Cyclodextrin Nanosponges as adsorbent material to remove hazardous pollutants from water: the case of Ciprofloxacin

Abstract This study was developed inside the European Project Life “Clean up” (LIFE 16 ENV/ES/000169) to search for suitable adsorbents to purify treated water from emerging pollutants. Notably, among pollutants, the attention was focused on Ciprofloxacin removal, selecting as recyclable adsorbent Cyclodextrin-based nanosponges, characterized by using FTIR-ATR, DSC, TG, SEM, EDX, gas-volumetric analysis, and XRD analyses. Indeed, the in-batch adsorption process was quite complete removing, in a few minutes, 90% of the pollutant from water, with a maximum adsorption capacity of 2 mg/g. A better comprehension of the adsorption mechanism was obtained by studying the effect of various experimental parameters on the process, i.e. ionic strength, pH values, adsorbent/pollutant ratio, and temperature values. The thermodynamics (ΔG° 0), the adsorption isotherms (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich), and kinetics of the process were also investigated. In particular, the applicability of all the proposed isotherms, except the Langmuir model, was observed, and the finding highlighted the heterogeneous character of the adsorption process. The pseudo-second-order kinetic model well described the process and the application of the Weber-Morris model suggested that two main consecutive steps constituted the adsorption. Despite the relatively low adsorption capacity, desorption experiments, recycling 80% of the pollutant for each cycle, were performed, and for the purpose, 0.1 M NaCl was used, lowering the environmental impact. Moreover, other contaminants, such as Diclofenac, Carbendazim, Furosemide, and Sulfamethoxazole were successfully removed from the water, also if present in a quaternary mixture, opening the possibility to use this adsorbent for real water treatments.