Chlorine Axial Coordination Enables Peroxidase Mimicking and Lignin Depolymerization in Fe–N₃O Single-Atom Nanozymes

Single-atom nanozymes (SAzymes) precisely emulate enzyme catalytic centers at the atomic level, offering exceptional catalytic efficiency and selectivity. Inspired by the heme structure of natural enzymes, this study introduces chlorine axial coordination into the Fe-N₃O single-atom nanozyme, constructing a unique Fe-N₃O-Cl catalytic site (Fe-N/O/Cl-C SA). As a result, the Fe-N/O/Cl-C SA demonstrates remarkable peroxidase-like activity toward the substrate 3,3',5,5'-tetramethylbenzidine (TMB), achieving a catalytic efficiency 1.96-fold greater than horseradish peroxidase (HRP). Density functional theory (DFT) calculations further reveal that axial chlorine coordination significantly reduces the reaction energy barrier, complementing the planar oxygen coordination, which shortens the activation pathway for H₂O₂. Moreover, the Fe-N/O/Cl-C SA efficiently catalyzes the oxidative depolymerization of birch lignin under mild conditions, producing high-value aromatic monomers such as vanillin and cinnamaldehyde. These findings underscore the critical role of chlorine axial coordination in enhancing catalytic performance and highlight the great potential of single-atom nanozymes in biomass conversion and renewable energy applications.