The Controllable Constructure And Photocatalytic Properties Of SnIn₄S₈/Oxide Heterojunction

In order to promote green development and low-carbon transformation for constructing a community of life for man and nature,the developments of new green chemical production method and highly efficient and environmental water treatment technology have become the current research focus.Semiconductor photocatalytic technology powered by solar energy is an ideal technology to realize green chemical production and environmentally friendly water treatment.However,it is a major challenge to develop and design efficient,stable,cheap,wide spectrum response and safe semiconductor photocatalyst to achieve efficient conversion and utilization of solar energy.In recent years,ternary sulfide has been considered as an ideal candidate material for promoting the practical application of semiconductor photocatalytic technology,of which,SnIn₄S₈ has received more and more research due to its excellent photoelectric properties.The practical application of SnIn₄S₈ is severely restricted by its inherent defects of the rapid recombination of photogenerated charge and limited reports of SnIn₄S₈.Therefore,it is of great research value and practical significance to adopt practical and effective strategies to modify SnIn₄S₈ to improve its solar absorption and utilization performance.In this paper,different SnIn₄S₈-oxide heterojunction composites were constructed based on SnIn₄S₈ nanosheets,which showed excellent photocatalytic properties through the synergistic effect of structure and material.The structure,composition,interface contact and photoelectric properties of the composites were systematically characterized.The photocatalytic redox performance and practical application prospect of the composites were evaluated by photocatalytic degradation of pollutants,reduction of Cr（Ⅵ）and synthesis of H₂O₂.Finally,the mechanisms of the improved photocatalytic performance and electron transport in the photocatalytic reaction process were proposed.The main research contents were as follows:（1）A novel light driven double-shell SnIn₄S₈/TiO₂ heterostructure with close interface contact was constructed by covering with SnIn₄S₈ nanosheets onto the surfaces of TiO₂ hollow spheres through in-situ hydrothermal method.The double-shell SnIn₄S₈/TiO₂ heterostructure had excellent photocatalytic activity for MO degradation and Cr（Ⅵ）reduction,and the optimized SISTOHS2 has the best photocatalytic efficiency.The kinetic rates of MO removal and Cr（Ⅵ）clean-up of SISTOHS2 were 2.37 and 4.02 times than those of SnIn₄S₈,and 15.03 and 28.39times as high as those of TiO₂,respectively.The significant enhancement of photocatalytic activities was mainly due to the innovative synergistic effect of photocatalysis and double shell structure,which effectively solved the defects of low light utilization rate of single photocatalyst and rapid recombination of photoexcited carriers.Finally,the possible photocatalytic mechanism of MO removal and Cr（Ⅵ）clean-up over as-prepared samples were discussed.（2）Multifunctional core-shell SnIn₄S₈ nanosheets/CeO₂ nanorods heterojunction were successfully fabricated by in-situ hydrothermal growing method.The photocatalytic degradation of MO,production of H₂O₂ and reduction of Cr（Ⅵ）were used to evaluate its multifunctional and practical application prospects of the prepared materials.The results showed that the photocatalytic activities of the composites were significantly improved compared with the original SnIn₄S₈ nanosheets and CeO₂ nanorods,and the optimized COSIS2 showed the best photocatalytic activities.The kinetic rates of MO degradation,Cr（Ⅵ）reduction and H₂O₂production over COSIS2 were 2.5,3.1 and 7.2 times than those of SnIn₄S₈,and10.2,14.3 and40.0 times than those of CeO₂,respectively.The improved photocatalytic performance could be attributed to the construction of coaxial core-shell heterostructure to effectively improve the charge separation efficiency and photocatalytic activity.Meanwhile,the cyclic experiments of the three applications and XRD patterns before and after recycling runs over COSIS2 composite confirmed its good sustainability and recycling.Finally,based on the active species capture experiment,a direct Z-scheme mechanism was proposed to explain the photocatalytic reaction.（3）SnIn₄S₈ nanosheets/Bi₂MoO₆ nanospheres heterojunction composite was constructed by ultrasonic self-assembly coating method.The as-prepared composites had stronger visible light response ability and larger specific surface area than SnIn₄S₈and Bi₂MoO₆,which enhanced light absorption and increased reactive site.Moreover,the close contact heterostructure interface and built-in electric field greatly promoted the separation and migration of charges between semiconductors to improve the photocatalytic reaction.BMOSIS2 displayed the best performance of photocatalytic MO removal and H₂O₂ production,and the kinetic rate of photocatalytic MO removal and H₂O₂ production over BMOSIS2 were 2.03 and 5.97 times than those of SnIn₄S₈,and 10.40 and 28.35 times than those of Bi₂MoO₆,respectively.In addition,the photocatalytic performance of BMOSIS2 did not decrease significantly after four consecutive cycles,which confirmed its excellent stability.The possible photocatalytic reaction pathway of MO removal over BMOSIS2 was analyzed by mass spectrometry.Finally,a reasonable electron transport model was proposed to explain the photocatalytic reaction mechanism according to the results of the active species capture experiment.