Preparation Of Iron Oxide-Modified BiVO₄ Photocatalyst And The Degradation Of Sulfadiazine In Water

Sulfadiazine（SD）is one of the most commonly used sulfonamide drugs for treating human and livestock infections.The discharge of SD wastewater from various industries worldwide has largely caused water environmental pollution,posing great harm to human health and ecological safety.Bismuth vanadate（BiVO₄）,as a solar driven photocatalyst,is non-toxic and corrosion resistant.However,its low electron mobility and high free carrier recombination rate limit its application in the degradation of persistent organic compounds in water.Several widely used iron oxides have suitable bandgaps,and their modification of BiVO₄has broad prospects in the field of photocatalysis.Therefore,this study used iron oxide to modify BiVO₄through heterostructure construction,introducing Ag nanoparticles with surface plasmon resonance effect and high abundance and activity Cu element respectively,to prepare two types of iron oxide/BiVO₄based photocatalysts.SD was used as the target pollutant,and the physicochemical properties and degradation performance of the composite photocatalyst were explored through a series of characterization and experiments.At the same time,a photocatalytic flexible composite membrane coated with PVDF was prepared,and the properties of the membrane were thoroughly studied and explored.The main research content and conclusions of the paper are as follows:（1）A 2D Ag-γ-Fe₂O₃/BiVO₄with oxygen vacancies was designed,and the results of steady-state fluorescence and phosphorescence spectroscopy demonstrated that it could generate ¹O₂mainly through exciton-based energy transfer.The construction of Z-type heterojunction significantly improved the performance of the prepared photocatalyst.The introduction of Ag played an electronic mediating role in Z-type heterojunctions,not only increasing the free charge carriers in the system but also promoting the generation of singlet excitons.The presence of oxygen vacancies at appropriate concentrations in Ag-γ-Fe₂O₃/BiVO₄further promoted the generation of¹O₂.Ag-γ-Fe₂O₃/BiVO₄could degrade 99.4%of SD within 90 minutes.Electron paramagnetic resonance（EPR）spectroscopy and active species capture experiments indicated that h⁺and ¹O₂played a major role in the degradation of SD.Ecological toxicity prediction indicated that the main by-product of Ag-γ-Fe₂O₃/BiVO₄degradation of SD had low toxicity.The prepared photocatalysts provide new research ideas for the development of efficient and highly selective photocatalysts.（2）CuO/α-Fe₂O₃/BiVO₄with double heterojunction was prepared.The construction of a Z-type heterojunction between BiVO₄andα-Fe₂O₃promoted the generation of free carriers,and the close contact between CuO andα-Fe₂O₃created a p-n junction.This further improved the separation efficiency of photogenerated carriers and increased the concentration of free carriers in the photocatalytic system,exhibiting strong photocatalytic degradation ability for SD.The results of active species capture experiments and EPR testing demonstrated that·O₂^-and h⁺were the main active species in the photocatalytic degradation of SD.At the same time,Fe/Cu participated in the Fenton like reaction and produced·OH,which also contributed to the degradation of SD.CuO/α-Fe₂O₃/BiVO₄had good stability and could degrade98.59%of SD within 20 minutes,and almost completely degraded other organic pollutants.（3）The PVDF/CBF composite photocatalytic membrane was prepared by loading CuO/α-Fe₂O₃/BiVO₄（CBF）onto the PVDF membrane through phase invasion method,achieving the immobilization of CBF.PVDF/CBF could remove89.18%of SD in static water within 60 minutes,and 92.96%of SD in flowing water within 180 minutes.It could also maintain a high degradation rate in actual water.The introduction of CBF brought more abundant hydrophilic groups to the surface of the composite membrane,changing the inherent hydrophobic characteristics of PVDF.Meanwhile,PVDF/CBF had excellent physical/chemical pollutant removal ability and low energy consumption,providing a high-efficiency,low energy consumption,and green solution for the practical application of photocatalysis.