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

Activation of peroxydisulfate (PDS, S2O82-) 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 center dot- generated via S2O82- dissociation under visible light irradiation, O-2(center dot-) and O-1(2) are also produced in both systems. However, in the absence of ATZ, H2O2 and O-2(center dot-) are key intermediates and precursors for O-1(2), whereas in the presence of ATZ, a different pathway was followed to produce O-2(center dot-) and O-1(2). Both radical and nonradical processes contribute to the degradation of ATZ in the PDS visible light system. The active role of O-1(2) in the degradation of ATZ besides SO4 center dot- is manifested by the enhanced degradation of contaminants and electron paramagnetic resonance spectroscopy measurements in D2O.