The adsorption and desorption behavior of several long chain alkyl thiols on gold electrodes were studied using the electrochemical quartz crystal microbalance (EQCM). The rate of adsorption of the self-assembled monolayer (SAM) from various nonaqueous solutions was determined by using the EQCM to monitor the mass change at the electrode surface caused by the formation of the SAM. The EQCM method also allowed for monitoring the mass change due to reductive desorption of the SAM. Significantly different behavior was observed for the SAM formation in acetonitrile (ACN) and dimethylformamide (DMF). For example, exposure of a bare gold electrode to alkyl thiol in ACN leads to multilayer formation which slowly evolves to a stable SAM, while in DMF no initial multilayer formation is observed. Also, the time scale for deposition of submonolayer amounts of alkyl thiols was much shorter in DMF (ca. seconds at millimolar concentrations) than in ACN (ca. minutes at millimolar concentrations). Detailed comparisons of charge consumption and mass change during the reductive desorption, along with some model calculations for the amount of double layer charge passed during the desorption event, suggest that a considerable fraction of the charge harvested during reductive desorption could originate from charging the double layer.
ASJC Scopus subject areas
- Colloid and Surface Chemistry