Rapid and selective removal of Cs+ and Sr2+ ions by two zeolite-type sulfides via ion exchange method

The selective capture of Cs-137 and 90Sr with strong radiotoxicity is of great significance for environmental remediation and human health. However, it is challenging to efficiently sequester Cs-137+ and Sr-90(2+) ions from aqueous solutions due to their high solubility and environmental mobility. Herein, two three-dimensional (3D) clusters-based microporous metal sulfides with gamma radiation resistance were used for the removal of Cs+ and Sr2+ ions by the ion exchange method, namely [MeNH3](5.5)[Me2NH2](0.5)In10S18.7H2O (1) and [Me2NH2](6)In10S(18) (2). Both compounds feature two-fold interpenetrating zeolite-type frameworks of [In10S18]n6n-, and small protonated methylamine and/or dimethylamine cations are located in the pores of 1 and 2. Prior to this work, the protonated organic amines with large size were normally presented in Tn cluster-based microporous sulfides as structure-directing agents (SDA). As a result, a stepwise activation strategy was usually applied to activate their ion exchange properties. Herein, the application of small-molecule amines as SDA imparts the direct and excellent Cs+ and Sr2+ ion exchange properties of title Tn cluster-based sulfides. They exhibit ultrafast kinetics, high adsorption capacities, wide pH durability and high selectivity for Cs+ and Sr2+ ions. Especially, 1 shows not only extremely high ion exchange capacity (qmCs = 564.2 mg/g and qmSr = 151.2 mg/g) superior to other reported adsorbents, but also high affinity and selectivity for Sr2+. Moreover, both compounds can be easily regenerated and reused for 5 cycles. This work shows that zeolite-type sulfides based on supertetrahedral clusters are promising adsorbents for the effective removal of Cs+ and Sr2+ ions for environmental remediation.