Evolution of singlet oxygen in peroxymonosulfate activation: a review

Abstract

Given that sulfate-radical-based advanced oxidation processes (SR-AOPs) have attracted great attention in recent years, PMS activation has been reckoned to be an alternative method to the Fenton process in environmental remediation. Hence, in this review, we deliberately retrospect and study the recent progress using singlet oxygen (¹O₂) in SR-AOPs since 2016. First, the fundamental principles and means of characterization of ¹O₂ are carefully presented. Several categories of activators, such as metal-free catalysts (e.g., carbon tubes and graphene), metal-based (i.e., the elements Co and Mo), and other metallic-based catalysts (i.e., the elements Fe, Mn, and noble metals), are then specifically proposed. Under these circumstances, the mechanisms of ¹O₂ formation via direct electron transfer, self-decomposition, superoxide radical mediation, oxygen vacancy, perxoymonosulfate radical recombination, etc., have been deliberately summarized in sections. Notably, the research gaps and perspectives for ¹O₂ in environmental remediation have been critically put forward. Hopefully, this review can offer detailed and theoretical guidance for researchers participating in the study of ¹O₂ in SR-AOPs.