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

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 (similar to 280 wt%) via wet-incipient technique with glutaraldehyde acetalization. Adsorption results of all TCE@PP reveal high Ag+ capacities with q(e) similar to 124-179 mg g(-1), excellent Ag+ selectivities with K-d similar to 291-778 Lg(-1) and rapid uptake rate within 1 h. But DH19-TCE4 or 19TCE@PP is the most effective as it achieved 96% Ag+ complexation compared with others similar to 53-86% at feed C-o = 1.5 mM. Density functional theory calculations reveal that DH19-TCE4 had the closest cavity size (empty set(c)= 235 angstrom) with Ag+ (empty set(Ag+)= 2.30 angstrom), the most negative binding energy (BE = -65.76 kcal mol(-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. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.