Morphology-tuned MnO/TiO nanocatalysts for recycling PET plastic waste using biomass-derived ethylene glycol.

This study presents a decisive role of TiO morphology on the catalytic activity of MnO/TiO nanomaterials for the chemical recycling of PET waste bottles using biomass-derived ethylene glycol to produce a valuable monomer, bis(2-hydroxyethyl) terephthalate (BHET). Three types of MnO/TiO nanocatalysts were prepared by varying the TiO morphology (nanosheets: NS, nanotubes: NT, and nanorods: NR). The combination of MnO nanoparticles and TiO nanorods (MnO/TiO-NR) showed significantly enhanced catalytic activity in PET glycolysis, with a 91% isolated yield of BHET at 190 °C in 3 h, whereas 74% and 82% yields of BHET were attained with MnO/TiO-NS and MnO/TiO-NT nanocatalysts, respectively. The morphology of TiO and the uniform dispersion of MnO on TiO-NR were confirmed by electron microscopic analysis. The MnO/TiO-NR catalyst contains optimum basic sites, which play a key role, along with surface hydroxyl species and Mn/Mn species, in activating ethylene glycol and PET/its oligomers towards BHET formation. The excellent stability of the MnO/TiO-NR nanocatalyst, as confirmed by the hot-filtration test, good catalytic reusability up to four cycles, non-toxic nature, and the low cost of the MnO/TiO materials indicate the practical feasibility of the developed catalytic protocol for the plastic recycling industry.