EVALUATION OF DIFFUSIBILITY OF ADSORBED PROPIONALDEHYDE ON TITANIUM DIOXIDE-LOADED ADSORBENT PHOTOCATALYST FILMS FROM ITS PHOTODECOMPOSITION RATE

Photocatalytic degradation of gaseous propionaldehyde over TiO2-loaded adsorbent films was investigated after adsorption equilibrium was obt ained using silica, alumina, activated carbon, and several kinds of ze olites as adsorbents. Irradiation of one-tenth of the TiO2-loaded adso rbent film caused complete mineralization of the adsorbed substrate in the entire film, although the rates obtained in that case were much l ower than one-tenth of the rates obtained with the total area irradiat ion, indicating a considerable contribution of supply of the adsorbed substrate from the nonirradiated part of the film to the irradiated pa rt. The apparent diffusion coefficient D-app of adsorbed substrate was evaluated by applying the time course of CO2 evolution obtained in th e area-selective photodecomposition reaction to a one-dimensional diff usion model. The D-app values estimated for various kinds of TiO2-load ed adsorbent supports explain well the differences in the photodecompo sition rates obtained at these photocatalysts. On the basis of experim ental results, the effect of diffusion of the adsorbed substrate on th e photodecomposition kinetics is quantitatively discussed.