Understanding the Ion Transport Behavior across Nanofluidic Membranes in Response to the Charge Variations

Biological pores regulate the cellular traffic of a diverse collection of molecules, often with extremely high selectivity. Given the ubiquity of charge-based separation in nature, understanding the link between the charged functionalities and the ion transport activities is essential for designing delicate separations, with the correlation being comparatively underdeveloped. Herein, the effect of charge density from the impact of pore structure is decoupled using a multivariate strategy for the construction of covalent organic framework-based membranes. How the density of charged sites in the nanofluidic membranes affect the ion transport activity with particular emphasis on Li⁺ and Mg²⁺ ions, relevant to the challenge of salt-lake lithium mining is systematically investigated. Systematic control of the charge distribution produces membranes with numerous advantages, overcoming the long-term challenge of Li⁺/Mg²⁺ separation. The top membrane exhibits an outstanding equilibrium selectivity for Li⁺ over Mg²⁺ and operational stability under diffusion dialysis and electrodialysis conditions (Li⁺/Mg²⁺ up to 500), qualifying it as a potential candidate for lithium extraction. It is anticipated that the developed nanofluidic membrane platform can be further leveraged to tackle other challenges in controlled separation processes.