PET recycling under mild conditions via substituent-modulated intramolecular hydrolysis

Shengbo Zhang; Yingying Xue; Yanfen Wu; Yu-Xiao Zhang; Ting Tan; Zhiqiang Niu

doi:10.1039/d3sc01161e

PET recycling under mild conditions via substituent-modulated intramolecular hydrolysis

Chem Sci. 2023 May 25;14(24):6558-6563. doi: 10.1039/d3sc01161e. eCollection 2023 Jun 21.

Authors

Shengbo Zhang¹, Yingying Xue², Yanfen Wu¹, Yu-Xiao Zhang¹, Ting Tan², Zhiqiang Niu¹

Affiliations

¹ Department State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University Beijing 100084 China niuzq@tsinghua.edu.cn.
² Laboratory of Theoretical and Computational Nanoscience, CAS Key Laboratory of Nanophotonic Materials and Devices, National Center for Nanoscience and Technology, Chinese Academy of Sciences Beijing 100190 China tant@nanoctr.cn.

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.