Sol-gel transition in simple silicates

Brinker, C.J.; Keefer, Keith D.; Schaefer, Dale W.; Ashley, Carol S.

doi:10.1016/0022-3093(82)90245-9

Cited by 627 publications

(248 citation statements)

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“…The NMR of the hydrolysis reaction was distinct from tetraethoxysilane hydrolysis indicating no loss of the hydroxymethylene group (Scheme 2, Fig. 3 Gels formed from hydroxymethyltriethoxysilane when subjected to conditions similar to those described for gel formation of tetraethoxysilane [30]. The dried gels were indefinitely stable to water and, in contrast to gels formed from acetoxymethyltriethoxysilane, did not dissolve in cold sulfuric acid.…”

Section: Compound Characterization and Behaviormentioning

confidence: 95%

Hydroxymethylsilanetriol – A Simple Analog of Silicic Acid

Arkles

King

Pannell

2013

Silicon

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Hydroxymethyltriethoxysilane and hydroxymethyltrimethoxysilane, precursors by hydrolysis to a simple analog of silicic acid, hydroxymethylsilanetriol, were prepared. Hydroxymethyltrialkoxysilanes undergo condensation to form silmethyleneoxide oligomers and dimeric 2,2,5,5-tetraalkoxy-2,5-disila-1,4-dioxanes. Hydroxymethylsilanetriol undergoes condensation reactions similar to silicic acid and readily forms organosilicate structures by sol-gel processing techniques which may be converted at relatively low temperatures to silicon dioxide. Hydroxmethylsilanetriol derived gels were subject to less stresscracking during drying than conventional tetraethoxysilane derived gels, suggesting that Si-O-C bond equilibration during drying provides a mechanism for stress-relief. In screening experiments, hydroxymethylsilanetriol appears to be a competitive inhibitor of the growth of the diatom C. fusiformis, a silicate dependent species, which produces silicate structures.

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Section: Compound Characterization and Behaviormentioning

confidence: 95%

Hydroxymethylsilanetriol – A Simple Analog of Silicic Acid

Arkles

King

Pannell

2013

Silicon

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“…The matrices were prepared via the ''two-step'' method [20] from a mixture of the alkenyltrimethoxy silane (RTS) and TMOS with a molar ratio of RTS:TMOS = 1:2, by the following procedure: a mixture of 0.9 mol RTS (VTS: 0.140 ml; PTS: 0.160 ml; BTS: 0.145 ml; ATS: 0.150 ml), 0.265 ml TMOS (1.8 mol) and 0.491 ml HCl (2.5 mM) was mixed for 30 min at 30°C. For obtaining a pure silica matrix 0.400 ml TMOS (2.7 mol) was used instead of the silane mixture mentioned above.…”

Section: Enzyme Entrapment Proceduresmentioning

confidence: 99%

Erratum to: Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Frenkel-Mullerad

Ben-Knaz

Avnir

2014

J Sol-Gel Sci Technol

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Chemically reactive sol-gel matrices hold the ability of protecting entrapped enzymes from destruction by external harsh chemicals. We show this concept by exposing alkaline phosphatase (AlP) to a strong oxidizing agent-bromine. In solution, AlP is immediately destroyed by this oxidant. When AlP was entrapped in hybrid silica sol-gel materials carrying double bonds, the reactivity of AlP was preserved after exposure to bromine under conditions which totally destroy it in solution. The matrices studied were vinylated and allylated silicas, and their protectability was compared to n-alkylated silicas and to silica itself. For instance, the reactivity of AlP entrapped in allylated silica after exposure to 25.6 mM bromine solution is 40 times higher than its reactivity when entrapped in pure silica; and in solution the enzyme is totally destroyed at this concentration. Molecular level mechanisms for these observations are proposed.Keywords Sol-gel Á Sol-gel preserved enzymes Á Oxidizing agent Á Ormosil BackgroundAlkaline phosphatase (AlP), like most other enzymes, is totally destructed when exposed to a strong oxidant such as bromine. Here we show how to protect an enzyme when exposed to such conditions. We do so by using the sol-gel materials methodology for enzyme entrapment [1]. Sol-gel entrapped enzymes [2-4] have already been shown to provide significant thermal stability [5][6][7][8], stability to extreme pH values [9][10][11], and stability to non-native environments [12][13][14]. In these earlier studies the protectability was attributed to the encaging itself [15]; here we extend these observations by showing protection against an oxidant due to active chemical scavenging of the destructive chemical by the matrix. Thus when the enzyme is entrapped within sol-gel derived olefinated silicas, and then exposed to bromine solution, the double bonds react with the bromine, and protect the enzyme. By comparing this mode of protection to entrapments in non-reactive matrices-sol-gel derived silicas and sol-gel-derived alkylated silicas-we were able to evaluate the weights of the bromine scavenging and of the physical entrapment to the protection of the enzyme; we find that this relative weight depends on the alkyl and alkenyl chain. Thus, the hybrid sol-gel material we used was based on vinyl (CH 2 =CH-Si; VTS; here and below we use the name of the monomer as the name of the material), or allyl (CH 2 =CH-CH 2 -Si; ATS). In earlier studies we showed these olefinated sol-gel materials are highly reactive towards bromine, undergoing in water an hydrobromination reaction [16,17] which proceeds according to Markovnikov's rule [18], as shown in Scheme 1, resulting in a bromohydrin and HBr. The formation of an acid is an environmental change that the entrapped enzyme can withstand. We recall that we showed that sol-gel entrapped alkaline phosphataseThe online version of the original article can be found under

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“…This relatively large weight loss observed above 200 • C for the pure polymeric membrane may be caused by the presence of significant number of chemically bound alkoxy groups because of the re-esterification reactions occurring during drying. It was reported that polymeric structures show enhanced densification at lower temperatures due to the removal of alkyl groups by condensation [22,23]. Structural relaxation and micropore collapse both combined with additional cross-linking might be expected to produce denser structures at lower temperatures because less hydrolysed species form in the acid catalysed polymeric systems [23].…”

Section: Thermal/densification Behaviour Of Unsupported Membranesmentioning

confidence: 99%

“…It was claimed that in polymeric systems, the gel to glass transition occur due to the combination of silanol ( Si-OH) groups on the surface of the pores, releasing H 2 O and forming Si-O-Si bonds. On the other hand, sintering by viscous flow was assumed to be effective for the base catalysed systems [22,23].…”

Section: Thermal/densification Behaviour Of Unsupported Membranesmentioning

confidence: 99%

Preparation of particulate/polymeric sol–gel derived microporous silica membranes and determination of their gas permeation properties

Topuz

Çiftçioğlu

2010

Journal of Membrane Science

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a b s t r a c tMonodisperse silica sols with well-defined spherical particles ranging in size from 5 to 310 nm were prepared through Stober process. Both particulate and polymeric sol-gel routes were employed for the preparation of stable silica sols. The use of polymeric species in combination with particulate silica spheres may allow the design of predefined membrane pore structures with high thermal stability by cubic/random/close packing of monodisperse spherical particles incorporated into the polymeric network. The size and volume content of spheres were varied in order to modify the consolidation behaviour of 2-structural silica membranes which would enhance the thermal stability. The low shrinkage level for sphere loaded 2-structural systems compared to the pure polymeric counterparts might be explained by the decrease in the structural free energy of the polymeric/particulate 2-structural system. The thermal stability of the microporous membranes may thus be improved by incorporating particulates into the polymeric network through the formation of a lower extent of thermally induced microcrack formation. The N 2 permeation through 90 nm silica sphere added silica membranes remained constant when they were heat treated in the 250-400 • C range indicating the stability of the pore network.

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Sol-gel transition in simple silicates

Cited by 627 publications

References 10 publications

Hydroxymethylsilanetriol – A Simple Analog of Silicic Acid

Hydroxymethylsilanetriol – A Simple Analog of Silicic Acid

Erratum to: Preserving the activity of enzymes under harsh oxidizing conditions: sol–gel entrapped alkaline phosphatase exposed to bromine

Preparation of particulate/polymeric sol–gel derived microporous silica membranes and determination of their gas permeation properties

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