Exploration of low-dose ozone-activated periodate (O₃/IO₄⁻) for rapid degradation of the β-Blocker pindolol: efficiency and radical mechanism.

The emergence of recalcitrant organic pollutants poses a significant threat to aquatic environments. PI-based AOPs have been widely used in water treatment and show great potential in degrading these pollutants. This study pioneers the application of low-dose ozone-activated periodate (O₃/IO₄⁻), a novel advanced oxidation process (AOP), for rapid degradation of β-blocker contaminants exemplified by pindolol (PIN). The O₃/PI system exhibits broad pH applicability. Under optimal conditions of 0.175 mg/L O₃, 0.1 mM IO₄⁻, and pH 7.0, the system achieved 99.2 % PIN degradation within 20 s (kobs = 0.254 s⁻¹) when treating an initial PIN concentration of 1 µM, indicating a strong synergistic effect between low-dose O₃ and PI activation. Radical quenching experiments coupled with electron paramagnetic resonance (EPR) spectroscopy revealed a multi-radical mechanism involving iodine species (IO₃•) and reactive oxygen species (ROS) (•OH, •O₂⁻, ¹O₂), with density functional theory (DFT) calculations confirming ozone-periodate adduct formation (OOOIO₄⁻) as the initiation step for radical chain propagation. The degradation of PIN by the O₃/PI system was minimally affected by coexisting substances in the aqueous matrix, with only high concentrations of HCO₃⁻ and humic acid (HA) showing some influence, while Cl⁻ had negligible effects. This highlights the stability of the O₃/PI system and its potential for practical water treatment applications. The identification of transformation products (TPs) and theoretical calculations elucidated the key ROS (IO₃• and •OH) in the PIN degradation process and their attack pathways (HAA, RAF, and SET). Potential degradation pathways for PIN are proposed. Zebrafish toxicity experiments showed that the O₃/PI system effectively detoxifies PIN, though the toxicity of intermediates warrants attention. In conclusion, the developed O₃/PI system offers an efficient and environmentally friendly strategy for PI activation and the treatment of emerging organic pollutants such as PIN.