ACID AND BASE CATALYSTS IN THE HYBRID SILICA SOL-GEL PROCESS

Sol-gel silicas were synthesized from the hydrolysis of tetraethoxysil ane and -beta-aminoethyl-gamma-aminopropyltrimethoxysilane in the pres ence of water and ethanol by using ammonium hydroxide or hydrochloric acid as base or acid catalysts, respectively. The influence of the typ e of the catalyst employed was studied by comparing the surface areas and pore sizes and volumes for both sol-gel silicas. Nitrogen elementa l analysis and C-13 and Si-29 NMR spectra showed that both silicas pre sent similar chemical compositions and structures. The electron-micros cope results demonstrated that the particles are uniformly spherical a nd well shaped in both cases. The sol-gel silica obtained via basic ca talysis presented relatively small spherical particles in comparison t o 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.