Efficient removal of anionic dyes from aqueous solution using CTAB and β-cyclodextrin-induced dye aggregation

Abstract

Abstract In this work, we developed a novel method for removal of anionic dyes-insoluble aggregation of anionic dyes induced by cetyl trimethyl ammonium bromide (CTAB) and β-cyclodextrin (β-CD). Firstly, the removal mechanisms were analyzed using the methods of electrical conductivity, surface tension, UV–visible spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscope with Eriochome black T (EBT) as a model anionic dye. The results show that EBT and CTAB interacted via electrostatic attraction to form a 1:1 complex and this complex could aggregate. β-CD was able to separate some CTAB molecules from the aggregates of the EBT-CTAB complex and interact with other CTAB molecules in the aggregates. In this case, these aggregates became unstable and tended to form nanoscale insoluble particles via self-assembly. Then, we studied the effects of pH, CTAB concentration, β-CD concentration and NaCl concentration on the removal of EBT. At EBT concentrations of 0.11, 0.22 and 0.44 mM, the removal ratio of EBT reached 100% within 10 min at pH from 5.0 to 10.0, molar ratio of EBT vs CTAB vs β-CD of 1:1:1 and NaCl concentration 20 mM. Finally, we used CTAB and β-CD for the removal of CBB-G250 and ARS. At a dye concentration of 0.22 mM, the removal ratios of CBB-G250 and ARS of 100% were obtained within 15 min and 10 min, respectively, at the molar ratio of dye vs CTAB vs β-CD of 1:1:1, suitable pH values (11.0 and 5.0, respectively) and NaCl concentration 20 mM. Therefore, CTAB and β-CD were effective and efficient in removal of anionic dyes.