2011 Vol. 26, No. 6

Synthesis of carbon nanotubes on silicon nanowires by thermal chemical vapor deposition
Shih-Fong Lee, Yung-Ping Chang, Li-Ying Lee
2011, 26(6): 401-407. doi: 10.1016/S1872-5805(11)60090-5
Abstract(1719) PDF(1450)
Abstract:
Carbon nanotubes (CNTs) were grown on a silicon nanowire substrate with Ni-catalyst layers of different thicknesses using thermal chemical vapor deposition. Scanning electron microscopy was used to observe the surface morphology, and Raman spectroscopy was used to investigate the structural changes in relation to the thicknesses of the catalyst deposited on the substrate. Field-emission characteristics of CNTs were also correlated with the catalyst thicknesses. The catalyst thickness was found to effectively change the field-emission characteristics of the CNTs. Obvious changes in the diameters, population density, and morphology of CNTs were found with differences in catalyst thickness. The field-emission characteristics of CNTs were dependent on their diameter.
Dependence of mechanical characteristics and the fracture and buckling behavior of single-walled carbon nanotubes on their geometry
K. Talukdar, R. Agrawala, A. K. Mitra
2011, 26(6): 408-416. doi: 10.1016/S1872-5805(11)60091-7
Abstract(1895) PDF(1341)
Abstract:
The dependence of the mechanical characteristics of single-walled carbon nanotubes on their length, radius, and chirality is investigated by molecular dynamics simulation. The observed changes in the mechanical properties with radii are compared with the results reported by other authors under both tensile and compressive loading. The tensile properties of zigzag and armchair CNTs are not dependent on their lengths. Slight changes in the mechanical properties with chirality are also reported. However, their compressive properties, primarily their stiffness and critical compressive stress, vary with length for all types of CNTs. The fracture patterns show different modes in each case. Buckling produces kinks, wavy structures, shell-wall buckling, columnar buckling, bending, and twisting.
Preparation of nano Au/C catalysts and their performance as a direct borohydride fuel cell electrode
YANG Zi-qin, ZHAO Peng-cheng, XIE Zi-li
2011, 26(6): 417-421.
Abstract(1860) PDF(1104)
Abstract:
Au/C catalysts were prepared by immobilizing the gold sol having a mean particle size of 5.0 nm with a quite narrow size distribution on carbon nanotubes (CNTs), Vxc-72R or ECP 600JD carbon black. Electrocatalytic activities of different Au/C catalysts with and without acid treatment (first with concentrated HCl then with concentrated HNO3) for the carbon supports for BH-4 oxidation were investigated. The hydrophilicity of all carbon supports and the Brunauer-Emmett-Teller (BET) surface area of CNTs increased, but the BET surface area of Vxc-72R or ECP 600JD decreased after the acid treatment. The Au loading on the carbon supports was closely related to the BET surface area of the supports. Acid treatment of the carbon supports was also an important factor for improving the electrocatalytic activity of the catalysts. Au supported by the acid-treated ECP 600JD exhibited the best electrocatalystic activity for BH-4 oxidation as an anode catalyst for the direct sodium borohydride fuel cell.
The mechanism of expansion during the baking of a hot-pressed graphite green body
ZHANG Can, LU Gui-min, YU Jian-guo
2011, 26(6): 422-427.
Abstract(1749) PDF(1244)
Abstract:
Controlling the volumetric dilation during baking is a key factor in the preparation of excellent graphite and carbon materials. The mechanism of expansion of shaped carbonaceous products at different forming temperatures during baking was investigated. Results showed that the green body hot-pressed at 170℃ can easily form a convex surface, cracks and other deformations during baking, which is in accordance with the gas dilation mechanism because of the poor gas permeability of the green body. The expansion and deformation can be inhibited by lowering the heating rate during baking. The expansion of the green body hot-pressed at 135℃ was caused by both the relaxation of residual stress and the gas dilation mechanism. The gas permeability of green body hot-pressed at 135℃ is superior to that hot-pressed at 170℃ and the dilation of the former mainly occurred at the pitch softening stage, and was also affected by heating rate during baking. The performance of the baked products can be improved by optimizing pitch/carbon ratio, molding temperature and pressure and by lowering the heating rate during baking.
The influence of a magnetic field during carbonization on the microstructure and electrical conductivity of needle cokes
2011, 26(6): 429-434.
Abstract(1679) PDF(1082)
Abstract:
The influence of a magnetic field during thermal polycondensation and carbonization of intermediate coal tar pitch on the electrical conductivity of the resulting needle cokes was explored using a pressure vessel under an external magnetic field. The microstructure of the cokes was analyzed by X-ray diffraction and polarized light microscopy. The electrical conductivity was measured during the coke forming process. Results indicated that aromatic molecules were ordered under the magnetic field during carbonization, leading to an improvement in the microcrystalline structure and an increase in the electrical conductivity of the cokes. Resistance-temperature curves also indicated that the magnetic field can accelerate the polymerization rate and reduce the dependence of the polymerization on temperature, which can be explained by the Zeeman effect.
Formation of SiC nano-micro rods from silica-sol infiltrated bamboo charcoal through carbothermal reduction
LIU Dong, YU Yan, ZHANG Qiu-hui, TIAN Gen-lin, CHENG Hai-tao
2011, 26(6): 435-440.
Abstract(1608) PDF(1046)
Abstract:
Carbonized bamboo was vacuum-infiltrated by a tetraethylorthosilicate solution and then heated at 1450℃ for 5h under an Ar atmosphere to prepare SiC nano-micro rods. Scanning electron microscopy revealed that many nano-micro rods with diameters of 100-500nm and length of around 30μm formed hexagonal layers that stacked to form a bamboo-like morphology. X-ray energy-dispersive spectra and X-ray diffraction patterns showed that the nano-micro rods were mainly silicon carbide. It was further found that nearly all the SiC nano-micro rods were located in the ducts derived from the tubular tissue of the bamboo and the weight gain by the infiltration determined the morphology and yield of the SiC nano-micro rods. This study indicates that bamboo would be an ideal biological template for preparing SiC nano-micro rods on a large scale.
Effect of oxidation time on the complex permittivity
of hollow, porous carbon fibers
XIE Wei, CHEN Zhao-hui, CHENG Hai-feng, CHU Zeng-yong| KUANG Jia-cai
2011, 26(6): 441-445.
Abstract(1666) PDF(1070)
Abstract:
Polyacrylonitrile-based hollow, porous carbon fibers (PAN-HPCFs) as lightweight radar wave absorbers were prepared by the oxidation of PAN hollow fibers in air followed by carbonization in nitrogen. The effects of oxidation time and carbonization temperature on the microstructure, composition, electrical conductivity and complex permittivity of the resulting PAN-HPCFs were investigated. Results indicated that heat-treatment parameters had no obvious effect on the microstructure of the PAN-HPCFs. The carbon content of the PAN-HPCF decreased, the nitrogen content increased and the electrical conductivity decreased with oxidation time. The real and imaginary parts of the complex permittivity (ε' and ε″) decreased with oxidation time. The electrical conductivity and complex permittivity of the PAN-HPCFs can be adjusted by changing the heat-treatment parameters. The values of ε' and ε″ of PAN-PHCFs were 17.20 and 11.90 respectively and the electrical conductivity was 564.50Ω-1 · m-1 when oxidation time was 60 min and carbonization temperature was 800℃.
Synthesis and electrochemical performance of Si/natural graphite/pitch carbon composites as the anode of a lithium ion battery
LI Ming-qi, XIANG Wei-min, REN Zhao-gang, WANG Jing
2011, 26(6): 446-452.
Abstract(1779) PDF(1142)
Abstract:
Composites with a pitch-based carbon (PC) matrix and a mixture of nanoparticle silicon and natural flake graphite (NG) as filler (Si-NG/PC) was prepared by high energy mechanical milling of mixtures of nano-Si, NG and high softening point pitch, followed by pyrolysis at 1000℃ for 2h to convert the pitch into carbon. The influence of the preparation conditions on the electrochemical properties of the composites for use as the anode of a lithium ion battery was investigated. This included milling time, rotation speed and the precursor formulations. XRD and SEM were used to examine the composition and structure of the composites. Results indicated that the optimum milling time is 21h at a rotation speed of 300r/min, and the optimum proportions of nano-Si and pitch carbon in the composites were less than 35wt.% and around 30wt.%, respectively. Under the optimized conditions, the Si-NG/PC composite presented a high specific capacity and a good cycling stability when tested for 50 cycles.
Electrochemical behavior of a carbonaceous mesophase sphere/activated carbon composite
YANG Juan| ZHOU Xiang-yang, LOU Shi-ju
2011, 26(6): 453-458.
Abstract(1551) PDF(1029)
Abstract:
Carbonaceous mesophase spheres and medium coal tar pitch with a weight ratio of 3 were mixed in absolute ethanol solution, to which KOH was added to form a slurry. The slurry was heated to 800℃ to carry out KOH activation. The structure of the resulting material was examined by scanning electron microscopy and X-ray diffraction. Electric double layer capacitors and half-cells were fabricated to investigate its electrochemical performance. The material exhibited good performance in both LiPF6/(ethylene carbonate + dimethyl carbonate) and Et4NBF4/acetonitrile electrolytes with a high reversible capacity of 306.6mAh/g (0.2C) in the half-cell and a capacitance of 25.8F/g in the capacitor. The material showed a favorable rate performance and good cycle stability.
Degradation of methyl orange in artificial wastewater through electrochemical oxidation using exfoliated graphite electrode
KONG Yong, WANG Zhi-liang, WANG Yu, YUAN Jia, CHEN Zhi-dong
2011, 26(6): 459-464. doi: 10.1016/S1872-5805(11)60092-9
Abstract(1986) PDF(1337)
Abstract:
Exfoliated graphite (EG), with good electronic conductivity, was used as an anode material for the electrochemical degradation of methyl orange (MO), an artificial textile wastewater. Through the electrochemical degradation, 98.6% color removal and 58.5% chemical oxygen demand reduction was achieved at a pH of 2.0, a current density of 13mA · cm-2, an electrolyte (NaCl) concentration of 0.1mol · dm-3 and an electrolysis time of 20 min. The degradation is based on chemical adsorption and electro-oxidation. MO molecules are first adsorbed on the EG surface by hydrogen bonds between the —OH functional groups on EG and the MO molecules, which are then degraded by electrochemical oxidation. EG can therefore be regarded as an excellent material for the treatment of textile wastewater.
Preparation of highly-expandable graphite using waste liquid propellants of nitric-27S as one of intercalating agents
CHEN Ya-ping, LUO Rui-ying, LI Shu-yan, ZHANG Jian, LI Hui, WANG Xuan-jun
2011, 26(6): 465-469.
Abstract(1837) PDF(1306)
Abstract:
Highly-expandable graphite was prepared by chemical oxidization using flake graphite as the host material and waste liquid propellants of nitric-27S, potassium permanganate, sulfuric acid and acetic acid as guest compounds. Various factors influencing the volume expansion were studied, such as the amounts of potassium permanganate, nitric-27S and acetic acid. Optimum preparation conditions were obtained using orthogonal experimental design. The preparation of graphite intercalation compounds was confirmed by SEM and XRD. Results showed that the most expandable graphite with a expansion volume of 320mL · g-1 was obtained at 40℃ for 90min using flake graphite, potassium permanganate, nitric-27S, sulfuric acid and acetic acid in the following respective amounts: 1g, 1g, 1.25mL, 1.25mL and 2mL. The amount of potassium permanganate is the most important factor affecting the expansion volume.
The role of surface oxygen-containing functional groups in liquid-phase adsorptive denitrogenation by activated carbon
LI Na, Masoud Almarri, MA Xiao-liang, ZHA Qing-fang
2011, 26(6): 470-478. doi: 10.1016/S1872-5805(11)60093-0
Abstract(1943) PDF(1145)
Abstract:
Twelve activated carbon (AC) samples with different physical and chemical properties were selected to investigate their ability for the adsorptive denitrogenation of liquid hydrocarbons using two model fuels containing typical nitrogen compounds, indole and quinoline in decane. The surface oxygen-containing groups of the ACs were characterized by temperature-programmed desorption with a mass spectrometer to identify and quantify the type and concentration of the oxygen-containing functional groups based on the CO- and CO2-evolution profiles. The adsorption behavior of AC for nitrogen compounds in decane was found to obey the Langmuir adsorption isotherm. The adsorption parameters (the maximum capacity and the adsorption constant) were estimated. With these results, the correlation between the adsorption performance of the AC samples and their physical/chemical properties was evaluated by a multiple linear-regression analysis, which indicated that the physical properties were not the key factors for the removal of the nitrogen compounds in decane. Furthermore, the oxygen-containing groups of ACs, especially the carboxylic acid groups, were found to be mainly responsible for nitrogen adsorption.
A brief overview of the Tenth National Symposium on New Carbon Materials
SONG Yan, LI Bao-hua, CHEN Yu-qin
2011, 26(6): 479-480.
Abstract(1408) PDF(1107)
Abstract:
The Tenth National Symposium on New Carbon Materials was held in Shenzhen, P. R. China during Dec. 10-14, 2011, which was hosted by Institute of Coal Chemistry, Chinese Academy of Sciences and Graduate School at Shenzhen, Tsinghua University. About 200 attendees participated in the conference, and 136 papers were accepted for presentation, including 3 plenary lectures, 13 keynotes talks and 120 orals. The papers were classified into the following seven topics: carbon fibers, carbon-based composites, nano-structured carbons,porous carbons for adsorption and catalysis, intercalated and modified carbons,carbon materials for energy storage, and carbon materials for industrial application. Research and development of carbon-based composites, porous carbons for adsorption and catalysis are quite active, and rapid progress has also been made on the energy storage uses of carbon materials.