<b>Electrohemical Properties of Carbon Nanotube Paste Electrodes Modified with Redox Cationic Dyes</b> - doi: 10.4025/actascitechnol.v34i3.15250

Abstract

The present work describes the electrochemical behavior of cationic dyes (methylene blue and toluidine blue) as electron mediators adsorbed in the multiwall carbon nanotubes paste in 0.5 KCl at pH 7.0 by using cyclic voltammetry. Based on midpoint potential [E_m = (E_ap + E_cp)/2] and separation of cathodic and anodic peaks (ΔE), it was not observed interaction of different eletrolytes (LiCl, KCl, BaCl₂, CaCl₂, NaCl, NaNO₃, Na₂SO₄ and NaClO₄), with the cationic dyes by an ion exchange reaction and, as a consequence, absence of leaching of cationic dyes to the solution phase.  The kinetics of electron transfer on the surface electrode was not sufficiently fast showing a fairly resistence of carbon nanotube paste modified with the cationic dyes.  The midpoint potential and ΔE also were insentive to the pH range (4-8), confirming the protective effect of carbon nanotubes matrix, owing to strong interaction of between the latter and the nitrogen of nitrogen of cationic dyes with carbon nanotube matrix, minimizing the proton interaction under cationic dye. This result is very important for sensor/biosensor preparation, because the eletrooxidation behavior of the analyte will be only affected by its formal potencial shifting.  Carbon nanotubes proved to be an efficient solid matrix for the adsorption of mediator electron in comparison to the electrochemical behavior of free cationic dyes in solution phase.