Layered Thiostannates with Distinct Arrangements of Mixed Cations for the Selective Capture of Cs+, Sr2+, and Eu3+ Ions

The selective capture of radioactive cesium, strontium, and lanthanides from liquid nuclear waste is of great significance to environmental remediation and human health. Herein, the rapid and selective removal of Cs+, Sr2+, and Eu3+ ions is achieved by two metal sulfides (FJSM-SnS-2 and FJSM-SnS-3). Both structures feature [Sn3S7]n2n– layers with the mixed cations of [CH3NH3]+ and [Bmmim]+ (1-butyl-2,3-dimethylimidazolium) as templates. However, the ratios and arrangements of mixed cations in the interlayered spaces are distinct. It is unprecedented that [CH3NH3]+ and [Bmmim]+ in FJSM-SnS-2 are alternatingly arranged in different interlayered spaces, whereas they in FJSM-SnS-3 are located in the same interlayered spaces. It is the first time that the ionic liquid cation and protonated organic amine have been simultaneously incorporated into metal sulfides. Both compounds show high capacities, rapid kinetics, and a wide pH active range for Cs+, Sr2+, and Eu3+. Even under excess Na+ ions, both show excellent selectivity in capturing trace Sr2+ and Eu3+ ions. FJSM-SnS-3 presents the highest KdEu to date. They still retain high removal efficiency even after intense β and γ radiation. Moreover, it is first confirmed by the in situ tracking method of mass spectrometry that the large-sized [Bmmim]+ ions are exchangeable. It is found that the arrangement of cations between interlayered spaces is a crucial factor affecting ion exchange performance. This work will likely change the consensus that large-sized organic cations are difficult to be exchanged and thus further highlight the great potential of metal sulfide ion exchangers for radionuclide remediation.从液态核废液中选择性捕获放射性铯、锶及镧系元素，对于环境修复与人类健康具有重要意义。本文通过两种金属硫化物（FJSM-SnS-2与FJSM-SnS-3），实现了对Cs+、Sr2+与Eu3+离子的快速选择性去除。两种材料的结构均具有[Sn3S7]ₙ²ⁿ⁻层状骨架，且以[CH3NH3]+与[Bmmim]+（1-丁基-2,3-二甲基咪唑鎓，1-butyl-2,3-dimethylimidazolium）的混合阳离子作为结构模板。但二者层间空间内混合阳离子的比例与排布方式存在显著差异。前所未有的是，FJSM-SnS-2中的[CH3NH3]+与[Bmmim]+在不同层间空间交替排布，而FJSM-SnS-3中的两种阳离子则共存于同一层间空间。这是首次将离子液体阳离子与质子化有机胺同时引入金属硫化物材料中。两种化合物对Cs+、Sr2+与Eu3+均表现出高吸附容量、快速吸附动力学及宽泛的pH适用范围。即便在过量Na+离子存在的条件下，二者仍可高效选择性捕获痕量Sr2+与Eu3+。其中FJSM-SnS-3对Eu3+的分配系数（KdEu）达到目前已报道的最高值。即使经过高强度β与γ射线辐照后，材料仍保持较高的去除效率。此外，本研究首次通过质谱原位追踪法证实，大尺寸的[Bmmim]+阳离子具有可交换性。研究发现，层间空间的阳离子排布是影响离子交换性能的关键因素。本工作或将改变“大尺寸有机阳离子难以被交换”的学界共识，进一步凸显金属硫化物离子交换剂在放射性核素修复领域的巨大应用潜力。