Structure and chemistry of graphene oxide in liquid water from first principles

Félix Mouhat,Marie-Laure Bocquet,François-Xavier Coudert

doi:10.1038/s41467-020-15381-y

Abstract

Graphene oxide is a rising star among 2D materials, yet its interaction with liquid water remains a fundamentally open question: experimental characterization at the atomic scale is difficult, and modeling by classical approaches cannot properly describe chemical reactivity. Here, we bridge the gap between simple computational models and complex experimental systems, by realistic first-principles molecular simulations of graphene oxide (GO) in liquid water. We construct chemically accurate GO models and study their behavior in water, showing that oxygen-bearing functional groups (hydroxyl and epoxides) are preferentially clustered on the graphene oxide layer. We demonstrated the specific properties of GO in water, an unusual combination of both hydrophilicity and fast water dynamics. Finally, we evidence that GO is chemically active in water, acquiring an average negative charge of the order of 10 mC m−2. The ab initio modeling highlights the uniqueness of GO structures for applications as innovative membranes for desalination and water purification.

Highlights

Graphene oxide is a rising star among 2D materials, yet its interaction with liquid water remains a fundamentally open question: experimental characterization at the atomic scale is difficult, and modeling by classical approaches cannot properly describe chemical reactivity
Our as generated graphene oxide (GO) layers are first studied without solvent, and among the stable ones, six of them are placed in liquid water at room temperature by means of long ab initio molecular dynamics (AIMD) simulations
We note that the choice of O/C ratio results from a compromise: taking values closer to the higher experimental limit would have decreased the number of possible independent replicas; while a lower ratio would require more simulation replicas in order to measure statistically significant changes in behavior

Summary

Introduction

Graphene oxide is a rising star among 2D materials, yet its interaction with liquid water remains a fundamentally open question: experimental characterization at the atomic scale is difficult, and modeling by classical approaches cannot properly describe chemical reactivity. Despite some further refinements, such as the anti position of the hydroxyl pairs in the basal plane[19,20], there is to the best of our knowledge, no clear statement about the spatial arrangement of the oxidized functions along the graphene layer Are they randomly distributed along the surface or not? To date there are mostly classical MD simulations, treating the oxygen chemical groups as passive in water[21,22,23,24,25] In this manuscript, we propose a realistic model of the GO basal plane surface, describing both water and the chemical groups at the electronic level. We perform a thorough statistical analysis by averaging over time and over replicas in order to quantitatively measures some of the physical and chemical properties of valuable interest for the community working on 2D materials and water/solid interfaces

Methods

Results

Conclusion