Ultra-fast ¹³⁷Cs sequestration via a layered inorganic indium thioantimonate

As a non-actinide fission product of uranium, Cs-137 has a long half-life, high-energy gamma-ray emissions, and facile accessibility to ecosystems due to the high solubility and mobility of Cs+ ions. Hence, rapid remediation of Cs-137 from radioactive wastewater is an urgent task. Here, we have developed a layered inorganic indium thioantimonate K2In2Sb2S72.2H(2)O (KIAS) prepared via cationic substitution from [(CH3)(2)NH2](2)In2Sb2S7 (NIAS) for the efficient enrichment and sequestration of Cs+ from complex aqueous solutions. KIAS possesses excellent radiation resistance, hydrolytic stability (In3+ leaching rates <= 0.01% at pH 1-13) and high Cs+ adsorption activity. Compared to unactivated NIAS, KIAS has enlarged interlayer spacing and exchangeable interlayer K+ ions. It exhibits extremely fast adsorption kinetics towards Cs+ with high removal rate (similar to 93%) in only 1 min, a record for Cs+ adsorbents. It also displays high adsorption capacity (309.60 mg g(-1)) and outstanding selectivity for Cs+ under the interference of large amounts of alkali (earth) metal ions, anions, and humic acid and even in actual tap water or lake water. Furthermore, KIAS can reversibly trap and release Cs+ ions for at least five adsorption-desorption cycles in an easy-to-operate and environmentally friendly elution procedure. The adsorption mechanism of Cs+ on KIAS, revealed by batch adsorption experiments and characterizations, is ion exchange between Cs+ and interlayer K+ ions. This work not only highlights KIAS as a promising Cs+ scavenger to minimize contamination in complicated wastewater, but also presents a cation activation strategy to greatly enhance the adsorption performance of layered metal sulfides.