Synthesis of mesoporous iron oxide nanoparticles for adsorptive removal of levofloxacin from aqueous solutions: Kinetics, isotherms, thermodynamics and mechanism

This study describes the synthesis, characterization, and application of mesoporous Fe₂O₃ as an adsorbent for levofloxacin removal from aqueous solutions. The characterization results indicated that at calcination temperatures between 250 and 350 °C, the annealed Fe₂O₃ showed highest surface area values of 73.6 and 90.6 m² g⁻¹ and lowest particle sizes of 87.8 and 48.4 nm, respectively. Furthermore, adsorption experiments revealed that calcination temperatures had a noticeable effect on the adsorption affinity of Fe₂O₃, and the 350 °C calcined sample exhibited higher adsorption activity (33.1 mg g⁻¹), which was the maximum adsorption capacity (q_max) for the removal of levofloxacin. Under optimum conditions (pH: 7.5, contact time: 10 min, temperature: 25 °C, levofloxacin concentration: 10 mg L^-1 and Fe₂O₃ dose: 0.02 g), the proposed system favored pseudo-second-order model, confirming chemisorption. Moreover, the intraparticle diffusion model demonstrated that the mechanism of levofloxacin adsorption was driven by both the surface adsorption and the intraparticle diffusion. It is worthy to indicate that, levofloxacin adsorption equilibrium data was in alignment with Langmuir isotherm model (R² = 0.9851) and these findings were further supported by Redlich-Peterson model, signifying monolayer adsorption process. The adsorptive removal of levofloxacin from aqueous solutions was exothermic and spontaneous, as revealed by the thermodynamics parameters.