Aerosol Cross-Linked Crown Ether Diols Melded with Poly(vinyl alcohol) as Specialized Microfibrous Li⁺ Adsorbents

Abstract

Crown ether (CE)-based Li adsorbent microfibers (MFs) were successfully fabricated through a combined use of CE diols, electrospinning, and aerosol cross-linking. The 14- to 16-membered CEs, with varied ring subunits and cavity dimensions, have two hydroxyl groups for covalent attachments to poly(vinyl alcohol) (PVA) as the chosen matrix. The CE diols were blended with PVA and transformed into microfibers via electrospinning, a highly effective technique in minimizing CE loss during MF fabrication. Subsequent aerosol glutaraldehyde (GA) cross-linking of the electrospun CE/PVA MFs stabilized the adsorbents in water. The aerosol technique is highly effective in cross-linking the MFs at short time (5 h) with minimal volume requirement of GA solution (2.4 mL g MF). GA cross-linking alleviated CE leakage from the fibers as the CEs were securely attached with PVA through covalent CE-GA-PVA linkages. Three types of CE/PVA MFs were fabricated and characterized through Fourier transform infrared-attenuated total reflection, C cross-polarization magic angle spinning NMR, field emission scanning electron microscope, N adsorption/desorption, and universal testing machine. The MFs exhibited pseudo-second-order rate and Langmuir-type Li adsorption. At their saturated states, the MFs were able to use 90-99% CEs for 1:1 Li complexation, suggesting favorability of their microfibrous structures for CE accessibility to Li. The MFs were highly Li-selective in seawater. Neopentyl-bearing CE was most effective in blocking larger monovalents Na and K, whereas the dibenzo CE was best in discriminating divalents Mg and Ca. Experimental selectivity trends concur with the reaction enthalpies from density functional theory calculations, confirming the influence of CE structures and cavity dimensions in their "size-match" Li selectivity.

Aqueous Synthesis of 14‐15‐Membered Crown Ethers with Mixed O, N and S Heteroatoms: Experimental and Theoretical Binding Studies with Platinum‐Group Metals

“…Nonetheless, the cyclization yields of CEs 2 a – 2 i starting from the diol intermediates gave good to excellent yields (56 %–93 %) in comparison to other reported values for CEs with mixed heteroatoms ,. More importantly, the resulting CEs are dihydroxy‐terminated which can be further functionalized for extraction or covalently attached on solid supports as PGM adsorbent materials ,…”

“…[13,24] More importantly, the resulting CEs are dihydroxy-terminated which can be further functionalized for extraction or covalently attached on solid supports as PGM adsorbent materials. [8,25]…”

Preparation of Crown‐Ether‐Functionalized Polysulfone Membrane by In Situ Surface Grafting for Selective Adsorption and Separation of Li+

“…For the sake to study the regeneration performance of as‐prepared PSf‐sg‐AB12 C4 membrane, the adsorption/desorption cycle experiment was carried out for ten cycles. The membrane which adsorbed Li + was regenerated by dynamic cyclic elution with 80 mL 0.1 mol⋅L ‐1 HCl, and Li + was displaced by H + from B12 C4 cavities on membrane . After that about 240 mL pure water was used to wash the membrane until neutral pH.…”

Materials for lithium recovery from salt lake brine

“…As shown in Fig. 11a, various (crown ether)-based lithium adsorbent microfibers can be synthesized using PVA as an electrospinning matrix and glutaraldehyde as a cross-linker during aerosol crosslinking [132]. The modified crown ether diols with different dimensions and ring subunits were prepared via a reaction with catechol, and the properties of the corresponding microfiber adsorbents were systematically investigated.…”