Radiocesium remediation is desirable for ecological protection, human health and sustainable development of nuclear energy. Effective capture of Cs+ from acidic solutions is still challenging, mainly due to the low stability of the adsorbing materials and the competitive adsorption of protons. Herein, the rapid and highly selective capture of Cs+ from strongly acidic solutions is achieved by a robust K+-directed layered metal sulfide KInSnS4 (InSnS-1) that exhibits excellent acid and radiation resistance. InSnS-1 possesses high adsorption capacity for Cs+ and can serve as the stationary phase in ion exchange columns to effectively remove Cs+ from neutral and acidic solutions. The adsorption of Cs+ and H3O+ is monitored by single-crystal structure analysis, and thus the underlying mechanism of selective Cs+ capture from acidic solutions is elucidated at the molecular level.

137 Cs with strong radioactivity and a long half-life is highly hazardous to human health and the environment. The efficient removal of 137 Cs from complex solutions is still challenging because of its high solubility and easy mobility and the influence of interfering ions. It is highly desirable to develop effective scavengers for radiocesium remediation. Here, the highly efficient uptake of Cs + has been realized by two robust layered metal–organic frameworks (MOFs), namely [(CH 3 ) 2 NH 2 ]In(L) 2 ·DMF·H 2 O (DMF = N , N ′-dimethylformamide, H 2 L= H 2 aip (5-aminoisophthalic acid) for 1 and H 2 hip (5-hydroxyisophthalic acid) for 2 ). Remarkably, 1 and 2 hold excellent acid and alkali resistance and radiation stabilities. They exhibit fast kinetics, high capacities ( q m Cs = 270.86 and 297.67 mg/g for 1 and 2 , respectively), excellent selectivity for Cs + uptake, and facile elution for the regeneration of materials. Particularly, 1 and 2 can achieve efficient Cs + /Sr 2+ separation in a wide range of Sr/Cs molar ratios. For example, the separation factor ( SF Cs/Sr ) is up to ∼320 for 1 . Moreover, the Cs + uptake and elution mechanisms have been directly elucidated at the molecular level by an unprecedented single-crystal to single-crystal (SC-SC) structural transformation, which is attributed to the strong interactions between COO – functional groups and Cs + ions, easily exchangeable [(CH 3 ) 2 NH 2 ] + , and flexible and robust anionic layer frameworks with open windows as “pockets”. This work highlights layered MOFs for the highly efficient uptake of Cs + ions in the field of radionuclide remediation.

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