Adsorption behavior of methylene blue on Fe₃O₄-embedded hybrid magnetic metal–organic framework

Abstract

A magnetic hybrid material (Fe₃O₄-embedded-MOF) consisting of a stable metal–organic framework HKUST-1 embedded with poly(N-vinyl-2-pyrrolidone) coated Fe₃O₄ microspheres was simply prepared under refluxing conditions for 4 h. The as-synthesized material was characterized using powder X-ray diffraction, scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), energy dispersive spectroscopy (EDS) and N₂ adsorption–desorption at 77 K. The hybrid material was studied for the adsorption of methylene blue from aqueous solution. The effects of dye concentration, adsorbent dose, and initial pH on the adsorption of methylene blue were measured, and from these experimental data, adsorption isotherms, kinetics, and thermodynamics were obtained. The results showed that a pseudo-second-order kinetic model and Langmuir isotherm (with R² = 0.937) matched well for the adsorption of methylene blue onto Fe₃O₄-embedded-MOF. Thermodynamic parameters including free energy, enthalpy, and entropy of methylene blue adsorption were calculated, and the results showed that the adsorption of methylene blue were favorable on Fe₃O₄-embedded-MOF. The magnetic hybrid Fe₃O₄-embedded-MOF material features both magnetic separation characteristics as well as excellent adsorption performance for methylene blue in aqueous solution. The results of the present study demonstrate that Fe₃O₄-embedded-MOF is a promising adsorbent for the removal of dye from wastewater.

Keywords:

• Hybrid material
• Adsorption
• Magnetic separation
• Kinetics
• Isotherm
• Thermodynamics

Acknowledgments

This work was supported by the National Natural Science Foundation of China (grant number 21401018) and the Fundamental Research Funds for the Central Universities (No. N130305003).