High-Purity, High-Yield Synthesis of Covalent Organic Framework Nanosheets for Fast and Selective Molecular Separation

Covalent organic framework nanosheets (CONs) with extremely thin thicknesses and inborn penetrating nanopores are attractive in transport-related applications. However, the strong tendency of π–π stacking between adjacent laminates hinders their mass production. Herein, we report a facile glycerol-mediated strategy for synthesizing various well-dispersed CONs in liquid phases. The CONs are readily prepared by dissolving monomers in glycerol and subsequent thermal condensation. Experimental and computational investigations reveal that the strong hydrogen bonds between glycerol and CONs suppress the π–π stacking interaction, leading to well-dispersed CONs. Additionally, glycerol acetalization with aldehyde monomers also contributes to the formation of CONs by decreasing the diffusion rate of reactants. The synthesized CONs show a lateral size of over 10 μm and a uniform thickness of ∼4 nm, and their yield is as high as ∼73%. CONs deposited on porous substrates exhibit remarkable permselectivities surpassing most reported membranes and exceptional dye/salt separation performances. This study provides a new strategy for synthesizing CONs and increases the understanding of the important role of solvents in the synthesis of two-dimensional materials.