Magnetically recyclable Fe3O4/ZnO for efficient depolymerization and atom-economical upcycling of polyester waste

The efficient deconstruction and upcycling of polyester waste are critical to the circular plastics economy. Herein, we report a magnetically separable Fe 3 O 4 /ZnO nanocatalyst engineered for efficient polyester depolymerization. Synergistic electronic interactions between Fe 3 O 4 and ZnO modulate surface acidity, maximizing Lewis acidity at an Fe/Zn molar ratio of 1:9. Kinetic and thermodynamic analyses reveal that the depolymerization follows a surface reaction-controlled shrinking-core mechanism, where the enhanced Lewis acidity minimizes Gibbs Free Energy ( ΔG ‡ d ) by lowering activation enthalpy ( ΔH ‡ d ), effectively compensating for the entropic penalty (ΔS ‡ d ) of transition state formation. Under mild conditions (1 atm, 196 ℃, 30 min, 1 wt% catalyst loading), the catalyst delivers 100 % poly(ethylene terephthalate) (PET) conversion and 94 % bis(2-hydroxyethyl) terephthalate (BHET) yield with excellent recyclability. Furthermore, a “one-pot” upcycling strategy is demonstrated where the unpurified depolymerization mixture serves directly as a chain extender for the synthesis of high-value waterborne alkyd resins. This protocol, characterized by near-100 % atom economy and the elimination of costly separation steps, offers a sustainable route for industrial polyester valorization.