Low-temperature high-pressure cryogelation of nanooxides

Gun’ko, Vladimir M.; Zarko, V.I.; Pakhlov, E.M.; Remez, O.S.; Charmas, B.; Skubiszewska–Zięba, J.

doi:10.1007/s10971-014-3575-2

Cited by 8 publications

(1 citation statement)

References 32 publications

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“…However, the morphology of NPNP per se (size, shape and surface structure) does not practically change because wetting-drying and hand stirring of samples in a porcelain mortar provides relatively low mechanical loading (smaller than 100 kg/cm 2 ). Note that treatment of nanosilicas at high pressure (up to 1050 atm) does not practically change the specific surface area, but the pore volume changes due to the compaction of the secondary particles [53,54]. Stirring of a blend with dense A-300 and AM1 (1:5) leads to the powders with the value of  b smaller (~0.13 g/cm 3 ) than that of dense A-300 because surface hydrophobic functionalities of NPNP of AM1 prevent the formation of tight contacts between neighboring particles.…”

Section: Resultsmentioning

confidence: 99%

Interfacial behavior of methane and organic solvents with low freezing points upon interaction with hydrophilic and hydrophobic nanosilicas

Gun’ko¹,

Туров²,

Krupska³

2018

Him. Fiz. Tehnol. Poverhni

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Phase state features of adsorbed substance vs. temperature are often unknown or poorly defined due to strong effects of confined space in pores onto bound compounds. The adsorption theory considers that on a surface or in pores of adsorbents, adsorbate fluid forms structures with the density intermediate between ones of a gas and a liquid. The aim of the work was to study possibility for adsorbed substances to transform into solid state at temperature higher than freezing point. Solvent (acetone and ethanol) adsorption onto hydro-compacted nanosilica A-300 and its blend with hydrophobic AM1 (dimethyldichlorosilane hydrophobized A-300), methane adsorption onto hydrated (h = 0.1 g/g) silicas, and water behavior vs. temperature were analyzed using 1 H NMR spectroscopy, cryoporometry, and quantum chemistry. A fraction of organics bound to silicas is immobile at temperatures higher than its freezing point since it does not contribute to 1 H NMR spectra of static samples. Methane signal increases with temperature because of enhanced molecular mobility and structure changes in mobile water clusters bound in voids between silica nanoparticles in their aggregates. Stronger compaction of A-300 than that of stirred A-300/AM1 (due to a negative effect of AM1 nanoparticles preventing formation of tight contacts between A-300 nanoparticles) leads to a decrease in adsorption of methane onto dense A-300 alone. Stronger stirring of the A-300/AM1 blend (at h = 0.1 g/g) leads to enhanced adsorption of methane. This effect is due to enhanced mobility of the methane molecules with T, because at low temperatures these molecules are practically immobile in voids between nanoparticles and frozen or poorly mobile water clusters, which partially fill narrow pores (voids) in NPNP aggregates and agglomerates.

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Section: Resultsmentioning

confidence: 99%