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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, izvirni znanstveni članek

Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Fe EXAFS, XANES, MIL100, MOF, magnetizem...
Ključne besede: Fe EXAFS, XANES, MIL100, MOF, magnetizem
Objavljeno: 26.03.2019; Ogledov: 336; Prenosov: 0
.pdf Polno besedilo (2,57 MB)

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, izvirni znanstveni članek

Opis: 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).
Najdeno v: ključnih besedah
Povzetek najdenega: ...MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis...
Ključne besede: MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis
Objavljeno: 06.05.2019; Ogledov: 293; Prenosov: 0
.pdf Polno besedilo (9,33 MB)

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, samostojni znanstveni sestavek ali poglavje v monografski publikaciji

Najdeno v: ključnih besedah
Povzetek najdenega: ...2D Imiging, XRF, XANES, synchrotron light...
Ključne besede: 2D Imiging, XRF, XANES, synchrotron light
Objavljeno: 05.09.2019; Ogledov: 137; Prenosov: 0
.pdf Polno besedilo (8,41 MB)

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, izvirni znanstveni članek

Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...antiferomagnetiki, Mn XANES, struktura...
Ključne besede: antiferomagnetiki, Mn XANES, struktura
Objavljeno: 23.10.2019; Ogledov: 159; Prenosov: 0
.pdf Polno besedilo (4,14 MB)

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