Molecularly imprinted polymers based on magnetic fly-ash-cenosphere composites for bisphenol A recognition

Abstract

Magnetic composites (MCs) were achieved via coating a chitosan layer containing γ-Fe₂O₃ nanoparticles onto the surface of aldehyde-functionalized fly-ash-cenospheres. Based on these MCs, the magnetic molecularly imprinted polymers (MMIPs) were further synthesized and characterized, and used to selectively recognise bisphenol A (BPA) molecules. Owing to the intrinsic advantages of cross-linked chitosan, magnetic γ-Fe₂O₃ nanoparticles and spherical FACs, the results demonstrated that these spherical shaped MMIPs particles had magnetic sensitivity (M_s = 2.221 emu g⁻¹) and magnetic stability (especially over the pH range of 6.0–12). Batch mode adsorption studies were carried out to investigate the specific adsorption equilibrium, kinetics and selective recognition. The Langmuir isotherm model was fitted well to the equilibrium data of the MMIPs, and the monolayer adsorption capacity of the MMIPs was 135.1 mg g⁻¹ at 298 K. The kinetic properties of the MMIPs were well described by the pseudo-second-order equation, indicating the chemical process could be the rate-limiting step in the adsorption process for BPA. Selective recognition experiments demonstrated the high affinity and selectivity of MMIPs towards BPA over competitive phenolic compounds. The molecular interaction between BPA and methacrylic acid (MAA) was investigated by the ¹H-NMR spectrum. Hydrogen bonding was proved to be mainly responsible for the recognition mechanism, and the specific recognition effect may be based on the distinct size, structure and functional group of the template molecules.