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

[Display omitted] • A step-by-step oxidation process including electron transfer and 1O 2 was proposed. • Electron transfer and 1O 2 occurred on OMS-2 surface and in solution, respectively. • O 2 •− on the surface of OMS-2 could significantly extended its half-life. • The step-by-step oxidation driven by the adsorption-desorption of O 2 •− on OMS-2. 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 MnO 2 -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 (1O 2) 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 1O 2 was unveiled by radical scavenging tests, electron paramagnetic resonance (EPR), and solvent-exchange experiment (from H 2 O to D 2 O). Moreover, superoxide radical (O 2 •−) generated from the reaction between PMS and metastable manganese intermediate was identified as the precursor of 1O 2. O 2 •− generated in the first stage could significantly extend its half-life by adsorbing on the (2 1 1) plane of OMS-2, and then desorbed in the second stage and contributed to the formation of 1O 2. 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 O 2 •− adsorption–desorption process was uncovered. [ABSTRACT FROM AUTHOR]