Ultrasound-assisted synthesis of the β-cyclodextrin based cationic polymeric flocculants and evaluation of flocculation performance: Role of β-cyclodextrin

In this work, the novel beta-cyclodextrin based polymeric flocculants (CADs) were synthesized and applied on the treatment of humic acid (HA)-kaolin wastewater. Acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (DAC) were grafted onto beta-cyclodextrin (beta-CD) by ultrasound assisted initiation using ceric ammonium nitrate as initiator. The synthesized conditions were optimized by evaluating the intrinsic viscosity and grafting efficiency of CADs. Furthermore, the characterization methods including Fourier transform infrared spectroscopy (FTIR), H-1 nuclear magnetic resonance spectroscopy (H-1 NMR), thermogravimetric/differential scanning calorimetry (TG/DSC) and scanning electron microscopy (SEM) were used to evaluate and analyze the molecular structure and surface morphology of graft copolymers. In flocculation experiments, the effects of dosage, flocculent types, solution pH and flocs properties on flocculation performance were investigate in detail. CADs exhibited more satisfactory turbidity and HA removal performance than the synthetic cationic flocculants (PAD) and the non-ionic graft polymers (CAM). At the optimum dosage 4 mg/L, the maximum turbidity and HA removal rate of CAD 1# was 97.5% and 68.3%, respectively. Furthermore, CAD 1# exhibited a good flocculation performance and wide flocculation window in the pH range of 2.0-8.0. Lastly, the flocculation mechanism of CAD was detailed discussed by the investigation of zeta potential, surface tension, flocs FTIR and XPS spectra. Results indicated the unique hydrophobic internal structure of beta-CD played an important role in improving the removal rate HA of CAD.