Nitrite electro-oxidation mediated by Co(II)-[tetra(4-aminophenyl)porphyrin]-modified electrodes: behavior as an amperometric sensor

Electro-oxidation of nitrite mediated by Co(II)-[tetra(4-aminophenyl)porphyrin]-modified electrodes (4-CoTAPP) is presented in this article. Catalytic activity of electrodes modified with porphyrin polymeric films (poly-4-CoTAPP) and with multilayer of monomers (m-4-CoTAPP) for the oxidation of nitrite was compared. The number of cycles for the electrosynthesis of poly-4-CoTAPP determines the activity of the electrode toward nitrite oxidation because the system loses its catalytic activity as the number of polymerization cycles increases above 15. The effect of pH on activity is also reported. The response for the nitrite oxidation of electrodes modified with 4-CoTAPP and with metal-free ligand, that is, tetra(4-aminophenyl)porphyrin, either as multilayer of monomers or as polymer (m-4-H2TAPP and poly-4-H2TAPP, respectively), was compared. An increase of activity in the presence of the metal was found. Furthermore, when the device was tested as an amperometric sensor for different nitrite concentrations under the optimum working conditions, only poly-4-CoTAPP exhibited a linear response throughout the concentration range studied with a reasonably low limit of detection, while m-4-CoTAPP and poly-H2TAPP systems have no linear response throughout the range of concentration. Finally, the number of electrons involved and the Tafel slope for the reaction were estimated.