Synthesis of High-Molecular-Weight Poly (Itaconic-Co-Methacrylic Acid) Copolymers for the Fabrication of Nanocomposite Hydrogels for Cationic Dye Removal

Abstract This study introduces a novel class of physically crosslinked hydrogels synthesized from high-molecular-weight copolymers consisting of itaconic acid (IA), methacrylic acid (MAA) and laponite RD, which efficiently removes cationic dyes. The copolymers synthesized via free-radical polymerization in a deep eutectic solvent demonstrated increased thermal stability with increasing MAA content. Rheological assessments revealed elastic solid behavior (G′ > G″), with decreased stiffness correlated with increased MAA content, which was attributed to diminished electrostatic interactions. Structural analyses, including WAXS/SAXS and TEM, confirmed the complete exfoliation of the clay and the formation of a hierarchical network; upon dye adsorption, an expansion of the basal spacing to 15–20 nm was observed. The hydrogels exhibited a swelling capacity of up to 38 g/g in pure water, which was reduced to 10 g/g in saline conditions. The highest adsorption capacity of basic fuchsin was determined to be 70 mg/g, achieving a 99.5% removal efficiency using 0.05 g/L of adsorbent over a 2-hour period. The adsorption process followed the Freundlich isotherm and was well described by a nonlinear pseudo-first-order (PFO) kinetic model. The dye adsorption process was spontaneous, and exothermic and followed physisorption. Crosslinking with calcium ions substantially increased the storage modulus by 252-fold and controlled the swelling ratio to 15.9 ± 0.7 g/g, facilitating regeneration cycles with 99.2 ± 0.2% efficiency. These findings position IA-MAA laponite RD hydrogels as sustainable materials with significant potential for application in dye-contaminated wastewater treatment.