Extraction Preferences of Crown Ether-Functionalized Ag-over-Au Nanoparticles from the Bulk Aqueous Phase by Gemini Surfactant-Stabilized Magnetic Nanoparticles at the Air–Aqueous Interface

Nonspecific interactions, without forming inclusion complexes, drove the extraction of crown ether (CE)-functionalized Au and Ag nanoparticles (NPs) across the air–aqueous interface by surfactant-stabilized iron oxide surface-active magnetic NPs. The amount of magnetic NPs consumed was monitored with UV–visible and DLS measurements. DLS also determined the surface potential and size of the complex formed between the Au/Ag and magnetic NPs. Elemental analyses with XPS, TEM, and FESEM quantified the extraction of Au/Ag NPs from the aqueous bulk. The preferential adsorption of CE on Ag NPs over Au NPs facilitated the extraction of Ag NPs. Density functional theory (DFT) fully supported the experimental findings and indicated a stronger adsorption energy of CE on Ag than on Au surfaces. A longer spacer of the Gemini surfactant made it easier for alkylammonium head groups to engage in nonspecific interactions with CE. The protocol highlighted the extraction of metallic pollutants across the immiscible air–aqueous interface without incorporating the magnetic NPs into the aqueous bulk and demonstrated the unique applicability of surface-active magnetic NPs in water purification.