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| 2. |
- Bochatay, Laurence, et al.
(författare)
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Metal Ion Coordination at the Water–Manganite (γ-MnOOH) Interface : I. An EXAFS Study of Cadmium(II)
- 2000
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 229:12, s. 584-92
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Tidskriftsartikel (refereegranskat)abstract
- The local structure of Cd(II) surface complexes adsorbed onto manganite (γ-MnOOH) has been investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. Adsorption experiments were carried out within the pH range 7.4–9.8 and with surface coverage from 2.2 to 8.9 μmol/m2. Quantitative analysis of the EXAFS spectra shows little difference in the local coordination environment of Cd regardless of the coverage. Analysis of the first shell required a third cumulant in an asymmetric distribution model (i.e., non-Gaussian distribution), indicating distorted CdO6 octahedra with an average Cd–O distance of 2.31 Å. A single second shell of Mn neighbors at a constant distance of 3.33 Å was detected. This comparatively short distance shows that inner-sphere complexes are formed. No Cd neighbor was found which means that cadmium hydroxide precipitation or cluster formation does not occur at the surface at the experimental conditions probed in this study. We assign the Cd–Mn distance to edge sharing between CdO6 and MnO6 octahedra, with a geometry similar to that in the mixed solid Cd2Mn3O8. This adsorption mode is possible on the {110} and {010} cleavage planes of manganite.
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| 3. |
- Bodor, Andrea, et al.
(författare)
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Studies of equilibrium, structure, and dynamics in the aqueous Al(iii)-oxalate-fluoride system by potentiometry, 13C and 19F NMR spectroscopy
- 2003
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Ingår i: Geochimica et Cosmochimica Acta. ; 67:15, s. 2793-2803
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Tidskriftsartikel (refereegranskat)abstract
- The AlOx1–3 (Ox = oxalate) species were identified in 0.6 M aqueous NaCl by 13C nuclear magnetic resonance (NMR). Rate constants and activation parameters for intramolecular cis/trans isomerization of the Werner-type AlOx2− complex (k(298 K) = 5 s−1, ΔH# = 67 ± 5 kJ mol−1, ΔS# = −6 ± 6 J mol−1 K−1, the rate determining step could be the breaking of the Al–O(C=O) bond) and a very slow intermolecular ligand exchange reaction of AlOx33− complex and the free ligand (k30(298 K) = 6.6 · 10−5 s−1, ΔH# = 164 ± 17 kJ mol−1, ΔS# = 225 ± 51 J mol−1 K−1, D/Id mechanism) were determined by dynamic 1D and 2D 13C NMR measurements. Mixed complexes, AlFOx, AlFOx22–, AlF2Ox−, and AlF2Ox23–, with overall stability (logβ) of 11.53 ± 0.03, 15.67 ± 0.03, 15.74 ± 0.02, and 19.10 ± 0.04 were measured by potentiometry using pH- and fluoride-selective electrodes and confirmed by 13C and19F NMR. The role of these complexes in gibbsite dissolution was modeled. The mixed Al(III)-Ox2–-F− complexes have to be considered as the chemical speciation of Al(III) in natural waters is discussed.
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| 4. |
- Boily, Jean-Francois, et al.
(författare)
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Benzenecarboxylate surface complexation at the goethite (-FeOOH)/water interface: II. Linking IR spectroscopic observations to mechanistic surface complexation models for phthalate, trimellitate, and pyromellitate
- 2000
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Ingår i: Geochimica et Cosmochimica Acta. ; 64:20, s. 3453-70
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Tidskriftsartikel (refereegranskat)abstract
- A study combining information from infrared spectroscopy and adsorption experiments was carried out to investigate phthalate, trimellitate, and pyromellitate complexes at the goethite (-FeOOH)/water interface. Infrared spectra showed evidence for inner-sphere complexes below pH 6 and outer-sphere complexes in the pH range 3 to 9. Normalized infrared peak areas were used as a semi-quantitative tool to devise diagrams showing the molecular level surface speciation as a function of pH. Surface complexation models that simultaneously predict these diagrams, the proton balance data and the ligand adsorption data were developed with surface complexation theory. Surface complexation modeling was carried out with a Charge Distribution Multisite Complexation Model (CD-MUSIC), assuming goethite particles with surfaces represented by the {110} plane (90% of total particle surface area) and by the {001} plane (10% of total particle surface area). Inner-sphere complexes were described as mononuclear chelates at the {001} plane, whereas outer-sphere complexes were described as binuclear complexes with singly coordinated sites on the {110} plane. The Three-Plane Model (TPM) was used to described surface electrostatics and to distribute the charges of the inner- and the outer-sphere complexes on different planes of adsorption.
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| 5. |
- Boily, Jean-Francois, et al.
(författare)
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Benzenecarboxylate surface complexation at the goethite (α-FEOOH)/water interface. III. The influence of particle surface area and the significance of modeling parameters
- 2000
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Ingår i: Journal of colloid and interface science. ; 227:1, s. 132-40
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Boily, Jean-Francois, et al.
(författare)
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Modeling proton binding at the goethite (-FeOOH)-water interface
- 2001
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. ; 179:1, s. 11-27
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Cardenas, Juan, et al.
(författare)
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Investigation of the titaniumdioxide-aqueous solution interface using XPS and cryogenics
- 2003
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Ingår i: Surface Science. ; 532-35, s. 1104-8
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of Na[+] and Cl[-] electrolyte ions from an aqueous solution onto single crystal TiO[2] has been the subject of an investigation using XPS in combination with in situ cryogenics. In particular the samples were decontaminated from adventitious carbon by annealing at 600 °C prior to the exposure to aqueous solution. Further, the subsequent transfer of the sample to the spectrometer was performed in a liquid nitrogen filled hollow sample holder in order to preserve the chemistry and structure at the sample surface. The presence of an ionic layer consisting of H[2]O, Na[+] and Cl has been confirmed using angular dependent XPS, where the electrolyte ions are distributed in at least 2-3 monolayers.
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| 8. |
- Johnson, Bruce B, et al.
(författare)
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Surface Complexation of Mellitic Acid to Goethite: An Attenuated Total Reflection Fourier Transform Infrared Study
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:3, s. 823-8
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Tidskriftsartikel (refereegranskat)abstract
- The nature of the interaction between mellitic acid (benzene hexacarboxylic acid) and the common soil mineral goethite (-FeOOH) has been investigated as a function of pH and ionic strength by use of attenuated total reflection Fourier transform infrared spectroscopy. Molecular orbital calculations of the theoretical vibrational frequencies of the mellitate ion (L6-) and dihydrogen mellitate (H2L4-) have allowed the measured absorption frequencies to be accurately assigned. At pH values above 6, adsorption involves outer-sphere complexation of the deprotonated L6- ion. At lower pH values, there is evidence of a second outer-sphere surface complex involving a partially protonated species, although the extent of protonation of the surface species is significantly less than that found for the solution species at the same pH. While there is no evidence of inner-sphere complexation, increasing the ionic strength to 2.0 M does not displace the adsorbed species but does increase the fraction present on the surface as the fully deprotonated L6-. The small effect of ionic strength suggests that the adsorptive interaction, although outer-sphere in character, is still relatively strong, which indicates that hydrogen bonds may play a significant role. Hydrogen bonding may also help to account for the observed outer-sphere complexation at pH values above the pHiep of goethite.
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| 10. |
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