Degradation of methyl orange using persulfate activated by magnetic CuS/Fe3O4 catalyst: Catalytic performance and mechanisms

Abstract

While magnetic Fe3O4 provides Fe2+ to activate persulfate (PS) to produce sulfate radicals (SO4·-), Fe2+ tends to be oxidized to Fe3+, declining the activation efficiency. The low-valent sulfur in transition metal sulfide could convert Fe3+ to Fe2+ due to its strong reducibility, and CuS was used as the activator of PS. However, its separation and recovery posed great challenges to practical application. Magnetic CuS/Fe3O4 was prepared with a purpose to simultaneously convert Fe3+ to Fe2+ and rapidly separate CuS as a catalyst for the degradation of methyl orange (MO) by activating PS. The results showed that CuS/Fe3O4 exhibited higher activity than sole CuS or Fe3O4 as 94 % of MO was removed within 30 min. SO4·-, hydroxyl radical (·OH), superoxide radical (·O2–) and singlet oxygen (1O2) were detected in the CuS/Fe3O4/PS system and ·OH was the dominant active species. S2- and Sn2- provided electrons for the cycle of Fe3+/Fe2+ and Cu2+/Cu+, resulting in excellent catalytic activity of CuS/Fe3O4. The NC bond cleavage, the breakage of NN bond and the loss of SO2 bond were identified as three possible degradation pathways of MO. This work provided an effective strategy to enhance the catalytic activity and recovery of the catalyst, and improved the understanding of MO degradation mechanisms.