The effect of anions on the phase transition in the adsorbed layer of thiourea at the mercury-aqueous solution interface

Abstract

The condensation of thiourea (TU) molecules at a mercury electrode in concentrated aqueous solutions was investigated by using impedance measurements and cyclic voltammetric techniques. The effects of the nature and concentration of the supporting electrolyte, the temperature and the thiourea concentration on the position of the phase transition potentials are discussed. It is concluded that the hydrogen bonds between the-NH 2 groups of TU and water molecules from the outer part of the double layer are an immobilizing agent for the adsorbed TU molecules, which leads to a stable structure in the “pit” zone. Electrostatic interaction between the TU dipoles and anions is responsibile for the formation of a condensed structure at the positively-charged mercury electrode.