A guanidinium-based ionic COF for selective and efficient capture of 99TcO4−: A synergistic effect of ion exchange and hydrogen bond

Abstract

The efficient capture of ⁹⁹Tc from radioactive wastewater is crucial for the sustainable development of nuclear energy and human safety. In this study, a guanidinium-based ionic covalent organic framework (DhBa-TG_Cl) was synthesized using 1,2,3-Triaminoguanidine hydrochloride (TG_Cl) and 3,3′-dihydroxy-[1,1-biphenyl]-4,4′-dicarboxaldehyde (DhBa) to capture ⁹⁹TcO₄⁻/ReO₄⁻ in aqueous solutions. Batch experiments were conducted to investigate the effects of solution pH, adsorbent concentration, contact time, initial concentration and competing anions. The experiments demonstrated that within the pH range of 3–10, the removal efficiency of ReO₄⁻, an analogue of ⁹⁹TcO₄⁻, remained stable, with rapid adsorption kinetics (over 80 % of ⁹⁹TcO₄⁻ removed within 30 s) and a high adsorption capacity (227.21 mg•g⁻¹ for ReO₄⁻). Furthermore, competition experiments in binary systems with excess coexisting anions (Cl⁻, NO₃⁻, SO₄²⁻, and MoO₄²⁻) and the DFT calculation results revealed that DhBa-TG_Cl maintained good selectivity for ReO₄⁻ and ⁹⁹TcO₄⁻. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the adsorption mechanism involved a synergistic effect of electrostatic attraction and hydrogen bonding. Additionally, DhBa-TG_Cl can withstand 200 kGy of γ-ray irradiation and demonstrates excellent reusability after five adsorption–desorption cycles. The excellent properties of DhBa-TG_Cl highlight its great potential for rapid and selective removal of ⁹⁹TcO₄⁻ from radioactive waste liquids.