F-doped FeNC catalyst with axial ligand engineering: breaking the strong adsorption barrier for efficient non-radical peroxymonosulfate (PMS) activation and antibiotic removal.

Conventional Fe-Nx sites exhibit excessively strong electronic coupling between metal centers and oxygen species during peroxymonosulfate (PMS) activation, which inevitably induces non-selective radical pathways and fundamentally restricts the efficient and selective oxidative degradation of organic pollutants. Herein, we introduce highly electronegative fluorine atoms as a proposed axial ligand to potentially regulate the electronic structure of Fe-Nx sites, and develop an F-FeNC catalyst for highly efficient tetracycline degradation. The as-fabricated catalyst achieved 94.1% tetracycline (TC) removal within 15 min with a rate constant of 1.01 min-1-4.75 times higher than that of FeNC-while retaining stable and excellent catalytic performance in complex water matrices. Mechanistic investigations combined with density functional theory (DFT) calculations suggest that axial F coordination elevates the positive charge density of the Fe center and induces a downshift of the d-band center, thus weakening the excessively strong adsorption of oxygen-containing intermediates, optimizing the reaction kinetics, and remarkably boosting the selective generation of 1O2. Furthermore, open-circuit voltage and salt-bridge experiments confirm a prominent electron transfer process (ETP) in the system, establishing a non-radical degradation mechanism dominated by 1O2 and synergistically assisted by ETP. This work highlights the great potential of the proposed axial F-coordination engineering concept for PMS activation, offering new design principles for the construction of selective and robust non-radical PMS activation systems.