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

Abstract

We simulate sum-frequency generation (SFG) spectra of isotopically diluted water at the water-graphene and water-hexagonal boron-nitride (hBN) sheet interfaces, using ab initio molecular dynamics simulations. A sharp 'dangling' O-D peak around ∼2640 cm-1 appearing in both simulated SFG spectra evidences that both graphene and hBN are hydrophobic. The dangling O-D peak is 10 cm-1 red-shifted at the water-hBN interface relative to the peak at the water-graphene interface. This frequency difference gives a stronger O-DN intermolecular interaction between water and hBN than the O-DC interaction between water and graphene. Accordingly, the anisotropy decay of such a dangling O-D group slows down near hBN compared with near graphene, illustrating that the dynamics of the dangling O-D group are also affected by the stronger O-DN interaction than the O-DC interaction. We discuss molecular-level insights into the structure and dynamics of interfacial water in the context of the friction of hBN and graphene.

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

“…The signal from the water molecules sandwiched between the substrate and the graphene layer would then counteract the signal from the water molecules on the side of the graphene layer in contact with bulk water. In line with the second possible explanation, the presence of a free OH at the graphene water interface in simulations and its absence in experiments, has been attributed by Ohto et al 6 to the presence of a substrate in the experiments.…”

“…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.…”

Effect of Oxidation Level on the Interfacial Water at the Graphene Oxide–Water Interface: From Spectroscopic Signatures to Hydrogen-Bonding Environment

“…These simulated systems, compared to the experimental one, possess no sapphire support for the graphene oxide sheet, and any interpenetrated waters between the substrate and GO are absent. 100 For GO 2/1 , the peaks are slightly red-shifted (100 cm –1 ) 105 compared to the experimental results, with a major peak at 3600 cm –1 and a neighboring shoulder at 3300 cm –1 . Most of the low-frequency range (lower than 3200 cm –1 ) is absent in the simulated vSFG spectra from GO 2/1 .…”

“…For the unreduced system, there is a major peak in the high-frequency region at 3700 cm –1 and a very broad intensity within the 3200–3500 cm –1 range with a minor peak at 3375 cm –1 . In the literature, this peak around 3700 cm –1 is typically attributed to dangling OH bonds pointing toward the air–water interface 50 , 53 , 59 , 97 − 99 or the graphene–water interface, 100 whereas the range between 3200 and 3500 cm –1 is typically attributed to hydrogen-bonded OH bonds (from water and hydroxyl groups) whether pointing away from or toward the interface. 50 , 53 , 59 , 97 − 99 , 101 − 103 After 10 min of reduction, one can see the disappearance of the 3700 cm –1 peak, a growth of a peak around 3500 cm –1 , and a specific peak growing at 2900 cm –1 , which can be attributed to methine groups resulting from the reduction of the graphene oxide.…”

Impact of intermolecular vibrational coupling effects on the sum-frequency generation spectra of the water/air interface

“…Typically, these simulations include intra-and intermolecular vibrational couplings of O-H stretch modes [40][41][42][43], which strongly affects the speed and time scales of spectral diffusion and alters the SFG response of the O-H stretch frequency [18,22]. Yet, in practical SFG simulations, only the intramolecular vibrational coupling effects are explicitly included, while the intermolecular vibrational couplings are generally neglected [11,28,44,45], or just partially treated using a short correlation cutoff [27]. An alternative approach to compute SFG spectra is via the dipole moment-polarisability (μ-α) time-correlation function (TCF) [25,28,30], which however is computationally rather expensive since it requires relatively long trajectories (several ns) to reach numerical convergence [11].…”