Engineering Charge Spatial Configuration: A Paradigm Shift from Homogeneous Donnan Exclusion to Charge-mosaic Induced Cotransport

Abstract

The precise extraction of strategic resources such as lithium and rare earth elements from complex aqueous systems like salt lake brines and industrial effluents presents a major challenge for sustainable water utilization and the circular economy. The core solution lies in developing separation technologies with ultimate ion selectivity. Traditional nanofiltration membranes rely on the Donnan exclusion effect generated by homogeneous surface charges. However, when facing ion pairs with similar hydration radii but different valences (e.g., Li⁺/Mg²⁺), their selectivity falls short of practical resource recovery requirements. The key to overcoming this bottleneck is to reconstruct the charge distribution of the membrane from a static, uniform background to a spatially specific arrangement tailored for the separation target. This article explains the principle of charge-mosaic membranes, which are characterized by the formation of ordered positive and negative charge microdomains on their surface or interior (known as charge-mosaic structures). These microdomains are designed to match the characteristics of target ions, creating electrostatic recognition sites and distinct transport pathways for specific ions. The microscopic physical mechanisms, key fabrication routes, and advanced characterization methods for realizing this paradigm are reviewed. By integrating multiscale simulations and materials informatics, this review aims to provide a clear framework for the rational design and engineered application of electrostatic microenvironments at membrane interfaces, driving a paradigm shift in water treatment and strategic resource recovery technologies.