Crosslinked PolyCyclodextrin/PolyBenzoxazine electrospun microfibers for selective removal of methylene blue from an aqueous system

Abstract

In this study, a blend solution of hydroxypropyl-beta-cyclodextrin (HP beta CD) and benzoxazine monomer (BA-a) was prepared in dimethylformamide to obtain HP beta CD/BA-a microfibers by electrospinning technique. The electrospun HP beta CD/BA-a microfibers were then thermally cured to obtain crosslinked PolyHP beta CD/PolyBA-a microfibers. The compositions of HP beta CD (120%, w/v) and BA-a (25%, w/v) were determined as an optimum concentration for producing bead-free and uniform microfibers from blend of HP beta CD and BA-a (HP beta CD/BA-a). Afterwards, the HP beta CD/BA-a microfibers were thermally cured using step-wise curing method to obtain water-insoluble crosslinked PolyHP beta CD/PolyBA-a fibrous membrane (FM). However, the fibrous structure of PolyHPOCD/PolyBA-a membrane was subjected to some morphological deformation during thermal curing. Therefore, citric acid (CTR, 5% and 15%, w/v) was incorporated into blend of HP beta CD15/BA-a and it was named as HP beta CDx/BA-a where x represents the amount of CTR (w/v) in the system. Blend solution of HP beta CD15/BA-a was electrospun into microfibers to facilitate the crosslinking and to improve thermal resistance of the crosslinked fibrous membrane (PolyHP beta CD15/PolyBA-a). Structural changes and thermal properties of the microfibers before and after curing were studied. Scanning electron microscopy was further used to monitor the morphology and stability of crosslinked PolyHPDCD/PolyBA-a microfibers in water and organic solvents. Consequently, PolyHP beta CD15/PolyBA-a microfibers showed an enhanced structural stability in water and organic solvents along with thermal resistance, indicating successful crosslinking. Afterwards, the molecular separation ability of self-standing PolyHP beta CD15/PolyBA-a FM was evaluated using dye mixture of Methylene Blue (MB) and Methyl Orange (MO). While both dye molecules are able to form a host-guest interaction between cyclodextrin molecules, crosslinked PolyHP beta CD15/PolyBA-a FM showed sorption selectivity against cationic MB dye due to favorable electrostatic attractions between MB and HP beta CD compared to anionic MO dye and HP beta CD. In addition to selective sorption behavior of MB dye over MO dye, crosslinked PolyHP beta CD15/PolyBA-a FM exhibited a decent adsorption capacity for MB in water.