Scrutinizing the vital role of various ultraviolet irradiations on the comparative photocatalytic ozonation of albendazole and metronidazole: Integration and synergistic reactions mechanism

Herein, TiO₂ nanoparticles were immobilized on the ceramic surface using the sol-gel dip-coating method, which confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Then, a semi-batch reactor containing the prepared ceramic plates, which irradiated by the various UV lights was used for the degradation of the albendazole (ALZ) and metronidazole (MTZ) pharmaceuticals by the photocatalytic ozonation process. The control experiments were performed to compare the photocatalysis, ozonation, photo-ozonation and photocatalytic ozonation processes under the same operational conditions with the UV-A, UV-B and UV-C irradiations. The synergistic effect of photocatalysis and ozonation was observed; moreover, the results revealed that the UV-A/TiO₂/O₃ had the highest efficiency for the ALZ and MTZ degradation owing to the synergistic heterogeneous reactions (SHRs), which led to more reactive oxygen species (ROS). The MTZ and ALZ degradation were probed by monitoring the dissolved ozone, oxygen and hydrogen peroxide concentrations during the various processes including the UV-A/TiO₂/O₃ process. The obtained results disclose that the ALZ degradation is lower than the MTZ due to its resistant nature with more direct attacks of the ozone in the bulk solution compared to the MTZ. Furthermore, the various compounds as the holes (h⁺) and ROS scavengers or ozone solubility enhancers were added to the reaction bulk to investigate the exact mechanism of the photocatalytic-ozonation. Eventually, the degradation intermediates of the pharmaceuticals generated in the photocatalytic-ozonation process were successfully recognized by the Gas chromatography–mass spectrometry (GC–MS) and the possible degradation paths were suggested for the degradation of pollutants considering the responsible ROS in each case.