"I admit it does sound crazy," says Michael Wong of his idea to use gold to clean up toxic waste. Wong plans to combine gold with palladium—an even more precious metal—to treat polluted groundwater beneath waste dumps and contaminated factories and military sites. "It not only works faster [than current methods], but a hundred times faster," Wong says, "and I bet it will be cheaper too."
A golden detergent? Here is Wong's trick: he creates nanoparticles of gold. In his realm, the work product is measured not in carats but in atoms. A thimbleful of coffee-colored solution contains 100 trillion gold spheres—each only 15 atoms wide, or about the width of a virus. Upon every golden nanosphere, Wong and his team dust a dash of palladium atoms. Think of an infinitely small ice-cream scoop flecked with sprinkles.
The 35-year-old Caltech and MIT graduate says he had not given toxic waste much thought until three years ago when one of his colleagues at Rice University (where he is a recently tenured professor of chemical engineering) came to him and said, "I have a problem," meaning something interesting to work on.
The problem concerned the suspected carcinogen trichloroethene, or TCE, "one of the most ubiquitous pollutants out there," says Wong, and "a really nasty molecule." The clear, sweet-smelling solvent has been used for decades to degrease metal parts in factories and government facilities. "It's everywhere," Wong adds. "We used TCE in our own labs." NASA assembly plants are contaminated with it, as are some of the most advanced research laboratories in the nation. The Environmental Protection Agency says 60 percent of Superfund cleanup sites harbor TCE; the Department of Defense says 1,400 of its facilities do. Estimated cleanup costs run to $5 billion just for the Defense sites.
TCE lingers like a bad houseguest, especially if handled carelessly. It accumulates in soil and can persist for years in groundwater. In a report last year, the National Research Council found that TCE was a potential cause of kidney cancer; it's also associated with liver problems, autoimmune disease and impaired neurological function.
Currently, the most common method of removing TCE from groundwater is to "pump and treat," Wong says—to pump the water out of the ground and run it through a filter made of activated carbon. ("Think of it as a big Brita water filter," he says.) The carbon grains soak up TCE like a sponge, but the process leaves behind TCE-laden filters that have to be stored or burned. "So you haven't really gotten rid of anything," Wong says. "You've just moved it from one place to another."
This is where Wong comes in. He began thinking about using nanoparticles as a catalyst to react with the TCE and break it down into what he calls "happy byproducts."
From the scientific literature, Wong knew that palladium had shown some promise at deconstructing TCE. "Palladium works OK, but it didn't work hard enough," Wong says. So he and his team began trying
various recipes, and after six months reached a eureka moment when they sculpted a palladium-covered core of gold atoms.
"We didn't believe it at first, because the gold-palladium nanoparticles were just so much more efficient—like, a hundred times more efficient," he says. "You see, gold itself doesn't do anything to TCE." But something very interesting happens at the interface where gold, palladium and TCE meet.