The photooxidation of 4-chlorophenol by singlet oxygen was studied in aqueous solution. The reactions were carried in a heterogeneous system using tetra(4-carboxyphenyl)porphyrin as a sensitizer adsorbed on silicon dioxide (TcPPH/SiO2). The generation of singlet oxygen produced during photosensitization of TcPPH/SiO2 with visible light was analyzed by electron paramagnetic resonance (EPR) studies using spin trapping technique. Hydroquinone and benzoquinone were identified by HPLC as the main products of the photooxidation. The photooxidation of 4-chlorophenol followed a global kinetic Langmuir-Hinshelwood.