High performance functionalized UiO metal organic frameworks for the efficient and selective adsorption of Pb (II) ions in concentrated multi-ion systems

In this work, we report novel amine-functionalized zirconium-based metal organic frameworks (MOFs) 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. This is the first report on grafting of amidinothiourea onto MOFs. Successful grafting was confirmed by Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. A mechanism involving dehydration, ionization and coordination steps was proposed for grafting and subsequent Pb (II) binding. The microporous amidinothiourea modified UiO-66 and UiO-67 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. The developed MOFs can thus be utilized as reliable adsorbents for Pb (II) removal from industrial wastewater effluents.