Heterointerface-Engineered ZnO@ZnFe2O4 Catalysts with Lewis Acid–Base Cooperativity for Closed-Loop PET Upcycling

Abstract Polyethylene terephthalate (PET) waste remains a major environmental challenge due to its chemical robustness, massive accumulation, and limited mechanical recyclability. Glycolysis enables PET depolymerization into bis(2-hydroxyethyl) terephthalate (BHET) for closed-loop production, but is hindered by sluggish kinetics, insufficient selectivity, and poor catalyst recyclability. Herein, ZnO@ZnFe2O4 heterostructured catalysts with tunable Zn/Fe ratios are developed via a coprecipitation–hydrothermal strategy followed by thermal annealing. The optimized ZF-2.5:1 catalyst integrates intimate ZnO/ZnFe2O4 heterointerfaces and hierarchical mesoporosity with abundant Lewis acid–base sites, while the moderate oxygen vacancies further contribute to the cooperative activation of PET ester carbonyls and ethylene glycol hydroxyls. As a result, ZF-2.5:1 achieves a high BHET yield of 97.68% at 190 °C within 60 min with an ultralow catalyst loading of only 0.5 wt%, which is among the most efficient heterogeneous catalysts reported for PET glycolysis. Benefiting from magnetic recoverability and structural robustness, it retains 92.88% BHET yield after five cycles and efficiently converts real PET products. This work provides a magnetically recyclable Lewis acid–base cooperative oxide platform for sustainable PET upcycling.