PET recycling under mild conditions via substituent-modulated intramolecular hydrolysis†

Abstract

Catalytic depolymerization represents a promising approach for the closed-loop recycling of plastic wastes. Here, we report a knowledge-driven catalyst development for poly(ethylene terephthalate) (PET) recycling, which not only achieves more than 23-fold enhancement in specific activity but also reduces the alkali concentration by an order of magnitude compared with the conventional hydrolysis. Substituted binuclear zinc catalysts are developed to regulate biomimetic intramolecular PET hydrolysis. Hammett studies and density functional theory (DFT) calculations indicate that the substituents modify the charge densities of the active centers, and an optimal substituent should slightly increase the electron richness of the zinc sites to facilitate the formation of a six-membered ring intermediate. The understanding of the structure–activity relationship leads to an advanced catalyst with a specific activity of 778 ± 40 g_PET h⁻¹ g_catal⁻¹ in 0.1 M NaOH, far outcompeting the conventional hydrolysis using caustic bases (<33.3 g_PET h⁻¹ g_catal⁻¹ in 1–5 M NaOH). This work opens new avenues for environmentally benign PET recycling.