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

Biological proton channels play important roles in the delicate metabolism process, and have led to great interest in mimicking selective proton transport. Herein, we designed a bioinspired proton transport membrane by incorporating 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 about 8.2 GPa. The 14C4 units could grab water, thereby 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. Furthermore, the 14C4 moieties could bond alkali ions through host–guest interactions. Thus, the ion conductance follows H⁺≫K⁺>Na⁺>Li⁺, and an ultrahigh selectivity of H⁺/Li⁺ (ca. 215) is obtained. This study provides an effective avenue for developing ion-selective membranes by embedding macrocycle motifs with inherent cavities.