J. Jablonski et al., Mechanism of adsorption of selected monovalent and divalent inorganic ionsat the alumina/electrolyte interface, POL J CHEM, 74(10), 2000, pp. 1399-1409
The mechanism of adsorption of selected mono- and divalent ions (Na+, Ca2+,
Cl-, SO42-) at the metal oxide (Al2O3)/electrolyte interface has been stud
ied using different experimental techniques: potentiometric titration, zeta
potential and adsorption density measurements. Radiotracers and ion-select
ive electrodes were used to measure the adsorption densities of ions. It wa
s found that the accuracy of both methods was almost the same. Ion-selectiv
e electrodes allowed to acquire adsorption data for shorter times of contac
t between the oxide and electrolyte solution. Based on the potentiometric t
itration data, ionization and complexation constants of surface hydroxyl gr
oups were calculated using the site binding theory of the electrical interf
acial layer. The adsorption density of Ca2+, at the same pH and ion concent
ration, was significantly higher than that observed for sodium ions and rev
ealed strong pH dependence (adsorption edge). A shift of the pzc and iep of
alumina was observed in the systems containing chloride, sulphate or calci
um ions, due to the specific adsorption of those ions at the oxide/electrol
yte interface. The calculated pK(A) values for different anions showed that
the stability of surface complexes increased in the following sequence: Cl
O4- < Cl- < SO42-.