Advanced oxidation processes based on non-radical pathways in persulfate systems: a comprehensive review of their characteristics, detection methods, and catalyst design

Peroxysulfate-based advanced oxidation processes (AOPs) are increasingly employed for the degradation of organic contaminants in wastewater. However, conventional AOPs primarily rely on highly oxidative free radicals, which are often scavenged by inorganic anions and dissolved organic matter, leading to low selectivity. Recently, non-radical oxidation technologies, particularly those utilizing persulfate, have emerged as promising alternatives due to their enhanced selectivity and stability in complex wastewater environments. Despite their potential, the mechanisms underlying non-radical oxidation are not yet fully understood, and challenges related to catalytic processes and catalyst regulation hinder their broader application. This review provides a comprehensive analysis of recent advancements in persulfate-based non-radical oxidation technologies, focusing on the generation mechanisms, characteristics, and identification of non-radical species, including singlet oxygen and high-valent metal oxides, as well as electron transfer processes. Additionally, the review examines the role of catalysts in regulating non-radical oxidation processes. Finally, it outlines future research directions aimed at advancing non-radical oxidation technologies, with a particular emphasis on oxidation mechanisms, active species identification, and catalyst design.