In our density functional theory calculations, we illustrated the atomistic details of NiO surface and presented the mechanism of ozone decomposition, peroxide radical ion generation, and hydroxyl radical generation on the surfaces. And the electronic properties were further investigated to discuss the electronic structure and adsorption characteristics of the catalytic ozonation systems. Furthermore, the hydroxyl radicals were truly identified by spin-trapping/electron paramagnetic resonance (EPR) technique. Results suggest that the presence of NiO nanoparticles promote the decomposition of ozone, the generation of superoxide ions, and the generation of hydroxyl groups favoring the chain reaction for the generation of hydroxyl radicals, promoting the degradation of organic pollutants. (C) 2009 Elsevier B.V. All rights reserved.