Structural, optical and photocatalytic properties of erbium (Er(3+)) and yttrium (Y(3+)) doped TiO(2) thin films with remarkable self-cleaning super-hydrophilic properties

The self-cleaning and super hydrophilic properties of pristine TiO(2) and of TiO(2) doped with Er(3+) or Y(3+) transparent thin films deposited onto glass substrates were investigated. The thin films prepared by multiple dipping and drying cycles of the glass substrate into the pristine TiO(2) sol and Er(3+) or Y(3+)-doped TiO(2) sol were characterized by X-ray diffraction, UV-vis spectrophotometry, and atomic force microscopy (AFM). The self-cleaning photocatalytic activity of the thin films towards the removal of oleic acid deposited on the surface under UVA irradiation was evaluated. A remarkable enhancement was observed in the hydrophilic nature of the TiO(2) thin films under irradiation. The optical properties and wettability of TiO(2) were not affected by Er(3+) or Y(3+) doping. However, the photocatalytic degradation of oleic acid under UVA irradiation improved up to 1.83 or 1.95 fold as the Er(3+) or Y(3+) content increased, respectively, due to the enhanced separation of the photogenerated carriers and reduced crystallite size. AFM analysis showed that the surface roughness increased by increasing the Er(3+) or Y(3+) content due to the formation of large aggregates. This in turn contributes to the increase of the active surface area enhancing the photodegradation process. This study demonstrates that TiO(2) doped with low amounts of Er(3+) or Y(3+) down to 0.5 mol% can produce transparent, super-hydrophilic, thin film surfaces with remarkable self-cleaning properties.