Dual functional adsorption of benzoic acid from wastewater by biological-based chitosan grafted β-cyclodextrin

Removal of benzoic acid from industrial wastewater is important for the water treatment, and adsorption is an efficient treatment process. Chitosan and β-cyclodextrin (β-CD) are well investigated as feedstock for preparing polysaccharide-based toxic compounds removing adsorbents. In this study, chitosan grafted β-CD (CGC) was synthesized using glutaraldehyde as cross-linker in acidic aqueous solution. The successful grafting of β-CD onto chitosan was confirmed by FTIR and XRD. Compared with β-CD-epichlorohydrin copolymer (CDP) and cross-linked chitosan resin (CCR), CGC showed an excellent ability to adsorb benzoic acid. The CGC adsorption kinetics toward benzoic acid at 298.15 K, and isotherms at varying temperatures were studied systematically. Kinetics of the adsorption process agreed well with the pseudo-second-order kinetic model, and the experimental data of equilibrium isotherms fitted well with Langmuir model (R2 > 0.99). Furthermore, thermodynamic parameters revealed the spontaneity and exothermic nature of the adsorption process. The adsorption–desorption of benzoic acid by CGC and other two commercial adsorbents were evaluated and compared in five cycles, demonstrating high regeneration efficiency of CGC. The reversibility of benzoic acid adsorption by CGC was further proved by column recycle test. Finally, the adsorption mechanism was proposed according to the inclusion behavior of β-CD toward benzoic acid as well as the electrostatic interaction between chitosan units and benzoic acid.

► Biological-based chitosan grafted β-CD (CGC) was synthesized and characterized.
► CGC shows an excellent ability and regeneration capability for adsorbing benzoic acid.
► The adsorption process shows spontaneous, exothermic and orderly nature.
► The mechanism of dual functional adsorption process is proposed.