Visible Light-Induced Catalyst-Free Activation of Peroxydisulfate: Pollutant-Dependent Production of Reactive Species

Activation of peroxydisulfate (PDS, S₂O₈^2-) via various catalysts to degrade pollutants in water has been extensively investigated. However, catalyst-free activation of PDS by visible light has been largely ignored. This paper reports effective visible light activation of PDS without any additional catalyst, leading to the degradation of a wide range of organic compounds of high environmental and human health concerns. Importantly, the formation of reactive species is distinctively different in the PDS visible light system with and without pollutants [e.g., atrazine (ATZ)]. In addition to SO₄^•- generated via S₂O₈^2- dissociation under visible light irradiation, O₂^•- and ¹O₂ are also produced in both systems. However, in the absence of ATZ, H₂O₂ and O₂^•- are key intermediates and precursors for ¹O₂, whereas in the presence of ATZ, a different pathway was followed to produce O₂^•- and ¹O₂. Both radical and nonradical processes contribute to the degradation of ATZ in the PDS visible light system. The active role of ¹O₂ in the degradation of ATZ besides SO₄^•- is manifested by the enhanced degradation of contaminants and electron paramagnetic resonance spectroscopy measurements in D₂O.