The role of mass transfer in solution photocatalysis at a supported titanium dioxide surface

The kinetics of Cl(-) production from the UV-photocatalysed degradation of aqueous 4-chlorophenol (CP), by a thin TiO(2) (Degussa P25) film, in both aerated and oxygenated solutions, have been determined by the channel flow method with electrochemical detection. The experimental approach allows surface kinetics and mass transport effects to be readily resolved. For typical irradiation intensities of (0.7-2.0)x10(17) quanta cm(-2) s(-1), the results obtained with dilute CP solutions (less than or equal to 0.5 mM), in particular, clearly demonstrate that there is a range of practically important conditions where mass transport plays a role in controlling the kinetics of the process. When these effects are considered, the surface kinetics are consistent with the Langmuir-Hinshelwood model.