2015 Vol. 30, No. 5

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2015, 30(5): .
Abstract(339) PDF(444)
Abstract:
An observation of the radial breathing mode in the Raman spectra of CVD-grown multi-wall carbon nanotubes
Valeriy V. Bolotov, Vasiliy E. Kan, Egor V. Knyazev, Peter M. Korusenko, Sergey N. Nesov, Yuriy A. Sten'kin, Viktor A. Sachkov, Irina V. Ponomareva
2015, 30(5): 385-390. doi: 10.1016/S1872-5805(15)60197-4
Abstract(805) PDF(714)
Abstract:
MWCNTs grown by chemical vapor deposition on SiO2/Si substrates were investigated by Raman spectroscopy, transmission electron microscopy (TEM), Auger spectroscopy, and X-ray photoelectron spectroscopy before and after an annealing at 390℃ for 120 min in air or chemical treatment with a HCl solution. The Raman spectroscopy was focused on the low-frequency (250-300 cm-1) band. It is found that the positions and full widths at half maximum of the peaks forming the 250-300 cm-1 Raman band change little with the annealing or chemical treatment. The measured inner diameters of small-diameter CNTs from TEM agree well with those from Raman spectroscopy. These indicate that the low-frequency band originates from the radial breathing oscillations of carbon atoms in the inner walls of small-diameter MWCNTs.
Fabrication and characterization of a multi-walled carbon nanotube-based counter electrode for dye-sensitized solar cells
ZHENG Wei, QI Tao, ZHANG Yong-chao, SHI Hai-ying, TIAN Jun-qing
2015, 30(5): 391-396. doi: 10.1016/S1872-5805(15)60198-6
Abstract(652) PDF(596)
Abstract:
A counter-electrode (CE) for dye-sensitized solar cells (DSSCs) was prepared by coating a slurry containing acid-oxidized multi-wall carbon nanotubes and nano-graphite powder onto a fluorine-doped tin oxide conducting glass substrate. The samples were characterized by SEM, TEM, EDS and IR spectroscopy. The CE performance in the DSSCs with MgO-doped TiO2 as the photoanode was investigated by measurements of current-voltage curves, cyclic voltammetry and electrochemical impedance spectroscopy. Results show that the cell with the CE exhibits the best photoelectric properties of all the carbon-based CEs investigated. The short-circuit current density (Jsc) is 4.67 mA/cm2, the open-circuit voltage (Voc) is 0.53 V and photoelectric conversion efficiency is up to 4.10%, which are comparable with those of the Pt-based CE in DSSCs.
Synthesis of a novel CNT/polyamide composite containing phosphine oxide groups and its flame retardancy and thermal properties
Meisam Shabanian, Mohsen Hajibeygi, Mehdi Roohani
2015, 30(5): 397-403. doi: 10.1016/S1872-5805(15)60199-8
Abstract(557) PDF(692)
Abstract:
A novel composite based on a semi-aromatic polyamide (PA) reinforced by multiwall carbon nanotubes (CNTs) was prepared by a solution mixing method. PA was synthesized through a direct polycondensation between azelaic acid and bis (3-amino phenyl) phenyl phosphine oxide. The effect of the CNT addition on the thermal and flammability properties of the composite were studied by thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry. The temperature at which 5% weight loss occurs is increased by over 70℃ by incorporating CNTs into the PA matrix. CNTs improve the flame retardancy of PA, which is manifested by a decrease of the heat release rate and the total heat release of the composite compared with pure PA.
Preparation of reduced graphene oxide-reinforced epoxy resin composites and their shape memory properties
ZHANG Zhi-yi, ZHANG Huang, SHOU Jin-quan, SUN You-yi, LIU Ya-qing
2015, 30(5): 404-411.
Abstract(657) PDF(847)
Abstract:
Novel shape memory composites based on reduced graphene oxide (rGO)-reinforced epoxy resin (EP) composites were prepared by a solution mixing and solvothermal reduction method. The effect of rGO content on the mechanical and shape memory properties of the rGO/EP composites was investigated. Results showed that the GO uniformly dispersed in the EP matrix was reduced in-situ to rGO by the solvothermal reduction. The composite had the maximum tensile strength and modulus when the mass fraction of rGO was 0.2%. When the mass fraction of rGO was 0.6%, the glass transition temperature (Tg) of the composite was 102℃, 45℃ higher than that of pure EP, and the corresponding composite has a good shape memory property with its deformation fully recovered.
Pyrolysis behavior of graphene/phenolic resin composites
HUANG Gui-rong, LIU Hong-bo, YANG Li, HE Yue-de, XIA Xiao-hong, CHEN Hui
2015, 30(5): 412-418.
Abstract(979) PDF(1072)
Abstract:
A graphene/phenolic(GNS/PF) resin composite was prepared by blending a graphene oxide suspension with an emulsion of phenolic resin in water, followed by reduction with hydrazine and curing at 160℃. AFM, SEM, FT-IR and TG-DTG were performed to reveal the effects of graphene on the morphology, structure, thermal stability and char yield of the composites. Results showed that GNS was uniformly dispersed in the PF matrix. Strong adsorption of GNS on the PF resulted in an ordered arrangement of PF along the GNS plane. The density of crosslinks in the PF matrix was drastically increased after curing and its thermal stability and char yield were remarkably improved. The thermal decomposition peak temperature was increased from 382.7℃ for pure PF to 408℃ for the GNS/PF composites and the char yield of pure PF at 900℃ was increased from 46.2% to 59.4% for that in the composite containing 0.65 wt% graphene oxide.
Preparation and electrochemical performance of expanded graphites as anode materials for a lithium-ion battery
GUO De-chao, ZENG Xie-rong, DENG Fei, ZOU Ji-zhao, SHENG Hong-chao
2015, 30(5): 419-424.
Abstract(834) PDF(634)
Abstract:
Expanded flake graphites (EFGs) with different expansion volumes were prepared by an electrophoresis intercalation method using natural flake graphite as the raw material, concentrated HNO3 and acetic anhydride as intercalates and KMnO4 as oxidant. Results indicate that the density of structural defects, and the surface area and d002 increase after the intercalation. EFG-0.7 obtained with a KMnO4 mass percentage of 0.7 wt% has a capacity of 521 mAh/g when used as the anode of a lithium ion battery, which is significantly higher than the theoretical capacity of natural graphite. EFG-0.7 retains more than 99% of its capacity after 30 cycles at 0.2 C and its capacity stabilizes at 188 mAh/g after 50 cycles at 1.0 C. All the EFGs exhibit excellent performance in high-rate charge-discharge. The resistance of the solid-electrolyte interface film and the charge transfer resistance of the EFGs are smaller than natural flake graphite as revealed by electrochemical impedance spectroscopy. The improved electrochemical performance of the EFGs can be ascribed to their increased surface area and d002, and the larger number of structural defects.
Preparation and oil absorption performance of sponge-like activated carbon/organic composites
MA Wei, XU Sai-nan, CHEN Ke, GUO Yu-qiang, ZHAO Feng-hui, CHEN Yong
2015, 30(5): 425-431.
Abstract(714) PDF(834)
Abstract:
Activated carbons in powder and monolithic form easily form sediments in water, leading to the failure to adsorb an oil film on the water surface. To solve these problems, coconut shell activated carbons were modified to increase their oil-absorption ability and a 3D sponge-like activated carbon/organic composite was then prepared through polymerization of polyvinyl alcohol with formalin in the presence of a foaming agent and the modified activated carbon. The effects of the amounts of water, activated carbon, dilute sulfuric acid (9%) and formaldehyde solution (40%), and reaction temperature on the oil adsorption performance of the composites were investigated. The composites had a hierarchical porous structure and floated on the water surface due to their low density (about 0.197 7 g/cm3). A composite prepared under optimal conditions can adsorb approximately 1.5 times as much oil as the original activated carbon. Its robust and flexible properties make it suitable for recycling during use.
Expanded graphite as a filler for epoxy matrix composites to improve their thermal, mechanical and electrical properties
Subhra Gantayat, Gyanaranjan Prusty, Dibya Ranjan Rout, Sarat K Swain
2015, 30(5): 432-437. doi: 10.1016/S1872-5805(15)60200-1
Abstract(443) PDF(745)
Abstract:
Expanded graphite (EG)-reinforced epoxy composites were prepared by a solution mixing method. The structure and morphology of the EG/epoxy composites were investigated by XRD, FE-SEM and HR-TEM. The EG prepared by acid oxidation and thermal expansion shows good compatibility with the epoxy resin that enters the EG layers to decrease their thickness to 60-70 nm, owing to its abundant oxygen-containing functional groups. With the addition of 9 wt% EG, the thermal decomposition temperature of the composite increases from 340 to 480℃, the electrical conductivity from 10-15 to 10-5 S/cm and the tensile stress is increased by more than 30%. These improvements are attributed to the good dispersion of EG sheets in the epoxy matrix.
Preparation and expansion properties of a graphite intercalation compound containing phosphorus
ZHOU Ming-shan, HUANG Yao, TAO Yong
2015, 30(5): 438-444.
Abstract(660) PDF(867)
Abstract:
A graphite intercalation compound (GIC) was prepared by the chemical oxidation method using natural graphite flakes, HClO4, H3PO4 and CrO3 as raw materials with mass ratios of 1:1:2:0.3. It was characterized by SEM, EDS, XPS, FT-IR, XRD and TGA. The expansion volume of the GIC was 350 mL·g-1 at 300℃ and reached the highest value of 610 mL·g-1 at 800℃. The expansion volume of this GIC was obviously higher than the GICs using H2SO4 as an intercalating agent. The intercalating agents of the GIC were PO43-, ClO4- and Cr2O72-.
Synthesis of Al2O3-silica fibers supported on a V2O5-K2SO4 catalyst used for soot combustion
WU Qiang, ZHAO Li, WU Mei-xia, YAO Wei-feng
2015, 30(5): 445-450.
Abstract(491) PDF(505)
Abstract:
An Al2O3-silica fiber support was prepared by first impregnating a Al(NO3)3 solution on a silica fiber mat on which sacrificial carbon nanofibers had been formed by chemical-vapor deposition, followed by burning in air. The support was further impregnated with a solution containing NH4VO3 and K2SO4 to prepare the Al2O3-silica fiber supported V2O5-K2SO4 catalyst. The catalyst can greatly decrease the combustion temperature of soot by around 200℃, which is promising for decreasing soot emission in diesel-powered vehicles.
The influence of hot-pressing temperature on the structure and properties of an organic modified nanoclay-reinforced carbon/carbon composite
KONG Chui-zhou, GAO Xiao-qing, GUO Quan-gui, SONG Jin-ren, YANG Yu
2015, 30(5): 451-458.
Abstract(438) PDF(551)
Abstract:
A 1D-carbon/carbon composite (C/C) with an organic- modified nanoclay filler was fabricated by hot-pressing and densification at temperatures of 1 000, 1 100, 1 200 and 1 300℃. The organic modified nanoclay was prepared by substituting ions between the layers of an inorganic clay with an organic quaternary ammonium salt. The thermal transformation of the nanoclay following the hot-pressing was investigated by X-ray diffraction and Raman spectroscopy and the effect of the transformation on the bulk density, porosity, thermal conductivity, flexural strength and modulus of the C/C were characterized. The microstructure of the specimens was observed by scanning electron microscopy. Results indicate that the hot-pressing temperature has a significant impact on the structure and properties of the nanoclay-reinforced C/C composite. The C/C composite with the nanoclay filler hot-pressed at 1 200℃ exhibited the best mechanical properties with a flexural strength of 230.1 MPa and modulus of 87.3 GPa. At this temperature, the nanoclay transformed into mullite, cristobalite, disordered nanoclay, ordered carbon and disordered carbon dispersed uniformly in the carbon matrix. This modified the structure of the carbon matrix and tightened the interface between the matrix and the fibers, thus increasing the mechanical properties of the C/C. Carbothermal reduction took place between SiO2 and the carbon matrix at 1 300℃, which damaged the matrix structure and decreased flexural strength and modulus of the composite. However, the presence of, the reaction product (SiC) increased the thermal conductivity.
Pyrolysis of polyimide membranes from the same dianhydride monomer and different diamines to form carbon membranes
LI Lin, QI Wen-bo, WANG Hong, ZHANG Ping-ping, SUN Mei-yue, WANG Tong-hua, LI Jian-xin, CAO Yi-ming
2015, 30(5): 459-465.
Abstract(597) PDF(727)
Abstract:
Polyimide membranes were synthesized by the polymerization of five diamines, p-phenylenediamine (PPD), 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPPD), 4,4'-oxydianiline (ODA), 4,4'-(4,4'-isopropylidenediphenyl-1,1'-diyldioxy)dianiline (BAPP) and 4,4'-(hexafluoroisopropylidene)bis(p-phenyleneoxy) dianiline (BDAF), and the same dianhydride monomer, 1,2,4,5-benzenetetracarboxylic anhydride (PMDA). The chemical structures of the membranes pyrolyzed at different temperatures were investigated by TGA, TG-MS, FT-IR and XPS. Results indicate that there are five stages during pyrolysis: (a) the removal of the solvents, adsorbed oxygen and water, (b) imidization, (c) cross-linking and carbonization, which are accompanied by main chain breaking, (d) deoxygenation and dehydrogenation, (e) aromatization and turbostratic carbon formation. The chemical structure of the precursor is the main factor that causes the great differences in chemical structures during pyrolysis. Imidization in the pyrolysis of the PPD-PMDA and TMPPD-PMDA occurs at higher temperatures than those for ODA-PMDA, BDAF-PMDA and BAPP-PMDA. The order of temperatures for the release of CH4, CO2 and C6H6 during the pyrolysis is ODA-PMDA >BDAF-PMDA >BAPP-PMDA. Elemental F in the BDAF-PMDA disappears after pyrolysis at 700℃. The chemical structures of the polyimides have a great influence on the microstructures of the carbon membranes obtained.
Polydimethylsiloxane-modified super hydrophobic porous graphene filled with palmitic acid as a phase change energy storage material
LIANG Wei-dong, ZHANG Guo-dong, LIU Ye, CHEN Pin-song, ZHU Zhao-qi, LIU Xiao-yu
2015, 30(5): 466-470.
Abstract(672) PDF(1211)
Abstract:
A porous graphene (PG) was synthesized using calcium carbonate micro-spheres as a hard template, graphene oxide prepared by the Hummers' method as graphene precursor, hydrazine hydrate as a reduction agent and N,N-dimethylformamide as a dispersion agent. The as-prepared PG was modified by chemical vapor deposition of polydimethylsiloxane (PDMS) to obtain a super hydrophobic porous material (PG-PDMS) with a water contact angle of 152.3°, which was used as a porous host for palmitic acid. It was found that the pores of the PG-PDMS were completely filled with palmitic acid. The hydrophobic modification significantly increased the palmitic acid content from 62.3 to 80.2%. The incorporation of palmitic acid did not change the crystal structure of the PG and PG-PDMS. The latent heats of melting and crystallization for the palmitic acid-filled PG-PDMS are 167.8 and 170.1 kJ·kg1, respectively. This phase change material has great potential for energy saving applications and solar energy storage.
Template-free preparation of mesoporous carbon from rice husks for use in supercapacitors
WU Ming-bo, LI Ling-yan, LIU Jun, LI Yang, AI Pei-pei, WU Wen-ting, ZHENG Jing-tang
2015, 30(5): 471-475. doi: 10.1016/S1872-5805(15)60201-3
Abstract(679) PDF(736)
Abstract:
Mesoporous carbon (MC) was prepared from rice husk (RH) by a simple and template-free method which combines H3PO4 activation with a pretreatment of the RH with a NaOH solution and pre-oxidation in air. The pretreatment of RH with NaOH removes silicon and damages the crystal structure of the cellulose in the RH, both of which are beneficial to the preparation of MC with a high surface area and high mesoporosity. The MC has a specific surface area of 2 009 m2·g-1 and a mesoporosity of 90.8%. Its specific capacitance can reach 176 F·g-1 at a current density of 50 mA·g-1, and a value of 126 F·g-1 is retained at 1 000 mA·g-1, indicating an excellent rate capability. A MC electrode has a stable specific capacitance of about 150 F/g at 200 mA·g-1 with no apparent capacitance fade after 1 000 cycles, indicating good electrochemical stability.
Microstructural heterogeneity on the cylindrical surface of carbon fibers analyzed by Raman spectroscopy
REN Gui-zhi, CHEN Cong-jie, DENG Li-hui, QUAN Hai-yu, LU Yong-gen, WU Qi-lin
2015, 30(5): 476-480. doi: 10.1016/S1872-5805(15)60202-5
Abstract(468) PDF(772)
Abstract:
A polyacrylonitrile-based carbon fiber monofilament was characterized by a confocal micro Raman spectrometer with the aid of a stage that allowed the axial rotation of the fiber so that the whole surface area could be examined. Results indicate that disorder is localized and aligned along the axial direction of the fiber. La values in defective regions are relatively lower than in others. The changes in the amount of amorphous carbon in different regions are significant.

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