Fellow: Sita Krajangpan
Advisor: Achintya Bezbaruah, Ph.D., Assistant Professor, Department of Civil Engineering, North Dakota State University.
Co-Advisor: Bret Chisholm, Senior Research Scientist, Center for Nanoscale Science and Engineering and Adjunct Professor, Polymers and Coatings, North Dakota State University.
Matching Support: North Dakota State University.
Degree Progress: Ph.D. in Environmental Engineering expected in Spring 2009.

Project Background:

Zero-valent iron nanoparticles (nZVI) have been used for groundwater remediation of various contaminants because of their unique physiochemical properties. Various chlorinated aliphatic hydrocarbons, explosives, and metals have been successfully decontaminated with nZVI. However, nZVI are not only highly reactive with the contaminants, but also rapidly react with surrounding media in the subsurface (dissolved oxygen and/or water) and other non-target compounds. Thus, significant loss of nZVI reactivity occurs before the particles reach the target contaminants. Additionally, strong magnetic interactions between particles cause agglomeration, limiting colloidal stability and reduction in reactive surface area. For nZVI to effective, the particles should remain dispersed, protected from non-target compounds, and suspended for longer time. The inherent problems associated with bare nZVI can be overcome by designing a delivery vehicle. Considering the requirements of an effective delivery vehicle for nZVI, functionalized amphiphilic polysiloxanes are an ideal class of polymers for this application. Amphiphilic polysiloxane graft co-polymers (APGC) have been synthesized by hydrosilylation of hydride-functional polysiloxanes, poly ethylene glycol ( PEG) and tert-butyl acrylate (tBA) (supported by 2007 NDWRRI fellowship). The water-soluble grafts, PEG, allow for dispersibility and colloidal stability in an aqueous medium. The hydrophobicity of the polysiloxane polymer backbone protects the nZVI from excessive oxidation by creating a barrier to water while also creating an affinity of the coated nZVI for the water/contaminant interface. The polymer also readily allows permeation of contaminants to the nZVI surface.

The present research is in continuation of the work proposed for the 2007 NDWRRI program.

Project Objectives:

1. Synthesize and characterize the nZVI using transmission electron microscopy (TEM), scanning electron microscopy with Energy Dispersive Spectroscopy or X-ray microanalysis ( SEM/ EDS), X-ray diffraction (XRD), and BET surface area analysis. Completed.
2. Synthesize APGC by hydrosilylation and characterize the APGC using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy techniques. Completed.
3. Study colloidal stability of APGC coated nZVI and compare with uncoated (bare) nZVI. Completed.
4. Compare the degree of oxidation of APGC coated and bare nZVI by non-target compounds. In progress.
5. Study of reaction kinetics for APGC coated nZVI mediated degradation of various contaminants [As, TCE and RDX] and compare with bare nZVI. In progress.
6. Identification of As, TCE, and RDX degradation by-products. Inductively coupled plasma mass spectroscopy (ICP-MS), gas chromatography (GC), and High performance liquid chromatography (HPLC), respectively, will be used in As, TCE, and RDX studies. In progress.

Progress:

APGC, nZVI, and APGC coated nZVI are successfully synthesized and characterized. The colloidal stability studies of APGC coated nZVI and comparison with bare nZVI (proposed in the 2007 NDWRRI program) are completed. The batch experiments for kinetic analyses of groundwater contaminant (As, TCE, and RDX) degradation are in progress and expected to be completed by the end of 2008. The preliminary results are encouraging. The effectiveness of the new co-polymer in protecting the nZVI from oxidation by non-target compounds is being investigated. A provisional patent on the new nZVI delivery vehicle has been granted by the United States Patent and Trademark Office. A manuscript (base on the work done so far) is under preparation and will be submitted shortly to a peer reviewed journal

Research Outcomes:

         Krajangpan, S. , Jarabek, L., Jepperson, J., Chisholm, B., Bezbaruah, A. September 7 2007. Protecting Iron Nanoparticles from Oxidation by Non-target Compounds and Their Effective Subsurface Delivery Using Amphiphilic Polysiloxane Graft Copolymers, ND/SD ESPCoR 6th Biennial Joint Conference 2007, Fargo, ND. [Poster]

         Krajangpan, S. , Chisholm, B., Bezbaruah, A., December 11 2007. Comparative Studies of Colloidal Stability of Bare and Amphiphilic Polysiloxane Graft Copolymer Coated Iron Nanoparticles and Their TCE Degradation Kinetics. ISNEPP 2007 Nanotechnology in Environmental Protection and Pollution, Ft. Lauderdale, FL. [Presentation]

         Krajangpan, S., Elorza, J., Bezbaruah, A., Khan, E., Chisholm, B., December 11 2007. Nitrate Removal by Zero-Valent Iron Nanoparticles Entrapped in Calcium Alginate. ISNEPP 2007 Nanotechnology in Environmental Protection and Pollution, Ft. Lauderdale, FL. [Presentation]

         Krajangpan, S., Jarabek, L., Jepperson, J., Chisholm, B., Bezbaruah, A. April 10 2008 The Use of Multifunctional Polymers to Effective Deliver Iron Nanoparticles to Subsurface Contaminants. 235th ACS National Meeting, New Orleans, LA. [Poster]

Significance:

Successful development of a delivery vehicle for iron nanoparticles will have broader ramifications in the field of groundwater remediation. The synthesis, characterization, and analysis phases of the polymeric delivery vehicle development process have and will result in fundamental knowledge on the behavior of the polymer coated nanoparticles. Kinetic studies for As/ TCE/ RDX will help us in quantifying the advantages and disadvantages of using polymer coated iron nanoparticles for remediation. Identification and analysis of degradation by-products will also help in identifying future research directions in this area. The results of this research will be useful for the pilot tested to create a reactive barrier/wall to contain the arsenic trioxide plume in southeast North Dakota. The results from this project will stimulate further research for the development of target specific delivery vehicles for contaminants of environmental concern.