Theory-guided multifunctional Zn-Salen molecular catalyst for sustainable polyester plastic recycling

Abstract

The escalating global challenge of plastic waste calls for innovative recycling solutions that overcome the high energy requirements of traditional chemical recycling and the inefficiency of enzymatic methods. Here, inspired by the structure of Salen-based molecular catalysts and the hydrolase-mediated degradation mechanism of poly(ethylene terephthalate) (PET), we report a multifunctional Zn-Salen molecular catalyst identified through theoretical screening and experimental validation. This catalyst achieves high PET conversion efficiency under mild conditions with low energy consumption. Mechanistic investigations reveal that its Zn metal site, quaternary ammonium component, and aromatic groups synergistically promote adsorption, activation, and nucleophilic attack towards the O–C=O group in PET via a proximity effect, mimicking key features of PET hydrolases. Notably, the synthetic catalyst demonstrates high resistance to external interference, achieving an industrially viable productivity of 75 gTPA L-1 h-1 at COH- =0.1 M and T=90 °C. This catalyst is also effective for diverse substrates, including real-world PET waste, mixed plastics containing PET, and biodegradable PLA plastic. Techno-economic and environmental analyses indicate that this recycling system can significantly reduce carbon emissions and has potential commercial value.