Preparation And Application Of A 3D Flower-shaped Z-scheme Heterojunction Photoelectrocatalyst Zn₃In₂S₆@a-Fe₂O₃

The shortage of energy and the pollution of environmental water are becoming more and more serious,which have become the hot issues to be solved all over the world.Therefore,we urgently need to seek suitable new energy generation and water purification technology.The photoelectrocatalytic hydrogen peroxide production and water treatment technology based on semiconductor heterojunction is an effective method to solve the current global energy problems and environmental crisis.The key of this technique is to construct a novel,highly efficient and visible light responsive semiconductor heterojunction photoelectrocatalyst.A three-dimensional layered Z-scheme Zn₃In₂S₆@α-Fe₂O₃heterojunction photoelectrocatalyst has been constructed in this paper.We tested the ability of the photoelectrocatalyst in which used to produce hydrogen peroxide.Meanwhile,the water purification ability was explored with tetracycline and Cr（Ⅵ）as the pollutants.1.In this paper,a new 3D hierarchical flower-like Zn₃In₂S₆@α-Fe₂O₃heterostructure photocatalyst was constructed and which is characterized by XRD,SEM,TEM,XPS,DRS,Mott-Schottky and other means.The results show that Zn₃In₂S₆has a typical three-dimensional micro-flower-like structure,which is composed of two-dimensional Zn₃In₂S₆nanosheets stacked.In this flower-like Zn₃In₂S₆,α-Fe₂O₃can be uniformly loaded on its surface as proppant,forming a uniform,stable and efficient Z-scheme heterojunction structure.The formation of this n-n type Z-scheme heterojunction structure can accelerate the separation and transfer of photogenerated carriers,effectively reduce the recombination of electron hole pairs,increase the specific surface area of the microstructure,increase the reactive active site of the material,and significantly expand the absorption range of the material to visible light.At the same time,due to the superior photoelectric properties and narrow band gap of metal sulfide,the accelerated absorption of molecular oxygen is conducive to the efficient photocatalytic reaction.In this paper,the stability of the catalyst was proved by 7.5h photocurrent test,and the stability of the material was proved by comparing the XRD,XPS and SEM before and after the reaction.2.The photocatalyst of Zn₃In₂S₆@α-Fe₂O₃heterojunction was used for hydrogen peroxide generation,tetracycline oxidation and Cr（Ⅵ）reduction.（i）H₂O₂production:The experiments showed that 5%Zn₃In₂S₆@α-Fe₂O₃exhibited the best hydrogen peroxide production capacity compared to pure Zn₃In₂S₆andα-Fe₂O₃and different proportions of heterojunctions.It was found that 1.028mmol L^-1hydrogen peroxide could be produced in a perchloric acid acidified potassium perchlorate solution with p H=3,under the sealing condition of 180min by applying-0.7 V voltage and continuously pumping oxygen.The superoxide radical（·O₂^-）is the main active substance of the reaction,and the reaction mechanism is confirmed by free radical capture experiments.By comparing the efficiency of photoelectric catalysis,photocatalytic catalysis and electrocatalytic hydrogen peroxide production,it is proved that the material has the synergistic effect of light and electricity in the photoelectric catalysis system,which can enhance the efficiency of hydrogen peroxide reaction and accelerate the reaction process.（ii）Catalytic oxidation of tetracycline hydrochloride:The experimental results show that the catalytic performance of 5%Zn₃In₂S₆@α-Fe₂O₃composite material is the best compared with the original Zn₃In₂S₆,originalα-Fe₂O₃and the composite materials with different proportions when the loading amount ofα-Fe₂O₃is 5%.When the p H=8,the degradation efficiency of tetracycline can reach 86.7%in 120minutes.By free radicals to capture the reaction activity of free radicals is verified by the experiments for the super oxygen free radical（·O₂^-）and holes（h⁺）and small amounts of hydroxyl radical（·OH）,through exploring the semiconductor bandgap and valence band location and the relationship between the activity of free radicals,determine the reaction mechanism of this reaction,its efficiency is due to the n-n type Z-scheme heterojunction formed by Zn₃In₂S₆andα-Fe₂O₃.（iii）Reduction of Cr（Ⅵ）:The experimental results show that the best reaction condition is determined by comparing the catalytic performance of different proportions of Zn₃In₂S₆@α-Fe₂O₃with the original Zn₃In₂S₆and the originalα-Fe₂O₃as well as the study of reaction conditions such as p H,that is,the photoelectric catalytic experiment in sodium sulfate system with p H=3.In this system,the reduction efficiency of Cr（Ⅵ）can be increased by 78.1%.Combined with the results of free radical capture and Mott-Schottky,it is proved that the composite Zn₃In₂S₆@α-Fe₂O₃forms a Z-scheme n-n heterojunction,which promotes the photocatalytic effect,and also explores the synergistic effect of photocatalytic effect,that is,the photocatalytic effect is greater than the addition of photocatalytic and electrocatalytic efficiency.It is hoped that the method of H₂O₂production by using Zn₃In₂S₆@α-Fe₂O₃could be applied to replace traditional fossil fuels to solve the energy problem,and at the same time,the removal of pollutant substance in the environmental water could be realized,so as to achieve the purpose of repairing and improving the water environment.