Hydrophobic interaction is considered to be responsible for the adsorption of perfluorooctane sulfonate (PFOS) on the surface of hydrophobic carbon nanotubes (CNTs), which is inconsistent with the oleophobicity of the long C-F chain in PFOS. In this study, we propose that it is air bubbles on the surface of hydrophobic CNTs that is directly involved in the adsorption of PFOS, rather than their hydrophobic interaction. PFOS adsorption on different CNTs all decreases after vacuum degassing. Vacuum degassing time and pressure significantly affect PFOS removal by CNTs. After vacuum degassing at 0.01 atm for 36 h, PFOS removal by the pristine CNTs decreases 79%, indicating the main contribution of air bubbles to PFOS adsorption. When the degassed solution is re-contacted with air during the adsorption process, PFOS removal recovers to the value obtained without vacuum degassing, further verifying the key role of air bubbles in PFOS adsorption. By theoretical calculation, PFOS distribution in air bubbles on CNT surfaces is discussed, and a new sorption schematic model of PFOS on CNTs is proposed in the presence of air bubbles. PFOS accumulation at the interface of air bubbles on the adsorbents is primarily responsible for its adsorption, providing a new mechanistic insight into PFOS transport, fate and removal.

Role of air bubbles overlooked in the adsorption of perfluorooctane sulfonate on carbon nanotubes

249th National Meeting (2015)

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