Diego Villagra

Electrochemical reduction of SO2 on poly-Co-3-tetraaminophenylporphyrin glassy carbon modified electrode¶

This article describes the electrochemical reduction of sulfite in water–ethanol mixtures under acidic conditions on a glassy carbon electrode modified with a conducting film formed by Co(II) tetra-3-aminophenyl porphyrin. Rotating disc electrode experiments show a kinetic limitation related with the formation of an adduct between the reduced porphyrin and the sulfur compound. UV–Visible spectroelectrochemical data suggest that Co(I) is not stabilized; thus the adduct should involve a radical species of the porphyrin. However, the resulting modified electrode is stable and shows a linear relationship between current and concentration of the sulfur species at pH 1. The detection range of sulfite by the modified electrode goes from 12 to 150 mg L−1. The detection limit is 4.15 mg L−1. ¶This article is dedicated to Professor A. Mederos.

ELECTROCHEMICAL REDUCTION OF NITRITE AT POLYMERIC Co (II)-TETRA-3-AMINO-PHENYL-PORPHYRIN MODIFIED ELECTRODE

This paper describes the electrochemical reduction of nitrite ion in basic media 0.2M KHC03, with glassy carbon or ITO electrodes modified with a conducting polymer derived from Co(II)tetra-3-aminophenyl-porphyrin. Cyclic voltammetry results show an enhancement in the current of the corresponding Co(II)/Co(I) redox couple when the solution contains 0.02M nitrite. When spectroelectrochemical experiments were performed in the support electrolyte, the modified electrode does not stabilize Co(I) oxidation state, but when there is nitrite in the solution a band at 549nm appears, indicating the stabilization of Co(I) oxidation state probably due to the formation of an intermediary complex between the Co(I) and nitrite. Controlled potential electrolysis experiments verify the production of ammonia and hydrazine even at very negative potentials, showing the electrocatalytic character and the stability of this modified electrode

EFFECT OF THE NUMBER OF SUBSTITUENTS ON THE BEHAVIOR OF MODIFIED ELECTRODES WITH COBALT PORPHYRINS SUBSTITUTED WITH A DIFFERENT NUMBERS OF BIS(METHOXYPHENYL) GROUPS TOWARD THE OXIDATION OF SULFITE

In this study, we compared four glassy carbon electrodes modified with adsorbed porphyrins of cobalt containing one, two, three, or four bis(methoxyphenyl) groups as substituents of the ligand. The aim of this work was to determine the effect of these donating groups on the electrocatalyst behavior of the modified electrodes for the reduction or oxidation of sulfite in water or in mixtures of 12% ethanol in water (v/v) at different pHs. The results showed that the modified electrodes are not catalytic toward the electro-reduction of sulfite in the whole range of pH studied (2-12). However, all the electrodes showed a catalytic toward the oxidation of sulfite at basic pHs. We found that the best catalytic system was the four-substituted porphyrin modified electrode at pH 9.8. This system performed well as an amperometric sensor for sulfite in ethanol-water mixtures and in aqueous solutions at the same pH. When the calibration curve was carried out by cyclic voltammetry, a detection limit of 0.10 mg L-1 for the four-substituted cobalt porphyrin modified electrode in water and in ethanol-water mixtures was found.