"The advantages of palladium-based trichloroethene remediation are well-documented, but so is the cost," said Michael Wong of Rice University. "Using nanotechnology, we were able to maximize the number of palladium atoms that come into contact with trichloroethene molecules and improve efficiency by several orders of magnitude over bulk palladium catalysts."
Palladium catalyzes the hydrodechlorination of trichloroethene in water at room temperature and in the presence of hydrogen. The reaction produces ethane without the formation of vinyl chloride and other toxic chlorinated intermediates. Alternative trichloroethene treatment techniques such as bioremediation or reduction by iron nanoparticles can lead to the temporary creation of vinyl chloride, which is actually more toxic than trichloroethene.
The researchers found that palladium-coated gold nanoparticles were more active catalysts for breaking down trichloroethene than either palladium nanoparticles, alumina-supported palladium or palladium powder (in the form of palladium black). Gold nanoparticles that were only partially coated with palladium proved the most effective of all. Since palladium is a costly material, increasing its efficiency is obviously of considerable benefit.
Trichloroethene is used as a solvent to degrease metals and electronics parts. It is one of the most common organic pollutants in US groundwater. Exposure to the chemical is believed to cause liver damage, impaired pregnancies and cancer.
"The next step is engineering a system that will allow us to get at the polluted groundwater," said Joe Hughes of Georgia Institute of Technology. "The scale of trichloroethene contamination is enormous, so any new scheme for trichloroethene remediation has got to clean large volumes of water very quickly for just a few pennies."
The team plans to put a catalytic membrane of the gold-palladium nanoparticles inside a cylindrical pump. The pump could sit at the bottom of existing wells, continuously pumping and removing trichloroethene from water. This would eliminate drilling costs for new wells, energy costs for lifting water to the surface and construction costs for surface treatment facilities.
The researchers will report their work in Environmental Science and Technology.