Oxygen Surrounding Research Articles

In-Situ Soft X-ray Absorption of Over-exchanged Fe/ZSM5

In-situ soft X-ray absorption spectroscopy (XAS) has been applied to study the iron redox behavior in over-exchanged Fe/ZSM5. The Fe L2,3 XAS and O K spectral shapes of the Fe/ZSM5 surface have been measured during heat treatments and reduction/oxidation cycles. Charge-transfer multiplet calculations provide a detailed understanding of the L2,3 spectra of iron in Fe/ZSM5. The oxidized form of Fe/ZSM5 contains FeIII ions in an octahedral surrounding, with a total crystal field splitting of ∼1.0 eV. This value is significantly smaller than that for Fe2O3, which is indicative of a much weaker Fe−O bonding. The reduced form of Fe/ZSM5 has FeII ions in a tetrahedral oxygen surrounding. The Fe L2,3 spectra show that iron in calcined Fe/ZSM5 is reduced in 15 min to an average valence state of 2.65, under 10 mbar of pure helium at room temperature. This value has a relative uncertainty on the order of 0.01. Heating in helium up to 350 °C under the same pressure further reduces the iron valence to 2.15. The oxygen spectra show that the autoreduction is accompanied by a loss of molecular oxygen and water. Reoxidation with 5% O2 in helium yields a valence of >2.90 after 10 min.

Crystal Structure of U(VI) Peroxo Complex with Triphenylphosphine Oxide {(UO2)2O2[OP(C6H5)3]6}(ClO4)2

The peroxo complex {(UO2)2O2[OP(C6H5)3]6}(ClO4)2 was synthesized, and its crystal structure was determined [triclinic unit cell: a = 10.523(2), b = 16.242(3), c = 16.978(3) A, α = 65.79(3)°, β = 85.06(3)°, γ = 77.14(3)°, space group P-1, Z = 1, V = 2580.1(9) A3, d c a l c = 2.789 g cm- 3; CAD4, MoK α, graphite monochromator, direct method, R 1 = 0.0368 for 3115 observed reflections, wR 2 = 0.1107 for 4403 unique reflections, 622 refined parameters]. {(UO2)2O2[OP(C6H5)3]6}(ClO4)2 has monomeric structure and consists of the complex cations {(UO2)2O2[OP(C6H5)3]6}2 + and ClO4 - anions. The uranium atom has a pentagonal-bipyramidal oxygen surrounding (CN 7). Uranyl groups UO2 2 + are linear and symmetrical, the U = O bond lengths are 1.780(8) and 1.787(8) A, the O(1) = U = O(2) bond angles are 178.7(4) A. The equatorial planes of bipyramids are formed by oxygen atoms of three TPPO molecules [U-OT P P O 2.352(8)-2.368(7) A, average 2.362 A] and peroxo group O2 2 - [U-Op e r 2.285(8) and 2.323(8) A, average 2.305 A]. Two pentagonal bipyramids sharing the common edge O(3)-O(3)(a) form the centrosymmetrical peroxo-bridged diuranyl complex {(UO2)2O2[OP(C6H5)3]6}2 + with the [UO2O2UO2]2 + core. The length of the O(3)-O(3)( 9a ) edge is 1.426(15) A.

Crystal Structure and Electronic Absorption Spectrum of Double Neptunium(V) Phthalate Co(NH3)6NpO2[(OOC)2C6H4]2·2H2O

Single crystals of Co(NH3)6NpO2[(OOC)2C6H4]2·2H2O were grown. The crystal structure of this compound [monoclinic cell: a = 7.748(2), b = 23.051(5), c = 14.608(3) A, β = 96.21(3)°, space group P21/c, Z = 4, V = 2593.7(9) A3, dcalc = 2.034 g cm-3, CAD4 automatic diffractometer, MoKα, graphite monochromator, R1 = 0.041 for all 3567 reflections observed, wR2 = 0.1344 for all 4445 unique reflections, 325 refined parameters] was studied. The structure consists of infinite anionic chains {NpO2[(OOC)2C6H4]2} n 3 n -, [Co(NH3)6]3+ cations, and molecules of crystallization water. Neptunium(V) atom is in pentagonal-bipyramidal oxygen surrounding (CN 7); the neptunyl(V) group is linear and symmetrical; the Np = O bond lengths are 1.830(6) and 1.833(5)A, the O = Np = O angle is 176.4(2)°. The equatorial plane of the bipyramid is formed by five oxygen atoms of phthalate anions. The Np-Oeq bond length correlates with the denticity of the phthalate anions. Two types of phthalate anions are localized in the structure. The first tridentate ligand is a bridge between Np(V) atoms in the chains. The second ligand is coordinated to Np in the bidentate fashion to form NpOCCCCO seven-membered chelate ring. The cation [Co(NH3)6]3+ has an octahedral structure. The average Co-N distance in the octahedron is 1.961 A the N-Co-N bond angles are close to 90°. Two water molecules along with [Co(NH3)6]3+ cations are located between the anionic chains {NpO2[(OOC)2C6H4]2} n 3 n -. The chains are additionally bonded along the Z-axis of the crystal by Ow-H···O hydrogen bonds.

Microstructure study of amorphous vanadium oxide films

Conversion films of vanadium oxides are potentiodynamically generated on vanadium in acetate electrolyte systems at high voltages. The microstructure of the about 5 μm thin anodic films is investigated. X-ray diffraction and transmission electron microscopy indicate the films are complete amorphous. X-ray photoelectron spectroscopy (XPS) measurements show V 2p 3/2 binding energies of mixed valance vanadium sub oxides. Electron spin resonance (ESR) experiments on isolated films at 130 K point to paramagnetic V 4+ centers in a disordered octahedral oxygen surrounding.

Superoxide production by phagocytosing macrophages in relation to the intracellular distribution of oxygen.

We simultaneously measured the concentration of oxygen ([O2]) within the phagosomal and extracellular compartments of macrophages. By combining electron paramagnetic resonance (EPR) oximetry techniques with that of spin-trapping, we found that a significant difference in oxygen concentration ([O2]) exists between these two compartments and we were able to monitor (1) how [O2] in the extracellular compartment and the rate of mitochondrial consumption affected this difference in [O2], and (2) to what extent this gradient of [O2] influenced production of reactive oxygen species by phagosomes. Under conditions where the [O2] in the inflowing gas was high (210 microM; air), the [O2] in the extracellular and phagosomal compartments was 180 and 141 microM, respectively. This was sufficient to maintain maximum superoxide production in these cells. When extracellular [O2] was reduced to 84 or 36 microM, the [O2] in phagosomes within the cells (31.7 and 7.7 microM, respectively) was too low to maintain superoxide production by the NADPH-oxidase system within the phagosomes. The [O2] in the extracellular compartments of these samples, however, was always sufficient to maintain superoxide production by phagosomes at the cell surface. Our findings suggest that the distribution of oxygen surrounding and within macrophages can influence their ability to perform microbicidal and tumoricidal functions, even at an [O2] in the media that appears to be adequate.

Nanocomposite materials consisting of alternating layers of molybdenum disulfide and cobalt or nickel hydroxides: Magnetic characterization

Magnetization measurements were performed from 5 to 300 K on nanocomposite compounds obtained by precipitation of MoS 2 single-layer dispersion in the presence of Co 2+ or Ni 2+ ions. Ni(II) and high spin Co(II) were evidenced, both in octahedral oxygen surrounding. From similarity of their temperature magnetic behavior with that of lamellar references Ni(OH) 2 and β-Co(OH) 2 powders, it can be inferred that the nanocomposites contain 2D nickel or cobalt hydroxide species. The low temperature magnetic behavior is discussed on the basis of dimensionality and finite particle size effects.

The "In Situ" Research of the Synthesis of NiMoO4

The formation of the crystal structure of the NiMoO4 high temperature phase the solid phase reaction NiO+α-MoO3→β-NiMoO4 at 600 C has been in situ studied with the high temperature synchrotron technique. We have performed the measurements of the Extended X-ray Absorption Fine Structure (EXAFS) and the X-ray Absorption Near Edge Structure (XANES) at the K-edge of Ni atom during the -niMoO4synthesis. The analysis of the XANES data and the Fourier transformants of the EXAFS data has led us to the conclusion that at the initial stage of synthesis the nearest oxygen surrounding of Ni atoms the final production reaction has got an unique geometry that differs from the octahedral oxygen surrounding of Ni atoms the both structures of NiO and β-NiMoO4. At the initial stage of the β-NiMoO4 synthesis there is not the final product of the synthesis, but the formation of the β-NiMoO4 crystal structure takes place essentially later, contrary to how it has been considered so far. We have concluded that at the original stage of the β-NiMoO4 synthesis the some intermediate phase is formed that is characterized with the low concentration of nickel and the low symmetrical geometry for the nearest oxygen surrounding of Ni atoms.

Awaxs study of amorphous WO3 and WO3 · nH2O

Anomalous Wide Angle X-Ray Scattering (AWAXS) has been applied to glassy bulk WO3. In this system the partial distribution of pairs WW and WO may be reliably extracted. Glasses have been prepared by non-reactive grinding from both the metastable pyrochlore type structure and from the hydrates WO3· nH2O. A weighted differential analysis has been developed, leading to the knowledge of the oxygen surrounding and to the extraction of the partial WW first correlations. The influence of water content on the octahedra's network in the amorphous states is analyzed and the medium range order are considered in the framework of hexagonal, pyrochlore and ReO3 type structures.

Nonstoichiometry in the perovskite-type oxides: an evolution from the classical Schottky-Wagner model to the recent high T c superconductors

It will be shown on hand of many examples that the oxygen surrounding of the transition elements in the defect perovskite-type oxides and derived compounds depends on the electronic configuration, the d-electron localization and the ability to disproportionate. Possibilities of A-cation (and eventually B-cation) ordering or of oxygen excess will also be mentioned. Superconductivity will be presented as a logical property closely related to the crystal structure of the involved materials.

Luminescence spectra of non-stoichiometric aluminates doped with Eu 2+ ions

Luminescence measurements indicate that in Al 2O 3-deficient aluminate phosphors with the magnetoplumbit crystal structure, aprt of the Eu 2+ activator ions occur in β-alumina-type oxygen surroundings rather than in magnetoplumbite-type oxygen surroundings. In Al 2O 3-rich β-alumina type aluminate phosphors part of the Eu 2+ ions has a magnetoplumbite-type oxygen surrounding.