Emerging Selective Ion Transport via 2D Confined Space for the Innovations in Separation and Energy Technologies

Ion transport technology is pivotal in energy and environmental applications, yet traditional bulk materials, such as ion exchange membranes (IEMs) and porous ceramics, face limitations in selectivity, mechanical stability, and adaptability under dynamic conditions. Two-dimensional (2D) materials, including graphene oxide (GO), MXene, and covalent organic frameworks (COFs), offer transformative potential due to their tunable nanochannels, surface chemistry, and confinement effects. However, challenges persist in long-term structural stability, selectivity decay in complex environments, and scalable fabrication, alongside an insufficient mechanistic understanding of ion-material interactions under nanoconfinement. This review systematically analyzes ion transport mechanisms in 2D nanochannels, focusing on material design strategies (e.g., layer spacing regulation, heterostructures, and external field modulation), performance optimization, and applications in membrane separation, osmotic energy harvesting, energy storage, and sensing. Key findings reveal that 2D materials enhance ion selectivity via size exclusion, charge regulation, and solvation modification, while photothermal synergy, voltage-controlled pores, and dynamic hydrogen-bond networks enable breakthroughs in efficiency and adaptability. For instance, MXene/metal-organic framework (MOF) composites achieve osmotic power densities up to 8.29 W/m² and COF membranes attain Li⁺/Mg²⁺ selectivity of 190. The integration of machine learning and advanced simulations is highlighted for future mechanistic exploration. This work provides critical insights into designing high-performance, intelligent ion transport systems, bridging fundamental research with practical applications in desalination, energy conversion, and biomedicine, thereby advancing the development of next-generation membrane technologies.