R. Klenze

Institute for Transuranium Elements, Carlsruhe, Baden-Württemberg, Germany

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Publications (50)87.83 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Density functional theory calculations and classical Monte Carlo simulations are applied to study the behavior of water in contact with a hydroxylated corundum (001) surface. Using DFT with periodic boundary conditions at $T=0$ K, we systematically study the influence of the number of water molecules on the surface geometry and on the structure of the contact water layer. Only little effect of the thickness of the water layer on the geometry of the surface hydroxyl groups is observed. On the other hand, the molecules in the second layer have strong influence on the arrangement of water molecules in direct contact with the solid surface. In order to mimic macroscopic systems at room temperature, we perform inhomogeneous MC simulations of model corundum surface in contact with water phase modeled by SPC/E model. The water molecules are clasified according to their hydrogen-bonded partners into several groups. It is found that the preferential orientation of interfacial water molecules is primarily determined by the type of their hydrogen bonding. The hydroxyl groups at the corundum surface can serve as hydrogen bond donor or acceptor, depending on their orientation. No surface hydroxyls are found to coordinate two water molecules at the same time. On the other hand, water molecules coordinated by two different surface groups appear in MC simulations.
    Langmuir 02/2014; · 4.19 Impact Factor
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    ABSTRACT: The formation of hydrated CmF2+ and CmF2+ species in aqueous solutions are studied in the temperature range of 20−90 °C at different fluoride concentrations and at constant ionic strength as well as at constant fluoride concentration and different ionic strengths by means of time-resolved laser fluorescence spectroscopy (TRLFS). The molar fractions of the Cm3+ aqua ion, CmF2+, and CmF2+ species are determined by peak deconvolution of the emission spectra. An increase of the mono- and difluoro complexes is observed with increasing fluoride concentration and/or increasing temperature. Using the specific ion interaction theory (SIT), the thermodynamic stability constants log K10 (CmF2+) and log K20 (CmF2+) as well as the values of Δε1 and Δε2 are determined as a function of temperature. The log K10 values increase from 3.56 ± 0.07 to 3.98 ± 0.06 and the log K20 values increase from 2.20 ± 0.84 to 3.34 ± 0.21 with increasing temperature from 20 to 90 °C. The value of Δε1 determined at 25 °C is in good agreement with literature data and shows a negligible temperature dependency in the studied temperature range. The value of Δε2 also shows only a moderate variation in the studied temperature range. The thermodynamic standard state data (ΔrHm0, ΔrSm0, ΔrGm0) are determined from the temperature dependence of the equilibrium constants at Im = 0 using the integrated Van’t Hoff equation. The fluorescence lifetime of the 6D′7/2(Cm3+) state is found to be constant at 63 ± 5 μs with increasing fluoride concentration. A model based on density functional theory (DFT) calculations is introduced to account for the additional quenching occurring through the near second sphere waters in the [Cm(H2O)8F]2+(H2O)18 complex.
    The Journal of Physical Chemistry B 11/2010; 114(47):15626-34. · 3.61 Impact Factor
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    ABSTRACT: In the present study, the sorption of europium and lutetium onto titanium dioxide from aqueous solutions is presented, as a function of pH, ionic strength and concentration. An acid base model for the titanium dioxide surface was determined from potentiometric titrations and zeta-potential measurements. The common intersection point of potentiometric titrations coincided with the isoelectric point from electrokinetic experiments, resulting in a pristine point of zero charge of about 6.1. The experimental data were in agreement with previously published results and a previously published MUSIC-type model was used as the basis to model the acid-base behavior. Comparison of europium and lutetium showed no difference in the adsorption behavior. Furthermore, no difference was observed both in uptake and spectroscopic studies whether carbonate was absent or present. The absence of a noticeable effect of the ionic strength on the adsorption behavior was indicative of strong binding. EXAFS revealed rough conservation of the coordination with 9-8 water and surface hydroxyl groups upon sorption. EXAFS results suggested the existence of different metal-oxygen distances, more varied than that observed for the respective aquo complex and thus indicative for inner-sphere surface complexation. A clear differentiation of surface complexation denticity was not possible based on spectroscopic data. A multisite surface complexation model approach was applied by assuming monodentate and multidentate binding to describe the trivalent metal uptake data. It is conceivable that mono- and multidentate species contribute to lanthanide sorption to titanium dioxide. In other words a distribution of states occurs in cation surface complexation reactions.
    Journal of Colloid and Interface Science 10/2010; 350(2):551-61. · 3.17 Impact Factor
  • Angewandte Chemie International Edition 08/2010; 49(36):6343-7. · 13.73 Impact Factor
  • Reinhardt Klenze, Thomas Fanghänel
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    ABSTRACT: Die Mobilität von Actiniden in aquatischen Systemen lässt sich auf der Basis von Prozessverständnis und fundierten thermondynamischem Daten wesentlich zuverlässiger beschreiben als bislang mit rein phänomenologischen Ansätzen. Berücksichtigt man das geochemische Verhalten der Actiniden, werden belastbare Prognosen zur Langzeitsicherheit der Endlagerung nuklearer Abfälle in einer tiefen geologischen Formation möglich.
    Nachrichten aus der Chemie 05/2010; 53(10):1004 - 1009. · 0.20 Impact Factor
  • Angewandte Chemie. 01/2010; 122(36):6367-6367.
  • ChemInform 01/2010; 41(26).
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    ABSTRACT: For the reliable long-term modeling of the actinide migration in geological formations, the adsorption/desorption properties and the reactivity of mineral surfaces must be understood at the molecular level. The adsorption of radioisotopes at mineral surfaces of the aquifer is an important process that leads to the retention of contaminants such as radionuclides. Their transport by the ground water is either retarded or even completely inhibited by the presence of such a surface. Accordingly, this subject is of main importance for the safety assessment of nuclear waste repositories. As part of a joint theoretical/experimental effort, the interaction of water with the corundum (0001) surface is studied using several theoretical methods (Moller-Plesset perturbation theory, coupled cluster singles doubles with triplet corrections, as well as density functional theory). We focus in this study on the determination of the bond lengths and tilt angles of the surface OH species and their respective vibrational frequencies. The theoretical results are confirmed by subsequent simulation of the interface selective nonlinear sum frequency spectra. The excellent agreement of the simulated with the experimental spectra allows an assignment of the observed peaks in the sum frequency spectra of the water/corundum (0001) interface on the basis of our theoretical data. In this theoretical study we are able to give a unique interpretation of the observed sum frequency spectra of the water/corundum (0001) interface.
    The Journal of Chemical Physics 03/2009; 130(6):064702. · 3.16 Impact Factor
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    ABSTRACT: Previous systematic C 1s-NEXAFS studies carried out for humic acid (HA) loaded with polyvalent metal cations (Mn+) reveal spectral features which were postulated to result from metal ion complexation: a strong decrease of the C 1s (COO−) → π*CO transition intensity and the appearance of a new absorption feature at slightly lower energy adjacent to the carboxyl resonance. Although spectroscopic results for the Mn+-PAA (polyacrylic acid) system (selected as model for structurally ill-defined HA) reveal the same spectral features, evidence by an independent approach for interpretation of these features is desirable. It is well established that quantum chemical calculations are capable of reproducing transition features in C 1s core excitation spectra of small organic molecules, e.g., acetate, which is chosen here as a fragment containing the complexing group to model the macromolecular HA and PAA systems. In this study, the RI-ADC(2) approach, as implemented in the TURBOMOLE program package, is applied to calculate vertical core excitation spectra of various metal acetates and the acetate anion. An energy shift (Δf) between the C 1s (COO−) → π*CO transition of the acetate anion and various metal cation acetates is established. Calculated shifts are very similar to the experimentally observed values for the energy difference between the C 1s (COO−) → π*CO peak and the absorption feature appearing after metal ion complexation in Mn+-PAA/PAA. According to our computations, structural changes of the acetate complexes (e.g., the O–C–O bond angle) compared to the free acetate anion are predominantly responsible for the spectral changes observed upon metal ion complexation.
    Journal of Electron Spectroscopy and Related Phenomena. 01/2009;
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    ABSTRACT: Humic acids (HA) are potentially important in binding traces of actinides or lanthanides, thus affecting their transport in aquatic systems. Eu(III) induced HA colloid aggregation has been investigated by a combination of Scanning Transmission X-ray Microscopy (STXM) and Laser Scanning Luminescence Microscopy (LSLM). Both methods reveal the same aggregate morphology - optically dense zones embedded in a matrix of less dense material observed by STXM correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. From these comparative measurements we infer the enrichment of Eu(III) cations in the optically dense zones. These areas also exhibit a C 1s-NEXAFS signature strongly differing from the signal extracted from the less dense areas. Spectral filtering of Eu(III) luminescence lines corresponding to valence transitions affected by organic acid complexation indicates that Eu(III) cations are more strongly bound in the dense zones.
    Journal of Physics Conference Series 01/2009; 186(1).
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    ABSTRACT: Fluorescence emission and excitation spectra of [Cm(H2O)9 ]3+ ions with regular and distorted tricapped trigonal prismatic coordination geometries are reported at temperatures of 293 and 20 K. The Cm3+ impurities are incorporated into the hexagonal crystal lattices of the isotypic [M(H2O)9](CF3SO3)3 (M) La (1), Y (2)), and [Y(H2O) ](C2H5SO4)3 (3) salts, and into the low symmetry [La(H2O)9]Cl3·15-crown-5·H2O (4) salt. Small but significant structural differences in the MO9 polyhedra influence the crystal-field levels of the 8 S′ 7/2 ground-state and the 6 D′ 7/2 excited-state multiplets. Thus, the total 6 D′ 7/2 splitting is smaller in 1-3 (376-393 cm-1) than in 4 (430 cm-1), which explains the marked blue shifts of the emission spectra of 1-3 to those of 4 and Cm 3+ (aq) at 293 K. The transitions between the ground state and the two lowest crystal-field levels of the 6 D′ 7/2 multiplets in 1-3 give rise to narrow fluorescence lines at the emitting level at 20 K, resolving the crystal-field levels of the ground state as sharp and narrowly spaced lines. The total ground-state splittings in 1 (8.0 cm-1), 2 (6.0 cm-1), and 3 (7.5 cm-1) are about three to four times larger than those for Cm3+ in LaCl3 (2.0 cm-1), but four to six times smaller than those for Cm3+ in [Y(H2O)8]Cl3·15-crown-5 (35 cm-1). Inhomogeneous line broadening prevents resolving the ground multiplet levels in 4. Vibronic side bands associated with the 8S′ 7/2 -6D′ 7/2 transition are observed in the low temperature emission and excitation spectra. The intensities of these side bands are <1% of the parent electronic transition, the stronger ones being located below ∼400 cm-1 and correspond to various CmO9 skeletal modes. The luminescence lifetimes in 1-4 are between 63 and 74 µs.
    The Journal of Physical Chemistry C 01/2009; 113:449-458. · 4.81 Impact Factor
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    ABSTRACT: The formation of aqueous Cm(III) nitrate com-plexes is studied in the temperature range from 5 to 200 °C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex forma-tion is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H2O. The mono-and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (ΔrH°m, ΔrS°m , ΔrG°m, ΔrC°p,m) are determined from the temperature dependence of the equilibrium constants at I = 0. The equilibrium constants up to 75 °C are well described by the Van't Hoff equation (ΔrH°m independent of T and ΔrC°p,m = 0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (ΔrC°p,m).
    Radiochimica Acta 01/2009; 97:385-393. · 1.37 Impact Factor
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    ABSTRACT: By employing the nonlinear optical, interface selective experiment of sum frequency spectroscopy together with independent ab initio and density functional theory calculations, we determine the functional species of a corundum (001) surface: doubly coordinated OH groups which differ in their bond tilt angles. The interaction of the functional species with the adjacent water molecules is also observed. In a large pH range around the point of zero charge, the interaction is not controlled electrostatically but by hydrogen bonding. The functional species' tilt angles are crucial parameters, determining whether the species act as hydrogen bond donors or acceptors.
    Langmuir 12/2008; 24(23):13434-9. · 4.19 Impact Factor
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    ABSTRACT: Three samples of calcite homogeneously doped with Eu(3+) were synthesized in a mixed-flow reactor. By means of selective excitation of the 5D0-->7F0 transition at low temperatures (T<20 K), three different Eu(3+) species (species A, B, and C, respectively) could be discriminated. For each one, the emission spectrum and lifetime were obtained after selective excitation of the single species. On the basis of these data, species C could be identified as Eu(3+) incorporated into the calcite lattice on the (nearly) octahedral Ca(2+) site. Species B was also identified as Eu(3+) incorporated into the calcite lattice, but the ligand field shows a much weaker symmetry. Species A, however, is not incorporated into the crystal's bulk, having 1-2 H(2)O ligands left in its first coordination sphere and showing very little symmetry, and is considered as Eu(3+) adsorbed onto the calcite surface. The emission spectra of species C for Eu:calcite grown in the presence of Na(+) were found to differ from those of Eu:calcite synthesized in the presence of K(+). The latter revealed a strong distortion in site symmetry, which was not observed in the samples grown in Na(+) solutions. This finding provides spectroscopic evidence in favor of an incorporation mechanism based on the charge-balanced coupled substitution of Na(+)+Eu(3+)<-->2Ca(2+).
    Journal of Colloid and Interface Science 05/2008; 321(2):323-31. · 3.17 Impact Factor
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    ABSTRACT: The research programme of the Institut fuer Nukleare Entsorgung (INE) at the Forschungszentrum Karlsruhe is dedicated to elaborate the fundamental understanding of radionuclide/actinide interactions with various components of the groundwater and with the relevant host rock materials at disposal relevant trace concentrations. INE's research programme was not biased after enactment of the Gorleben moratorium in 2001. This paper presents current R and D with respect to application in performance assessment/safety case of nuclear waste disposal. Focus is given to the leading role of the institute in various projects within EU framework programmes. (authors)
    06/2007
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    ABSTRACT: In Germany the safe disposal of radioactive waste is in the responsibility of the federal government. The R and D performed in the Institute for Nuclear Waste Disposal (INE) at the Research Center Karlsruhe contributes to the German provident research in the field of long-term safety for final disposal of high level heat producing nuclear wastes. INE's research is focused on the actinide elements and long lived fission products since these dominate the radiotoxicity over a long time. The research strategy synergistically combines fundamental science of aquatic radionuclide chemistry with applied investigations of real systems (waste form, host rock, aquifer), studied on laboratory scale and in underground laboratories. Because Germany has not yet selected a site for a high-level waste repository, all host rock formations under discussion in the international community (salt, hard rock, clay/tone) are investigated. Emphasis in long-term safety R and D at INE is on the development of actinide speciation methods and techniques in the trace concentration range. (authors)
    06/2007
  • Angewandte Chemie International Edition 02/2007; 46(6):919-22. · 13.73 Impact Factor
  • Angewandte Chemie-international Edition - ANGEW CHEM INT ED. 01/2007; 46(6):808-808.
  • Angewandte Chemie. 01/2007; 119(6):822-822.
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    ABSTRACT: Selected soft N-donor ligands are highly effective extractants for the separation of trivalent actinides (An(III)) from lanthanides (Ln(III)) in the partitioning and transmutation (P&T) strategy. Comparative structural investigations using X-ray absorption spectroscopy (EXAFS) on An(III) and Ln(III) complexed with tris[(2-pyrazinyl)methyl]amine (TPZA) and 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (BTP) are performed in order to evaluate if ligand extraction performance is reflected in coordination structure differences, specifically in variations in the metal cation–N bond lengths. We observe U(III) to generally exhibit a decrease in the bond distance over that expected for pure ionic binding for the ligand complexes investigated and interpret this as higher covalent character of the U(III)–N binding. In contrast, no measurable differences for Am(III), Cm(III), and the Ln(III) elements in the middle of the 4f series are observed. Time-resolved laser fluorescence spectroscopy (TRLFS) investigations on solution BTP complexed with Cm(III) and Eu(III) reveal that the selective extraction behavior of this ligand can be explained by the large difference in conditional stability constants of their 1:3 complexes (K13). The K13 value for Cm–BTP3 is a number of orders of magnitude larger than that for Eu–BTP3.
    Comptes Rendus Chimie - C R CHIM. 01/2007; 10(10):872-882.

Publication Stats

299 Citations
238 Downloads
2k Views
87.83 Total Impact Points

Institutions

  • 2010
    • Institute for Transuranium Elements
      Carlsruhe, Baden-Württemberg, Germany
  • 2008
    • Paul Scherrer Institut
      Aargau, Switzerland
  • 2006
    • Northeast Institute of Geography and Agroecology
      • Institute of Plasma Physics
      Beijing, Beijing Shi, China
    • Institut National de Physique Nucléaire et de Physique des Particules
      France