PHOTOOXIDATIVE SELF-CLEANING TRANSPARENT TITANIUM-DIOXIDE FILMS ON GLASS

In the context of studying the feasibility of photocatalytically self- cleaning windows and windshields, clear, abrasion resistant, photocata lytic films of TiO2 were formed on soda lime glass and on fused quartz by a sol-gel process. The rate of photooxidation of contaminant depos its was estimated by measuring the rate of decrease in the integrated IR absorbance associated with the C-H stretching vibrations of a thin solution-cast film of stearic acid under 365 nm (2.4 mW/cm(2)) or 254 nm (0.8 mW/cm(2) irradiation. Approximately 3 x 10(-4) stearic acid mo lecules were stripped per 365 nm photon in either front- or back-illum inated soda lime glass, and 6 x 10(-4) molecules when the films were c oated on fused quartz. For thin TiO2 films on fused quartz, the rate o f photooxidation, normalized by the number of photons absorbed per uni t area, was independent of the wavelength, In contrast, for films on s oda lime glass, the rate of photooxidation, when similarly normalized, was higher for the less penetrating wavelength. The reduced photoacti vity on glass at the deeply penetrating wavelength (365 nm), as well a s the greater photoefficiency on quartz than on glass, are attributed to diffusion of sodium oxide from the glass into the inner glass-conta cting zone of the TiO2 layer.