In situ spectroelectrochemical studies of phenothiazine dyes at clay coated electrodes

Abstract

Phenothiazine dye exchanged bentonite clay coated electrodes were prepared and their electrochemical and in situ spectroelectrochemical studies were carried out. Electrodes coated with pre-exchanged phenothiazine dyes did not exhibit voltammetric responses when immersed in solution containing only supporting electrolyte. However, the dye cations were readily incorporated into the clay film from solution and exhibited voltammetric responses. The D_app values are of the order of 10^-8-10^-9 cm² s^-1 suggesting that the ionic diffusion of the electroactive species occurs predominantly. A diffusion mechanism similar to the polyelectrolyte Nafion^® modified electrodes and the bottleneck effect are observed at the clay modified electrodes. For the first time, the in situ spectroelectrochemical behavior of clay modified electrodes was studied to address the electroactivity of the different forms of the adsorbed dyes. The in situ spectroelectrochemical studies showed that part of the dimer dye was readily reduced at clay modified electrodes compared to the monomer and its protonated form. The dimer dye molecules are present on the surface of the clay film and also in the interlamelar region of the clay whereas the monomer and the protonated dye molecules occupy the interlamelar space of the clay. The fraction of the monomer and the dimer dye molecules adsorbed on the surface of the clay were electroactive.