Studies On The Preparation And Properties Of Graphene/Metal Sulfide Semiconductor Composites

Graphite resource is abundant and widely distributed in our country. It has come into focus to prepare high-performance graphene and its composite materials with cheap natural flake graphite as raw material. Graphene is a kind of promising photoelectric functional materials due to its unique surface of the honeycomb structure, good optical transmittance and excellent electric conductivity. Semiconductor nanocrystals have tunable optical properties with varied chemical composition, and potentially used in optoelectronics and other areas. Since the high surface energy leads to aggreation of semiconductor nanoparticles and results in the limited optoelectronics application, it is a good way to load semiconductor particles on the surface of graphene to prevent the aggregation of the semiconductor nanoparticles and make the semiconductor particles dispersed evenly in the graphene sheets. In this paper, graphene/ZnS and graphene/ZnxCd1-xS semiconductor composites were synthesized and its electrochemical performance and photoelectric properties were explored on electrochemical workstation. The research content is divided into the following two parts:(1) The high-quality graphite is prepared by hydrofluoric acid purification,and the carbon content of the graphite is increased from 97.5% to 99.49%. Graphite oxide was prepared by Hummers method with the high-quality graphite as raw materials, and further reduced to graphene by chemical reduction method. Graphene/ZnS composites were synthesized via a simple solvothermal method with ethylene glycol and ethylene diamine as reaction solvent, sodium sulphide and thiourea as sulfur source, respectively. The crystalline and morphology of composite materials were characterized by X-ray diffraction(XRD) analysis and electronic scanning electron microscopy(SEM). The electrochemical and photoelectric properties of composites were detected by cyclic voltammetry(CV), transient photocurrent responses(i-t) and electrochemical impedance spectra(EIS) analysis taken on the electrochemical working station. The results show that the specific capacitance and the transient photocurrent reach the maximum of 35.10F/g and 1.186 × 10-5A/cm2 for graphene/ZnS with thiourea as sulfur source and ethylene glycol as solvent.(2) Composition-tunable ternary graphene/ZnxCd1-xS composites were synthesized by a one-step hydrothermal and solvothermal process using zinc acetate as zinc source and cadmium acetate as cadmium source, in which the ratio of Zn to Cd in the composites was controlled by adjusting the relative amounts of the starting materials. The crystalline structure and morphology of composites were characterized by XRD and SEM analysis. It can be seen that the XRD patterns of graphene/ZnxCd1-xS composites by hydrothermal method show hexagonal crystal structure, while those of graphene/ZnxCd1-xS composites by solvothermal method transform from a hexagonal structure to a cubic structure with the content of Zn increasing. The electrochemical and photoelectric properties of composites were detected by CV and i-t analysis taken on the electrochemical working station. The results show that the specific electrochemical capacitance and transient photocurrent values gradually increase with the increase of the Zn/Cd ratio. The specific capacitance and the transient photocurrent of graphene/Zn0.8 Cd0.2S reach the maximum of 84.71 F/g and 3.53×10-4A/cm2 by hydrothermal method, and those of graphene/Zn0.8Cd0.2S reach the maximum of 54.38 F/g and 5.20×10-5A/cm2 by solvothermal method.