Halogen microregulation in metal-organic frameworks for enhanced adsorption performance of ReO4-/TcO4

Effective and selective removal of 99TcO4- , one of the most nuisance radionuclides in nuclear waste, is highly desirable but remains a significant challenge. Herein, two isostructural MOFs, NCU-3-X (X = Cl, Br) were constructed by ZnX2 coordinated to nitrogen-containing neutral ligand tri(4-(1H-imidazole-1-l) phenyl) amine for efficient adsorption ReO4- /TcO4- . Owning to the twofold interpenetrating structure, both of them exhibit strong alkaline resistance. Consequently, NCU-3-Br exhibited superior adsorption performances with a maximum capacity as high as 483 mg/g, which is 2.23 times larger than that of NCU-3-Cl. The primary reasons accounting for the enhanced adsorption performances of NCU-3-Br are that compared to chlorine atoms, the smaller electronegativity of bromine atoms as halogen bonds donor can facilitate the formation of Sigma-holes, enhance positively charged skeleton, and reduce the adsorption energy associated with ReO4- /TcO4- . In addition, the onedimensional hydrophobic channels in the NCU-3-Br framework enable NCU-3-Br to have highly selective toward ReO4- , which has a low relative charge density against interfering ions. The SRS simulation removal experiment further confirmed the excellent adsorption capacity of NCU-3-Br to ReO4- /TcO4- . This work illustrated that the halogenated new strategy incorporated different halogen atoms into MOF skeletons can dramatically modulate the adsorption performances for ReO4-/TcO4-.

Automated summary

Researchers have successfully constructed two isostructural MOFs, NCU-3-X (X = Cl, Br), for efficient adsorption of ReO4-/TcO4- in nuclear waste. NCU-3-Br exhibited superior adsorption performances due to the smaller electronegativity of bromine atoms and the presence of one-dimensional hydrophobic channels in its framework. The adsorption capacity of NCU-3-Br to ReO4-/TcO4- was confirmed through experiments.