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2018, 33(5): .

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Abstract:

Functional carbon materials in marine science and technology

ZHANG Chen, TANG Quan-jun, TAO Ying, WU Hong-bing, LING Guo-wei, YANG Quan-hong

2018, 33(5): 385-391.

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China's marine strategy has become one of the most important national strategies for our future development. Our knowledge of the oceans is still limited. Owing to the extreme physiochemical environment, advanced functional materials are highly required in marine exploration, transportation, construction, national defense and equipment, et al. Carbon materials, which have been widely used in many important fields such as aerospace, are good candidates for use in marine science and technology. In this review, such use is systematically highlighted, particularly in some emerging fields including the treatment of oil spills, anti-corrosion, anti-fouling, structural materials for offshore facilities and seawater purification. The roles, mechanisms and effects of carbon materials are comprehensively discussed, and some promising applications are also presented for their use in marine energy storage, desalination, coatings and other fields, both from the academic and industrial requirements.

Synthesis of S, N co-doped porous carbons from polybenzoxazine for CO₂ capture

JIN Zu-er, WANG Jian-long, ZHAO Ri-jie, GUAN Tao-tao, ZHANG Dong-dong, LI Kai-xi

2018, 33(5): 392-401. doi: 10.1016/S1872-5805(18)60347-6

Abstract(385)

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S, N co-doped porous carbons were synthesized from polybenzoxazine through solidification, carbonization and KOH activation using 4-cyanophenol, thiourea and formaldehyde as the monomers and a triblock copolymer (Pluronic F127) as a soft template. The samples were characterized by FT-IR, SEM, N₂ adsorption, elemental analysis and XPS. Results indicate that the activated samples had high surface areas of 1 511.6-2 385.1 m² g^-1 with a large number of micropores and abundant sulfur and nitrogen functionalities. The templated samples had apparently lower contents of sulfur, nitrogen and oxygen than the un-templated ones due to the easy escape of volatile sulfur, nitrogen and oxygen compounds during carbonization and KOH activation. CO₂ uptake had contributions from both physical and chemical adsorption and depended on the volume of narrow micropores less than 0.8 nm and the numbers of basic sulfur and nitrogen functional groups. The un-templated sample activated at 600℃ had the highest CO₂ uptakes of 6.96 and 4.55 mmol g^-1 under 1 bar at 0 and 25℃, respectively, and was highly selective for CO₂/N₂ separation and had a high recyclable stability for CO₂ capture.

A two-step method for the preparation of high performance corncob-based activated carbons as supercapacitor electrodes using ammonium chloride as a pore forming additive

WEI Qing-ling, CHEN Zhi-min, WANG Xiao-feng, YANG Xiao-min, WANG Zi-chen

2018, 33(5): 402-408. doi: 10.1016/S1872-5805(18)60348-8

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Activated carbons were prepared from corncobs by an initial hydrothermal treatment using ammonium chloride as a pore forming additive and then by KOH activation. Samples were characterized by SEM, XRD, TG analysis and nitrogen adsorption. The effects of preparation conditions on the iodine number, yield and their electrochemical performance as supercapacitor electrodes were investigated. Results indicate that NH₄Cl is helpful for the formation of activated carbons with a hierarchical pore structure. The best activated carbon prepared has a good rate performance with a capacitance of 175 F·g^-1 at 0.5 A·g^-1 and a capacity retention ratio of 73.0% at 20 A·g^-1, and a good cycling stability with a specific capacity change from 175 to 173 F·g^-1 after a 10 000 charge/discharge test.

Effects of the ultrasound-assisted H₃PO₄ impregnation of sawdust on the properties of activated carbons produced from it

ZHANG Zong-bo, LIU Xiao-yang, LI Da-wei, GAO Tian-tian, LEI Yu-qi, WU Bao-gui, ZHAO Jia-wei, WANG Yan-kui, WEI Ling

2018, 33(5): 409-416. doi: 10.1016/S1872-5805(18)60349-X

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The effects of the ultrasound-assisted H₃PO₄ impregnation of sawdust on the pore structure, morphology, surface functional groups, and adsorption capacities for iodine and methylene blue of activated carbons produced from it were investigated. Results showed that ultrasonic impregnation promoted the mass transfer and uptake of H₃PO₄, which simultaneously increased specific surface area, pore volumes of micropores, mesopores and ultramicropores, and adsorption capacities for iodine and methylene blue. Long ultrasonic impregnation times were unnecessary. The maximum surface area (1 504 m²/g) was achieved at a total impregnation time of 45 min with 5 min ultrasound irradiation. Compared with impregnation without the ultrasound treatment, the ultrasonic-assisted impregnation reduced the impregnation time by 85%.

Preparation of Ni-rice husk carbon catalysts for the hydrodeoxygenation of vanillin

CHEN Zhi-hao, CHAO Wei, FENG Yi, JIN Lu, ZHU Yan-chao, YANG Xiao-min, WANG Zi-chen

2018, 33(5): 417-423.

Abstract(380)

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Ni-rice husk carbon catalysts with Ni loadings from 2 to 8 wt% were prepared by impregnating rice husk activated carbon with Ni(NO₃)₂·6H₂O solutions, followed by carbothermal reduction at temperatures from 500 to 950℃. The valance, particle size and dispersion of nickel nanoparticles on the carbon, the graphitization extent of the carbon, and the pore structure of the catalysts were investigated by XRD, TEM, Raman spectroscopy and nitrogen adsorption. The activity and selectivity of the catalysts for the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol were evaluated. Results indicate that by increasing the carbothermal reduction temperature, the specific surface area and micropore volume decrease, mesopore volume and average pore size increase, nickel particle size increases and the (002) peak of carbon appears and becomes sharp above 900℃. The selectivity of all catalysts investigated is 100%. The catalytic activity is closely related to the Ni content and its dispersion on the carbon. A high Ni loading of over 6 wt% and reduction at temperatures higher than 800℃ lead to aggregation of the nickel nanoparticles, which lowers the catalytic activity.

Preparation and process optimization of randomly oriented C/C composites by a novel method

Thakur Sudesh Kumar Raunija, Rajeev K. Gautam, Sharad Chandra Sharma, Anil Verma

2018, 33(5): 424-433. doi: 10.1016/S1872-5805(18)60350-6

Abstract(358)

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Conventional ways of fabricating C/C composites are unable to achieve wetting in the core of the carbon fiber tow by molten pitch because a single tow has thousands of fibers. Pitch stabilization after infiltration into the carbon fiber preform results in local oozing of the pitch and a non-uniform microstructure due to non-uniform pitch stabilization in the preform. The objective of this research was to devise a method by which complete wetting of fibers in the tow with mesophase pitch is attained by mixing stabilized pitch and chopped and scattered carbon fibers, followed by hot-pressing and carbonization. The influence of process parameters on the carbon yield of the stabilized mesophase pitch is evaluated. The carbon yield divided by processing time and the carbon yield multiplied by the ratio of the apparent density to real density of the C/C composites are used to optimize process parameters. Results show that complete wetting of fibers with mesophase pitch is attained by this method. The carbon yield of the stabilized mesophase pitch decreases with heating rate and the mass ratio of stabilized pitch to carbon fibers, and increases with hot-pressing pressure. At high pressures and high mass ratios, local oozing of the stabilized pitch occurs. The optimum C/C composite was prepared under a hot-pressing pressure of 15 MPa, a heating rate of 0.2℃/min and a mass ratio of stabilized pitch to carbon fibers of 1:1.

Ablation and oxidation resistance properties of C/C composites densified by xylene pyrocarbon using LaCl₃ as a catalyst and resin carbon

DENG Hai-liang, ZHENG Jin-huang, CAO Jun-ning, YAO Dong-mei, CUI Hong, ZHANG Xiao-hu, SU Hong

2018, 33(5): 434-441.

Abstract(355)

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Carbon/carbon composites with densities of 1.72-1.73 g/cm³ were prepared by densification with pyrocarbon produced from xylene using a LaCl₃-catalyzed film boiling chemical vapor infiltration method, followed by resin impregnation, carbonization and graphitization. The ablation and oxidation resistance of the composites were respectively tested by an oxyacetylene torch and air oxidation methods. The phase composition and morphology of the ablated and oxidized surfaces were studied by XRD and SEM, respectively. Results show that the ablation rate and oxidation loss exhibit minima at catalyst contents from 0 to 15 wt%. During the ablation and oxidation, the La₂O₃ film formed from LaC₂ oxidation protects the composites from further oxidation. Catalytically-formed carbon nanofilaments prevent mechanical separation of the carbon fibers from the matrix. As a result, mass ablation and volume ablation rates and the weight loss of the composites due to oxidation are decreased by 7.6%-15.2%, 10.7%-20.0% and 17.7%-38.5%, respectively compared with those formed without the catalyst. The composites produced at catalyst contents of 6 and 10 wt% have higher ablation and oxidation resistance than samples with 0, 3 and 15 wt% contents. Both the thicker isotropic pyrocarbon when the catalyst content is more than 10 wt% and the lower fraction of carbon nanofilaments when the catalyst content is less than 6 wt% are unfavorable for the improvement of the ablation and oxidation resistance properties. The ablation and oxidation resistance of the composites are improved by graphitization from 1 800℃ to 2 250℃.

Effect of nozzle thermal environment on the ablation rate of the throat inserts of solid rocket motors

SU Jun-ming, ZHOU Shao-jian, XUE Ning-juan, XIAO Chun, SUN Jian-tao, LI Rui-zhen, CUI Hong

2018, 33(5): 442-448.

Abstract(817)

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Solid rocket motors using five different C/C composites (radially woven 4D C/C, axially woven 4D C/C, integral felt C/C, needle felt C/C and punctured 3D C/C) and two kinds of graphite (T705 graphite and an anisotropic pyrolytic graphite with a density of 2.18 g/cm³, a porosity of 1% and graphene layers perpendicular to throat surface) as the throat inserts were propelled by hydroxyl terminated polybutadiene or a high energy fuel to test the ablation rates of the throat inserts. The effect of nozzle thermal environment (propellant type and combustion chamber pressure) on the ablation rates of the throat insert materials was investigated under identical conditions. Results show that the ablation rates of the carbon materials are closely related to the concentration of the oxidative gases (H₂O and CO₂) and the chamber pressure. The chamber pressure is of primary importance, and doubling it leads to an increase of ablation rates by 1.8-2.6 times. The ablation rates using the hydroxyl terminated polybutadiene propellant are 51.6%-65.1% higher than those using the high energy propellant because the concentration of oxidizing H₂O in the former is 1.26 times higher than that in the latter. The pyrolytic graphite has the lowest ablation rate followed by the integral felt C/C, needle felt C/C and axially woven 4D C/C. The radially woven 4D C/C has the highest rate, and the punctured 3D C/C and T705 graphite have similar ablation rates. The ablation rates of the five composites and two graphites made in China are similar or superior to the C/C composites and Graphnol graphite made in other countries.

Analysis of the interaction energies between and within graphite particles during mechanical exfoliation

YIN Li, DENG Chuan, DENG Fei, GE Xiao-ling

2018, 33(5): 449-459. doi: 10.1016/S1872-5805(18)60351-8

Abstract(250)

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A method for calculating the interaction energies between and within graphite particles is established by analyzing their thickness and lateral size distribution from AFM and SEM images of 300 particles during mechanical exfoliation at different times. The energy for exfoliating graphite sheets by breaking van der Waals (vdW) bonds, the energy for fracturing graphite sheets by breaking covalent bonds, the potential energies for restacking graphite sheets and the lateral aggregation of graphite particles are analyzed. Results show that the vdW interaction between graphite sheets is the key factor that leads to their restacking. Restacking and lateral aggregation become more active than exfoliation as exfoliation progresses. The energy for exfoliating graphite sheets by breaking vdW bonds is 4 times less than that the potential energy for restacking graphite sheets, and 2 orders of magnitude less than that the energy for fracturing graphite sheets by breaking covalent bonds. The increased number of exfoliated and fractured graphite sheets leads to a considerable increase in the restacking and lateral aggregation by vdW interaction. The coulombic energy is weak and can be ignored. The model has implications for the fabrication of aggregation-free graphite sheets with high aspect ratios.

Preparation and biological properties of a graphene oxide/silk fibroin barrier membrane loaded with simvastatin

ZHAO Bin, WU Feng, BAI Ying-ying, FANG Min, WANG Lu

2018, 33(5): 460-468.

Abstract(325)

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A graphene oxide/silk fibroin (GO/SF) barrier membrane loaded with simvastatin (SIM) was prepared by a freeze-drying method. The biocompatibility of the barrier membrane in vitro and its applicability in guided bone regeneration were investigated. The morphology,structure and the drug release behavior of the membrane were characterized by SEM, XRD and UV-spectroscopy. Laser confocal microscopy and CCK-8 tests were used to evaluate the attachment and proliferation of MC3T3-E1 dermal cells. Defective skulls of Sprague Dawley rats were covered with four membranes (GO/SF/SIM membrane, GO/SF membrane, SF/SIM membrane and SF membrane) and their effectiveness for bone regeneration was evaluated. Results indicated that the GO/SF/SIM membrane had a double-layer (dense surface and porous inside) and stable silk Ⅱ structure. SIM was continuously released from the barrier membrane over 15 days. The GO/SF membrane supported the attachment, growth and proliferation of MC3T3-E1 cells. The GO/SF/SIM exhibited the best bone repairing ability among the four membranes and a better biocompatibility in vitro than the GO/SF. The local application of GO had no damage to important organs (liver, spleen and kidney) of the rats in the short-term observation.

A Boltzmann model for calculating the microscopic ablation morphology of C/C composites

YUAN Jing-chao, ZHU Zi-di, ZHANG Fang-zhou, ZHANG Dan, ZHANG Wei-gang, LI Ai-jun

2018, 33(5): 469-475.

Abstract(355)

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A two-solid-phase cell ablation model involving an oxidative gas phase, a carbon fiber and a carbon matrix is proposed and the Boltzmann equation of non-equilibrium statistical physics was numerically solved to simulate the spatial evolution of each phase at the mesoscopic scale during the diffusion-surface reaction process. The predicted results of the model are in a good agreement with those of the analytical solution. A more complex three-solid-phase cell model that considered a fiber/matrix interphase was numerically simulated. The simulation results show that the roughness of the composites after oxidative ablation mainly depends on the morphology of the interphase between the fiber and the matrix. The hypothesis of a linear distribution of the concentrations of gas species is reasonable only away from the interphase, but not near the interphase. A maximum ablation depth exists due to diffusion limitation near the fiber/matrix interphase, which depends on parameters such as the Sherwood number, the fiber radius and the reaction rate ratio of the fiber to the interphase with the oxidative gas. This interphase tracking algorithm has good stability during numerical calculations.

A diode based on a chemically-doped SWCNT

SONG Chuan-juan, YANG Jun-ru, LIAO Cheng-hao, LIU Xiao-dong, WANG Ying, HE Rong, DONG Xu-sheng, ZHONG Han-qing, LIU Yi-jian, ZHANG Li-ying, CHEN Chang-xin

2018, 33(5): 476-480.

Abstract(302)

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Carbon nanotube p-n junction diodes are expected to be the building block of next generation integrated circuits. A p-i-n junction diode was prepared from a SWCNT with one end p-type doped, the other end n-type doped and the middle segment undoped. The p-type doping was performed using triethyloxonium hexachloroantimonate to form an air stable charge transfer complex (SWCNT⁺-SbCl₆^-) while polyethylene imine was used as an electron donor for the n-type doping. The device showed an excellent performance with a high rectification ratio of 10³ and a low reverse saturation current of 23 pA.

2018 Vol. 33, No. 5

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