The sol-gel preparation and characterization of nanoporous silica membranewith controlled pore size

A thin nanoporous silica membrane was prepared by the two-step sol-gel meth od. First, silica membrane was formed onto the alpha -alumina support as an intermediate layer with fibrous silica colloid. Then, silica nanoparticles were deposited on the first layer of silica membrane surface again by the sol-gel method. It is generally found that gelation process, as liquid evap orates during drying, begins with the formation of fractal aggregates. Sinc e an aggregate having the higher fractal dimension has the more complex voi d space than the aggregate having the lower fractal dimension, the silica n anoparticle concentration in the coating solution for the second step modif ication was selected low enough to avoid the aggregates with the higher fra ctal dimension. Thus, the prepared membrane had a dense skin layer with a n anospace as interparticle void space, which was proved by the AFM surface i mage analysis and the result from nitrogen adsorption porosimetry. (C) 2001 Elsevier Science B.V. All rights reserved.