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Field emission studies of amorphous carbon deposited on copper nanowires grown by cathodic arc plasma deposition

Bohr-Ran Huang, Chun-Shin Yeh, Dau-Chung Wang, J.T.Tan| J. Sung

2009, 24(02): 97-101. doi: 10.1016/S1872-5805(08)60040-2

Abstract(2370)

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Abstract:
The field emission properties of amorphous carbon/copper nanowire (CuNW)/Si composites have been investigated. The CuNWs (50-80nm in diameters) were deposited anodically within the pores of a porous anodic aluminum oxide (AAO) nano-template by electrolysis of a CuSO₄-H₂SO₄solution at room temperature using DC current. Two kinds of structure, amorphous carbon/Si and amorphous carbon/CuNWs/Si , were used. Both of them can emit electrons in vacuum towards an anode at a very low turnon field. Field emission from the amorphous carbon/CuNWs/Si shows a fourfold decrease in turn-on field compared with the amorphous carbon/Si. Results indicated that the electrons were emitted under the effect of an enhanced field because of the geometry of the amorphous carbon sample.

Formation of an icosahedral diamond crystal and its computer simulation

YU Zhi-ming, WEI Qiu-ping, YE Jun, A. Flodrstr-m

2009, 24(02): 102-108.

Abstract(2132)

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Icosahedral diamond crystals (IDCs) were found in chemical vapour deposited diamond by a field emission scanning electron microscope, using. YG13 (cemented tungsten carbide containing 13% of Co) as a substrate. It is found that the nanometer sized IDCs are in the shape of a nearly perfect icosahedron and the micrometer sized IDCs are in the shape of a icosahedron with dimples or grooves. A simulation on atomistic scale is performed by assuming a nucleation-growth model in order to elaborate the mechanism of IDC formation. Results show that the nucleus of IDCs is dodecahedrane, C₂₀H₂₀. For the tetrahedral cubic packing, the dihedral angle of {111} facets of IDCs is 2.87^o larger than that of the normal {111} twin plane. The geometric position of the bilateral atoms on the {111} twin plane of IDCs is mismatched, resulting in a distorted twin plane (DTP) in IDCs. The high energy of DTP induces the dimples or grooves that occurred in IDCs.

Fabrication of carbon nanofibres and bambooshaped carbon nanotubes with open ends from anthracite coal by arc discharge

ZHAO Xue-fei, SUN Ye-xin, HAO Ce, SUN Tian-jun, CUI Ling-we

2009, 24(02): 109-113.

Abstract(1659)

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Abstract:
Bamboolike carbon nanotube (BCNTs) with open ends, and carbon nanofibers (CNFs) were prepared from a coalbased carbon rod by a DC arc discharge. The coalbased carbon rod was made by carbonizing Chinese Bai-Yang-Shu anthracite with coal tar and pitch as binder . The BCNTs and CNFs were characterized by scanning and transmission electron microscopy, energy dispersive spectroscopy, and Xray diffraction. It is found that BCNTs and CNFs grow as a deposit on the anode at a low helium pressure of 0.020MPa with the coalbased carbon rod as anode. Most of the BCNTs have an open end and a diameter of 50nm. CNFs with a diameter of 30-50nm form fluffy balls on the surface of the remaining anode.

Preparation of paraffin/expanded graphite phase change composites for thermal storage

ZHAO Jian-guo, GUO Quan-gui, Gao Xiao-qing, WEI Xing-hai, SHI Jing-li, YA

2009, 24(02): 114-118.

Abstract(2027)

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Abstract:
A paraffin/expanded graphite phase change material for thermal storage was prepared by impregnating a compressed expanded graphite block with paraffin. The thermal properties of the phase change materials were characterized by DSC．Results show that the latent heat of the phase change materials increases with paraffin fraction and the phase change temperature remains constant. The thermal diffusivity of the paraffin/expanded graphite phase change materials decreases with paraffin fraction. Paraffin can be uniformly absorbed in the worm-like pores of the expanded graphite by capillary forces, which can prevent paraffin from permeating outwards.

Synthesis of high purity multiwalled carbon nanotubes over Co-Mo/ MgO catalyst by the catalytic chemical vapor deposition of methane

Wei-Ming Yeoh, Kim-Yang Lee, Siang-Piao Chai, Keat-Teong Lee, Abdul Rahman M

2009, 24(02): 119-123. doi: 10.1016/S1872-5805(08)60041-4

Abstract(1968)

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Abstract:
Nearly uniform diameter multiwalled carbon nanotubes (MWCNTs) were synthesized over a magnesia supported Co-Mo bimetallic catalyst through the catalytic chemical vapor deposition of methane. The bimetallic catalyst with a composition of Co∶Mo∶MgO=5∶20∶75 (mass ratio) was prepared by a sol-gel method. Thermagravimetric analysis shows that MWCNTs were synthesized in high yield. The selectivity of the catalyst for MWCNTs over undesired amorphous carbon was 91.17%. Transmission electron microscopy indicates that the MWCNTs grown on the catalyst have an average diameter of 6.2±0.5nm (mean±standard deviation). Through simple purification by mild acid treatment, the catalyst residue for the purified samples was reduced to 0.72%.

In situ growth of a carbon nanofiber/Si composite and its application in Li-ion storage

LIU Hong-peng, QIAO Wen-ming, ZHAN Liang, LING Li-cheng

2009, 24(02): 124-130. doi: 10.1016/S1872-5805(08)60042-6

Abstract(2145)

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A CNF/Si composite was synthesized in situ by growing carbon nanofibers on the surface of silicon particles through catalytic chemical vapor deposition. Microstructures of the composites were characterized by scanning and transmission electron microscopy, and X-ray diffraction. Electrochemical measurements indicated that the composite showed higher reversible capacity (1042mAh/g) and better cyclability than did a CNF-Si mixture prepared by simple mechanical milling. A structural evolution mechanism is proposed to explain the superior electrochemical performance of the CNF/Si composite electrode in comparison with the CNF-Si mixture. Scanning electron microscopy and ac impedance analysis indicated that the electrochemical performance can be attributed to the good contact of the in situ grown carbon fiber with the silicon particles.

Adsorption and degradation of toluene over TiO₂ supported on bamboo charcoal

ZHOU Jian-bin| DENG Cong-jing | FU Jin-he| ZHANG Qi-sheng

2009, 24(02): 131-135.

Abstract(2734)

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Abstract:
TiO₂ supported on bamboo charcoal (TiO₂/C) was prepared by impregnating the charcoal with a TiO₂ precursor and baking. The resulting material was characterized by SEM and EPR. Adsorption and degradation of toluene over the TiO₂/C under a UV lamp, fluorescent lamp, incandescent lamp and sunlight was determined. Results showed that pore size in bamboo charcoal was centered around 200 nm and TiO₂ was loaded on the rim and surface of the pores. The number of the un-paired electrons increased from 8.7×10¹³ for bamboo charcoal to 8.9 ×10¹⁷ for TiO₂/C. The oxidationreduction ability of TiO₂/C was significantly higher than that of bamboo charcoal. The toluene removal efficiency and the released CO₂ were 94.50% and 122mg/m³ respectively after toluene was exposed to TiO₂/C under UV for 12h. The corresponding figures were 76.80% and 60mg/m³ under sunlight for 12h in TiO₂/C.

Microwave assisted chemical vapor infiltration to prepare carbon/carbon composites

ZOU Ji-zhao| ZENG Xie-rong| XIONG Xin-bo

2009, 24(02): 136-140.

Abstract(1856)

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Microwave assisted chemical vapor infiltration (CVI) was carried out to prepare carbon/carbon composites in a homemade microwave furnace in the temperature range of 1075-1150℃, using carbon fiber felt as the substrate and and methane as the pyrolytic carbon precursor. The felts were heated by absorbing microwave energy. Because the selective heating of the carbon fiber surface by polarization of polar groups on the carbon fiber surface and the catalytic effect of homogeneous gasphase reactions by microwaves, the preform was densified from center to surface to a bulk density 1.70g/cm³ after CVI for 90h. The densification rate was increased to 0.0189g/(cm³ · h). The pyrolytic carbon has a smooth laminar structure along carbon fiber surface. The radial density distribution of carbon investigated by optical microscopy indicates that plugging of the surface pores is avoided in the carbon fiber felts and the microstructure of the materials is uniform, having a medium texture.

Regulation of pore size distribution in coal-based activated carbon

GONG Guo-zhuo, XIE Qiang, ZHENG Yan-feng, YE Shu-feng, CHEN Yun-fa

2009, 24(02): 141-146.

Abstract(1894)

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Abstract:
An approach to regulating the pore size distribution of coal-based activated carbon was proposed and studied by potassiumcatalyzed steam activation. Activated carbons were prepared from coal in the presence of different amounts of KOH in the raw materials, and in the process of which, delicate acid washing was performed to change the amount of Kcontaining compounds left in chars after carbonization and before steam activation. Then, the activated carbons were characterized by nitrogen adsorption, scanning electron microscopy, and XRay energy spectrometry, and their adsorption capacity was determined. Results show that the content of Kcontaining compounds left in the char can be controlled jointly by changing the amount of KOH added to the precursor and subsequent washing with 5% mass fraction acid after carbonization. With increasing amount of KOH, the adsorption capacity of the resulting activated carbon becomes greater. The average pore size of the activated carbons gradually increases from 2.379 to 2.636nm, and the mesoporosity increases from 30.9 to 46.1%. The principles for the regulation of pore size distribution in activated carbon were discussed.

In situ synthesis of graphene oxide and its composites with iron oxide

V. K. Singh, M. K. Patra, M. Manoth, G. S. Gowd, S. R. Vadera, N. Kumar

2009, 24(02): 147-152. doi: 10.1016/S1872-5805(08)60044-X

Abstract(3947)

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A single step method was developed for the preparation of graphene oxide/Fe₂O₃ composites by exfoliation of graphite oxide with an oxygen-rich ferric acetyl acetonate complex. The synthesized materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, atomic force microscopy, and low temperature dc conductivity measurements. After exfoliation, the Fourier transform infrared studies reveal the decomposition of epoxy groups and the simultaneous formation of composites of iron oxide particles within the graphene oxide. Atomic force microscopy reveals the formation of an ~5nm thick graphene oxide stack with layered morphology. The layered morphology of graphene oxide degrades at higher concentrations of iron oxide. The vibrating sample magnetometer studies show ferromagnetic behavior of all composites in the range of 0.13-5.5emu/g at room temperature. The conductivity of these composites is found to be governed by a quasi 1D hopping mechanism.

A comparison of crystallite and pore structures in different polyacrylonitrilebased carbon fibers

WEN Yue-fang, GUO Jian-qiang, GAO Zhong-min, LI Xiang-shan

2009, 24(02): 153-158.

Abstract(1762)

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Abstract:
Homemade polyacrylonitrile-based carbon fiber and the T300B, T700SC and M55JB products of Toray were investigated and compared by WAXD and SAXS. The WAXD results show that, the Lc, d002, Lc/d002 and pore content of the homemade carbon fiber were all between that of T300B and T700SC, and its La value was close to that of T700SC. The SAXS results suggest that the cylindrical pores with a m value (length of semi-major axis) less than 5nm were 99.72% in T700SC, and there were no pores with m value around 30nm, which was better than that of homemade carbon fiber and T300B. There was a large number of pores with m≈7-15nm in M55JB, as a result, the strength of M55JB was less than that of T700SC. The pores in T700SC and M55JB had the ratios of m to pore radius larger than that of the homemade carbon fiber . The pore orientation angle of homemade carbon fiber, and Toray T300 and T700 carbon fibers are all about 21-22. However, the pore orientation angle of M55JB graphite fiber is 8°, less than that of the others. In order to improve the performance of homemade carbon fiber, efforts should be made to increase the degree of graphitization, to reduce the d002 and pore content and to increase degree of densification. The number of larger pores should be reduced and eliminated, and the number of smaller pores should be increased from the spinning of the precursor fiber through stabilization and carbonization.

Synthesis, characterization, and photocatalytic analysis of CNT/TiO₂ composites derived from MWCNTs and titanium sources

CHEN Ming-liang, ZHANG Feng-jun, Won-Chun Oh

2009, 24(02): 159-166. doi: 10.1016/S1872-5805(08)60045-1

Abstract(2601)

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Abstract:
CNT/TiO₂ composites were prepared using multiwalled carbon nanotubes (MWCNTs) as a starting material, and titanium(IV) isopropoxide, titanium(IV) propoxide and titanium(IV) nbutoxide as titanium sources and benzene as a solvent. The composites were characterized by N₂ adsorption, scanning electron microscopy, Xray diffraction, energy dispersive X-ray analysis, and UV-vis absorption spectroscopy. The photoactivity of the prepared materials was evaluated by the conversion of methylene blue (MB, C₁₆H₁₈N₃S · Cl · 3H₂O) in aqueous solution under UV irradiation. It can be found that the MB removal effect of the CNT/TiO₂ composites is not only due to the adsorption of MWCNTs and the photocatalytic degradation of TiO₂ but also to electron transfer between MWCNTs and TiO₂.

In-situ synthesis of Fe-filled carbon nanotubes by a floating CVD method with FeCl₃ as catalyst precursor

ZHU Wei, ZHAO Zong-Bin, QIU Jie-Shan

2009, 24(02): 167-172.

Abstract(2168)

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Abstract:
Large-scale insitu synthesis of Fe-filled carbon nanotubes was achieved by chemical vapor deposition (CVD) with anhydrous FeCl₃ as floating catalyst precursor and ethylene as carbon source. The effects of catalyst and carrier gas were studied. The as-grown products were characterized using SEM, TEM, XRD, Raman, and vibrating sample magnetometer techniques. It has been found that for the floating CVD technique, anhydrous FeCl₃ is a good yet cheap catalyst precursor that is better than the traditional ferrocene catalyst in terms of the purity and filling ratio of the Fe-filled carbon nanotubes produced. The superparamagnetic property of the carbon nanotubes was also demonstrated by vibrating sample magnetometry.

The influence of high temperature exposure to air on the damage to 3D-C/SiC composites

HOU Jun-tao, QIAO Sheng-ru, ZHANG Cheng-yu, ZHANG Yue-bing

2009, 24(02): 173-177. doi: 10.1016/S1872-5805(08)60046-3

Abstract(1549)

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3D-C/SiC composites, exposed in air at 600, 900, and 1300℃ for 0 to 15h, were investigated by three point bend tests at room temperature, SEM, and energy dispersive spectroscopy. The results show that the damage curves, expressed as a relative change of elastic modulus, of the composites for a 15h exposure, could be divided into a sharply increasing stage (stage I) and a steady increasing stage (stage II). Stage I may be caused by a direct oxidation of the carbon fibers and interface carbon layers by the oxygen in air, and stage II may be caused by a diffuse controlled oxidation of the inner part of the composites. The matrix micro-cracks, induced by a difference of coefficients of thermal expansion between matrix and carbon fibers in the cooling process after composite preparation act as oxygen diffuse paths and are where the oxidation takes place. The fact that the damage decreases with temperature for the same exposure time may be caused by the crack shrinking at high temperature, which decreases the oxidizable surface area and inhibits the diffusion of oxygen into the composites.

Preparation of carbon membranes from poly ( urethane imide ) and poly-imide copolymers

LI Zhen, LIU Jin, ZHENG Kou-song

2009, 24(02): 178-182.

Abstract(1888)

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Pyrolysis of poly ( urethane imide ), polyimide and their copolymer was investigated by FTIR spectroscopy and the resultant carbon membrane was characterized by SEM, nitrogen adsorption and a water flux test. Results indicate that the urethane group is decomposed at 200-300℃ while the imide group is decomposed at 500-700℃. The macropores and micropores are formed during the pyrolysis in the thermally labile urethane component and the thermally stable imide component, respectively. The shrinkage of the polymers during pyrolysis decreases with increasing number of urethane groups or decreasing number of imide groups. The pore size of the carbon membrane can be controlled over a wide range by changing the ratio of imide and urethane components. The addition of carbon black can effectively reduce the shrinkage and apparently increase specific surface area and micropore volume.

Preparation of a SWCNT-DNA modified electrode and its electrochemical detection property

XIANG Dong-ya| SU Zhen| ZHAO Zhuo| YANG Liu-quan| YANG Quan-hong

2009, 24(02): 183-186.

Abstract(2443)

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Abstract:
SWCNT-DNA hybrids were prepared by a selfassembly process of SWCNTs and single strand DNA (ssDNA) and all nanotubes were isolated into individual nanotubes in these hybrids. The SWCNT-DNA hybrids attach strongly to a glassy carbon (GC) electrode surface and easily form a uniform film, to produce a SWCNT-DNA modified electrode. Compared with unmodified and bundled SWCNT modified GC electrodes, the SWCNT-DNA modified one shows strong current signals responding to a K₃Fe(CN)₆ solution in the cyclic voltammetric analysis. Moreover, such electrochemical signals are stable, and of high sensitivity and respond to the concentration of K3Fe(CN)6 solution in a linear relationship. In the SWCNT-DNA modified electrode, the wrapping of ssDNA around the SWCNT increases the specific surface area and enhances electron transfer in the Fe(CN)₃-6/ Fe(CN)₄- 6system, indicating that this novel electrode could be a promising candidate for electrochemical detection.

New mesoporous carbons prepared from pitch by simultaneous templating and carbonization

WANG Yan-su| WANG Cheng-yang| CHEN Ming-ming

2009, 24(02): 187-190. doi: 10.1016/S1872-5805(08)60047-5

Abstract(1949)

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Mesoporous carbons with high surface area were successfully prepared from a pitch using MgO as a template. The mixtures of the pitch and the MgO precursors (magnesium acetate and citrate) with different mass ratios in powder form were carbonized at 950℃ in nitrogen. The MgO was dissolved using a 1mol/L hydrochloric acid aqueous solution after carbonization and the porous carbons formed were isolated. The results indicated that most of the pores in the carbons were mesopores, which were generated as a result of the templating action of MgO formed by pyrolysis of the MgO precursors. The BET surface area of the carbons could reach up to 1295m²/g although no activation was performed. The carbon yield was as high as 50% mass fraction when magnesium citrate was used as the MgO precursor.

Introduction to the 15th international symposium on intercalation compounds

ZOU Lin, LU Rui-tao, KANG Fei-yu

2009, 24(02): 191-192.

Abstract(1599)

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This is a brief report on the 15th International Symposium on Intercalation Compounds (ISIC15), which was held in Tsinghua University, Beijing, May 11-15, 2009. More than 210 experts from 19 countries and regions presented 294 contributions in ISIC15. The presentations covered 15 topics, including the mechanism, synthesis and applications of intercalation compounds and related materials. As with the previous ISIC conferences, scientists with a physical background were invited to present their research, which provided new insights into the intercalation phenomena and materials. Moreover, several new layered materials were highlighted in the conference, such as the highly crystalline graphene ribbons, and metalorganic frameworks.

2009 Vol. 24, No. 02

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