Environmental Engineering Reference
In-Depth Information
Hence, graphene adsorbents and membranes have this added advantage that there will be
only minimal microbial contamination.
Photo-inactivation of bacteria (
E. coli
) by a GO-TiO
2
ilm under solar illumination was
reported by Akhavan and Ghaderi.
148
The composite exhibited about 7.5× increased antibac-
terial activity compared with native TiO
2
. The same group have reported an interesting pro-
cess where interactions of GO with
E. coli
living in a mixed-acid fermentation environment
in an anaerobic condition result in the formation of highly antibacterial graphenic mate-
rial.
149
Reduction of GO to RGO occurs owing to the metabolic activity of the surviving bac-
teria through their glycolysis process. After the reduction process, the RGO sheets exhibited
an inhibition for proliferation of the bacteria on their surfaces and the already proliferated
bacteria became detached from the surface of these sheets, pointing to the antibacterial activ-
ity. Some et al.
150
devised a graphene-poly(l-lysine) composite that promotes the growth of
human cell culture and exhibits high antibacterial activity. Antibacterial composites of gra-
phene in combination with ZnO,
151
polyvinyl-
N
-carbazole,
152
lanthanum(III),
153
and chloro-
phenyl pendant
154
have also been reported. Another different effort to construct antibacterial
graphene-based composite was reported by Wang et al.
155
where they prepared GO-benzyl-
penicillin (BP) anion intercalated Mg-Al layered double hydroxide (GO-BP-LDH) hybrid
ilms. The hybrid ilms were fabricated via a simple solvent evaporation process. The ilms
can release BP ions, and the release can be tuned by adjusting the composition of the ilm,
and hence the strategy can be used for drug release applications as well. The antibacterial
activity of the ilm was due to the presence of GO as well as the release of BP.
34.2 Graphene-Based Contaminant Sensing Strategies
The last section illustrated graphene-based strategies employed to remove contaminants
from the water stream. Detecting these contaminants is as important as it is to remove these
toxic materials from drinking water. However, detecting strategies should be able to detect
contaminants at ultralow concentrations, since their permissible limits are very low. The
maximum permissible limits of most of these contaminants are in parts per billion (ppb)
or parts per trillion (ppt). Hence, smart materials have to be used to sense these toxins in a
fast, sensitive, selective, reliable, and reproducible manner. Various NPs with their diverse
physicochemical properties are being employed for this purpose. This section outlines the
various approaches undertaken to construct graphene-based contaminant sensors.
34.2.1 Graphene-Based FET Sensors
Graphene electrically behaves as a semimetal with zero band gap. It has the maximum
room temperature mobility reported. For sensors, this can be helpful for rapid signal trans-
mission. Graphene has many other interesting properties such as ballistic transport of its
charge carriers with very low scattering at room temperature,
1
a tunable band gap,
156-159
quantum interference,
160
and a large quantum capacitance.
8
Hence, a small perturbation
in its electrical characteristics can lead to rapid, ampliied signal response with minimal
background. Therefore, graphene has been widely used for constructing various sen-
sors based on sensitive changes of their electrical properties. Graphene-based ield-effect
transistors (FETs) are one of the most utilized classes of devices for sensor applications.
Schedin et al.
161
did pioneering work on graphene-based sensors. In this study, single gas
