Enhanced photodecomposition of 4-chlorophenol in aqueous solution by deposition of CdS on TiO2

The photocatalyzed degradation of 4-chlorophenol (4-CP) in water is comparatively examined with TiO2 powder, TiO2/CdS powder, TiO2 thin him electrodes and TiOl/CdS thin him electrodes in the initial stages of the reaction. The apparent intermediates of 4-CP photodegradation with TiO2 and TiO2/CdS powders in suspensions are found to be 1,4-benzoquinone (BQ) and hydroquinone (HQ), with HQ rapidly converting into BQ with TiO2 and TiO2/CdS electrodes at an applied anodic potential of 0.6 V vs Ag/AgCl. The apparent reaction rate constants using the Langmuir-Hinshelwood equation with TiO2/CdS powder and the TiO2/CdS electrode are obtained to be about 90% and 33% larger than with TiO2/CdS powder and the TiO2 electrode, respectively, indicating that the TiO2/CdS catalysts have more photocatalytic activities than the TiO2 catalysts in the initial stages. The adsorption coefficient (K) of 4-CP on TiO2/CdS powder is one and a half times larger than that on TiO2 powder. With the electrode catalysts at 0.6 V, the value of K increases several times with respect to the corresponding powder catalysts and shows essentially no difference between the TiO2/CdS electrode and the TiO2 electrode. Thus, the value of K may strongly depend on the electrostatic interaction between 4-CP and the electrode surface, but not very much on the type of electrode surface, (C) 1999 Elsevier Science S.A. All rights reserved.