41. 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.
Ključne besede: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides
Objavljeno v RUNG: 01.06.2018; Ogledov: 4776; Prenosov: 0
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42. Določanje atomske strukture snovi z rentgensko absorpcijsko spektrometrijo s sinhrotronsko svetloboIztok 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: 6854; Prenosov: 0
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43. Role of Surface Cu-O-Zr Sites in the Photocatalytic Activity of TiO2 Nanoscale ParticlesOlena 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: 6138; Prenosov: 0
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44. Electrochemical dissolution of iridium and iridium oxide particles in acidic media : transmission electron microscopy, electrochemical flow cell coupled to inductively coupled plasma mass spectrometry and X-ray absorption spectroscopy studyPrimož Jovanovič, Nejc Hodnik, Francisco Ruiz-Zepeda, Iztok Arčon, Barbara Jozinović, Milena Zorko, Marjan Bele, Martin Šala, Vid Simon Šelih, Samo B. Hočevar, Miran Gaberšček, 2017, izvirni znanstveni članek Opis: Iridium based particles as the most promising proton exchange membrane electrolyser electrocatalysts were investigated
by transmission electron microscopy (TEM), and by coupling of electrochemical flow cell (EFC) with online inductively
coupled plasma mass spectrometer (ICP-MS). Additionally, a thin-film rotating disc electrode (RDE), an identical location transmission
and scanning electron microscopy (IL-TEM and IL-SEM) as well as an X-ray absorption spectroscopy (XAS) studies have
been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that iridium
particles dissolved already well below oxygen evolution reaction (OER) potentials, presumably induced by iridium surface oxidation
and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile type IrO2 particles (T-IrO2)
are substantially more stable and less active in comparison to as prepared metallic (A-Ir) and electrochemically pretreated (E-Ir)
analogues. Interestingly, under OER relevant conditions E-Ir particles exhibit superior stability and activity owing to the altered
corrosion mechanism where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance,
electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low temperature
electrochemical hydrogen production device, namely a proton exchange membrane electrolyser.
Ključne besede: Iridium Oxide Par-ticles, Electrochemical Dissolution of Iridium, Ir L3-edge XANES
Objavljeno v RUNG: 23.08.2017; Ogledov: 5397; Prenosov: 0
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48. Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2–SiO2 nanoparticle compositesT. Čižmar, Urška Lavrenčič Štangar, Iztok Arčon, 2016, izvirni znanstveni članek Opis: Copper-modified TiO2–SiO2photocatalysts were prepared by sol–gel method based on organic copper,silicon and titanium precursors. Copper concentration varied from 0.1 to 3.0 mol%. A widely appliedmodel reaction of photocatalytic oxidation of terephtalic acid (TPA) in water solution was used in order toevaluate the catalytic activities of elaborated samples. The crystal structures of the titania components ofall tested titania–silica species were studied using XRD analysis. The influence of Cu2+cation incorporationon the crystal structure of titania, as well as the chemical states and the neighbouring structures of coppercations, have been examined by means of Cu K-edge EXAFS and XANES analysis. The experimental datashow that there is a ten times increase in photocatalytic activity when TiO2–SiO2matrix is modified with0.1 mol% of Cu. It can be supposed that an enhancement of photocatalytic activity of low-concentratedcopper-modified titania–silica nanocomposites is probably due to a close attachment of Cu2+cationsto the surfaces of photocatalytically active TiO2nanoparticles. In this case, Cu2+cations may possiblyact as free electron traps reducing the intensity of recombination between opposite free charge carriers(electrons, holes) available at the photocatalyst’s surface.
Ključne besede: Cu-modified TiO2–SiO2photocatalysts, Titanium dioxide, Metal doping, Cu K-edge XANES, EXAFS, Photocatalytic activitya
Objavljeno v RUNG: 17.01.2017; Ogledov: 6704; Prenosov: 0
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49. Arbuscular mycorrhizal fungi alter Hg root uptake and ligand environment as studied by X-ray absorption fine structureAlojz Kodre, Iztok Arčon, Marta Debeljak, Mateja Potisek, Matevž Likar, Katarina Vogel-Mikuš, 2017, izvirni znanstveni članek Opis: Mercury (Hg) – plant – fungal interactions are only poorly studied. Hg speciation and ligand environment
in maize roots inoculated with arbuscular mycorrhizal (AM) fungi were investigated in order to better
understand the role of AM in Hg soil to root transfer.
The maize plants were grown in Hg polluted substrate (50 mg g1 as dissolved HgCl2) and inoculated
with AM fungi originating from: a) highly Hg polluted environment of a former Hg smelting site in Idrija,
Slovenia, (Glomus sp. – sample AmI), and b) non-polluted environment (commercial AM inoculum
Symbivit1 – sample AmC). Hg speciation and ligand environment in maize roots was studied by Hg-L3
XANES and EXAFS with emphasis on XAS methodology – modelling and fitting the XAFS spectra to extract in a reliable way as much information on Hg coordination as possible. The AmI plants developed more arbuscules and less vesicles than the AmC plants, and also
accumulated more Hg in the roots. A clear difference in Hg coordination between the AM (AmC & AmI)
and the control (ConC & ConI) plants is recognized in Hg L3-edge EXAFS analysis: in the ConC & ConI
maize roots 73–80% of Hg is attached between two sulphur atoms at the distance of 2.34 Å. The remaining
ligand is nitrogen at 2.04 Å. In AmI & AmC roots another Hg-S attachment encompassing four thiol groups
at the S-distance of 2.50 Å are identified, accounting for 21–26%. AM fungi can modify Hg ligand environment in plant roots, thus playing an important role in biogeochemical cycling of Hg in terrestrial
ecosystems.
Ključne besede: EXAFS
XANES
Arbuscular mycorrhiza
Phytoremediation
Toxicity
Hg coordination
Ligand environment
Objavljeno v RUNG: 27.09.2016; Ogledov: 7944; Prenosov: 0
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50. Identifikacija, porazdelitev in vezavne oblike železa v rižu (Oryza sativa L.) z rentgensko absorpcijsko in emisijsko mikro-spektroskopijoBojan Šuc, 2016, diplomsko delo Opis: V diplomskem delu smo raziskali vezavne oblike železa v različnih delih korenin riža s kombinacijo rentgenske absorpcijske spektroskopije in mikroskopije z metodo mikro-XANES. S tem smo želeli izboljšati razumevanje vnosa železovih spojin v rastline riža (Oryza sativa L.) na tkivnem nivoju. Rastline riža so bile vzgojene v hidroponskem sistemu z dodanim železom Fe2+ (kot FeSO4). Spektri mikro-XANES na absorpcijskem robu K železa so bili pomerjeni na prečnih rezinah korenin, zamrznjenih v tekočem dušiku, na žarkovni liniji ID21 sinhrotrona ESRF v Grenoblu v fluorescenčnem načinu. Pri analizi spektrov mikro-XANES smo preučili uporabnost metode linearnega kombiniranja referenčnih spektrov XANES železa izmerjenih na nizu referenčnih dvo- in trivalentnih železovih spojin. Rezultati so pokazali, da je možno s to metodo v rastlinskih vzorcih jasno ločiti med dvo- in trivalentnimi železovimi kompleksi in določiti njihov delež z natančnostjo ±1%. Prevladujoča valenca železa v vzorcih korenin je Fe3+. Prepoznavanje in razločevanje različnih železovih kompleksov je manj natančno. Natančnost pri določanju deleža različnih trivalentnih železovih kompleksov je med 10% in 30%. Nekaterih železovih kompleksov s to metodo ni mogoče razločiti med sabo, ker se njihovi spektri XANES premalo razlikujejo. Kot najpogostejše železove komplekse v koreninah riža smo prepoznali Fe2+-fitat med dvovalentnimi spojinami, med trivalentnimi pa: železov oksid/hidroxid Goethit α-FeOOH Fe3+-citrat in Fe3+-fitat. Na natančnost pri razločevanju železovih spojin znatno vplivajo statistični šum in sistematske napake v izmerjenih spektrih mikro-XANES. Rezultati razmerij med dvo- in trivalentnimi železovimi kompleksi v različnih delih korenin kažejo, da se rastline riža zaščitijo pred strupenim toksičnim dvovalentnim železom tako, da ga oksidirajo in tvorijo tako imenovani plak, oziroma oborino, s čimer omejijo vnos dvovalentnega železa.
Ključne besede: Rentgenska absorpcijska spektrometrija, riž, železo, mikro-XANES, metoda linearnega kombiniranja referenčnih spektrov
Objavljeno v RUNG: 06.09.2016; Ogledov: 9826; Prenosov: 256
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