Preparation of porous anatase coating from sol-gel-derived titanium dioxide and titanium dioxide-silica by water-vapor exposure

The effects of water vapor on the crystallization behavior of sol-gel-deriv ed titanium dioxide (TiO2) thin films that contained 0-50 mol% silica (SiO2 ) were investigated. Anatase formed on exposure to water vapor at 60 degree s-180 degrees C, with a simultaneous decrease in the concentration of OH gr oups. An increase in the SiO2 content of the exposed films led to an increa se in the average crystalline size. Because crystallization of the exposed films of the films was not accompanied by shrinkage, porous anatase coating s were obtained via exposure at a relatively low temperature. Phase separat ion of the,immiscible TiO2-SiO2 system was induced with:water vapor, which resulted in acceleration of the crystallization-df the sol-gel films.