Dual-cation covalent organic polymers with sufficient adsorption sites for enhancing 99TcO4−/ReO4− removal

Abstract

Ultrafast removal of high-radioactivity and toxic ⁹⁹TcO₄⁻ anion from nuclear wastewater is imperative for human well-being and surroundings, notwithstanding the formidable challenges. Herein, we constructed a dual-cation covalent organic polymer (DCOP) with high charge density and sufficient active sites for ultra-fast and efficient ⁹⁹TcO₄⁻/ReO₄⁻ removal, employing a bi-cationic strategy for the first time. Alkyl-functionalized pyridinium was used to crosslink guanidinium, accomplishing the dual-cation strategy, which not only increased the charge density by charge re-distribution but also exposed more active sites on the COP materials, enhancing ReO₄⁻ removal. Batch experiment results showed that DCOP exhibited ultrafast removal kinetics (R>99 %, equilibrium within 30 s), high removal capacity (708.9 mg/g), high selectivity (R of 77.5 % and 85.5 %, respectively, at 1000 times excess of NO₃⁻ and SO₄²⁻), excellent stability (even under extreme conditions such as 240 kGy γ radiation), good recyclability (six times), and high application potential (R of 90.7 % from simulated Hanford’s waste liquid) for ReO₄⁻. Spectral characterization results, combined with theoretical calculations, indicated that the superior removal properties were related to introducing a dual-cationic strategy. This study exhibits the great potential of dual-cation covalent organic polymers for enhancing ⁹⁹TcO₄⁻/ReO₄⁻ removal from nuclear wastewater, providing a new and valuable perspective for designing high-performance COP materials for nuclear wastewater treatment.