Enhancement of selective heavy metal adsorption ability due to amino acid in MOF-808

Abstract

N-Acethyl-L-cysteine (AcC)-grafted MOF-808 was prepared by exchanging formates at Zr metal centers of MOF-808 exposed in the solvent pore. Since MOF-808 has six formates per Zr6O4(OH)4 cluster, N-Acethyl-L-cysteine with thiol residue can be introduced into the pore up to six molecules by exchanging formate with N-Acethyl-L-cysteine. The amount of N-Acethyl-L-cysteine molecules was confirmed by NMR and the presence of thiol group was confirmed by FT-IR. Heavy metal adsorption process of AcC-grafted MOF-808 followed pseudo 2nd order kinetic model. AcC-grafted MOF-808 showed 95.9% removal of Cd2+ and its Kd value is 2.31×104, which is moderate compared to other porous systems. The maximum uptake of Cd2+ was 225.1 mg/g, which is the highest value among MOFsystems. In addition, AcC-grafted MOF-808 showed excellent selectivity for Cd2+ and Pb2+ over other alkali and transition metal ions.