Sol±Gel Synthesis and Characterization of Microporous Silica Membranes

It has been reported in the literature that the composition Unsupported silica membranes were prepared by acid-catalyzed of the synthesis solution influences the structure of the spe-hydrolysis and condensation of tetraethylorthosilicate. The possi- cies in the sol (3) and, hence, the final structure of the bility of tailoring the pore size and porosity of microporous silica membrane. This possibility to tailor-make membranes can membranes was investigated by varying the amounts of reactants. be of advantage in manufacturing application-oriented mem-A wide range of porosities of 0 to 30 % could be obtained. Of the branes with different porosity or pore size. To prepare mem-varied parameters, the acid concentration in the reaction mixture branes with predefined properties, it is important to under-is of most importance for the variation in porosity. The pore size stand the relationship between the synthesis conditions anddistribution was calculated from nitrogen adsorption isotherms, the resulting structure of the membranes. The first step inby using the Horva th±Kawazoe method. This resulted in an aver-age pore diameter of 5 AÊ with a broad tail up to 10 AÊ. q 1996 this investigation was to study the relationship between the Academic Press, Inc. synthesis composition and the structure of the species in the Key Words: membrane; silica; microporous; sol±gel. sol. Part of these results have been published in a previous publication [part I (4)]. That article presented a detailed account of small-angle X-ray scattering (SAXS) of silic