Preparation of transparent nanostructured N-doped TiO₂ thin films by combination of sonochemical and CVD methods with visible light photocatalytic activity

Pollution of water resources with pesticide compounds has raised serious environmental problems, and for photocatalytic degradation of these pollutants, thin film photocatalysts are preferred to colloidal ones due to the separation problem of colloidal nanoparticles. In this work, nanostructured TiO₂ and N-doped TiO₂ thin films with high transparency were deposited on glass and quartz substrates through sonochemical–chemical vapor deposition (CVD) method. The films prepared on glass and quartz substrates had nanocubic and nanospherical morphology, respectively. The presence of N atoms in the structure of TiO₂ resulted in a decrease in the band gap energy of TiO₂ and also in the reduction of photogenerated electron–hole recombination rate. Furthermore, the presence of N atoms induced the formation of Ti³⁺ species which can act as hole trapping centers. The prepared thin films were also used for the visible light photocatalytic degradation of paraoxon pesticide. According to these results among the prepared thin films, the N-doped TiO₂ thin films have higher photocatalytic activity than pure TiO₂ thin films. Moreover, in comparison with the thin films deposited on quartz substrate, the films on glass substrate have higher photocatalytic performance, which can be related to the special nanocubic morphology of these samples.