Project 6: Contaminant oxidation using nanoparticulate and granular zero-valent iron
The main objective of this project is to assess the potential for using oxidants produced during the corrosion of granular and nanoparticulate zero-valent iron (ZVI) by oxygen to remediate contaminated groundwater and soil. These objectives are being realized by studying the reaction mechanisms involved in oxidant production and contaminant transformation and the efficiency of potential treatment methods under conditions similar to those that are likely to be employed in treatment systems. The overall hypothesis is that the oxidative ZVI system offers a practical, cost-effective means of remediating contaminants that have the greatest impact on human health at Superfund sites. This investigation of the reaction mechanisms focuses on the role of solution chemistry and surface structure on the rate of contaminant transformation. To gain insight into the processes occurring on or near ZVI surfaces, chemical processes occurring in the solution phase are being measured in conjunction with studies conducted using techniques designed to probe the surface, such as potentiometry, surface enhanced Raman spectroscopy and electrochemical quartz microbalance methods. This investigation of the potential applications of the oxidative ZVI system to contaminant remediation focuses on permeable reactive barriers and water infiltration systems used to treat organic contaminants and drinking water treatment systems used to remove arsenic. These studies extend the research in oxidant formation mechanisms to account for the effect of oxide coatings on the ZVI surfaces on contaminant oxidation rates and transport of contaminants to and from the corroding iron surfaces. This research has the potential to provide innovative and cost-effective ways of removing contaminants from groundwater and drinking water that are difficult or expensive to treat by conventional methods. The development of these technologies could reduce human exposure to organic and inorganic contaminants of concern.
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The investigators aim to develop and test new approaches for oxidizing contaminants that are difficult to treat with existing technologies (e.g., PCBs, 1,4-dioxane and perfluorinated compounds) and apply these approaches to make treatment systems more robust and efficient. Successful completion of the proposed research will result in new oxidative treatment systems that will substantially reduce the costs of remediating contaminants that are difficult to clean-up.
What we have done so far
The investigators facilitate the reaction of iron with oxygen or hydrogen peroxide so that it produces large amounts of powerful oxidants, such as hydroxyl radicals, that are capable of degrading chemical contaminants. Due to their high surface area and reactivity, these reactions are especially fast on iron nanoparticles, raising the possibility of using iron nanoparticles for oxidative remediation of contaminants.
In the first phase of the research, the investigators demonstrated that, under conditions normally encountered in contaminated soil and groundwater, only a small fraction of the oxygen or hydrogen peroxide reacts with the iron-containing particles to produce hydroxyl radicals. The reaction pathway responsible for much of the loss of oxidant appeared to produce reactive species that were incapable of oxidizing most important organic contaminants encountered at Superfund sites.
To make more efficient use of the potential for iron-containing particles to facilitate oxidation of recalcitrant contaminants, their subsequent research has focused on ways of increasing the yield of hydroxyl radicals when oxygen or hydrogen peroxide reacts with iron. Research showed that using a heterogeneous catalyst in which the iron was associated with silica or aluminum oxide increased oxidant yields from hydrogen peroxide by almost two orders of magnitude at near-neutral pH values relative to hydrogen peroxide decomposition on iron oxides.
During the past year they have shown that when iron is associated with aluminosilicate clay minerals it exhibits high yields for oxidant production. They also observed that dissolved silica present in groundwater interacts with the surfaces of iron oxides to decrease their catalytic activity, prolonging the lifetime of hydrogen peroxide in the subsurface.
The results are significant to Superfund site chemical oxidation applications in which hydrogen peroxide is added to soil or groundwater to remediate recalcitrant organic contaminants. The research suggests that hydrogen peroxide addition is much more likely to succeed when the soil or aquifer contains iron in association with aluminosilicate clay minerals. Furthermore, it may be possible to manipulate the subsurface to remove iron oxides or increase the amount of iron associated with aluminosilicate clays as a means of improving the performance of these remediation systems.
- Pham AL, Doyle FM, Sedlak DL (2012) Kinetics and efficiency of H2O2 activation by iron-containing minerals and aquifer materials. Water Research. Dec 1;46(19):6454-6462. PMID: 23047055. (PMC Journal- In Progress). [PDF]
- Pham AL, Doyle FM, Sedlak DL (2012) Dissolution of mesoporous silica supports in aqueous solutions: Implications for mesoporous silica-based water treatment processes. Applied Catalysis B: Environmental. Sep 25;126: 258-264. PMCID: PMC3465675. [PDF]
- Gui MH, Smuleac V, Ormsbee LE, Sedlak DL, Bhattacharyya D (2012) Iron oxide nanoparticle synthesis in aqueous and membrane systems for oxidative degradation of trichloroethylene from water. J. Nanoparticle Res. 14(5):861. doi: 10.1007/s11051-012-0861-1. (PMC Journal – In Process). [PDF]
- Pham AL, Doyle FM, Sedlak DL (2102) Inhibitory Effect of Dissolved Silica on H2O2 Decomposition by Iron(III) and Manganese(IV) Oxides: Implications for H2O2-Based In Situ Chemical Oxidation. Environ. Sci. Technol. Jan 17;46(2):1055-1062. PMCID: PMC3262894. [PDF]
- Pham AL, Lee C, Doyle FM, Sedlak DL (2009) A silica-supported iron oxide catalyst capable of activating hydrogen peroxide at neutral pH values. Environ Sci Technol. Dec 1; 43(23):8930-5. PMID: 19943668. PMCID: PMC2792909. [PDF]
- Keenan CR, Goth-Goldstein R, Lucas D, Sedlak DL (2009) Oxidative stress induced by zero-valent iron nanoparticles and Fe(II) in human bronchial epithelial cells. Environ Sci Technol. Jun 15; 43(12):4555-60. PMID: 19603676. [PDF]
- Lee C, Sedlak DL (2009) A novel homogeneous Fenton-like system with Fe(III)-phosphotungstate for oxidation of organic compounds at neutral pH values. J Molec Catal A. 311(1-2):1-6. NIHMS131170. [PDF]
- Lee C, Sedlak DL (2008) Enhanced formation of oxidants from bimetallic nickel-iron nanoparticles in the presence of oxygen. Environ Sci Technol. Nov 15; 42(22):8528-33. PMID: 19068843. PMCID: PMC2628954. [PDF]
- Keenan CR, Sedlak DL (2008) Ligand-enhanced reactive oxidant generation by nanoparticulate zero-valent iron and oxygen. Environ Sci Technol. Sep 15; 42(18):6936-41. PMID: 18853812. PMCID: PMC2701397. [PDF]
- Lee C, Keenan CR, Sedlak DL (2008) Polyoxometalate-enhanced oxidation of organic compounds by nanoparticulate zero-valent iron and ferrous ion in the presence of oxygen. Environ Sci Technol. Jul 1; 42(13):4921-6. PMID: 18678027. PMCID: PMC2536720. [PDF]
- Lee C, Kim JY, Lee WI, Nelson KL, Yoon J, Sedlak DL (2008) Bactericidal effect of zero-valent iron nanoparticles on Escherichia coli. Environ Sci Technol. Jul 1; 42(13):4927-33. PMID: 18678028. PMCID: PMC2536719. [PDF]
- Keenan CR, Sedlak DL (2008) Factors affecting the yield of oxidants from the reaction of nanoparticulate zero-valent iron and oxygen. Environ Sci Technol. Feb 15; 42(4):1262-7. PMID: 18351103. [PDF]