A. Jitianu

Influence of the silica based matrix on the formation of iron oxide nanoparticles in the Fe2O3–SiO2 system, obtained by sol–gel method

Composite iron oxide–SiO2 materials were prepared by a sol–gel method starting with two types of precursors, tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS), as the SiO2 source. As the iron source a soluble Fe2+ salt, mainly Fe(SO4)2·7H2O, was used, the iron oxides were generated during the sol–gel process. The amorphous gels obtained were thermally treated up to 1000 °C in order to obtain iron oxides with different structures and grain size. The initial gels and the thermally treated samples were characterised by DTA/TGA analysis, DR-UV–VIS and IR-spectroscopy, EPR measurements, transmission electron microscopy (TEM) and BET surface area methods. The matrices obtained from the precursors play a major role in the evolution of the process. In both cases the initial gels are amorphous. In the non-porous matrix obtained by thermal treatment using methyltriethoxysilane (MTEOS), the tendency for crystallisation increases, and the iron oxide particle size is increased.

Al2TiO5 preparation starting with reactive powders obtained by sol-gel method

Abstract Individual Al 2 O 3 , TiO 2 and SiO 2 , as well as binary Al 2 O 3 -TiO 2 powders have been obtained by sol-gel method, polymeric route. The obtained powders have been characterized by X-ray diffraction (XRD), IR-spectrometry and transmission electron microscopy (TEM) methods. In the used experimental conditions amorphous, submicronic, monodisperse powders have been obtained. The preparation of Al 2 TiO 5 and of some compositions situated in the Al 2 TiO 5 -Al 6 Si 2 O 13 pseudobinary system has been realized by solid-state reaction starting with the mentioned above powders. The thermal treatment schedule of the pressed powder mixtures has been established according to the results of differential thermal and thermogravimetric analysis (DTA/TGA). The formation of the compound has been followed by XRD, dimensional variation of the samples and apparent density measurements. The results obtained starting with reactive powders have been compared with those obtained starting with commercial powders. The samples have shown a high reactivity and the formation of tialite was enhanced. However the sintering tendency was not essentially increased.

Sol‐Gel Mono‐ and Poly‐component Nanosized Powders in the Al2O3–TiO2–SiO2–MgO System

Abstract Sol‐gel processes allow for the synthesis of powders with a more elaborate structure from the point view of composition, purity, size, and size distribution. In the powder case, sol‐gel refers to processing in a liquid medium to obtain a solid, which does not settle under gravity due to the formation of a diffuse network structure (the gel) comprising interparticle contacts. In the presence of water, the precursors undertake the following succession of transformations: hydrolysis→polymerisation→nucleation→growth. Sol‐gel monocomponent Al2O3, TiO2, MgO, and SiO2 powders as well as polycomponent powders in the Al2O3–TiO2–SiO2–MgO system have been obtained and have been characterized by x‐ray diffraction (XRD), IR‐spectroscopy, DTA/TG analysis, transmission electron microscopy (TEM), and BET specific surface area methods. Amorphous and nanosized powders with a tendency towards aggregation have been obtained. In the case of binary and ternary powders the dimension of the particles decreases and the specific surface area increases. The great value of specific surface area and the tendency towards crystallization underlines the high reactivity of these powders. Such powders may be used as pigments, catalysts, supports in chromatography or as raw materials for advanced polycrystalline ceramics.

NANOCOMPOSITE MATERIALS FOR As(V) REMOVAL BY MAGNETICALLY INTENSIFIED ADSORPTION

New nanocomposite adsorbent based on silica and iron(III) oxide, thermally treated at 200°C has been used for the arsenic(V) removal. Adsorbents were prepared by sol–gel method, the iron oxides being generated in situ during the sol–gel process. Nanocomposite materials thus obtained have a convenient porosity and nanosized iron oxide content. The sorption experiments have been carried out in a batch mode by using aqueous solutions containing 1000 ppm As. The influence of different experimental parameters on the adsorption capacity was investigated. The effect of magnetic field on the enhancement of adsorption process was also revealed.

Spectroellipsometric Characterization of Multilayer Sol-Gel Fe2O3 Films

Multilayer Fe2O3 films were deposited by the sol-gel method on glass substrates using three successive deposition procedures. The films were thermally treated for 1 h at 300°C.The optical and microstructural properties of these films were investigated by spectroscopic ellipsometry (SE) in the 500–1000 nm range. The optical gap was found by fitting the dispersion of the film refractive index (n) with the Wemple-DiDomenico (WDD) formula.The ellipsometric measurements showed also that the Fe2O3 films are anisotropic. The birefringence values (Δn) of the sol-gel films (0.05–0.08) are smaller than the large values of the Fe2O3 (which are around 0.28) but increase with the crystalization of the films. AFM mesurements showed that the films treated at 300°C start to crystallize.

Composite SiO2—Iron Oxide Materials for Magnetically Intensified Adsorption

Composite SiO2—iron oxide materials were prepared by three experimental procedures. In the first case, the iron oxides were precipitated during a sol-gel process. In the second case, a SiO2 matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe2+ salt in the previously processed matrix. In the third method, ferrite powders, prepared by wet chemical method, were embedded into a SiO2 based sol-gel matrix. Materials with convenient porosity and nano-sized iron oxide content could be prepared using the mentioned methods. The prepared composite has been tested for arsenic(V) removal.

Structural Evolution During Reaction to Form Aluminum Titanate from Sol-Gel Precursors

Abstract Aluminum titanate ceramic materials have been obtained by field-activated sintering of amorphous sol-gel powder precursors. Aluminum titanate formation started at 1000°C. The structural evolution with temperature from the amorphous sol-gel state to the final fully densified ceramic product has been monitored by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and electron microscopy. The full crystallization of aluminum titanate occurred at 1200°C. The grain size of the specimen densified at 1300°C was between 150 and 500 nm.

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al2O3–TiO2–MgO and Al2O3–TiO2–SiO2 systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al2TiO5. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.

SiO2-Iron Oxide Composites Obtained by Sol-Gel Method

Composite SiO2-iron oxide materials were prepared by three experimental procedures. In the first case (1), the iron oxides were precipitated during the sol-gel process. In the second case (2), the SiO2 matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe2+ salt in the previously processed matrix. In the third method (3), ferrite powders, prepared by wet chemical method, were embedded into a SiO2 based sol-gel matrix. Two type of precursors (tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS) were used as SiO2 sources. Various properties versus both type of precursor and on the method of preparation were noticed. Materials with high porosity and nano-sized iron oxide content could be prepared using the mentioned above methods.

Contribution to the Sol-Gel Chemistry in Silica Based Systems

In the present work the sol-gel process in the silica base systems, starting with different alkoxides, was approached by gas chromatography coupled with mass spectrometry (CG-MS). The influence of the type of alkoxide, type of solvent and the water amount on the molecular species formed in the early stages of the hydrolysis-polycondenstion process were analyzed, as well as the influence of the molecular species present in the solution at the moment of gelation on the structure of the obtained gels.