Mechanistic Insights into Salt Resistance of Commercial Ozone Catalysts for Hypersaline Wastewater Decontamination
Yinhao Dai, Fuqiang Liu, Zhenhua Dai, Wei Miao, Hongyu Dong, Irene M.C. Lo, Xiaohong Guan
Abstract
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.