Water Permeation through Layered Graphene-based Membranes: A Fully Atomistic Molecular Dynamics Investigation

TL;DR

This study uses atomistic molecular dynamics simulations to explore water permeation mechanisms in layered graphene and graphene oxide membranes, revealing how interlayer spacing and functional groups influence water flux and transport efficiency.

Contribution

It provides detailed atomistic insights into water transport in graphene-based membranes, highlighting the impact of functional groups and interlayer distance on permeation rates.

Findings

Water flux is higher in pristine graphene than in graphene oxide membranes.

Hydrogen bonding with oxide groups traps water, reducing flow rates.

Transport efficiency depends on interlayer spacing and membrane functionalization.

Abstract

Graphene-based membranes have been investigated as promising candidates for water filtration and gas separation applications. Experimental evidences have shown that graphene oxide can be impermeable to liquids, vapors and gases, while allowing a fast permeation of water molecules. This phenomenon has been attributed to the formation of a network of nano capillaries that allow nearly frictionless water flow while blocking other molecules by steric hindrance effects. It is supposed that water molecules are transported through the percolated two-dimensional channels formed between graphene-based sheets. Although these channels allow fast water permeation in such materials, the flow rates are strongly dependent on how the membranes are fabricated. Also, some fundamental issues regarding the nanoscale mechanisms of water permeation are still not fully understood and their interpretation remains controversial. In this work, we have investigated the dynamics of water permeation through pristine graphene and graphene oxide model membranes. We have carried out fully atomistic classical molecular dynamics simulations of systems composed of multiple layered graphene-based sheets into contact with a water reservoir under controlled thermodynamics conditions (e. g., by varying temperature and pressure values). We have systematically analyzed how the transport dynamics of the confined nanofluids depend on the interlayer distances and the role of the oxide functional groups. Our results show the water flux is much more effective for graphene than for graphene oxide membranes. These results are attributed to the H-bonds formation between oxide functional groups and water, which traps the water molecules and precludes ultrafast water transport through the nanochannels.