Transparent nitrogen doped TiO₂/WO₃ composite films for self-cleaning glass applications with improved photodegradation activity

TiO₂-based photocatalyst has been widely used by modifying the band structure owing its large band gap (∼3.2 eV) and fast recombination of electron-hole pairs. In order to modify the TiO₂ base structure, WO₃ component is used as the sensitizer and electron accepting species with additional dopant materials. Nitrogen-doped TiO₂/WO₃ composite film with high transmittance was successfully synthesized by the sol-gel spin coating method, and the nitrogen doping changes the base crystal sizes by the diffusion of nitrogen atoms into the base lattice. Photocatalytic activity is directly related to the energy band structure and surface morphology of materials. Optimally doped nitrogen atoms improve the photocatalytic activity of the TiO₂/WO₃ base materials, but overly doped nitrogen reduces the activity because of the electron hole recombination in the localized band state. Therefore, it is important to use the optimum amount of dopant species to improve the photocatalytic activity of the composite photocatalysts.