Preparation And Photocatalytic Properties Of P-BiOX?X=Cl,Br?/n-ZnFe₂O₄ Composite Nanofibers

In recent years,as people's needs for life and the improvement of life quality,environmental pollution has become more and more serious.Water pollution is an important part of environmental pollution,and it is also one of the major issues before us.So it is imminent to treat water pollution.Among many methods of controlling water pollution,semiconductor photocatalytic technology has attracted much attention due to its low cost,high efficiency and no secondary pollution to environment.Zinc ferrite?ZnFe₂O₄?is an n-type semiconductor with a narrow band gap of 1.9 eV and a spinel crystallographic structure.It is a new visible light photocatalyst because its prominent visible light absorption properties,excellent photochemical stabilities and magnetic separation properties.But the following problems still exist in the nanostructured ZnFe₂O₄:Firstly,ZnFe₂O₄ powders are easy to reunite,resulting in significant reduction of the active sites.This may affect the photocatalytic performances.Secondly,the photo-generated electron-hole pairs are easy to recombine because of its narrow band gap,leading to the sharp decreasing of the separation efficiency.To solve the above problems,we prepared one-dimensional Zn Fe₂O₄ nanofibers via electrospinning technology to reduce agglomeration.And then p-BiOX?X=Cl,Br?nanosheets were evenly assembled on the electrospun ZnFe₂O₄ nanofibers by the solvothermal method using the n-ZnFe₂O₄ nanofibers as hard templates to obtain p-n heterojunctions which can improve the separation efficiency of photo-generated electron-hole pairs.The obtained one-dimensional p-BiOX?X=Cl,Br?/n-ZnFe₂O₄ composite nanofiber photocatalyst by the two-step experiment can greatly improve photocatalytic activities.The specific research contents are as follows:?1?One-dimensional p-BiOX?X=Cl,Br?/n-ZnFe₂O₄ composite nanofiber photocatalyst was successfully prepared by using the electrospun n-ZnFe₂O₄ nanofibers as templates via solvothermal method.Then,p-BiOX?X=Cl,Br?nanosheets could be controlled to grow on ZnFe₂O₄ nanofibers by adjusting the precursor solution concentration of p-BiOX?X=Cl,Br?in the solvothermal process.Thus,the different p-BiOX?X=Cl,Br?/n-ZnFe₂O₄ heterojunction photocatalysts were constructed.The results of morphology and structure show that BiOX?X=Cl,Br?nanosheets with different density can be uniformly loaded on ZnFe₂O₄nanofibers.And there may be surface interaction between BiOX?X=Cl,Br?and ZnFe₂O₄molecules in the heterojunction.?2?p-BiOX?X=Cl,Br?/n-ZnFe₂O₄ heterojunction photocatalyst exhibits better photocatalytic activity than pure BiOCl powders,ZnFe₂O₄ nanofibers and their mechanical mixing for the degradation of Rhodamine B?RhB?under visible light irradiation.This result indicates that the existence of heterojunctions can effectively increase the separation efficiency of photo-generated electrons and holes.The larger specific surface area of photocatalysts is beneficial to the full contact with dye molecules during photocatalysis.Moreover,the different heterojunctions also show different photocatalytic properties,indicating that the surface morphology,the number of heterojunctions,the specific surface area and the light absorption all will affect the photocatalytic performances.In addition,compared with these two parts,p-BiOBr/n-ZnFe2O4 photocatalyst has better photocatalytic activity,which may be closely related to the optical absorption properties of the material.BiOBr has stronger visible light absorption capacity,but BiOCl can only be stimulated by ultraviolet light.?3?In the practical application of photocatalysts,p-BiOX?X=Cl,Br?/n-ZnFe2O4heterojunction photocatalyst can be efficiently separated from liquid phase solution under the action of external magnetic field because of the ferromagnetic behavior of the ZnFe2O4nanofibers.Furthermore,the results of the cyclic experiments show that the p-BiOX?X=Cl,Br?/n-ZnFe2O4 heterojunction photocatalysts exhibit good cycling stability.Therefore,it is easy to separate and recycle from the liquid phase solution.In addition,the possible photocatalytic mechanism is also discussed in detail.The results show that four active groups play a certain role in the photocatalytic reaction process,of which holes?h⁺?play the most important role.