IR Studies of the Zirconia-Water Interface
|dc.contributor.advisor||McQuillan, A James|
|dc.identifier.citation||Scholz, J. (2012). IR Studies of the Zirconia-Water Interface (Thesis, Doctor of Philosophy). Retrieved from http://hdl.handle.net/10523/2092||en|
|dc.description.abstract||The aim of the present work was to contribute to an understanding of the reactivity of hydroxylated zirconia surfaces towards hydration and anion adsorption. IR spectroscopy was used to characterise the structure and bonding of surface functional groups and interfacial water molecules, to study slow surface reconstruction processes and to obtain insights into the specific adsorption of chloride, sulphate, phosphate and tungstate ions. To account for the structural diversity of the zirconia-water interface and hence its spectral complexity, both zirconia nanoparticle films and structurally related materials including crystalline zirconyl chloride n-hydrates, zirconia hydro gels and aqueous zirconia sols were studied spectroscopically. Thermal and isothermal dehydration and humidity-controlled hydration studies of zirconyl chloride octahydrate, zirconia hydro gels and zirconia nanoparticle films as well as anion adsorption studies to zirconia nanoparticle films from aqueous solutions under static conditions were conducted. Further, X-ray single crystal, thermogravimetric, mass spectrometric and calorimetric data as well as electrophoretic mobility measurements were used to infer additional structural information. Vibrational data for hydroxylated zirconia polymorphs, crystalline hydrogen chloride n-hydrates and size-selected water clusters was employed for spectral assignments. The characteristic vibrational signature of stoichiometric zirconyl chloride n-hydrates was obtained and assignments for vibrational modes of discrete Cl-•••H+-O, Cl-H•••O, O•••H+•••O, O-H•••O and Zr-(OH2)3 groups are given. H2O52+- and H3O2--like entities were evident in zirconyl chloride octa and -hexahydrate. A hydrolysis mechanism for the reaction of H2O(g) and HCl(aq) with Zr4+ sites in Zr-O-Zr groups is proposed (chemisorption). The formation of a strongly H-bonded network of surface-bound water molecules at the zirconia surface was observed (physisorption), and the role of continuous yet slow Zr-O-Zr bond cleavage in the formation of a gel-like surface layer is highlighted. The loss in crystallinity of the zirconia surface led to a gradual increase in the positive net surface charge of zirconia particles. The latter seems to be accountable for the embedding of chloride ions into the network of surface-bound water molecules; and a specific chloride adsorption mechanism is suggested. Sulphate, phosphate and tungstate adsorption studies to zirconia nanoparticle films revealed binding motifs of the oxoanions at pH 3 and 1; and their adsorption affinities were compared in view of considerable differences in Langmuir equilibrium constants, Kads.|
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|dc.title||IR Studies of the Zirconia-Water Interface|
|thesis.degree.name||Doctor of Philosophy|
|thesis.degree.grantor||University of Otago|
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