Intrinsic interface adsorption drives selectivity in atomically smooth nanofluidic channels

TL;DR

This paper combines molecular dynamics, linear response theory, and hydrodynamics to explain how intrinsic molecular interactions at interfaces cause ion selectivity in atomically smooth nanofluidic channels, enabling desalination.

Contribution

It introduces a comprehensive framework integrating simulations and theory to understand ion selectivity driven by interface adsorption in nanofluidic channels.

Findings

Intrinsic molecular interactions cause ion adsorption at interfaces.

Ion selectivity arises without surface charge due to molecular interactions.

Nanochannels can be used as desalination membranes.

Abstract

Specific molecular interactions underlie unexpected and useful phenomena in nanofluidic systems, but require descriptions that go beyond traditional macroscopic hydrodynamics. In this letter, we demonstrate how equilibrium molecular dynamics simulations and linear response theory can be synthesized with hydrodynamics to provide a comprehensive characterization of nanofluidic transport. Specifically, we study the pressure driven flows of ionic solutions in nanochannels comprised of two-dimensional crystalline substrates made from graphite and hexagonal boron nitride. While simple hydrodynamic descriptions do not predict a streaming electrical current or salt selectivity in such simple systems, we observe that both arise due to the intrinsic molecular interactions that act to selectively adsorb ions to the interface in the absence of a net surface charge. Notably, this emergent selectivity indicates that these nanochannels can serve as desalination membranes.