Voltammetric and impedance studies of phenols and its derivatives at carbon nanotubes/prussian blue films platinum modified electrode

The electrochemical oxidation of phenol (Ph), 4-chlorophenol (4-ClPh) and 4-nitrophenol (4-NPh) at a platinum electrode modified with and without multi-walled carbon nanotubes/Prussian blue nanocomposite in a pH 7.0 phosphate buffer electrolyte was investigated by cyclic voltammetry (CV) and impedance measurements. The modified electrodes were characterised using techniques such as transmission electron microscopy (TEM), electron X-ray dispersive spectroscopy (XRD), cyclic voltammetry (CVs) and electrochemical impedance spectroscopy (EIS). The phenol produced an irreversible CV oxidation peak whose potential increased for 4-ClPh and 4-NPh derivatives. Pt-MWCNT-SO3--PB electrode gave the highest electro-oxidation current compared to the other electrodes studied. The oxidation of the phenol compounds was not completely diffusion controlled especially at higher scan rate, and the electrode was characterized by some level of adsorption. The degree of adsorption was depicted by the Tafel values of 4292.4, 663.2 and 203.8 mVdec-1 for Ph, 4-ClPh and 4-NPh respectively. The limits of detection were in the micro molar range and the Gibbs free energy change (δG⁰) due to adsorption was estimated as -33.8, -35.8 and -36.0 kJmol-1 for Ph, 4-ClPh and 4-NPh. Impedance data showed that the MWCNT-SO3--PB film was so porous and behaved as a pseudocapacitor towards the oxidation of the analytes.