Amphoteric starch-based flocculants can flocculate different contaminants with even opposite surface charges from water through molecular structure control

Flocculation is one of the most widely applied techniques in water treatment. Polysaccharide-based flocculants have been paid much attention for their eco-friendliness recently. However, precise molecular structure control is greatly important in improving their flocculation performance. In this work, a series of amphoteric starch-based flocculants with different substitution degrees of functional groups (3-chloro-2-hydroxypropyl trimethyl ammonium chloride modified carboxymethyl starch, denoted as CMS-CTA) was synthesized. The flocculation experiments confirmed that the well-designed CMS-CTA flocculants exhibited improved performance in both optimal dosage and pH sensitivity, for not only kaolin, but also hematite suspensions, which have opposite surface charges. Further quantitative mathematical correlations among the preparation recipe, structural features, and flocculation properties were built, providing operational feasibility in the precise molecular control of the flocculants to achieve their desired flocculation performance. Additional experimental results demonstrated that a suitable flocculant could be designed successfully according to the characteristics of the targeted contaminants and structure–activity relationship, proving the effectiveness of molecular structure control for optimization of the flocculation process.