Defect engineering of ZnO nanoparticles by graphene oxide leading to enhanced visible light photocatalysis

Photocatalysis by visible light is important for a wide range of applications. In this work, graphene oxide (GO) based hybrid photocatalyst ZnO/(Fe3O4@SiO2)/rGO (GZF) composites were prepared via microwave synthesis by introducing ZnO nanoparticles (ZnO NPs) and Fe3O4@SiO2 onto the surface of reduced GO (rGO). GZF composites possess magnetism therefore easy to separate from the solution simply by a hand-held magnet. They exhibit excellent photo-catalysis for the oxidative degradation of methylene blue, which is 3.6 times higher under visible light when compared to the ZnO NPs. The surface defects in the ZnO nanoparticles before and after graphene hybridization were studied. The optical results show that the visible emission consists of violet, blue and green regions, attributed to the zinc interstitial, zinc vacancy and oxygen vacancy defects. After hybridization with the graphene the vacancy sites in the ZnO nanoparticles were significantly decreased, oxygen vacancies were healed, albeit oxygen interstitial defect (Of) levels appeared as a new defect. The superoxide and hydroxyl radicals are responsible for the photocatalytic reaction. The present results are important for exploring graphene based magnetic photocatalysts for various applications. (C) 2016 Elsevier B.V. All rights reserved.