Nonradical oxidation has been determined to be a promising pathway for the degradation of organic pollutants in heterogeneous catalytic ozonation (HCO). However, the bottlenecks are the rational design of catalysts to selectively induce nonradicals and the interpretation of detailed nonradical generation mechanisms. Herein, we propose a new HCO process based on single-atom iron catalysts, in which Fe-N 4 sites anchored on the carbon skeleton exhibited outstanding catalytic ozonation activity and stability for the degradation of oxalic acid (OA) and phydroxybenzoic acid (pHBA) as well as the advanced treatment of a landfill leachate secondary effluent. Unlike traditional radical oxidation, nonradical pathways based on surface-adsorbed atomic oxygen (*O ad ) and singlet oxygen ( 1 O 2 ) were identified. A substrate-dependent behavior was also observed. OA was adsorbed on the catalyst surface and mainly degraded by *O ad , while pHBA was mostly removed by O 3 and 1 O 2 in the bulk solution. Density functional theory calculations and molecular dynamics simulations revealed that one terminal oxygen atom of ozone preferred bonding with the central iron atom of Fe-N 4 , subsequently inducing the cleavage of the O−O bond near the catalyst surface to produce *O ad and 1 O 2 . These findings highlight the structural design of an ozone catalyst and an atomic-level understanding of the nonradical HCO process.

Heterogeneous catalytic ozonation is regarded as a feasible technology in advanced wastewater treatment. Catalytic performance, mass transfer, and mechanical strength are the key elements for large-scale applications of catalysts. To optimize those elements, Fe was selected for its dual role in graphitization and catalytic ozonation. A Fe/N-doped micron-scale carbon−Al 2 O 3 framework (CAF) was designed and applied to a fluidized catalytic process for the treatment of secondary effluent from coal gasification. The chemical oxygen demand removal rate constant and the hydroxyl radical generation efficiency (R ct ) of the Fe/Ndoped CAF were 190% and 429% higher than those of pure ozone, respectively. Theoretical calculations revealed that higher Fe valence promoted ozone decomposition, which implied increasing Fe III content for further catalyst optimization. The rate constant and R ct with a higher Fe III -proportion catalyst were increased by 13% and 16%, respectively, compared to those with the lower one. Molecular dynamics and density functional theory calculations were performed to analyze the reaction kinetics qualitatively and quantitatively. The energy barrier corresponding to Fe III configuration was 1.32 kcal mol −1 , 27% lower than that for Fe II configuration. These theoretical calculations guided the catalyst optimization and provided a novel solution for designing ozonation catalysts. The Fe/N-doped CAF demonstrated a great potential for practical applications.

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