Enhanced adsorption of three fluoroquinolone antibiotics using polypyrrole functionalized Calotropis gigantea fiber

Fluoroquinolone antibiotics (FQs) have been detected frequently in aquatic environment with the concentration level of up to mg/L. As an emerging class of environmental micropollutants, it’s significant to remove FQs from water by developing adsorbents with low cost and high efficiency. Calotropis gigantea fiber (CGF) comes from the seeds of C. procera and is featured with large, hollow lumens and inherent waxy layer. When the attached wax was removed by treating with NaClO2, this fiber was then utilized as the bio-template to produce a green and sustainable adsorbent via FeCl3-triggered oxidative polymerization of pyrrole along the fiber surface. With adsorption capacity for enrofloxacin (Enr), ciprofloxacin (Cip) and norfloxacin (Nor) as the responses, the polymerization conditions including reaction time, pyrrole amount and acetonitrile percentage in solvent were optimized via Box-Behnken design using response surface method. The optimized adsorbent material, i.e. polypyrrole (PPy) modified CGF (PPy-O-CGF), was well characterized and its adsorption performance for three FQs was systematically investigated by varying PPy amount, contact time, initial concentration, initial pH and ion strength. The results indicated that PPy-O-CGF showed outstanding adsorption capacity, with 78.27 mg/g for Enr, 76.61 mg/g for Cip and 68.90 mg/g for Nor at pH = 6.0 and initial concentration of 100 mg/L. The adsorption kinetics proved that Enr, Cip and Nor adsorption rapidly reached > 40% within 5 min, > 55% within 10 min, and > 75% within 30 min. PPy-O-CGF can be regenerated and reused, showing good recyclability. Preliminary breakthrough study gave an indication that the adsorption capacity of PPy-O-CGF was 9.97–20.7 mg/g for three FQs.