51. X-ray absorption spectroscopy set-up for unstable gases: A study of 5p HydridesRobert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, 2020, izvirni znanstveni članek Opis: An absorption cell is constructed for x-ray absorption spectroscopy of reactive, unstable or hazardous gases at
room temperature. In conjunction with in-situ micro-synthesis technique relying on handling the gas in syringes
it enabled a first measurement of x-ray absorption spectra in the region of K and L edges for the series of hydrides
of 5p elements (SnH4, SbH3, TeH2, HI). The signal-to-noise ratio above 103 was achieved, whereby fine detail is
discerned in the spectra, in particular the small sharp features above each absorption edge, testifying of coexcitations
of outer electrons in the core photoeffect. Ključne besede: X-ray absorption spectroscopy
Micro-synthesis absorption cell
Gaseous hydrides
Multielectron photoexcitations Objavljeno v RUNG: 10.02.2020; Ogledov: 3560; Prenosov: 0 Gradivo ima več datotek! Več... |
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53. Role of Cu current collector on electrochemical mechanism of Mg–S batteryAna Robba, Maja Mežnar, Alen Vižintin, Jan Bitenc, Jernej Bobnar, Iztok Arčon, Anna Randon-Vitanova, Robert Dominko, 2020, izvirni znanstveni članek Opis: Development of magnesium sulfur battery is accompanied with all known difficulties present in Li–S batteries,
however with even more limited choice of electrolytes. In the present work, the influence of current collector on
electrochemical mechanism was investigated in light of different reports where improved behavior was ascribed
to electrolyte. Notable differences in cycling behavior are reported when Al current collector is replaced by Cu
current collector independent of electrolyte. The initial reduction of sulfur follows similar reaction path no mater
of current collector, but formation of MgS can be in competition with formation of CuS in the presence of Cu
cations. With the subsequent cycling cells prepared from cathodes deposited on Cu current collector show
decrease in the voltage and formation of single plateau during cycling. The change corresponds to the
involvement of Cu into the reaction and formation of redox couple Mg/CuS as determined by Cu K-edge XANES
measurements. Corrosion of Cu foil is identified by SEM and serves as a source of Cu cations for the chemical
reaction between Cu and polysulfides. Mg/CuS redox couple shows improved cycling stability, but theoretical
energy density is severely reduced due to substitution of S with CuS as cathode active material. Ključne besede: Magnesium
Sulfur
Rechargeable batteries
Current collector
Copper
Corrosion Objavljeno v RUNG: 16.01.2020; Ogledov: 3068; Prenosov: 0 Gradivo ima več datotek! Več... |
54. Arabidopsis halleri shows hyperbioindicator behaviour for Pb and leaf Pb accumulation spatially separated from ZnStephan Höreth, Paula Pongrac, Marta Debeljak, Katarina Vogel-Mikuš, Matic Pečovnik, Primož Vavpetič, Iztok Arčon, izvirni znanstveni članek Opis: Lead (Pb) ranks among the most problematic environmental pollutants. Background contamination of soils is nearly ubiquitous, yet plant Pb accumulation is barely understood. In a survey covering 165 European populations of the metallophyte Arabidopsis halleri, several field samples had indicated Pb hyperaccumulation, offering a chance to dissect plant Pb accumulation.
Accumulation of Pb was analysed in A. halleri individuals from contrasting habitats under controlled conditions to rule out aerial deposition as a source of apparent Pb accumulation. Several elemental imaging techniques were employed to study the spatial distribution and ligand environment of Pb.
Regardless of genetic background, A. halleri individuals showed higher shoot Pb accumulation than A. thaliana. However, dose–response curves revealed indicator rather than hyperaccumulator behaviour. Xylem sap data and elemental imaging unequivocally demonstrated the in planta mobility of Pb. Highest Pb concentrations were found in epidermal and vascular tissues. Distribution of Pb was distinct from that of the hyperaccumulated metal zinc. Most Pb was bound by oxygen ligands in bidentate coordination.
A. halleri accumulates Pb whenever soil conditions render Pb phytoavailable. Considerable Pb accumulation under such circumstances, even in leaves of A. thaliana, strongly suggests that Pb can enter food webs and may pose a food safety risk. Ključne besede: Pb accumulation, XANES, EXAFS, Arabidopsis halleri Objavljeno v RUNG: 16.01.2020; Ogledov: 3116; Prenosov: 0 Gradivo ima več datotek! Več... |
55. Mineral element composition in grain of awned and awnletted wheat (Triticum aestivum L.) cultivars tissue-specific iron speciation and phytate and non-phytate ligand ratioPaula Pongrac, Iztok Arčon, Hiram Castillo Michel, Katarina Vogel-Mikuš, 2020, izvirni znanstveni članek Opis: In wheat (Triticum aestivum L.), the awns—the bristle-like structures extending from
lemmas—are photosynthetically active. Compared to awned cultivars, awnletted cultivars produce
more grains per unit area and per spike, resulting in significant reduction in grain size, but their
mineral element composition remains unstudied. Nine awned and 11 awnletted cultivars were
grown simultaneously in the field. With no difference in 1000-grain weight, a larger calcium and
manganese—but smaller iron (Fe) concentrations—were found in whole grain of awned than in
awnletted cultivars. Micro X-ray absorption near edge structure analysis of different tissues of
frozen-hydrated grain cross-sections revealed that differences in total Fe concentration were not
accompanied by differences in Fe speciation (64% of Fe existed as ferric and 36% as ferrous species) or
Fe ligands (53% were phytate and 47% were non-phytate ligands). In contrast, there was a distinct
tissue-specificity with pericarp containing the largest proportion (86%) of ferric species and nucellar
projection (49%) the smallest. Phytate ligand was predominant in aleurone, scutellum and embryo
(72%, 70%, and 56%, respectively), while nucellar projection and pericarp contained only non-phytate
ligands. Assuming Fe bioavailability depends on Fe ligands, we conclude that Fe bioavailability from
wheat grain is tissue specific. Ključne besede: biofortification, phytate, iron, awn, X-ray fluorescence, X-ray absorption spectrometry, phosphorus, sulphur, nicotianamine Objavljeno v RUNG: 16.01.2020; Ogledov: 2927; Prenosov: 0 Gradivo ima več datotek! Več... |
56. Spremljanje, ugotavljanje in zagotavljanje kakovosti : Poročilo za študijsko leto 2018/2019, Fakulteta za znanosti o okolju, Univerza Nova GoricaBlaž Belec, Iztok Arčon, Marina Artico, Tea Stibilj Nemec, Nivec Štefančič, Maja Terčon, Matjaž Valant, Sabina Zelinšček, elaborat, predštudija, študija Ključne besede: Samoevalvacijsko poročilo Objavljeno v RUNG: 06.01.2020; Ogledov: 3184; Prenosov: 0 Gradivo ima več datotek! Več... |
57. Localization, ligand environment, bioavailability and toxicity of mercury in Boletus spp. and Scutiger pes-caprae mushroomsAnja Kavčič, Klemen Mikuš, Marta Debeljak, Johannes Teun van Elteren, Iztok Arčon, Alojz Kodre, Peter Kump, Andreas-Germanos Karydas, Alessandro Migliori, Mateusz Czyzycki, Katarina Vogel-Mikuš, 2019, izvirni znanstveni članek Opis: This study provides information on mercury (Hg) localization, speciation and ligand environment in edible mushrooms: Boletus edulis, B. aereus and Scutiger pes-caprae collected at non-polluted and Hg polluted sites, by LA-ICP-MS, SR-μ-XRF and Hg L3-edge XANES and EXAFS. Mushrooms (especially young ones) collected at Hg polluted sites can contain more than 100 μg Hg g−1 of dry mass. Imaging of the element distribution shows that Hg accumulates mainly in the spore-forming part (hymenium) of the cap. Removal of hymenium before consumption can eliminate more than 50% of accumulated Hg.
Mercury is mainly coordinated to di-thiols (43–82%), followed by di-selenols (13–35%) and tetra-thiols (12–20%). Mercury bioavailability, as determined by feeding the mushrooms to Spanish slugs (known metal bioindicators owing to accumulation of metals in their digestive gland), ranged from 4% (S. pes-caprae) to 30% (B. aereus), and decreased with increasing selenium (Se) levels in the mushrooms. Elevated Hg levels in mushrooms fed to the slugs induced toxic effects, but these effects were counteracted with increasing Se concentrations in the mushrooms, pointing to a protective role of Se against Hg toxicity through HgSe complexation. Nevertheless, consumption of the studied mushroom species from Hg polluted sites should be avoided. Ključne besede: edible mushrooms, HgSe complex, imaging of elemental distribution, LA-ICP-MS, alpha-XRF, XAS Objavljeno v RUNG: 24.10.2019; Ogledov: 4636; Prenosov: 0 Gradivo ima več datotek! Več... |
58. Comparing magnetism in isostructural oxides A[sub](0.8)La[sub](1.2)MnO[sub](4.1) : anisotropic spin glass (A = Ba) versus long range order (A = Sr)Mirela Dragomir, Paul A. Dube, Iztok Arčon, Chad Boyer, Meghan Rutherford, Christopher Wiebe, Graham King, Hanna Dabkowska, John E. Greedan, 2019, izvirni znanstveni članek Opis: This study presents the strikingly distinct magnetic properties of two isostructural compounds, Ba0.8La1.2MnO4.1
and Sr0.8La1.2MnO4.1 (K2NiF4
type, I4/mmm). Spectroscopic studies have shown that Mn is in a +3.0(1) oxidation state only,
in both compounds; therefore, the charge is balanced by accommodating extra oxygen at interstitial sites, as confirmed by
neutron powder diffraction. We found that the Ba compound exhibits an exceedingly rare anisotropic spin glass behavior, Tg =
26.4(4) K, with the moment freezing along the c-axis only while the in-plane spin components remain dynamic well below Tg.
Experimental results including neutron diffraction, heat capacity, and magnetic (dc and ac) measurements performed on an
oriented single crystal support this conclusion. This is a remarkable result, the only other known example of an anisotropic spin
glass being Fe2TiO5. The spin glass state in Ba0.8La1.2MnO4.1 is argued to arise due to competing antiferromagnetic and
ferromagnetic 180° Mn3+−O−Mn3+ superexchange interactions. In contrast, the Sr analogue shows 2D antiferromagnetic
correlations and long-range antiferromagnetic order below 95(1) K with a remarkably reduced ordered moment of 1.449(49)
μB/Mn3+ instead of the ∼4 μB expected for an S = 2 ion. Ključne besede: antiferomagnetiki, Mn XANES, struktura Objavljeno v RUNG: 23.10.2019; Ogledov: 3171; Prenosov: 0 Gradivo ima več datotek! Več... |
59. In-depth structural characterization and magnetic properties ofquaternary ferrite systems Co0.5Zn0.25M0.25Fe2O4(M¼Ni, Cu, Mn, Mg)Radu-G. Ciocarlan, Iztok Arčon, Aurel Pui, Myrjam Mertens, Nataša Novak Tušar, Elena M. Seftel, Pegie Cool, 2019, izvirni znanstveni članek Opis: This paper investigates the structural and magnetic properties of a mixed series of ferrites having generalformula Co0.5Zn0.25M0.25Fe2O4(M¼Ni, Cu, Mn, Mg). Insights on surface chemistry, structural andmorphological parameters are presented in order to achieve highly tuned ferrite systems with specificcharacteristics. The site occupancy of the cations in the spinel structure was determined using XAS, XRDand Raman spectroscopy. A 100% occupancy of the tetrahedral sites was observed for the Zn cations forall the samples. Co cations occupied the octahedral sites in proportion of 100% for CoeZneCu, CoeZneMg and around 80% for CoeZneNi, CoeZneMn. Ni cations were found only in the octahedral sites,while Cu 80% in the octahedral sites and Mn 60% in the octahedral sites. The cation distribution resultswere correlated with the magnetic properties data. At the same time, not only the cation distribution, butalso the particles size distribution was observed to have a great influence on magnetic and opticalproperties of the ferrites. Given the importance of the surface chemistry of the nanoparticles, XPS and FT-IR analysis were used to prove the functionalization with groups belonging to the surfactant. Moreover,the peculiar behavior of manganese in spinel structures was clarified and the origin of the multiple states(Mn2þand Mn4þ) was elucidated. Finally, parallels have been drawn between the use of different cationsin mixed ferrites in order to gain specific properties. Ključne besede: FerritesMagnetic propertiesSpinel nanoparticlesX-ray absorption spectroscopyCo-precipitation Objavljeno v RUNG: 23.10.2019; Ogledov: 3313; Prenosov: 0 Gradivo ima več datotek! Več... |
60. Effects of the molecular potential on coexcitations of valence electrons in the K-shell photoeffect of 3p and 4p elementsRobert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Giuliana Aquilanti, 2019, izvirni znanstveni članek Opis: Photoabsorption spectra of gaseous hydrides of 3p (PH3, H2S, HCl) and 4p elements (GeH4, AsH3 , H2Se,
HBr) are measured in the energy region within 50 eV above the K edge, to study coexcitations of valence
electrons by photoeffect in the K shell. The analysis of the valence coexcitations is extended to Ar, Kr, and
SiH4. Relative probabilities and energies of states in the individual coexcitation channels are recovered by
modeling the spectral features with a minimal ansatz based on the features in the contiguous noble gas. The
extracted parameters are compared to the results of theoretical calculations for molecules (ORCA code) and
free atoms (Hartree-Fock code). The experimental results confirm that the valence coexcitations in the 3p and
4p hydride molecules can be satisfactorily described by a two-step process, with the shake of the outer electron
following the excitation of the core electron. The total probability—relative to the K-edge jump—of the shake-up
processes shows a steady decrease from 19% in Si to 14% in Cl, and from 15% in Ge to 12% in Br. The
experimental values for Ar (12%) and Kr (10%) are in accord with the trend. The dominant contribution is
the transition to quasiatomic orbitals, in contrast with the deeper coexcitation channels in hydride molecules
where transition to molecular orbitals prevails. Ključne besede: X-ray absorption spectra, gaseous hydrides, 3p K-edge spectra, DFT Objavljeno v RUNG: 05.09.2019; Ogledov: 2976; Prenosov: 0 Gradivo ima več datotek! Več... |