Molecular Level Insights into Carbon Capture at Liquid Surfaces
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Implementing effective and environmentally responsible carbon capture technologies is one of the principle challenges of this century. Successful implementation requires a host of engineering advancements, but also a fundamental understanding of the underlying physics, chemistry, and materials science at play in these highly complex systems. A large body of scholarship examines both current technologies as well as future strategies, but to date little exploration of the surface behavior of these systems has been examined. As these carbon capture systems involve uptake of gaseous CO2 to either aqueous or solid substrates, understanding the chemistry and physics governing the boundary between the two reactant phases is critical. Yet probing the unique chemistry and physics of these interfacial systems is very difficult. This dissertation addresses this knowledge gap by examining the surface chemistry of monoethanolamine and CO2. Monoethanolamine is a simple organic amine currently used in small scale CO2 scrubbing, and acts as an industrial benchmark for CO2 capture efficiency. The studies presented throughout this dissertation employ surface selective techniques, including vibrational sum frequency spectroscopy, surface tensiometry, and computation methodologies, in order to determine the behavior governing aqueous amine interfaces. The adsorption behavior and surface orientation of aqueous monoethanolamine is examined first. The results show monoethanolamine is present at the surface, highly ordered, and solvated. Perturbations to this amine surface from gaseous CO2 and SO2, as well as from liquid HCl, are examined in the remainder of the dissertation. Reactions between the amine and acids are shown to cause immediate changes to the interface, but the interface then remains largely unaffected as further reaction evolves. The studies presented herein provide a needed exploration of the interfacial picture of these highly reactive systems, with implications for future carbon capture materials and design.