11. Monitoring of chemical processes at the atomic level by X-ray absorption spectrometry using extremely bright synchrotron radiation sourcesIztok Arčon, predavanje na tuji univerzi 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. Ključne besede: XAS, operando XANES, EXAFS, functional materials Objavljeno v RUNG: 01.06.2022; Ogledov: 1505; Prenosov: 0 Gradivo ima več datotek! Več... |
12. Insight into the interdependence of Ni and Al in bifunctional Ni/ZSM-5 catalysts at the nanoscaleHue-Tong Vu, Iztok Arčon, Danilo Oliveira de Souza, Simone Pollastri, Goran Dražić, Janez Volavšek, Gregor Mali, Nataša Zabukovec Logar, Nataša Novak Tušar, 2022, izvirni znanstveni članek Opis: Catalyst design is crucial for improving catalytic activity and product selectivity. In a bifunctional Ni/ZSM-5
zeolite type catalyst, catalytic properties are usually tuned via varying Al and Ni contents. While changes in
acid properties associated with Al sites are usually closely investigated, Ni phases, however, receive
inadequate attention. Herein, we present a systematic structural study of Ni in the Ni/ZSM-5 materials by
using Ni K-edge XANES and EXAFS analyses, complemented by XRD and TEM, to resolve the changes in
the local environment of Ni species induced by the different Al contents of the parent ZSM-5 prepared
by a “green”, template free technique. Ni species in Ni/ZSM-5 exist as NiO crystals (3–50 nm) and as
charge compensating Ni2+ cations. The Ni K-edge XANES and EXAFS results enabled the quantification
of Ni-containing species. At a low Al to Si ratio (nAl/nSi # 0.04), the NiO nanoparticles predominate in
the samples and account for over 65% of Ni phases. However, NiO is outnumbered by Ni2+ cations
attached to the zeolite framework in ZSM-5 with a high Al to Si ratio (nAl/nSi ¼ 0.05) due to a higher
number of framework negative charges imparted by Al. The obtained results show that the number of
highly reducible and active NiO crystals is strongly correlated with the framework Al sites present in
ZSM-5 zeolites, which depend greatly on the synthesis conditions. Therefore, this kind of study is
beneficial for any further investigation of the catalytic activities of Ni/ZSM-5 and other metal-modified
bifunctional catalysts. Ključne besede: Ni/ZSM-5 catalysts, zeolite, Ni XANES, EXAFS Objavljeno v RUNG: 11.05.2022; Ogledov: 1823; Prenosov: 46 Celotno besedilo (1,25 MB) Gradivo ima več datotek! Več... |
13. Characterization of electrochemical processes in metal-organic batteries by X-ray Raman spectroscopyAva Rajh, Iztok Arčon, Klemen Bučar, Matjaž Žitnik, Marko Petric, Alen Vižintin, Jan Bitenc, Urban Košir, Robert Dominko, Hlynur Gretarsson, Martin Sundermann, Matjaž Kavčič, 2022, izvirni znanstveni članek Opis: X-ray Raman spectroscopy (XRS) is an emerging
spectroscopic technique that utilizes inelastic scattering of hard Xrays
to study X-ray absorption edges of low Z elements in bulk
material. It was used to identify and quantify the amount of
carbonyl bonds in a cathode sample, in order to track the redox
reaction inside metal−organic batteries during the charge/
discharge cycle. XRS was used to record the oxygen K-edge
absorption spectra of organic polymer cathodes from different
multivalent metal−organic batteries. The amount of carbonyl bond
in each sample was determined by modeling the oxygen K-edge
XRS spectra with the linear combination of two reference compounds that mimicked the fully charged and the fully discharged
phases of the battery. To interpret experimental XRS spectra, theoretical calculations of oxygen K-edge absorption spectra based on
density functional theory were performed. Overall, a good agreement between the amount of carbonyl bond present during different
stages of battery cycle, calculated from linear combination of standards, and the amount obtained from electrochemical
characterization based on measured capacity was achieved. The electrochemical mechanism in all studied batteries was confirmed to
be a reduction of double carbonyl bond and the intermediate anion was identified with the help of theoretical calculations. X-ray
Raman spectroscopy of the oxygen K-edge was shown to be a viable characterization technique for accurate tracking of the redox
reaction inside metal−organic batteries. Ključne besede: X-ray Raman spectroscopy, meta-organic batteries, oxygen K-edge XANES, electrochemical processes Objavljeno v RUNG: 24.03.2022; Ogledov: 1874; Prenosov: 20 Povezava na celotno besedilo Gradivo ima več datotek! Več... |
14. 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: 2009; Prenosov: 0 Gradivo ima več datotek! Več... |
15. Resolving the dilemma of Fe-N-C catalysts by the selective synthesis of tetrapyrrolic active sites via an imprinting strategyDavide Menga, Jian Liang Low, Yan-Sheng Li, Iztok Arčon, Burak Koyutürk, Friedrich Wagner, Francisco Ruiz-Zepeda, Miran Gaberšček, Beate Paulus, Tim-Patrick Fellinger, 2021, izvirni znanstveni članek Opis: Combining the abundance and inexpensiveness of
their constituent elements with their atomic dispersion, atomically
dispersed Fe−N−C catalysts represent the most promising
alternative to precious-metal-based materials in proton exchange
membrane (PEM) fuel cells. Due to the high temperatures
involved in their synthesis and the sensitivity of Fe ions toward
carbothermal reduction, current synthetic methods are intrinsically
limited in type and amount of the desired, catalytically active Fe−
N4 sites, and high active site densities have been out of reach
(dilemma of Fe−N−C catalysts). We herein identify a paradigm
change in the synthesis of Fe−N−C catalysts arising from the
developments of other M−N−C single-atom catalysts. Supported
by DFT calculations we propose fundamental principles for the synthesis of M−N−C materials. We further exploit the proposed
principles in a novel synthetic strategy to surpass the dilemma of Fe−N−C catalysts. The selective formation of tetrapyrrolic Zn−N4
sites in a tailor-made Zn−N−C material is utilized as an active-site imprint for the preparation of a corresponding Fe−N−C catalyst.
By successive low- and high-temperature ion exchange reactions, we obtain a phase-pure Fe−N−C catalyst, with a high loading of
atomically dispersed Fe (>3 wt %). Moreover, the catalyst is entirely composed of tetrapyrrolic Fe−N4 sites. The density of
tetrapyrrolic Fe−N4 sites is more than six times as high as for previously reported tetrapyrrolic single-site Fe−N−C fuel cell catalysts Ključne besede: Fe-N-C catalysts, selective synthesis, tetrapyrrolic active sites, EXAFS, XANES, single atom, DFT Objavljeno v RUNG: 25.10.2021; Ogledov: 2127; Prenosov: 54 Povezava na celotno besedilo Gradivo ima več datotek! Več... |
16. Photo-Chemically-Deposited and Industrial Cu/ZnO/Al2O3 Catalyst Material Surface Structures During CO2 Hydrogenation to Methanol: EXAFS, XANES and XPS Analyses of Phases After Oxidation, Reduction, and ReactionMaja Pori, Iztok Arčon, Venkata Dasireddy, Blaž Likozar, 2021, izvirni znanstveni članek Opis: Industrial Cu/ZnO/Al2O3 or novel rate catalysts, prepared with a photochemical deposition method, were studied under functional CH3OH synthesis conditions at the set temperature (T) range of 240–350 °C, 20 bar pressure, and stoichiometric carbon dioxide/hydrogen composition. Analytical scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray adsorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) methods were systematically utilized to investigate the interfaces, measured local geometry, and chemical state electronics around the structured active sites of commercially available Cu/ZnO/Al2O3 material or synthesized Cu/ZnO. Processed Cu K-edge EXAFS analysis suggested that various Cu atom species, clusters, metallic fcc Cu, Cu oxides (Cu2O or CuO) and the Cu0.7Zn2 alloy with hexagonal crystalline particles are contained after testing. It was proposed that in addition to the model’s Cu surface area, the amount, ratio and dispersion of the mentioned bonded Cu compounds significantly influenced activity. Additionally, XPS revealed that carbon may be deposited on the commercial Cu/ZnO/Al2O3, forming the inactive carbide coating with Cu or/and Zn, which may be the cause of basicity’s severe deactivation during reactions. The selectivity to methanol decreased with increasing T, whereas more Cu0.7Zn2 inhibited the CO formation through reverse water–gas shift (RWGS) CO2 reduction. Ključne besede: CH3OH synthesis, Cu/ZnO-based catalyst, XPS, XANES, EXAFS analyses, Catalyst selectivity and activity Objavljeno v RUNG: 03.06.2021; Ogledov: 2431; Prenosov: 0 Gradivo ima več datotek! Več... |
17. Laser ablation-single-particle-inductively coupled plasma mass spectrometry as a multimodality bioimaging tool in nano-based omicsDino Metarapi, Johannes Teun van Elteren, Martin Šala, Katarina Vogel-Mikuš, Iztok Arčon, Vid Simon Šelih, Mitja Kolar, Samo B. Hočevar, 2021, izvirni znanstveni članek Opis: Advanced data processing and visualization techniques were applied to laser ablation-single particleinductively
coupled plasma mass spectrometry (LA-sp-ICPMS) data obtained from imaging of roots of
sunflower (Helianthus annuus L.) which were exposed to ionic silver (Ag+). Highly multiplexed images with
tissue level resolution were generated, showing the uptake and transformation of Ag+ to silver
nanoparticles (AgNPs) in whole root cross-sections, and revealing that the size of biosynthesized AgNPs is
predisposed by the reducing power of particular root compartments. Various Ag+ and AgNP visualization
strategies are shown with special emphasis on spatially resolved information associated with the number
and spherical-equivalent size of individual AgNPs in user-selected root cross-sectional regions, including
statistical analysis of the AgNP distribution. Normally, this multimodality information can only be obtained
by combining the results of techniques from several complementary platforms. Ključne besede: Laser ablation, Ag XANES, bioimaging Objavljeno v RUNG: 03.06.2021; Ogledov: 2291; Prenosov: 50 Povezava na celotno besedilo Gradivo ima več datotek! Več... |
18. 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: 3274; Prenosov: 0 Gradivo ima več datotek! Več... |
19. 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 Objavljeno v RUNG: 17.10.2020; Ogledov: 3073; Prenosov: 0 Gradivo ima več datotek! Več... |
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