Redox properties of phenosafranine at zeolite-modified electrodes - Effect of surface modification and solution pH

Redox properties of cationic dye phenosafranine (3,7-diamino-5-phenylphenazenium chloride) (PS+) were studied at zeolite-modified electrodes using Zeolite-Y and NaZSM-5. The peak current and peak potential of phenosafranine-adsorbed zeolite were found to be influenced by the pH of the electrolyte solution. Observation of a second redox couple is suggested to be due to formation of new species at low concentration from the reduced phenosafranine at the zeolite-modified electrodes. Titanium dioxide nanoparticles encapsulated in the cavities of the zeolite or anchored on the external surface of the zeolite do not seem to affect the redox properties of adsorbed PS+. When the cyclic voltammograms are recorded immediately after the electrode is immersed into the solution, the redox potential of PS+ is found to be sensitive to the nature of the zeolite surface. The peak potential shifts towards positive region under continuous cycles as the surface hydroxyl groups get protonated in acidic electrolyte solution thereby forcing the movement of dye molecules from the zeolite surface to the zeolite electrode solution interface. The electron transfer rate constants for the adsorbed dye at the electrode are calculated to be 2.5 +/- 0.2 s(-1) and 3.5 +/- 0.2 s(-1) for the zeolite-Y electrode and the ZSM-5 electrode, respectively by the Laviron equation. (c) 2007 Elsevier B.V. All rights reserved.