A review on the role of high-valent metals in peracetic acid-based advanced oxidation processes

In contrast to center dot OH and CH3C(O)O center dot/CH3C(O)OO center dot radicals, which are commonly considered to be the primary reactive oxidants, high-valent metals generated during peracetic acid (PAA) activation have only recently been proposed. Compared with radicals, high-valent metals possess longer lifetimes (e.g., 0.02 mu s for center dot OH versus 7 s for Fe(IV)) and are more tolerant to background ions despite their relatively moderate oxidation power. Although several review papers on high-valent metals have been published, there is a lack of information on the generation of high-valent metals in peracetic acid systems. Therefore, the aim of this work was to review highvalence metals generated during peracetic acid activation, primarily focusing on i) formation pathways based on homo- and heterogeneous Fe(II)/PAA and Co(II)/PAA systems, ii) reaction mechanisms involving hydride/Hatom transfer, oxygen atom transfer, electrophilic addition, and nucleophilic attack, iii) oxidation performance including substrate-specific reactivity, influencing factors, and environmental water matrices. Furthermore, critical thinking and further prospects for high-valent metal-mediated oxidation processes are proposed.