A simple, efficient and selective catalyst for closed-loop recycling of PEF in situ towards a circular materials economy approach†

Developing plastics from biomass and performing chemical recycling are two essential strategies in circular materials economy. Herein, we present an innovative technique for the closed-loop, in situ chemical recycling of bio-derived poly(ethylene 2,5-furandicarboxylate) (PEF), utilizing the exceptional capabilities of monodisperse nano γ-Ga₂O₃ with tunable oxygen vacancy density. This framework enables seamless cycling of bio-based plastics from polymerization to de-polymerization and re-polymerization, promoting a sustainable polymer economy. The introduction of oxygen vacancy defects in the structure of gallium oxide, a low toxicity and transparent metal oxide, is considered to be an effective strategy for improving catalytic activity. The polymerization process was controlled by using novel oxygen vacancy-defective Ga₂O₃, which catalyzed the reaction between bio-based 2,5-furandicarboxylic acid and ethylene glycol to produce high molecular weight PEF. (M_n = 41 kg mol⁻¹). This PEF can then undergo efficient in situ glycolysis, achieving complete de-polymerization under moderate conditions without the need for external catalysts. The glycolysis derivatives of PEF can be directly re-polymerized to polyester rPEF, achieving a significant molecular weight (M_n = 43 kg mol⁻¹) and a remarkable yield (93%). Notably, γ-Ga₂O₃ with nano oxygen vacancy defects exhibits the ability to selectively de-polymerize PEF within composite material systems containing commercial PET. This research highlights the significant utility of a green catalyst in in situ closed-loop recycling processes.