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2015, 30(4): .

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Preparation of aligned polyimide-based carbon nanofibers by electrospinning

ZHANG Zhen-xing, DU Hong-da, LI Jia, GAN Lin, CHIANG Sum-wai, LI Bao-hua, KANG Fei-yu

2015, 30(4): 289-294.

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Polyimide (PI) is a good carbon precursor owing to its high carbon yield and easy graphitization. PI nanofibers prepared by electrospinning were carbonized and graphitized to prepare aligned carbon nanofibers. Pyromelliticdianhydride and 4,4'-diaminodiphenyl ether were dissolved in N,N-dimethylacetamide at room temperature and stirred for 2 h to obtain a polyamide acid (PAA) solution, which was electrospun into aligned PAA nanofibers at 20 kV and collected by a rolling cylinder 18 cm below the needle with a rolling speed of 2 800 r/min. The PAA nanofibers were first imidized into the PI nanofibers at 350 ℃, then carbonized at 900 ℃ at a heating rate of 5 ℃/min and finally graphitized at 3 000 ℃ to obtain continuous and aligned polyimide-based carbon nanofibers. The PAA solution with a concentration of 20% was the most suitable for electrospinning. SEM characterization shows that the average diameter of the carbon nanofibers is around 100 nm. The carbon nanofibers after graphitization at 3 000 ℃ have a typical graphite structure.

Preparation of nitrogen-enriched porous carbon nanofibers and their electrochemical performance as electrode materials of supercapacitors

MA Chang, SHI Jing-li, LI Ya-juan, SONG Yan, LIU Lang

2015, 30(4): 295-301.

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Nitrogen-enriched porous carbon nanofibers were prepared from a commercial polyimide resin by electrospinning, followed by carbonization. The products were characterized by scanning electron microscopy, nitrogen sorption and X-ray photoelectron spectroscopy. As-prepared carbon nanofibers were directly used as a supercapacitor electrode, and their electrochemical performance was investigated by cyclic voltammetry, charge-discharge tests and electrochemical impedance spectroscopy. The evolution of the porous structure and the surface nitrogen-containing functionality of the carbon nanofibers with carbonization temperature was also investigated. Results showed the carbon nanofibers with developed micropores and enriched with nitrogen were obtained by carbonization of polyimide nanofibers. Both the specific surface area and surface nitrogen content decreased gradually with the carbonization temperature. The carbon nanofibers obtained at 700 ℃ had the highest specific surface area of 447 m²/g, a fiber diameter of 234 nm and a nitrogen content of 4.1%. They also exhibited a specific capacity of 214 F/g or 0.57 F/m².

Mesoporous carbons for supercapacitors obtained by the pyrolysis of block copolymers

WANG Yong, KONG Ling-bin, LI Xiao-ming, RAN Fen, LUO Yong-chun, KANG Long

2015, 30(4): 302-309. doi: 10.1016/S1872-5805(15)60191-3

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Novel mesoporous carbons were prepared by the simple pyrolysis of block-copolymers, polyacrylonitrile-b-polystyrene-b-polyacrylonitrile (PAN-b-PS-b-PAN), in which PAN generates a carbon network and PS is released to form mesopores after pyrolysis. The block-copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and the molecular weight of each polymer block can be designed to tailor the porous structure of the mesoporous carbons. The carbons have high specific surface areas and a well-controlled mesopore size. The best mesoporous carbon has a high specific capacitance of 185 F·g^-1 at 0.625 A·g^-1 with a high power capability and a remarkable cycle stability in 2 mol/L KOH aqueous electrolyte.

A preliminary study of the preparation of porous carbon from oil sludge for water treatment by simple pyrolysis or KOH activation

Shohreh Mohammadi, Nourollah Mirghaffari

2015, 30(4): 310-318. doi: 10.1016/S1872-5805(15)60192-5

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The production and disposal of large amounts of oil sludge are considered a most critical environmental issue in the petroleum industry. The possible conversion of oil sludge produced in a fuel oil storage tank to porous carbons by simple pyrolysis or KOH activation was investigated and the feasibility of their use to treat drinking water and to adsorb were evaluated. The oil sludge contains 80% of carbon and consists of mainly aliphatic compounds. The porous carbon obtained by KOH activation has a BET surface area, total pore volume and micropore surface area of 328.0 m²·g^-1, 0.21 cm³·g^-1 and 289.10 m²·g^-1, respectively, while that produced by pyrolysis has a much lower surface area of 3.6 m²·g^-1. Although Cd, Cu, Zn, Mn, and Fe are enriched in the porous carbons compared with the oil sludge, their leaching in distilled water is low and below the allowed standard limits except for Cr which is close to the limit. The Cd adsorption removal rates for the KOH activated porous carbon and the pyrolysed one are 97.36 and 77.74%, respectively. The former is comparable to three commercial activated carbons under the same conditions. The recovery of the oil sludge through KOH activation to prepare porous adsorbents for waste water treatment can be suggested as an alternative to the conventional disposal methods.

Preparation and electrochemical performance of a hierarchically porous activated carbon aerogel /sulfur cathode for lithium-sulfur batteries

TANG Zhi-wei, XU Fei, LIANG Ye-ru, WU Ding-cai, FU Ruo-wen

2015, 30(4): 319-326.

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An activated carbon aerogel with a hierarchical pore structure was prepared through KOH activation with a KOH/organic aerogel with mass ratio 3:1, followed by carbonization at 900 ℃ for 3 h. The activated carbon aerogel was used as a conductive host of elemental sulfur to prepare a composite by a melt-infiltration method. Nitrogen adsorption, SEM, TEM, XRD and XPS were used to characterize the structure and morphology of the samples before and after the sulfur infiltration. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy were used to evaluate the electrochemical performance of the composite as a cathode in lithium ion batteries. It is found that the composite has a sulfur content of up to 66.2%, a high initial discharge capacity of 1 287 mAh·g^-1 at a current density of 0.2 C and a retained capacity of 643 mAh·g^-1 after 200 cycles, which are much higher than those of a sulfur cathode without the carbon host. The composite also exhibits excellent rate capability.

Microstructure of a carbon produced from a lignin-modified phenol-formaldehyde resin using a nickel nitrate catalyst

FANG Wei, ZHAO Lei, LIANG Feng, CHEN Hui, GONG Shi-shun, LEI Zhong-xing, CHEN Huan

2015, 30(4): 327-334.

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Calcium lignosulfonate-phenol-formaldehyde resin (LPF) was prepared by the polymerization of a mixture of calcium lignosulfonate and phenol with formaldehyde using a NaOH catalyst. Nickel nitrate was used as a catalyst for the carbon formation and was added to the LPF before dehydration and curing. The LPF was carbonized at 800, 1 000 and 1 200 ℃ for 3 h. The dispersion of the catalyst (Ni) in the cured LPF and the microstructure of the carbon were investigated by SEM, HR-TEM, XRD and Raman spectroscopy. Results show that Ni is dispersed homogeneously in the LPF. The carbon is a kind of foam with closed cells. The metallic Ni in the carbon catalyzes the formation of carbon nanotubes that extend from the carbon matrix into the closed cells. The number and length of the carbon nanotubes increase and their crystallinity is improved with increasing carbonization temperature and/or the amount of nickel nitrate added.

Preparation of reinforced carbon foams with different fillers

HUO Yun-xia, HE Zi-guo, ZHAN Liang, LIU Xiang, WANG Yan-li

2015, 30(4): 335-341.

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Carbon foam composites were prepared by a self-foaming method from mesophase pitch using mesocarbon microbeads (MCMBs), PAN based carbon fibers (PAN-CFs) and ZrO₂ nanoparticles were used as the fillers for reinforcement. The effects of the fillers on the foaming behavior and the compressive strength were investigated. Results show that ZrO₂ nanoparticles produce a larger increase in the compressive strength of the carbon foam than do MCMBs and PAN-CFs. The compressive strength of the carbon foam increases from 7.57 to 31.4 MPa when 30% of the ZrO₂ nanoparticles is added to the mesophase pitch. The foam formation obeys the hot-point nucleation mechanism, in which gaseous products released from light hydrocarbons are heated to generate nuclei by localized condensation reaction heat.

Single-wall carbon nanotube hybridized graphene films: self assembly and electrical properties

Prashanta Dhoj Adhikari, Yong-hun Ko, Daesung Jung, Chung-Yun Park

2015, 30(4): 342-348. doi: 10.1016/S1872-5805(15)60193-7

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A SWCNT-G/Si hybrid film was fabricated from graphene (G) film by chemical vapor deposition and single-walled carbon nanotubes (SWCNTs) by an immobilization method, in which a 3-aminopropyltriethoxysilane monolayer was formed on a UV irradiated graphene film by self-assembly, and acid-oxidized SWCNTs were chemisorbed on it. The G/Si, 3-aminopropyltrie-thoxysilane immobilized G/Si and SWCNT-G/Si hybrid films were characterized by SEM, Raman spectroscopy, XPS, and conductivity and electrochemical tests. Results indicate that the immobilization changes the p-type G/Si into n-type by electron donation from a lone electron pair on the amine and the chemisorption reduces the n-type behavior. The SWCNT-G/Si hybrid film has a higher specific capacitance than the G/Si film. This approach could be of great use in the fabrication of supercapacitors, flexible hybrid electrodes and other devices.

Influence of graphene oxide additions on the microstructure and mechanical strength of cement

WANG Qin, WANG Jian, LU Chun-xiang, LIU Bo-wei, ZHANG Kun, LI Chong-zhi

2015, 30(4): 349-356. doi: 10.1016/S1872-5805(15)60194-9

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The effect of adding graphene oxide (GO) to cement on its microstructure and mechanical strength was investigated. A paste of cement (16.5% of water)and GO (0.05%) was prepared together with an identical mixture to which sand (3x the weight of the cement) had been added to form a mortar. The fluidity, viscosity and setting time of the mortar and the morphology, pore structure and compressive and flexural strengths of both the hardened cement paste and mortar, were investigated using SEM, nitrogen adsorption, and fluidity, viscosity, mechanical and hydration tests. The influence of the GO addition on the hydration heat of the cement was also tested. Results show that the addition of GO increases the viscosity, decreases the fluidity and shortens the setting time of the mortar. It also reduces the heat of hydration of the cement. The compressive and flexural strengths of the hardened cement paste at different times are increased by the addition of GO. The flexural strength was greater by 86.1%, 68.5% and 90.5% after 3, 7 and 28 days, respectively, and the corresponding compressive strength increases were 52.4%, 46.5% and 40.4% For the hardened mortar, the corresponding increases are 69.4%, 106.4% and 70.5% for flexural strength and 43.2%, 33% and 24.4% for compressive strength. The addition of GO promotes hydration, decreases pore volume, accelerates crystallite formation and causes the crystallites to align, which increases the tightness of both the hardened cement paste and mortar.

Enhanced photocatalytic activity of a TiO₂/graphene composite by improving the reduction degree of graphene

WANG Jian, WANG Meng, XIONG Ji-ru, LU Chun-hua

2015, 30(4): 357-363. doi: 10.1016/S1872-5805(15)60195-0

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Two kinds of graphene prepared by a high-temperature exfoliation and a solvothermal method were used as supports of a TiO₂ catalyst (P25) from Degussa, Inc to prepare TiO₂/graphene composites. The photocatalytic activities of the composites were evaluated by their degradation of Rhodamine B in aqueous solutions under visible light. Results indicate that the composites prepared by high-temperature exfoliation have much higher photocatalytic activities than those produced by the solvothermal method or the unsupported P25. Both the adsorption capacity of Rhodamine B on the composites and their light absorption characteristics are independent of the kind of graphene used. The activity increases with exfoliation temperature and reduction degree of the graphene regardless of the methods and conditions used, indicating that a high degree of reduction of graphene can inhibit the recombination of electron-hole pairs generated by light irradiation by increasing electron transfer from TiO₂ to the graphene layer.

Effect of carrier gases on densification rate, bulk density and microstructure of carbon/carbon composites

HOU Zhen-hua, HAO Ming-yang, LUO Rui-ying, XIANG Qiao, YANG Wei, SHANG Hai-dong, XU Huai-zhe

2015, 30(4): 364-371. doi: 10.1016/S1872-5805(15)60196-2

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Effect of carrier gases(H₂ and CO₂) on the densification rate, bulk density and microstructure of carbon/carbon composites fabricated by isothermalchemical vapor infiltration from methane (CH₄) was investigated.In the initial 50 h, the densification rate obtained from CH₄-H₂ is obviously higher than that from CH₄-CO₂, while the densification rate from CH₄-H₂ is lower than that from CH₄-CO₂with a further increase of infiltration time. When the carrier gas is switched from H₂ to CO₂, the average bulk density of the compositeincreases from 1.626 to 1.723 g/cm³, the maximum radial density gradient decreases from 0.074 to 0.056 g/cm³, the matrix changes from the pure rough laminar to hybrid rough laminar pyrocarbon with overgrowth cones, and the average degree of graphitization reduces from 62.7% to 50.8%. These significant changes are caused by the fact that CO₂ can effectively reduce the surface deposition rate but does not inhibit the in-pore infiltration, and thatdefects are formed in the deposits by a CO₂ introduction in gas phase and the resulting overgrowth cones deteriorate the texture degree of pyrocarbon.

Influence of a pre-coated pyrocarbon layer on the microstructure and mechanical properties of ZrC-doped C/C composites

LI He-jun, TAO Jun, YAO Dong-jia, FU Qian-gang, LI Ke-zhi

2015, 30(4): 372-377.

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A carbon fiber preform was pre-coated with a carbon layer (PyC) with different thicknesses by chemical vapor infiltration (CVI), then impregnated with a ZrOCl₂ ethanol solution, carbonized at 1 800 ℃ to form ZrC, densified by CVI to a density of 1.75 g/cm³ and graphitized at 2 300 ℃ to obtain ZrC-doped C/C composites. The microstructure and composition of the composites were analyzed by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The mechanical properties were studied by three-point bend tests. The influence of the PyC layer on the microstructure, ZrC distribution and mechanical properties was investigated. Results show that the average flexural strength is 256.85 MPa when the thickness of PyC layer is 1.5-1.7 μm, which is a 67.01% increase compared with the sample without the PyC layer. The cross sections of the composites after flexural failure show a brittle-fracture mode. The ablation resistance of the composites was slightly improved as a result of the PyC layer.

Synthesis and characterization of CNT/thermoplastic polyurethane composites with a high-toughness

JIA Run-ping, DAI Li, TENG Na, HE Xin-yao, HUANG Mao-song

2015, 30(4): 378-384.

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Carbon nanotubes (CNTs) were grafted with acrylic acid-3-(perfluoro-3-methykbutyl)-2-hydroxypropylate by an oxygen plasma-assisted method to increase their dispersion in thermoplastic polyurethane (TPU). The TPU monomers and the grafted CNTs were mixed and polymerized to prepare the CNT/TPU composites. Results show that the grafting procedure has little effect on the structure of the CNTs. The grafted CNTs have a fluorine content of 10.40% and a diameter of about 30 nm, and are uniformly dispersed in the TPU matrix. The tensile strength and elongation at fracture of the composites have maxima of 36.5 MPa and 630%, respectively, at a CNT content of 0.3%, and these are respectively 40.4% and 26.5% higher than those of pure TPU. Moreover, the surface free energy of the composites decreases from 27.3 to 9.9 mN/m with increasing CNT content from 0 to 0.8%.

Innovation with carbon materials——A report on the annual world conference on carbon, Carbon 2015

ZHANG Qiang

2015, 30(4): 385-388.

Abstract(699)

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The annual world conference on carbon, Carbon 2015, was held in Dresden, Germany, and was hosted by the German Carbon Group and German Ceramic Society, during July 12~17, 2015. About 582 attendees from 40 countries participated in the conference, and 540 papers were accepted for discussion, including 4 plenary lectures, 256 oral presentations, and 280 posters involved in 12 topics, namely, activated carbon, biomass derived carbon, carbon black, carbon fiber and composites, granular/nuclear carbon, natural graphite, nanoforms, industrial, conversion process, physical & chemical properties, environmental & medical, and energy storage. Carbon fiber, graphite, carbon black, and carbon alloy were the subjects of the plenary lectures. The innovation of the traditional carbon materials and new nanocarbon, the critical role of carbon in energy, environment, and healthcare application, as well as the new insights on the relationship of structure and properties at the molecular scale were strongly considered in this event. Carbon materials required continuous innovation to meet the rising requirement of sustainable society.

2015 Vol. 30, No. 4

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