Construction of lacunary α-K8SiW11O39 polyoxometalate/MIL-101(Cr) MOF/CoFe2O4 magnetic nanocomposites for adsorptive removal of toxic azo dyes and antibiotics from wastewater

Abstract

In this work, a ternary magnetic nanocomposite based on the MIL-101(Cr) metal–organic framework hybridized with lacunary Keggin-type polyoxometalate (α-K₈SiW₁₁O₃₉·13H₂O; LPOM) and cobalt ferrite nanoparticles (CoFe₂O₄; CFO) as a magnetic component was synthesized through a hydrothermal route. The ternary magnetic nanocomposite with the feature LPOM@MIL-101(Cr)/CFO was characterized via FT-IR, XRD, Raman, FE-SEM, EDX, TEM, VSM, zeta potential, BET, TGA, and UV-vis spectroscopy. The results confirmed that heteropolyanions were successfully encapsulated in MIL-101(Cr) cavities. The surface area and pore volume in the ternary magnetic nanocomposite have been significantly decreased compared to the metal–organic framework due to the integration of polyoxometalate and cobalt ferrite nanoparticles. The ability of the ternary magnetic nanocomposite to remove organic dyes methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) and antibiotic drug ciprofloxacin (CIP) from aqueous solutions was investigated. The ternary magnetic nanocomposite revealed effective CIP drug adsorption. Additionally, it demonstrated rapid and selective adsorption for cationic dyes from the mixed dye solutions of MB/MO, MB/RhB, RhB/MO, and MB/RhB/MO. In comparison with its single and double components, the ternary magnetic LPOM@MIL-101(Cr)/CFO nanocomposite demonstrated superior adsorption performance. The adsorption process followed both the pseudo-second-order model and the Langmuir model, indicating that the reaction was spontaneous and achieved a maximum adsorption capacity of 103 and 64 mg g⁻¹ for MB and CIP pollutants. Electrostatic attraction was found to be the primary driving force behind the adsorption process, and the material retained 95% of its maximum adsorption capacity even after four cycles. The magnetic nanocomposite LPOM@MIL-101(Cr)/CFO is easily separated using a magnet and recycled without any change in the structure.