Synthesis Of Micro-mesoporous Silicas With The Complex Template Of Chitosan And CTAB

Micro-mesoporous complex materials have the advantages over either microporous or mesoporous materials and have potential wide applications in the field of adsorption and catalysis. The meso-scale pores are benefit to the diffusion of larger molecules with low resistance, while the micro-scale pores can provide effective catalytic sites of small molecules with high selectivity.This dissertation investigated the synthesis of micro-meosporous silicas with complex template of chitosan and surfactant cetyltrimethylammonium bromide (CTAB), and studied influences of complex tempate on pore structures.Firstly, steady-state fluorescence measurement and atomic force microscopy were carried out to study the aggregation behavior of chitosan with different degrees of deacetylation (DD) in 0.3mol/L acetic acid aqueous solution and 0.67mol/L acetic acid-ethanol mixture. It was concluded that critical aggregation concentration(CAC) increased with the decreasing of chitosan DD and the CAC in acetic acid-ethanol mixture was higher than that in acetic acid aqueous solution. Aggregates of chitosan observed were about nanometers in height and hundreds of nanometers in length.Secondly, steady-state fluorescence and fluorescence-quecher technique were adopted to study the influence of hydrochloric acid, temperature and ethanol on the self-assemble of CTAB. In aqueous solution at 30℃, critical micelle concentration(CMC) of CTAB decreased from 1.07mmol/Lto 0.35mmol/L after hydrochloric acid was added to a final concentration of 1.0×10^-2mol/L, while the critical aggregation number increased from 28.9 to 38.2. When the temperature increased to 80℃, CMC of CTAB increased to 1.18mmol/L and critical aggregation number decreased to 12.2 as the hydrochloric acid concentration reached 1.0×10^-2mol/L. In the presence of ethanol aqueous solvent with a hydrochloric acid concentration of 1.0×10^-2mol/L, CMC of CTAB was 0.060mol/L and the critical aggregation number was 18.2.Finally, micro-mesoprous silicas were synthesized using TEOS as the precursor, and chitosan, chitosan-CTAB and CTAB as the template respectively. Silica synthesized using the template of chitosan was rich in micro-scale pores and DD of chitosan influenced the proportion of micro-scale and meso-scale pores in the synthesized silica. Silica synthesized using the complex template of chitosan and CTAB has a higher meso-scale pore content and higher BET surface area and total pore volume. Addition of CTAB made the pore structure well ordered. Silica synthesized with higher temperature has a lower BET surface area, a lower micro-scale pores content and a higher pore sizes. Total pore volume was the same as that of lower temperature. BET surface area and pore volume of silica were decreased with the decreasing of pH value. The decreasing of pH value did not alter the micro-scale pores content and pore size distribution of silica. The decreasing of pH made the pore structure more ordered. Molecular dynamics simulation of chitosan-CTAB-water system indicated that chitosan has little influence on the self-assemble of CTAB. The hydrophobic interaction of the tail of CTAB made CTAB self-asemble and form the"tail-in and head-out"structure. Chitosan and CTAB can self-assemble respectively.