One of the biggest obstacles in the use of nanotechnology is the cost of manufacture. Scientists working in labs come up with all sorts of interesting nanomaterials that have qualities superior to existing materials for many applications. These discoveries regularly receive glowing media reports. But too many such discoveries are going unused because of a lack of ways to make these nanomaterials cheaply in bulk. Nanotubes are a great example. They are considered to have enormous promise but in spite of the interest they have attracted no team has found a cheap way to make them. Therefore reports of nanotech production cost reduction advances are important.
UCLA chemists report in the Feb. 28 issue of Science a room-temperature chemical method for producing a new form of carbon called carbon nanoscrolls. Nanoscrolls are closely related to the much touted carbon nanotubes -- which may have numerous industrial applications -- but have significant advantages over them, said Lisa Viculis and Julia Mack, the lead authors of the Science article and graduate students in the laboratory of Richard B. Kaner, UCLA professor of chemistry and biochemistry.
"If nanotubes can live up to all their predicted promise, then we believe that we have a method for making analogous materials for a fraction of the cost," Mack said.
Nanotubes are pure carbon sheets in a tubular form, capped at each end. Viculis and Mack's carbon nanoscrolls are also pure carbon but the sheets are curled up, without the caps on the ends, potentially allowing access to significant additional surface area. While nanotubes are normally made at high temperatures, nanoscrolls can be produced at room temperature.
"Our method involves scrolling sheets of graphite, which could give us a much higher surface area," Viculis said.
"If we can access the entire surface area on both sides of the carbon sheets -- unlike with carbon nanotubes, where only the outside surface is accessible -- then we could adsorb twice the amount of hydrogen -- an enormous increase," Mack said, "improving on hydrogen storage for fuel (an alternative to fossil fuels)."
"Nanoscrolls can be made by a relatively inexpensive and scalable process at low temperatures," Mack said. "Our starting materials are just graphite and potassium metal. The idea is beautiful in its simplicity."
"Carbon surfaces are known to adsorb hydrogen. A difficulty with using hydrogen as a fuel source for cars, instead of gas, is obtaining a material capable of storing enough hydrogen to make the approach feasible," Viculis said.
"Carbon nanoscrolls could make pollution-free, hydrogen-powered cars better than they would otherwise be," said Kaner, the third co-author on the Science paper. "This research is a good start. We have a long way to go. For this approach to work well, we need to get down to individual carbon layers, and we are not there yet. On average, the nanoscrolls are 40 layers thick. We have not yet realized the full surface area or all the properties we are after. The challenge is to reduce the nanoscrolls to individual layers. We have many good leads, and have started new collaborations."
The research may lead to numerous applications.
"For electronic applications, nanotubes may work well," Kaner said. "For applications where high surface area is important -- such as hydrogen storage, or energy storage in super-capacitors -- these nanoscrolls may be better."
Other possible applications for nanoscrolls, Kaner said, include lightweight but strong materials for planes and cars, and improved graphite-based tennis rackets and golf clubs.
The use of nanoscrolls for energy storage is especially interesting. Liquifying hydrogen requires considerable energy expenditure to cool it and also requires extremely well insulated tanks to hold it. But gaseous hydrogen takes up too much space. If nanoscrolls could be used either to store hydrogen densely at room temperature or to make a better kind of battery then they'd be very attractive.
|Share |||Randall Parker, 2003 March 07 10:57 AM Nanotech Advances|