Ion-disrupted hydrogen-bond networks enable fast water transport under two-dimensional confinement

Water transport under nanoscale confinement often exhibits anomalously high flow rates that defy classical hydrodynamic descriptions. While such behavior is commonly analyzed assuming pure water, confined water under realistic conditions inevitably contains dissolved ions. How ion-water interactions reshape hydrogen-bond networks and regulate nanoscale water transport therefore remains poorly understood. Here we study ion-modulated water transport using vermiculite-based two-dimensional nanochannels with tunable, exchangeable interlayer cations. Despite larger interlayer spacings, membranes hosting strongly hydrated ions exhibit markedly slower water transport, whereas weakly hydrated ions enable ultrafast permeation. Infrared spectroscopy reveals ion-dependent restructuring of the hydrogen-bond network, with weakly hydrated cations disrupting hydrogen-bond connectivity and shifting the O-H stretching band toward higher frequencies. Molecular dynamics simulations further show that such disruption enhances the population and mobility of dynamically exchanging hydration water, which dominates two-dimensional water diffusion under confinement. These findings establish ionic effects as an essential component of confined water transport and provide a molecular framework for understanding anomalous water flow across natural and engineered nanochannels.