Solar driven photocatalytic colored co–TixOyNz amorphous film prepared through air plasma treatment of sputtered titanium film

Colored co–titanium oxides and oxynitride amorphous thin film were fabricated through air plasma treatment of sputtered titanium films. Air plasma treatment led to the removal of the passive film that developed on the titanium film surface, and changes in the structural and optical properties of the films. The amorphous nature, grain size, and thickness of the films remained invariant after the treatment process. The surface roughness of the films increased upon plasma treatment. UV-vis spectroscopy study showed the reduction of the bandgap energy of the films after the air plasma treatment and the maximum reduction was found for the thinner film. The 60min air plasma treatment of the thinner film (AD5: film with 5 min deposition time) leads to the changes in bandgap from 4.11 eV to 3.26 eV, and significant Urbach energy values pointed to the formation of defect states. XPS analysis highlighted that the plasma treatment process led to the formation of titanium oxides (TiO2, Ti2O3) and oxynitrides (TiON), accompanied with Ti2+ defect states in the bandgap. The degradation of methylene blue dye solution with plasma-treated film (PT5) as the photocatalyst resulted in 88% degradation efficiency under 240min irradiation of solar simulator. The degradation has also been checked with natural solar illumination and is found to have a 90% degradation efficiency in 480min. [Display omitted] •Colored co-titanium oxides and oxynitrides amorphous thin films are fabricated by air plasma treatment.•Plasma treatment of thinner film shows better photocatalytic activity.•The bandgap energy of the film is around 3.26 eV with extended tail towards visible region.•Urbach energy values indicate the formation of Ti2+ defect states inside the bandgap.•Nearly 90% degradation efficiency is achieved for methylene blue dye under solar illumination.