Electrochemical oxidative adsorption and reductive desorption of a self-assembled monolayer of decanethiol on the Au(111) surface in KOH+ethanol solution

Abstract

The electrochemical characteristics of an Au(111) electrode were investigated in 0.1 M KOH ethanol solutions containing various concentrations of decanethiol. Anodic and cathodic peaks corresponding to the oxidative adsorption and reductive desorption, respectively, of a self-assembled monolayer (SAM) of decanethiol were observed. Both peaks negatively shifted with the increase in the thiol concentration by ca. 57 mV/decade, showing that the redox process is a one-electron process. The adsorbed amount determined from the charge corresponding to the reductive desorption increased with an increase in the decanethiol concentration but never reached the saturated amount as long as the cyclic voltammograms were continuously recorded with the sweep rate of 10 -200 mV s-1. It increased with the holding time at +0.1 V, which was much more positive than the anodic peak potential, and reached the saturated amount in ca. 10 min in the 10 μM thiol solution. The reductive peak potential also negatively shifted with the holding time but for a longer period. It kept shifting for ca. 60 min in the 10 μM thiol solution, which is much longer than the time when the adsorbed amount reached the saturated value. These results suggest that the formation of a highly ordered SAM requires a much longer time than the adsorption of the thiol.2

Effects of concentration and temperature on the formation process of decanethiol self-assembled monolayer on Au(1 1 1) followed by electrochemical reductive desorption

“…[ [18,35,36,38,39]. This discrepancy may be caused by an error in the estimation of real surface area.…”

“…From the area, shape, and position of the cathodic peak corresponding to reductive desorption of the SAM, one can obtain much information on the SAM such as the amount adsorbed thiol molecules and stability and conformational order of the SAM. We have shown that the SAM can be formed by anodic oxidative adsorption, i.e., a reverse reaction of the reductive desorption, in an alkaline ethanolic solution containing thiol and the coverage of SAM increased and the peak position shifted negatively with adsorption time and the rates of formation and the conformational order of the SAM are higher in the decanethiol solution of higher concentration [39,40].…”

“…Since Widrig et al reported that an alkanethiol SAM is desorbed from gold surface by a one-electron electrochemical reduction process in an alkaline aqueous solution [35], many electrochemical studies on this reaction have been carried out [34][35][36][37][38][39][40][41]. From the area, shape, and position of the cathodic peak corresponding to reductive desorption of the SAM, one can obtain much information on the SAM such as the amount adsorbed thiol molecules and stability and conformational order of the SAM.…”

Electrochemical Oxidative Formation and Reductive Desorption of a Self-Assembled Monolayer of Decanethiol on a Au(111) Surface in KOH Ethanol Solution

“…[52][53][54][55][56][57][58][59][60][61] Recently, we briefly reported that quantitative analysis of the reductive desorption of an electrodeposited thiolate layer provided us with useful information about the formation process of a SAM such as the time dependency of the adsorbed amount and the order of the SAM. 62 In this work, we studied in detail the anodic oxidative adsorption and cathodic reductive desorption of decanethiol layers on Au(111) electrodes in 0.1 M KOH ethanol solutions containing various concentrations of decanethiol. The effects of sweep rate and thiol concentration under the condition of continuous potential cycling as well as the effects of holding time and thiol concentration under the condition of potentiostatic oxidative SAM formation on the amount of adsorbed thiolate and the order of the SAM were evaluated from the charge and position of the reductive peak, respectively.…”

Self-Assembly Process of Flatly Adsorbed Porphyrin Self-Assembled Monolayer on a Au(111) Surface Studied by ex situ Scanning Tunneling Microscopy and Electrochemical Reductive Desorption Measurements

“…It is well known that alkylthiol SAMs are electrochemically desorbed from a gold surface by the following reduction process in an alkaline aqueous solution: [56][57][58][59][60][61][62][63][64][65] Au Figure 2 shows LSVs of the Au(111) electrodes modified with the TMMPP SAMs, which were prepared for various dipping periods, measured in 0.1 M KOH at a scan rate of 20 mV s ¹1 when the potential was negatively scanned from 0 to ¹1.4 V. Between ¹0.7 and ¹1.1 V, three cathodic peaks, which seemed to be due to the reductive desorption of the SAM, were observed. The two more negative peaks observed around ¹0.9 and ¹1.0 V were reported only in the case of the mercaptopyridine and mercaptopyrrole SAMs.…”