Structural characteristics of gels prepared from sonohydrolysis and conventional hydrolysis of TEOS: an emphasis on the mass fractal as determined from the pore size distribution

Abstract

Silica gels were preparated from fixed proportion mixtures of tetraethoxysilane, water and hydrocloric acid, using either ultrasound stimulation (US) or conventional method (CO) in the hydrolysis step of the process. Wet gels were obtained with the same silica volume concentration and density. According to small‐angle X‐ray scattering, the structure of the wet gels can be described as mass fractal structures with mass fractal dimension D = 2.20 in a length scale ξ = 7.9 nm, in the case of wet gels US, and D = 2.26 in a length scale ξ = 6.9 nm, in the case of wet gels CO. The mass fractal characteristics of the wet gels US and CO account for the different structures evolved in the drying of the gels US and CO in the obtaining of xerogels and aerogels. The pore structure of the dried gels was studied by nitrogen adsorption as a function of the temperature. Aerogels (US and CO) present high porosity with pore size distribution (PSD) curves in the mesopore region while xerogels (US and CO) present minor porosity with PSD curves mainly in the micropore region. The dried gels US (aerogels and xerogels) generally present pore volume and specific surface area greater than the dried gels CO. The mass fractal structure of the aerogels has been studied from an approach based on the PSD curves exclusively. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrasonic preparation of mesoporous silica using pyridinium ionic liquid

“…No appreciable difference could be seen between the structure of sonogels and xerogels. In general, sonication applied during synthesis does not affect the size of monomer particles but may influence their secondary aggregation [36,37,39]. In the present materials, the SANS data did not reveal any influence of ultrasonication on the level of the primary particle formation, while the presence of ionic liquid appears to slow down the polycondensation reaction thus leading to increase of the primary particle size.…”

Combined SANS and SAXS study of the action of ultrasound on the structure of amorphous zirconia gels

“…Contrariwise, our later experiments [46,47] revealed the increase in the surface fractal dimension and in the size of individual particles in sonochemically prepared amorphous zirconia gels [47]. Up to now, studies on the fractal structure of gels forming under the action of ultrasound were conducted primarily for hydrous silica [48,49]. For example, Vollet et al [49] have shown that ultrasound-stimulated wet silica gels possessed a lower fractal dimension than conventional ones.…”

“…Up to now, studies on the fractal structure of gels forming under the action of ultrasound were conducted primarily for hydrous silica [48,49]. For example, Vollet et al [49] have shown that ultrasound-stimulated wet silica gels possessed a lower fractal dimension than conventional ones. However, upon drying the former has shown a higher pore volume and specific surface area.…”

Aerogels Synthesis by Sonocatalysis: Sonogels

“…7) magnifies the structural effects induced by the ultrasound, that is, the formation of small statistical balls [26]. Donatti, Vollet, and their collaborators carried out a systematic study [66][67][68][69] of wet sonogels 1 prepared in excess of water, by previous pH adjusting with different amounts of diluted NH 4 OH.…”