When mixed with natural organic matter in water from the Suwannee River -- a relatively unpolluted waterway that originates in southern Georgia -- multiwalled carbon nanotubes (MWNTs) remain suspended for more than a month, making them more likely to be transported in the environment, according to research led by the Georgia Institute of Technology.
Carbon nanotubes, which can be single- or multiwalled, are cylindrical carbon structures with novel properties that make them potentially useful in a wide variety of applications including electronics, composites, optics and pharmaceuticals.
"We found that natural organic matter, or NOM as we call it, was efficient at suspending the nanotubes in water," said Jaehong Kim, an assistant professor in the Georgia Tech School of Civil and Environmental Engineering.
The research will be published in the January issue of the American Chemical Society journal Environmental Science & Technology. Kim is the senior author and conducted the research with Professor Joseph Hughes, graduate student Hoon Hyung, both at Georgia Tech, and postdoctoral researcher John Fortner from Georgia Tech and Rice University. The U.S. Environmental Protection Agency funded the research.
"We don't know for certain why NOM is so efficient at suspending these nanotubes in the laboratory," Kim said. "We think NOM has some chemical characteristics that promote adhesion to the nanotubes more than to some surfactants. We are now studying this further."
In the lab, Kim and his colleagues compared the interactions of various concentrations of MWNTs with different aqueous environments organic-free water, water containing a 1 percent solution of the surfactant sodium dodecyl sulfate (SDS), water containing a commercially available sample of Suwannee River NOM and an actual sample of Suwannee River water from the same location as the commercially available preparation. They agitated each sample for one hour and then let it sit for up to one month.
The researchers then used transmission electron microscopy (TEM), measurements of opacity and turbidity, and other analyses to determine the behavior of MWNTs in these environments. The results were:
MWNTs added to organic-free water settled quickly, and the water became completely transparent in less than an hour.
When added to the SDS solution, the nanotubes immediately made the water dark and cloudy. After one day of settling, some nanotubes remained suspended, and the water was a light gray color.
Water containing the commercially available sample of Suwannee River NOM originally appeared dark and cloudy, then gradually lightened after four days of settling. Some MWNTs remained suspended for more than a month.
The results with an actual Suwannee River sample were similar to those with the commercially available preparation.
In addition, Kim and his colleagues used TEM to find that most MWNTs in both samples of NOM were suspended as individually dispersed nanotubes, rather than being clustered together as some other nanomaterials do in water. "This individual dispersion might make them more likely to be transported in a natural environment," Kim explained.
In light of these findings, Kim and his colleagues have expanded their research to other nanomaterials, including single-walled carbon nanotubes and C60, the so-called "buckyball" molecules in the same family as carbon nanotubes. They are also experimenting with other NOM sources and studying different mixing conditions. "We are getting some interesting results, though our findings are still preliminary," Kim noted.
While researchers explore applications of nanomaterials and industry nears commercial manufacture of these novel products, it's essential for scientists and engineers to study the materials' potential environmental impact, Kim added.
"Natural organic matter is heterogeneous," he explained. "It's a complex mixture made from plants and microorganisms, and it's largely undefined and variable depending on the source. So we have to continue to study nanomaterial transport in the lab using various NOM sources to try to better understand their potential interaction in the natural environment."
In related research, Kim's research team is studying various other aspects of the fate of nanomaterials in water -- including photochemical and chemical reactions of C60 colloidal aggregates -- with the ultimate goal of understanding the environmental implications of nanotechnology.
Jane M. Sanders | EurekAlert!
Successful calculation of human and natural influence on cloud formation
04.11.2016 | Goethe-Universität Frankfurt am Main
Invasive Insects Cost the World Billions Per Year
04.10.2016 | University of Adelaide
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
05.12.2016 | Earth Sciences
05.12.2016 | Physics and Astronomy
05.12.2016 | Life Sciences