Hydrophobic Deep Eutectic Solvents: A Circular Approach to Purify Water Contaminated with Ciprofloxacin

Clean water became one of the major concerns of the 21st century. The occurrence of micropollutants in aquatic ecosystems poses serious public health and environmental problems, leading to true challenges in the development of sustainable and cost-effective alternative technologies for wastewater treatment processes. As a result, hydrophobic deep eutectic solvents (DESs) have been emerging as easy-to-prepare, inexpensive, and environmentally benign media showing a high potential for water applications. The main goal of this work is the development of hydrophobic DESs for the removal of ciprofloxacin, identified as one of the top 10 priority micropollutants, from water environments. In particular, DESs composed of natural neutral components, such as menthol and fatty acids, and also DESs based on the combination of quaternary ammonium salts and natural fatty acids were evaluated as potential extractants. The molar ratio of C12:C10 displays the second highest solubility value of ciprofloxacin and the lowest water solubility, which leads to the best extraction efficiency of ciprofloxacin. Moreover, extraction efficiencies were maximized by optimizing the experimental factors using a central composite design combined with a response surface methodology. Finally, aiming at full sustainability, a circular process was developed by recycling and reusing the hydrophobic DES through the use of activated carbon.