Heterogeneous activation of persulfate by Ag doped BiFeO₃ composites for tetracycline degradation

Persulfate (PS) activation have been extensively considered as a promising technology for removing recalcitrant pollutants, due to their production of radicals with superior oxidation reactivity. However, a catalyst with high reactive and convenient recovery for PS activation still remains to be developed. In this work, the silver-doped bismuth ferrite (Ag_x-BiFeO₃, x = 0.1, 0.2, 0.3 and 0.4) catalysts with variable Ag content were synthesized via a facile sol-gel method and applied as heterogeneous catalyst in PS activation for tetracycline (TC) degradation. Ag_0.4-BiFeO₃ presented the best catalytic activity compared with other Ag doped BiFeO₃ composites, 91% TC could be efficiently removed within 60 min under optimized conditions and the reaction rate constant was 0.0338 min^-1. On the basis of the characterization analysis and catalytic test results, Ag could be the effective active site in PS activation and had a significant effect on PS activation. Moreover, the initial pH has negligible effect on the catalytic performance, indicating that Ag_0.4-BiFeO₃/PS system could work in a wide pH range. The results of electron spin-resonance spectroscopy and radical quenching tests suggested that both SO₄^- and OH radicals were involved in the Ag_0.4-BiFeO₃/PS system. The possible mechanism of Ag_0.4-BiFeO₃ activating PS and the major degradation pathway of TC degradation were proposed. At last, the reusability experiment results proved that Ag_0.4-BiFeO₃ catalyst still has a high catalytic performance after 4 times used.