Preparation Of ZnIn₂S₄-Based Heterostructure And Their Photocatalytic Performance

Photocatalyts,as an important potential method for clean energy production and environmental pollution treatment by utilizing solar energy directly,has received much attention in recent years.In order to efficiently utilize the sunlight,it is necessary to develop novel visible-light-driven photocatalysts.ZnIn₂S₄,as a typical ternary sulfur compound,exhibits absorption ability in the visible-light range.However,the performance of pure ZnIn₂S₄ is still far from the application requirement due to serious charge carriers recombination.In order to solve these issues,constructing a heterojunction and loading cocatalyst are common and effective method that have been employed.In this paper,the unique ZnIn₂S₄ 2D nanosheets was chose.The specific research was as follows:（1）Constructing ZnIn₂S₄/SnS₂ 3D heterojunction is an effective method to enhance the catalytic activity of pure ZnIn₂S₄.The 3D heterostructure can effectively promote charge transfer and suppress recombination of photogenerated electrons and holes,leading to the enhanced photocatalytic reduction of aqueous Cr（VI）.The ZnIn₂S₄/SnS₂ 3D heterojunction was successfully prepared by a simple hydrothermal method.All the as-prepared ZnIn₂S₄/SnS₂ heterojunction exhibite higher photocatalytic activity compared with pure ZnIn₂S₄ and SnS₂.When the mass ratio of SnS₂to ZnIn₂S₄ is 1:10,the ZnIn₂S₄/SnS₂ heterojunction exhibits the highest photocatalytic activity with 100%efficiency for Cr（VI）（50 mg/L）reduction within 70 min under visible light irradiation.The improved photocatalytic performance is attributed to the effective charge transfer across the heterojunction interface,as evidenced by the steady-state photoluminescence spectroscopy.In addition,no obvious decrease of activity for the catalyst is observed after three cycles of testing,indicating its excellent photostability.（2）Single Ni atoms anchored on the ZnIn₂S₄ nanosheets with rich sulfur vacancies were successfully synthesized.The single-atom co-catalyst can realize maximum atom efficiency and significantly boost electron-hole separation efficiency of ZnIn₂S₄nanosheets,generating a greatly enhanced photocatalytic hydrogen evolution performance.The ZnIn₂S₄nanosheets with rich sulfur vacancies（denoted as ZnIn₂S₄-RV_s）was successfully prepared by the solvothermal method.Then we realized the decoration of isolated Ni atoms onto the surface of ZnIn₂S₄ nanosheets by an electrostatic adsorption method.The 0.9%Ni/ZnIn₂S₄-RV_sexhibits an excellent H₂ generation rate of 1786.9μmol/g/h under the visible light,which is as nearly 2.3 times and 5.7 times higher than those of ZnIn₂S₄ -RV_sand ZnIn₂S₄-PV_s（ZnIn₂S₄ with poor sulfur vacancies）,respectively.The charge carriers separation and transfer are significantly enhanced by the synergistic effect of sulfur vacancies and single-atom Ni,which are the reason of the enhanced hydrogen evolution performance.In addition,in situ electron spin resonance spectroscopy（ESR）detect the valance states change of single Ni atoms during photocatalytic reaction process from+2 to zero,and then to+2,directly confirming as an electron trapping center for protons reduction.