Selective adsorption of fluoroquinolones by a chemically modified β-cyclodextrin composite: Combined contributions of hydrophobic cavity and functional groups.

Water pollution by fluoroquinolones requires the development of efficient treatment techniques. In this study, β-cyclodextrin (β-CD) was chemically modified by acrylamide (AM) and sodium styrene sulfonate (SSS) copolymerization, and crosslinked with citric acid (CA) to prepare a composite material (CA/β-CD-P(AM-SSS)) for the selective removal of fluoroquinolones from aqueous solutions. The preparation conditions were optimized through single-factor experiments and response surface methodology, and the obtained CA/β-CD-P(AM-SSS) was fully characterized by SEM, BET, FTIR, and XPS. Batch adsorption experiments showed that CA/β-CD-P(AM-SSS) had an excellent adsorption performance for representative fluoroquinolone antibiotic norfloxacin (NOR), with maximum adsorption capacity of 733 mg/g at 298 K, much higher than unmodified crosslinked β-cyclodextrin (CA/β-CD). Besides, with the coexistence of nutrient elements, cations, and other impurities in actual wastewater, the adsorption capacity of CA/β-CD-P(AM-SSS) towards NOR was still satisfactory. After eight adsorption-desorption cycles, the regeneration rate of CA/β-CD-P(AM-SSS) was higher than 83%, demonstrating its strong stability and reusability. In single-antibiotic system and ternary-antibiotic system, CA/β-CD-P(AM-SSS) presented a superior selective adsorption capability towards fluoroquinolones. XPS analysis and DFT calculation revealed that this high selectivity was attributed to the combined contributions of hydrophobic cavity and functional groups, mainly including host-guest inclusion interaction, hydrophobic interaction, and electrostatic attraction. In addition, hydrogen bonding and π-π conjugation also participated in the adsorption process. This study provides an effective strategy for the design of fluoroquinolone selective adsorption materials based on hydrophobic cavity-functional group dual binding sites and a valuable guidance for the elimination of fluoroquinolones in wastewater treatment field.