Chemical vapor deposition (CVD) of tetramethoxysilane was carried out on alumina after the pre-adsorption of aldehyde as the molecular template, in order to form a molecular-sieving silica overlayer with controlled cavities. The adsorption of a molecule (1-naphthaldehyde) larger than the template was almost completely suppressed when acetic acid was added during CVD, showing a high selectivity based upon the shapes of the controlled cavity and the adsorbed molecule, while the selectivity was low when acetic acid was not used. The infrared (IR) spectrum and nuclear magnetic resonance (NMR) of 29Si showed that the acetic acid enhanced the oligomerization of Si alkoxide via hydrolysis, probably by acid catalysis, resulting in the formation of a dense network of siloxane. Such a dense wall of silica is speculated to determine the shape of the adsorption cavity precisely, and to generate high selectivity.

The CVD of silicon alkoxide was carried out on a tin oxide surface coated with pre-adsorbed carboxylate anions as templates. During the deposition of alkoxide, acetic acid was added in order to accelerate the formation of siloxane. After removal of the template and acetic acid, both the template molecule itself and the smaller molecule were adsorbed, while the adsorption of larger molecules was almost completely suppressed. The shape-selective adsorption capacity was thus observed, and the presence of a cavity, the shape and size of which were controlled by the template molecule, is suggested.

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