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

AbstractHg2+ ions are bound to a 1,4‐benzenedimethanethiol (BDMT) monolayer assembled on a Au electrode. Electrochemical reduction of the Hg2+–BDMT monolayer to Hg+–BDMT (at E°=0.48 V) and subsequently to Hg0–BDMT (at E°=0.2 V) proceeds with electron‐transfer rate constants of 8 and 11 s−1, respectively. The Hg0 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 Hg2+ ions proceeds with electron‐transfer rate constants corresponding to 9 and 43 s−1, respectively, and the redistribution of Hg2+ on the thiolated monolayer occurs within approximately 15 s. The reduction of the Hg2+ ions to the Hg0 nanoclusters and their reverse electrochemical oxidation proceed without the dissolution of mercury species to the electrolyte, implying high affinities of Hg2+, Hg+, and Hg0 to the thiolated monolayer. The electrochemical transformation of the Hg2+‐thiolated monolayer to the Hg0‐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 Hg0‐nanocluster‐modified surface reveals enhanced hydrophobicity (contact angle 76°) as compared to the Hg2+‐thiolated monolayer (contact angle 57°). The hydrophobic properties of the Hg0‐nanocluster‐modified electrode are further supported by force measurements employing a hydrophobically modified AFM tip.