Title: 29Si NMR and UV-Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol-Gel Chemistry
Authors: Depla, Anouschka ×
Lesthaeghe, David
Van Erp, Titus
Aerts, Alexander
Houthoofd, Kristof
Fan, Fengtao
Li, Can
Van Speybroeck, Veronique
Waroquier, Michel
Kirschhock, Christine
Martens, Johan #
Issue Date: Mar-2011
Publisher: American Chemical Society
Series Title: Journal of Physical Chemistry C vol:115 issue:9 pages:3562-3571
Abstract: The initial molecular steps of the acid-catalyzed silica sol-gel process departing from tetraethylorthosilicate (TEOS) were investigated by in situ Si-29 NMR and UV-Raman spectroscopy. The use of a substoichiometric H2O:TEOS molar ratio (r-value 0.2-1.2) slowed the silicate oligomerization reaction and allowed unraveling the initial steps of silica condensation. Molecular modeling confirmed Raman signal and Si-29 NMR shift assignment. A comprehensive listing of all Raman and Si-29 NMR assignments is provided, including unique Raman assignments of cyclosilicates and the linear tetramer. The combination of experiment and modeling allowed an analysis of the reaction kinetics. The derived kinetic model and the experimental observation both revealed that the H2O:TEOS molar ratio had a strong influence on the reaction kinetics but not on the reaction pathways. The multianalytical approach led to development of an oligomerization scheme. As dominant oligomerizations, chain growth, cyclodimerization, and branching were identified. Under the investigated conditions, chains did not grow longer than pentamer, and ring sizes were limited to 6-rings. Chains of 4 Si atoms and 4-rings were abundant species. Branched rings and chains were formed by attachment of dimers and trimers. Gelation proceeded from branched 4-rings and branched chains with limited hydroxyl functionalities.
ISSN: 1932-7447
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Centre for Surface Chemistry and Catalysis
× corresponding author
# (joint) last author

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