21. 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, izvirni znanstveni članek Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides...
Ključne besede: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides
Objavljeno: 01.06.2018; Ogledov: 839; Prenosov: 0
 Polno besedilo (579,89 KB) |
22. 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, izvirni znanstveni članek Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Cu modified TiO2-SiO2 photocatalyst
Cu EXAFS, XANES,
Organic pollutants...
Ključne besede: Cu modified TiO2-SiO2 photocatalyst
Cu EXAFS, XANES, Organic pollutants
Objavljeno: 30.08.2018; Ogledov: 766; Prenosov: 0
Polno besedilo (1,53 MB) |
23. 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, izvirni znanstveni članek Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Cd XANES, Cd oxalate, Gomphrena claussenii...
Ključne besede: Cd XANES, Cd oxalate, Gomphrena claussenii
Objavljeno: 06.09.2018; Ogledov: 640; Prenosov: 0
Polno besedilo (3,68 MB) |
24. X-ray spectrometry in plant biologyPrimož Pelicon, Peter Kump, Anja Kavčič, Alojz Kodre, Iztok Arčon, Katarina Vogel-Mikuš, 2018, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje) Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...X-ray spectrometry, plants, XANES, EXAFS...
Ključne besede: X-ray spectrometry, plants, XANES, EXAFS
Objavljeno: 12.09.2018; Ogledov: 741; Prenosov: 0
Polno besedilo (62,44 KB) |
25. Operando XAS analysis of CuO/SiO2 and CuO/CeO2 catalystsAlbin Pintar, Maxim Zabilsky, Petar Djinović, Janvit Teržan, Iztok Arčon, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...reaction [2].
Operando Cu K-edge and Ce L3-edge XANES and EXAFS analysis was performed during
catalytic reactions...
Ključne besede: katalizatorji, Cu XANES, EXAFS
Objavljeno: 12.09.2018; Ogledov: 788; Prenosov: 0
Polno besedilo (62,04 KB) |
26. 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, objavljeni povzetek znanstvenega prispevka na konferenci Najdeno v: ključnih besedah
Ključne besede: Cu Zr modified TiO2, EXAFS, XANES
Objavljeno: 12.09.2018; Ogledov: 666; Prenosov: 0
Polno besedilo (990,75 KB) |
27. 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, objavljeni povzetek znanstvenega prispevka na konferenci Najdeno v: ključnih besedah
Povzetek najdenega: ...Li-žveplive baterije, XANES, polisulfidi...
Ključne besede: Li-žveplive baterije, XANES, polisulfidi
Objavljeno: 12.09.2018; Ogledov: 587; Prenosov: 0
Polno besedilo (148,44 KB) |
28. Sulfur based batteries studied by in-operando S K-edge RIXS and XAS spectroscopyMatjaž Žitnik, Iztok Arčon, Alen Vižintin, Janez Bitenc, Ana Robba, Matjaž Kavčič, Klemen Bučar, Robert Dominko, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Sulfur based batteries are considered as very attractive energy storage devices. Sulfur is one of the most abundant elements in the earth, it is electrochemically active material which can accept up to two electrons per atom. In combination with alkali metals, sulfur forms electrochemical couples with much higher theoretical energy density compared to Li-ion batteries commonly available today. At the moment, the electrochemical couple with Li is most extensively studied. While the main principle of operation is known the relevant operation mechanism(s) is not completely clear. Even more promising is the electrochemical couple with Mg providing almost twofold higher volumetric energy density due to its ability to provide two electrons during oxidation. However, Mg-S batteries are still in the very early stage of research and development and the complex mechanism of sulfur conversion has been less extensively studied.
In order to improve the understanding of sulfur electrochemical conversion and its interactions within electrode, we need to apply new experimental approaches capable to provide precise information about local environment of S in the cathode during battery operation. In our work, resonant inelastic X-ray scattering (RIXS) and XAS measurements at the sulfur K-edge performed in operando mode were used to study the lithium-polysulfide formation during the discharge process. Measurements were performed at ID26 beamline of the ESRF synchrotron using tender X-ray emission spectrometer [1]. Resonant excitation condition enhanced the sensitivity for the lithium−polysulfide detection. On the other hand, the sulfate signal from the electrolyte was heavily suppressed and the self-absorption effects minimized due to fixed excitation energy.
This experimental methodology was used to provide quantitative analysis of sulfur compounds in the cathode of a Li−S battery cell during the discharge process [2]. The high-voltage plateau in the discharge curve was characterized by a rapid conversion of solid sulfur into liquid phase Li polysulfides reaching its maximum at the end of this plateau. At this point the starting point for the precipitation of the Li2S from the liquid polysulfide phase was observed. The same approach has been used also for the Mg-S battery revealing similar mechanism as in case of Li-S battery [3]. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and Mg polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau).
Najdeno v: ključnih besedah
Povzetek najdenega: ...Mg-Sulphur batteries, XANES, RIXS...
Ključne besede: Mg-Sulphur batteries, XANES, RIXS
Objavljeno: 13.09.2018; Ogledov: 968; Prenosov: 0
Polno besedilo (123,32 KB) |
29. Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2-SiO2 nanoparticle compositesT. Čižmar, doktorska disertacija Opis: The objective of this dissertation was to examine how copper modification can improve the photocatalytic activity of TiO2-SiO2 and to explain the correlation between Cu concentration and chemical state of Cu cations in the TiO2-SiO2 matrix, as well as the photocatalytic activity under the UV/solar irradiation.
The Cu-modified TiO2-SiO2 photocatalysts were prepared by a low temperature sol-gel method based on organic copper, silicon and titanium precursors with varied Cu concentrations (from 0.05 to 3 mol%). The sol-gels were dried at 150 °C to obtain the photocatalysts in the powder form. To test thermal stability, additional set of photocatalysts was obtained by calcinating dried samples in air at 500 °C for 1 h.
The photocatalytic activity was determined by a fluorescence-based method of terephthalic acid decomposition. Up to three times increase in photocatalytic activity of air-dried samples is obtained when 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 Cu-modified photocatalyst is smaller than in the unmodified reference TiO2-SiO2 photocatalyst. Calcined samples showed significantly reduced photocatalytic activity compared to air-dried samples.
XRD analysis showed that all Cu-modified TiO2-SiO2 nanocomposites with different Cu concentrations have the same crystalline structure as unmodified TiO2-SiO2 nanocomposites (air-dried or calcined). The addition of Cu does not change the relative ratio between the anatase and brookite phase or unit cell parameters of the two TiO2 crystalline structures. TEM analysis showed that the addition of Cu does not change the morphology of TiO2-SiO2 catalyst dried at 150 °C.
The Cu K-edge XANES and EXAFS analysis were used to determine valence state and local structure of Cu cations in Cu-modified TiO2-SiO2 photocatalyst. The results elucidate the mechanism responsible for the improved or hindered photocatalytic activity. In the air-dried samples with low Cu content, which exhibit largest activity, Cu-O-Ti connections are formed, suggesting that the activity enhancement is due to Cu(II) cations attachment on the surface of the photocatalytically active TiO2 nanoparticles, so Cu(II) cations may act as free electron traps, reducing the intensity of recombination between electrons and holes at the TiO2 photocatalyst’s surface. At higher Cu loadings no additional Cu-O-Ti connections are formed, instead only Cu-O-Cu connections are established, indicating the formation of amorphous or nanocrystalline Cu(II) oxide, which hinders the photocatalytic activity of TiO2. Calcination of Cu-modified TiO2-SiO2 photocatalysts at 500 °C induces significant structural changes: Cu-O-Ti connections are lost, Cu partially incorporates into the SiO2 matrix and amorphous copper oxides, which again reduce the photocatalytic activity of the material, are formed.
Najdeno v: ključnih besedah
Povzetek najdenega: ...catalyst dried at 150 °C.
The Cu K-edge XANES and EXAFS analysis were used to determine...
Ključne besede: titanium dioxide, Cu-modified TiO2-SiO2 photocatalyst, photocatalytic activity, Cu K-edge XANES, EXAFS.
Objavljeno: 17.12.2018; Ogledov: 1041; Prenosov: 53
Polno besedilo (3,05 MB) |
30. Alternative Recovery and Valorization of Metals from Exhausted Catalytic Converters in a New Smart Polymetallic CatalystOreste Piccolo, Laura Sperni, Michele Gallo, Katarina Vogel-Mikuš, Iztok Arčon, Franco Baldi, Sebastiano Tieuli, 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...(I) were investigated by X-ray absorption spectroscopy
methods ( XANES and EXAFS). No metallic alloy seems to
be...
Ključne besede: Biogenerated polymetallic exopolysaccharide, biphasic catalysis, hydrogenation, metals-polymeric
composite, new catalyst from metallic wastes, EXAFS, XANES
Objavljeno: 06.05.2019; Ogledov: 435; Prenosov: 0
Polno besedilo (2,87 MB) |
