Controllable Preparation And Visible Light Photocatalytic Properties Of Janus-like ZnFe₂O₄/ZnO Heterojunction Hollow Nanofibers

The industrialization rapid developmenthas provid people a better living environment and also bring great pollution problems.The problem of water pollution is particularly serious.Therefore,the management of water pollution is imminent.Photocatalytic technology has attracted much attention in the treatment of water pollution because of its low cost,high efficiency,thorough treatment,and no secondary pollution to the environment.Zinc ferrite?ZnFe₂O₄?is a narrow-bandgap semiconductor with a spinel structure with a band gap width of about 1.9 eV.It has good visible light absorption,good light stability and magnetically separable properties.Many of the above advantages make ZnFe₂O₄ a new type of visible light photocatalyst with very good development prospects.However,there are still some problems with ZnFe₂O₄:First,the powder structure of ZnFe₂O₄ is extremely easy to agglomerate,resulting in exposed active sites,thereby reducing its photocatalytic activity.Second,the band gap of ZnFe₂O₄ is narrow,and the generated photogenerated electrons and holes are easily recombined,resulting in a relatively low quantum yield.In view of the above problems,it can be considered to make ZnFe₂O₄ into a one-dimensional nanofiber structure by electrospinning technology.This structure not only has a large specific surface area,but also reduces agglomeration and exposes more active sites.Then ZnFe₂O₄ is combined with zinc oxide?ZnO?to construct a ZnFe₂O₄/ZnO heterojunction,which promotes the separation of photogenerated electrons and holes,thereby improving the photocatalytic activity of the material.The specific research contents are as follows:?1?Preparation of hollow nanofiber ZnFe₂O₄/ZnO mixed heterojunction by electrospinning technique.Fe?NO₃?₃ and Zn?NO₃?₂ were mixed and added to a polymer-containing organic solvent in a molar ratio of1:1.After stirring,the nanofibers were obtained by electrospinning,and the ZnFe₂O₄/ZnO mixed heterojunction was finally obtained by calcination.The photocatalytic experiment on the degradation of methylene blue?MB?under visible light showed that the ZnFe₂O₄/ZnO mixed heterojunction showed higher photocatalytic activity than the pure ZnFe₂O₄ nanofiber.Its photocatalytic degradation rate constant is eight times that of ZnFe₂O₄ nanofibers.This result indicates that the heterojunction plays an important role in promoting the separation of electrons and holes and improving the photocatalytic activity.?2?Fe?NO₃?₃/Zn?NO₃?₂/PVP nanofiber prepared by electrospinning technology as a hard template,ZnO is deposited on the surface of Fe?NO₃?₃/Zn?NO₃?₂/PVP nanofiber by atomic layer deposition technology.After calcination,a one-dimensional hollow nanofiber structure of ZnFe₂O₄/ZnO Janus-like heterojunction photocatalyst is obtained.The photocatalytic results show that the ZnFe₂O₄/ZnO Janus-like heterojunction exhibits higher photocatalytic activity than that of the ZnFe₂O₄/ZnO mix heterojunction and pure ZnFe₂O₄ nanofibers.The photocatalytic degradation rate constant of ZnFe₂O₄/ZnO Janus-like heterojunction is two times that of the ZnFe₂O₄/ZnO mix heterojunction and seventeen times that of pure ZnFe₂O₄ nanofibers.It is indicated that the ZnFe₂O₄/ZnO Janus-like heterojunction is superior in promoting the separation of electrons and holes and improving the photocatalytic activity.In order to further prove the role of the heterojunction in improving photocatalytic activity,an Al₂O₃ barrier layer was add between ZnFe₂O₄ and ZnO to obtain a ZnFe₂O₄/Al₂O₃/ZnO composite nanofibers..Compared with the ZnFe₂O₄/ZnO Janus-like heterojunction,the photocatalytic activity of ZnFe₂O₄/Al₂O₃/ZnO composites for MB degradation is greatly reduced,which is almost consistent with pure ZnFe₂O₄.The ZnFe₂O₄/ZnO Janus-like heterojunction photocatalyst can be separated and recovered under the action of an external magnetic field.The photocatalytic cycle experimental test results show that the photocatalyst has good cycle stability.The ZnFe₂O₄/ZnO Janus-like heterojunction photocatalyst can be separated and recovered under the action of an external magnetic field.The photocatalytic cycle experimental test results show that the photocatalyst has good cycle stability.Finally,the results of the reaction mechanism in the photocatalytic process show that the four active substances play different roles in the photocatalytic process.The active substance which plays a major role is a hydroxyl radical??OH?.