Date of Award
Campus Access Dissertation
Doctor of Philosophy (PhD)
The enhanced properties of nanoparticles are not singularly due to the high surface area to volume ratio, but also to the plentiful reactive sites. The inherently hydroxylated surfaces of various sized nanoparticles of rutile TiO2 are examined using in situ DRIFTS throughout cycles of annealing and water exposure (rehydroxylation). The defect nature of the nanoparticles is rather resilient, the types of hydroxyl sites on the surface persist after cycles of heating and rehydroxylation; there is only about a 10% loss in the overall concentration of surface hydroxyls. The hydroxyl stretching region in the spectrum for a microparticle rutile titania is much less defined in comparison and indicates a rather hydrophilic surface. However, after undergoing cycles of heating and rehydroxylation the surface becomes more hydrophobic; this is not observed for the nanoparticle surfaces. Surface hydroxyl sites are very active and may either hinder or promote certain transformations. The reactivity and adsorption of acetic acid over rutile, anatase, and P25 ( ~85% anatase, ~15% rutile) nanoparticle surfaces are examined. There are two competing reactions, the adsorption of acetic acid to form surface acetates and/or adsorbed acetone, which is capable of desorbing from the anatase surface and not the rutile surface. Adsorbed acetone on the rutile surface undergoes a self-condensation to form a chemically bound mesityl oxide surface moiety. Acetic acid over P25 reacts with surface hydroxyls to form surface acetates at higher pressures (0.5 Torr) than rutile and anatase alone. The presence of rutile in P25 hinders acetone formation. The investigation validates that P25 is a true mixture of rutile and anatase, whose enhanced acetate adsorption properties are due to the rutile component. Exposure of acetic acid to monoclinic ZrO2 nanoparticles indicates that surface acetates, when formed, hinder the desorption of adsorbed acetone; surface hydroxyls are promoting the ketonization of acetic acid and their removal occurs in conjunction with formation of surface acetates. The chemical intricacies of surface hydroxyl chemistry and reactivity on metal oxide nanoparticle substrates explored in this dissertation using innovate IR methodologies offer a perspective to enhance and tailor mechanisms for catalytic processes.
Kipreos, Maria Dimitra, "Revealing the Molecular Details of Metal Oxide Nanoparticle Surface Hydroxyl Chemistry and Reactivity Using In Situ DRIFTS" (2018). Graduate Doctoral Dissertations. 444.