Imine-linkage covalent organic framework synthesis in deep eutectic solvent at ambient conditions

Covalent organic frameworks (COFs) are important porous materials with large surface areas and adjustable pore channels with the ability of being effective adsorbents. The solvothermal synthesis of COFs usually requires elevated temperature, closed systems under high pressure, and harmful organic solvents. In addition, different conditions are needed to produce different COFs depending in part on the type of monomers used, meaning there is no 'one size fits all' approach synthesis route for COFs. In this work, a green synthesis routine was proposed for a series of imine-linkage COFs by using deep eutectic solvent (DES) as the reaction media at room temperature and atmospheric pressure. The obtained COFs are equipped with a large surface area (∼1300 m2 g−1), mesopore structure, high degree of crystallization and were synthesized with high yield. In addition, the stability of the DES structure under different temperatures and the effect of adding acetic acid (AC) for the catalytic synthesis of the COFs was also verified for the first time. Finally, the proposed routine showed good reusability which can fabricate COFs with good crystallization after four times. The synthesized COFs also showed excellent adsorption performance for dye solutions with ultra-fast kinetics, achieving nearly 100 % dye removal within 3 min with an adsorption rate of 7.399 g mg−1 min−1. The proposed routine showed clear advantages of using DES as a reaction media which includes lower synthesis temperature and pressure (i.e. room temperature and atmospheric pressure), open-air vessels, eco-friendly solvents, and good reaction media reusability.