Amino acid functionalized Zr-MOF for heterogeneous catalysis and heavy metal adsorption

Abstract

Metal-organic frameworks (MOFs) are a class of microporous materials composed of metal ions and organic ligands through coordination bonding. Open metal sites and functionalized residues at the pore make them promising candidates as heterogeneous catalysts and adsorbents. Recently, Zr-based MOFs such as UiO-66 series, NU-1000 and MOF-808 are spotlighted because of their water stability and chemical reactivity. In MOF-808 with (3,6)-c spn net topology, 6-c [Zr6O4(OH)4(COO)12] clusters are interconnected by using 3-c trimesic acid (btc) ligands. Only six carboxylates among the 12 carboxylates of the Zr cluster are connected to btc ligands and the remaining six carboxylates are terminating ligands. The terminating carboxylate ligands can be further replaced by other carboxylate ligands including amino acids and their derivatives. For example, the MOF-808 grafted by using cysteine, MOF-808-Cys, can be prepared and used for the selective and efficient captures of heavy atoms such as Cd and Hg ions since the thiol residue of the cysteine has strong binding affinity for soft heavy atoms. The MOF-808 grafted by using other amino acid, MOF-808-Amino, can also be used for biomimetic catalysis such as various hydrolysis and aldol condensation reactions.