A novel amphoteric β-cyclodextrin-based adsorbent for simultaneous removal of cationic/anionic dyes and bisphenol A

The coexistence of anionic dye, cationic dye and endocrine-disrupting chemicals (EDCs) in dyeing wastewater has highlighted a great necessity to develop new and effective approaches for their simultaneous removal. In this study, a novel amphoteric adsorbent was successfully synthesized using a two-step strategy, starting with the preparation of citric acid (CA) crosslinked β-cyclodextrin (CD) polymer (CD/CA) through esterification reactions, followed by the grafting of 2-dimethylamino ethyl methacrylate monomer (PDMAEMA) through polymerization reaction. Adsorption performance of the synthesized material (CD/CA-g-PDMAEMA) toward EDCs (bisphenol A, BPA), cationic dye (methylene blue, MB) and anionic dye (methyl orange, MO) in the monocomponent and multicomponent systems were evaluated. The adsorbent showed a maximum adsorption capacity (qmax) of 79.0 mg/g for BPA at pH 6.5, 165.8 mg/g for MO at pH 4.0 and 335.5 mg/g for MB at pH 11.0, respectively. By altering the solution pH, zeta-potential of the adsorbent could be changed, endowing the material with selective adsorption properties toward anionic or cationic dyes, while BPA adsorption efficiency was vastly insusceptible to the changes in solution pH from 2.0 to 10.0. These characteristics are beneficial for the application of CD/CA-g-PDMAEMA in real wastewaters treatment. In addition, the pseudo-second-order model fitted well with the experimental data in both monocomponent and multicomponent systems, and the adsorption mechanisms were proposed: BPA could form inclusion complex with β-cyclodextrin cavities, while MB and MO molecules could interact with the carboxyl and tertiary amino groups on CD/CA-g-PDMAEMA through electrostatic attractions.