Surface engineering on natural stone through TiO2 photocatalytic coatings

The application of semiconductor photocatalytic films on natural stone has been investigated for surface protection and selfcleaning. Sol Gel and hydrothermal processes were used to synthesize TiO2 sols with enhanced photocatalytic activity and without the need of thermal curing of the coated surface. The stone was a local (apulian) carbonatic sedimentary and porous stone. Films and powders prepared from the TiO2 sols were studied using x-ray diffraction to evaluate the microstructural evolution and identify rutile and anatase phases. A morphological and physical characterization was carried on the coated stone to establish the coating adhesion and the changes of aspect, colour and hydric behaviour. The photocatalytic activity was evaluated by dye degradation rate under UV irradiation measuring the color change with a colorimeter. The hydrothermal process proved to be effective for obtaining photocatalytic surfaces with selfcleaning and antipollution properties. With no need of high temperature post cure treatments the hydrothermal TiO2 nanostructured sols look ideal candidate for coating application on architectural materials including natural stone