Two consecutive Langmuir isotherms were used in this study to describe copper(II) phthalocyaninetetrasulfonic acid-tetrasodium salt (CuPc) adsorption by TiO2-Degussa-P25. UV-vis reflectance spectroscopy confirmed CuPc adsorption on the TiO2 surface. FTIR spectra revealed less TiO-sulfonic interactions for maximum CuPc surface coverage (39 mg g(-1)) of the second Langmuir than the maximum coverage (8 mg g(-1)) of the first Langmuir. This finding indicates that there is more than one TiO-sulfonic interaction per CuPc molecule. Dichlorvos (DDVP)-water solutions were degraded with the modified TiO2 catalyst and visible simulated solar light. The highest degradation rates were obtained using 8 mg g(-1) CuPc at a neutral pH with a maximum K-obs = 0.0072 min(-1). Under this condition, a rate vs. DDVP concentration (C-DDVP) bell-shaped profile was observed. This tendency can be explained in terms of dissolved oxygen singlet formation via visible light surface sensitization. This process was diminished at high C-DDVP because of DDVP competition with dissolved oxygen to reach the catalyst surface. DDVP degradation and mineralization have the same rate limiting step. Therefore, there is no intermediate accumulation during treatment. The modified TiO2-CuPc catalyst activity was further improved when solar simulated light (including UV) was used to degrade DDVP. In fact, the fastest degradation rate constant (k(obs) = 0.011 min(-1)) was obtained using high CuPc coverage (39 mg g(-1)). (C) 2014 Elsevier B.V. All rights reserved.