posted on 2022-05-19, 07:05authored byTingting Xu, Bin Wu, Linxiao Hou, Yanran Zhu, Fangmeng Sheng, Zhang Zhao, Yun Dong, Jiandang Liu, Bangjiao Ye, Xingya Li, Liang Ge, Huanting Wang, Tongwen Xu
Membranes
of high ion permselectivity are significant for the separation
of ion species at the subnanometer scale. Here, we report porous organic
cage (i.e., CC3) membranes with hierarchical channels including discrete
internal cavities and cage-aligned external cavities connected by
subnanometer-sized windows. The windows of CC3 sieve monovalent ions
from divalent ones and the dual nanometer-sized cavities provide pathways
for fast ion transport with a flux of 1.0 mol m–2 h–1 and a mono-/divalent ion selectivity (e.g.,
K+/Mg2+) up to 103, several orders
of magnitude higher than the permselectivities of reported membranes.
Molecular dynamics simulations illustrate the ion transport trajectory
from the external to internal cavity via the CC3 window, where ions
migrate in diverse hydration states following the energy barrier sequence
of K+ < Na+ < Li+ ≪
Mg2+. This work sheds light on ion transport properties
in porous organic cage channels of discrete frameworks and offers
guidelines for developing membranes with hierarchical channels for
efficient ion separation.