In Situ Photoelectrochemical Chloride Activation Using a WO3 Electrode for Oxidative Treatment with Simultaneous H2 Evolution under Visible Light.

Reactive chlorine species (RCS) such as HOCl and chlorine radical species is a strong oxidant and has been widely used for water disinfection. This study investigated a photoelectrochemical (PEC) method of RCS production from ubiquitous chloride ions using a WO3 film electrode and visible light. The degradation of organic substrates coupled with H2 evolution using a WO3 electrode was compared among electrochemical (EC), photocatalytic (PC), and PEC conditions (potential bias: +0.5 V vs Ag/AgCl; λ > 420 nm). The degradation of 4-chlorophenol, bisphenol A, acetaminophen, carbamazepine, humic acid, and fulvic acid and the inactivation of E. coli were remarkably enhanced by in situ RCS generated in PEC conditions, whereas the activities of the PC and EC processes were negligible. The activities of the WO3 film were limited by rapid charge recombination in the PC condition, and the potential bias of +0.5 V did not induce any significant reactions in the EC condition. The PEC activities of WO3 were limited in the absence of Cl- but significantly enhanced in the presence of Cl-, which confirmed the essential role of RCS in this PEC system. The PEC mineralization of organic compounds was also markedly enhanced in the presence of Cl- where dark chemical chlorination by NaOCl addition induced a negligible mineralization. The H2 generation was observed only at the PEC condition and was negligible at PC and EC conditions. On the other hand, the oxidation of chloride on a WO3 photoanode produced chlorate (ClO3-) as a toxic byproduct under UV irradiation, but the visible light-irradiated PEC system generated no chlorate.