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31.
X-ray spectrometry in plant biology
Katarina Vogel-Mikuš, Iztok Arčon, Alojz Kodre, Anja Kavčič, Peter Kump, Primož Pelicon, 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.
Ključne besede: X-ray spectrometry, plants, XANES, EXAFS
Objavljeno v RUNG: 12.09.2018; Ogledov: 3449; Prenosov: 0
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32.
Effects of Different Copper Loadings on the Photocatalytic Activity of TiO2-SiO2 Prepared at a Low Temperature for the Oxidation of Organic Pollutants in Water
T. 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.
Ključne besede: Cu modified TiO2-SiO2 photocatalyst Cu EXAFS, XANES, Organic pollutants
Objavljeno v RUNG: 30.08.2018; Ogledov: 3483; Prenosov: 0
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33.
Surface modified titanium dioxide using transition metals : nickel as a winning transition metal for solar light photocatalysis
Andraž Šuligoj, Iztok Arčon, Matjaž Mazaj, Goran Dražić, Denis Arčon, Pegie Cool, Urška Lavrenčič Štangar, Nataša Novak Tušar, 2018, izvirni znanstveni članek

Opis: 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.
Ključne besede: surface modified TiO2, XANES, EXAFS, Nickel, solar light photocatalyst
Objavljeno v RUNG: 01.06.2018; Ogledov: 3420; Prenosov: 0
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34.
Polysulfides formation in different electrolytes from the perspective of X-ray absorption spectroscopy
Robert 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.
Ključne besede: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides
Objavljeno v RUNG: 01.06.2018; Ogledov: 3512; Prenosov: 0
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35.
Določanje atomske strukture snovi z rentgensko absorpcijsko spektrometrijo s sinhrotronsko svetlobo
Iztok Arčon, predavanje na tuji univerzi

Opis: 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.
Ključne besede: rentgenska absorpcijska spektroskopija, XANES, EXAFS, strukturna analiza, sinhrotronska svetloba
Objavljeno v RUNG: 01.06.2018; Ogledov: 4185; Prenosov: 0
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36.
Role of Surface Cu-O-Zr Sites in the Photocatalytic Activity of TiO2 Nanoscale Particles
Olena Pliekhova, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2016, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: Photocatalysis, Titanium dioxide, Copper, Zirconia, co-doping, EXAFS, XANES
Objavljeno v RUNG: 23.08.2017; Ogledov: 4585; Prenosov: 0
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37.
Structural analysis of sunlight efficient Cu and Zr modified TiO2 photocatalyst
Olena Pliekhova, Iztok Arčon, Urška Lavrenčič Štangar, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: TiO2, photocatalysis, EXAFS, surface modification
Objavljeno v RUNG: 23.08.2017; Ogledov: 4146; Prenosov: 0
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38.
39.
Correlations between photocatalytic activity and Cu structure in Cu-modified TiO2-SiO2
T. Čižmar, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: Titanium dioxide, Cu-modified, TiO2-SiO2, photocatalysts, photocatalytic activity, Cu K-edge XANES, EXAFS
Objavljeno v RUNG: 26.06.2017; Ogledov: 4503; Prenosov: 0
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40.
An extracellular polymeric substance quickly chelates mercury(II) with N-heterocyclic groups
Franco Baldi, Michele Gallo, Salvatore Daniale, Dario Battistel, Claudia Faleri, Alojz Kodre, Iztok Arčon, 2017, izvirni znanstveni članek

Opis: A strain of Klebsiella oxytoca DSM 29614 is grown on sodium citrate in the presence of 50 mg l−1 of Hg as Hg(NO3)2. During growth, the strain produces an extracellular polymeric substance (EPS), constituted by a mixture of proteins and a specific exopolysaccharide. The protein components, derived from the outer membrane of cells, are co-extracted with the extracellular exopolysaccharide using ethanol. The extracted EPS contains 7.5% of Hg (total amount). This indicates that EPS is an excellent material for the biosorption of Hg2+, through chemical complexation with the EPS components. The binding capacity of these species towards Hg2+ is studied by cyclic voltammetry, and Hg L3-edge XANES and EXAFS spectroscopy. The results found indicate that Hg2+ is mainly bound to the nitrogen of the imidazole ring or other N-heterocycle compounds. The hydroxyl moities of sugars and/or the carboxyl groups of two glucuronic acids in the polysaccharide can also play an important role in sequestring Hg2+ ions. However, N-heterocyclic groups of proteins bind Hg2+ faster than hydroxyl and carboxyl groups of the polysaccharide.
Ključne besede: Klebsiella oxytoca, Biosorption, Proteins, Polysaccharide, Cyclic voltammetry, EXAFS analysis
Objavljeno v RUNG: 03.03.2017; Ogledov: 4561; Prenosov: 0
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