Efficient catalytic activity of NiO and CeO₂ films in benzoic acid removal using ozone

This research focuses on the synthesis of NiO and CeO₂ thin films using spray pyrolysis for the removal of benzoic acid using ozone as an oxidant. The results indicate that the addition of CeO₂ films significantly enhances the mineralization of benzoic acid, achieving a rate of over 80% as the CeO₂ films react with ozone to produce strong oxidant species, such as hydroxyl radicals, superoxide radicals, and singlet oxygen as demonstrated by the presence of quenchers in the reaction system. The difference in catalytic activity between NiO and CeO₂ films was analyzed via XPS technique; specifically, hydroxyl oxygen groups in the CeO₂ film were greater in number than those in the NiO film, thus benefitting catalytic oxidation as these species are considered active oxidation sites. The effects of nozzle-substrate distances and deposition time during the synthesis of the films on benzoic acid removal efficiency were also explored. Based on XRD characterization, it was established that the NiO and CeO₂ films were polycrystalline with a cubic structure. NiO spherical nanoparticles were well-distributed on the substrate surface, while some pin holes and overgrown clusters were observed in the CeO₂ films according to the SEM results. The stability of the CeO₂ films after five consecutive cycles confirms their reusability. The retrieval of films is easy because it does not require additional separation methods, unlike the catalyst in powder form. The obtained results indicate that the CeO₂ films have potential application in pollutant removal from water through catalytic ozonation.