3D NiFe₂O₄@ZnFe₂O₄ Z-scheme Hollow Spheres Photoelectrocatalytic Materials For H₂O₂ Production And In : Situ Repair Of Arsenic Pollution

The energy crisis is an important issue restricting the development of the world economy,and converting energy-rich,clean and renewable solar energy into chemical energy is an important technology to ensure the sustained and stable energy supply.Hydrogen peroxide has the advantages of easy storage,high energy density,green and pollution-free products,and is a promising energy carrier.On the other hand,theFenton reaction,which relies on hydrogen peroxide,also shows great potential for the treatment of water pollution,and the strong oxidizing active free radicals produced by hydrogen peroxide decomposition can effectively oxidize and degrade pollutants in water.Therefore,as an important green chemical,hydrogen peroxide has important application value in energy supply and pollutant treatment.However,the anthraquinone process for the industrial production of hydrogen peroxide is expensive,and the use of organic solvents poses serious environmental problems.The photoelectrocatalytic（PEC）process requires only sunlight and a low electrical energy input,is an environmentally friendly and inexpensive H₂O₂ production process.However,due to the low efficiency of catalyst light utilization and charge transmission,there is still a big gap between the current H₂O₂ output of photocatalytic systems and the output of industrial production,which limits the practical application of H₂O₂ in photoelectric systems.Therefore,in view of the above problems,we designed a 3D NiFe₂O₄@ZnFe₂O₄ Z-scheme hollow spheres photoelectrocatalytic material,the suitable energy band position and wide visible light response range make it can be used as photoelectrocathode to achieve high H₂O₂ yield,and by using theFe sheet anode,the in situFenton photoelectrocatalytical system is constructed,the H₂O₂ product is applied to the water pollution treatment,and the high toxicity As（III）can be convert to the low toxicity As（V）and degradation of organic arsenic contaminants（roxoarone）can be decomeposed.The research content of this article is as follows:（1）3D NiFe₂O₄ hollow spheres were synthesized by a hydrothermal methed,ZnFe₂O₄ nanoparticles uniformly modified to the surface of 3D NiFe₂O₄ hollow spheres,then 3D NiFe₂O₄@ZnFe₂O₄ Z-scheme hollow spheres photoelectrocatalytic material was constructed.Material properties are characterized by SEM,transient photocurrent,electrochemical AC impedance spectroscopy,PL spectroscopy,etc.The results show that the formation of heterojunction improves the electron and hole separation efficiency of the material,and reasonable band matching of the material effectively enhances the ability of H₂O₂ production.The design of hollow structure gives the material a larger specific surface area and more catalytically active sites,the visible light utilization efficiency can be improved by reflecting and scattering visible light multiple times.The 3D NiFe₂O₄@ZnFe₂O₄ Z-scheme hollow spheres photoelectrocatalytic material is used as a photocathode for H₂O₂ production,under visible light irradiation and-0.7V（vs.Ag/Ag Cl）external bias,the H₂O₂ yield of540m M·gcat-1·h-1 is obtained,and the Faraday efficiency can reach 75%.The results of free radical capture and rotating disc electrode tests show that the production of H₂O₂is dominated by ORR process,and there are both direct and indirect ORR processes to produce H₂O₂.Finally,through the results of free radical capture and the analysis of XPS electron flow direction,it was proved that the Z-type electron transport pathway of the material,the electrons were transferred from the NiFe₂O₄ conduction band to the ZnFe₂O₄ valence band,which reduced the carrier recombination and enabled the electron to accumulate in the conduction band of ZnFe₂O₄,thus promoting the catalytic process of ORR production of H₂O₂.Our work clarifies the mechanism of 3D NiFe₂O₄@ZnFe₂O₄ Z-scheme hollow spheres photocatalytic H₂O₂ production,which provides a theoretical basis for the design of efficient inorganic semiconductor photocathodes.（2）Based on the excellent production performance of 3D NiFe₂O₄@ZnFe₂O₄ Z-scheme hollow spheres photoelectrocatalytic materials,an in situFenton photoelectrocatalytic system withFe sheet as anode was constructed for the treatment of inorganic arsenic and organic arsenic pollutants in water.Under this photoelectrocatalytic system,more than 95%of As（III）can be converted to As（V）within 45 minutes,and nearly 100%degradation rate of roxoarone can be achieved within 2 hours.After the reaction is completed,theFe³⁺produced by theFenton reaction can form iron hydroxides in situ by adjusting p H,more than 90%of arsenic in the water can be removed by using its flocculation effect.By comparing with the Pt anode,it is clear that withFe sheet as the anode can improve the effect of pollutant treatment.The results of the capture experiment showed that good transformation or degradation effects depended on the synergy of·OH,?O₂^-and h⁺,where·OH plays a leading role.A large number of·OH is derived from theFenton reaction between H₂O₂produced by the cathode ORR andFe²⁺produced by anodic electrolysis,the strong oxidation of·OH can realize the conversion of As（III）to As（V）and the degradation of roxoarone.The in situFenton photoelectrocatalytic system designed in this paper innovatively combines H₂O₂ production withFenton advanced oxidation technology,without the addition of H₂O₂ andFe²⁺,only relying on sunlight and low electrical energy input can achieve sustainable arsenic pollution treatment,the in situ generation of iron flocculants in the system realizes the complete removal of arsenic.The work provides new strategies for innovative photoelectrocatalytic system design and green,efficient and sustainable arsenic pollution remediation.