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"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," said center
director and lead author Vicki Colvin. "Our approach is simple and
requires no electricity. 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."
CBEN's technology is based on a newly discovered magnetic interaction
that takes place between particles of rust that are smaller than
viruses.
"Magnetic particles this small were thought to only interact with a
strong magnetic field," Colvin said. "Because we had just figured out
how to make these particles in different sizes, we decided to study
just how big of magnetic field we needed to pull the particles out of
suspension. We were surprised to find that we didn't need large
electromagnets to move our nanoparticles, and that in some cases
hand-held magnets could do the trick."
The experiments involved suspending pure samples of uniform-sized iron
oxide particles in water. A magnetic field was used to pull the
particles to out of solution, leaving only the purified water.
Colvin's team measured the tiny particles after they were removed from
the water and ruled out the most obvious explanation: the particles
were not clumping together after being tractored by the magnetic field.
Colvin, professor of chemistry, said the experimental evidence instead
points to a magnetic interaction between the nanoparticles themselves.
Co-author Doug Natelson explains, "As particle size is reduced the
force on the particles does drop rapidly, and the old models were
correct in predicting that very big magnetic fields would be needed to
move these particles.
"In this case, it turns out that the nanoparticles actually exert
forces on each other," said Natelson, associate professor of physics
and astronomy and in electrical and computer engineering. "So, once
the hand-held magnets start gently pulling on a few nanoparticles and
get things going, the nanoparticles effectively work together to pull
themselves out of the water."
Colvin said, "It's yet another example of the unique sorts of
interactions we see at the nanoscale."
Because iron is well known for its ability to bind arsenic, Colvin's
group repeated the experiments in arsenic-contaminated water and found
that the particles would reduce the amount of arsenic in contaminated
water to levels well below the EPA's threshold for U.S. drinking water.
Colvin's group has been collaborating with researchers from Rice
Professor Mason Tomson's group in civil and environmental engineering
to further develop the technology for arsenic remediation. Colvin said
Tomson's preliminary calculations indicate the method could be
practical for settings where traditional water treatment technologies
are not possible. Because the starting materials for generating the
nanorust are inexpensive, she said the cost of the materials could be
quite low if manufacturing methods are scaled up. In addition,
Colvin's graduate student, Cafer Yuvez, has been working for several
months to refine a method that villagers in the developing world could
use to prepare the iron oxide nanoparticles. The primary raw materials
are rust and fatty acids, which can be obtained from olive oil or
coconut oil, Colvin said.
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