Preparation And Activity Study Of Immobilized Z-scheme-heterojunction ZnO/ZnCo₂O₄-Co₃O₄|Co Photocatalyst Composite Film

In recent years,the problems of energy crisis and environmental pollution have become increasingly serious.Therefore,the development of renewable energy and efficient environmental governance technology are necessary.Thereinto,the photocatalytic technology has attracted extensive concern of researchers due to its characteristics of low cost,clean and no pollution.At present,many semiconductor materials are used to conduct photocatalytic reactions,but there are still problems such as low utilization of sunlight and easy recombination of photon-generated carriers.In order to achieve photocatalytic degradation and hydrogen production more effectively,some researchers have tried to combine two or more semiconductor materials with matching band gap to form a composite photocatalytic system.This not only broadens the response range of sunlight,but also makes the photocatalytic system show stronger redox ability.On the one hand,hydrogen can be generated more effectively on the conduction band.On the other hand,some substances with strong reductive ability,such as organic pollutants in wastewater,can be effectively oxidized into water,carbon dioxide and some inorganic ions on the valence band.This not only alleviates the problem of energy crisis,but also solves the problem of environmental pollution to some extent.In this paper,an immobilized Z-scheme-heterojunction ZnO/ZnCo₂O₄-Co₃O₄|Co photocatalyst composite film was constructed by using spin-coating method and incomplete solid-state chemical reaction method.After the photocatalytic reaction,the cobalt foil is directly recycled,which can be used for large-scale production and application in the future.In the photocatalyst system,cobalt foil is used as the carrier of the photocatalyst to realize the immobilization of the photocatalyst.In addition,cobalt foil is also a cathode.Under the irradiation of sunlight,the electrons on the CB of Co₃O₄ and Zn Co₂O₄ can be easily transferred to the other side surface of the cobalt foil,so the degradation reaction of organic pollutants and hydrogen production reaction can be realized on both sides of the cobalt foil,respectively.Consequently,the H₂ and CO₂ can be collected separately on both sides of the photocatalyst composite film without further separation and purification.The XRD,SEM,TEM,XPS,PL,EIS and other characterization techniques were used to study the structural composition,microstructure,forming process and photoelectric properties of the photocatalyst composite film.Besides,the effects of important conditions such as coating Zn（OH）₂layer number,cobalt foil thickness,calcination temperature and calcination time on photocatalyst degradation with simultaneous hydrogen production were investigated.Under the condition of different preparation,the photocatalytic activity of ZnO/ZnCo₂O₄-Co₃O₄|Co photocatalyst composite film is different.For the obtained photocatalyst composite film with the best photocatalytic activity,after simulated sunlight irradiation 180 min,the degradation ratio of norfloxacin and hydrogen production amount reach 80.70%and 357.12μmol/dm²,respectively.Moreover,the four-cycle experiments of degradation and hydrogen production show that the immobilized Z-scheme ZnO/ZnCo₂O₄-Co₃O₄|Co photocatalyst composite film gives good stability,which is easy to recycle and reuse.The existence of active substances is verified in the photocatalytic degradation process.Finally,a mechanism of norfloxacin degradation with synchronous hydrogen production caused by immobilized Z-scheme-Type II-heterojunction ZnO/ZnCo₂O₄-Co₃O₄|Co photocatalyst composite film is proposed.It is hoped that this study has certain guiding significance for designing an immobilized photocatalyst film for the large-scale photocatalytic degradation of organic pollutants with simultaneous hydrogen production.