Electrocatalytic oxidation of nitrite on a carbon paste electrode modified with Co(II) porphyrin adsorbed on SiO2/SnO2/phosphate prepared by the sol-gel method

This paper describes the immobilization of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphyrin ion on SiO2/SnO2/Phosphate obtained by the sol-gel processing method. The porphyrin was adsorbed on the surface of the modified material and furthermore metallized in situ with Co(II) ion. The porphyrin metallation process was followed using UV-Vis spectroscopy by inspecting the Q bands of the free and metallated porphyrin. A carbon paste electrode modified with material containing metallated porphyrin was used to study the electro-catalytic oxidation of nitrite ions by means of cyclic voltammetry, chronoamperometry and RDE voltammetry. The modified electrode was very stable and exhibited the electro-catalytic oxidation of nitrite ions at 0.72 V vs. SCE by a two electron mechanism producing nitrate ions at pH 5.4. The kinetic parameters of the electrode reaction process were calculated; (1 - alpha)n(a) was 0.479, D was (5.3 +/- 0.11) x 10(-5) cm s(-1), and k(0) could be determined as (5.4 +/- 10.14) x 10(-3) cm s(-1). (c) 2005 Elsevier B.V. All rights reserved.