A great deal of attention has been drawn to the coating of transparent photocatalytic TiO2 onto outdoor building materials, such as glass, tile and stone, for utilizing the self-cleaning effect originating from the hydrophilic behavior of the coated layer under ultraviolet irradiation. Two key technologies should be developed for the successful commercialization of a hydrophilic photocatalyst, i.e., superior activity of the TiO2 sol, and a transparent and strong adhesive coating. A photocatalytic TiO2 sol showing a high degree of hydrophilicity was prepared by a sol-gel technique using titanium (IV) isoproxide as a starting materials. The concentration of TiO2 was controlled by varying the amount of water and ethanol. The sol was coated on the glass substrate by either a spray or dip coating technique. The characteristics of the coated layer were evaluated in terms of wetting angle, transparency and adhesion strength under the conditions of ultraviolet irradiation. The wettability of a water drop for the wetting angle, UV-visible spectrometer for transparency and pencil hardness for adhesive strength were employed for the evaluations. The coated TiO2 layer using 1.54 wt% TiO2 sol showed more than 95% transparency, less than 10 o of wetting angel and an adhesive strength of 7H. As a result of this study, photocatalytic TiO2 coated stone for the application of outdoor building materials has been successfully commercialized.

Keywords: Photocatalytic TiO2 sol, Hydrophilicity, Coating, Transparency.