Synthesis and application of novel hydroxylated thia-crown ethers as composite ionophores for selective recovery of Ag+ from aqueous sources

Abstract

Selective recovery of silver ions Ag+ has been a big challenge due to its difficult separation from complex aqueous feed streams. Herein, four novel highly selective 13- to 19-membered thia-crown ethers (TCEs) were successfully developed by intermolecular cyclization of S- and O-containing intermediates. The TCEs have reactive hydroxyl group(s) for coating on solid supports. To evaluate their ability to capture Ag+, the TCEs were coated on polypropylene (PP) membrane (TCE@PP) at high loading (∼280wt%) via wet-incipient technique with glutaraldehyde acetalization. Adsorption results of all TCE@PP reveal high Ag+ capacities with qe ∼124–179mgg−1, excellent Ag+ selectivities with Kd ∼291–778Lg−1 and rapid uptake rate within 1h. But DH19-TCE4 or 19TCE@PP is the most effective as it achieved 96% Ag+ complexation compared with others ∼53–86% at feed Co=1.5mM. Density functional theory calculations reveal that DH19-TCE4 had the closest cavity size (∅c=2.35Å) with Ag+ (∅Ag+=2.30Å), the most negative binding energy (BE=−65.76kcalmol−1), and the least cavity distortion during Ag+ complexation. All adsorbents are reusable and stable with consistent performance even after five cycles of adsorption/desorption runs. Overall results demonstrate the effectiveness of the synthesis strategies for TCEs and their high potential as adsorbents, especially DH19-TCE4, for selective Ag+ recovery from aqueous sources.