Programming Permeation Inversion in Nanoconfined Ionic Liquid Membranes for Ultra-Selective CO₂/H₂ Separation.

Abstract

To bypass the enduring limitations intrinsic to traditional size-sieving separation, alternative materials for CO₂/H₂ separation need to be developed. Here, we program a permeation inversion in CO₂/H₂ transport by constructing a nanoconfined ionic liquid membrane through the synergistic engineering of graphene oxide nanosheets and ionic liquids. A substrate-assisted size-selection strategy enables the preferential incorporation of large nanosheets, which form ordered laminates, while short-chain CO₂-philic ionic liquids are precisely confined within the interlayer galleries. The resulting membrane exhibits inverted transport behavior, achieving an ultrahigh CO₂ permeance of 358.2 GPU and a mixed-gas CO₂/H₂ selectivity of 201.9 under a 10:90 CO₂/H₂ feed─surpassing the upper bounds of conventional polymeric and mixed-matrix membranes. Scalability is demonstrated using a five-cell module, in which CO₂ flux increases linearly without selectivity loss. Molecular dynamics simulations and spectroscopic studies reveal that the nanoconfined ionic liquid phase creates a continuous, high-solubility pathway for CO₂, whereas H₂ is largely excluded from the graphene oxide interfaces. This study establishes nanosheet-ionic liquid synergy as a programmable design platform to engineer permeation inversion, offering a scalable route to advanced CO₂/H₂ separation membranes.