Bifunctional asymmetric Fe-O4/Co-O4 sites in 2D porphyrin-based monolayer for deep mineralization of contaminants

Dual single-atom 2D monolayer catalysts with asymmetric sites present a formidable synthetic challenge. Herein, we successfully synthesized a monolayer dual-atom catalyst (0.5 nm, PML-Fe-Co) featuring an asymmetric Fe-O ₄ /Co-O ₄ coordination configuration based on porphyrin rings using a solvothermal method. It achieved complete degradation of acetaminophen (APAP) with a degradation rate constant of 0.346 min⁻¹ in 10 min. The asymmetric Fe-O ₄ /Co-O ₄ sites realize the degradation of pollutants through the free radical/non-free radical mixed mechanism: the Fe site generates SO ₄ ^•– / •OH through PMS activation, while the Co site generates ¹ O ₂ through spin state modulation. DFT calculation and characterization results revealed that the asymmetric structure modulated the d-orbital spin state of the Co site from low-spin (t _2g ⁶e _g ¹/LS) to high-spin (t _2g ⁵e _g ²/HS) state. The Co site of high-spin exhibited unpaired electrons in e _g orbital, which facilitated electron acquisition from the O 2p orbital in HSO ₅ ^– , thereby accelerating the generation of reactive oxygen species and enhancing the APAP mineralization rate. This approach provided a reference for the development of 2D monolayer catalysts and their application in Fenton-like systems.