This investigation evaluated the photocatalytic degradation of monochlorobenzene (MCB) in an aqueous TiO2 suspension. In accordance with the experimental results, the degradation of MCB was a function of the initial substrate concentration, incident light intensity, and TiO2 dosage. However, the solution pH had insignificant effect on the degradation efficiency. The heterogeneous photocatalytic degradation of MCB followed the Langmuir-Hinshelwood kinetics. The adsorption coefficient of MCB (K) and the observed degradation rate constant (k) were calculated as 13.4 mM(-1) and 0.0054 mM min(-1), respectively. In addition, a 0.255 dependency of the initial degradation rate on the light intensity revealed the considerable adverse effect of e(-)-h(+) pair recombination. Both mineralization and dechlorination occurred during the photocatalytic degradation of MCB. Under the operating condition of initial MCB concentration of 0.1 mM, light intensity of 5.68 mu Einstein s(-1), TiO2 dosage of 1.0 g L-1, and solution pH of 7, about 93.7% of MCB was mineralized after 240 min of irradiation. Nevertheless, 64.3% of the stoichiometric amount of Cl- ions was released into the bulk solution. The simulation results derived from the X-ray photoelectron spectroscopy (XPS) analysis was suggested that the interaction between Cl- ions and TiO2 Surface tended to lower the released amount of Cl- ions. (C) 2007 Elsevier B.V. All rights reserved.