Abstract
The properties of a methylene blue layer adsorbed onto a sulphur-modified gold electrode have been studied by electrochemical and in-situ reflectance spectroscopy in the visible region. At saturation coverage, methylene blue monomer and dimer bands were observed in the double-layer region through the electrochromism of the adsorbed film arising from the effect of the double-layer field on the molecule transition moment. Possible dye orientations in the adsorbed state are discussed with the aid of the optical measurements. At low surface concentrations, the optical signal stems from modulation of the monomer/dimer interconversion. Repeated electrochemical reduction and oxidation of adsorbed methylene blue result in gradual desorption of the dimer species, probably due to a change in the molecular geometry upon reduction which may evolve from a planar configuration to a folded structure.
Highlights
In recent years, the study of electrodeposited organic layers on electrodes has become a field of increasing interest owing to their potential application in, for instance, electrochromic devices, synthetic conducting materials, photogalvanic cells and electrocatalysis [l-4].Methylene blue cation (MB+) is known in connection with the determination of surface areas and cation exchange capacity of clays [5]
The electrochemical behaviour of methylene blue adsorbed on a sulphur-modified gold electrode has been reported by Svetlicic et al [16]
Region characterized by a pair of sharp current peaks corresponding to the reversible MB+/methylene blue in the leuco (MBH) reaction
Summary
The study of electrodeposited organic layers on electrodes has become a field of increasing interest owing to their potential application in, for instance, electrochromic devices, synthetic conducting materials, photogalvanic cells and electrocatalysis [l-4].Methylene blue cation (MB+) is known in connection with the determination of surface areas and cation exchange capacity of clays [5]. High coverage When the electrode potential is modulated at 11 Hz, with a 100 mV,_, sinusoidal wave and bias potentials ranging from + 0.20 to - 0.15 V, two bands are detected at 1.79 and 2.05 eV, corresponding to the absorption of polarized radiation at the positive limit of the modulation by bound methylene blue monomer and dimer, respectively (Fig. 2).
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