Abstract.A kind of hexagonal ZnO (HZO) was synthesized in N-methyl-2-pyrrolidone (NMP)/H2O mixed solvent for a high exposure of polar ±(0001) facets to get a highefficiency photocatalyst. The amine-functionalized HZO particles were coated with graphene oxide (GO) by electrostatic force-induced self-assemby and thermal reduction to form HZO@Gr core/shell structure. The as-prepared HZO and HZO@Gr were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and UV-visible diffuse reflectance spectroscopy (UV-vis/DRS). The results indicate that the graphene on HZO@Gr remains high quality and the optical properties of the composite change a lot with sunlight absorption improving, bandgap and photoluminescence (PL) intensity decreasing. The obtained HZO photocatalyst shows good photocatalytic activity for methylene blue (MB) under UV-visible irradiation. Furthermore, the HZO@Gr photocatalyst exhibits the best photodegradation rate of MB reaching up to 98.2% within 50 minutes. The graphene-coated HZO structure could offer new directions which would further extend the scope for synthesis of various ZnO/graphene composites with improved properties useful for various applications.
IntroductionCurrently, organic dyes and their effluents have become one of the main sources of water pollution due to the greater demand in industry such as textile, paper and plastic. Thus, it is of great significance to develop a high-efficiency, energy-saving and low-cost treatment method for the elimination of dyes in wastewater.As one of the most important semiconductor photocatalysts, ZnO has attracted considerable interests because of its high photosensitivity and stability [1]. However, despite its great potential, the photocatalytic efficiency remains very low because of the fast recombination of the photogenerated electron-hole pairs in the single-phase semiconductor [2]. As a rising star of carbonaceous materials, graphene has become the focus of considerable interest for its great potential to enhance the photodegradation activity of ZnO [3]. According to recent research, there are mainly three factors that attribute to the increasing photocatalytic efficiency: the increasing adsorpticity of pollutansts, extended light absorption range and efficient charge transportation and separation [4], which conquer the obstacles that hinder the photodegradation process.