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Kinetics of Zero Valent Iron Nanoparticle Oxidation in Oxygenated Water
journal contribution
posted on 2012-12-04, 00:00 authored by Lauren F. Greenlee, Jessica D. Torrey, Robert
L. Amaro, Justin M. ShawZero 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*, H2(g), H2O2) 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 (H2O and O2) 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.