Fe(0) nanoparticles for nitrate reduction: stability, reactivity, and transformation.

The pyrophoric character of zerovalent iron nanoparticles and cumbersome handling of this material has been a drawback in practical applications, despite the expectation of an enhanced reactivity. We have been interested in how the iron nanoparticles can gain stability in air without significantly sacrificing reactivity. The freshly synthesized iron nanoparticles ignited spontaneously upon exposure to air. However, when exposed slowly to air, an approximately 5 nm coating of iron oxide was formed on the surface of particles. The oxide shell did not thicken for at least two months, indicating no sign of further corrosion of iron particles. The reactivity studies on nitrate reduction showed that the freshly synthesized iron reacted at the fastest rate. After formation of the oxide shell the rate constants decreased by ca. 50% of that of fresh iron, but were still higher than that of commercial grade micro- or milli-sized iron powder. Nitrate (50 ppm/350 mL) can be recharged 6 times into a bottle containing 0.5 g of iron nanoparticles. The reduction rate of the second cycle was the fastest among the six cycles, which can be attributed to the increase of surface area and the fresh iron surfaces that were bared by the dissolution of oxidized iron species on the surface. The oxidized iron was transformed to crystalline magnetite (Fe3O4) in solution.

[1]  Paul G Tratnyek,et al.  Characterization and properties of metallic iron nanoparticles: spectroscopy, electrochemistry, and kinetics. , 2005, Environmental science & technology.

[2]  Gerald R. Eykholt and,et al.  Dechlorination of the Chloroacetanilide Herbicides Alachlor and Metolachlor by Iron Metal , 1998 .

[3]  E. E. Carpenter,et al.  Passivated Iron as Core−Shell Nanoparticles , 2003 .

[4]  Wei-xian Zhang,et al.  Transformation of chlorinated methanes by nanoscale iron particles , 1999 .

[5]  U. Schwertmann,et al.  Iron Oxides , 2003, SSSA Book Series.

[6]  Hsing-Lung Lien,et al.  Nanoscale iron particles for complete reduction of chlorinated ethenes , 2001 .

[7]  R. Puls,et al.  Nitrate reduction by zerovalent iron: effects of formate, oxalate, citrate, chloride, sulfate, borate, and phosphate. , 2004, Environmental science & technology.

[8]  James Farrell,et al.  Investigation of the Long-Term Performance of Zero-Valent Iron for Reductive Dechlorination of Trichloroethylene , 2000 .

[9]  D. Shriver,et al.  The manipulation of air-sensitive compounds , 1969 .

[10]  Pedro J. J. Alvarez,et al.  Fe(0)-Supported Autotrophic Denitrification , 1998 .

[11]  M. Conklin,et al.  Understanding soluble arsenate removal kinetics by zerovalent iron media. , 2002, Environmental science & technology.

[12]  D. Sholl,et al.  TCE dechlorination rates, pathways, and efficiency of nanoscale iron particles with different properties. , 2005, Environmental science & technology.

[13]  M. Reinhard,et al.  Treatment of 1,2-dibromo-3-chloropropane and nitrate-contaminated water with zero-valent iron or hydrogen/palladium catalysts , 1996 .

[14]  Cumaraswamy Vipulanandan,et al.  Microemulsion and solution approaches to nanoparticle iron production for degradation of trichloroethylene , 2003 .

[15]  Wei-xian Zhang,et al.  Synthesizing Nanoscale Iron Particles for Rapid and Complete Dechlorination of TCE and PCBs , 1997 .

[16]  John F. Devlin,et al.  The effects of electron donor and granular iron on nitrate transformation rates in sediments from a municipal water supply aquifer , 2000 .

[17]  T. Mallouk,et al.  Remediation of Cr(VI) and Pb(II) aqueous solutions using supported, nanoscale zero-valent iron , 2000 .

[18]  Paul G Tratnyek,et al.  Diversity of contaminant reduction reactions by zerovalent iron: role of the reductate. , 2004, Environmental science & technology.

[19]  C. Huang,et al.  Nitrate reduction by metallic iron , 1998 .

[20]  A. E. Greenberg,et al.  Standard methods for the examination of water and wastewater : supplement to the sixteenth edition , 1988 .

[21]  M. Scherer,et al.  Kinetics of nitrate, nitrite, and Cr(VI) reduction by iron metal. , 2002, Environmental science & technology.

[22]  G. Hadjipanayis,et al.  Chemistry of Borohydride Reduction of Iron(II) and Iron(III) Ions in Aqueous and Nonaqueous Media. Formation of Nanoscale Fe, FeB, and Fe2B Powders , 1995 .

[23]  Tian C. Zhang,et al.  The effects of pH and addition of an organic buffer (HEPES) on nitrate transformation in Fe0-water systems , 1998 .

[24]  J. Khim,et al.  Kinetics of reductive denitrification by nanoscale zero-valent iron. , 2000, Chemosphere.

[25]  Timothy L. Johnson,et al.  Kinetics of Halogenated Organic Compound Degradation by Iron Metal , 1996 .