1. Beyond surface area : enhanced pseudocapacitive properties of cobalt layered double hydroxide through structural modificationsAnja Siher, Ksenija Maver, Uroš Luin, Albin Pintar, Iztok Arčon, Andraž Mavrič, 2025, izvirni znanstveni članek Opis: Cobalt hydroxide and other first-row transition metal hydroxides have gained significant attention as pseudocapacitor materials due to their rapid and reversible redox processes. Their layered structures facilitate interactions between electrolyte anions and cobalt cation sites within the bulk of the material, enabling higher charge density and extending redox activity beyond the particle surface. By controlled precipitation under hydrothermal conditions, the structure and morphology of cobalt hydroxides can be optimized to enhance electrochemical performance. Challenging conventional assumptions, surface area alone is not the primary factor driving increased pseudocapacitive performance. The hexagonal hydrotalcite-like structure, characterized by lower skeletal density and larger basal plane spacing, outperforms the monoclinic cobalt carbonate hydroxide structure, achieving an order of magnitude higher capacitance. In situ X-ray absorption spectroscopy provides critical insights into the pseudocapacitive behavior, revealing enhanced accessibility of Co2+ sites for electrochemical oxidation. While monoclinic cobalt carbonate hydroxide exhibits minimal changes in the Co2+ oxidation state, indicative of surface-limited redox activity, the hydrotalcite-like cobalt hydroxides show substantial shifts in the Co K-edge position, highlighting oxidation of Co2+ sites throughout the bulk.
Ključne besede: pseudocapacitors, layered-double hydroxides, cobalt hydroxide, redox processes, in situ x-ray absorption spectroscopy
Objavljeno v RUNG: 14.03.2025; Ogledov: 343; Prenosov: 6
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2. Iodine K- and L-edge X-ray absorption spectra of HI : the effect of molecular orbitals and core subshellsRobert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Uroš Luin, 2024, izvirni znanstveni članek Opis: Analysis of the recently measured absorption spectra of molecular HI at K and L edges of iodine, in parallel with
previously measured spectra of noble gas Xe and the K edge spectrum of atomic I, is presented. A strong
dependence of some valence multielectron photoexcitation features on the orbital momentum of the core vacancy
is found, attributed to the change of the symmetry of the HI molecule: the shake-up coexcitation of a
valence electron to a free molecular orbital is much stronger at L3 than L1 edge. The effect of angular momentum
of the core hole on the shake processes of deeper multielectron photoexcitations is found negligible. Both HI and
Xe exhibit a much weaker one-electron transition [1s]6p than monatomic I. At the K edge, the strength of
coexcitations of 4d, 4p and 3d subshells in atomic I is close to the HI and Xe. The same is found for HI and Xe at
the L edges, due to a weak contribution of the additional free molecular orbital in HI.
Ključne besede: X-ray absorption spectroscopy, K edge spectrum of atomic I, multielectron photoexcitations (MEPE), core vacancy angular momentum
Objavljeno v RUNG: 09.01.2025; Ogledov: 530; Prenosov: 6
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3. GasesAlojz Kodre, Iztok Arčon, Jana Padežnik Gomilšek, 2024, znanstveni sestavek v slovarju, enciklopediji, leksikonu Opis: X-ray absorption spectroscopy of gases is seldom used for structural analysis,
except in as much as the extended X-ray absorption fine-structure (EXAFS)
signal is used to monitor some specific molecular process. Gas spectroscopy,
however, has been the main tool in the systematic study of higher-order
photoabsorption processes, multielectron photoexcitations (MEEs), which were
introduced with an experiment at the K edge of argon. Along with noble gases,
where MEEs are studied in the pure form, free of the structural signal,
measurements have been extended to monatomic metal vapours, although at the
cost of considerable experimental difficulties. Several types of absorption cells
have been devised, among them the ceramic double cell and the heat-pipe cell
for experiments in the low-energy region. In a high-temperature oven with
considerable technical refinement, edge profiles of nonvolatile metals were
measured up to 2500 K. Edge profiles and MEEs, which are strongly dependent
on electron correlation, provide sensitive tests of the theory of atomic and
molecular structure.
Ključne besede: X-ray absorption spectroscopy, absorption cells, gas and vapour samples, multielectron photoexcitation, effects of electron
correlation
Objavljeno v RUNG: 05.09.2024; Ogledov: 1104; Prenosov: 4
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4. Monitoring chemical processes in (photo)catalysts and energy storage materials by operando X-ray absorption spectroscopyIztok Arčon, 2022, 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. The rapid development of extremely bright synchrotron sources of X-ray and ultraviolet light in recent years has opened new possibilities for research of matter at the atomic or molecular level, indispensable in the development of new functional nanostructured materials with desired properties. The talk will present the possibilities offered by X-ray absorption spectroscopy with synchrotron light for ex-situ or operando characterization of various functional porous and other nanomaterials, before, after and during their operation [1,2,3,4]. New generation of synchrotron light sources also opened the possibility of combining X-ray absorption with high-resolution emission [5] and inelastic scattering spectroscopy [6], and microscopy with sub-micron resolution [7]. Examples of operando XANES and EXAFS analysis to track changes in the valence states and local structures of selected elements in different energy storage materials and in various (photo)catalysts, during chemical reactions under controlled reaction conditions, will be presented, which provided insight into the dynamic functional properties and reaction mechanisms of these materials. Access to SR facilities of Petra III (beamlines P65, P64 and P01), ESRF (beamlines BM23, ID21, ID26) and Elettra (beamlines XAFS, XRF), for the presented research is kindly acknowledged.
Ključne besede: X-ray absorption spectroscopy, operando XANES, EXAFS, catalysts, batteries
Objavljeno v RUNG: 07.10.2022; Ogledov: 2174; Prenosov: 0
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5. Structure and population of complex ionic species in FeCl[sub]2 aqueous solution by X-ray absorption spectroscopyUroš Luin, Iztok Arčon, Matjaž Valant, 2022, izvirni znanstveni članek Opis: Technologies for mass production require cheap and abundant materials such as ferrous chloride (FeCl2). The literature survey shows the lack of experimental studies to validate theoretical conclusions related to the population of ionic Fe-species in the aqueous FeCl2 solution. Here, we present an in situ X-ray absorption study of the structure of the ionic species in the FeCl2 aqueous solution at different concentrations (1–4 molL−1) and temperatures (25–80 ◦C). We found that at low temperature and low FeCl2 concentration, the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five water molecules at a distance of 2.095 (±0.005) Å. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical water molecule is substituted by a chlorine ion to yield a neutral Fe[Cl2(H2O)4]0. The observed substitutional mechanism is facilitated by the presence of the intramolecular hydrogen bonds as well as entropic reasons. The transition from the single charged Fe[Cl(H2O)5]+ to the neutral Fe[Cl2(H2O)4]0 causes a significant drop in the solution conductivity, which well correlates with the existing conductivity models.
Ključne besede: structure, population, ionic species, aqueous ferrous chloride, in situ X-ray absorption spectroscopy
Objavljeno v RUNG: 24.01.2022; Ogledov: 3078; Prenosov: 44 (1 glas)
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6. Monitoring of chemical processes at the atomic level by X-ray absorption spectrometry using extremely bright synchrotron radiation sourcesIztok Arčon, vabljeno predavanje na konferenci brez natisa 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. The rapid development of extremely bright synchrotron sources of X-ray and ultraviolet light in recent years has opened new possibilities for research of matter at the atomic or molecular level, indispensable in the development of new functional nanostructured materials with desired properties. The lecture will present the possibilities offered by X-ray absorption spectroscopy with synchrotron light for ex-situ and in-situ or operando characterization of various functional porous and other nanomaterials before, after and during their operation. With the operando micro-XANES and EXAFS methods it is possible to track changes in the valence states and local structures of selected elements in different energy storage materials or in various (photo)catalysts, during chemical reactions under controlled reaction conditions, thus gaining insight into the dynamic functional properties and reaction mechanisms of these materials. New synchrotron light sources also opened the possibility of combining X-ray absorption or emission spectroscopy and microscopy with a resolution of up to a few tens of nanometres, crucial for analysis of environmental and biological samples on sub-cellular level, to understand the mechanisms of uptake, transport, accumulation, and complexation of metal cations on subcellular level in various plant tissues or accumulation in environment, to develop effective remediation approaches.
Ključne besede: X-ray absorption spectroscopy, EXAFS, XANES, synchrotron radiation sources, operando
Objavljeno v RUNG: 15.12.2021; Ogledov: 3064; Prenosov: 0
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7. Removal of copper from aqueous solutions with zeolites and possible treatment of exhaust materialsNataša Zabukovec Logar, Iztok Arčon, Janez Kovač, Margarita Popova, 2021, izvirni znanstveni članek Opis: The mechanism of Cu2+ loading into commercially available natural HEU-type and synthetic LTA-type zeolites for their
possible use in environmental processes, such as water and air treatment applications, was studied. Elemental analysis,
SEM/EDXS, XRD, XAS and XPS analyses revealed 4-fold coordination of Cu2+ cations with oxygen atoms in the pores, a
predominant location of copper atoms on the surface of crystallites and retained crystallinity of zeolites throughout the
processes. The post-treatment of Cu2+-loaded samples with HCl and/or NaCl solutions confirmed the predominantly
reversible sorption of copper on zeolites from aqueous solutions by ion-exchange mechanism and, therefore, excellent
regeneration possibilities for both types of zeolites. Furthermore, with the calcination of exhaust metal-loaded zeolites,
catalysts for total toluene oxidation reaction, as a model VOC pollutant, were obtained.
Ključne besede: Cu2+ ion exchange, Total toluene oxidation, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Zeolite
Objavljeno v RUNG: 03.06.2021; Ogledov: 3155; Prenosov: 156
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8. 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: 6322; Prenosov: 0
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9. 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: 4926; Prenosov: 0
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10. Trace detection of C2H2 in ambient air using continuous wave cavity ring-down spectroscopy combined with sample pre-concentrationManik Pradhan, Ruth Lindley, Roberto Grilli, Iain R. White, Damien Martin, Orr-Ewing Andrew, 2008, izvirni znanstveni članek Opis: Continuous wave cavity ring-down spectroscopy (cw-CRDS) coupled with sample pre-concentration has been used to measure acetylene (C2H2) mixing ratios in ambient air. Measurements were made in the near-infrared region (λ∼1535.393 nm), using the P(17) rotational line of the (ν1+ν3) vibrational combination band, a region free from interference by overlapping spectral absorption features of other air constituents. The spectrometer is shown to be capable of fast, quantitative and precise C2H2 mixing ratio determinations without the need for gas chromatographic (GC) separation. The current detection limit of the spectrometer following sample pre-concentration is estimated to be 35 parts per trillion by volume (pptv), which is sufficient for direct atmospheric detection of C2H2 at concentrations typical of both urban and rural environments. The CRDS apparatus performance was compared with an instrument using GC separation and flame ionization detection (GC-FID); both techniques were used to analyze air samples collected within and outside the laboratory. These measurements were shown to be in quantitative agreement. The indoor air sample was found to contain C2H2 at a mixing ratio of 3.87±0.22 ppbv (3.90±0.23 ppbv by GC-FID), and the C2H2 fractions in the outside air samples collected on two separate days from urban locations were 1.83±0.20 and 0.69±0.14 ppbv (1.18±0.09 and 0.60±0.04 ppbv by GC-FID). The discrepancy in the first outdoor air sample is attributed to degradation over a 2-month interval between the cw-CRDS and GC-FID analyses.
Ključne besede: Rotational Line, Cavity Enhance Absorption Spectroscopy, Adsorbent Trap, Trace Atmospheric Constituent, CRDS Instrument
Objavljeno v RUNG: 15.07.2019; Ogledov: 4518; Prenosov: 0
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