Probing the Structure of Water at the Interface with Graphene Oxide Using Sum Frequency Generation Vibrational Spectroscopy

The structure of water at the graphene oxide (GO)/water interface has received considerable attention due to the high performance of GO in a wide number of applications. In this work, a face-up geometry of sum frequency generation (SFG) vibrational spectroscopy was employed to deduce the structure of water at the GO/water interface in which GO nanosheets were covered onto the water surface via Langmuir compression. The SFG results showed that the intense OH stretching bands at the range of 3000–3600 cm–1were predominant in the spectrum with high GO coverage, which is mainly due to the third-order susceptibility χ(3)response from the water orientation in the electrical double layer induced by the static electric field of the negatively charged GO surface. In addition, the second-order susceptibility χ(2)response was relatively weak, suggesting that a few water molecules formed a H-bonding network within the closest GO surface. This work is beneficial to the in-depth understanding of water in contact with GO-based materials.