A versatile route to organically-modified silicas and porous silicas via the non-hydrolytic sol–gel process

Abstract

The non-hydrolytic sol±gel route has been used to provide a versatile synthesis of organically-modi®ed silicas (ormosils), via a rapid, facile reaction in the absence of any solvent. The ormosils are synthesised by reaction of silicon halides with alkoxides, where one or both of the reactants contains the organic substituent. The products are organic±inorganic hybrid nanocomposite materials, where the organic modi®cation is an alkyl, aryl or vinyl group covalently bonded to silicon. The ormosils have low surface areas, but may be converted to high surface area, largely microporous silicas by thermal degradation of the organic component.

The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review

“…The synthesis of 3D cross-linked polysiloxanes has been described by Vioux and coworkers [78,112], and Hay and Raval [113][114][115]. Redistribution reactions of alkoxy and chloro groups take place readily at r.t., while the condensation reactions occur at temperatures from 35 to 150 • C and were catalyzed by Lewis acidic metal chlorides, similar to the syntheses of metal oxides (Section 2.1).…”

“…The homogeneity was further negatively influenced by other side reactions. Dialkylether was observed as a condensation product together with alkyl halide in some cases [78], and cleavage of the Si-C bonds was observed during the synthesis of phenylsilsesquioxanes in sealed ampoules [112] (these bonds were stable when the Schlenk vessel was opened to N 2 atmosphere allowing for the release of alkyl halide from the reaction mixture) [113]. In spite of these side reactions the homogeneity and stability of 3D cross-linked siloxanes prepared by alkyl halide elimination were still superior to the materials prepared by HSG syntheses [78].…”

Siloxane‐Bond Formation Promoted by Lewis Acids: A Nonhydrolytic Sol–Gel Process and the Piers–Rubinsztajn Reaction

“…[7][8][9] For example, in the 1970s, reactions of alkoxysilane and chlorosilanes were studied as "heterofunctional condensation". [10][11][12][13][14] ) Therefore, a clear understanding of the fundamentals of nonhydrolytic sol-gel processing surely contributes to the synthetic chemistry of various inorganic oxides including silica and silsesquioxanes. Nonhydrolytic sol-gel processing is applicable not only for silica but also for other oxides such as TiO 2 , SnO 2 , ZrO 2 , SiO 2 ÀTiO 2 , SiO 2 ÀZrO 2 , and more.…”

“…(Please see reviews of NHSG for various inorganic oxides including SiO 2 . [10][11][12][13][14] ) Therefore, a clear understanding of the fundamentals of nonhydrolytic sol-gel processing surely contributes to the synthetic chemistry of various inorganic oxides including silica and silsesquioxanes.…”

Novel Materials through Non-Hydrolytic Sol-Gel Processing: Negative Thermal Expansion Oxides and Beyond

“…The term NHSG reaction has not only been applied to systems that result in monolithic gels, but based on a common reaction mechanism also to precursors that yield precipitates. This method was later adapted to other complex oxide systems [73,74,75,76], as well as the preparation of hybrid organic-inorganic gels [77,78,79,80]. Our group has been exploring NHSG routes to negative thermal expansion (NTE) materials in the A 2 M 3 O 12 family (A = trivalent metal; M = Mo, W) [81,82,83].…”