Preparation of fractal-like silica particles based on Stöber method by using tetrabutylammonium hydroxide as co-catalyst

Abstract

Conventional Stöber method, in which ammonia is used to catalyze the hydrolysis/condensation of tetraethyl orthosilicate (TEOS), has been proven to be very powerful for preparation of different sized, spherical silica particles. In this work, a modified Stöber method was developed, in which tetrabutylammonium hydroxide (TBAOH) was used as a co-catalyst of ammonia, for preparation of silica particles fractal-like in shape. In this method, the hydrolysis/condensation of TEOS was promoted due to the stronger alkalinity of TBAOH than ammonia, profitable for the formation of loosely condensed silica networks less negatively charged. Meanwhile, incorporation of the positively charged tetrabutylammonium ion (TBA+), generated by dissociation of TBAOH, into the negatively charged silica networks may further suppress the electrostatic repulsion among the silica particles along the reaction. As a result, growth of the silica particles in such modified Stöber method primary followed the aggregation-only model, allowing the growth of silica particles with different fractal dimensions (df) by simply changing the concentration of TBAOH.