Photocatalytic activity and photo-induced superhydrophilicity of sol–gel derived TiO2 films

TiO2 thin films have been deposited using various sol–gel routes. X-ray diffraction, ellipsometry, atomic force microscopy, and scanning electron microscopy characterizations show that the film morphology is strongly influenced by the sol nature and post-deposition heat-treatment temperature. Photo-induced properties of the films have been studied in relation to their morphology. In aqueous medium, photocatalytic properties are governed by a migration of photo-generated charge carriers, which occurs through the whole film thickness and closely depends on the film morphology, in particular the crystallization and densification degrees, as well as the primary and secondary particle sizes. Correlations between photocatalytic activity and photo-induced superhydrophilicity show that both properties are influenced by same mechanisms. Photo-wettability mechanisms are less critically influenced by morphologic properties because they only involve a very thin active surface layer.