Intrinsic Electric Field Triggers Phenol Oxidative Degradation at Microbubble Interfaces

Phenol, recognized for its environmental persistence and toxicity, typically necessitates high-energy or costly catalytic methods for its removal from industrial wastewater. In this study, we demonstrate the oxidative degradation of phenol at air-water interfaces (AWIs) by microbubbling air through water. High-resolution mass spectrometry revealed the transformation of phenol into progressively oxidized intermediates and ultimately into acetic acid, with a degradation rate of over 96% after 3 h for a 2 mM phenol solution. Complementary vortex experiments constructed a detailed degradation pathway involving sequential hydroxylation, dehydrogenation, and ring-cleavage processes. Radical scavenger experiments and DFT calculations indicate that the mechanism may follow an interfacial electric field-induced excitation pathway via radical reactions. The oxidation trend of para-halogenated phenols (F < Cl < Br < (H) < I) aligns with each radical's HOMO-LUMO gap, supporting the interfacial field-induced molecular activation mechanism. Compared to conventional advanced oxidation processes, our method offers reagent-free operation, reduced secondary pollution, and high efficiency under mild conditions. These findings highlight the AWI-mediated oxidation as a sustainable strategy for degrading phenolic pollutants in water.