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Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of Colloid And Interface Science, Sept 1, 2013, Vol.405, p.44(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jcis.2013.05.041 Byline: Matthias Handel, Thilo Rennert, Kai U. Totsche Abstract: Display Omitted Article History: Received 20 February 2013; Accepted 17 May 2013
    Keywords: Oxides ; Manganese Compounds
    ISSN: 0021-9797
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Geoderma, Feb, 2013, Vol.193-194, p.117(5)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.geoderma.2012.09.002 Byline: Matthias Handel, Thilo Rennert, Kai U. Totsche Keywords: FTIR; XRD; Specific surface area; Manganese oxide; Remediation; Sol-gel synthesis Abstract: The synthesis of pure birnessite ([delta]-MnO.sub.2) by a simple, fast and reliable method is introduced. Birnessite was synthesized by a sol-gel reaction involving the reduction of KMnO.sub.4 by lactate at ambient pressure and temperature. Our method does not include the use of strong acids and bases and does not produce toxic residues. The results from both X-ray diffraction and Fourier-transform infrared spectroscopy, compared with a synthesized reference material, verified our synthesized mineral as birnessite. Secondary electron images showed a micro-porous structure of aggregated birnessite colloids, and consistently, we measured a very large specific BET surface area of 249.15[+ or -]0.05m.sup.2 g.sup.-1. Birnessite is known to have a variable mineral formula, and the elemental composition of our mineral is within the range of other birnessites. Birnessite obtained by this procedure could serve as a model mineral for laboratory experiments on the biogeochemistry of Mn, and furthermore it may also have a potential as electron acceptor for remediation purposes. Article History: Received 21 March 2012; Revised 25 July 2012; Accepted 16 September 2012
    Keywords: Manganese Compounds -- Methods ; Manganese Compounds -- Analysis
    ISSN: 0016-7061
    Source: Cengage Learning, Inc.
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  • 3
    In: Physical Chemistry Chemical Physics, 2014, Vol.16(7), pp.2827-2830
    Description: Establishing high-resolution structures of biological macromolecules in heterogeneous environments by MAS solid-state NMR is an important challenge where development of advanced experimental procedures is in high demand. Promising new methods take advantage of samples with extensive 2 H, 13 C, and 15 N isotope labelling, effectively diluting 1 H spins. In many cases, a sufficient amount of 1 H at exchangeable sites cannot be re-established during the purification procedure, hence it is necessary to exploit also the potential of 2 H as a starting point in pulse sequences, capitalizing on its short T 1 as compared to 13 C, and to detect carbon or proton spins as appropriate. Here we present a new method that enables the required high-efficiency 2 H to 13 C or 15 N polarization transfer to be accomplished under the limited 2 H rf power conditions using current 1 H, 2 H, 13 C and 15 N quadruple-resonance MAS NMR instrumentation.
    Keywords: Labelling ; Exchange ; Carbon ; Physical Chemistry ; Instrumentation ; Purification ; Polarization ; Nuclear Magnetic Resonance ; Miscellaneous Sciences (So);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 4
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 November 2015, Vol.169, pp.167-183
    Description: Iron oxides represent a substantial fraction of secondary minerals and particularly affect the reactive properties of natural systems in which they formed, e.g. in soils and sediments. Yet, it is still obscure how transient conditions in the solution will affect the properties of in situ precipitated Fe oxides. Transient compositions, i.e. compositions that change with time, arise due to predominant non-equilibrium states in natural systems, e.g. between liquid and solid phases in soils. In this study, we characterize Fe–OM co-precipitates that formed in pH-neutral exfiltrates from anoxic topsoils under transient conditions. We applied soil column outflow experiments, in which Fe was discharged with the effluent from anoxic soil and subsequently oxidized in the effluent due to contact with air. Our study features three novel aspects being unconsidered so far: (i) the transient composition of soil-derived solutions, (ii) that pedogenic Fe oxides instead of Fe salts serve as major source for Fe in soil solution and (iii) the presence of exclusively soil-derived organic and inorganic compounds during precipitation. The experiments were carried out with two topsoil materials that differed in composition, texture and land use. Derived from Mössbauer spectroscopy, broad distributions in quadrupole splittings (0–2 mm s ) and magnetic hyperfine fields (35–53 T) indicated the presence of low-crystalline ferrihydrite and even lower crystalline Fe phases in all Fe–OM co-precipitates. There was no unequivocal evidence for other Fe oxides, i.e. lepidocrocite and (nano)goethite. The Fe–OM co-precipitates contained inorganic (P, sulfate, silicate, Al, As) and organic compounds (proteins, polysaccharides), which were concurrently discharged from the soils. Their content in the Fe–OM co-precipitates was controlled by their respective concentration in the soil-derived solution. On a molar basis, OC and Fe were the main components in the Fe–OM co-precipitates (OC/Fe ratio = 0.5–2). The elemental composition of the Fe–OM co-precipitates was in accordance with the sequential precipitation of Fe(III)phosphates/arsenates prior to the formation of ferrihydrite. This explains decreasing Si contents in the Fe–OM co-precipitates with increasing availability of P. With respect to constant mean quadrupole splittings and slightly decreasing mean magnetic hyperfine fields, increasing contents of OC, P and Al in the Fe–OM co-precipitates did not further increase the structural disorder of the Fe polyhedra, while the crystallite interactions slightly decreased. Scanning electron microscopy and dynamic light scattering revealed the coincidental presence of variably sized aggregates and a considerable amount of Fe–OM co-precipitates, which remained dispersed in solution for months. Thus, variably composed Fe–OM co-precipitates with highly diverse aggregate sizes and comparably constant poor crystallinity can be expected after the oxidation of Fe in transient, soil-derived solutions.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 5
    Language: English
    In: Journal of Colloid And Interface Science, 01 September 2013, Vol.405, pp.44-50
    Description: Cryptomelane-type octahedral molecular sieves (K-OMS-2) were successfully synthesized at ambient pressure and temperature by a simple one-step reaction pathway. We designed three synthesis mixes based on redox reactions of either MnSO or MnCl together with KMnO in aqueous solution. The synthesis products were characterized structurally (XRD, FTIR spectroscopy), morphologically (SEM, BET surface area), and chemically (SEM-EDX, ICP-OES). For all mixes, a precursor octahedral layered K-birnessite (K-OL-1) was formed after 1 d that subsequently transformed into K-OMS-2. This transformation process depends on the pH of the reaction solution, the respective Mn(II) salt and time. We obtained K-OMS-2 materials with BET surface areas between 50.4 and 104.5 m g and different crystallinities. The described method is reliable, reproducible, easy to handle and may be the basis to produce well defined Mn oxides that could be used for remediation and catalysis purposes.
    Keywords: Octahedral Molecular Sieve ; K-Oms-2 ; K-Ol-1 ; Nanowires ; Mn Oxide ; Bet Surface ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 6
    Language: English
    In: Journal of colloid and interface science, 2013, Vol.405, pp.44-50
    Description: Cryptomelane-type octahedral molecular sieves (K-OMS-2) were successfully synthesized at ambient pressure and temperature by a simple one-step reaction pathway. We designed three synthesis mixes based on redox reactions of either MnSO₄ or MnCl₂ together with KMnO₄ in aqueous solution. The synthesis products were characterized structurally (XRD, FTIR spectroscopy), morphologically (SEM, BET surface area), and chemically (SEM-EDX, ICP-OES). For all mixes, a precursor octahedral layered K-birnessite (K-OL-1) was formed after 1d that subsequently transformed into K-OMS-2. This transformation process depends on the pH of the reaction solution, the respective Mn(II) salt and time. We obtained K-OMS-2 materials with BET surface areas between 50.4 and 104.5m²g⁻¹ and different crystallinities. The described method is reliable, reproducible, easy to handle and may be the basis to produce well defined Mn oxides that could be used for remediation and catalysis purposes. ; p. 44-50.
    Keywords: Redox Reactions ; Potassium Permanganate ; Aqueous Solutions ; X-Ray Diffraction ; Manganese ; Temperature ; Remediation ; Manganese Oxides ; Catalytic Activity ; Scanning Electron Microscopy ; Ph ; Fourier Transform Infrared Spectroscopy ; Surface Area
    ISSN: 0021-9797
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 7
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 August 2014, Vol.139, pp.434-446
    Description: Microbial reduction of ferric iron is partly dependent on Fe hydroxide particle size: nanosized Fe hydroxides greatly exceed the bioavailability of their counterparts larger than 1 μm. Citrate as a low molecular weight organic acid can likewise stabilize colloidal suspensions against aggregation by electrostatic repulsion but also increase Fe bioavailability by enhancing Fe hydroxide solubility. The aim of this study was to see whether adsorption of citrate onto surfaces of large ferrihydrite aggregates results in the formation of a stable colloidal suspension by electrostatic repulsion and how this effect influences microbial Fe reduction. Furthermore, we wanted to discriminate between citrate-mediated colloid stabilization out of larger aggregates and ferrihydrite dissolution and their influence on microbial Fe hydroxide reduction. Dissolution kinetics of ferrihydrite aggregates induced by different concentrations of citrate and humic acids were compared to microbial reduction kinetics with . Dynamic light scattering results showed the formation of a stable colloidal suspension and colloids with hydrodynamic diameters of 69 (±37) to 165 (± 65) nm for molar citrate:Fe ratios of 0.1 to 0.5 and partial dissolution of ferrihydrite at citrate:Fe ratios ⩾ 0.1. No dissolution or colloid stabilization was detected in the presence of humic acids. Adsorption of citrate, necessary for dissolution, reversed the surface charge and led to electrostatic repulsion between sub-aggregates of ferrihydrite and colloid stabilization when the citrate:Fe ratio was above a critical value (⩽ 0.1). Lower ratios resulted in stronger ferrihydrite aggregation instead of formation of a stable colloidal suspension, owing to neutralization of the positive surface charge. At the same time, microbial ferrihydrite reduction increased from 0.029 to 0.184 mM h indicating that colloids stabilized by citrate addition enhanced microbial Fe reduction. Modelling of abiotic dissolution kinetics revealed that colloid stabilization was most pronounced at citrate:Fe ratios of 0.1 – 0.5, whereas higher ratios led to enhanced dissolution of both colloidal and larger aggregated fractions. Mathematical simulation of the microbial reduction kinetics under consideration of partial dissolution and colloid stabilization showed that the bioaccessibility increases in the order large aggregates 〈 stable colloids 〈 Fe-citrate. These findings indicate that much of the organic acid driven mobilization of Fe oxy(hydr)oxides is most likely due to colloid formation and stabilization rather than solubilisation.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 8
    Language: English
    In: Applied and environmental microbiology, August 2014, Vol.80(16), pp.5086-97
    Description: Biological Mn oxidation is responsible for producing highly reactive and abundant Mn oxide phases in the environment that can mitigate metal contamination. However, little is known about Mn oxidation in low-pH environments, where metal contamination often is a problem as the result of mining activities. We isolated two Mn(II)-oxidizing bacteria (MOB) at pH 5.5 (Duganella isolate AB_14 and Albidiferax isolate TB-2) and nine strains at pH 7 from a former uranium mining site. Isolate TB-2 may contribute to Mn oxidation in the acidic Mn-rich subsoil, as a closely related clone represented 16% of the total community. All isolates oxidized Mn over a small pH range, and isolates from low-pH samples only oxidized Mn below pH 6. Two strains with different pH optima differed in their Fe requirements for Mn oxidation, suggesting that Mn oxidation by the strain found at neutral pH was linked to Fe oxidation. Isolates tolerated Ni, Cu, and Cd and produced Mn oxides with similarities to todorokite and birnessite, with the latter being present in subsurface layers where metal enrichment was associated with Mn oxides. This demonstrates that MOB can be involved in the formation of biogenic Mn oxides in both moderately acidic and neutral pH environments.
    Keywords: Soil Microbiology ; Bacteria -- Isolation & Purification ; Manganese Compounds -- Metabolism ; Uranium -- Metabolism
    ISSN: 00992240
    E-ISSN: 1098-5336
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  • 9
    Language: English
    In: Geoderma, February 2013, Vol.193-194, pp.117-121
    Description: The synthesis of pure birnessite (δ-MnO ) by a simple, fast and reliable method is introduced. Birnessite was synthesized by a sol–gel reaction involving the reduction of KMnO by lactate at ambient pressure and temperature. Our method does not include the use of strong acids and bases and does not produce toxic residues. The results from both X-ray diffraction and Fourier-transform infrared spectroscopy, compared with a synthesized reference material, verified our synthesized mineral as birnessite. Secondary electron images showed a micro-porous structure of aggregated birnessite colloids, and consistently, we measured a very large specific BET surface area of 249.15 ± 0.05 m g . Birnessite is known to have a variable mineral formula, and the elemental composition of our mineral is within the range of other birnessites. Birnessite obtained by this procedure could serve as a model mineral for laboratory experiments on the biogeochemistry of Mn, and furthermore it may also have a potential as electron acceptor for remediation purposes. ► Pure birnessite was synthesized by a simple, fast, reliable and inexpensive method. ► This birnessite can serve as a model mineral in studies on the biogeochemistry of Mn. ► It may have potential for the remediation of contaminated soils.
    Keywords: Ftir ; Xrd ; Specific Surface Area ; Manganese Oxide ; Remediation ; Sol–Gel Synthesis ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 10
    Language: English
    In: Geoderma, 2013, Vol.193, pp.117-121
    Description: The synthesis of pure birnessite (δ-MnO₂) by a simple, fast and reliable method is introduced. Birnessite was synthesized by a sol–gel reaction involving the reduction of KMnO₄ by lactate at ambient pressure and temperature. Our method does not include the use of strong acids and bases and does not produce toxic residues. The results from both X-ray diffraction and Fourier-transform infrared spectroscopy, compared with a synthesized reference material, verified our synthesized mineral as birnessite. Secondary electron images showed a micro-porous structure of aggregated birnessite colloids, and consistently, we measured a very large specific BET surface area of 249.15±0.05m²g⁻¹. Birnessite is known to have a variable mineral formula, and the elemental composition of our mineral is within the range of other birnessites. Birnessite obtained by this procedure could serve as a model mineral for laboratory experiments on the biogeochemistry of Mn, and furthermore it may also have a potential as electron acceptor for remediation purposes. ; p. 117-121.
    Keywords: Acids ; Biogeochemistry ; Elemental Composition ; X-Ray Diffraction ; Manganese ; Remediation ; Temperature ; Colloids ; Infrared Spectroscopy ; Toxicity ; Birnessite ; Laboratory Experimentation ; Surface Area
    ISSN: 0016-7061
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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