Environmental Engineering Reference
In-Depth Information
tablE 23.4
contaminants remediated by nanoscale zero-valent iron (nzVi) [49]
Carbon tetrachloride
Chrysoidine
cis
-Dichloroethene
Dichlorobenzenes
Chloroform
Tropaeolin
trans
-Dichloroethene
Bromoform
Dichloromethane
Acid orange
1,1-Dichloroethene
TNT
Chloromethane
Acid Red
Vinyl chloride
Chlorobenzene
Hexachlorobenzene
Mercury
PCBs
Dibromochloromethane
Pentachlorobenzene
Nickel
Dioxins
Dichromate
Tetrachlorobenzenes
Silver
Pentachlorophenol
DDT
Trichlorobenzenes
Cadmium
NDMA
Dichlorobromomethane
Arsenic
lindane
Tetrachloroethene
Perchlorate
orange II
Trichloroethene
Nitrate
oil membrane, which in turn acts as a driving force to allow additional TCE migration into the membrane and additional
degradation is carried out. A potential benefit of EZVI over nZVI for environmental applications is that the hydrophobic mem-
brane surrounding the nZVI protects it from other groundwater constituents, such as some inorganic compounds, which might
otherwise react with the nZVI, reducing its capacity or passivating the iron [52].
Another type of nanoparticle used for environmental applications is the bi-metallic nanoparticle (BNP). Bi-metallic nanopar-
ticles consist of elemental iron or other metals in conjunction with a metal catalyst, such as platinum (Pt), gold (Au), nickel
(Ni), or palladium [51]. The combination of metals to form a nanoparticle increases the kinetics of redox reaction, therefore
catalyzing the reaction. The most commonly used and commercially available BNPs are the palladium and iron BNPs (Pd/Fe).
The surface area normalized rate constant of iron BNPs combined with palladium (nZVI/Pd) was two orders of magnitude
higher than that of nZVI [53]. Palladium and iron BNPs are generally used for the removal of TCE. In one of the studies, pal-
ladium was used to convert TCE into ethane with minimal formation of vinyl chloride and other chlorinated intermediates that
often occur with anaerobic bioremediation and with iron metal [54].
nZVI and reactive nanoscale iron product (RNIP) comprise the most basic form of the nano iron technology [49, 55].
Particles of nZVI, typically about 100-200 nm in diameter, consist solely of ZVI (Fe
0
). The most common approach to nZVI
synthesis employs sodium borohydride as the key reductant [49]. In 1997, Wang et al. first produced the nanoscale iron particles
in the laboratory using the method of sodium borohydride (NaBH
4
) reduction [56]. By mixing NaBH
4
with FeCl
3
·6H
2
o, Fe
3+
is
reduced according to the following reaction:
(
)
3
+
+ →+
(
)
+
0
Fe HO
+
3
BH HO Fe BOH
3
3
105
.
H
2
4
2
2
6
3
In a laboratory-scale production of nZVI, Wang et al. achieved a particle size distribution of less than 100 nm for 90% of the
particles produced. The BET surface area (Brunauer-Emmett-Teller (BET) theory that explains adsorption of gas molecules
on a solid surface and is a important analysis technique for the measurement of the specific surface area of a material) for the
particles was determined to be 33.5 m
2
/g [56]. Following the reaction, the reduced particles of iron (Fe
0
) created could be
directly used for contaminant destruction. The stoichiometry of the reduction of TCE to ethane, a typical decontamination reac-
tion, would proceed as follows:
0
+
2
+
−
CHCl
+
4
Fe HCH e l
+ →+
5
4
+
3
2
3
26
RNIP particles vary slightly from nZVI particles, in that RNIP particles consist of approximately a 50:50 wt.% mixture of
iron and magnetite (Fe
3
o
4
). The core of the particles consists of the elemental iron (α-Fe), while the Fe
3
o
4
surrounds the Fe,
forming an outer shell [55].
23.14
conclusions
The aim of this chapter is to give an overall perspective of the use of nanoparticles to solve potential issues such as the more
effective treatment of contaminated water for the purposes of drinking and reuse than through conventional means. Nanoremediation
has the potential to clean up large contaminated sites
in situ
, reduce cleanup time, and eliminate the need for the removal of con-
taminants, hence reducing the contaminant concentration to near zero. A great deal of care needs to be taken if it has to be imple-
mented in real life to avoid deleterious effects of unhygienic water. The success of these techniques in field conditions is a factor
for interdisciplinary collaboration of chemistry, material science, and geology to cope with the challenges of this research.
