2D nanofluidic vermiculite membranes with self-confinement channels and recognition sites for ultrafast lithium ion-selective transport

Two-dimensional (2D) membranes with lamina nanofluidic channels hold great promise for ion selective transport. However, the complex nanosheets preparation process and undesirable ion sieving ability of 2D channels in aqueous environment hindered the further application of 2D membranes. Herein, we designed and constructed 2D vermiculite-based nanofluidic membranes with ultrafast lithium ion-selective transport channels through interlayer chemical modification-to introduce sulfonated polyvinyl alcohol (SPVA). As for salt concentration of 0.2 M, the optimal VmMS-1 membrane with stable and sub-nanometer ion selective channels exhibited high Li⁺ permeation rate up to ∼1.3 mol m⁻² h⁻¹ driven by concentration gradient difference, while the selectivity of Li⁺/Mg²⁺, Li⁺/Na⁺, and Li⁺/K⁺ reached 23.8, 14.9, 19.1, respectively. Self-confinement ion recognition (SCIR) mechanism was proposed to describe the superior lithium ion-selective transport process in 2D confined channels. Self-confinement interlayer channel could manipulate the water-shell layer of ions and sulfonic acid groups could effectively recognize lithium ion to accelerate them transport. This study provides a new vermiculite membrane design insight based on SCIR mechanism that is expected to achieve high lithium extraction, as well as providing a new insight of membrane design for other 2D materials.