2016 Vol. 31, No. 6

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2016, 31(6): .
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Research progress and potential applications for graphene/polymer composites
ZENG You, WANG Han, CHENG Hui-ming
2016, 31(6): 555-567.
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With the rapid development and technological breakthroughs in the synthesis of graphene on a large scale at low cost, the commercial application of graphene materials has been arousing great interest from both academic and industrial fields. We review the latest research progress on graphene/polymer composites, focusing on their mechanical reinforcement, improvement of electrical and thermal conductivity, corrosion resistance, and flame-retardance. The current situation regarding commercial graphene products is summarized, and the main problems and future development of graphene/polymer composites are discussed.
Large-scale synthesis of novel vertically-aligned helical carbon nanotube arrays
ZHANG Ji-cheng, TANG Yong-jian, YI Yong, MA Kang-fu, ZHOU Min-jie, WU Wei-dong, WANG Chao-yang
2016, 31(6): 568-573. doi: 10.1016/S1872-5805(16)60032-X
Abstract(656) PDF(578)
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The large-scale synthesis of vertically-aligned carbon nanotube arrays with different helical pitches and diameters was achieved using the floating catalyst method. Results indicate that they are aligned perpendicular to the substrate surface and have a well-graphitized structure and their growth is accompanied by the production of pentagonal, heptagonal and hexagonal carbon rings. The hexagonal carbon ring is the basic structure unit to form the graphite lattice. When paired pentagon-heptagon atomic rings arrange themselves periodically within the hexagonal carbon network, helical carbon nanotubes are formed. The growth rate of the helical carbon nanotubes is about 4.5mg/cm2·h.
Rheological behavior of fresh cement pastes with a graphene oxide additive
WANG Qin, WANG Jian, LU Chun-xiang, CUI Xin-you, LI Shi-yu, WANG Xi
2016, 31(6): 574-584. doi: 10.1016/S1872-5805(16)60033-1
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The rheological properties and morphology of fresh cement pastes with different contents of graphene oxide (GO) were investigated by a rheometer and a laser confocal scanning microscope, respectively. The rheological data were fitted by the Modified-Bingham (M-B) model and Herschel-Bulkley (H-B) model. A mechanism for the effect of GO on the rheological properties is proposed. Results show that the cement particles are re-agglomerated and new flocculation structures are generated by the addition of GO. The new flocculation structures significantly alter the rheological properties of the pastes. The degree of re-agglomeration and the number of new flocculation structures increase with increasing GO content, leading to a sharp increase in the yield stress, plastic viscosity and the area of the hysteresis loop. GO can effectively reduce the degree of shear-thickening, and increase the critical shear rate and the stability of the pastes.
Microstructure and molten salt impregnation characteristics of a micro-fine grain graphite for use in molten salt reactors
ZHANG Wen-ting, ZHANG Bao-liang, SONG Jin-liang, QI Wei, HE Xiu-jie, LIU Zhan-jun, LIAN Peng-fei, HE Zhou-tong, GAO Li-na, XIA Hui-hao, LIU Xiang-dong, ZHOU Xing-tai, SUN Li-bin, WU Xin-xin
2016, 31(6): 585-593. doi: 10.1016/S1872-5805(16)60034-3
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The microstructure and molten salt impregnation characteristics of a micro-fine grain isotropic graphite ZXF-5Q from Poco Inc. was investigated. The microstructural characteristics of the pores caused by gas evolution, calcination cracks, Mrozowski cracks, and the crystal structure were characterized by optical microscopy, mercury porosimetry, helium pycnometry, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. Results show that the ZXF-5Q has uniformly-distributed pores caused by gas evolution with very small entrance diameters (~0.4 μm), and numerous lenticular Mrozowski cracks. Molten salt impregnation with a molten eutectic fluoride salt at 650℃ and 1, 3 and 5 atm, indicate that ZXF-5Q could not be infiltrated even at 5 atm due to its very small pore entrance diameter. Some scattered global salt particles found inside the ZXF-5Q are possibly formed by condensation of the fluoride salt steam during cooling.
Preparation and electrochemical performance of a polyaniline-carbon microsphere hybrid as a supercapacitor electrode
LIU Wei-feng, YANG Yong-zhen, LIU Xu-guang, XU Bing-she
2016, 31(6): 594-599. doi: 10.1016/S1872-5805(16)60035-5
Abstract(564) PDF(661)
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A polyaniline-carbon microsphere (PANI-CMS) hybrid was prepared by an electrochemical deposition method and used as an electrode for supercapacitors. Field emission scanning electron microscopy and Fourier transform infra-red spectroscopy were used to characterize its morphology and structure. The supercapacitive performance of the hybrid was investigated by cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy and cycling tests. Results indicate that polyaniline is uniformly coated on the outer surfaces of the CMSs by the electrochemical deposition. The hybrid has a specific capacitance of 206 F·g-1 at a current density of 1 A·g-1. It has a higher specific capacitance and more stable cycle performance than PANI, which is ascribed to a synergistic effect between the PANI and the CMSs.
Preparation of carbon microspheres by inverse emulsion polymerization and their electrochemical performance as electrode materials of supercapacitors
FENG Chong, ZHAO Jiang-hong, HAN Bai-xin, SUN Ya-hui, WANG Jian-long, LI Kai-xi
2016, 31(6): 600-608.
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Porous phenolic resin-based carbon microspheres were prepared by inverse emulsion polymerization, followed by carbonization at 800℃ for 1 h and KOH activation at 800℃ for 1 h with a KOH/coke mass ratio of 4. Thermal setting phenolic resin in ethanol was used as one phase and a mixture oil of silicone oil and heat transfer oil as the other phase in the inverse emulsion polymerization. The performance of the porous spheres as electrode materials in supercapacitors was investigated. Results indicate that the size and morphology of the spheres are mainly determined by the mass ratio of silicone oil to heat conduction oil, the mass ratio of alcohol to phenolic resin and the stirring speed. The heat transfer oil with alkyl benzene size chains interacts with phenolic resin by a π-π interaction, which is beneficial for the formation of microspheres. The porous spheres prepared under the optimum conditions have a high specific capacitance of 206 and 134 F/g at current densities of 1 A/g and 20 A/g, respectively in a 6 M KOH electrolyte. The good capacitive and rate performance can be ascribed to the high specific surface area and the pore structures.
Synthesis and electrochemical performance of a spherical flower-like MoS2/graphene anode material for lithium ion batteries
MOU Yan-pu, WANG Cong, ZHAN Liang, LIU Xiang, Wang Yan-li
2016, 31(6): 609-614.
Abstract(527) PDF(731)
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A MoS2/graphene composite was synthesized at 240℃ by a hydrothermal method using graphene oxide, Na2MoO4 and CS(NH2)2 as the raw materials. Results indicate that the spherical flower-like MoS2 structure was self-assembled by thin MoS2 micrometer size layers and dispersed uniformly on the surface of graphene. The MoS2/graphene composite as an anode material retains a capacity of 735.2 mAh/g after 100 cycles under a current density of 100 mA/g and has a good rate performance (490.3 mAh/g at 400 mA/g and 411.9 mAh/g at 800 mA/g). The excellent electrochemical performance of the composite is attributed to its special structure. The thin MoS2 layers shorten the diffusion and transport paths for Li+ ions and electrons. The abundant mesopores are beneficial for ion diffusion and act as a buffer to inhibit volume changes during charge-discharge. Graphene increases the charge-discharge rate of MoS2 effectively owing to its high conductivity and high surface area.
Preparation and electrochemical properties of nanostructured MnO2/exfoliated graphite composites
XU De-fang, SONG Yan, TIAN Xiao-dong, WANG Kai, GUO Quan-gui, LIU Lang
2016, 31(6): 615-620.
Abstract(570) PDF(676)
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Nanostructured MnO2/exfoliated graphite (EG) composites were prepared by an in-situ hydrothermal method, and were characterized by scanning electron microscopy, X-ray diffraction and thermal gravimetric analysis. Their electrochemical performance was investigated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. Results show that the nanostructured MnO2 is inserted between the EG layers, and their conductivity and electrochemical stability are significantly improved. The composites have an improved rate performance compared with the pure MnO2. The capacitance retention rate of the composites and pure MnO2 are 100 and 94.3% after 1000 cycles at a current density of 1 A/g, indicating that the stability of the composites is better than that of pure MnO2.
Microstructures of carbon nanoscrolls characterized by polarized micro-Raman spectroscopy
G. Carotenuto, A. Longo, C. Camerlingo, S. De Nicola, G. P. Pepe
2016, 31(6): 621-627. doi: 10.1016/S1872-5805(16)60036-7
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Carbon nanoscrolls (CNSs) are produced by rolling up the graphite layer in graphene nanoplatelets on a nanofibrous bi-axially oriented polypropylene surface by a shear-friction mechanism. Microstructures of the CNSs are characterized by optical and scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and micro-Raman spectroscopy. Results indicate that the CNSs have a long tubular and fusiform structure with a hollow core surrounded by few graphene layers. The orientation of the graphite lattice with respect to the scroll axis is accurately determined from the split of the vibrational G mode by polarized micro-Raman spectroscopy. Morphological changes produced by the rolling are also described.
Microstructures and ablation properties of Al-Si modified C/C composites produced by the reactive melt infiltration method
CHANG Ya-bin, SUN Wei, XIONG Xiang, PENG Zheng, CHEN Zhao-ke, WANG Ya-lei, XU Yong-long
2016, 31(6): 628-638.
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C/C composites with densities around 1.3 g/cm3 were infiltrated with Al and Si powder mixtures to densities of 1.9-2.2 g/cm3 using reactive melt infiltration to improve their anti-ablation properties. The effects of the Si/Al mass ratio, infiltration temperature, time and atmosphere on the microstructures and ablation properties of the modified composites were investigated by XRD, SEM equipped with EDS, electron-probe micro analysis and oxygen-acetylene ablation tests. Results indicate that homogeneous Al+SiC and Al4SiC4+SiC were respectively formed in the C/C composites after infiltration at 1 500℃ for 2 h and 1 600℃ for 6 h in argon. A gradient of SiC+Al was formed after treatment at 1 600℃ for 6 h under vacuum with the Al content decreasing from the inside to the outside of the composite. The gradient C/C modified by SiC+Al with a Si/Al ratio of 3 has the best ablation resistance of the three, with a mass ablation rate of -1.0×10-3 g/s in an ablation test at 2 500℃ for 60 s.
The mechanism of the fluorescence quenching of L-tryptophan by graphene oxide
GONG Qiao-juan, WANG Yong-dong, YANG Hai-ying, YUAN Mei-ni
2016, 31(6): 639-645.
Abstract(712) PDF(662)
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Graphene oxide (GO) was prepared by the modified Hummers method and used as a fluorescence quenching reagent of L-tryptophan (L-Trp). The structure of GO was characterized by FT-IR and Raman spectroscopy. The binding mechanism of L-Trp on GO and their reaction were investigated by UV spectroscopy and the fluorescence method. Results show that GO has a strong fluorescence quenching ability for L-Trp. The quenching efficiency is 95.6% for L-Trp with a concentration of 2×10-5 mol·L-1 when the GO concentration is 16×10-5 g·mL-1. The binding constants of L-Trp on GO were 2.03×105, 1.83×105 and 1.63×105 mL·g-1 at 25, 30 and 35℃, respectively, as revealed by the Lineweawer-Burk equation, indicating a strong interaction between GO and L-Trp. GO quenches the intrinsic fluorescence of L-Trp by the formation of a complex, and is a static quenching mechanism. The quenching rate constant was 6.65×1012 mL·(g·s)-1 at 25℃ as determined by the Stern-Volmer equation.
Simulation of the fracture behavior of single-walled carbon nanotubes with a single atom vacancy by the finite element method
ZHANG Xu, QI Le-hua, SHU Yang, FU Qian-gang, LI He-jun
2016, 31(6): 646-650.
Abstract(456) PDF(628)
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A finite element model of single-walled carbon nanotubes (SWCNTs) was established using ANSYS parametric design language, by which their fracture behavior was simulated on the platform of ANSYS using the criterion of the fracture of a carbon-carbon bond based on the Morse potential. The influence of a single atomic vacancy on the tensile strength and ultimate strain of SWCNTs was investigated. Results showed that the tensile strength and ultimate strain of perfect SWCNTs are about 120 GPa and 22%, respectively. Values for SWCNTs with the single vacancy are 20-30% and 12-18% less than those of the perfect ones. This is why the experimental tensile strengths of SWCNTs are far less than the theoretical predicted values. In addition, the tensile strengths of SWCNTs are anisotropic at large deformations, which agrees well with the simulation results obtained using molecular mechanics.

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