Das, Manash R. and Borah, Jayanta M. and Kunz, Werner and Ninham, Barry W. and Mahiuddin, Sekh (2010) Ion specificity of the zeta potential of alpha-alumina, and of the adsorption of p-hydroxybenzoate at the alpha-alumina-water interface. JOURNAL OF COLLOID AND INTERFACE SCIENCE, 344 (2). pp. 482-491. ISSN 0021-9797, 1095-7103
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The influence of inorganic anions (NO3, I-, Br-, Cl-, SO42-, and S2O32-) and of divalent canons (Ca2+ and Mg2+) on the zeta potential and on the isoelectric point of a-alumina in aqueous medium has been studied. The effect of the anions is highly ion specific even at salt concentrations as low as 5 x 10(-4) M. This unexpected finding is in line with a recent report [Bostrom et al., J. Chem. Phys. 128 (2008) 135104]. It is also in agreement with an earlier theoretical prediction [B.W. Ninham, V.V. Yaminsky, Langmuir 13 (1997) 2097]. 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 alpha-alumina in aqueous medium, more precisely; S2O3 produced large negative zeta potential (similar to-12 to -47 mV) within the pH range of the study without the isoelectric point (IEP) of alpha-alumina. However, the SO42- decreased the zeta potential of alpha-alumina of different magnitudes (maximum similar to 25 mV at both ends of the experimental acidic and basic pH scale) with a minor shift of the IEP (similar to 0.5 unit) toward lower pH. Ca2+ and Mg2+ produce zeta potentials of alpha-alumina roughly equal to that of neat alpha-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 density of p-hydroxybenz oate onto alpha-alumina surfaces. The sequence of anions (with common cation) for the adsorption density of p-hydroxybenzoate on the alpha-alumina surfaces follows the Hofmeister series sequence: S2O32- < SO4(2-) < Cl- > Br- > l(-) > NO3-. The divalent cations (Ca2+ and Mg2+) exhibit a roughly equivalent effect on the adsorption of p-hydroxybenzoate onto a-alumina surfaces. Using the frequency shifts of v(as)(-COO-) and v(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 alpha-alumina surfaces at pH 5 and 6 and inner-sphere complexes at pH 7, 8, and 9 in the presence of 5 x 10(-4) M NaCl(aq). (C) 2009 Elsevier Inc. All rights reserved.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | TRANSFORM INFRARED-SPECTROSCOPY; NATURAL ORGANIC-MATTER; SITU ATR-FTIR; AQUEOUS-SOLUTION; MINERAL/WATER INTERFACES; HOFMEISTER SERIES; HUMIC SUBSTANCES; ZERO CHARGE; COMPETITIVE ADSORPTION; ELECTROLYTE INTERFACE; Adsorption; Alumina; DRIFT; Hofmeister effect; Ion specificity; p-Hydroxybenzoate; Surface complexation; Zeta potential |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry VI - Physical Chemistry (Solution Chemistry) > Prof. Dr. Werner Kunz |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 03 Aug 2020 07:14 |
| Last Modified: | 03 Aug 2020 07:14 |
| URI: | https://pred.uni-regensburg.de/id/eprint/24823 |
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