Study On The Preparation, Modification And Adsorption Properties Of Vapor Grown CMSs From DOA

Carbon micro spheres(CMSs),one important member of carbon family, have excellent properties and potential applications because of their special structure.Many potential applications for CMSs have been proposed,such as anode material of secondary Lithium ion batteries,catalyst supporters,fillers in composite,porous conductive and super-high hydrogen storage materials. Deoiled asphalt(DOA)is a carbon-rich by-product of petroleum industry.CMSs can be synthesized from synergic effects of the gaseous species released during the pyrolysis of DOA,including CH₄,CO,H₂,N₂,H₂S and low molecular hydrocarbons.Utilization of DOA can provide a new approach for expansion of product chains of petroleum processing and comprehensive utilization of petroleum resource.In this paper,DOA was chosen as carbon source in order to prepare CMSs by chemical vapor deposition(CVD).Various conditions influencing the growth of products were studied.In addition,air oxidation and KOH activation were performed to modify CMSs.Morphologies and structures of the products were characterized by field emission scanning electron microscopy(FESEM),high resolution transmission electron microscopy(HESEM),X-ray.diffraction(XRD) and Raman spectroscopy,and the functional groups on the surface of CMSs were characterized by Fourier transformation infra-red spectrometry(FTIR).The main conclusions are as follows:1.A series of size-controllable CMSs were synthesized from DOA by CVD, with the emphasis on the influences of experimental parameters,including reaction temperature,argon flow rate and reaction zone.As the reaction temperature increased from 900 to 1100℃,the size of CMSs distributed in the range of 650 to 750 nm and the yield increased from 21%to 35.6%.With increasing Ar flow rate from 60 to 300 ml/min,the size of CMSs decreased from 1μm to 220 nm,and the yield of CMSs decreased from 44.7%to 30.7%.The products collected in low temperature zone were CMSs with smaller size and broader size distribution than that obtained in high temperature zone.And results show that an effective mass production of size-controllable CMSs,with diameters ranging from 100nm to 1μm,was achieved.The obtained high purity CMSs were of spherical shape with uniform size and amorphous structure.After vacuum treatment at 2000℃for 1 hour,the graphitization degree was enhanced greatly and clear graphitic layer appeared inside the CMSs.In addition,the effect of catalyst was investigated.Results show that vapor grown carbon fibers (VGCFs)were synthesized by CVD in the mixed atmosphere of argon and hydrogen,using DOA as carbon source and FeCl₃ as catalyst precursor.The VGCFs exhibited a tree annual-ring-type structure and had a hollow core.Their walls were divided into two different kinds of structures,that is,the high-graphitized inner layer shells and low-graphitized outer layer shells.2.Air oxidation and KOH activation were performed to modify CMSs. After air oxidation,some oxygen-containing functional groups were introduced onto the surface of CMSs,including anion carboxylate,carboxylic group and hydroxyl group,which would provide the probability of CMSs as catalyst and biomolecules supporters.After activated by KOH,the adsorption isotherms of samples translated to typeâ…¡,and the specific surface area increased from 3.981m²/g to 60.376m²/g.The pore volume of as-synthesized CMSs was composed by micropores and mesopores,but after activation,macropores was found.