Conformationally Adaptive Crown Ether Embedded in a Metal Sulfide for Exceptional Strontium Capture

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Environmental Remediation

Background:

• Efficient host-guest recognition in adsorbents requires precise conformational control of flexible moieties like crown ethers.
• Conventional covalent strategies for adsorbent modification often involve complex synthesis or limit molecular flexibility.

Purpose of the Study:

• To develop a simple, non-covalent anchoring strategy for incorporating 18-crown-6 (18Cr6) into a perforated thiostannate framework.
• To create a crystalline-state adsorbent (18Cr6-SnS) with enhanced strontium (Sr²⁺) binding affinity and selectivity.

Main Methods:

• One-pot synthesis to in-situ embed 18-crown-6 molecules within the interlayer galleries of a perforated thiostannate framework.
• Characterization using experimental and theoretical analyses to understand the adsorption mechanism and performance.
• Evaluation of Sr²⁺ binding affinity and selectivity against other metal ions in simulated acidic high-level liquid waste.

Main Results:

• The 18Cr6-SnS adsorbent achieved a record-high distribution coefficient for Sr²⁺ (K_d = 4.9 × 10⁶ mL/g) under neutral conditions.
• Demonstrated excellent selectivity for Sr²⁺ over Cs⁺, Eu³⁺, and Ni²⁺ in 1 M HNO₃, with high separation factors.
• Conformational adaptability of intercalated 18-crown-6 and adjustable interlayer spacing were identified as key factors for superior Sr²⁺ recognition.

Conclusions:

• The non-covalent anchoring strategy provides an effective and scalable route for designing advanced adsorbents.
• Synergistic integration of host materials with flexible supramolecular receptors enables high-performance separation of target ions.
• This approach holds significant potential for critical energy and environmental applications, particularly in nuclear waste management.