Efficient removal of toxic methylene blue (MB) dye from aqueous solution using a metal-organic framework (MOF) MIL-101(Fe): isotherms, kinetics, and thermodynamic studies

MIL-101(Fe) iron-benzene dicarboxylate based metal-organic framework (MOF) was synthesized via a solvothermal method for adsorptive removal of cationic methylene blue (MB) dye from aqueous solution. The prepared MIL-101(Fe) was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analyzer, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller analysis tools. Various parameters affecting the removal efficiency were deliberated such as pH medium, contact time, solution temperature, MOF dosage, and initial MB dye concentrations. Results showed that MIL-101(Fe) has a maximum adsorption capacity of 58.82 mg/g at pH 9. Moreover, data obtained from isotherm studies were more fitted to the Langmuir isotherm model (R-2 = 0.997), while the adsorption kinetics followed the pseudo-second-order model. The thermodynamic studies proved that the adsorption process of MB dye onto MIL-101(Fe) was spontaneous and endothermic. Besides, MIL-101(Fe) showed higher adsorption ability towards cationic MB dye compared to the anionic methyl orange dye. Finally, the MIL-101(Fe) adsorbent showed excellent reusability for removing MB dye with efficiency exceeded 70% after ten consecutive cycles. Therefore, the as-prepared MIL101(Fe) could be applied as a reusable adsorbent for removing cationic dyes from their aqueous solutions.