Enhancing the stability of poly(ionic liquids)@MOFs@COFs via core-shell protection strategy for (TcO4-)-Tc-99 sequestration

Sequestration of (TcO4-)-Tc-99 from the acidic or alkaline nuclear waste is highly desirable and necessary for energy sustainability and environmental safety. However, it currently remains an unmet challenge given the harsh working environment, including extreme pH conditions, high salinity, and strong radiation. Herein, we propose an "impregnation-coating" hierarchical composite strategy to fabricate ReO4- (a surrogate of (TcO4-)-Tc-99) sorbent to achieve a combination of high capture efficiency and superior structural stability under both acidic and alkaline conditions. In situ polymerization of ionic liquids (ILs) impregnated into the pores of NH2-UiO-66 forms polyILs@NH2-UiO-66, which is then covalently coated by chemically stable COF on the surface, generating a core-shell polyILs@NH2-UiO-66@COF composite. The resulting composite can maintain structural integrity in 3 M HNO3 or 2 M NaOH solutions. More importantly, this material shows good performance to remove 80.4% and 44.6% of ReO4- from the simulated Hanford low-activity waste and high-level radioactive waste in the U.S. Savannah River Site (SRS), respectively. This strategy provides a constructive way to design hierarchical core-shell composites and extends the applications of polyILs@MOF@COF hybrids.