Rapid and efficient Sr(ii) capture by lanthanide-cluster based metal–organic frameworks containing alkali metal ions

Abstract

⁹⁰Sr, with a long half-life and strong radioactivity, will pose a huge threat to ecological security once exposed to the environment. Its high solubility and easy mobility, coupled with the interference of competitive ions, make the efficient removal of ⁹⁰Sr from complex aqueous solutions highly challenging. In this work, two three-dimensional (3D) lanthanide-cluster based metal–organic frameworks (MOFs) containing alkali metal ions have been screened and synthesized, namely {M₅[Dy₅(IDC)₄(ox)₄]}_n·(20H₂O)_n (denoted as K-Dy and Na-Dy; M = Na, K; IDC = imidazole-4,5-dicarboxylate, ox = oxalate). Both compounds show Sr²⁺ ion capture performance. K-Dy as a representative has been studied in detail. It can rapidly and highly selectively capture Sr²⁺ from aqueous solutions. In the presence of interfering ions (Na⁺, Cs⁺, Mg²⁺, Ca²⁺, and Sr²⁺) and even in actual water samples (such as river water and tap water), it still shows high selectivity for Sr²⁺ capture. In addition, the good regeneration of materials can be achieved via facile elution. The Sr²⁺ capture mechanism is elucidated by various characterization techniques. The efficient Sr²⁺ capture is attributed to the readily exchangeable K⁺ ions in channels of K-Dy and the C₂O₄²⁻ groups in K-Dy with the affinity for Sr²⁺. This work not only shows the great potential of lanthanide-cluster based MOFs in radionuclide remediation, but also provides ideas for the design and synthesis of MOF based ion exchange materials with high selectivity for Sr²⁺.