Environmental Engineering Reference
In-Depth Information
and heavy metals. Besides iron, other metal nanoparticles like Co, Ni, and Pd are also widely used as magnetic nanoparticles
for the removal of contaminants from water. Titanium dioxide (Tio
2
) is a naturally occurring oxide of titanium and is found in
nature as the well-known minerals rutile, anatase, and brookite. Titanium dioxide nanoparticles are commonly used as a photo-
catalyst. Magnetite (Fe
3
o
4
) is a mineral with the chemical formula Fe
3
o
4
, one of several iron oxides [41].
23.11
graPhEnE
A graphene sheet is an infinite two-dimensional (2D) layer consisting of sp-hybridized carbon atoms that belongs to one of the
five 2D Bravais lattices called the hexagonal (triangular) lattice. It is noteworthy that by piling up graphene layers, in an orderly
way, one can form 3D graphite. Graphene was initially considered as a theoretical building block used to describe the graphite
crystal, and to study the formation of CNTs (rolled graphene sheets).
Gold nanoparticle-graphene nanocomposites have been used for desalination purposes and it was observed that this nano-
composite system can enhance the palatability of water fulfilling several criteria. This nanocomposite was prepared by the
reduction of gold ions using sodium citrate as the reducing and capping material. Both graphene-gold and graphene-silver
nanocomposites are efficient photothermal materials used for water desalination. In one method, a mixture of 0.1 g graphene
and 50 µg gold particles was added to 1 l of seawater, and exposed to sunlight. The rate of temperature rise upon exposure to
light from a halogen lamp after adding different nanomaterials was measured. The mixture of gold and graphene was much
more efficient than plasmonic nanomaterials alone. The obtained water via desalination using the graphene nanocomposite was
tested chemically and biologically. All chemical testing was carried out according to the standard international protocols in
order to determine water quality, namely, salinity, pH, dissolved oxygen test, hardness, heavy metal content, and the total
amount of phosphate, sulfate, and carbonate ions (Table 23.3). The result indicated that water obtained from this nanocomposite
was totally pure and free from all salts, metal ions, and heavy metals.
Many protozoa, bacteria, viruses, algae, and fungi are found in natural water systems. Some are pathogenic (typhoid, cholera,
and amebic dysentry can result from waterborne pathogens). The obtained distilled water using this nanocomposite was exam-
ined and indicated that the water was totally clean and did not contain any microorganism. This might be because of the photo-
thermal effect of the nanocomposite, which raises the temperature and causes bacterial death.
23.12
WatEr sitE rEmEdiation/nanorEmEdiation
In recent years, nanoremediation has become the main focus of research and development. There is great potential for the use
of this technology to clean up contaminated sites and protect the environment from pollution. This eco-friendly technology is
considered to be an effective alternative to the current practices of site remediation.
Nanoremediation methods involve the application of reactive materials for the detoxification and transformation of pollut-
ants. These materials initiate both chemical reduction and catalysis of the pollutants of concern. The unique properties of nano-
materials make them best suited for
in situ
applications. Their small size and novel surface coatings enable them to achieve
farther and wider distribution when compared to large-sized particles.
over the years, the field of remediation has grown and evolved significantly into new technologies in attempts to improve
the remediation process. one of the most established systems is “pump-and-treat” [42]. Pump-and-treat systems operate on
the basis of removing contaminated groundwater from the ground, downstream of the contamination site, and then treating it
tablE 23.3 comparative analysis of gold-graphene nanocomposite for its efficacy in the removal
of major ionic contaminants and also on various other parameters of water palatability
SN
Water quality
Graphene-gold nanocomposite
Common drinking water
1
pH
7
6.8
2
Calcium content
0
50 ppm
3
Chlorine content
0
100 ppm
4
oxygen
1.5%
2.2%
5
Sulfate ions
0
20 ppm
6
Mg ions
0
30 ppm
7
Salinity
0
0.03%
8
Hardness
0
2%
