Recyclable Enzymatic Hydrolysis with Metal–Organic Framework Stabilized Humicola insolens Cutinase (HiC) for Potential PET Upcycling

The degradation and recycling of plastics, such as poly(ethylene terephthalate) (PET), often require energy-intensive processes with significant waste generation. Moreover, prevalent methods primarily entail physical recycling, yielding subpar materials. In contrast, upcycling involves breaking down polymers into monomers, generating valuable chemicals and materials for alternative products. Enzyme-catalyzed depolymerization presents a promising approach to break down PET without the need for extreme conditions and unstable or toxic metal catalysts, which are typical of traditional recycling methods. However, the practical application of enzymes has been hindered by their high cost and low stability. In this study, we stabilized the enzyme Humicola insolens cutinase (HiC) by encapsulating it within a mesoporous zirconium-based metal-organic framework, NU-1000. HiC@NU-1000 exhibited a quantitative degradation of the PET surrogate, ethylene glycol dibenzoate (EGDB), with greater selectivity than native HiC in producing the fully hydrolyzed product benzoic acid in partial organic solvent. Additionally, the heterogeneous catalyst is also active toward the hydrolysis of PET and has demonstrated recyclability for at least four catalytic cycles. The HiC@NU-1000 model system represents a promising approach to stabilize industrially relevant enzymes under conditions involving elevated temperatures and organic solvents, offering a potential solution for relevant protein-related applications.