Selective perrhenate/pertechnetate removal by a MOF-based molecular trap

Abstract

A rational design of anion-exchange materials for the selective elimination of radioactive anionic contaminants poses a great challenge. Rather than relying on a size-compatible effect, the combination of a nano-sieve pore, hydrophobic cationic cavity, and soft-acidic open metal sites within one sorbent is an emerging strategy for meeting the requirement. Here, we designed a porous cationic Ag(I) metal-organic framework (MOF), TNU-132, which combined multiple features and showed superior perrhenate/pertechnetate capture selectivity in the presence of a large excess of 300-fold NO₃^- and 2000-fold SO₄^2-. The mechanism of this high selectivity can be well elucidated by the anion exchange experiments of TNU-132 in the Cr₂O₇^2-/ReO₄^- mixture. That is, the separation process underwent two sequential steps, the nano-sieving procedure and then a reconstruction process in the crystalline sorbent. These results were further confirmed by scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and/or single-crystal X-ray diffraction (SC-XRD) of oxoanion-loaded materials.