Synergetic multiple free radicals lower the organohalide conversion barrier and potentiate effective contaminant mineralization

Here we investigated the synergetic multiple free radicals (atomic hydrogen (H*), superoxide anion (•O₂⁻), and hydroxyl radicals (•OH)) in enhancing removal efficiencies of the halogen organic pollutants, such as p-chlorophenol (4-CP). A TiO₂ photoanode and a palladium and carbon layer co-modified Cu/Cu₂O/CuO (Cu_xO@C/Pd) photocathode were combined to construct a photoelectrocatalytic platform that enabled the synchronous production of multiple free radicals. It was found that the conversion and mineralization rates of 4-CP were up to ∼0.044 min⁻¹ and ∼71.3% respectively, representing an increase of ∼4.3 times and ∼2.1 times compared to conventional •OH mediated oxidation. Theoretical calculations and experiments indicated that the conversion barrier of 4-CP was significantly reduced through the redox synergies of H* and •OH and the simultaneous nucleophilic-electrophilic addition of •O₂⁻ effectively inhibited the accumulation of benzoquinone intermediates. This work is beneficial for the study and application of advanced oxidation processes mediated by multiple free radicals. © 2023 Elsevier B.V.