Environmental Engineering Reference
In-Depth Information
34.1.5 Graphene-Based Catalyst for Other Catalytic Degradation Methods
Graphenic materials have been used for other catalytic processes to remove contaminants
as well. Sun et al.
128
demonstrated that RGO having an
I
D
/
I
G
>1.4 can activate peroxymono-
sulfate to produce active sulfate radicals such as
SO
4
−
, which, in turn, can decompose
various aqueous contaminants owing to the powerful oxidizing character of the radicals.
The study proved that compared with other allotropes of carbon such as AC, graphite
powder, GO, and multiwalled CNTs, RGO has better activity. It was also reported that
RGO-based catalysis is better compared with transition metal oxide-based catalysis for
the degradation of phenol, 2,4-dichlorophenol and MB, in water. A graphene-MnOOH
composite prepared by a solvothermal process involving the dissolution-crystallization
and oriented attachment of MnOOH on graphene exhibited unusual catalytic perfor-
mance for the thermal decomposition of ammonium perchlorate.
129
The concerted effect
of graphene and MnOOH is reported to be the reason for the enhanced performance.
A graphene-horseradish peroxidase composite for enzyme-catalyzed degradation of phe-
nolic compounds was reported by Zhang et al.
130
An ethylenediamine-RGO (ED-RGO)
composite for the indirect reduction of Cr(VI) to less toxic Cr(III) and subsequent removal
was reported by Ma et al.
131
The removal was explained via a three-step mechanism. In
the irst step, Cr(VI) binds to the composite through an electrostatic interaction between
the negatively charged Cr(VI) species
HCrO
( )
and the protonated amine groups on ED.
Later in the second step, π electrons on the six-membered carbon ring of RGO reduced
Cr(VI) to Cr(III). This Cr(III) will be liberated into the solution and will attach onto the
ionized carboxylic groups on the RGO in the third step to complete the removal process.
Electro-enzymatic degradation of carbofuran on a ternary GO-Fe
3
O
4
-hemoglobin hybrid
structure was reported by Zhu et al.
132
The composite can be easily separated magnetically
after the remediation process. Graphene-CdS composites were used to sonocatalytically
degrade various azo dyes from water in the absence of light.
133
Shi et al.
134
reported a cobalt
oxide (Co
3
O
4
) supported on graphene that can be used as catalyst for the sulfate radical-
based oxidative removal of orange II from water.
34.1.6 Antibacterial Properties of Graphene
Drinking water contamination due to the presence of microbes is a recurring problem. Not
only water bodies but also the ilters used for puriication purpose are also susceptible to
microbial attacks. The formation of bioilms on the ilter surface due to bacterial growth
can impart unwanted tastes and odors to the puriied water.
135
After some time, this bio-
ilm can also lead to premature clogging of ilters. Graphene can also be a solution for this
problem. The antibacterial activity of GO and RGO was irst investigated by Hu et al.
136
They found that graphenic materials could effectively inhibit the growth of
Escherichia
coli
bacteria while showing minimal cytotoxicity toward human cells. This is an added
advantage since other carbon allotropes such as CNTs are known to have cytotoxic effects.
Krishnamoorthy et al.
137
studied the mechanism behind the antibacterial activity of GO/
RGO. The study was conducted on four different species of pathogenic bacteria. The study
indicated that the production of ROS by graphene leads to an increase of intracellular ROS
levels of the cells, making them susceptible to oxidative stress. Such oxidative stress can
induce damage to cellular components, including DNA, lipids, and proteins.
138,139
Speciic
studies have indicated that oxidation of fatty acids by ROS can generate lipid peroxides
and can subsequently stimulate a chain reaction, leading to the disintegration of the cell
membrane followed by cell death.
