Highly efficient selective adsorption of anionic dyes by modified β-cyclodextrin polymers

Abstract

The nitrile groups in the tetrafluoroterephthalonitrile-crosslinked β-cyclodextrin (β-CD) were modified by (1) the reaction with the diethanolamine resulting in the hydroxyalkylaminoalkylamide groups or the hydroxyalkylaminoimide groups (2) the reduction of the borane-tetrahydrofuran complex resulting in the amide groups to form two novel β-CD based polymers (CDPs), namely the CDP-DEA and the CDP-NH₂, correspondingly. Furthermore, the dye adsorption abilities of these two CDPs in the aqueous solution were investigated using the anionic dyes including the Congo red (CR) and the orange G (OG). For both the CDP-DEA and the CDP-NH₂, the pseudo second-order model fitted well with their adsorption dynamics and their equilibrium adsorption process followed the Langmuir isotherm model. The maximum adsorption capacities of the CDP-DEA for CR at pH = 5 and OG at pH = 3 were 813 mg/g and 442 mg/g, respectively, while the corresponding values of the CDP-NH₂ were 40 mg/g and 446 mg/g, respectively. It was found that the electrostatic attraction played an important role in the anionic dye adsorption of the CDP-DEA and the CDP-NH₂.