Influence of Dissolved Organic Matter on Organic Pollutant Removal by Multiwalled Carbon Nanotubes

Influence of dissolved organic matter (DOM) on removal efficiency of phenanthrene and 1-naphthol by multiwalled carbon nanotubes (MWCNTs) was examined. A model DOM, succinic acid, did not reduce removal efficiency of phenanthrene and 1-naphthol by MWCNTs with varying outer diameters (ODs), due to its very low sorption to these sorbents and thus minimal influence on their surface properties. In contrast, humic acid (HA) introduction highly reduced their removal by MWCNTs. Molecular size and sorption strength of tested HAs by a given MWCNT generally followed the order: HA1<HA4<HA7. However, relative sorption reduction percentage of phenanthrene and 1-naphthol to a given MWCNT resulting from addition of HA1, HA4, or HA7 was comparable. This was because sorption strength of both phenanthrene and 1-naphthol by all HAs also followed the order: HA1<HA4<HA7. A greater number of phenanthrene or 1-naphthol molecules would be sorbed to MWCNTs with HA7 as compared to HA1 in the form of an hydrophobic organic contaminant (HOC)-HA complex in the bi-solute sorption systems. Great difference in sorption reduction of phenanthrene and 1-naphthol to MWCNTs induced by introduction of succinic acid or various HAs implied that chemical composition of DOMs greatly influenced their removal efficiency by MWCNTs. This study highlights that if MWCNTs can be used as a sorbent for HOC removal in the future, as its production cost will be considerably reduced, influence of DOMs on pollutant removal efficiency needs to be taken into consideration.