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Graphene oxide (GO) laminate membranes for water purification have surged in popularity due to their hydrophilicity, high throughput and excellent separation abilities. However, concerns about swelling and stability in water persist. Herein, we prepared high stability, composite reduced graphene oxide (rGO)/graphene oxide (GO) membranes. The composite membranes (i.e. rGO/GO composite membranes) displayed excellent rejection performance for methylene blue (MB) of up to 99.0%, together with ultrahigh water permeance (201.7 L m−2 h−1 bar−1) compared to pristine GO membranes (54.8 L m−2 h−1 bar−1). This study broadens the applications of graphene-based membranes and enhances their performance in water treatment. [ABSTRACT FROM AUTHOR]

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 -2 h -1 bar -1 ) and high Na 2 SO 4 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., (© 2025 Wiley‐VCH GmbH.)