“Very few technologies are capable of locating and destroying dense non-aqueous phase liquids (DNAPLs) trapped in the subsurface,” Greg Lowry of Carnegie Mellon University told nanotechweb.org. “Often contamination is in very small pores in the soil matrix and difficult to access. We were inspired by targeted drug delivery methods that use thermodynamic or chemical affinity to get specific drugs to target organs and/or tissues.”
Lowry and colleagues used nanoparticles with an iron core and a shell made up of several types of polymer, including an inner shell of hydrophobic poly(methyl methacrylate) (PMMA) and an outer hydrophilic coating of sulphonated polystyrene. The hydrophilic coating made the nanoparticles soluble in water, while the hydrophobic layer gave them an affinity to the trichloroethylene. The iron core of the nanoparticle reacted with the trichloroethylene and dechlorinated it, decomposing the pollutant into non-toxic materials.
“The nanoparticles, at roughly 50-100 nm, are small enough to be transported in the aquifer and to access DNAPL trapped in very small pores,” said Lowry. “The novel polymer shells - amphiphilic block copolymers - provide charge stabilization of the particles, which allows them to transport in the aquifer and also the affinity to the hydrophobic DNAPL. The particles essentially home in on their target by themselves once introduced into the subsurface.”
The researchers believe they could target other subsurface contaminants simply by changing the reactive core and polymer shells. “One could imagine delivering agents to set up an impermeable barrier at a specific location in the subsurface,” added Lowry. “This may come in handy to control the lateral spread of carbon dioxide injected into deep saline aquifers.”
The team is currently 18 months into a three-year $1.7 m study. At the end of this period the scientists plan to test the technology at a DNAPL-contaminated aquifer in the US or in a controlled large tank experiment.
The researchers reported their work at the American Chemical Society meeting in the US.