In Situ Embedding Of BiFeO₃ Into G-C₃N₄ For The Construction Of OVs Active-site Fenton-like Catalysts

The mechanism of traditional heterogeneous Fenton catalysts activating H₂O₂through transition valence changes of surface transition metals has been demonstrated to have drawbacks of low catalytic activity and active metal leaching in practical applications.So that,the construction of non-metallic active site heterogeneous Fenton catalysts is expected to address this mechanistic deficiency.This study integrated basic theories such as double reaction center theory,cation-πtheory,and conditions for producing surface oxygen vacancies（OVs）to address this mechanical defect.The heterogeneous Fenton catalyst BiFeO₃@g-C₃N₄（BFO/CN）with OVs as active sites was prepared by mixed calcination using urea and pre-prepared BiFeO₃as precursors.The catalytic performance,conformational relationships between structure and performance,and potential for practical applications have been systematically investigated.Results as follows:（1）Calcination causes the in situ embedding of BiFeO₃into the g-C₃N₄skeleton and increases the concentration of its oxygen vacancies（OVs）.Fe-N bonds link BiFeO₃and g-C₃N₄in BFO/CN,and Fe-πinteractions induce the formation of OVs active sites on the BiFeO3 side and electron-poor triazine carbon（N-C=N）sites on the g-C₃N₄side,this indicates the successful preparation of Fenton-like catalytic materials with OVs active sites.（2）BFO/CN exhibits high catalytic activity at high pH（pH=11）as the electron-rich OVs site is unaffected by surface hydroxyl complexation.When the BFO/CN dosage was 0.8 g/L and the H₂O₂concentration was 10 m M,the Rh B（20mg/L）removal rate was up to 92%within 5 min and the TOC removal rate was up to43%within 60 min of the initial reaction.The remaining experiments show that BFO/CN can be adapted to a wide range of pollutant concentrations（20-100 mg/L）and that the reaction is less influenced by conventional inorganic anions,with pollutant removal rates above 90%and TOC removal rates above 31%for all six cycles,and only trace amounts of Fe and Bi leaching in each cycle.At the same time,BFO/CN can be used for the catalytic degradation of different types of dyestuffs（Rh B,MB,AO7）and antibiotic（tetracycline）organic pollutants.The above results show that BFO/CN has excellent Fenton-like performance.（3）In terms of the reaction mechanism,H₂O₂is electrophilically adsorbed to the electron-rich OVs site and reduced to-OH,thus gradually mineralising the contaminant;the contaminant is nucleophilically adsorbed to the electron-poor triazine carbon,whose electrons are trapped and transferred to the BiFeO₃side OVs via Fe-N bond bridges to maintain the surface charge balance.Surface Fe is not the main active site,but forms Fe-N bonds as a connecting bridge between organic（g-C₃N₄）and inorganic（BiFeO₃）in BFO/CN.（4）The simulated wastewater treated by the BFO/CN type Fenton system resulted in BOD5 and COD removal rates of 84%and 92%respectively,with the BOD₅/COD value increasing from 0.228 to 0.463,indicating that the Fenton-like catalytic material has strong potential for practical application.