Adsorption Of The Cs+, Sr2+ And Co(ii) Ions
Adsorption of the Cs+, Sr2+ and Co(II) ions
at the zirconium dioxide/electrolyte interface
W. Janusz
Faculty of Chemistry, Maria Curie-Sklodowska University,
Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland,
e-mail:wjanusz@hermes.umcs.lublin.pl;
Some properties of the zirconium dioxide/electrolyte systems have been investigated extensively due to many practical application of this oxide.
Owing to its chemical and thermal resistance it is widely used as catalyst supporter and material in ceramics and nuclear technology. Applied as a model system it is interesting for understanding the processes taking place at the metal oxide/electrolyte interface.In this paper the adsorption of the selected cations (Cs+, Sr2+ and Co(II)) at the zirconium dioxide/electrolyte interface and its result on the properties of the electrical double layer (edl) of this system has been presented.
The adsorption of ions was investigated using radioisotopic method, the surface charge at the metal oxide electrolyte was determined by means of the potentiometric titration. The z potential was measured using Zetasizer 3000 (Malvern, England).
The adsorption of Cs+ ions at the ZrO2/electrolyte interface increases with increase of the pH of solution, due to exchange of Cs+ ions with hydrogen in hydroxyl groups, Fig 1. This process leads to the increase of negatively charged groups on the ZrO2 surface at the concentrations higher than 0.001MCs+ ions. Ionisation and complexation constants (pKa1=2.0, pKCl=6.37, pKCs=7.0, pKa2=9.69) were determined using numerical optimisation method on the basis of the experimental data i.e. density of the surface charge as a function of pH and concentration of CsCl.
The edge of the adsorption of Sr2+ ions is above pHpzc of ZrO2, compare Figs 1 and 2. Adsorption of Sr2+ takes place either on one or two surface hydroxyl groups with release of hydrogen from these groups. The respective reaction constants are pK1=6.0 and pb=8.8.
At initial concentration of 0.001 M of Sr2+ ions the overcharging of the compact layer of electrical double layer takes place so the charge reversal at the z potential vs. pH plot was observed.
Figure1.The adsorption of cations (Cs+, Sr2+ and Co(II)) at the ZrO2/aqueous solution interface form initial concentration of 10-4 M of cation
Figure2.The surface charge density at ZrO2/aqueous solution of cations (Cs+, Sr2+ and Co(II) at initial concentration of 10-3 mole/dm3.
Adsorption edge of Co(II) at the ZrO2/aqueous solution of 0.001 NaCl is pH50% below pHpzc and the adsorption process of Co(II) ions leads to release of H+ ions. In this way the surface charge in presence of Co(II) ions is significantly lower as the result of increase of negatively charged groups at the ZrO2/solution interface. The adsorption reaction constants on one and two hydroxyl groups are pK1=4.7 and pb=6.5.
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