Papers by Author: V. Dondur

Abstract: Ceramic materials, barium and strontium diphyllosilicates doped with ytterbium ions, were obtained by thermal treatment from Ba–LTA and Sr–LTA zeolites. The samples were characterized with Differential Scanning Calorimetry, Infra–Red Spectroscopy and Scanning Electron Microscopy. The crystal structures of diphyllosilacetes have been refined.

Abstract: In this work, a series of iron-containing zeolitic materials has been tested as heterogeneous catalysts for decomposition of H2O2 and for oxidation of the cationic dye Methylene Blue with H2O2 in aqueous solutions. FeAPO and FeBEA zeolites, synthesized through hydrothermal crystallization of basic hydrogels, and FeY and FeZSM-5 zeolites, prepared by ionexchange procedures, have been studied. The ion exchange with Fe(III) cations was performed from different salt solutions. Fe-exchange procedure carried out in Fe-citrate solution has been identified as an attractive option for the preparation of highly effective FeZSM-5 catalysts in wet oxidation processes. It has been shown that both tetrahedral, framework Fe, and octahedral, extra-framework Fe species incorporated into zeolite structure are catalytically active in wet oxidation reactions.

Abstract: In this paper the adsorption and oxidation of CO on nanocrystalline Au/γ-Fe2O3, Au/α- Fe2O3, γ-Fe2O3 and a series of mixed ferrite with MnxZn1-xFe2O4 composition are investigated. The catalysts were prepared by co-precipitation method and characterized using X-ray diffraction (XRPD), specific surface (BET), transition electron spectroscopy (TEM) and magnetization measurements. A temperature programmed desorption (TPD) study of the water and CO interaction with nanocrystalline adsorbents is presented. The catalytic activities towards CO oxidation increased in the following order: γ-Fe2O3 < MnxZn1-xFe2O4 < Au/γ-Fe2O3 .

Abstract: The surface properties of zeolites A, X, Y and natural zeolite clinoptilolite (CLI) functionalized by cationic surfactants were investigated. The quaternary ammonium type surfactants, such as hexadecyltrimethylammonium (HDTMA) chloride, stearildimethylbenzylammonium (SDMBA) chloride and distearildimethylammonium (DSDMA) chloride, replaced inorganic cations like Na+ and Ca2+ on the external surface of zeolites. The adsorption capacities of all organic cations followed the order of CLI>CaY>CaX>CaA>NaY>NaX>NaA and increased with the increase of Si/Al molar ratio in zeolite structure. This modification resulted in an alteration in the surface property of zeolites - it changed from hydrophilic to hydrophobic. The adsorption of selected pesticides with different hydrophobicity on surfactant-modified zeolites was studied. It is shown that surfactant-modified zeolites can be used for removal of pesticides from the environment. The increase in hydrophobicity of pesticides resulted in an increase in pesticide adsorption on SDMBA and DSDMA modified zeolites.

Abstract: A series of hexacelsians with different compositions were synthesized by thermally induced transformation of a LTA zeolite. Various forms of hexacelsians have been characterized by XRPD, IR, Raman and 29Si MAS NMR method. The phase transformation a
b hexacelsian was investigated by DSC method. This phase transformation is sensitive to synthesis conditions, doping and thermal treatment. The peak maximum temperature, Tm, varies from 302 up to 353 oC. Heat of transformation changes from 0.42 to 1.77 kJ/mol.