Ion and water transport in charge-modified graphene nanopores

TL;DR

This study uses molecular dynamics simulations to explore how charge modifications on graphene nanopores influence ion selectivity and water transport, revealing charge-dependent ion rejection and enhanced water flow.

Contribution

It demonstrates how edge charge modifications on graphene nanopores can control ion selectivity and significantly enhance water transport, providing insights for membrane design.

Findings

Nanopores are selective to counterions based on charge.

Total ionic currents exhibit an increase-decrease profile with charge.

Water transport is notably enhanced by charge modification, especially positive charges.

Abstract

Porous graphene has high mechanical strength and atomic layer thickness, which make it a promising material for material separation and biomolecule sensing. Electrostatic interactions between charges in aqueous solution are a kind of strong long-range interaction which may have great influence on the fluid transport through nanopores. Here, molecular dynamics simulations were conducted to investigate ion and water transport through a 1.05-nm-in-diameter monolayer graphene nanopore with its edge charge-modified. From the results, it is found that the nanopores are selective to counterions when they are charged. As the charge amount increases, the total ionic currents show an increase-decrease profile while the co-ion currents monotonously decrease. The co-ions rejection can reach 75% and 90% when the nanopores are negatively and positively charged, respectively. Cl ions current increases and reaches a plateau, and Na+ current decreases with the charge amount in the systems where they act as counterions. Besides, the charge modification can enhance the water transport through nanopores obviously. This is mainly due to the ion selection of nanopores. Especially, positive charges on the pore edge facilitate the water transport much more than negative charges.