Understanding the details of water interacting with graphene is essential for various applications, such as water desalination, energy storage, and catalysis. However, the hydrogen-bonding structure of the water at the graphene-water interface has not been fully understood. Vibrational sum frequency generation (VSFG) spectroscopy is suited to elucidate the water structure at graphene-water interfaces. With varying numbers of graphene layers or tuning the doping level of a single monolayer, the interfacial water structure differs substantially. Specifically, as the number of graphene layers increases, water molecules with non-H-bonded, dangling OH groups become increasingly apparent. The fraction of dangling OH groups inferred from the VSFG spectrum correlates with the water adhesion energy of graphene. This observation suggests that VSFG could be an incisive technique for measuring the water adhesion energy on any spatially confined interface where the water contact angle cannot be measured. We anticipate that VSFG spectroscopy will shed light on the wettability of low-dimensional materials.

了解水与石墨烯相互作用的细节对于水淡化、储能和催化等各种应用至关重要。然而，石墨烯-水界面处水的氢键结构尚未完全清楚。振动和频产生 (VSFG) 光谱适用于阐明石墨烯-水界面处的水结构。随着石墨烯层数的变化或调整单个单层的掺杂水平，界面水结构有很大不同。具体来说，随着石墨烯层数的增加，具有非 H 键、悬空 OH 基团的水分子变得越来越明显。从 VSFG 光谱推断出的悬空 OH 基团的比例与石墨烯的水粘附能相关。这一观察结果表明，VSFG 可以成为一种精巧的技术，用于测量无法测量水接触角的任何空间受限界面上的水粘附能。我们预计 VSFG 光谱将揭示低维材料的润湿性。