Chemical Characteristics of Ciprofloxacin and Its Degradation Products: On the Road to Understanding Its Potential Hazards

Antibiotics such as ciprofloxacin (CIP) are considered emerging contaminants because of their widespread use in human and veterinary medicine, their persistence in the environment, and their incomplete removal during wastewater treatment. To mitigate pollution, the photocatalytic degradation of antibiotics is an available option. However, some of the degradation products could be more harmful than the original compound. The main idea of this investigation is to determine the chemical properties of the main photodegradation products of CIP to understand the positive or negative consequences of degrading CIP. Density functional theory calculations were performed to investigate the electron transfer capacity of CIP and 20 selected degradation products. Fukui functions were also calculated to determine the reactive atoms. To identify the degradation products, this investigation presents theoretical and experimental ultraviolet (UV)/visible spectra of the photocatalytic degradation of CIP using zinc oxide nanowires (ZnO NW). The 3 h photocatalytic reaction showed an 89% of CIP degradation, indicating the effectiveness of ZnO NW photocatalyst. The agreement between the experiment and theory indicates that two degradation products (B5 and B8) are formed during the photocatalytic experiment. Concerning the electron transfer capacity, B8 is a better electron donor and could help to prevent oxidative stress by donating electrons to free radicals. B5 is a better electron acceptor, but it is not as good as ^•OOH, and therefore, it is not expected that this molecule will oxidize other molecules. Fukui functions reveal that B5 and B8 have more reactive atoms than CIP, and this could have consequences for health and the environment. With this information on the chemical characteristics of the degradation products, it is possible to determine whether or not it is advisable to degrade the CIP using this photocatalytic degradation procedure, and the risks of not achieving its complete mineralization. Understanding the chemical reactivity from these theoretical results facilitates the analysis of the potential hazards in subsequent studies.