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

The selective capture of 137Cs and 90Sr with strong radiotoxicity is of great significance for environmental remediation and human health. However, it is challenging to efficiently sequester 137Cs+ and 90Sr2+ ions from aqueous solutions due to their high solubility and environmental mobility. Herein, two three-dimensional (3D) clusters-based microporous metal sulfides with γ radiation resistance were used for the removal of Cs+ and Sr2+ ions by the ion exchange method, namely [MeNH3]5.5[Me2NH2]0.5In10S18·7H2O (1) and [Me2NH2]6In10S18 (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.