pH-Regulated Interfacial Charge of Ozone Micro-Nanobubbles Controls ROS Selectivity and Sulfamethoxazole Transformation Pathways

Micronanobubbles (MNBs) offer enhanced interfacial area and distinct interfacial physicochemical properties, but the mechanistic role of interfacial charge in governing ozone-derived reactive oxygen species (ROS) remains inadequately understood. Herein, the pH-dependent interfacial charge characteristics of ozone micronanobubbles (O 3 -MNBs) were systematically examined to elucidate their influence on sulfamethoxazole (SMX) degradation. O 3 -MNBs increased the apparent degradation rate by approximately 4-fold relative to macrobubbles, with initial enhancement driven by facilitated ozone dissolution and subsequent acceleration governed by interfacial reaction processes. ζ potential measurements and ROS probe analyses demonstrated that solution pH modulates MNB interfacial charge, thereby regulating pollutant interfacial enrichment and shifting ROS dominance. Acidic conditions promoted hydroxyl radical ( • OH) formation through interfacial instability, whereas neutral and alkaline conditions favored the generation of superoxide radicals (O 2 •– ) and singlet oxygen ( 1 O 2 ). Quadrupole time-of-flight mass spectrometry (Q-TOF-MS) further confirmed that these distinct ROS regimes correspond to divergent SMX transformation pathways. The findings establish interfacial charge regulation as a critical determinant of reaction selectivity in O 3 -MNB systems and provide mechanistic guidance for optimizing MNB-assisted ozonation in advanced water treatment.