Dehydration induced selective ion trapping by topology constrained atomically thin graphene-crown membranes†

Abstract

Inspired by the host–guest recognition of crown ethers, the current era is evolving around the graphene-crown-based atomically thin membranes that will profoundly impact diverse fields of science and engineering. Using extensive MD simulations and DFT calculations, we investigate the binding affinities of graphene-embedded 18-crown-6, 16-crown-5, and 14-crown-4 for Li⁺, Na⁺, K⁺, Mg²⁺, and Ca²⁺ metal ions. We highlight that the binding preference of these membranes depends not only on the size of the crown ether cavity but also on the stability of the hydration shell of binding ions, as demonstrated by the hydration-induced energy transfer barrier. The diverse transport behavior of these membranes is attributed to ion transport over a free energy barrier raised from ionic dehydration. Results designate that the deformation of the hydration shell is a necessary condition for the adsorption of metal ions within crown ether pores, which controls the selectivity of the membrane for particular metal ions. The findings from microstructure analysis about the ion location and pore occupancy reveal how sub-nanopores of graphene-crown membranes are capable of distinguishing ions of similar characteristics. The observed ion dehydration and kinetic behavior are sensitive to pore size and the chemical environment lining the pore, similar to those observed with biological ion channels.