新型炭材料

2017, 32(1): .

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Controllable synthesis of sandwich-like graphene-supported structures for energy storage and conversion

WU Wei-ming, ZHANG Chang-song, YANG Shu-bin

2017, 32(1): 1-14. doi: 10.1016/S1872-5805(17)60101-X

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This paper reviews recent progress on the controllable synthesis of sandwich-like graphene-supported structures for energy storage and conversion by harnessing the two-dimensional structure of graphene. These structures could be divided into three major categories:graphene-supported nanoparticles (0D), graphene-supported nanorods, nanowires or nanoribbons (1D), and graphene-supported nanoplates (2D). In these structures, the intrinsic incompatibility between graphene and the functional materials was circumvented by modifying or functionalizing the graphene or graphene oxide. A graphene intermediate provides a fast electron-transfer pathway for energy storage and conversion. It also gives a way to design and fabricate sandwich-like graphene and even graphene-analogue-supported functional materials with well-defined structures for broad applications such as catalysts, sensors, energy storage and conversion.

Oxidation of graphite by different modified Hummers methods

Roksana Muzyka, Monika Kwoka, Lukasz Smedowski, Noel Díez, Grazyna Gryglewicz

2017, 32(1): 15-20. doi: 10.1016/S1872-5805(17)60102-1

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Graphite oxides with different oxygen contents and specifications were prepared from a commercial graphite by different versions of the Hummers method and by oxidation with sodium dichromate. The chemical and structural characteristics of the graphite oxides were studied by elemental analysis(EA), Fourier-transform infrared spectroscopy(FT-IR), X-ray photoelectron spectroscopy(XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Dichromate oxidation provided a low oxygen fixation, mainly in the form of hydroxyl and epoxy groups. A much more efficient oxidation was achieved by using the Hummers method. The use of NaNO₃ and a reaction time of 2 h led to the highest oxygen content in the graphite oxide, over 40 wt%, and oxygen was found to be single- and double-bonded to carbon. SEM and XRD observations showed a high spacing of the graphitic layers under these conditions. These results prove that, even using the same oxidizing method, the chemical structure of graphite oxides can be tailored by changing reaction conditions.

A comparative study of graphene oxide reduction in vapor and liquid phases

CHANG Yun-zhen, HAN Gao-yi, XIAO Yao-ming, ZHOU Hai-han, DONG Jian-hua

2017, 32(1): 21-26. doi: 10.1016/S1872-5805(17)60103-3

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Graphene oxide (GO) was reduced by formaldehyde or formic acid in vapor or liquid phases below 200℃. The influence of the concentrations of reducing agents, reaction temperature and time on the electrical conductivity of the reduced graphene oxide (rGO) was investigated. The rGOs were characterized by XRD, XPS and Raman spectroscopy. Results show that the optimum reaction temperatures are 150 and 175℃ in the vapor phase and the liquid phase, respectively, based on the electrical conductivities of the rGOs. The ratio of the areas of the C 1s peaks related to the C-C and C-O (R_cc/co) from XPS decreases with reaction time from 9 to 24 h in the vapor phase, and increases from 2 to 24 h in the liquid phase, which are in agreement with the electrical conductivities and Raman results. Gasification of carbon atoms in GO sheets may be responsible for the decrease of R_cc/co with prolonged reaction time in the vapor phase.
Supporting information

Organic photovoltaic cells using MWCNTs

Samrat Paul, Bijumani Rajbongshi, Birinchi Bora, Ranjith G Nair, S K Samdarshi

2017, 32(1): 27-34. doi: 10.1016/S1872-5805(17)60104-5

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MWCNTs were synthesized by chemical vapor deposition from Sesamum indicum oil, functionalized, cut into short lengths and used as additives in organic photovoltaic solar cells (OPVs) using poly (3-octylthiophene) (P3OT) as a photoactive molecule and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) as an exciton dissociation agent. Results indicate that the addition of the MWCNTs and the functionalized and cut MWCNTs increases the power conversion efficiency of the OPVs by 22% and 40%, respectively. MWCNTs improve the collection and transportation of holes from the P3OT after exciton dissociation owing to their high hole mobility. The functionalization and cutting of MWCNTs improves their dispersion in P3OT and PCBM, which further increases the power conversion efficiency.

Preparation of a silicalite/ACF composite and its catalytic activity for NO oxidation to NO₂

LI Yu, LI Jun-ping, XUE Ze-hui

2017, 32(1): 35-40. doi: 10.1016/S1872-5805(17)60105-7

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A silicalite/activated carbon fiber (ACF) composite was prepared by a two-step method, in which nitric acid oxidation was used to incorporate hydrophilic groups to improve crystal seed impregnation and a hydrothermal process was used to grow silicalite on the ACFs. The samples were characterized by SEM, XRD and N₂ adsorption. Results showed that the surface of the ACFs was covered with a silicalite layer, and the specific surface area, pore volume and average pore size of the composite were 826 m²·g^-1, 0.42 cm³·g^-1 and 0.64 nm, respectively. The catalytic activity of the ACFs for NO oxidation to NO₂ was higher than that of a composite loaded with 10 wt% silicalite under dry conditions. However, the latter had a much better resistance to vapor and exhibited a more stable catalytic activity than the ACFs under moist conditions.

Preparation of carbon fibers from low-molecular-weight compounds obtained from low-rank coal and biomass by solvent extraction

LI Xian, ZHU Xian-qing, Kenshiro Okuda, ZHANG Zong, Ryuichi Ashida, YAO Hong, Kouichi Miura

2017, 32(1): 41-47. doi: 10.1016/S1872-5805(17)60106-9

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The practical use of carbon fibers is limited by their high price mainly due to the high price of precursors. We have examined a high temperature solvent extraction method to prepare carbon fiber precursors from low-rank coals and biomass, using a lignite from Australia and rice straw. 1-methylnaphthalene at 350℃ was used for the extraction and some of the extract in the solvent was precipated at room temperature. The soluble fractions at room temperature were obtained for use as the precursors by solvent evaporation. They were spun into fibers by a centrifuge spinning system and were then were extracted by cyclohexane to increase the softening point, stabilized by a temperature-programmed thermal treatment in air from 80℃ to 330℃ and carbonized at 1 000℃ for 1 h in N₂ to obtain carbon fibers. The carbon and oxygen contents of the final carbon fibers were 92 and 6.0 wt%, respectively, similar to those of commercial carbon fibers. The fiber diameter was around 4-6 μm. The soluble fractions were found to be promising low-cost precursors for carbon fibers.

Effect of graphene oxide addition on the interlaminar shear property of carbon fiber-reinforced epoxy composites

HAN Xiao, ZHAO Yan, SUN Jian-ming, LI Ye, ZHANG Jin-dong, HAO Yue

2017, 32(1): 48-55. doi: 10.1016/S1872-5805(17)60107-0

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Carbon fiber-reinforced composites were manufactured by hot pressing stacked carbon fiber prepregs using graphene oxide (GO)-modified epoxy resin as the matrix. Tetrahydrofuran was used as the solvent to disperse GO in the epoxy resin. Results showed that a homogeneous GO-modified epoxy system could be obtained, which was stable for approximately 3 h, long enough to produce the prepreg. The incorporation of 0.10 wt% GO into the epoxy resin achieved the largest interlaminar shear strength (ILSS) of 96.14 MPa for laminates, 8.05% higher than that without GO. Also, the glass transition temperature of the composite was increased by approximately 5℃. The improvement of ILSS could be attributed to the toughening of the epoxy resin and an improvement in the interfacial adhesion between carbon fibers and epoxy matrix.

Fabrication and performance of a C/C composite using a needled non-woven carbon fiber felt as a preform

LI Yan, CUI Hong, ZHENG Rui, JI A-lin, ZHOU Shao-jian

2017, 32(1): 56-62.

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A C/C composite was prepared by chemical vapor infiltration followed by repeated pitch impregnation and high pressure carbonization to a final density of 1.9 g/cm³ using a needled non-woven carbon fiber felt preform. Its mechanical properties were compared with a 3D woven C/C composite. Results indicated that the axial tensile strength of the needled C/C composite was 24.5 and 52.88 MPa at room temperature and 2 800℃, respectively, correspondingly 138 and 170% higher than that of the 3D woven C/C composite. The failure mode of the needled composite was pseudoplastic. The axial thermal expansion coefficient of the needled composite at 1 000℃ was only 1.409×10^-6/℃, 64% lower than that of the 3D woven composite. The needled C/C composite exhibits excellent mechanical strength and thermal physical properties which make it potentially useful for a solid rocket motor.

A graphene/PVDF/PP multilayer composite separator for long-life and high power lithium-ion batteries

BU Ai-xiu, TAN Yong, FANG Ruo-pian, LI Feng, PEI Song-feng, REN Wen-cai

2017, 32(1): 63-70.

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The separator is an important part of lithium-ion batteries and its optimization from both material and structural considerations can improve the performance of the battery. We prepared multilayer separators by coating a slurry containing graphene and PVDF in N-methylpyrrolidone on one side of a commercial polypropylene (PP) separator, followed by water treatment at 60℃ for 6 h and vacuum drying at 60℃ for 12 h to manipulate the pore structure of the composite layer. Results indicate that the discharge capacities of batteries using PP and the composite separator were nearly the same at a low rate of 0.5 C. However, the capacity of the former at a high rate of 5 C fades quickly while that of the latter remains almost unchanged after 600 cycles. The composite separators have a high absorption and wettability of the electrolyte, resulting in an improved conductivity.

Effects of a dioctyl phthalate addition to coal tar pitch on the microstructures and electrochemical properties of derived semi-cokes

GUO Liang-cheng, JIN Li-e, ZHONG Cun-gui, WANG Ying, CAO Qing

2017, 32(1): 71-76.

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Coal tar pitch (CTP) and dioctyl phthalate (DOP) were co-carbonized and the effects of the DOP addition on the thermal behavior of CTP, and the microstructures and electrochemical properties of semi-cokes derived from it were investigated by TGA, polarized light microscopy, SEM, XRD and electrochemical impedance spectroscopy (EIS). Results indicate that the weight loss rates of mixtures of CTP and DOP are slower than that of CTP, indicating that polycondensation between CTP and DOP takes place during co-carbonization. The Lc values of the CTP-DOP cokes are larger while their d₀₀₂ values are smaller than those of the CTP coke. The electrical conductivities of the CTP-DOP cokes are better than that of the CTP coke as revealed by EIS.

Modelling and optimization of the pore structure of carbon aerogels using an artificial neural network

YANG Zhen, QIAO Wen-ming, LIANG Xiao-yi

2017, 32(1): 77-85. doi: 10.1016/S1872-5805(17)60108-2

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An intelligent simulation method for predicting and optimizing the pore structure of carbon aerogels is proposed by using an artificial neural network (ANN) algorithm. The ANN model has been optimized based on an improved genetic algorithm from six typical training algorithms. The volumes and diameters of pores in the simulated samples are predicted by the optimized ANN model, which shows correlation coefficients R² of 0.992 and 0.981 and root-mean-square prediction errors (RMSPE) of 0.077 and 0.054 between the predicted and experimental values for the volumes and diameters of pores, respectively. The proposed model is expected to have practical applications in the pore structure control of carbon aerogels.

Carbon foams produced from lignin-phenol-formaldehyde resin for oil/water separation

QU Jiang-ying, HAN Qing, GAO Feng, QIU Jie-shan

2017, 32(1): 86-91. doi: 10.1016/S1872-5805(17)60108-2

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Carbon foams for oil/water separation were synthesized using lignin-phenol-formaldehyde (LPF) resin as the carbon source and polyurethane (PU) foam as the template. Lignin was extracted from sedge grass and was used to replace 25 wt% of the phenol to prepare a LPF resin in an alkaline medium. The carbon foams exhibit unique properties such as open macropores, low bulk density, good water repellency and efficient oil absorption. The absorption capacities of the carbon foams are 12 to 41 times their own weight for a wide range of oils and organic solvents. The foams can be recycled by directly burning the oil within their pores and absorption capacity remains above 83% after 10 absorption test cycles, indicating that the carbon foams are promising oil sorbents with a good recyclability.

Homoepitaxial growth of single crystal diamond by microwave plasma chemical vapor deposition

YAN Lei, MA Zhi-bin, CHEN Lin, FU Qiu-ming, WU Chao, GAO Pan

2017, 32(1): 92-96.

Abstract(855)

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Homoepitaxial growth of single crystal diamond on a diamond substrate prepared by the high pressure high temperature method was carried out by microwave plasma chemical vapor deposition and the effects of methane concentration and substrate temperature on the quality of the as-grown diamond were investigated. The diamond was characterized by scanning electron microscopy and Raman spectroscopy. Results show that step growth and hillock growth are two main homoepitaxial growth modes, where a polycrystalline structure appears to form easily in the latter case. The surface roughness of the diamond is effectively improved by decreasing the methane concentration because it suppresses hillock growth. The homoepitaxial growth rate increases with increasing methane concentration, pressure and substrate temperature. However, the quality of the diamond is decreased by increasing the methane concentration and substrate temperature above 2% and 1 150 ℃, respectively. The content of amorphous carbon increases with growth layer thickness. A diamond with a high crystallinity and low defect concentration is obtained under optimal conditions.

2017 Vol. 32, No. 1

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