Synthesis And Hydrogen Production Performance Research Of MOF-derived Sulfide Photocatalysts

Photocatalytic water splitting to obtain solar fuels are attractive strategies to address the environmental crises and energy shortage issues.Metal chalcogenides have been extensively studied due to their excellent luminescence properties and photochemical properties.Among them,ZnS and CdS have become the hotspots of research as a typical semiconductor material.However,the wide band gap of ZnS and the severe photoetching of CdS limit its photocatalytic activity.In recent years,the construction of composites with metal-organic framework（MOF）precursors has been paid close attention for application of versatile functionalities.Such materials usually have controlled morphology,higher surface area and porosity.Many methods have been developed and applied to improve photocatalytic performance,such as heterojunction.This paper is a catalyst for the preparation of heterostructure using MOF as a precursor.The main contents are as follows:（1）A visible light-driven porous ZnS/rGO/CuS heterojunction photocatalyst was synthesized by simple hydrothermal and cation exchange methods using a zeolitic imidazolate framework（ZIF-8）as the template.The composition,morphology and electrochemistry of the samples are characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and electrochemical impedance spectroscopy（EIS）.These results showed that ZnS/rGO/CuS nanocomposites were obtained,and the ZnS/CuS nanoparticles were evenly distributed on the rGO surface.Due to the ZIF-8 templated high porous microstructure and/or the high carrier conductivity of the graphene（rGO）,the ZnS/rGO/CuS heterojunction exhibited high photocatalytic H₂-production activity under visible light irradiation.The significant enhancement in photoactivity can be ascribed to be the porous morphology of ZnS nanoparticles in the nanocomposites and the introduction of graphene and CuS which reinforced the absorptivity of the photocatalysts,suppressed the electron-hole pairs recombination,and extended the light absorption range in the as-synthesized ZnS/rGO/CuS nanocomposite photocatalyst.（2）Complex uniform ternary heavy metal-free CuZnIn₂S₄/rGO/g-C₃N₄ heterojunction photocatalyst were fabricated using the in-situ formed MOF heterostructure as template,and coupled with the g-C₃N₄,and the conductive rGO inserted into the heterostructure as charge carrier mediator for the first time.The composition,morphology and electrochemistry of the samples are characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and electrochemical impedance spectroscopy（EIS）.These results showed that the CuZnIn₂S₄/rGO/g-C₃N₄ heterojunction was obtained,and CuZnIn₂S₄,g-C₃N₄ and rGO were evenly distributed.Due to the MOFs templated high porous microstructure,and the high carrier conductivity of the rGO,CuZnIn₂S₄ and CuZnIn₂S₄/rGO/g-C₃N₄ heterojunctions exhibited an excellent photocatalytic H₂-production activity under visible-light irradiation.（3）The CdS/PVP/NiO heterojunction photocatalyst was prepared by a simple hydrothermal method using Ni-MOF as a template and PVP-modified CdS.The composition,morphology and electrochemistry of the samples are characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and electrochemical impedance spectroscopy（EIS）.These results showed that the reaction resulted in a CdS/PVP/NiO heterojunction photocatalyst,and the CdS nanoparticles were uniformly distributed on NiO.The introduction of NiO solved the problem of rapid recombination of electron-hole pairs in CdS,and increased the specific surface area of the catalyst and improved the photocatalytic activity.