Relative importance of multiple mechanisms in sorption of organic compounds by multiwalled carbon nanotubes

Abstract

Sorption of hydrophobic organic compounds (HOCs) (phenanthrene, lindane and atrazine) by original and OH-functionalized multiwalled carbon nanotubes (F-MWCNTs) was examined. Functionalization of MWCNTs with hydrophilic moieties greatly reduced their ability to sorb HOCs. The surface area (SA) and sum of meso- and macropore volumes of MWCNTs were governing characteristics that influenced their affinity and capacity for sorption of HOCs. Molecular size of HOCs markedly influenced their volume sorption capacity ( Q 0) by the original MWCNTs, and the differences in Q 0 values between various HOCs were less for F-MWCNTs, than for the original MWCNTs. The introduced hydroxyl groups may have reduced accessibility of a large portion of sites in meso- and macropores of MWCNTs that were originally available for smaller HOCs, but not for those with larger molecular size. Sorption of HOCs by MWCNTs was dominantly controlled by hydrophobic interaction regardless of their chemical structure. K ow-normalized sorption coefficients ( K d/ K ow) of the tested compounds for all MWCNTs followed the order: atrazine > phenanthrene > lindane, implying that π–π interactions enhanced sorption of aromatics by MWCNTs. The enhancement was more pronounced for chemicals with activating groups and larger molecular size relative to those with smaller molecular size and without any substituent.