Chemical Recycling of Mixed-Color Polyethylene Terephthalate Plastic Waste Using a Colorant-Tolerant, Reusable Magnetic MnO _x /Fe ₃ O ₄ Nanocatalyst

Recycling mixed-color PET plastic waste into monomers is challenging due to dye/pigment effects on catalyst stability and monomer purity yet crucial for a circular plastic economy. To achieve this, we developed a colorant-tolerant and highly reusable magnetic MnO x /Fe 3 O 4 nanocatalyst (calcined at 400 °C, MnO x /Fe 3 O 4 -4) for the efficient methanolysis of mixed-color PET bottles to produce a value-added dimethyl terephthalate (DMT) monomer. The Mn 3+ /Mn 4+ species, uniformly dispersed on the surface of morphology-controlled Fe 3 O 4, are the primary active sites in the cleavage of PET polymer toward DMT monomer. The innate magnetic strength of Fe 3 O 4 played a key role in improving the stability of the MnO x /Fe 3 O 4 -4 catalyst in colored PET solution and easy recovery of the catalyst after the reaction. This dual functionality (Mn 3+ /Mn 4+ and magnetic Fe 3 O 4 ) bolstered efficient methanolysis of various PET plastic materials, including industrial PET scrap, transparent PET, and mixed-color PET bottles (transparent, blue, and green), with a 96–98% isolated yield of DMT at mild reaction conditions. The PET methanolysis process was scaled up to 5 g using both transparent and mixed-color (blue and green) PET bottles. The MnO x /Fe 3 O 4 -4 nanocatalyst exhibited excellent reusability across various colored PET plastics with 86–87% isolated DMT yields even after seven cycles, offering promising practical solutions for the PET plastic recycling industry.