Photocatalytic degradation of 4chlorobenzoic acid in water was studied using different TiO2 catalysts (Degussa P-25, Ishihara ST01 and Hombikat UV-100) and solution characteristics. Mineralization of 4chlorobenzoic acid was achieved in all the experiments and total recovery of the chlorine as free Cl- was obtained. The catalyst concentration influenced the photocatalytic rates and the optimum loading concentration was determined to be different for Degussa P-25 and Ishihara ST01, mainly due to the difference in their adsorption and scattering characteristics. Comparison between the catalysts for their photocatalytic activity revealed that other factors must influence the photocatalytic reaction rates beside the surface area of the catalysts. The photocatalytic reaction rates were found to obey the Langmuir-Hinshelwood adsorptionreaction model. At pH = 7.0, the presence of Cl did not inhibit the reaction rates. At pH = 3.0, however, the photocatalytic reaction rates were higher for the solution containing NO-3 instead of Cl- at the same molar concentration.

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