Surface-Specific Spectroscopy of Water at a Potentiostatically Controlled Supported Graphene Monolayer.

L B Dreier,M Bonn,M.-J Van Zadel,E H G Backus,Z Liu,A Narita,K.-J Tielrooij,K Müllen

doi:10.1021/acs.jpcc.9b05844

Abstract

Knowledge of the structure of interfacial water molecules at electrified solid materials is the first step toward a better understanding of important processes at such surfaces, in, e.g., electrochemistry, atmospheric chemistry, and membrane biophysics. As graphene is an interesting material with multiple potential applications such as in transistors or sensors, we specifically investigate the graphene–water interface. We use sum-frequency generation spectroscopy to investigate the pH- and potential-dependence of the interfacial water structure in contact with a chemical vapor deposited (CVD) grown graphene surface. Our results show that the SFG signal from the interfacial water molecules at the graphene layer is dominated by the underlying substrate and that there are water molecules between the graphene and the (hydrophilic) supporting substrate.

Highlights

Due to the importance of the graphene−water interactions in various technological applications, it is of great interest to improve our understanding of the water structure at the graphene−water interface
Our results show that the sum-frequency generation (SFG) signal from the interfacial water molecules at the graphene layer is dominated by the underlying substrate and that there are water molecules between the graphene and the supporting substrate
The reported water contact angles for graphene range from 20° to 127°.4,5. These variations are often attributed to chemical doping or substrate effects.[6−8] Given that materials with a water contact angle below 90° are defined as hydrophilic,[9] this implies that it is debated whether graphene is hydrophilic or hydrophobic

Summary

Introduction

Due to the importance of the graphene−water interactions in various technological applications, it is of great interest to improve our understanding of the water structure at the graphene−water interface. There is still no scientific consensus regarding the wettability of graphene, one of the most fundamental properties of the graphene−water interface. The reported water contact angles for graphene range from 20° to 127°.4,5. These variations are often attributed to chemical doping or substrate effects.[6−8] Given that materials with a water contact angle below (above) 90° are defined as hydrophilic (hydrophobic),[9] this implies that it is debated whether graphene is hydrophilic or hydrophobic The reported water contact angles for graphene range from 20° to 127°.4,5 These variations are often attributed to chemical doping or substrate effects.[6−8] Given that materials with a water contact angle below (above) 90° are defined as hydrophilic (hydrophobic),[9] this implies that it is debated whether graphene is hydrophilic or hydrophobic

Methods

Results

Conclusion