Recyclable Enzymatic Hydrolysis with Metal–Organic\nFramework Stabilized Humicola insolens Cutinase (HiC) for Potential\nPET Upcycling

The degradation and recycling of\nplastics, such as poly(ethylene\nterephthalate) (PET), often require energy-intensive processes with\nsignificant waste generation. Moreover, prevalent methods primarily\nentail physical recycling, yielding subpar materials. In contrast,\nupcycling involves breaking down polymers into monomers, generating\nvaluable chemicals and materials for alternative products. Enzyme-catalyzed\ndepolymerization presents a promising approach to break down PET without\nthe need for extreme conditions and unstable or toxic metal catalysts,\nwhich are typical of traditional recycling methods. However, the practical\napplication of enzymes has been hindered by their high cost and low\nstability. In this study, we stabilized the enzyme Humicola insolens\ncutinase (HiC) by encapsulating it within a mesoporous zirconium-based\nmetal–organic framework, NU-1000. HiC@NU-1000 exhibited a quantitative\ndegradation of the PET surrogate, ethylene glycol dibenzoate (EGDB),\nwith greater selectivity than native HiC in producing the fully hydrolyzed\nproduct benzoic acid in partial organic solvent. Additionally, the\nheterogeneous catalyst is also active toward the hydrolysis of PET\nand has demonstrated recyclability for at least four catalytic cycles.\nThe HiC@NU-1000 model system represents a promising approach to stabilize\nindustrially relevant enzymes under conditions involving elevated\ntemperatures and organic solvents, offering a potential solution for\nrelevant protein-related applications.