Environmental Engineering Reference
In-Depth Information
between iron and target pollutant, chlorinated hydrocarbons can be reduced by accepting
electrons produced from the oxidation of ZVI:
Fe
0
→ Fe
2+
+ 2e
−
(4.1)
RX + H
+
+ 2e
−
→ RH + X
−
(4.2)
Fe
0
+ RX + H
+
→ Fe
2+
+ RH + X
−
(4.3)
Recent studies on the metal iron chemistry, however, showed that ZVI has several draw-
backs in application [17]. These include the formation of iron oxides on the surface, the
increase in solution pH, and decline in reactivity with time [18,19]. Several attempts, includ-
ing the use of hydrogen gas, noble catalysts, and nanoparticles, have been made to enhance
the reduction rates of priority pollutants [20-22]. The enhancement of the reactivity and
change in end-product distribution by nanoscale ZVI (nZVI) has recently attracted much
attention because of their small particle size (1-100 nm), large speciic surface area, and
unique surface morphology [7].
The robust development of nanotechnology has triggered the use of nanomaterials to
environmental applications. Most environmental applications of nanotechnology fall into
the following categories: treatment/remediation, nanocatalysts, nanosensing/sensor sys-
tem, nano-enable energy, and green technology/pollution prevention [7]. Although sev-
eral nanosized ZVMs and nanostructured materials such as nZVI, carbon nanotube, and
hierarchical titanium dioxide have been synthesized and applied to the removal of many
priority pollutants such as chlorinated hydrocarbons, nitroaromatics, nitrate, and heavy
metal, nZVI is becoming an increasingly popular method for the treatment of hazard-
ous and toxic chemicals in the contaminated soil and groundwater. In this chapter, an
overview of using the microscale and nanoscale ZVI system for the reduction of priority
pollutants under anaerobic conditions is provided. The preparation and characterization
of different kinds of nZVI are irst introduced and compared. The reactivity of bare ZVI
and bimetallic iron systems toward reduction of priority pollutants under various envi-
ronmental conditions are summarized. In addition, the stability and mobility of nZVI in
the environments is discussed.
4.2 Preparation and Characterization of nZVI
Several techniques can be employed for the preparation of nZVI. The use of physical syn-
thetic methods, such as inert gas condensation, severe plastic deformation, high-energy
ball milling, and ultrasonic shot peening, can synthesize ZVI nanoparticles with diam-
eters of 10−30 nm [23]. However, the surface reactivity of these physically synthesized iron
nanoparticles is strong and is dificult for storage and application. In addition, the surface
reactivity of nZVI will gradually decrease owing to the agglomeration of nanoparticles.
The chemical methods include microemulsion, chemical coprecipitation, chemical vapor
condensation, pulse electrodeposition, and chemical wet reduction [23]. Chemical meth-
ods are often used for the synthesis of small quantities of nZVI. In addition, the diam-
eter of synthesized nZVI can be adjusted to the desired particle sizes, depending on the
