An alkali-resistant metal-organic framework as halogen bond donor for efficient and selective removing of ReO4-/TcO4.

Abstract

99Tc is one of the most problematic nuclear fuel products due to its long half-life and high environmental mobility. Direct removal of TcO4- from the highly alkaline solution of nuclear fuel is a serious and challenging environmental issue. In this work, the first efficient synthetic approach introducing halogens into a two-dimensional metal-organic framework, named Mn-MOF, is established using MnCl2·4H2O coordinating with neutral nitrogen-donor ligand, showing ultrahigh stability in alkaline aqueous even under 1M NaOH. The luxuriant Mn-Cl bonds and ordered hydrophobic pore channels enable the Mn-MOF to have an efficient adsorption capacity for ReO4- with a large capacity (403mgg-1), which is higher than most MOF adsorbents. More importantly, the Mn-MOF shows an excellent selectivity toward ReO4- in high-density competitive anions, such as NO3- and SO42-. Moreover, the outstanding performance of Mn-MOF in removing ReO4- endowed it successfully separated ReO4- from the simulated Savannah River Site (SRS) high-level waste (HLW) stream with high removal of 66.84% at the phase ratio of 10. The adsorption mechanism is further demonstrated by FT-IR, XPS analysis, and DFT calculation, showing that the ReO4- can selectively interact with Mn-Cl bonds and imidazole groups, forming unique halogen bonds Cl-O-Re, and a series of hydrogen bonds, respectively. This work suggests a new approach to the removal of TcO4- from nuclear fuel.