Rapid and selective removal of Cs⁺ from water by layered potassium antimony thiostannate

¹³⁷Cs is radioactive and highly hazardous to human health and the environment and its efficient removal from water is still challenging. In this study, potassium antimony tin sulfide (KATS-2) was synthesized using a hydrothermal method and utilized for the first time for cesium removal from water. KATS-2 showed a high maximum ion exchange capacity (358 mg g^-1) and distribution coefficient (1.59 × 10⁵ mL g^-1) toward Cs⁺. In particular, KATS-2 showed rapid ion exchange kinetics and reached the adsorption equilibrium within 5 min with 99% removal efficiency. The adsorption was good at a wide active pH range (1-12) even in extreme alkaline conditions (K_d = 3.26 × 10⁴ mL g^-1 at pH 12). The effect of coexisting ions was also investigated, and a high selectivity toward Cs⁺ was maintained even in artificial seawater (K_d = 3.28 × 10³ mL g^-1). Powder X-ray diffraction and thermogravimetric analysis demonstrated that KATS-2 was chemically and thermally stable. The results showed that owing to its excellent adsorption performance as well as chemical and thermal stability, KATS-2 is a promising adsorbent for Cs⁺ removal from contaminated water.