Wang Rui, Ding Li, Xue Jian, Wu Haoyu, Cai Chengzhi, Qiao Zhiwei, Caro Jürgen, Wang Haihui
Beijing Key Laboratory for Membrane Materials and Engineering, Department of Chemical Engineering, Tsinghua University, Beijing, 100084, China.
Guangdong Provincial Key Lab of Green Chemical Product Technology, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, 510640, China.
Small Methods. 2025 Mar;9(3):e2401111. doi: 10.1002/smtd.202401111. Epub 2024 Oct 15.
Artificial membranes with ion-selective nanochannels for high-efficiency mono/divalent ion separation are of great significance in water desalination and lithium-ion extraction, but they remain a great challenge due to the slight physicochemical property differences of various ions. Here, the successful synthesis of two-dimensional TpEBr-based covalent organic framework (COF) nanosheets, and the stacking of them as consecutive membranes for efficient mono/divalent ion separation is reported. The obtained COF nanosheet membranes with intrinsic one-dimensional pores and abundant cationic sites display high permeation rates for monovalent cations (K, Na, Li) of ≈0.1-0.3 mol m h, while the value of divalent cations (Ca, Mg) is two orders of magnitude lower, resulting in an ultrahigh mono/divalent cation separation selectivity up to 130.4, superior to the state-of-the-art ion sieving membranes. Molecular dynamics simulations further confirm that electrostatic interaction controls the confined transport of cations through the cationic COF nanopores, where multivalent cations face i) strong electrostatic repulsion and ii) steric transport hindrance since the large hydrated divalent cations are retarded due to a layer of strongly adsorbed chloride ions at the pore wall, while smaller monovalent cations can swiftly permeate through the nanopores.
具有离子选择性纳米通道的人工膜用于高效单/二价离子分离，在海水淡化和锂离子提取方面具有重要意义，但由于各种离子的物理化学性质差异微小，仍然是一个巨大的挑战。在此，报道了二维基于TpEBr的共价有机框架（COF）纳米片的成功合成，以及将它们堆叠成连续膜用于高效单/二价离子分离。所获得的具有固有一维孔和丰富阳离子位点的COF纳米片膜对单价阳离子（K、Na、Li）显示出约0.1 - 0.3 mol m⁻² h⁻¹的高渗透速率，而二价阳离子（Ca、Mg）的值低两个数量级，从而导致高达130.4的超高单/二价阳离子分离选择性，优于目前最先进的离子筛分膜。分子动力学模拟进一步证实，静电相互作用控制阳离子通过阳离子COF纳米孔的受限传输，其中多价阳离子面临：i）强静电排斥，ii）空间传输阻碍，因为大的水合二价阳离子由于孔壁上一层强烈吸附的氯离子而受阻，而较小的单价阳离子可以迅速渗透通过纳米孔。
