Metal sulfides enhance Fe(II)/Fe(III) redox cycling to promote catalytic Ozonation: Efficient utilization of superoxide radicals

Iron oxides are widely utilized in catalytic ozonation, but their effectiveness is often limited by the slow Fe(II)/Fe(III) redox cycle. In this study, a series of metal sulfide–iron oxide composites were synthesized, all of which exhibited enhanced catalytic performance, with MoS 2 @Fe 3 O 4 showing outstanding efficiency. The catalytic system decomposes ozone (O 3 ) into hydroxyl radicals (·OH) and singlet oxygen ( 1 O 2 ), with ·OH predominantly contributing to the oxidation process. The catalytic process was significantly enhanced through three key pathways: (i) metal sulfides themselves demonstrate superior ozonation catalytic performance compared to iron oxides; (ii) the presence of Mo(IV) effectively promotes the Fe(II)/Fe(III) redox cycle; and (iii) the transient superoxide radical (·O 2 − ), a crucial intermediate in ozone chain decomposition, rapidly reduces high-valence Mo(VI) to Mo(IV), thereby reinforcing the Mo redox cycle, further strengthening the Fe redox cycle, and leading to the accumulation of 1 O 2 . Notably, the efficient utilization of ·O 2 − represents a unique mechanism in the catalytic ozonation system. These findings emphasize the critical role of the Mo redox cycle in enhancing Fe redox activity to promote catalytic ozonation, providing valuable insights for the development of advanced metal sulfide–iron oxide catalysts for environmental applications.