Facile synthesis of high performance porous magnetic chitosan - polyethylenimine polymer composite for Congo red removal.

A new porous magnetic chitosan-polyethylenimine (Fe3O4/CS-PEI) polymer composite was synthesized by crosslinking chitosan (CS) with polyethylenimine (PEI) in the present of FeCl3·6H2O and FeCl2·4H2O in alkaline condition and applied to remove congo red (CoR) from aqueous solutions. The Fe3O4/CS-PEI composite was characterized by SEM, XRD, TGA and FT-IR analysis. The polymer composite owned high positive charge, large surface area, multi-level pore distribution and magnetic responsiveness. The porous magnetic Fe3O4/CS-PEI composite showed ultrahigh capacity (1876mg/g) for CoR removal. It removed over 99.3% of CoR (100mg/L) when the dosage was over 1.4g/L. A higher temperature was benefit to CoR removal. The Fe3O4/CS-PEI composite was effective for CoR removal in a wide pH range (3-13). Kinetics studies suggested that the adsorption mechanism of CoR followed the pseudo-second model and it was also affected by the boundary layer diffusion. The adsorption process followed the Redlich-Peterson isotherm equation. Thermodynamic studies also demonstrated that this adsorption process was spontaneous, favorable and endothermic. The activation energy (Ea) of the adsorption process was 34.08kJ/mol, indicating that chemisorption existed in the process. The results demonstrated that the porous magnetic Fe3O4/CS-PEI polymer composite is a promising adsorbent for the efficient removal of dye pollutants from aqueous solution.