Adsorption of common solvent molecules on graphene and MoS$_2$ from first-principles

TL;DR

This study uses first-principles calculations to investigate how common solvent molecules interact with graphene and MoS$_2$, revealing weak physisorption but notable charge rearrangements at the interface, which could influence material processing.

Contribution

It provides detailed atomic-scale insights into solvent-layer interactions, challenging the assumption that solvents do not significantly affect 2D materials.

Findings

Solvent molecules are physisorbed with negligible charge transfer.

Adsorption strength is independent of solvent polarity.

Significant charge rearrangement occurs at the interface after adsorption.

Abstract

Solvents are an essential element in the production and processing of two-dimensional (2D) materials. For example, the liquid phase exfoliation of layered materials requires a solvent to prevent the resulting monolayers from re-aggregating, while solutions of functional atoms and molecules are routinely used to modify the properties of the layers. It is generally assumed that these solvents do not interact strongly with the layer and so their effects can be neglected. Yet experimental evidence has suggested that explicit atomic-scale interactions between the solvent and layered material may play a crucial role in exfoliation and cause unintended electronic changes in the layer. Little is known about the precise nature of the interaction between the solvent molecules and the 2D layer. Here, we use density functional theory calculations to determine the adsorption configuration and binding energy of a variety of common solvent molecules, both polar and non-polar, on two of the most popular 2D materials, namely graphene and MoS$_2$. We show that these molecules are physisorbed on the surface with negligible charge transferred between them. We find that the adsorption strength of the different molecules is independent of the polar nature of the solvent. However, we show the molecules induce a significant charge rearrangement at the interface after adsorption as a result of polar bonds in the molecule.