MAPTAC-Functionalized Poly(acrylic acid-co-sodium acrylate) Hydrogels for Enhanced Pb(II) and Cd(II) Adsorption

Abstract Heavy metals are among the most hazardous environmental pollutants, necessitating the development of efficient materials for their removal from contaminated water. In this study, a poly(acrylic acid-co-sodium acrylate) hydrogel was synthesized and functionalized with 3-(Methacryloylamino)propyltrimethylammonium chloride (MAPTAC). The synthesized hydrogels were characterized using various analytical techniques. Rheological and dynamic mechanical thermal analysis demonstrated that MAPTAC modification enhanced the storage modulus and improved the thermo-mechanical stability of the hydrogel by forming a stronger and more stable polymer network. The modification also reduced the equilibrium swelling capacity while improving the structural integrity of the hydrogel, indicating the formation of a more compact and mechanically stable polymer network. Their adsorption behavior of synthesized hydrogels toward Pb(II) and Cd(II) ions was investigated. Among all formulations, the hydrogel containing 10 g MAPTAC showed the highest adsorption capacities of 118 mg/g for Pb(II) and 117 mg/g for Cd(II), with corresponding removal efficiencies of 94.5% and 94%. Adsorption was systematically evaluated as a function of solution pH, contact time, adsorbent dosage, temperature, and initial metal-ion concentration. The optimal adsorption conditions were pH 6, a contact time of 60 min, a temperature of 25°C, and an adsorbent dosage of 0.008 g. The equilibrium data were best described by the Freundlich isotherm model, while adsorption kinetics followed the pseudo-second-order model. Thermodynamic analyses indicated that the adsorption process was spontaneous and most favorable at 25°C. These findings demonstrate that the MAPTAC-functionalized poly(acrylic acid-co-sodium acrylate) hydrogel is an efficient and promising adsorbent for removing Pb(II) and Cd(II) from aqueous media.