Mechanistic insights into PET and PU degradation on bio-inspired dual-metal catalysts

Understanding how polymer backbone chemistry governs catalytic hydrolysis remains essential for designing efficient plastic-degrading catalysts. Here, we combine molecular dynamics (MD) and density functional theory (DFT) analyses to construct a unified mechanistic picture of polyethylene terephthalate (PET) and polyurethane (PU) degradation on bio-inspired dual-metal catalysts. Tetramers are taken for MD simulations, and model molecules containing key fragments of the two polymers are used for DFT investigations. MD simulations reveal that PET adopts flexible, weakly hydrated conformations, while PU forms compact hydrogen-bond networks stabilized by intramolecular N–H···O=C interactions. Guided by enzymatic motifs, a family of dual-atom catalysts hosted on nitrogen-doped carbon supports (M₂N₆@C, M = Fe, Co, Ni, Cu, Zn) was designed to emulate cooperative active sites found in metalloenzymes. DFT results show that both reactions proceed through a five-state cycle—adsorption, nucleophilic attack, tetrahedral intermediate, bond cleavage, and product desorption—but exhibit distinct rate-determining steps. Cu₂N₆@C achieves the lowest barrier for PET (0.226 eV, desorption-controlled), while Fe₂N₆@C most effectively activates PU (0.416 eV, polarization-controlled). Electronic-structure analyses show that shorter Fe–Fe pairs excel at activating compact, strongly bound urethane groups of PU through polarization, whereas longer Cu–Cu pairs optimally engage extended ester bonds of PET through adaptive coordination and charge delocalization. These findings establish direct correlations between metal–metal distance, spin state, and substrate selectivity, providing molecular design principles that bridge enzymatic cooperativity with heterogeneous dual-metal catalysis for selective plastic depolymerization.