Synthesis and photocatalytic activity of ZnO/ZnO2 composite

ZnO/ZnO2composite photocatalysts were synthesized by hydrothermal treatment at 120–180 °C of ZnO2, which in turn was obtained from an aqueous solution of ZnSO4 and H2O2. The composite particles showed morphology of ZnO prismatic crystallites with small ZnO2 granules “fused” at surface. Photocatalytic activity was characterized based on photocatalytic degradation of methyl orange under UV-light (300 nm) illumination, and the maximum activity was observed for the powder with an intermediate ZnO2-to-ZnO conversion. The enhanced activity, as compared with the pure ZnO crystallites, has been attributed to the presence of the intimately bonded ZnO/ZnO2 surface hetero-structure. This study also points out a new approach to synthesize a composite photocatalyst containing strongly coupled constituents by phase transformation reactions among the constituents.