Anomalous Ion Transport in 2D Graphene Oxide Nanochannels Enabled by Hydration Mimicry with Confined Amino Acids

Inspired by biological ion channels, we design graphene oxide (GO) membranes functionalized with aspartic acid to introduce ion-specific binding sites within angstrom-scale confinement. This leads to a notable suppression of monovalent ion mobility, contributing to unexpected selectivity for divalent calcium ions, with Ca²⁺/Li⁺ and Ca²⁺/Na⁺ selectivities of ∼9.8 and ∼4.8, respectively. With the combination of transition-state theory and molecular dynamics simulations, the complex interplay of hydration energy, spatial confinement, and ion-ligand coordination strength is highlighted, offering a mechanistic basis for designing membranes with nonclassical selectivity profiles.