Efficient Ion Sieving in Covalent Organic Framework Membranes with Sub-2-Nanometer Channels

Membranes of sub-2-nanometer channels show high ion transport rates, but it remains a great challenge to design such membranes with desirable ion selectivities for ion separation applications. Here, covalent organic framework (COF) membranes with a channel size of approximate to 1.4 nm and abundant hydrogen bonding sites, exhibiting efficient ion sieving properties are demonstrated. The COF membranes have high monovalent cation permeation rates of 0.1-0.2 mol m(-2) h(-1) and extremely low multivalent cation permeabilities, leading to high monovalent over divalent ion selectivities for K+/Mg2+ of approximate to 765, Na+/Mg2+ of approximate to 680, and Li+/Mg2+ of approximate to 217. Experimental measurements and theoretical simulations reveal that the hydrogen bonding interaction between hydrated cations and the COF channel wall governs the high selectivity, and divalent cations transport through the channel needs to overcome higher energy barriers than monovalent cations. These findings provide an effective strategy for developing sub-2-nanometer sized membranes with specific interaction sites for high-efficiency ionic separation.

Automated summary

Research demonstrates that COF membranes with a channel size of approximately 1.4 nm exhibit efficient ion sieving properties, with high monovalent cation permeation rates and low multivalent cation permeabilities.