Silica-Based Aerogels with Tunable Properties: The Highly Efficient BF₃-Catalyzed Preparation and Look inside Their Structure

Abstract

This work presents a solution to one of the most fundamentally and practically important challenges in the production of silica-based aerogels, time consumption and expensiveness of these processes, with the main focus on the sol−gel process. We suggested a highly efficient BF 3 -catalyzed method for the production of aerogels, which allows one to shorten the stage of the formation of a (wet) gel to 5 min, the stage of gel aging to 0, while the stage of gel workup is not required; the duration of these stages, according to the literature, ranges from days to weeks. The process is performed using commercially available, simple, and inexpensive reagents and under mild reaction conditions: BF 3 •Et 2 O as the catalyst, acetone as the solvent, room temperature, and at atmospheric pressure. This approach allows one to quickly obtain both classic opaque and transparent silica-based aerogels from Si(OMe) 4 or Si(OEt) 4 as well as transparent superhydrophobic ones from their mixtures with MeSi(OMe) 3 or Me 2 Si(OMe) 2 . In addition, we succeeded in obtaining a series of aerogels with various organic and inorganic additives, in particular, in this way, luminescent and metallasiloxane ones were prepared. Also, the effect of the method for producing silica-based aerogels on their (supra)molecular structure and morphology was thoroughly studied by a set of physicochemical methods of analysis: scanning electron and light microscopy, X-ray microtomography, and NMR experiments. These findings allow to tune the density, transparency, mechanical strength, hydrophobicity, and other properties depending on the need by choosing the right technique.

Novel, flexible, and transparent thin film polyimide aerogels with enhanced thermal insulation and high service temperature

“…[76][77][78] Though some previously reported inorganic silica aerogels showed higher optical transparency compared to the fabricated PI aerogels, in this work, the fabricated PI aerogels presented significantly higher mechanical flexibility and thermal stability. [79][80][81][82]…”

Ionic Cyclopropenium-Derived Triplatinum Cluster Complex [(Ph3C3)2Pt3(MeCN)4]2+(BF4–)2: Synthesis, Structure, and Perspectives for Use as a Catalyst for Hydrosilylation Reactions

“…Detailed structural NMR studies − of complex A in a MeCN and chloroform solutions, in which it is well soluble and stable, show the complete identity of its structure with respect to the crystalline state. 1 H, 13 C, 19 F and 11 B NMR spectra show typical chemical shift values for similar types of structures (see the Supporting Information).…”

Synthesis of mono- and polyfunctional organosilicon derivatives of polyhedral carboranes for the preparation of hybrid polymer materials

“…54,55 Compound 8 can be used as a binder and as a precursor for the creation of organoelement aerogels, which are in high demand in modern materials science. 56,57 At the same time, during the hydrosilylation reactions, the migration of the allyl double bond in carborane 1 in some cases was found to form 9-propenyl-m-carborane 9. It was found that the double bond migration in allylcarborane 1 to the internal position with the formation of pure propenylcarborane 9 proceeded in the presence of an excess of Karstedt's catalyst compared to the amount of catalyst utilized in the hydrosilylation reaction (carborane : catalyst ratio was 5.4 : 9.13 Â It is worth noting that for compounds containing an allyl group, a similar phenomenon has been described earlier, with the migration of a double bond to the internal position being observed in the presence of transition metal complexes, including palladium, rhodium, and iron, [58][59][60][61] but the carborane polyhedra intensified this process.…”

“…54,55 Compound 8 can be used as a binder and as a precursor for the creation of organoelement aerogels, which are in high demand in modern materials science. 56,57…”