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| Item type: | Article | ||||||
|---|---|---|---|---|---|---|---|
| Journal or Publication Title: | Journal of Colloid and Interface Science | ||||||
| Publisher: | Elsevier B.V. | ||||||
| Volume: | 344 | ||||||
| Number of Issue or Book Chapter: | 20 | ||||||
| Page Range: | pp. 482-491 | ||||||
| Date: | 2010 | ||||||
| Institutions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry VI - Physical Chemistry (Solution Chemistry) > Prof. Dr. Werner Kunz | ||||||
| Identification Number: |
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| Keywords: | ion specificity zeta potential isoelec point alumina adsorption | ||||||
| Dewey Decimal Classification: | 500 Science > 540 Chemistry & allied sciences | ||||||
| Status: | Published | ||||||
| Refereed: | Yes, this version has been refereed | ||||||
| Created at the University of Regensburg: | Yes | ||||||
| Item ID: | 24415 |
Abstract
The influence of inorg. anions (NO-3, I-, Br-, Cl-, SO42-, and S2O32-) and divalent cations (Ca2+ and Mg2+) on the zeta potential and isoelec. point of α-alumina in aq. medium has been studied. The effect of the anions is highly ion specific even at salt concns. as low as 5 × 10-4 M. This unexpected finding is in line with a recent report. It is also in agreement with an earlier theor. ...
Abstract
The influence of inorg. anions (NO-3, I-, Br-, Cl-, SO42-, and S2O32-) and divalent cations (Ca2+ and Mg2+) on the zeta potential and isoelec. point of α-alumina in aq. medium has been studied. The effect of the anions is highly ion specific even at salt concns. as low as 5 × 10-4 M. This unexpected finding is in line with a recent report. It is also in agreement with an earlier theor. prediction. The results are consistent with the classical Hofmeister series, except for the case of NO3-. Divalent anions (SO42- and S2O32-) decrease the magnitude of the zeta potential of α-alumina in aq. medium, more precisely; S2O32- produced large neg. zeta potential (∼-12 to -47 mV) within the pH range of the study without the isoelec. point (IEP) of α-alumina. However, the SO42- decreased the zeta potential of α-alumina of different magnitudes (max. ∼25 mV at both ends of the exptl. acidic and basic pH scale) with a minor shift of the IEP (∼0.5 unit) toward lower pH. Ca2+ and Mg2+ produce zeta potentials of α-alumina roughly equal to that of neat α-alumina but slightly higher than that of Na+ at both sides of the IEP. We have shown further that the same ion specificity or equivalently competitive ion effects occur with the adsorption d. of p-hydroxybenzoate onto α-alumina surfaces. The sequence of anions (with common cation) for the adsorption d. of p-hydroxybenzoate on the α-alumina surfaces follows the Hofmeister series sequence: S2O32- < SO42- < Cl- > Br- > I- > NO3-. The divalent cations (Ca2+ and Mg2+) exhibit a roughly equiv. effect on the adsorption of p-hydroxybenzoate onto α-alumina surfaces. Using the frequency shifts of ν as(-COO-) and ν s(-COO-) in the DRIFT spectra of p-hydroxybenzoate after adsorption and other characteristic peaks, we have demonstrated that p-hydroxybenzoate forms outer-sphere complexes onto α-alumina surfaces at pH 5 and 6 and inner-sphere complexes at pH 7, 8, and 9 in the presence of 5 × 10-4 M NaCl(aq).
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