Metronidazole photodegradation under solar light with UiO-66-NH2 photocatalyst: Mechanisms, pathway, and toxicity assessment

Metronidazole is a nitroimidazole antibiotic that is increasingly detected in aquatic bodies. Therefore, there is an urgent need to research methodologies to remove this and other antibiotics. One of the alternatives is the application of solar photocatalysis, which requires the use of an efficient photocatalyst. In this work, UiO-66-NH2 was synthesized by a facile solvothermal method and evaluated for the degradation of metronidazole under simulated solar light. The effects of catalyst dosage, initial pH, and metronidazole concentration were discussed, establishing the best operation conditions. In addition, the stability and reproducibility of UiO-66-NH2 activity were also verified. The quenching reaction showed that holes and superoxide radicals coexisted as the main active species, being responsible for the metronidazole degradation. The pathway of metronidazole photo-degradation was proposed by means of density functional theory calculations and LC/ESI-MS analysis. It is noteworthy that this study detected for the first time C6H11N3O4, C4H6N2O3, and C4H8N2O4 as metronidazole photodegradation byproducts. ECOSAR toxicity analysis showed that all byproducts were less toxic than the original metronidazole, supporting the potential feasibility of this method for treating water polluted with this antibiotic.