Novel Chitosan-Alginate/Polyacrylamide Ternary Hydrogel Synthesized via Gamma Irradiation for Effective Remediation of Iron and Manganese Ions

Abstract Chitosan–alginate/polyacrylamide (CS–Alg/PAAm) ternary hydrogel was successfully synthesized via gamma irradiation for the removal of Fe 3 ⁺ and Mn 2 ⁺ ions from aqueous solutions and groundwater. The highest gel fraction (96.4%) was achieved at 15 kGy, 15 wt% acrylamide, and equal CS:Alg. The hydrogel was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Energy-dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET), Thermogravimetric analysis (TGA), and zeta potential. The hydrogel exhibited a point of zero charge (pHpzc) of pH 3.9, favoring cation adsorption, and optimum adsorption was achieved at pH 5. Adsorption followed the Langmuir isotherm with q max values of 20.68 and 17.26 mg g −1 for Fe 3 ⁺ and Mn 2 ⁺, respectively, indicating monolayer adsorption. The pseudo-second-order kinetic model, suggests a chemisorption-controlling mechanism. Adsorption is spontaneous and endothermic, according to thermodynamic analysis. Application to groundwater samples collected from Bahariya Oasis demonstrated effective removal of both metal ions, with adsorption efficiencies reaching 53.18% for Mn 2 ⁺ and 32.26% for Fe 3 ⁺. Adsorption was governed by Complexation, ion exchange, and electrostatic interactions.