Experimental and Theoretical Investigation of the Catalytic Ozonation on the Surface of NiO−CuO Nanoparticles

Abstract

NiO-CuO nanoparticles prepared by the sol-gel method were used as catalyst for the degradation of dichloroacetic acid by ozone. Catalyst samples were characterized by measuring the specific area (SBET), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The catalytic activity of NiO-CuO nanoparticles was investigated for the removal of dichloroacetic acid in aqueous solutions, using different experimental conditions like catalyst dose, initial reaction temperature, and pH have been examined. Ozonation processes were significantly influenced by tert-butyl alcohol, which confirmed that NiO-CuO catalytic ozonation follows a radical-type mechanism, which the hydroxyl radicals were truly identified by spin-trapping/electron spin resonance (EPR) technique and density functional theory (DFT) calculation. In our DFT calculation, we illustrated the atomistic details with three surface models of NiO-CuO nanoparticle and presented a mechanism depicting how an ozone molecule interacted with the surface and how hydroxyl radicals were generated on the surface with a quantitative and qualitative discussion including electronic structure characteristics and relative energetic diagrams. We found partial electron transfer from these surfaces to the adsorbed ozone, which directly led to the decomposition of ozone and promoted the generation of superoxide radical ions and hydroxyl radicals. Results suggested that the introduction of NiO-CuO nanoparticles led to violent interaction between ozone and the catalyst surface, hence promoting the decomposition of ozone and the generation of .OH which, in turn, might lead to an increase in their catalytic ozonation efficiency.