A CBET Nugget
Notable Accomplishments from CBET Awards
 

Environmental Protection by Targeted Delivery of Nanoparticulate Iron

Robert D. Tilton, Carnegie Mellon University

Background:  This research focuses on efficient remediation of groundwater contaminated by chlorinated organic compounds, with new technologies that work at the source of the contamination. Typically denser than water and only sparingly soluble in water, chlorinated organic compounds migrate downward in aquifers due to gravity and accumulate as saturated pools and ganglia trapped in the microporous soil. Leaching from these trapped sources creates long-lived plumes carried by the groundwater flow.  Zero valent iron has a known ability to reduce chlorinated organic compounds to less toxic compounds.  This research group has synthesized novel copolymers that adsorb to iron nanoparticles, to promote nanoparticle transport through aquifers, and cause them to accumulate in the contaminant source zone.  By concentrating the reactive nanoparticles directly in the source zone, decontamination rates will be significantly faster than current technologies allow.

Methodology:  Linear triblock copolymers consisting of poly(methacrylic acid), poly(methyl- or butyl-methacrylate) and poly(styrenesulfonate) were synthesized to achieve precise control over the relative sizes of the three blocks.  The poly(methacrylic acid) block causes the iron nanoparticles to be “sticky” to the organic contaminant.  The poly(styrenesulfonate) block provides strong repulsive forces to stop the nanoparticles from sticking to each other and to the minerals in the groundwater.  The poly(methyl- or butyl-methacrylate) block is designed to swell the nanoparticles when they contact the chlorinated organic phase.  Experiments were conducted to test the ability of polymer-coated iron nanoparticles to travel through sand columns and to adsorb to water/chlorinated organic compound interfaces.

Results:  The triblock copolymers achieved the objectives of transporting nanoparticles to the contaminants and sticking them to the contaminant surfaces.  The triblock copolymer-modified iron nanoparticles were extremely effective in removing the organic compounds, producing trichloroethylene-in-water emulsions that were stable for at least 6 months.  This demonstrated that the polymer-coated nanoparticles could be used for removing organic contaminants from groundwater.


Robert Tilton Image 1   Robert Tilton Image 2

Inefficient transport of particles
causes clogging so that the
contaminants cannot be removed.
  The polymer coatings on the nanoparticles anchor them to oil/water interface as demonstrated in this emulsion.
 
Credit:  Robert D. Tilton, Carnegie Mellon University


Scientific Uniqueness:  Without surface modification, zero valent iron nanoparticles are insufficiently mobile in saturated soils to provide source zone remediation of groundwater contamination by chlorinated organic compounds.  This research program has developed polymeric surface modifiers that not only enhance zero valent iron nanoparticle transport by minimizing particle aggregation and adhesion, but also provide the novel capability of accumulating in the contaminant source zone by anchoring the particle at the contaminant/water interface.  It does so by virtue of a polymer block that responds to the interface by swelling into the organic phase.

Impact on Industry and/or Society:  These polymers have the properties needed to deliver remediation chemistry directly to underground pools of chlorinated organic contaminants in groundwater.  Providing such source zone remediation has the potential to significantly reduce the total time and operating expense to meet cleanup targets, compared to current technologies that emphasize plume remediation.  Faster remediation promises diminished ecological damage and human exposure risk.  The high emulsifying power observed for nanoparticles stabilized by the newly developed triblock copolymers suggests new classes of particulate emulsifiers for emulsion technology in general, providing ancillary benefits to industries as diverse as personal care products or oil recovery.

Work is notable because it exploits the unique ability of atom transfer radical polymerization to precisely synthesize polymers whose composition is designed according to the principles of electrosteric colloidal stabilization and block copolymer adsorption, in order to provide nanoparticle transport and adsorption properties that are needed to achieve specific objectives for source zone environmental contaminant remediation.

This Work is multidisciplinary.  The conception and execution of the project was based on close collaboration among a chemical engineer with particular experience in colloid and interface science, a chemist with particular experience in polymer synthesis, and an environmental engineer with particular experience in chlorinated organic contaminant remediation.  The graduate student supported by this grant has learned to integrate the unique capabilities provided by each of these disciplines into a functional project.

This work strongly addresses the goals of the NSF Strategic Plan 2006-2011 in the following ways:

- - Primary Strategic Outcome Goal:  Discovery (Foster research that will advance the frontiers of knowledge, emphasizing areas of greatest opportunity and potential benefit and establishing the national as a global leader in fundamental transformational science and engineering.):  This work is at the forefront of discovering new techniques and mechanisms for interaction of nanoparticle iron and organic materials as well as the mixing and emulsification required to remove the organics from contaminated groundwater.

- - Secondary Strategic Outcome Goal:  Learning (Cultivate a world-class, broadly inclusive science and engineering workforce, and expand the scientific literacy of all citizens.):  The multidisciplinary approach fostered by the research team will equip the graduate students with the tools and skills to work collaboratively with scientists, engineers and environmentalists.  Results from this project will be used to enhance graduate and undergraduate curricula to ensure that the most current up-to-date material is presented to the future workforce.

This work represents transformative research.  Remediation of contaminated sites could be transformed to an in-situ approach eliminating the need for removal and transportation of contaminated groundwaters.



     
Program Officer:   Judy Raper
     
NSF Award Number:   0521721
     
Award Title:   Development of a Copolymer-Based System for Targeted Delivery of Nanoparticulate Iron to Environmental Non-Aqueous Phase Liquids
     
PI Names:   Robert D. Tilton
     
Institution Name:   Carnegie Mellon University
     
Program Element:   1415
     

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This Nugget was Updated on 16 January 2007.