Non-hydrolytic sol-gel routes to silica

Silica was prepared by solvent-free non-hydrolytic condensation reactions f rom silicon tetrachloride with different oxygen donors: benzyl alcohol and tetrabenzyloxysilane (no catalysis), tetraethoxysilane, tetraisopropoxysila ne, diethylether and diisopropylether (catalyzed by FeCl3, TiCl4, AlCl3 or ZrCl4). Highly condensed gels with a low hydroxyl content were obtained in high yields. A solution Si-29 NMR study showed that in the presence of FeCl 3 the condensation of SiCl4 with Si((OPr)-Pr-i)(4) was accompanied by exten sive redistribution of Si-Cl and Si-(OPr)-Pr-i bonds, leading to increasing ly complex mixtures. Non-hydrolytic silica xerogels were characterized by c hemical analysis, IR and Si-29 NMR spectroscopy and thermogravimetric analy sis. Porosity and specific surface area were determined using nitrogen adso rption-desorption. Xerogels displayed a wide variety of textures depending on the nature of the oxygen donor and of the catalyst. (C) 1998 Elsevier Sc ience B.V. All rights reserved.