Regulate Ion Transport in Subnanochannel Membranes by Ion-Pairing

The ability of biological ion channels to respond to environmental stimuli, regulate ion permeation rates, and selectively transport specific ions is essential for sustaining physiological functions and holds immense potential for various practical applications. In this study, we report a highly selective ion separation membrane capable of responding to ionic stimuli, thereby regulating the permeation rate of the target ions. This membrane is constructed from two-dimensional MXene nanosheets functionalized with γ-poly(glutamic acid) (γ-PGA) molecules. Its biomimetic ion channel structure provides spatial confinements, as well as ion recognition and response sites. Remarkably, the membrane demonstrates the ability to respond to stimulus ions, achieving regulation of target ion permeation rates by over 2 orders of magnitude and achieving a K⁺/Mg²⁺ selectivity exceeding 10.³ Unlike traditional nanochannel membranes, where ion transport is predominantly driven by ion-channel interactions, this membrane operates through an ion-ion interaction-dominated mechanism. The introduction of stimulus ions dynamically alters ion-pair formation within the subnanochannels, thereby modulating the permeation rates of target ions. This study provides a fresh perspective on ion transport mechanisms in nanoconfined environments, reflecting conditions closer to those in real-world systems. It underscores the pivotal role of ion-ion interactions in regulating ion transport and offers valuable insights into the design of next-generation ion separation membranes with tailored responsiveness.