Three-Dimensional Macro-mesoporous Cobalt–Manganese Spinel Oxides for Heterogeneous Catalytic Ozonation: Efficacy, Structure–Performance Relationship, and Mechanism Insight

Heterogeneous catalytic ozonation (HCO) is a promising technology for wastewater treatment, which requires the development of catalysts having both high intrinsic activity and facile mass transfer properties in the tri-phase reaction process. This study investigated the HCO performances of a novel type of Co-Mn spinel oxide catalysts and the structure-performance relationship. The catalysts were prepared via the molecular foaming method. They possess interpenetrating macro-mesopores, rich surface Mn sites, and excellent redox activities. The optimized sample showed an ultrafast carbamazepine (CBZ) degradation rate (rate constant ∼1.69 min-1), excellent total organic carbon (TOC) removal (∼70%), superior O3 utilization efficiency, general applicability under different pH and co-existing anions and various pollutants, and high stability with minimized metal leaching. Relationships between performance factors (O3 decomposition and utilization, CBZ degradation, and TOC removal) and structural properties were established. Surface Mn is the active site, and there is a negative linear relationship between TOC removal rate and the average oxidation state of Mn. The interpenetrating macropores and facile electron transfer of the catalyst can enhance O3 transfer and utilization. Mechanism study reveals that O3, hydroxyl radical (•OH), and singlet oxygen (1O2) are responsible for CBZ oxidation, while surface-bonded •OH is the major attribute for mineralization. This study would contribute to designing efficient spinel oxide catalysts and deepening the understanding of their HCO performance for potential wastewater treatment.