Preparation of a ZnO/TiO2 vertical-nanoneedle-on-film heterojunction and its photocatalytic properties

This paper introduces a process to prepare a novel ZnO/TiO2 heterojunction composite with ZnO nanoneedles vertically grown on a TiO2 film via micro-arc oxidation (MAO), pulse plating and thermal oxidation. Firstly a TiO2 thin film was prepared on a titanium substrate using MAO; then a Zn nanocrystalline film was pulse plated on the MAO film; finally the composite film was thermally treated at 380 degrees for several hours, which transformed the Zn film into ZnO nanoneedles. SEM observations revealed that the ZnO nanoneedles were vertically grown on the TiO2 film. The advantage of the ZnO/TiO2 heterojunction was that during heat treatment, in addition to the phase transformation from Zn into ZnO, simultaneous short-range atom diffusion occurred at the interface between the ZnO nanoneedles and the TiO2 layer, which encouraged the formation of a highly efficient, strong and stable heterojunction. Photocatalytic experiments demonstrated that, compared with pure ZnO or TiO2, the as-prepared ZnO/TiO2 composites showed greater efficiency and stability in photogenerated carriers and a significantly improved photocatalytic performance, due to this special heterojunction structure.