Hexanethiol, adsorption

Formation of the Au-S bond in hexanethiol adsorption leads to a localized a resonance which broadens and shifts when the hexanethiol molecules, initially lying flat at low coverages, realign vertically at higher coverages. Extensive studies of the model system C61 v>/Cu(111) have shown the presence of a transient anionic resonance, and similar studies are now being carried out on other systems. 

Eyring and Wadsworth (59) used the pressed-salt method to study the adsorption of hexanethiol on ZnS, ZnO, and willemite (Zn2Si04). The ZnS... 

It was pointed out that adsorption of propanethiol or hexanethiol occurs according to the following reaction (58) RSH —> RSads + H+ + e desorption can occur by an electrooxidation, RSads + 3H20—> RSO,H + 5H + + 5e. A comparative study of the amount of thiol adsorbed and the effect of this adsorption on hydrogen chemisorption showed that one molecule of thiol is adsorbed on one accessible platinum atom (58). 

According to Maxted (36), at low temperatures the molecule would be adsorbed through sulfur atom anchoring. Around this point the hydrocarbon chain could, thanks to its free rotation, inhibit adsorption over the whole adjacent surface. A comparison of the toxicities of hexanethiol and propanethiol shows that the ratio of these toxicities is exactly equal to the ratio of the surface area covered by the two molecules. 

Wadsworth and coworkers (13, 14) have found considerable evidence for surface polarization in double-beam infrared spectroscopy. Not only do new differential peaks due to adsorption appear in the spectrograms but also the bands due entirely to the adsorbent are frequently appreciably shifted by adsorption. This occurred, for example, in calcium fluorite treated with oleic acid, in samples of bentonites taken from aqueous solutions of different pH, and in various minerals treated by flotation collectors. In fact, it is more the rule than the exception that the spectrograms of finely divided solids dispersed in the KI or KBr window exhibit distortion due to adsorption, whether adsorption occurs at the solid-aqueous solution or at the solid-vapor interface. For example, Eyring and Wadsworth (13) found that two (differential) peaks were produced by adsorption on willemite either from the vapor or aqueous solution of hexanethiol. These peaks were due to the influence of adsorption of the hexanethiol on the Si-O bands of the willemite and occurred at about 9.2 and 12.3 microns. 

The mpe was determined for the reductive desorption of alkanethiol SAMs of various chain lengths from hexanethiol (C6SH)toC18SHina0.1 M KOH/ethanol solution. It linearly increases with the chain length with a slope close to the mass of CH2, as expected for a one-electron process. However, the mpe is much smaller (by 148 g mol ) than the molar mass of the desorbed alkanethiol. This difference is attributed to the simultaneous adsorption of cation species from solution, which is supported by the observed cation dependence of mpe and by the fact that the pzc of a bare gold electrode is more positive than the desorption potential. 

Cyclic Voltammetry [12]. The composition of the mixed monolayer of 6-ferrocenyl-hexanethiol and 2-hydroxy-ethanethiol used in the AFM-measurements was determined by separate cyclic voltammetric experiments. The redox signal of the ferrocene unit was integrated in cyclic voltammograms measured in 0.1 M NaC104 for monolayers of different ratios of the two adsorbates in the adsorption solution (1-100% Fc). 

Wano, H. Uosaki, K. 2005. In sim dynamic monitoring of electrochemical oxidative adsorption and reductive desorption processes of a self-assembled monolayer of hexanethiol on a Au(lll) surface in KOH ethanol solution by scanning tunneling microscopy. Langmuir 21 4024-4033. 

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