2011 Vol. 26, No. 2

Growth of carbon nanotubes and nitrogen-doped carbon nanotubes on “carbon nanotube seeds”
WANG Can, WANG Yan-li, ZHAN Liang, HUANG Zheng-hong, QIAO Wen-ming
2011, 26(2): 81-84.
Abstract(2235) PDF(1465)
Abstract:
Carbon and nitrogen-doped carbon (CNx) nanotubes were synthesized by detonation-assisted chemical vapor deposition with CNTs as seeds and paraffin as the carbon source and melamine as the carbon/nitrogen source. Transmission electron microscopy and electron energy loss spectroscopy were performed to characterize both materials. CNx nanotubes exhibited a compartmentalized bamboo-like structure and contained a high concentration of nitrogen (17.3 at %), while the new pure CNTs had hollow cores. The role of the original CNTs added to the raw materials could be ascribed to their curvature and open tip edges, which adsorbed Cn/CN species and assembled them into carbon and CNx nanotubes.
A green precursor for carbon nanotube synthesis
S. Paul, S. K. Samdarshi
2011, 26(2): 85-88. doi: 10.1016/S1872-5805(11)60068-1
Abstract(2606) PDF(1741)
Abstract:
The present work aims to explore a natural renewable precursor for the synthesis of multiwalled carbon nanotubes (MWCNTs), conforming to the principles of green chemistry. MWCNTs were synthesized by chemical vapor deposition using a natural renewable precursor (coconut oil). Nitrogen gas was used as an inert atmosphere as well as a carrier for the evaporated precursor (flow rate: 100mL/min). The synthesized MWCNTs are characterized by scanning and transmission electron microscopy, electron dispersive X-ray analysis, and Raman spectroscopy. The diameters of the synthesized nanotubes are in the range of 80nm to 90nm under optimum conditions.
Preparation of amine-modified multiwalled carbon nanotubes and their use in composites
WANG Guo-jian, ZU Mei| QIU Jun
2011, 26(2): 89-97.
Abstract(2879) PDF(1985)
Abstract:
Multiwalled carbon nanotubes (MWCNTs) were modified by a graft reaction of diamines with different chain lengths, such as ethylenediamine(EDA), hexamethylene diamine(HMDA) and decamethylene diamine(DMDA). FTIR, Raman spectroscopy, XPS and TEM were used to characterize their chemical structure. XPS indicated that the molar content of N on the surface of MWCNTs-EDA, MWCNTs-HMDA and MWCNTs-DMDA reached 3.52%, 4.18% and 2.88% respectively under the same reaction conditions. The dispersion of MWCNTs in organic solvents before and after the modification was measured semi-quantitatively using UV-Vis spectra and a Turbiscan analyzer. It was found that the amino-modified MWCNTs improved their dispersion in polar solvents and MWCNTs-HMDA had the best dispersion stability. MWCNTs-HMDA were introduced into a traditional carbon fiber reinforced epoxy system to prepare three phase composites which showed remarkably improved flexural and impact strengths.
Preparation of spongy microspheres consisting of functionalized multiwalled carbon nanotubes
Dhiraj Dutta, Rama Dubey, Jitendra Yadav, T. C. Shami, K.U. Bhasker Rao
2011, 26(2): 98-102. doi: 10.1016/S1872-5805(11)60069-3
Abstract(1937) PDF(1414)
Abstract:
Multiwalled carbon nanotubes (MWCNTs) were synthesized by catalytic chemical vapor deposition and functionalized by oxidation with potassium permanganate at room temperature using a phase transfer catalyst, methyl trioctyl ammonium chloride as a dispersion agent. The functionalized nanotubes were characterized by Fourier transform infrared spectroscopy and thermogravimetry. Sonication was used to assist their dispersion in dichloromethane and the resulting suspension was added dropwise to a stirred polyvinyl alcohol aqueous solution and spongy microspheres were formed. SEM showed that the microspheres consisted of loosely entangled MWCNTs that had diameters in the range 50-150μm. The microspheres may be useful for lightweight energy absorbing coatings, catalyst and electronics applications.
The preparation, characterization and acidic catalytic function of sulfonated bamboo char
XU Qiong, XIA Yue, YIN Du-lin, FAN Chang-ling, XU Zhong-yu
2011, 26(2): 103-108.
Abstract(1835) PDF(1827)
Abstract:
Bamboo sawdust was soaked in phosphoric acid for 48-72h and bamboo char was obtained by pyrolysis of the soaked sawdust at 200℃ for 2h. The latter was treated at 100℃ for 2h in fuming sulfuric acid to produce sulfonated bamboo char. The results of XRD and FTIR showed that the product a solid amorphous material with polycyclic aromatic rings and acidic functional groups. The result of pyridine adsorption DRIFT showed that the surface acid sites were proton type. The amount of acid in sulfonated bamboo char was 2.02mmol · g-1 as determined by ion exchange and titration. Sulfonated bamboo char had a good catalytic activity and can be reused in the acetalization of ethylene glycol with different aldehydes or ketones.
Performance analysis of a carbon cloth/felt layer needled perform
JI A-lin, CUI Hong, LI He-jun, CHENG Wen, JI Ling-ling
2011, 26(2): 109-116. doi: 10.1016/S1872-5805(11)60070-X
Abstract(2430) PDF(1795)
Abstract:
The structural characteristics of a carbon cloth/felt layer needled preform are investigated. X-Y direction tensile strength, Z direction peel-off stress, and the Naval Ordnance Laboratory (NOL) ring-integrated tensile strength were tested. The X-Y direction tensile strength decreased with the increase of needling density. The law of surface density of fiber felt affecting the Z direction stress is not obvious. Peel-off stress of a 3K carbon cloth/felt needled preform is higher than that of 6K and 12K cloth/felt, and the peel-off stress of a diagonal carbon cloth/felt needled preform is better than that of a satin one. There are three different damage modes for the NOL-integrated tensile ring, namely complete rupture, incomplete rupture, and interlayer peel-off. For 3K satin carbon cloth/felt needling preform, its NOL ring-integrated tensile strength is the lowest and only 3MPa, and it shows complete rupture. For the 12K satin carbon cloth/felt needled preform, the damage mode is interlayer peel-off , and for the 6K satin carbon cloth/felt needled preform, the damage mode is incomplete rupture, and its integrated mechanical performance is excellent. NOL ring-integrated tensile strength is much higher than X-Y tensile intensity for the preforms made by same process.
Preparation of low density and high mesoporosity carbon aerogels by an organic/inorganic hybrid method
ZHOU Bei, ZHANG Rui, GUO Quan-gui, LI Zhi-hong, HU Zi-jun, LI Jun-ning
2011, 26(2): 117-122.
Abstract(1966) PDF(1505)
Abstract:
Carbon aerogels were synthesized by the solution-sol-gel polymerization of resorcinol (R) and formaldehyde (F) with silica colloidal nanoparticles as additives in a basic aqueous solution followed by supercritical drying, pyrolysis and HF etching. The R/F molar ratio was maintained at 0.5 and the concentration of R+F in solution was varied. The evolution of porosity from hydrogels to carbon aerogels was investigated by nitrogen adsorption. The effect of R+F concentration and size of the silica colloidal nanoparticles on porosity and mesopore ratios were investigated under the same concentration of silica colloidal nanoparticles at 15g/100mL. Results indicated that the volume shrinkage of carbon precursors during supercritical drying and pyrolysis can be reduced by the presence of silica colloidal nanoparticles. The mesopore ratio increased with increasing R+F concentration and porosity decreased with increasing size of the silica colloidal nanoparticles. When the R+F concentration was 20g/100mL, the densities of the carbon aerogels were 0.22 and 0.26g/cm3 with mesopore ratios of 96 and 98% for 7 and 12nm silica colloidal nanoparticles respectively.
Simple synthesis of semi-graphitized ordered mesoporous carbons with tunable pore sizes
LI Ying, ZHONG Jian, YANG Xia-zhen, LAN Guo-jun, TANG Hao-dong, LIU Hua-zhang
2011, 26(2): 123-129. doi: 10.1016/S1872-5805(11)60071-1
Abstract(1910) PDF(1591)
Abstract:
Ordered mesoporous carbons (OMCs) with adjustable pores were synthesized by using an ordered mesoporous silica, SBA-15 as a hard template and boric acid as a pore expanding agent. The prepared samples were characterized by X-ray diffraction, N2 porosimetry, thermogravimetry, transmission and scanning electron microscopy, and Raman spectroscopy. Results show that the pore size of the prepared samples can be finely tuned in the range of 3-7nm by using boric acid as the pore expanding agent. The OMCs possess extensive graphitic domains as evidenced by the well-resolved powder X-ray diffraction peaks, Raman spectra, transmission electron microscope images and thermogravimetric curves. This approach gives a simple method that can be widely used in the controlled synthesis of mesoporous carbons.
Synthesis and characterization of activated carbon with a high mesoporosity
LI Yan-qiu, LI Kai-xi, SUN Guo-hua, WANG Jian-long
2011, 26(2): 130-136.
Abstract(2033) PDF(1582)
Abstract:
Activated carbon with a high mesoporosity was prepared by yttrium-phenolic resin complex formation, carbonization and steam activation, using novolac phenolic resin as the carbon precursor. The resins and corresponding carbons were characterized by infrared spectrometry, thermogravimetry, nitrogen adsorption scanning electron microscopy and X-ray diffraction. Results indicated that complexes were formed between yttrium and methyl methacrylate-grafted phenolic resin, and the corresponding activated carbon had a mesoporosity up to 88%. The formation of the complexes obviously improved the compatibility between the organic precursor and the inorganic salt, leading to a homogenous distribution of yttrium and its increased catalytic efficiency. And as a result, activated carbons rich in mesopores were obtained.
Thermal properties of porous copolymers of BM-DVB and their carbonization products
M. Sobiesiak, B. Gawdzik, A.M. Puziy, O.I. Poddubnaya
2011, 26(2): 137-144. doi: 10.1016/S1872-5805(11)60072-3
Abstract(1895) PDF(1393)
Abstract:
Thermogravimetry and differential scanning calorimetry were used for characterization of the thermal properties of new 4,4’ -bismaleimidodiphenylmethane (BM) and divinylbenzene (DVB) porous copolymers and their carbonization products. Bead-shaped porous copolymers BM-DVB with the following monomer ratios 1∶4, 1∶1, 4∶1 were synthesized using suspension copolymerization under the same conditions. Differences in the monomer ratio caused a different degree of cross-linking of the starting polymers. Before carbonization, the BM-DVB copolymers were pretreated using two methods. In one method, the starting material was stabilized in hot air (product was labeled PO-C800). In the other method, the copolymer was soaked in H3PO4 (product was named P800). Then, materials obtained by both methods were carbonized at 800℃ in an argon atmosphere. To characterize the heat resistance of the BM-DVB copolymers and their carbonized derivatives, their thermostabilities were evaluated. The data suggest the existence of a relationship between the composition and thermal stability of the copolymers and their carbonized derivatives. The most thermally resistant copolymer was that obtained with a 4∶1 molar ratio of BM to DVB. Its thermal stability is caused by the high concentration of nitrogen atoms in the polymeric structure. 1∶4 BM-DVB copolymer with a high degree of cross-linking was the least thermally stable, which might be caused by its microporous nature and small fraction of nitrogen. The derived carbons have very similar thermal properties, and an insignificant influence of the nature of the polymer precursor was observed. More important factors affecting thermal stability were the porosity and surface chemistry, which were created in the thermal pretreatment processes.
Fabrication and properties of porous C/SiC composites
JI Hong-liang, ZHANG Chang-rui, ZHOU Xin-gui, CAO Ying-bin
2011, 26(2): 145-150.
Abstract(2449) PDF(1458)
Abstract:
Preforms made of carbon fibers and sacrificial tungsten fibers as a pore forming agent were repeatedly infiltrated with polycarbosilane and pyrolysed for 14 cycles, followed by aqua regia leaching to remove the tungsten fibers to form porous C/SiC composites. The pore structure, mechanical properties and permeability of the porous C/SiC composites to water and kerosene were respectively studied by a scanning electron microscope, a universal materials testing machine and home-made permeation equipment based on a fluid flow model in capillaries. Results showed that the pores of the porous C/SiC composites were mostly straight and that the open porosity can be controlled by the volume fraction of tungsten fibers used. The bend strength, Young’ s modulus and fracture toughness were 358MPa, 124GPa and 16.7MPa · m1/2 respectively when the open porosity of the composite was 23.5%. The fluids permeated through the porous C/SiC composites by linear laminar flow(the osmosis rate value is 1.02×10-3mm2). The composites exhibited tough fracture behavior and the presence of pores didn’t lead to a significant deterioration of their mechanical properties.
Preparation of mesoporous carbons by a template method
CHUAN Xiu-yun, ZHOU Shu-hui
2011, 26(2): 151-160.
Abstract(2660) PDF(2212)
Abstract:
Inorganic and organic template methods were reviewed, and it was assumed that the mineral template method and the composite template method could be efficient ways to synthesize mesoporous carbons with a low cost and a wide availability. The composite template method has advantages of both “soft-template” and “hard-template”, and can be used to synthesize mesoporous carbons with a variety of structures and characteristics, and therefore expand their range of applications.