Electrochemically synthesized graphene@ZnO@MnO₂ composite as an advanced adsorbent for levofloxacin removal

Levofloxacin (LEV), a third-generation fluoroquinolone antibiotic, is increasingly detected in aquatic environments due to its widespread use and incomplete removal in conventional wastewater treatment systems. In this study, a ternary composite based on electrochemically exfoliated graphene (EG) decorated with ZnO and MnO₂ nanoparticles (EG@ZnO@MnO₂) was fabricated and evaluated for LEV adsorption from aqueous solutions. The material was characterized by SEM, EDS, XRD, FTIR, BET, zeta potential analysis, and Raman analyses. Batch adsorption experiments were conducted to examine the effects of pH, contact time, and initial LEV concentration. The highest removal occurred at pH 7, where zwitterionic LEV likely interacted with the surface through cooperative electrostatic association and noncovalent interactions, with a plausible contribution from π-π interactions on graphene domains and hydrogen bonding with oxygenated surface groups. The zeta potential became less negative after adsorption (-14.1 to -8.3 mV), indicating partial charge neutralization upon LEV adsorption. Kinetic followed the pseudo-second-order model (R² = 0.979), and equilibrium was best described by the Langmuir isotherm (R² = 0.994), with a model-estimated capacity of 132.80 mg g^-1 and a maximum experimental uptake of 109.50 mg g^-1 (90.01% removal). Thermodynamic analysis indicated an exothermic process (ΔH^o < 0). The composite retained 78.31% of its initial removal efficiency after five regeneration cycles, and Zn/Mn were not detected in adsorption supernatants while only trace levels appeared in dilute-acid regeneration eluates. Overall, EG@ZnO@MnO₂ is a reusable adsorbent for LEV removal in synthetic single-solute systems, and further validation in real wastewater matrices is warranted.