Mesoporous silica matrices derived from sol-gel process assisted by low power ultrasonic activation

Abstract

The present work contributes to elucidating the differences between silica gels obtained by low doses ultrasonic activation, and those obtained by the conventional method, termed as classical sol gel. Silica matrices were produced by sol-gel synthesis process, assisted and non-assisted by an ultrasonic field, and subsequently characterized by various methods. Nitrogen adsorption and small-angle neutron scattering (SANS) measurements provided texture and microstructure of the dried gels. The adsorption results show that the sample sonicated for 2 hours presents the most ordered microstructure, characterized by pore shape close to spherical and the narrowest size distribution - about 90 % of the pores for this sample fall into the mesopore range (2-50 nm). SANS data reveal the formation of primary structural units of sizes around 1.5-2 nm which are small linear or branched polymeric species of roughly spherical shape and with rough surface. They are generated in the very early stage of sol gel process, as a result of hydrolysis and condensation reactions. The aggregated primary units form the secondary porous structure which can be described as a rough surface with fractal dimension above 2. The best porosity characteristics were obtained for the sample activated for 2 hours, indicating the optimal doses of sonication in the present conditions. Our results demonstrate the possibility of tailoring the pore size distribution using a low power ultrasonic bath. .

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

“…In all the cases, r c lies within a range of 2.4-2.6 nm. Primary clusters of similar sizes were obtained by Ayral et al [69] for zirconia hydrogels synthesized from acidic media, and by Savii et al [26] for silica gels obtained in US-assisted synthesis. Thus we can conclude that sonication does not affect the size of monomer hydrous zirconia particles, but results in substantial changes in their aggregation patterns.…”

“…Similarly, layered double hydroxides obtained by an ultrasound-enhanced technique showed larger adsorption capacity for humic substances [24]. Recently, formation of high specific surface area porous adsorbents with the use of ultrasound was also reported [25,26].…”

Small-angle scattering investigation of silica xerogels and sonogels prepared with ionic liquid pyridinium tetrafluoroborate

“…The q-range of the SAXS instrument was broader, therefore the increase of scattering at q < 0.02 Å -1 can be seen only in the SAXS data. In general, for dry xerogels this part is described by a power law decay of the scattering curves, the power exponent being −4 for smooth surfaces of the large aggregates [25]. In the present case, only the IL-free samples show a power-law behaviour over a sufficiently large range, while for the other samples it is shifted to smaller q, which prevented the accurate determination of the slope.…”

“…Various theoretical models can be used to describe the behaviour of small-angle scattering from structures consisting of nanometer sized particles. The simplest models are the assemblies of mono-or polydisperse particles of spherical or other shapes, with or without interactions [25,26]. Here we use model of polydisperse spherical particles for describing the SANS spectra, and for the SAXS spectra a power law function is added for taking into account the structural organization of the agglomerated particles on the secondary level.…”

Synthesis, morphology, microstructure and magnetic properties of hematite nanoparticles

“…Nanočestični maghemit je jedan od najinteresantnijih magnetnih materijala zbog svojih potencijalnih primena u informacionim tehnologijama, medicini, magneto-optičkim ureĎajima i ferofluidima [59][60][61]. Magnetne osobine nanočestičnih γ-Fe 2 O 3 materijala istraţuju se intenzivno i uzorci se sintetišu različitim metodama [62][63][64][65]. Pokazano je da se magnetne osobine maghemita znatno razlikuju u zavisnosti od metoda sinteze.…”