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

90 Sr, 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 )H2 O], 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 )H2 O] has a high chemical stability (resistance of pH=~3-12) and thermal stability (≥~300 °C). It possesses an excellent adsorption selectivity (Kd =~6.1×104  mL ⋅ g-1 ) and a maximum adsorption capacity of qm =~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 )H2 O] 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.