| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Simpson, Stuart L, et al.
(författare)
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Pyrocatechol Violet Complexation at the Boehmite–Water Interface
- 2000
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 229:2, s. 568-74
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Tidskriftsartikel (refereegranskat)abstract
- Acid/base reactions and pyrocatechol violet complexation at the boehmite–solution interface have been investigated in 0.10 M K(Cl) solution at 298.2 K in the range 5.0≤−log h≤9.0. Equilibrium measurements were performed as potentiometric titrations complemented by spectrophotometric analysis of a ligand (batch adsorption experiments). The experimental data were evaluated on the basis of the extended constant capacitance model, allowing for inner-sphere and/or outer-sphere complexation. The acid/base properties are described by the equilibria: H++≡AlOH ≡AlOH2+; log β1,1,0(int)=7.46±0.04 and ≡AlOH ≡AlO−+H+; log β−1,1,0(int)=−9.87±0.12. The specific capacitance was determined as 1.00 F m−2. The binding of pyrocatechol violet {PCV, 2-[(3,4-dihydroxyphenyl)(3-hydroxy-4-oxocyclohexa-2,5-diene-1-ylidene)methyl]benzenesulfonic acid}, H4L, was described by the formation of a single inner-sphere complex according to the reaction ≡AlOH+H4L≡AlL3−+3H++H2O. Allowing for a charge distribution of this complex between the inner plane and β-plane (−2, −1), a significant improvement of the fit was obtained. The adsorbed complex exhibited a dark blue color over the pH range 5–8.5, indicative of proton loss from the 1,2-dihydroxyl moiety. Furthermore, DRIFT spectra showed the bonding environment of PCV bound to the surface to exhibit similarities with corresponding catechol adsorption to different aluminium (hydr)oxides. These spectral features turned out to be very similar to soluble catechol complexes of Al(III). Thus, it is suggested that PCV forms a mononuclear chelating complex at the boehmite–water interface. The maximum surface coverage reached was ca. 33%, indicating that the high negative charge of the species may result in surface charge “saturation” rather than saturation of surface binding sites. Steric hindrances caused by the large size of PCV may also contribute to the low surface coverage.
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