Electrochemical studies of a new iron porphyrin entrapped in a propylpyridiniumsilsesquioxane polymer immobilized on a SiO2/Al2O3 surface

In this work, a new porphyrin, the 5,10,15,20-tetrakis-(2,6-difluoro-3-sulfonatophenyl) porphyrinato iron(III) chloride (denoted as FeTsP) was immobilized on SiO2/Al2O3 (SiAl) coated with n-propylpyridiniumsilsesquioxane polymer (SiPy+Cl-). The FeTsP was adsorbed on SiAl/SiPyCl by an ion exchange reaction, obtaining a modified solid, SiAl/ SiPy/FeTsP, where the porphyrin complex was strongly adhered. Cyclic voltammograms of the SiAl/SiPy/FeTsP carbon paste electrode showed an irreversible response, with an oxidation peak at E-Pa=0.40 V and nondefined reduction peak at E-pc = 0.15 V (vs. SCE). These peaks were not observed for the nonmetallated porphyrin, indicating that they probably correspond to the Fe(III)/Fe(II) process. Studies made in solutions having different pH, (between pH 2 and 9) using the modified electrode showed that the peak potentials and the current density were not affect by pH changes, indicating that the iron porphyrin is very stable and strongly entrapped in the matrix. The modified electrode presented the property to electrocatalyze the eletrooxidation of hydrazine at 0.41 V (vs. SCE), at pH 7. The potentiality of the SiAl/SiPy/FeTsP electrode as a sensor for hydrazine was evaluated by the using the chronoamperometric technique. A linear response was obtained in the concentration range between 5 x 10(-5) and 6 x 10(-4) mol L-1 of hydrazine.