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Interactions of amino-bearing organic acids at the ferrihydrite-water interface: a flow adsorption microcalorimetry-ultra violet visible spectroscopy study
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2022-04-22
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In-tandem flow adsorption microcalorimetry-UV-Vis spectroscopy was used to study the dynamics, kinetics, energetics, and effects on surface charge for amino-bearing organic acids at the ferrihydrite-water interface. The amino-bearing organic acids sorbed to ferrihydrite via multiple, enthalpy- or entropy-driven steps at different rates involving a mixture of van der Waals, ion exchange and ligand exchange reactions. The nature of interaction varied across speciation, molecular size, conformation, and hydrolizability. For instance, glycine sorption to NO3--saturated ferrihydrite was a two-step enthalpy-driven, completely reversible ion exchange process with overall heat of sorption (DHsorp) of -3.66 kJ mol-1 and after the desorption reaction, the anion exchange energy (NO3-/Cl- and Cl-/NO3-) at the ferrihydrite-water interface was doubled. By comparison, a-alanine, with similar speciation as glycine, had two-stepped and enthalpy-driven sorption that occurred via mixed van der Waals and ion exchange reactions with DHsorp of -1.24 kJ mol-1, and 10% reversibility by NO3- with no impact on anion exchange energy. The thesis further covers comparison in interactions at the ferrihydrite-water interface across molecular conformation (a-alanine versus ß-alanine) and hydrolyzability (G3.5-COOH, ATP).
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Geological Sciences