Electrochemical stuy of the redox dyes Nile Blue and Toluidine Blue adsorbed ongraphite and zirconium phosphate modified graphite

摘要

Solid graphite electrodes were modified with the redox dyes Nile Blue (NB) and Toluidine Blue (TB), follwing irreversible adsorption from ethanol solution,and a droplet evaporationprocedure. The shift of redox potential for both dyes to the negative direction upon adsorption on graphite was estimated from cycliv voltammetry, and from extrapolation of the dependence of E_p versus I_p to I_p = 0, to vary between 60 and 110 mV. For electrodes containing a controlled amount of NB or TB, heteogeneous charge transfer rate constants of 31 and 11.6 s~(-1), respectively, were estimated by extrapolationof the data to zero coverage of the electrode surface. The rate constants obtained are several times higher thanthose obtained for multilayer coatings with the dyes. The modification of solid graphite electrodes with zirconium phosphate (ZrP), followed by the adsorption of NB and TB was performed. For NB, two forms of the dye were found to be present, one of them presenting an usual adsorbate of NB on graphite, and another one having E_(pc) SHIFTED BY CA. 0.15-0.30 V to more positive potential values. The latter form is ascribed to NB, included in the ZrP host matrix, as follws by comparing its electrochemical behavior with that observed for NB, included in carbon paste containing ZrP.