Magnetically recoverable Co-ZIF-L-derived catalysts for decolorized BHET recovery and oligomer-to-TPA valorization from colored PET waste.

The accumulation of colored polyethylene terephthalate (PET) waste poses an environmental challenge, as conventional recycling often results in downcycling due to persistent dye contamination. Here, a magnetically recoverable Co-ZIF-L-derived catalyst has been developed for the catalytic glycolysis of colored PET waste, enabling PET depolymerization, catalyst recovery, and decolorized bis(2-hydroxyethyl) terephthalate (BHET) recovery. The catalyst contained finely dispersed Co/CoOx nanoparticles with an average size of 2.9 nm and a high saturation magnetization of 71.49 emu g-1, allowing rapid magnetic separation (>90%) and reuse over five consecutive cycles. Under optimized glycolysis conditions (200 °C, 4 h), the system achieved a 96.1% PET conversion with a 75.34% yield of BHET. Kinetic analysis gave an apparent activation energy of 148 kJ mol-1, lower than those of several reported magnetic catalysts. To further utilize dye-containing oligomeric residues, the oligomers underwent subsequent acid hydrolysis, alkaline dissolution, and precipitation. This integrated post-treatment converted oligomeric residues into purified terephthalic acid (TPA) with a yield of up to 88.64%, while further separating residual dye-containing species. The recovered BHET exhibited low residual chromaticity, with American Dye Manufacturers Institute (ADMI) values below 20 for most colored PET samples. This work demonstrates an integrated catalytic route for converting colored PET waste into reusable aromatic monomers through magnetically recoverable glycolysis, decolorized BHET recovery, and oligomer-to-TPA valorization.