Effects of Zn/S ratios on the photoelectric properties of ZnS/microcrystalline graphene composites

Microcrystalline graphite oxide was prepared by the Hummers method using the microcrystalline graphite as raw material. ZnS/microcrystalline graphene (ZnS/MGR) composites were synthesized by a solvothermal method using zinc acetate as zinc source, thiourea as sulfur source and microcrystalline graphite oxide as a carrier. The structure and morphology of the composites were characterized by XRD and SEM. The results show that the cubic ZnS nanoparticles with size of 50-100 nm are uniformly dispersed on the microcrystalline graphene sheets which offer an ideal platform for smaller ZnS nanoparticles and prevent the aggregation of ZnS nanoparticles. The effects of different Zn/S ratios on the photoelectric and electrochemical properties of ZnS/MGR were investigated. As the Zn/S ratio changes from 1: 1, 1: 2 to 1: 3, the photocurrent density first increases, reaches a maximum of 4.62 x 10(-5)A/cm(2) at the Zn/S ratio of 1:2, and then decreases as the Zn/S ratio further decreases. The electrochemical impedance of ZnS/MGR reaches a minimum at the Zn/S ratio of 1:2, and the specific capacitance of ZnS/MGR at the same ratio reaches a maximum of 55.66F/g, which is about 180 times as large as that of pure ZnS.