Sulfate Radicals-Mediated Chemiluminescence Production with Peroxydisulfate and Hydroquinone as Coreactants: Mechanism and Environmental Applications

Chemiluminescence (CL) is an attractive method for real-time quantification of toxic contaminants or intermediates generated during advanced oxidation processes due to its high sensitivity, low detection limit, and wide linear range. In this study, we present an unprecedented intrinsic CL phenomenon observed in an alkaline aqueous solution containing hydroquinone (HQ) and peroxydisulfate (PDS, S₂O₈^2-). Mechanistic investigations unveil a two-stage process for CL production: sulfate radical (SO₄^•-) generation and CL emission. Initially, the highly oxidizing SO₄^•- are formed via the decomposition of PDS by semiquinone radicals, originating from the comproportionation reaction of HQ with benzoquinone that is generated by the reaction of HQ with OH^- in the presence of dissolved oxygen. Subsequently, SO₄^•- promptly oxidizes the residual HQ to an excited-state light-emitting species, which returns to its ground-state, accompanied by a transient and intense light emission. Notably, HQ plays dual roles in the CL process by both participating in the generation of SO₄^•- and serving as the precursor of the light-emitting substrate. The proposed CL system is developed to quantify trace amounts of HQ and real-time monitor the degradation kinetics of phenols. These findings hold considerable significance in chemical analysis, intermediate identification, and advanced oxidation processes.