Laminated self-standing covalent organic framework membrane with uniformly distributed subnanopores for ionic and molecular sieving

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. Fabrication of large scale and defect free covalent organic framework (COF) membranes with pores small enough for gas sieving remains challenging. Here, the authors report a scalable fabrication method to grow large area defect free COF membranes and to tune the pore size in the sub-nm region by adjusting the stacking modes of the COF layers.