21. X-ray absorption spectroscopy analysis: in situ, operando, in vivoIztok Arčon, 2020, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje) Opis: X-ray absorption spectroscopy (XAS) is a powerful tool for characterisation of local structure and chemical state of selected elements in different new functional materials and biological or environmental samples. The XAS spectroscopy is based on extremely bright synchrotron radiation X-rays sources, which allow precise characterisation of bulk, nanostructured or highly diluted samples. With its two methods (XANES and EXAFS) it enables monitoring changes in valence states and local structures of constituent elements during chemical reactions under controlled reaction conditions, and it offers a possibility of a combination of X-ray spectroscopy and microscopy with sub-micron lateral resolution, crucial for analysis of biological samples on sub-cellular level. In this talk some typical examples of advanced XAS analysis will be presented.
Ključne besede: X-ray absorption spectroscopy, EXAFS, XANES, in-situ, operando
Objavljeno v RUNG: 17.10.2020; Ogledov: 6542; Prenosov: 0
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22. Spectroscopic insights into the electrochemical mechanism of rechargeable calcium/sulfur batteriesAntonio Scafuri, Romain Berthelot, Klemen Pirnat, Alen Vižintin, Jan Bitenc, Giuliana Aquilanti, Dominique Foix, Rémi Dedryvère, Iztok Arčon, Robert Dominko, Lorenzo Stievano, 2020, izvirni znanstveni članek Opis: Calcium batteries represent a promising alternative to lithium metal systems. The combination of the low redox potential and low cost and the energy-dense calcium anode (2073 mAh/cm3, similar to 2044 mAh/cm3 for Li) with appropriate low-cost cathode materials such as sulfur could produce a game-changing technology in several fields of applications. In this work, we present the reversible activity of a proof-of-concept Ca/S battery at room temperature, characterized by a surprising medium-term cycling stability with low polarization, promoted by the use of a simple positive electrode made of sulfur supported on an activated carbon cloth scaffold, and a state-of-the-art fluorinated alkoxyborate-based electrolyte. Insights into the electrochemical mechanism governing the chemistry of the Ca/S system were obtained for the first time by combining X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The mechanism implies the formation of different types of soluble polysulfide species during both charge and discharge at room temperature, and the formation of solid CaS at the end of discharge. The reversible electrochemical activity is proven by the reformation of elemental sulfur at the end of the following charge. These promising results open the way to the comprehension of emerging Ca/S systems, which may represent a valid alternative to Mg/S and Li/S batteries.
Ključne besede: Calcium/Sulfur Batteries
EXAFS, XANES
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24. Study of water adsorption on EDTA dealuminated zeolite YO. L. Pliekhov, Olena Pliekhova, Iztok Arčon, Federica Bondino, Elena Magnano, Gregor Mali, Nataša Zabukovec Logar, 2020, izvirni znanstveni članek Opis: Zeolite Y was synthesized and modified with EDTA dealumination procedure. The modified zeolites were
analyzed by X-ray diffraction, X-ray absorption spectroscopy, chemical analysis and water adsorption measurements.
We demonstrated that dealumination with bulk organic acid such as EDTA is able to reduce the
original intense water affinity. Furthermore, it was found that dealumination with EDTA, in contrast with
steaming and HCl dealumination, provides fully controllable, predictable and secure process of Al removal from
the zeolites’ frameworks. The shift of the adsorption isotherm in the low partial pressure range represents an
interesting result for adsorption-based applications.
Ključne besede: Zeolite Y
Water sorption
Dealumination
Al XANES
EDTA treatment
Objavljeno v RUNG: 05.06.2020; Ogledov: 4300; Prenosov: 0
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25. Effects of a Mixed O/F Ligand in the Tavorite-Type LiVPO4O StructureSorour Semsari Parapari, Jean-Marcel Ateba Mba, Elena Tchernychova, Gregor Mali, Iztok Arčon, Gregor Kapun, Mehmet Ali Gülgün, Robert Dominko, 2020, izvirni znanstveni članek Opis: We report the synthesis and detailed structural
and chemical characterization including electrochemical
properties of a lithium vanadium oxy/fluoro-phosphate
material. To the best of our knowledge, we have for the first
time synthesized a LiVPO4O-type phase with a mixed O/F
ligand. In the synthesis procedure, the LiVPO4O precursor
compound was fluorinated via LiF incorporation, with
preservation of the LiVPO4O framework structure. The
operating potential of the synthesized material is increased
compared to that of the LiVPO4O precursor (4.12 V vs 3.95 V
versus metallic lithium, respectively). The related increase in
operating potential was assigned to the effect of the
intermixing O/F ligand, which is attained via the successful
fluorine incorporation into the LiVPO4O structure. A characterization of the investigated materials was performed using
microscale-covering XRD, XANES, and NMR techniques as well as nanoscale spatially resolved imaging and analytical STEM
techniques. The obtained oxy/fluoro-phosphate phase is isostructural to LiVPO4O; however, the presence of the mixed O/F
ligand promoted a higher symmetry of vanadium octahedra. These variations of the vanadium local environment along with the
observed inhomogeneous distribution of the incorporated fluorine gave rise to the minor local deviations in vanadium valence.
Our results clearly emphasize the connection among the fluorine ligand incorporation, its local distribution, and the
electrochemical properties of the material.
Ključne besede: LiVPO4O, XRD, SEM, V XANES, Tavorite-Type, electrochemical properties
Objavljeno v RUNG: 17.02.2020; Ogledov: 4223; Prenosov: 0
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26. 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: 4470; Prenosov: 0
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27. 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: 4378; Prenosov: 0
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28. Recent advances in 2D imaging of element distribution in Plants by focused beam techniquesKatarina Vogel-Mikuš, Johannes Teun van Elteren, Marjana Regvar, Jitrin Chaiprapa, Boštjan Jenčič, Iztok Arčon, Alojz Kodre, Peter Kump, Anja Kavčič, Mitja Kelemen, Dino Metarapi, Marijan Nečemer, Primož Vavpetič, Primož Pelicon, Paula Pongrac, 2019, samostojni znanstveni sestavek ali poglavje v monografski publikaciji Ključne besede: 2D Imiging, XRF, XANES, synchrotron light
Objavljeno v RUNG: 05.09.2019; Ogledov: 4552; Prenosov: 0
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29. New Insights into Manganese Local Environment in MnS-1NanocrystalsAlenka Ristić, Matjaž Mazaj, Iztok Arčon, Nina Daneu, Nataša Zabukovec Logar, Roger Glaser, Nataša Novak Tušar, 2019, izvirni znanstveni članek Opis: Manganese plays an important role in redox catalysis using zeolites as inorganic support materials, but the formation of the preferred redox manganese species (framework or extraframework) is still not well understood. Herein, the influence of the amount of manganese together with conventional and microwave-assisted hydrothermal synthesis paths on the formation of manganese species within the zeolite silicalite-1 (S-1) with MFI structure was investigated. It was found out that both synthesis procedures led to the formation of framework and extraframework manganese species, but in different molar ratios. However, the conventional synthesis procedure with all Mn/Si molar ratios generates more framework Mn in comparison to the microwave procedure. Additionally, the diminution of the zeolite crystals to nanoscale from 100 to 200 nm was achieved via the conventional procedure for the first time. UV–vis, Raman, and X-ray absorption spectroscopic analyses revealed different local environments of manganese: Mn3+ incorporated into the silicalite-1 framework as “framework manganese” and Mn2+/3+ present as “extraframework manganese” (Mn2O3, Mn3O4). TEM reveals the presence of Mn3O4 nanorods. Both framework manganese and extraframework manganese exhibit good catalytic activity for styrene epoxidation. Catalytic results suggest that, in oxidation reactions of hydrocarbons, framework manganese is more active at lower Mn contents (Mn/Si < 0.015), whereas extraframework manganese is more active at higher loadings (Mn/Si > 0.015).
Ključne besede: MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis
Objavljeno v RUNG: 06.05.2019; Ogledov: 4722; Prenosov: 0
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30. Alternative Recovery and Valorization of Metals from Exhausted Catalytic Converters in a New Smart Polymetallic CatalystSebastiano Tieuli, Franco Baldi, Iztok Arčon, Katarina Vogel-Mikuš, Michele Gallo, Laura Sperni, Oreste Piccolo, Stefano Paganelli, 2019, izvirni znanstveni članek Opis: A new metals-polymeric composite, Metx-EPS (I), was prepared
to be used as catalyst in water or in two-phase aqueous
conditions. The metals source was an exhausted catalytic
converter that was grinded and treated with an acidic solution at room temperature. After filtration, the solution was concentrated, neutralized and added to a broth of Klebsiella oxytoca DSM 29614 to produce (I) where metals are embedded in a peculiar polysaccharide structure (EPS). The composite was easily recovered from the fermentation broth and purified. The process protocol was verified many times and was shown to be reproducible satisfactorily. The % recovery of metals, originally present in the converter, was good as determined by atomic
absorption. The morphology and the chemical state of main
metals in (I) were investigated by X-ray absorption spectroscopy
methods (XANES and EXAFS). No metallic alloy seems to
be evident. The catalytic activity and a possible synergic effect due to the presence of the different metals was valuated in the hydrogenation of some substrates, valuable precursors for theproduction of fine chemicals.
Ključne besede: Biogenerated polymetallic exopolysaccharide, biphasic catalysis, hydrogenation, metals-polymeric
composite, new catalyst from metallic wastes, EXAFS, XANES
Objavljeno v RUNG: 06.05.2019; Ogledov: 4676; Prenosov: 0
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