Preparation And Photocatalytic Performance Of Doping ZnIn₂S₄/g-C₃N₄ Heterostructure

Energy crisis,water pollution and environmental degradation gradually attract people’s attention to the environment in modern society.Colored impurities are the main cause of water pollution in industrial wastewater,which seriously endanger aquatic organisms and human health.The colored impurities include synthetic organic pollutants that are difficult to degrade.Such as methylene blue,methyl orange and antibiotics.Therefore,we need to develop an environmentally friendly,low-cost and effective organic degradation technology to remove pollutants.Photocatalytic technology not only reduces the harm of pollutants to the environment,but also realizes the purification of the environment.Photocatalytic technology makes the best use of resources.It is undoubtedly the best choice to deal with organic pollution.In semiconductor nanomaterials,indium zinc tetrasulfide（ZnIn₂S₄）is widely used as a ternary sulfide with low toxicity and appropriate band gap.Graphite phase carbon nitride（g-C₃N₄）is selected because of its band gap matching ZnIn₂S₄ and easy preparation.However,pure ZnIn₂S₄and g-C₃N₄ usually have some disadvantages,such as rapid carrier recombination,poor charge transfer ability,insufficient visible light absorption and so on.These limitations lead to relatively short carrier lifetime,low quantum yield and low solar energy conversion efficiency.Based on the synthesis of heterostructure,metal and non-metal doping are used to improve the photocatalytic activity,in order to synthesize efficient photocatalysts.B doped ZnIn₂S₄/g-C₃N₄,Mo,N doped and（Mo,N）codoped ZnIn₂S₄/g-C₃N₄ composites are prepared by sol-gel method and solid-state method.Their photocatalytic properties are studied,such as optical,photoelectrochemical and charge transfer mechanisms.B doped g-C₃N₄/ZnIn₂S₄ can expand the optical absorption range and reduce the energy band width.The optical study shows that B doped g-C₃N₄/ZnIn₂S₄can make the two substances in close contact and shorten the charge transfer path.The photoelectric results indicate that the photocurrent intensity of B doped g-C₃N₄/ZnIn₂S₄ increases.It has relatively small electrochemical impedance and inhibits the recombination of carriers.After irradiating methylene blue solution with 500 W xenon lamp for 120 min,the degradation efficiency of 5%B doped g-C₃N₄/ZnIn₂S₄ nanocomposite is as high as 90%,which is 14%higher than that of B doped g-C₃N₄.The prepared Mo,N（co）doped ZnIn₂S₄/g-C₃N₄ nanosheets show that heterostructure and co doping can significantly prolong the light absorption edge and have a large number of active sites.In addition,electrochemical station test and photoluminescence spectroscopy show that（Mo,N）codoped ZnIn₂S₄/g-C₃N₄ greatly improve the separation and transfer of photoinduced electron hole pairs.（Mo,N）codoped ZnIn₂S₄/g-C₃N₄ nanosheets form a Z-scheme charge transfer mechanism.Under the strong synergistic effect of the internal electric field of the heterostructure and（Mo,N）codoping,the optimized（0.35%Mo,2.4%N）codoped ZnIn₂S₄/g-C₃N₄ Z-scheme heterostructure has excellent photocatalytic activity and photocatalytic stability for the degradation of methylene blue.After 120 min of illumination,the degradation rate reaches 97%,which is 1.3 and 2.6 times higher than that of ZnIn₂S₄/g-C₃N₄ heterostructure and pure ZnIn₂S₄,respectively.The synergistic strategy of codoping and Z-scheme charge transfer provides a simple and easy way to improve photocatalytic activity.The design of two-dimensional nanosheets promotes the research progress of photcatalysts for pollutant degradation.