Direct Observation of the Orientational Anisotropy of Buried Hydroxyl Groups inside Muscovite Mica

Abstract

Muscovite mica (001) is a widely used model surface for controlling molecular assembly and a common substrate for environmental adsorption processes. The mica (001) surface displays near-trigonal symmetry, but many molecular adsorbatesincluding waterexhibit unequal probabilities of alignment along its three nominally equivalent lattice directions. Buried hydroxyl groups within the muscovite structure are speculated to be responsible, but direct evidence is lacking. Here, we utilize vibrational sum frequency generation spectroscopy (vSFG) to characterize the orientation and hydrogen-bonding environment of near-surface hydroxyls inside mica. Multiple distinct peaks are detected in the O–H stretch region, which we attribute to Si/Al substitution in the SiO4 tetrahedron and K+ ion adsorption above the hydroxyls based on density functional theory simulations. Our findings demonstrate that vSFG can identify the absolute orientation of −OH groups and, hence, the surface termination at a mica surface, providing a means to investigate how −OH groups influence molecular adsorption and better understand mica stacking-sequences and physical behavior.

Probing the Mineral–Water Interface with Nonlinear Optical Spectroscopy

“…They concluded that, as the humidity increases, the sub‐monolayer water structure evolves into a more ordered D‐bonding network with the complete absence of the free‐OD peak at full monolayer coverage. Another SFG study employing the SA geometry demonstrated an azimuthal angle dependence of the OH‐stretch response at mica (001), which indicated the mica crystal structure imposes anisotropy on the interfacial water response [64] . As discussed in more detail in Section 8.2.2, several groups [65] have studied the mica–water interface in the context of ice nucleation, concluding that the surface‐induced ordering of water plays an important role in the freezing process of water.…”

Factors Governing the Enhancement of Hydrocarbon Recovery via H2S and/or CO2 Injection: Insights from a Molecular Dynamics Study in Dry Nanopores

“…Muscovite with this surface termination has been used in several studies. [41][42][43][45][46][47] No water is considered in the present study, although it would certainly affect the results, for example via the solvation of the K + ions.…”

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

“…To probe interfaces, several surface-specific techniques can be used such as environmental scanning electron microscopy (ESEM), secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), etc. 42 − 46 One method, vibrational sum-frequency generation (vSFG), 47 , 48 has received a lot of attention for characterizing interfaces experimentally 49 − 57 and in conjunction with simulations. 51 , 52 , 58 − 62 The synergy between vSFG experiments and molecular simulations allows for an in-depth probing of the interface, permitting a finer molecular interpretation of the underlying interfacial region.…”