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

Abstract

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, 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 concentration 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.

Bioaccumulation, stress, and swimming impairment in Daphnia magna exposed to multiwalled carbon nanotubes, graphene, and graphene oxide

“…Multiwalled carbon nanotubes were stabilized with SDBS for uniform dispersion in aqueous solutions; however, natural cations (Naþ, Kþ, Ca 2þ , and Mg 2þ ) may have altered steric/ electrostatic repulsion forces induced by surfactants, causing aggregation to occur [32]. Calculated MWCNT D. magna uptake rates were significantly different in moderately hard and hard freshwater (Table 1, x 2 ¼ 41.61, p ¼ 0.01).…”

Environmental risks of engineered nanomaterials

“…Similar phenomenon was observed for the stablized C 60 suspension , i.e., DOM could enhance the colloidal stability in Na + solution but decrease the stability significantly in Ca 2+ and La 3+ solutions. However, we observed that single-walled CNTs (SWCNTs) powders could not be stabilized in water even in the presence of surfactants, without the assistance of extreme agitation such as by sonication in dispersion (Yang et al, 2014). C 60 powders were also observed unable to be stably suspended in water or in DOM solution even with the assistance of sonication in dispersion .…”

“…C 60 powders were also observed unable to be stably suspended in water or in DOM solution even with the assistance of sonication in dispersion . Moreover, the stably suspended nanoparticles may not remain stable in the presence of environmentally relevant cations (e.g., Na + , K + , Ca 2+ , Mg 2+ , and La 3+ ) (Hu et al, 2014;Yang et al, 2014;Zhang et al, 2014), especially once they were diluted (Yang et al, 2014). Dilution is a process commonly occurring once contaminants are released into the environment.…”

“…Dilution is a process commonly occurring once contaminants are released into the environment. Therefore, nanoparticles such as bulk SWCNTs will not travel long distances in significant concentrations in the natural environment (Yang et al, 2014). The results of dispersion experiments using vigorous sonication could be inappropriate for assessing and predicting the dispersion and suspension of bulk CNTs in the aqueous environment because sonication induces more extreme agitation than that is encountered in the natural aqueous environment (Yang et al, 2014).…”

“…Therefore, nanoparticles such as bulk SWCNTs will not travel long distances in significant concentrations in the natural environment (Yang et al, 2014). The results of dispersion experiments using vigorous sonication could be inappropriate for assessing and predicting the dispersion and suspension of bulk CNTs in the aqueous environment because sonication induces more extreme agitation than that is encountered in the natural aqueous environment (Yang et al, 2014). Multi-walled CNTs with bigger diameters than C 60 and SWCNTs could be much easier to be dispersed and suspended stably in water because of lower sonication energy needed in dispersion (Yang et al, 2013), and thus could travel longer distances in the environment and pose greater risks.…”