A means to an interface: investigating monoethanolamine behavior at an aqueous surface

Abstract

The use of amine scrubbers to trap carbon dioxide from flue gas streams is one of the most promising avenues for atmospheric carbon dioxide reduction. However, modifications are necessary to efficiently scale these scrubbers for use in fossil fuel plants. Current advances in tailoring amines for CO2 capture involve improvements of bulk kinetic and thermodynamic parameters, with little consideration to surface chemistry and behavior. Aqueous alkanolamine solutions, such as monoethanolamine (MEA), are currently highly favored sorbents in CO2 post-combustion capture. Although numerous studies have explored MEA-CO2 chemistry at the macroscopic scale, few have investigated the role of the interface in the gas adsorption process. Additionally, as these amines become more industrially ubiquitous, their presence on and the need to understand their behavior at atmospheric and environmental surfaces will increase. This study investigates the surface behavior of monoethanolamine at the vapor/water interface, with particular focus on MEA's surface orientation and footprint. Using vibrational sum frequency spectroscopy, surface tensiometry, and computational techniques, MEA is found to adopt a constrained gauche interfacial conformation with its methylene backbone oriented toward the vapor phase and its functional groups solvated in the bulk solution. Computational and experimental analysis agree well, giving a complete picture with vibrational mode assignments and surface orientation of MEA. These findings can assist in the tailoring of amine structures or to facilitate improvements in engineering design to exploit favorable surface chemistry, as well as to serve as a starting point toward understanding aqueous amine surface behavior relevant to environmental systems.

Successive Surface Reactions on Hydrophilic Silica for Modified Magnetic Nanoparticle Attachment Probed by Sum-Frequency Generation Spectroscopy

“…For the SFG peak profile of this sample, the same vibrational mode assignments in the CH stretching region as those used for the COCl-terminated substrate could be applied, since most of the organo-layer structures on the silica were not removed after attaching the NPs. Thus, CH 2 SS, CH 2 FR, and CH 2 AS from the CH 2 group adjacent to the O atom of the ethanolamine-functionalized NP can be assigned to the peaks positioned at ∼2855 cm –1 ( ssp and ppp ), ,, ∼2890 cm –1 ( ppp ), and ∼2925 cm –1 ( ppp ), respectively (Figure A). The peaks located at ∼2878 cm –1 ( ssp ), ∼2934 cm –1 ( ssp ), and ∼2960 cm –1 ( ppp ) were assigned to the CH 2 SS, CH 2 FR, , and CH 2 AS , of the CH 2 group adjacent to the N atom of the ethanolamine-functionalized NP, respectively (Figure A).…”

On the Rise: Experimental and Computational Vibrational Sum Frequency Spectroscopy Studies of Pyruvic Acid and Its Surface-Active Oligomer Species at the Air–Water Interface

“…Vibrational sum frequency (VSF) spectroscopy is an inherently surface-selective nonlinear optical technique that provides a vibrational spectrum of surface-active molecules that are anisotropically ordered and noncentrosymmetric. − At asymmetric interfaces, VSF spectroscopy is a well-established technique that has been used extensively by the Richmond lab ,− and others − to study liquid interfaces. By overlapping a fixed visible and a tunable-frequency IR beam in time and space, a third sum frequency beam is generated, which is the sum of the incident frequencies.…”

“…These techniques also provide vital structural and behavioral insights about the simulated system, such as depth-dependent molecular partitioning. This approach has been shown to be robust, efficient, and highly adaptable for numerous and varied chemical systems when compared with experimental spectra. ,− …”

“…Molecular dynamics (MD) simulations are performed using the Amber 12 suite of programs using parameters and force fields derived in the same manner as in previous studies, ,− and starting configurations were generated by PACKMOL . In each simulation, a specific number of PA and water molecules are arranged to form a 30 Å cube within a 30 Å × 120 Å × 30 Å simulation box, with periodic boundary conditions, forming a water slab with two interfaces.…”

Computational Vibrational Sum Frequency Spectra of Formaldehyde and Hydroxymethanesulfonate at Aqueous Interfaces

“…Finally, the in-house code generates VSF spectra by combining the requisite information from the classical MD and DFT calculations. Reasonably accurate VSF spectra for similar small organic molecules at aqueous interfaces have been obtained using this approach. − This computational methodology is applied in an effort to elucidate specific information relating to the formaldehyde and hydroxymethanesulfonate aqueous interfaces previously studied experimentally.…”