Dibenzo-18-crown-6/polycaprolactone composite nanofibers for selective adsorption of cations

Abstract

Electrospun nanofibers are attractive alternatives to traditional adsorbents due to their high surface-to-volume ratio, porosity, and loading capacity. Functionalization of nanofibers with macrocycles can contribute to further enhancement in selective adsorption of ions. In this study, polycaprolactone (PCL) nanofibers were functionalized with a crown ether, namely dibenzo-18-crown-6 (DB18C6), and the potential of the resultant electrospun PCL/DB18C6 nanofibers for selective ion adsorption, particularly the selective recovery for K+, was investigated. The morphology, chemical structure and thermal properties of PCL/DB18C6 nanofibers were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The average diameter of PCL/DB18C6 nanofibers was 529±196 nm. Single-ion adsorption experiments indicated that the adsorption capacity for K+ ion was 137 mg·g−1 and the selectivity sequence was found as K+>Ca2+>Na+. The adsorption selectivity coefficients of K+/Ca2+ and K+/Na+ were calculated respectively as 1.37 and 4.28 for single ion experiments and as 1.13 and 5.11 for mixed ion adsorptions which illustrate that the difference between the adsorption capacities of K+ and Ca2+ decreased in mixed ion adsorption experiments. Overall results demonstrate that the electrospun PCL/DB18C6 nanofibers are amenable for use as polymer adsorbents for the selective ion recovery.