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usually insensitive to high ionic strengths for which double layer repulsions would be greatly
shielded. Examples of iron nanoparticles stabilization follow:
Coatings such as polyelectrolytes or triblock polymers can be added in the suspension (He
et al ., 2009; Hydutsky et al ., 2007; Lin et al ., 2010; Saleh et al ., 2007; 2008; Wang and
Roman, 2011; Zhang, 2003) to stabilize the iron nanoparticles and improve their mobility.
The nanoparticles are encased in emulsified vegetable oil droplets (EZVI) (Quinn et al ., 2005)
to improve stability and to improve reactivity by improving contact with the contaminant.
Multi-functional nanocomposites (MFNC) are developed by incorporating nZVI into porous
submicron particles (nanocomposites) of silica (Zhan et al ., 2008; Zheng et al ., 2008) or carbon
(Zhan et al ., 2011), to prevent agglomeration and couple iron reactivity with high silica/carbon
adsorptivity.
Guar gum is used as the stabilizing agent of aqueous suspension to reduce the attachment
efficiency of NP in soil grains under varying conditions (Tiraferri and Sethi, 2009).
Some nanoscale materials are made with catalysts (bimetallic nanoparticles, BNP) that enhance
the intrinsic reactivity of the surface sites (Tratnyek and Johnson, 2006). In bench-scale tests,
BNPs of iron combined with Pd achieved contaminant degradation two orders of magnitude
greater than microscale iron particles alone: these particles were 99.9% iron and less than 0.1%
Pd (Zhang et al ., 2011). BNPs are generally incorporated into a slurry which may be stabilized
by a combination of the aforementioned procedures (Schrick et al ., 2004; Zhan et al ., 2009),
and can be injected by gravity or pressure feed.
Research indicates that nanoscale materials such as nZVI, BNPs, EZVI, MFNC may
chemically reduce effectively PCE, TCE, cis-1,2-dichloroethylene, vinyl chloride, and 1-1-1-
tetrachloroethane, polychlorinated biphenyls, halogenated aromatics, nitro-aromatics, heavy
metals such as, lead and chromium, and arsenic, nitrate, perchlorate, sulfate, and cyanide (Bennett
et al ., 2010; Cundy et al ., 2008; Kanel et al ., 2005; Ponder et al ., 2000; Zhang, 2003).
1.6.5 Other zerovalent nanoparticles used in soil and
groundwater remediation
While iron is the most extensively examined metal for reductive processes like dechlorination,
other metals such as Cu can also degrade halogenated hydrocarbons (Liou et al ., 2007). Although
nanosized and microsized ZVI are capable of degrading a wide array of highly chlorinated con-
taminants, e.g., trichloroethylene, the reactivity of ZVI towards as for example 1,2-dichloroethane
is very low, but Cu zerovalent nanoparticles are rather effective (Huang et al ., 2011). Moreover,
unlike nZVI, Cu nanoparticles exhibit relative stability in water, avoiding unwanted reactions
with surrounding media.
Various types of metal-oxides nanopowders (Al 2 O 3 ,TiO 2 ,Fe 3 O 4 , MgO, ZrO 2 , etc.) have been
tested as adsorbents of arsenate ions from groundwater (Hristowski et al ., 2007). Nanocrys-
talline metal salts have recently been tested to immobilize heavy metals in soils, sediments,
and groundwater; for example, iron phosphate nanoparticles was tested for Pb (Liu and Zhao,
2007), iron sulfide nanoparticles for Hg (Xiong et al ., 2009), and nanohydroxyapatite for Cd
and Pb (Zhang et al ., 2010). Nanoparticles of iron (oxyhydr)-oxides of controlled shape and
size (goethite nanorods, hematite nanocubes, magnetite nanoparticles) were obtained from amor-
phous hydrous ferric- or ferrous-oxide by using a cost-effective hydrothermal method. These
materials demonstrated to have 6-50 times higher adsorption capacity for As(III) compared to
microsized particles (Zhao et al ., 2011). The use of clays and iron-oxide minerals as nanocatalysts
of Fenton-like reactions is a promising alternative for the decontamination of soils, groundwa-
ter, and sediments (Garrido-Ramirez et al ., 2010; Zelmanov and Semiat, 2008). Recent studies
suggest that nanoparticles of calcium peroxide (CaO 2 ) are a more effective source of hydrogen per-
oxide for in-situ chemical oxidation of organic pollutants dissolved in groundwater (Khodaveisi
et al ., 2011). Nanoparticulate magnetite is a potentially important reductant for environmental
contaminants, including several halogenated organics and heavy metals (Gorski et al ., 2010; Lee
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