Robust and Flexible Thioantimonate Materials for Cs+ Remediation with Distinctive Structural Transformation: A Clear Insight into the Ion-Exchange Mechanism

It is imperative yet challenging to efficiently sequester the ¹³⁷Cs⁺ ion from aqueous solutions because of its highly environmental mobility and extremely high radiotoxicity. The systematical clarification for underlying mechanism of Cs⁺ removal and elution at the molecular level is rare. Here, efficient Cs⁺ capture is achieved by a thioantimonate [MeNH₃]₃Sb₉S₁₅ (FJSM-SbS) with high capacity, fast kinetics, wide pH durability, excellent β and γ radiation resistances, and facile elution. The Cs⁺ removal is not significantly impacted by coexisting Na⁺, K⁺, Ca²⁺, Mg²⁺, and Sr²⁺ ions which is beneficial to the remediation of Cs⁺-contaminated real waters. Importantly, the mechanism is directly illuminated by revealing an unprecedented single-crystal to single-crystal structural transformation upon Cs⁺ uptake and elution processes. The superior Cs⁺ removal results from an unusual synergy from strong affinity of soft S^2- with Cs⁺, easily exchangeable [MeNH₃]⁺ cations, and the flexible and robust framework of FJSM-SbS with open windows as trappers.