Polyoxotitanates and their role in titania sol-gel polymerization

Chen, Yuewu

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https://hdl.handle.net/2142/23673 Copy

Description

Title

Polyoxotitanates and their role in titania sol-gel polymerization

Author(s)

Chen, Yuewu

Issue Date

1996

Doctoral Committee Chair(s)

Klemperer, Walter G.

Department of Study

• 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 Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Chemistry, Inorganic
• Chemistry, Polymer
• Engineering, Materials Science

Language

eng

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.

Type of Resource

text

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Copyright 1996 Chen, Yuewu

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