At a time when the global electronics industry is going gaga over graphene and other carbon-based nanomaterials, two studies have found the 'miracle' graphene may not be that good.
In one research, scientists have found that graphene oxide nanoparticles are very mobile in lakes or streams and, therefore, likely to cause negative environmental impacts if released in surface water.
Another study revealed that while the carbon material is possibly the strongest material produced today, it is also as brittle as ordinary ceramic and can crack easily.
"As production of these nanomaterials increase, it is important for regulators, such as the Environmental Protection Agency, to understand their potential environmental impacts," said Jacob D. Lanphere from University of California, Riverside's Bourns College of Engineering.
Graphene oxide nanoparticles are an oxidised form of graphene, a single layer of carbon atoms prized for its strength, conductivity and flexibility.
Applications for graphene include everything from cell phones, tablet and computers to biomedical devices and solar panels.
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The use of graphene and other carbon-based nanomaterials, such as carbon nanotubes, are growing rapidly. At the same time, recent studies have suggested graphene oxide may be toxic to humans.
"The situation today is similar to where we were with chemicals and pharmaceuticals 30 years ago," Lanphere said.
We just do not know much about what happens when these engineered nanomaterials get into the ground or water. "So we have to be proactive," he cautioned in a paper published in the journal Environmental Engineering Science.
In groundwater, which typically has a higher degree of hardness and a lower concentration of natural organic matter, the graphene oxide nanoparticles tended to become less stable and eventually settle out or be removed in subsurface environments.
In surface waters, where there is more organic material and less hardness, the nanoparticles remained stable and moved farther, especially in the subsurface layers of the water bodies.
In an another study, researchers from Rice University and Georgia Institute of Technology tested small pieces of "bilayer" graphene by making tiny cracks in them with focused beams of ions.
They then pulled the graphene, to see how fast the cracks expanded until the material broke.
"It is very sensitive to the presence of a crack. In steel if you have a crack, there, it's not so dangerous. Steel has a huge resistance to crack extension. Graphene is more like window glass," explained Ting Zhu, an associate professor of mechanical engineering at Georgia Tech.
Zhu, working with Jun Lou at Rice, found that graphene with cracks is 10 times more prone to breakage than steel.