Two-Dimensional Graphene-Based Potassium Channels Built at an Oil/Water Interface

Graphene-based laminar membranes exhibit remarkable ion sieving properties, but their monovalent ion selectivity is still low and much less than the natural ion channels. Inspired by the elementary structure/function relationships of biological ion channels embedded in biomembranes, a new strategy is proposed herein to mimic biological K⁺ channels by using the graphene laminar membrane (GLM) composed of two-dimensional (2D) angstrom(Å)-scale channels to support a simple model of semi-biomembrane, namely oil/water (O/W) interface. It is found that K⁺ is strongly preferred over Na⁺ and Li⁺ for transferring across the GLM-supported water/1,2-dichloroethane (W/DCE) interface within the same potential window (-0.1-0.6 V), although the monovalent ion selectivity of GLM under the aqueous solution is still low (K⁺/Na⁺~1.11 and K⁺/Li⁺~1.35). Moreover, the voltammetric responses corresponding to the ion transfer of NH₄⁺ observed at the GLM-supported W/DCE interface also show that NH₄⁺ can often pass through the biological K⁺ channels due to their comparable hydration-free energies and cation-π interactions. The underlying mechanism of as-observed K⁺ selective voltammetric responses is discussed and found to be consistent with the energy balance of cationic partial-dehydration (energetic costs) and cation-π interaction (energetic gains) as involved in biological K⁺ channels.