A Matthew MXene (Ti3C2Tx) Lamellar Membrane as a Potassium-Sieving Amplifier

Abstract

Transport channels with ultrahigh K⁺ selectivity over other ions play a crucial role for living beings, but constructing ionic channels with promising K⁺ selectivity and permeability remains a challenge. Here, an asymmetric bilayer membrane based on MXene (Ti₃C₂T_x) lamellar channels consisting of a recognition layer (RL) on top of an enhancement layer (EL) exhibits an amazing Matthew effect: amplification of the preferred transport of K⁺, resulting in an excellent K⁺-separation performance. The K⁺ ion is selected by the 1-aza-18-crown-6 ether-modified RL, owing to preferential affinity energy, and then rapidly transported as a hydrated ion through the EL, based on the confinement effect. Other undesired ions such as Na⁺ are hindered from entering the RL by the preferred K⁺ occupation of the crown ether. The MXene (Ti₃C₂T_x)-based Matthew membrane presents high K⁺-permeation rates of 0.1–0.2 mol∙m⁻²∙h⁻¹, with a significant K⁺/Na⁺ selectivity of 5–9. The molecular separation mechanism of the Matthew membrane is investigated deeply to explore the nature of the Matthew amplification effect on K⁺ sieving, where the precise matching of the RL and EL within the membrane governs the fast K⁺ permeation with good selectivity. The asymmetric structure of our Matthew membrane is the key to understanding the biological function of ion channels for precise and fast ion transport, which will guide us in the creation of artificial ion channels or membranes.