Theoretical/Experimental Study of the Heavy Metals in Poly(vinylalcohol)/Carboxymethyl Starch-g-Poly(vinyl imidazole)-Based Magnetic Hydrogel Microspheres

Heavy metal contamination of water is a critical environmental problem due to its toxicity and persistence in ecosystems. In this study, magnetic hydrogel spheres composed of carboxymethylated starch modified with poly(1-vinylimidazole) (CMS-g-PVI) and polyvinyl alcohol (PVA), combined with Fe3O4 nanoparticles, were synthesized and characterized to evaluate their efficiency in adsorbing metal ions such as Cu2+, Pb2+, and Cd2+. Structural characterization by FT-IR spectroscopy confirmed the successful integration of all functional components into the hydrogel matrix. Additionally, scanning electron microscopy (SEM) revealed a rough and porous surface morphology favorable for adsorption and an average bead diameter of 3.2 mm, influenced by the stirring rate during synthesis. Adsorption studies demonstrated maximum capacities of 82.4 mg·g−1 for Cu2+, 66.5 mg·g−1 for Pb2+, and 51.8 mg·g−1 for Cd2+, with optimal removal efficiencies at pH 6.2 and 5.7. From a theoretical perspective, density functional theory (DFT) calculations using the B3LYP/6-311+G(d,p) method allowed the optimization of molecular structures and analysis of electronic properties. The total dipole moment (TDM) of the CMS-g-PVI/PVA system reached 20.81 Debye. A significant reduction in the HOMO-LUMO energy gap was observed upon metal adsorption, with values of 0.0308 eV for Cu2+, 0.0175 eV for Pb2+, and 0.0235 eV for Cd2+, confirming strong interactions between the hydrogel matrix and the metal ions. The combined experimental and computational approach provides a comprehensive understanding of the adsorption mechanisms and supports the development of efficient materials for water decontamination.