Preparation Of ZnFe₂O₄/Bi Based Composite Photocatalytic Materials And Their Water Treatment Properties Study

Photocatalysis technology is an effective way to solve the problem of environmental pollution.Bi based photocatalytic materials have attracted attention due to their unique layered structure,excellent photochemical properties and good stability.However,the single Bi based materials have some problems such as limited visible light response range,easy recombination of photogenerated carriers,and difficult recovery of powder materials,which inhibit their photocatalytic degradation efficiency.The construction of magnetic heterojunction materials can improve the light absorption capacity of Bi based materials,and improve the migration and separation efficiency of photogenerated carriers.In addition,the composite material is also endowed with magnetic properties,which is conducive to efficient recycling,and has important significance for the modification of Bi based materials.Based on the unique photoelectric and magnetic properties of ZnFe₂O₄,Bi based materials were modified from the two starting points of heterojunction construction and magnetization,and were applied to the purification of azo dye wastewater,antibiotic wastewater and wastewater containing heavy metals.The main research contents are as follows:（1）Spinel ferrite ZnFe₂O₄was prepared by“soft template”method with bismuth oxyhalide Bi OBr and oxysalts of bismuth Bi₂WO₆as matrix,respectively.Two kinds of magnetic ZnFe₂O₄/Bi OBr（ZFB）and ZnFe₂O₄/Bi₂WO₆（ZBW）composite photocatalytic materials were prepared by two steps solvothermic and solvothermic hydrothermal methods.The introduction of ZnFe₂O₄induced the growth of nanosheet structure on the surface of Bi OBr microspheres,and the nanosheet structure on the surface of Bi OBr microspheres gradually evolved into a three-dimensional flower-like layered structure,and the specific surface area increased from 12.28 m²/g to 15.78 m²/g.The flaky structure on the surface of Bi₂WO₆evolved into orderly stacked sheets,and the specific surface area increased from 26.02 m²/g to 29.74 m²/g.Compared with monomer Bi OBr and Bi₂WO₆,the band gap of ZFB and ZBW decreases,the visible light response range widths and the light response intensity increases,and the photogenerated carrier migration and separation efficiency are significantly improved.（2）The two magnetic heterostructural materials showed excellent degradation performance and cycle stability in water treatment pollutants.The degradation efficiency of ZFB on Rhodamine B（Rh B）wastewater,norfloxacin（NOR）and sulfadiazine（SDZ）wastewater reached 99.04%,91.70%and 66.85%,respectively,within 60 min,which continued to prolong the degradation time of SDZ.The degradation efficiency of SDZ by ZFB reached 86.64%within 120 min.In addition,the retention rate of Rh B,NOR and SDZ for five cycles under the magnetic recovery of ZFB reached over 92%.The degradation efficiency of ZBW for Rh B wastewater and Cr（Ⅵ）containing heavy metal reached 99.41%and 77.47%respectively within 60 min.The degradation time of Cr（Ⅵ）was continued to extend.The reduction efficiency of ZBW for Cr（Ⅵ）reached 96.93%within 120 min.The performance retention rate of Rh B degradation and Cr（Ⅵ）reduction by ZBW reached more than 93%.（3）Capture experiments and ESR studies confirmed that the excellent catalytic performance of ZFB was due to the construction of magnetic heterojunction containing oxygen vacancy,and the strong oxidation of active species holes（h⁺）and superoxide radical（·O₂^-）under the synergistic effect effectively promoted the degradation of organic pollutants.The excellent oxidation and reducibility of ZBW were attributed to the migration and separation of space charge.In the degradation Rh B system,the active species were superoxide radical（·O₂^-）and hydroxyl radical（·OH）.In the reduced Cr（Ⅵ）system,the active species were superoxide radical（·O₂^-）and electron（e^-）.Under the synergistic action of the three active species,the photocatalytic degradation ability of the catalyst was effectively improved.