Kinetic analysis of the photocatalytic degradation of gas-phase 2-propanol under mass transport-limited conditions with a TiO2 film photocatalyst

A kinetic study of the degradation of gas-phase 2-propanol was carried out using a TiO(2) film photocatalyst in a batch-type reactor under relatively high-intensity UV light illumination; the incident UV intensity was varied from 35 mu W cm(-2) to 60 mW cm(-2), and the initial 2-propanol concentration was varied from 0.1 ppmv to 100 ppmv. Although the degradation rate increased with increasing numbers of absorbed photons at lower light intensities, it gradually saturated and finally reached completely mass transport-limited conditions. We simulated the decrease in gas-phase 2-propanol concentration as a function of time under mass transport-limited conditions using the one-dimensional diffusion equation, assuming a boundary layer thickness of 1.5 cm. On the basis of these results, together with previously reported results obtained under extremely low-intensity UV light illumination (36 nW cm(-2)-45 mu W cm(-2)), we have mapped various regions on a light intensity vs initial reactant concentration plot, corresponding to pure mass transport-limited conditions and pure light intensity-limited conditions for the photocatalytic degradation of gas-phase organic compounds.