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-derived titanium dioxide (TiO₂) thin films that contained 0-50 mol% silica (SiO₂) were investigated. Anatase formed on exposure to water vapor at 60°-180°C, with a simultaneous decrease in the concentration of OH groups. An increase in the SiO₂ content of the exposed films led to an increase in the average crystalline size. Because crystallization of the exposed films of the films was not accompanied by shrinkage, porous anatase coatings were obtained via exposure at a relatively low temperature. Phase separation of the immiscible TiO₂-SiO₂ system was induced with water vapor, which resulted in acceleration of the crystallization of the sol-gel films.