Yimiao Jing, Jie Wang, Yu Fang, Zhongshan Liu*. Chem. Sci., 2026, DOI: 10.1039/D5SC09502F

Covalent organic frameworks (COFs), featuring customizable topologies and permanent porosities, have demonstrated potential applications in adsorption, separation, catalysis, and sensing. Unlike booming synthetic methods and applications, the chemical recycling of end-of-life COFs remains undeveloped. Several studies have attempted physical recovery strategies by means of adsorption-desorption or magnetic separation. However, these methods struggle to retain the structural integrity and performance stability of the recovered COFs and also fail to recycle physically inseparable COF moieties from composite materials. Therefore, developing a chemical recycling strategy that can regenerate high-quality COFs is highly desired.

This work reported closed-loop recycling methods for imine-linked COFs, realizing their chemical depolymerization and reconstruction through dynamic imine chemistry. An alkyl monoamine with a stronger nucleophilicity is adopted to attack aromatic imine linkages of COFs at room temperature, depolymerizing the crosslinked frameworks into small molecular alkyl-imines and aromatic amine monomers. The alkyl-substituted imines are unstable in the presence of acetic acid and easily revert back to the aromatic imines via reversible transamination. Based on this, this work proposed two in situ recycling methods, including room-temperature recycling (RTR) and solvothermal recycling (STR), enabling in situ regeneration of COFs without tedious monomer purification and with recoveries up to 92%. As evidenced by powder X-ray diffraction and nitrogen and benzene vapor adsorption measurements, the recovered COFs retain their crystallinity, characteristic pore size and adsorption performance. The successful recycling of imine-linked COFs offers a promising strategy for the sustainable development of porous organic materials.

Figure 1. Chemical recycling routes and characterization of recovered COFs

First Author: Jing Yimiao, master’s student, Shaanxi Normal University

Correspondence Author: Assoc. Prof. Liu Zhongshan, Shaanxi Normal University

Full Text Link: https://doi.org/10.1039/D5SC09502F