Study On The Synthesis Of Carbon Nanotubes By Silica-supported Cobalt Sulfide Catalyst

Carbon nanotubes（CNTs）,as a new type of inorganic non-metallic nanomaterials with good properties of mechanics,thermals,electric conduction,biochemistry,magnetism,adsorption,storage etc.,have become a research hotspot in the material science field since its discovery in 1991.It is necessary to develop a new type of efficient catalyst for the synthesis of carbon nanotubes because the catalyst directly affects the properties of CNTs.Previous studies reported that silica-supported cobalt sulfate catalyst（CoSO4/SiO₂）demonstrated an excellent selectivity towards（9,8）tubes and cobalt sulfide（CoS）was an intermediate reduction product in the synthesis of CNTs from cobalt sulfate.Therefore,this paper mainly studies the preparation of silica-supported cobalt sulfide（CoS/SiO₂）catalyst and its application in synthesis of CNTs by chemical vapor deposition（CVD）.A silica-supported cobalt sulfide catalyst was prepared via two different methods.First,the catalyst precursor was prepared by chemical reaction of cobalt salt and ammonium sulfide solution on a fumed silica support,followed by heat-treatment at 400～600℃ in hydrogen or at 600-900℃ in argon to obtain the CoS/SiO₂ catalyst.The another method is directly mixing up of pure cobalt sulfide and silica support by ultrasonication,cell pulverization and stirring in order to obtain P-CoS/SiO₂(CoS is composed of Co₉S₈ and Co_1-xS).Then,CNTs were synthesized on CoS/SiO₂ and P-CoS/SiO₂ catalysts using ethanol as the carbon source,and the effects of reduction temperature and Co loadings on CNT synthesis were investigated.The results showed that catalysts reduced at 700℃ synthesized SWCNTs with better quality and higher yiled.CoS/SiO₂ synthesized CNTs,but the yield and chirality selectivity were not good.Whereas P-CoS/SiO₂ catalyst with Co loading less than 5 wt%can synthesize SWCNTs with high quality,P-CoS/SiO₂ catalyst with high Co loading of 7 wt%and 10 wt%obtained CNTs with yields up to 20 wt%.Finally,the mechanism about synthesis of CNTs by P-CoS/SiO₂ catalyst was explored.