Targeted removal of enrofloxacin by 1-hexadecyl-3-methylimidazolium-chloride-modified attapulgite: a recyclable green adsorbent

Fluoroquinolone antibiotics such as enrofloxacin (ENR) persist in aquatic environments, posing risks to ecosystems and human health. In this study, 1-hexadecyl-3-methylimidazolium-chloride-modified attapulgite (IL-ATP), which exhibits excellent adsorption performance for ENR, was prepared. The adsorption kinetics follow a pseudo-second-order model (Q
e,cal
= 51.38 mg/g, R
2
= 0.9968), showing good agreement with the experimental equilibrium adsorption capacity (Q
e
= 49.99). This suggests chemisorption dominates the process, with diffusion resistance contributing in the later stage. Isotherm analysis showed that both Langmuir and Freundlich models exhibit good fitting performance. The Langmuir model showed a maximum monolayer adsorption capacity of 415.82 mg/g at 299 K. Thermodynamic analysis showed negative ΔG values (−6.30 to −7.92 kJ·mol⁻
1
), a positive ΔH (17.13 kJ·mol⁻
1
), and a positive ΔS (81.8 J·mol⁻
1
·K⁻
1
), indicating that the adsorption process is spontaneous, endothermic, and accompanied by increased disorder at the solid–liquid interface. The spent IL-ATP can be efficiently regenerated via ultrasonic treatment, with a regeneration efficiency of 95.68% under optimized conditions (5 min, 80 W, pH = 6). Even after five adsorption–regeneration cycles, IL-ATP retained 75.01% of its initial adsorption capacity, demonstrating its excellent reusability. Mechanistic studies indicated a dual-driven regeneration process: physical desorption induced by cavitation-generated microjets, and chemical desorption mediated by hydroxyl radicals (OH) disrupting hydrogen bonding and hydrophobic interactions. This work demonstrates that IL-ATP is an efficient, sustainable, and cost-effective adsorbent for fluoroquinolone removal from wastewater, with promising potential for practical applications.