Kooperativer Bibliotheksverbund

Berlin Brandenburg

and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
Type of Medium
Language
Year
  • 1
    Language: English
    In: The journal of physical chemistry. A, 05 November 2009, Vol.113(44), pp.12171-8
    Description: Pre-edge spectral features below the main X-ray absorption K-edge of transition metals show a pronounced chemical sensitivity and are promising sources of structural information. Nevertheless, the use of pre-edge analysis in applied research is limited because of the lack of definite theoretical peak-assignments. The aim of this study was to determine the factors affecting the chromium K-pre-edge features in trivalent chromium-bearing oxides and oxyhydroxides. The selected phases varied in the degree of octahedral polymerization and the degree of iron-for-chromium substitution in the crystal structure. We investigated the pre-edge fine structure by means of high-energy-resolution fluorescence detected X-ray absorption spectroscopy and by 1s2p resonant X-ray emission spectroscopy. Multiplet theory and full multiple-scattering calculations were used to analyze the experimental data. We show that the chromium K-pre-edge contains localized and nonlocalized transitions. Contributions arising from nonlocalized metal-metal transitions are sensitive to the nearest metal type and to the linkage mode between neighboring metal octahedra. Analyzing these transitions opens up new opportunities for investigating the local coordination environment of chromium in poorly ordered solids of environmental relevance.
    Keywords: Spectrometry, X-Ray Emission ; X-Ray Absorption Spectroscopy ; Chromium -- Analysis ; Oxides -- Analysis
    ISSN: 10895639
    E-ISSN: 1520-5215
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, 2010, Vol.74(1), pp.164-186
    Description: We studied the local coordination and structure of Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water (buffered to pH 7 by 8 mM bicarbonate) using synchrotron-based X-ray absorption spectroscopy (XAS) at the -edges of Fe, P, Ca, and As. Dissolved phosphate, silicate, and Ca at different ratios relative to each other and to Fe affect the forming Fe(III)-phases in a complex manner. The high affinity of phosphate for Fe(III) results in the predominant precipitation of Fe(III)-phosphate as long as dissolved phosphate is present, with Fe(III) polymerization limited to small oligomers. In Ca-containing solution, Ca uptake by Fe(III)–Ca-phosphate involves the linkage and coagulation of negatively charged Fe(III)-phosphate oligomers via Ca–O–P bonds. In the absence of phosphate, dissolved silicate at Si/Fe ratios above ∼0.5 results in the formation of hydrous ferric oxide (HFO) with mainly edge-sharing Fe–Fe linkage. At lower Si/Fe ratios of ∼0.5–0.1, mainly 2-line ferrihydrite (2L-Fh) with both edge- and corner-sharing Fe–Fe linkage forms. Only in the absence of phosphate at low Si/Fe ratio, lepidocrocite (Lp) forms. In solutions containing sufficient Fe(II), aeration results in the sequential precipitation of Fe(III)-(Ca-)phosphate, HFO or 2L-Fh (depending on solution Si/Fe), and finally Lp. The amount and oxidation state of As co-precipitated with Fe(III) are controlled by the co-oxidation of As(III) with Fe(II), which increases with initial Fe/As ratio, and the competitive uptake of phosphate, As(V) and less strongly sorbing silicate and As(III). This study demonstrates that the diversity and sequence of short-range-ordered Fe(III)-precipitates forming by Fe(II) oxidation in near-neutral natural waters depend on water chemistry. Because differences in the colloidal stability and biogeochemical reactivity of these phases will affect the fate of associated major and trace elements, the different Fe(III)-precipitates and their specific biogeochemical properties must be taken into account when addressing nutrient and contaminant dynamics at redox boundaries in natural and engineered systems.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Language: English
    In: Geochimica et Cosmochimica Acta, 2010, Vol.74(19), pp.5574-5592
    Description: In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, ‘2-line’ Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0–50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH) octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe–O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 Å for Fe–O, 3.03 Å for Fe–Fe1, and 3.45 Å for Fe–Fe2. Likewise, citrate had no effect on the As–Fe (3.31 Å) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear ( C) As(V) surface complexes and (ii) combinations of C, monodentate mononuclear ( V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing V/ C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3–6.6, ∼0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios ⩾25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: Geochimica et Cosmochimica Acta, 2011, Vol.75(19), pp.5559-5573
    Description: The chemical weathering of primary Fe-bearing minerals, such as biotite and chlorite, is a key step of soil formation and an important nutrient source for the establishment of plant and microbial life. The understanding of the relevant processes and the associated Fe isotope fractionation is therefore of major importance for the further development of stable Fe isotopes as a tracer of the biogeochemical Fe cycle in terrestrial environments. We investigated the Fe mineral transformations and associated Fe isotope fractionation in a soil chronosequence of the Swiss Alps covering 150 years of soil formation on granite. For this purpose, we combined for the first time stable Fe isotope analyses with synchrotron-based Fe-EXAFS spectroscopy, which allowed us to interpret changes in Fe isotopic composition of bulk soils, size fractions, and chemically separated Fe pools over time in terms of weathering processes. Bulk soils and rocks exhibited constant isotopic compositions along the chronosequence, whereas soil Fe pools in grain size fractions spanned a range of 0.4‰ in δ Fe. The clay fractions (〈2 μm), in which newly formed Fe(III)-(hydr)oxides contributed up to 50% of the total Fe, were significantly enriched in light Fe isotopes, whereas the isotopic composition of silt and sand fractions, containing most of the soil Fe, remained in the range described by biotite/chlorite samples and bulk soils. Iron pools separated by a sequential extraction procedure covered a range of 0.8‰ in δ Fe. For all soils the lightest isotopic composition was observed in a 1 M NH OH–HCl–25% acetic acid extract, targeting poorly-crystalline Fe(III)-(hydr)oxides, compared with easily leachable Fe in primary phyllosilicates (0.5 M HCl extract) and Fe in residual silicates. The combination of the Fe isotope measurements with the speciation data obtained by Fe-EXAFS spectroscopy permitted to quantitatively relate the different isotope pools forming in the soils to the mineral weathering reactions which have taken place at the field site. A kinetic isotope effect during the Fe detachment from the phyllosilicates was identified as the dominant fractionation mechanism in young weathering environments, controlling not only the light isotope signature of secondary Fe(III)-(hydr)oxides but also significantly contributing to the isotope signature of plants. The present study further revealed that this kinetic fractionation effect can persist over considerable reaction advance during chemical weathering in field systems and is not only an initial transient phenomenon.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Language: English
    In: Geochimica et Cosmochimica Acta, 2010, Vol.74(11), pp.3112-3128
    Description: We studied stable iron isotope fractionation during dissolution of a biotite and chlorite enriched mineral fraction from granite by HCl and 5 mM oxalic acid in a pH range of 4–5.9. Batch experiments covered a time period from 2 h to 100 days and were performed at initial potassium concentrations of 0, 0.5, and 5 mM to induce different levels of biotite exfoliation. All experiments were kept anoxic to investigate solely the dissolution step without the influence of oxidation and precipitation of secondary Fe oxyhydroxides. Oxalic acid increased the release of Fe by a factor of ∼15 compared with the HCl experiments. Addition of 0.5 mM K to initial solutions in proton-promoted dissolution decreased the release of Fe by 30–65% depending on the dissolution stage. In ligand-controlled dissolution, K reduced the Fe release only to a minor extent. All solutions of the early dissolution stages were enriched in light Fe isotopes by up to −1.4‰ in δ Fe compared with the isotopic composition of biotite and chlorite mineral separates, which we explained by a kinetic isotope effect. In proton-promoted dissolution, early released fractions of K-enriched experiments were significantly lighter (−0.7‰ to −0.9‰) than in the initially K-free experiments. The evolution of Fe isotope ratios in solution was modeled by a linear combination of kinetic isotope effects during two independent dissolution processes attacking different crystallographic sites. In ligand-controlled dissolution, K did not influence the kinetic isotope effect and the Fe isotope composition in solution in the late dissolution stages remained slightly lighter than the bulk composition of the biotite/chlorite enriched mineral fraction. This study demonstrates that the initial Fe weathering flux should be enriched in light Fe isotopes and that Fe isotope data in combination with dissolution kinetics and stoichiometry provide new insights into dissolution mechanisms.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: International Journal of Mass Spectrometry, 2011, Vol.307(1), pp.39-45
    Description: ► Ablation cell design for fast washout of laser generated aerosol. ► High spatial resolution LA-ICP-MS for analysis of large heterogeneous samples. ► Detection of Hg-derivatised ovalbumin in electrophoresis gel with LA-ICP-MS. An ablation cell was developed to host large or several small samples (up to dimensions 230 mm × 34 mm × 16 mm, × × ) for high spatial resolution analysis. The performance of the cell was tested using silicate glass NIST SRM 610 and steel CRM JK-2D. To obtain high resolution profiles of trace element distributions, the ablation cell must offer fast washout of the aerosol to decrease mixing of the particles from different laser pulses. The washout of the new ablation cell is 70% faster when compared to the standard ablation cell previously applied in our laboratory and provides washout times within 2.6 s for 99.9% of the signal. Gas flow patterns in the cell were modeled by computational fluid dynamics (CFD) and validated by measurements on two reference materials. To demonstrate the potential of the ablation cell, p-(hydroxymercuri)benzoic acid (pHMB) derivatised ovalbumin was ablated from polyacrylamide gels after electrophoretic separation. The evaluation of the ablation cell demonstrates high resolution capabilities on large solid samples. It promises to have a significant impact on numerous applications, such as imaging of biological samples or trace element determinations on climate archives (e.g., stalagmites).
    Keywords: La-Icp-MS ; Ablation Cell ; Large Sample ; Fast Washout ; Gel Electrophoresis ; CFD Modeling ; Physics
    ISSN: 1387-3806
    E-ISSN: 1873-2798
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    In: American Mineralogist, 2010, Vol.95(8), pp.1202-1213
    Description: Poorly crystalline solids play an important role in many low-temperature geochemical processes, such as trace element speciation and biomineralization. Yet, the structures of many such naturally occurring phases are poorly understood. X-ray absorption spectroscopy is a powerful tool that permits chemically and spatially resolved investigations of poorly crystalline materials. In this study, we compare structural and electronic information derived from different regions of chromium K-edge X-ray absorption spectra for a series of poorly ordered iron(III)-chromium(III)-oxyhydroxides. These phases regularly form after the reduction of Cr(VI) by Fe(II) and often dictate the long-term fate of Cr in the environment. The distinct parts of the X-ray absorption spectrum, namely the pre-edge region, the near edge (XANES) region, and the extended (EXAFS) region, provide complementary information about the local chemical environment of Cr. Analysis of the XANES and EXAFS spectra showed that the structure around Cr in the Cr-poor sample is primarily composed of edge-sharing octahedra, whereas the octahedra in the Cr-rich samples are connected by edge-sharing and cornersharing linkages. The analysis of non-local transitions in the pre-edge spectra indicated the absence of Cr clustering at low Cr substitution. This study demonstrates the advantage of complementary pre-edge, XANES, and EXAFS analysis to deduce information on the medium-range environment around Cr in poorly ordered solids.
    Keywords: Xanes ; Exafs ; Pre-Edge ; Chromium ; Iron ; Oxyhydroxides ; Poorly Crystalline
    ISSN: 0003-004X
    E-ISSN: 1945-3027
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Language: English
    In: Geomicrobiology Journal, 01 March 2012, Vol.29(2), pp.173-185
    Description: Pseudomonas corrugata 28 represents a microorganism that can potentially be applied for in situ bioremediation of Cr(VI) contaminated sites. This strain combines a high resistance toward toxic Cr(VI) with the ability to reduce Cr(VI) to Cr(III) under oxic conditions. In this study, the...
    Keywords: Hexavalent Chromium ; Microbial Reduction ; Aerobic Conditions ; Organic Metal Complexes ; Scanning Transmission X-Ray Microscopy (Stxm) ; Pseudomonas Corrugata 28 ; Biology ; Chemistry
    ISSN: 0149-0451
    E-ISSN: 1521-0529
    Source: Taylor & Francis (Taylor & Francis Group)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Language: German
    In: Ökologisches Wirtschaften, 2014, Vol.29(4), pp. 39-43
    ISSN: 14308800
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Language: English
    In: Journal of Environmental Assessment Policy and Management, September 2015, Vol.17(3)
    Description: The Federal Environment Agency of Germany (Umweltbundesamt: UBA) is expected to provide information regarding the environmental performance of products and technologies — even in cases with limited time and data availability. Therefore, the streamlined environmental assessment (StreamEA) methodology has been developed which combines the competences available throughout the agency. Based on scientific assessment models, a ranking of alternatives can be determined for 15 impact categories, like greenhouse gas (GHG) emissions, nuisance, pathogenic emissions or physical killing of animals. Since the overall environmental burden depends on the specific impact per product and the total number of products, a macroeconomic assessment at the level of the product entirety is included. The applicability of the method, which can be adapted to other regions, and the robustness of results have been tested by means of case studies. The method is currently applied in the daily work of the agency to provide guidance to the general public and policy makers.
    Keywords: Streamlined Environmental Assessment ; Federal Environment Agency ; Life Cycle Assessment ; Environmental Guidance ; Environmental Sciences
    ISSN: 1464-3332
    E-ISSN: 1757-5605
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages