A cationic nanotubular metal-organic framework for the removal of Cr2O72− and iodine

Abstract

In this work, two new metal-organic frameworks (MOFs) based on a pyrazole-imidazole heterotopic ligand, namely, SCNU-Z8(Co) and SCNU-Z8(Ni), are constructed. They are isostructural, and the crystal structure of SCNU-Z8(Co) is further analyzed by single-crystal X-ray diffraction. They are 3D cationic frameworks with 1D tubular channels and possess a highly (3,9)-connected binodal gfy network topology. SCNU-Z8(Ni) can be synthesized in high yield with high phase purity; thus, it is selected to be further explored. A stability study shows that its framework is stable in water at different pH values and in many organic solvents. It can be applied to capture Cr2O72− anions in water with a moderate adsorption capacity of 130 ​mg/g via anion-exchanged process. Iodine molecules in vapour phase and cyclohexane solution can also be captured by SCNU-Z8(Ni). In the case of iodine vapours and iodine cyclohexane solution, the adsorption capacity reaches up to 4.1 ​g/g and 640 ​mg/g, respectively, which are among the best in MOFs. Most of the absorbed iodine molecules are stably captured in the framework and hard to release, which may be conducive to allow the permanent storage of radioactive iodine.