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1 2000

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Mechanism of Adsorption of Selected Monovalent and Divalent Inorganic Ions at the Alumina/Electrolyte Interface

Jabłoński J., Janusz W., Reszka M., Sprycha R., Szczypa J.

Polish Journal of Chemistry

2000

Vol. 74, nr 10

1399-1409

The mechanism of adsorption of selected mono- and divalent ions (Na+, Ca2+, Cl–, SO4 2- ) at the metal oxide (Al2O3)/electrolyte interface has been studied using different experimental techniques: potentiometric titration, zeta potential and adsorption density measurements. Radiotracers and ion-selective electrodes were used to measure the adsorption densities of ions. It was found that the accuracy of both methods was almost the same. Ion-selective electrodes allowed to acquire adsorption data for shorter times of contact between the oxide and electrolyte solution. Based on the potentiometric titration data, ionization and complexation constants of surface hydroxyl groups were calculated using the site binding theory of the electrical interfacial layer. The adsorption density of Ca2+, at the same pH and ion concentration, was significantly higher than that observed for sodium ions and revealed strong pH dependence (adsorption edge). A shift of the pzc and iep of alumina was observed in the systems containing chloride, sulphate or calcium ions, due to the specific adsorption of those ions at the oxide/electrolyte interface. The calculated pKA values for different anions showed that the stability of surface complexes increased in the following sequence: ClO4 < Cl– < SO4