▎ 摘　　要

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(-1) were predominant in the spectrum with high GO coverage, which is mainly due to the third-order susceptibility chi((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 chi((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.