Effects of aging time on V2O5 sol-gel coatings

Preparing Catalytic Materials by the Sol-Gel Method

“…For example, Assink and Kay used 29Si NMR to monitor silicates, thereby obtaining functional group kinetics of tetramethoxysilane (TMOS) (92) and tetraethoxysilane (TEOS) (93). The technique can also be used to study the effects of prehydrolysis (94), complexation (95), and aging (96) on the properties of sol-gel materials. These are all important issues of which a fundamental understanding is presently lacking.…”

A Detailed Study of the Synthesis of Aqueous Vanadium Pentoxide Nematic Gels

“…One of the most popular methods of synthesis consists of the acidification of a NaVO 3 solution by ion-exchange because no foreign ions are thus introduced . Previous studies of the synthesis of V 2 O 5 gels have mostly focused on the determination of the chemical mechanism by which vanadium molecular species polymerize into ribbons. − However, the mechanism of this synthesis still remains unclear from the physical point of view. In this work, we compare three different methods of synthesis: by ion-exchange, by reaction with H 2 O 2 , and by direct dissolution in water.…”

The role of transesterification in the multistep “prehydrolysis” sol/gel synthesis of aluminum-rich aluminosilicate gels

“…1], the prehydrolysis of the silicon alkoxide can allow the formation of transparent gels. 2 Provided the aluminum to silicon ratio is kept low enough so that all of the aluminum can be protected by silanols, a homogeneous aluminosilicate gel can be obtained in several tetra-alkoxysilane/alcohol/aluminum sec-butoxide [TROS͞ROH͞Al(OBu s ) 3 , where R alkyl group] systems. 2 Provided the aluminum to silicon ratio is kept low enough so that all of the aluminum can be protected by silanols, a homogeneous aluminosilicate gel can be obtained in several tetra-alkoxysilane/alcohol/aluminum sec-butoxide [TROS͞ROH͞Al(OBu s ) 3 , where R alkyl group] systems.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] We have recently shown that one reason this protocol works is that the silanols prepared in the prehydrolysis step react with the aluminum precursor, protecting aluminum sites from direct hydrolysis by water (which is added only after the "protecting" reaction has been accomplished). [1][2][3] At high ratios of aluminum to silicon precursors (Al͞Si . [1][2][3] At high ratios of aluminum to silicon precursors (Al͞Si .…”

“…[1][2][3] At high ratios of aluminum to silicon precursors (Al͞Si . 1,3 In this paper we provide evidence that transesterification with Pr i OH can operate to protect the excess aluminum from permanent hydrolysis and to avoid aluminate precipitation. 2 This usually allows the aluminum precursor to be directly attacked by water, and hence leads to alumina precipitation.…”