Investigation of local structures and photo-induced surface properties on transparent Me(Ti, Cr)-containing mesoporous silica thin films

Abstract

Using a sol–gel/spin coating method, the transparent metal(Ti, Cr)-containing mesoporous silica thin films could be prepared on quarts plates. In the case of the Ti-containing mesoporous silica (TMS) thin film, the formation of isolated and tetrahedrally-coordinated Ti oxide species in the frameworks was confirmed by XRD, UV–vis, and Ti K-edge XAFS measurements. The TMS thin film has been proved to exhibit a strong hydrophilic property even before UV irradiation compared to the common mesoporous silica and TiO 2 thin films. After UV-light irradiation, the contact angle of water droplet on the TMS thin film become extremely lower, indicating the appearance of the photo-induced super-hydrophilic property. We have also synthesized the transparent Cr-containing mesoporous silica (CMS) thin film containing tetrahedrally-coordinated Cr oxide species, which showed the super-hydrophilic property even under visible light irradiation. By using the polymerization ability of the isolated Cr oxide species under UV light irradiation, the polyethylene phase was successfully formed on the surface of the CMS thin film. It was demonstrated that the surface property of the CMS was converted into hydrophobic while keeping its transparency. The single-site Cr oxide moieties are responsible for the photo-induced surface reaction as well as controlling the surface hydrophilic–hydrophobic properties.