Mild and Scalable Conditions for the Solvothermal Synthesis of Imine-Linked Covalent Organic Frameworks

A convenient method was developed that allows for the synthesis of highly crystalline and porous imine-linked covalent organic frameworks (COFs) in hours. The use of an apolar solvent in combination with a precise amount of water and acetic acid was crucial to obtain materials of optimal quality. Twelve different COFs could be produced under the same reaction conditions, using a green solvent mixture of n-butanol, acetic acid and water at 70 °C for 16 hours with stirring. The crystallinity of the COFs produced in this manner is similar or better than that obtained by traditional solvothermal synthesis. The method could be easily scaled to synthesize over ten grams of COF in one batch. Optical microscopy, FTIR spectroscopy and in situ Raman spectroscopy gave insight in the role of the solvent on the aggregation of COF nanosheets and the resulting crystallinity, porosity and robustness of the material.