" Development of Polymer-Decorated Nanoparticles for Targeted Delivery of Remediation Agents to the Trichloroethylene/Water Interface"

Kevin Sirk (Advisor: Bob Tilton)

Dense non-aqueous phase liquids (DNAPL) are a persistent contamination problem at many of the Superfund sites across the country. Examples of DNAPL include dichloroethene (DCE), trichloroethylene (TCE), and carbon tetrachloride (CCl4). Current remediation technologies such as “pump and treat” methods only target the dissolved plume and not the source, so they tend to be inefficient, costly, and require decades of time to meet clean up requirements. The goal of this work is in situ delivery of nanoiron particles to the source contamination zone. Nanoiron refers to particles with an iron oxide shell and a reactive zero valent iron core that have been shown to reduce compounds like TCE into less toxic products, but delivering them to the source zone has been difficult due to colloidal instability and poor transport of these particles in groundwater environments. To overcome these difficulties and provide a means for these particles to accumulate at the DNAPL source zone, we are modifying the surfaces of these particles with environmentally responsive ABC triblock copolymers prepared by atom transfer radical polymerization (ATRP). A poly(methacrylic acid) “A block” anchors the polymers to the nanoiron surface. A poly(styrene sulfonate) “C block” disperses the nanoparticles in water and helps repel attachment to soil minerals and humic substances. A hydrophobic poly(methyl or butyl methacrylate) “B block” swells in contact with DNAPL and anchors the particles at the DNAPL/water interface.

Figure 1. ABC triblock: poly(methacrylic acid) left block, poly(methyl methacrylate) center block, poly(styrene sulfonate) right block. N,M,P are the degrees of polymerization for each block respectively.

Figure 2. The vial on the left is an unmodified nanoiron suspension. Most of the particles have settled out of suspension within minutes. The vial on the right is a nanoiron suspension with our triblock adsorbed to the surface of the particles. This suspension is stable for weeks.

One interesting result of this work is how well this polymer enhances the particle transport in porous media. We chose silica as the test media because it is the most abundant mineral in soil. We flowed suspensions of these particles through packed sand columns and compared the amount of iron eluted for both unmodified and polymer modified particles. The graph below shows that as you increase the nanoiron particle concentration, the amount of eluted iron decreases for the unmodified reactive nanoiron particles (RNIP), resulting in a plugged column. Particles with one of our triblocks adsorbed (PMAA48-PMMA17-PSS650, the subscripts are the degrees of polymerization for each block) to the surface show enhanced transportability at all particle concentrations.

Figure 3. Unmodified reactive nanoiron particle (RNIP) transport in a packed sand column vs. polymer modified RNIP. The highest particle concentration sample is a practical concentration needed for use in field applications.