Mechanistic aspects for the enhanced adsorption of bromophenol blue and atrazine over cyclodextrin modified polyacrylonitrile nanofiber membranes

The present work describes a unique modification process for electrospun polyacrylonitrile (PAN) nanofiber membranes modified with β-cyclodextrin (β-CD) monomers and their application in the adsorption of bromophenol blue and atrazine from aqueous systems. PAN and β-CD were successfully crosslinked using citric acid followed by electrospinning of PAN-CD nanofiber membranes. XRD and FTIR spectroscopy demonstrated successful crosslinking of PAN, β-CD, and citric acid to form PAN-CD nanofiber membranes. The microstructure and surface morphology of nanofibers were investigated using SEM and AFM and our data show that the nanofibers are uniform, have an average diameter range of 497–557 nm and possess rougher surfaces. UV-Vis spectroscopic technique was used to determine the nanofiber membranes’ adsorption efficiency and to evaluate their adsorption capacity. Batch adsorption studies at optimized conditions revealed that the removal of 66% and 89% was achieved for bromophenol blue using PAN and PAN-CD nanofibers with adsorption capacity of 0.886 and 1.197 mg/g, respectively. PAN and PAN-CD nanofibers removed 67% and 91% atrazine with adsorption capacity of 0.603 and 0.817 mg/g, respectively. The adsorptive removal of these pollutants followed the pseudo-second order kinetics and best fitted the Freundlich isotherm model. The increased removal is therefore credited to the increased surface area per volume ratio obtained from reduced diameters, intermolecular interactions, and inclusion complexation after the incorporation of β-CD monomers. Thus, it is shown that the addition of CDs improved the adsorption capacity of the hybrid materials via distinctive adsorption mechanisms. Thus, the uniqueness of this work lies on the mechanistic adsorption of bromophenol blue and atrazine through modified PAN-CD nanofiber matrix induced by the grafting of citric acid crosslinked β-CD.