111. Photocatalytic Activity of Zirconium- and Manganese- Codoped Titania in Aqueous Media: The Role of the Metal Dopant and its Incorporation SiteO. L. Pliekhov, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2016, original scientific article Abstract: The development of efficient TiO2-based photocatalysts for
water treatment is mainly performed by doping with transition
metals or by establishing junctions between different phases,
metal–semiconductor or semiconductor–semiconductor. We
present, for the first time, the synthesis of Zr- and Mn-modified
TiO2 by a redesigned sol–gel technique that allows the formation
of heterometallic bridges on the TiO2 surface. Cations of
the doping metals are located in the pores of mesoporous
anatase and attached to the crystalline TiO2 walls. The presence
of the Zr enhances the photoactivity of the TiO2 catalyst.
However, the introduction of Mn decreases the photocatalytic
efficiency in a nonadditive manner. The inhibition effect was
assigned to the side reaction between hydroxyl radicals and
Mn ions. The fact that Mn effectively scavenges the hydroxyl
radicals and, consequently, inhibits the whole oxidation process
is direct proof that hydroxyl radicals are the main reactive
species in the photocatalytic oxidative processes on TiO2 surfaces
in aqueous media and the process of COH generation is the
rate-determining step, which was confirmed using a method
based on the decolorization of a commercial dye Bezaktiv Blau
in a reaction with Fenton’s reagent as a source of hydroxyl radicals.
Keywords: doping, manganese, oxidation, X-ray absorption spectroscopy, zirconium
Published in RUNG: 21.07.2016; Views: 4274; Downloads: 0
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113. Study of Li-S batteries by S K-edge RIXS spectroscopyMatjaž Kavčič, Matjaž Žitnik, Klemen Bučar, Marko Petrič, Iztok Arčon, Robert Dominko, Alen Vižintin, 2016, published scientific conference contribution abstract Abstract: Li-S batteries are considered as one of the most promising candidates for future batteries in applications where high energy density is required [1]. Despite that the general principle of operation is known for a long time [2], the lack of detailed understanding of relevant operation mechanisms has so far prevented their extensive use. A Li-S battery is composed of a lithium metal anode and a sulfur based cathode, separated by a porous separator wetted with electrolyte. During the battery cycle the reduction and oxidation of S to Li2S and back proceeds through a complicated equilibrium mixture of compounds that are typically dissolved in the electrolyte in the form of long and short chain polysulfides. In order to improve our understanding of polysulfide formation and its interactions within electrode, which are essential to achieve the long term cycling stability, development and application of new analytical tools is required.
In this work sulfur K-edge resonant X-ray emission (RXES) measurements were performed on the Li-S battery in operando mode. The experiment was performed at the ID26 beamline at ESRF using the Johansson type tender x-ray emission spectrometer [3]. Full K-L RIXS maps were recorded on a set of chemically prepared Li2Sx sample standards characterized by different Li:S stoichiometric ratio, followed by the operando measurements on Li-S battery. Using the spectra recorded on Li2Sx standards two excitation energies were chosen and RXES spectra from the back of the battery cathode were sequentially acquired during one discharge cycle (C20). The relative amounts of each sulfur compound in the cathode during the discharge cycle were determined from the linear combination fit using measured reference standard spectra. Because of resonant excitation conditions the sensitivity for the polysulfide detection was significantly enhanced. Our work sets up S K-edge RIXS spectroscopy as an important analytical tool to study the mechanism of Li-polysulfide formation in the cathode and their interaction with the host matrix and electrolyte.
Keywords: RIXS, RXES, Li-S battery, operando, Sulphur K-edge XANES, Lithium polysulphides, Li2S
Published in RUNG: 28.06.2016; Views: 5745; Downloads: 0
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114. XAS and micro-XRF analysis of mono and bi-metallic exopolysaccharide (FePd-EPS) bio-generated by K. oxytocaIztok Arčon, Stefano Paganelli, Oreste Piccolo, Michele Gallo, Katarina Vogel-Mikuš, Franco Baldi, 2016, published scientific conference contribution abstract Abstract: Bacteria Klebsiella oxytoca (DSM 29614) secret a specific exopolysaccharide (EPS) in the presence of Fe(III)-citrate, as sole carbon and energy source, and produces after 7 days an iron gel precipitate (Fe-EPS) [1]. In the presence of palladium or other metal species, the culture of K. oxytoca can produce other mono or bimetal species (Pd-EPS, FePd-EPS) [2]. These bio-materials may be used as green biogenerated catalysts or for other biotechnological purposes. In this work we present the analysis of the morphology and the chemical state of the metals in mono and bi-metallic (Fe-EPS, Pd-EPS, FePd-EPS) complexes, by a combination of micro X-ray fluorescence, X-ray absorption spectroscopy methods (XANES and EXAFS), and transmission electron microscopy. The results show that iron in monometallic Fe-EPS and bimetalic FePd-EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe3+, with a small amount of Fe2+ in the structure, as a mixture of different nano-crystalline iron oxides and hydroxides. Palladium on the other hand is found as Pd(0) in the form of metallic nanoparticles with fcc structure in both, bi-metallic (FePd-EPS) and mono-metallic (Pd-EPS) species. In bi-metallic species Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. Access to the SR facilities at ESRF (beamline ID21, project LS-2225), DESY (beamline C) Hamburg (project I-20110511 EC) and ELETTRA (beamline XAFS, project 20115112) is acknowledged.
Keywords: Klebsiella oxytoca, Fe, Pd, XANES, EXAFS, exopolysaccharide, FePd-EPS
Published in RUNG: 28.06.2016; Views: 5640; Downloads: 0
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115. |
116. The first example of a mixed valence ternary compound of silver with random distribution of Ag(I) and Ag(II) cationsIztok Arčon, Zvonko Jagličić, Wojciech Grochala, Zoran Mazej, Evgeny A. Goreshnik, Tomasz Michałowski, Jadwiga Szydłowska, 2015, original scientific article Keywords: srebrov fluorid, mešana valenca, srebro, XANES
Published in RUNG: 16.06.2016; Views: 4225; Downloads: 159
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119. Removal of manganese in batch and fluidized bed systems using beads of zeolite a as adsorbentMina Jovanovic, Iztok Arčon, Janez Kovač, Nataša Novak Tušar, Bojana Obradovic, Nevenka Rajić, 2016, original scientific article Abstract: In this study the uptake capacity of Mn(II) ions by zeolite A beads was investigated for different initial Mn concentration (100e400 mg Mn dm^-3) in batch mode at 25e55 C. The obtained adsorption capacity varying from 30 to 50 mg Mn g^-1 demonstrated a high affinity of zeolite A towards Mn(II) present in solutions. Kinetic studies indicated the intra-particle diffusion as the rate limiting step up to 45 C with apparent diffusivities in the range (1.2e2.0) x 10^-13 m2 s^-1 and the activation energy of 21.9 kJ mol^-1, which implies strong interactions between the zeolite A and Mn ions. At 55 C ion-exchange became the rate limiting step. The adsorption isotherms were studied at 25 C showing that the Mn adsorption is the best described by the Langmuir model suggesting a homogenous zeolite surface. XPS analysis of the Mnloaded beads showed that there is no surface accumulation of Mn but an almost uniform Mn distribution inside zeolite A, whereas XANES and EXAFS suggested that the adsorption of Mn(II) was followed by the Mn(II) oxidation and oxide formation. Regeneration of the spent zeolite was examined in 8 adsorption/desorption cycles by a chelating Na2EDTA in a fluidized column. It has been found that zeolite A beads could be reused for at least 4 cycles with satisfactory Mn(II) adsorption efficiencies of about 70%.
Keywords: Zeolite A
Manganese
Adsorption kinetics
EXAFS/XANES
XPS
Published in RUNG: 01.04.2016; Views: 5334; Downloads: 0
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