Selective Capture of 99TcO4–/ReO4– Using a Novel Functionalized Cationic Organic Polymer via Synergistic Electrostatic-Chelation Interactions

The continued expansion of nuclear power has brought increasing attention to the management of technetium-99 (99Tc) in radioactive waste. However, the efficient removal of pertechnetate (99TcO4-) under extreme conditions, such as strong acid/alkali, high radiation, and high salinity, remains a major bottleneck. Here, TJU-COP-2, a porous organic polymer, was prepared through a hexadecyl trimethylammonium bromide (CTAB)-assisted Schiff-base condensation and evaluated for the selective removal of ReO4-, a nonradioactive surrogate for 99TcO4-, from aqueous media. Characterization via scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller surface-area analysis (BET), and Fourier transform infrared spectroscopy (FTIR) confirmed that TJU-COP-2 possesses a porous internal structure and is rich in imidazolium cations and Schiff base functional groups. Batch adsorption experiments gave a maximum ReO4- uptake of 1033.07 mg·g-1 for TJU-COP-2, approximately 20% higher than that of the previously reported TJU-COP-1. Not only does TJU-COP-2 exhibit a high adsorption capacity, but it also has a fast adsorption rate, reaching equilibrium within 5 min. Furthermore, the material maintained structural integrity and exceptional adsorption performance under various extreme conditions, retaining a 97.99% removal efficiency, especially in strongly alkaline simulated wastewater. TJU-COP-2 maintained a ReO4- removal efficiency above 95% after 10 adsorption-desorption cycles and achieved 95.74% removal from a simulated Hanford waste solution. To gain deeper insight into the extraction mechanism, FTIR, energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS), together with quantum-chemical simulations, were employed to systematically investigate the interactions between the material and ReO4-, while the potential recognition ability of the polymer toward 99TcO4- was further evaluated through quantum-chemical calculations. These investigations revealed that the superior performance originates from a predominant Cl-/ReO4- anion-exchange mechanism, with the imidazolium cation providing the primary driving force through electrostatic attraction and the Schiff-base groups playing a supplementary role via weak noncovalent interactions. Consequently, TJU-COP-2 holds promise as a potential candidate for the efficient removal of 99TcO4-/ReO4- from nuclear wastewater.