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

Abstract

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 (O3-MNBs) were systematically examined to elucidate their influence on sulfamethoxazole (SMX) degradation. O3-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 (O2•–) and singlet oxygen (1O2). 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 O3-MNB systems and provide mechanistic guidance for optimizing MNB-assisted ozonation in advanced water treatment.