Modification of highly dispersed silica with zirconium acetylacetonate

Abstract

UDC 541.183 N. V. Borisenko, I. Ya. Sulim, and L. I. BorisenkoThe chemisorption of Zr(acac) 4 and the formation of nanoparticles of ZrO 2 on the surface of silica were studied by IR spectroscopy, thermogravimetry, thermal and X-ray phase analysis. The composition was established and the hydrolytic and thermal properties of ºSiOZr(acac) 3 groups were investigated.Chemical reactions of metal (M) chlorides and oxochlorides with surface hydroxyl groups are widely used for the formation of nanoparticles of metal oxides in silica matrices. The most completely studied is the chemisorption of metal chlorides on the surface of silica with subsequent hydrolysis and condensation. However, the hydrogen chloride, evolved during the reaction, interacts with the SiO-M bond leads to restrictions in the conditions of the modification process. Therefore in recent years researchers have paid considerable attention to the modification of SiO 2 with metal acetylacetonates [1]. As a result of the chemical transformations of the modifying compounds nanoparticles of metal oxide in the surface layer of silica. In this case the chemisorption of the metal on the silica surface is an intermediate but very important stage. The formation and stability of the adsorbed complexes, the chemisorption processes proceeding with the participation of silanol groups of the silica surface, the structural-adsorption characteristics of the silica matrix, the thermal and hydrolytic properties of the surface compounds have a considerable influence on the structure of the surface oxides in the M x O y /SiO 2 nanocomposites.Gas phase modification of SiO 2 with zirconium compounds, ZrCl 4 in particular, and also subsequent hydrolysis, dehydration, and phase condensation has been previously studied in detail [2][3][4][5]. We have established [5] that the SiO-Zr bond underwent hydrolysis at temperatures above 400°C. Zirconium dioxide, formed as a result of subsequent modification of the silica surface (chemisorption of ZrCl 4 , hydrolysis, dehydration), has a crystal structure which depends on the temperature of calcination. The average size of the crystallites of ZrO 2 , formed on the surface of pyrogenic silica, increased from 46 to 109 nm with increasing numbers of stratification from 1 to 4. The tetragonal modification of ZrO 2 is stabilized by pyrogenic silica, inhibiting its transition to the monoclinic form on heating to 1000°C. An analogous effect was observed by the authors of [6] on introducing calcium cations and silicate ions into ZrO 2 . On calcining silica containing zirconium to a temperature of 1500°C the monoclinic modification is formed along with the tetragonal form [4].It should be noted that the chemisorption of zirconium acetylacetonate has not been investigated previously. The present work is associated with the chemical reaction of Zr(acac) 4 with the SiO 2 surface and also the formation of nanoparticles of ZrO 2 in a silica matrix.In this work highly dispersed pyrogenic silica (HDS), mark A 300 (Kalush Pilot Plant of the Chemical Insti...

Silica-supported ceria–zirconia and titania–zirconia nanocomposites: Structural characteristics and electrosurface properties

“…For both composites, the mass loss in the range 50-190 • C arises primarily due to desorption of intact water [6]. The mass loss in the 190-500 • C range corresponds to destruction of acetylacetonates ligands and removal of volatile carbon components upon oxide formation [29]. This agrees with the DTA curves having the corresponding exothermic peaks.…”

Excitonic Quasimolecules in Quasi-Zero-Dimensional Nanosystems

“…By using the variational method, we obtain the total energy and the binding energy of the biexciton singlet ground state in such system as a function of the spacing between the QD surfaces and of the QD radius. Moreover we establish that the spectral shift of the lowtemperature absorption peak [1,2] in such a nanosystem is due to quantum confinement of the energy of the biexciton ground state.…”

“…In Refs [1][2][3][4][5], a shift of the spectral peak of the low-temperature absorption was observed also for samples with a QD content of x ≈ (1-2) %. It was noted that, at such a QD content in the samples, one must take into account the interaction between charge carriers localized above the QD surfaces [1 -5].…”

“…The optical properties of quasi-zero-dimensional semiconductor nanosystems that consist of spherically shaped semiconductor quantum dots (QDs) grown to a radius of a ≈ (1-30) nm in transparent insulator matrices are defined in a large extent by the energy spectra of charge carriers localized close to the QD surface [1][2][3][4][5]. In Refs [1,2], the optical properties of silicate glassy samples containing CuO QDs were experimentally studied. The average radii of such QDs were in the range of a ≈ (2 -30) nm.…”

Silica-Supported Titania–Zirconia Nanocomposites: Structural and Morphological Characteristics in Different Media

“…The reaction mixture was stirred in the refluxing tube for 1 h. Then, IPA and acetylacetone were removed from the mixture by evacuation. The solid products were dried and calcined at 550 °С and 1100 °С for 1 h. According to [22], the temperature range 500–550 °C corresponds to the destruction of acetylacetonate ligands and complete removal of the volatile carbon components upon oxide formation. But at 550 °C, a high probability of the formation of the amorphous structure takes place, while the temperature of 1100 °C was chosen as sufficient for crystalline structure formation.…”