Application of Zero-valent Iron Nanoparticles for Environmental Clean Up - Advanced Materials for Agriculture, Food and Environmental Safety - page 389

density of surface reactive sites and greater intrinsic reactivity; all these
properties make it a potential remediation tool for organic as well as inor-
ganic contaminants. Owing to its size and surface characteristics, nFe 0 can
be injected or pumped straight into subsurface aquifers and groundwater
to treat contaminated plumes. Not only does nFe 0 reduce the total content
of contaminants, but it also lowers the amount of mobile and bioavailable
fractions of contaminant. In addition, it also provides enormous l exibility
for both in situ and ex situ applications.

14.2.4.1.1 Organic Contaminants
Zero-valent iron nanoparticle can reduce a number of halogenated hydro-
carbons to benign products such as hydrocarbons, chloride and water.
Wang and Zhang [26] reported complete dechlorination of 20 mg/L tri-
chloroethylene (TCE) to hydrocarbons including ethene, ethane, propene,
propane, butene, butane and pentane in the presence of 1.0 g nFe 0 . Similarly,
Zhang [30] studied the dechlorination reaction of trichloroethane, trichlo-
roethene and tetrachloroethene by nFe 0 and found a 99% reduction within
24 hours with ethane as the major product. Other chlorinated compounds
which are reported to undergo partial or complete dechlorination include
tetrachloromethane, trichloromethane [31], polychlorinated biphenyls
[32, 33], etc. Regarding the dechlorination pathway of chlorinated eth-
anes in a nFe 0 system, Song and Caraway [34] proposed that reductive
β- elimination will be the major pathway for chlorinated ethanes pos-
sessing α , β -pairs of chlorine atoms whereas reductive α -elimination and
hydrogenolysis will be concurrently followed by compounds having chlo-
rine substitution on one carbon only. Zero-valent iron nanoparticle has
also been proven as an ei cient reductant for chlorinated pesticides such
as Lindane and Atrazine [35-40]. Organophosphate compounds such as
chlorpyrifos, tributyl phosphate have also been reported to degrade in the
presence of nFe 0 [41, 42] .
As a strong reductant, nFe 0 degrades organochlorine compounds fol-
lowing Eq. 7. h e Fe 2+ ion formed during iron oxidation reaction is a good
electron donor and contributes in reducing the chlorinated compounds
(Eq. 14.8).

Fe 0 + R-Cl + H + Fe 2+ + R-H + Cl - (14.7)

Fe 2+ + R-Cl + H 2 O 2Fe 3+ + R-H + OH - + Cl - (14.8)

Other organic contaminants ef ectively degraded by nFe 0 include:
nitroamines [43], nitroaromatic compounds [44], azo dyes [45, 46], poly-
brominated diphenyl ethers [47], polycyclic aromatic hydrocarbon [48], etc.