Abstract
The preparation of subnanoporous covalent-organic-framework (COF) membranes with high performance for ion/molecule sieving still remains a great challenge. In addition to the difficulties in fabricating large-area COF membranes, the main reason is that the pore size of 2D COFs is much larger than that of most gas molecules and/or ions. It is urgently required to further narrow their pore sizes to meet different separation demands. Herein, we report a simple and scalable way to grow large-area, pliable, free-standing COF membranes via a one-step route at organic–organic interface. The pore sizes of the membranes can be adjusted from >1 nm to sub-nm scale by changing the stacking mode of COF layers from AA to AB stacking. The obtained AB stacking COF membrane composed of highly-ordered nanoflakes is demonstrated to have narrow aperture (∼0.6 nm), uniform pore distribution and shows good potential in organic solvent nanofiltration, water treatment and gas separation.
Highlights
The preparation of subnanoporous covalent-organic-framework (COF) membranes with high performance for ion/molecule sieving still remains a great challenge
The solubility problem confronted by traditional water–organic interfacial polymerization for covalent organic frameworks (COFs) membrane preparation can be partially or all solved by the above two methods, so far the pore sizes (>1 nm) of the obtained COF membranes are usually much larger than small molecules (H2, N2, CO2, etc.) and ions, which limits their applications in selectively molecule sieving and desalination, etc
We wonder if the stacking mode of COF layers could be adjusted by merely changing the number of functional groups on COF monomers, for the reason that the steric resistance increases as the number of functional groups increases to some extent
Summary
The preparation of subnanoporous covalent-organic-framework (COF) membranes with high performance for ion/molecule sieving still remains a great challenge. In order to obtain subnanoporous COF membrane, we tried to increase the number of phenolic hydroxyl groups on triformylbenzene monomers for adjusting the stacking mode of 2D COF layers from AA stacking to AB stacking mode, so as to reduce the pore size from >1 nm to sub-nm scale (Fig. 1). Two resulting laminated free-standing covalent-organic-framework membranes (FS-COM-1 and FSCOM-2) with different pore sizes are successfully synthesized and systematically studied, and their selective separation performance for molecules and ions are investigated and compared.
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