Efficient one-pot synthesis of magnetic MIL-100(Fe) using nitric acid without additional Fe ion addition and adsorption behavior of charged organic compounds

Magnetically separable Co0.6Fe2.4O4/MIL-101-NH2 adsorbent for Congo red efficient removal

The development of effective and practical adsorbents for eliminating pollutants still remains a significant challenge. Herein, we synthesized a novel magnetically separable composite, Co0.6Fe2.4O4/MIL-101-NH2, through the in-situ growth of MIL-101-NH2 on magnetic nanoparticles, designed specifically for the removal of Congo red (CR) from aqueous solutions. MIL-101-NH2 possessed high BET surface area (240.485 m2•g-1) and facile magnetic separation function and can be swiftly separated (within 30 s) through an external magnetic field post-adsorption. The investigation systematically explored the influence of crucial parameters, including adsorbent dosage, pH, adsorption duration, temperature, and the presence of interfering ions, on CR adsorption performance. Findings indicate that CR adsorption adheres to the pseudo-second-order (PSO) kinetic model and the Langmuir isotherm model. Thermodynamic analysis reveals the spontaneity, endothermic nature, and orderly progression of the adsorption process. Remarkably, the adsorbent with 0.1 g•L-1 boasts an impressive maximum adsorption capacity of 1756.19 mg•g-1 for CR at 298.15 K, establishing its competitive advantage. The reuse of the adsorbent over 5 cycles remains 78% of the initial adsorption. The CR adsorption mechanisms were elucidated, emphasizing the roles of π-π interactions, electrostatic forces, hydrogen bonding, and metal coordination. Comparison with other dyes, such as methylene blue (MB) and methyl orange (MO), and exploration of adsorption performance in binary dye systems, demonstrates the superior capacity and selectivity of this adsorbent for CR. In conclusion, our magnetically separable metal-organic framework (MOF)based composite presents a versatile and effective solution for CR removal, with promising applications in water treatment and environmental remediation.