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Improved sorption of perfluorooctanoic acid on carbon nanotubes hybridized by metal oxide nanoparticles

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Abstract

Multi-walled carbon nanotubes (MWCNTs) are often used as adsorbent because of their strong adsorption capacity. However, due to the nature of MWCNTs, their ability to adsorb perfluorooctanoic acid (PFOA), a highly hydrophobic pollutant, is low. In this study, MWCNTs were modified by three nano metal oxides (nano iron oxide, copper oxide, and zinc oxide). The pristine (as the control) and modified MWCNTs were characterized by BET-N2, TEM, FTIR, XPS, and XRD, which showed that nano metal oxides were well hybridized on the surface of MWCNTs. Radioactive-labeled PFOA (14C-PFOA) was used to quantify it at trace level. Adsorption kinetics showed that intra-particle diffusion was the control step of PFOA adsorbing on metal oxides hybridized MWCNTs (MOHCNTs). Adsorption capacity of PFOA on the MOHCNTs was higher than that on the control due to electrostatic and hydrophobic interactions. In addition, PFOA formed inner-sphere complexes with metal oxide nanoparticles via ligand exchange. The alteration of PFOA adsorption capacity by increasing ionic strength was attributed to the aggregation degree of MWCNTs, electrostatic shielding, and/or salting out effect. The presence of Ca2+ increased the adsorption, owing to not only its higher electrostatic shielding ability than Na+ but also its formation of bridge between PFOA and MOHCNTs. PFOA adsorption on MOHCNTs strongly depended on medium pH value. These results provide an innovative approach for removing trace PFOA from liquid medium.

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Acknowledgments

This work was financially supported by the National Nature Science Foundation of China (Project No. 21377074) and Collaborative Fund between National Nature Science Foundation of China and Swiss National Science Foundation (Project No. 21661132004). We also thanked Dr. Bin Gao, Florida University to improve English in the manuscript.

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Correspondence to Chengliang Li or Rong Ji.

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Responsible editor: Guilherme L. Dotto

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Liu, L., Liu, Y., Li, C. et al. Improved sorption of perfluorooctanoic acid on carbon nanotubes hybridized by metal oxide nanoparticles. Environ Sci Pollut Res 25, 15507–15517 (2018). https://doi.org/10.1007/s11356-018-1728-5

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  • DOI: https://doi.org/10.1007/s11356-018-1728-5

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