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41.
Correlations between photocatalytic activity and chemical structure of Cu-modified TiO [sub] 2-SiO [sub] 2 nanoparticle composites
T. Čižmar, Iztok Arčon, Urška Lavrenčič Štangar, 2016, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: Cu-modified TiO2-SiO2, sol-gel, XANES, EXAFS
Objavljeno v RUNG: 06.02.2017; Ogledov: 4113; Prenosov: 0
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42.
Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2–SiO2 nanoparticle composites
T. Čižmar, Urška Lavrenčič Štangar, Iztok Arčon, 2016, izvirni znanstveni članek

Opis: Copper-modified TiO2–SiO2photocatalysts were prepared by sol–gel method based on organic copper,silicon and titanium precursors. Copper concentration varied from 0.1 to 3.0 mol%. A widely appliedmodel reaction of photocatalytic oxidation of terephtalic acid (TPA) in water solution was used in order toevaluate the catalytic activities of elaborated samples. The crystal structures of the titania components ofall tested titania–silica species were studied using XRD analysis. The influence of Cu2+cation incorporationon the crystal structure of titania, as well as the chemical states and the neighbouring structures of coppercations, have been examined by means of Cu K-edge EXAFS and XANES analysis. The experimental datashow that there is a ten times increase in photocatalytic activity when TiO2–SiO2matrix is modified with0.1 mol% of Cu. It can be supposed that an enhancement of photocatalytic activity of low-concentratedcopper-modified titania–silica nanocomposites is probably due to a close attachment of Cu2+cationsto the surfaces of photocatalytically active TiO2nanoparticles. In this case, Cu2+cations may possiblyact as free electron traps reducing the intensity of recombination between opposite free charge carriers(electrons, holes) available at the photocatalyst’s surface.
Ključne besede: Cu-modified TiO2–SiO2photocatalysts, Titanium dioxide, Metal doping, Cu K-edge XANES, EXAFS, Photocatalytic activitya
Objavljeno v RUNG: 17.01.2017; Ogledov: 5123; Prenosov: 0
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43.
Arbuscular mycorrhizal fungi alter Hg root uptake and ligand environment as studied by X-ray absorption fine structure
Alojz Kodre, Iztok Arčon, Marta Debeljak, Mateja Potisek, Matevž Likar, Katarina Vogel-Mikuš, 2017, izvirni znanstveni članek

Opis: Mercury (Hg) – plant – fungal interactions are only poorly studied. Hg speciation and ligand environment in maize roots inoculated with arbuscular mycorrhizal (AM) fungi were investigated in order to better understand the role of AM in Hg soil to root transfer. The maize plants were grown in Hg polluted substrate (50 mg g1 as dissolved HgCl2) and inoculated with AM fungi originating from: a) highly Hg polluted environment of a former Hg smelting site in Idrija, Slovenia, (Glomus sp. – sample AmI), and b) non-polluted environment (commercial AM inoculum Symbivit1 – sample AmC). Hg speciation and ligand environment in maize roots was studied by Hg-L3 XANES and EXAFS with emphasis on XAS methodology – modelling and fitting the XAFS spectra to extract in a reliable way as much information on Hg coordination as possible. The AmI plants developed more arbuscules and less vesicles than the AmC plants, and also accumulated more Hg in the roots. A clear difference in Hg coordination between the AM (AmC & AmI) and the control (ConC & ConI) plants is recognized in Hg L3-edge EXAFS analysis: in the ConC & ConI maize roots 73–80% of Hg is attached between two sulphur atoms at the distance of 2.34 Å. The remaining ligand is nitrogen at 2.04 Å. In AmI & AmC roots another Hg-S attachment encompassing four thiol groups at the S-distance of 2.50 Å are identified, accounting for 21–26%. AM fungi can modify Hg ligand environment in plant roots, thus playing an important role in biogeochemical cycling of Hg in terrestrial ecosystems.
Ključne besede: EXAFS XANES Arbuscular mycorrhiza Phytoremediation Toxicity Hg coordination Ligand environment
Objavljeno v RUNG: 27.09.2016; Ogledov: 6092; Prenosov: 0
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44.
XAS and micro-XRF analysis of mono and bi-metallic exopolysaccharide (FePd-EPS) bio-generated by K. oxytoca
Iztok 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: 5481; Prenosov: 0
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45.
46.
Specific EXAFS tools in analysis of MoSI nanowires
Anton Meden, Alojz Kodre, Iztok Arčon, Jana Padežnik Gomilšek, Dragan Mihailović, 2006, izvirni znanstveni članek

Opis: Specific EXAFS tools in analysis of MoSI nanowires
Ključne besede: EXAFS, MoSI, nanocevke, struktura
Objavljeno v RUNG: 17.05.2016; Ogledov: 4899; Prenosov: 20
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47.
Removal of manganese in batch and fluidized bed systems using beads of zeolite a as adsorbent
Mina 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: 5178; Prenosov: 0
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48.
Operando (micro) XAFS analysis
Iztok Arčon, Robert Dominko, Katarina Vogel-Mikuš, 2016, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje)

Opis: In the talk the principles of XAS methods were presented with practical examples which illustrate the possibilities and advanced approaches for their use in structural analysis of different types of materials. The emphasis will be on to the use of XAS spectroscopy in operando mode and in combination with X-ray microscopy.
Ključne besede: X-ray absorption spectroscopy, X-ray microscopy, EXAFS, XANES, opearndo mode
Objavljeno v RUNG: 25.03.2016; Ogledov: 6074; Prenosov: 165
.pdf Celotno besedilo (18,40 MB)

49.
High-resolution X-ray absorption spectrometry of atomic vapors
Iztok 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: 4911; Prenosov: 27
URL Povezava na celotno besedilo

50.
X-ray absorption spectroscopy and related techniques
Iztok 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: 4686; Prenosov: 26
URL Povezava na celotno besedilo

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