning electron microscopy and transmission electron microscopy. Electrochemical performance of LiFePO(4)/CNT/C composite nanofibers was evaluated in coin-type cells. Functionalized CNTs were found to be well-dispersed in the carbonaceous matrix and increased the electrochemical performance of the composite nanofibers. As a result, cells using LiFePO(4)/CNT/C composite nanofibers have good performance, in terms of large capacity, extended cycle life, and good rate capability.

Toprakci O; Toprakci HA; Ji L; Xu G; Lin Z; Zhang X

2012-03-01

312

Synthesis of palladium nanoparticles decorated helical carbon nanofiber as highly active anodic catalyst for direct formic acid fuel cells  

International Nuclear Information System (INIS)

[en] Highlights: ? We present a single metal synthesis of highly active catalysts based on Pd-helical carbon fibers. ? Our catalyst material show better performance than Pd-decorated multi-walled nanotubes. ? Formic acid fuel cell tests with Pd-helical carbon nanofibers as anode show high power densities. ? Helical carbon nanofibers have several good properties for electrochemical applications. - Abstract: We present a single metal approach to produce highly active catalyst materials based on Pd-decorated helical carbon nanofibers. Helical carbon fibers are synthesized by a chemical vapor deposition process on a C60 supported Pd catalyst and the obtained fibers are functionalized by H2O2 followed by a decoration with Pd nanoparticles. Although transmission electron microscopy images show that the decoration is relatively inhomogeneous the electrocatalytic activity for formic acid oxidation is very high. Cyclic voltammetry measurements (CV) show that the generated current peak value for Pd-decorated helical carbon nanofibers is 300 mA/mgPd for a scan rate of 10 mV/s. This is significantly higher than the corresponding value of a reference sample of multiwalled carbon nanotubes decorated with Pd nanoparticles by the same process. Fuel cell tests for our Pd-decorated helical carbon nanofibers also displayed a high power density, although not as superior to Pd-decorated multiwalled nanotubes as measured by CV. Our results show that helical carbon nanofibers have several good properties, such as a rigid anchoring of catalyst nanoparticles and a suitable structure for creating functionalization defects which make them an interesting candidate for electrochemical applications.

2012-02-29

313

Controlled transport of latex beads through vertically aligned carbon nanofiber membranes  

Science.gov (United States)

Stripes of vertically aligned carbon nanofibers (VACNFs) have been used to form membranes for size selectively controlling the transport of latex beads. Fluidic structures were created in poly(dimethylsiloxane) (PDMS) and interfaced to the VACNF structures for characterization of the membrane pore size. Solutions of fluorescently labeled latex beads were introduced into the PDMS channels and characterized by fluorescence and scanning electron microscopy. Results show that the beads size selectively pass through the nanofiber barriers and the size restriction limit correlates with the interfiber spacing. The results suggest that altering VACNF array density can alter fractionation properties of the membrane. Such membranes may be useful for molecular sorting and for mimicking the properties of natural membranes.

Zhang, L.; Melechko, A. V.; Merkulov, V. I.; Guillorn, M. A.; Simpson, M. L.; Lowndes, D. H.; Doktycz, M. J.

2002-07-01

314

Solid-state NMR and EPR study of fluorinated carbon nanofibers  

International Nuclear Information System (INIS)

Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF4 during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF)n structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C2F)n type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O2), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined. - Graphical abstract: Scheme of the fluorination process using F2 and TbF4 as fluorinating agent.

2008-01-01

315

Non-lithographic organization of nickel catalyst for carbon nanofiber synthesis on laser-induced periodic surface structures  

Science.gov (United States)

We present a non-lithographic technique that produces organized nanoscale nickel catalyst for carbon nanofiber growth on a silicon substrate. This technique involves three consecutive steps: first, the substrate is laser-irradiated to produce a periodic nanorippled structure; second, a thin film of nickel is deposited using glancing-angle ion-beam sputter deposition, followed by heat treatment, and third, a catalytic dc plasma-enhanced chemical vapor deposition (PECVD) process is conducted to produce the vertically aligned carbon nanofibers (VACNF). The nickel catalyst is distributed along the laser-induced periodic surface structure (LIPSS) and the Ni particle dimension varies as a function of the location on the LIPSS and is correlated to the nanoripple dimensions. The glancing angle, the distance between the ion beam collimators and the total deposition time all play important roles in determining the final catalyst size and subsequent carbon nanofiber properties. Due to the gradual aspect ratio change of the nanoripples across the sample, Ni catalyst nanoparticles of different dimensions were obtained. After the prescribed three minute PECVD growth, it was observed that, in order for the carbon nanofibers to survive, the nickel catalyst dimension should be larger than a critical value of ~19 nm, below which the Ni is insufficient to sustain carbon nanofiber growth.

Guan, Y. F.; Melechko, A. V.; Pedraza, A. J.; Simpson, M. L.; Rack, P. D.

2007-08-01

316

Non-lithographic organization of nickel catalyst for carbon nanofiber synthesis on laser-induced periodic surface structures  

International Nuclear Information System (INIS)

We present a non-lithographic technique that produces organized nanoscale nickel catalyst for carbon nanofiber growth on a silicon substrate. This technique involves three consecutive steps: first, the substrate is laser-irradiated to produce a periodic nanorippled structure; second, a thin film of nickel is deposited using glancing-angle ion-beam sputter deposition, followed by heat treatment, and third, a catalytic dc plasma-enhanced chemical vapor deposition (PECVD) process is conducted to produce the vertically aligned carbon nanofibers (VACNF). The nickel catalyst is distributed along the laser-induced periodic surface structure (LIPSS) and the Ni particle dimension varies as a function of the location on the LIPSS and is correlated to the nanoripple dimensions. The glancing angle, the distance between the ion beam collimators and the total deposition time all play important roles in determining the final catalyst size and subsequent carbon nanofiber properties. Due to the gradual aspect ratio change of the nanoripples across the sample, Ni catalyst nanoparticles of different dimensions were obtained. After the prescribed three minute PECVD growth, it was observed that, in order for the carbon nanofibers to survive, the nickel catalyst dimension should be larger than a critical value of ?19 nm, below which the Ni is insufficient to sustain carbon nanofiber growth.

2007-08-22

317

Influence of oxygen-containing surface groups on the activity and selectivity of carbon nanofiber-supported ruthenium catalysts in the hydrogenation of cinnamaldehyde  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Carbon-nanofiber-supported ruthenium catalysts were employed to study the influence of oxygen-containing surface groups on catalytic performance in the liquid-phase hydrogenation of cinnamaldehyde. The carbon nanofibers were oxidized to introduce oxygen-containing groups and the metal precursor was ...

Toebes, M.L.; Prinsloo, F.F.; Bitter, J.H.; Dillen, A.J. van; Jong, K.P. de

318

Electrospinning of carbon/CdS coaxial nanofibers with photoluminescence and conductive properties  

International Nuclear Information System (INIS)

Carbon/CdS coaxial nanofibers (NFs) have been prepared using polyacrylonitrile (PAN)/CdS composite NFs as precursors. The synthesis strategy involves immersing the as-spun PAN fibers into cadmium acetate aqueous solution, followed by reaction with H2S gas and carbonization. SEM and TEM showed the morphology of the obtained coaxial NFs. The structures were examined by XRD, FT-IR and Raman spectra. The NFs displayed photoluminescence and conductive properties which were characterized by room-temperature photoluminescent spectra and standard four-probe method.

2007-05-25

319

Influence of copper on the structural characteristics of carbon nanofibers produced from the cobalt-catalyzed decomposition of ethylene  

Energy Technology Data Exchange (ETDEWEB)

We have used a combination of techniques to examine modifications in the structural characteristics of carbon nanofibers produced from the interaction of cobalt and copper-cobalt powders with ethylene at temperatures over the range 425 to 700{degree}C. The nanofibers generated from the interaction of cobalt with ethylene at 600{degree}C were found to be highly crystalline in nature. Incorporation of as little as 2{percent} copper into the cobalt created a major modification in the conformation of the solid carbon deposit, which was composed of multiple nanofiber limbs emanating from a single catalyst particle, and in this state the carbon structures tended to be disordered. As the composition of the bimetallic was progressively changed to the point where copper became the major component, there was a significant increase in the degree of crystalline perfection of the nanofibers even though they maintained their multidirectional form. The transformation in structural characteristics of the carbon nanofibers is rationalized, according to a concept wherein the crystalline order of the deposit is related to the wetting properties of the bimetallic particles with graphite. {copyright} {ital 1996 Materials Research Society.}

Chambers, A.; Rodriguez, N.M.; Baker, R.T. [Catalytic Materials Center, Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802-4800 (United States)

1996-02-01

320

Carbon nanotube-templated polyaniline nanofibers: synthesis, flash welding and ultrafiltration membranes.  

UK PubMed Central (United Kingdom)

Electro-active switchable ultrafiltration membranes are of great interest due to the possibility of external control over permeability, selectivity, anti-fouling and cleaning. Here, we report on hybrid single-walled carbon nanotube (SWCNT)-polyaniline (PANi) nanofibers synthesized by in situ polymerization of aniline in the presence of oxidized SWCNTs. The composite nanofibers exhibit unique morphology of core-shell (SWCNT-PANi) structures with average total diameters of 60 nm with 10 to 30 nm thick PANi coatings. The composite nanofibers are easily dispersed in polar aprotic solvents and cast into asymmetric membranes via a nonsolvent induced phase separation. The hybrid SWCNT-PANi membranes are electrically conductive at neutral pH and exhibit ultrafiltration-like permeability and selectivity when filtering aqueous suspensions of 6 nm diameter bovine serum albumin and 48 nm diameter silica particles. A novel flash welding technique is utilized to tune the morphology, porosity, conductivity, permeability and nanoparticle rejection of the SWCNT-PANi composite ultrafiltration membranes. Upon flash welding, both conductivity and pure water permeability of the membranes improves by nearly a factor of 10, while maintaining silica nanoparticle rejection levels above 90%. Flash welding of SWCNT-PANi composite membranes holds promise for formation of electrochemically tunable membranes.

Liao Y; Yu DG; Wang X; Chain W; Li XG; Hoek EM; Kaner RB

2013-05-01

 
 
 
 
321

Carbon nanotube-templated polyaniline nanofibers: synthesis, flash welding and ultrafiltration membranes.  

Science.gov (United States)

Electro-active switchable ultrafiltration membranes are of great interest due to the possibility of external control over permeability, selectivity, anti-fouling and cleaning. Here, we report on hybrid single-walled carbon nanotube (SWCNT)-polyaniline (PANi) nanofibers synthesized by in situ polymerization of aniline in the presence of oxidized SWCNTs. The composite nanofibers exhibit unique morphology of core-shell (SWCNT-PANi) structures with average total diameters of 60 nm with 10 to 30 nm thick PANi coatings. The composite nanofibers are easily dispersed in polar aprotic solvents and cast into asymmetric membranes via a nonsolvent induced phase separation. The hybrid SWCNT-PANi membranes are electrically conductive at neutral pH and exhibit ultrafiltration-like permeability and selectivity when filtering aqueous suspensions of 6 nm diameter bovine serum albumin and 48 nm diameter silica particles. A novel flash welding technique is utilized to tune the morphology, porosity, conductivity, permeability and nanoparticle rejection of the SWCNT-PANi composite ultrafiltration membranes. Upon flash welding, both conductivity and pure water permeability of the membranes improves by nearly a factor of 10, while maintaining silica nanoparticle rejection levels above 90%. Flash welding of SWCNT-PANi composite membranes holds promise for formation of electrochemically tunable membranes. PMID:23525119

Liao, Yaozu; Yu, Deng-Guang; Wang, Xia; Chain, Wei; Li, Xin-Gui; Hoek, Eric M V; Kaner, Richard B

2013-03-25

322

Transport properties of spiral carbon nanofiber mats containing Pd metal clusters using Pd2(dba)3 as catalyst  

CERN Document Server

We have grown spiral carbon nanofibers containing Pd metal clusters using the Pd2(dba)3 catalyzed decomposition of gaseous acetylene on molecular sieves (AlPO4-5) support. The microstructure and composition of the spiral carbon nanofibers were examined by the powder x-ray diffractometer and transmission electron microscope. The conductivity of the mat in the temperature range from 14 to 250 K could be described by the form of exp[-(T-1/4)]. The thermopower shows a remarkably linear behavior down to 40 K, reminiscent of some conducting polymers. The sign change of the thermopower suggests there exists more than one type of charge carrier, which could be ascribed to the different types of nanotube with various sizes of radius. The transport behavior of spiral carbon nanofibers containing Pd metal clusters will be discussed in the framework of the heterogeneous model.

Liu, C J; Hsu, L S; Su, C J; Wang, C C; Shieu, F S

2004-01-01

323

Destructive Adsorption of Diazinon Pesticide by Activated Carbon Nanofibers Containing Al2O 3 and MgO Nanoparticles.  

UK PubMed Central (United Kingdom)

We report the destructive adsorption of Diazinon pesticide by porous webs of activated carbon nanofibers containing Al2O3 and MgO nanoparticles. The results show that, the presence of Al2O3 and MgO nanoparticles in the activated carbon nanofibers increases the amount of destructively adsorbed Diazinon pesticide by activated carbon nanofibers. Moreover, type, amount, and specific surface area of metal oxide nanoparticles affect the adsorption rate as well as the total destructively adsorbed Diazinon. Liquid chromatography proved the degradation of Diazinon by chemical reaction with Al2O3 and MgO nanoparticles. Liquid chromatography-mass spectrometry showed that the main product of reaction between Diazinon and the metal oxides is 2-isopropyl-6-methyl-4-pyrimidinol with less toxicity than Diazinon.

Behnam R; Morshed M; Tavanai H; Ghiaci M

2013-08-01

324

Effect of heat-treatment temperature on carbon corrosion in polymer electrolyte membrane fuel cells  

Energy Technology Data Exchange (ETDEWEB)

This study examines the effect of heat-treatment temperature on the electrochemical corrosion of carbon nanofibers (CNFs) in polymer electrolyte membrane (PEM) fuel cells. Corrosion is investigated by monitoring the generation of CO{sub 2} using an on-line mass spectrometer at a constant potential of 1.4 V for 30 min. The experimental results show that the generation of CO{sub 2} decreases with increasing heat-treatment temperature, indicating that less electrochemical carbon corrosion occurs. In particular, when the heat-treatment temperature is 2400 C, the change intensifies. X-ray photoelectron spectroscopic analysis shows that oxygen functional groups on the carbon surface decrease with increasing heat-treatment temperature. A reduction in oxygen functional groups increases the hydrophobic nature of the carbon surface, which is responsible for the increased corrosion resistance of CNFs. (author)

Ko, Young-Jin; Oh, Hyung-Suk; Kim, Hansung [Dept. of Chemical and Biomolecular Engineering, Yonsei University, 134 Shinchon-Dong, Seodaemun-gu, 120-749 Seoul (Korea)

2010-05-01

325

Self-aligned gated field emission devices using single carbon nanofiber cathodes  

Science.gov (United States)

We report on the fabrication and operation of integrated gated field emission devices using single vertically aligned carbon nanofiber (VACNF) cathodes where the gate aperture has been formed using a self-aligned technique based on chemical mechanical polishing. We find that this method for producing gated cathode devices easily achieves structures with gate apertures on the order of 2 mum that show good concentric alignment to the VACNF emitter. The operation of these devices was explored and field emission characteristics that fit well to the Fowler-Nordheim model of emission was demonstrated.

Guillorn, M. A.; Melechko, A. V.; Merkulov, V. I.; Hensley, D. K.; Simpson, M. L.; Lowndes, D. H.

2002-11-01

326

Effects of ligand monolayers on catalytic nickel nanoparticles for synthesizing vertically aligned carbon nanofibers.  

Science.gov (United States)

Vertically aligned carbon nanofibers (VACNFs) were synthesized using ligand-stabilized Ni nanoparticle (NP) catalysts and plasma-enhanced chemical vapor deposition. Using chemically synthesized Ni NPs enables facile preparation of VACNF arrays with monodisperse diameters below the size limit of thin film lithography. During pregrowth heating, the ligands catalytically convert into graphitic shells that prevent the catalyst NPs from agglomerating and coalescing, resulting in a monodisperse VACNF size distribution. In comparison, significant agglomeration occurs when the ligands are removed before VACNF growth, giving a broad distribution of VACNF sizes. The ligand shells are also promising for patterning the NPs and synthesizing complex VACNF arrays. PMID:21410229

Sarac, Mehmet F; Wilson, Robert M; Johnston-Peck, Aaron C; Wang, Junwei; Pearce, Ryan; Klein, Kate L; Melechko, Anatoli V; Tracy, Joseph B

2011-03-16

327

Effects of ligand monolayers on catalytic nickel nanoparticles for synthesizing vertically aligned carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Vertically aligned carbon nanofibers (VACNFs) were synthesized using ligand-stabilized Ni nanoparticle (NP) catalysts and plasmaenhanced chemical vapor deposition. Using chemically synthesized Ni NPs enables facile preparation of VACNF arrays with monodisperse diameters below the size limit of thin film lithography. During pregrowth heating, the ligands catalytically convert into graphitic shells that prevent the catalyst NPs from agglomerating and coalescing, resulting in a monodisperse VACNF size distribution. In comparison, significant agglomeration occurs when the ligands are removed before VACNF growth, giving a broad distribution of VACNF sizes. The ligand shells are also promising for patterning the NPs and synthesizing complex VACNF arrays.

Sarac, Mehmet [North Carolina State University; Robert, Wilson [North Carolina State University; Johnsont-Peck, Aaron [North Carolina State University; Wang, Junwei [North Carolina State University; Pearce, Ryan [North Carolina State University; Klein, Kate [National Institute of Standards and Technology (NIST); Melechko, Anatoli [North Carolina State University; Tracy, Joseph [North Carolina State University

2011-03-01

328

Control Mechanisms for the Growth of Isolated Vertically Aligned Carbon Nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Isolated vertically aligned carbon nanofibers (VACNFs) have been grown using dc plasma-enhanced chemical vapor deposition, and the effects of the growth conditions on VACNF morphology and composition have been determined in substantial detail. The dependence of the growth rate, tip and base diameters, and chemical composition of isolated VACNFs on the growth parameters is described, including the effects of plasma power and gas mixture. Phenomenological models explaining the observed growth behavior are presented. The results indicate the importance of plasma control for the deterministic growth of isolated VACNFs, which are promising elements for the fabrication of practical nanoscale devices.

Merkulov, Vladimir I [ORNL; Hensley, Dale K [ORNL; Melechko, Anatoli Vasilievich [ORNL; Guillorn, M. A. [Cornell University; Lowndes, Douglas H [ORNL; Simpson, Michael L [ORNL

2002-01-01

329

Effects of ligand monolayers on catalytic nickel nanoparticles for synthesizing vertically aligned carbon nanofibers.  

UK PubMed Central (United Kingdom)

Vertically aligned carbon nanofibers (VACNFs) were synthesized using ligand-stabilized Ni nanoparticle (NP) catalysts and plasma-enhanced chemical vapor deposition. Using chemically synthesized Ni NPs enables facile preparation of VACNF arrays with monodisperse diameters below the size limit of thin film lithography. During pregrowth heating, the ligands catalytically convert into graphitic shells that prevent the catalyst NPs from agglomerating and coalescing, resulting in a monodisperse VACNF size distribution. In comparison, significant agglomeration occurs when the ligands are removed before VACNF growth, giving a broad distribution of VACNF sizes. The ligand shells are also promising for patterning the NPs and synthesizing complex VACNF arrays.

Sarac MF; Wilson RM; Johnston-Peck AC; Wang J; Pearce R; Klein KL; Melechko AV; Tracy JB

2011-04-01

330

Synthesis and Field Emission Properties of Hybrid Structures of Ultrananocrystalline Diamond and Vertically Aligned Carbon Nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Ultrananocrystalline diamond (UNCD) films with and without nitrogen doping were deposited onto vertically aligned carbon nanofibers (VACNFs). The field emission properties of these hybrid structures were studied. It is found that the UNCD films were deposited on VACNFs with a high degree of conformality using an optimized seeding process. This hybrid structures exhibited greatly improved macroscopic field emission performance compared with uncoated VACNFs. Further enhancement was observed for nitrogen-doped UNCD on VACNFs, with low threshold field emission (2.5 V/{micro}m) and low work functions for the field emission. The stability of the emission was also improved as compared to the uncoated VACNFs.

Xiao, X. [Argonne National Laboratory (ANL); Auciello, O. [Argonne National Laboratory (ANL); Cui, Hongtao [ORNL; Lowndes, Douglas H [ORNL; Merkulov, Vladimir I [ORNL; Carlisle, J. [Argonne National Laboratory (ANL)

2006-01-01

331

Residual gas analysis of a dc plasma for carbon nanofiber growth  

International Nuclear Information System (INIS)

[en] We report the analysis of a plasma enhanced chemical vapor deposition process for carbon nanofiber growth. A direct current (dc) plasma is employed with a mixture of acetylene and ammonia. Residual gas analysis is performed on the downstream plasma effluent to determine degrees of precursor dissociation and high molecular weight species formation. Results are correlated to growth quality obtained in the plasma as a function of dc voltage/power, gas mixture, and pressure. Behaviors in plasma chemistry are understood through application of a zero-dimensional model

2004-11-01

332

Fabrication of carbon nanofiber-polyaniline composite flexible paper for supercapacitor.  

UK PubMed Central (United Kingdom)

In this work we report a low cost technique, via simple rapid-mixture polymerization of aniline using an electrospun carbon nanofiber (CNF) paper as substrate, to fabricate free-standing, flexible CNF-PANI (PANI=polyaniline) composite paper. The morphology and microstructure of the obtained products are characterized by FESEM, FTIR, Raman and XRD. As results, PANI nanoparticles are homogeneously deposited on the surface of each CNF, forming a thin, light-weight and flexible composite paper. The resulting composite paper displays remarkably enhanced electrochemical capacitance compared with the CNF paper, making it attractive for high-performance flexible capacitors.

Yan X; Tai Z; Chen J; Xue Q

2011-01-01

333

X-ray generation using carbon-nanofiber-based flexible field emitters  

International Nuclear Information System (INIS)

Carbon nanofibers were grown on flexible polyimide substrates using an ion-beam sputtering technique. Field emission measurement showed a fairly low threshold voltage of 1.5 V/?m with a current density of 1 ?A/cm2. The field enhancement factor was determined to be 4400. The emitter showed resilience when exploited as a high voltage electron source for x-ray generation. The x-ray generated by the flexible emitter is capable of delivering fine images of biological samples with superior sharpness, resolution, and contrast.

2006-03-06

334

Microarrays of Biomimetic Cells Formed by the Controlled Synthesis of Carbon Nanofiber Membranes  

Energy Technology Data Exchange (ETDEWEB)

Biological processes are carried out in a small physical volume, the cell, where molecular composition coupled with defined nanometer-scale architecture bring about function. A major challenge inherent in copying this engineering ideal is the fabrication and filling of enclosed membrane structures. Described here is the combination of deterministically grown carbon nanofibers, micromachining techniques, and piezo-based ink jet technology to create cellular mimics. The synthesis, testing, and application of coupled arrays of semipermeable microstructures with defined, sub-nanoliter fluid contents are demonstrated.

Fletcher, Benjamin L [ORNL; Hullander, Eric D [ORNL; Melechko, Anatoli Vasilievich [ORNL; McKnight, Timothy E [ORNL; Klein, Kate L [ORNL; Hensley, Dale K [ORNL; Morrell, Jennifer L. [University of Tennessee, Knoxville (UTK); Simpson, Michael L [ORNL; Doktycz, Mitchel John [ORNL

2004-01-01

335

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

Science.gov (United States)

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; Caillard, Amaël; Charles, Christine; Boswell, Rod W.; Graves, David B.

2012-12-01

336

Fabrication of carbon nanofiber-polyaniline composite flexible paper for supercapacitor  

Science.gov (United States)

In this work we report a low cost technique, via simple rapid-mixture polymerization of aniline using an electrospun carbon nanofiber (CNF) paper as substrate, to fabricate free-standing, flexible CNF-PANI (PANI = polyaniline) composite paper. The morphology and microstructure of the obtained products are characterized by FESEM, FTIR, Raman and XRD. As results, PANI nanoparticles are homogeneously deposited on the surface of each CNF, forming a thin, light-weight and flexible composite paper. The resulting composite paper displays remarkably enhanced electrochemical capacitance compared with the CNF paper, making it attractive for high-performance flexible capacitors.

Yan, Xingbin; Tai, Zhixin; Chen, Jiangtao; Xue, Qunji

2011-01-01

337

Self-Aligned Gated Field Emission Devices Using Single Carbon Nanofiber Cathodes  

Energy Technology Data Exchange (ETDEWEB)

We report on the fabrication and operation of integrated gated field emission devices using single vertically aligned carbon nanofiber (VACNF) cathodes where the gate aperture has been formed using a self-aligned technique based on chemical mechanical polishing. We find that this method for producing gated cathode devices easily achieves structures with gate apertures on the order of 2 {mu}m that show good concentric alignment to the VACNF emitter. The operation of these devices was explored and field emission characteristics that fit well to the Fowler-Nordheim model of emission was demonstrated.

Guillorn, M. A. [Cornell University; Melechko, Anatoli Vasilievich [ORNL; Merkulov, Vladimir I [ORNL; Hensley, Dale K [ORNL; Simpson, Michael L [ORNL; Lowndes, Douglas H [ORNL

2002-01-01

338

Integrated field emission electron guns with single vertically aligned carbon nanofiber cathodes  

Science.gov (United States)

Nanostructured carbon-based materials hold great promise as field emission (FE) cathodes for integrated FE devices. These materials display remarkable FE properties as a consequence of their unique chemical and physical properties. Among this class of materials, the vertically aligned carbon nanofiber (VACNF) is exceptional in that its synthesis can be deterministically controlled. This has enabled the characterization of the FE properties of individual VACNF grown on Si substrates. The results of these studies indicate that the VACNF is an excellent candidate for integrated FE electron sources where the generation of a focused electron beam from a microscale structure is required. In this dissertation, the design, fabrication and characterization of FE electron sources using single VACNF cathodes is presented. This work emphasized the construction of devices using standard wafer-scale microfabrication techniques. Consequently, the compatibility of VACNF with these processes was explored in detail. Results showed that the VACNF could be incorporated into well established processes for synthesizing integrated FE electron sources. Gated cathode electron sources and sources incorporating an integrated electrostatic focusing electrode were designed using single carbon nanofiber cathodes. Numerical simulations of the device structures were performed to analyze the electric field structure within the devices. Following fabrication of these devices, testing was performed to verify device operation demonstrating their functionality.

Guillorn, Michael Alberto

2003-10-01

339

Growth of verically aligned carbon nanofibers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition  

Energy Technology Data Exchange (ETDEWEB)

Vertically aligned carbon nanofibers (VACNFs) have been grown using a low-pressure, plasma-enhanced, chemical vapor deposition process. The nanofibers are grown from a nickel catalyst that can be patterned to form arrays of individual, isolated VACNFs. The fibers are grown at pressures below 100 mTorr, using an inductively coupled plasma source with a radio-frequency bias on the sample substrate to allow for independent control of the ion energies. Plasma conditions are related to growth results by comparing optical emission from the plasma to the physical structure of the nanofibers. We find that the ratio of etching species in the plasma to depositing species is critical to the final shape of the carbon structures that are formed.

Caughman, John B [ORNL; Baylor, Larry R [ORNL; Guillorn, Michael A [ORNL; Merkulov, Vladimir I [ORNL; Lowndes, Douglas H [ORNL; Allard Jr, Lawrence Frederick [ORNL

2003-08-01

340

Role of ion flux on alignment of carbon nanofibers synthesized by DC plasma on transparent insulating substrates.  

UK PubMed Central (United Kingdom)

A key factor to the implementation of devices with vertically aligned carbon nanofibers (VACNFs) is fundamental understanding of how to control fluctuations in the growth direction of the fibers. Here we demonstrate synthesis of VACNF on transparent and insulating substrates by continuous direct current (DC) plasma for realization of cellular interface suitable for transmission optical microscopy. To maintain continuous glow discharge above the substrate, a metal grid electrode layer (Cr) was deposited over silica with windows of exposed silica ranging in size from 200 ?m to 1 mm. This electrode geometry allows for synthesis of VACNFs even within an insulating window. This observation and the observed trends in the alignment of nanofibers in the vicinity of grid electrodes have indicated that the alignment does not correspond to the direction of the electric field at the substrate level, contrary to previously proposed alignment mechanism. Computational modeling of the plasma with this grid cathode geometry has shown that nanofiber alignment trends follow calculated ion flux direction rather than electrical field. The new proposed alignment mechanism is that ion sputtering of the carbon film on a catalyst particle defines the growth direction of the nanofibers. With this development, fiber growth direction can be better manipulated through changes in ionic flux direction, opening the possibility for growth of nanofibers on substrates with unique geometries.

Pearce RC; Vasenkov AV; Hensley DK; Simpson ML; McKnight TE; Melechko AV

2011-09-01

 
 
 
 
341

Role of ion flux on alignment of carbon nanofibers synthesized by DC plasma on transparent insulating substrates.  

Science.gov (United States)

A key factor to the implementation of devices with vertically aligned carbon nanofibers (VACNFs) is fundamental understanding of how to control fluctuations in the growth direction of the fibers. Here we demonstrate synthesis of VACNF on transparent and insulating substrates by continuous direct current (DC) plasma for realization of cellular interface suitable for transmission optical microscopy. To maintain continuous glow discharge above the substrate, a metal grid electrode layer (Cr) was deposited over silica with windows of exposed silica ranging in size from 200 ?m to 1 mm. This electrode geometry allows for synthesis of VACNFs even within an insulating window. This observation and the observed trends in the alignment of nanofibers in the vicinity of grid electrodes have indicated that the alignment does not correspond to the direction of the electric field at the substrate level, contrary to previously proposed alignment mechanism. Computational modeling of the plasma with this grid cathode geometry has shown that nanofiber alignment trends follow calculated ion flux direction rather than electrical field. The new proposed alignment mechanism is that ion sputtering of the carbon film on a catalyst particle defines the growth direction of the nanofibers. With this development, fiber growth direction can be better manipulated through changes in ionic flux direction, opening the possibility for growth of nanofibers on substrates with unique geometries. PMID:21786800

Pearce, Ryan C; Vasenkov, Alexei V; Hensley, Dale K; Simpson, Michael L; McKnight, Timothy E; Melechko, Anatoli V

2011-08-09

342

A reagentless enzymatic amperometric biosensor using vertically aligned carbon nanofibers (VACNF)  

Energy Technology Data Exchange (ETDEWEB)

A reagentless amperometric enzymatic biosensor is constructed on a carbon substrate for detection of ethanol. Yeast alcohol dehydrogenase (YADH), an oxidoreductase, and its cofactor nicotinamide adenine dinucleotide (NAD+) are immobilized by adsorption and covalent attachment to the carbon substrate. Carbon nanofibers grown by plasma enhanced chemical vapor deposition (PECVD) are chosen as the electrode material due to their excellent structural and electrical properties. Electrochemical techniques are employed to test the functionality and performance of the biosensor using reduced form of nicotinamide adenine dinucleotide (NADH) which also determines the oxidation peak potential of NADH. Subsequently, amperometric measurements are conducted for detection of ethanol to determine the electrical current response due to the increase in analyte concentration. The detection range, storage stability, reusability, and response time of the biosensor are also examined.

Weeks, Martha L [University of Tennessee, Knoxville (UTK); Rahman, Touhidur [ORNL; Frymier, Paul Dexter [ORNL; Islam, Syed K [University of Tennessee, Knoxville (UTK); McKnight, Timothy E [ORNL

2008-01-01

343

Properties that Influence the Specific Surface Areas of Carbon Nanotubes and Nanofibers.  

UK PubMed Central (United Kingdom)

Commercially available carbon nanotubes and nanofibers were analyzed to examine possible relationships between their Brunauer-Emmett-Teller specific surface areas (SSAs) and their physical and chemical properties. Properties found to influence surface area were number of walls/diameter, impurities, and surface functionalization with hydroxyl and carboxyl groups. Characterization by electron microscopy, energy-dispersive X-ray spectrometry, thermogravimetric analysis, and elemental analysis indicates that SSA can provide insight on carbon nanomaterials properties, which can differ vastly depending on synthesis parameters and post-production treatments. In this study, how different properties may influence surface area is discussed. The materials examined have a wide range of surface areas. The measured surface areas differed from product specifications, to varying degrees, and between similar products. Findings emphasize the multiple factors that influence surface area and mark its utility in carbon nanomaterial characterization, a prerequisite to understanding their potential applications and toxicities. Implications for occupational monitoring are discussed.

Birch ME; Ruda-Eberenz TA; Chai M; Andrews R; Hatfield RL

2013-09-01

344

Carbon-nanofiber-based probing arrays for multipoint integration with cellular matrices  

Science.gov (United States)

The self-assembling and controlled synthesis properties of vertically-aligned carbon nanofibers (VACNF) have been exploited to provide parallel subcellular and molecular-scale probes for biological manipulation and monitoring. VACNFs possess many attributes that make them very attractive for implementation as functional, nanoscale features of microfabricated devices. For example, they can be synthesized at precise locations upon a substrate, can be grown many microns long, and feature sharp, nano-dimensioned tips. They also exhibit characteristic electrochemical responses similar to conventionally studied materials such as the edge plane of pyrolytic graphite and surface-activated glassy carbon. This, and their needlelike, vertical orientation upon a substrate, makes them particularly attractive as multielement cellular scale probes or as a parallel embodiment of traditional single-point microinjection or microelectrophysiological systems. We will overview our efforts at fabricating and characterizing several embodiments of VACNF cell probing systems. We will also overview surface modification techniques that exploit the rich surface chemistries of VACNF arrays to allow immobilization of active enzymes and transcriptionally active DNA, which can provide sensitivity to specific biological analytes and application of the nanofiber architecture for controlled biochemical manipulation within the cell. Finally, we will overview our techniques of integrating these probing structures with intact cells and how these structures may be used on a massively parallel basis for measurement and control of the intracellular domain.

McKnight, Tim E.; Melechko, Anatoli; Griffin, Guy D.; Austin, Derek W.; Sims, Tyler; Guillorn, Michael; Merkulov, Vladimir I.; Simpson, Michael L.

2004-03-01

345

Electrically conductive carbon nanofiber/paraffin wax composites for electric thermal storage  

International Nuclear Information System (INIS)

Highlights: ? Carbon nanofiber (CNF)/paraffin wax composite is found to be a promising electric thermal storage material. ? The thermal storage capacity of CNF/paraffin wax composite is five times of traditional electric thermal storage material. ? CNF is shown to be an effective conductive filler for the composite. - Abstract: The research of electric thermal storage (ETS) has attracted a lot of attention recently, which converts off-peak electrical energy into thermal energy and release it later at peak hours. In this study, new electric thermal storage composites are developed by employing paraffin wax as thermal storage media and carbon nanofiber (CNF) as conductive fillers. Electric heating and thermal energy release performances of the CNF/paraffin wax composites are experimentally investigated. Experimental results show that, when the composites are heated to about 70 °C, the developed electrically conductive CNF/paraffin wax composites present a thermal storage capacity of about 280 kJ/kg, which is five times of that of traditional thermal storage medium such as ceramic bricks (54 kJ/kg). The CNF/paraffin wax composites can also effectively store the thermal energy and release the thermal energy in later hours.

2012-01-01

346

Superhydrophobic and conductive carbon nanofiber/PTFE composite coatings for EMI shielding.  

UK PubMed Central (United Kingdom)

This paper presents a solvent-based, mild method to prepare superhydrophobic, carbon nanofiber/PTFE-filled polymer composite coatings with high electrical conductivity and reports the first data on the effectiveness of such coatings as electromagnetic interference (EMI) shielding materials. The coatings are fabricated by spraying dispersions of carbon nanofibers and sub-micron PTFE particles in a polymer blend solution of poly(vinyledene fluoride) and poly(methyl methacrylate) on cellulosic substrates. Upon drying, coatings display static water contact angles as high as 158° (superhydrophobic) and droplet roll-off angles of 10° indicating self-cleaning ability along with high electrical conductivities (up to 309 S/m). 100 ?m-thick coatings are characterized in terms of their EMI shielding effectiveness in the X-band (8.2-12.4 GHz). Results show up to 25 dB of shielding effectiveness, which changed little with frequency at a fixed composition, thus indicating the potential of these coatings for EMI shielding applications and other technologies requiring both extreme liquid repellency and high electrical conductivity.

Das A; Hayvaci HT; Tiwari MK; Bayer IS; Erricolo D; Megaridis CM

2011-01-01

347

Controlling thin film structure for the dewetting of catalyst nanoparticle arrays for subsequent carbon nanofiber growth  

International Nuclear Information System (INIS)

Vertically aligned carbon nanofiber (CNF) growth is a catalytic chemical vapor deposition process in which structure and functionality is controlled by the plasma conditions and the properties of the catalyst nanoparticles that template the fiber growth. We have found that the resultant catalyst nanoparticle network that forms by the dewetting of a continuous catalyst thin film is dependent on the initial properties of the thin film. Here we report the ability to tailor the crystallographic texture and composition of the nickel catalyst film and subsequently the nanoparticle template by varying the rf magnetron sputter deposition conditions. After sputtering the Ni catalyst thin films, the films are heated and exposed to an ammonia dc plasma, to chemically reduce the native oxide on the films and induce dewetting of the film to form nanoparticles. Subsequent nanoparticle treatment in an acetylene plasma at high substrate temperature results in CNF growth. Evidence is presented that the texture and composition of the nickel thin film has a significant impact on the structure and composition of the formed nanoparticle, as well as the resultant CNF morphology. Nickel films with a preferred (111) or (100) texture were produced and conditions favoring interfacial silicidation reactions were identified and investigated. Both compositional and structural analysis of the films and nanoparticles indicate that the properties of the as-deposited Ni catalyst film influences the subsequent nanoparticle formation and ultimately the catalytic growth of the carbon nanofibers.

2007-11-21

348

Morphological characterization of carbon-nanofiber-reinforced epoxy nanocomposites using ultra-small angle scattering  

International Nuclear Information System (INIS)

Studies of the properties of nanocomposites reinforced with vapor-grown carbon nanofibers (VGCFs) can be found throughout the literature. Electrical, mechanical, viscoelastic, and rheological properties are just a few of the characteristics that have been well discussed. Although these properties depend on morphology, morphological characterization is rare. Due to its 2-dimensional nature, microscopy is of limited value when analyzing network morphologies. This work will show how the characterization of the three-dimensional geometry and network formation of VGCFs can be determined using ultra-small angle scattering techniques. Ultra-small angle x-ray and neutron scattering (USAXS and USANS) were used to characterize the morphology of carbon nanofibers suspended in epoxy. Using a simplified tube model, we estimate the dimensions of suspended fibers. The assumption of tubular fibers accounts for the increased surface area observed with USAXS that is not accounted for using a solid rod model. Furthermore, USANS was used to search for a structural signature associated with the electrical percolation threshold. USANS extends to longer dimensional scales than USAXS, which measures a smaller range of momentum transfer. To determine the electrical percolation threshold, AC impedance spectroscopy was employed to verify that an electrically conductive, percolated network forms at VGCNF loadings of 0.8%

2005-11-04

349

Improving microstructure of silicon/carbon nanofiber composites as a Li battery anode  

Energy Technology Data Exchange (ETDEWEB)

We report the interfacial study of a silicon/carbon nanofiber (Si/CNF) nanocomposite material as a potentially high performance anode for rechargeable lithium ion batteries. The carbon nanofiber is hollow, with a graphitic interior and turbostratic exterior. Amorphous silicon layers were uniformly coated via chemical vapor deposition on both the exterior and interior surfaces of the CNF. The resulting Si/CNF composites were tested as anodes for Li ion batteries and exhibited capacities near 800 mAh g1 for 100 cycles. After cycling, we found that more Si had fallen off from the outer wall than from the innerwall of CNF. Theoretical calculations confirmed that this is due to a higher interfacial strength at the Si/Cedge interface at the inner wall than that of the Si/C-basal interface at the outer wall. Based upon the experimental analysis and theoretical calculation, we have proposed several interfacial engineering approaches to improve the performance of the electrodes by optimizing the microstructure of this nanocomposite.

Howe, Jane Y [ORNL; Meyer III, Harry M [ORNL; Burton, David J. [Applied Sciences, Inc.; Qi, Dr. Yue [General Motors Corporation; Nazri, Maryam [Applied Sciences, Inc.; Nazri, G. Abbas [General Motors Corporation-R& D; Palmer, Andrew C. [Applied Sciences, Inc.; Lake, Patrick D. [Applied Sciences, Inc.

2013-01-01

350

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

UK PubMed Central (United Kingdom)

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.

Liu D; Zhang X; Sun Z; You T

2013-08-01

351

Fabrication of carbon nanofiber-driven electrodes from electrospun polyacrylonitrile/polypyrrole bicomponents for high-performance rechargeable lithium-ion batteries  

Energy Technology Data Exchange (ETDEWEB)

Carbon nanofibers were prepared through electrospinning a blend solution of polyacrylonitrile and polypyrrole, followed by carbonization at 700 C. Structural features of electrospun polyacrylonitrile/polypyrrole bicomponent nanofibers and their corresponding carbon nanofibers were characterized using scanning electron microscopy, differential scanning calorimeter, thermo-gravimetric analysis, wide-angle X-ray diffraction, and Raman spectroscopy. It was found that intermolecular interactions are formed between two different polymers, which influence the thermal properties of electrospun bicomponent nanofibers. In addition, with the increase of polypyrrole concentration, the resultant carbon nanofibers exhibit increasing disordered structure. These carbon nanofibers were used as anodes for rechargeable lithium-ion batteries without adding any polymer binder or conductive material and they display high reversible capacity, improved cycle performance, relatively good rate capability, and clear fibrous morphology even after 50 charge/discharge cycles. The improved electrochemical performance of these carbon nanofibers can be attributed to their unusual surface properties and unique structural features, which amplify both surface area and extensive intermingling between electrode and electrolyte phases over small length scales, thereby leading to fast kinetics and short pathways for both Li ions and electrons. (author)

Ji, Liwen; Yao, Yingfang; Toprakci, Ozan; Lin, Zhan; Liang, Yinzheng; Shi, Quan; Medford, Andrew J.; Millns, Christopher R.; 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)

2010-04-02

352

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)

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 dispersio...

Cardoso, Paulo; Silva, Jaime; Klosterman, Donald; Covas, José A; van Hattum, Ferrie WJ; Simoes, Ricardo; Lanceros-Mendez, Senentxu

353

LiFePO4 - 3D carbon nanofiber composites as cathode materials for Li-ions batteries  

Science.gov (United States)

The characterization of carbon nanofiber 3D nonwovens, prepared by electrospinning process, coated with olivine structured lithium iron phosphate is reported. The LiFePO4 as cathode material for lithium ion batteries was prepared by a Pechini-assisted reversed polyol process. The coating has been successfully performed on carbon nanofiber 3D nonwovens by soaking in aqueous solution containing lithium, iron salts and phosphates at 70 °C for 2-4 h. After drying-out, the composites were annealed at 600 °C for 5 h under nitrogen. The surface investigation of the prepared composites showed a uniform coating of the carbon nonwoven nanofibers as well as the formation of cauliflower-like crystalline structures which are uniformly distributed all over the surface area of the carbon nanofibers. The electrochemical measurements on the composites showed good performances delivering a discharge specific capacity of 156 mAhg- 1 at a discharging rate of C/25 and 152 mAhg- 1 at a discharging rate of C/10 at room temperature.

Dimesso, L.; Spanheimer, C.; Jaegermann, W.; Zhang, Y.; Yarin, A. L.

2012-03-01

354

One-dimensional confinement of a nanosized metal organic framework in carbon nanofibers for improved gas adsorption.  

UK PubMed Central (United Kingdom)

The loading of a Zn-terephthalate based MOF in the inner cavity as well as on the outer walls of a hollow carbon nanofiber (CNF) creates MOF@CNF hybrids. This hybrid ''MOF@CNF'' displayed improved thermal stability as well as gas adsorption compared to the individual counterparts.

Pachfule P; Balan BK; Kurungot S; Banerjee R

2012-02-01

355

Early Combination of Material Characteristics and Toxicology Is Useful in the Design of Low Toxicity Carbon Nanofiber  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper describes an approach for the early combination of material characterization and toxicology testing in order to design carbon nanofiber (CNF) with low toxicity. The aim was to investigate how the adjustment of production parameters and purification procedures can result in a CNF product w...

Ellen K. Jensen; Sten Y. Larsen; Unni C. Nygaard; Calin D. Marioara; Tore Syversen

356

Preparation and electrochemical properties of carbon nanofiber composite dispersed with silver nanoparticles using polyacrylonitrile and beta-cyclodextrin.  

UK PubMed Central (United Kingdom)

A simple one-step method was used for preparing the beta-cyclodextrin/polyacrylonitrile (PAN) nanofibers deposited with silver nanoparticles by electrospinning and followed by the reduction of the Ag+ ions. The nano-composite fibers were stabilized at 280 degrees C in air and activated at 800 degrees C for 1 h in steam/N2. The structures of nano-composite fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction analysis (XRD). The electrochemical behaviors of the composite of carbon nano-fibers were investigated by cyclic voltammetry and charge/discharge tests.

Kim BH; Yang KS; Woo HG

2011-08-01

357

Preparation and electrochemical properties of carbon nanofiber composite dispersed with silver nanoparticles using polyacrylonitrile and beta-cyclodextrin.  

Science.gov (United States)

A simple one-step method was used for preparing the beta-cyclodextrin/polyacrylonitrile (PAN) nanofibers deposited with silver nanoparticles by electrospinning and followed by the reduction of the Ag+ ions. The nano-composite fibers were stabilized at 280 degrees C in air and activated at 800 degrees C for 1 h in steam/N2. The structures of nano-composite fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction analysis (XRD). The electrochemical behaviors of the composite of carbon nano-fibers were investigated by cyclic voltammetry and charge/discharge tests. PMID:22103155

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

2011-08-01

358

The influence of the dispersion method on the electrical properties of vapor-grown carbon nanofiber/epoxy composites  

Science.gov (United States)

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: 72.80.Tm; 73.63.Fg; 81.05.Qk

Cardoso, Paulo; Silva, Jaime; Klosterman, Donald; Covas, José A.; van Hattum, Ferrie Wj; Simoes, Ricardo; Lanceros-Mendez, Senentxu

2011-05-01

359

The influence of the dispersion method on the electrical properties of vapor-grown carbon nanofiber/epoxy composites.  

UK PubMed Central (United Kingdom)

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: 72.80.Tm; 73.63.Fg; 81.05.Qk.

Cardoso P; Silva J; Klosterman D; Covas JA; van Hattum FW; Simoes R; Lanceros-Mendez S

2011-01-01

360

The influence of the dispersion method on the electrical properties of vapor-grown carbon nanofiber/epoxy composites  

Directory of Open Access Journals (Sweden)

Full Text Available 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: 72.80.Tm; 73.63.Fg; 81.05.Qk

Cardoso Paulo; Silva Jaime; Klosterman Donald; Covas José; van Hattum Ferrie; Simoes Ricardo; Lanceros-Mendez Senentxu

2011-01-01

 
 
 
 
361

Carbon nanotube-templated polyaniline nanofibers: synthesis, flash welding and ultrafiltration membranes  

Science.gov (United States)

Electro-active switchable ultrafiltration membranes are of great interest due to the possibility of external control over permeability, selectivity, anti-fouling and cleaning. Here, we report on hybrid single-walled carbon nanotube (SWCNT)-polyaniline (PANi) nanofibers synthesized by in situ polymerization of aniline in the presence of oxidized SWCNTs. The composite nanofibers exhibit unique morphology of core-shell (SWCNT-PANi) structures with average total diameters of 60 nm with 10 to 30 nm thick PANi coatings. The composite nanofibers are easily dispersed in polar aprotic solvents and cast into asymmetric membranes via a nonsolvent induced phase separation. The hybrid SWCNT-PANi membranes are electrically conductive at neutral pH and exhibit ultrafiltration-like permeability and selectivity when filtering aqueous suspensions of 6 nm diameter bovine serum albumin and 48 nm diameter silica particles. A novel flash welding technique is utilized to tune the morphology, porosity, conductivity, permeability and nanoparticle rejection of the SWCNT-PANi composite ultrafiltration membranes. Upon flash welding, both conductivity and pure water permeability of the membranes improves by nearly a factor of 10, while maintaining silica nanoparticle rejection levels above 90%. Flash welding of SWCNT-PANi composite membranes holds promise for formation of electrochemically tunable membranes.Electro-active switchable ultrafiltration membranes are of great interest due to the possibility of external control over permeability, selectivity, anti-fouling and cleaning. Here, we report on hybrid single-walled carbon nanotube (SWCNT)-polyaniline (PANi) nanofibers synthesized by in situ polymerization of aniline in the presence of oxidized SWCNTs. The composite nanofibers exhibit unique morphology of core-shell (SWCNT-PANi) structures with average total diameters of 60 nm with 10 to 30 nm thick PANi coatings. The composite nanofibers are easily dispersed in polar aprotic solvents and cast into asymmetric membranes via a nonsolvent induced phase separation. The hybrid SWCNT-PANi membranes are electrically conductive at neutral pH and exhibit ultrafiltration-like permeability and selectivity when filtering aqueous suspensions of 6 nm diameter bovine serum albumin and 48 nm diameter silica particles. A novel flash welding technique is utilized to tune the morphology, porosity, conductivity, permeability and nanoparticle rejection of the SWCNT-PANi composite ultrafiltration membranes. Upon flash welding, both conductivity and pure water permeability of the membranes improves by nearly a factor of 10, while maintaining silica nanoparticle rejection levels above 90%. Flash welding of SWCNT-PANi composite membranes holds promise for formation of electrochemically tunable membranes. Electronic supplementary information (ESI) available: Characteristic chemical shifts/transmittances of ATR/FT-IR spectral bands for SWCNT-PANi EB composite membranes under different numbers of flash welds at full power can be seen in Table S1. See DOI: 10.1039/c3nr00441d

Liao, Yaozu; Yu, Deng-Guang; Wang, Xia; Chain, Wei; Li, Xin-Gui; Hoek, Eric M. V.; Kaner, Richard B.

2013-04-01

362

Effect of the nature the carbon precursor on the physico-chemical characteristics of the resulting activated carbon materials  

Energy Technology Data Exchange (ETDEWEB)

Carbon materials, including amorphous carbon, graphite, carbon nanospheres (CNSs) and different types of carbon nanofibers (CNFs) [platelet, herringbone and ribbon], were chemically activated using KOH. The pore structure of carbon materials was analyzed using N{sub 2}/77 K adsorption isotherms. The presence of oxygen groups was analyzed by temperature programmed desorption in He and acid-base titration. The structural order of the materials was studied by X-ray diffraction and temperature programmed oxidation. The morphology and diameter distribution of CNFs and CNSs were characterized by transmission electron microscopy. The materials were also characterized by temperature-desorption programmed of H{sub 2} and elemental composition. The ways in which the different structures were activated are described, showing the type of pores generated. Relationships between carbon yield, removed carbon, activation degree and graphitic character were also examined. The oxygen content in the form of oxygen-containing surface groups increased after the activation giving qualitative information about them. The average diameter of both CNFs and CNSs was decreased after the activation process as consequence of the changes produced on the material surface.

Jimenez, Vicente, E-mail: vicente.jimenez@uclm.es [Facultad de Ciencias Quimicas, Departamento de Ingenieria Quimica, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Sanchez, Paula; Valverde, Jose Luis [Facultad de Ciencias Quimicas, Departamento de Ingenieria Quimica, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Romero, Amaya [Escuela Tecnica Agricola, Departamento de Ingenieria Quimica, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)

2010-11-01

363

Effect of the nature the carbon precursor on the physico-chemical characteristics of the resulting activated carbon materials  

International Nuclear Information System (INIS)

Carbon materials, including amorphous carbon, graphite, carbon nanospheres (CNSs) and different types of carbon nanofibers (CNFs) [platelet, herringbone and ribbon], were chemically activated using KOH. The pore structure of carbon materials was analyzed using N2/77 K adsorption isotherms. The presence of oxygen groups was analyzed by temperature programmed desorption in He and acid-base titration. The structural order of the materials was studied by X-ray diffraction and temperature programmed oxidation. The morphology and diameter distribution of CNFs and CNSs were characterized by transmission electron microscopy. The materials were also characterized by temperature-desorption programmed of H2 and elemental composition. The ways in which the different structures were activated are described, showing the type of pores generated. Relationships between carbon yield, removed carbon, activation degree and graphitic character were also examined. The oxygen content in the form of oxygen-containing surface groups increased after the activation giving qualitative information about them. The average diameter of both CNFs and CNSs was decreased after the activation process as consequence of the changes produced on the material surface.

2010-11-01

364

In situ Polymerization of Multi-Walled Carbon Nanotube/Nylon-6 Nanocomposites and Their Electrospun Nanofibers  

Science.gov (United States)

Multiwalled carbon nanotube/nylon-6 nanocomposites (MWNT/nylon-6) were prepared by in situ polymerization, whereby functionalized MWNTs (F-MWNTs) and pristine MWNTs (P-MWNTs) were used as reinforcing materials. The F-MWNTs were functionalized by Friedel-Crafts acylation, which introduced aromatic amine (COC6H4-NH2) groups onto the side wall. Scanning electron microscopy (SEM) images obtained from the fractured surfaces of the nanocomposites showed that the F-MWNTs in the nylon-6 matrix were well dispersed as compared to those of the P-MWNTs. Both nanocomposites could be electrospun into nanofibers in which the MWNTs were embedded and oriented along the nanofiber axis, as confirmed by transmission electron microscopy. The specific strength and modulus of the MWNTs-reinforced nanofibers increased as compared to those of the neat nylon-6 nanofibers. The crystal structure of the nylon-6 in the MWNT/nylon-6 nanofibers was mostly ?-phase, although that of the MWNT/nylon-6 films, which were prepared by hot-pressing the pellets between two aluminum plates and then quenching them in icy water, was mostly ?-phase, indicating that the shear force during electrospinning might favor the ?-phase, similarly to the conventional fiber spinning.

Saeed, Khalid; Park, Soo-Young; Haider, Sajjad; Baek, Jong-Beom

2009-01-01

365

In situ Polymerization of Multi-Walled Carbon Nanotube/Nylon-6 Nanocomposites and Their Electrospun Nanofibers  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Multiwalled carbon nanotube/nylon-6 nanocomposites (MWNT/nylon-6) were prepared by in situ polymerization, whereby functionalized MWNTs (F-MWNTs) and pristine MWNTs (P-MWNTs) were used as reinforcing materials. The F-MWNTs were functionalized by Friedel-Crafts acylation, which introduced aromatic amine (COC6H4-NH2) groups onto the side wall. Scanning electron microscopy (SEM) images obtained from the fractured surfaces of the nanocomposites showed that the F-MWNTs in the nylon-6 matrix were well dispersed as compared to those of the P-MWNTs. Both nanocomposites could be electrospun into nanofibers in which the MWNTs were embedded and oriented along the nanofiber axis, as confirmed by transmission electron microscopy. The specific strength and modulus of the MWNTs-reinforced nanofibers increased as compared to those of the neat nylon-6 nanofibers. The crystal structure of the nylon-6 in the MWNT/nylon-6 nanofibers was mostly ?-phase, although that of the MWNT/nylon-6 films, which were prepared by hot-pressing the pellets between two aluminum plates and then quenching them in icy water, was mostly ?-phase, indicating that the shear force during electrospinning might favor the ?-phase, similarly to the conventional fiber spinning.

Saeed Khalid; Park Soo-Young; Haider Sajjad; Baek Jong-Beom

2008-01-01

366

A New Strategy to Pretreat Carbon Nanofiber and Its Application in Determination of Dopamine  

Directory of Open Access Journals (Sweden)

Full Text Available 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 oxidation of DA. A carbon paste electrode modified by CNF (CPE-CNF) was used to determine the dopamine (DA) in the presence of ascorbic acid (AA). The detection limit is 0.05??M, with the linear range from 0.05??M to 6.4??M.

Dong Liu; Yang Liu; Haoqing Hou; Tianyan You

2010-01-01

367

Effects of spatial separation on the growth of vertically aligned carbon nanofibers produced by plasma-enhanced chemical vapor deposition  

International Nuclear Information System (INIS)

Vertically aligned carbon nanofibers (VACNFs) with vastly different spacing were grown by catalytically controlled dc glow discharge chemical vapor deposition. Both densely packed VACNFs and essentially isolated VACNFs were studied using scanning electron microscopy and x-ray energy dispersive spectroscopy. The morphology and chemical composition of isolated VACNFs were found to have a strong dependence upon the growth conditions, in particular on the C2H2/NH3 gas mixture used. This is attributed to the sidewalls of isolated VACNFs being exposed to reactive species during growth. In contrast, the sidewalls of densely packed VACNFs were shielded by the neighboring VACNFs, so that their growth occurred mainly in the vertical direction, by diffusion of carbon through the catalyst nanoparticle and subsequent precipitation at the nanofiber/nanoparticle interface. These striking differences in the growth process result in the formation of flattened carbon nanostructures (carbon nanotriangles) and also are quite important for the realization of VACNF-based devices

2002-01-21

368

Effects of spatial separation on the growth of vertically aligned carbon nanofibers produced by plasma-enhanced chemical vapor deposition  

Science.gov (United States)

Vertically aligned carbon nanofibers (VACNFs) with vastly different spacing were grown by catalytically controlled dc glow discharge chemical vapor deposition. Both densely packed VACNFs and essentially isolated VACNFs were studied using scanning electron microscopy and x-ray energy dispersive spectroscopy. The morphology and chemical composition of isolated VACNFs were found to have a strong dependence upon the growth conditions, in particular on the C2H2/NH3 gas mixture used. This is attributed to the sidewalls of isolated VACNFs being exposed to reactive species during growth. In contrast, the sidewalls of densely packed VACNFs were shielded by the neighboring VACNFs, so that their growth occurred mainly in the vertical direction, by diffusion of carbon through the catalyst nanoparticle and subsequent precipitation at the nanofiber/nanoparticle interface. These striking differences in the growth process result in the formation of flattened carbon nanostructures (carbon nanotriangles) and also are quite important for the realization of VACNF-based devices.

Merkulov, Vladimir I.; Melechko, Anatoli V.; Guillorn, Michael A.; Lowndes, Douglas H.; Simpson, Michael L.

2002-01-01

369

X-ray absorption fine structure (XAFS) analyses of Ni species trapped in graphene sheet of carbon nanofibers  

International Nuclear Information System (INIS)

Metal impurities in the carbon nanotubes and carbon nanofibers play an important role in understanding their physical and chemical properties. We apply the Ni K-edge x-ray absorption fine structure analyses to the local electronic and geometric structures around embedded Ni impurities used as catalysts in a carbon nanofiber in combination with multiple scattering analyses. We find almost Ni catalysts as metal particles are removed by the purification treatment. Even after the purification, residual 100 ppm Ni species are still absorbed; most of them are in monomer structure with Ni-C bond length 1.83 A, and each of them is substituted for a carbon atom in a graphene sheet.

2006-04-01

370

Decomposition of Fe{sub 5}C{sub 2} catalyst particles in carbon nanofibers during TEM observation  

Energy Technology Data Exchange (ETDEWEB)

The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite ({theta}-Fe{sub 3}C). However, for Haegg carbide nanoparticles ({chi}-Fe{sub 5}C{sub 2}), explosive decay is observed after exposure for 5-10 s. This produces small particles of cementite and {gamma}-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Haegg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.

Blank, Vladimir D; Kulnitskiy, Boris A; Perezhogin, Igor A; Alshevskiy, Yuriy L; Kazennov, Nikita V [Technological Institute for Superhard and Novel Carbon Materials, 7a Centralnaya Street, Troitsk 142190, Moscow region (Russian Federation)], E-mail: boris@ntcstm.troitsk.ru

2009-01-15

371

Actuatable membranes based on polypyrrole-coated vertically aligned carbon nanofibers.  

UK PubMed Central (United Kingdom)

Nanoporous membranes are applicable to a variety of research fields due to their ability to selectively separate molecules with high efficiency. Of particular interest are methods for controlling membrane selectivity through externally applied stimuli and integrating such membrane structures within multiscale systems. Membranes comprised of deterministically grown, vertically aligned carbon nanofibers (VACNFs) are compatible with these needs. VACNF membranes can regulate molecular transport by physically selecting species as they pass between the fibers. Defined interfiber spacing allows for nanoscale control of membrane pore structure and resultant size selectivity. Subsequent physical or chemical modification of VACNF structures enables the tuning of physical pore size and chemical specificity allowing further control of membrane permeability. In this work, the dynamic physical modulation of membrane permeability that results when VACNFs are coated with an electrically actuatable polymer, polypyrrole, is demonstrated. Electrochemical reduction of polypyrrole on the VACNFs results in controlled swelling of the diameter of the nanofibers that in turn decreases the pore size. Dynamic control of membrane pore size enables selective transport and gating of nanoscale pores.

Fletcher BL; Retterer ST; McKnight TE; Melechko AV; Fowlkes JD; Simpson ML; Doktycz MJ

2008-02-01

372

Actuatable membranes based on polypyrrole-coated vertically aligned carbon nanofibers.  

Science.gov (United States)

Nanoporous membranes are applicable to a variety of research fields due to their ability to selectively separate molecules with high efficiency. Of particular interest are methods for controlling membrane selectivity through externally applied stimuli and integrating such membrane structures within multiscale systems. Membranes comprised of deterministically grown, vertically aligned carbon nanofibers (VACNFs) are compatible with these needs. VACNF membranes can regulate molecular transport by physically selecting species as they pass between the fibers. Defined interfiber spacing allows for nanoscale control of membrane pore structure and resultant size selectivity. Subsequent physical or chemical modification of VACNF structures enables the tuning of physical pore size and chemical specificity allowing further control of membrane permeability. In this work, the dynamic physical modulation of membrane permeability that results when VACNFs are coated with an electrically actuatable polymer, polypyrrole, is demonstrated. Electrochemical reduction of polypyrrole on the VACNFs results in controlled swelling of the diameter of the nanofibers that in turn decreases the pore size. Dynamic control of membrane pore size enables selective transport and gating of nanoscale pores. PMID:19206624

Fletcher, Benjamin L; Retterer, Scott T; McKnight, Timothy E; Melechko, Anatoli V; Fowlkes, Jason D; Simpson, Michael L; Doktycz, Mitchel J

2008-02-01

373

Optically and electrically addressed carbon nanofiber electrode arrays for intracellular interfacing  

Science.gov (United States)

Progress in the application of vertically-aligned carbon nanofibers (VACNF) as parallel subcellular and molecular-scale probes for biological manipulation and monitoring is reported. VACNFs possess many attributes that make them very attractive for implementation as functional, nanoscale features of microfabricated devices. For example, they can be synthesized at precise locations upon a substrate, can be grown many microns long, and feature sharp, nano-dimensioned tips. This, and their needlelike, vertical orientation upon a substrate, makes them particularly attractive as multielement cellular scale probes or as a parallel embodiment of traditional single-point microinjection or microelectrophysiological systems. We will overview our progress with fabricating and characterizing several embodiments of VACNF cell probing systems, which all feature arrays of nanoscale electrochemically-active probing regions at the tips of individually electrically-addressed nanofiber elements. We also overview our techniques of integrating these probing structures with intact cells and how these structures may be used on a massively parallel basis for measurement and control around and within viable cells.

McKnight, Timothy E.; Melechko, Anatoli V.; Griffin, Guy D.; Jun, Seong-Ik; Rack, Philip D.; Guillorn, Michael A.; Merkulov, Vladimir I.; Simpson, Michael L.

2004-10-01

374

Actuatable membranes based on polypyrrole-coated vertically aligned carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Nanoporous membranes are applicable to a variety of research fields due to their ability to selectively separate molecules with high efficiency. Of particular interest are methods for controlling membrane selectivity through externally applied stimuli and integrating such membrane structures within multiscale systems. Membranes comprised of deterministically grown, vertically aligned carbon nanofibers (VACNFs) are compatible with these needs. VACNF membranes can regulate molecular transport by physically selecting species as they pass between the fibers. Defined interfiber spacing allows for nanoscale control of membrane pore structure and resultant size selectivity. Subsequent physical or chemical modification of VACNF structures enables the tuning of physical pore size and chemical specificity allowing further control of membrane permeability. In this work, the dynamic physical modulation of membrane permeability that results when VACNFs are coated with an electrically actuatable polymer, polypyrrole, is demonstrated. Electrochemical reduction of polypyrrole on the VACNFs results in controlled swelling of the diameter of the nanofibers that in turn decreases the pore size. Dynamic control of membrane pore size enables selective transport and gating of nanoscale pores.

Fletcher, Benjamin L [ORNL; McKnight, Timothy E [ORNL; Melechko, Anatoli Vasilievich [ORNL; Fowlkes, Jason Davidson [ORNL; Simpson, Michael L [ORNL; Doktycz, Mitchel [ORNL

2008-01-01

375

Synthesis and characterization of magnetically active carbon nanofiber/iron oxide composites with hierarchical pore structures  

Science.gov (United States)

Polyacrylonitrile (PAN) solution containing the iron oxide precursor iron (III) acetylacetonate (AAI) was electrospun and thermally treated to produce electrically conducting, magnetic carbon nanofiber mats with hierarchical pore structures. The morphology and material properties of the resulting multifunctional nanofiber mats including the surface area and the electric and magnetic properties were examined using various characterization techniques. Scanning electron microscopy images show that uniform fibers were produced with a fiber diameter of ~600 nm, and this uniform fiber morphology is maintained after graphitization with a fiber diameter of ~330 nm. X-ray diffraction (XRD) and Raman studies reveal that both graphite and Fe3O4 crystals are formed after thermal treatment, and graphitization can be enhanced by the presence of iron. A combination of XRD and transmission electron microscopy experiments reveals the formation of pores with graphitic nanoparticles in the walls as well as the formation of magnetite nanoparticles distributed throughout the fibers. Physisorption experiments show that the multifunctional fiber mats exhibit a high surface area (200-400 m2 g-1) and their pore size is dependent on the amount of iron added and graphitization conditions. Finally, we have demonstrated that the fibers are electrically conducting as well as magnetically active.

Panels, Jeanne E.; Lee, Jinwoo; Park, Kang Yeol; Kang, Seung Yeon; Marquez, Manuel; Wiesner, Ulrich; Lak Joo, Yong

2008-11-01

376

Morphological characterization of carbon nanofiber aerosol using tandem mobility and aerodynamic size measurements  

Energy Technology Data Exchange (ETDEWEB)

Characterizing microstructural and transport properties of non-spherical particles, such as carbon nanofibers (CNF), is important for understanding their transport and deposition in human respiratory system and engineered devices such as particle filters. We describe an approach to obtain morphological information of non-spherical particles using a tandem system of differential mobility analyzer (DMA) and an electrical low-pressure impactor (ELPI). Effective density, dynamic shape factors (DSF), particle mass, and fractal dimension-like mass-scaling exponent of nanofibers were derived using the measured mobility and aerodynamic diameters, along with the known material density of CNF. Multiple charging of particles during DMA classification, which tends to bias the measured shape factors and particle mass toward higher values, was accounted for using a correction procedure. Particle mass derived from DMA-ELPI measurements agreed well with the direct mass measurements using an aerosol particle mass analyzer. Effective densities, based on mobility diameters, ranged from 0.32 to 0.67 g cm{sup -3}. The DSF of the CNF ranged from 1.8 to 2.3, indicating highly non-spherical particle morphologies.

Deye, Gregory J.; Kulkarni, Pramod, E-mail: pskulkarni@cdc.gov; Ku, Bon Ki [National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention (United States)

2012-09-15

377

Morphological characterization of carbon nanofiber aerosol using tandem mobility and aerodynamic size measurements  

International Nuclear Information System (INIS)

Characterizing microstructural and transport properties of non-spherical particles, such as carbon nanofibers (CNF), is important for understanding their transport and deposition in human respiratory system and engineered devices such as particle filters. We describe an approach to obtain morphological information of non-spherical particles using a tandem system of differential mobility analyzer (DMA) and an electrical low-pressure impactor (ELPI). Effective density, dynamic shape factors (DSF), particle mass, and fractal dimension-like mass-scaling exponent of nanofibers were derived using the measured mobility and aerodynamic diameters, along with the known material density of CNF. Multiple charging of particles during DMA classification, which tends to bias the measured shape factors and particle mass toward higher values, was accounted for using a correction procedure. Particle mass derived from DMA–ELPI measurements agreed well with the direct mass measurements using an aerosol particle mass analyzer. Effective densities, based on mobility diameters, ranged from 0.32 to 0.67 g cm?3. The DSF of the CNF ranged from 1.8 to 2.3, indicating highly non-spherical particle morphologies.

2012-01-01

378

Magnetic Properties of Fe-alloy Catalyst Nanoparticles for Carbon Nanofiber Synthesis  

Science.gov (United States)

The magnetic properties of Fe-alloy nanoparticles, used as catalysts in vertically-aligned carbon nanofiber (VACNF) growth, has been investigated. First, Fe and Co or Ni were co-sputtered onto Si substrates in order to make a catalyst alloy film. These substrates were then placed in a plasma-enhanced CVD chamber with a substrate temperature of 700^oC and a flowing mixture of acetylene (C2H2) and ammonia (NH3) gas. During the PECVD, the catalyst film breaks into nanoparticles of 50--200 nm and VACNFs are grown. EDX shows that the catalyst nanoparticles nominally have the deposited alloy ratio. In addition, the nanoparticles are still magnetic and have a non-negligible remanence and hysteresis. Their magnetic properties are investigated by SQUID magnetometry in applied field of |H| VACNF system.

Sorge, K. D.; Leventouri, Th.; Finkel, C.; Malkina, O.; Rack, P. D.; Melechko, A. V.; Fowlkes, J. D.; Klein, K. L.; Simpson, M. L.

2006-03-01

379

Magnetic Properties of Fe-Co Catalysts for Carbon Nanofiber Synthesis  

Science.gov (United States)

The magnetic properties of Fe-Co alloys used as catalysts for vertically-aligned carbon nanofiber (VACNF) growth are presented. 10 nm thick layers of FexCo100-x of varying composition (10 <=x <=75) are deposited on Si wafers by a co-sputtering technique. VACNFs are then grown by Plasma-Enhanced Chemical Vapor Deposition (PECVD) in an atmosphere of NH3 and C2H2 at a temperature of ˜570^oC. The catalyst particles on the tips of the VACNFs are 30--80 nm in size after growth. The magnetic properties are investigated at various stages of the fabrication process by SQUID magnetometry in a field range of |H|<=10 kOe and temperatures of T = 5--300 K. The particles are ferromagnetic with moderate coercivity and remanence. The magnetization, however, is lower than expected at each stage.

Malkina, O.; Finkel, C.; Sorge, K. D.; Leventouri, T.; Fowlkes, J. D.; Rack, P. D.; Klein, K. L.; Melechko, A. V.; Simpson, M. L.

2007-03-01

380

Scanned-probe field-emission studies of vertically aligned carbon nanofibers  

Energy Technology Data Exchange (ETDEWEB)

Field emission properties of dense and sparse ''forests'' of randomly placed, vertically aligned carbon nanofibers (VACNFs) were studied using a scanned probe with a small tip diameter of {approx}1 {mu}m. The probe was scanned in directions perpendicular and parallel to the sample plane, which allowed for measuring not only the emission turn-on field at fixed locations but also the emission site density over large surface areas. The results show that dense forests of VACNFs are not good field emitters as they require high extracting (turn-on) fields. This is attributed to the screening of the local electric field by the neighboring VACNFs. In contrast, sparse forests of VACNFs exhibit moderate-to-low turn-on fields as well as high emission site and current densities, and long emission lifetime, which makes them very promising for various field emission applications.

Merkulov, Vladimir I.; Lowndes, Douglas H.; Baylor, Larry R.

2001-02-01

 
 
 
 
381

Design and synthesis of superhydrophobic carbon nanofiber composite coatings for terahertz frequency shielding and attenuation  

Science.gov (United States)

We report design and synthesis of polymer-based large-area superhydrophobic carbon nanofiber (CNF) composite coatings for tunable electromagnetic interference shielding and attenuation in the terahertz (THz) frequency regime. Such coatings with different CNF/polymer weight ratios are characterized by a frequency domain THz spectroscopy system. A maximum THz shielding effectiveness of ~32 dB was measured in the examined frequency range of 570-630 GHz. Coating attenuation level varied with CNF loading. Two-dimensional distributions of power attenuation at 600 GHz showed good spatial uniformity. The present composite coatings, in addition to their self-cleaning property, have high potential for advanced technology high-frequency applications.

Das, Arindam; Megaridis, Constantine M.; Liu, Lei; Wang, Tao; Biswas, Abhijit

2011-04-01

382

Self-sensing of carbon nanofiber concrete columns subjected to reversed cyclic loading  

Science.gov (United States)

Civil infrastructures are generally a country's most expensive investment, and concrete is the most widely used material in the construction of civil infrastructures. During a structure's service life, concrete ages and deteriorates, leading to substantial loss of structural integrity and potentially resulting in catastrophic disasters such as highway bridge collapses. A solution for preventing such occurrences is the use of structural health monitoring (SHM) technology for concrete structures containing carbon nanofibers (CNF). CNF concrete has many structural benefits. CNF restricts the growth of nanocracks in addition to yielding higher strength and ductility. Additionally, test results indicate a relationship between electrical resistance and concrete strain, which can be well utilized for SHM. A series of reinforced concrete (RC) columns were built and tested under a reversed cyclic loading using CNF as a SHM device. The SHM device detected and assessed the level of damage in the RC columns, providing a real-time health monitoring system for the structure's overall integrity.

Howser, R. N.; Dhonde, H. B.; Mo, Y. L.

2011-08-01

383