Preparation And Properties Of Graphene Quantum Dots/Doped Semiconductor Composites

Microcrystalline graphite is a kind of graphite mineral and formed by nondirectional alignment of graphite crystallites with a crystal diameter of less than 1?m.Its natural defect of "long-range order,short-range disorder" has greatly limited the application range of this graphite mineral.Graphene has many advantages such as large specific surface area,good electrical conductivity and stable properties.Graphene quantum dots(GQDs)can be obtained by reducing the size of graphene to below 100 nm.GQDs not only have many advantages of graphene,but also have adjustable bandgap.Therefore,processing microcrystalline graphite into graphene and GQDs can not only effectively remedy the disadvantage of small crystal size,but also improve the application range of microcrystalline graphite by the excellent properties of graphene and GQDs.Zinc sulphide(ZnS)is a direct bandgap semiconductor.The photoelectric performance of ZnS semiconductor can be enhanced through aluminum doping.The photogenerated electrons conduction of Al doped ZnS semiconductor particles can be accelerated by the combination of GQDs and Al doped ZnS semiconductors due to the high carrier mobility of GQDs.Meanwhile,the combination of GQDs and Al doped ZnS semiconductor particles can also prevent the aggregation of the semiconductor particles.In this paper,graphene and GQDs were prepared by using microcrystalline graphite as raw material.GQDs/Al doped ZnS semiconductor(Al-ZnS/GQDs)composites with different GQDs mass fractions were prepared.The electrochemical properties of graphene and GQDs and the photoelectric properties of Al-ZnS/GQDs were explored.The research contents the following three parts:(1)The graphene was prepared by the redox process.The test results showed that after thermal reduction,the oxygen containing functional groups between the microcrystalline graphite oxide sheets were removed and graphene was successfully prepared.Meanwhile,the graphene obtained by thermal reduction at 250 °C has the largest specific capacitance value and the smallest interfacial charge transfer resistance.(2)GQDs were prepared by hydrothermal cutting.The GQDs were concentrated between 20-35 nm and the height of GQDs was about 0.5-2 nm.The prepared GQDs still maintained good graphene structure.In addition,the GQDs have better reversible specific capacitance performance and higher charge carrier conduction efficiency than graphene.(3)A series of Al-ZnS/GQDs composites with different GQDs mass fractions were prepared by solvothermal method.The photoelectric properties of doped semiconductors were significantly improved by compounding with GQDs.Meanwhile,the photocurrent of Al-ZnS/GQDs composites first improved with the increasing GQDs content,reaching a maximum at the GQDs content of 1.2 wt%,and declined with the further increasing of GQD content.The photocurrent density value of Al-ZnS/GQDs is about 700% and 200% of pure ZnS and Al-ZnS,respectively.