Amphiphilic Janus nanoparticles for effective foam fractionation of perfluorooctanoic acid (PFOA): Effect of modifier type

Perfluorooctanoic acid (PFOA), a persistent organic pollutant, is gaining attention for its detrimental effects on human health and ubiquity in aquatic environments. Herein, we introduce a novel foam fractionation method that uses Janus nanoparticles as foam stabilizers and collectors for the efficient removal and enrichment of PFOA from water. The amphiphilic Janus-SiO₂ nanoparticles (SNPs) were successfully synthesized through anisotropic modification with perfluoroalkylsilanes and aminosilanes. The amphiphilicity of constructed F₁₇-SNPs-N₂ enhanced foam stability due to high detachment energy and a bridging mechanism. The fluorine and amino groups on F₁₇-SNPs-N₂ surface facilitated efficient PFOA adsorption via fluorine-fluorine interactions, hydrophobic-hydrophobic interactions, hydrogen bonding, and electrostatic attraction, as supported by experimental analysis and DFT calculation. We also explored the mechanisms governing foam fractionation under different parameters. Under optimal conditions, we achieved PFOA removal efficiencies and enrichment ratios of 98 % and 98, respectively, within a bubbling duration of 180 s. F₁₇-SNPs-N₂, as a bifunctional material for PFOA foam fractionation, demonstrated reusability and excellent performance even in the presence of competing contaminants, highlighting its broad environmental application potential. This research provides a strategy for designing amphiphilic Janus-based foam fractionation agents through post-modification and enhances our understanding of the mechanisms behind highly efficient PFOA foam fractionation.