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Title:Polyoxotitanates and their role in titania sol-gel polymerization
Author(s):Chen, Yuewu
Doctoral Committee Chair(s):Klemperer, Walter G.
Department / Program:Chemistry, Inorganic
Chemistry, Polymer
Engineering, Materials Science
Discipline:Chemistry, Inorganic
Chemistry, Polymer
Engineering, Materials Science
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Chemistry, Inorganic
Chemistry, Polymer
Engineering, Materials Science
Abstract:Hydrolysis of Ti(OBu$\sp{\rm t})\sb4$ with 1 equiv of water in t-BuOH at 100$\sp\circ$C yielded a new polyoxotitanate complex $\rm\lbrack Ti\sb{18}O\sb{28}H\rbrack (OBu\sp{t})\sb{17}$. A single crystal X-ray diffraction study of its t-BuOH solvate revealed a $\rm Ti\sb{18}O\sb{45}$ metal-oxygen framework having a pentacapped Keggin structure Reaction of the complex with t-amyl alcohol led to the product $\rm\lbrack Ti\sb{18}O\sb{28}H\rbrack (OBu\sp{t})\sb{12}(OAm\sp{t})\sb5$, identified using NMR spectroscopy.
Partial hydrolysis and condensation of titanium alkoxides were studied in situ by using solution 170 NMR spectroscopy. The speciation and rates of formation were found to be greatly affected by reaction conditions such as the choice of alkoxide ligand, degree of hydrolysis, solvent and pH. The low molecular weight species formed did not appear to be intermediates formed under sol-gel polymerization conditions.
Solution $\sp{17}$O NMR and static light scattering techniques were used to examine molecular size distributions in hydrolyzed Ti(OEt)$\sb4$ and $\rm\lbrack Ti\sb{16}O\sb{16}\rbrack (OEt)\sb{32}$ solutions under acidic and basic (or neutral) conditions as a function of the degree of hydrolysis. Sol-gel polymerization of Ti(OEt)$\sb4$ was observed to involve the initial formation of stable polyoxotitanates which then serve as monomers for sol-gel polymerization.
A building block approach in titania sol-gel polymerization was explored using two polyoxotitanates, $\rm\lbrack Ti\sb7O\sb4\rbrack (OEt)\sb{20}$ and $\rm\lbrack Ti\sb{16}O\sb{16}\rbrack (OEt)\sb{32}$, as potential precursors. First, the stability of the $\rm\lbrack Ti\sb7O\sb4\rbrack (OEt)\sb{20}$ and $\rm\lbrack Ti\sb{16}O\sb{16}\rbrack (OEt)\sb{32}$ core structures toward ethanol was studied. Ethanolic solution of $\rm\lbrack Ti\sb7O\sb4\rbrack (OEt)\sb{20}$ showed significant decomposition of the $\rm\lbrack Ti\sb7O\sb4$) core structure, while solution of $\rm\lbrack Ti\sb{16}O\sb{16}\rbrack (OEt)\sb{32}$ showed no signs of decomposition under the same conditions. Solid state $\sp{17}$O MAS NMR experiments using selective $\sp{17}$O labeling techniques indicated that the $\rm\lbrack Ti\sb{16}O\sb{16}$) core was largely preserved during sol-gel polymerization. Dynamic light scattering studies comparing kinetics of $\rm\lbrack Ti\sb7O\sb4\rbrack (OEt)\sb{20}$, $\rm\lbrack Ti\sb{16}O\sb{16}\rbrack (OEt)\sb{32}$ and Ti(OEt)$\sb4$ sol-gel polymerization revealed that two different molecular growth pathways were followed. Nitrogen adsorption studies showed different porosities for $\rm\lbrack Ti\sb7O\sb4\rbrack (OEt)\sb{20}$-, $\rm\lbrack Ti\sb{16}O\sb{16}\rbrack (OEt)\sb{32}$- and Ti(OEt)$\sb4$-derived xerogels arising from the different precursors employed.
Issue Date:1996
Type:Text
Language:English
URI:http://hdl.handle.net/2142/23673
ISBN:9780591197716
Rights Information:Copyright 1996 Chen, Yuewu
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712230
OCLC Identifier:(UMI)AAI9712230


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