Laccase-Inspired Single-Atom Fe-N₄ Nanozymes for Pollutant Degradation and Lignin Valorization

Single-atom nanozymes can accurately mimic the catalytic centers of enzymes at the atomic scale, showing high catalytic efficiency and selectivity. Inspired by the active center of natural laccase, we constructed a nitrogen-doped carbon-based single-atom nanozyme (Fe-NC) featuring planar Fe-N₄ active sites using a zeolitic imidazolate framework (Fe/ZIF-8) as a precursor. The resulting Fe-NC showed high laccase-like activity toward phenolic substrates such as 2,4-dichlorophenol, with a catalytic efficiency 77 times higher than that of natural laccase. Furthermore, Fe-NC efficiently catalyzed the degradation of tetracycline hydrochloride (77.14%) under mild conditions, with an activity 13 times that of laccase. It also selectively and oxidatively depolymerized birch lignin into valuable aromatic monomers, including vanillin and vanillic acid. These findings highlight the key role of planar Fe-N₄ coordination in improving bioinspired catalysis and reveal the great potential of single-atom nanozymes in biomass valorization.