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.