High-efficient M-NC single-atom catalysts for catalytic ozonation in water purification: Performance and mechanisms

Heterogeneous catalytic ozonation (HCO) holds promise in water purification but suffers from limited accessible metal sites, metal leaching, and unclear structure-activity relationships. This work reported M-NC (M=Co, Ni, Fe, and Mn) single-atom catalysts (SACs) with high atomic efficiency and minimal metal release. The new HCO systems, especially the Co-based system, exhibited impressive performance in various refractory contaminant removal, involving various reactive species generation, such as center dot OHads, center dot OHfree, *O, and 1O2. For sulfamethoxazole removal, the normalized kobs for Co-NC, Ni-NC, Fe-NC, and Mn-NC were determined as 13.53, 3.94, 3.55, and 4.13 min 1mMmetal 1 g & sdot;m 2 correspondingly, attributed to the abundant acid sites, faster electron transfer, and lower energy required for O3 decomposition and conversion. The metal atoms and hydroxyl groups, individually serving as Lewis and Bronsted acid sites (LAS and BAS), were the primary centers for center dot OH generation and O3 adsorption. The relationships between active sites and both O3 utilization and center dot OH generation were found. LAS and BAS were responsible for O3 3 adsorption, while strong LAS facilitated O3 3 conversion into center dot OH. Theoretical calculations revealed the catalytic mechanisms involved O3 -> 3 -> *O -> -> *OO -> -> O 3 center dot- -> center dot OH. This work highlights the significance of SAC design for HCO and advances the understanding of atomic-level HCO behavior.