Cyclic Control of the Surface Properties of a Monolayer‐Functionalized Electrode by the Electrochemical Generation of Hg Nanoclusters

Hg 2+ ions are bound to a 1,4‐benzenedimethanethiol (BDMT) monolayer assembled on a Au electrode. Electrochemical reduction of the Hg 2+ –BDMT monolayer to Hg + –BDMT (at E° =0.48 V) and subsequently to Hg 0 –BDMT (at E° =0.2 V) proceeds with electron‐transfer rate constants of 8 and 11 s −1 , respectively. The Hg 0 atoms cluster into aggregates that exhibit dimensions of 30 nm to 2 μm, within a time interval of minutes. Electrochemical oxidation of the nanoclusters to Hg + and further oxidation to Hg 2+ ions proceeds with electron‐transfer rate constants corresponding to 9 and 43 s −1 , respectively, and the redistribution of Hg 2+ on the thiolated monolayer occurs within approximately 15 s. The reduction of the Hg 2+ ions to the Hg 0 nanoclusters and their reverse electrochemical oxidation proceed without the dissolution of mercury species to the electrolyte, implying high affinities of Hg 2+ , Hg + , and Hg 0 to the thiolated monolayer. The electrochemical transformation of the Hg 2+ ‐thiolated monolayer to the Hg 0 ‐nanocluster‐functionalized monolayer is characterized by electrochemical means, surface plasmon resonance (SPR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact‐angle measurements. The Hg 0 ‐nanocluster‐modified surface reveals enhanced hydrophobicity (contact angle 76°) as compared to the Hg 2+ ‐thiolated monolayer (contact angle 57°). The hydrophobic properties of the Hg 0 ‐nanocluster‐modified electrode are further supported by force measurements employing a hydrophobically modified AFM tip.