Eco-friendly flocculants from chitosan grafted with PNVCL and PAAc: Hybrid materials with enhanced removal properties for water remediation

Abstract

Currently, there is still a demand concerning processes for appropriate treatment of wastewater containing toxic heavy metals and emerging contaminants (pharmaceuticals and pesticides). Regarding that, water remediation can be enhanced by the development of next-generation flocculants that may tackle the current need. Therefore, this study addressed the preparation of environmental friendly flocculants derived from biobased chitosan grafted with biocompatible poly(N-vinylcaprolactam) (PNVCL) and poly(acrylic acid) (PAAc), as well as their evaluation in the removal of turbidity, ciprofloxacin (CIP) and cadmium (Cd(II)) from contaminated water. After flocculation trials, it was found that unmodified chitosan worked well at a specific dosage as flocculant (5 μg mL−1), whilst its graft copolymers having tuned properties showed a wide range of concentrations (from 1 to 10 μg mL−1) reducing contaminants levels. Besides, graft copolymers led to better results (residual turbidity < 30 NTU) than using PNVCL homopolymer alone (residual turbidity > 200 NTU). Increased temperature yielded higher pollutant removal due to the thermoresponsivity of the PNVCL grafted to the chitosan backbone (turbidity removal using CS-g-PNVCL at pH 7: < 60% at 25 °C, but around 90% at 50 °C); while the pH of the medium influenced greatly the pollutants removal in general. Flocculants containing both PNVCL and PAAc grafts allowed CIP and Cd(II) removal close to 95% in single contaminant flocculation experiments.