21. 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, original scientific article Abstract: 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.
Keywords: Ni/ZSM-5 catalysts, zeolite, Ni XANES, EXAFS
Published in RUNG: 11.05.2022; Views: 1686; Downloads: 43
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23. 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, original scientific article Abstract: 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.
Keywords: X-ray Raman spectroscopy, meta-organic batteries, oxygen K-edge XANES, electrochemical processes
Published in RUNG: 24.03.2022; Views: 1769; Downloads: 20
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24. Nutritional quality and safety of the spirulina dietary supplements sold on the Slovenian marketJasmina Masten, Marta Jagodic Hudobivnik, Marijan Nečemer, Katarina Vogel-Mikuš, Iztok Arčon, Nives Ogrinc, 2022, original scientific article Abstract: The microalgae Spirulina may be a popular dietary supplement rich in essential nutrients
and vitamins, but oversight of the supplement industry, in general, remains limited, and increasing
incidents of adulteration, misbranding, and undeclared ingredients together with misleading claims
create potential risks. In response, this study characterized the elemental, amino acid and fatty acid
content of commercially available Spirulina supplements in Slovenia using EDXRF, ICP-MS and
GC-MS and compared the results with their nutritional declaration. The gathered data confirm that
Spirulina supplements are a good source of calcium (0.15 to 29.5% of RDA), phosphorous (3.36–26.7%
of RDA), potassium (0.5 to 7.69% of RDA) and selenium (0.01 to 38.6% of RDA) when consumed
within recommended amounts. However, although iron contents were relatively high (7.64 to 316%
of RDA), the actual bioavailability of iron was much lower since it was mainly present as the ferric
cation. This study also confirms that pure Spirulina supplements are a good source of essential
and non-essential amino acids, and !-6 but not !-3 polyunsaturated fatty acids. The presence of
additives resulted in significant variation in nutrient content and, in some instances, lower product
quality. Moreover, a high proportion (86.7%) of inappropriate declarations regarding the elemental
content was observed. Overall, the study conclusions underline the need for a stricter control system
for Spirulina-based supplements.
Keywords: Spirulina, microalgae, cyanobacteria, elements, toxic elements, amino acids, fatty acids, authenticity, safety, quality
Published in RUNG: 24.03.2022; Views: 1626; Downloads: 0
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25. Structure and population of complex ionic species in FeCl[sub]2 aqueous solution by X-ray absorption spectroscopyUroš Luin, Iztok Arčon, Matjaž Valant, 2022, original scientific article Abstract: 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.
Keywords: structure, population, ionic species, aqueous ferrous chloride, in situ X-ray absorption spectroscopy
Published in RUNG: 24.01.2022; Views: 1812; Downloads: 42 (1 vote)
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26. Photoexcitation processes in atomsAlojz Kodre, Iztok Arčon, Jana Padežnik Gomilšek, 2021, independent scientific component part or a chapter in a monograph Abstract: Photoelectric absorption is characterized by a smooth power-law decrease of the
cross section with photon energy. Absorption edges reveal rich structure, which
continues into the high-energy side. The quasiperiodic signal, superposed onto
the smooth basis, due to scattering of the photoelectron on the neighbours of the
target atom provides the basis for the structural (XAFS) analysis of the material.
Irregular tiny resonances and edges that appear over the same general range as
XAFS are recognized as intra-atomic effects: multielectron excitations (MEE)
owing to correlated motion in the electronic cloud. The systematic study of MEE
began on noble gases and metallic vapours, both of which are gases of free
atoms. With some extremely strong MEE, mostly coexcitations of the subvalence
d and f electrons, the structural XAFS analysis may be compromised;
hence, there is a need to independently determine the MEE signal, the atomic
absorption background (AAB) for the analyzed element, and remove it prior to
analysis. In view of the scarcity of elements which can practically be prepared in
a free-atom gas state, several approaches to approximate the AAB have been
developed: analysis of disordered compounds, where the weak and simple
XAFS signal can be modelled and removed, and correlation analysis of the
absorption spectra of several independent samples, where the AAB is extracted
in an iterative procedure.
Keywords: photoexcitation, XAFS, multielectron excitations, atomic
absorption background
Published in RUNG: 15.12.2021; Views: 1733; Downloads: 0
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27. Monitoring of chemical processes at the atomic level by X-ray absorption spectrometry using extremely bright synchrotron radiation sourcesIztok Arčon, unpublished invited conference lecture Abstract: 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.
Keywords: X-ray absorption spectroscopy, EXAFS, XANES, synchrotron radiation sources, operando
Published in RUNG: 15.12.2021; Views: 1886; Downloads: 0
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28. 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, original scientific article Abstract: 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
Keywords: Fe-N-C catalysts, selective synthesis, tetrapyrrolic active sites, EXAFS, XANES, single atom, DFT
Published in RUNG: 25.10.2021; Views: 1997; Downloads: 54
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29. Analiza vinskega turizma kot priložnost za vinarje vinorodnega okoliša slovenska Istra : diplomsko deloMatej Zaro, 2021, undergraduate thesis Abstract: Vinski turizem je hitro rastoča ekonomska panoga, ki bi jo glede na geografske danosti slovenske regije in kakovost pridelanega vina bilo vredno ne samo izkoristiti, temveč tudi poglobiti. V diplomski nalogi predstavljamo in preučujemo vinarstvo ter vinogradništvo v povezavi s turizmom v Sloveniji, s poudarkom na okolišu slovenska Istra. Pod drobnogled vzamemo konzorcij Vin Istre in društvo Vinol, kjer izpostavljamo tako dobre prakse, kakor pomankljivosti. Osredotočimo se na vinske festivale, njihov pomen, s poudarkom na festival maceriranih belih vin Orange Wine Festival Izola. Dotaknemo se tudi svetovnih trendov vinske panoge ter kakšen je bil vpliv pandemije Covid-19 na vinski turizem. V diplomski nalogi predstavljamo podjetje Vina Zaro, njegove začetke in možnosti razvoja za prihodnost. Rdeča nit diplomske naloge je iskanje že delujočih dobrih praks in trendov, ki bodo pripomogle k spremembi odnosa do vinskega turizma in odkrivanju novih aktivnosti za razvoj le-tega. Zavedamo se potrebe po mednarodnosti in zgledovanju po tujih uveljavljenih praksah, vendar prepoznamo jedro razvoja tudi v odnosu do mednarodnih potrošnikov, v lokalnih sortah grozdja, reinterpretaciji tradicionalnih pridelovalnih tehnikah, vrednotenju lastne kulturne dediščine, razširitvi ekološke pridelave in spodbujanju interakcije med različni turističnimi panogami.
Keywords: diplomske naloge, vinski turizem, slovenska Istra, vinski festivali, blagovne znamke, Slovenija, vinarstvo Zaro, udomačene sorte
Published in RUNG: 07.10.2021; Views: 2300; Downloads: 159
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30. 1,8-dihydroxy naphthalene (DHN) - melanin confers tolerance to cadmium in isolates of melanised dark septate endophytesMateja Potisek, Matevž Likar, Katarina Vogel-Mikuš, Iztok Arčon, Jože Grdadolnik, Marjana Regvar, 2021, original scientific article Abstract: The contribution of 1,8-dihydroxy naphthalene (DHN) melanin to cadmium (Cd) tolerance in two dark septate
endophytes (DSE) of the genus Cadophora with different melanin content was investigated in vitro. The DSE
isolate Cad#148 with higher melanin content showed higher tolerance to Cd than the less melanised Cad#149.
Melanin synthesis was significantly reduced by Cd in both isolates with uninhibited melanin synthesis, in a dosedependent
manner. Inhibition of melanin synthesis by tricyclazole reduced the relative growth of Cad#148
exposed to Cd and did not affect Cad#149. Cd accumulation was not altered by tricyclazole in the two isolates,
but it increased catalase and reduced glutathione reductase activity in more melanised Cad#148, indicating
higher stress levels. In contrast, in Cad#149 the enzyme activity was less affected by tricyclazole, indicating a
more pronounced role of melanin-independent Cd tolerance mechanisms. Cd ligand environment in fungal
mycelia was analysed by extended EXAFS (X-ray absorption fine structure). It revealed that Cd was mainly bound
to O- and S-ligands, including hydroxyl, carboxyl, phosphate and thiol groups. A similar proportion of S- and Oligands
(~35% and ~65%) were found in both isolates with uninhibited melanin synthesis. Among O-ligands
two types with Cd-O-C- and Cd-O-P- coordination were identified. Tricyclazole altered Cd-O- ligand environment
in both fungal isolates by reducing the proportion of Cd-O-C- and increasing the proportion of Cd-O-P coordination.
DHN-melanin, among other tolerance mechanisms, significantly contributes to Cd tolerance in more
melanised DSE fungi by immobilising Cd to hydroxyl groups and maintaining the integrity of the fungal cell wall.
Keywords: DSE, melanin, Cd tolerance, inhibitor tricyclazole, antioxidant enzymes, EXAFS
Published in RUNG: 13.07.2021; Views: 2126; Downloads: 0
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