One-step electrodeposition of ZnO/eosin Y hybrid films from a hydrogen peroxide oxygen precursor

The deposition of eosin Y/zinc oxide hybrid films is performed by cathodic electrodeposition from a hydrogen peroxide oxygen precursor in chloride medium. Typically the deposition bath contains 5 mM ZnCl2, 10 mM H2O2 and less than 10 muM eosin Y. A rotating disk substrate is used with a rotation speed of 500 rpm. The deposition potentials range between - 1.25 and - 1.50 V versus the mercurous sulfate electrode (MSE). The resulting films are well crystallised and highly textured with the C axis perpendicular to the substrate. They exhibit an electrocatalytic activity for hydrogen peroxide reduction during the deposition. The role of reduced eosin bound to ZnO in the electrocatalysis is discussed. We have measured a maximum of dye loading at 0.21 M and we show that the dye is concentrated in the film compared to the dye/zinc ion molecular ratio in solution. The dye loading decreases slightly with deposition overvoltage. We discuss the loading mechanism in the light of the dye diffusion behaviour in solution and of the relationship between dye loading and film growth rate. The chemical diffusion coefficient of eosin Y under the present conditions is measured an equal to 1.9 x -10(-5) cm(2) s(-1). We show that the complexation between reduced eosin Y and free zinc ion in solution and the coprecipitation reaction of this complex are likely to be the key steps of the loading process. (C) 2002 Elsevier Science B.V. All rights reserved.