Di-lacunary [In₆S₁₅]¹²⁻ cluster: the building block of a highly negatively charged framework for superior Sr²⁺ adsorption capacities

In this study, the construction of a highly negatively charged layered material [CH₃CH₂NH₃]₆In₆S₁₂ (InS-1) by introducing a lacunary cluster as the building block is reported. The pronounced framework negative charge density (5.59 × 10⁻³) and the soft Lewis basic S component endow InS-1 with an effective ion exchange performance toward heavier Sr²⁺, with a top-level adsorption capacity q_m of 105.35 mg g⁻¹. InS-1 exhibits a good exchange activity over pH 3–12, and the Sr²⁺-laden product can be facilely eluted.