scholarly journals Changes in u(VI) SPeciation Upon Sorption onto Montmorillonite from Aqueous and Organic Solutions

1991 ◽  
Vol 257 ◽  
Author(s):  
Catherine Chisholm-Brause ◽  
Steven D. Conradson ◽  
P. Gary Eller ◽  
David E. Morris
Keyword(s):  
Oxidation State ◽  
Aqueous Systems ◽  
X Ray ◽  
Ph Values ◽  
Uranium Oxidation ◽  
Organic Solutions ◽  
X Ray Absorption ◽  
Hydrolysis Of ◽  
Uranium Species ◽  
Lines Of Evidence

ABSTRACTThe speciation of UO22+ and UO22+/ TBP mixtures has been investigated in solution and intercalated with the reference smectite clay SAz-1 using x-ray absorption, Raman, andluminescence spectroscopies. Neither aquated UO22+ nor its TBP complex undergoes any detectable changes in uranium oxidation state on intercalation. Further, at the pH values employed in this work, there is no evidence for hydrolysis of the uranium species to generate dimeric or higher order uranium oligomers. However, we do find indications that the structures of the solution complexes are altered on intercalation, particularly for the UO22+TBP system and for more dilute UO22+/aqueous systems. In addition, several lines of evidence suggest that, at the loading levels used in this study, the uranyl species is interacting with two or more spectroscopically distinguishable sites on SAz-1.

Characterization and Dissolution of ZrTh3UO10 and Th3UO8 Ceramics

2002 ◽  
Vol 713 ◽  
Author(s):  
Gini Curran ◽  
Yoann Sevestre ◽  
Wendy Rattray ◽  
Patrick G. Allen ◽  
Ken R. Czerwinski
Keyword(s):  
Oxidation State ◽  
X Ray Diffraction ◽  
X Ray ◽  
Uranium Oxidation ◽  
Absorption Studies ◽  
The Matrix ◽  
Microscopy Techniques ◽  
Long Term Behavior ◽  
Electron Energy Loss ◽  
X Ray Absorption

ABSTRACTThoria-urania-zirconia ceramics were studied in order to investigate the long-term behavior of potential thorium fuels in a repository environment. The ceramics were prepared by coprecipitation of the metal salts. Zirconia was added to determine if further stabilization against dissolution of the thoria-urania system could be achieved. In addition, 0.5 wt% MgO was added to some samples to increase stability and density. The inclusion of Zr in the ceramics did not dramatically decrease the leaching of thorium from the matrix.Material properties of the ceramic were analyzed using electron microscopy techniques such as Energy Dispersive X-ray (EDX) analysis and Electron Energy Loss Spectroscopy (EELS). X-ray diffraction and synchrotron-based x-ray absorption studies including extended xray fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES) were also used to reveal elements of the phase structure and chemistry of the ceramics. X-ray diffraction (XRD) and EDX show that these ceramics separate into a zirconium-based phase and an actinide-based phase with low mutual affinity of thorium and zirconium, as well as partial solubilization of uranium in zirconium. The comparison of EELS spectra collected for the ceramics with spectra collected for UO2 and U3O8 reference materials also allow the assessment of uranium oxidation state independently in the two separate phases. Assessment of the bulk oxidation state using XANES correlated well with the EELS analysis. Interatomic distances and the bulk crystal structure were determined using EXAFS.

Reduction of antimony by nano-particulate magnetite and mackinawite

2008 ◽  
Vol 72 (1) ◽  
pp. 185-189 ◽  
Author(s):  
R. Kirsch ◽  
A. C. Scheinost ◽  
A. Rossberg ◽  
D. Banerjee ◽  
L. Charlet
Keyword(s):  
Oxidation State ◽  
Photoelectron Spectroscopy ◽  
Redox Processes ◽  
Environmental Behaviour ◽  
X Ray ◽  
Ph Values ◽  
Wide Ph Range ◽  
Ph Range ◽  
X Ray Absorption

AbstractThe speciation of antimony is strongly influenced by its oxidation state (V, III, 0, —III). Redox processes under anaerobic groundwater conditions may therefore greatly alter the environmental behaviour of Sb. Employing X-ray absorption and photoelectron spectroscopy, we show here that Sb(V) is reduced to Sb(III) by magnetite and mackinawite, two ubiquitous Fe(II)-containing minerals, while Sb(III) is not reduced further. At the surface of magnetite, Sb(III) forms a highly symmetrical sorption complex at the position otherwise occupied by tetrahedral Fe(III). The Sb(V) reduction increases with pH, and at pH values >6.5 Sb(V) is completely reduced to Sb(III) within 30 days. In contrast, at the mackinawite surface, Sb(V) is completely reduced across a wide pH range and within 1 h. The Sb(V) reduction proceeds solely by oxidation of surface Fe(II), while the oxidation state of sulphide is conserved. Independent of whether Sb(V) or Sb(III) was added, an amorphous or nano-particulate SbS3-like solid formed.

scholarly journals Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 116
Author(s):  
Gian Luca Chiarello ◽  
Ye Lu ◽  
Miren Agote-Arán ◽  
Riccardo Pellegrini ◽  
Davide Ferri
Keyword(s):  
Particle Size ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Oxidation State ◽  
Diffuse Reflectance ◽  
X Ray ◽  
Spectral Changes ◽  
Diffuse Reflectance Infrared ◽  
X Ray Absorption ◽  
Reversible Reduction

Infrared spectroscopy is typically not used to establish the oxidation state of metal-based catalysts. In this work, we show that the baseline of spectra collected in diffuse reflectance mode of a series of Pd/Al2O3 samples of increasing Pd content varies significantly and reversibly under alternate pulses of CO or H2 and O2. Moreover, these baseline changes are proportional to the Pd content in Pd/Al2O3 samples exhibiting comparable Pd particle size. Similar measurements by X-ray absorption spectroscopy on a different 2 wt.% Pd/Al2O3 confirm that the baseline changes reflect the reversible reduction-oxidation of Pd. Hence, we demonstrate that changes in oxidation state of metal-based catalysts can be determined using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and that this behavior is part of the spectral changes that are returned by experiments under operando conditions.

Preparation and structural analysis of (±)-threo-ritalinic acid

2013 ◽  
Vol 69 (11) ◽  
pp. 1225-1228 ◽  
Author(s):  
Sara Wyss ◽  
Irmgard A. Werner ◽  
W. Bernd Schweizer ◽  
Simon M. Ametamey ◽  
Selena Milicevic Sephton
Keyword(s):  
Methyl Ester ◽  
Free Acid ◽  
Nmr Analysis ◽  
Intermolecular Hydrogen Bonds ◽  
X Ray ◽  
X Ray Crystallography ◽  
Ph Values ◽  
Ritalinic Acid ◽  
Methyl Phenidate ◽  
Hydrolysis Of

Hydrolysis of the methyl ester (±)-threo-methyl phenidate afforded the free acid in 40% yield,viz.(±)-threo-ritalinic acid, C13H17NO2. Hydrolysis and subsequent crystallization were accomplished at pH values between 5 and 7 to yield colourless prisms which were analysed by X-ray crystallography. Crystals of (±)-threo-ritalinic acid belong to theP21/nspace group and form intermolecular hydrogen bonds. An antiperiplanar disposition of the H atoms of the (HOOC—)CH—CHpygroup (py is pyridine) was found in both the solid (diffraction analysis) and solution state (NMR analysis). It was also determined that (±)-threo-ritalinic acid conforms to the minimization of negativegauche+–gauche−interactions.

scholarly journals Magnetic spectroscopy of nanoparticulate greigite, Fe3S4

2017 ◽  
Vol 81 (4) ◽  
pp. 857-872 ◽  
Author(s):  
Richard A. D. Pattrick ◽  
Victoria S. Coker ◽  
Masood Akhtar ◽  
M. Azad Malik ◽  
Edward Lewis ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Oxidation State ◽  
Magnetic Circular Dichroism ◽  
Covalent Character ◽  
X Ray ◽  
Positive Feature ◽  
A Site ◽  
Intermediate Oxidation ◽  
X Ray Absorption ◽  
Ferrite Spinel

AbstractSynthesis of Ni and Zn substituted nano-greigite, Fe3S4, is achieved from single source diethyldithiocarbamato precursor compounds, producing particles typically 50–100 nm in diameter with plate-like pseudohexagonal morphologies. Up to 12 wt.% Ni is incorporated into the greigite structure, and there is evidence that Zn is also incorporated but Co is not substituted into the lattice. The FeL3X-ray absorption spectra for these materials have a narrow single peak at 707.7 eV and the resulting main X-ray magnetic circular dichroism (XMCD) has the same sign at 708.75 eV. All XMCD spectra also have a broad positive feature at 711 eV, a characteristic of covalent mixing. The greigite XMCD spectra contrast with the three clearly defined XMCD site specific peaks found in the ferrite spinel, magnetite. The FeL2,3X-ray absorption spectra and XMCD spectra of the greigite reflect and reveal the high conductivity of greigite and the very strong covalency of the Fe–S bonding. The electron hopping between Fe3+and Fe2+on octahedral sites results in an intermediate oxidation state of the Fe in the Ohsite of Fe2.5+producing an effective formula of [Fe3+↑]A-site[2Fe2.5+↓]B-siteS42–]. The NiL2,3X-ray absorption spectra and XMCD reveal substitution on the Ohsite with a strongly covalent character and an oxidation state <Ni1.5+in a representative formula [Fe3+↑]A[[(2 – x)Fe2.5+↓][Nix1.5+]]BS42–.

scholarly journals Probing the variability in oxidation states of magnetite nanoparticles by single-particle spectroscopy

2018 ◽  
Vol 6 (4) ◽  
pp. 875-882 ◽  
Author(s):  
A. Fraile Rodríguez ◽  
C. Moya ◽  
M. Escoda-Torroella ◽  
A. Romero ◽  
A. Labarta ◽  
...  
Keyword(s):  
Oxidation State ◽  
Absorption Spectroscopy ◽  
Magnetite Nanoparticles ◽  
Single Particle ◽  
Cation Distribution ◽  
Oxidation States ◽  
Magnetic Response ◽  
X Ray ◽  
Single Particle Spectroscopy ◽  
X Ray Absorption

Single-particle X-ray absorption spectroscopy reveals that the oxidation state and cation distribution of individual magnetite nanoparticles may be largely heterogeneous even when the macroscopic structural and magnetic response of the ensembles is uniform.

Insights into sulfur poisoning and regeneration of Cu-SSZ-13 catalysts: In situ Cu and S K-edge XAS studies

2021 ◽  
Author(s):  
Vitaly Mesilov ◽  
Sandra Dahlin ◽  
Susanna Liljegren Bergman ◽  
Peter Sams Hammershøi ◽  
Shibo Xi ◽  
...  
Keyword(s):  
Selective Catalytic Reduction ◽  
Oxidation State ◽  
Absorption Spectroscopy ◽  
Catalytic Reduction ◽  
Sulfur Poisoning ◽  
X Ray ◽  
Scr Catalysts ◽  
X Ray Absorption

In situ Cu and S K-edge X-ray absorption spectroscopy (XAS) was used for the investigation of sulfur-poisoned and regenerated Cu-SSZ-13 selective catalytic reduction (SCR) catalysts. Sulfur in the oxidation state...

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