Facile Synthesis of MIL-53(Fe) by Microwave Irradiation and its Application for Robust Removal of Heavy Metals from Aqueous Solution by Experimental Design Approach: Kinetic and Equilibrium

MIL-53(Fe) with huge porosity has been synthesized by microwave radiation in the different ‎conditions: various powers (80, 100W) and time (5, 10 min). Nano-sized crystals were ‎characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier ‎transform infrared spectroscopy (FTIR) and specific surface area analysis. After performing the characterization, MIL-53(Fe)-1 with the best porous structure for Pb (II) and Cd (II)‎ removal was used for all tests from aqueous solution. The best condition for synthesis was 5 min and 80 W. Then the best porous structure was selected for removal of Pb (II) / Cd (II) from aqueous solution. The ‎response surface methodology (RSM) based on central composite design (CCD) was applied to ‎optimize the removal capacity. In these experimental designs, four independent variables were studied and the best condition was evaluated as ‎‎pH(in the range of 6-8), temperature (40-50◦C), contact time (50 min), and adsorbent amount (0.1-0.3 g.L-1). The removal efficiency and ‎capacity of MIL-53(Fe) for Pb (II) and Cd (II) was further surveyed. Langmuir equation was the ‎best isotherm to describe the adsorption manner of Pb (II) and Cd (II) ions (qmax values ( 178.57 and 714.28 mg g−1) for Pb (II) and Cd (II)). The adsorption ‎process was confirmed by a pseudo-second-order kinetic pattern. The result of thermodynamic ‎studies displayed that the sorption process was spontaneous and exothermal.