Origin of Anomalous Water Permeation through Graphene Oxide Membrane

TL;DR

This study uses first-principles calculations to explain the atomic-level mechanisms behind the anomalous water permeation through graphene oxide membranes, focusing on ice bilayer formation and layer spacing effects.

Contribution

It introduces atomistic models that reveal how ice bilayer formation and layer spacing control water permeation in graphene oxide structures.

Findings

Formation of hexagonal ice bilayer is crucial for water permeation.

Layer spacing influences water flow and can be controlled by pressure or reduction.

Melting at flake edges affects water transport dynamics.

Abstract

Water inside the low dimensional carbon structures has been considered seriously owing to fundamental interest in its flow and structures as well as its practical impact. Recently, the anomalous perfect penetration of water through graphene oxide membrane was demonstrated although the membrane was impenetrable for other liquids and even gases. The unusual auxetic behavior of graphene oxide in the presence of water was also reported. Here, based on first-principles calculations, we establish atomistic models for hybrid systems composed of water and graphene oxides revealing the anomalous water behavior inside the stacked graphene oxides. We show that formation of hexagonal ice bilayer in between the flakes as well as melting transition of ice at the edges of flakes are crucial to realize the perfect water permeation across the whole stacked structures. The distance between adjacent layers that can be controlled either by oxygen reduction process or pressure is shown to determine the water flow thus highlighting a unique water dynamics in randomly connected two-dimensional spaces.