Microstructure modulation of α-MnO₂ via mild urea-induced phase transition for enhanced catalytic ozonation of emerging contaminants

While facet engineering and heterostructure construction are recognized as effective strategies for enhancing catalytic performance through defect creation, their integration remains scarce and challenging. This study develops a mild urea-assisted thermal strategy to construct an oxygen vacancy (OV)-rich α-MnO₂(310)/Mn₃O₄ heterojunction (Mn400-0.125U), comprising 48.6% α-MnO₂ with preferentially exposed (310) facets and 51.4% Mn₃O₄. The low OV formation energy on (310) facets coupled with heterojunction interfaces effects leads to a high OV concentration. Mn400-0.125U demonstrated exceptional catalytic ozonation performance, achieving a sulfamethoxazole degradation rate constant (7.7×10⁻² min⁻¹), which is 1.8-, 1.6-, and 3.3-fold higher than those of α-MnO₂, Mn₃O₄, and single ozonation, respectively. Operational advantages include ultralow catalyst dosage (0.1 g/L), broad pH adaptability (3.5–10.5), and remarkable resilience against aqueous matrix interference (≤ 12.4% efficiency loss). Both experimental and theoretical calculations demonstrate that the abundant OVs, combined with the proper hydrophilicity of Mn400-0.125U, synergistically trigger barrier-free activation and decomposition of ozone, subsequently generating a series of reactive species via chain reactions. A hybrid oxidation regime was identified where the non-radical pathway mediated by electron-transfer, O* (surface oxygen atoms), and 1O₂ predominates over radical pathways (•O₂−/•OH). This work establishes a facile coupled modulation protocol for creating defect-rich manganese oxides applied in catalytic ozonation of emerging contaminants. © 2026, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.