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/MnO 2 (#15), Mn 2 O 3 (#22), and Fe 3 O 4 (#23), respectively. Increasing the salinity from 15 to 200 g L –1 significantly inhibited OA removal in the CuO/O 3 system, while no inhibitory effect was observed in the other three systems. Mechanistic studies revealed that Cl – inhibited OA removal in the CuO/O 3 system by quenching the aqueous-phase hydroxyl radicals (HO aq • ). Although HO aq • was also the dominant oxidant in both Mn 2 O 3 /O 3 and Fe 3 O 4 /O 3 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/MnO 2 /O 3 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.