Biosynthesis of MgFe₂O₄ Nanoparticles Using Plant Extract for Efficient Lead and Mercury Removal from Water: Adsorption Isotherms, Kinetics, Regeneration Performance and DFT Studies

Heavy metal contamination in water poses severe environmental and health challenges, creating an urgent need for sustainable remediation strategies. In this study, magnesium ferrite (MgFe₂O₄) nanoparticles were biosynthesized using natural plant extracts and explored as bioadsorbents for the removal of Pb²⁺ and Hg²⁺ from wastewater. The nanoparticles were thoroughly characterized by SEM, FTIR, and XRD, confirming the formation of well-defined spinel structures (∼3.77 nm) and the presence of hydroxyl and cyano groups as active adsorption sites. Batch adsorption experiments demonstrated high removal efficiencies, with maximum capacities of 94.85 mg/g for Pb²⁺ and 97.37 mg/g for Hg²⁺, best described by the Langmuir isotherm. Kinetic analysis indicated pseudo-second-order behavior, suggesting chemisorption-driven mechanisms. Complementary DFT calculations revealed strong electronic interactions between the metal ions and the MgFe₂O₄ surface, supporting the experimental findings. Additionally, the nanoparticles retained their adsorption performance over five reuse cycles, highlighting their stability and cost-effectiveness. These results position biosynthesized MgFe₂O₄ nanoparticles as promising, sustainable materials for heavy metal remediation in water treatment applications.