Interactions between organic flocculant PAN–DCD and dyes

Organic flocculant polyacrylonitrile–dicyandiamide (PAN–DCD) was characterized by IR, 1H NMR and 13C NMR spectra. Polar groups, such as triazine, carboxyl, amidine, carbonamide and non-polar groups, such as methylene were identified in the macromolecular chain of PAN–DCD. The flocculant effectively decolorized the examined dyes in their aqueous solutions under acid condition. By comparing the IR spectra of dyes with that of PAN–DCD and that of flocs formed, weak chemical interactions between amino in PAN–DCD side chain and sulfonic acid group in the dye molecules were observed through the formation of –NH3+SO3−–,–NH2+SO3−– or/and =NH+SO3−–. By using equilibrium dialysis technique, the hydrophobic interactions between PAN–DCD and the dyes in the binding process were also observed from the experimental results. The binding extent of PAN–DCD to dye KN-R was greater than that of MO. The addition of urea into the binding system of KN-R by PAN–DCD reduced the first binding constant K from 12.2×105 (without urea) to 3.48×105 (with urea).