Post-Modification of a Robust Covalent Organic Framework for Efficient Sequestration of ⁹⁹ TcO₄ ^- /ReO₄

Nuclear industry spent fuel reprocessing and some radioactive contamination sites often involve high acidity and salinity environments. Currently developed and reported sorbents in ⁹⁹ TcO₄ ^- sequestration from the nuclear waste are unstable and show low adsorption efficiency in harsh conditions. To address this issue, we developed a post-synthetic modification strategy by grafting imidazole-based ionic liquids (ILs) onto the backbone of covalent organic framework (COF) via vinyl polymerization. The resultant COF-polyILs sorbent exhibits fast adsorption kinetics (<5 min) and good sorption capacity (388 mg g^-1 ) for ReO₄ ^- (a nonradioactive surrogate of ⁹⁹ TcO₄ ^- ). Outstandingly, COF-polyILs composite shows superior ReO₄ ^- removal even under highly acidic conditions and in the presence of excess competing ions of Hanford low-level radioactive waste stream, benefiting from the stable covalent bonds between the COF and polyILs, mass of imidazole rings, and hydrophobic pores in COF.