Crown Ether-Based Covalent Organic Framework Packed Nanofiltration Membrane for Efficient Mg²⁺/Li⁺ Ion Sieving

Developing new highly selective ion separation membranes is of great significance, but it remains a major challenge. This article reports a type of covalent organic framework (ZUT-CEs-COF) using crown ether organic units. ZUT-CEs-COF has a high specific surface area, good crystallinity, and excellent stability. The ZUT-CEs-COF functionalized with crown ethers structure is introduced as a nanofiller into the nanofiltration membrane separation system for ion separation. Interestingly, the thin-film nanocomposite membrane regulated by ZUT-CEs-COF shows a significant increase in the selectivity coefficient for magnesium/lithium (Li⁺/Mg²⁺) and water flux, achieving a high flux of up to 52.4 L m^-2 h^-1, while achieving an excellent molecular screening coefficient of 26.5 for Li⁺/Mg²⁺. Density functional theory calculations further confirm that the modulation of the binding energy of ions anchored by the nanopores can provide ideas for the construction of separation membranes and promote their potential applications in the selective separation of similar ions with high selectivity.