Identification of step-by-step oxidation process and its driving mechanism in the peroxymonosulfate catalytically activated with redox metal oxides

This study proposed a step-by-step oxidation process based on the in-depth analysis of the catalytic mechanism of peroxymonosulfate (PMS) activated by the common MnO2-based catalyst-manganese octahedral molecular sieve (OMS-2). In the first stage, OMS-2-mediated electron transfer dominated the oxidation process. When PMS was completely consumed, the reaction entered the second stage, at which singlet oxygen (1O2) gradually turned into primary oxidation source. OMS-2-mediated electron transfer was proved based on the results of electrochemical analysis, phosphate substitution experiments, and Raman tests. Meanwhile, the oxidation process of 1O2 was unveiled by radical scavenging tests, electron paramagnetic resonance (EPR), and solvent-exchange experiment (from H2O to D2O). Moreover, superoxide radical (O2 center dot- ) generated from the reaction between PMS and metastable manganese intermediate was identified as the precursor of 1O2. O2 center dot- generated in the first stage could significantly extend its half-life by adsorbing on the (211) plane of OMS-2, and then desorbed in the second stage and contributed to the formation of 1O2. More importantly, through the transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and DFT calculations, the essence of step-by-step oxidation driven by O2 center dot- adsorption-desorption process was uncovered.

Automated summary

This study proposed a step-by-step oxidation process using peroxymonosulfate (PMS) activated by manganese octahedral molecular sieve (OMS-2) catalyst. The oxidation process is dominated by OMS-2-mediated electron transfer in the first stage and gradually transitions to singlet oxygen (1O2) as the primary oxidation source in the second stage. The generation of 1O2 is attributed to the reaction between PMS and metastable manganese intermediate, with O2 center dot- identified as the precursor. The step-by-step oxidation mechanism driven by O2 center dot- adsorption-desorption process was revealed through various experiments and analysis.