Highly efficient and selective removal of cationic and anionic dyes from aqueous solutions by poly-cyclodextrin...

Cyclodextrins (CDs) are cyclic oligosaccharides derived from starch and are widely recognized as natural, non-toxic materials. In this study, electrospinning followed by various crosslinking strategies was used to create nanofibrous membranes (NMs) based on cyclodextrin (CD). Functionalization with 1,2,3,4-butanetetracarboxylic acid (BTCA) or glutaraldehyde along with polyethyleneimine (PEI), gave the otherwise insoluble poly-CD NMs different ionization properties, allowing for selective adsorption of cationic or anionic dyes through electrostatic attraction. BTCA-crosslinked poly-CD NM effectively adsorbed the cationic dye methylene blue (MB), while PEI-functionalized poly-CD NM showed a strong affinity for the anionic dye methyl orange (MO). Structural analysis confirmed the formation of imine (Schiff base) linkages between PEI's amine groups and glutaraldehyde, which improved thermal stability. The poly-CD/PEI NM achieved an impressive MO adsorption capacity of 814.30 mg/g, significantly higher than that of a PVA/PEI NM (478.85 mg/g) with similar PEI content, highlighting the effectiveness of cyclodextrins as structural components. Adsorption isotherm studies indicated that MO adsorption followed the Langmuir model, implying monolayer adsorption driven primarily by electrostatic attraction between the positively charged PEI groups and the negatively charged dye molecules. The membrane maintained about 90 % of its original capacity after five adsorption/desorption cycles.