Preparation Of ZnO-based Core-shell Nanorods Vertically Grown On Reduced Graphene Oxide And Their Enhanced Photocatalytic Performance

In this paper, four reduced graphene oxide/ZnO nanocomposites with different morphologies, including RGO/ZnO nanoparticles, RGO/ZnO nanosheets, RGO/ZnO nanospheres and RGO/ZnO nanorods were prepared through hydrothermal process, characterized by XRD, IR, TEM, SEM, UV-vis spectra and electrochemical analysis and tested in photocatalytic hydrogen production from ethanol-triethylamine aqueous solution. The results show that the as-prepared RGO/ZnO nanorods display a sandwich-liked 3D structure?upright ZnO nanorods/RGO/upright ZnO nanorods three-layer construction? or carpet-liked 2D structure?upright ZnO nanorods/RGO two-layer construction?; the strong chemical interaction between graphene sheets and upright ZnO nanorods and order arrangement of upright ZnO nanorods is helpful to restrain the electron-hole recombination and enhance optical absorption performance.Based on the RGO/ZnO nanocomposites above, ZnS-CdS solid solution or ZnS-Cu2 S shell sensitized RGO/ZnO nanorods were synthesized by hydrothermal treat and ion-exchange, and the important influences of content of CdS or Cu2 S in shell on the morphology, composition and structure, light absorption properties and photocatalytic performance were investigated. The results illustrate that Sensitized RGO/ZnO nanorods were composed of graphene sheets, vertical ZnO nanorods and ZnS-Cu2 S or Zn_xCd_1-xS shell. Compared to RGO/ZnO nanorods and RGO/ZnO core-shell nanorods, the light absorption of solid solution-sensitized nanomaterials were strengthened and the absorption edge shfited to red. Fluorescence emission spectrum showed the optimal proportion of Cu₂S/ZnS or CdS/ZnS in shell and the introduction of graphene is helpful for improving charge separation efficiency. Photocatalytic activity tests reveal that RGO/ZnO@ZnS-Cu2 S and RGO/ZnO@Zn_xCd_1-xS have much higher hydrogen production rates than RGO/ZnO and RGO/ZnO@ZnS. Under irradiation of 300 W Xe lamp, the hydrogen production rate of RGO/ZnO@Cu₂S is 1451 ?mol·h-1·g-1, which is 1.37 and 0.84 times higher than that of RGO/ZnO and RGO/ZnO@ZnS respectively. The highest photocatalytic hydrogen production rate of 1865 ?mol·h-1·g-1 is observed over RGO/ZnO@Zn0.6Cd0.4S sample, which is about 2.1 and 1.4 times more active than RGO/ZnO and RGO/ZnO@ZnS respectively, its quantum efficiency could reach to 22.6%. Under the irradiation of visible light?>420 nm?, RGO/ZnO and RGO/ZnO@ZnS nanorods are barely active, whereas RGO/ZnO@Zn0.6Cd0.4S displays a hydrogen production rate of 160 ?mol·h-1·g-1. The highly improved performance of the sensitized composites can be ascribed to the increased light absorption and efficient charge separation.