Electrodeposited mesoporous ZnO thin films as efficient photocatalysts for the degradation of dye pollutants

Thin mesoporous films of ZnO were prepared by electrochemical deposition using eosin Y as a structure-directing agent. After removal of the eosin from the structure, transparent porous ZnO films were obtained. The porosity and surface area of these films were determined by performing krypton BET measurements. Electrochemical deposition parameters, such as the deposition time and the eosin concentration in the plating bath, were optimized to prepare films with large internal surface areas and good mechanical properties. Eosin concentrations of 50-60 mu M were found to give the best-quality mesoporous zinc oxide films with film thicknesses ranging from 2 to 3 mu m. The photodegradations of a heteropolyaromatic dye (methylene blue) and a diazo dye (congo red) served as model reactions to assess the photocatalytic activity of the zinc oxide films. For both dyes, the photodegradation rate reached its maximum for mesoporous films that were prepared with eosin concentrations above 40 mu M. As the photodegradation was found to occur preferentially in the larger-diameter pores of the films, the development of a very large surface area owing to a fine network of mesopores narrower than 8 nm did not significantly enhance the photocatalytic performance of ZnO films.