umu.sePublications
Change search
Refine search result
12 1 - 50 of 63
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    The Variable Capacitance Model: A Strategy for Treating Contrasting Charge-Neutralizing Capabilities of Counterions at the Mineral/Water Interface2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 8, 2009-2018 p.Article in journal (Refereed)
    Abstract [en]

    Thermodynamic models predicting ion adsorption at mineral/water interfaces can have limitations from the simplifying assumptions that compact plane thicknesses and capacitance values are constant, and that charge densities of electrolyte counterions of different charge-to-size ratios lie at the same planes of adsorption, or split between different planes. To address these limitations a thermodynamic adsorption modeling framework was developed to account for coexisting compact planes for each type of counterion complexes formed on a single mineral surface. This framework was developed to predict charge development at lepidocrocite (gamma-FeOOH) particle surfaces suspended in aqueous solutions of NaCl and NaClO4. The model incorporates properties of Cl-, ClO4-, and Na+ complexes formed at the (001) and (010) faces of this mineral obtained by molecular dynamics (MD) simulations. This concept was incorporated in a thermodynamic adsorption model that predicts an overall variable compact plane capacitance in terms of a linear combination of the capacitances of ion-specific EDL structures scaled for their relative surface loadings. These capacitance values are in turn constrained by compact plane thicknesses of every Cl-, ClO4-, and Na+ complex, based on their MD-derived structures and atomic densities. The model predicts experimental potential-determining (H+, OH-) data for submicrometer-sized synthetic lepidocrocite particles exhibiting both (001) and (010) faces. It also isolates electrostatic contributions from these faces. A computer code solving for this Variable Capacitance Model-VCM-is provided in the Supporting Information section of this article, and can be readily modified to predict molecular-level details of any other mineral/water interface systems using this methodology.

  • 2.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Water Structure and Hydrogen Bonding at Goethite/Water Interfaces: Implications for Proton Affinities2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 7, 4714-4724 p.Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics simulations of four crystallographic terminations of goethite (alpha-FeOOH) in contact with liquid water (300 K, 1 bar) were performed to resolve interfacial water structures in the vicinity of surface (hydr)oxo groups. Interfacial water molecules adopted highly surface-specific configurations on (010), 100), (110), and (021) planes of goethite. Water molecules generally had weaker hydrogen bond numbers and strengths, as well as smaller self-diffusion coefficients, than their bulk liquid counterparts. Relaxed surface Fe-O and H acceptor distances and populations were used to estimate proton affinity constants of singly-, and triply-coordinated (hydr)oxo groups using the multisite complexation model. These calculations confirmed that singly coordinated groups are mainly responsible for charge uptake under normal environmental conditions. However, revised proton affinity constants showed that protonation of doubly-coordinated hydroxo groups and one type of triply-coordinated oxo group may be favored in the presence of strongly binding negatively charged ligands. These calculations should facilitate elucidation of surface complexation mechanisms on this environmentally important material.

  • 3.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kozin, Philipp A.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Particle Morphological and Roughness Controls on Mineral Surface Charge Development2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 141, no 15 September, 567-578 p.Article in journal (Other academic)
    Abstract [en]

    Effects of mineral particle morphology and roughness on potential determining ion (p.d.i.; H+, OH) loadings achieved at synthetic lepidocrocite (γ-FeOOH) surfaces were predominantly investigated by potentiometry and thermodynamic modeling. Nanosized rod- (RL) and lath-shaped (LL) particles exhibiting different proportions of the same predominant crystallographic faces acquired largely comparable pH, ionic strength and counterion (NaCl, NaClO4) dependencies on p.d.i. loadings. These results supported previous claims that faces ideally containing proton silent sites only, are likely populated by additional proton active sites. This concept was supported further by results of roughened LL-like particles (LLR) also showing highly congruent pH-, ionic strength- and composition-dependent p.d.i. loadings with those of LL and RL. These loadings thereby correspond to maximal levels allowed by net attractive and repulsive forces at each solution composition, irrespective of particle morphology. Contrasting equilibration times required to achieve these loadings revealed considerably slower exchange of p.d.i. and electrolyte ions near the point of zero charge in the rough LLR than in the more idealized LL and RL particles.

    Thermodynamic modeling was used to test various concepts accounting for these results. The model made use of a novel framework capable of isolating electrostatic contributions from different faces, and of accounting for ion-specific double-layer properties within a single crystallographic face. These efforts made use of capacitance values for each electrolyte ions within the framework of a recently developed Variable Capacitance Model. Attempts at modeling all three particle types were used to suggest that the (0 1 0) face contains ∼0.9 site nm−2 of proton active sites, a value notably constrained by recently published Na+, Cl, and ClO4 loadings derived by cryogenic X-ray photoelectron spectroscopy. The model presented in this work thus provides a means to predict p.d.i. loadings on multifaceted mineral particle surfaces, and can therefore be used to constrain further our understanding of mineral/water interface reactivity.

  • 4.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lins, Roberto D
    Pacific Northwest National Laboratory, Richland Washington, USA .
    Electrostatic cooperativity of hydroxyl groups at metal oxide surfaces2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 38, 16568-16570 p.Article in journal (Refereed)
    Abstract [en]

    The O−H bond distribution of hydroxyl groups at the {110} goethite (α-FeOOH) surface was investigated by molecular dynamics. This distribution was strongly affected by electrostatic interactions with neighboring oxo and hydroxo groups. The effects of proton surface loading, simulated by emplacing two protons at different distances of separation, were diverse and generated several sets of O−H bond distributions. DFT calculations of a representative molecular cluster were also carried out to demonstrate the impact of these effects on the orientation of oxygen lone pairs in neighboring oxo groups. These effects should have strong repercussions on O−H stretching vibrations of metal oxide surfaces.

  • 5.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lutzenkirchen, Johannes
    Balmes, Oliver
    Beattie, James
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Modeling proton binding at the goethite (-FeOOH)-water interface2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 179, no 1, 11-27 p.Article in journal (Refereed)
    Abstract [en]

    The basic charging behaviours of goethite particles with different surfaces area (23, 37 and 85 m2 g-1) in 0.003-2.0 M NaNO3 were interpreted using surface complexation theory with the basic Stern model (BSM). The affinity of the goethite surface functional groups for protons was evaluated using the multisite complexation model (MUSIC) framework considering singly, doubly, and triply-coordinated surface oxygens with respect to underlying Fe(III) atoms. The affinity of these functional groups for protons was investigated first by using a calibration curve devised in Hiemstra et al. [J. Colloid Interface Science, 184 (1996) 680]. The calibration curve correlates the proton affinity constants of aqueous metal monomers to the undersaturation of the coordination environment of oxygens by considering the actual bond valences of Fe&unknown;O bonds in goethite, short hydroxyl bonds and hydrogen bonds. The results show that the predictions are sensitive to the range of short hydroxyl bonds/hydrogen bonds found in the literature. The singly- and one type of the triply coordinated sites are, however, most likely responsible for the basic charging behavior of goethite in the pH 2-11. The proton affinity constants of the singly- and triply coordinated sites were also optimized using titration data at different ionic strengths by co-optimizing values for electrolyte ion pairs and the capacitance of the Stern Layer. The optimal proton binding constants were in the range of the predicted values using the aforementioned calibration curve, although the modeling parameters are interdependent. A narrow range of CStern and electrolyte ion pairs was chosen to model the charging behavior of goethite by considering, (i), the range of proton binding constants from the aforementioned calibration curve; and (ii), the success of the models to predict zeta potential measurements assuming that the shear plane coincides with the head of the diffuse layer. Modeling parameters were also produced with the '1pK approximation' whereby the proton affinity constant of the singly- and of the triply-coordinated sites were set to the pH of zero charge and CStern and the electrolyte ion binding constants were co-optimized. In both cases, the values of CStern and of the electrolyte ion binding constants are slightly larger for the 23 and 37 m2 g-1 goethites than for the 85 m2 g-1. This indicates a larger proton uptake capacity of the 23 and 37 m2 g-1 goethites, putatively resulting from the larger surface roughness at the termination of the particles.

  • 6.
    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, 132-40 p.Article 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.

  • 7.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions. 2. tracing the relationship between surface charge and electrolyte adsorption2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 6, 2613-2616 p.Article in journal (Refereed)
    Abstract [en]

    Colloidal-sized hematite spheroids exposed to aqueous NaCl solutions were investigated by X-ray photoelectron spectroscopy using the fast-frozen technique. The O 1s region provided evidence for (de)protonation reactions of surface (hydr)oxo groups of OH-enriched/O-depleted hematite Surfaces. These results were also correlated to changes in sodium (Na 1s) and chloride (Cl 2p) contents with pH. Electrolyte ion surface loadings were successfully predicted using a classic thermodynamic adsorption model normalized for surface site density. These efforts pointed to ion-specific inner-Helmholtz plane capacitances.

  • 8.
    Boily, Jean-Francois
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Yesilbas, Merve
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Uddin, Munshi Md. Musleh
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Baiqing, Lu
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Trushkina, Yulia
    Salazar-Alvarez, German
    Thin Water Films at Multifaceted Hematite Particle Surfaces2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 48, 13127-13137 p.Article in journal (Refereed)
    Abstract [en]

    Mineral surfaces exposed to moist air stabilize nanometer- to micrometer-thick water films. This study resolves the nature of thin water film formation at multifaceted hematite (alpha-Fe2O3) nanoparticle surfaces with crystallographic faces resolved by selected area electron diffraction. Dynamic vapor adsorption (DVA) in the 0-19 Torr range at 298 K showed that these particles stabilize water films consisting of up to 4-5 monolayers. Modeling of these data predicts water loadings in terms of an "adsorption regime" (up to 16 H2O/nm(2)) involving direct water binding to hematite surface sites, and of a "condensation regime" (up to 34 H2O/nm(2)) involving water binding to hematite-bound water nanodusters. Vibration spectroscopy identified the predominant hematite surface hydroxo groups (-OH, mu-OH, mu(3)-OH) through which first layer water molecules formed hydrogen bonds, as well as surface iron sites directly coordinating water molecules (i.e., as geminal eta-(OH2)(2) sites). Chemometric analyses of the vibration spectra also revealed a strong correspondence in the response of hematite surface hydroxo groups to DVA-derived water loadings. These findings point to a near-saturation of the hydrogen-bonding environment of surface hydroxo groups at a partial water vapor pressure of similar to 8 Torr (similar to 40% relative humidity). Classical molecular dynamics (MD) resolved the interfacial water structures and hydrogen bonding populations at five representative crystallographic faces expressed in these nanoparticles. Simulations of single oriented slabs underscored the individual roles of all (hydro)oxo groups in donating and accepting hydrogen bonds with first layer water in the "adsorption regime". These analyses pointed to the preponderance of hydrogen bond-donating -OH groups in the stabilization of thin water films. Contributions of mu-OH and mu(3)-OH groups are secondary, yet remain essential in the stabilization of thin water films. MD simulations also helped resolve crystallographic controls on water water interactions occurring in the "condensation regime". Water water hydrogen bond populations are greatest on the (001) face, and decrease in importance in the order (001) > (012) approximate to (110) > (014) >> (100). Simulations of a single (similar to 5 nm x similar to 6 nm x similar to 6 nm) nanometric hematite particle terminated by the (001), (110), (012), and (100) faces also highlighted the key roles that sites at particle edges play in interconnecting thin water films grown along contiguous crystallographic faces. Hydroxo water hydrogen bond populations showed that edges were the preferential loci of binding. These simulations also suggested that equilibration times for water binding at edges were slower than on crystallographic faces. In this regard, edges, and by extension roughened surfaces, are expected to play commanding roles in the stabilization of thin water films. Thus, in focusing on the properties of nanometric-thick water layers at hematite surfaces, this study revealed the nature of interactions between water and multifaced particle surfaces. Our results pave the way for furthering our understanding of mineral-thin water film interfacial structure and reactivity on a broader range of materials.

  • 9.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Chemistry.
    Elucidation of oxyanion coordination geometries at solid surfaces of varied electric field strengths2009In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, no 37, 8133-5 p.Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations of oxyanions exposed to external electric fields revealed systematic variations in molecular geometries and vibration stretching frequencies. These variations can be used in laboratory studies to determine coordination geometries of oxyanions adsorbed on solid surfaces using infrared spectroscopy.

  • 10.
    Boily, Jean-François
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Chatman, Shawn
    Rosso, Kevin M
    Inner-Helmholtz potential development at the hematite (α-Fe2O3) (0 0 1) surface2011In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, no 15, 4113-4124 p.Article in journal (Refereed)
    Abstract [en]

    Electric potentials of the (0 0 1) surface of hematite were measured as a function of pH and ionic strength in solutions of sodium nitrate and oxalic acid using the single-crystal electrode approach. The surface is predominantly charge-neutral in the pH 4–14 range, and develops a positive surface potential below pH 4 due to protonation of μ-OH0 sites (pK1,1,0,int = −1.32). This site is resilient to deprotonation up to at least pH 14 (−pK−1,1,0,int ≫ 19). The associated Stern layer capacitance of 0.31–0.73 F/m2 is smaller than typical values of powders, and possibly arises from a lower degree of surface solvation. Acid-promoted dissolution under elevated concentrations of HNO3 etches the (0 0 1) surface, yielding a convoluted surface populated by sites. The resulting surface potential was therefore larger under these conditions than in the absence of dissolution. Oxalate ions also promoted (0 0 1) dissolution. Associated electric potentials were strongly negative, with values as large as −0.5 V, possibly from metal-bonded interactions with oxalate. The hematite surface can also acquire negative potentials in the pH 7–11 range due to surface complexation and/or precipitation of iron species (0.0038 Fe/nm2) produced from acidic conditions. Oxalate-bearing systems also result in negative potentials in the same pH range, and may include ferric-oxalate surface complexes and/or surface precipitates. All measurements can be modeled by a thermodynamic model that can be used to predict inner-Helmholtz potentials of hematite surfaces.

  • 11.
    Boily, Jean-François
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Fein, Jeremy B
    Proton binding to humic acids and sorption of Pb(II) and humic acid to the corundum surface2000In: Chemical Geology, Vol. 168, no 3-4, 239-53 p.Article in journal (Refereed)
    Abstract [en]

    An experimental investigation of proton binding to a humic acid, and of the co-adsorption of humic acid and Pb(II) to the corundum surface was conducted in 0.01 M NaNO3. We attempt to model the acid–base properties of the humic acid using both discrete and continuous distributions of proton affinity constants, also testing both nonelectrostatic and electrostatic approaches. The best-fitting models indicate that an average of three dominant proton-active functional groups are present on the humic acid with proton affinity constant logβ1,1,0 (int) equal to 2.6, 5.2 and 7.6. These values may be applied as intrinsic constants in a Constant Capacitance Model (CCM) or as means of distribution functions in a Langmuir–Freundlich isotherm where the humate is treated as a mixture of three monoprotic acids. The adsorption of humic acid onto corundum is best described using a Surface Complexation Model (SCM) with the Extended Constant Capacitance Model. The humate surface complexes, which best describe the experimental data, are the outer-sphere (>AlOH2+)0.1Hf1∑L(0.1–3.0+f1) and (>AlOH2+)0.1(H(f1+f2)∑L)(0.1–3.0+f1+f2) complexes, where f1 and f2 are the mole fractions of the sites with logβ1,1,0 (int)=7.6 and logβ1,1,0 (int)=5.2, respectively. Experimental data also show that the presence of calcium increases the adsorption of humate. The adsorption of Pb in the presence of humate was interpreted to proceed by the formation of the surface ternary complex >AlOH2+–L−z–Pb+2 at low to circumneutral pH. At high pH, aqueous Pb–humate complexation competes with Pb surface complexes and significantly reduces Pb adsorption.

  • 12.
    Boily, Jean-François
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gassman, Paul L
    Peretyazhko, Tetyana
    Szanyi, János
    Zachara, John M
    FTIR spectral components of schwertmannite2010In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, no 4, 1185-1190 p.Article in journal (Refereed)
    Abstract [en]

    Fourier transform infrared (FTIR) spectral components of three dominant groups of sulfate species in synthetic schwertmannite (Fe8O8(OH)6-x(SO4)x*nH2O) are presented. These components were extracted by multivariate curve resolution analysis of spectra obtained from N2(g)-dry samples initially reacted in aqueous solutions (pH 3-9) at room temperature. Each component contains complex sets of bands that correspond to mixtures of similar species. We tentatively assign these components to sulfate ions that are hydrogen- (components I and III) and iron-bonded (component I) to schwertmannite. Another component (II) is assigned to protonated sulfate species. Heating experiments to 130 degrees C moreover confirmed this possibility for component II. The spectral components extracted from this study can be used to identify dominant sulfate species in FTIR spectra of naturally occurring schwertmannite samples.

  • 13.
    Boily, Jean-François
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Ilton, Eugene S.
    An independent confirmation of the correlation of Uf4 primary peaks and satellite structures of UVI, UV and UIV in mixed valence uranium oxides by two-dimensional correlation spectroscopy2008In: Surface Science: Volume 602, Issue 24, 15 December 2008, Pages, Vol. 602, no 24, 3637-46 p.Article in journal (Refereed)
    Abstract [en]

    Two-dimensional (2D) correlation spectroscopy was used to resolve the positions and correlations among U4f primary peaks and satellite structures of UIV, UV and UVI components on a dry mica surface. These different species resulted from the reduction of UVI, initially sorbed/precipitated from solution, upon exposure to a high flux of monochromatic Al Kα X-rays during X-ray photoelectron spectroscopy. Synchronous and asynchronous 2D maps of these results are consistent with previous assignments to UIV, UV and UVI components of the solid. The synchronous spectra confirmed the negative correlation between UVI and UIV components and the asynchronous spectra confirmed the role of UV as a reactive intermediate in the reduction reaction of UVI to UIV. Simulations of 2D correlation maps using synthetic spectra of the primary peaks showed that the presence of highly overlapped peaks centered within 2 eV of each other cannot be distinguished without the presence of additional cross-peaks. The maps have therefore confirmed the existence of three dominant oxidation states, and identified positions of UIV, UV and UVI U4f primary peaks and satellite structures that are consistent with previous peak-fitting efforts. Satellite structures also showed out-of-phase correlations among the different oxidation states, further confirming their use as reliable indicators of oxidation state.

  • 14.
    Boily, Jean-François
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rosso, Kevin M
    Crystallographic controls on uranyl binding at the quartz/water interface2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 17, 7845-7851 p.Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics methods were used to simulate UO(2)(OH)(2)(0) binding to pairs of oxo sites (O(S)) on three low-index planes of α-SiO(2) in contact with water. Differences in binding site distributions on the (001), (010) and (101) planes produced distinct sets of stable U inner-sphere species. Steric constraints prevented bidentate coordination to the (001) surface, resulting in a mononuclear monodentate complex, [UO(2)(OH)(2)(H(2)O)(n)O(S)] (90% for n = 1 and 10% for n = 2 over 5 ns production runs). Binuclear bidentate coordination, [UO(2)(OH)(2)(H(2)O)(n)(O(S))(2)], was however favored on the (010) (99% for n = 0 and 1% for n = 1) and the (101) (72% for n = 0 and 28% for n = 1) planes. These results underscore a predominant four-coordinated equatorial shell for U when complexed to the quartz/water interface. Potential of mean force calculations uncovered a diversity of metastable outer- and inner-sphere complexes at local energy minima up to ∼0.4 nm from the surface. These calculations point to important differences in both energetic requirements and mechanisms for the approach of UO(2)(OH)(2)(0) to different quartz surfaces. Binding strengths are affected by binding site distribution, steric freedom, U hydration and OH orientation, and increase in the order (001) (3.7 kJ mol(-1)) < (101) (5.6 kJ mol(-1)) < (010) (6.5 kJ mol(-1)). A general binding mechanism involves (1) formation of monodentate outer-sphere complexes, (2) removal of oxo-bound waters, (3) formation of one (monodentate), then two (bidentate) direct U-O(S) bonds (inner-sphere), and (4) expulsion of excessive waters from the equatorial shell of U.

  • 15.
    Ding, Xiangbin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Song, Xiaowei
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Identification of fluoride and phosphate binding sites at FeOOH surfaces2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 41, 21939-21947 p.Article in journal (Refereed)
    Abstract [en]

    Iron oxyhydroxide minerals occur widely in nature and play important roles in environmental and industrial processes. Owing to their high reactivity, these minerals can act as sinks and/or transformation centers for a variety of inorganic and organic ions. Interfacial reactions are often mediated by surface (hydr)oxo groups. These groups can be singly, doubly, or triply coordinated with respect to underlying Fe atoms. In order to investigate the reactivity of these differently coordinated groups, Fourier transform infrared (FTIR) spectroscopy was used to examine adsorption products formed on iron oxyhydroxide surfaces. The absence of water was required to probe the O-H stretching region after initial reactions in aqueous media. This work was specifically focused on synthetic, submicrometer-sized lepidocrocite and goethite particles reacted with aqueous solutions of sodium fluoride and monosodium phosphate. Langmuir-Freundlich adsorption isotherms were calibrated on adsorption data in aqueous media at various pH values to obtain the maximum sorption densities for these ions under these conditions. FTIR measurements of the resulting solids dried under N-2(g) show that fluoride and phosphate ions preferentially exchange with singly coordinated hydroxyls. Doubly coordinated groups can, however, be exchanged with fluoride ions at relatively high loading densities. Triply coordinated groups remain, in contrast, resilient to exchange. They may, however, stabilize phosphate species by hydrogen bonding. These findings add further constraints to our understanding of adsorption reactions and to the formulation of molecularly adequate thermodynamic models.

  • 16.
    Feng, Wenting
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Erhagen, Bjoern
    Nilsson, Mats B.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Millennia-old organic carbon in a boreal paleosol: chemical properties and their link to mineralizable carbon fraction2016In: Journal of Soils and Sediments, ISSN 1439-0108, E-ISSN 1614-7480, Vol. 16, no 1, 85-94 p.Article in journal (Refereed)
    Abstract [en]

    Little is known about the biogeochemical properties of millennia-old soil organic matter (SOM) in boreal forest paleosols and whether these properties contribute to the persistence of several millennia-old SOM. In this study, we assessed the physicochemical properties of a well-drained paleosol and looked for links between these properties and the mineralizable carbon (C) fraction. We studied a well-drained paleosol located under a typical forest podzol in Northern Sweden, in which up to 7-kyr-old SOM was preserved according to C-14 dating. We assessed the elemental compositions of the outermost 2-mu m and 10-nm soil particle surfaces by using energy-dispersive X-ray scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. We also conducted a 5-week laboratory incubation of samples from both the paleosol and the podzol to quantify their mineralizable C fractions and analyzed the thermal stability of soil samples before and after incubation by using temperature-programmed desorption coupled with mass spectrometry techniques. Proxies for weathering (i.e., total mineral surface area and Al/Si and Fe/Si ratios of particle surfaces) suggested that the paleosol was at the same weathering stage as the contemporary forming podzol. Mineral soil particle surfaces of both the paleosol and podzol were dominated by aliphatic and ether/alcohol C functional groups. The incubation and thermal analysis showed that the mineralizable C fraction of the paleosol was smaller than that of the podzol, and losses of thermally labile SOM due to microbial degradation during the incubations were only detected in the mineral free O horizon of the podzol. Moreover, the mineralizable C fraction of the sampled podzol-paleosol sequence was correlated to the proportion of ether/alcohol C functional groups at the outermost 10-nm soil particle surfaces. Based on the links between microbial decomposition and the chemistry of soil particle surfaces and the thermal stability difference between organic and mineral soils induced by microbial decomposition, we conclude that the intrinsic chemical properties of SOM and its chemical surroundings is important for SOM preservation over a millennia timescale in the studied soil.

  • 17.
    Feng, Wenting
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Thermal Stability of Goethite-Bound Natural Organic Matter Is Impacted by Carbon Loading2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 51, 12790-12796 p.Article in journal (Refereed)
    Abstract [en]

    Dissolved natural organic matter (NOM) sorption at mineral surfaces can significantly affect the persistence. of organic carbon in soils and sediments. Consequently, determining the mechanisms that stabilize sorbed NOM is crucial for predicting the persistence of carbon in nature. This study determined the effects of loadings and pH on the thermal stability of NOM associated: With synthetic goethite (alpha-FeOOH) particle surfaces, as a proxy for NOM mineral interactions taking place in nature.. NOM thermal stability was investigated using temperature programmed desorption (TPD) in the 30-700 degrees C range to collect vibration spectra of thermally decomposing goethite NOM assemblages, and to concomitantly analyze evolved gases using mass spectrometry Results showed that NOM thermal stability, indicated by the range of temperatures in which CO2 evolved during thermal decomposition, was greatest in unbound NOM and lowest when NOM was bound to goethite. NOM thermal Stability was also loading dependent. It decreased:when loadings were in increased the 0.01 to 042 mg C m(-2) range, where the upper value corresponds to a Langmuirian adsorption maximum. Concomitant Fourier transform infrared (FTIR) spectroscopy measurement showed that these lowered stabilities could be ascribed to direct NOM-goethite interactions that dominated the NOM binding environment. Mineral surface interactions at larger loadings involved, on the contrary, a smaller fraction of the sorbed NOM, thus increasing thermal stability toward that of its unbound counterpart. This study thus identifies a sorption threshold below which NOM sorption to goethite decreases NOM thermal stability, and above which no strong effects are Manifested. This should likely influence the fate of organic carbon exposed to thermal gradients in natural environments.

  • 18.
    Hakobyan, Shoghik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Proton and gallium(III) binding properties of a biologically active salicylidene acylhydrazide2014In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 138, 9-15 p.Article in journal (Refereed)
    Abstract [en]

    Bacterial biofilm formation causes a range of problems in our society, especially in health care. Salicylidene acylhydrazides (hydrazones) are promising antivirulence drugs targeting secretion systems used during bacterial infection of host cells. When mixed with the gallium ion they become especially potent as bacterial and biofilm growth-suppressing agents, although the mechanisms through which this occurs are not fully understood. At the base of this uncertainty lies the nature of hydrazone-metal interactions. This study addresses this issue by resolving the equilibrium speciation of hydrazone-gallium aqueous solutions. The protonation constants of the target 2-oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (ME0163) hydrazone species and of its 2,4,6-trihydroxybenzaldehyde and oxamic acid hydrazide building blocks were determined by UV-visible spectrophotometry to achieve this goal. These studies show that the hydrazone is an excessively strong complexing agent for gallium and that its antivirulence properties are predominantly ascribed to monomeric 1:1Ga-ME0163 complexes of various Ga hydrolysis and ME0163 protonation states. The chelation of Ga(III) to the hydrazone also increased the stability of the compounds against acid-induced hydrolysis, making this group of compounds very interesting for biological applications where the Fe-antagonist action of both Ga(III) and the hydrazone can be combined for enhanced biological effect.

  • 19.
    Hakobyan, Shoghik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rzhepishevska, Olena
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Influence of Chelation Strength and Bacterial Uptake of Gallium Salicylidene Acylhydrazide on Biofilm Formation and Virulence by Pseudomonas aeruginosa2016In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 160, 24-32 p.Article in journal (Refereed)
    Abstract [en]

    Development of antibiotic resistance in bacteria causes major challenges for our society and has prompted a great need for new and alternative treatment methods for infection. One promising approach is to target bacterial virulence using for example salicylidene acylhydrazides (hydrazones). Hydrazones coordinate metal ions such as Fe(III) and Ga(III) through a five-membered and a six-membered chelation ring. One suggested mode of action is via restricting bacterial Fe uptake. Thus, it was hypothesized that the chelating strength of these substances could be used to predict their biological activity on bacterial cells. This was investigated by comparing Ga chelation strength of two hydrazone complexes, as well as bacterial Ga uptake, biofilm formation, and virulence in the form of production and secretion of a toxin (ExoS) by Pseudomonas aeruginosa. Equilibrium constants for deprotonation and Ga(III) binding of the hydrazone N′-(5-chloro-2-hydroxy-3-methylbenzylidene)-2,4-dihydroxybenzhydrazide (ME0329), with anti-virulence effect against P. aeruginosa, were determined and compared to bacterial siderophores and the previously described Ga(III) 2-oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (Ga-ME0163) and Ga-citrate complexes. In comparison with these two complexes, it was shown that the uptake of Ga(III) was higher from the Ga-ME0329 complex. The results further show that the Ga-ME0329 complex reduced ExoS expression and secretion to a higher extent than Ga-citrate, Ga-ME0163 or the non-coordinated hydrazone. However, the effect against biofilm formation by P. aeruginosa, by the ME0329 complex, was similar to Ga-citrate and lower than what has been reported for Ga-ME0163.

  • 20. Hanna, K
    et al.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sorption of two naphthoic acids to goethite surface under flow through conditions2010In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, no 23, 8863-8869 p.Article in journal (Refereed)
    Abstract [en]

    While the transport of low molecular weight organic acids was widely investigated, little is known about the mobility of the carboxylated aromatic compounds containing double rings in natural porous media. This study combines macroscopic (batch and column), microscropic (vibration spectroscopy), and surface complexation modeling to evaluate the mobility of two PAH degradation products: naphthoic acid (1-naphthoic acid (NA) and 1-hydroxy-2-naphthoic acid (HNA)), in porous media consisting of goethite-coated sand. The loss of ligands from aqueous solution was attributed to (1) a hydrogen-bonded surface complex present over the entire 3−10 pH range as well as protonated (2) surface and (3) bulk precipitates below pH 5. Mobility in column experiments was strongly affected by ligand functionality. Adsorption breakthrough predictions that make use of surface complexation parameters accurately predicted NA mobility. Those for HNA however predicted much less adsorption reactions than in the batch sorption experiments. Additional breakthrough experiments and test calculations confirmed that these differences were not related to sorption kinetics. HNA adsorption breakthrough data could only be predicted by lowering intrinsic complexation constant of the formation of hydrogen-bonded species, thereby suggesting modifications of the diffuse layer properties under flow conditions. These findings have strong implications in the assessment and prediction of contaminant transport and environmental remediation.

  • 21. Hanna, K.
    et al.
    Martin, S.
    Quiles, F.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sorption of Phthalic Acid at Goethite Surfaces under Flow-Through Conditions2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 23, 6800-6807 p.Article in journal (Refereed)
    Abstract [en]

    The objectives of this investigation were to improve our understanding of organic acid transport in porous media by focusing on a model system involving phthalic acid and goethite-coated sand (GCS). This was specifically made by first recalibrating a molecularly sound phthalate surface complexation model to GCS and then applying this model to describe breakthrough curves (BTC) in a GCS packed column. ATR-FTIR spectra of phthalic acid adsorbed at goethite surfaces at pH 3.0 and 6.0 and at loadings from 2.0 to 40.8 mu mol/m(2) confirmed the coexistence of metal-bonded (MB) and hydrogen-bonded (HB) complexes at low pH and the predominance of HB complexes at high pH. This concept was incorporated into a surface complexation model used to describe BTC at influent pH (pH(in)) values of 3.0, 6.0, and 7.8. The BTC revealed strongly pH-dependent behaviors. At pH(in) 3.0, the BTC revealed one front/plateau behavior while at pH(in) 6.0 two fronts/plateaus occurred. The existence of a second front/plateau led to an overestimation of the sorbed amount compared to that observed in the batch and caused a failure in the prediction of BTC. Additional column investigations suggested that surface loadings of nonspecifically adsorbed complexes could vary with pH and ionic strength and that the two-step breakthrough behavior may have emerged as a result of the formation of surface species of different natures than those during the first step, with the latter even serving as attachment sites corresponding to the second step. These findings call for refinements in current day modeling approaches used in reactive transport studies.

  • 22. Ilton, Eugene S
    et al.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Chemistry.
    Buck, Edgar C
    Skomurski, Frances N
    Rosso, Kevin M
    Cahill, Christopher L
    Bargar, John R
    Felmy, Andrew R
    Influence of Dynamical Conditions on the Reduction of U(VI) at the Magnetite-Solution Interface2010In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, no 1, 170-6 p.Article in journal (Refereed)
    Abstract [en]

    The heterogeneous reduction of U(VI) to U(IV) by ferrous iron is believed to be a key process influencing the fate and transport of U in the environment. The reactivity of both sorbed and structural Fe(II) has been studied for numerous substrates, including magnetite. Published results from U(VI)-magnetite experiments have been variable, ranging from no reduction to clear evidence for the formation of U(IV). In this contribution, we used XAS and high resolution (+/-cryogenic) XPS to study the interaction of U(VI) with nanoparticulate magnetite. The results indicated that U(VI) was partially reduced to U(V) with no evidence of U(IV). However, thermodynamic calculations indicated that U phases with average oxidation states below (V) should have been stable, indicating that the system was not in redox equilibrium. A reaction pathway that involves incorporation and stabilization of U(V) and U(VI) into secondary phases is invoked to explain the observations. The results suggest an important and previously unappreciated role of U(V) in the fate and transport of uranium in the environment.

  • 23. Ilton, Eugene S
    et al.
    Wang, Zheming
    Boily, Jean-François
    Qafoku, Odeta
    Rosso, Kevin M
    Smith, Steven C
    The Effect of pH and Time on the Extractability and Speciation of Uranium(VI) Sorbed to SiO(2)2012In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, no 12, 6604-6611 p.Article in journal (Refereed)
    Abstract [en]

    The effect of pH and contact time on uranium extractability from quartz surfaces was investigated using either acidic or carbonate (CARB) extraction solutions, time-delayed spikes of different U isotopes ((238)U and (233)U), and liquid helium temperature time-resolved laser-induced fluorescence spectroscopy (TRLFS). Quartz powders were reacted with (238)U(VI) bearing solutions equilibrated with atmospheric CO(2) at pH 6, 7, and 8. After 42 days, the suspensions were spiked with (233)U(VI) and reacted for an additional 7 days. Sorbed U was then extracted with either dilute nitric acid or CARB. For the CARB, but not the acid, extraction there was a systematic decrease in extraction efficiency for both isotopes from pH 6 to 8, which was mimicked by less desorption of (238)U, after the (233)U spike, from pH 6 to 8. The efficiency of (233)U extraction was consistently greater than that of (238)U, indicating a strong temporal component to the strength of U association with the surface that was accentuated with increasing pH. TRLFS revealed a strong correlation between CARB extraction efficiency and sorbed U speciation as a function of pH and time. Collectively, the observations show that aging and pH are critical factors in determining the form and strength of uranium-silica interactions.

  • 24.
    Kozin, Philipp A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mineral surface charge development in mixed electrolyte solutions2014In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 418, 246-253 p.Article in journal (Refereed)
    Abstract [en]

    Abstract Effects of competing counterions with different charge-to-size ratios on potential-determining ion (pdi; H+, OH−) adsorption at mineral/water interfaces were resolved in mixtures of aqueous solutions of NaCl and NaClO4 solutions. These effects were monitored on two synthetic goethite (α-FeOOH) particle preparations with distinct charge uptake capacities arising from differences in surface roughness. Charge development at these mineral surfaces was chiefly explored by high precision potentiometric titrations at 25 °C. These measurements confirmed that the greater charge-to-size ratio chloride ion not only promoted greater surface charge, but also had pronounced effects in perchlorate-dominated solutions. Cryogenic X-ray photoelectron spectroscopic measurements confirmed that perchlorate retains significant loadings at the goethite surface, even in the presence of chloride. Molecular dynamics simulations of the (1 1 0) plane of goethite exposed to these mixed solutions showed that chloride compressed the interfacial region containing electrolyte ions. Perchlorate, on the other hand, is not only present over a thicker region of the interface but also promotes an additional outer-sphere sodium species. These findings were used to develop a thermodynamic adsorption model predicting charge development at these mineral surfaces. The model involves a new formulation accounting for coexisting ion-specific regions each with their distinct compact plane capacitance values. The model can predict charge development in any mixtures of NaCl and NaClO4 contacted with goethite particles of contrasting charge uptake capacities without any additional parameters. This model can also be applied to a broader range of material surfaces.

  • 25.
    Kozin, Philipp A
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Proton Binding and Ion Exchange at the Akaganéite/Water Interface2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 12, 6409-6419 p.Article in journal (Refereed)
    Abstract [en]

    Proton exchange in nanosized synthetic akaganéite particles suspended in aqueous media and in ionic strengths of 3–100 mM NaCl and NaClO4 was monitored by high precision potentiometry at 25 °C. Proton budgets in the pH 3–10 range pertain to simultaneously occurring surface complexation and bulk ionic exchange reactions. Surface complexation reactions involve proton binding to (hydr)oxo groups of the dominant crystallographic planes of the particles. These are responsible for the colloidal attributes of the akaganéite particles, as confirmed by electrophoretic mobility measurements. Bulk ionic exchange involves the codiffusion of protons and chloride ions through the tunnel structure of the hollandite-type akaganéite bulk. Chloride ions migrate to bulk complexation sites that are ideally defined by eight surrounding hydroxyl groups, ≡(OH)8. Protons are in turn considered to be bound to neighboring oxo groups, ≡O. Collectively, the complexes are referred as [≡(OH)8···Cl······HO≡]. A thermodynamic model accounting for these two processes was developed to predict the pH (3–9), ionic strength (3–100 mM), and ionic medium (NaCl, NaClO4) dependence of the potentiometric data. This model is supported by new zeta potential data pointing to an isoelectric point of 9.6–10.3 for pristine akaganéite particles and by Fourier transform infrared spectra showing the impact of pH and ionic medium on bulk proton-chloride loadings. Our proposed stoichiometry for a chloride-rich solid of β-FeOOH·(HCl)0.192 corresponds to a maximal occupancy of 75% for chloride ions in the [≡(OH)8···Cl······HO≡] bulk complexation sites. Samples equilibrated in pure aqueous solutions should have a composition of β-FeOOH·(HCl)0.151, corresponding to a 60% occupancy for chloride ions due to a partial exchange of HCl. Our model can be used to predict compositional changes in the akaganéite bulk and surfaces upon any variations in pH and ionic media considered in this work.

  • 26.
    Kozin, Philipp A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Salazar-Alvarez, German
    Materials and Environmental Chemistry, Stockholm University, 114 18 Stockholm, Sweden.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Oriented Aggregation of Lepidocrocite and Impact on Surface Charge Development2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 30, 9017-9021 p.Article in journal (Refereed)
    Abstract [en]

    The impact of lepidocrocite (gamma-FeOOH) nanoparticle aggregation on mineral surface charge development was resolved in aqueous solutions of NaCl and NaClO4. Synthetic rod-like particles exhibiting charged edge (100) and neutrally/low-charged (010) faces self-aggregated in salt-free solutions. Aggregation was notably imaged by high-resolution transmission electron microscopy, and inferred by decreases in N-2(g)-B.E.T. specific surface area from 94 m(2)/g to 77 m(2)/g after 12 months, and to 66 m(2)/g after 33 months storage. Potential determining (H+, OH-) ions loadings in the 4-11 pH range were unchanged only if the particles remained aggregated in NaCI but only if they were disaggregated in NaClO4. These differences, alongside molecular simulations and experimental ion loadings resolved in other studies from our group, point to important controls on background electrolyte ion identity on the aggregation and charge development in lepidocrocite. These results may apply further to other mineral surfaces of comparable surface (hydr)oxo populations.

  • 27.
    Kozin, Philipp A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Salazar-Alvarez, German
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Oriented Aggregation of Lepidocrocite and Its Impact on Surface Charge DevelopmentManuscript (preprint) (Other academic)
  • 28.
    Kozin, Philipp A
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Electrolyte Ion Binding at Iron Oxyhydroxide Mineral Surfaces2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 39, 12129-12137 p.Article in journal (Refereed)
    Abstract [en]

    Electrolyte ion loadings at the surfaces of synthetic goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) particles that were pre-equilibrated in aqueous solutions of 10 mM NaCl and NaClO4 at 25 °C were investigated by cryogenic X-ray photoelectron spectroscopy (XPS). Atomic concentrations of Cl(-), ClO4(-), and Na(+) were correlated to potential determining ion (pdi; H(+), OH(-)) loadings obtained by potentiometric titrations. While Cl(-) promoted more pdi adsorption than ClO4(-), due to its greater charge-to-size ratio, both ions followed the same loading dependence on pdi adsorption, in contrast to previous studies supporting the concept for negligible perchlorate adorption. Lepidocrocite particles exhibited a stronger response of electrolyte adsorption to pdi loadings due electrolyte ion adsorption on the proton inactive (010) plane. These particles also acquired greater sodium loadings than goethite. These loadings were moreover considerably enhanced by perchlorate adsorption, possibly due to a thickening of the interfacial region in NaClO4 on the (010) plane. Finally, goethite particles with rougher surfaces acquired greater pdi and ion loadings than on those with smoother surfaces. No strong differences could be discerned between Cl(-) and ClO4(-) loadings on these materials. This work thus identified key aspects underpinning the relationship between pdi and electrolyte loadings at FeOOH mineral surfaces of environmental and technological importance.

  • 29. Lower, Brian H
    et al.
    Yongsunthon, Ruchirej
    Shi, Liang
    Wildling, Linda
    Gruber, Hermann J
    Wigginton, Nicholas S
    Reardon, Catherine L
    Pinchuk, Grigoriy E
    Droubay, Timothy C
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lower, Steven K
    Antibody Recognition Force Microscopy Shows that Outer Membrane Cytochromes OmcA and MtrC Are Expressed on the Exterior Surface of Shewanella oneidensis MR-12009In: Applied and environmental microbiology, ISSN 1098-5336, Vol. 75, no 9, 2931-5 p.Article in journal (Refereed)
    Abstract [en]

    Antibody-recognition force microscopy showed that OmcA and MtrC are expressed on the exterior surface of living Shewanella oneidensis MR-1 cells when Fe(III), including solid phase hematite (Fe2O3), was the terminal electron acceptor. OmcA was localized to the interface between the cell and mineral. MtrC displayed a more uniform distribution across the cell surface. Both cytochromes were associated with an extracellular polymeric substance.

  • 30.
    Lucas, Marie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mapping Electrochemical Heterogeneity at Iron Oxide Surfaces: A Local Electrochemical Impedance Study2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 50, 13618-13624 p.Article in journal (Refereed)
    Abstract [en]

    Alternating current scanning electrochemical microscopy (AC-SECM) was used for the first time to map key electrochemical attributes of oriented hematite (alpha-Fe2O3) single crystal surfaces at the micron-scale. Localized electrochemical impedance spectra (LEIS) of the (001) and (012) faces provided insight into the spatial variations of local double layer capacitance (C-dl) and charge transfer resistance (R-ad). These parameters were extracted by LEIS measurements in the 0.4-8000 Hz range to probe the impedance response generated by the redistribution of water molecules and charge carriers (ions) under an applied AC. These were attributed to local variations in the local conductivity of the sample surfaces. Comparison with global EIS measurements on the same Samples uncovered highly comparable frequency-resolved processes, that were broken: down into contributions fromthe bulk hematite, the interface as well as the microelectrode/tip :assembly. This work paves the way for new studies aimed at mapping electrochemical processes at the mesoscale on this environmentally and technologically important material.

  • 31. Lützenkirchen, Johannes
    et al.
    Boily, Jean-François
    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.
    Limitations of the potentiometric titration technique in determining the proton active site density of goethite surfaces2002In: Geochimica et Cosmochimica Acta: Volume 66, Issue 19, 1 October 2002, Pages, Vol. 66, no 19, 3389-96 p.Article in journal (Refereed)
    Abstract [en]

    Density of proton active surface sites at mineral surfaces is a property of fundamental importance in equilibrium modeling of surface complexation reactions. In this article, methods for an experimental determination of these sites at the surface of α-FeOOH (goethite) are explored. It is shown that previously obtained saturation data of goethite with respect to protons do not yield a site density that can be considered as an intrinsic sorbent property: the results are below crystallographically expected values and values for different ionic media in terms of composition and concentration yield different numbers—for example, chloride would yield higher values than nitrate at the same concentration, and higher electrolyte concentration would favor higher apparent maxima. Although site saturation might be explained by electrostatic repulsion, which is more efficient at high electrolyte concentration or for certain ions, further independent experimental results show that no saturation occurs on goethite down to ph ≡ −log[H+] = 2.2 and possibly to PH = 1.0 in 0.6 M NaCl. For those very low pH values, the experimental charging curve was obtained by coulometric back titration (using the Gran plot) or titrations with tris (hydroxymethyl)-aminomethane of the supernatant of acidified goethite suspension. These experimental data are to our knowledge the first high quality data at such low pHs. However, small errors in the determination of proton concentrations (1%) are shown to strongly affect the shape of the charging curve for ph < 2. Furthermore, goethite dissolution (proton consumption and iron reduction in coulometric titrations) and liquid junction effects interfere at low ph, hampering the straightforward application of coulometric Gran titrations over the whole pH range. From these experiments, it can nonetheless be ascertained that a minimum of 2.5 protons/nm2 can be adsorbed at the goethite surface from the point of zero charge (ph 9.4) to pH 0.9. Although these studies are restricted to goethite, those studies in which titrations with excess acid and base have been used for the determination of proton active site concentrations of sorbents should be reconsidered.

  • 32. Lützenkirchena, J
    et al.
    Boily, J F
    Gunneriusson, L
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Chemistry.
    Protonation of different goethite surfaces—Unified models for NaNO3 and NaCl media2008In: Journal of Colloid and Interface Science, Vol. 317, no 1, 155-65 p.Article in journal (Refereed)
    Abstract [en]

    Acid–base titration data for two goethites samples in sodium nitrate and sodium chloride media are discussed. The data are modeled based on various surface complexation models in the framework of the multi site complexation (MUSIC) model. Various assumptions with respect to the goethite morphology are considered in determining the site density of the surface functional groups. The results from the various model applications are not statistically significant in terms of goodness of fit. More importantly, various published assumptions with respect to the goethite morphology (i.e., the contributions of different crystal planes and their repercussions on the “overall” site densities of the various surface functional groups) do not significantly affect the final model parameters within simple 1-pK approximations. The simultaneous fit of the chloride and nitrate data results in electrolyte binding constants, which are applicable over a wide range of electrolyte concentrations including mixtures of chloride and nitrate. Model parameters for the goethite sample with 90 m2/g specific surface area are in excellent agreement with parameters that were independently obtained by another group on different goethite titration data sets.

  • 33.
    Martin, Sebastien
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Rennes Cedex 7, France.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hanna, Khalil
    Rennes Cedex 7, France.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kinetics and Mechanisms of Ciprofloxacin Oxidation on Hematite Surfaces2015In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 20, 12197-12205 p.Article in journal (Refereed)
    Abstract [en]

    Adsorption of antibiotics at mineral surfaces has been extensively studied over the past 20 years, yet much remains to be learned on their interfacial properties and transformation mechanisms. In this study, interactions of Ciprofloxacin (CIP), a fluoroquinolone antibiotic with two sets of synthetic nanosized hematite particles, with relatively smooth (H10, 10-20 nm in diameter) and roughened (H80, 80-90 nm in diameter) surfaces, were studied by means of liquid chromatography (LC), mass spectrometry (MS), and spectroscopy (vibration and X-ray photoelectron). Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy provides evidence for inner-sphere bidentate complex formation of CIP at hematite surfaces in 0.01 M NaCl, irrespective of pH and particle size. ATR-FTIR spectroscopy also revealed that the sorbed mother CIP molecule decayed to other surface species over a period of at least 65 h. This was supported by the detection of three daughter products in the aqueous phase by LC/MS. The appearance of NH3+ groups during the course of these experiments, revealed by cryogenic XPS, provides further evidence that CIP oxidation proceeds through an opening of piperazine ring via N-dealkylation. Additional in vacuo FTIR experiments under temperature-programmed desorption also showed that oxidation of sorbed byproducts were effectively degraded beyond 450 degrees C, a result denoting considerably strong (inter)molecular bonds of both mother and daughter products. This work also showed that rougher, possibly multidomainic particles (H80) generated slower rates of CIP decomposition but occurring through more complex schemes than at smoother particle surfaces (H10). This work thus uncovered key aspects of the binding of an important antibiotic at iron oxide surfaces, and therefore provided additional constraints to our growing understanding of the fate of emerging contaminants in the environment.

  • 34. Michel, F Marc
    et al.
    Barrón, Vidal
    Torrent, José
    Morales, María P
    Serna, Carlos J
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Liu, Qingsong
    Ambrosini, Andrea
    Cismasu, A Cristina
    Brown, Gordon E
    Ordered ferrimagnetic form of ferrihydrite reveals links among structure, composition, and magnetism2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 7, 2787-92 p.Article in journal (Refereed)
    Abstract [en]

    The natural nanomineral ferrihydrite is an important component of many environmental and soil systems and has been implicated as the inorganic core of ferritin in biological systems. Knowledge of its basic structure, composition, and extent of structural disorder is essential for understanding its reactivity, stability, and magnetic behavior, as well as changes in these properties during aging. Here we investigate compositional, structural, and magnetic changes that occur upon aging of "2-line" ferrihydrite in the presence of adsorbed citrate at elevated temperature. Whereas aging under these conditions ultimately results in the formation of hematite, analysis of the atomic pair distribution function and complementary physicochemical and magnetic data indicate formation of an intermediate ferrihydrite phase of larger particle size with few defects, more structural relaxation and electron spin ordering, and pronounced ferrimagnetism relative to its disordered ferrihydrite precursor. Our results represent an important conceptual advance in understanding the nature of structural disorder in ferrihydrite and its relation to the magnetic structure and also serve to validate a controversial, recently proposed structural model for this phase. In addition, the pathway we identify for forming ferrimagnetic ferrihydrite potentially explains the magnetic enhancement that typically precedes formation of hematite in aerobic soil and weathering environments. Such magnetic enhancement has been attributed to the formation of poorly understood, nano-sized ferrimagnets from a ferrihydrite precursor. Whereas elevated temperatures drive the transformation on timescales feasible for laboratory studies, our results also suggest that ferrimagnetic ferrihydrite could form naturally at ambient temperature given sufficient time.

  • 35.
    Mitev, Pavlin D.
    et al.
    Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, S-751 21 Uppsala, Sweden .
    Eriksson, Anders
    Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, S-751 21 Uppsala, Sweden .
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hermansson, Kersti
    Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, S-751 21 Uppsala, Sweden .
    Vibrational models for a crystal with 36 water molecules in the unit cell: IR spectra from experiment and calculation2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 16, 10520-10531 p.Article in journal (Refereed)
    Abstract [en]

    We present experimental and calculated IR spectra of the water molecules in crystalline aluminium nitrate nonahydrate and a method to generate a realistic and well resolved isotope-isolated spectrum from periodic DFT calculations. Our sample crystal contains 18 structurally different OH groups and is a perfect benchmark compound to validate vibrational models and the structure-property relationship of bound water molecules. FTIR spectra (ATR technique) were recorded for the Al(NO3)(3)center dot 9H(2)O crystal at 138 and 298 K, and due to a multitude of OH contributions and couplings, they are naturally poorly resolved and yield a broad OH band in the range 3500 to 2700 cm(-1) at both temperatures. Isotope-isolated IR spectra have the clear advantage over non-deuterated spectra that they are better resolved and easier to interpret - here we have extended the experimental study by simulating the isotope-isolated IR spectrum, using PBE-D2 and auxiliary B3LYP calculations and an anharmonic OH vibrational model. We find excellent agreement between the shapes and frequency ranges of the experimental and calculated OH spectral bands. We make use of four different vibrational models: (i) a harmonic lattice-dynamical model for the isotope-isolated crystal with 1 H among 71 D, (ii) a harmonic lattice-dynamical model for the normal undeuterated crystal involving all the vibrational couplings, (iii) a harmonic 1-dimensional uncoupled OH vibrational model, and (iv) the anharmonic variant of the previous model, which yields the final spectrum. We also use the individual frequencies, resolved by the calculations, to quantify new or extended relationships involving OH frequencies versus local electric fields and H-bond distances. We explore the correlation between OH frequency and molecular dipole moment for bound water molecules.

  • 36.
    Phan, Duong Ngoc Chau
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Marklund, Stellan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    A link between fly ash chemistry and the thermal formation of PCDDs, PCDFs, PCBs, and PCNs during waste incinerationManuscript (preprint) (Other academic)
    Abstract [en]

    The relationship between the properties of fly ash generated during waste incineration and the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) was investigated using a laboratory incinerator and two artificial wastes that were designed to reflect regional differences in municipal solid waste composition. Flue gas and fly ash samples were collected isokinetically via a sampling port in the post-combustion zone at a flue gas temperature of 300 °C. The mineralogical properties, morphology and sub-surface composition, surface composition and elemental oxidation states of the fly ash samples were determined. The flue gas samples were analyzed for Mo-OCDDs, Mo-OCDFs, Tri-DCBs, and Di-OCNs. Orthogonal Projections to Latent Structures (OPLS) modeling was used to study the relationship between the properties of the fly ash and the post-combustion formation of polychlorinated aromatics. The presence of high levels of ash-forming elements (i.e. Na, Mg, Fe, Ti, etc…) in the waste reduced the S content of the flue gas and thereby promoted the production of Cl2 via the Deacon process. Because this process is vital for the formation of polyaromatic species, wastes with depleted levels of fly ash-building elements should be favored to minimize the release of toxic PCDDs, PCDFs, PCBs, and PCNs during incineration.

  • 37.
    Phan, Duong Ngoc Chau
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Link between fly ash properties and polychlorinated organic pollutants formed during simulated municipal solid waste incineration2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 4, 2761-2769 p.Article in journal (Refereed)
    Abstract [en]

    The relationship between the properties of fly ash generated during waste incineration and the thermal formation of persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs), was investigated on two artificial wastes using a laboratory incinerator. Fly ash particles were sampled in the post-combustion zone at approximately 300 degrees C and were characterized with the following complementary techniques: X-ray diffraction (XRD), scanning electron microscopy energy-dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Flue gas samples were collected at the same location and analyzed for Mo-OCDDs, Mo-OCDFs, Tri-DCBs, and Di-OCNs. A strong correlation between fly ash characteristics and waste composition exists for several of the elements considered in this work. For instance, the waste containing the highest levels of Al produced more abundant Al-bearing minerals and elemental Al in the resulting fly ashes. Copper, an especially important POP formation catalyst, was not detected in the top 10 nm surface of fly ash particles but rather occurred within the top 2 pm, indicating that surface copper of catalytic importance for POP formation reactions was not available. Important contributions of ferric iron present in the abundant fly ash-building hematite phase could have also played an important role, especially given its documented contributions in chlorination pathways. Orthogonal projections to latent structures (OPLS) modeling resolved the relationship between fly ash properties and the post-combustion POP formation. These efforts showed that low levels of ash-forming elements (i.e., Na, Mg, Fe, Ti, etc.) were associated with an increase in flue gas S levels, which, in turn, poison the Cl-2 production via the Deacon process. Wastes with depleted levels of fly-ash-building elements should therefore be favored for minimizing PCDD, PCDF, PCB, and PCN release caused by incineration.

  • 38.
    Phan, Duong Ngoc Chau
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Physicochemical properties of fly ash particles formed during municipal solid waste combustionManuscript (preprint) (Other academic)
    Abstract [en]

    Fly ashes generated from two artificial wastes were investigated with regard to physicochemical properties of importance for thermal formation of persistent organic pollutants (POPs). The ash samples were collected in the post-combustion zone at approximately 300 °C and were characterized using complementary techniques: X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray (SEM/EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The results showed a strong correlation between ash chemistry and waste composition. The waste containing higher levels of Al resulted in more abundant Al-bearing minerals, as well as the element Al, in the fly ash. In the case of Fe, no such correlation was found. Copper, an especially important reaction catalyst, was not detected by in the top 10-nm layer of ash but rather occurred within the top 2-µm, indicating that POPs formation reactions may have depleted the available surface Cu. The possibly inaccessible buried forms of Cu may also be a limiting factor in the production of POPs. Furthermore, organic forms of carbon were present at fly ash surfaces, although not significantly in their chlorinated forms. Taken collectively, these results contribute to understanding the correlations between fly ash chemistry and the thermal formation of POPs.

  • 39.
    Ramstedt, Madeleine
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nakao, Ryoma
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Nyunt Wai, Sun
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Monitoring surface chemistry changes in the bacterial cell wall: multivariate analysis of Cryo-X-ray photoelectron spectroscopy data2011In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, no 14, 12389-12396 p.Article in journal (Refereed)
    Abstract [en]

    Gram-negative bacteria can alter the composition of the Lipopolysaccharide (LPS) layer of the outer membrane as a response to different growth conditions and external stimuli. These alterations can, for example, promote attachment to surfaces and biofilm formation. The changes occur in the outermost layer of the cell and may consequently influence interactions between bacterial cells and surrounding host tissue, as well as other surfaces. Microscopic analyses, fractionation of bacterial cells or other traditional microbiological assays have previously been used to study these alterations. These methods can, however, be time consuming and do not always give detailed chemical information about the bacterial cell surface. We here present an analytical method that provides chemical information on the outermost portion of bacterial cells with respect to protein, peptidoglycan, lipid and polysaccharide content. The method involves cryo-X-ray Photoelectron Spectroscopy (XPS) analyses of the outermost portion (within ~10 nm of the surface) of intact bacterial cells, followed by a multivariate curve resolution analysis of carbon spectra. It can be used as a tool for characterizing and monitoring variations in the chemical composition of bacterial cell walls or of isolated outer membrane vesicles, variations that result from e.g. mutations or external stimuli. The method enabled us to accurately predict the alterations in polysaccharide content and surface chemistries of a set of well characterized Escherichia coli LPS mutants. The described approach may moreover be applied to monitor surface chemical composition of other biological samples.

  • 40. Rustad, James R
    et al.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Letter: Density functional calculation of the infrared spectrum of surface hydroxyl groups on goethite (-FeOOH)2010In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 95, no 2-3, 414-417 p.Article in journal (Other academic)
    Abstract [en]

    We present density functional calculations of vibrational frequencies of OH groups on an idealized goethite (110) surface, represented by a large embedded cluster model. The calculations show that isolated surface groups bound to one, two, and three metal ions can have nearly identical OH stretching frequencies. This finding provides a strong constraint on interpretations of infrared spectra of oxide surfaces, and resolves a long-standing problem in OH vibrational assignments on goethite surfaces, where, in general, too few peaks have been observed relative to the expected heterogeneity of surface functional groups. 

  • 41.
    Rzhepishevska, Olena
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hakobyan, Shoghik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ekstrand-Hammarström, Barbro
    Swedish Defense Research Institute (FOI), Umeå, Sweden.
    Nygren, Yvonne
    Swedish Defense Research Institute (FOI), Umeå, Sweden.
    Karlsson, Torbjörn
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bucht, Anders
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Pulmonary Medicine. Swedish Defense Research Institute (FOI), Umeå, Sweden.
    Elofsson, Mikael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    The gallium(III)-salicylidene acylhydrazide complex shows synergistic anti-biofilm effect and inhibits toxin production by Pseudomonas aeruginosa2014In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 138, 1-8 p.Article in journal (Refereed)
    Abstract [en]

    Bacterial biofilms cause a range of problems in many areas and especially in health care. Biofilms are difficult to eradicate with traditional antibiotics and consequently there is a need for alternative ways to prevent and/or remove bacterial biofilms. Furthermore, the emergence of antibiotic resistance in bacteria creates a challenge to find new types of antibiotics with a lower evolutionary pressure for resistance development. One route to develop such drugs is to target the so called virulence factors, i.e. bacterial systems used when bacteria infect a host cell. This study investigates synergy effects between Ga(III) ions, previously reported to suppress biofilm formation and growth in bacteria, and salicylidene acylhydrazides (hydrazones) that have been proposed as antivirulence drugs targeting the type three secretion system used by several Gram-negative pathogens, including Pseudomonas aerugionosa, during bacterial infection of host cells. A library of hydrazones was screened for: Fe(III) binding, enhanced anti-biofilm effect with Ga(III) on P. aeruginosa, and low cytotoxicity to mammalian cells. The metal coordination for the most promising ligand, 2-Oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (ME0163) with Ga(III) was investigated using extended X-ray absorption fine structure spectroscopy as well as density functional theory. The results showed that Ga(III) chelates the hydrazone with 5- and 6-membered chelating rings, and that the Ga(III)-ME0163 complex enhanced the antibiofilm effect of Ga(III) while suppressing the type three secretion system in P. aeruginosa. The latter effect was not observed for the hydrazone alone and was similar for Ga(III)-citrate and Ga(III)-ME0163 complexes, indicating that the inhibition of virulence was caused by Ga(III).

  • 42.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Chemistry.
    XPS study of the hematite-aqueous solution interface2008In: Surface and Interface Analysis, Vol. 40, no 3-4, 349-53 p.Article in journal (Refereed)
    Abstract [en]

    The interaction between the surface of hematite colloidal platelets and Na+ and Cl- ions was investigated by XPS using the cryogenic technique. Pastes in ionic strengths of 0 and 10 mM NaCl contained about 10 at. % water and water/NaCl atomic ratios of 3 to 6. These results fall within the range of values obtained for a variety of minerals studied with this technique. Pastes in 100 mM NaCl background electrolyte, however, contained an unusually larger water content of 25 at. %, yielding a Na+: Cl-: H2O ratio of 1:1:2. This result is in strong contrast with other minerals at the same ionic strength, which typically reveal about 10 at. % water. Substituting Na+ for Cs+ in the hematite paste with 100 mM CsCl yielded, on the other hand, the same amount of water as in the pastes with 0 and 10 mM NaCl, and underpinned the role of Na+ ions in the large water content of the hematite paste. As surface concentrations of Na+ and Cl- exceeded those of hematite surface structural hydroxyl groups and Na 1s and Cl 2p spectra exhibited energy loss features, the electrolyte ions are proposed to be distributed in a three-dimensional array in the fast-frozen paste, possibly in a hydrohalite-like (NaCl·2H2O) phase. In addition, because the fast-frozen solution of 100 mM NaCl yields a water/NaCl ratio of about 70, hematite is proposed to play an important role in the stabilization of this three-dimensional distribution of Na+ and Cl- ions. The role of the neutrally charged {001} plane, a predominant feature in the hematite particles of this study, is notably discussed in the light of recent molecular models showing that this plane can stabilize several layers of hydrated ions up to 15 Å from the surface.

  • 43.
    Shchukarev, Andrey
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Chemistry.
    Felmy, Andrew R
    XPS of Fast-Frozen Hematite Colloids in NaCl Aqueous Solutions: I. Evidence for the Formation of Multiple Layers of Hydrated Sodium and Chloride Ions Induced by the {001} Basal Plane2007In: The Journal of Physical Chemistry C, Vol. 111, no 49, 18307-16 p.Article in journal (Refereed)
    Abstract [en]

    The composition of fast-frozen wet pastes of hematite particles of different morphologies equilibrated in NaCl aqueous solutions was investigated by X-ray photoelectron spectroscopy. Two hematite preparations consisted of micrometer-sized platelets with 42% (HEM-1) and 82% (HEM-8) of the surface terminated by the {001} basal plane and a third of spheroids with no recognizable crystal plane (HEM-control). All hematite samples responded to changes in pH (4 and 9) and ionic strength (0, 10, 100 mM), showing that acid/base reactions of surface hydroxyl groups impact the composition of the paste. The HEM-1 and HEM-8 sample exhibited unusually large Na, Cl, and water contents at the highest ionic strength (100 mM) compared to HEM-control and all other minerals studied with this technique previously. The Na 1s and Cl 2p spectra occurred at binding energies typical of hydrated Na+ and Cl- ions and possessed energy-loss features, suggesting a three-dimensional distribution of these ions in the paste. An approximate stochiometric Na/Cl/H2O ratio of 1:1:2 was obtained in all samples in 100 mM NaCl as well as a strong correlation between the these compounds and the fraction of the {001} basal plane present in the hematite particles. The basal plane of hematite is proposed to induce the formation of a hydrated NaCl structure in the fast-frozen pastes, one that is compositionally reminiscent of hydrohalite (NaCl·2H2O), by stabilizing multiple layers of hydrated Na+ and Cl- ions prior to freezing.

  • 44.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Electrochemical Properties and Relaxation Times of the Hematite/Water Interface2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 31, 9591-9598 p.Article in journal (Refereed)
    Abstract [en]

    Electric double layer properties and protonation rates at the surface of a mechanically and chemically polished (001) surface of hematite (alpha-Fe2O3) contacted with aqueous solutions of NaCl were extracted by electrochemical impedance spectroscopy (EIS). Effects of pH (4-12) and ionic strength (10-1000 mM) on the EIS response of the electrode were predicted using an electrical equivalent circuit model accounting for hematite bulk and interfacial processes. These efforts generated diffuse layer as well as compact layer capacitances and resistance values pertaining to interfacial processes. Diffuse layer capacitance values lie in the 0.5-0.6 mu F cm(-2) region and are about 1.5 times smaller than those obtained on a roughened hematite surface. Compact layer capacitances are strongly pH dependent as they pertain to the transfer of ions (charge carriers) from the diffuse layer onto surface (hydr)oxo groups. These values, alongside those of resistance adsorption, pointed a 50% decrease in proton adsorption/desorption resistance under acidic and alkaline conditions relative to that of the point of zero charge (pH 8-9). Increasing ionic strength generally induces larger diffuse layer capacitances, larger adsorption capacitances, and lower resistance values. Such a response is in line with the concept for thinner electric double layers and facilitated proton adsorption reactions by solutions of high ionic strengths. Relaxation times pertaining to the transfer of charge carriers across the compact plane induced by the EIS experiments lie in the 0.7-4.2 s range and become larger under acidic conditions. Decreases in site availability and increases in electrostatic repulsion are two possible contributing factors impeding reaction rates below the point of zero charge. Collectively, these finding are underpinning important relationships between classical views on mineral surface complexation reactions and electrochemical views of semiconductor/water interfaces.

  • 45.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Electrochemical Signatures of Crystallographic Orientation and Counterion Binding at the Hematite/Water Interface2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 11, 5988-5994 p.Article in journal (Refereed)
    Abstract [en]

    The interfacial electrochemistry of hematite (α-Fe2O3) is a key aspect for understanding the behavior of this important mineral phase in photocatalytic water-splitting devices as well as in terrestrial and atmospheric systems. Nano- to microsized particles are often multifaceted and exhibit terminations of varied crystallographic orientations and structures. As structure often controls reactivity, this study was devised to identify the impact of crystallographic orientation on the electrochemical response of hematite electrode surfaces contacted with technologically, geochemically, and environmentally important solutions of inorganic ions (NaCl, NaHCO3, and NH4Cl). Electrochemical impedance spectroscopy (EIS) measurements of single hematite crystals oriented along the (001) and (012) faces were used for this purpose. The EIS responses of the electrodes were described in terms of an equivalent electrical circuit that accounts for fast bulk and slower interfacial processes. Capacitance and resistance values for the bulk processes confirmed the anisotropic conductivity attributes of hematite and supported the use of the EIS data for interpreting the crystallographic orientation dependence of interfacial processes. These efforts extracted diffuse (C-dl) and compact (T-ad) layer capacitances and resistance (R-ad), as well as relaxation times pertaining to the re-equilibration of interfacial species during EIS. Capacitance values confirmed the greater charge-storing capability of the (012) face (C-dl = 110 mu F.cm(-2); T-ad = 335 mu F.cm(-2).s(-phi)) compared to the (001) face (C-dl = 0.20.6 mu F.cm(-2); T-ad = 0.20.6 mu F.cm(-2).s(-phi)). This was also confirmed through the resistance values pertaining to the transfer of charge carriers across the compact plane, which were lower (R-ad = 0.00.8 M Omega.cm(-2)) on the (012) face than on the (001) face (R-ad = 14 M Omega.cm(-2)). Binding of chloride and (bi)carbonate on the (012) face under acidic conditions was associated with an increase in capacitance values and relaxation times. The lowest capacitances and relaxation times occurred in the pH 8-9 region, which correspond to a likely point of zero charge. The capacitance values in NH4Cl were considerably lower than in NaCl and NaHCO3, owing to hydrogen bonding between the NH4+/NH3 species and surface (hydr)oxo groups. Such interactions can block protonation reactions and can be translated to negligible relaxation times for this system. Collectively, these findings underpin the interdependency of the hematite electrode surface orientation on its electrochemical signatures for important inorganic ions of direct relevance to technological and natural systems.

  • 46.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, UK.
    Driver, Gordon W.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lucas, Marie
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sparrman, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bifluoride ([HF2](-)) formation at the fluoridated aluminium hydroxide/water interface2016In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 22, 9045-9050 p.Article in journal (Refereed)
    Abstract [en]

    This study uncovers bifluoride-type (difluorohydrogenate(I); [HF2](-)) species formed at mineral/water interfaces. Bifluoride forms at equivalent to Al-F surface sites resulting from the partial fluoridation of gibbsite (gamma-Al(OH3)) and bayerite (alpha-Al(OH3)) particles exposed to aqueous solutions of 50 mM NaF. Fluoride removal from these solutions is proton-promoted and results in a strongly self-buffered suspensions at circumneutral pH, proceeds at a F : H consumption ratio of 2 : 1, and with recorded losses of up to 17 mM fluoride (58 F nm(-2)). These loadings exceed crystallographic site densities by a factor of 3-4, yet the reactions have no resolvable impact on particle size, shape and mineralogy. X-ray photoelectron spectroscopy (XPS) of frozen (-155 degrees C) wet mineral pastes revealed coexisting surface F- and HF0 species. Electron energy loss features pointed to multilayer distribution of these species at the mineral/water interface. XPS also uncovered a distinct form of Na+ involved in binding fluoride-bearing species. XPS and solid state magic angle spinning F-19 nuclear magnetic resonance measurements showed that these fluoride species were highly comparable to a sodium-bifluoride (NaHF2) reference. First layer surface species are represented as =Al-F-H-F-Al= and =Al-F-Na-F-Al=, and may form multi-layered species into the mineral/water interface. These results consequently point to a potentially overlooked inorganic fluorine species in a technologically relevant mineral/water interfacial systems.

  • 47.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lasia, Andrzej
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    An electrochemical impedance study of the hematite/water interface2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 20, 7914-7920 p.Article in journal (Refereed)
    Abstract [en]

    Reactions taking place on hematite (α-Fe2O3) surfaces contacted with aqueous solutions are of paramount importance for environmental and technological processes. Electrochemical properties of the hematite/water interface are central to these processes and can be probed by open circuit potentials and cyclic voltammetric measurements of semiconducting electrodes. In this study electrochemical impedance spectroscopy (EIS) was used to extract resistive and capacitive attributes of this interface on mm-sized single-body hematite electrodes. This was carried out by developing equivalent circuit models to impedance data collected on a semi-conducting hematite specimen equilibrated in solutions of 0.1 M NaCl and NH4Cl at various pH values. These efforts produced distinct sets of capacitance values for the diffuse and compact layers of the interface. Diffuse layer capacitances shift in the pH 3-11 range from 2.32 to 2.50 μF⋅cm-2 in NaCl and from 1.43 to 1.99 μF⋅cm-2 in NH4Cl. Furthermore, these values reach a minimum capacitance at pH 9, near a probable point of zero charge for an undefined hematite surface exposing a variety of (hydr)oxo functional groups. Compact layer capacitances pertain to transfer of ions (charge carriers) from the diffuse layer to surface hydroxyls, and are independent of pH in NaCl, with values of 32.57±0.49 μF·cm-2·s-ϕ. They however decrease with pH in NH4Cl from 33.77 at pH 3.5 to 21.02 μF·cm-2·s-ϕ at pH 10.6 due to interactions of ammonium species with surface (hydr)oxo groups. Values of ϕ (0.71-0.73 in NaCl and 0.56-0.67 in NH4Cl) denote the non-ideal behavior of this capacitor, here treated as a constant phase element. As electrode-based techniques are generally not applicable to the commonly insulating metal (oxyhydr)oxides found in the environment, this study opens opportunities for exploring mineral/water interface chemistry by EIS studies of single-body hematite specimens.

  • 48.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nyström, J.
    Geladi, P.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Electrolyte ion adsorption and charge blocking effect at the hematite/aqueous solution interface: an electrochemical impedance study using multivariate data analysis2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 17, 11560-11568 p.Article in journal (Refereed)
    Abstract [en]

    A model-free multivariate analysis using singular value decomposition is employed to refine an equivalent electrical circuit model in order to probe the electrochemical properties of the hematite/water interface in dilute NaCl and NH4Cl solutions using electrochemical impedance spectroscopy. The result shows that the surface protonation is directly related to the mobility and trapping of charge carriers at the mineral surface. Moreover, the point of zero charge can be found at pH where the charge transfer resistance is the highest, in addition to the minimum double layer capacitance. The innersphere interaction of the NH4+ ion with the surface is indicated by an increase of capacitance for charge carrier trapping from the protonated surface as well as lower double layer capacitance and open circuit potential. It is clear that the intrinsic electrochemical activity of hematite depends on the degree of surface (de) protonation and other inner-sphere adsorption, as these processes affect the charge carrier density in the surface state. This work also highlights an important synergistic effect of the two spectral analyses that enables EIS to be utilized in an in-depth investigation of mineral/water interfaces.

  • 49.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions: 3. stabilization of ammonium species by surface (hydr)oxo groups2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 14, 6796-6801 p.Article in journal (Refereed)
    Abstract [en]

    The speciation of ammonium at the hematite/water interface was probed by cryogenic X-ray photoelectron spectroscopy. Wet pastes of colloidal hematite spheroids equilibrated in aqueous solutions of 50 mM NH4Cl exhibit distinctive pH-sensitive N 1s peaks for both NH4+ (401.7 eV) and NH3 (400.1 eV), yet total N/Fe ratios remain relatively invariant (0.029 ± 0.006) throughout the pH 2.2−10.5 range. Both NH4+ and NH3 species coexist throughout most of the tested pH range. NH4+ is most likely stabilized at the interface by hydrogen bonding with surface (hydr)oxo groups. A cationic sorption edge for NH3 is driven by proton abstraction of NH4+ by (hydr)oxo groups, forming surface complexes of the type ≡Fe−OH···NH3. These interactions shift the NH4+/NH3 equilibrium from pKa = 9.3 in water to 8.4 at the interface. Removal of excess water by vacuum dehydration induces, on the other hand, formation of NH2 directly bound to surface Fe atoms. These results underscore distinct ammonium species in contact with mineral surfaces and should be considered in understanding environmental and catalytic reactions in this medium.

  • 50.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kozin, Philipp A
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions. 5. halide ion (F, Cl, Br, I) adsorption2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 8, 2623-2630 p.Article in journal (Refereed)
    Abstract [en]

    Halide anion (F, Cl, Br, and I) adsorption and its impact on sodium adsorption at the hematite/water interface were studied by cryogenic X-ray photoelectron spectroscopy (XPS). Measurements were carried out on frozen, centrifuged wet hematite pastes that were previously equilibrated in 50 mM electrolytic solutions in the pH 2–11 range. XPS-derived halide ion surface loadings decreased in the order F > I ≈ Cl > Br, whereas sodium loadings were in the order Na(F) > Na(I) > Na(Br) > Na(Cl). The greater sodium loadings in NaF and in NaI resulted from larger anion loadings in these systems. Bromide ion had the lowest loading among all halide ions despite having a charge-to-size ratio that is intermediate between those of Cl and I. This unexpected result may have arisen from specific properties of the hematite/water interface, such as water structure and electric double layer thickness. Fluoride ion adsorption proceeded via the formation of hydrogen bonds with the surface hydroxo groups (e.g., ≡Fe–OH2···F or ≡Fe–OH···F). Surface-bound fluoride ions exert a greater charge-screening effect than the other halide anions, as demonstrated by considerably small zeta potential values. Fe–F bond formation was excluded as a possible interfacial process as the F 1s peak binding energy (684.2 eV) was more comparable to that of NaF (684.6 eV) than FeF3 (685.4 eV). Overall, these findings motivate further refinements of existing thermodynamic adsorption models for predicting the ionic composition of hematite particle surfaces contacted with sodium halide aqueous solutions.

12 1 - 50 of 63
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf