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Cited by 34Per- and polyfluoroalkyl substances researchSurfactants and Colloidal SystemsSurface Modification and Superhydrophobicity

The DOI matches its Crossref record; 41 of the 41 references it cites were found in a registry or an index; none of the 10 sources its claims cite is checked for support yet.

Effect of hydro-oleophobic perfluorocarbon chain on interfacial behavior and mechanism of perfluorooctane sulfonate in oil-water mixture

Open access
Meng, Pingping, Deng, Shubo, Du, Ziwen, Wang, Bin, Huang, Jun, Wang, Yujue, Yu, Gang, Xing, Baoshan·2017·Scientific Reports
DOI 10.1038/srep44694PMC PMC5353549
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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.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

PFOS emulsifies oil-water mixtures only in the presence of air, unlike hydrocarbon surfactant OS, because its hydro-oleophobic perfluorocarbon chain partitions to air-bubble interfaces rather than oil-water interfaces. This air-dependent emulsification moves PFOS from water into oil/emulsion and releases it back to water as the emulsion settles.

Key findings

  • In hexane-water, no air: PFOS water concentration was 9.9 mg/L (initial 10 mg/L) and hexane was 12 μg/L; with air (5 mL hexane + 15 mL 10 mg/L PFOS in a 30-mL vial), water was 7.3 mg/L and hexane was 4.2 mg/L, with emulsion mainly in hexane.
  • Air/oil volumes and shaking controlled transfer: increasing mixture volume from 10 to 50 mL in 60-mL vials raised water PFOS from 6.8 to 8.0 mg/L; increasing hexane from 1 to 10 mL lowered water PFOS from 9.7 to 7.2 mg/L; after 36 h shaking, about 76% of initial PFOS remained in water.
  • Octanol-water with airspace gave water/octanol PFOS of 5.5/12.4 mg/L versus 6.9/8.6 mg/L without airspace; during settling, PFOS at air-bubble interfaces in hexane fell from 33.5% at 10 min to 6.1% at 33 h, and after 7 h about 12.8% of total PFOS was concentrated in the octanol emulsion.
  • OS control showed no air effect: hexane-water OS water was 3.70 vs 3.78 mg/L and hexane 0.97 vs 0.88 mg/L with/without air; PFOS solubility decreased with solvent polarity (e.g., 25 mg/L in carbon tetrachloride, 18 mg/L in hexane, 37.1 g/L in methanol, 0.11 g/L in octanol).

Methods

  • Bottle tests mixed PFOS or OS aqueous solution with hexane or octanol, shaken at 150 rpm at 25 °C, with or without airspace, then sampled water and oil phases after settling; typical initial PFOS was 10 mg/L, OS 4.3 mg/L, and settling experiments used 0.0186 mmol/L PFOS.
  • Solubility experiments added excess PFOS to 10 mL of different solvents, shook at 150 rpm at 25 °C for 96 h, settled 24 h, dried supernatant under nitrogen, and re-dissolved residues in methanol; all experiments were run in triplicate.
  • PFOS and OS were measured by HPLC with conductivity detection for >1 mg/L PFOS and OS (LOD 0.149 mg/L PFOS, 0.033 mg/L OS) and by HPLC-MS/MS for <1 mg/L PFOS (LOD 0.112 μg/L), using external standard calibration.

Limitations

  • The paper does not state a dedicated limitations section.
  • Evident from the text: suspended emulsion in water meant measured residual PFOS concentrations in water were likely higher than actual values, and calculated PFOS percentages at air-bubble interfaces before 7 h in the octanol system were not reliable because of suspended emulsion.
  • Evident from the text: in the hexane emulsion, air bubbles could not be distinguished from water droplets microscopically, and the experiments used model oils and largely high PFOS concentrations, with some additional tests from 10 μg/L to 1 mg/L.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/srep44694

Cites

41 of 41 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

0 of 10 cited sources checked · 0 supported · 0 flagged

  • Findingreasoning

    PFOS can emulsify oil-water mixture only in the presence of air, unlike hydrocarbon surfactants.

    “For the first time, we propose that PFOS can emulsify oil-water mixture only in the presence of air, completely different from hydrocarbon surfactants.”
    Quote in the paperSubstantial claim
  • Findingown data

    Emulsification of perfluorooctane with organic solvents increases in the order hexane < toluene < acetone < acetonitrile, consistent with solvent polarity order.

    “After shaking, the emulsification increases in the order of hexane-perfluorooctane < toluene-perfluorooctane < acetone-perfluorooctane < acetonitrile-perfluorooctane, consistent with the polarity order of these solvents (Figure S14).”
    Quote in the paperSubstantial claim
  • Findingown data

    PFOS solubility in alcoholic solvents decreases with increasing hydrocarbon chain length of the solvent.

    “Figure 7b shows the solubility of PFOS in different alcoholic solvents, and PFOS solubility values decrease with increasing hydrocarbon chain length in the solvents.”
    Quote in the paperSubstantial claim
  • Findingcitation

    PFOS solubility in acetone is higher than in methanol.

    “PFOS solubility in acetone is higher than that in methanol because the cavity energy for acetone is smaller than that for methanol38.”
    Quote in the paperNot a substantial claim
  • Findingown data

    The involvement of air bubbles is verified by the increased volume after shaking in the presence of air for both hexane-water and octanol-water mixtures.

    “The involvement of air bubbles is also verified by the increased volume after shaking in the presence of air for both hexane-water and octanol-water mixtures (Figure S15).”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one. 29
  • Probably not a substantial claim. 8

  • It may state two separate claims as one.

    Findingown data

    After 8 min settling, emulsification of the four mixtures all disappears, and higher polar solvents require longer time for emulsion disappearance.

    “After 8 min settling, the emulsification of four mixtures all disappears, and the higher polar solvents require longer time for emulsion disappearance.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingreasoning

    In the octanol-water system, the mixture is emulsified well after shaking, and it takes much longer for the water phase to become transparent.

    “In the octanol-water system, the mixture is emulsified well after shaking, and it takes much longer time for water phase to become transparent.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Findingreasoning

    During settling, the emulsion gradually disappears and concentrated PFOS is released into water.

    “During the settling process, the emulsion gradually disappears and the concentrated PFOS is released into water.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    PFOS solubility in carbon tetrachloride and hexane is 25 and 18 mg/L, respectively, much lower than in polar methanol, acetonitrile, and acetone.

    “PFOS solubility values in the nonpolar solvents including carbon tetrachloride and hexane are 25 and 18 mg/L, respectively, much lower than those in polar methanol, acetonitrile, and acetone.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingreasoning

    After settling, only a few water-air bubble aggregates remain at the bottom of the hexane phase, and PFOS concentrations in water increase significantly.

    “After settling, only a few water-air bubble aggregates remain at the bottom of hexane phase, and PFOS concentrations in water increase significantly (Fig. 8b).”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    PFOS concentrations in hexane and octanol are up to 46.8 and 233.0 mg/L, respectively, when the initial PFOS concentration is 100 mg/L, much higher than their solubility.

    “It is notable that PFOS concentrations in hexane and octanol are up to 46.8 and 233.0 mg/L, respectively (Figure S8), when the initial PFOS concentration is 100 mg/L, much higher than their solubility obtained in Fig. 7.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    After 2 h settling, PFOS concentrations in both water and octanol almost keep constant, and aggregates of water droplets and air bubbles exist at the bottom of the octanol phase.

    “After 2 h settling, PFOS concentrations in both water and octanol almost keep constant, and the aggregates of water droplets and air bubbles exist at the bottom of octanol phase (Fig. 8d).”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    The octanol-perfluorooctane mixture has similar emulsification to the acetone-perfluorooctane mixture, and its emulsion disappears after 3 min, faster than the acetonitrile-perfluorooctane mixture (8 min).

    “The octanol-perfluorooctane mixture has the similar emulsification to the acetone-perfluorooctane mixture, and its emulsion disappears after 3 min, faster than that of acetonitrile-perfluorooctane mixture (8 min).”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Findingreasoning

    Increasing shaking speed and time, oil volume, and air volume all increase emulsification and decrease PFOS concentrations 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.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    PFOS solubility in methanol is up to 37.1 g/L and decreases to 0.11 g/L in octanol.

    “The solubility of PFOS in methanol is up to 37.1 g/L, while this value decreases to 0.11 g/L in octanol.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingreasoning

    The emulsion formed in the oil phase contains high concentrations of PFOS, resulting in decreased PFOS concentration in water.

    “The formed emulsion in oil phase contains high concentrations of PFOS, resulting in PFOS decrease in water.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    Both emulsified layers of water-perfluorooctane and hexane-perfluorooctane mixtures disappear fast and become transparent within 3 min.

    “Both emulsified layers disappear fast and the mixtures become transparent within 3 min.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. The paper’s conclusions may not depend on it.

    Study design and conductown data

    The limit of detection for low PFOS concentrations by HPLC-MS/MS was 0.112 μg/L.

    “The LOD was measured to be 0.112 μg/L.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Interpretationreasoning

    PFOS partitions to the interfaces of air bubbles, with the hydro-oleophobic perfluorocarbon chain stretching into air bubbles and the polar head in water.

    “PFOS partitions to the interfaces of air bubbles with the hydro-oleophobic perfluorocarbon chain stretching into air bubbles and the polar head in water.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: PFOS prefers to stay at the air-water interface in the emulsion, rather than at the oil-water interface or in the bulk oil phase.

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Study design and conductnone given

    All experiments were operated thrice and the mean value was adopted.

    “All experiments were operated thrice and the mean value was adopted.”
    • Also stated in: § Emulsification Experiments · plain
      “All the experiments were operated thrice and the mean value was adopted.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Interpretationown data

    Air facilitates the formation of emulsion and some PFOS molecules are transferred to the hexane phase.

    “Thus, air facilitates the formation of emulsion and some PFOS molecules are transferred to hexane phase.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationown data

    The emulsion gradually disappears and concentrated PFOS is released into water during the settling process.

    “The emulsion gradually disappears and the concentrated PFOS is released into water during the settling process.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Study design and conductown data

    The limit of detection was 0.149 mg/L for PFOS and 0.033 mg/L for OS by HPLC.

    “the limit of detection (LOD) was 0.149 mg/L for PFOS and 0.033 mg/L for OS.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim.

    Interpretationreasoning

    Because of the strong hydrophobicity of hexane, water droplets should be covered by air bubbles to make them stable in the hexane phase.

    “Because of the strong hydrophobicity of hexane, water droplets should be covered by air bubbles to make them stable in hexane phase.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationreasoning

    Water droplets may re-enter the water phase, and small air bubbles could merge into big ones and disappear on the hexane surface.

    “Water droplets may re-enter into water phase, and small air bubbles could merge into big ones and disappear on hexane surface.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationown data

    Perfluorooctane has a higher repulsive force for water than for hexane, i.e., its hydrophobicity is greater than its oleophobicity for hexane.

    “the hexane-perfluorooctane mixture has more obvious emulsified layer than the water-perfluorooctane mixture (Figure S13a and b), suggesting that perfluorooctane has a higher repulsive force for water than for hexane, i.e., hydrophobicity of perfluorooctane is greater than its oleophobicity for hexane.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationreasoning

    Air bubbles attached by hexane droplets in the water phase may go up quickly and enter the hexane phase, leading to fast water clarification and decreased PFOS concentration in water within 10 min settling.

    “The air bubbles attached by hexane droplets (model A) in water phase may go up quickly and enter hexane phase, leading to the fast water clarification and the decrease of PFOS concentration in water within 10 min settling.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim.

    Interpretationreasoning

    PFOS accumulation at air bubble surfaces implies possible approaches for efficient removal of PFOS from water or wastewater.

    “PFOS accumulation at air bubble surfaces implies the possible approaches for efficient removal of PFOS from water or wastewater.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. It may be too vague to check against evidence.

    Interpretationreasoning

    The finding has important implications for the transport and fate of PFOS or other PFCs in aquatic environments, oil-contaminated soil, and the accumulation of PFOS in animal bodies.

    “Because air bubbles and oils are ubiquitous in surface water or wastewater, this new finding has important implications for the transport and fate of PFOS or other PFCs in aquatic environments, oil-contaminated soil, and the accumulation of PFOS in animal bodies.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: Air bubbles and oils are ubiquitous in surface water or wastewater.

  • It may state two separate claims as one.

    Interpretationnone given

    PFOS at high concentrations in water or wastewater would partition to the interfaces of air bubbles in organic phase if oils are present in the system and air may be involved in the formation of emulsion with the help of external force.

    “PFOS at high concentrations in water or wastewater would partition to the interfaces of air bubbles in organic phase if oils are present in the system and air may be involved in the formation of emulsion with the help of the external force.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim.

    Interpretationown data

    Hydrocarbon surfactants such as OS may emulsify oil-water mixture via the stretching of nonpolar hydrocarbon chain into oils.

    “The hydrocarbon surfactants such as OS may emulsify oil-water mixture via the stretching of nonpolar hydrocarbon chain into oils (Figure S16)”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Study design and conductown data

    All PFOS and OS concentrations were measured using an external standard method, with calibration curves shown in Figure S17.

    “All PFOS and OS concentrations were measured using external standard method, and their calibration curves are shown in Figure S17.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Interpretationown data

    Octanol droplets are dispersed in the water phase and may attach on air bubbles to form aggregates.

    “Octanol droplets are dispersed in water phase (model E), and they may also attach on air bubbles (model F) to form the aggregates (model G) (Fig. 8c).”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Interpretationown data

    The perfluorocarbon chain of PFOS is oleophobic and repels the hydrophobic parts of organic solvents.

    “The lower solubility of PFOS in lower polar solvents is contrary to that of hydrocarbon compounds41, indicating that the perfluorocarbon chain of PFOS is oleophobic and repels the hydrophobic parts of organic solvents.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [41] Craft, N. E. & Soares, J. H. Relative solubility, stability, and absorptivity of lutein and.beta.-carotene in organic solvents. J. Agr. Food Chem. 40, 431–434 (1992). source

  • It may state two separate claims as one.

    Interpretationown data

    The perfluorocarbon chain of perfluorooctane is both hydrophobic and oleophobic.

    “When hexane, water and perfluorooctane are mixed together, they separate quickly and three clear phases (hexane, water and perfluorooctane from top to bottom) are observed after 3 min settling (Figure S13c), further verifying that the perfluorocarbon chain of perfluorooctane is both hydrophobic and oleophobic.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationreasoning

    PFOS can only emulsify oil-water mixture in the presence of air bubbles, different from hydrocarbon surfactant OS.

    “PFOS can only emulsify oil-water mixture in the presence of air bubbles, different from hydrocarbon surfactant OS”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationown data

    The foam formed by PFOS at the solution surface is not stable and disappears fast.

    “Hence, the foam formed by PFOS at the solution surface is not stable and disappears fast.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Interpretationown data

    Air has no effect on OS distribution in the mixture, completely different from PFOS.

    “These results indicate that air has no effect on OS distribution in the mixture, completely different from PFOS.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationnone given

    The perfluorocarbon chain of PFOS repels hydrophobic compounds, and its oleophobicity increases with decreasing polarity of organic solvents.

    “The perfluorocarbon chain repels hydrophobic compounds and its oleophobicity increases with decreasing polarity of organic solvents.”
    Quote in the paperSubstantial claim
34 of 34

  • The authors state this as an assumption.

    Air bubbles might also be involved in PFOS fate in oil-water systems based on its hydro-oleophobicity.

    “Therefore, we assume that air bubbles might also be involved in PFOS fate in oil-water systems based on its hydro-oleophobicity, which has also never been addressed before.”

  • The authors state this as an assumption.

    PFOS prefers to stay at the air-water interface in the emulsion, rather than at the oil-water interface or in the bulk oil phase.

    “Due to the hydro-oleophobic perfluorocarbon chain of PFOS, we assume that PFOS prefers to stay at the air-water interface in the emulsion, rather than at oil-water interface or in the bulk oil phase.”

  • The paper relies on this without support.

    Air bubbles and oils are ubiquitous in surface water or wastewater.

    “Because air bubbles and oils are ubiquitous in surface water or wastewater”

  • The paper relies on this without support.

    Perfluorooctane has the same perfluorocarbon chain as PFOS.

    “since it has the same perfluorocarbon chain as PFOS”

  • The paper relies on this without support.

    There are no surfactants to stabilize air bubbles in the perfluorooctane-solvent mixtures.

    “since there are not surfactants to stabilize the air bubbles in the mixture”
5 of 5

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Metadata

Authors
Meng, P., Deng, S., Du, Z., Wang, B., Huang, J., Wang, Y., Yu, G., & Xing, B.
Affiliations
  • State Key Joint Laboratory of Environment Simulation and Pollution Control (CN)
  • University of Massachusetts Amherst (US)
Corresponding author
  • Deng, Shubo
  • Wang, Bin
ORCID
Venue
Scientific Reports
Publisher
Springer Science and Business Media LLC
Published
2017-03-16
Volume
7
Issue
1
Pages
44694-44694
ISSN
2045-2322 (ISSN-L)
DOI
10.1038/srep44694
PMC
PMC5353549
OpenAlex
W2596594097
Semantic Scholar
8eea18fb825cc787e43e39adbfdf75fea1be49a5
Cited by
34
References
40
Citations by year
2026: 5 · 2025: 7 · 2024: 6 · 2023: 4 · 2022: 1 · 2021: 3 · 2020: 2 · 2019: 3 · 2018: 2
FWCI
0.98
Type
journal article
Language
en
Open access
Licence
Locations
  • Scientific Reports (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
Funders
  • National Natural Science Foundation of China (21577074, IRT1261)
  • Tsinghua University (20141081174, IRT1261, 20131089251)
  • Collaborative Innovation Center for Regional Environmental Quality
  • Tsinghua Initiative Scientific Research Program
  • Program for Changjiang Scholars and Innovative Research Team in University (IRT 1261)
Topics
  • Physical Sciences › Environmental Science › Environmental Chemistry › Per- and polyfluoroalkyl substances research
  • Physical Sciences › Chemistry › Physical and Theoretical Chemistry › Surfactants and Colloidal Systems
  • Physical Sciences › Materials Science › Surfaces, Coatings and Films › Surface Modification and Superhydrophobicity
Keywords
PFOS, oil-water mixtures, emulsification, air bubbles, interfacial behavior

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