Size effect induced activity enhancement and anti-photocorrosion of reduced graphene oxide/ZnO composites for degradation of organic dyes and reduction of Cr(VI) in water

The composites of reduced graphene oxide/ZnO (RGO/ZnO) with different particles size of ZnO have been prepared via a facile solvothermal reaction of graphene oxide (GO) and ZnO in an ethanol-water solvent. It is found that the RGO/ZnO-S1 composite with ZnO particle size of 20-100 nm exhibits the enhanced photoactivity toward degradation of organic dyes and reduction of heavy metal ions Cr(VI) in water as compared to the bare ZnO-S1 sample under UV light irradiation. However, the RGO/ZnO-S2 composite with ZnO particle size of 50-500 nm shows decreased photoactivity as compared to bare ZnO-S2. The recycled photoactivity testing shows that, for RGO/ZnO-S1, the photocorrosion of ZnO-S1 is efficiently inhibited by the hybridization with RGO whereas the case is not for RGO/ZnO-S2. A collection of characterization techniques disclose that the smaller particles size for RGO/ZnO-S1 than that for RGO/ZnO-S2 leads to a more interfacial contact and a chemical bonding between RGO and ZnO-S1, thereby resulting in enhanced photoactivity and efficient anti-photocorrosion as observed for RGO/ZnO-S1. Furthermore, the possible reaction mechanism for degradation of dyes and reduction of Cr(VI) over RGO/ZnO-S1 has also been studied. Our results suggest that the semiconductor particles size has an important effect on the photocatalytic performance of RGO/semiconductor composites photocatalysts. The hybridization of RGO with ZnO in an appropriate manner is able to significantly inhibit the well-known photocorrosion of semiconductor ZnO. It is anticipated that this work would enrich the applications of RGO/semiconductor photocatalysts in environment purification. (C) 2013 Elsevier B.V. All rights reserved.