Eco-Friendly Fabrication of Biogenic Nanocomposites and their Application in Selective Removal of Heavy Metal Ions from Aqueous Systems

Abstract

The present study investigates the eco-friendly synthesis of a biogenic chitosan–Fe₃O₄ nanocomposite using Moringa oleifera leaf extract as a natural reducing and stabilising agent, and its application in the selective removal of heavy metal ions from aqueous systems. Magnetite nanoparticles were first synthesised via a green co-precipitation method and subsequently incorporated into a chitosan matrix to develop a magnetically separable adsorbent. The structural and functional properties of the prepared nanocomposite were confirmed through standard characterisation techniques, indicating successful integration of iron oxide nanoparticles within the biopolymer framework. Batch adsorption experiments were performed to evaluate the removal efficiency of Pb(II), Cd(II), Cu(II), Ni(II), and Cr(VI) under varying experimental conditions, including pH, contact time, initial concentration, and competitive multi-metal systems. The results indicated strong pH-dependent adsorption behaviour, in which divalent cations exhibited maximum uptake under near-neutral conditions, whereas Cr(VI) showed higher removal efficiency under acidic conditions. Among all tested ions, Pb(II) demonstrated the highest adsorption capacity and selectivity in both single- and mixed-metal systems. Kinetic analysis revealed that adsorption followed a pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Equilibrium data were well described by the Langmuir isotherm, indicating monolayer adsorption on a homogeneous surface. Regeneration studies confirmed that the nanocomposite retained significant adsorption efficiency over multiple cycles, demonstrating its stability and reusability. Overall, the findings suggest that biogenic chitosan–Fe₃O₄ nanocomposites offer a sustainable, efficient, and reusable approach for heavy metal remediation in contaminated water systems.