Facile synthesis and photocatalytic properties of ZnO core/ZnS–CdS solid solution shell nanorods grown vertically on reductive graphene oxide

Abstract

In the present study, ZnS–CdS solid solution sensitized ZnO nanorods were anchored on graphene sheets by combining a hydrothermal process and ion exchange technique, and the significant influence of CdS content in the shell on photo absorption and photocatalytic performance were investigated. Electron microscopic images reveal that the as-prepared nanocomposites display a sandwich-like 3D structure, consisting of ZnO nanorods with a Zn_xCd_1−xS or CdS shell grown vertically on both sides of the graphene sheets. UV/Vis DRS shows that the solid solution sensitized nanocomposites have enhanced visible light absorption and also exhibited a red-shift of the band-edge as compared to RGO/ZnO and RGO/ZnO@ZnS. Fluorescence emission spectra indicate that the deposition of CdS on the shell with an appropriate CdS/ZnS ratio and the incorporation of graphene causes improved charge separation. The photocatalytic experiments demonstrate that the RGO/ZnO@Zn_xCd_1−xS nanocomposites possess much higher photocatalytic activity for H₂ evolution than the RGO/ZnO nanorods and RGO/ZnO@ZnS core/shell nanorods. Under the irradiation of a 300 W Xe lamp, the highest photocatalytic hydrogen production rate of 1865 μmol h⁻¹ g⁻¹ is observed over the RGO/ZnO@Zn_0.6Zn_0.4S sample, which is about 2.1 and 1.4 times more active than RGO/ZnO and RGO/ZnO@ZnS, respectively. Under the irradiation of visible light (>420 nm), the RGO/ZnO and RGO/ZnO@ZnS nanorods are barely active, whereas RGO/ZnO@Zn_0.6Zn_0.4S displays a hydrogen production rate of 160 μmol h⁻¹ g⁻¹. The highly improved performance of the composites can be ascribed to the increased light absorption and efficient charge separation.