Reclaiming Monomers from Waste Polyester Textiles with 4d Metal-Doped ZnO and g-C 3 N 4 Nanocomposites

Our investigation focuses on breaking down 100% PET polyester (PES) threads using bimetallic ZnO and g-C 3 N 4 nanocomposites. To do this, we used the sol-gel method to create tin, silver, and cadmium-doped bimetallic ZnO nanoparticles and impregnated them on g-CN. We analyzed the nanocomposites using XRD, FT-IR, UV-visible, and SEM-EDX and found that they had a wurtzite crystalline pattern and a lower optical bandgap than the bimetallic ZnO nanoparticles. Next, we carried out aminolytic and glycolytic depolymerization of the waste polyester threads under microwave irradiation. This resulted in the production of two monomers: bis(2-hydroxyethyl)terephthalamide (BHETA) and bis(2-hydroxyethyl)terephthalate (BHET) from aminolysis and glycolysis, respectively. We confirmed the monomers using FT-IR, 1 H & 13 C NMR, and MS techniques. Under optimized reaction conditions, we were able to completely depolymerize both blue and green-dyed waste polyester threads and yield colorless monomers. This process has the potential to recycle waste polyester threads and produce valuable monomers that could be used to make virgin polymers.