Principal Investigator Dr. Mamadou S. Diallo Department of Civil Engineering Howard University

1. Fe(0)/FeS Dendrimer Nanocomposites for Reductive Dehalogenation of Chlorinated Haliphatic Compounds: Synthesis, Characterization and Bench Scale Laboratory Evaluation of Materials Performance Principal Investigator Dr. Mamadou S. Diallo Department of Civil Engineering Howard University Co-Principal Investigators: Dr. Paul F. Hudrlik and Dr. Ann Hudrlik Department of Chemistry Howard University

2. Presentation Outline • Background • Objectives and Research Plan • Expected Results

3. Number of sites with contaminated groundwater: 300, 000 to 400, 000 Chlorinated haliphatic compounds (e. .g, PCE and TCE): among the 25 most commonly found contaminants at DOE, DOD and EPA Superfund Sites Chlorinated haliphatic compounds are not easily degraded to less toxic compounds in oxic environments. Chlorinated haliphatic compounds undergo rapid reductive transformations to less toxic products in an anoxic environment Reactive media that promote such transformations under reducing conditions are increasingly being used as functional materials to develop permeable reactive barriers (PRB) for groundwater remediation Background: National Research Council. Innovations in Groundwater and Soil Cleanup: From Concept to Commercialization. National Academy Press, Washington, D.C., 1997

4. Permeable Reactive Barrier Collection Trench w/ Impermeable Barrier Plumes Remediated Groundwater Water Table Reactor Cells w/ Reactive Media Flow Direction USDOE Rocky Flats Mound Site Plume, Tetra Tech EM, Inc. 1998

5. Reactive Medium of Choice for Remediation of Chlorinated Aliphatic Compounds: Zero Valent Iron (ZVI)

6. Reductive Dehalogenation of Chlorinated Aliphatic Compounds by Zero Valent Ironhttp://clu-in.org/conf/itrc/prb_031902 Fe0 = Fe+2 + 2e- 2H2O = 2H+ + 2OH- 2H+ + 2e- = H2(g) X-Cl + H+ + 2e- = X-H + Cl- C2HCl3 + 3H+ + 6e- = C2H4 + 3Cl-

7. Degradation Pathways of Chlorinated Haliphatic Compounds by Zero Valent IronLynn A. Robert et al. (1996), Env Sci. Technol Roberts, A. L., et. al, 1996 Reductive Elimination of Chlorinated Ethylene by Zero-Valent Metals. Environmental Science and Technology,

8. Limitations of Zero Valent Iron (ZVI) • Low surface area (5 m2/g) • Tendency to generate toxic by products such as vinyl chloride • Deposition of hydroxide precipitates • Buildup of biofilms • Limited delivery modes: e.g., cannot be delivered to DNAP pools

9. Project Objectives: Synthesis and Evaluation Fe(O)/FeS Dendrimer Nanocomposites Figure 3b

10. PAMAM Dendrimers with Ethylene Diamine Core and Terminal NH2 Groups: Will be Used to Prepare the Fe(0)/FeS Nanoparticles

11. Extent of Binding and Fractional Binding of Selected Metal Ions in Aqueous Solutions of G3 and G3.5 PAMAM Dendrimers

12. Expected Results • High surface area Fe(O)/FeS particles • Particle with tunable redox activity • Less tendency to generate toxic by products • More flexible delivery: e . g.,can be delivered to DNAPL pools

13. Permeable Reactive Barrier Construction: Conventional ExcavationandHigh Pressure Jetting

14. Acknowledgments • DOE HBCU-MI Environmental Technology Consortium (Funding) • EPA Star Grant (Partial Funding) • Howard University Keck Center for the Design of Nanomaterials for Molecular Recognition (Partial Funding)