Electrochemical property of methylene blue redox dye immobilized on porous silica–zirconia–antimonia mixed oxide

Abstract

The mixed oxide SiO 2/ZrO 2 obtained by the sol–gel processing method adsorbs Sb(V) from acid solution, forming a new phase on the matrix surface designated as SiO 2/ZrO 2/Sb 2O 5. The amount of Zr(IV) in the matrix was 8.1 wt.%, corresponding to 0.89 mmol g −1, and the amount of Sb(V) incorporated in the matrix was 6.3 wt.% (0.52 mmol g −1). This material presented a specific surface area, S BET=590 m 2 g −1. The immobilized Sb 2O 5 is a good cation exchanger and adsorbs methylene blue (MB) cationic dye with an average surface density δ=1.1×10 −11 mol cm −2 (about 0.07 molecule nm −2). The dye is strongly entrapped in the pores of the matrix and it is not leached off in KCl solutions as concentrated as 1.0 M. A carbon paste of the SiO 2/ZrO 2/Sb 2O 5/MB material showed a reversible redox pair with midpoint potential E m=−0.1 V versus SCE. This midpoint potential is not affected by solution pH change between 2 and 7. The immobilized dye mediated NADH catalytic oxidation at ca. 50 mV.