Crown ether-doped sol-gel materials for strontium(II) separation

Hybrid organic/inorganic sol-gel materials containingan encapsulated crown ether ligand were found to selectively remove 91.4 ± 1.3% of Sr²⁺ from a solution containing excess of competing ions such as Ca²⁺. The crown ether ligand, 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,-16-bis(malonate) ligand (Na₄oddm), with known high affinity for Sr²⁺ was encapsulated in hydrophilic SiO₂ through a simple sol-gel process. Washing the Sr²⁺-loaded gel with acid or ethylenediaminetetraacetic acid disodium salt recovered the Sr²⁺ from the sol-gel sorbent and regenerated the doped gel for subsequent Sr²⁺ intake. The approach reported here is a new alternative to the use of crown ethers in metal ion separation through, for example, solvent extraction or the use of sorbents containing chemically grafted crown ether ligands.