Study On Design And Visible-light Photocatalytic Performance Of UiO-66 And ZIF-8 Based Heterostructures

As a potential environmentally friendly and low-cost method for dealing with environmental pollution and solving energy shortages,photocatalytic technology has attracted great attention.Many researchers are working to modify existing semiconductor photocatalysts or to develop new photocatalytic materials.Compared with traditional semiconductor photocatalysts,metal-organic framework compounds（MOFs）are a new type of porous materials formed by coordination of metal ions or metal cluster units with organic ligands.They have large specific surface area,adjustable pore size and variable structure.Easy to regulate and modify.Therefore,more and more MOFs materials are used in the fields of photocatalytic degradation,hydrogen production and CO₂ reduction.However,MOFs materials also have some shortcomings,such as poor thermal stability,can not absorb visible light,etc.,which limits the application of MOFs in the field of photocatalysis,it is necessary to modify it,inhibit its shortcomings,and make it have good visible light catalytic performance.In this paper,two kinds of MOFs materials with good water stability,UiO-66 and ZIF-8,were selected for modification,which combined with semiconductor materials to form a heterostructure and enhance the visible light catalytic performance.First,we synthesized UiO-66 by solvothermal method and removed the reactant molecules in the channels by solvent exchange.Heat treatment thereof increases the pore size of the UiO-66,making it easier for ions to enter its pores.Neutral acetylacetonate was used as the precursor,which was introduced into the pores of UiO-66 by vacuum adsorption,and converted intoα-Fe₂O₃ by calcination to constructα-Fe₂O₃@UiO-66 heterostructure.α-Fe₂O₃ is confined in the pores of UiO-66,effectively inhibiting the growth ofα-Fe₂O₃ particles.The limited-grownα-Fe₂O₃ nanoclusters will greatly reduce the probability of complex photogenerated electrons and holes.Compared with UiO-66,theα-Fe₂O₃@UiO-66 heterostructure exhibits a good visible light response,the ability of visible light to degrade methylene blue（MB）is significantly enhanced,and the photocurrent intensity is also significantly enhanced.The pollutants in the water are diverse,and not only the photocatalytic oxidation can be used to degrade organic pollutants,but also the photocatalytic reduction of heavy metal ions.In order to improve the diversity of photocatalytic reactions,we chose ZIF-8 with good water stability to modify and improve the photocatalytic performance.ZIF-8 was grown in situ on the surface of ZnO nanosheets to construct a ZIF-8@ZnO heterostructure.Heat treatment is used to remove some parts of ZIF-8,and self-defects are built to introduce visible light absorption.Compared with the pure phase ZnO,ZIF-8 and ZIF-8@ZnO heterostructures,the ZIF-8@ZnO heterostructure containing self-defects exhibits good visible light degradation of Cr（VI）and a significant increase in photoelectric conversion efficiency..In addition,we also optimized the ZIF-8 loading and defect amount to optimize the photocatalytic degradation efficiency and photoelectric conversion efficiency of the defect ZIF-8@ZnO heterostructure.Finally,in order to achieve CO₂ reduction by ZIF-8 under visible light irradiation,defects were formed by calcination at 350°C,and visible light absorption was introduced and the pore diameter thereof was enlarged.Then,the defective ZIF-8 is vulcanized to construct a defective ZnS@ZIF-8 heterostructure to enhance its photoreduction ability.Since ZnS is grown in situ in ZIF-8,it can form a stable transitional fusion interface,which facilitates the smooth migration of photogenerated carriers at its interface,thereby enhancing the synergistic effect and improving the photoreduction CO₂ performance.Compared to pure phase ZIF-8 and ZnS,the ZnS@ZIF-8 heterostructure has a higher visible light catalytic ability to reduce CO₂.