Incidence of UV or visible light on ZnO powder in O2 atmosphere of low pressure either enhances or reduces the adsorption of O2. The phenomenon depends quantitatively upon the history of sample powders as well as the measuring conditions such as wavelength, intensity of exciting light, temperature, atmospheric pressure and so on.
Three types of powders showing the positive effect (photoadsorption), negative effect (photodesorption) and almost no effect were prepared. The detailed measurements were carried out at various conditions on the powders of photoadsorption type, and the following conclusions were derived; (1) the spectral response showed the fundamental absorption to induce the phenomenon and (2) the relative photoadsorption rate was proportional to the atmospheric pressure and also to the root of light intensity. A mechanism was proposed to the photo-effect on O2 adsorption.
The photoadsorption of H2 on ZnO powder was very slight compared to that of O2. The pressure changes by incidence of light for H2 and O2 were enough to separate each other. Thus the separation between H2 and O2 was found to be possible by the use of ZnO powder and solar light.
