Insight into the degradation of Orange G by persulfate activated with biochar modified by iron and manganese oxides: Synergism between Fe and Mn

Abstract In this study, sludge-derived biochar (SDBC) loaded with metal oxides was successfully synthesized via a simple impregnation method, including monometallic-based SDBC (Fe, F-SDBC; Mn, M-SDBC) and bimetallic-based SDBC (Fe and Mn, FM-SDBC). Results demonstrated that FM-SDBC possessed higher activation capacity than F/M-SDBC. The degradation of Orange G (OG) under different pH were explored. Leaching of metal ions and cycling test showed that FM-SDBC possess extraordinary stability and reusability during repeated activation of persulfate (PS). It was evidenced by quenching studies that both SO4·－ and ·OH were generated in FM-SDBC/PS. The XPS spectra of Fe 2p and Mn 2p before and after reactions indicated that the activation of PS on FM-SDBC was in company with the redox cycling of Fe and Mn species. Through the kinetics study, the contribution of Mn occupied the dominant position at the beginning, and Fe did in subsequent activation process in FM-SDBC/PS system. Synergistic mechanism between Fe and Mn in FM-SDBC could be attributed to (1) mutual electron transfer between Fe and Mn; (2) the formation of Fe-Mn bonds, which facilitated electron transfer between Fe and Mn to some extent. Based on the synergistic mechanism aforementioned, bimetallic-based biochar, especially FM-SDBC prepared in this study, had the benefits of high efficiency, stability, reusability and waste control by waste, which provided new insights into sulfate radical (SO4·－)-based advanced oxidation processes in practical application.