Nanochannel membranes for ion-selective electrodialysis: principles, materials, and environmental applications

Abstract

Ion-selective electrodialysis (SED) has emerged as a promising approach for water purification, resource recovery, and electrochemical processes. While conventional ion-exchange membranes (IEMs) enable efficient charge-based ion separation, their disordered polymer networks lack the structural precision needed to distinguish ions with similar valence or hydrated size. As separation demands become increasingly stringent, IEMs have evolved toward advanced ion-selective membranes that introduce nanoscale confinement and engineered interfacial chemistries. These developments have culminated in the emergence of nanochannel membranes, which feature geometrically defined sub-nanometer channels that promote surface-governed ion transport and enable ion–ion selectivity far beyond the capabilities of traditional IEMs. This review integrates fundamental principles of electrochemical ion transport with recent advances in nanochannel membrane design for SED. We first elucidate the key mechanisms governing ion selectivity, including dehydration-based partitioning at the channel entrance, intra-channel ion–pore interactions, and dimensionality-dependent transport in 1D, 2D, and 3D nanochannels. We then survey major material platforms used to construct nanochannel membranes, such as ultrathin polymeric layers, two-dimensional nanosheet laminates, crystalline porous frameworks, and ceramic nanochannels. Finally, we outline design principles for controlling channel dimensions, interfacial charge, and structural stability, and discuss remaining challenges in translating nanochannel-enabled SED into efficient, durable, and industrially relevant ion-separation technologies.