Ciprofloxacin adsorption onto Azolla filiculoides activated carbon from aqueous solutions

Abstract

The adsorption of ciprofloxacin (CIP) from aqueous solutions by Azolla filiculoides activated carbon (AFAC) was studied in a batch adsorption system. Results revealed that at CIP concentration of 10 mg/L, AFAC dose of 2.5 g/L, the contact time of 75 min, the temperature of 50°C, the CIP removal reached about 99.1%. Langmuir, Freundlich and Dubinin–Radushkevich isotherm models were studied to determine the adsorption mechanism. Langmuir isotherm best fits the equilibrium adsorption data and the maximum capacity was 35.14 mg/g. The adsorption intensity obtained from the Freundlich model and the energy of adsorption obtained from the Dubinin–Radushkevich model (2.25 kJ/mol) suggested that physisorption dominates the adsorption of CIP onto the AFAC. All the error functions in the Langmuir isotherms showed that the error in the least. Thermodynamic parameters were calculated for the CIP–AFAC system and the positive value of ΔH° (52.7 kJ/mol) and negative values of ΔG° (–0.079 to –5.61) showed that the adsorption was endothermic, spontaneous and physical in nature. The results of sequential adsorption–desorption showed that the AFAC could be successfully reused for five cycles. The characteristic results showed that AFAC can be employed as an alternative to commercial adsorbents in the removal of antibiotics from wastewater.