Final Report: Magnetite Nanoparticles for Enhanced Environmental RemediationEPA Contract Number: EPD05027
Title: Magnetite Nanoparticles for Enhanced Environmental Remediation
Investigators: Hull, Matthew
Small Business: Luna Innovations Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2005 through August 31, 2005
Project Amount: $69,939
RFA: Small Business Innovation Research (SBIR) - Phase I (2005) RFA Text | Recipients Lists
Research Category: SBIR - Nanotechnology , Small Business Innovation Research (SBIR) , Nanotechnology
Luna Innovations Incorporated is developing commercial-scale suspensions of nanoscale magnetite (Fe3O4) particles for enhanced, reduced-cost remediation of contaminated groundwater. Magnetite nanoparticles are ubiquitous in the environment and can be found in weathered clays and soils, atmospheric aerosols, and recently deposited marine and freshwater sediments. Preliminary studies conducted by Luna Innovations indicate that, as a result of their small size, Fe3O4 nanoparticles have a reductive capacity that may be considerably higher than that of an equal mass of larger-sized particles. In addition, Luna Innovations attests that the potential importance of these particles as reductive components in anoxic subsurface environments has not been adequately recognized and that a detailed analysis of the activity of these particles is warranted. Luna Innovations will develop a strategic commercialization strategy to transition the magnetite nanoparticle technology to end users in the $8-$10 billion global remediation market. Penetration of this market requires advanced tools that can improve cost efficiency and enhance environmental remediation practices. Luna Innovations’ stabilized magnetite nanoparticle technology is responsive to those needs.
Recently, it has been shown that nanoscale iron can be used to reduce a wide variety of contaminants prioritized for remediation by federal agencies such as the U.S. Environmental Protection Agency, Department of Energy, and Department of Defense. These contaminants include chlorinated ethylenes, hexavalent chromium, and perchlorate. Reaction rates reported for nanoparticulate iron typically are two- to threefold greater than the reaction rates reported for granular irons (diameter approximately 1 to 2 mm). This disparity may be the result of size-mediated changes in surface reactivity. The original Phase I plan was to investigate the reactivity of magnetite nanoparticles toward a model contaminant, carbon tetrachloride (CT). The hypothesis was that as a direct result of their size, magnetite nanoparticles will exhibit reactivity that differs significantly from that of larger (greater than 100 nm diameter) bulk particles. To test this, Luna Innovations proposed to carefully synthesize monodisperse suspensions of Fe3O4 under anoxic conditions and then evaluate the reactivity of these suspensions toward CT in laboratory experiments. Finally, Luna Innovations planned to leverage its experience in nanomaterials development and manufacturing to refine the application of the nanoparticles for environmental remediation and to optimize the particle production process for commercial scale-up and field application during Phase II.
CT readily degrades when mixed with the magnetite particles in batch reactors.
On a mass basis,
“bulk,” or micron-scale magnetite was the least reactive. On a surface area normalized basis, however, the nano- and microscale particles behaved similarly. The observed reaction rate, as described by pseudo-first-order rate constants, is a linear function of the magnetite mass load (given in m2/L) at the different pH values investigated. Furthermore, the results indicate that the surface area normalized reaction rates increase by an order of magnitude as the pH is increased. This result is consistent with prior reports in the contaminant remediation literature (e.g., Danielsen and Hayes, 2004).
Solution pH strongly affects the observed reaction rates. At acidic pH, the measured rates are fairly slow. As the pH is raised, however, the rates increase by roughly an order of magnitude. Between a pH of 7.5 and 8, the reaction rates rise sharply; this may reflect the pH dependence of the surface reaction.
Some of the observed differences in reactivity and product distribution may suggest that particles produced using different methodologies are not the same and may differ in terms of particle size and/or FeII to FeIII ratio. Efforts will be undertaken during Phase II to determine particle characteristics most affected by methods of preparation and, subsequently, which characteristics have the greatest effect on particle reactivity and the generation of toxic intermediate compounds.
The magnetite nanoparticles prepared during Phase I also are applicable for treatment of arsenic-contaminated waste streams. In preliminary experiments, adsorption of As(III) by magnetite nanoparticles compared very well to results reported by other researchers using zero-valent iron (ZVI), particularly given the fact that Luna Innovations Incorporated’s studies employed one-third fewer particles (by mass) and a 10-fold greater concentration of As(III) than typically is reported.
Luna Innovations evaluated dozens of different formulations and methods of preparations during Phase I to achieve cost-efficient particles with performance characteristics desirable for environmental remediation applications (e.g., low cost, high reactivity, and mobility in porous media). Nanoparticle production and stabilization techniques were identified that can be controlled or “tuned” to improve particle stability and mobility in aqueous media, as well as enhance particle reactivity with chlorinated hydrocarbons and adsorption of As(III) from solution. These production processes can be optimized further to reduce, or perhaps eliminate entirely, the formation of toxic intermediates, such as chloroform, which are known to occur during reductive dechlorination of chlorinated hydrocarbons.
Based on Luna Innovations’ initial observations and the published literature, the reaction rates measured with nanoscale magnetite, although lower than those measured with nanoscale ZVI, appear to be rapid enough to remediate many contaminated sites. The slightly lower reactivity of nanoscale magnetite could be advantageous because the particles are presumably less reactive with water and thus would not be subject to the same losses in reactivity observed with nanoscale ZVI. More importantly, magnetite nanoparticles may impart a significant cost advantage over the popular ZVI or bimetallic particles frequently described in the literature. A detailed cost-versus-benefit analysis of nanoscale magnetite relative to other remediation strategies will be undertaken during Phase II, when more information is available regarding actual costs and quantities of magnetite particles required to achieve field performance comparable to conventional approaches.
Planned Phase II studies include: (1) optimizing the nanoparticle manufacturing process for more controlled and reproducible particles and stabilizing suspension chemistries; (2) investigating additional environmentally compatible surface coating and particle stabilization/delivery techniques; (3) expanding the number of contaminants degraded; (4) incorporating the technology with appropriate nanoparticle delivery methods; (5) conducting field-scale demonstrations; and (6) conducting a thorough cost-benefit analysis comparing the proposed magnetite approach to existing technologies for in situ remediation.