Environmental Engineering Reference
In-Depth Information
V(L
s
)/V
n
s
=1+4 L
s
/r (Eq. 15.99)
where, V(L
S
) = the experimentally observed flow velocity (cm/s), V
n
s
= the flow
velocity calculated from the Hagen-Poiseuille Equation, r is the radius of the
nanotube. Majumder et al. (2005) reported that L
s
was 39-54 urn for water, 3.4 for
decane, and 28 for ethanol. This is like having a garden hose that can deliver as
much water in the same amount of time as a fire hose that is 10 times larger.
(3)
NMs have the potential to react with a variety of chemicals with increased or novel
reactivity and catalytic activity.
The greater chemical reactivity of NPs results in
increased production of reactive oxygen species (ROS), including free radicals. ROS
production has been found in a diverse range of NPs, including carbon fullerenes,
carbon nanotubes and metal oxide NPs. ROS (and free radical production) is one of
the primary mechanisms of NP toxicity; it may result in oxidative stress,
inflammation, and consequent damage to proteins, membranes and DNA (Nel et al.,
2006; Xia et al., 2006). Currently, oxidative stress has been viewed as the most
appealing paradigm for discriminating the adverse effects of different NMs at the
cellular and molecular level (Stone and Donaldson, 2006).
Recently, deep oxidation of xenobiotics was found to occur in the presence of
ZVI, ethylenetetraaminediacetic acid (EDTA), and air (ZEA) under aqueous
conditions (Noradoun and Cheng, 2005). The mechanism by which the ZEA
reaction proceeds is hypothesized to be through ROS as shown in the following
reactions (Joo and Cheng, 2006):
Fe° -> Fe
2
+
+ 2e"
(Eq. 15.100)
Fe
2
+
+ L^Fe
n
L
(Eq. 15.101)
Fe
n
L + O
2
-> Fe
nl
L + O
2
'"
(Eq. 15.102)
Fe
n
L + O
2
'" + 2H
+
-> Fe
m
L + H
2
O
2
(Eq. 15.103)
Fe
n
L + H
2
O
2
-> Fe
m
L + OH' + HO"
(Eq. 15.104)
where L indicates a suitable ligand (e.g., EDTA). In a ZEA system, ZVI is used as a
pool of reducing agent. The Fe
+
ions are produced by the spontaneous corrosion of
ZVI (eq. 15.100) and are complexed by EDTA forming FE
n
EDTA (eq. 15.101).
Aqueous oxygen is either reduced by the ZVI (a heterogeneous O
2
activation) or
FE
n
EDTA (homogeneous O
2
activation) or by both routes to more reactive forms
(O
2
*~, eq. 15.102) that leads to the production of H
2
O
2
(eq. 15.103) and eventually
the Fenton reaction (eq. 15.104). The ZEA system is capable of degrading the
phosphorus-sulfur groups present in malathion as well as cleaving aromatic rings in
chlorinated phenols to carbonates and simple carboxylates in a one-step process,
eliminating the need for secondary oxidation processes.
(4)
Free NPs or part of f-NMs may be released upon the release of NMs into the
environment.
The behavior of NMs is a function of their size, shape and surface
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