Strong acid- and irradiation-resistant nitrogen-rich covalent organic polymers with high iodine adsorption capacity

The removal of radioactive iodine from nuclear waste is very important for the development of nuclear energy. Covalent organic polymers (COPs) have been widely investigated for iodine capture due to their simple operation, diverse structures, and abundant pores. However, the disposal of nuclear waste in a strongly acidic and radioactive environment is still a great challenge. Herein, three nitrogen-rich COPs were successfully designed and synthesized by Schiff-base polycondensation reactions. The high density of N atoms in triazines and imines enhanced the binding capacity of iodine molecules, with an optimal gas-phase iodine adsorption capacity of 4.98 g g⁻¹ and a liquid-phase iodine adsorption capacity of 1224.6 mg g⁻¹. The backbone structure of the hydrazone bond connection and the introduction of thiophene effectively enhanced the stability of the TZ-COPs. The adsorption performance of TZ-2 was maintained after 6 M HNO₃ immersion and 100 kGy radiation irradiation, respectively. In addition, TZ-2 still has 92.32 % adsorption performance in five cycles, with excellent reversible regeneration ability. Therefore, this work is important for the preparation of nitrogen-rich COPs for the efficient and reversible removal of radioiodine from nuclear waste.