Wei-xian Zhang

Nanoscale Iron Particles for Environmental Remediation: An Overview

Nanoscale iron particles represent a new generation of environmental remediation technologies that could provide cost-effective solutions to some of the most challenging environmental cleanup problems. Nanoscale iron particles have large surface areas and high surface reactivity. Equally important, they provide enormous flexibility for in situ applications. Research has shown that nanoscale iron particles are very effective for the transformation and detoxification of a wide variety of common environmental contaminants, such as chlorinated organic solvents, organochlorine pesticides, and PCBs. Modified iron nanoparticles, such as catalyzed and supported nanoparticles have been synthesized to further enhance the speed and efficiency of remediation. In this paper, recent developments in both laboratory and pilot studies are assessed, including: (1) synthesis of nanoscale iron particles (10–100nm, >99.5% Fe) from common precursors such as Fe(II) and Fe(III); (2) reactivity of the nanoparticles towards contaminants in soil and water over extended periods of time (e.g., weeks); (3) field tests validating the injection of nanoparticles into aquifer, and (4) in situ reactions of the nanoparticles in the subsurface.

Zero-Valent Iron Nanoparticles for Abatement of Environmental Pollutants: Materials and Engineering Aspects

Zero-valent iron nanoparticle technology is becoming an increasingly popular choice for treatment of hazardous and toxic wastes, and for remediation of contaminated sites. In the U.S. alone, more than 20 projects have been completed since 2001. More are planned or ongoing in North America, Europe, and Asia. The diminutive size of the iron nanoparticles helps to foster effective subsurface dispersion whereas their large specific surface area corresponds to enhanced reactivity for rapid contaminant transformation. Recent innovations in nanoparticle synthesis and production have resulted in substantial cost reductions and increased availability of nanoscale zero-valent iron (nZVI) for large scale applications. In this work, methods of nZVI synthesis and characterization are highlighted. Applications of nZVI for treatment of both organic and inorganic contaminants are reviewed. Key issues related to field applications such as fate/transport and potential environmental impact are also explored.

Treatment of chlorinated organic contaminants with nanoscale bimetallic particles

Abstract Nanoscale bimetallic particles (Pd/Fe, Pd/Zn, Pt/Fe, Ni/Fe) have been synthesized in the laboratory for treatment of chlorinated organic pollutants. Specific surface areas of the nanoscale particles are tens of times larger than those of commercially available microscale metal particles. Rapid and complete dechlorination of several chlorinated organic solvents and chlorinated aromatic compounds was achieved by using the nanoscale bimetallic particles. Evidence observed suggests that within the bimetallic complex, one metal (Fe, Zn) serves primarily as electron donor while the other as catalyst (Pd, Pt). Surface-area-normalized reactivity constants are about 100 times higher than those of microscale iron particles. Production of chlorinated byproducts, frequently reported in studies with iron particles, is notably reduced due to the presence of catalyst. The nano-particle technology offers great opportunities for both fundamental research and technological applications in environmental engineering and science.

Nanoscale iron particles for complete reduction of chlorinated ethenes

Abstract This paper examines the potential for using laboratory synthesized nanoscale Pd/Fe bimetallic particles to reduce chlorinated ethenes. Rapid and complete dechlorination was achieved for six chlorinated ethenes: tetrachloroethene (PCE, C 2 Cl 4 ), trichloroethene (TCE, C 2 HCl 3 ), 1,1-dichloroethene (1,1-DCE, C 2 H 2 Cl 2 ), cis - and trans -1,2-dichloroethene (c-DCE, t-DCE, C 2 H 2 Cl 2 ), and vinyl chloride (VC, C 2 H 3 Cl). The chlorinated ethenes (20 mg l −1 ) were completely reduced within 90 min at a metal loading of 5 g l −1 . Ethane was the primary product from these reactions, amount to 60–90% of the total carbon. Ethene (3–20%) was produced during the transformation of TCE, DCEs and VC. No chlorinated intermediates or final products were detected above the method detection limit ( −1 ). The remarkable performance of the nanoscale particles can be attributed to: (1) High specific surface area of the nanoscale metal particles, approximately 35 m 2 g −1 , tens to hundreds of times higher than commercial grade micro- or milli-scale iron particles; (2) Increased reactivity per unit metal surface area, largely due to the presence of the noble metal (Pd) on the surface. Values of the surface-area-normalized rate coefficients ( k SA ) were two orders of magnitude higher than those reported in the literature for larger iron particles. Due to their small particle size and high reactivity, the nanoscale bimetallic particles may be useful in a wide array of environmental applications including subsurface injection for groundwater treatment.

Dechlorination of pentachlorophenol using nanoscale Fe/Ni particles: role of nano-Ni and its size effect.

The dechlorination of pentachlorophenol (PCP) using nano-Fe together with different size of nano-Ni particles (30, 50, 80, and 100nm) was investigated. The results indicated that nano-Ni particles could improve the dechlorination of PCP. The X-ray powder diffraction (XRD) analysis suggested that nano-Ni particles might serve as catalyst for dechlorination. The decrease of nano-Ni particle size resulted in the increase of PCP transformation and chloride release. The accumulation of several intermediates, such as phenol, 2-chlorophenol, 3-chlorophenol and 4-chlorophenol indicated the probable changes of the reaction pathway for PCP dechlorination. The corrosion products of Fe were detected using XRD analysis. In the system without nano-Ni particles, they were lepidocrocite (gamma-FeOOH) and magnetite (Fe(3)O(4)) and/or maghemite (Fe(2)O(3)), however, in the systems with nano-Ni particles, they were still magnetite/maghemite but no lepidocrocite existed. The size of nano-Ni particles might affect the crystallization of corrosion products of Fe, but did not affect the species distribution of corrosion products.

Zerovalent iron nanoparticles for treatment of ground water contaminated by hexachlorocyclohexanes.

Ground water and aquifer samples from a site contaminated by hexachlorocyclohexanes (HCHs; C(6)H(6)Cl(6)) were exposed to nanoscale iron particles to evaluate the technology as a potential remediation method. The summed concentration of the HCH isomers in ground water was approximately 5.16 micromol L(-1) (1500 microg L(-1)). Batch experiments with 2.2 to 27.0 g L(-1) iron nanoparticles showed that more than 95% of the HCHs were removed from solution within 48 h. Using a pseudo first-order kinetics model, the HCH isomers were removed in accordance with the trend gamma congruent with alpha > beta > delta. This seems to be correlated with the orientation (axial vs. equatorial) of the chlorine atoms lost in the dihaloelimination steps. Although the reactivity of the HCH isomers has been investigated in the classical organic chemistry literature, the present study was the first in the environmental remediation arena. The rate of removal is directly correlated to the number of axial chlorines. The observed rate constant varied from 0.04 to 0.65 h(-1), and the rate constant normalized to the iron surface area concentration ranged from 5.4 x 10(-4) to 8.8 x 10(-4) L m(-2) h(-1). Post-test extractions of the reactor contents detected little HCH remaining in solution or on the iron surfaces, reinforcing the contention that reaction rather than sorption was the operative mechanism for the HCH removal. Together with previously published work on a wide variety of chlorinated organic solvents, this work further demonstrates the potential of zerovalent iron nanoparticles for treatment and remediation of persistent organic pollutants.