Rational tuning of thorium-organic frameworks by reticular chemistry for boosting radionuclide sequestration

The reticular chemistry strategy presents a powerful molecule-design tool to tailor the physical and chemical properties of metal-organic framework (MOF). In this work, we for the first time investigated the effect of organic ligands on the radionuclide sequestration (TcO4-) of thorium-organic framework. Through a coordination modulation technique, two novel isoreticular thorium-organic frameworks, namely Th-MOF-67 and Th-MOF-68, were obtained. Relative to the antetype MOF of Th-MOF-66 that shows extremely low uptake of ReO4- (a chemical surrogate of radioactive TcO4-), the isoreticular MOFs of Th-MOF-67 and Th-MOF-68 enable ultrahigh uptake of ReO4-, giving an impressively 36.8-fold or 56-fold enhancement, respectively. The adsorption capacity of Th-MOF-68 is as high as 560 mg/g, exceeding most reported adsorbents for such use. The mechanism for such exceptional outstanding performance, as unveiled by both the single crystal X-ray diffraction and theoretical calculation, is due to coordination interaction for Th-MOF-67, when a tetrazolate ligand was used, or a combined effect from both coordination interaction and anion-exchange for Th-MOF-68, if using a triazolate ligand.