Effects of foreign metal doping on the step-by-step oxidation process in M-OMS-2 catalyzed activation of PMS

Various metal cations M (M = Mg²⁺, Ca²⁺, Zn²⁺, Cu²⁺, Fe³⁺) were doped into the tunnel of manganese octahedral molecular sieve (OMS-2). Redox-inactive metal (Ca, Mg and Zn) doped OMS-2 exhibited better peroxymonosulfate (PMS) catalytic activity than redox metal-doped Cu-OMS-2 and Fe-OMS-2. Redox-inactive metals doping improves the conductivity and reducibility of the catalyst, while transition metal doping reduces the dispersion of manganese. More importantly, the degradation of ACE can be divided into two stages. In the first stage, ACE was oxidized dominantly through mediated electron transfer process. Subsequently, singlet oxygen (¹O₂) gradually dominated oxidative degradation in the second stage, which was derived from the reaction between superoxide radical (O₂^•-) and metastable manganese intermediates. The long half-life of O₂^•- on the surface of OMS-2 ensured the delay generation of ¹O₂. This study not only provides a new idea for improving the efficiency of heterogeneous catalysts activation of PMS, but also meaningful for the in-depth study of multiple reaction mechanisms in PMS activation processes.