The Uptake of Hazardous Metal Ions into a High-Nuclearity Cluster-Based Compound with Structural Transformation and Proton Conduction

The discovery of novel high-nuclearity oxo-clusters considerably promotes the development of cluster science. We report a high-nuclearity oxo-cluster-based compound with acid/alkali-resistance and radiation stabilities, namely, (H3O)7[Cd7Sb24O24(l-tta)9(l-Htta)3(H2O)6]·29H2O (FJSM-CA; l-H4tta = l-tartaric acid), which features a two-dimensionally anionic layer based on the largest Sb-oxo-clusters with 28-metal-ion-core [Cd4Sb24O24]. It is challenging to efficiently capture Sr2+, Ba2+ (analogue of 226Ra), and [UO2]2+ ions from aqueous solutions due to their high water solubility and environmental mobility, while it is unprecedented that a novel Sb-oxo-cluster-based framework material FJSM-CA can efficiently remove these hazardous ions accompanied with intriguing structural transformations. Especially, it shows fast ion-exchange abilities for Sr2+, Ba2+, and [UO2]2+ (reaches equilibrium within 2, 10, and 20 min, respectively) and high exchange capacity (121.91 mg/g), removal rate R (96%), and distribution coefficient KdU (2.46 × 104 mL/g) for uranium. Moreover, the underlying mechanism is clearly revealed, which is attributed to strong electrostatic interactions between exchanged cations and highly negative-charged frameworks and the strong affinity of (COO)− groups for these cations. Proton conduction of the pristine and Sr2+, Ba2+, [UO2]2+-loaded products was investigated. This work highlights the design of new oxo-cluster-based materials for radionuclide remediation and proton conduction performance.