Environmental Engineering Reference
In-Depth Information
particularly effective decontaminants for several
classes of environmentally problematic com-
pounds at elevated temperatures, enabling com-
plete destruction of these compounds at
considerably lower temperatures than that
required for incineration (Decker et al.
2002
).
The application of nanocrystalline materials as
destructive adsorbents for acid gases such as
HCl, HBr, CO
2
, H
2
S, NO
X
, and SO
X
has been
found to be more effective than commercially
available oxides (Klabunde et al.
1996
; Stark and
Klabunde
1996
; Carnes et al.
2002
). In waste and
wastewater treatment, MgO facilitates the adsorp-
tion and precipitation of silica and heavy metals
and helps in preventing scale formation in boil-
ers, heat exchangers, and piping. For soil reme-
diation, it is an excellent pH modifi er and heavy
metal scavenger in contaminated soils and also
effectively precipitates heavy metals, thus pre-
venting subsequent leaching from treated soils
(
http://www.baymag.com
). Copper oxide
nanoparticles have been synthesized using gram-
negative bacterium of the genus
Serratia
and
Aloe vera
extract (Saif Hasan et al.
2008
;
Sangeetha et al.
2012
). Cupric oxide can safely
dispose hazardous materials like
cyanide
,
hydro-
carbons
,
halogenated hydrocarbons
,
and
dioxins
through
oxidation
(Kenney and Uchida
2007
).
Copper oxide nanocrystals also possess photo-
catalytic, photovoltaic, and photoconductive
functionalities (Kwak and Kim
2005
). Titanium
oxide has been synthesized via the “green” route
using leaf extracts of
Catharanthus roseus
and
Nyctanthes arbor-tristis
and R5 peptide derived
from diatom
Cylindrotheca fusiformis
and also
using
Lactobacillus
sp. and Saccharomyces cere-
visiae (Sewell and Wright
2006
; Jha et al.
2009
;
Sundrarajan and Gowri
2011
; Velayutham et al.
2012
). It serves as photocatalyst in detoxifi cation
of wastewater (Jones et al.
2007
). Semiconducting
properties of TiO
2
materials are responsible for
the removal of various organic pollutants
(Makarova et al.
2000
). Degradation of nitroben-
zene has been achieved using nano-TiO
2
(Yang
et al.
2007
). The bacterium
Actinobacter
sp. has
been shown to be capable of synthesizing iron-
based nanoparticles under ambient conditions
depending on the nature of precursors used
(Bharde et al.
2005
,
2008
). They are being used
to clean carbon tetrachloride in groundwater and
arsenic from water wells. The use of zerovalent
iron (ZVI or Fe
0
) for in situ remedial treatment
has been expanded to include all different kinds
of contaminants (Ponder et al.
2000
).
6.5
Platinum Nanoparticles
They have been synthesized using >10 %
Diospyros kaki
leaf extract as reducing agent
from an aqueous H
2
PtCl
6
.6H
2
O solution at a
reaction temperature of 95 °C and as reducing
agent from aqueous chloroplatinic acid at a reac-
tion temperature of 100 °C that fi nds application
in water electrolysis (Song et al.
2010
;
Soundarrajan et al.
2012
). Preferential oxidation
of carbon monoxide is important for purifi cation
of H
2
for use in polymer electrolyte fuel cells
which has been possible with platinum nanopar-
ticles in mesoporous silica with unprecedented
activity, selectivity, and durability below 353 K
(Fukuoka et al.
2007
).
7
Barriers and Challenges
to Commercialization
of Green Nanotechnology
(ACS
2011
)
1. Lack of clear design guidelines for researchers
in initial discovery phases of green nanosci-
ence. The choices made for the synthesis of
new green nanomaterials can affect throughout
the development and commercialization pro-
cess which most researchers are unaware of.
2. Many green nanomaterials require new com-
mercial production techniques, which
increases the need for basic research, engi-
neering research, and coordination of the
two between the industrial and research
communities, as the challenges do not
appear until fi rms begin to produce in large
quantities. This problem is common for
small companies and start-ups and solutions
rely at least partially on work done by the
research community.
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