Crown Ether Rotaxane-Induced Construction of COF Membranes With Recognition Channels for High-Efficiency Ion Sieving

Biological ion channels can achieve high ion discrimination through the synergy between pore structure and microenvironment. However, constructing biomimetic ion-sieving membranes with precise recognition capabilities for target ions remains challenging. Herein, we propose a rotaxane-induced stacking method for constructing COF membranes integrated with ion-recognition sub-nanoscale channels. The dibenzo-crown ether rotaxane COF (CRCOF) nanosheets are fabricated and subsequently stacked into membranes. Driven by π-π interactions between rotaxane moieties and CRCOF nanosheets, as well as the specific ion-recognition ability of rotaxanes, the nanosheets undergo oriented stacking, yielding well-defined sub-nanoscale channels equipped with recognition sites. The angstrom-scale pore size and specific binding channels synergistically enhance selectivity and minimize transport energy penalties of target ions. By modulating the ion recognition capability of channels, the obtained CRCOF membrane demonstrates an exceptional Li⁺ permeation rate of 0.04 mol m^-2 h^-1 (approximately five times higher than reported polymer membranes) and high Li⁺ selectivity (Li⁺/Mg²⁺ selectivity of 315 and Li⁺/Na⁺ selectivity of 12) in a mixture solution. This work provides a new avenue for the accurate construction of biomimetic ion-sieving membranes and offers new insights into the mechanisms of high-efficiency ion separation in sub-nanoscale confined recognition channels.