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Chemistry of Sol-Gel Synthesis of Aluminum Oxides with In Situ Water Formation: Control of the Morphology and Texture

Rezgui, Saloua and Gates, Bruce C. and Burkett, Sandra L. and Davis, Mark E. (1994) Chemistry of Sol-Gel Synthesis of Aluminum Oxides with In Situ Water Formation: Control of the Morphology and Texture. Chemistry of Materials, 6 (12). pp. 2390-2397. ISSN 0897-4756. doi:10.1021/cm00048a029.

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Sol-gel synthesis of aluminum oxide from mixtures containing Al(O-s-Bu)_3, acetic acid, and sec-butyl alcohol, whereby water was produced in situ, was characterized by infrared, ^1H NMR, ^(13)C NMR, and ^(13)C and ^(27)Al magic angle spinning NMR spectroscopies. The molar ratio (R) of acetic acid to Al(O-s-Bu)_3 strongly influenced the nature of the product. When R was < 2, the product was an opaque gelatinous precipitate, and when R was ≥ 2, transparent gels were formed. Acetic acid played crucial roles in both the hydrolysis and condensation reactions that constitute the essential chemistry of the sol-gel synthesis. Acetic acid influenced the rate of hydrolysis by (1) reacting rapidly with Al(O-s-Bu)_3 to give Al(O-s-Bu_2-OCOCH_3), which is much less reactive than Al(O-S-BU)_3 in hydrolysis, (2) catalyzing condensation reactions, and (3) catalyzing the dehydration of sec-butyl alcohol to give water. Acetic acid is involved in all the reactions of the sol-gel synthesis and thus provides a delicate control of the chemistry. The ratio R also influenced the morphology of the products formed as a result of drying at temperatures in the range 50-300 °C; these products were characterized by infrared spectroscopy, scanning electron microscopy, and surface area/pore volume measurements. Upon heating, the gelatinous precipitate was transformed into a dense material with a low surface area and low pore volume. Prior to drying, this material contained principally oligomeric species with few OH ligands and little unreacted acetic acid, thus favoring intermolecular condensation reactions and collapse of the structure during drying. In contrast, gels produced at values of R ≥ 2 gave materials with higher surface areas and higher pore volumes. Prior to drying, these materials contained principally polymeric species incorporating acetate and OH ligands located close to each other, thus favoring intramolecular condensation reactions during drying. Removal of unreacted acetic acid from the gel led to high-surface-area and high-pore-volume materials.

Item Type:Article
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URLURL TypeDescription
Gates, Bruce C.0000-0003-0274-4882
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 1994 American Chemical Society. Received June 29, 1994. Revised Manuscript Received October 3, 1994. S. Rezgui was supported by a Fulbright Fellowship sponsored by AMIDEAST and was on leave from Faculté des Sciences de Bizerte, Tunisia.
Funding AgencyGrant Number
Fulbright FoundationUNSPECIFIED
Issue or Number:12
Record Number:CaltechAUTHORS:20180507-141346360
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Official Citation:Chemistry of Sol-Gel Synthesis of Aluminum Oxides with In Situ Water Formation: Control of the Morphology and Texture Saloua Rezgui, Bruce C. Gates, Sandra L. Burkett, and Mark E. Davis Chemistry of Materials 1994 6 (12), 2390-2397 DOI: 10.1021/cm00048a029
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86259
Deposited By: George Porter
Deposited On:07 May 2018 22:51
Last Modified:15 Nov 2021 20:36

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