Abstract
Perfluorocarbon chain of perfluorooctane sulfonate (PFOS) is not only hydrophobic but also oleophobic, and its effect on PFOS distribution in oil-water mixture and underlying mechanism are unclear. For the first time, we propose that PFOS can emulsify oil-water mixture only in the presence of air, completely different from hydrocarbon surfactants. The perfluorocarbon chain repels hydrophobic compounds and its oleophobicity increases with decreasing polarity of organic solvents. The formed emulsion in oil phase contains high concentrations of PFOS, resulting in PFOS decrease in water. The increase of shaking speed and time as well as oil and air volume all increase the emulsification and decrease PFOS concentrations in water. During the settling process, the emulsion gradually disappears and the concentrated PFOS is released into water. The emulsification mechanism of PFOS based on air bubbles is proposed, and PFOS partitions to the interfaces of air bubbles with the hydro-oleophobic perfluorocarbon chain stretching into air bubbles and the polar head in water. This study clarifies the ambiguous understanding of the oleophobicity of perfluorocarbon chain in PFOS, and it is helpful for the understanding of the transport and fate of PFOS at oil-water interfaces in aquatic environments as well as the enhanced removal of PFOS from wastewater.
Highlights
IntroductionSoil-trichloroethylene-water system with the involvement of sodium dodecyl sulfate (SDS) has been studied[24], and the joint formation of hemi-micelles by mixed SDS and PFAAs (the attachment of perfluorocarbon chain on hydrocarbon chain) was attributed to the enhanced sorption of PFAAs on soils
Soil-trichloroethylene-water system with the involvement of sodium dodecyl sulfate (SDS) has been studied[24], and the joint formation of hemi-micelles by mixed SDS and PFAAs was attributed to the enhanced sorption of PFAAs on soils
Perfluorooctane sulfonate (PFOS) aqueous solution and oil were shaken in a bottle for emulsification, and samples were taken from the water phase or both the water and oil phases to measure PFOS concentrations after settling for different time
Summary
Soil-trichloroethylene-water system with the involvement of sodium dodecyl sulfate (SDS) has been studied[24], and the joint formation of hemi-micelles by mixed SDS and PFAAs (the attachment of perfluorocarbon chain on hydrocarbon chain) was attributed to the enhanced sorption of PFAAs on soils. These phenomena are not consistent with the oleophobicity of perfluorocarbon chain, which stays away from hydrophobic oil phases. Typical oil-water mixtures are selected to investigate the transport and distribution of PFOS, especially the essential role of air bubbles in the system is examined. The interfacial mechanism of PFOS distribution in oil-water mixtures invoking air bubbles is proposed
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