Researchers at the University of North Carolina have demonstrated that vertical carbon nanofibers (VACNFs) can be produced using ambient air, making the manufacturing process safer and less expensive.
![Researchers have demonstrated that they are able to produce vertical carbon nanofibers (VACNFs) using ambient air instead of ammonia gas. [Courtesy of Anatoli Melechko]](https://www.hayadan.org.il/images/content3/2014/05/Melechko-carbon-nanofibers-2014-image-500x330.jpg)
"Our discovery makes the production of vertical carbon nanofibers (from Wikipedia) safer and cheaper, because there is no need to consider the risks and costs of neutralization and treatment associated with ammonia gas," explains Dr. Anatoli Melechko, professor of materials science and engineering at North Carolina State University and the author The main body of an article describing the research findings. "Our discovery also promotes the possibility of producing these materials on a much larger scale."
In the most common production method of vertical carbon nanofibers, a substrate coated with nickel nanoparticles is placed in a vacuum chamber and heated to a temperature of 700 degrees Celsius. In the next step, the cell is filled with ammonia gas together with acetylene or acetone gas, which are a source of carbon atoms. When the substrate is exposed to an electric voltage, the gas is ionized. This process creates a plasma that directs the growth shape of the nanofibers. The carbon atoms that are not attached to the nickel nanoparticles begin to form carbon nanofibers under the nanoparticles. However, if too much carbon atoms are piled up on top of the nanoparticles, this may result in the formation of a layer that is too high, blocking the passage of additional carbon atoms required for the growth of the increasingly elongated nanofibers. The role of the ammonia gas is to prevent the carbon atoms from forming a membrane on top of the nanoparticles, one that will prevent the continued growth of the nanofibers. "We didn't think we could make these fibers without using ammonia or hydrogen," said the lead researcher. But the researchers tried anyway.
The team of researchers tried the usual vacuum chamber method, using acetone. However, they replaced the ammonia gas with air from the environment - and it worked successfully - the size, shape and directionality of the resulting carbon nanofibers were the same as those obtained by common manufacturing methods.
"We achieved this by using the vacuum method in the absence of ammonia," says the lead researcher. "Our discovery advances the theoretical possibility of producing vertical carbon nanofibers without the use of a vacuum chamber. If this can be done, we will be able to produce these materials on a much larger scale."
