Environmental Engineering Reference
In-Depth Information
for bioremediation purposes. A recent interesting development is single enzyme nanoparticles (SENs). A SEN is nothing but a
single molecule of an enzyme, surrounded by a protective silicate cage of a few nanometers, but the active sites are chemically
accessible to the ligands [23]. The use of individual enzymes for remediation processes has recently become more common
since it offers a variety of advantages as compared to traditional microbial methods. Major advantages are their stability under
extreme conditions such as high and low pH, high salinity, and temperature.
23.6
carbon nanotubEs
Significant advancements in nanotube research have been witnessed in recent years, especially in CNT. A wide range of
commercial applications have been identified for CNTs [24]. In recent years, several new reports pertaining to the role of CNTs
in pollution control, waste water purification [25], and desalination [26] have created a new surge of interest in nanotube
research (Table 23.1).
CNTs are the most versatile adsorbents for an array of pollutants like heavy metals, environmental residues, and organic
pollutants such as chloroform, benzene, dichlorobenzene, trihalomethanes, and polyaromatic hydrocarbon [27]. CNTs
also have a phenomenal sorbent potential for inorganic pollutants such as fluoride, along with several divalent metal ions
(Table 23.2). Interestingly, it was observed that crude and poor-quality CNTs having a high surface area have shown better
adsorption capacity as compare to aligned CNTs. This suggests that modification and surface activation of functional
groups of CNTs causes the removal of amorphous carbon [28]. Activation of CNTs under oxidizing conditions with
chemicals such as HNo
3
, KMno
4
, H
2
o
2
, NaoCl, H
2
So
4
, KoH, and NaoH has been widely reported. During activation,
the impurities and catalyst-supporting materials that alter the surface characteristics by introducing new functional groups
are dissolved.
Recently it was reported that ceramic pore channels inducted with CNTs can efficiently remove oils from water [29]. This is
a significant development for the control of oil spillage in water bodies. CNT-embedded magnesium oxide composite is reported
to efficiently remove lead (II) from water [30].
tablE 23.1
basic advantages and functions of cnt-based water filtration systems
functions
applications
Removal of organic molecules and metal ions
Water filtration and remediation
Removal of bacteria and viruses
Point-of-use treatment systems
advance performances
applications
1. High and fast retention of pollutants
Improved adsorption efficiency and capacity
2. Fast mass transport
Gravity driven or low-pressure operation
3. High mechanical properties and light weight
High compacted and portable filters
4. Possible regeneration by heat or chemical treatment
Reusable and economical systems
tablE 23.2
Various types of cnt-based nanomaterials used in water purification specifically for pollutants
Nanomaterials
Pollutants
Sorption
References
SWCNTs
Chloroform (CHCl
3
)
3.158 mg/g
lu et al. (2005)
CNT polymer composite
Trichloroethylene
Nondetectable <0.01 PPB
Salipira et al. (2007)
CNT polymer composite
P
-Nitrophenol
99% removal from a 10 mg/l
spiked water
Salipira et al. (2007)
Ceo
2
-CNT
As (V)
82 mg/g
Peng (2005)
Ceo
2
-aligned CNT
Cr (V)
30.2 mg/g
Di (2006)
Acid-treated MWCNTs
Pb (II)
97.08 mg/g
li et al. (2003)
Cu (II)
24.49 mg/g
Cd (II)
10.86 mg/g
CNTs (diameter 2 nm)
Microcystin toxin (MC)
14.8 mg/g
Yan et al. (2006)
Herbicides
