Nanomaterials for Environmental Burden Reduction, Waste Treatment and Non-Point Source Pollution Control - Nanotechnologies for Water Environment Applications - page 450

sorbent materials. For example, when chlorine is present, the bulk sorbents do not
effectively suppress the nucleation of the heavy metal species, resulting in the formation
of submicrometer-sized aerosols that are difficult to be captured in conventional particle
control devices (Scotto et al., 1994). It is essential that the sorbent particle is in a size
range (preferably < 500 nm) that would result in its effective capture in a particle control
device (Owens and Biswas, 1996a, b). The use of a nanostructured sorbent injection
method to capture heavy metals in combustion environments has been widely studied.
Several sorbent materials, including calcium, silica, complexes of aluminum-silicon, and
other oxides, can have very high capture efficiencies. For example, capture efficiencies
of lead exceeded 95% in a high-temperature environment by utilizing a nanostructured
silica sorbent. Nanocrystals have been used to remove carbon dioxide released from the
smokestack. When carbon dioxide lands on a nanocrystal composed of cadmium,
selenium, and indium, the nanocrystal donates an electron to the carbon dioxide. This
extra electron allows the carbon dioxide to react with other molecules and then becomes
harmless (Booker and Boysen, 2005).
Mercury, a toxic element, primarily emitted from coal combustion systems
(Rodriguez et al., 2004), is a pollutant transported on a global scale. Brown et al. (1999)
have indicated that one of the most touted methods is that of activated and other forms
of carbon. The carbon sorbents have been found to be most effective at the nanoscale
with functional groups that have a high affinity for mercury, such as halogens and other
chelating groups (Kwon and Vidic, 2000). Another mercury-containment method being
investigated uses titanium oxide nanocrystals under UV light, which turns the mercury
vapor into mercury oxide, a solid that can be easily removed. Placing a UV light source
in the smokestack poses a possible maintenance problem. Therefore, other nanocrystals
(e.g., iron oxide nanoparticles) can be used as long as they require heat rather than UV
light to make the reaction work (Booker and Boysen, 2005).
Sometimes, valuable byproducts can be obtained from nanoparticle emission,
thereby reducing emissions to the environment. Zimmer and Biswas (2000) suggested
the use of magnetic fields to capture magnetic nanoparticles in a welding plume and
obtain high-value magnetic oxides; they demonstrated the viability of using captured
welding-generated aerosol particles for the treatment of contaminated water streams.
14.2.3 Desulfurization/Denitrification of Non-Renewable Energy Sources
Utilization and combustion of nonrenewable energy sources produce serious
NPS pollutions, which mainly result from the release of sulfur- and nitrogen-containing
compounds that are common impurities in the nonrenewable energy sources such as
petroleum. For example, automobile emissions are one category of NPS pollutions. SO2
and NO2 are serious air pollutants (frequently produced during the combustion of fossil
derived fuels) that contribute to the generation of acid rain; they are also known as a