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101.
Ceramic synthesis of disordered lithium rich oxyfluoride materials
Jean-Marcel Ateba Mba, Iztok Arčon, Gregor Mali, Elena Tchernychova, Ralf Witte, Robert Kruk, Miran Gaberšček, Robert Dominko, 2020, original scientific article

Abstract: Disordered lithium-rich transition metal oxyfluorides with a general formula Li1þxMO2Fx (M being a transition metal) are gaining more attention due to their high specific capacity which can be delivered from the facecentered cubic (fcc) structure. The most common synthesis procedure involves use of mechanosynthesis. In this work, ceramic synthesis of lithium rich iron oxyfluoride and lithium rich titanium oxyfluoride are reported. Two ceramic synthesis routes are developed each leading to the different level of doping with Li and F and different levels of cationic disorder in the structure. Three different Li1þxMO2Fx samples (x ¼ 0.25, 0.3 and 1) are compared with a sample prepared by mechanochemical synthesis and non-doped LiFeO2 with fcc structure. The obtained lithium rich iron oxyfluoride are characterized by use of M€ossbauer spectroscopy, X-ray absorption spectroscopy, NMR and TEM. Successful incorporation of Li and F have been confirmed and specific capacity that can be obtained from the samples is in the correlation with the level of disorder introduced with doping, nevertheless oxidation state of iron in all samples is very similar. Conclusions obtained from lithium rich iron oxyfluoride are validated by lithium rich titanium oxyfluoride.
Found in: osebi
Keywords: Lithium batteries Face centered-cubic Oxyfluoride Li-rich Disorder
Published: 05.06.2020; Views: 1140; Downloads: 0
.pdf Fulltext (2,37 MB)

102.
Effect of Na, Cs and Ca on propylene epoxidation selectivity over CuOx/SiO2 catalysts studied by catalytic tests, in-situ XAS and DFT
Janvit Teržan, Matej Huš, Iztok Arčon, Blaž Likozar, Petar Djinović, 2020, original scientific article

Abstract: This research focuses on epoxidation of propylene over pristine, Na, Ca and Cs modified CuOx/SiO2 catalysts using O2. The selectivity of the reaction is analyzed using a combination of catalytic tests, in-situ XAS and DFT calculations. The initially present subnanometer CuO clusters are present in all catalysts which re-disperse/flatten during reaction. During catalytic reaction, the Cu1+ becomes the predominant oxidation state. There is no correlation between propylene oxide (PO) selectivity and copper oxidation state. DFT analysis of the propylene reaction pathway revealed that Na, Cs, and Ca addition decreases the bonding strength of propylene to CuO and decreases the O2 activation barrier, while simultaneously increase the exothermicity of O2 dissociation. The Na induced Cu-O bond modification decreases the activation barrier from 0.87 to 0.71 eV for the oxametallacycle (OMC) ring closure (first step in the reaction pathway favoring selectivity towards PO) compared to pristine 5Cu catalyst. At the same time, we observed an increase (from 0.45 to 0.72 eV) of the barrier for the abstraction of allylic hydrogen. The opposite effect is achieved by Ca addition: the activation barrier for OMC ring closure increases to 1.08 eV and that for allylic hydrogen stripping decreases to 0.16 eV.
Found in: osebi
Keywords: Alkali modification, propylene epoxidation, reaction mechanism, copper oxide, activation barrier.
Published: 05.06.2020; Views: 1164; Downloads: 0
.pdf Fulltext (22,78 MB)

103.
104.
VELIKOKRAT NAS JE PRESENETILO, KAJ ATOMI DEJANSKO POČNEJO
Nina Slaček, Iztok Arčon, radio or television broadcast

Abstract: Razvoj novih materialov, nanotehnologije, molekularne biologije in še številnih drugih področij sodobnih znanosti je tesno povezan s podrobnim razumevanjem tega, kaj se dejansko dogaja na molekularnem oziroma atomskem nivoju. Za razvoj denimo novih nanostrukturnih materialov za baterije prihodnosti je nujno videti, kaj se v njih dejansko dogaja med samim delovanjem. To omogoča rentgenska absorpcijska spektroskopija s sinhrotronsko svetlobo. »Ko z rentgenskim žarkom posvetimo na snov, iz atoma izbijemo elektron in ta odleti v okolico, se od nje odbija in nam na ta način sporoči, kaj se v njegovi okolici nahaja,« razlaga osnovni princip te metode prof. dr. Iztok Arčon. Na ta način je mogoče pridobiti številne ključne podatke, ki pogosto na glavo postavijo predhodne domneve raziskovalcev. A za takšne raziskave je nujen sinhrotron. Tovrstnih pospeševalnikov ni veliko in merilni čas na sinhrotronu je potrebno pridobiti z vrhunsko zastavljenimi raziskavami. A tokratni gost Podob znanja, dr. Iztok Arčon, redni profesor na Univerzi v Novi Gorici, ima po zaslugi svojega znanstvenega dela na tem področju na široko odprta vrata, sodeluje pa raziskovalnimi skupinami z zelo različnih področij. Letos je za svoje dosežke prejel tudi Preglovo nagrado. Foto: iz osebnega arhiva Iztoka Arčona
Found in: osebi
Summary of found: ...osnovni princip te metode prof. dr. Iztok Arčon. Na ta način je mogoče pridobiti številne ključne...
Keywords: rentgenska absorpcijska spektroskopija, sinhrotronsko sevanje, raziskave nanomaterialov, Preglova nagrada 2020
Published: 19.10.2020; Views: 939; Downloads: 0
.pdf Fulltext (160,86 KB)

105.
Effect of the Morphology of the High-Surface-Area Support on the Performance of the Oxygen-Evolution Reaction for Iridium Nanoparticles
Leonard Moriau, Marjan Bele, Živa Marinko, Francisco Ruiz-Zepeda, Gorazd Koderman, Martin Šala, Angelija Kjara Šurca, Janez Kovač, Iztok Arčon, Primož Jovanovič, Nejc Hodnik, Luka Suhadolnik, 2021, original scientific article

Abstract: The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiONx) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst’s OER activity and stability. Our study is supported by various state-of-the-art materials’ characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO2 benchmarks as well as the Ir-supported samples on morphologically different TiONx from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.
Found in: osebi
Keywords: electrocatalysis, oxygen-evolution reaction, TiONx-Ir powder catalyst, iridium nanoparticles, anodic oxidation, morphology−activity correlation
Published: 04.01.2021; Views: 769; Downloads: 0
.pdf Fulltext (6,36 MB)

106.
Ni več treba tipati v temi!
Iztok Arčon, 2020, other performed works

Abstract: Vidna svetloba, ki jo lahko zaznajo naše oči, predstavlja le droben delček v širokem spektru različnih vrst svetlobe, ki jih ponuja narava. V predavanju si bomo ogledali, kako so velika znanstvena odkritja o nenavadnih lastnostih svetlobe odprla pogled neposredno v čarobni svet atomov, omogočila razvoj sodobnih merskih tehnologij in s tem izjemen preboj v razvoju novih tehnološko zanimivih materialov.
Found in: osebi
Keywords: svetloba, rentgenske spektroskopije, karakterizacija materialov
Published: 21.01.2021; Views: 742; Downloads: 0
.pdf Fulltext (256,81 KB)

107.
108.
In-situ XAS study of catalytic N[sub]2O decomposition over CuO/CeO[sub]2 catalysts
Elena Tchernychova, Petar Djinović, Iztok Arčon, Maxim Zabilsky, Albin Pintar, 2021, original scientific article

Abstract: We performed in‐situ XAS study of N 2 O decomposition over CuO/CeO 2 catalysts. The Cu K‐edge and Ce L 3 ‐edge XANES and EXAFS analyses revealed the dynamic and crucial role of Cu 2+ /Cu + and Ce 4+ /Ce 3+ ionic pairs during the catalytic reaction. We observed the initial formation of reduced Cu + and Ce 3+ species during activation in helium atmosphere at 400 °C, while concentration of these species decreased significantly during steady‐state nitrous oxide degradation reaction (2500 ppm N 2 O in He at 400 °C). In‐situ EXAFS analysis further revealed a crucial role of copper‐ceria interface in this catalytic reaction. We observed dynamic changes in average number of Cu‐Ce scatters under reaction conditions, indicating an enlarging the interface between both copper and ceria phases, where electron and oxygen transfer occurs.
Found in: osebi
Keywords: in-situ XAS, Cu EXAFS, CuO/CeO2 nanorod catalys, N2O decomposition
Published: 29.01.2021; Views: 702; Downloads: 0
.pdf Fulltext (1,31 MB)

109.
Sn-modified TiO[sub]2 thin film photocatalysts prepared by low-temperature sol-gel processing
Ksenija Maver, 2021, doctoral dissertation

Abstract: Due to many advantageous physiochemical properties, titanium dioxide (TiO2) is the most widely used photocatalyst in numerous applications, such as wastewater treatment and air purification, self-cleaning surfaces and energy conversion (H2 generation). However, one of its disadvantages is the high electron-hole recombination rate, and coupling with other semiconductors is one of the strategies to improve it. The objective of this dissertation was to investigate how the photocatalytic activity of pure TiO2 can be improved by tin modification and to explain the mechanism of increased or hindered photoactivity in correlation with the structural properties of the modified TiO2 photocatalysts. A new low-temperature sol-gel synthesis route was developed to prepare Sn- or SnO2-modified TiO2 photocatalysts. In both cases, organic tin and titanium precursors were used. Tin in the form of Sn cations was used to prepare Sn-modified TiO2. In this case, the precursors went through the sol-gel reaction together to form a Sn-TiO2 sol. In the case of SnO2 modification, the SnO2 sol was prepared separately and additionally mixed with the TiO2 sol to form a TiO2/SnO2 bicomponent semiconductor system. Different molar ratios of tin to titanium were prepared to investigate the correlation between the tin concentration and the photocatalytic properties of the photocatalysts in the form of thin films. The results were used to optimize the synthesis conditions to obtain an improved activity of the modified TiO2 photocatalysts under UV-irradiation. The photocatalytic activity of the thin films was determined by measuring the degradation rate of an azo dye. An increase of up to 40 % in the photocatalytic activity of the dried samples (at 150 °C) was achieved when the TiO2 was modified with the Sn or SnO2 in a concentration range of 0.1 to 1 mol.%. At higher Sn or SnO2 loadings and after calcination of the samples at 500 °C, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. Different characterization techniques (UV-Vis, XRD, nitrogen physisorption, TEM, SEM and XAS) were employed to clarify the mechanism responsible for the enhanced and hindered photocatalytic performance of the Sn- and SnO2-modified TiO2 photocatalysts. The results showed that a nanocrystalline structure is already achieved in the samples by the low-temperature film treatment (drying at 150 °C) and that the photocatalytic efficiency is mainly influenced by the crystalline phase composition: anatase/rutile in the case of Sn-modified and TiO2/SnO2 in the case of SnO2-modified TiO2. The crystal size and specific surface area differ insignificantly between the equally thermally treated samples and partly explain the differences in photoefficiency of the calcined samples compared to the dried samples. The structural study at the atomic level, using the Sn K-edge EXAFS, revealed that Sn cations act as nucleation sites for the anatase to rutile transformation in the Sn-modified TiO2 photocatalysts, while in the SnO2-modified TiO2 samples the nanocrystalline cassiterite SnO2 is bound to the TiO2 nanocrystallites via the Sn-O-Ti bond. In both cases, the advantage of coupling the two semiconductors was achieved by separating the charge carriers and thus prolonging their lifetime for accessibility to participate in the redox reactions. The maximum activity enhancement was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases are obtained for the given physical parameters, such as particle size, shape and specific surface area of the catalyst.
Found in: osebi
Keywords: Sn-modified TiO2, SnO2-modified TiO2, low-temperature sol-gel, thin films, photocatalytic activity, anatase/rutile system, Sn K-edge EXAFS, dissertations
Published: 09.06.2021; Views: 773; Downloads: 49
URL Fulltext (0,00 KB)
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110.
Removal of copper from aqueous solutions with zeolites and possible treatment of exhaust materials
Iztok Arčon, Janez Kovač, Margarita Popova, Nataša Zabukovec Logar, 2021, original scientific article

Abstract: 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.
Found in: osebi
Keywords: Cu2+ ion exchange, Total toluene oxidation, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Zeolite
Published: 03.06.2021; Views: 359; Downloads: 14
URL Fulltext (0,00 KB)
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