Coupling solute interactions with functionalized graphene membranes: towards facile membrane-level engineering

Optimizing ion transport through nanoporous graphene membranes with intricate engineering at nanoscale levels finds applications ranging from ion segregation to desalination. Such membrane-level engineering often requires futuristic and state-of-the-art micro- and nanofabrication infrastructure making it less accessible to widespread applications. In this study, the effective membrane pore size is modulated using macroscopic membrane functionalization, which, when combined with the solute concentration, can prove to be facile nanoscale engineering towards achieving selectivity. By performing robust molecular dynamics (MD) simulations of aqueous NaCl solution through a nanoporous graphene membrane, we demonstrate that varying membrane wettability influences the structural organization of ions and water molecules both in the vicinity and inside the nanopore, which is manifested in the form of altered permeation characteristics. Moreover, the disparate solvation characteristics of the ionic species in conjunction with the variable van der Waals interactive forces affect the ion-selective nature (Cl- over Na+) of the membrane. The relative hydrophilization, resulting from the effective functionalization of the nanoporous graphene membrane, not only allows greater control over the permeation characteristics of ions and water molecules mediated by an altered depletion ratio but also gives rise to the ion-selective nature of the membrane, thus providing a sound understanding of the transport properties of ion-water solutions through nanoporous materials.

Automated summary

This study demonstrates the facile nanoscale engineering of ion transport through nanoporous graphene membranes by modulating the effective membrane pore size using macroscopic membrane functionalization. Molecular dynamics simulations reveal that the varying membrane wettability influences the structural organization of ions and water molecules in the nanopore, leading to altered permeation characteristics. The solvation characteristics of ionic species and van der Waals interactive forces also play a role in the ion-selective nature of the membrane. The relative hydrophilization of the nanoporous graphene membrane allows control over the permeation characteristics and results in ion selectivity.