Fe3O4 Nanodispersions as Efficient and Recoverable Magnetic Nanocatalysts for Sustainable PET Glycolysis

Polyethylene terephthalate (PET), as one of the most indispensable synthetic organic compounds with high strength and transparency properties, can be widely used for textile and food packaging. With the increasing demand for PET production, the recycling of discarded PET has attracted great interest. In this work, we first proposed ethylene glycol (EG) dispersions of highly dispersed Fe3O4 nanoparticles, which were prepared through a co-precipitation route, as efficient and recoverable nanocatalysts for a PET chemical depolymerization achieved by a glycolysis reaction. The as-prepared Fe3O4 nanoparticles have an average size of 11 nm and can be stably dispersed in EG for up to 6 months. This glycolysis process was optimized in terms of catalyst concentrations, EG dosages, degradation temperature, and reaction time. Furthermore, the possible reaction mechanism of PET glycolysis using Fe3O4 as a catalyst was presented. More importantly, 100% PET conversion was achieved, and the bis(2-hydroxyethyl) terephthalate (BHET) yield reached more than 93% under optimal conditions (Fe3O4/PET = 2%, EG/PET = 13, 210 °C 30 min) even after three cycles. The Fe3O4 nanocatalysts are relatively stable during recycling and have great application prospects in chemocatalysis for future research.