Assessing the occurrence and ecotoxicology of ciprofloxacin in aquatic environments: Insights into clay-based adsorptive remediation measures

Ciprofloxacin (CIP) is one of the emerging contaminants of environmental concern because of its continual and heavy use. Concerns about CIP are ascribed to its persistence and incomplete degradation in the environment, which could lead to the spread of drug-resistant bacterial strains. Adsorption of CIP has played a remarkable role in the treatment of CIP-laden (waste)water, and the role of clay adsorbents has increasingly emerged. However, limited studies have been reported on the use of clay-based adsorbents for CIP adsorption, compared to the use of other adsorbents. Second, the lack of understanding of interaction pathways and the effectiveness of clays might limit its practical application in wastewater treatment. Given this gap, this paper present state-of-the-art review on the adsorption of CIP using clay-based adsorbents. Our findings revealed that composite of graphene oxide–kaolinite and activated montmorillonite–kaolin are synergistically effective to remove CIP sorption with demonstrated sorption capacities of 408.16 mg/g and 344.82 mg/g, respectively. Bentonite-based composites showed the best performance, particularly ZnO/CuO–bentonite, with 451 mg/g experimentally and about 1249.3 mg/g calculated capacity, with a removal efficiency of nearly 99 %. Overall, pH was found to play dominant role in controlling CIP adsorption as well as the electrostatic attraction as dominant mechanism of uptake. Isotherm modelling suggested that the best fit model was Langmuir isotherm ($r^2>0.96-0.99)$ which confirms chemisorption as the dominant mechanism. This state-of-the-art synthesis recommends the adoption of clay and clay-composites for further interdisciplinary research in order to optimize adsorption systems for probable real-world applications.