Intellectual Merit. Organic contamination of subsurface soil and groundwater is an extensive and vexing environmental problem that stands to benefit from nanotechnology. The Environmental Protection Agency reports that contamination by organic pollutants, especially chlorinated volatile organic compounds, are primary concerns at over half of the Superfund National Priorities List sites [Common Chemicals Found at Superfund Sites, U.S. E.P.A., 2003]. Health risks associated with these compounds have led to an extensive, but relatively unsuccessful, remediation effort for the past 30 years. The limited success of past remediation efforts is primarily because most organic pollutants have limited solubility in water and tend to remain as a separate non-aqueous phase liquid (NAPL) in the subsurface. Residual NAPL pools act as long-term sources for contaminant leaching to the groundwater, resulting in large plumes of dissolved contaminants and very long remediation times.
Prior research indicates that suspended iron nanoparticles react with NAPLs to convert them to non-toxic products. The major goal of this proposal is to develop and optimize polymer assemblies that preferentially target iron-containing nanoparticles to the NAPL-water interface, so the remediation activity can be concentrated at the NAPL source. The research focuses on the interfacial behaviors that are required to successfully develop a targeted nanoparticle delivery system. The polymers are designed to be multifunctional - they disperse the iron nanoparticles into water for good aqueous transportability through porous media, minimize undesirable adsorption to mineral and natural organic matter (NOM) surfaces, and preferentially anchor nanoparticles to accumulate at the NAPL/water interface. Experimental metrics include the polymers' effects on colloidal stability, transport through porous sand columns, adsorption to model mineral and NOM surfaces, and partitioning to the NAPL/water interface. The composition and architecture of the block copolymers will be systematically varied. Use of controlled radical polymerization schemes will provide tight control over block lengths. Finally, two modes of polymer attachment to the nanoparticle will be compared - physisorption of soluble block copolymers and block copolymer grafting from nanoparticle surfaces.
Broader Impact. Several decades are typically required to reach NAPL cleanup targets using the prevailing "pump-and-treat" technologies, because they address primarily the NAPL plume, not the source. Accordingly, the Department of Energy currently advocates the development of novel in situ technologies to remediate its contaminated sites [Guidance for Optimizing Ground Water Response Actions at Department of Energy Sites, U.S. D.O.E. Office of Environmental Management, 2002]. The proposed nanoparticle system is envisioned as the basis for a new in situ remediation technology with the potential to accelerate cleanup by directly targeting remediation action to the source, rather than the plume.
One Ph.D. student will receive research training through this grant. Further educational benefits will accrue through the involvement of undergraduate students in the conduct of the research, especially by leveraging Carnegie Mellon's Summer Institute for Minority Undergraduate Students. Participating students and faculty will prepare hands-on "smart polymer" and "nanotechnology in the environment" modules for Carnegie Mellon's Engineering Your Future program that increases technology awareness among female high school students in the Pittsburgh area.
