Ion-selective channels play a key role in physiological processes and are used in many technologies. Although biological channels can efficiently separate same-charge ions with similar hydration shells, it remains a challenge to mimic such exquisite selectivity using artificial solid-state channels. Although there are several nanoporous membranes that show high selectivity with respect to certain ions, the underlying mechanisms are based on the hydrated ion size and/or charge. There is a need to rationalize the design of artificial channels to make them capable of selecting between similar-sized same-charge ions, which, in turn, requires an understanding of why and how such selectivity can occur. Here we study ångström-scale artificial channels made by van der Waals assembly, which are comparable in size with typical ions and carry little residual charge on the channel walls. This allows us to exclude the first-order effects of steric- and Coulomb-based exclusion. We show that the studied two-dimensional ångström-scale capillaries can distinguish between same-charge ions with similar hydrated diameters. The selectivity is attributed to different positions occupied by ions within the layered structure of nanoconfined water, which depend on the ion-core size and differ for anions and cations. The revealed mechanism points at the possibilities of ion separation beyond simple steric sieving.

离子选择性通道在生理过程中起着关键作用，并用于许多技术中。尽管生物通道可以有效地分离具有相似水化壳的相同电荷离子，但使用人工固态通道来模拟这种精妙的选择性仍然是一个挑战。尽管有几种纳米多孔膜对某些离子表现出高选择性，但潜在的机制是基于水合离子的大小和/或电荷。有必要使人工通道的设计合理化，使它们能够在大小相似、电荷相同的离子之间进行选择，而这反过来又需要了解这种选择性发生的原因和方式。在这里，我们研究了由范德瓦尔斯装配制成的 ångström 级人工通道，它们的大小与典型离子相当，并且在通道壁上几乎没有残留电荷。这使我们能够排除基于空间和库仑排斥的一阶效应。我们表明所研究的二维 ångström 级毛细管可以区分具有相似水合直径的相同电荷离子。选择性归因于离子在纳米承压水的层状结构中占据的不同位置，这取决于离子核尺寸并且阴离子和阳离子不同。揭示的机制指出了离子分离超越简单空间筛分的可能性。我们表明所研究的二维 ångström 级毛细管可以区分具有相似水合直径的相同电荷离子。选择性归因于离子在纳米承压水的层状结构中占据的不同位置，这取决于离子核尺寸并且阴离子和阳离子不同。揭示的机制指出了离子分离超越简单空间筛分的可能性。我们表明所研究的二维 ångström 级毛细管可以区分具有相似水合直径的相同电荷离子。选择性归因于离子在纳米承压水的层状结构中占据的不同位置，这取决于离子核尺寸并且阴离子和阳离子不同。揭示的机制指出了离子分离超越简单空间筛分的可能性。