Dissolved Humic Acids Can Disperse Carbon Nanotubes and Increase Their Adsorption.

Dissolved organic matter (DOM) has been reported to effectively disperse and suspend the carbon nanotubes (CNTs), but the subsequent impact on the fate and risk of CNTs and their interaction with pollutants are unknown. In this study, two humic acids (HA) were treated through bleaching and hydrolysis to selectively remove the aromatic and aliphatic components, respectively, and original and treated HAs were used as DOM. Adsorption of rigid, aromatic moieties-rich HAs on CNTs was lower than the flexible, aliphatic components-rich ones, but the former was better at dispersing CNTs due to stronger steric hindrance. Adsorption coefficients of sulfamethoxazole on HA-suspended CNTs were much higher than that of aggregated CNTs. As measured by ¹H NMR relaxometry, the significantly increased surface area of HA-dispersed CNTs relative to the aggregated ones provided the direct evidence for the enhanced adsorption. This work emphasizes that the DOM-suspended CNTs can have more exposed surface area, thus potentially having greater environmental impact.