In this study, molecular simulation is utilized to explore the charge effect in COF membranes on separation performance. Three types of COF membranes with different functional groups (Tp-Tta-COOH, Tp-Tta-COO⁻ and Tp-Tta-NH₃⁺) and thus different charges are designed. It is found that the positively charged membrane (Tp-Tta-NH₃⁺) shows higher ion selectivity in mixed Li⁺/Mg²⁺ ion solution, compared with the negatively charged and neutral membranes. In Tp-Tta-NH₃⁺ membrane, the effective pore size is reduced by the secondary confinement effect of Cl⁻ ions. The orderly arranged anions (Cl⁻) reduce the actual pore size and generate the secondary confinement effect, which fortifies the pore-entrance sieving effect, and due to the large difference in hydration energies of Li⁺ and Mg²⁺ ions, the former is easier to dehydrate and enter the pore. The charge effect in Li⁺/Mg²⁺ separation uncovered by molecular simulation is microscopically insightful toward the design of COF membranes and other organic framework membranes for high-performance ion separation.

在本研究中，分子模拟用于探索 COF 膜中的电荷对分离性能的影响。设计了三种具有不同官能团（Tp-Tta-COOH、Tp-Tta-COO ^-和Tp-Tta-NH ₃ ⁺）并因此具有不同电荷的COF膜。发现带正电的膜(Tp-Tta-NH ₃ ⁺ )在混合的Li ⁺ /Mg ²⁺离子溶液中表现出比带负电和中性膜更高的离子选择性。在Tp-Tta-NH ₃ ⁺膜中，有效孔径因Cl ^-离子的二次限制效应而减小。有序排列的阴离子（Cl ^-) 减小实际孔径，产生二次限制效应，强化了入孔筛分效果，由于Li ⁺和Mg ²⁺离子的水合能差异较大，前者更容易脱水进入孔隙. 通过分子模拟揭示的Li ⁺ /Mg ²⁺分离中的电荷效应在微观上对 COF 膜和其他用于高性能离子分离的有机骨架膜的设计具有重要意义。