New research has shown that that organic matter is highly effective in suspending carbon nanotubes in water, making them more likely to be transported and dispersed in the natural environment.
The work was funded by the Environmental Protection Agency in the US, and published in the January 2007 issue of Environmental Science & Technology.
Chemist Jaehong Kim, from the Georgia Tech School of Civil Engineering, and colleagues studied water from the Suwanee River in southern Georgia, and found that when mixed with natural organic matter (NOM), multi-walled carbon nanotubes (MWNTs) remain suspended for more than a month.
In the laboratory, Kim and his co-workers compared various concentrations of nanotubes in different aqueous solutions, including organic-free water and a sample of actual Suwanee River water. Each sample was agitated for an hour and then left to settle for up to one month.
The researchers then measured the opacity and turbidity of the various solutions using transmission electron microscopy, and found that MWNTs settle quickly when added to pure water, which becomes completely transparent within 30 minutes. Water containing NOM gradually lightens after four days. Other nanomaterials are also being studied in the same way.
‘This study demonstrated that a model carbon nanotube could be dispersed in water with the aid of organic matter that is naturally present,’ says Kim. ‘This suggests that dispersal of carbon nanomaterials could occur following a route that has not been considered in past environmental studies.’
Mason Tomson, from Rice University in Texas, has studied fullerene nanoparticles in soils, and found that they travel only a few metres before becoming bound to organic matter. But the results are puzzling, showing sudden drops in fullerene levels in effluent followed by sharp spikes.
Kim, acknowledging that organic material is a complex and undefined mixture of plant and animal debris, intends to look at other NOM sources, so as to better understand the interaction between nanomaterials and organic matter in the environment.
Figure: From left to right: organic-free water with nanotubes; 1% surfacant solution with nanotubes; NOM solution with nanotubes; NOM without nanotubes; Suwanee River water with nanotubes; Suwanee water without nanotubes. All solutions were agitated for 1 hour and left to settle for 4 days. Taken from the journal Environmental Science and Technology.
Article first published in Nanomaterials News.