Different photochemical approaches have been investigated to prepare supported nickel nanoparticles to be used in the catalytic ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D). Direct photochemical (lambda = 365 nm, without TiO2) and photocatalytic deposition in presence or absence of sensitizers (TiO2, acetone or benzophenone) were employed. The characterization of the catalysts was carried out by Xray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The photocatalytic deposition without any sensitizer resulted to be the most suitable method to obtain in very short irradiation time. Ni nanoparticles randomly distributed over the support with a particle size ranging from 7 to 15 nm. An optimization of this technique was performed by varying the mass of TiO2 and the light intensity. According to the results of 2,4-D degradation, the catalytic ozonation with Ni/TiO2 catalyst presented a slightly higher conversion than TiO2 or ozonation alone. These results were explained in terms of the two phases (NiO/Ni) present on the surface of TiO2 which favor the ozone decomposition forming OH radicals useful for 2,4-D degradation. A reaction pathway including all the intermediates formed during the direct attack of ozone and the produced OH radicals was proposed. (C) 2011 Elsevier B.V. All rights reserved.