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Abstract  

The effects of pH, ionic strength, competing ions and initial metal concentrations on the uptake behavior and mechanism of radioactive Ni(II) onto MnO2 was investigated using a combination of classical macroscopic methods and the extended X-ray absorption fine structure (EXAFS) spectroscopy technique. The results indicated that the uptake of Ni(II) on MnO2 is obviously dependent on pH but independent of ionic strength, which suggested that the uptake of Ni(II) onto MnO2 is attributed to an inner-sphere surface complex rather than an outer-sphere surface complex. EXAFS analysis shows that the hydrated Ni(II) is adsorbed through six-fold coordination with an average Ni–O interatomic distance of 2.04 ± 0.01 Å. It can be inferred from the EXAFS analysis that the inner-sphere surface complex of Ni(II) onto MnO2 is involved in both edge-sharing and corner-sharing linkages. Both the macroscopic uptake data and the molecular level evidence of Ni(II) surface speciation at the MnO2-water interfaces should be factored into better prediction of the bioavailability and mobility of Ni(II) in soil and water environment.

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Abstract  

Structural studies of lanthanide ions (Nd3+≈Lu3+: about 1 mol/l) in the aqueous chloride (HCl: 0≈6 mol/l) and nitrate (HNO3: 0−13 mol/l) solutions were carried out by extended X-ray absorption fine structure (EXAFS). The radial structural functions appeared to be mainly characterized by hydration in both chloride and nitrate systems and coordination of nitrate ion in nitrate systems. These results indicated that nitrate ion forms inner-sphere complex with lanthanide but chloride ion hardly forms one. The quantitative analyses of EXAFS data have revealed that the total coordination numbers of lanthanide ranged from about 9 for light lanthanides to about 8 for heavy lanthanides in all the samples. The bond distances of Ln−O were from about 2.3 to 2.5 Å for Ln−OH2 and from about 2.4 to 2.6 Å for Ln−O2NO. Nitrate ion locates at 0.1 Å longer position than water, it suggested that nitrate ion ligates more weakly than water.

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Abstract  

The reduction of ammonium pertechnetate by sodium borohydride in 0.1 M NaOH/glacial acetic acid has been studied. The reduction products (solids and solutions) have been characterized by UV–Visible spectroscopy, Scanning Electron Microscopy/Energy-dispersive X-ray emission spectroscopy (SEM/EDS), and X-ray absorption fine structure (XAFS) spectroscopy. UV–Visible spectra of the solution, after reduction, exhibit bands at 350 and 500 nm that have been attributed to the formation of polymeric Tc(IV) species. SEM/EDS on the solid (X-ray amorphous) indicates the absence of metallic Tc and the presence of oxygen. EXAFS measurements further indicate that the precipitate exhibits a [Tc(μ-O)2Tc] core structure. XANES is consistent with the formation of Tc(III) and/or Tc(IV). Results infer that reduction of aqueous Tc(VII) by borohydride in the presence of acetic acid does not produce metallic Tc, but a mixture of various oxidation states of Tc near Tc(III) and Tc(IV).

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Frederic Poineau, Charles Yeamans, G. Silva, Gary Cerefice, Alfred Sattelberger, and Kenneth Czerwinski

Abstract  

Uranium mononitride (UN), sesquinitride (U2N3) and dinitride (UN2) were characterized by extended X-Ray absorption fine structure spectroscopy. Analysis on UN indicate the presence of three uranium shells at distances of 3.46(3), 4.89(5) and 6.01(6) Å and a nitrogen shell at a distance of 2.46(2) Å. For U2N3, two absorbing uranium atoms at different crystallographic positions are present in the structure. One of the uranium atoms is surrounded by nitrogen atoms at 2.28(2) Å and by uranium atoms at 3.66(4) and 3.95(4) Å. The second type of uranium atom is surrounded by nitrogen atoms at 2.33(2) and 2.64(3) Å and by uranium atoms at 3.66(4), 3.95(4) and 5.31(5) Å. Results on UN2 indicate two uranium shells at 3.71(4) and 5.32(5) Å and two nitrogen shells at 2.28(2) and 4.34(4) Å. The lattice parameters of UN, U2N3 and UN2 unit cells were respectively determined to be 4.89(5), 10.62(10) and 5.32(5) Å. Those results are well in agreement with those obtained by X-Ray diffraction analysis.

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Abstract  

LIII edge X-ray Absorption Fine Structure (XAFS) spectroscopic study of Eu(III) sorbed on γ-alumina from aqueous solutions of different pH (values ranging from 6 to 8) has been carried out at XAFS beam line of Elettra Synchrotron facility, Italy, in transmission mode. Extended X-ray Absorption Fine Structure spectra of reference compounds, namely, Eu2O3, Eu(OH)3 and Eu-aquo complex in solution, were also measured. The data were analyzed using the IFEFFIT suite of code. XAFS spectra of the sorption samples is dominated by the Eu–O near neighbor co-ordination at distance 2.4 ± 0.1 Å. 8–9 oxygen atoms, coming from both coordinating water molecule and oxygen atoms from alumina surface, surround the Eu(III) in the surface complex. Next near neighbor atoms in all the sorption samples consist of Al at distance ~3.6 and 3.8 Å, which on comparison with literature data indicates towards Eu(III) bidentate binding to apical oxygen of two different alumina octahedra on γ-alumina surface.

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Abstract  

X-ray spectrometric technique has been described to determine the X-ray mass attenuation coefficient, μ/ρ, of X-rays employing HPGe X-ray detector and radioactive sources. The photon intensity is measured by gating the channel of the spectrometer at FWHM/photo peak. Using the technique the “best value” values of μ/ρ were obtained for those thicknesses which lie in the transmission (T) range 0.5 ≥ T ≥ 0.02. Total attenuation cross sections for other elements and lead compounds were measured at photon energies from 17 to 88 keV to study the Bragg’s additivity law near the absorption edge of the lead. The measured values of mass attenuation coefficient values are compared with theoretical values obtained using Winxcom (programme). This study suggests that measured mass attenuation coefficient values at and near absorption edges differ from the theoretical value by about 17–23%.

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Abstract  

The uptake of rare earth elements (REE) by Euglena gracilis cells has been investigated in Fudan University. The remarkable ability to transport REEs to these cell’s compartments had been observed. X-ray absorption fine structure experiments (XAFS) of cerium in Euglena gracilis were performed at Beijing Synchrotron Radiation Facility (BSRF) to directly determine the cerium valence state and coordination structure in situ. Extended X-ray absorption fine structure (EXAFS) derived calculation showed that cerium was surrounded by 8 N atoms with bond length of 0.258 nm. Combining with other measurements, it may indicate that most likely REEs are mainly located in chlorophyll molecules.

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Abstract  

Complexes of adenosine and related compounds (adenosine-5’-monophosphate, adenosine-5’-triphosphate and pyridoxal-5-phosphate) with Bu2SnO and/or BuSnCl2 were prepared in the solid state. The compositions of the complexes were determined by standard analytical methods. It was found that the complexes contain the organotin(IV) moiety and the ligand in a ratio of 1:1. The FT-IR spectra demonstrated that Bu2SnO reacts with the D-ribose moiety of the ligands, while Bu2SnCl2 is coordinated to the deprotonated phosphate group. The basic part of the ligands does not participate directly in complex formation. Comparison of the experimental Mössbauer Δ (quadrupole splitting) values with those calculated on the basis of the pqs concept revealed that the organotin(IV) moiety has Tbp and in some cases also Th geometry. The adenosine complex contains the organotin(IV) cation in two different surroundings (Tbp and Th). The local structures of the complexes were determined by means of EXAFS measurements. At the same time a number of organotin(IV) complexes containing different organo moieties of calf thymus DNA were also prepared. Similarly as above, EXAFS data were obtained for these compounds and analyzed by using multishell models up to 300 pm. These results are the first structural data (bond lengths) on complexes formed with organotin(IV)-DNA and related compounds.

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Abstract  

Thermal and structural changes of lanthanum hexacyanocobaltate(III) pentahydrate, La[Co(CN)6]⋅5H2O were investigated by means of thermal analysis, visible electronic spectra, IR, powder X-ray diffraction, EXAFS and TG-MS. The dehydration of La[Co(CN)6]⋅5H2O proceeded reversibly through three steps and steps corresponded to the losses of H2O, 3H2O and H2O, and the enthalpy changes for these steps were 51.3, 211.0 and 38.7 kJ mol−1, respectively. After the dehydration, the colour of the anhydride changed from white to blue around 290C and an abrupt mass loss occurred at 350C. The colour change seems to be attributable to the change of coordination geometry around the Co ions from an octahedral structure to a tetrahedral one. LnCoO3 was obtained as a final product by heating the sample to 1000C.

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Abstract  

A number of dibutyltin(IV) complexes of polyhydroxyalkyl carboxylic acids (O donor atoms) and amino acids (O,N donor atoms) were prepared in the solid state. The binding sites of the ligands were determined by means of FT-IR, Raman and 13C NMR spectroscopy. Partial quadrupole splitting calculations were utilized to determine the coordination geometry around the Sn(IV) centre by means of Mössbauer measurements. The results showed that in the solid state oligomeric complexes are formed, with the -COO- groups as bridges between the organometallic cations. The {Sn} atoms are mostly in trigonal bipyramidal surroundings. The Sn-O and Sn-C bond distances were determined by EXAFS measurements to be 207-234 and 295 pm, respectively. Evaluation of the pH-metric and NMR titration curves in Me2Sn(IV)-D-gluconic acid system revealed that the equilibria in aqueous solution are fairly complicated. In acidic solution, the formation of 1 : 1 and 1 : 2 -COO- coordinated species predominate, but deprotonation of the alcoholic -OH groups also starts at very low pH. In the pH range 5-9, NMR provides experimental evidence of ligand-exchange reactions without pH-metrically detectable proton release. In alkaline solution, further deprotonation processes occur, resulting in either alkoxo or mixed hydroxo complexes. The carboxylate coordination is expected for the amino acid ligands but the shift of the νN-H stretching vibrations in the FT-IR spectra demonstrated that the ammine group also binds to the metal ion in the solid Bu2Sn(IV)complexes.

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