High-performance MnFe2O4@ZIF-8 magnetic composite and its effectiveness in doxycycline removal

Abstract

A high-performance MnFe₂O₄@ZIF-8 magnetic composite was successfully designed and synthesized, and its adsorption behavior toward doxycycline (DOX) was systematically investigated. Structural characterization by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) confirmed the effective incorporation of MnFe₂O₄ nanoparticles into the ZIF-8 framework, while magnetic hysteresis measurements demonstrated favorable magnetic responsiveness, enabling rapid separation under an external magnetic field. Adsorption equilibrium data were well described by the Langmuir isotherm model, which yielded a model-derived maximum monolayer adsorption capacity (q_m) of 3235.5 mg/g at 25 °C. Kinetic, thermodynamic, and adsorption behavior analyses indicated that the adsorption process was spontaneous and endothermic. Based on the combined results of FT-IR spectroscopy, zeta potential analysis, pH-dependent adsorption experiments, and adsorption studies, the adsorption of DOX onto MnFe₂O₄@ZIF-8 is proposed to involve multiple cooperative interactions, including electrostatic attraction, hydrogen bonding, π–π interactions, possible metal–DOX coordination, and pore-filling/spatial confinement effects. In addition, the composite maintained good adsorption performance after four consecutive adsorption–desorption cycles, demonstrating promising recyclability. The results suggest that MnFe₂O₄@ZIF-8 is a promising magnetic adsorbent for the removal of antibiotic contaminants from aqueous environments and provide useful insights for the design of multifunctional MOF-based adsorbents for water treatment applications.