title: Molecular insights of oxidation process of iron nanoparticles: spectroscopic, magnetic, and microscopic evidence.
abstract: Oxidation behavior of nano-Fe(0) particles in an anoxic environment was determined using different state-of-the-art analytical approaches, including high resolution transmission electron microscopy (HR-TEM) combined with energy filtered transmission electron microscopy (EFTEM), X-ray absorption spectroscopy (XAS), and magnetic measurements. Oxidation in controlled experiments was compared in standard double distilled (DD) water, DD water spiked with trichloroethene (TCE), and TCE contaminated site water. Using HR-TEM and EFTEM, we observed a surface oxide layer (∼3 nm) formed immediately after the particles were exposed to water. XAS analysis followed the dynamic change in total metallic iron concentration and iron oxide concentration for the experimental duration of 35 days. The metallic iron concentration in nano-Fe(0) particles exposed to water, was ∼40% after 35 days; in contrast, the samples containing TCE were reduced to ∼15% and even to nil in the case of TCE contaminated site water, suggesting that the contaminants enhance the oxidation of nano-Fe(0). Frequency dependence measurements confirmed the formation of superparamagnetic particles in the system. Overall, our results suggest that nano-Fe(0) oxidized via the Fe(0) - Fe(OH)2 - Fe3O4 - (γ-Fe2O3) route and the formation of superparamagnetic maghemite nanoparticles due to disruption of the surface oxide layer.
authors.affiliation: CNRS-Aix-Marseille Université , CEREGE, UMR 7330, Marseille, Aix en Provence 13545, France.
authors.forename: Naresh
authors.initials: N
authors.lastname: Kumar
authors.forename: Mélanie
authors.initials: M
authors.lastname: Auffan
authors.forename: Jérôme
authors.initials: J
authors.lastname: Gattacceca
authors.forename: Jérôme
authors.initials: J
authors.lastname: Rose
authors.forename: Luca
authors.initials: L
authors.lastname: Olivi
authors.forename: Daniel
authors.initials: D
authors.lastname: Borschneck
authors.forename: Petr
authors.initials: P
authors.lastname: Kvapil
authors.forename: Michael
authors.initials: M
authors.lastname: Jublot
authors.forename: Delphine
authors.initials: D
authors.lastname: Kaifas
authors.forename: Laure
authors.initials: L
authors.lastname: Malleret
authors.forename: Pierre
authors.initials: P
authors.lastname: Doumenq
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Bottero
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D036103:Nanotechnology / Q000379:methods; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry; D014241:Trichloroethylene / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D010087:Oxides; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D014241:Trichloroethylene; D007501:Iron