Preparation Of Polvacrylonitrile-based Mesoporous Carbon Via Silica Templating Method

Mesoporous carbons are novel carbon materials with pore size of2-50nm, high surface areas and narrow pore size distribution. They have a broad application prospects on adsoption separation of materials with greater molecule size, catalytic support and double layer capacitors electrode and so on. Inorganic templating is the most general method to prepare mesoporous carbon materials with good performance, and homogeneous distribution of high content inorganic particles in carbon precursor is the key step to prepare mesoporous carbon with greater meso-porosity and surface area. In this thesis, polyacrylonitrile (PAN)/nanosilica composite particles with different silica content were synthesized through emulsion polymerization of acrylonitrile (AN) in the presence of nanosilica modified by cationic emulsifier and reactive surfactant, and further carbonized and template removed to obtain carbon materials with high surface area and high porosities. The mechanism of modification of silica by cationic emulsifier and reactive surfactant, in-situ emulsion polymerization behavior and the morphology of composite particles were investigated. The influences of polymerization way and the content of silica on the morphology and pore structure of mesoporous carbons were studied. Furthermore, the formation mechanism of mesoporous carbons was discussed.The aqueous dispersion of silica particles with5-20nm size were used as inorganic template. Cationic emulsifier cetyltrimethylammonium bromide (CTAB) could be effectively adsorbed onto the surface of silica by electrostatic action when pH value was adjusted to11and the surface of silica exhibited negative electrocity. It was proved by energy spectrum and infrared spectrum that part of the reactive surfactant a-allylalkylphenol ethoxylate (30)(RN-30) could be anchored onto nanosilica when reactive surfactant was added into the aqueous dispersion of silica, through the reaction between the hydroxy groups of RN-30and silanol (Si-OH) groups of the silica. Introduction of vinyl groups not only enhanced the affinity between silica and monomers, but also could take part in the copolymerization with monomers.PAN/nanosilica composite particles were synthesized through in-situ emulsion polymerization of AN in the presence of nanosilica modified by cationic emulsifier and reactive surfactant. The average size of composite particles was increased and size distribution was broadened with the increase of the content of nanosilica. When the content of nanosilica were greater then50%mass fraction of monomers, more composite particles would be aggregated and "free" nanosilica in the continuous phase increased. It was shown by transmission electon microscope (TEM) that the composite particles exhibited rough surface, which proved that nanosilica particles were coated in the composites and part of the silica embedded in the surface of the composite particles.Mesoporous carbons were prepared after carbonization and template removing. FT-IR spectroscopy, scanning electron microscopy (SEM), TEM and nitrogen adsorption-desorption were used to characterize the structure and property of the carbon materials. The results showed that the silica templates could be completely removed after the treatment with ethier NaOH or HF aqueous solution. All of the nitrogen adsorbption-desorption isotherms curves of porous carbons prepared by composite particles with different silica content exhibited IV type absorption behavior, with a hysteresis loop at relatively high pressure, which indicated the presence of meso-pores. The prepared mesoporous exhibited a maximum specific surface area of862.3m2/g, a maximum mesoporisity degree of89.64%, and the average pore size ranged from5to10nm. Combined with the FT-IR spectroscopy and morphology analysis of the composite particles and mesoporous carbons, nano-silica particles are proved to be acted as templates in the formation of mesopores. Preparing of PAN composite with high content and uniformly dispersed nanosilica particles is the key to obtain mesoporous carbons with great specific surface area, pore volume and mesoporosity.