2006 Progress Report: Nanostructured Materials for Environmental Decontamination of Chlorinated CompoundsEPA Grant Number: GR832374
Title: Nanostructured Materials for Environmental Decontamination of Chlorinated Compounds
Investigators: Lu, Yunfeng , John, Vijay T.
Institution: Tulane University
EPA Project Officer: Hahn, Intaek
Project Period: August 1, 2005 through July 31, 2008 (Extended to July 31, 2009)
Project Period Covered by this Report: August 1, 2005 through July 31, 2006
Project Amount: $320,000
RFA: Greater Research Opportunities: Research in Nanoscale Science Engineering and Technology (2004) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Nanotechnology , Safer Chemicals
Our research is directed towards the development of novel mesoporous materials that act as supports for zerovalent iron nanoparticles used in the breakdown of chlorinated compounds. Halogenated organic compounds such as chlorinated aromatics, chlorinated aliphatics, and polychlorinated biphenyls are typical of dense nonaqueous phase liquids (DNAPLs) that are prevalent at contaminant sites. In recent years, the use of zerovalent iron has represented a promising and innovative approach to the destruction of these compounds. Of particular interest is the use of nanoparticles of Fe in remediation through hydrodechlorination. The enormous surface area of nanoparticles leads to enhanced efficiencies. However, due to the high surface energy of nanoparticles, the particles tend to aggregate, leading to larger units that do not maintain colloidal stability and are not easily transported in sediments. Fe nanoparticles exceeding 10-15 nm additionally exhibit ferromagnetism also leading to aggregation and precipitation from solution. Finally, it is difficult to functionalize iron with organic compounds in order to maintain stability in aqueous or in organic systems.
Our technical approach combines the simplicity and affordability of the sol-gel processing techniques for ceramic synthesis with the efficiency and spontaneity of surfactant/silica cooperative assembly to manufacture nanostructured decontamination materials using a simple aerosol processing technique.
Our results to date have been extremely promising. Starting with a solution of the iron and silica precursors, the aerosol apparatus atomizes the solution into droplets that undergo a drying and solidification step, generating nanoparticles that are collected in a filter. During this process, solvent evaporation enriches the surfactant and silicate from the air-liquid interface of the droplet towards its interior, resulting in their co-assembly and in the formation of nanostructures growing from the interface towards the interior. Subsequent condensation reactions of silica during the drying and heating steps freezes the mesophases and results in silica particles that contain iron hydroxides. These are contacted with sodium borohyride to form particles containing zerovalent iron. Figure 1 illustrates such composite particles, where the dark spots are nanoparticles of zerovalent iron.
Figure 1. Silica Particles Containing Zerovalent Iron
The following are our major conclusions:
- We are able to efficiently prepare silica particles containing zerovalent iron nanoparticles.
- These particles show efficient partitioning to the TCE-water interface. Figure 2 illustrates a droplet of TCE in a microcapillary containing water and composite Fe/Silica particles. The tendency of the particles to accumulate at the TCE-water interface is clearly shown. The partitioning can be controlled by functionalizing the silica with nonpolar ligands.
- The particles are efficient in the reductive dehalogenation of TCE, as shown in Figure 3, where M/M0 is the ratio of TCE remaining to the original TCE content. Most importantly, we present a new concept, namely that by functionalizing the silica with hydrocarbon groups, TCE is absorbed onto the particles and these particles are in close proximity with zerovalent iron. The removal of TCE through a combined adsorptive-reactive process is a novel way of designing functional nanomaterials for environmental decontamination of chlorinated compounds.
Figure 2. Microcapillary Experiments Showing Silica Particles Partitioning to the Oil-Trichloroethylene (TCE) interface
Figure 3. Characteristics of TCE Destruction Using the Composite Nanoparticles
The following activities are planned:
- Continuation of research in optimizing silica particle functionalization to enhance TCE partitioning to the proximity of iron nanoparticles.
- Column and capillary transport studies of particles for effective remediation technologies.
- Publication of observations.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 26 publications||7 publications in selected types||All 5 journal articles|
||Zheng T, Pang J, Tan G, He J, McPherson GL, Lu Y, John VT, Zhan J. Surfactant templating effects on the encapsulation of iron oxide nanoparticles within silica microspheres. Langmuir 2007;23(9):5143-5147.||