Visible light-induced degradation of blue textile azo dye on TiO2/CdO–ZnO coupled nanoporous films

The photodegradation of a typical textile blue azo dye, followed by UV–VIS spectra analysis, has been carried out successfully under white light illumination on TiO₂/CdO–ZnO nanoporous coupled thin films. A relatively fast degradation occurs in dye solutions with concentrations of 100 mg/l (pH=3), at temperatures of 85°C, and with the aid of 400 mg/l hydrogen peroxide. Photodegradation also occurs on nanoporous TiO₂ films but with significant lower efficiency than on TiO₂/CdO–ZnO coupled nanoporous films. Dye photodegradation does not occur on TiO₂/CdO or TiO₂/ZnO nanoporous films, suggesting that both CdO and ZnO components are required on the sensitization of TiO₂ nanoporous films. A combined effect of new sensitizing interband states (response to white illumination) and/or rectification phenomena (improved charge separation) may be responsible of the higher photocatalytic activity of the TiO₂/CdO–ZnO nanoporous films. Similarly, the alternative route for visible degradation, the photosensitized degradation mechanism, could also benefit from the coupled nanoporous films due to a higher driving force for electron injection (dye oxidation).