Fabrication of magnetic bimetallic Co–Zn based zeolitic imidazolate frameworks composites as catalyst of glycolysis of mixed plastic

Abstract With the increasing awareness of environmental protection, the degradation of waste plastic has attracted more and more attention. In this study, the glycolysis of PET and PBT which are widely used in daily life were investigated using CoFe2O4@ZIF-8/ZIF-67 composite as catalyst. Moreover, the glycolysis of PET/PBT mixed plastic was also studied. The result showed that CoFe2O4@ZIF-8/ZIF-67 has ideally catalytic effect in glycolysis of plastic, especially in glycolysis of PET/PBT mixed plastic. PET/PBT (5 g), CoFe2O4@ZIF-8/ZIF-67 (0.05 g) and ethylene glycol (25 g) were at 200 °C for 60 min, plastic conversion is up to 100% and BHET yield reached 84.3%. The main product of glycolysis of PBT and PET/PBT was characterized and confirmed to be bis(hydroxyalkyl) terephthalate (BHET). The result of UPLC indicated that purity of main product of glycolysis of PET/PBT was 92%. The as-synthesized catalysts were characterized by XRD, FT-IR, SEM, TGA, N2 adsorption–desorption and VSM. The catalytic performance of catalysts was significantly influenced by external BET surface area. More importantly, the magnetic catalyst could be collected quickly by external magnetic field. The catalytic performance of CoFe2O4@ZIF-8/ZIF-67 did not obviously decrease and element content of Zn and Co in catalyst was just decreased by less than 10% after it was reused for five times.