Amide-linked imidazolium-based cationic organic polymer for efficient 99TcO4−/ReO4− removal via synergistic electrostatic and ion-exchange interactions

An amide-linked imidazolium polymer P(BIPTA/Xy) was developed for efficient 99 TcO 4 - /ReO₄ - sequestration. • 88.38% ReO₄ - was removed within 10 s, reaching 741.96 mg g -1 uptake capacity. • High removal efficiency was retained under wide pH, irradiation, and recycling conditions. • The comprehensive adsorption performance index Ψ was proposed for the first time, with values of 123.73 and 80.36 L·g -1 ·min -1 under 1000-fold excess NO₃ - and SO₄ 2- . • Ion exchange dominated ReO₄ - uptake and was enhanced by electrostatic interactions. Adsorptive extraction of 99 TcO 4 − from nuclear wastewater is recognized as a promising remediation strategy. However, its practical application remains challenging because nuclear wastewater often contains highly acidic or alkaline media, high ionic strengths, intense radiation fields, and massive competing anions. Herein, an amide-linked imidazolium-based cationic organic polymer, P(BIPTA/Xy), was designed and synthesized via a two-step route involving nucleophilic substitution and subsequent quaternization in this work. This polymer incorporates abundant imidazolium cation sites and amide groups into a robust porous structure, allowing these functional motifs to be spatially organized for efficient anion capture. For a 200 mg/L ReO 4 − solution, P(BIPTA/Xy) achieved 88.38% removal within 10 s and reached adsorption equilibrium within 1 min, corresponding to a removal efficiency of 97.92%. The maximum adsorption capacity was 741.96 mg g −1 . More importantly, P(BIPTA/Xy) combines second-scale adsorption with high adsorption capacity and strong tolerance toward competing anions. Even in the presence of 1000-fold excess NO 3 − and SO 4 2− , the ReO 4 − removal efficiencies remained as high as 85.22% and 68.68%, respectively. To quantitatively describe this multidimensional performance, a competition-corrected comprehensive adsorption performance index (Ψ) was further employed to integrate adsorption capacity, contact-time scale, and competitive tolerance into a unified evaluation metric. The polymer maintained a ReO 4 − removal efficiency above 94% over a wide pH range of 3–11. Under conditions of 1000-fold excess NO 3 − and SO 4 2− , the corresponding Ψ values were 123.73 and 80.36 L·g −1 ·min −1 , respectively. The material further showed outstanding radiation resistance and excellent recyclability with negligible performance attenuation after 10 adsorption-desorption cycles. Additionally, P(BIPTA/Xy) achieves a ReO 4 − removal efficiency of 81.06% in simulated Hanford wastewater. Experimental characterization and density functional theory calculations revealed an adsorption mechanism dominated by Br − /ReO 4 − anion exchange and imidazolium-mediated electrostatic interactions, with a possible auxiliary contribution from the amide-containing local interaction environment. These results demonstrate that the advantage of P(BIPTA/Xy) does not arise from any single adsorption parameter, but rather from a favorable balance among rapid adsorption, high capacity, and competitive tolerance, providing useful guidance for the structural design of 99 TcO 4 − /ReO 4 − adsorbents for complex nuclear wastewater. Download: Download high-res image (370KB) Download: Download full-size image