Efficient capture of Tc/Re(VII, IV) by a viologen-based organic polymer containing tetraaza macrocycles

Abstract 99Tc is a β-emitting radionuclide with high fission yield, long half-time and it is urgent to remove Tc from liquid radioactive waste due to its potential toxicity for human. Herein, we presented a viologen-based cationic organic polymer (VBCOP) as a novel adsorbent with cationic sites and functional groups for efficient capture of Re/Tc(VII, IV) from aqueous medium. The results showed that this material could rapidly remove TcO4−/ReO4− from aqueous solution within 5 min and the maximum sorption capacity for Re(VII) could reach up to 444 mg g−1, and the distribution coefficient (Kd) towards Re(VII) and Tc(VII) reached 4.0 × 105 and 7.2 × 105 mL g−1, respectively. And more, the adsorption mechanism was also studied by X-ray photoelectron spectroscopy (XPS), Energy dispersive spectrometer (EDS) mapping and Ion chromatography (IC), the results suggested an ion-exchange process in which the Cl− in this material was replaced by ReO4−. Additionally, we investigated its adsorption mechanism towards low-valent Re which was prepared by reducing ReO4− with NaBH4, and the flexible tetraaza macrocycle introduced in the material chelated with Re(IV) was confirmed by X-ray photoelectron spectroscopy (XPS) and Extended X-ray absorption fine structure (EXAFS) analysis. In general, the research exhibits a new sorbent material that can remove both TcO4−/ReO4− and the low-valent Tc/Re, and provide a new strategy to treat radioactive waste containing Tc with different valences.