131. XAS and micro-XRF analysis of mono and bi-metallic exopolysaccharide (FePd-EPS) bio-generated by K. oxytocaIztok Arčon, Stefano Paganelli, Oreste Piccolo, Michele Gallo, Katarina Vogel-Mikuš, Franco Baldi, 2016, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Bacteria Klebsiella oxytoca (DSM 29614) secret a specific exopolysaccharide (EPS) in the presence of Fe(III)-citrate, as sole carbon and energy source, and produces after 7 days an iron gel precipitate (Fe-EPS) [1]. In the presence of palladium or other metal species, the culture of K. oxytoca can produce other mono or bimetal species (Pd-EPS, FePd-EPS) [2]. These bio-materials may be used as green biogenerated catalysts or for other biotechnological purposes. In this work we present the analysis of the morphology and the chemical state of the metals in mono and bi-metallic (Fe-EPS, Pd-EPS, FePd-EPS) complexes, by a combination of micro X-ray fluorescence, X-ray absorption spectroscopy methods (XANES and EXAFS), and transmission electron microscopy. The results show that iron in monometallic Fe-EPS and bimetalic FePd-EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe3+, with a small amount of Fe2+ in the structure, as a mixture of different nano-crystalline iron oxides and hydroxides. Palladium on the other hand is found as Pd(0) in the form of metallic nanoparticles with fcc structure in both, bi-metallic (FePd-EPS) and mono-metallic (Pd-EPS) species. In bi-metallic species Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. Access to the SR facilities at ESRF (beamline ID21, project LS-2225), DESY (beamline C) Hamburg (project I-20110511 EC) and ELETTRA (beamline XAFS, project 20115112) is acknowledged.
Ključne besede: Klebsiella oxytoca, Fe, Pd, XANES, EXAFS, exopolysaccharide, FePd-EPS
Objavljeno v RUNG: 28.06.2016; Ogledov: 5631; Prenosov: 0
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133. The first example of a mixed valence ternary compound of silver with random distribution of Ag(I) and Ag(II) cationsIztok Arčon, Zvonko Jagličić, Wojciech Grochala, Zoran Mazej, Evgeny A. Goreshnik, Tomasz Michałowski, Jadwiga Szydłowska, 2015, izvirni znanstveni članek Ključne besede: srebrov fluorid, mešana valenca, srebro, XANES
Objavljeno v RUNG: 16.06.2016; Ogledov: 4216; Prenosov: 159
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136. Removal of manganese in batch and fluidized bed systems using beads of zeolite a as adsorbentMina Jovanovic, Iztok Arčon, Janez Kovač, Nataša Novak Tušar, Bojana Obradovic, Nevenka Rajić, 2016, izvirni znanstveni članek Opis: In this study the uptake capacity of Mn(II) ions by zeolite A beads was investigated for different initial Mn concentration (100e400 mg Mn dm^-3) in batch mode at 25e55 C. The obtained adsorption capacity varying from 30 to 50 mg Mn g^-1 demonstrated a high affinity of zeolite A towards Mn(II) present in solutions. Kinetic studies indicated the intra-particle diffusion as the rate limiting step up to 45 C with apparent diffusivities in the range (1.2e2.0) x 10^-13 m2 s^-1 and the activation energy of 21.9 kJ mol^-1, which implies strong interactions between the zeolite A and Mn ions. At 55 C ion-exchange became the rate limiting step. The adsorption isotherms were studied at 25 C showing that the Mn adsorption is the best described by the Langmuir model suggesting a homogenous zeolite surface. XPS analysis of the Mnloaded beads showed that there is no surface accumulation of Mn but an almost uniform Mn distribution inside zeolite A, whereas XANES and EXAFS suggested that the adsorption of Mn(II) was followed by the Mn(II) oxidation and oxide formation. Regeneration of the spent zeolite was examined in 8 adsorption/desorption cycles by a chelating Na2EDTA in a fluidized column. It has been found that zeolite A beads could be reused for at least 4 cycles with satisfactory Mn(II) adsorption efficiencies of about 70%.
Ključne besede: Zeolite A
Manganese
Adsorption kinetics
EXAFS/XANES
XPS
Objavljeno v RUNG: 01.04.2016; Ogledov: 5326; Prenosov: 0
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139. High-resolution X-ray absorption spectrometry of atomic vaporsIztok Arčon, Jana Padežnik Gomilšek, Alojz Kodre, Andrej Mihelič, 2004, izvirni znanstveni članek Opis: A measurement of an x-ray absorption spectrum of a monatomic sample yields pure atomic absorption essential for the EXAFS (Extended X-ray Absorption FineStructure) analysis in cases of a weak structural signal. A construction of an absorption cell to contain vapor sample takes into account specific properties of the investigated element. Metal-vapor absorption cells for the elements K, zn, Rb, Cd, Cs, and Hg are presented and comments are made on the use of materials and the operating mechanisms of the cells.
Ključne besede: X-žarki, absorpcija, EXAFS, absorpcijske celice
Objavljeno v RUNG: 10.07.2015; Ogledov: 5056; Prenosov: 27
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140. X-ray absorption spectroscopy and related techniquesIztok Arčon, Alojz Kodre, Jana Padežnik Gomilšek, 2004, izvirni znanstveni članek Opis: In the extensive field of X-ray diagnostic techniques, nowadays mostly implemented on synchrotron X-ray sources, the X-ray absorption methods offer a relatively simple tool for structural analysis of materials. The advantage of the methods is the sensitivity to chemical species and the insensitivity to the long-range order. An overview of various detection techniques is given together with the discussion of accuracy of the method with regard to the spatial resolution and the possible contamination by intra-atomic contributions, the multielectron photoexcitations.
Ključne besede: X-žarki, absorpcija, EXAFS, XANES
Objavljeno v RUNG: 10.07.2015; Ogledov: 4802; Prenosov: 26
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