21. Določanje atomske strukture snovi z rentgensko absorpcijsko spektrometrijo s sinhrotronsko svetloboIztok Arčon, invited lecture at foreign university Abstract: Zakaj so velike evropske države pripravljene investirati ogromna sredstva v izgradnjo in delovanje sinhrotronov? Gre za izjemno svetle vire ultravijolične in rentgenske svetlobe, ki so v zadnjih dveh ali treh desetletjih postali nepogrešljivo orodje pri analizi snovi na atomskem oziroma molekularnem nivoju. Razvoja in sinteze novih materialov z želenimi lastnostmi si ne moremo predstavljati brez sodobnih preiskovalnih metod, ki temeljijo na sinhrotronski svetlobi.
V predavanju bo predstavljen princip delovanja in primeri uporabe ene od rentgenskih metod s sinhrotronsko svetlobo – rentgensko absorpcijsko spektroskopijo, s katero lahko določamo atomsko oz. molekularno strukturo snovi v vseh agregatnih stanjih. Za take raziskave so danes zanimivi predvsem različni nanostrukturni materiali, kot so katalizatorji, katodni materiali za Li-ionske in Li-žveplove baterije, tanke zaščitne plasti, in drugi, pri katerih atomska struktura določa njihove funkcionalne lastnosti. Na predavanju bodo izpostavljeni v prvi vrsti primeri in-operando karakterizacije z metodama XANES in EXAFS ki omogoča zelo natančno in neposredno spremljanje postopnih sprememb valence kovinskih kationov in njihove lokalne atomske strukture v nanozrnih v katodnem materialu med polnjenjem in praznjenjem baterije, ali kovinskih kationov na površini nanostrukturnega (foto)katalitskega materiala med samo katalitsko reakcijo.
Sodobni sinhrotronski viri rentgenske svetlobe pa omogočajo tudi uporabo kombinacije rentgenske absorpcijske spektroskopije z rentgenskimi mikroskopskimi metodami, z ločljivostjo do nekaj deset nanometrov. Na predavanju bodo predstavljeni primeri mikro-XANES in EXAFS analize lokalizacije in vezave toksičnih kovinskih kationov na sub-celičnem nivoju v različnih tkivih rastlin, s čimer lahko ključno prispevamo k razumevanju mehanizmov zajemanja, transporta, akumulacije in kompleksacije kovinskih kationov na sub-celičnem nivoju v različnih tkivih rastlin, ki te polutante (hiper)akumulirajo, in jih s tem prenašajo v prehranjevalno verigo, s čimer je ogroženo zdravje ljudi.
Found in: ključnih besedah
Summary of found: ...prvi vrsti primeri in-operando karakterizacije z metodama XANES in EXAFS ki omogoča zelo natančno in...
Keywords: rentgenska absorpcijska spektroskopija, XANES, EXAFS, strukturna analiza, sinhrotronska svetloba
Published: 01.06.2018; Views: 3206; Downloads: 0
 Fulltext (151,01 KB) |
22. Surface modified titanium dioxide using transition metalsAndraž Šuligoj, Iztok Arčon, Matjaž Mazaj, Goran Dražić, Denis Arčon, Pegie Cool, Urška Lavrenčič Štangar, Nataša Novak Tušar, 2018, original scientific article Abstract: Titanium dioxide has been widely used as an antimicrobial agent, UV-filter and catalyst for pollution abatement. Herein, surface modifications with selected transition metals (Me) over colloidal TiO2 nanoparticles and immobilization with a colloidal SiO2 binder as composite films (MeTiO2/SiO2) on a glass carrier were used to enhance solar-light photoactivity. Colloidal TiO2 nanoparticles were modified by loading selected transition metals (Me ¼ Mn, Fe, Co, Ni, Cu, and Zn) in the form of chlorides on their surface. They were present primarily as oxo-nanoclusters and a portion as metal oxides. The structural characteristics of bare TiO2 were preserved up to an optimal metal loading of 0.5 wt%. We have shown in situ that metal-oxo-nanoclusters with a redox potential close to that of O2/O2 were able to function as co-catalysts on the TiO2 surface which was excited by solar-light irradiation. The materials were tested for photocatalytic activity by two opposite methods; one detecting O2 (reduction, Rz ink test) while the other detecting OH (oxidation, terephthalic acid test). It was shown that the enhancement of the solar-light activity of TiO2 by the deposition of transition metal oxo-nanoclusters on the surface depends strongly on the combination of the reduction potential of such species and appropriate band positions of their oxides. The latter prevented excessive self-recombination of the photogenerated charge carriers by the nanoclusters in Ni and Zn modification, which was probably the case in other metal modifications.
Overall, only Ni modification had a positive effect on solar photoactivity in both oxidation and reduction reactions.
Found in: ključnih besedah
Summary of found: ...surface modified TiO2, XANES, EXAFS, Nickel, solar light photocatalyst...
Keywords: surface modified TiO2, XANES, EXAFS, Nickel, solar light photocatalyst
Published: 01.06.2018; Views: 2681; Downloads: 0
Fulltext (1,24 MB) |
23. Polysulfides formation in different electrolytes from the perspective of X-ray absorption spectroscopyRobert Dominko, Alen Vižintin, Giuliana Aquilanti, Lorenzo Stievano, Maria Joseph Helen, Anji Reddy Munnangi, Maximilian Fichtner, Iztok Arčon, 2018, original scientific article Abstract: Li-S batteries are promising energy storage technology for the future, however there two major problems remained which need to be
solved before successful commercialization. Capacity fading due to polysulfide shuttle and corrosion of lithium metal are directly
connected with the type and quantity of electrolyte used in the cells. Several recent works show dependence of the electrochemical
behavior of Li-S batteries on type of the electrolyte. In this work we compare and discuss a discharge mechanism of sulfur conversion
in three different electrolytes based on measurements with sulfur K-edge XAS. The sulfur conversion mechanism in the ether based
electrolytes, the most studied type of solvents in the Li-S batteries, which are enabling high solubility of polysulfides are compared
with the fluorinated ether based electrolytes with a reduced polysulfide solubility and in carbonate based electrolytes with the sulfur
confined into a ultramicroporous carbon. In all three cases the sulfur reduction proceeds through polysulfide intermediate phases
with a difference on the type polysulfides detected at different steps of discharge.
Found in: ključnih besedah
Summary of found: ...Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides...
Keywords: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides
Published: 01.06.2018; Views: 2811; Downloads: 0
Fulltext (579,89 KB) |
24. A mechanistic study of metal sulfur batteriesIztok Arčon, Ana Robba, Sara Drvarič Talian, Alen Vižintin, Robert Dominko, 2018, published scientific conference contribution abstract (invited lecture) Found in: ključnih besedah
Summary of found: ...Li-sulphur batteries, Sulphur XANES, magnesium...
Keywords: Li-sulphur batteries, Sulphur XANES, magnesium
Published: 15.10.2020; Views: 1646; Downloads: 0 |
25. Effects of Different Copper Loadings on the Photocatalytic Activity of TiO2-SiO2 Prepared at a Low Temperature for the Oxidation of Organic Pollutants in WaterT. Čižmar, Iztok Arčon, Mattia Fanetti, Urška Lavrenčič Štangar, 2018, original scientific article Abstract: The objective of this research is to examine how Cu modification can improve the photocatalytic activity of TiO2-SiO2, to explainthe correlation between the Cu concentration and the chemical state of Cu cations in the TiO2-SiO2 matrix, and the photocatalytic activity under UV/solar irradiation. The Cu-modified TiO2-SiO2 photocatalysts were prepared by a low-temperature sol–gel method from organic Cu, Si and Ti precursors with various Cu concentrations (0.05–3 mol %). The sol–gels were dried at 150 8C to obtain the photocatalysts in a powder form. The photocatalytic activity was determined by using a fluorescence- based method of terephthalic acid decomposition. An up to three times increase in photocatalytic activity is obtained if the TiO2-SiO2 matrix is modified with Cu in a narrow concentration
range from 0.05 to 0.1 mol%. At higher Cu loadings,
the photocatalytic activity of the Cu-modified photocatalysts is lower than that of the un-modified reference TiO2-SiO2 photocatalyst. XRD was used to show that all Cu-modified TiO2-SiO2 composites with different Cu concentrations have the same crystalline structure as un-modified TiO2-SiO2 composites. The addition of Cu does not change the relative ratio between the anatase and brookite phases or unit cell parameters of the two TiO2 crystalline structures. We used Cu K-edge X-ray absorption near edge structure and extended X-ray absorption fine structure analyses to determine the valence state and local structure of Cu cations in the Cu-modified TiO2-SiO2 photocatalysts. The results elucidate the mechanism responsible for the improved photocatalytic activity. In samples with a low Cu content,
which exhibit the highest activity, Cu@O@Ti connections
are formed, which suggests that the activity enhancement is
caused by the attachment of CuII cations on the surface of the photocatalytically active TiO2 nanoparticles, so CuII cations may act as free-electron traps, which reduce the intensity of recombination between electrons and holes at the TiO2 photocatalyst surface. At higher Cu loadings no additional Cu@O@Ti connections are formed, instead only Cu@O@Cu connections are established. This indicates the formation of amorphous or nanocrystalline
copper oxide, which hinders the photocatalytic activity
of TiO2.
Found in: ključnih besedah
Summary of found: ...Cu modified TiO2-SiO2 photocatalyst
Cu EXAFS, XANES,
Organic pollutants...
Keywords: Cu modified TiO2-SiO2 photocatalyst
Cu EXAFS, XANES, Organic pollutants
Published: 30.08.2018; Views: 2745; Downloads: 0
Fulltext (1,53 MB) |
26. Cadmium associates with oxalate in calcium oxalate crystals and competes with calcium for translocation to stems in the cadmium bioindicator Gomphrena clausseniiPaula Pongrac, Tania Serra, Hiram Castillo Michel, Katarina Vogel-Mikuš, Iztok Arčon, Mitja Klemen, Boštjan Jencic, Anja Kavčič, Mina T. Villafort Carvalho, Mark G. M. Aarts, 2018, original scientific article Abstract: Cadmium (Cd) was shown to co-localise with calcium (Ca) in oxalate crystals in the stems and leaves of
Cd tolerant Gomphrena claussenii, but Cd binding remained unresolved. Using synchrotron radiation
X-ray absorption near edge spectroscopy we demonstrate that in oxalate crystals of hydroponically
grown G. claussenii the vast majority of Cd is bound to oxygen ligands in oxalate crystals (488%;
Cd–O–C coordination) and the remaining Cd is bound to sulphur ligands (Cd–S–C coordination). Cadmium
binding to oxalate does not depend on the amount of Ca supplied or from which organs the crystals
originate (stems and mature leaves). By contrast, roots contain no oxalate crystals and therein Cd is
bound predominantly by S ligands. The potential to remove Cd by extraction of Cd-rich oxalate crystals
from plant material should be tested in phytoextraction or phytomining strategies.
Found in: ključnih besedah
Summary of found: ...Cd XANES, Cd oxalate, Gomphrena claussenii...
Keywords: Cd XANES, Cd oxalate, Gomphrena claussenii
Published: 06.09.2018; Views: 2578; Downloads: 0
Fulltext (3,68 MB) |
27. X-ray spectrometry in plant biologyPrimož Pelicon, Peter Kump, Anja Kavčič, Alojz Kodre, Iztok Arčon, Katarina Vogel-Mikuš, 2018, published scientific conference contribution abstract (invited lecture) Abstract: Trace elements are essential components of living systems, but at the same time they can be toxic at concentrations beyond those necessary for their biological functions. In addition, the toxicity can be extended to other non-essential elements of very similar atomic characteristics that can mimic the properties of a trace element.
Trace element malnutrition affects more than half of the world’s population, while on the other hand industrialization, traffic and extensive use of fertilizers have resulted in exceedingly high concentrations of non-essential elements in food crops, posing risks to human health.
In order to be able to develop and improve phyto-technologies that enable production of safe and quality food, knowledge on the basic mechanisms involved in trace and non-essential element uptake, transport, accumulation and ligand environment in plants is needed.
Such studies are nowadays supported by highly sophisticated X-ray based techniques, such as synchrotron based X-ray fluorescence spectrometry, proton induced X-ray emission and X-ray absorption spectroscopy, enabling imaging of element distribution and determination of speciation and ligand environment of trace elements in biological tissues and cells with high spatial resolution and sensitivity.
Selected case studies of metal distribution and speciation in selected model and crop plants, achieved by interdisciplinary work, will be presented.
Found in: ključnih besedah
Summary of found: ...X-ray spectrometry, plants, XANES, EXAFS...
Keywords: X-ray spectrometry, plants, XANES, EXAFS
Published: 12.09.2018; Views: 2772; Downloads: 0
Fulltext (62,44 KB) |
28. Operando XAS analysis of CuO/SiO2 and CuO/CeO2 catalystsAlbin Pintar, Maxim Zabilsky, Petar Djinović, Janvit Teržan, Iztok Arčon, 2018, published scientific conference contribution abstract Abstract: The possibilities of the operando XAS analysis of catalysts will be presented on two case
studies of promising new catalytic materials: alkali doped nano-dispersed copper oxide
clusters on ordered mesoporous SiO2, which is highly active and selective towards propylene
epoxidation [1], and nanoshaped CuO/CeO2 catalysts used in N2O decomposition reaction [2].
Operando Cu K-edge and Ce L3-edge XANES and EXAFS analysis was performed during
catalytic reactions under controlled reaction conditions in a tubular reactor filled with
protective He atmosphere at 1 bar. The spectra were measured before the reaction at RT, then
during heating, and during catalytic reaction at 400 °C under controlled atmosphere.
Operando XANES analysis is used to monitor the changes in valence states and local
symmetries of Cu and Ce cations in the catalysts. A partial reduction of Cu2+ to Cu+ and Cu0
and Ce4+ to Ce3+ species was detected during catalyst activation, and re-oxidation during
catalytic reaction. Different dynamics of reaching a quasi-steady oxidation state were revealed
as the tested catalysts approached the quasi-steady state after 300 min of reaction.
Operando EXAFS spectra are used to precisely determine local structure of Cu and Ce
cations, to identify structural characteristics and changes of Cu and Ce species during the
catalytic reactions. In this way, the active site in the catalytic reactions can be identified and
the mechanism of the reaction clarified.
The results of operando XAS analyses are crucial to guide further material modification, to
obtain more effective catalyst, and material which is more resistant to inhibiting effects that
cause catalyst deactivation during catalytic reaction.
Found in: ključnih besedah
Summary of found: ...reaction [2].
Operando Cu K-edge and Ce L3-edge XANES and EXAFS analysis was performed during
catalytic reactions...
Keywords: katalizatorji, Cu XANES, EXAFS
Published: 12.09.2018; Views: 2725; Downloads: 0
Fulltext (62,04 KB) |
29. The effect of Zr loading on photocatalytic activity of Cu modified TiO [sub] 2Urška Lavrenčič Štangar, Nataša Novak Tušar, Iztok Arčon, Mattia Fanetti, O. L. Pliekhov, Olena Pliekhova, 2018, published scientific conference contribution abstract Found in: ključnih besedah
Keywords: Cu Zr modified TiO2, EXAFS, XANES
Published: 12.09.2018; Views: 2609; Downloads: 0
Fulltext (990,75 KB) |
30. Fluorinated ether based electrolyte for high-energy lithium-sulfur batteriesRobert Dominko, Patrik Johansson, Giuliana Aquilanti, Iztok Arčon, Klemen Pirnat, Alen Vižintin, Steffen Jeschke, Sara Drvarič Talian, 2018, published scientific conference contribution abstract Found in: ključnih besedah
Summary of found: ...Li-žveplive baterije, XANES, polisulfidi...
Keywords: Li-žveplive baterije, XANES, polisulfidi
Published: 12.09.2018; Views: 2447; Downloads: 0
Fulltext (148,44 KB) |
