Adsorption of Hydrophobic Organic Contaminants on Carbon Nanotubes in Different Organic Solvents

Carbon nanotubes (CNTs) have attracted increasing research attention because of their unique properties, such as electrical conductivity, optical activity and mechanical strength. This fascinating new class of materials shows promising application potentials in many areas. However, CNTs have been reported to be toxic to various organisms and thus may be considered as emerging contaminants. In addition, the interaction between CNTs and hydrophobic organic contaminants (HOCs) has been observed to be strong and could significantly affect the environmental behavior of HOCs. Their interaction mechanisms generally include hydrophobic effect, hydrogen bond, Ĉ-Ĉ bond, and electrostatic interaction. Different mechanisms may respond differently to the change of environmental conditions. Therefore, it is of great importance to understand the relative contribution of individual mechanisms in order to properly predict the fate of HOCs in the presence of CNTs. Adsorption of HOCs by CNTs in solvents with different polarities may reflect the contribution of hydrophobic effect to the overall adsorption. Therefore, in this study, several HOC-CNT (multi-walled, diameter 10-15 nm) interaction systems were compared in different solvents (e.g., water, methanol, and hexadecane). The results showed that the adsorption of HOCs by CNT in hexadecane is around 10% of that in water indicating hydrophobic effect is the dominant interaction mechanism. Experiments were also conducted in water-methanol mixtures with various ratios. The calculated polarity indexes of the solvents and the adsorption coefficients did not linearly related. This result indicates that mechanisms other than hydrophobic effect may be also involved.