Asymmetric Fe-Ov-Co Synergizing Free Nitrogen Sites in Carbon-Support Spinel Nanodots: Dual-Engineered Electronic States for High-Efficiency Peroxymonosulfate Activation

Oxygen vacancies (Ov) play an important role in promoting peroxymonosulfate (PMS) activation. However, conventional symmetric Ov exhibits low electron transfer efficiency due to symmetric adjacent cations, constraining their catalytic performance. Asymmetric vacancies (M1-Ov-M2) offer enhanced catalytic potential, yet developing catalysts featuring uniformly distributed asymmetric Ov remains challenging. Incorporating supports with N-bonded functionalities can modulate the electronic structure of metal oxides, providing a promising strategy to overcome these limitations. Here, we designed a 3D porous N-bonded carbon-supported CoFe2O4-x spinel nanodots catalyst featuring rich and structurally uniform asymmetric Fe-Ov-Co sites and free nitrogen sites for PMS activation in p-nitrophenol degradation. Through carrier engineering and the integration of functional nonmetallic sites, this catalyst achieves a high degradation rate constant (0.12 min-1) and exceptional cycling stability. The synergistic catalytic mechanism between asymmetric vacancies and free N species in PMS activation was elucidated. Specifically, asymmetric Ov in the spinel, combined with N-bonded functionalities in the support, optimizes the electronic states near the Fermi level, promoting faster electron transfer and enhancing reactive oxygen species (ROS) generation. The synergy between asymmetric Ov and pyrrolic N sites improves PMS adsorption and activation, while the combination of Ov and pyridinic N lowers the catalyst's d-band center by 0.29 eV, facilitating ROS release. Additionally, Ov and pyrrolic N cooperatively enhance p-nitrophenol adsorption, enabling in situ degradation by surface ROS and accelerating degradation kinetics. This work not only advances defect engineering in catalysts but also unveils the "oxygen vacancy-nitrogen synergy" mechanism, providing valuable insights for designing multiactive-site catalysts in complex environmental systems.