A natural-biopolymer sodium alginate magnetic multifunctional adsorbent with high capacity for broad-spectrum fluoroquinolone antibiotic removal from water.

Persistent fluoroquinolone (FQ) antibiotics in water bodies boost bacterial resistance and endanger aquatic ecosystems, necessitating efficient removal. In this work, a natural-biopolymer sodium alginate-based adsorbent (SA@Fe3O4-SPABS) was prepared via cross-linking and amidation to introduce multiple functional groups onto the adsorbent framework. Gatifloxacin (GAT) was selected as a representative fluoroquinolone to evaluate the adsorption performance. The kinetic data were well described by the pseudo-first-order model. Based on the Langmuir model, SA@Fe3O4-SPABS exhibited an adsorption capacity of 857.97 mg g-1 for GAT at 288.15 K and pH 6.0, exceeding that of most reported FQ adsorbents. Moreover, SA@Fe3O4-SPABS displayed high adsorption capacities for other FQs, namely 693.4 mg g-1 for levofloxacin, 536.1 mg g-1 for moxifloxacin, 366.5 mg g-1 for ofloxacin, and 362.3 mg g-1 for ciprofloxacin. Its strong magnetism (saturation magnetization of 35.93 emu·g-1) enabled rapid separation of SA@Fe3O4-SPABS from treated water and its recovery for reuse, retaining approximately 65% of its initial adsorption capacity after eight regeneration cycles. Characterization revealed that SA@Fe3O4-SPABS binds GAT through multiple mechanisms, including electrostatic attraction, cation exchange, hydrogen bonding, and π-π electron donor-acceptor interactions. In simulated wastewater, SA@Fe3O4-SPABS achieved a GAT removal efficiency of up to 86.7%. In summary, SA@Fe3O4-SPABS represents a high-capacity, broad-spectrum, and easily recoverable adsorbent for removing fluoroquinolone residues from water.