Effective Cross-Linked Chelating Polymer for the Removal of Ferrous Ions: Synthesis, Characterization, and Application

A new chelating material was designed and applied for the treatment of aqueous solutions containing ferrous ions (Fe²+). A cross-linked chelating polymer was developed through two steps. First, ethane-1,2-diamine was condensed with methacrylic acid using N,N′-dicyclohexylcarbodiimide as a dehydrating agent to obtain the vinyl monomer N,N′-(ethane-1,2-diyl)bis(2-methacrylamide). In the second step, the vinyl monomer was polymerized via free-radical polymerization in the presence of benzoyl peroxide as a thermal initiator. The structures of both the vinyl monomer and the resulting polymer were elucidated by FT-IR and ¹H NMR spectroscopy. The thermal behavior of the synthesized cross-linked chelating polymer was studied by thermogravimetric analysis (TGA). The surface morphology and elemental composition of the polymer were investigated by SEM-EDX analysis. The adsorption of Fe(II) ions onto the chelating polymer was evaluated using batch experiments. The adsorption capacity was studied as a function of pH, initial ion concentration, and polymer dosage. The results showed that the highest removal efficiency occurred at pH 5.7, with an adsorption capacity of 33.84 mg/g. The data revealed that the Langmuir isotherm model provided a better fit for Fe(II) adsorption, with a maximum adsorption capacity of 122.88 mg/g, compared with the Freundlich model.Thermodynamic studies indicated that adsorption was favored at higher temperatures, confirming the endothermic nature of the process. The positive value of ΔH further supports the endothermic behavior, while the positive value of ΔS suggests an increase in randomness or disorder at the solid–solution interface during adsorption.