Adsorption of the lanthanum and thorium cryptates at mercury electrode

The adsorption behavior of cryptates of La3+ and Th4+ cations at the Hg/aqueous solution interface is studied by using the electrochemical impedance spectroscopy method. It was shown that the studied complexes have high surface activity at the interface. The lanthanum cryptate adsorption parameters are found using the regression analysis based on the two parallel capacitor model supplemented by the Frumkin adsorption isotherm. The differential capacitance curves calculated by using these parameters agree satisfactorily with the experimental ones. The more complicated adsorption behavior of lanthanum cryptate, as compared with the complexes of lower valence cations, is interpreted with taking into consideration the strong interaction of the La3+ cation contained in the [2.2.2.] cryptand intramolecular cavity with the supporting electrolyte anions.