Asymmetric coordination in iron single atom catalysts enables rapid hydroxyl radical turnover and sustainable water purification

Abstract

Asymmetric coordination engineering offers a powerful yet underexplored route to boost the performance of single-atom catalysts (SACs) for solar-driven advanced oxidation and water purification. In iron-based SACs (Fe-SACs), radical turnover and charge dynamics are limited by the conventional symmetric Fe–N₄ coordination, thereby constraining their practical efficiency in photocatalytic degradation of pollutants. Herein, we report an asymmetrically coordinated single Fe atom-dispersed carbon nitride foam (Fe-CNF) photocatalyst, in which an electron-withdrawing hydroxyl ligand is introduced directly into the first coordination shell of the Fe–N₄ site. This asymmetric coordination modulation downshifts the Fe d-band center, facilitates –O–O– bond cleavage in H₂O₂, and critically promotes the desorption of hydroxyl radicals (˙OH) from the photocatalytic material. The optimized Fe-CNF catalyst achieves a remarkable ˙OH yield of 137.3 μM g⁻¹ and a 30.2-fold increase in the photocatalytic degradation rate compared to bulk CN, enabling rapid removal of multiple antibiotics from real wastewater matrices. Furthermore, the treated water exhibits minimal toxicity toward aquatic microorganisms, confirming its environmental safety. This work demonstrates that ligand engineering provides an effective strategy to achieve asymmetric coordination for designing high-performance SACs aimed at sustainable water purification.