Designing a biomimetic graphene nanopore with valence selectivity between cations

Biological ion channels exhibit many remarkable mass-transport properties, including high selectivity and permeability, which are also highly desired in practical applications. Herein, using molecular dynamics simulations, we design a biomimetic graphene nanopore with valence selectivity for monovalent cations, by tailoring pore size and modifying the pore rim with four negatively charged carboxylate groups to mimic the selectivity filter of bacterial Na⁺ channels such as NavAb. The results indicate that under electric fields, the biomimetic nanopore preferentially conducts Na⁺ over Ca²⁺, as the carboxylate groups in the nanopore selectively bind Ca²⁺ and slow down its passage through the nanopore. In contrast, Na⁺ interacts with the carboxylate groups less strongly and passes across the nanopore quickly. Under strong fields, a Cl⁻ concentration polarization layer quickly forms on one side of the nanopore and promotes the formation of stable clusters of Cl⁻ and Ca²⁺ pairs bound at the carboxylate groups, which severely hinders the transport of Cl⁻ and occasionally suspends the transport of cations across the nanopore. These molecular insights provide some design principles and implications for fabricating nanoporous graphene membranes for separation applications, such as heavy metal removal from wastewater.