Acid and base catalysts in the hybrid silica sol-gel process

Sol-gel silicas were synthesized from the hydrolysis of tetraethoxysilane and N-beta-aminoethyl-gamma-aminopropyltrimethoxysilane in the presence of water and ethanol by using ammonium hydroxide or hydrochloric acid as base or acid catalysts, respectively. The influence of the type of the catalyst employed was studied by comparing the surface areas and pore sizes and volumes for both sol-gel silicas. Nitrogen elemental analysis and C-13 and Si-29 NMR spectra showed that both silicas present similar chemical compositions and structures. The electron-microscope results demonstrated that the particles are uniformly spherical and well shaped in both cases. The sol-gel silica obtained via basic catalysis presented relatively small spherical particles in comparison to those synthesized by acidic catalysis. The results obtained suggest that acidic catalysis is a better procedure for the synthesis of these organofunctionalized hybrid sol-gel silicas. (C) 1997 Academic Press.