Photocatalytic Hydrogen Generation Properties Of Metal Sulfide/Graphene Composite Nanomaterials

Along with the increasing depletion of fossil fuels,the continuous growth of global energy demand and environmental pollution has become the biggest and most serious challenge that the human have to face.It is a strategic issue that to develop enviornmental friendly and new energy is associated with the sustainable development of the country and the basic life of people in order to deal with the energy crisis.To produce hydrogen by decomposing the water with semiconductor photocatalyst is one of the most attractive ways undoubtedly.Among the many photocatalytic materials,metal sulfide photocatalysts have attracted more and more attention because of their excellent photocatalytic performance and a lot of achievements in this field has also been made.This paper uses a series of simple method to synthesize a series of metal sulfide based photocatalysts with excellent photocatalytic performance and systematically studies the relationship of the crystal structure,morphology,cocatalyst,valence band structure and the catalytic performance.A kind of molecular self-assembly method was used to synthesize CdS/MoS₂/graphene hollow spheres in this paper.The molecular structure of cysteine is the key to control the morphology of composites.Due to the unique hollow sphere structure and the promoting ability of charge separation,CdS/5 wt%MoS₂/2 wt% graphene hollow spheres exhibit superior hydrogen production under light conditions.The synergistic effect of graphene and molybdenum disulfide was studied by fluorescence spectrum,electrochemical impedance spectroscopy and the Mott-Schottky measurement.On this basis,in order to adjust the valence band structure of the catalyst and reduce the amount of toxic metal Cd,the non-toxic metal Zn was used to replace partial Cd.Cd1-xZnxS/MoS₂ graphene hollow spheres were prepared by the same self-assembly method.Cd0.8Zn0.2S/MoS₂/graphene shows excellent photocatalytic hydrogen production performance,which is 63 times of Cd0.8Zn0.2S and also higherthan Cd/MoS₂ graphene and Cd0.8Zn0.2S/Pt respectively 2 and 3.8 times.At the same time,the reasons of improving the performance of the catalyst were further explored,and it was found that the abundantly defective molybdenum disulfide as cocatalyst promoted the separation of electron and hole.Finally,the Cu₂ZnSnS₄（CZTS）system was explored in order to further reduce the amount of toxic metal Cd ions,and we chose Cu,Zn,Sn metal ions to synthesize a solid solution of metal sulfide which has suitable valence band structure.The microstructure of the CZTS nano crystal with a diameter of about20-30 nm in diameter has been synthesized by thermal injection method.Then weused high temperature liquid phase method to compound CZTS,MoS₂ and graphene.The crystal phase and valence elements were characterized by XRD and XPS and the final test was the photocatalytic properties under visible light.