Extraction of Heavy Metal Ions via Multimetallic Nanoparticles: A Convenient Methodology for the Synthesis of High Entropy Alloys through Surface Reduction of Iron Oxide Magnetic Nanoparticles

Iron oxide magnetic nanoparticles (NPs) were utilized to reduce and extract transition-metal ions of groups 10 and 11 in the form of multimetallic NPs as a step forward toward the synthesis of high entropy alloy (HEA) NPs through surface catalysis in aqueous phase at room temperature. The extraction of multimetallic NPs in the compositional range of ∼1–60 atomic % was carried out in the form of metal–magnetic composite NPs responsive to an external magnetic field. UV–visible and ICP measurements determined that extraction followed largely the reduction potential of metal ions, whereas XPS analysis explored their oxidation states. Au and Ag ions were extracted in their metallic states, whereas most of the Pd and Pt ions were extracted as oxides. Microscopic and EDS analyses highlighted the shape, structure, and composition of HEA NPs. Two prominent morphologies of multimetallic NPs centered on Au and Ag with prominent Au–Cu and Ag–Cu bimetallic compositions, respectively, were emerged. The protocol presented a methodology based on surface reduction and extraction of heavy metal ions as the most convenient strategy toward the synthesis of HEA NPs from contaminated water by utilizing magnetic NPs.