Abstract
The first stages of the electroadsorption of ethyl xanthate (EX) on polycrystalline gold have been studied by optical and electrochemical techniques covering the 5 × 10 −6 to 1 × 10 −3 M concentration range. According to ac voltammetry and electroreflectance measurements, the adsorption of EX begins at −1.4 V (vs. SCE), in the HER potential region, followed by a capacitative process at −1.0 V. Both stages can be ascribed to the formation of different bonds between the EX and the gold surface through the sulphur atoms of the molecule. The following electroadsorption stage at −0.7 V implies the formation of a surface compound leading subsequently to layer growth. Differential reflectivity was particularly useful in providing information'on this type of complex adsorption process without appreciable interference from charging currents or stray faradaic reactions.
Highlights
Organic monolayers of well-defined structures supported on electrodes have proved useful for a variety of applications in microelectronics, batteries, biology, etc
Cyclic voltammetric experiments were conducted in order to get a rough picture of the system behaviour and to delimit the potential regions of the different processes
Voltammograms run at 70 mV/s for 1 X 10e4 M KEX (Fig. la) and spanning the potential region positive of the HER, between -1.2 and 0.65 V, show two anodic current peaks, one at -0.07 V and another one at 0.04 V
Summary
Organic monolayers of well-defined structures supported on electrodes have proved useful for a variety of applications in microelectronics, batteries, biology, etc. The fundamental problem of charge transfer across long distances is of considerable importance to electrochemical systems. This type of organic layer with variable controlled distances provides a means of separating redox centres from metal surfaces in the process of electron tunnelling. From the practical point of view, the specific adsorption of collectors such as potassium ethyl xanthate (KEX) on mineral surfaces is used in the industrial process of flotation for separating different minerals from each other and from ore (gangue). The method has been applied to metallic sulphides for many years, the fundamental chemistry of the adsorption-desorption processes is not properly understood [2-161. In order to achieve a better understanding of the surface
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