1 research outputs found
Aerosol Cross-Linked Crown Ether Diols Melded with Poly(vinyl alcohol) as Specialized Microfibrous Li<sup>+</sup> Adsorbents
Crown
ether (CE)-based Li<sup>+</sup> 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 polyÂ(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<sup>–1</sup> 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, <sup>13</sup>C cross-polarization magic angle spinning NMR, field emission
scanning electron microscope, N<sub>2</sub> adsorption/desorption,
and universal testing machine. The MFs exhibited pseudo-second-order
rate and Langmuir-type Li<sup>+</sup> adsorption. At their saturated
states, the MFs were able to use 90–99% CEs for 1:1 Li<sup>+</sup> complexation, suggesting favorability of their microfibrous
structures for CE accessibility to Li<sup>+</sup>. The MFs were highly
Li<sup>+</sup>-selective in seawater. Neopentyl-bearing CE was most
effective in blocking larger monovalents Na<sup>+</sup> and K<sup>+</sup>, whereas the dibenzo CE was best in discriminating divalents
Mg<sup>2+</sup> and Ca<sup>2+</sup>. 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<sup>+</sup> selectivity