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

Abstract

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° 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.