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 a huge porosity has been synthesized by microwave radiation in different conditions: various powers (80, 100 W) and time (5, 10 min). Nano-sized crystals were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and specific surface area analysis. After 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 the 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) were 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.