Preparation And Photocatalytic Performance Of M-Fe₂O₄/ZnO_1-x（M=Mg,Ni） Heterojunctions

In recent years,wastewater containing estrogen-17αethoestradiol（EE2）has adverse effects on the endocrine system of humans and other living organisms,which seriously endangers human health and ecosystem.Presently,the technology which using traditional preparation is not only cannot effectively remove 17αethinylestradiol（EE2）,but also cause harm to the environment seriously.In this case,the ways of photocatalytic degradation have energy saving,high efficiency and green environmental protection,it becomes one of the most promising methods.The results show that the main factors effecting the efficiency of photocatalyst are the visible light absorption capacity and carrier recombination rate.The construction of heterojunction can not only effectively separate the electron-hole pairs in the system,but also improve the utilization rate of solar energy.Secondly,it has been found that surface oxygen vacancy,as a typical crystal defect and electron capture site,can not only improve visible light absorption by reducing the semiconductor band gap,inhibit the recombination of carriers in the crystal,but also improve the level of charge transfer to the defect,so as to achieve the purpose of improving the photocatalytic degradation efficiency.In this paper,we studied the MgFe₂O₄/ZnO_1-x heterojunction’s related properties and NiFe₂O₄/ZnO_1-x heterojunction’s related properties,and compared the photocatalytic activity,analyzed the reasons for the different degradation efficiency,explored the photocatalytic degradation mechanism and the repeatability and recyclability of the catalyst.The specific research contents are as follows:（1）Preparation、optical and degradation properties of MgFe₂O₄/ZnO_1-x heterojunction catalysts.The flower-like ZnO_1-x with oxygen vacancy defect was prepared by water bath and high temperature reduction method.We synthesized ZnO_1-xwith MgFe₂O₄ by co-precipitation method,and obtained that MgFe₂O₄ was uniformly distributed on the surface of ZnO_1-x by SEM and TEM characterization methods.The photocatalytic degradation results showed that the degradation rate of MgFe₂O₄/ZnO_1-x to estradiol17α（EE2）was 96%within 60 min,which was 76%and 83%higher than that of pure ZnO_1-x and MgFe₂O₄ materials.Through the characterization and analysis of the optical and electrical properties of the materials,it is concluded that the enhancement of the photocatalytic activity of MgFe₂O₄/ZnO_1-xmay be due to the formation of heterojunction and the presence of oxygen vacancies（OVs）.ZnO_1-x formed a heterojunction composite material with magnetic material MgFe₂O₄,which can be magnetically separated,and the recyclability and recycling performance of the photocatalyst have been greatly improved,reducing the secondary pollution to the environment.（2）In order to explore the photocatalytic mechanism of prepared heterojunction materials detailly,we used the same method to prepare the flower-like NiFe₂O₄/ZnO_1-xheterojunction catalyst with the same structure as MgFe₂O₄/ZnO_1-x.By controlling the mass ratio of ZnO_1-x to NiFe₂O₄ and further changing the area of heterojunction,the optimum ratio of heterojunction photocatalyst was prepared.The results of photocatalytic degradation experiments showed that the photocatalytic activity was the best when the mass fraction of ZnO_1-x was 60%among all the NiFe₂O₄/ZnO_1-xheterojunction samples.The final degradation rate of estrogen-17αethoestradiol（EE2）within 60 min was 98.9%,which was 78.9%and 83.7%higher than that of pure ZnO_1-xand NiFe₂O₄ materials,respectively.In addition,The degradation rate of the composite can still reach 97%after repeated use for five times.