Secondary coordination sphere modulation in covalent organic framework immobilized Co single-atom for Fenton-like catalysis

While the significance of the coordination microenvironment in single-atom catalysts (SACs) is well recognized, precise modulation of the more extended coordination sphere remains a substantial challenge. Herein, a series of cobalt-based SACs (Co/TpHz, Co/TpPa, Co/TpBD) were fabricated via a secondary coordination sphere (SCS) modulation strategy. This was achieved by anchoring isolated Co sites into three β-ketoenamine-linked covalent organic frameworks (COFs) with tailored conjugation degrees in their frameworks, which resulted from the controlled variation in the number of aromatic rings within the aminobenzene-based linkers. Remarkably, the monobenzene-type Co/TpPa catalyst exhibited superior performance in the removal of bisphenol A via Peroxymonosulfate (PMS) based Fenton-like reactions, achieving an exceptional reaction rate constant ( k ) of 0.54 min −1 , which is 2.6 times and 49 times higher than those of Co/TpHz and to Co/TpBD, respectively. Density functional theory (DFT) calculations revealed that modulation of the SCS significantly influences the electronic structure of the Co sites. Notably, the active sites in Co/TpPa exhibited the strongest adsorption energy (–1.60 eV) toward PMS, along with the lowest reaction energy barrier. This work offers valuable insights into the role of the SCS in SACs and opens a new avenue for the rational design of high-performance Fenton-like catalysts.