Researchers at Rice University have successfully conducted side-by-side tests involving palladium-gold nanoparticles and iron catalysts for removing Trichloroethene (TCE) from groundwater and have discovered palladium-gold to perform billion times faster than iron.
Lead author, Michael Wong(Credit: Rice University)
TCE is a carcinogenic substance that is used as a solvent and chemical degreaser and is a common contaminant of groundwater. The TCE molecule has a stable structure comprising three chlorine atoms and two carbon atoms making it an industrial user’s dream and an environmental engineer’s nightmare. Preferred methods of TCE clean-up are carbon adsorption and air-stripping which physically eliminate TCE from water rather than breaking the bonds. But these are expensive methods albeit being easy to implement. In the U.S, the Pentagon pegs the cost of TCE elimination from ground water in U.S. military bases at $5 billion.
Researchers have identified pure palladium and pure iron as successful candidates capable of breaking down TCE into nontoxic constituents. Palladium acts as a catalyst for reactions that subsequently break up the carbon-chlorine bonds. Iron causes deterioration of TCE while it gets corroded in water. Use of iron may at times lead to formation of harmful byproduct, vinyl chloride. Palladium has been largely limited to research trials due to the expenses involved. While it has been established that palladium and palladium-gold are quicker than iron, there has been no effort in the past to test the two materials side-by-side for comparison.
Rice University researchers led by Professor Michael Wong ran parallel tests on six different formulations of iron and palladium. Two of these were iron nanoparticles; two were palladium nanoparticles including the palladium-gold nanoparticle developed by Wong in 2005 and the final two were powdered samples of palladium-aluminum oxide and iron. The results of the tests showed that palladium catalysts took less than 15 minutes to breakdown 90% of TCE while the iron nanoparticles took 25 hours each. Wong’s expectation of the test results is to aid in the cost comparison of catalyst-based TCE treatment methods.