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  • 1. Alessi, Daniel S.
    et al.
    Lezama-Pacheco, Juan S.
    Stubbs, Joanne E.
    Janousch, Markus
    Bargar, John R.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bernier-Latmani, Rizlan
    The product of microbial uranium reduction includes multiple species with U(IV)-phosphate coordination2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 131, p. 115-127Article in journal (Refereed)
    Abstract [en]

    Until recently, the reduction of U(VI) to U(IV) during bioremediation was assumed to produce solely the sparingly soluble mineral uraninite, UO2(s). However, results from several laboratories reveal other species of U(IV) characterized by the absence of an EXAFS U-U pair correlation (referred to here as noncrystalline U(IV)). Because it lacks the crystalline structure of uraninite, this species is likely to be more labile and susceptible to reoxidation. In the case of single species cultures, analyses of U extended X-ray fine structure (EXAFS) spectra have previously suggested U(IV) coordination to carboxyl, phosphoryl or carbonate groups. In spite of this evidence, little is understood about the species that make up noncrystalline U(IV), their structural chemistry and the nature of the U(IV)-ligand interactions. Here, we use infrared spectroscopy (IR), uranium L-III-edge X-ray absorption spectroscopy (XAS), and phosphorus K-edge XAS analyses to constrain the binding environments of phosphate and uranium associated with Shewanella oneidensis MR-1 bacterial cells. Systems tested as a function of pH included: cells under metal-reducing conditions without uranium, cells under reducing conditions that produced primarily uraninite, and cells under reducing conditions that produced primarily biomass-associated noncrystalline U(IV). P X-ray absorption near-edge structure (XANES) results provided clear and direct evidence of U(IV) coordination to phosphate. Infrared (IR) spectroscopy revealed a pronounced perturbation of phosphate functional groups in the presence of uranium. Analysis of these data provides evidence that U(IV) is coordinated to a range of phosphate species, including monomers and polymerized networks. U EXAFS analyses and a chemical extraction measurements support these conclusions. The results of this study provide new insights into the binding mechanisms of biomass-associated U(IV) species which in turn sheds light on the mechanisms of biological U(VI) reduction. (C) 2014 Elsevier Ltd. All rights reserved.

  • 2.
    Andersson, Tove
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Giesler, Reiner
    Ecology and Environmental Science.
    Adsorption of Monomethyl Phosphate to the Goethite (-FeOOH)/water Interface2002Conference paper (Other academic)
  • 3.
    Axe, Kristina
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Time-dependent surface speciation of oxalate at the water-boehmite (γ-AlOOH) interface: implications for dissolution2001In: Geochimica et Cosmochimica Acta, Vol. 65, no 24, p. 4481-92Article in journal (Refereed)
    Abstract [en]

    The surface speciation of oxalate at the water-boehmite (γ-AlOOH) interface during adsorption and dissolution reactions was studied by means of attenuated total reflectance infrared spectroscopy. The structural interpretations of infrared (IR) data were based on comparison with results from theoretical frequency calculations. Two different surface complexes were identified: an inner-sphere complex with a bidentate five-membered chelate structure involving both carboxylate groups; and a hydrogen-bonded surface complex with no direct bonding to Al atoms. A scheme was developed by which the surface concentrations of these complexes could be determined from IR spectroscopy data. The concentration of the hydrogen bonded complex was shown to be strongly dependent on the experimental conditions, and the concentration of the inner-sphere complex was comparatively insensitive to the conditions within the studied experimental range. The dissolution data indicated that an excess of oxalate with respect to a critical surface concentration of oxalate was necessary to induce significant boehmite dissolution. Under dissolving conditions, the concentration of the inner-sphere complex was shown to be almost identical to this critical concentration and thus a stable entity.

  • 4.
    Bengtsson, Åsa
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lindegren, Malin
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Dissolution, adsorption and phase transformation in the fluorapatite–goethite system2007In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 22, no 9, p. 2016-2028Article in journal (Refereed)
    Abstract [en]

    An aqueous system containing fluorapatite (Ca5(PO4)3F), (FAP) and varying amounts of goethite (α-FeOOH) has been investigated. Batch experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to monitor the dissolution products of FAP, as well as the adsorption, and phase transformation of phosphate at the goethite surface over a period of 129 days. The results show that the presence of goethite increases dissolution of FAP, mainly due to the high affinity of phosphate for the goethite surface: Besides monitoring the pH changes associated with this reaction, the concentrations of Ca2+ and fluoride were determined. Furthermore, the amount of phosphate adsorbed was quantified from ATR-FTIR spectra. In addition to adsorbed phosphate, phase transformations of goethite into a Fe phosphate phase (FePO4(s)) are seen in the samples with relatively high phosphate to goethite ratios (excess phosphate to available surface sites) equilibrated for 15–129 days.

    An equilibrium model that takes into account (i) FAP dissolution, (ii) solution complexation, (iii) surface complexation of phosphate species onto goethite and (iv) possible phase transformation Ca5(PO4)3F–CaF2 and FeOOH–FePO4 was designed. This model was found to be in very good agreement with experimental observations and could thus be used to give qualitative and quantitative information about goethite promoted dissolution of FAP under other pH conditions than those studied in the present work.

  • 5.
    Bengtsson, Åsa
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    A comparative study of the dissolution of hydroxyapatite and fluorapatite in the absence and presence of organic ligands2005In: GEOCHIMICA ET COSMOCHIMICA ACTA 69 (10): A68-A68 Suppl. S, MAY 2005, ISSN 0016-7037, Vol. 69, no 10, p. A68-Article in journal (Other academic)
  • 6.
    Bengtsson, Åsa
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    A kinetic and spectroscopic study of fluorapatite dissolution2004Conference paper (Other academic)
  • 7. Bengtsson, Åsa
    et al.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Phase Transformations, Ion-Exchange, Adsorption, and Dissolution Processes in Aquatic Fluorapatite Systems2009In: Langmuir, Vol. 25, no 4, p. 2355-2362Article in journal (Refereed)
    Abstract [en]

    A synthetic fluorapatite was prepared that undergoes a phase transformation generated during a dialysis step. A surface layer with the composition Ca9(HPO4)2(PO4)4F2 is formed, which is suggested to form as one calcium atom is replaced by two protons. A surface complexation model, based upon XPS measurements, potentiometric titration data, batch experiments, and zeta-potential measurements was presented. The CaOH and OPO3H2 sites were assumed to have similar protolytic properties as in a corresponding nonstoichiometric HAP (Ca8.4(HPO4)1.6(PO4)4.4(OH)0.4) system. Besides a determination of the solubility product of Ca9(HPO4)2(PO4)4F2, two additional surface complexation reactions were introduced; one that accounts for a F/OH ion exchange reaction, resulting in the release of quite high fluoride concentrations (∼1 mM) that turned out to be dependent on the surface area of the particles. Furthermore, to explain the lowering of pHiep from around 8 in nonstoichiometric HAP suspensions to about 5.7 in FAP suspensions, a reaction that lowers the surface charge due to the readsorption of fluoride ions to the positively charged Ca sites was introduced: ≡CaOH2+ + F− ⇋ ≡CaF + H2O. The resulting model also agrees with predictions based upon XPS and ATR-FTIR observations claiming the formation of CaF2(s) in the most acidic pH range.

  • 8.
    Bengtsson, Åsa
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    A solubility and surface complexation study of a non-stoichiometric hydroxyapatite2009In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, no 2, p. 257-267Article in journal (Refereed)
    Abstract [en]

    The dissolution and surface complexation of a non-stoichiometric hydroxyapatite (Ca8.4(HPO4)1.6(PO4)4.4(OH)0.4), (HAP) was studied in the pH range 3.5 – 10.5, at 25 ºC in 0.1 M Na(Cl). The results from well-equilibrated batch experiments, potentiometric titrations, and zeta-potential measurements were combined with information provided by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The information from the analyses was used to design an equilibration model that takes in to account dissolution, surface potential, solution and surface complexation, as well as possible phase transformations. The results from the XPS measurements clearly show that the surface of the mineral has a different composition than the bulk and that the Ca/P ratio of the surface layer is 1.4 ± 0.1. This ratio was also found in solution in the batches equilibrated at low pH where the dominating reaction is dissolution. In the batches equilibrated at near neutral pH values, however, the Ca/P ratio in solution attains values as high as 25, which is due to re-adsorption of phosphate ions to the HAP surface. The total concentration of protons as well as the total concentration of dissolved calcium and phosphate in solution were used to calculate a model for the dissolution and surface complexation of HAP. The constant capacitance model was applied in designing the following surface complexation model.

  • 9. Bergknut, Magnus
    et al.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Molecular characterization of brominated persistent pollutants using extended X-ray absorption fine structure (EXAFS) spectroscopy2008In: Analytical and Bioanalytical Chemistry: Volume 390, Number 3 / February, 2008, ISSN 1618-2642 (Print) 1618-2650 (Online), Vol. 390, no 3, p. 921-8Article in journal (Refereed)
    Abstract [en]

    X-ray absorption fine structure (EXAFS) spectroscopy spectra were collected for three brominated persistent pollutants: 6-bromo-2,4,5-trichlorophenol (BrTriClP), pentabromophenol (PentaBrP) and 3,3',5,5'-tetrabromobisphenol A (TBBA). The substances were selected to be symmetrical (BrTriClP and TBBA) or asymmetrical (PentaBrP) with respect to the atomic Br positions and to differ in the number of bromine and other halide atoms, as well as their relative positions. The asymmetrical PentaBrP was modelled with special detail as not all bromine atoms have identical coordination environments. The studied substances displayed unique EXAFS spectra, which could be used to determine the molecular structure in fair detail. We conclude that EXAFS spectroscopy is a suitable technique for molecular characterization of the comparatively complex molecules within the class of compounds of brominated organic persistent pollutants. A detailed understanding of the EXAFS spectra of the pure compounds opens up possibilities to study the interactions with soil and sediment matrices by means of EXAFS spectroscopy. Figure Brominated organic persistent pollutants are characterized by EXAFS spectroscopy.

  • 10.
    Bochatay, Laurence
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Metal Ion Coordination at the Water–Manganite (γ-MnOOH) Interface II. An EXAFS Study of Zinc(II)2000In: Journal of Colloid and Interface Science, Vol. 229, no 2, p. 593-9Article in journal (Refereed)
    Abstract [en]

    The local structure of Zn(II) adsorbed at the water—manganite (γ-MnOOH) interface has been investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. Adsorption experiments were carried out within the pH range 6.17—9.87 and surface coverages of 0.9 to 9.7 μmol/m2Zn(II) coordination was observed to change from six to four as pH was increased. This was indicated by a change in Zn—O distance from 2.04 to 1.96 Å and by a decrease in the obtained coordination numbers. Two higher shells were detected at about 3.08 and 3.33 Å, at all pH values and surface coverage investigated. As the backscattering phase and amplitude functions of Mn and Zn are similar, we used structural and chemical considerations to assign the backscattering at 3.08 Å to Mn neighbors, and the one at 3.33 Å to Zn atoms. Indeed the size of the Zn polyhedra, especially of ZnO4, does not quite match the structure of the manganite surface. We conclude that Zn(II) forms multinuclear hydroxo-complexes or a zinc hydroxide phase at the surface, as it might be easier for an additional Zn(II) to bond to an already sorbed Zn. These results were compared to our previous EXAFS study of Cd(II) adsorption onto manganite, where mononuclear inner-sphere complexes bound to the surface via edges were found.

  • 11.
    Bochatay, Laurence
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Metal Ion Coordination at the Water–Manganite (γ-MnOOH) Interface: I. An EXAFS Study of Cadmium(II)2000In: Journal of Colloid and Interface Science, Vol. 229, no 12, p. 584-92Article in journal (Refereed)
    Abstract [en]

    The local structure of Cd(II) surface complexes adsorbed onto manganite (γ-MnOOH) has been investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. Adsorption experiments were carried out within the pH range 7.4–9.8 and with surface coverage from 2.2 to 8.9 μmol/m2. Quantitative analysis of the EXAFS spectra shows little difference in the local coordination environment of Cd regardless of the coverage. Analysis of the first shell required a third cumulant in an asymmetric distribution model (i.e., non-Gaussian distribution), indicating distorted CdO6 octahedra with an average Cd–O distance of 2.31 Å. A single second shell of Mn neighbors at a constant distance of 3.33 Å was detected. This comparatively short distance shows that inner-sphere complexes are formed. No Cd neighbor was found which means that cadmium hydroxide precipitation or cluster formation does not occur at the surface at the experimental conditions probed in this study. We assign the Cd–Mn distance to edge sharing between CdO6 and MnO6 octahedra, with a geometry similar to that in the mixed solid Cd2Mn3O8. This adsorption mode is possible on the {110} and {010} cleavage planes of manganite.

  • 12.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Benzenecarboxylate surface complexation at the goethite (-FeOOH)/water interface: II. Linking IR spectroscopic observations to mechanistic surface complexation models for phthalate, trimellitate, and pyromellitate2000In: Geochimica et Cosmochimica Acta, Vol. 64, no 20, p. 3453-70Article in journal (Refereed)
    Abstract [en]

    A study combining information from infrared spectroscopy and adsorption experiments was carried out to investigate phthalate, trimellitate, and pyromellitate complexes at the goethite (-FeOOH)/water interface. Infrared spectra showed evidence for inner-sphere complexes below pH 6 and outer-sphere complexes in the pH range 3 to 9. Normalized infrared peak areas were used as a semi-quantitative tool to devise diagrams showing the molecular level surface speciation as a function of pH. Surface complexation models that simultaneously predict these diagrams, the proton balance data and the ligand adsorption data were developed with surface complexation theory. Surface complexation modeling was carried out with a Charge Distribution Multisite Complexation Model (CD-MUSIC), assuming goethite particles with surfaces represented by the {110} plane (90% of total particle surface area) and by the {001} plane (10% of total particle surface area). Inner-sphere complexes were described as mononuclear chelates at the {001} plane, whereas outer-sphere complexes were described as binuclear complexes with singly coordinated sites on the {110} plane. The Three-Plane Model (TPM) was used to described surface electrostatics and to distribute the charges of the inner- and the outer-sphere complexes on different planes of adsorption.

  • 13.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Benzenecarboxylate surface complexation at the goethite (α-FEOOH)/water interface. III. The influence of particle surface area and the significance of modeling parameters2000In: Journal of colloid and interface science, Vol. 227, no 1, p. 132-40Article in journal (Refereed)
    Abstract [en]

    A surface complexation model describing the adsorption of three benzenecarboxylates (phthalate, trimellitate, and pyromellitate) on goethite (α-FeOOH) was calibrated on data using goethite particles of 37 and 43 m[2]/g surface area. The models predict potentiometric titration and batch adsorption data with the multisite complexation model coupled with the three-plane model to account for surface electrostatics. The modeling parameters were found to be similar to those calibrated on benzenecarboxylate adsorption data on goethite particles of 90 m[2]/g (Boily et al. Geochim. Cosmochim. Acta, in press). The significance of the benzenecarboxylate-dependent values of the modeling parameters is also discussed. The values of the capacitances of the inner- and outer-Helmholtz planes were shown to be important modeling parameters to model the benzenecarboxylate-dependent slopes of the adsorption edges. It was shown that the larger the charge of the ligand, the larger the capacitance of the outer-Helmholtz plane.

  • 14. Boily, Jean-François
    et al.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Structures and stabilities of Cd(II) and Cd(II)-phthalate complexes at the goethite/water interface2005In: GEOCHIMICA ET COSMOCHIMICA ACTA, ISSN 0016-7037, Vol. 69, no 13, p. 3219-35Article in journal (Refereed)
    Abstract [en]

    The complexation of Cd(II) and Cd(II)-phthalate at the goethite/water interface were investigated by EXAFS and IR spectroscopy, by batch adsorption experiments and by potentiometric titrations at 298.15 K. The EXAFS spectra showed Cd(II) to form only inner-sphere corner-sharing complexes with the goethite surface sites in the presence and absence of phthalate. EXAFS spectra also showed the presence of Cd(II)-chloride complexes in 0.1 mol/L NaCl. IR spectra also showed phthalate to form (1) an inner-sphere complex with adsorbed corner-sharing Cd(II) surface complexes in the pH 3.5 to 9.5 and (2) an outer-sphere complex with the same type of corner-sharing Cd(II) complex however at pH > 6, in addition to the inner- and outer-sphere complexes of phthalate reported in a previous study. The potentiometric titration and the batch adsorption data were used to constrain the formation constants of the different Cd(II)-phthalate surface complexes on the dominant {110} and the {001} planes of the goethite. The models were carried out with the Charge Distribution Multisite Complexation model coupled to the Three Plane Model and can predict the molecular-scale speciation of cadmium and phthalate in the presence of goethite. Cd(II) adsorption models calibrated on a 90 m2/g goethite also could accurately predict experimental data for a 37 m2/g goethite of slightly different basic charging properties.

  • 15.
    Clausén, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Öhman, Lars-Olof
    Umeå University, Faculty of Science and Technology, Chemistry.
    Axe, Kristina
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Spectroscopic studies of aluminum and gallium complexes with oxalate and malonate in aqueous solution2003In: Journal of Molecular Structure, Vol. 648, no 3, p. 225-35Article in journal (Refereed)
    Abstract [en]

    The local structures of Ga(III) in aqueous oxalate and malonate complexes were studied by means of Ga K-edge EXAFS spectroscopy. Irrespective of the number and type of coordinated ligands, the EXAFS results showed very regular first coordination shells consisting of six oxygen atoms. Scattering paths from more distant atoms revealed that both oxalate and malonate form mononuclear chelate structures where one oxygen from each carboxylate group binds to Ga(III). Again, very little variation in bond distances and no changes in coordination modes were detected as the number of ligands coordinated to Ga(III) was varied. Based on the very close resemblance of IR spectra of oxalate and malonate complexes of Al(III), and the corresponding complexes of Ga(III), it is believed that the local structures of the Al(III) complexes are similar to those of the Ga(III) complexes in terms of ligand coordination modes and distortions. This conclusion was corroborated by results from theoretical frequency calculations.

  • 16. Clausén, Maria
    et al.
    Öhman, Lars-Olof
    Umeå University, Faculty of Science and Technology, Chemistry.
    Kubicki, James D
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Characterisation of gallium(III)-acetate complexes in aqueous solution: A potentiometric, EXAFS, IR and molecular orbital modelling study2002In: Journal of Chemical Society Dalton Transactions, p. 2559-64Article in journal (Refereed)
    Abstract [en]

    The aqueous gallium(III)-acetate system was studied in 0.6 M Na(Cl) at 25 °C using a multi-technique approach, including potentiometry, IR spectroscopy, EXAFS spectroscopy and molecular orbital calculations. The potentiometric data were satisfactorily explained by a model which includes one mononuclear and one binuclear complex. The corresponding equilibrium constants defined according to the reactionsGa3++ HAc GaAc2++ H+2Ga3++ HAc + 2H2O Ga2(OH)2Ac3++ 3H+are log –1,1,1=–2.08 ± 0.09 and log –3,2,1=–5.65 ± 0.06, respectively. The latter complex has a stoichiometry identical to that previously identified in the aluminium(III)-acetate system. Also in agreement with this system, the IR and EXAFS data strongly indicates that this complex consists of two edge-sharing Ga octahedra bridged with an acetate ion, and should be formulated [Ga2(µ-OH)2(µ-O2CCH3)]3+. This interpretation is further supported by the molcular orbital calculations.

  • 17.
    Clausén, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Öhman, Lars-Olof
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Spectroscopic studies of aqueous gallium(III) and aluminum(III) citrate complexes2005In: JOURNAL OF INORGANIC BIOCHEMISTRY, ISSN 0162-0134, Vol. 99, no 3, p. 716-26Article in journal (Refereed)
    Abstract [en]

    Aqueous gallium(III) citrate complexes have been studied in the 10(-2) M concentration range with extended X-ray absorption fine structure (EXAFS) and FTIR techniques. From EXAFS data, one mononuclear and one oligomeric species were identified at different Ga(III) to citrate ratios. The first shell of the mononuclear complex was found to be distorted, with average Ga-O bond lengths of 1.95 and 2.06 Angstrom, in agreement with the solid-state structure of Ga(Cit)(2)(3-) (Cit = citrate). Also the oligomeric species was found to have a distorted first shell, with average Ga-O bond lengths of 1.95 and 2.04 Angstrom. This complex was found to contain two Ga-Ga distances at 3.03 and 3.56 Angstrom, typical for edge and corner sharing GaO6 octahedra, respectively. The gallium(III) and aluminum(III) citrate systems were compared by means of FTIR, and were found to be analogous. The IR results suggest that the bond lengths derived from EXAFS for the 1:2 gallium(III) citrate complex also provide a good estimate of the corresponding distances in the mononuclear 1: 1 complex. Direct coordination of citrate to the metal ions in the oligomeric gallium(III) citrate complex was indicated from both EXAFS and IR results, and this complex is stoichiometrically analogous to the Al-3(H(-1)Cit)(3)(OH)(H2O)(4-) complex, which has been structurally determined. However, while the formation of the aluminum trimer has been shown to be slow, the gallium trimer was significantly more labile with a rate of formation indicated to be in the order of seconds or faster.

  • 18.
    Cunningham, Laura
    et al.
    Umeå University, Faculty of Science and Technology. Climate Impacts Research Centre (CIRC), Umeå University, 98107 Abisko, Sweden.
    Vogel, Hendrik
    Nowaczyk, Norbert
    Wennrich, Volker
    Juschus, Olaf
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rosen, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre (CIRC), Umeå University, 98107 Abisko, Sweden.
    Climatic variability during the last interglacial inferred from geochemical proxies in the Lake El'gygytgyn sediment record2013In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 386, p. 408-414Article in journal (Refereed)
    Abstract [en]

    The Last Interglacial Period (LIP) is often regarded as a good analogue for potential climatic conditions under predicted global warming scenarios. Despite this, there is still debate over the nature, duration and frequency of climatic changes during this period. One particularly contentious issue has been the apparent evidence of climatic instability identified in many marine cores but seemingly lacking from many terrestrial archives, especially within the Arctic, a key region for global climate change research. In this paper, geochemical records from Lake El'gygytgyn, north-eastern Russia, are used to infer past climatic changes during the LIP from within the high Arctic. With a sampling resolution of similar to 20-similar to 90 years, these records offer the potential for detailed, high-resolution palaeoclimate reconstruction. This study shows that the LIP commenced in central Chukotka similar to 129 thousand years ago (ka), with the warmest climatic conditions occurring between similar to 128 and 127 ka before being interrupted by a short-lived cold reversal. Mild climatic conditions then persisted until similar to 122 ka when a marked reduction in the sedimentation rate suggests a decrease in precipitation. A further climatic deterioration at similar to 118 ka marks the return to glacial conditions. This study highlights the value of incorporating several geochemical proxies when inferring past climatic conditions, thus providing the potential to identify signals related to environmental change within the catchment. We also demonstrate the importance of considering how changes in sedimentation rate influence proxy records, in order to develop robust palaeoenvironmental reconstructions. (C) 2013 Elsevier B.V. All rights reserved.

  • 19.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Andersson, Tove
    Chemistry.
    Lövgren, Lars
    Chemistry.
    Persson, Per
    Chemistry.
    Phosphate sorption in aluminum- and iron-rich humus soils2005In: Soil Science Society of America Journal, Vol. 69, no 1, p. 77-86Article in journal (Refereed)
    Abstract [en]

    Groundwater discharge areas in boreal forest ecosystems can potentially be areas where Fe and Al accumulate in the forest floor and affect the solubility of P. This study was conducted to determine phosphate sorption properties using humus soils containing high native amounts of Al and Fe. Humus soils were collected from two different forested groundwater discharge areas varying in pH and amount and distribution of At and Fe species. The phosphate sorption capacities were 265 and 216 mmol P kg(-1) dry wt. soil, respectively, for the two humus soils. Pyrophosphate extractable Al and Fe dominated in the first soil, 738 mmol kg(-1) dry wt. The concentration of pyrophosphate extractable Al and Fe in the second soil was 317 mmol kg(-1) dry wt.. whereas citrate-dithionite (CD) extracted 548 mmol Al and Fe kg(-1) dry wt. Using 0.1 mol dm(-3) NaCl as ionic medium gave a higher phosphate sorption compared with deionized water at the midrange additions, but no difference at the highest addition. Phosphate sorption was pH independent when 0.1 mol dm(-3) NaCl was used, whereas deionized water gave a sorption minimum at approximately pH 6. Dissolved organic carbon (DOC) release in solution was positively correlated with phosphate sorption, especially in 0.1 mol dm(-3) NaCl ionic medium. However, dissolved organic P (DOP) was unaffected by the phosphate sorption. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) indicated that precipitation of Al and Fe phosphates dominated at higher phosphate additions in the soil with mainly organically bound At and Fe, whereas both surface sorption and precipitation occurs in the soil with a larger amount of CD-extractable Fe.

  • 20.
    Gorzsás, András
    et al.
    Swedish University of Agricultural Sciences (SLU), Sweden.
    Stenlund, Hans
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Trygg, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sundberg, Björn
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences (SLU), Sweden.
    Cell specific chemotyping and multivariate imaging by combined FT-IR microspectroscopy and OPLS analysis reveals the chemical landscape of secondary xylem2011In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 66, no 5, p. 903-914Article in journal (Refereed)
    Abstract [en]

    Fourier-transform infrared (FT-IR) spectroscopy combined with microscopy enables acquiring chemical information from native plant cell walls with high spatial resolution. Combined with a 64 x 64 focal plane array (FPA) detector 4096 spectra from a 0.3 x 0.3 mm image can be simultaneously obtained, where each spectrum represents a compositional and structural "fingerprint" of all cell wall components. For optimal use and analysis of such large amount of information, multivariate approaches are preferred. Here, FT-IR microspectroscopy with FPA detection is combined with orthogonal projections to latent structures discriminant analysis (OPLS-DA). This allows for 1) the extraction of spectra from specific cell types, 2) identification and characterization of different chemotypes using the full spectral information, and 3) further visualising the pattern of identified chemotypes by multivariate imaging. As proof of concept, the chemotypes of Populus tremula xylem cell types are described. The approach revealed unknown features about chemical plasticity and patterns of lignin composition in wood fibers that would have remained hidden in the dataset with traditional data analysis. The applicability of the method on Arabidopsis xylem, and its usefulness in mutant chemotyping is also demonstrated. The methodological approach is not limited to xylem tissues but can be applied to any plant organ/tissue also using other microspectroscopy techniques such as Raman- and UV-microspectroscopy.

  • 21. Jalilehvand, Farideh
    et al.
    Maliarik, Mikhail
    Sandström, Magnus
    Mink, János
    Persson, Ingmar
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Tóth, Imre
    Glaser, Julius
    New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal-Metal Bond: 5. Structure Determination of Heterodimetallic Cyano Complexes in Aqueous Solution by EXAFS and Vibrational Spectroscopy2001In: Inorganic Chemistry, Vol. 40, no 16, p. 3889-99Article in journal (Refereed)
    Abstract [en]

    The structures of three closely related heterodimetallic cyano complexes, [(NC)5Pt-Tl(CN)n]n- (n = 1-3), formed in reactions between [PtII(CN)4]2- and TlIII cyano complexes, have been studied in aqueous solution. Multinuclear NMR data (205Tl, 195Pt, and 13C) were used for identification and quantitative analysis. X-ray absorption spectra were recorded at the Pt and Tl LIII edges. The EXAFS data show, after developing a model describing the extensive multiple scattering within the linearly coordinated cyano ligands, short Pt-Tl bond distances in the [(NC)5Pt-Tl(CN)n]n- complexes: 2.60(1), 2.62(1), and 2.64(1) Å for n = 1-3, respectively. Thus, the Pt-Tl bond distance increases with increasing number of cyano ligands on the thallium atom. In all three complexes the thallium atom and five cyano ligands, with a mean Pt-C distance of 2.00-2.01 Å, octahedrally coordinate the platinum atom. In the hydrated [(NC)5Pt-Tl(CN)(H2O)4]- species the thallium atom coordinates one cyano ligand, probably as a linear Pt-Tl-CN entity with a Tl-C bond distance of 2.13(1) Å, and possibly four loosely bound water molecules with a mean Tl-O bond distance of about 2.51 Å. In the [(NC)5Pt-Tl(CN)2]2- species, the thallium atom probably coordinates the cyano ligands trigonally with two Tl-C bond distances at 2.20(2) Å, and in [(NC)5Pt-Tl(CN)3]3- Tl coordinates tetrahedrally with three Tl-C distances at 2.22(2) Å. EXAFS data were reevaluated for previously studied mononuclear thallium(III)-cyano complexes in aqueous solution, [Tl(CN)2(H2O)4]+, [Tl(CN)3(H2O)], and [Tl(CN)4]-, and also for the solid K[Tl(CN)4] compound. A comparison shows that the Tl-C bond distances are longer in the dinuclear complexes [(NC)5Pt-Tl(CN)n]n- (n = 1-3) for the same coordination number. Relative oxidation states of the metal atoms were estimated from their 195Pt and 205Tl chemical shifts, confirming that the [(NC)5Pt-Tl(CN)n]n- complexes can be considered as metastable intermediates in a two-electron-transfer redox reaction from platinum(II) to thallium(III). Vibrational spectra were recorded and force constants from normal-coordinate analyses are used for discussing the delocalized bonding in these species.

  • 22.
    Johnson, Bruce B
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Surface Complexation of Mellitic Acid to Goethite: An Attenuated Total Reflection Fourier Transform Infrared Study2004In: Langmuir, ISSN 0743-7463, Vol. 20, no 3, p. 823-8Article in journal (Refereed)
    Abstract [en]

    The nature of the interaction between mellitic acid (benzene hexacarboxylic acid) and the common soil mineral goethite (-FeOOH) has been investigated as a function of pH and ionic strength by use of attenuated total reflection Fourier transform infrared spectroscopy. Molecular orbital calculations of the theoretical vibrational frequencies of the mellitate ion (L6-) and dihydrogen mellitate (H2L4-) have allowed the measured absorption frequencies to be accurately assigned. At pH values above 6, adsorption involves outer-sphere complexation of the deprotonated L6- ion. At lower pH values, there is evidence of a second outer-sphere surface complex involving a partially protonated species, although the extent of protonation of the surface species is significantly less than that found for the solution species at the same pH. While there is no evidence of inner-sphere complexation, increasing the ionic strength to 2.0 M does not displace the adsorbed species but does increase the fraction present on the surface as the fully deprotonated L6-. The small effect of ionic strength suggests that the adsorptive interaction, although outer-sphere in character, is still relatively strong, which indicates that hydrogen bonds may play a significant role. Hydrogen bonding may also help to account for the observed outer-sphere complexation at pH values above the pHiep of goethite.

  • 23.
    Jonsson, Caroline M.
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Jönsson, Julia
    Andersson, Ingegärd
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John S.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Glyphosate complexation to aluminium(III) in solution and to the surface of aged gamma-Al2O3: chemical speciation models combining spectroscopic and macroscopic dataManuscript (Other (popular science, discussion, etc.))
  • 24.
    Jonsson, Caroline
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John
    Umeå University, Faculty of Science and Technology, Chemistry.
    Adsorption of Glyphosate on Goethite (α-FeOOH): surface complexation modeling combining spectroscopic and adsorption data2008In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 42, no 7, p. 2464-2469Article in journal (Refereed)
    Abstract [en]

    N-(phosphonomethyl)glycine (glyphosate, PMG) is the most widely used herbicide, and its adsorption onto soil minerals plays a significant role in its mobility and rate of degradation. In this work, we present the results of the first serious effort to find a realistic surface complexation model that fits both adsorption and total proton concentration data for PMG on the common soil mineral, goethite. Special attention was focused on making sure that the final model was in good semiquantitative agreement with previously reported X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopic measurements. Electrostatic effects were accounted for using the Basic Stern model, and the charges of the PMG-containing surface complexes were assumed to be distributed across the 0- and β-planes. The reactions for the protonation of the goethite surface were described using the 1 pK model. We optimized on the intrinsic formation constants and the charge distributions of the complexes, as well as the initial total proton concentration (I = 0.1 M Na(NO3), 25.0 °C), and the following model was obtained.

    Here, β is the intrinsic formation constant, Q0 is the charge at the 0-plane, and the errors are reported as one standard deviation. The charge distributions of the complexes are rationalized by considering intramolecular hydrogen bonding between the protons of the amine group and both the phosphonate and carboxylate groups.

  • 25.
    Jönsson, Jörgen
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Schwertmannite precipitated from acid mine drainage: phase transformation, sulphate release and surface properties2005In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 20, no 1, p. 179-191Article in journal (Refereed)
    Abstract [en]

    Schwertmannite precipitated from acid mine drainage at the Kristineberg Zn-Cu mine in northern Sweden has been characterised regarding elemental composition, phase transformation as a function of pH and time. SO42- release and speciation of SO42- associated with the solid. The elemental analysis gave the composition FeSOS(OH)(5.02)(-SO4)(1.49) . 0.5H(2)O where approximately 1/3 of the SO42- is adsorbed to the surface. The conversion of schwertmannite to goethite at pH 9 was complete within 187 days; at pH 6. the conversion was still incomplete after 514 days. Lower pH and relatively high SO42- concentration decreased the conversion even further. Also temperature was shown to be an important parameter for this process and low temperature (+4 degreesC) effectively stopped the transformation at pH 3. The release of SO42- was linear with pH and X-ray photoelectron spectroscopy measurements confirming that the surface bound SO42- was released before bulk SO42-. Zeta potential measurements indicate a pH(IEP) of 7.2 for the schwertmannite sample. Prior to conversion into goethite, the SO42- associated with schwertmannite was indicated by attenuated total reflectance FTIR spectroscopy to be present both as bulk and surface species. Furthermore: the speciation of surface SO42- was shown to vary with pH and two predominating species were detected. As pH increases. SO42- is increasingly Coordinated in an outer sphere mode whereas a stronger. possibly inner sphere, complex dominates. at low pH.

  • 26.
    Kaplun, Marina
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nordin, Agneta
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    On the Anomalous Adsorption of [Pd(edta)](2-) at the Water/Goethite Interface: Spectroscopic Evidence for Two Types of Surface Complexes.2008In: Langmuir, ISSN 0743-7463, Vol. 24, no 2, p. 483-9Article in journal (Refereed)
    Abstract [en]

    The structure of palladium(II) ethylenediaminetetraacetate (edta) in aqueous solutions and its adsorption on the surface of goethite (-FeOOH) were studied using extended X-ray absorption fine structure spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. The obtained results show that in aqueous solutions, Pd-edta exists as a 1:1 complex, [Pd(edta)]2-, with edta acting as a quadridentate ligand. On the surface of goethite, [Pd(edta)]2- forms two different types of complexes over a pH range of 3.40-8.12. At pH < 5, [Pd(edta)]2- adsorbs as an outer-sphere species with possible hydrogen bonding. At higher pH values, the formation of inner-sphere complexes of the cation-type sets in after a cleavage of one glycinate ring and the formation of an (edta)Pd-O-Fe linkage.

  • 27.
    Kaplun, Marina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sandström, Malin
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boström, Dan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Crystal structures and spectroscopic properties of palladium complexes isolated from Pd–EDTA solutions2005In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 358, no 3, p. 527-534Article in journal (Refereed)
    Abstract [en]

    Two complexes were isolated from aqueous Pd(NO3)2–Na2H2EDTA solutions and studied by single crystal X-ray diffraction, IR/Raman spectroscopy, and photoelectron spectroscopy. The first complex, Pd(Hkpda)2 (kpda = ketopiperazinediacetate dianion, C8H10N2O5), forms yellow parallelepipeds during slow evaporation of Pd(NO3)2–Na2H2EDTA solution at 25 °C, and is a result of EDTA oxidation. The second one, [Pd(μ-H2EDTA)]2 · 2NaNO3 · 7.5H2O, with two EDTA molecules acting as bridges between two palladium atoms, forms yellow bipyramides during fast evaporation at 60 °C. In both complexes, the palladium atoms adopt a planar trans-geometry by bonding to two nitrogen and two oxygen atoms of two ligand molecules.

  • 28.
    Karlsson, Torbjörn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Mörth, Carl-Magnus
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Characterization of Iron(III) in Organic Soils Using Extended X-ray Absorption Fine Structure Spectroscopy2008In: Environmental Science & Technology, Vol. 42, no 15, p. 5449-54Article in journal (Refereed)
    Abstract [en]

    The distribution of different iron (Fe) species in soils, sediments, and surface waters has a large influence on the mobility and availability of Fe, other nutrients, and potentially toxic trace elements. However, the knowledge about the specific forms of Fe that occurs in these systems is limited, especially regarding associations of Fe with natural organic matter (NOM). In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize Fe(III) in organic soils (pH 4.6-6.0) with varying natural Fe content. The EXAFS data were subjected to wavelet transform analysis, to facilitate the identification of the nature of backscattering atoms, and to conventional EXAFS data fitting. The collective results showed the existence of two pools of iron: mononuclear Fe(III)-NOM complexes and precipitated Fe(III) (hydr)oxides. In the soil with lowest pH (4.6) and Fe content mononuclear organic complexes were the completely dominating fraction whereas in soils with higher pH and Fe content increasing amounts of Fe (hydr)oxides were detected. These results are of environmental importance, as the different iron pools most likely have markedly different reactivities.

  • 29.
    Karlsson, Torbjörn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Complexes with aquatic organic matter suppress hydrolysis and precipitation of Fe(III)2012In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 322-323, p. 19-27Article in journal (Refereed)
    Abstract [en]

    The fate of iron (Fe) in freshwaters is largely influenced by chemical interactions with natural organic matter (NOM). However, the knowledge about the molecular structure of the Fe species formed in association with aquatic NOM is still limited. In this work we have studied the interactions between Fe(III) and aquatic organic matter from the Suwannee River at a range of pH values and Fe concentrations (6489–55,659 μg g− 1 dry weight, pH 3.0–6.8) by means of extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopy. Our results showed that Fe(III) formed stable complexes with aquatic NOM, and that carboxylates were the predominant functional group involved in these interactions. At low Fe concentrations (6489–11,953 μg g− 1; pH 3.0–6.7) mononuclear Fe(III)–NOM complexes dominated the speciation while at higher pH values and Fe concentrations (~ 23,000 μg g− 1 pH 5.0–6.2 and 55,659 μg g− 1 pH 3.1–6.7) we detected mixtures of mononuclear Fe(III)–NOM complexes and a polymeric Fe(III) (hydr)oxide phase. The structure of the latter was indicated to be ferrihydrite-like. It was evident that the strong complexation between Fe and aquatic NOM suppressed the hydrolysis and polymerization of Fe(III), and it is likely that presence of NOM favored the formation of presumably small ferrihydrite particles with an inherent large reactivity due to high surface area per unit mass. Furthermore, our IR data showed that the formation of hydrolyzed Fe(III) was accompanied with structural changes of the NOM material, which implied that these interactions potentially also could affect the reactivity of NOM. Thus, our aggregative results highlight the importance of Fe(III)–NOM interactions for the geochemistry of Fe and NOM as well as for other elements (e.g. P and As), that is known to be strongly associated with Fe(III), in freshwater systems.

  • 30.
    Karlsson, Torbjörn
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Coordination chemistry and hydrolysis of Fe(III) in a peat humic acid studied by X-ray absorption spectroscopy2010In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, no 1, p. 30-40Article in journal (Refereed)
    Abstract [en]

    The speciation of iron (Fe) in soils, sediments and surface waters is highly dependent on chemical interactions with natural organic matter (NOM). However, the molecular structure and hydrolysis of the Fe species formed in association with NOM is still poorly described. In this study extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the coordination chemistry and hydrolysis of Fe(III) in solution of a peat humic acid (5010–49,200 μg Fe g−1 dry weight, pH 3.0–7.2). Data were analyzed by both conventional EXAFS data fitting and by wavelet transforms in order to facilitate the identification of the nature of backscattering atoms. Our results show that Fe occurs predominantly in the oxidized form as ferric ions and that the speciation varies with pH and Fe concentration. At low Fe concentrations (5010–9920 μg g−1; pH 3.0–7.2) mononuclear Fe(III)–NOM complexes completely dominates the speciation. The determined bond distances for the Fe(III)–NOM complexes are similar to distances obtained for Fe(III) complexed by desferrioxamine B and oxalate indicating the formation of a five-membered chelate ring structure. At higher Fe concentrations (49,200 μg g−1; pH 4.2–6.9) we detect a mixture of mononuclear Fe(III)–NOM complexes and polymeric Fe(III) (hydr)oxides with an increasing amount of Fe(III) (hydr)oxides at higher pH. However, even at pH 6.9 and a Fe concentration of 49,200 μg g−1 our data indicates that a substantial amount of the total Fe (>50%) is in the form of organic complexes. Thus, in environments with significant amounts of organic matter organic Fe complexes will be of great importance for the geochemistry of Fe. Furthermore, the formation of five-membered chelate ring structures is in line with the strong complexation and limited hydrolytic polymerization of Fe(III) in our samples and also agrees with EXAFS derived structures of Fe(III) in organic soils.

  • 31. Karlsson, Torbjörn
    et al.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Complexation of Copper(II) in Organic Soils and in Dissolved Organic Matter - EXAFS Evidence for Chelate Ring Structures2006In: Environmental Science and Technology, Vol. 40, no 8, p. 2623-8Article in journal (Refereed)
    Abstract [en]

    Associations with functional groups of natural organic matter (NOM) are of great importance for bioavailability, toxicity, and mobility of trace metals in soils and waters. In this study, the coordination chemistry of copper, Cu(II), in organic soils and dissolved organic matter (DOM) from soils and streams was investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. In both soil organic matter (SOM) and DOM (990-11 000 g Cu g-1 dry weight, pH 2.8-6.3), Cu(II) was coordinated by 4 oxygen/nitrogen (O/N) atoms at a distance of 1.92-1.95 Å in the first coordination shell. These four atoms are positioned in the equatorial plane of a Jahn-Teller distorted octahedron. In samples with a pH of 4.8-6.3, a second coordination shell with 2.0-3.8 C atoms was located at a distance of 2.76-2.86 Å. A significant improvement (19-39%) of the fit was obtained by including a third coordination shell with 2.0-3.8 O/C atoms involved in single scattering at an average distance of 3.69 Å and multiple scattering at an average distance of 4.19 Å. Our results provide evidence for inner-sphere complexation of Cu(II) in NOM and suggest that Cu(II) is complexed by either one or two five-membered chelate rings involving possible combinations of amino, carboxyl, or carbonyl functional groups. Ion activity measurements showed that less than 0.2% of total Cu was in the form of free Cu2+ in our samples at pH 4.8-6.3.

  • 32. Karlsson, Torbjörn
    et al.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Extended X-ray absorption fine structure spectroscopy evidence for the complexation of cadmium by reduced sulfur groups in natural organic matter2005In: ENVIRONMENTAL SCIENCE & TECHNOLOGY, ISSN 0013-936X, Vol. 39, no 9, p. 3048-55Article in journal (Refereed)
    Abstract [en]

    It is widely accepted that the bioavaiiability, toxicity, and mobility of trace metals are highly dependent on complexation reactions with functional groups in natural organic matter (NOM). In this study, the coordination chemistry of Cd in NOM was investigated by extended X-ray absorption fine structure spectroscopy. Soil organic matter (SOM) from different types of organic soils and dissolved organic matter (DOM) from an organic and a mineral soil horizon of a Spodosol and aquatic DOM from Suwannee River were investigated. In SOM samples (1000-25000 mu g of Cd g(-1), pH 4.6-6.6), Cd was coordinated by 1.0-2.5 S atoms at a distance of 2.49-2.55 angstrom and by 3.0-4.5 O/N atoms at a distance of 2.22-2.25 angstrom. In DOM samples (1750-4250 mu g of Cd g(-1), pH 5.4-6.3), Cd was coordinated by 0.3-1.8 S atoms at a distance of 2.51-2.56 angstrom and 3.6-4.5 O/N atoms at a distance of 2.23-2.26 angstrom. In both SOM and DOM samples a second coordination shell of 1.7-6.0 carbon atoms was found at an average distance of 3.12 angstrom. This is direct evidence for inner-sphere complexation of Cd by functional groups in NOM. Furthermore, ion activity measurements showed that less than 1% of total Cd was in the form of free Cd2+ in our samples. Bond distances and coordination numbers suggest that Cd complexed in SOM and DOM is a mixture of a 4-coordination with S (thiols) and 4- and 6-coordinations with O/N ligands. Given that Cd-S associations on average are stronger than Cd-O/N associations, our results strongly indicate that reduced S ligands are involved in the complexation of Cd by NOM also at native concentrations of metal in oxidized organic-rich soils and in humic streams.

  • 33.
    Leone, Laura
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Ferri, Diego
    Umeå University, Faculty of Science and Technology, Chemistry.
    Manfredri, Carla
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John
    Umeå University, Faculty of Science and Technology, Chemistry.
    Modeling the Acid-Base Properties of Bacterial Surfaces: A Combined Spectroscopic and Potentiometric Study of the Gram-Positive Bacterium Bacillus subtilis2007In: Environmental Science & Technology, Vol. 41, no 18, p. 6465-71Article in journal (Refereed)
    Abstract [en]

    In this study, macroscopic and spectroscopic data were combined to develop a surface complexation model that describes the acid-base properties of Bacillus subtilis. The bacteria were freeze-dried and then resuspended in 0.1 M NaCl ionic medium. Macroscopic measurements included potentiometric acid-base titrations and electrophoretic mobility measurements. In addition, ATR-FTIR spectra of wet pastes from suspensions of Bacillus subtilis at different pH values were collected. The least-squares program MAGPIE was used to generate a surface complexation model that takes into account the presence of three acid-base sites on the surface: COOH, NH+, and PO-, which were identified previously by XPS measurements. Both potentiometric titration data and ATR-FTIR spectra were used quantitatively, and electrostatic effects at the charged bacterial surface were accounted for using the constant capacitance model. The model was calculated using two different approaches: in the first one XPS data were used to constrain the ratio of the total concentrations of all three surface sites. The capacitance of the double layer, the total buffer capacity, and the deprotonation constants of the NH+, POH, and COOH species were determined in the fit. A second approach is presented in which the ratio determined by XPS of the total concentrations of NH+ to PO- sites is relaxed. The total concentration of PO- sites was determined in the fit, while the deprotonation constant for POH was manually varied until the minimization led to a model which predicted an isoelectric point that resulted in consistency with electrophoretic mobility data. The model explains well the buffering capacity of Bacillus subtilis suspensions in a wide pH range (between pH = 3 and pH = 9) which is of considerable environmental interest. In particular, a similar quantitative use of the IR data opens up possibilities to model other bacterial surfaces at the laboratory scale and help estimate the buffering capacity of carboxylate-containing compounds in natural samples.

  • 34.
    Leone, Laura
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Shchukarev, Andrey
    Surface characterization of the Gram-positive bacteria Bacillus subtilis-an XPS study2006In: Surface and Interface Analytsis, Vol. 38, p. 202-5Article in journal (Refereed)
    Abstract [en]

    Interactions at the bacteria-solid interface in aquatic environments are of crucial importance in biofilm formation processes. The characterization of microbial surfaces properties is therefore a very important step for the understanding of these interactions. In this study, XPS spectra of Bacillus subtilis wet pastes centrifuged from suspensions over a span of pH values were recorded using a fast-freezing procedure. The chemical composition of the bacterial surface was elucidated and the presence of surface sites containing carboxylate, phosphate and amine functional groups was established. It was possible to distinguish between charged and uncharged amine sites on the surface and follow their deprotonation reactions as a function of pH. It is suggested that increased metabolic activity around the physiological pH results in the excretion of proteins and/or peptides which are possibly related to the production of extracellular polymeric substances (EPS). Copyright © 2006 John Wiley & Sons, Ltd.

  • 35.
    Lindegren, Malin
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John
    Redden, G
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Citrate adsorption at the water-goethite interface: A spectroscopic evaluation of surface complexes2005In: GEOCHIMICA ET COSMOCHIMICA ACTA, ISSN 0016-7037, Vol. 69, no 10Article in journal (Other academic)
  • 36.
    Lindegren, Malin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Loring, John S
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Molecular structures of citrate and tricarballylate adsorbed on α-FeOOH particles in aqueous suspensions2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 18, p. 10639-10647Article in journal (Refereed)
    Abstract [en]

    In this work, the adsorption of citric (2-hydroxypropane-1,2,3-tricarboxylic acid) and tricarballylic (propane-1,2,3-tricarboxylic acid) acids onto α-FeOOH (goethite) in aqueous suspensions was studied as a function of pH and total ligand concentration in 0.1 M NaCl at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The adsorption experiments were carried out as a series of batch experiments, and a newly developed simultaneous infrared and potentiometric titration technique was used to collect in situ infrared spectra with high signal-to-noise ratios. The high quality of the infrared spectra allowed analysis by means of two-dimensional correlation spectroscopy formalism that aided the resolution of pH-dependent spectral features. This has enabled the detection of two previously unidentified citrate-goethite surface complexes: one protonated species at low pH, and one inner sphere complex prevailing at high pH and coordinated via a combination of hydroxyl and carboxylate groups. In addition, an inner sphere complex involving only carboxylate coordination predominating at low pH and an outer sphere complex existing in the circumneutral pH region were identified. The behavior of tricarballylate parallels that of citrate, except no inner sphere surface complex is formed at high pH values, which is in accordance with the lack of an α-hydroxyl group. The comparison between citrate and tricarballylate reinforces previous observations showing that inner sphere surface complexes of pure carboxylates at water-iron oxide interfaces are suppressed at high pH values, where outer sphere species are relatively more predominant. It also shows that significant amounts of inner sphere surface complexes of carboxylates only seem to form in the basic pH region when the ligands contain complementary functional groups, such as the hydroxyl or amine groups.

  • 37.
    Lindegren, Malin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Competitive adsorption between phosphate and carboxylic acids: quantitative effects and molecular mechanisms2009In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 60, no 6, p. 982-993Article in journal (Refereed)
    Abstract [en]

    The competitive adsorption at the water-goethite interface between phosphate and a carboxylic acid, either oxalate, citrate, 1,2,3,4-butanetetracarboxylic acid (BTCA), mellitate or Suwannee River Standard Fulvic Acid 1S101F (FA), was investigated over a wide pH range (3–9) by means of batch experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The quantitative results from the competitive adsorption measurements show that the efficiency of the organic acids in competing with phosphate was in the order oxalate < citrate < BTCA ≅ FA < mellitate. Oxalate showed no detectable effect, whereas the effect in the mellitate system was strong, and the aggregative results indicate that an increasing number of carboxylic groups favours competitive ability towards phosphate. The infrared spectroscopic results show conclusively that competition for goethite surface sites between carboxylic acids and phosphate is not a ligand-exchange reaction between inner-sphere surface complexes. Instead, ligands capable of multiple H-bonding interactions are required to out-compete and desorb surface complexes of phosphate. The fact that partially protonated organic acids are the most efficient emphasizes the importance of both H-accepting carboxylate groups and H-donating carboxylic acid groups for the competitive effect.

  • 38.
    Lindegren, Malin
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Competitive adsorption involving phosphate and benzenecarboxylic acids on goethite: Effects of molecular structures2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 343, no 1, p. 263-70Article in journal (Other academic)
    Abstract [en]

    The competitive adsorption between phosphate and either one of seven benzenecarboxylates (benzoate, phthalate, trimellitate, trimesoate, hemimellitate, pyromellitate, and mellitate) on the surfaces of fine-particulate goethite (α-FeOOH) was investigated as a function of pH. The series of ligands contained molecules with an increasing number of functional groups as well as three structural isomers of the tricarboxylates. Thus, the effects of both the number of carboxylate groups and the relative positions of these groups on the competitive efficiency toward phosphate were probed in this study. Quantitative adsorption experiments in batch mode and infrared spectroscopy were collectively used to evaluate the competitive adsorption reactions. Under the conditions probed, mono- and dicarboxylates had no detectable effect on phosphate adsorption whereas the ligands containing three or more carboxylate groups were able to partially outcompete phosphate. However, the pH dependency and the extent of these competitive effects were strongly dependent on the structure and composition of the benzenecarboxylate. The collective results showed that it was the competition for hydrogen-bonding surface sites rather than inner sphere surface sites that primarily determined the outcome of the competitive adsorption experiments, and it was the ability of the organic ligand to act as hydrogen-bonding acceptor and/or donor in various parts of the pH range that also determined the competitive pH dependency. The importance of H-bonding for the competitive adsorption between phosphate and benzenecarboxylic acids suggested that H-bonding interactions contributed substantially to the stabilities of both the adsorbed benzenecarboxylates and the phosphate ions and that these interactions were structurally specific; i.e., they were sensitive to the locations and the directional properties of the H-acceptor and H-donor surface sites.

  • 39. Lindgren, Johan
    et al.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Öhman, Lars-Olof
    Umeå University, Faculty of Science and Technology, Chemistry.
    Interactions of calcium(II), copper(II) and aluminium(III) ions with two chemically modified wood fibres2001In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 16, no 3, p. 225-34Article in journal (Refereed)
    Abstract [en]

    Two chemically modified softwood fibres, carboxymethylated cellulose (CMC) and 2,3-dicarboxylic cellulose (DCC), have been characterised with respect to acid/base properties and metal ion affinity. The experiments were performed as series of potentiometric titrations at 25 degreesC and at constant ionic strengths of 50 and 100 mM Na(Cl). Data showed that the amount of acidity in each pulp was independent of the ionic strength employed.

    In modelling the acid/base properties of both pulps, equilibrium models comprising two intrinsic dissociation constants and a co-optimised specific capacitance value were found capable of explaining all data collected at -log[H+]less than or equal to6. However, the acidity of the functional groups on the fibres increased, and the influence from electrostatic effects decreased, with increasing ionic strength. The metal ion affinity studies involved the ions Ca2+, Cu2+ and Al3+. Complementary information concerning metal ion-fibre interactions at the molecular level was obtained from IR measurements. It was found that the simple Donnan equilibrium model was inadequate for modelling these interactions and it was concluded that specific metal ion-fibre interactions occurred. For an equilibrium reaction in which two fibre sites interact with one metal ion, an equilibrium model was found that could explain all data in the examined -log[H+] and metal ion concentration ranges, for both pulps, and for all three metal ions examined. In the aluminium(III)-DCC system, also a tendency to hydrolysis of the Al-fibre complex was indicated. The two pulps had significantly different acid/base- and metal ion affinity properties, which mirrors significant differences in the local chemical environment of the carboxylic groups in the two pulps. The IR measurements indicated no direct interactions between the Ca2+ and Cu2+ ions and these carboxylic groups, implying that the complexes formed have a predominant outer-sphere character. In contrast, IR data clearly showed an inner-sphere coordination between Al3+ and the carboxylic groups on the fibres.

  • 40.
    Loring, John
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Simultaneous potentiometric and infrared spectroscopic titrations of mineral suspensions2004In: ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, ISSN 0065-7727, Vol. 227, p. U1220-U1220Article in journal (Other academic)
  • 41.
    Loring, John
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Simanova, Anna
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Highly Mobile Iron Pool from a Dissolution-Readsorption Process2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 14, p. 7054-7057Article in journal (Refereed)
    Abstract [en]

    Oxalate (C2O42−) acts synergistically on the dissolution of goethite (α-FeOOH) in the presence of siderophores that are secreted by plants and microorganisms to sequester iron. We report here the first in situ molecular-scale observations of synergistic ligand-promoted dissolution processes. We show that there are conditions under which oxalate promotes goethite dissolution, but dissolved Fe(III) concentrations do not increase because Fe(III)-oxalate complexes readsorb to the mineral surface. We demonstrate that these readsorbed Fe(III)-oxalate complexes are highly mobile, extremely reactive in the presence of uncomplexed siderophores, and responsible for the synergistic effects on the dissolution of goethite.

  • 42.
    Loring, John
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Combined infrared and potentiometric titrations of mineral suspensions2004In: GEOCHIMICA ET COSMOCHIMICA ACTA, ISSN 0016-7037, Vol. 68, no 11, p. A158-A158Article in journal (Other academic)
  • 43.
    Mäkie, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Österlund, Lars
    Adsorption of trimethyl phosphate and triethyl phosphate on dry and water pre-covered hematite, maghemite, and goethite nanoparticles2013In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 392, p. 349-358Article in journal (Refereed)
    Abstract [en]

    Adsorption of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on well-characterized nanoparticles of hematite (α-Fe(2)O(3)), maghemite (γ-Fe(2)O(3)), and goethite (α-FeOOH) has been studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 2D correlation DRIFTS analysis, and X-ray photoelectron spectroscopy (XPS) on dry and water pre-covered surfaces. It is shown that, at room temperature and low coverage, both TMP and TEP coordinate to Lewis acid Fe sites through the O phosphoryl atom on hematite and maghemite, while hydrogen bonding to Brønstedt acid surface OH groups dominates on goethite. At room temperature, slow dissociation of TMP occurs on the iron (hydr)oxide nanoparticles, whereby a methoxy group is displaced to form surface methoxy, leaving adsorbed dimethyl phosphate (DMP). Methoxy is further decomposed to formate, suggesting an oxidative degradation pathway in synthetic air on the oxide particles. Relatively, larger amounts of DMP and surface methoxy form on maghemite, while more formate is produced on hematite. Upon TMP adsorption on dry goethite nanoparticles, no oxidation surface products were detected. Instead, a slow TMP hydrolysis pathway is observed, yielding orthophosphate. It is found that pre-adsorbed water stimulates the hydrolysis of TMP. In contrast to TMP, TEP adsorbs molecularly on all iron hydr(oxide) nanoparticles. This is attributed to the longer aliphatic chain, which stabilizes the loss of charge on the methoxy CO bonds by charge redistribution upon phosphoryl O coordination to Fe surface atoms. The presented results implicate different reactivity depending on specific molecular structure of the organophosphorus compound (larger functional groups can compensate loss of charge due to surface coordination) and iron (hydr)oxide surface structure (exposing Lewis acid or Brønstedt acid sites).

  • 44.
    Mäkie, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Österlund, Lars
    Solar Light Degradation of Trimethyl Phosphate and Triethyl Phosphate on Dry and Water-Precovered Hematite and Goethite Nanoparticles2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 28, p. 14917-14929Article in journal (Refereed)
    Abstract [en]

    We report on the solar-light-mediated degradation of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on hematite and goethite nanoparticles in synthetic air. Adsorption and photoreactions of TMP and TEP were studied by in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) on dry and water-precovered nanoparticles in dark and under simulated solar light irradiation. Two-dimensional correlation analysis of infrared spectra was used to identify surface products as a function of reaction time. The optical properties of the hematite and goethite nanoparticles were investigated with optical spectrophotometry. The optical band gap was determined by analysis of the Tauc relationship around the band gap energy, E-g, yielding band gap energies of 2.14 and 2.28 eV for hematite and goethite nanoparticles, respectively. It is found that both TMP and TEP are readily photodegraded upon solar light irradiation (employing AM1.5 filters with 1735 W m(-2)), yielding surface orthophosphate as the final product. The first step in the dissociation of TMP and TEP is displacement of the methoxy and ethoxy groups, respectively, yielding adsorbed dimethyl phosphate (DMP) and methoxy, and diethyl phosphate (DEP) and ethoxy intermediates. Further photodegradation displaces additional methoxy and ethoxy groups with adsorbed orthophosphate as final reaction product. Methoxy and ethoxy fragments are simultaneously oxidized to carboxylates and carbonates. Photodegradation of TMP and TEP is promoted by OH radicals, which is evidenced by the higher photodegradation rate on water-precovered surfaces. The rate of TMP degradation is higher than that for TEP contrary to what is expected from their corresponding bulk hydrolysis rates, but consistent with their surface reactivity in dark, where TMP is observed to dissociate at room temperature but not TEP (or only very slowly). The photodegradation rate is higher on the goethite nanoparticles than the hematite nanoparticles on both dry and water precovered surfaces. The TMP and TEP photodegradation rate constants are found to be 0.025 (0.058) and 0.008 (0.023) min(-1), respectively, on water-precovered hematite (goethite) nanoparticles.

  • 45.
    Mäkie, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Westin, Gunnar
    Department of Materials Chemistry, The Ångstrom Laboratory, Uppsala University.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Österlund, Lars
    Department of Engineering Sciences, The Ångstrom Laboratory, Uppsala University.
    Adsorption of Trimethyl Phosphate on Maghemite, Hematite and Goethite Nanoparticles2011In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 32, p. 8948-8959Article in journal (Refereed)
    Abstract [en]

    Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanoparticles was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy show that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl atom (-P=O-Fe) on hematite and maghemite. On goethite most TMP molecules bond to Brønstedt acid surface OH groups and form hydrogen bonded surface complexes. The vibrational mode analysis and uptake kinetics suggest two main reasons for the observed trend of reactivity towards TMP (hematite > maghemite > goethite): (i) Larger number of accessible Lewis acid adsorption sites on hematite, (ii) stronger interaction between the Lewis acid Fe sites and the phosphoryl O atom on TMP for hematite and maghemite compared to goethite with concomitant formation of surface coordinated TMP and dimethyl phosphate intermediates. As a result, on the oxides a surface oxidation pathways dominates during the initial adsorption, which results in the formation of surface methoxy and formate. In contrast, on goethite a slower hydrolysis pathway is identified which eventually yields phosphoric acid. The observed trends of the reactivity and analysis of the corresponding surface structure and particle morphology suggest an intimate relation between the surface chemistry of exposed crystal facets on the iron minerals. These results are important to understand OP surface chemistry on iron minerals.

  • 46.
    Nelson, Hanna
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Loring, John
    Umeå University, Faculty of Science and Technology, Chemistry.
    Arsenate adsorption to goethite studied by combining spectroscopy and potentiometry2006Conference paper (Other academic)
  • 47.
    Norgren, Caroline
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lutzenkirchen, Johannes
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Metal-glyphosate complexation in solution and at the goethite-solution interface2004In: GEOCHIMICA ET COSMOCHIMICA ACTA, ISSN 0016-7037, Vol. 68, no 11, p. A167-A167Article in journal (Other academic)
  • 48.
    Norén, Katarina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Loring, John
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Adsorption of alpha amino acids at the water/goethite interface2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 319, no 2, p. 416-428Article in journal (Refereed)
    Abstract [en]

    The adsorption of amino acids onto mineral surfaces plays an important role in a wide range of areas, e.g., low-temperature aqueous geochemistry, bone formation and protein-bone interactions. In this work, the adsorption of three alpha aminoacids (sarcosine, MIDA and EDDA) onto goethite (α-FeOOH) was studied as a function of pH and background electrolyte concentration at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The results showed that adsorption of alpha amino acids were strongly dependent on the functionality and structure of the ligands. No adsorption was detected for the zwitterionic sarcosine indicating that simple alpha amino acids without other ionizable and/or functional groups display insignificant affinity for mineral surfaces such as goethite. With respect to the more complex amino acids, which are surface reactive, the number and relative positions of carboxylate and amine groups determine the types of surface interactions. These interactions range from non-specific outer-sphere to specific inner-sphere interactions as shown by the MIDA and EDDA results, respectively. The results presented herein suggest that isomerically-selective adsorption might only occur for amino acids that are capable of specific surface interactions, either through site-specific hydrogen bonding or inner-sphere complexation.

  • 49.
    Norén, Katarina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Loring, John S
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bargar, John R
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Adsorption mechanisms of EDTA at the water−iron oxide interface: implications for dissolution2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 18, p. 7762-7771Article in journal (Refereed)
    Abstract [en]

    The interactions between chelating agents and metal oxide particles play important roles for the distribution and availability of metal ions in aquatic environments. In this work, the adsorption of ethylenediaminetetraacetate (EDTA) onto goethite (α-FeOOH) was studied as a function of pH, time, and background electrolyte concentration at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of infrared spectroscopy using the attenuated total reflectance sampling technique. The collective infrared spectroscopic results of this study show that two surface complexes consisting of HEDTA3− and H2EDTA2− predominate at the water−goethite interface within the pH range of 3−9. No direct interactions of these complexes with surface Fe(III) ions were detected; hence, most likely the surface complexes are stabilized at the interface by electrostatic and hydrogen-bonding forces. The formation of the EDTA surface complexes is fast (time scale of minutes), but a slower (time scale of hours to days) dissolution reaction also occurs. The dissolved iron in solution is in the form of the highly stable FeEDTA solution complex, and the experimental evidence presented indicates that this complex can readsorb to the mineral surface. As dissolution proceeds, the concentration of FeEDTA in the solution phase increases, and this in turn leads to a buildup of readsorbed FeEDTA onto goethite. In the pH range of 4−7, this dissolution and readsorption process increases the total EDTA concentration at the surface. Under the experimental conditions in the present study, it is primarily the presence of uncomplexed EDTA in solution that drives the dissolution of goethite resulting in the subsequent readsorption of FeEDTA, while the HEDTA3− and H2EDTA2− surface complexes are stable during this process.

  • 50.
    Norén, Katarina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Adsorption of monocarboxylates at the water/goethite interface: The importance of hydrogen bonding2007In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 71, no 23, p. 5717-5730Article in journal (Refereed)
    Abstract [en]

    The adsorption of monocarboxylates (acetate, benzoate and cyclohexanecarboxylate) at the water/goethite interface was studied as a function of pH and ionic strength by means of quantitative adsorption measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR spectra were obtained of suspensions prepared in both H2O and D2O. In order to identify the number of predominating surface complexes and to improve the resolution of overlapping peaks the ATR-FTIR spectra were subjected to a 2D correlation spectroscopic analysis. The adsorption envelopes of acetate, benzoate and cyclohexanecarboxylate are similar and depend strongly on pH and ionic strength, but the pH dependence is also correlated to the slightly different pKa values of the monocarboxylic acids. At the molecular level, the ATR-FTIR spectroscopic results reveal two surface complexes: one solvent-surface hydration-separated ion pair and one surface hydration-shared ion pair. The former predominates at circumneutral pH values while the latter forms mainly in the acidic pH range. We find no evidence for direct inner-sphere coordination between the carboxylic oxygens and the Fe(III) ions present at the surface. The identification of surface hydration-shared ion pairs emphasizes the importance of comparatively strong ionic hydrogen-bonding interactions for adsorption processes at the water/goethite interface.

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