Electrochemical study and complete factorial design of Toluidine Blue immobilized on SiO2/Sb2O3 binary oxide

SiO₂/Sb₂O₃ of specific surface area S _BET = 788 m² g^–1 and 4.7 wt % of Sb was prepared by the sol–gel method. Toluidine Blue (TB⁺) was immobilized on SiO₂/Sb₂O₃ by ion exchange reactions and the amount of dye bonded to the substrate surface was 13.72 mol g^–1 for SiO₂/Sb₂O₃. This material was used to modify carbon paste electrodes and the electrochemical properties of Toluidine Blue (TB⁺) immobilized on a silica surface modified with antimonium trioxide were investigated by cyclic voltammetry. The electron mediator property of toluidine blue was optimized using a factorial design, consisting of four factors each at two levels. Factorial analysis was carried out by searching for better reversibility of the redox process, that is, the lowest separation between anodic and cathodic peak potentials and a current ratio near unity. The aqueous phase pH does not appear to influence the peak separation, E, and the |I _pa//I _pc| current ratio response. The other factors studied, the scan rate, type of electrolyte and electrolyte concentration are important for this chemically modified electrode system demonstrating significant influences on the reversibility of electron transfer. The experimental observations and data analyses on this system indicate that the smallest peak separation occurs using 20 mV s^–1 and 1.0 mol L^–1 KCl while values of |I _pa//I _pc| close to unity are found for 20 mV s^–1 with 1.0 mol L^–1 concentrations of either KCl or CH₃COONa. The electrodes presented reproducible responses and were chemically stable for various oxidation-reduction cycles.