Cobalt Porphyrin Immobilized on a Niobium(V) Oxide Grafted – Silica Gel Surface: Study of the Catalytic Oxidation of Hydrazine

Abstract

meso-Tetracarboxyphenylporphyrin (4,4′,4″,4′′′(21H-23H-Porphine-5,10,15,20-tetrayl) tetrakis-(benzoic acid)), designated as H2TCPP, was efficiently immobilized onto niobium oxide grafted on the silica gel surface, SiO2/Nb2O5, by the -COO-Nb bond formed between the porphyrin carboxyl groups and Nb2O5. This immobilized porphyrin, SiO2/Nb2O5/H2TCPP, was then in situ metallated with Co(II) in dimethylformamide solution. The metallation process was followed by inspection of the UV-vis spectra which showed a decrease in the number of Q bands (a2u → eg transition) after the metallation, indicating that the symmetry of the porphyrin ring changed from D2h to D4h upon incorporation of Co(II). This material, when incorporated into a carbon paste electrode, electrocatalyzed hydrazine oxidation. Amperometric studies showed the potential of the modified electrode as a sensor for determination of hydrazine. The response time of the modified electrode was less than 1 s. A linear response was obtained between 1×10−5 and 5×10−4 mol L−1 at pH 7.