From Ambiguity to Application: Deciphering Non-Radical Pathways in Heterogeneous Persulfate Activation

Non-radical pathways have emerged as a critical research frontier in persulfate-based heterogeneous advanced oxidation processes (PS-HAOPs), offering superior selectivity and thereby resistance to background interference compared to conventional radical-based routes. However, the practical implementation remains hindered by mechanistic ambiguities, stemming from the coexistence of multiple reactive species and difficulty in direct verification. Current studies remain fragmented, lacking a unified framework to connect catalyst properties, operational parameters, and dominant oxidation mechanisms. This review examines the formation mechanism, identification methodologies, and reactivity patterns of non-radical species, such as singlet oxygen, high-valent metal oxide species, and electron transfer pathways. Particular emphasis is placed on rational catalyst design strategies, including spin-state tuning, coordination environment manipulation, and structural engineering, which directly modulate the steric and electronic structures of active sites and thereby influence the dominant oxidation pathway and overall catalytic efficiency. By integrating insights into temporal evolution, multi-pathway coupling, and polymerization behavior, a comprehensive model that links catalyst properties, operational conditions, and pollutant characteristics to pathway selectivity is formulated. This review provides mechanistic clarity and design principles to guide the future development of controllable, efficient, and application-oriented non-radical PS-HAOPs systems.