A review of the antibiotic ofloxacin: Current status of ecotoxicology and scientific advances in its removal from aqueous systems by adsorption technology

It is estimated that the growth of the population, the augmented expectancy of life, and the emergence of new pandemics will significantly increase the consumption of pharmaceutical drugs in the coming years. Due to its high efficiency, the group of fluoroquinolones, where the antibiotic ofloxacin hydrochloride (OFL) is found, is widely used to combat bacterial infections in humans and animals. The big problem is concentrated in the effluents generated by industries and hospitals. Additionally, most of the drug is not absorbed by the body and is released directly into domestic effluents. On the other hand, treatment stations have removal limitations for small concentrations. This review analyzed all adsorbents developed and used in OFL removal, listing the main parameters influencing the process. In the end, the other existing technologies in the literature and the gaps and future prospects were described. OFL adsorption in most studies occurs under basic conditions (pH between 6.5 and 8). The increase in concentration provides an increase in adsorption capacity. The adsorbents analyzed showed moderate kinetics, reaching equilibrium before 250 min for most studies. The pseudo-second-order model showed the best statistical fit. In most of the studies, the increase in temperature (313, 315, and 328 K) favored the adsorption of OFL. The Langmuir monolayer model represented most of the isothermal studies. The adsorption capacity varied from 3702 to 0.3986 mg g−1. In this aspect, factors such as OFL concentration and textural characteristics of the adsorbent exerted great influence. The thermodynamic parameters were compatible with the isothermal data, where the endothermic nature of the studies was confirmed. Physical interactions (π-π stacking, H bonding, hydrophobic and electrostatic interactions) governed the main adsorption mechanism. Although some studies stated that chemosorption occurred, thermodynamic parameters cannot validate the same. Coexisting ions in the solution can positively and negatively influence OFL adsorption. The listed studies are all applied to batch processes, where fixed bed studies should be better explored. From this review, it can be concluded that adsorption is a promising technique for OFL removal. However, it is extremely necessary to break the laboratory scale barrier and analyze possible conditions for applying these materials in treating real effluents together with combining technologies.