Efficient degradation of 2,4-dichlorophenoxyacetic acid (2,4-D, herbicide) aqueous solutions was achieved on NiO/SiO2 catalysts in presence of ozone. NiO nanoparticles were deposited on the silica surface by impregnation (I) and liquid phase photodeposition (P) in presence of sensitizers (acetone or benzophenone). The most promising method of preparation appears to be the sensitized photodeposition allowing a higher reduction of the precursor (Ni(acac)(2)) at short irradiation time. The resulting catalysts were characterized by transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). It was found from TEM observations, that the size of NiO nanoparticles was smaller than 2 nm for both preparation methods, however the particle size distribution for impregnated catalyst was broader than that of photodeposited catalyst. On the other hand, the surface composition of both catalysts was similar, showing Ni(0), NiO, Ni(OH)(2) as the main species for impregnation, in the case of photodeposition an additional contribution of Ni(acac)(2) were detected. According to the results of catalytic ozonation of 2,4-D, the initial specific activity of the photodeposited catalyst was almost 7 times higher compared with that of impregnation catalyst. (C) 2014 Elsevier B.V. All rights reserved.