Degradation of norfloxacin by the synergistic effect of micro–nano bubbles and sodium hypochlorite: kinetics, influencing factors and pathways†

This study thoroughly investigated the degradation of norfloxacin (NOR) under the influence of micro–nanobubbles (MNBs) and sodium hypochlorite (NaClO), focusing on their synergistic effects. The impact of various environmental factors, including NaClO concentration, pH, inorganic anions, and surfactants, on NOR degradation efficiency within the MNBs/NaClO system was systematically assessed. The basic properties of the MNBs/NaClO system and the degradation kinetics of NOR were explored. The degradation products and pathways of NOR were explored to reveal the degradation mechanism of antibiotics in the MNBs/NaClO system by employing density functional theory (DFT) and high-performance liquid chromatography-mass spectrometry (HPLC-MS). The redox potential of the MNBs/NaClO system exhibited significantly superior properties than the single system, with bubble sizes predominantly in the nanoscale. The degradation kinetics of NOR adhered to a pseudo-first-order reaction model, with optimal degradation occurring at a 0.025% NaClO volume concentration. Acidic conditions promoted the degradation of NOR, and alkaline conditions inhibited the degradation of NOR. Inorganic anions PO₄³⁻, HCO₃⁻, and CO₃²⁻ in the water matrix led to strong inhibition of NOR degradation. Cationic surfactants accelerated the degradation process of NOR, while anionic and nonionic surfactants had a consistent inhibitory effect on the degradation of NOR. Based on the degradation behavior, three potential pathways for NOR degradation were proposed: quinolone group transformation, defluorination reaction, piperazine ring cracking and quinolone ring decomposition. This research contributes a novel technical approach for addressing antibiotic pollution and offers a theoretical framework for understanding the fate of antibiotics in the environment.