Asymmetric Fe-Ov-Co Synergizing Free Nitrogen Sites in Carbon-Support Spinel Nanodots: Dual-Engineered Electronic...

Oxygen vacancies (O_v) play an important role in promoting peroxymonosulfate (PMS) activation. However, conventional symmetric O_v exhibits low electron transfer efficiency due to symmetric adjacent cations, constraining their catalytic performance. Asymmetric vacancies (M₁-O_v-M₂) offer enhanced catalytic potential, yet developing catalysts featuring uniformly distributed asymmetric O_v 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 CoFe₂O_4-x spinel nanodots catalyst featuring rich and structurally uniform asymmetric Fe-O_v-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 O_v 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 O_v and pyrrolic N sites improves PMS adsorption and activation, while the combination of O_v and pyridinic N lowers the catalyst's d-band center by 0.29 eV, facilitating ROS release. Additionally, O_v 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.