Size-Matching and Soft-Base Synergy: A 3D Supertetrahedral Cluster Based Oxysulfide Open Framework for Exceptional...

The selective sequestration of strontium-90 (⁹⁰Sr) from complex nuclear wastewater remains critically important yet challenging due to competitive interference from abundant coexisting ions. Herein, we present the first application of an anionic oxysulfide three-dimensional (3D) open framework based on pseudo-T4 supertetrahedral [In₈Sn₁₂O₁₀S₃₄]^16- clusters, named InSnOS, as a superior Sr²⁺ adsorbent. InSnOS exhibits outstanding Sr²⁺ adsorption performance, achieving a maximum capacity of 144.39 mg·g^-1. This value is comparable to the best performing layered materials such as FJSM-SnS-4 (141.22 mg·g^-1) and InS-2 (143.29 mg·g^-1). In addition, InSnOS shows exceptionally fast kinetics, reaching equilibrium within 5 min. It also exhibits high selectivity, exceeding 97.7% removal efficiency (R) across a wide pH range of 4 to 10, as well as in the presence of Na⁺, K⁺, Mg²⁺, Ca²⁺ cations and HCO₃^-, CO₃^2-, SO₄^2-, HPO₄^2-, Cl^- anions. The superior Sr²⁺ uptake of InSnOS arises from synergistic electrostatic attraction, rapid diffusion, Hard and Soft Acids and Bases (HSAB) governed soft-base binding, and coordination-site spacing matching that selectively accommodates Sr²⁺ over competing ions. This work establishes supertetrahedral cluster-based open frameworks as a versatile platform for designing advanced ion exchangers.