Structural Design And Photocatalytic Activities Of Multicomponent Metal Sulfide ZnIn₂S₄

Abstract:The interest of converting solar energy into hydrogen（H₂）through direct photocatalytic water splitting arises from its potential application in solving two critical global issues of fossil energy shortage and environmental pollution.In recent years,researchers have explored various photocatalytic materials in the field of photocatalytic H₂ evolution.Among existing photocatalysts,metal sulfides have been extensively studied due to their excellent solar spectral response and high photocatalytic activity.This thesis mainly studies the ternary metal sulfide ZnIn₂S₄（ZIS）to understand and solve the problems of sulfide-based photocatalysts:How to effectively suppress the recombination of photo-generated carriers under visible light and how to improve the separation and migration efficiency of photo-generated carriers,and finally achieve efficient photocatalytic H₂ evolution efficiency.The research content of this thesis mainly includes:1.Six groups of pristine phase hexagonal ZIS were prepared under different hydrothermal conditions.The experimental results showed that ZIS-6 prepared under hydrothermal conditions of 200°C/24 h had excellent crystallinity,good surface morphology,potential light absorption performance,and could effectively respond to visible light.Moreover,ZIS-6 had higher photocatalytic activity and stability than other five samples because the fully crystallized petal-like nanosheets on the surface of ZIS-6 could efficiently transport photogenerated carriers and reduce the corrosion of photogenerated holes.2.Pristine ZIS was first prepared by hydrothermal method,and the hydrogenated ZIS photocatalyst（H-ZIS）was obtained under high temperature and high hydrogen pressure treatmented.Hydrogenation could produce a large number of defects on the H-ZIS surface,and the presence of defects could enhance the absorption of visible light by H-ZIS.It was found that the surface defects were S vacancies,and the S vacancies under the visible light could capture the photogenerated electrons generated by H-ZIS,promoted the separation and migration process of photogenerated carriers,effectively inhibited the photogenerated electron-hole recombination.Finally,H-ZIS showed excellent photocatalytic activity,and the H₂ evolution rate was as high as 1.9mmol h^-1 g^-1,which was about 8.6 times that of pristine ZIS.3.A series of WO₃ nanoparticle（WNp）with different weight ratios loaded on the surface of ZIS composite photocatalysts were successfully prepared by hydrothermal method.The loaded WNp significantly enhanced the photocatalytic H₂ evolution ability of ZIS under visible light irradiation.Through a series of experiments and characterizations,the enhanced photocatalytic mechanism was explored.It was found that WNp could not only improve the separation efficiency of ZIS photogenerated carriers,but also prolong the lifetime of photogenerated electrons.The W5-ZIS composite photocatalyst with a final loading of 5 wt%WNp exhibited the best photocatalytic activity,proving the Z-scheme charge transfer mechanism with synergistic effect between WNp and ZIS.