title: Role of air bubbles overlooked in the adsorption of perfluorooctanesulfonate on hydrophobic carbonaceous adsorbents.
abstract: Hydrophobic interaction has been considered to be responsible for adsorption of perfluorooctanesulfonate (PFOS) on the surface of hydrophobic adsorbents, but the long C-F chain in PFOS is not only hydrophobic but also oleophobic. In this study, for the first time we propose that air bubbles on the surface of hydrophobic carbonaceous adsorbents play an important role in the adsorption of PFOS. The level of adsorption of PFOS on carbon nanotubes (CNTs), graphite (GI), graphene (GE), and powdered activated carbon (PAC) decreases after vacuum degassing. Vacuum degassing time and pressure significantly affect the removal of PFOS by these adsorbents. After vacuum degassing at 0.01 atm for 36 h, the extent of removal of PFOS by the pristine CNTs and GI decreases 79% and 74%, respectively, indicating the main contribution of air bubbles to PFOS adsorption. When the degassed solution is recontacted with air during the adsorption process, the removal of PFOS recovers to the value obtained without vacuum degassing, further verifying the key role of air bubbles in PFOS adsorption. By theoretical calculation, the distribution of PFOS in air bubbles on the adsorbent surfaces is discussed, and a new schematic sorption model of PFOS on carbonaceous adsorbents in the presence of air bubbles is proposed. The accumulation of PFOS at the interface of air bubbles on the adsorbents is primarily responsible for its adsorption, providing a new mechanistic insight into the transport, fate, and removal of PFOS.
authors.affiliation: School of Environment, Beijing Key Laboratory for Emerging Organic Contaminants Control, State Key Joint Laboratory of Environment Simulation and Pollution Control (SKLESPC), Tsinghua University , Beijing 100084, China.
authors.forename: Pingping
authors.initials: P
authors.lastname: Meng
authors.forename: Shubo
authors.initials: S
authors.lastname: Deng
authors.forename: Xinyu
authors.initials: X
authors.lastname: Lu
authors.forename: Ziwen
authors.initials: Z
authors.lastname: Du
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Huang
authors.forename: Yujue
authors.initials: Y
authors.lastname: Wang
authors.forename: Gang
authors.initials: G
authors.lastname: Yu
authors.forename: Baoshan
authors.initials: B
authors.lastname: Xing
mesh_terms: D000327:Adsorption; D000388:Air / Q000032:analysis*; D017738:Alkanesulfonic Acids / Q000737:chemistry*; D002606:Charcoal / Q000737:chemistry*; D005466:Fluorocarbons / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D037742:Nanotubes, Carbon / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D017738:Alkanesulfonic Acids; D005466:Fluorocarbons; D037742:Nanotubes, Carbon; D014874:Water Pollutants, Chemical; D002606:Charcoal; C076994:perfluorooctane sulfonic acid