Site-dependent generation of surface-bound reactive oxygen species and oxidation behavior in cobalt-based spinels...

Surface-bound reactive oxygen species (ROS) are increasingly recognized in catalytic ozonation for their strong oxidation capability and superior resistance to wastewater matrix, enabling efficient emerging pollutants elimination. Cobalt-based spinel oxides exhibit remarkable potential for surface-bound ROS generation, whereas the intrinsic roles of tetrahedral and octahedral Co sites in regulating surface-bound ROS evolution and catalytic oxidation behavior remain unclear. Herein, three spinel catalysts (Co₃O₄, CoAl₂O₄, ZnCo₂O₄) were constructed by selectively substituting Co³⁺ and Co²⁺ with inert Al³⁺ and Zn²⁺, respectively, enabling the investigation of site-dependent ozone activation. Combined quenching experiments and in-situ characterizations revealed the differentiated ROS generation, wherein Co²⁺ sites preferentially generated surface‑bound hydroxyl radicals (•OH_ad) and surface atomic oxygen (*O_ad), while Co³⁺ sites favored *O_ad formation. Density functional theory (DFT) calculations further elucidated that Co²⁺ sites exhibited a d‑band center closer to the Fermi level than that of Co³⁺, thereby facilitating stronger O₃ adsorption and greater electron transfer. Due to the distinct formed ROS, Co³⁺‑dominated ZnCo₂O₄ showed selective oxidation toward electron‑rich pollutants, whereas Co₃O₄ and CoAl₂O₄ with mixed ROS displayed non‑selective degradation. Nevertheless, all systems demonstrated robust anti‑interference, broad pH adaptability, and excellent reusability. Moreover, the three catalytic systems fundamentally altered atrazine transformation pathways, enabling dechlorination and deeper oxidation, along with reducing acute toxicity and bioaccumulation. This work established a site‑dependent surface-bound ROS regulation paradigm, providing guidelines for rationally designing efficient ozonation catalysts in advanced wastewater treatment.