"Cation-Recognition" Effect of 2D Nanochannels in Graphene Oxide Membranes Intercalated with Ionic Liquid for High Desalination Performance.

Water and ion transport in nanochannels is crucial for membrane-based technology in biological systems. 2D materials, especially graphene oxide (GO), the most frequently used as the starting material, are ideal building blocks for developing synthetic membranes. However, the selective exclusion of small ions while maintaining in a pressured filtration process remains a challenge for GO membranes. Herein, a novel "cation-recognition" effect is introduced within the nanochannels of reduced GO (rGO) membranes modified by ionic liquids (IL) to enhance the desalination performance. The resulting IL-intercalated rGO (IL-rGO) membranes exhibit remarkable stability even under prolonged exposure to acidic and basic conditions, without damage or delamination and maintain approximately ultrahigh water permeance (≈32.0 L m h bar) and high NaSO rejection. The density functional theory calculations revealed that IL-rGO nanochannels exhibited different exclusion effects on cations (Na and /or K) and the attraction effect on water molecules, which led to the "cation-recognition" effect. Overall, this work provides a theoretical framework in sub-nanochannels for developing advanced 2D nanochannels to address the critical challenge of freshwater scarcity.