Electrocatalytic oxidation of phenolic compounds using an electrode modified with Ni(II) porphyrin adsorbed on SiO2/Nb2O5-phosphate synthesized by the sol-gel method

Phosphated silica-niobia, SiO2/Nb2O5/H2PO4, presenting high specific surface area (S-BET = 580 m(2) g(-1)) was used as substrate base to adsorb 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21-H,23-H-porphyrin and furthermore metallated with Ni(11). The adsorption of porphyrin and in situ metallation procedures with Ni(II) were accompanied by UV-visible spectroscopy and cyclic voltammetry under alkaline conditions, respectively. A carbon paste electrode of the material obtained (CPE-Ni) was used to investigate the detection of hydroquinone and 4-aminophenol by electrochemical methods in KCl supporting electrolyte solution The cyclic voltammogram corresponding to the Ni(II)/Ni(III) redox couple was recorded during 820 cycles and demonstrated exceptional high stability. CPE-Ni showed higher catalytic efficiency than the electrode whose oxidation is mediated by the semiconducting property of Nb2O5 (a carbon paste electrode of pure mixed SiO2/Nb2O5 oxides) since the former presented the anodic peak potential for phenolic compounds at remarkably less positive potential. Hydroquinone and 4-aminophenol were detected over wide linear ranges of concentrations and with satisfactory sensitivities for both electrochemical techniques used, cyclic voltammetry and chronoamperometry. CPE-Ni exhibited an excellent operational response even after 260 and 280 measurements, respectively for hydroquinone and 4-aminophenol. (c) 2006 Elsevier B.V. All rights reserved.