Transparent visible light activated C-N-F-codoped TiO₂ films for self-cleaning applications

The current work reports a potential technology for fabricating visible light activated doped TiO₂ coatings for self-cleaning applications. Transparent C-N-F-codoped TiO₂ films with enhanced visible light photocatalytic activity and non-light activated superwettability were successfully prepared by a simple layer-by-layer dip-coating method using TiO₂ sol and NH₄F methanol solution as precursors. The current coating method prevents the reactions of F^- ions with the glass substrate and hence resulting in a uniform and transparent coating. It also creates TiO₂ coating with high surface roughness without an additional pore-inducing agent and generates non-irradiated superhydrophilic surface. Contact angles of the C-N-F-codoped TiO₂ films were 2.3-3.1° in the absence of any illumination and they rose slowly in the dark (<1.8° in 30 days). The C-N-F-codoped TiO₂ films showed strong visible-light absorption and enhanced photocatalytic activity for stearic acid decomposition under visible light irradiation, which was 5 times higher than that of C-doped TiO₂ film. Our DFT calculations also showed that increasing N:F doping ratio leads to band gap narrowing of TiO₂.