Electrochemical properties of adsorbed alkanethiol monolayers on mercury electrode surfaces

n-Alkanethiols (CH3(CH2)nSH, n=3,5,11,13,15,17) have been adsorbed at mercury electrodes from ethanolic solutions. A. c. voltammetry has been carried out of the adsorbed alkanethiol on mercury electrodes in aqueous solutions containing 1 M KCl at 25°C. Cyclic d.c. voltammetry of several metal ions also has been performed at these electrodes. The results show that long-chain alkanethiols n ≥ 11 can form densely packed monolayers with fully extended alkyl chains in the potential range between 0 and -0. 7 volt vs. Ag/AgCl. Metal ions such as Pb2+ are unable to penetrate into the monolayer. In contrast, short-chain alkanethiols with n = 3 and 5 form less ordered and loosely packed adsorption layers, which are permeable to the metal ions. A pH dependent a.c. voltammetric peak is observed at a mercury electrode with adsorbed alkanethiol (n=5) in buffer solutions, which is attributable to the redox reaction of the adsorbed thiol: [CH3(CH2)5S]adHg + H+ + e- [CH3(CH2)SH]adHg.