Kinetics studies in heterogeneous photocatalysis. I. Photocatalytic degradation of chlorinated phenols in aerated aqueous solutions over titania supported on a glass matrix

The photocatalytic degradation of phenol, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,5-trichlorophenol over TiO/sub 2/ (anatase) has been investigated by using three photochemical reactors. TiO/sub 2/ was used as a thin film, coating the internal surface of a glass coil (reactors I and II) or the external surface of glass beads (reactor III). The degradation of the four phenolic compounds, in a continuous recirculation mode in all three reactors, approximates first-order kinetics to near-complete degradation. The Langmuir-Hinshelwood kinetics have been modified slightly to rationalize the first-order behavior in solid-liquid reactions and to argue in favor of a surface reaction; the degradation reactions occur on the TiO/sub 2/ particle surface. In the multipass mode experiments, both reactors I and II exhibit higher degradation rates for phenol at the higher flow rates. By contrast, the greater degradation is associated with the lower flow rates in the single-pass mode experiments.