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New research from Rice University's Center for Biological and Environmental Nanotechnology finds that nanoparticles of gold and palladium are the most effective catalysts yet identified for remediation of one of the nation's most pervasive and troublesome groundwater pollutants, trichloroethene or TCE. The research, conducted by engineers at Rice and the Georgia Institute of Technology, will appear next month in the journal Environmental Science and Technology, a publication of the American Chemical Society.
Tiny Particles Could Solve Billion-Dollar Problem
Bimetallic Nanoparticles Break Down TCE 100 Times Faster Than Bulk Catalysts
Houston, TX | February 23, 2005
New research from Rice University's Center for
Biological and Environmental Nanotechnology finds that nanoparticles of gold
and palladium are the most effective catalysts yet identified for
remediation of one of the nation's most pervasive and troublesome
groundwater pollutants, trichloroethene or TCE.
The research, conducted by engineers at Rice and the Georgia Institute of
Technology, will appear next month in the journal Environmental Science and
Technology, a publication of the American Chemical Society.
"The advantages of palladium-based TCE remediation are well-documented, but
so is the cost," said lead researcher Michael Wong, assistant professor of
chemical engineering and chemistry at Rice. "Using nanotechnology, we were
able to maximize the number of palladium atoms that come in contact with TCE
molecules and improve efficiency by several orders of magnitude over bulk
TCE, which is commonly used as a solvent to degrease metals and electronic
parts, is one of the most common and poisonous organic pollutants in U.S.
groundwater. It is found at 60 percent of the contaminated waste sites on
the Superfund National Priorities List, and it is considered one of the most
hazardous chemicals at these sites because of its prevalence and its
toxicity. Human exposure to TCE has been linked to liver damage, impaired
pregnancies and cancer.
Cleanup costs for TCE nationwide are estimated in the billions of dollars.
The Department of Defense alone estimates the cost of bringing its 1,400
TCE-contaminated sites into EPA compliance at more than $5 billion.
The typical approach to getting rid of TCE involves pumping polluted
groundwater to the surface, where it can be exposed to chemical catalysts or
microorganisms that break the TCE down into less toxic or non-toxic
constituents. In general, chemical catalysis offers faster reactions times
than bioremediation schemes but also tends to be more expensive.
One of the major advantages of using palladium catalysts to break down TCE
is that palladium converts TCE directly into non-toxic ethane. By contrast,
breaking down TCE with more common catalysts, like iron, produces
intermediate chemicals, like vinyl chloride, that are more toxic than TCE.
In the CBEN experiments, Wong and collaborators compared the effectiveness
of four varieties of palladium catalysts: bulk palladium, palladium powder
on an aluminum oxide support base, pure palladium nanoparticles and a hybrid
nanoparticle developed by Wong that consists of a gold nanoparticle covered
with a thin coat of palladium atoms.
As metal particles get progressively smaller, a higher percentage of the
atoms in the particle are found on the surface of the particle instead of
being locked away inside the metal where they cannot interact with other
chemicals. For example, in the bulk palladium, less than 4 percent of the
palladium atoms were on surface of the particle. Pure palladium
nanoparticles had 24 percent of the metal on the surface. In the
gold-palladium nanoparticles, 100 percent of the palladium atoms are
accessible for reaction.
"We've documented the efficiency of these catalysts in breaking down TCE,
and the next step is engineering a system that will allow us to get at the
polluted groundwater," said Joe Hughes, professor of civil and environmental
engineering at Georgia Institute of Technology and a co-leader of CBEN¹s
environmental research programs. "The scale of TCE contamination is
enormous, so any new scheme for TCE remediation has got to clean large
volumes of water very quickly for a just a few pennies."
Hughes, Wong and their collaborators hope to develop a device that would
include a cylindrical pump containing a catalytic membrane of the
gold-palladium nanoparticles. The device would be placed down existing wells
where it would pump water through continuously, breaking TCE into non-toxic
Cost is the primary hurdle to cleaning up TCE-polluted groundwater. CBEN's
team hopes to drive down costs by using every ounce of palladium to maximum
efficiency, and by eliminating drilling costs for new wells, construction
costs for surface treatment facilities and energy costs of lifting water to
Nanotechnology is critical to the scheme because only a nanoscale catalyst
will be efficient enough to provide the throughput needed to make the whole
approach effective. Tests in Wong's lab have found that the gold-palladium
nano-catalysts break TCE down about 100 times faster than bulk palladium
CBEN's research is funded by the National Science Foundation.
The Center for Biological and Environmental Nanotechnology is a National
Science Foundation Nanoscale Science and Engineering Center dedicated to
developing sustainable nanotechnologies that improve human health and the
environment. Located at Rice University in Houston, CBEN is a leader in
ensuring that nanotechnology develops responsibly and with strong public
For more information visit cben.rice.edu.
About Rice University
Rice University is consistently ranked one of America¹s best teaching and
research universities. It is distinguished by its: size - 2,850 undergraduates
and 1,950 graduate students; selectivity -10 applicants for each place in the
freshman class; resources - an undergraduate student-to-faculty ratio of
6-to-1, and the fifth largest endowment per student among American
universities; residential college system, which builds communities that are
both close-knit and diverse; and collaborative culture, which crosses
disciplines, integrates teaching and research, and intermingles
undergraduate and graduate work. Rice's wooded campus is located in the
nation's fourth largest city and on America's South Coast.
For more information visit www.rice.edu.
Copyright © Rice
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