Magnetic Chitosan‐Based Poly(Acrylic Acid‐ co ‐Methyl Methacrylate‐ co ‐2‐(Dimethylamino)ethyl Methacrylate)/ Fe 3 O 4 Composite Hydrogel for Adsorption of Anionic and Cationic Dyes

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The design of versatile adsorbents with maximum efficiency in dye removal and easy recovery is important in wastewater treatment. In this work, a chitosan‐based poly(acrylic acid‐co‐methyl methacrylate‐co‐2‐(dimethylamino)ethyl methacrylate)/Fe 3 O 4 hydrogel was synthesized for the removal of anionic Indigo Carmine (IC) and cationic Methylene Blue (MB) from water. The composite had a porous structure and magnetic properties, which made possible easy magnetic separation. Adsorption was strongly dependent on pH, with the optimal results obtained at pH 2 for IC and pH 12 for MB. The kinetics of adsorption was described by a pseudo‐second‐order kinetic model of adsorption with maximum adsorption capacities 1030 and 1137.73 mg g −1 , respectively. The nonlinear analysis showed that the best fitting model for IC was the Temkin model, while the best fitting model for MB was the Freundlich model. The thermodynamic analysis showed that adsorption was spontaneous and exothermic. After 5 cycles of adsorption–desorption, the hydrogel retained its initial removal efficiency, which was 92.51% and 83.37% for IC and MB, respectively.