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31.
Sulfur based batteries studied by in-operando S K-edge RIXS and XAS spectroscopy
Matjaž Žitnik, Iztok Arčon, Alen Vižintin, Janez Bitenc, Ana Robba, Matjaž Kavčič, Klemen Bučar, Robert Dominko, 2018, published scientific conference contribution abstract

Abstract: 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).
Found in: ključnih besedah
Summary of found: ...Mg-Sulphur batteries, XANES, RIXS...
Keywords: Mg-Sulphur batteries, XANES, RIXS
Published: 13.09.2018; Views: 1236; Downloads: 0
.pdf Fulltext (123,32 KB)

32.
Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2-SiO2 nanoparticle composites
T. Čižmar, doctoral dissertation

Abstract: 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.
Found in: ključnih besedah
Summary of found: ...catalyst dried at 150 °C. The Cu K-edge XANES and EXAFS analysis were used to determine...
Keywords: titanium dioxide, Cu-modified TiO2-SiO2 photocatalyst, photocatalytic activity, Cu K-edge XANES, EXAFS.
Published: 17.12.2018; Views: 1310; Downloads: 62
.pdf Fulltext (3,05 MB)

33.
Alternative Recovery and Valorization of Metals from Exhausted Catalytic Converters in a New Smart Polymetallic Catalyst
Oreste Piccolo, Laura Sperni, Michele Gallo, Katarina Vogel-Mikuš, Iztok Arčon, Franco Baldi, Sebastiano Tieuli, Stefano Paganelli, 2019, original scientific article

Abstract: 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.
Found in: ključnih besedah
Summary of found: ...(I) were investigated by X-ray absorption spectroscopy methods ( XANES and EXAFS). No metallic alloy seems to be...
Keywords: Biogenerated polymetallic exopolysaccharide, biphasic catalysis, hydrogenation, metals-polymeric composite, new catalyst from metallic wastes, EXAFS, XANES
Published: 06.05.2019; Views: 655; Downloads: 0
.pdf Fulltext (2,87 MB)

34.
Unraveling the arrangement of Al and Fe within the framework explains the magnetism of mixed-metal MIL-100(Al,Fe)
Gregor Mali, Matjaž Mazaj, Iztok Arčon, Darko Hanžel, Denis Arčon, Zvonko Jagličić, 2019, original scientific article

Abstract: Properties of mixed-metal MOFs depend on the distribution of different metals within their frameworks. Determination of this distribution is often very challenging. Using an example of aluminum- and iron-containing MIL-100, we demonstrate that 27Al NMR spectroscopy, when combined with first-principles calculations and magnetic, X-band electron paramagnetic resonance, Fe K-edge extended X-ray absorption fine structure, and Mössbauer measurements, enables one to accurately determine the arrangement of Al and Fe within the metal trimers, which are the basic building units of MIL-100. In this particular material, the incorporation of Fe and Al on the framework metal sites is random. Crucial for deciphering the arrangement is detecting NMR signals, shifted because of the strong hyperfine interaction between the 27Al nuclei and the unpaired electronic spins of Fe3+ ions, assigning the shifted signals aided by first-principles calculations of hyperfine couplings, and quantitatively evaluating the NMR intensities and the measured effective magnetic moment.
Found in: ključnih besedah
Summary of found: ...Fe EXAFS, XANES, MIL100, MOF, magnetizem...
Keywords: Fe EXAFS, XANES, MIL100, MOF, magnetizem
Published: 26.03.2019; Views: 816; Downloads: 0
.pdf Fulltext (2,57 MB)

35.
New Insights into Manganese Local Environment in MnS-1Nanocrystals
Alenka Ristić, Matjaž Mazaj, Iztok Arčon, Nina Daneu, Nataša Zabukovec Logar, Roger Glaser, Nataša Novak Tušar, 2019, original scientific article

Abstract: Manganese plays an important role in redox catalysis using zeolites as inorganic support materials, but the formation of the preferred redox manganese species (framework or extraframework) is still not well understood. Herein, the influence of the amount of manganese together with conventional and microwave-assisted hydrothermal synthesis paths on the formation of manganese species within the zeolite silicalite-1 (S-1) with MFI structure was investigated. It was found out that both synthesis procedures led to the formation of framework and extraframework manganese species, but in different molar ratios. However, the conventional synthesis procedure with all Mn/Si molar ratios generates more framework Mn in comparison to the microwave procedure. Additionally, the diminution of the zeolite crystals to nanoscale from 100 to 200 nm was achieved via the conventional procedure for the first time. UV–vis, Raman, and X-ray absorption spectroscopic analyses revealed different local environments of manganese: Mn3+ incorporated into the silicalite-1 framework as “framework manganese” and Mn2+/3+ present as “extraframework manganese” (Mn2O3, Mn3O4). TEM reveals the presence of Mn3O4 nanorods. Both framework manganese and extraframework manganese exhibit good catalytic activity for styrene epoxidation. Catalytic results suggest that, in oxidation reactions of hydrocarbons, framework manganese is more active at lower Mn contents (Mn/Si < 0.015), whereas extraframework manganese is more active at higher loadings (Mn/Si > 0.015).
Found in: ključnih besedah
Summary of found: ...MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis...
Keywords: MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis
Published: 06.05.2019; Views: 858; Downloads: 0
.pdf Fulltext (9,33 MB)

36.
Recent advances in 2D imaging of element distribution in Plants by focused beam techniques
Katarina Vogel-Mikuš, Johannes Teun van Elteren, Marjana Regvar, Jitrin Chaiprapa, Boštjan Jenčič, Iztok Arčon, Alojz Kodre, Peter Kump, Anja Kavčič, Mitja Kelemen, Dino Metarapi, Marijan Nečemer, Primož Vavpetič, Primož Pelicon, Paula Pongrac, 2019, independent scientific component part or a chapter in a monograph

Found in: ključnih besedah
Summary of found: ...2D Imiging, XRF, XANES, synchrotron light...
Keywords: 2D Imiging, XRF, XANES, synchrotron light
Published: 05.09.2019; Views: 610; Downloads: 0
.pdf Fulltext (8,41 MB)

37.
Comparing magnetism in isostructural oxides A[sub](0.8)La[sub](1.2)MnO[sub](4.1)
John E. Greedan, Hanna Dabkowska, Graham King, Christopher Wiebe, Meghan Rutherford, Chad Boyer, Iztok Arčon, Paul A. Dube, Mirela Dragomir, 2019, original scientific article

Abstract: This study presents the strikingly distinct magnetic properties of two isostructural compounds, Ba0.8La1.2MnO4.1 and Sr0.8La1.2MnO4.1 (K2NiF4 type, I4/mmm). Spectroscopic studies have shown that Mn is in a +3.0(1) oxidation state only, in both compounds; therefore, the charge is balanced by accommodating extra oxygen at interstitial sites, as confirmed by neutron powder diffraction. We found that the Ba compound exhibits an exceedingly rare anisotropic spin glass behavior, Tg = 26.4(4) K, with the moment freezing along the c-axis only while the in-plane spin components remain dynamic well below Tg. Experimental results including neutron diffraction, heat capacity, and magnetic (dc and ac) measurements performed on an oriented single crystal support this conclusion. This is a remarkable result, the only other known example of an anisotropic spin glass being Fe2TiO5. The spin glass state in Ba0.8La1.2MnO4.1 is argued to arise due to competing antiferromagnetic and ferromagnetic 180° Mn3+−O−Mn3+ superexchange interactions. In contrast, the Sr analogue shows 2D antiferromagnetic correlations and long-range antiferromagnetic order below 95(1) K with a remarkably reduced ordered moment of 1.449(49) μB/Mn3+ instead of the ∼4 μB expected for an S = 2 ion.
Found in: ključnih besedah
Summary of found: ...antiferomagnetiki, Mn XANES, struktura...
Keywords: antiferomagnetiki, Mn XANES, struktura
Published: 23.10.2019; Views: 705; Downloads: 0
.pdf Fulltext (4,14 MB)

38.
Arabidopsis halleri shows hyperbioindicator behaviour for Pb and leaf Pb accumulation spatially separated from Zn
Stephan Höreth, Paula Pongrac, Marta Debeljak, Katarina Vogel-Mikuš, Matic Pečovnik, Primož Vavpetič, Iztok Arčon, original scientific article

Abstract: Lead (Pb) ranks among the most problematic environmental pollutants. Background contamination of soils is nearly ubiquitous, yet plant Pb accumulation is barely understood. In a survey covering 165 European populations of the metallophyte Arabidopsis halleri, several field samples had indicated Pb hyperaccumulation, offering a chance to dissect plant Pb accumulation. Accumulation of Pb was analysed in A. halleri individuals from contrasting habitats under controlled conditions to rule out aerial deposition as a source of apparent Pb accumulation. Several elemental imaging techniques were employed to study the spatial distribution and ligand environment of Pb. Regardless of genetic background, A. halleri individuals showed higher shoot Pb accumulation than A. thaliana. However, dose–response curves revealed indicator rather than hyperaccumulator behaviour. Xylem sap data and elemental imaging unequivocally demonstrated the in planta mobility of Pb. Highest Pb concentrations were found in epidermal and vascular tissues. Distribution of Pb was distinct from that of the hyperaccumulated metal zinc. Most Pb was bound by oxygen ligands in bidentate coordination. A. halleri accumulates Pb whenever soil conditions render Pb phytoavailable. Considerable Pb accumulation under such circumstances, even in leaves of A. thaliana, strongly suggests that Pb can enter food webs and may pose a food safety risk.
Found in: ključnih besedah
Summary of found: ...Pb accumulation, XANES, EXAFS, Arabidopsis halleri...
Keywords: Pb accumulation, XANES, EXAFS, Arabidopsis halleri
Published: 16.01.2020; Views: 465; Downloads: 0
.pdf Fulltext (4,46 MB)

39.
Effects of a Mixed O/F Ligand in the Tavorite-Type LiVPO4O Structure
Sorour Semsari Parapari, Jean-Marcel Ateba Mba, Elena Tchernychova, Gregor Mali, Iztok Arčon, Gregor Kapun, Mehmet Ali Gülgün, Robert Dominko, 2020, original scientific article

Abstract: We report the synthesis and detailed structural and chemical characterization including electrochemical properties of a lithium vanadium oxy/fluoro-phosphate material. To the best of our knowledge, we have for the first time synthesized a LiVPO4O-type phase with a mixed O/F ligand. In the synthesis procedure, the LiVPO4O precursor compound was fluorinated via LiF incorporation, with preservation of the LiVPO4O framework structure. The operating potential of the synthesized material is increased compared to that of the LiVPO4O precursor (4.12 V vs 3.95 V versus metallic lithium, respectively). The related increase in operating potential was assigned to the effect of the intermixing O/F ligand, which is attained via the successful fluorine incorporation into the LiVPO4O structure. A characterization of the investigated materials was performed using microscale-covering XRD, XANES, and NMR techniques as well as nanoscale spatially resolved imaging and analytical STEM techniques. The obtained oxy/fluoro-phosphate phase is isostructural to LiVPO4O; however, the presence of the mixed O/F ligand promoted a higher symmetry of vanadium octahedra. These variations of the vanadium local environment along with the observed inhomogeneous distribution of the incorporated fluorine gave rise to the minor local deviations in vanadium valence. Our results clearly emphasize the connection among the fluorine ligand incorporation, its local distribution, and the electrochemical properties of the material.
Found in: ključnih besedah
Summary of found: ...the investigated materials was performed using microscale-covering XRD, XANES, and NMR techniques as well as nanoscale...
Keywords: LiVPO4O, XRD, SEM, V XANES, Tavorite-Type, electrochemical properties
Published: 17.02.2020; Views: 446; Downloads: 0
.pdf Fulltext (3,11 MB)

40.
Study of water adsorption on EDTA dealuminated zeolite Y
O. L. Pliekhov, Olena Pliekhova, Iztok Arčon, Federica Bondino, Elena Magnano, Gregor Mali, Nataša Zabukovec Logar, 2020, original scientific article

Abstract: Zeolite Y was synthesized and modified with EDTA dealumination procedure. The modified zeolites were analyzed by X-ray diffraction, X-ray absorption spectroscopy, chemical analysis and water adsorption measurements. We demonstrated that dealumination with bulk organic acid such as EDTA is able to reduce the original intense water affinity. Furthermore, it was found that dealumination with EDTA, in contrast with steaming and HCl dealumination, provides fully controllable, predictable and secure process of Al removal from the zeolites’ frameworks. The shift of the adsorption isotherm in the low partial pressure range represents an interesting result for adsorption-based applications.
Found in: ključnih besedah
Summary of found: ...Zeolite Y Water sorption Dealumination Al XANES EDTA treatment...
Keywords: Zeolite Y Water sorption Dealumination Al XANES EDTA treatment
Published: 05.06.2020; Views: 373; Downloads: 0
.pdf Fulltext (667,27 KB)

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