Studies On The Preparation Of Carbon Nanospheres From Polyacrylonitile Precursor

Due to their outstanding physical and chemical properties,such as chemical stability,thermal stability,excellent electrical conductivity,thermal conductivity,and so on,carbon nanospheres(CNSs) are emerging as a new kind of carbon materials with great development and application potentials.Chemical vapor deposition, solvothermal,and template method can be used to prepare carbon nanospheres of various structures.However,it is very difficult to accurately control the size of carbon nanospheres and prepare mono-dispersed carbon microspheres of high purity and size uniformity.In this paper,using acrylonitrile and methyl methacrylate as raw materials, several PAN nanoparticles precursors of various structures were firstly synthesized through emulsion polymerization and seeding emulsion polymerization.Then, through appropriate pre-oxidation and carbonization treatments,the PAN nanoparticles precursors were transformed into solid or hollow carbon nanospheres.The preparation process of carbon nanospheres from acrylonitrile mainly consists of two steps:the first step is the preparation of PAN nanoparticles precursors;the second step is the pre-oxidation and carbonization of the precursors.The most crucial step is the synthesis of PAN precursor nanospheres with uniform size and controllable structure.The influences of the initiator amount,surfactant amount,reaction temperature and reaction time on the emulsion polymerizations of AN or MMA were investigated. The results showed that too low reaction temperature and too much SDS led to a low conversion of MMA monomer.Raising the reaction temperature,increasing the amount of the initiator or the surfactant would lead to a significant decrease in the size of PMMA latex.The initiator's type and amount as well as the amount of the surfactant have a great influence on the conversion of AN monomer and the size of PAN nanospheres.Using water-soluble initiator and increasing the amount of initiator can increase the AN conversion.Using oil-soluble initiator and appropriately reducing the amount of surfactant can lead to PAN latex of smaller size.Through the appropriate choice of initiator,the addition of a small amount of crosslinker,as well as the optimization of the polymerization process,PAN/PMMA, PMMA/PAN and PMMA/PAN/PMMA core-shell structured nanoparticles were synthesized using seed emulsion.The influences of various factors such as the pre-oxidation temperature and carbonization temperature,on the size of carbon spheres were discussed.The results showed that,CNSs of small size can be obtained from PAN/PMMA core-shell nanoparticles.Oxidation at 200℃and carbonization at 600℃are the most suitable processing parameters for the preparation of small CNSs.The amount of precursor materials during the pre-oxidation also affected the dispersion of the resultant CNSs.The preparation of CNSs with hollow structure from the PMMA/PAN/PMMA core/shell/shell nanoparticles was tried.The influences of thepre-oxidation temperature and carbonization temperature on the size of the hollow CNSs were explored.The results showed that pre-oxidation temperature at 250℃and carbonization at 600℃are the most suitable conditions for the preparation of small CNSs.