Enhanced foam fractionation of perfluorooctane sulfonate (PFOS) from water using amphiphilic Janus SiO2 nanoparticles

Perfluorooctane sulfonate (PFOS), a persistent environmental contaminant, presents significant risks to human health and ecological balance. In response, our research introduces an innovative approach to tackle this challenge through the development of an efficient nanoparticle surfactant that enhances PFOS removal via foam fractionation. We synthesized a novel amphiphilic Janus nanoparticle (F-SNP-NH₂) by chemically modifying SiO₂ nanoparticles with 1H,1H,2H,2H-perfluorooctyltrimethoxysilane and aminopropyltriethoxysilane, employing an interface masking strategy. This unique particle, bearing hydrophobic fluorocarbon chains and hydrophilic amino groups, offers surface properties conducive to foam fractionation. We verified the structure and chemical composition of F-SNP-NH₂ through SEM-EDX, FTIR, and XPS. Its high surface activity enabled effective adsorption at the air–water interface, thereby promoting foam stability. Correspondingly, the foam height and half-life reached 24.5 mm and 316 s, respectively. Significantly, F-SNP-NH₂ reached PFOS adsorption equilibrium in a short duration of 40 min, achieving a maximum adsorption capacity of 1015.04 mg/g. Our analysis, supported by experimental data, theoretical models, and DFT calculations, pinpointed F–F and hydrophobic interactions as the primary forces driving PFOS collection. Under suitable conditions for foam fractionation, specifically at pH 5.0 and air flowrate 700 mL/min, the removal efficiency of PFOS achieved a high range of 98.8 % to 99.2 %, with corresponding enrichment ratios varying from 23.6 to 24.9. The foam fractionation process, employing F-SNP-NH₂, demonstrated high selectivity and efficiency for PFOS removal, showcased the reusability of the nanoparticle surfactant. These results highlight the potential of F-SNP-NH₂ in advancing foam fractionation technology for the targeted removal of PFOS and other per- and polyfluoroalkyl substances.