Multimetallic porphyrins/polyoxotungstate modified electrodes by layer-by-layer method: Electrochemical, spectroscopic and morphological characterization

This work describes the formation of modified electrodes layer-by-layer assembly of a mu-{meso-5,10,15,20-tetra(pyridyl)porphyrin}terrakis{bis(bipyridine)chloride ruthenium(II)} coordinated with Zn(II) and Mn(III) in its central cavity and an anionic polyoxotungstate [SiW12O40](4-). The bilayer formation was monitored using electrochemical and UV-vis techniques, following the oxidation process of the Ru-III/II couple and the absorbance of the Soret band of porphyrin complexes respectively. It was possible to form 10 stable bilayers onto ITO surface. SEM studies were carried out finding that the morphology of the film depends on the metal center in the porphyrin. The thickness of these films was estimated as 0.603 mu m for (Zn(II)TRP](4+)/[SiW12O40](4-) and 2.18 mu m for [Mn(III)TRP](5+)/[[SiW12O40](4-) modified electrodes respectively. Raman spectroscopy showed that new bands appeared for [Mn(III)TRP](5+)/[SIW12O40](4-) assembly confirming stronger interactions than only electrostatic forces. Kinetics parameters such as charge transfer coefficient, alpha, and heterogeneous electron transfer rate constant, k(s) were obtained for both electrodes. Using electrochemical and UV-vis data it was possible to estimate the energy levels involved in the charge transfer process through the films formed. Sensor properties of [Zn(II)TRP](4+)/(SiW12O40](4-) modified electrode toward chlorite oxidation was tested. The results show electrocatalytic activity, amperometric determination demonstrate a detection limit of 13.8 mu M. (C) 2012 Elsevier Ltd. All rights reserved.