Abstract
Isotherms of adsorption by zinc oxide of Rose Bengal dye from different solvents such as water, ethnol and water-ethanol mixtures were measured. The different amounts adsorbed at saturation were obtained from these isotherms, and the minimum adsorption value was obtained at about 70 vol.% of ethanol, which gives the minimum enthalpy of the mixed solvents. The maximum amount of dye adsorbed was obtained in the case of the pure water solvent, and the maximum coverage θBET(max) was about 0.5.
The dependence of the surface potential and the photovoltage of the dyed zinc oxide powder layers prepared by vaporization of solvents on the amounts of dye adsorbed was measured in air. The plots of the surface potential vs. the amount adsorbed showed M-shaped curves, and the plots of the photovoltage vs. the amount adsorbed showed N-sharped curves. Form these results, it was proposed that two types of adsorption sites for the sensitizing dye may exist on the zinc oxide sureface. The adsorption states of the dye molecules on the surface and the mechanisms responsible for the dye-sensitized photovoltages were dicussed.
