Nano-Seeds Shown to Grow Pure Materials
HOUSTON, Texas, November 17, 2006
Rice University chemists today revealed the first method for cutting carbon nanotubes into "seeds" and using those seeds to sprout new nanotubes. They hope that seeded growth may one day produce the large quantities of pure nanotubes needed for innovative materials applications.
First discovered just 15 years ago, single-walled carbon nanotubes are molecules of pure carbon with many unique properties.
Smaller in diameter than a virus, nanotubes are about 100 times stronger than steel, weigh about one-sixth as much and are among the world's best electrical conductors and semi-conductors.
"Carbon nanotubes come in lots of diameters and types, and our goal is to take a pure sample of just one type and duplicate it in large quantities," said corresponding author James Tour, director of Rice's Carbon Nanotechnology Laboratory, CNL.
"We've shown that the concept can work," said Tour.
The challenge of making mass quantities of pure tubes is one of the major unachieved goals of nanoscience. But Tour may be up to the challenge. He is renowned as the inventor of nanocars, which he unveiled in 2005.
Tour says CNL founder and nanotube pioneer Richard Smalley, died in October 2005 after a long battle with leukemia. In the last two years of his life Smalley devoted much time and energy to seeded-growth nanotube amplification research.
"Rick was intent on using nanotechnology to solve the world's energy problems, and he knew we needed to find a way to make large quantities of pure nanotubes of a particular type in order to re-wire power grids and make electrical energy widely available for future needs," said Tour.
Nanotechnology makes possible the creation of materials with new properties, perhaps leading to new ways to make, transmit and store energy.
Smalley was winner of the 1996 Nobel Prize in Chemistry for the discovery of a structure of carbon atoms known as a "buckyball."
Smalley had a way of making things happen, Tour said, and for six months of 2004, there were at least 50 researchers in four Rice laboratories devoting their effort to this problem.
"It was unprecedented," said Tour, "and it paid off."
The nanotube seeds are miniscule - 200 nanometers long and one nanometer wide. A nanometer is one billionth of a meter - one ten-thousandth the diameter of a human hair, and a thousand times smaller than a single red blood cell.
Smalley's vision was "a revolutionary system like PCR [polymerase chain reaction] where very small samples could be exponentially amplified," Tour said. "We're not there yet."
CNL's team has yet to prove that the added growth has the same atomic architecture of the seeds, he explained, but the added growth had the same diameter as the original seed, indicating that the method is successful.
The nanotube seeds are about 200 nanometers long and one nanometer wide. After cutting, they were chemically modified.
Bits of iron were attached at each end, and a polymer wrapper was added that allowed the seeds to stick to a smooth piece of silicon oxide.
After burning away the polymer and impurities, the seeds were placed inside a pressure-controlled furnace filled with ethylene gas.
With the iron acting as a catalyst, the seeds grew spontaneously from both ends, growing to more than 30 times their initial length in just a few minutes.
The nano-seed demonstration involves single nanotubes, and Tour calls the yields "very low," but he is satisfied that the amplified growth route is demonstrated.
Ray Baughman at the University of Texas - Dallas said that Tourís team has made a host of seminal advances that are inspiring a legion of nanotechnologists to build upon them.
The research is slated to appear in an upcoming issue of the "Journal of the American Chemical Society."
In other Rice nano-news, the discovery of magnetic interactions between specks of rust is leading scientists at Riceís Center for Biological and Environmental Nanotechnology, CBEN, to develop a low cost technology for cleaning arsenic from drinking water.
CBENís technology is based on a newly observed magnetic interaction that takes place between particles of rust that are smaller than viruses, dubbed "nanorust."
The technology holds promise for millions of people in India, Bangladesh and other developing countries where thousands of cases of arsenic poisoning each year are linked to poisoned wells.
Center director and lead author Vicki Colvin said, "Arsenic contamination in drinking water is a global problem, and while there are ways to remove arsenic, they require extensive hardware and high-pressure pumps that run on electricity."
"Our approach is simple and requires no electricity," she said. "While the nanoparticles used in the publication are expensive, we are working on new approaches to their production that use rust and olive oil and require no more facilities than a kitchen with a gas cooktop."
The new technique was described in the November 10 issue of the journal "Science."