Gentle and rapid synthesis of imine-linked covalent organic frameworks in acetic acid-based deep eutectic solvents

Abstract

Covalent organic frameworks (COFs) linked by imine bonds are generally synthesized using the solvothermal method, which often involves complex and toxic processes. In this study, we combined acetic acid, the most common catalyst for imine-linked COFs, with menthol to form a green acetic acid-based deep eutectic solvent (DES) that serves both as the solvent and catalyst. Three combinations of monomers, each with different chemically active functional groups, were selected to examine various synthesis conditions. The effects of the menthol : acetic acid molar ratio, reaction temperature, and reaction time on the formation of imine-linked COFs were systematically investigated. Through these optimizations, 23 imine-linked COFs were prepared by simply adjusting the menthol : acetic acid ratio, demonstrating the versatility of the method. This approach offers several advantages: it eliminates the need for strict vacuum environment, uses milder reaction conditions compared to traditional solvothermal method, and can be easily scaled up to the gram scale. Based on this approach, we synthesized the TAPB-TFP COF on a large scale for use as an adsorbent to selectively remove furfural from cellulose hydrolysate, while preserving the glucose and xylose content. Our strategy provides a sustainable, efficient route for the green synthesis and large-scale production of imine-linked COFs.