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Adsorption of Tri-n-butyl Phosphate (TBP) from NaClO_4 Aqueous Solution on Hg Electrode

The adsorption of TBP on Hg electrode from aqueous NaClO_4 media has been studied using differential capacity and chronocoulometric measurements. TBP adsorbs in two steps, the first corresponding to a flat and second to a perpendicular orientation. Both orientations were observed in the whole investigated potential range. The maximal measured surface concentration (*=gama_max) of TBP reaches a value of 1.55 x 10^-10 mol cm^-2, which corresponds to the theoretical value for densely packed molecules in perpendicular orientation. *=gama value of the first isotherm step plateau is about 7 to 15 % smaller than *=gama_max and decreases strongly at potentials more negative than -0.9 V due to the repelling of negative charges between the electrode and the phosphate group. The standard Gibbs energy of adsorption was found to reach the value of -34 kJ mol^-1.

Tri-n-butyl phosphate; adsorption; Hg electrode

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