Unified non-equilibrium simulation methodology for flow through nanoporous carbon membrane

TL;DR

This paper introduces a unified non-equilibrium molecular dynamics simulation method to study transport phenomena in nanoporous membranes, specifically applied to carbon nano membranes for water filtration and energy harvesting.

Contribution

The paper presents a novel NEMD methodology capable of simulating various external stimuli on nanoporous membranes, applied to demonstrate the performance of carbon nano membranes in desalination and energy harvesting.

Findings

High water permeability due to entrance effects and negligible friction inside nanopores.

Prediction of significant diffusio-osmotic current without surface charges.

CNMs as promising scalable membranes for osmotic energy harvesting.

Abstract

The emergence of new nanoporous materials, based e.g. on 2D materials, offers new avenues for water filtration and energy. There is accordingly a need to investigate the molecular mechanisms at the root of the advanced performances of these systems in terms of nanofluidic and ionic transport. In this work, we introduce a novel unified methodology for Non-Equilibrium classical Molecular Dynamic simulations (NEMD), allowing to apply likewise pressure, chemical potential and voltage drops across nanoporous membranes and quantifying the resulting observables characterizing confined liquid transport under such external stimuli. We apply the NEMD methodology to study a new type of synthetic Carbon NanoMembranes (CNM), which have recently shown outstanding performances for desalination, keeping high water permeability while maintaining full salt rejection. The high water permeance of CNM, as measured experimentally, is shown to originate in prominent entrance effects associated with negligible friction inside the nanopore. Beyond, our methodology allows to fully calculate the symmetric transport matrix and the cross-phenomena such as electro-osmosis, diffusio-osmosis, streaming currents, etc. In particular, we predict a large diffusio-osmotic current across the CNM pore under concentration gradient, despite the absence of surface charges. This suggests that CNMs are outstanding candidates as alternative, scalable membranes for osmotic energy harvesting.