新型炭材料

2014, 29(2)

Abstract(697)

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Abstract:

Fabrication of three-dimensional MoS₂-graphene hybrid monoliths and their catalytic performance for hydrodesulfurization

WANG Xu-Zhen-1, 2, 3, 　Liu-　Ning-1, 　Hu-　Han-2, 　Wang-Xin-Beng-1, 　Qiu-Ge-Shan-2

2014, 29(2): 81-88.

Abstract(1203)

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Abstract:
A simple process to synthesize three-dimensional molybdenum disulfide-graphene monolithic catalysts (3D-MoS₂-G) was developed. 3D-MoS₂-G hybrid monoliths were fabricated by a combined hydrothermal self-assembly and freeze-drying treatment, in which ammonium tetrathiomolybdate and graphite oxide were used as starting materials. The structure and morphology of the samples were characterized by X-ray diffraction, Fourier transform infrared spectrometry, Raman spectrometry, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption. The catalytic performance of the hybrid monoliths was investigated by evaluating the activity for the hydrodesulfurization (HDS) of carbonyl sulfide (COS). In addition, the influence of microwave irradiation on the catalytic property of the 3D-MoS₂-G monoliths was also investigated. It is demonstrated that after microwave irradiation the 3D-MoS₂-G monoliths show an excellent activity for COS hydrogenation compared with the traditional MoS₂/γ-Al₂O₃ catalyst prepared by impregnation-sulfidation. The 3D-MoS₂-G-160M monolith hydrothermally synthesized at 160℃ exhibits the highest COS conversion of 100% at a relatively low temperature (260℃) for the HDS reaction. The superior performance of the 3D-MoS₂-G-160M catalyst can be ascribed to the unique hybridized structure of the MoS₂ nanoparticles uniformly dispersed on graphene sheets in the monolith.

Preparation of N-doped activated carbons for electric double-layer capacitors from waste fiberboard by K₂CO₃activation

ZHANG Ming-Xiang, 　Jin-Xiao-Juan, 　ZHAO Qiang

2014, 29(2): 89-95. doi: 10.1016/S1872-5805(14)60128-1

Abstract(861)

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N-doped activated carbons for electric double-layer capacitors were prepared from waste medium density fiberboard using K₂CO₃ activation. The effects of carbonization temperature, activation temperature, activation time and K₂CO₃/coke mass ratios on surface chemical compositions, pore structure and electrochemical performance of the resulting activated carbons were investigated. Results indicated that the activated carbons had nitrogen contents from 0.93-2.86%, Brunauer-Emmett-Teller specific surface areas from 569m²/g to 1027m²/g and specific capacitances from 147F/g to 223F/g, depending on carbonization and activation conditions. The maximum specific capacitance was attributed to a high surface area, optimum pore size, large pore volume and high N-5 (the pyrrolic nitrogen and pyridinic nitrogen in association with oxygen functionality) content.

Surface modification of activated carbon for CO₂ adsorption

GAO 　Feng-1, 　Wang-　Yuan-1, 　Li-Cun-Mei-1, 　Xu-Zhi-Xiong-2, 　Zhang-Chang-Meng-2, 　Wang-Jian-Long-2, 　Li-Kai-Chi-2

2014, 29(2): 96-101.

Abstract(979)

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Activated carbon was oxidized by an acid mixture of concentrated HNO₃ and H₂SO₄ with a volume ratio of 1∶1 diluted with the same volume of de-ionized water, followed by reduction with iron dust to modify its surface chemical properties for CO₂ adsorption. The samples before and after the modification were characterized by N₂ adsorption, elemental analysis, FT-IR and XPS. CO2 adsorption properties of the samples were investigated by high pressure adsorption. It was found that the adsorption capacities of the modified sample were 17.72 and 14.01mmol/g at room temperature and 319.15K respectively, showing an increase of 49 and 70% respectively, based on the surface area of the samples. The modified activated carbon can be recycled 4 times at ambient conditions without a significant decrease in CO₂adsorption capacity. Surface basic nitrogen-containing functional groups on the modified sample, such as primary amino groups, are responsible for the increased adsorption.

Carbon nanomaterials produced by the catalytic decomposition of methane over Ni/ZSM-5: Significance of Ni content and temperature

Justyna Majewska, Beata Michalkiewicz

2014, 29(2): 102-108.

Abstract(878)

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Abstract:
Methane decomposition into hydrogen and carbon nanomaterials (CNMs) was carried out over Ni/ZSM-5 catalysts with different Ni contents at different temperatures. The yields of hydrogen and the CNMs increase significantly with Ni content and reaction temperature, but they level off at high temperatures when the Ni content is over 8 wt.%. The morphology of the CNMs strongly depended on the temperature. Multiwall carbon nanotubes were formed at higher temperature, while carbon nanofibers formed at the lower temperature. The catalytic activity of the Ni/ZSM-5 decreased with time.

Investigations on oxidation cutting and dispersibility of multi-walled carbon nanotubes

BI Song-1, 2, 　Su-Xun-Jia-1, 　Hou-Gen-Liang-1, 　Liu-Chao-Hui-1, 　Xiao-　Zhou-1, 　Xiao-Yong-Dong-2, 　Cao-Mao-Cheng-3

2014, 29(2): 109-117.

Abstract(939)

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Abstract:
Multi-wall carbon nanotubes (MWCNTs) were oxidized by soaking in mixed acids. Their microstructure and composition were characterized using transmission electron microscopy, atomic force microscopy, Raman spectroscopy and infrared spectroscopy. The influence of soaking time on microstructure and dispersibility of the cut MWCNTs in aqueous solution was investigated. Results show that the MWCNTs were oxidized at defect sites by the mixed acids and converted from highly tangled ropes into short, open-ended nanotubes with lengths of 200-1500nm. The isoelectric point was reduced from 4.5 to 3.5 due to hydroxyl and carboxyl groups on the surface and the open ends of the cut MWCNTs. The aggregation experiments and UV-vis absorbance spectra revealed that the cut MWCNTs can be best dispersed in an aqueous solution containing 0.1 wt.% of sodium dodecyl-benzenesulfonate when sonicated at a pH value of 2 for 40min.

Effect of the addition of carbon nanotubes on the properties of low carbon Al₂O₃ refractory materials

LIANG 　Feng-1, Li-　Nan-1, Liu-Bai-Kuan-2, He-Zhong-Yang-2

2014, 29(2): 118-125.

Abstract(966)

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Abstract:
A new type of low carbon Al₂O₃ refractory material was prepared using coarse-grain white fused alumina , tabular alumina (≤0.043mm), graphite flake (≤0.147mm), silicon powder (≤0.074mm) and carbon nanotubes (CNTs) as fillers, and thermosetting phenolic resol as binder. The CNTs were added directly to the fillers or coated onto tabular alumina by catalytic chemical vapor deposition (CVD). Properties of the samples were tested, such as apparent porosity, bulk density, mechanical strength, modulus of rupture at 1100℃, thermal shock resistance and oxidation resistance. The morphologies of the CNTs and fractured samples were examined by scanning and transmission electron microscopy. Results indicate that bulk density, mechanical strength, modulus of rupture at 1100℃, thermal shock resistance and oxidation resistance of the sample obtained by the CVD method are higher while apparent porosity is lower than for the sample obtained by the direct addition method. The addition of CNTs improves the oxidation resistance of the refractory materials. The direct addition method not only has no influence on thermal shock resistance, but also decreases the modulus of rupture at 1100℃.

A SiC/Mo(Six, Al1-x)₂oxidation-resistant coating for carbon/carbon composites

WANG Xiang-Hui-1, 　Weng-　Li-1, 　Zhang-Wei-Gang-2

2014, 29(2): 126-131.

Abstract(856)

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SiC/Mo(Six, Al1-x)₂ multilayer coatings were prepared on carbon/carbon (C/C) composites using a multi-phase reaction technique to improve their high temperature oxidation resistance. The microstructure and phase compositions of the multilayer coatings were investigated by SEM, XRD and EDS. The coating exhibits a binary-layer microstructure, i.e. an outer Mo(Six, Al1-x)₂layer and an inner SiC layer with a small amount of Mo_4.8Si₃C_0.6. The oxidation behavior of the coated C/C composites was evaluated in a supersonic flow of about 1500m·s^-1 at 1800K in a wind tunnel. No destruction of the coated C/C composites was found after 4s oxidation after 24 exposures and thermal cycling between room temperature and 2550K for 24 times in air. The excellent oxidation resistance and thermal shock resistance are attributed to a high cohesion between the layers and the C/C composite, and the formation of a continuous and stable glassy film consisting of SiO₂ and Al₂O₃ on the coated layers during oxidation.

Molecular modeling of the mechanical behavior of carbon fiber-amine functionalized multiwall carbon nanotube/epoxy composites

Kamal Sharma1, 　Mukul Shukla1, 2

2014, 29(2): 132-142.

Abstract(1080)

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Abstract:
This paper presents a molecular dynamics (MD) analysis to parametrically describe the mechanical behavior of carbon fiber-amine functionalized multiwall carbon nanotube (A-MWCNT)/epoxy composites. The functionalized CNTs are first embedded in epoxy and cured to increase the micromechanical interlocking between CNTs and matrix. Carbon fibers were later used as fillers to increase the overall mechanical properties of the three-component composites. Within the model, the carbon fiber volume fraction was fixed at 60% and the CNT volume fraction was changed from 0.25 to 5%. Results show that the Young’s modulus and tensile strength along the carbon fiber direction increased from 92 to 224.4GPa and from 1.35 to 2.85GPa, respectively, with increasing the CNT volume fraction from 0.25 to 5%.

Preparation of montmorillonite-modified carbon foams

WANG 　Qian, 　Li-He-Jun, 　Zhang-Yu-Lei, 　Li-Ke-Zhi, 　Wang-　Bin

2014, 29(2): 143-148.

Abstract(1028)

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Montmorillonite-modified carbon foams with a closed-pore structure were prepared by compressive molding of phenolic resin, phenolic hollow microspheres and montmorillonite, followed by thermosetting and carbonization at 800℃ under Ar flow. The effects of the montmorillonite content on the microstructure, compressive strength and thermal conductivity of the modified foams were investigated. Results show that the hollow microspheres, carbon matrix and montmorillonite combine more closely in the modified carbon foams than the unmodified one. Their compressive strength increases and the porosity decreases with increasing montmorillonite content from 0 to 7 wt.%. The highest compressive strength is 25.54MPa and the lowest thermal conductivity at 800℃ is 0.588W/(m·K) when the montmorillonite content is 7 wt.%.

Numerical simulation of the effect of heat conductive fillers on the heat conduction behavior of paraffin phase change energy storage system

HONG Xiang-Lei-1, 2, 　Guo-Quan-Gui-2, 　Zhong-E-Juan-3, 　Wang-Li-Yong-2, 　Hu-　Jian-1, 　Wang-Xiao-Dong-1, 　Tan-Chun-Jing-1

2014, 29(2): 149-154.

Abstract(902)

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A cylindrical phase change energy storage system was modeled numerically using the finite element method. The model system was composed of a cylindrical container into the center of which is inserted concentrically a copper pipe carrying hot water. Either copper fins or compressed expanded natural graphite (CENG) were placed as heat-conducting fillers between the container and the pipe for comparison. The former is radially positioned while the latter is randomly filled. The remaining space was filled with paraffin as a phase change energy storage material. Fluid flow, heat conduction and convection, and the paraffin phase change were simulated simultaneously. It was found that the heat transfer performance of the system increases with the number of copper fins when they were used as the filler. The time required to reach heat equilibrium is shortened significantly by increasing the density of the CENG when it was used. CENG is much more effective than copper fins to promote paraffin melting.

The effect of coal-tar pitch modification with polyethylene glycol on its properties and the semi-coke structure derived from it

JIE Xiao-Ling-1, 2, 　Diao-Cai-Xia-1, 　Zhang-Fu-Beng-2, 　Cao-　Jing-1

2014, 29(2): 155-160.

Abstract(1060)

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Polyethylene glycol-200 and-400 were used to modify coal-tar pitch using p-toluene sulfonic acid as a catalyst. The chemical properties of the modified pitches and the microstructure of the derived cokes were studied. Results showed that the β resin contents were increased by 52-55 wt.%, the residual carbon yield at 800℃ was increased by 18 wt.%, the vibration absorption frequency of bond in aromatic rings increased significantly, and the condensation degree was improved after the modification. The modification reactions occurred at the positions of aromatic hydrogen. The viscosities of the pitch modified with PG-400 and-200 are respectively lower and higher than that of the pristine pitch. The fibrous structure of the semi-coke from the PG-200 modified pitch was significantly improved and its degree of ordering and stack height of graphene layers were also increased significantly.

2014 Vol. 29, No. 2

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