Svetozar Musić

Chemical and micro structural properties of TiO2 synthesized by sol-gel procedure

Abstract Nanosized TiO 2 powders were prepared using the sol-gel procedure. The selected colloidal suspensions were stabilized with polyethylene glycol (PEG). This polymer prevented sintering of TiO 2 particles during the calcination of the starting material. X-ray powder diffraction (XRD) phase analysis showed that the samples, obtained up to 500°C, were a mixture of anatase and brookite. In the samples, obtained at 850°C and higher temperatures, rutile as a single phase was detected. The TGA/DTA curves were dependent on the preparation of TiO 2 samples. The samples were also characterized by Fourier transform infrared spectroscopy and laser Raman spectroscopy. A new method, based on low-frequency Raman scattering, was proposed for the size determination of nanosized TiO 2 . The size determination of nanosized TiO 2 by low-frequency Raman scattering was in a good agreement with crystallite size values obtained by XRD.

Precipitation of amorphous SiO2 particles and their properties

The experimental conditions were optimized for the synthesis of amorphous SiO2 particles by the reaction of neutralization of sodium silicate solution with H2SO4 solution. Amorphous SiO2 particles were characterized by XRD, FT-IR, FE-SEM, EDS and microelectrophoresis. The amorphous peak was located at 2θ = 21.8o in the XRD pattern. Primary SiO2 particles were ~ 15 to ~ 30 nm in size and they aggregated into bigger particles. Amorphous SiO2 particles showed a specific surface area up to 130 m2g-1, dependent on the parameters of the precipitation process. The EDS spectrum of amorphous SiO2 particles did not show contamination with sulfate or other ions, which cannot be excluded in traces. pHzpc =1.7 was obtained by microelectrophoresis.

Dependence of nanocrystalline SnO2 particle size on synthesis route

Very fine SnO2 powders were produced by (a) slow and (b) forced hydrolysis of aqueous SnCl4 solutions and (c) hydrolysis of tin(IV)-isopropoxide dissolved in isopropanol (sol–gel route) and then characterized by X-ray powder diffraction, Fourier transform infrared and laser Raman spectroscopies, TEM and BET. The XRD patterns showed the presence of the cassiterite structure. As found from XRD line broadening the crystallite sizes of all powders were in the nanometric range. TEM results also showed that the sizes of SnO2 particles in all powders are in nanometric range. Very fine SnO2 powders showed different features in the FT-IR spectra, depending on the route of their synthesis. The reference Raman spectrum of SnO2 showed four bands at 773, 630, 472 and 86 (shoulder) cm−1, as predicted by group theory. Very fine SnO2 powders showed additional Raman bands, in dependence on their synthesis. The broad Raman band at 571 cm−1 was ascribed to amorphous tin(IV)-hydrous oxide. The additional Raman bands at 500, 435 and 327 cm−1 were recorded for nanosized SnO2 particles produced by forced hydrolysis of SnCl4 solutions. However, these additional Raman bands were not observed for nanosized SnO2 particles produced by slow hydrolysis of SnCl4 solution or the sol–gel route. The aggregation effects of nanosized particles were considered in the interpretation of the Raman band at 327 cm−1. The method of low frequency Raman scattering was applied for SnO2 particle size determination. On the basis of these measurements it was concluded that the size of SnO2 particles was also in the nanometric range and that, the sol–gel particles heated to 400 °C consisted of several SnO2 crystallites.

Mössbauer spectroscopic study of the formation of Fe(III) oxyhydroxides and oxides by hydrolysis of aqueous Fe(III) salt solutions

Abstract Mossbauer spectroscopy has been used to investigate the precipitates formed by hydrolysis of 0.1 M solutions of Fe(NO 3 ) 3 , FeCl 3 , Fe 2 SO 4 ) 3 , and NH 4 Fe(SO) 2 at 90°C. The isomer shifts, electric quadrupole splittings, and nuclear magnetic splittings were used for the qualitative and quantitative identification of the hydrolysis products. Proposals were made concerning the mechanism of formation of the oxides and hydroxyoxides of iron. Hydrolysis in the nitrate and chloride solutions proceeds by the formation of monomers and dimers of iron III) ions, followed by the formation of polymeric species. The polymers formed in the nitrate solution are not presumed to include the nitrate ion in the polymer chain, whereas the polymers formed in the chloride solution contain some chloride ions in place of the hydroxyl ion. The next step in the precipitation process is the formation of oxybridges and the development of α-FeOOH and β-FeOOH structures. This step is followed by loss of water and internal crystallization of α-FeOOH to α-Fe 2 O 3 in nitrate solution or by dissolution of β-FeOOH and growth of α-FeOOH in chloride solution. In sulfate solutions the formation of an FeSO 4 + complex suppresses the polymerization process and the formation of oxyhydroxides and oxides. Basic Fe(III) sulfates are formed instead.

Hydrothermal crystallization of boehmite from freshly precipitated aluminium hydroxide

Abstract Hydrothermal crystallization of boehmite from freshly precipitated aluminium hydroxide was monitored using X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. Crystallite sizes and interplanar spacings for boehmite samples were determined. Changes in the crystallinity of boehmite influenced the corresponding FT-IR spectra. The maximum specific area for boehmite powder was 246 m2 g−1, as measured by the Brunauer–Emmet–Teller (BET) method. With an increase of the crystallinity of boehmite, the specific area decreased and for the best crystalline sample, was 91 m2 g−1. All boehmite samples contained particles of colloidal dimensions. For the best crystalline boehmite sample, hexagonal-like plates were observed and some of them were elongated.

Microstructure of nanosized TiO2 obtained by sol-gel synthesis

Abstract Nanosized TiO2 was prepared using a sol-gel procedure. The colloidal suspension was stabilized with hydroxypropyl cellulose (HPC). This polymer prevents sintering of TiO2 particles during the heating of the starting material in the form of a solid film. The TiO2 crystallite size increased from 5 to 12 nm with increase of temperature up to 500 °C, as determined by X-ray diffraction. XRD phase analysis showed that the studied samples were a mixture of anatase, as the dominant phase, and brookite. A new approach to size determination of nanophase TiO2, by low-frequency Raman scattering, was used

Raman investigation of nanosized TiO2

Nanosized TiO2 was prepared using the sol–gel procedure. The prepared powder was thermally treated up to 1000°C. X-ray diffraction (XRD) measurements showed that the starting powder and the samples obtained after heating this powder up to 500°C were mixtures of anatase, as the dominant phase, and brookite. The crystallite sizes of the samples were estimated using the Scherrer equation. A new approach to the size determination of nanosized TiO2, by low-wavenumber Raman scattering, was also applied. The particle sizes, determined by low-wavenumber Raman scattering, were in agreement with the crystallite sizes measured by XRD. Rutile was produced by heat treatment of the starting powder at 850°C and higher temperatures.

Influence of synthesis procedure on the YIG formation

The influence of synthesis procedure on the yttrium iron garnet (YIG; Y3Fe5O12) formation has been investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Mossbauer and magnetization measurements. The samples were prepared by coprecipitation or ceramic processing using the starting molar ratio Y2O3/Fe2O3=3:5. The fractions of Y2O3, α-Fe2O3, YFeO3 and YIG present in the samples depended on the method of materials processing and the calcination temperature. XRD of the thermally treated hydroxide coprecipitate at 1173 K showed the formation of YIG as a dominant phase, and YFeO3 and Y2O3 as associated phases, whereas upon heating at 1473 K, YIG and a small amount of YFeO3 were found. The samples produced by combining ball-milling of the starting powder and ceramic processing at 1573 K contained YIG and a smaller amount of YFeO3, as found by XRD. It was shown that high-energy ball-milling with stainless steel can be substituted by milling with agate bowl and balls, thus decreasing the contamination of the oxide system due to wear. FT-IR and 57Fe Mossbauer spectroscopic measurements were in agreement with XRD; however, the smaller amount of YFeO3 produced at 1573 K could not be detected with certainty by means of FT-IR and 57Fe Mossbauer spectroscopies. The magnetization values of end-products measured at 5 K were in agreement with their phase composition.

Synthesis of tungsten trioxide hydrates and their structural properties

Abstract Tungsten trioxide hydrates were synthesized by (a) cation exchange reaction from sodium tungstate solution and (b) precipitation from sodium tungstate solution by the addition of HCl solution. The samples were analyzed by XRD, DTA/TGA, Raman and FT-IR spectroscopy. XRD showed formation of WO 3 ·H 2 O by cation exchange reaction, whereas WO 3 ·0.33H 2 O was identified by XRD as a product of the acidification of sodium tungstate solution with HCl solution. After heating at 320°C, WO 3 ·H 2 O transformed into WO 3 , whereas the WO 3 ·0.33H 2 O crystal structure remained and these results were in agreement with DTA/TGA measurements. The WO 3 ·H 2 O sample synthesized by cation exchange reaction showed a weight loss corresponding to one molecule of water in the crystal structure. However, samples WO 3 ·0.33H 2 O showed a much greater weight loss upon heating than could be expected on the basis of the WO 3 0.33H 2 O formula. The phase transition WO 3 ·H 2 O→WO 3 was also monitored by Raman and FT-IR spectroscopy. In the case of WO 3 ·0.33H 2 O samples, the basic features of Raman and FT-IR spectra did not change on heating to 320°C, thus indicating that the heating of WO 3 ·0.33H 2 O up to this temperature did not destroy the original crystal structure. Contrary to this, after heating the WO 3 ·H 2 O sample to 320°C, the Raman and FT-IR spectra showed a series of new bands caused by the phase transition WO 3 ·H 2 O→WO 3 .

Thermal decomposition of β-FeOOH

Abstract β-FeOOH particles were prepared by a forced hydrolysis of the 0.1 M FeCl3 + 5·10−3 M HCl solution, whereas sulfated β-FeOOH particles were prepared by forced hydrolysis of the 0.1 M FeCl3 solution containing 5·10−3 M quinine hydrogen sulfate (QHS). β-FeOOH particles, as well as sulfated β-FeOOH particles, were thermally treated up to 600 °C. The samples were characterized using DTA, XRD, FT-IR and TEM. β-FeOOH particles showed a cigar-type morphology, whereas bundles of β-FeOOH needles were obtained in the presence of QHS. Heating of β-FeOOH particles at 300 °C and above yielded α-Fe2O3 particles. Specific adsorption of sulfate groups showed a strong effect on the thermal decomposition of β-FeOOH particles. Upon heating of sulfated particles between 300 and 500 °C the formation of an amorphous phase and a small fraction of α-Fe2O3 were observed. Needle-like morphology of amorphous particles in these samples was preserved. At 600 °C, α-Fe2O3 particles were obtained; however, they were much smaller than those obtained by heating a pure β-FeOOH.