Preparation of titania-impregnated silica aerogels and their application to removal of benzene in air

Silica-titania aerogels were prepared by impregnating titanium tetraisopropoxide modified with acetylacetone into a silica alcogel followed by supercritical drying. The effects of the impregnation conditions, the supercritical drying medium (ethanol, 2-propanol or CO₂) and the calcination temperature on the homogeneity of the aerogel and the nature of the impregnated titania were investigated. Aerogels prepared in this way had large specific surface areas and maximum titanium contents of ca. 32 at%. Ethanol and CO₂ dried samples were homogeneous, but 2-propanol dried samples were inhomogeneous because of the extraction of impregnated titania. Ethanol and 2-propanol dried samples contained anatase particles of < 10 nm agglomerated into clusters of 100-300 nm size, whereas CO₂ dried samples contained amorphous titania. Their application to the removal of benzene from air was attempted. Ethanol dried samples possessed excellent benzene adsorption capacities and the adsorbate could be decomposed to CO₂ by photocatalytic reaction.