Fe₃O₄@ZIF-8 core–shell nanocatalysts for highly efficient and magnetically recyclable glycolysis of PET waste

In this study, magnetic core-shell Fe3O4@ZIF-8 was synthesized via a hydrothermal method and applied to Polyethylene terephthalate(PET) degradation. The catalytic degradation of PET by Fe3O4@ZIF-8 was carried out under atmospheric pressure, yielding high-value bis(2-hydroxyethyl) terephthalate (BHET) monomers. The as-synthesized Fe3O4@ZIF-8 core-shell composites possess hierarchical porosity with tunable nanoscale cavities. SEM and TEM analyses confirmed the core-shell morphology, with nanoparticles having a size distribution of 180–280 nm. The degradation product was identified as a high-purity, colorless, and transparent monomeric BHET through 1H NMR and LC analyses. Based on a series of onefactor experiments and a Box-Behnken experimental design, the optimal process conditions were determined to be an alcoholysis temperature of 200°C, a catalyst dosage of 0.5 wt% (relative to PET mass), a reaction time of 50 min, and an ethylene glycol-to-PET mass ratio of 4.5:1. Under these conditions, the actual BHET yield reached 81.12%, closely matching the predicted value.