Investigating the potential of sepiolite-based adsorbents for levofloxacin removal from aqueous medium: experimental and optimization studies

This study evaluated the effectiveness of sepiolite nano-adsorbents (Sep) and Sep impregnated with manganese-oxide nanoparticles (Sep-MnO2) as cost-effective adsorbents for removing levofloxacin (LEV). Various analyses, including XRD, FTIR, and FESEM with EDS, were used to characterize the adsorbents. The Taguchi L25 experimental design was employed to optimize the adsorption process parameters (pH, contact time, adsorbent dose, initial concentration, and temperature) with the aim of maximizing LEV removal efficiency. Under optimal operating conditions, the maximum removal efficiencies for Sep and Sep-MnO₂ were 85.8% and 98.2%, respectively. The initial pH was identified as the most sensitive parameter, exhibiting peak performance at a pH of 3. The adsorption equilibrium data fit the Redlich–Peterson isotherm model more accurately. The maximum adsorption capacity was 11.46 and 30.98 mg/g for Sep and Sep-MnO2 adsorbents, respectively. The pseudo-second-order kinetic model provided the most accurate representation of the kinetic data. Thermodynamic analysis indicated that LEV adsorption on Sep is exothermic, whereas adsorption on Sep-MnO2 is endothermic and spontaneous. The adsorption mechanism was further explored through pH studies. The results showed that LEV adsorption involves cation exchange in acidic conditions, charge neutralization in neutral conditions, and proton transfer in alkaline conditions.