Design of hybrid Chitosan-Montmorillonite materials for water treatment: Study of the performance and stability

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Using hybrid chitosan-montmorillonite materials as environmentally-friendly alternatives to metallic salts in water treatment, and especially for drinking water production, is a new challenge. However, the coagulation-flocculation process requires minimization of polymer release and reactivity optimization to guarantee low Dissolved Organic Carbon content of the treated waters. To meet these requirements, hybrid materials were designed in this study to combine structural stability and good sorption efficiency, even in hard waters. The influence of preparation parameters (polymer molecular weight, polymer to clay mass ratio, addition method and post-preparation treatment) was evaluated and the obtained composites were fully characterized by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Jar-Test experiments were carried out to assess the performance of the hybrids toward MethylOrange, a model molecule for the hardly removable hydrophilic compounds. The best results were obtained by drying the hybrids prepared at a 0.5:1 polymer to clay mass ratio by the direct addition method. Structural analysis revealed that the polymer chains of the dried-hybrid were more strongly bound to the Montmorillonite particles while remaining accessible to the organic molecules. This structure prevented its destabilization in the presence of high ionic strength. Under these conditions, all chitosan based materials exhibited some reactivity loss. However, the dissolved chitosan release was reduced to 13% of the initial dosage for the optimized dried hybrid compared to 47% for the undried version. To conclude, the optimized hybrids still outperformed pristine chitosan, Montmorillonite and FeCl3 for the removal of MethylOrange, thus highlighting their potential for future use.