title: Characterization and properties of metallic iron nanoparticles: spectroscopy, electrochemistry, and kinetics.
abstract: There are reports that nano-sized zero-valent iron (Fe0) exhibits greater reactivity than micro-sized particles of Fe0, and it has been suggested that the higher reactivity of nano-Fe0 may impart advantages for groundwater remediation or other environmental applications. However, most of these reports are preliminary in that they leave a hostof potentiallysignificant(and often challenging) material or process variables either uncontrolled or unresolved. In an effort to better understand the reactivity of nano-Fe0, we have used a variety of complementary techniques to characterize two widely studied nano-Fe0 preparations: one synthesized by reduction of goethite with heat and H2 (Fe(H2)) and the other by reductive precipitation with borohydride (Fe(BH)). Fe(H2) is a two-phase material consisting of 40 nm alpha-Fe0 (made up of crystals approximately the size of the particles) and Fe3O4 particles of similar size or larger containing reduced sulfur; whereas Fe(BH) is mostly 20-80 nm metallic Fe particles (aggregates of <1.5 nm grains) with an oxide shell/coating that is high in oxidized boron. The FeBH particles further aggregate into chains. Both materials exhibit corrosion potentials that are more negative than nano-sized Fe2O3, Fe3O4, micro-sized Fe0, or a solid Fe0 disk, which is consistent with their rapid reduction of oxygen, benzoquinone, and carbon tetrachloride. Benzoquinone-which presumably probes inner-sphere surface reactions-reacts more rapidly with FeBH than Fe(H2), whereas carbon tetrachloride reacts at similar rates with FeBH and Fe(H2), presumably by outer-sphere electron transfer. Both types of nano-Fe0 react more rapidlythan micro-sized Fe0 based on mass-normalized rate constants, but surface area-normalized rate constants do not show a significant nano-size effect. The distribution of products from reduction of carbon tetrachloride is more favorable with Fe(H2), which produces less chloroform than reaction with Fe(BH).
authors.affiliation: Department of Environmental and Biomolecular Systems, Oregon Health & Science University, 20000 NW Walker Road, Portland, Oregon 97006, USA.
authors.forename: James T
authors.initials: JT
authors.lastname: Nurmi
authors.forename: Paul G
authors.initials: PG
authors.lastname: Tratnyek
authors.forename: Vaishnavi
authors.initials: V
authors.lastname: Sarathy
authors.forename: Donald R
authors.initials: DR
authors.lastname: Baer
authors.forename: James E
authors.initials: JE
authors.lastname: Amonette
authors.forename: Klaus
authors.initials: K
authors.lastname: Pecher
authors.forename: Chongmin
authors.initials: C
authors.lastname: Wang
authors.forename: John C
authors.initials: JC
authors.lastname: Linehan
authors.forename: Dean W
authors.initials: DW
authors.lastname: Matson
authors.forename: R Lee
authors.initials: RL
authors.lastname: Penn
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Driessen
mesh_terms: D011232:Chemical Precipitation; D003343:Corrosion; D004563:Electrochemistry; D058085:Iron Compounds / Q000737:chemistry*; D008422:Materials Testing; D049329:Nanostructures; D013057:Spectrum Analysis
chemical_list: D058085:Iron Compounds