Cationic covalent organic polymers based on guanidine with higher positive potential for selective sorption of ReO4−: Synthesis and DFT calculation

Removal of TcO4− from liquid radioactive waste is urgent due to its long half-life and high mobility. Herein, two guanidine-based cationic covalent organic polymers (TG-TPAL-H and TG-TPAL-OMe) were synthesized, and were used to research for the removal of ReO4−. TG-TPAL-H showed high removal efficiency, its sorption capacity got to 549 mg g−1 and distribution coefficient Kd was 1.17 × 106 mL g−1. What impressively, the TG-TPAL-H removed 80% of ReO4− even there was 1000 times of competing anions (Cl−, SO42−, H2PO4−). While TG-TPAL-OMe showed a poor performance on ReO4− with the capacity of 317 mg g−1 and Kd of 6.9 × 104 mL g−1. TG-TPAL-H can remove 87% ReO4− from simulated Hanford LAW stream sample, while TG-TPAL-OMe just can remove 35%. The difference between the two materials can be attributed to the electron donating group (Methoxy) in TG-TPAL-OMe reduced the positive charge density of guanidine, which was demonstrated by the ESP of density functional theory (DFT) calculation.