Insight on Structure of Water and Ice Next to Graphene Using Surface-Sensitive Spectroscopy

Abstract

The water/graphene interface has received considerable attention in the past decade due to its relevance in various potential applications including energy storage, sensing, desalination, and catalysis. Most of our knowledge about the interfacial water structure next to graphene stems from simulations, which use experimentally measured water contact angles (WCAs) on graphene (or graphite) to estimate the water-graphene interaction strength. However, the existence of a wide spectrum of reported WCAs on supported graphene and graphitic surfaces makes it difficult to interpret the water-graphene interactions. Here, we have used surface-sensitive infrared-visible sum frequency generation (SFG) spectroscopy to probe the interfacial water structure next to graphene supported on a sapphire substrate. In addition, the ice nucleation properties of graphene have been explored by performing in situ freezing experiments as graphitic surfaces are considered good ice nucleators. For graphene supported on sapphire, we observed a strong SFG peak associated with highly coordinated, ordered water next to graphene. Similar ordering was not detected next to bare sapphire, implying that the observed ordering of water molecules in the former case is a consequence of the presence of graphene. Our analysis indicates that graphene behaves like a hydrophobic (or negatively charged) surface, leading to enhanced ordering of water molecules. Although liquid water orders next to graphene, the ice formed is proton disordered. This research sheds light on water-graphene interactions relevant in optimizing the performance of graphene in various applications.

Understanding the Independent and Interdependent Role of Water and Oxidation on the Tribology of Ultrathin Molybdenum Disulfide (MoS2)

“…[15,40] Both pristine-MoS2 and graphene physically interact with water at the basal plane [35] and recent studies have suggested the formation of ice like water on the basal plane of other 2D materials. [41] Therefore the small increase in thickness of pristine-MoS2 by ~0.4nm is attributed to a single layer of water adsorbing on the pristine-MoS2 surface. [33] X-ray photoelectron spectroscopy (XPS) reveals the presence of 3.9at% of oxygen in the unannealed pristine-MoS2 sample (Figure 1c).…”

Structure and dynamics of water at water–graphene and water–hexagonal boron-nitride sheet interfaces revealed by ab initio sum-frequency generation spectroscopy

“…Interfacial water molecules neighboring the graphene interface have been probed by sum-frequency generation (SFG) spectroscopy. 9 An SFG signal is generated from the interaction of infrared and visible pulses with the interface, providing a second-order nonlinear optical response. Since the second-order nonlinear susceptibility is zero for centrosymmetric media owing to the selection rule of the even-order response, SFG can selectively probe the molecular response of the interfacial molecules.…”

“…Since this peak arises from the dangling, non-hydrogen-bonded, O-H group sticking out of the water-air interface, it constitutes a microscopic measure for the hydrophobicity of the materials. 14 In fact, a recent SFG study at the water-graphene interface 9 reported the absence of dangling O-H groups, suggesting that the graphene surface is not so hydrophobic.…”

Enhanced Nonlinear Absorption Performance of Reduced Graphene Oxide Nanohybrid Covalently Functionalized by Porphyrin via 1,3-Dipolar Cycloaddition

“…It is therefore very interesting to design and prepare graphene-based solution-processed organic/polymeric materials, due to its amenability to process in bulk-scale for the preparation of nanoscale hybrids, polymer blends and organic-inorganic nanocomposites, which are applicable in wide fields such as solar cells, optical sensors, and optical elements in lasers [7]. Remarkably, the hybrids are soluble enough to facilitate manipulation and solution studies in comparison with that of graphene [8]. Moreover, it can form donor-acceptor charge/electron-transfer complexes that bear great promise for major breakthroughs in converting solar energy into electricity, and also exhibit increased nonlinear optical (NLO) effects as potential optical limiting (OL) materials for the protection of human eyes and optical sensors [9].…”