Valorization of PES Textile Waste Through Glycolysis and Aminolysis Using Bimetallic ZnO and Carbon Nitride Nanocomposites

Chemical recycling of polyester (PES) textile fibers is a promising technology that has the potential to reduce the environmental impact of the textile industry. Polyester textile fibers breakdown into their monomers, which can then be used to produce new polyester fibers and alternative to mechanical recycling. However, impurities such as dyes and additives can make it difficult to chemically recycle polyester, and they can also reduce the quality of the recycled fibers. Despite these challenges, chemical recycling of polyester textiles has the potential to be a sustainable and environmentally friendly way to produce new polyester fibers. The PES textile fabrics are chemically recycled through aminolysis and glycolysis catalyzed by nanocomposites composed of Sb (or) In-doped ZnO and g-C₃N₄ nanocomposites prepared by the wet-impregnation method. The nanocomposites were characterized by XRD, UV‒Vis, FT-IR, and SEM‒EDS techniques. X-ray diffraction patterns as well as SEM-EDS showed the presence of amorphous g-C₃N₄ and doped ZnO. The extent of the optical band gaps of ZnO observed in doping with g-C₃N₄. The optical band gap of 3.31 eV of ZnO was reduced to 2.55–2.65 eV after doping with g-C₃N₄. SEM morphological analysis showed a sheet-like structure along with ZnO nanoparticles adsorbed on the surface of g-C₃N₄. Glycolysis and aminolysis of colored PES waste produced bis(2-hydroxyethyl) terephthalate (BHET) and bis(2-hydroxyethyl) terephthalamide (BHETA), respectively, as pure monomers in excellent yield (> 90%). In doped ZnO/g-C₃N₄, catalyzed aminolysis of blue- and green-colored PES produced a colorless monomer, BHETA. FT-IR, MS, ¹H, and ¹³C NMR were used to confirm the formation of BHET and BHETA.