First Potassium Fluoroaluminate Ionic Exchanger for Rapid and Selective Removal of Sr²⁺ with High Capacity

⁹⁰Sr, as a typical artificial radionuclide, poses a serious threat to human health and the ecological environment. The selective removal of this radionuclide from industrial nuclear waste is crucial for our environment. Here we report a novel potassium fluoroaluminate, K₂[(AlF₅)H₂O], which was synthesized by a simple low-temperature one-step method. It adopts a 1D AlF₆-chain structure, which consists of exchangeable potassium ions in between the infinite chains of octahedral Al centers. As a remarkable inorganic ionic exchanger, K₂[(AlF₅)H₂O] has a high chemical stability (resistance of pH=~3-12) and thermal stability (≥~300 °C). It possesses an excellent adsorption selectivity (K_d=~6.1×10⁴ mL ⋅ g^-1) and a maximum adsorption capacity of q_m=~120.32 mg ⋅ g^-1 for Sr²⁺. Importantly, it still keep a very good selectivity for Sr²⁺ ions even in the presence of competing Na⁺, Mg²⁺ and Ca²⁺ aqueous solutions. K₂[(AlF₅)H₂O] is the first example of fluoroaluminate ionic exchange materials that can capture Sr²⁺. This result opens up a new way to design and synthesize inorganic ionic exchangers for the selective removal of Sr²⁺ ions from radioactive waste water.