Surface molecular imprinting on polypropylene fibers for rhodamine B selective adsorption

A surface molecular imprinted fiber (MIF-B) for rhodamine B (RhB) was prepared by bonding polyethylenimine (PEI) onto polypropylene (PP) fibers and subsequently cross-linking with epichlorohydrin (ECH) in the presence of RhB. The chemical structures of composites in each synthetic step were traced by FTIR analyses. The MIF-B exhibited excellent static and dynamic adsorption properties for RhB. Its adsorption isotherm for RhB followed Langmuir model. The competitive adsorption results indicated that the MIF-B had much higher selectivity for RhB over a structural analog (rhodamine 6G) with a selectivity coefficient (K(c)) of 74.1. The MIF-B proved to be a pH-sensitive material. Poly(acrylic acid) (PAA) and PEI chains grafted on PP would stretch or shrink in response to pH, resulting in the change in size and shape of binding sites of the MIF-B. Basic condition could induce the lightly cross-linked MIF-B to swell and expand its surface area, thus providing more memory cavities and internal binding sites constructed by imprinting process and ultimately leading to higher binding capacity and better RhB recognition.