Study On The Construction Of ZnIn₂S₄-based Composite Photocatalysts And Its Photocatalytic Decemposition Of Water For Hydrogen Evolution

With the exhaustion of fossil energy,the energy crisis is becoming increasingly serious and the environmental problems caused by it are becoming increasingly prominent,which greatly hinders the sustainable development of the society.The development of new energy is extremely urgent.In recent years,the photocatalytic technology of energy conversion using solar energy has been developed rapidly,which provides a new way to solve the energy crisis.Photocatalytic decomposition of water for hydrogen evolution is widely regarded as a promising strategy to solve the energy problem.ZnIn₂S₄is widely used in photocatalytic hydrogen evolution reactions due to unique and excellent photoelectric chemical stability,narrow bandgap（2.0-2.6 e V）and decomposed water-matched energy level positions.Based on the above analysis,in this paper,pure ZnIn₂S₄,which possessed low toxicity and narrow bandgap with visible light response,was taken as the research object.In view of the shortcomings of ZnIn₂S₄,it existed the slow migration of photogenerated carrier and rapid recombination.We introduced surface vacancies,cocatalyst and a modified metal-organic framework to construct the heterostructure photocatalysts.The efficient separation of electron-hole pair was achieved,and the recombination of electron and hole was inhibited,thereby improving the photocatalytic activity of the composite photocatalysts.In addition,the mechanism of electron transfer at heterogeneous interface was further studied,which provided new insight for designing and synthesizing novel and highly-efficient ZnIn₂S₄-based composite photocatalyst.The results of the study were as follows:（1）The ZnIn₂S₄/MoS₂ nanosheets coupled with S-doped NH₂-UiO-66nanoparticles were successfully synthesized in sulfur-rich precursor solution by a simple two-step solvothermal method.Among them,S-doped NH₂-UiO-66acted as an electronic bridge,which promoted the migration of electrons from ZnIn₂S₄to MoS₂,realized the effective separation of photogenerated carriers,and improved the efficiency of photocatalytic hydrogen evolution.In this work,the ratio of MoS₂in the entire system was optimized,and finally reached photocatalytic hydrogen evolution rate of 5.69 mmol·h^-1·g^-1under visible light.In this system,XPS also revealed the presence of S atom doping in the NH₂-UiO-66 component of ZnIn₂S₄/NH₂-UiO-66/MoS₂ternary composites.Raman spectroscopy confirmed that transition metals（Zn,Mo）assist S in NH₂-UiO-66 was doped instead of carbonized.By means of FT-IR and XPS characterization for the ZnIn₂S₄/NH₂-UiO-66/MoS₂composite materials,we found that ZnIn₂S₄and NH₂-UiO-66 formed of Zn-O-C covalent bond at the interface.The photochemical results showed that the special charge transport channel promoted the migration of electrons from ZnIn₂S₄to NH₂-UiO-66,and realized the high photocatalytic efficiency.（2）Ni-MOF sheet material mediated by polyvinylpyrrolidone（PVP）was successfully prepared with solvothermal method,and then a novel core-shell structured Ni-P@C co-catalyst was obtained by derivation of Ni-MOF as a precursor at high temperature calcination and phosphating.The prepared visible light-driven Ni-P@C coupled with sulfur-vacancy（Vs）ZnIn₂S₄,the Ni-P@C/Vs-ZnIn₂S₄composite photocatalysts were successfully prepared.A composite catalyst was constructed by introducing Ni-P@C into ZnIn₂S₄by ultrasound,and the highest hydrogen evolution efficiency of the system reached11.06 mmol·h^-1·g^-1.Studies have shown that the metal-like characteristics core-shell Ni-P@C cocatalyst greatly promoted the separation of charge carriers in the composite system.This greatly promoted the transfer of electrons captured in the defect region of ZnIn₂S₄to Ni-P@C,thereby enhancing the photocatalytic activity.