Levofloxacin Adsorption onto MWCNTs/CoFe₂O₄ Nanocomposites: Mechanism, and Modeling Using Non-Linear Kinetics and Isotherm Equations

In the present work, the adsorption mechanism and capacity of MWCNTs/CoFe₂O₄ nanocomposite as an adsorbent were investigated. Levofloxacin (LFX), a widely used antibiotic, was selected as a hazardous model contaminant in aqueous solutions. The surface and inner characterization of MWCNTs/CoFe₂O₄ was obtained via SEM/TEM, XRD, BET/BJH, and pH_PZC. These analyses indicated that MWCNTs/CoFe₂O₄ possess excellent surface and pore characteristics, e.g., specific surface area, pore volume, and mean pore diameter, which were 72 m²/g, 0.51 cm³/g, and 65 nm, respectively. The results demonstrate that by supplementing 1 g/L of MWCNTs/CoFe₂O₄ at experimental conditions of pH value of 5, temperature of 30 °C, initial LFX concentration of 50 mg/L and mixing time of 90 min, a significant outcome of 99.3% removal was achieved. To identify the phenomenon of adsorption, the thermodynamic parameters of ΔH° and ΔS° were calculated, which indicated that the nature of LFX adsorption onto MWCNTs/CoFe₂O₄ nanocomposite was endothermic and spontaneous. Nine isotherm models, including four two-parameter and five three-parameter models, were investigated. In addition, the regression coefficient as well as five error coefficient models were calculated for nonlinear isotherm models. According to the goodness of fit tests, the equilibrium data were well coordinated with the Freundlich and Sips isotherms. The kinetics study showed that the LFX adsorption data well fitted with pseudo-second-order model, and the adsorption of LFX molecules occurred through several stages from surface to intraparticle diffusion. In conclusion, the present work evinces that LFX wastewater can be efficiently treated via an adsorption process using a MWCNTs/CoFe₂O₄ nanocomposite.