A Bioinspired Free-Standing 2D Crown-Ether-Based Polyimine Membrane for Selective Proton Transport.

Abstract

Biological proton channels play important roles in the delicate metabolism process, arousing great interest in mimicking selective proton transport. Herein, we designed a bioinspired proton transport membrane by bringing flexible 14-crown-4 (14C4) units into rigid frameworks of polyimine films by an interfacial Schiff base reaction. The Young's modulus of the membrane reaches ~8.2 GPa. The 14C4 units could grab water forming hydrogen bond-water networks and acting as jumping sites to lower the energy barrier of proton transport. The molecular chains present a vertical orientation to the membrane, and the ions travel between the quasi-planar molecular sheets. Also, the 14C4 moieties could bond alkali ions via host-guest interaction. Thus, the ion conductance follows H+ ≫ K+ > Na+> Li+, and an ultrahigh selectivity of H+/Li+ (~215) is resulted. This study provides an effective avenue for developing ion-selective membranes by embedding macrocycles motif with inherent cavities.