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2016, 31(4): .

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Theoretical research progress on the use of graphene in different electrochemical processes

SU Fang-yuan, XIE Li-jing, SUN Guo-hua, KONG Qing-qiang, LI Xiao-ming, LIU Zhuo, CHEN Cheng-meng

2016, 31(4): 363-377.

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Recent progress in the theoretical research on the band structures of perfect, defective and doped graphenes is reviewed. The relationship between the quantum capacitance of graphenes in supercapacitors and their band structures is analyzed. Electronic interactions and the diffusion behavior of Li ionsin different graphenestructures in lithium ion batteries are summarized. The role of different structures in the oxygen reduction reaction in the lithium-air battery is elaborated. This theoretical research lays a solid foundation for new ideas for novel graphene-based energy storage devices.

An asymmetrical activated carbon electrode configuration for increased pore utilization in a membrane-assisted capacitive deionization system

Jiyoung Kim, Dong-Hyun Peck, Byungrok Lee, Seong-Ho Yoon, Doo-Hwan Jung

2016, 31(4): 378-385. doi: 10.1016/S1872-5805(16)60020-3

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A membrane-assisted capacitive deionization (CDI) system was developed for the purification of water containing sodium chloride using activated carbon fibers (ACFs) as capacitor electrode materials. The ACFs have different degrees of activation with different surface areas and pore size distributions. Their desalination performance for sodium or chloride ions was investigated. Results indicate that the salt removal efficiency and surface area-normalized electrosorption capacity for each ion depend on the surface area, pore depth and the match between the pore sizes of the ACFs and the radius of each hydrated ion. A high surface area and shallow pores favor the salt removal efficiency and a high surface area-normalized electrosorption capacity. The ACF with a median pore size of 0.69 nm performs best for sodium ion removal and those with median pore sizes of 1.09 and 1.52 nm are best for chloride ion removal, which could be ascribed to the fact that the radius of a hydrated sodium ion (0.66 nm) is smaller than that of a hydrated chloride ion (0.72 nm). An asymmetric electrode material configuration is needed to optimize both the anion and cation adsorption in the membrane-assisted CDI system.
Supporting Information

Nitrogen-doped porous carbon with a 3D network structure produced from resorcinol-gelatin-formaldehyde co-polymers and its use as an electrode material for supercapacitors

ZHANG Ling, DONG Wei, LI Wen-cui

2016, 31(4): 386-392.

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Nitrogen-doped porous carbons (NPCs) with a three-dimensional network structure were prepared by the direct pyrolysis of resorcinol-gelatin-formaldehyde co-polymers, in which the biomacromolecule, gelatin acted as a nitrogen precursor. Their electrochemical properties as the electrodes of supercapacitors were evaluated with a three-electrode system. Since gelatin can affect the interfacial energy of the reaction liquid, the morphology of the co-polymers was changed into a three-dimensional framework consisting of small spheres. The nitrogen content of the NPCs increases from 1.04 to 2.03 wt% with the mass ratio of gelatin to resorcinol from 0.1 to 0.4. Their specific capacitance increases to 149 F·g^-1 with increasing nitrogen content and levels off when the nitrogen content is above 1.46%. After activation with water, the NPC has a high specific capacitance of 228 F·g^-1,and a specific surface area and nitrogen content of 1 174 m²·g^-1 and 1.51 wt%, respectively.

Electrospun N-doped porous carbon nanofiber webs as anodes for lithium-ion batteries

NAN Ding, HUANG Zheng-hong, KANG Fei-yu, SHEN Wan-ci

2016, 31(4): 393-398.

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Nitrogen-doped porous carbon nanofiber webs (NPCNFs) were prepared from mixtures of polyacrylonitrile and melamine byelectrospinning, followed by oxidative stabilization, carbonization and steam activation. The NPCNFs are free-standing,exhibit an interconnected non-woven nanofibrous morphology and a well-developed microporous structure, and can be used directly as anodes for lithium ion batteries without adding binder or conductive filler. The NPCNF from the mixture with a melamine/polyacrylonitrile mass ratio of 1:3 has a high specific capacity of 856 mAh·g^-1 and a satisfactory rate capability. These intriguing characteristics make the NPCNFs promising anode candidates for high-performance lithium ion batteries.

Preparation of MWCNTs-TiO₂ photocatalysts in thin liquid films under continuous flow conditions and their photocatalytic activities for quinoline degradation

CUI Jia-li, GAO Yong-hua, GAO Li-zhen

2016, 31(4): 399-406.

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MWCNTs-TiO₂ photocatalysts were formed within a very thin liquid film generated on a continuous flow spinning disc surface, in which two jets located in the center of the disc were fed with a suspension of HNO₃-purified MWCNTs (0.5 g) in a mixture of tetra-n-butyl titanate (40 mL), ethanol (100 mL) and acetic acid (10 mL), and a solution of ethanol (30 mL), acetic acid (20 mL) and water (8 mL). The collected products were gelled at room temperature for 24 h, dried at 80℃ for 4 h and calcined at 350, 400 and 450℃ for 4 h. The samples were characterized by XRD, FT-IR, SEM, TEM and UV-vis DRS. The photocatalytic properties were evaluated by the degradation of quinoline under visible light irradiation. Results showed that TiO₂ nanoparticles of the photocatalyst were smaller (5-10 nm) than when there were no MWCNTs present (10-15 nm), and were well distributed between the MWCNTs. MWCNTs promoted the visible light absorption of the samples. The photocatalyst calcined at 450℃ showed the strongest visible light absorption and best catalytic activity, andproduced a quinoline degradation of 86.6% after 180 min.

Hydrogen halide-promoted construction of 3D graphene aerogels

ZHANG Xu, ZHOU Ying, WANG Chun-lei, QIU Jie-shan

2016, 31(4): 407-414.

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Three-dimensional (3D) graphene aerogels were fabricated from graphene oxide using HBr, HCl and HI as promoters. The structures and properties of the aerogels were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and thermal gravimetric analysis. It was found that 3D graphene aerogels can be made in the presence of HI. Their formation is promoted by the synergistic effects of the acidic H⁺ and the reductive I^-. The electrical conductivity and thermal stability of the aerogels were significantly improved compared with those of graphene oxide. When the aerogels were used as supercapacitor electrodes, excellent specific capacitance and rate capability were achieved.

The use of carbon nanotube yarn as a filter medium to treat nitroaromatic-contaminated water

Sushil R. Kanel, Heath Misak, Dhriti Nepal, Shankar Mall, Seth W. Brittle, Ioana Sizemore, David M. Kempisty, Mark N. Goltz

2016, 31(4): 415-423. doi: 10.1016/S1872-5805(16)60021-5

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Carbon nanotube yarn (CNTY) is a promising material for the removal of organic contaminants from aqueous waste streams owing to its extraordinary mechanical strength, chemical stability, thermal stability and high surface area. CNTY was used to treat water contaminated with a model nitroaromatic compound, 2,4-dinitrotoluene (DNT). The isotherms and kinetics of DNT adsorption onto CNTY were investigated. The adsorption capacities of DNT were compared with the literature values of alternative sorbents. SEM-EDX, HR-TEM, Raman spectroscopy and XPS were used to characterize the size, surface morphology and surface chemistry of the CNTY before and after DNT adsorption. Results indicate that adsorption isotherm of DNT onto CNTY could be fitted by the Freundlich isotherm with a Freundlich constant, K_F, of 55.0 mg/g (L/mg)^1/n and a Freundlich exponent, 1/n, of 0.737. Adsorption kinetics can be formulated by the pseudo-second order kinetic model. This study demonstrates the ability of CNTY to remove organic contaminants from water.

Modification of asphalt by dispersing waste polyethylene and carbon fibers in it

ZHANG Mao-rong, FANG Chang-qing, ZHOU Shi-sheng, CHENG You-liang, HU Jing-bo

2016, 31(4): 424-430. doi: 10.1016/S1872-5805(16)60022-7

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Recycled waste packaging polyethylene (WPE) and chopped polyacrylonitrile-based carbon fibers (PAN-CFs) were dispersed in molten asphalt at 170℃ with a shearing machine at 3 800 r/min for 60 min to modify its properties to meet the demands of motorway paving. WPE and PAN-CFs were mixed by three methods before the dispersion:(a) simple blending, (b) first dissolving WPE in xylene, then mixing and evaporating and (c) blending and extrusion to rods of 1mm diameterat 170℃ which were fed directly into the hot asphalt. The PAN-CF content was varied in the range 0 to 0.12 wt% while the WPE content was constant(4 wt%). Results indicate that WPE and PAN-CFs are dispersed in asphalt to form a network structure by the xylene-assisted mixing or blending-extrusion methods. The softening points, penetration degree and ductility are improved with increasing content of PAN-CFs up to 0.1 wt%. Aggregation of the two modifiers occurs beyond 0.12 wt% of PAN-CFs, which degrades the properties of the modified asphalts. A fiber length of 5 mm is optimum for their best dispersion in the asphalt. Segregation of the modifiers from the modified asphalts can be prevented by increasing the content of PAN-CFs. The blending-extrusion method is best to form a fine network structure, which achieves a best performance. A model is proposed to explain the observed dispersion behavior in asphalt.

Electromagnetic and mechanical properties of La(NO₃)₃-doped multi-walled carbon nanotube/epoxy resin composites

HOU Cui-ling, SONG Shi-hua, WEI Jian-ning, LI Tie-hu

2016, 31(4): 431-436.

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La(NO₃)₃-doped MWCNT/epoxy resin (EP) composites were prepared by a solution bending method.Acid-oxidized MWCNTs were first used to adsorb La(NO₃)₃ and were then mixed with EP as matrix and ethylenediamine as a curing agent. The microstructure and morphology of the MWCNTs and MWCNTs-La(NO₃)₃ were investigated by TEM and XRD. The electromagnetic wave absorption properties, curing behavior and mechanical properties of MWCNT/EP and MWCNT-La(NO₃)₃/EP composites were measured by a vector network analyzer, differential scanning calorimetry, an electronic universal tester and a pendulum impact tester. Results indicate that the complex permittivity and permeability of the MWCNTs doped with La(NO₃)₃ are much improved, leading to a substantial increase in the dielectric and magnetic loss of the La(NO₃)₃-doped MWCNT/EP composite in the frequency range from 8.2 to 12.4 GHz and therefore an increase of its electromagnetic wave absorption. The curing rate of EP is accelerated by both the MWCNTs and La(NO₃)₃. The mechanical properties of the MWCNT/EP composite are degraded only slightly by the La(NO₃)₃ doping.

Bend properties and failure mechanism of a carbon/carbon composite with a 3D needle-punched preform at room and high temperatures

LI Dian-sen, YAO Qian-qian, JIANG Nan, JIANG Lei

2016, 31(4): 437-444. doi: 10.1016/S1872-5805(16)60023-9

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A 3D needle-punched C/C composite with a high density was fabricated and its bend properties were investigated at room and high temperatures. Macro-fracture and SEM micrographs were examined to understand the deformation and failure mechanism. Results show that the load-deflection curves below 400℃ exhibit a linear elastic and brittle fracture failure, while the curves at temperatures above 500℃ show an obvious tough and plastic failure. The bend strength and modulus decrease significantly with increasing temperature due to severe carbon oxidation. Below 500℃, the main damage to the composite is in the form of matrix cracking, 90° fiber/matrix debonding, local twisting and fracture of the 0° fibers. Above 500℃, the oxidation of the composite is significant and the interfacial adhesion between fibers and matrix is decreased significantly.

Effects of heating rate on the foaming behavior and pore structure of carbon foams derived from phenol-formaldehyde resin

GONG Qing, ZHAN Liang, ZHANG Yong-zheng, WANG Yan-li

2016, 31(4): 445-450.

Abstract(670)

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The effect of heating rate on the foaming behavior of phenol-formaldehyde resin and the pore structure and compressive strength of the carbon foams produced were investigated. Results indicate that the viscosity of the resin changes little with temperature between 135 and 225℃, but increases abruptly above 225℃. The foams are formed between 200 and 300℃ by gas released during pyrolysis and the foaming behavior follows the hot-spot nucleation mechanism. By increasing the heating rate from 0.5 to 3℃/min the average pore size decreases from 304 to 267 μm, and the density and compressive strength increase from 0.34 to 0.51 g/cm³ and 6.1 to 12.5 MPa, respectively. The heating rate affects the expansion velocity of the bubbles formed, and the average size and homogeneity of the pores in the foams.

Influence of ZrC on the microstructure of its surrounding resin-based carbon at high temperature

ZHANG Zhong-wei, MEI Min, LI Liang, NAN Ce-wen, WANG Jun-shan, XU Zheng-hui

2016, 31(4): 451-454. doi: 10.1016/S1872-5805(16)60024-0

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The microstructures of a refractory ZrC particle and its surrounding resin-based carbon treated above 2500℃ were investigated by SEM, TEM, HR-TEM and selected area electron diffraction. Results show that the ZrC particle is enclosed by a transition carbon layer that has a d₀₀₂ of 0.3375 nm, close to that of ideal graphite, indicating the formation of a well graphitized structure. The carbon far away from the ZrC particle remains isotropic and amorphous. These results are verified by selected area electron diffraction, and can be attributed to catalytic graphitization and stress-induced graphitization.

De-ashing of naphthalene-based mesophase pitch synthesized by the AlCl₃-catalyzed method

LIU Ben, ZHAO Hong-chao, LI Xiang-fen, ZHANG Xing-hua, GUO Quan-gui

2016, 31(4): 455-458.

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Naphthalene asphalt was synthesized at 160-240℃ using naphthalene as a raw material and AlCl₃ as a catalyst, and its de-ashing by ultrasonic treatment, stirring, heating, and acid and/or alkali washing was investigated. Results indicated that naphthalene-based mesophase asphalt with an ash content less than 500 ppm could be prepared by twice washing in an alkali followed by acid washing for 4 times and finally water washing for 10 times at 80-90℃ under ultrasonic or stirring conditions.

2016 Vol. 31, No. 4

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