Recent advances in monovalent ion selective membranes towards environmental remediation and energy harvesting

Advanced membranes are highly necessitated for critical industrial applications for alleviating contemporary environmental and energy issues coupled with increasing climate change. Especially, monovalent ion selective membranes (MISMs) with exceptionally high selectivity for mono/multivalent ions under low-pressure or low-voltage environments are appealing for precise ion separations with reduced energy consumption. Most recently, the rapid development of emerging materials (such as carbon nanomaterials, porous frameworks and polyelectrolytes) is conducive to enhancing the separation performance of MISMs. Therein, emerging materials with desirable structure and properties can supply supernumerary sub-nano pore sizes, wettability, charge density, and functional groups. With their unique virtues, MISMs are promising to improve separation efficiency and energy efficiency in diverse environmental and energy applications, including water treatment, lithium extraction, vanadium redox flow batteries (VRFBs) and reverse electrodialysis (RED). Herein, this review highlights ion transport mechanisms of MISMs and the structure–function relationship between the structure of membrane materials and membrane separation performance. The combination between conventional methods and emerging materials results in much higher ion selectivity of MISMs, which can be applied in both traditional fields and emerging areas. At last, the current challenges are discussed and future perspectives are also proposed.