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Enhanced Adsorption of Perfluorooctanoate (PFOA) on to Low Oxygen Content Ordered Mesoporous Carbon (OMC): Adsorption Behaviors and Mechanisms
Ordered mesoporous carbons (OMCs) with different oxygen contents were prepared and used first time for adsorbing perfluorooctanoate (PFOA) from aqueous solutions. Elemental analysis and X-ray Photoelectron Spectroscopy (XPS) results showed the oxygen content in OMC-900 was lower than that in OMC-700 due to the high calcination temperature used. The study results proved that the lower oxygen content OMC has a higher PFOA adsorption efficiency through the enhanced hydrophobic interaction. When the initial PFOA concentration was 10mg L-1, the adsorption capacity of OMC-900 was 83.4 mg g-1, which was 1.8 times higher than that of OMC-700, indicating the oxygen content in OMCs can affect the PFOA adsorption significantly. The adsorption kinetic experiments showed that the adsorption equilibrium was achieved within 1 h for both OMCs, and the kinetic data better fit the pseudo-second-order kinetic model. The isotherm data fit the Freundlich model very well, indicating the possible multilayer micelles and hemi-micelles structure formation through the hydraulic interaction. In addition, various background cations showed a positive effect on PFOA adsorption performance due to the salting-out and divalent bridge effects. The natural organic matter (NOM), represented by humic acid, can lead to a discernible reduction in adsorption capacity of PFOA by competing for adsorption sites on OMCs.
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