title: Kinetics of zero valent iron nanoparticle oxidation in oxygenated water.
abstract: Zero valent iron (ZVI) nanoparticles are versatile in their ability to remove a wide variety of water contaminants, and ZVI-based bimetallic nanoparticles show increased reactivity above that of ZVI alone. ZVI nanoparticles degrade contaminants through the reactive species (e.g., OH*, H(2(g)), H(2)O(2)) that are produced during iron oxidation. Measurement and modeling of aqueous ZVI nanoparticle oxidation kinetics are therefore necessary to optimize nanoparticle design. Stabilized ZVI and iron-nickel nanoparticles of approximately 150 nm in diameter were synthesized through solution chemistry, and nanoparticle oxidation kinetics were determined via measured mass change using a quartz crystal microbalance (QCM). Under flowing aerated water, ZVI nanoparticles had an initial exponential growth behavior indicating surface-dominated oxidation controlled by migration of species (H(2)O and O(2)) to the surface. A region of logarithmic growth followed the exponential growth which, based on the Mott-Cabrera model of thin oxide film growth, suggests a reaction dominated by movement of species (e.g., iron cations and oxygen anions) through the oxide layer. The presence of ethanol or a nickel shell on the ZVI nanoparticles delayed the onset of iron oxidation and reduced the extent of oxidation. In oxygenated water, ZVI nanoparticles oxidized primarily to the iron oxide-hydroxide lepidocrocite.
authors.affiliation: Applied Chemicals and Materials Division National Institute of Standards and Technology 325 Broadway, Boulder, Colorado 80305, USA. lauren.greenlee@nist.gov
authors.forename: Lauren F
authors.initials: LF
authors.lastname: Greenlee
authors.forename: Jessica D
authors.initials: JD
authors.lastname: Torrey
authors.forename: Robert L
authors.initials: RL
authors.lastname: Amaro
authors.forename: Justin M
authors.initials: JM
authors.lastname: Shaw
mesh_terms: D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D009532:Nickel / Q000737:chemistry; D010084:Oxidation-Reduction; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D009532:Nickel; D007501:Iron