Titania-Silica Nanocomposite Photocatalysts with Application in Stone Self-Cleaning

Mesoporous titania-silica composites that have photocatalytic activity have been synthesized by mixing ethoxysilane oligomers and titanium dioxide nanoparticles in the presence of a nonionic surfactant (n-octylamine). The resulting nanomaterials create effective adhesive and crack-free coatings for stone. These coatings give self-cleaning properties to stone and improve its mechanical resistance. In addition, the coating created has hydrophobic properties. For purposes of comparison, another two sets of photocatalytic materials have also been tested. The first of these has been obtained by an analogous synthesis in which n-octylamine is replaced by phosphoric acid; the second is a simple dispersion of titania nanoparticles in water. Both of these alternative materials produced coatings that crack and have poor adhesion on the stone tested; furthermore, they do not increase the mechanical resistance of the stone. These results confirm the valuable role played by n-octylamine in reducing the capillary pressure responsible for cracking, and in creating a mesoporous coating on the stone that enhances the self-cleaning properties, compared with the effect produced by the nanocomposite comprising similar particles embedded in a microporous silica matrix.