Effects of Au nanoparticles and ZnO morphology on the photocatalytic performance of Au doped ZnO/TiO2 films

Au doped ZnO nanocomposite films on TiO2 seeding layer (AuZ/T) were fabricated by hydrothermal processing and their photocatalytic performance was investigated. It could be found that the AuZ/T with micrometer(μm)-sized, lying ZnO bulks revealed optimal photocatalytic performance toward methyl orange under simulated sunlight, whose apparent degradation rate constant K app of 1.31 was about 20% higher compared to that of ZnO/TiO2 and 3 times higher compared to that of ZnO. The Au nanoparticles, TiO2 seeding layer and hydrothermal processing time imposed vital influence on the morphology of ZnO nanostructures, which played key roles in the formation of ZnO/TiO2 heterojunction and charge transfer (CT) inside it, as demonstrated by kinetics of transient photoluminescence (PL) decaying. The incorporation of Au nanoparticles not only induced the variations of ZnO crystallinity and reduction of ZnO band gap (E g), but also generated the Schottky heterojunction of metal-semiconductor, which would be beneficial to the CT inside nanocomposite films and separation of photo-generated electron-hole pairs, as verified by the remarkable PL suppression. The mechanism responsible for photocatalysis enhancement, which was resulted from the hybrid effects of Au nanoparticles and the ZnO morphology was discussed in details.