New Regularization Method for EXAFS Analysis

Reich, T.; Korshunov, M. E.; Antonova, T. V.; Ageev, A. L.; Moll, Henry; Reich, Tobias

doi:10.1063/1.2644459

Cited by 4 publications

(5 citation statements)

References 6 publications

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“…On this basis, it can be concluded that U(VI) forms two surface species on kaolinite that differ in the amount of water molecules in their coordination environment. Furthermore, from EXAFS measurements of U(VI) sorption onto kaolinite (33) it was concluded that U(VI) forms inner-sphere surface complexes. Moreover, two U-Si/Al interactions were found by EXAFS, which means that these surface complexes are bidentate.…”

Section: Disscusionmentioning

confidence: 99%

U(VI)-Kaolinite Surface Complexation in Absence and Presence of Humic Acid Studied by TRLFS

Křepelová

Brendler

Sachs

et al. 2007

Environ. Sci. Technol.

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Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the U(VI) surface complexes on kaolinite in the presence and absence of humic acid (HA). Two uranyl surface species with fluorescence lifetimes of 5.9 +/- 1.4 and 42.5 +/- 3.4 micros and 4.4 +/- 1.2 and 30.9 +/- 7.2 micros were identified in the binary (U(VI)-kaolinite) and ternary system (U(VI)-HA-kaolinite), respectively. The fluorescence spectra of adsorbed uranyl surface species are described with six and five fluorescence emission bands in the binary and ternary system, respectively. The positions of peak maxima are shifted significantly to higher wavelengths compared to the free uranyl ion in perchlorate medium. HA has no influence on positions of the fluorescence emission bands. In the binary system, both surface species can be attributed to adsorbed bidentate mononuclear surface complexes, which differ in the number of water molecules in their coordination environment. In the ternary system, U(VI) prefers direct binding on kaolinite rather than via HA, but it is sorbed as a uranyl-humate complex. Consequently, the hydration shell of the U(VI) surface complexes is displaced with complexed HA, which is simultaneously distributed between kaolinite particles. Aluminol binding sites are assumed to control the sorption of U(VI) onto kaolinite.

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Section: Disscusionmentioning

confidence: 99%

U(VI)-Kaolinite Surface Complexation in Absence and Presence of Humic Acid Studied by TRLFS

Křepelová

Brendler

Sachs

et al. 2007

Environ. Sci. Technol.

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“…On the other hand, sawteeth are also known to react back on the fast ion population during the sawtooth collapse. Measurements done just before and just after a sawtooth collapse indicate that in some conditions the sawtooth collapse itself is associated with a reduction of the central fast ion population of up to 50% [14][15][16][17][18]. The sawtooth collapse is also believed to reduce the fast ion density in certain parts of phase space.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of fast ions during sawtooth oscillations in the TEXTOR tokamak measured by collective Thomson scattering

et al. 2011

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Experimental investigations of sawteeth interaction with fast ions measured by collective Thomson scattering (CTS) on TEXTOR are presented. Time-resolved measurements of localised 1D fast-ion distribution functions allow us to study fast-ion dynamics during several sawtooth cycles. Sawtooth oscillations interact strongly with the fast ion population in a wide range of plasma parameters. The phase space density for large velocities along the resolved direction oscillates out of phase with the sawtooth oscillation during hydrogen neutral beam injection. These oscillations are interpreted to originate from fast hydrogen ions with energies close to the full injection energy. At lower energies the fast ions in the plasma centre are strongly redistributed. The redistribution of fast ions from deuterium neutral beam injection in the plasma centre is dependent on the resolved direction. We find no evidence of inverted sawteeth outside the inversion radius in the fast ion distribution function.

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“…RDFs reveal the relative positions of different pairs of atoms in a sample, avoiding the a priori reference to a structural model. Results for uranyl adsorption on kaolinite, obtained by conventional fitting [30][31][32][33][34], have independently been confirmed [40] with this approach; yet, it does not resolve the problem of differentiating Al and Si centers.…”

Section: Resultsmentioning

confidence: 54%

“…Recently an alternative regularization method for the analysis of EXAFS results was suggested [40]. Instead of trying to find the best structural model that fits the data, radial distribution functions (RDFs) have been determined directly from EXAFS data [40]. RDFs reveal the relative positions of different pairs of atoms in a sample, avoiding the a priori reference to a structural model.…”

Section: Resultsmentioning

confidence: 99%

“…Also, neighboring elements, like Al or Si, cannot be distinguished as they exhibit similar scattering abilities [12,34]; this holds for aluminol and silanol related sites at alumosilicate surfaces. Recently an alternative regularization method for the analysis of EXAFS results was suggested [40]. Instead of trying to find the best structural model that fits the data, radial distribution functions (RDFs) have been determined directly from EXAFS data [40].…”

Section: Resultsmentioning

confidence: 99%

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Quantum chemical modeling of uranyl adsorption on mineral surfaces

Kremleva

Krüger

Rösch³

2010

Ract

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We overview quantum mechanical simulations that model the adsorption of actinide ions at solvated mineral surfaces. Pertinent examples illustrate the status of this emerging field of computational chemistry. In particular, we describe our own studies on uranyl adsorption on kaolinite. Already the few available results, from applications of density functional methods to cluster models or periodic slab models, show that such calculations are a useful complement to experimental investigations. Detailed information at the atomic level from accurate electronic structure calculations on well defined model systems helps to refine current interpretations of the chemical nature of uranyl adsorption species and to discover new features of these interface systems. Results from quantum mechanical simulations also provide a valuable reference for future experimental investigations.

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New Regularization Method for EXAFS Analysis

Cited by 4 publications

References 6 publications

U(VI)-Kaolinite Surface Complexation in Absence and Presence of Humic Acid Studied by TRLFS

U(VI)-Kaolinite Surface Complexation in Absence and Presence of Humic Acid Studied by TRLFS

Dynamics of fast ions during sawtooth oscillations in the TEXTOR tokamak measured by collective Thomson scattering

Quantum chemical modeling of uranyl adsorption on mineral surfaces

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