Glycolysis of decolored waste polyethylene terephthalate fabrics catalyzed by zinc oxide nanocrystals

Chemical depolymerization and recycling of waste polyethylene terephthalate (PET) fibers represent an optimal sustainable approach. However, the presence of dyes in the fibers and the use of conventional homogeneous catalysts may have a detrimental impact on the depolymerization products. In this investigation, solvent extraction was employed to meticulously remove dispersed dyes from waste PET fibers, serving as a crucial preparatory step for subsequent chemical depolymerization. This process was followed by the synthesis of spherical hexagonal Wurtzite zinc oxide (ZnO) nanocrystals through a meticulously refined solution chemical method, with careful consideration given to the potential impacts of surface modification and the alcohol-water ratio on the morphological attributes and particle size distribution of these nanocrystals. These ZnO nanocrystals were subsequently utilized as a pseudo-heterogeneous catalyst, catalyzing the glycolysis of decolorized waste PET fabrics. Systematic investigations were conducted to elucidate the intricate relationships between the morphologies, particle sizes, and concentrations of ZnO nanocrystals and their corresponding catalytic activities, leading to the identification of optimal reaction conditions through a series of conditional experiments. Under these optimized conditions, namely a catalyst concentration of 0.5% (by weight), a reaction temperature of 195 °C, and a duration of 30 min, a remarkable yield of bis (2-hydroxyethyl) terephthalate (BHET) was achieved, reaching 82.07%, with a corresponding mass fraction of 97.62%. Graphical abstract