Optimization of heavy metal (As, Cd, and Hg) adsorption performance of green-synthesized TiO₂–Fe₃O₄ nanocomposite using aloe vera extract via taguchi method

This study presents the green synthesis of a TiO₂–Fe₃O₄ nanocomposite using Aloe vera extract as a natural reducing and stabilizing agent for the simultaneous removal of As(III), Cd(II), and Hg(II) ions from aqueous environments. The biomediated sol–gel synthesis produced a nanocomposite with a crystallite size of ~14 nm (XRD) and an agglomerated, quasi-spherical morphology (SEM) driven by surface biomolecules. Adsorption performance was systematically evaluated using a Taguchi L₁₆ orthogonal array to optimize pH, adsorbent dosage, initial concentration, and contact time. Results revealed pH as the most significant factor. Under optimal conditions (pH 6, 0.05% dosage, 60 min), the composite demonstrated an exceptional maximum adsorption capacity of 160.9 mg/g for Cd(II), following the selectivity order Cd(II) > Hg(II) > As(III). FTIR analysis provided direct evidence that this high capacity is governed by chemisorption via inner-sphere surface complexation with biogenic oxygen-bearing functional groups. Furthermore, desorption studies using 0.5 M HCl demonstrated excellent practical viability, with the magnetic adsorbent retaining 84.5% of its initial Cd(II) removal efficiency after five consecutive regeneration cycles. By integrating eco-friendly synthesis with statistical optimization and robust reusability, this work offers a highly efficient and scalable approach for multi-metal wastewater remediation.