Preparation And Photocatalytic Water Splitting Performances Of ZnIn₂S₄ Nanosheet And Their Composites

Solar-driven water splitting is a sustainable and clean method to produce renewable hydrogen,and it is one of the effective strategies to achieve the goal of emission peak and carbon neutrality.ZnIn₂S₄ nanosheets with layered structure are considered as a visible light response catalyst with the potential of photocatalytic overall water splitting due to their high activity and appropriate band gap.However,at present,the application of ZnIn₂S₄-based catalyst in photocatalytic water splitting mainly focuses on photocatalytic hydrogen production performance in the sacrificial agent system.In addition,the rapid recombination of photogenerated electrons and holes,and self photocorrosion caused by the oxidation of of surface sulfur atoms limit its practical application in photocatalytic overall water splitting.Therefore,in this paper,ZnIn₂S₄ nanosheets are modified by constructing heterojunction and surface defect engineering,and ZnIn₂S₄/oxide heterojunction,element doped ZnIn₂S₄ and ZnIn₂S₄/carbide composites are prepared.In addition,through characterization test and performance analysis,the acting mechanism of heterostructure and element doping in improving the photogenerated carrier separation efficiency of the catalyst was clarified,and the promotion effect of photothermal effect on the photocatalytic overall water splitting was deeply explored.HZIS/BTHS heterojunction catalyst with O,S-dual defects is prepared by low-temperature hydrogenation strategy.The amount of oxygen and sulfur defects can be controlled by adjusting the hydrogenation temperature.The hollow sphere structure can not only improve the utilization of sunlight through refracting incident light,but also serve as a substrate for the vertical growth of ZnIn₂S₄ nanosheets,which can make ZnIn₂S₄ expose more surface and edge active sites.The synergistic effect of O,S-dual defects provides more active sites for photocatalytic reaction,and improves the separation efficiency of photogenerated electrons and holes.Moreover,heterostructure can also accelerate the transmission of photogenerated carriers.Therefore,HZIS/BTHS heterojunction catalyst shows excellent photocatalytic hydrogen evolution performance(5.5 mmol·h^-1·g^-1)with lactic acid as sacrificial agent.Ultrathin ZnIn₂S₄ nanosheets with disordered structures（SRDZIS）are sythesized by one-step solvothermal method.Disordered structures can not only induce electrostatic potential difference to accelerate the separation efficiency of photogenerated carriers,but also increase the layer spacing of nanosheets,which can make ZnIn₂S₄ has larger specific surface area,surface active sites and surface carrier density.In addition,the charge redistribution caused by disordered structures result in the enrichment of positive charges surrounding Zn sites,and makes them become the active sites of O₂ evolution by enhancing the adsorption of hydroxide radical,and lowering the oxidation barriers of H₂O molecules.Therefore,the water oxidation process of SRDZIS nanosheets can compete with its own photocorrosion,result in SRDZIS nanosheets can achieve efficient and stable photocatalytic overall water splitting performance.ZIS nanosheet with Al doping（Al-ZIS）can be further prepared by adding aluminum n-butoxide into reaction solution.The introduction of Al atoms can further improve the separation efficiency of photogenerated electrons and holes,and thus can further improve the photocatalytic overall water splitting activity(H₂:77.2μmol·h^-1·g^-1;O₂:35.3μmol·h^-1·g^-1).WC/C composites are synthesized by one-step high temperature calcination.The phase state,size,particle spacing of WC nanoparticles,and carbon content can be controlled by adjusting the weight ratio of ammonium metatungstate to dicyanodiamine.The photothermal mechanism of WC/C is explored,and the WC/C with the best photothermal performance is determined through first-principles calculation and Finite Difference Time Domain Simulation simulation.The results show that WC/C has the best photothermal performance when the weight ratio of ammonium metatungstate to dicyandiamine is 3.0.On this basis,ZIS/WC/C composies are further prepared by solvothermal method.The results show that WC with localized surface plasmon resonance effect can produce a large number of hot electrons excited by light,and the hot electrons immediately recombine with the photogenerated holes in the ZnIn₂S₄ valence band.The thermal effect of WC/C can also act as a"heat island"to increase the surface temperature of catalyst and reaction system,and then increase the carrier mobility,and low reduction reaction barrier of catalyst,thus the photocatalytic pure water splitting perfoemance can be further improve,and the hydrogen evolution rate is up to 230μmol·h^-1·g^-1.In summary,heterojunction construction and element doping strategy can not only effectively enhance the utilization of sunlight of ZnIn₂S₄ nanosheets,but also increase the carrier density on the surface of material,and promote the separation and transmission of photogenerated carriers,so as to realize photocatalytic overall water splitting without cocatalysts and sacrificial agent under visible light irradiation.This thesis provides reliable scientific basis for the further design and synthesis of efficient photocatalytic overall water splitting photocatalyst.