Dispersion and aggregation of single-walled carbon nanotubes in aqueous solutions of anionic surfactants

Abstract

Understanding the dispersion and aggregation of carbon nanotubes (CNTs) in the aqueous environment are critical for the fate, bioavailability, and the environment and health risk assessment of them because the better suspended CNTs display a higher mobility and could transfer to a longer distance in the environment to possibly pose greater ecological and environmental risks. In this study, we have found that bulk single-walled carbon nanotubes (SWCNTs) could not be dispersed and stably suspended in water and sodium dodecylbenzene sulfonate (SDBS) solution by shaking at 140 r/min, although they could be stably suspended in SDBS solution by sonication. Even through sonication, SWCNTs suspended in SDBS solution do not remain stable at the presence of environmentally relevant cations (e.g., Na + , K + , Ca 2+ , and Mg 2+ ) after dilution. These observations suggest that SWCNTs will not travel long distances in significant concentrations in the natural environment to pose great ecological and environmental risks. We also observed that the re-aggregation of suspended SWCNTs in the presence of cations was dependent on the SDBS concen- tration rather than the SWCNT concentration in the suspension. Both SDBS and sonication play important roles in the dispersion of SWCNTs, with sonication breaking down large aggregates of SWCNTs, while SDBS adsorbed on the SWCNTs inhibits the coagulation and aggregation by steric/electrostatic repulsion to maintain the stability of the suspension in water.