Effective Magnetic MOFs Adsorbent for the Removal of Bisphenol A, Tetracycline, Congo Red and Methylene Blue Pollutions

A magnetic metal−organic frameworks adsorbent (Fe3O4@MIL-53(Al)) was prepared by a typical solvothermal method for the removal of bisphenol A (BPA), tetracycline (TC), congo red (CR), and methylene blue (MB). The prepared Fe3O4@MIL-53(Al) composite adsorbent was well characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and fourier transform infrared spectrometer (FTIR). The influence of adsorbent quantity, adsorption time, pH and ionic strength on the adsorption of the mentioned pollutants were also studied by a UV/Vis spectrophotometer. The adsorption capacities were found to be 160.9 mg/g for BPA, 47.8 mg/g for TC, 234.4 mg/g for CR, 70.8 mg/g for MB, respectively, which is superior to the other reported adsorbents. The adsorption of BPA, TC, and CR were well-fitted by the Langmuir adsorption isotherm model, while MB followed the Freundlich model, while the adsorption kinetics data of all pollutants followed the pseudo-second-order kinetic models. The thermodynamic values, including the enthalpy change (ΔH°), the Gibbs free energy change (ΔG°), and entropy change (ΔS°), showed that the adsorption processes were spontaneous and exothermic entropy-reduction process for BPA, but spontaneous and endothermic entropy-increasing processes for the others. The Fe3O4@MIL-53(Al) was also found to be easily separated after external magnetic field, can be a potential candidate for future water treatment.