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

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 (M 1 -O v -M 2 ) 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 CoFe 2 O 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.