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Title:Investigations of the early stages of titania sol-gel processing
Author(s):Park, Changwoo
Doctoral Committee Chair(s):Klemperer, Walter G.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:In order to understand the early stages of titania sol-gel polymerization, titanium alkoxides were hydrolyzed with controlled amounts of water, and the resulting solutions were investigated by NMR spectroscopy. A selective $\sp{17}$O isotope labeling technique was developed which allowed $\sp{17}$O NMR spectroscopy to be used to identify specific titanium polyoxoalkoxides present in the complex mixture of species formed in the hydrolyzed solution. Based on the $\sp{17}$O NMR spectra of several isolated titanium polyoxoalkoxides, $\sp{17}$O NMR chemical shift regions were defined as follow: $\delta$ 850-650 for Ti$\sb2$O, $\delta$ 650-450 for Ti$\sb3$O and $\delta$ 450-250 for Ti$\sb4$O oxide oxygens.
Titaniwn polyoxoalkoxides isolated and structurally characterized during the study of titanium ethoxide hydrolysis included (Ti$\sb7$O$\sb4$) (OEt)$\sb{20},$ (Ti$\sb8$O$\sb6$) (OBz)$\sb{20}$ and (Ti$\sb{10}$O$\sb8$) (OEt)$\sb{24},$ where Et = CH$\sb2$CH$\sb3$ and Bz = CH$\sb2$C$\sb6$H$\sb5.$ (Ti$\sb7$O$\sb4$) (OEt)$\sb{20}$ and (Ti$\sb8$O$\sb6$) (OEt)$\sb{20}$ were determined to be components of the titanium polyoxoalkoxide solution formed upon hydrolysis of Ti(OEt)$\sb4.$
While hydrolysis of Ti(OEt)$\sb4$ yielded a complex mixture of polyoxoethoxide species, hydrolysis of Ti(OPr$\sp{\rm i})\sb4$ at ambient temperature yielded $\alpha$- (Ti$\sb{11}$O$\sb{13}$) (OPr$\sp{\rm i})\sb{18}$ as the sole product in solution. Reaction of Ti(OPr$\sp{\rm i})\sb4$ with one equivalent of water in isopropanol at 100$\sp\circ$C for 3 days yielded as the sole products a 1:1 mixture of two isomeric complexes, $\alpha\sb1$- (Ti$\sb{12}$O$\sb{16}$) (OPr$\sp{\rm i})\sb{16}$ and $\alpha\sb2$- (Ti$\sb{12}$O$\sb{16}$) (OPr$\sp{\rm i})\sb{16}.$ All three of these compounds form a family of stable dodecatitanates which undergo regioselective ligand exchange upon reaction with alcohols.
The metal oxide framework stability of titanium polyoxoalkoxides was examined in methyl cyclohexane and alcohol solution at ambient and elevated temperature. The relative stabilities of the titanium polyoxoalkoxides examined were (Ti$\sb7$O$\sb4$) (OEt)$\sb{20} < $ (Ti$\sb8$O$\sb6$) (OBz)$\sb{20} < \alpha$- (Ti$\sb{11}$O$\sb{13}$) (OPr$\sp{\rm i})\sb{18} < \alpha\sb1$- (Ti$\sb{12}$O$\sb{16}$) (OPr$\sp{\rm i})\sb{16}.$ Among the compounds examined, $\alpha\sb1$- (Ti$\sb{12}$O$\sb{16}$) (OPr$\sp{\rm i})\sb{16}$ showed extremely low moisture sensitivity, failing to react with in 4 equivalent of water in 0.035M isopropanol solution after 12 hours, suggesting the compound be used as a molecular building block in sol-gel polymerization. $\sp{17}$O NMR studies of the hydrolysis and condensation behavior of $\alpha\sb1$- (Ti$\sb{12}$O$\sb{16}$) (OPr$\sp{\rm i})\sb{16}$ in toluene/acetonitrile showed that the metal oxide framework of the compound was retained during the early stages of sol-gel polymerization.
Issue Date:1993
Rights Information:Copyright 1993 Park, Changwoo
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9411746
OCLC Identifier:(UMI)AAI9411746

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