Mechanistic Insights into Salt Resistance of Commercial Ozone Catalysts for Hypersaline Wastewater Decontamination

The selection of effective ozone catalysts for hypersaline wastewater treatment remains a significant challenge due to the limited understanding of their salt-resistance mechanisms. Herein, 24 commercial ozone catalysts (denoted as #1-#24) were screened for salt-resistant catalytic performance, among which four catalysts (#1, #15, #22, and #23) demonstrated exceptional catalytic ozonation activity for oxalate (OA) removal in the presence of 15 g L^-1 NaCl. The active components of these four catalysts were identified as CuO (#1), CuO/MnO₂ (#15), Mn₂O₃ (#22), and Fe₃O₄ (#23), respectively. Increasing the salinity from 15 to 200 g L^-1 significantly inhibited OA removal in the CuO/O₃ system, while no inhibitory effect was observed in the other three systems. Mechanistic studies revealed that Cl^- inhibited OA removal in the CuO/O₃ system by quenching the aqueous-phase hydroxyl radicals (HO_aq^•). Although HO_aq^• was also the dominant oxidant in both Mn₂O₃/O₃ and Fe₃O₄/O₃ systems, their negatively charged surfaces electrostatically repelled Cl^-, preventing the depletion of HO_aq^• by Cl^- and thus maintaining the catalytic activity. Differently, surface-adsorbed hydroxyl radicals were generated in the CuO/MnO₂/O₃ system, enabling the salt-resistance performance of this system. This work paves the way for both selecting and designing effective catalysts for catalytic ozonation of hypersaline wastewater.