An Imidazopyridinium-Based Cationic Covalent Organic Framework for Selective Removal of Perrhenate Ions

Efficient removal of 99TcO4– is crucial for environmental protection and the optimal use of nuclear energy; however, existing adsorbents still face significant challenges in achieving excellent stability and high selectivity. In this work, a picolinaldehyde-based covalent organic framework (COF), TABT-COF, was converted into a chemically stable, imidazopyridinium-based, cationic N+-TABT-COF through a postmodification process. The as-synthesized N+-TABT-COF was used as an adsorbent for the selective adsorption of ReO4–, a nonradioactive substitute for radioactive 99TcO4–. Experimental results show that N+-TABT-COF achieves a ReO4– adsorption capacity of 370.6 mg·g–1, rapid adsorption kinetics (removing over 80% of ReO4– within 1 min), and good reusability. Notably, N+-TABT-COF can effectively remove ReO4– with good selectivity even in the presence of large amounts of competing ions. Combined spectral characterizations and theoretical calculations reveal that the removal of ReO4– is primarily driven by an anion-exchange mechanism between the counterion of N+-TABT-COF and ReO4–. This work offers an effective approach for developing high-performance adsorbents for the adsorption and separation of radioactive 99TcO4– in various types of contaminated environmental waters.