Elucidating molecular transport behaviors in vertically aligned GO membranes with tunable sub-nanometer interlayer spacing

Unraveling molecular transport behaviors in extremely confined two-dimensional (2D) nanochannels, especially the impact of sub-nanometer interlayer spacing, is essential for designing high-precision separation membranes. However, it remains a challenging issue due to the complex physical and chemical structures of conventional 2D lamellar membranes. Herein, vertically aligned graphene oxide (GO) membranes featuring stable and long-range nanochannels are constructed. Significantly, the interlayer spacing is precisely tuned from 0.76 to 0.98 nm by controlling relative humidity with saturated salt solutions. It is demonstrated that, for these GO membranes, organic solvent permeance generally increases monotonically with increasing interlayer spacing. In stark contrast, water transport exhibits an anomalous non-monotonic dependence, with a minimum permeance of 0.52 LMH bar −1 at a critical interlayer spacing of 0.87 nm, significantly lower than 4.35 and 3.46 LMH bar −1 at 0.81 and 0.92 nm, respectively. This phenomenon originates from the confinement-induced reconstruction of hydrogen-bond networks into an ice-like ordered structure at the critical spacing, which markedly elevates the diffusion energy barrier, thus leading to the lowest permeance. This work reveals the molecular transport behaviors under extreme confinement, providing novel theoretical insights into confined molecular transport.