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 (CuxO@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.