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

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 (•OHad) and surface atomic oxygen (*Oad), while Co3+ sites favored *Oad 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.