Production of FeCl3-Treated Amine Functional Polymer Gel for Enhanced Removal of Methyl Orange and Congo Red Anionic Dyes

Synthetic dyes such as Methyl Orange (MO) and Congo Red (CR) are recalcitrant, toxic, mutagenic and resistant to conventional biodegradation, and their industrial discharge continues to contaminate aqueous ecosystems worldwide. This study reports the synthesis and characterization of a poly(MMA-co-2-AEMA) copolymer gel (Fe-Copolymergel-NH2) treated with FeCl3. It evaluates its adsorption performance from aqueous solution against the anionic azo dyes MO and CR. Extensive characterization using N2 adsorption–desorption at 77 K, FTIR-ATR, XPS, SEM, and TEM revealed that Fe modification significantly improved the material’s textural properties, increasing its specific surface area from 8.11 m2/g to 12.55 m2/g and creating a highly irregular, interconnected, sponge-like morphology. Adsorption experiments showed that Fe-Copolymergel-NH2 achieved competitive Langmuir maximum monolayer adsorption capacities of 3201.9 mg/g for CR and 1089.8 mg/g for MO. Kinetic modeling demonstrated that adsorption strictly followed the PSO model, primarily governed by chemisorption via electrostatic attractions and complexation within the internal structure at Fe3+ coordination centers. Thermodynamic analysis revealed that the dye removal process was spontaneous and exothermic. Consequently, the successful integration of Fe3+ coordination centers resolves the adsorption and structural limitations of pure polymer matrices, positioning Fe-Copolymergel-NH2 as a highly promising and efficient adsorbent for the remediation of dye-contaminated industrial wastewater.