Functionalization of magnetic beads with chelating surfactants for metal ions extraction

• Divalent amino acid-based surfactants enhanced the stabilization and chelation of polystyrene/SPION beads. • The aspartate-based surfactant achieved up to 90 % extraction efficiency for Zn²⁺ and Ni²⁺ ions. • The synthesized beads exhibited excellent recyclability, indicating practical utility in metal ion extraction. Divalent amino acid-based surfactants were utilized in the preparation and functionalization of polystyrene/superparamagnetic iron oxide nanoparticle (SPION) beads. These surfactants were derived from aminomalonic acid, aspartic acid, and glutamic acid, all containing two carboxylic groups and differing only in the spacer size between these groups, coupled with a fatty acid moiety, resulting in N-acyl amino acid surfactants. In the process of beads formation, the surfactant played a dual role as a stabilizer and a chelating agent towards the targeted metal. The beads were obtained using an emulsion solvent evaporation method. In this process, an oil-in-water emulsion was formed, containing polystyrene and iron nanoparticles. By concentrating the oil and evaporating it, solid nanoparticles were obtained. The morphology of these particles was characterized using atomic force microscopy (AFM), dynamic light scattering (DLS), while streaming potential measurements were used to determine their charge density. The surfactant's capability to extract divalent ions, specifically Zn 2+ and Ni 2+ , was assessed both in its pure form and when they were attached to the particles. The aspartate-based surfactant showed the best chelating performance for divalent ions, and the combination of surfactant-functionalized particles with magnetic responsiveness led to highly efficient extraction (up to 90 %) results. Additionally, the recyclability of the beads was also assessed, highlighting their practical utility.