Rational Design Of SnS₂-based Heterostructures With Superior Photocatalytic Performance

Researchers have pay attention to semiconductor photocatalysis technology to realize the conversion and utilization of energy by using the photoelectric and other characteristics of semiconductor materials since the last century.After years of development,semiconductor photocatalysis technology have huge application prospects in producing high-efficiency clean energy(H₂,CH₄,CH₃OH,etc.),degrading pollutants and reducing inorganic pollutants(including heavy metal ions,etc.).SnS₂ is used in photocatalytic materials fields that have received extensive attention due to its narrow band gap(about 2.2 e V),low toxicity and good stability.However,the photo-generated carrier recombination of SnS₂ is severe,which greatly limits its photocatalytic activity.In this paper,we formulated different strategies including adjusting the morphology of SnS₂,constructing heterojunction with different semiconductor materials,and metal ion doping to improve its photocatalytic activity.The main research contents and conclusions are as follows:(1)SnO₂/SnS₂ heterojunction composite materials were prepared by solvothermal method and material heat treatment,and the ratio of SnS₂ to SnO₂ was changed through different heat treatments.The material composition and microscopic morphology were characterized that the surface of the as-prepared SnS₂ structure is uniformly covered by SnO₂ nanoparticles.This heterojunction has a large interface contact area and tight interface bonding,which is conducive to carrier transfer and improves the efficiency of electron-hole separation.The photocatalytic activity of SnO₂/SnS₂ composite material is 16.2 times that of SnS₂ by the photocatalytic reduction experiment of Cr(VI).Most importantly,the adsorption performance test of different dye molecules shows that the existence of SnO₂ is not only beneficial to the photocatalytic performance but also greatly increases the adsorption capacity of the material to Cr(VI).Combined with the analysis of XRD,PL and photoelectrochemical test results,it is considered caused by the defects on the surface of SnO₂ and the built-in electric field of the SnO₂/SnS₂ heterojunction.Finally,the PL photoluminescence spectrum,I-t transient photocurrent test and electrochemical impedance spectra(EIS)test results show that the SnO₂/SnS₂ heterojunction can effectively improve the separation of photogenerated carriers and restrain the recombination of photogenerated carriers which improve its photocatalytic activity.(2)WO₃/SnS₂ heterojunction composites were prepared on the basis of sheet SnS₂(obtained by changing sulfur sources in precursor solution).The structural composition,microscopic morphology,optical properties and photocatalytic activity of the material were characterized.The results show that the WO₃/SnS₂ composite material not only has a higher specific surface area,but also has a good separation and transport of photogenerated carriers.The degradation test of methylene blue and the reduction of potassium dichromate test show that the WO₃/SnS₂ composite has a Z-Scheme heterojunction structure,and its photocatalytic performance is significantly improved compared to SnS₂ and WO₃.Under simulated sunlight,the WO₃/SnS₂ composite material degrades MB at a rate of 3.4 times and 2.5 times that of SnS₂and WO₃;the WO₃/SnS₂composite material reduces Cr(VI)at a rate of 3.4 times and 35.0 times that of SnS₂and WO₃.Times.The as-prepared WO₃/SnS₂ composite material has stronger photocatalytic activity and is expected to be widely used in water treatment and other fields.(3)Mo-SnS₂ composites were prepared by adding a small amount of sodium molybdate into the precursor solution of SnS₂.Scanning Electron Microscopy and EDS element analysis show that the SnS₂ material has a bulk structure.The Mo element is beneficial to increase the dispersion performance of SnS₂,leading the particles on the block more obvious.In addition,Mo element can significantly improve the SnS₂ material light absorption performance.The photocatalytic performance test and photo-electrochemical test results showed the doping of a certain amount of Mo element can effectively reduce the charge transfer resistance of SnS₂,enhance transient photocurrent response density,improve the separation and transfer efficiency of photo-generated carriers and the photocatalytic activity of the material.From the potassium dichromate reduction test under visible light,it can be seen that the Mo-SnS₂-1 sample(3%Mo)reduces Cr(VI)at the fastest rate,which is about 3.7 times that of SnS₂.