A facile solvothermal method to produce ZnS quantum dots-decorated graphene nanosheets with superior photoactivity

Zinc sulfide-graphene (ZnS-GR) nanocomposites with a high degree of dispersion and high coverage of ZnS quantum dots (QDs) have been synthesized by a facile solvothermal method without any dispersant, during which the formation of ZnS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. ZnS-GR nanocomposites exhibit much higher photoactivity than nanoparticle crystal ZnS (NPC-ZnS) prepared in the absence of graphene (GR), as evaluated by degradation of methylene blue (MB) in the liquid phase under ultraviolet (UV) light. Among them, the ZnS-GR nanocomposite with a 5% mass fraction of GR prepared at 120 degrees C has the highest photocatalytic activity. The conversion and mineralization over MB are 96.7% and 57.1% respectively, which is much higher than that of NPC-ZnS. The high photoactivity of ZnS-GR nanocomposites can be ascribed to the integrated effect of an extremely high specific surface area and the excellent electron conductivity of GR and its significant influence on the morphology and structure of the samples. Moreover, it is found that the oxidation of MB is driven mainly by the participation of center dot OH radicals. Accordingly, a potential photocatalytic mechanism of ZnS-GR nanocomposites in the photocatalytic process has been proposed in this work. It is expected that our work could provide valuable information on the design of metal sulfide decorated GR with excellent properties.