Development of functional metal organic frameworks for wastewater treatment

Abstract

Novel amine-functionalized zirconium-based metal organic frameworks (MOFs) were solvothermally synthesized for the efficient and selective removal of Pb (II) in concentrated multi-component heavy metal ions systems. Pristine UiO-66 and UiO-67 MOFs were grafted with thiourea and amidinothiourea via a facile one-step post synthetic modification. Successful grafting was confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The microporous amidinothiourea modified MOFs demonstrated excellent performance in their high maximum adsorption capacities of 246 and 367 mg.g-1, respectively, as well as their remarkable selectivity for Pb (II) ions in highly concentrated multi-ion solutions. This is, in addition, to their effective removal efficiencies which reached up to more than 95% at a high range of Pb (II) concentrations (25 - 250 ppm). Furthermore, the structural stability of the MOF crystals was maintained after adsorption and the MOF was completely regenerated for up to four cycles. Additionally, an as-synthesized Zr-based MOF was solvothermally synthesized for the efficient removal of Diclofenac sodium (DCF) from an aqueous medium. The as-synthesized microporous DUT-67 MOF was characterized by XRD and BET. Equilibrium studies revealed that the sorption process followed the Langmuir isotherm, which accordingly demonstrated a significant adsorption capacity of 484 mg.g-1, attaining maximum removal efficiencies of about 90% at 75 and 150 ppm DCF initial concentrations. Kinetically, the adsorption process followed the pseudo-second order and the intraparticle diffusion models. The Dubinin-Radushkevich model along with thermodynamic analysis suggested a physisorption interaction that is exothermic and spontaneous.