新型炭材料

2016, 31(5): .

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The Li-Se battery and its C/Se composite electrode:Opportunities and challenges

LI Jing, ZHANG Chen, TAO Ying, LING Guo-wei, YANG Quan-hong

2016, 31(5): 459-466.

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Selenium is a novel and promising cathode material in lithium ion batteries owing to its high electronic conductivity and a theoretical volumetric capacity comparable to that of S.As a congener of sulfur (S), Se has a similar lithiation mechanism to S in charge/discharge when used as the cathode material of a Li-Se battery. However, similar to the Li-S battery, the Li-Se battery suffers from a shuttle effect that leads to poor cycle performance and low Coulombic efficiency. This review summarizes recent developments, highlights the excellent performance of Li-Se batteries and focuses on improvements to the carbon/Se composite electrode. The main obstacles are also discussed. The use of porous carbons, especially graphene-based materials, for improving the performance of the Se electrode in high performance Li-Se batteries is highlighted and discussed.

Preparation of carbon nanospheres by non-catalytic chemical vapor deposition and their formation mechanism

ZHANG You, YANG Wei, LUO Rui-ying, SHANG Hai-dong

2016, 31(5): 467-474. doi: 10.1016/S1872-5805(16)60025-2

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Carbon spheres with different sizes were prepared by non-catalytic chemical vapor deposition fromgas mixtures of CH₄ and H₂. The influence of the deposition temperature, pressure, and gas ratio on the formation and growth mechanism of the spheres was investigated. The carbon spheres obtained were characterized by XRD, SEM and TEM. Results indicated that carbon nanospheres (50-100 nm) could be obtained at 1 150℃ and 5 kPa from a gas mixture with a CH₄/H₂ volume ratio of 0.25. The deposition temperature had no obvious effect on the sphere size and structure. The sphere size increased with the deposition pressure and the gas ratio. A model was proposed to elucidate their formation and growth.

Porous carbons produced by the pyrolysis of green onion leaves and their capacitive behavior

YU Jing, GAO Li-zhen, LI Xue-lian, WU Chao, GAO Li-li, LI Chang-ming

2016, 31(5): 475-484. doi: 10.1016/S1872-5805(16)60026-4

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Porous carbons were prepared by the simple carbonization of green onion leaves at temperatures from 600 to 800℃ and used as the electrode materials of supercapacitors. SEM, FESEM, EDX, AAS, XRD, TGA and nitrogen adsorption were used to characterize their morphology, pore structure and surface elemental composition. Cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge were carried out to evaluate their specific capacitance, resistance and cycling life. Results showed that the initial mineral elements present in the leaves such as calcium (Ca) and potassium (K) play an activating role during the carbonization. All samples have a bimodal pore distribution of micropores (mainly 0.6-1.2 nm) and mesopores (mainly 3-5 nm). The carbon prepared at 800℃ had the highest surface area of 551.7 m²/g, a specific capacitance of 158.6 F/g at 0.2 A/g and an effective areal capacitance of 28.8 μF/cm². The effective areal capacitance of the carbon prepared at 800℃ is higher than of most porous carbons reported in the literature, which is ascribed to its pore size distribution that favors ion access to its pores.

Oxidative modification of multi-wall carbon nanotubes for the electrochemical detection of dopamine

GUO Cong-xiu, WANG Yun-wei, TONG Xi-li, GUO Xiang-yun

2016, 31(5): 485-491.

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Multi-wall carbon nanotubes (MWCNTs) with different degrees of oxidation were prepared by a wet chemical oxidation method. Their morphology and chemical composition were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The oxidized MWCNTs were coated on glassy carbon for use as electrodes and their electrocatalytic oxidation activities for dopamine, ascorbic acid and uric acid were investigated by cyclic voltammetry and differential pulse voltammetry in order to evaluate their performance for selective dopamine detection. Results indicated that the electrocatalytic oxidation activities are dependent on both the electron transfer resistance of the graphitic layers and the electrostatic attraction between dopamine and carboxyl groups on the MWCNTs. Optimized MWCNTs with an appropriate content of carboxyl groups and nearly complete graphitic layers have a wide linear response current range for dopamine contents from 2 to 100 μM, and can be used for the selective detection of dopamine in the presence of ascorbic acid and uric acid.

Optimizing the preparation conditions of activated carbons from olive cake using KOH activation

Nour T. Abdel-Ghani, Ghadir A. El-Chaghaby, Mohamed H. ElGammal, El-Shaimaa A. Rawash

2016, 31(5): 492-500. doi: 10.1016/S1872-5805(16)60027-6

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Activated carbons were prepared from olive cake waste by KOH activation. A full factorial 2³ experimental design was used to optimize their preparation conditions. The factors and levels included are activation temperature (600 and 900℃), activation time (1 and 3 h) and impregnation ratio (1:2 and 1:4). The surface area of the activated carbons was chosen as a measure of the optimization. The surface and pore properties of the activated carbon obtained at the optimum conditions were characterized by nitrogen adsorption, infrared spectroscopy and scanning electron microscopy. Results indicated that all factors and their interactions are significant (p<0.05). A function was used to correlate the surface area of the activated carbons to their preparation conditions with a correlation coefficient of 99.2%. The activated carbon prepared at the optimum conditions has a BET surface area of 672 m²/g and an average pore size of 2.05 nm with micro and mesopore volumes of 81.36 and 18.37%, respectively.

Removal of Cr(VI) from aqueous solution by pyrolytic charcoals

Türkan Altun, Yakup Kar

2016, 31(5): 501-509. doi: 10.1016/S1872-5805(16)60028-8

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Bio-chars produced by the pyrolysis of walnut shells at 450℃ (BC450) and theco-pyrolysis of walnut shells and 20 wt% tar sand (BCTS20)at the same temperature, were investigated as potential adsorbents for the removal of Cr(VI) ions from aqueous solutions using batch experiments. The BCTS20 has more abundant surface functional groups than BC450. The Cr(VI) removal percentages under optimal conditions were 80.47and 95.69% for BC450 and BCTS20, respectively. Langmuir, Freundlich and D-R models were used to fit the adsorption isotherms and the Langmuir model described the adsorption isotherms best. The adsorption of Cr(VI) was by a chemical process dominated by ion-exchange, electrostatic attraction and chelation. The maximum Langmuir adsorption capacities were 36.55 and 49.76 mg per g of BC450 and BCTS20, respectively. The maximum Langmuir adsorption capacity of BCTS20 is comparable to that of some reported commercial activated carbons.

Microstructure and mechanical properties of carbon/carbon composites densified with pyrocarbon from xylene using LaCl₃ as catalyst

ZHENG Jin-huang, DENG Hai-liang, YIN Zhong-yi, YAO Dong-mei, SU Hong, CUI Hong, ZHANG Xiao-hu, WANG Kun-jie

2016, 31(5): 510-517.

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Carbon/carbon composites with densities of 1.67-1.72 g/cm³ were prepared by film boiling chemical vapor infiltration at 1 000-1 100℃ using xylene and LaCl₃ as carbon source and catalyst, respectively. The influence of the catalyst content on the density, pyrocarbon (PyC) microstructure and mechanical properties of the composites was studied by polarized light microscopy, scanning and transmission electron microscopy and mechanical testing. Results show that the PyC deposition rate is remarkably increased by the presence of the catalyst. The microstructure of the PyC changes from a rough laminar (RL) to isotropic (ISO) with increasing catalyst content from 0 to 15 wt%. The density exhibits a maximum with the catalyst content at 3 wt% while the flexural strength and interlaminar shear strength exhibit maxima of 230.7 and 36.6 MPa, respectively, with the catalyst content at 6 wt%. Nanofilamentous carbon is found in the PyC when the catalyst content is above 3wt%. The catalyst particles are encapsulated by the PyC, resulting in the formation of a hybrid matrix consisting of RL and ISO PyCs. The thickness of the ISO layer increases with the catalyst content. The flexural and interlaminar shear strengths of the composites are increased by 8.1-33.0% and 15.3-55.7%, respectively, compared with the values for samples without the catalyst. The toughness of the composites is increased, but the flexural and interlaminar shear strengths are decreased by high temperature treatment. The maximum degradation of the flexural and interlaminar shear strengths is found at acatalyst content of 15 wt%, and these are 18.6 and 14.4% lower than the values for samples with no catalyst.

Preparation of nano-diamond films on GaN with a Si buffer layer

LIU Jin-long, TIAN Han-mei, CHEN Liang-xian, WEI Jun-jun, HEI Li-fu, LI Cheng-ming

2016, 31(5): 518-524. doi: 10.1016/S1872-5805(16)60029-X

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Gallium nitride (GaN) has been widely used in electronic and optoelectronic devices because of its unique electrical properties. However, its low thermal conductivity and the high thermal boundary resistance at the interface between GaN and substrates such as Si and Al₂O₃ prevent efficient heat dissipation from the heated regions, which limits the further development of GaN-based high power devices. Diamond, with the highest thermal conductivity, has been considered to be one of the most promising heat sink materials. However, it is hard to prepare a diamond film on a GaN substrate because there is a high thermal expansion coefficient difference and also a large lattice mismatch between them. An approach to prepare a nano-diamond film on a GaN substrate by incorporating a Si buffer layer has been proposed. A GaN substrate decomposes significantly from 560 to 680℃ when exposed to ahydrogen plasma for 5 min and no adhesive nano-diamond film can be directly grown on it. This decomposition is significantly suppressed by the presence of a Si buffer layer and a nano-diamond film about 2 μm thick can be deposited on a GaN substrate by microwave chemical vapor deposition using CH₄ as the carbon source. With an optimum Si layer of 10 nm, the adhesive force between the nano-diamond film and the GaN substrate reaches 10N, which is ascribed to the complete conversion of the Si layer to a silicon carbidetransition layer during the deposition.

Changing the chirality of single-wall carbon nanotubes during epitaxial growth: A density functional theory study

SHEN Wei, LI Feng, LIU Chang, YIN Li-chang

2016, 31(5): 525-531. doi: 10.1016/S1872-5805(16)60030-6

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The energetic of the change in the chirality of single-wall carbon nanotubes (SWCNTs)during epitaxial growth from (n, m) to (n±Δ, m Δ)(Δ=1, 2) was investigated by density functional theory calculations. The calculated energies for changing the chirality of different SWCNTs show a nearly linear decrease with decreasing tube diameter. In the case of Δ=1, more energy input is needed for near armchair (nAC) SWCNTs to change their chiralities than those for near zigzag (nZZ) SWCNTs with comparable diameters, due to the larger formation energies of pentagon-heptagon defects (5,7-defects) introduced in the nAC-SWCNTs. These larger formation energies for the nAC-SWCNTs come from the larger angles between the orientation of a 5,7-defect and the tube axis than those for nZZ-SWCNTs. The topological connection oftwo adjacent 5,7-defects, which is indispensable for changing the chirality during growth in the case of Δ=2, is found to be energetically most stable. The energies needed to change chirality in the case of Δ=2 are calculated to be less than twice those in the case of Δ=1 for SWCNTs with comparable diameters. These results may help us understand the change in chirality during the epitaxial growth of SWCNTs and guide the future synthesis of SWCNTs with a single-chirality.

A continuous high-temperature purification reactor for graphite using Freon-12

HU Xiang-long, TANG Xian, ZHOU Yue-bing, DAI Yu, HUANG Qi-zhong

2016, 31(5): 532-538.

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A new continuous high-temperature reactor for graphite purification using Freon-12 up to 2 600℃ was designed with a collection and disposal device for the exhaust such as off-gases, tar and dust. The reactor had an automatic graphite delivery system and amulti-zone temperature control system for feed-in, heating, reaction, cooling and feed-out regions that were controlled within ±5℃. The configuration of heat-insulating materials use da labyrinthine connection for irregularly-positioned multi-layer insulating pieces to isolate air and to prevent heat dissipation. Using this reactor the purity of the graphite can be increased from 88.2 to 99.5% with a production capacity of 90 kg/h.

Catalytic activity of carbon-based solid acids in the esterification synthesis of 1,4-butanediol disuccinate diisooctyl

HUA Ping, YU Hong-mei, LI Jian-hua, FANG Lue-tao, DAI Bao-jiang, ZHANG Hai-bin, ZHU Guo-hua

2016, 31(5): 539-544.

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Carbon-based solid acids were prepared by coking mixtures of p-toluene sulfonic acid and soluble starch with different ratios at different temperatures. The effects of the p-toluene sulfonic acid/soluble starch mass ratio, coking temperature and time on their catalytic activities in the esterification reaction of maleic anhydride with ethylene glycol were investigated. Results indicated that the activity of the acid was the highest when amixture with the mass ratio of 0.5 was coked at 200℃ for 8 h. The activity remained high after the solid acid had been used 5 times.

Preparation of MnO₂/coal-based graphene composites for supercapacitors

ZHANG Ya-ting, LI Jing-kai, LIU Guo-Yang, CAI Jiang-tao, ZHOU An-ning, QIU Jie-shan

2016, 31(5): 545-549.

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The low-cost production of high performance functional materials based on graphene remains a challenging task. One of the options for tackling this problem is to develop new processes based on cheap starting materials such as coal. Coal-based graphene precursors were prepared from purified Taixi anthracite by catalytic graphitization combined with an improved Hummers method. These were mixed with MnO₂ and reduced by a low temperature plasma to make MnO₂/coal-based graphene nanocomposites. The composites were studied by FT-IR, XRD, TEM and SEM. Their electrochemical performance was evaluated using cyclic voltammetry and galvanostatic charge/discharge. Results show that MnO₂ has been even lydeposited on the graphene surface and the specific capacitance of the composite as an electrode in a supercapacitor is much higher than that of coal-based graphene without MnO₂. The highest capacitance is 281.1 F/g, which is 261.2% of the value for coal-based graphene.

The densification mechanism of polyacrylonitrile carbon fibers during carbonization

MA Quan-sheng, GAO Ai-jun, TONG Yuan-jian, ZHANG Zuo-guang

2016, 31(5): 550-554. doi: 10.1016/S1872-5805(16)60031-8

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The densification mechanism of polyacrylonitrile carbon fibers during carbonization from 900 to 1 400℃ was investigated. The density, elemental composition, microstructure and weight loss of the fibers, as well as the gases released during the process were analyzed to reveal the mechanism. Results indicated that the density of the fibers was strongly dependent on the carbonization temperature and reactions involved indifferent temperature regimes. Condensation, pyrolysis and graphitization reactions were dominant at low (<1 050℃), medium (1 050-1 250℃) and high (>1 250℃) temperatures, respectively. The amount of small molecule gas released and the fiber density both increased rapidly with temperature when condensation reactions dominated. The fiber density decreased as a result of nitrogen release when pyrolysis reactions dominated above 1050℃ while the fiber density increased due to the growth and increase in order of the graphene layers during graphitization. The two fiber density maxima found with increasing carbonization temperature were attributed to the different reactions.

2016 Vol. 31, No. 5

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