Synthesis and Formation of Silica Aerogel Particles By a Novel Sol−Gel Route in Supercritical Carbon Dioxide

Abstract

A new method to obtain silica aerogel particles using acetic acid as the condensation agent for silicon alkoxides in supercritical carbon dioxide (scCO 2 ) is proposed. The objective of this study was to determine the mechanism of silica aerogel formation in scCO 2 using in situ analysis techniques. The synthesis and formation of silica aerogel particles was carried out by a modified sol-gel route, based on the hydroxylation and condensation of silicon alkoxides in scCO 2 ; both submicron and micron-size aerogel spheres were obtained. By means of in situ Fourier Transform infrared spectroscopy (FTIR), the activity of acetic, formic, benzoic, and chloroacetic acids were studied for the condensation of tetraethyl orthosilicate (TEOS). Formic and acetic acid gave slower rates than benzoic and chloroacetic acids. Increasing the concentration of acid and addition of extra water led to an acceleration of the reaction. The reactions were also studied as a function of temperature and pressure. Higher rates of reaction were obtained at higher temperatures and lower pressures. Results from particle formation studies indicated that by slowing the rate of reaction, precipitation and agglomeration of particles could be minimized. A submicron particle size range was obtained by depressurization of the sol-gel solution inside the reaction vessel, while the rapid expansion of supercritical solutions (RESS) process was found to yield particles in the size range of approximately 100 nm.

A novel approach to the synthesis of SiO2–PVAc nanocomposites using a one-pot synthesis in supercritical CO2

“…46,47 Low reaction rate could reduce agglomeration of particles and result in uniform and narrow distribution of particles. 44 Besides, these particles obtained from the one-pot synthesis route are significantly smaller than those from the two-step synthesis route discussed above. This may be due to an enhanced interaction of the TEOS/TMOS alkoxide with the silane linker groups in the copolymer that forms during the one-pot synthesis, compared with that of the two-step procedure, where the previously synthesized copolymer was placed in the reactor before subsequent hydrolysis.…”

Preparing titania aerogel monolithic chromatography columns using supercritical carbon dioxide

“…The method described in this research can be extended to preparing other monolithic columns, e.g., SiO 2 and ZrO 2 , and bimetallics using the direct sol-gel reactions in-scCO 2 techniques [37][38][39].…”

A new correlation to predict the stability of liquid jet in dense carbon dioxide

“…This includes readily accessible critical point, high compressibility, as well as being non-flammable, non-toxic, and inexpensive [5,6]. One such application involves precipitation of a solute and formation of particles from an organic solution using supercritical carbon dioxide (scCO 2 ) as an antisolvent.…”