A thermo-responsive chitosan-g-PNIPAM flocculant: a dual-phase mechanism for enhanced water treatment efficiency

The development of flocculants that can efficiently eliminate suspended solids and soluble pollutants from wastewater while mitigating the risk of secondary contamination holds paramount significance in scientific research. Biomass-derived flocculants have been extensively investigated due to their environmentally friendly and biodegradable characteristics. In this study, based on quaternate chitosan (QCS) and the temperature sensitive monomer N-isopropyl acrylamide (NIPAM), we prepared a thermo-responsive chitosan flocculant (QCS-g-PNIPAM). The prepared flocculant exhibited excellent removal efficiency for both humic acid and kaolin. In addition, the lower critical solution temperature (LCST) of the QCS-g-PNIPAM flocculant was about 36 °C. Below the LCST, PNIPAM's intermolecular hydrogen bonds enhanced hydrophilicity for pollutant adsorption; above the LCST, intramolecular hydrogen bonds induced hydrophobic transitions, triggering floc compaction through dehydration. This dual-phase mechanism synergistically improves contaminant removal, accelerates sedimentation, and boosts water recovery, advancing the design of intelligent biomass-based flocculants. The prepared temperature-responsive chitosan flocculant offers a novel approach for utilizing biomass materials to enhance water treatment efficiency and effectively mitigate secondary pollution.