Post‐Modification of a Robust Covalent Organic Framework for Efficient Sequestration of 99TcO4−/ReO4−

Abstract Nuclear industry spent fuel reprocessing and some radioactive contamination sites often involve high acidity and salinity environments. Currently developed and reported sorbents in 99 TcO 4 − 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 ReO 4 − (a nonradioactive surrogate of 99 TcO 4 − ). Outstandingly, COF‐polyILs composite shows superior ReO 4 − 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.