Construction of magnetically separable S-scheme BiFeO3/Cl-g-C3N4 heterostructure photocatalyst for simultaneous removal of Cr(Ⅵ) and tetracycline in aqueous solution: Performance and mechanism insight

A green, efficient and recyclable magnetic BiFeO₃/Cl-g-C₃N₄ photocatalyst was prepared for the simultaneous removal of Cr(Ⅵ) and tetracycline (TC) from water by wet chemical and thermal synthesis methods. Experimental results revealed that BiFeO₃/Cl-g-C₃N₄ achieved a removal efficiency of 96.1 % for Cr(Ⅵ) and 98.2 % for TC under visible light irradiation for 50 min at pH 6. The results of the work function, charge density difference, UV–vis DRS, PL, PC and EIS tests indicate the formation of S-scheme heterojunctions between BiFeO₃ and Cl-g-C₃N₄, which exhibits superior carrier separation and migration efficiency. The evidence for interfacial charge transfer from BiFeO₃ to Cl-g-C₃N₄ within BiFeO₃/Cl-g-C₃N₄ was further corroborated by means of ISIXPS, EPR and KPFM. Moreover, calculations of the density of states demonstrate that the introduction of Cl enhances the reduction capability of BiFeO₃/Cl-g-C₃N₄. Results from ESR tests and trapping experiments has demonstrated that the singlet oxygen (¹O₂) and electrons are the primary active species. Furthermore, the high removal rates of TC and Cr(VI) from industrial wastewater and groundwater, coupled with the lower ecotoxicity of TC degradation intermediates, indicate that BiFeO₃/Cl-g-C₃N₄ has the potential for practical applications. After five cycles, the BiFeO₃/Cl-g-C₃N₄ still removed 90.5 % of TC and 96 % of Cr(Ⅵ).