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.