Water-Insoluble Hydrophilic Electrospun Fibrous Mat of Cyclodextrin-Epichlorohydrin Polymer as Highly Effective Sorbent

The electrospinning of cyclodextrin (CD) functional fibers has emerged as a promising strategy to develop high performance fibers with great promising applications in many fields, including water treatment. Here, we report the fabrication of water-insoluble hydrophilic poly(cyclodextrin-epichlorohydrin) (poly(CD-ECH)) fibers by the electrospinning of an aqueous solution of hydroxypropyl-β-CD (HP-β-CD) and ECH and their cross-linking through heat treatment. The viscosity and time-dependent oscillatory deformation tests revealed that the cross-linking reactions between CD and ECH are highly sensitive to temperature, and main cross-linking takes place after the heat treatment of the electrospun mat, which was confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy analyses. The water contact angle measurement showed the hydrophilicity of the poly(CD-ECH) mat, which could maintain its fibrous structure in water. Furthermore, the poly(CD-ECH) fibers were stable in various organic solvents, i.e., acetonitrile, ethanol, methanol, trichloromethane, dimethylformamide, and dimethyl sulfoxide. Thermal gravimetric analysis showed that the cross-linking increased thermal stability of the poly(CD-ECH) fibers compared to the pristine CD, while X-ray diffraction analysis revealed the amorphous structure of the poly(CD-ECH) fibers. As a proof-of-concept study, the fiber and granule forms of the poly(CD-ECH) were exploited for the scavenging of an organic dye (i.e., phenolphthalein) and a polycyclic aromatic hydrocarbon (i.e., phenanthrene) from their aqueous solutions, and their rapid removal was observed for the poly(CD-ECH) fibers compared to its granule form. Given the hydrophilic nature of the poly(CD-ECH) electrospun mat, this high scavenging performance can be ascribed to the presence of high active CD content in the poly(CD-ECH) fibers, along with their high specific surface area.