Grantee Research Project Results
2004 Progress Report: Developing Functional Fe(0)-based Nanoparticles for In Situ Degradation of DNAPL Chlorinated Organic Solvents
EPA Grant Number: R830898Title: Developing Functional Fe(0)-based Nanoparticles for In Situ Degradation of DNAPL Chlorinated Organic Solvents
Investigators: Lowry, Gregory V. , Matyjaszewski, Krzysztof , Majetich, Sara A. , Tilton, Robert D.
Institution: Carnegie Mellon University
EPA Project Officer: Aja, Hayley
Project Period: May 1, 2003 through October 31, 2007
Project Period Covered by this Report: May 1, 2004 through October 31, 2005
Project Amount: $358,000
RFA: Environmental Futures Research in Nanoscale Science Engineering and Technology (2002) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
The project premise is that the surfaces of reactive Fe0 nanoparticles can be modified by amphiphilic block copolymers to be transportable in water through a porous matrix, to preferentially partition at a dense nonaqueous phase liquid (DNAPL)-water interface, and to degrade DNAPL to non-toxic products. Specific project objectives are to: (1) demonstrate the ability to provide targeted delivery of reactive nanoparticles to the DNAPL-water interface in saturated porous media; (2) increase the DNAPL degradation efficiency relative to unmodified particles; and (3) retain reactive particles at the DNAPL-water interface long enough to be fully utilized.
Progress Summary:
Nanoparticle Synthesis
Two iron nanoparticles were investigated, Reactive Nanoscale Iron Particles (RNIP; Toda American, Inc.) and Fe0 nanoparticles (Fe(B)) synthesized in our laboratory using aqueous sodium borohydride reduction of dissolved iron. RNIP particles are synthesized commercially by reduction of Fe-oxides in H2 gas. The particle size and N2-BET surface area of each particle are similar. The primary difference between the particle types is their degree of crystallinity. The amorphous nature of Fe(B) makes it more reactive with trichloroethylene (TCE) and with water (see below).
Implications. Commercially available RNIP appears to have the desired reactivity with chlorinated solvents and a low rate of oxidation by water. Particles synthesized by the reduction of Fe-oxides are preferable to those synthesized by borohydride reduction of dissolved Fe(II) because they remain reactive for longer.
Polymer Synthesis and Surface Modification
Polymer and Nanoparticle-Polymer Synthesis. Poly(methyl methacrylate) (PMMA) is a good candidate for the hydrophobic blocks. Sulfonated polystyrene (PSS) is a good hydrophilic block because of its high water solubility and degree of charge. A ratio 1/5-1/10 between hydrophobic and hydrophilic blocks is sufficient to provide water solubility of the hybrid nanoparticles. Nanoiron with an amphiphilic polymer shell (~2 mg/m2) was synthesized. It is water soluble and forms more stable particle suspensions than bare nanoiron.
Implications. Polymers adsorb fairly strongly (steep isotherm) to the iron surfaces in sufficient quantity to stabilize nanoparticle suspensions in water. Therefore, it is possible to modify the iron particle surfaces to provide them with NAPL-water targeting ability.
Nanoparticle Characterization
Particle Size Distributions. The polymer-modified RNIP showed a bimodal distribution of sizes, with the majority of particles having average particles diameters between 20-100 nm.
DNAPL-Water Partitioning. In emulsification studies, PSS-coated silica particles and nanoiron coated with PMAA42-b-PMMA26-b-PSS466 both demonstrated their ability to preferentially locate at the NAPL-water interface.
Implications. The PMAA42-PMMA26-PSS466 triblock polymer-modified nanoiron and PSS-grafted particles can target the TCE/water interface ex situ. Their ability to target the interface and their small size suggests that in situ targeting is possible and that an inexpensive PSS polymer may provide targeting of the NAPL-water interface.
Nanoparticle Reactivity
Fe(B) is highly reactive and transformed TCE into ethane (80%) and C3-C6 coupling products with a surface-area normalized rate constant that is approximately 4-fold higher than RNIP. All Fe0 in Fe(B) was accessible for TCE dechlorination. The amorphous nature of Fe(B) enabled it to activate H2 and use it for TCE hydrodechlorination, and is responsible for the very high reactivity of these particles. RNIP particles yielded acetylene under iron-limited conditions and ethylene using excess iron. Some Fe0 in the RNIP particles was unavailable for TCE dechlorination and remained in the particles. Adsorbed polymers did not lower the particle reactivity by more than a factor of 4.
Implications. Although more reactive, Fe(B) particles generate H2 quickly in water and have a limited lifetime. RNIP is more stable in water and has a longer lifetime. The efficiency of the RNIP particles is comparable with that of Fe(B) particles in terms of TCE degraded by unit mass of Fe0 because of the less saturated reaction products formed.
Transport
Transport studies conducted in laboratory columns demonstrated that less than 5 percent of unmodified nanoiron could be transported through 10 cm of a water-saturated porous media at a concentration of 3 g/L. Greater than 98 percent of the polymer-modified nanoiron was able to be transported through the same column indicating that the surface modifications can enhance transportability significantly. The enhancement was attributed to the higher surface charge of the modified nanoiron and the ability of the modified particles to resist flocculation.
Implications. Surface modification can enable nanoparticle transport in groundwater aquifers. This makes it possible to deliver reactive nanoparticles to subsurface contaminants, but also highlights the need to control the migration of these particles once released into the subsurface, as the health effects of these particles have not yet been established.
In Situ NAPL Targeting
A preliminary experiment in 2-D flow cell showed polymer-modified nanoiron aggregating near entrapped NAPL in the cell. Nanoiron was not retained in regions of the cell without NAPL.
Implications. This preliminary experiment suggests that polymer-modified nanoiron may have the ability to target entrapped NAPL in situ under flow conditions expected in natural aquifers, but more experiments are necessary to verify the hydrogeochemical conditions conducive to targeting.
Future Activities:
We will continue column experiments to understand the effects of geochemistry and hydrodynamics on the transportability of nanoiron and the ability to target NAPL in situ. We also will investigate the effect of geochemistry on the reactivity on RNIP.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 75 publications | 13 publications in selected types | All 11 journal articles |
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Liu Y, Majetich SA, Tilton RD, Sholl DS, Lowry GV. TCE dechlorination rates, pathways, and efficiency of nanoscale iron particles with different properties. Environmental Science & Technology 2005;39(5):1338-1345. |
R830898 (2003) R830898 (2004) R830898 (2005) R830898 (Final) |
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Liu Y, Choi H, Dionysiou D, Lowry GV. Trichloroethene hydrodechlorination in water by highly disordered monometallic nanoiron. Chemistry of Materials 2005;17(21):5315-5322. |
R830898 (2004) R830898 (2005) R830898 (Final) |
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Saleh N, Sarbu T, Sirk K, Lowry GV, Matyjaszewski K, Tilton RD. Oil-in-water emulsions stabilized by highly charged polyelectrolyte-grafted silica nanoparticles. Langmuir 2005;21(22):9873-9878. |
R830898 (2004) R830898 (2005) R830898 (Final) |
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Sarbu T, Lin K-Y, Ell J, Siegwart DJ, Spanswick J, Matyjaszewski K. Polystyrene with designed molecular weight distribution by atom transfer radical coupling. Macromolecules 2004;37(9):3120-3127. |
R830898 (2004) R830898 (2005) R830898 (Final) |
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Supplemental Keywords:
groundwater, VOC, trichloroethylene, TCE, NAPL, subsurface remediation, catalysis, zero valent iron, palladium, block copolymers, environmental chemistry, environmental engineering, source zone remediation, nanotechnology, reductive dechlorination, bimetallic particles, interdisciplinary research,, RFA, Scientific Discipline, TREATMENT/CONTROL, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Sustainable Industry/Business, Sustainable Environment, Environmental Chemistry, Remediation, Technology, Restoration, Technology for Sustainable Environment, New/Innovative technologies, Chemistry and Materials Science, Environmental Engineering, Engineering, Chemistry, & Physics, Aquatic Ecosystem Restoration, waste reduction, in situ remediation, DNAPL, remediation technologies, nanotechnology, environmental sustainability, reductive degradation of hazardous organics, environmentally applicable nanoparticles, aquifer remediation design, groundwater remediation, acuatic ecosystems, degradation rates, sustainability, reductive dechlorination, hazardous organics, groundwater contamination, innovative technologies, pollution prevention, contaminated aquifers, reductive detoxification, recycleRelevant Websites:
http://www.ce.cmu.edu/~glowry/ Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.