Sunlight induced catalytic degradation of bromophenol blue and antibacterial performance of graphene nanoplatelets/polypyrrole nanocomposites

Article abstract of DOI:10.1016/j.jssc.2019.03.045

Graphene-polymer nanocomposites are innovative materials that have attracted much attention due to their novel features. Herein, we report photocatalytic and antibacterial properties of GNP-PPy nanocomposites. The formation of nanocomposites was confirmed by various characterization techniques. The assembly of GNPs and PPy NPs with optimized GNP content amazingly increased the photocatalytic degradation of bromophenol blue (BPB) up to 93% under solar light irradiation in 120 min. The antibacterial assay revealed that 50% GNPs-PPy nanocomposite showed a best (32.43%) inhibition of growth against a Gram negative bacteria E. coli. The GNP-PPy nanocomposites can possibly be utilized as multifunctional material for wastewater treatment and as antimicrobial agent.

Full text of DOI:10.1016/j.jssc.2019.03.045

Accepted Manuscript
Sunlight induced catalytic degradation of bromophenol blue and antibacterial
performance of graphene nanoplatelets/polypyrrole nanocomposites
Hamsa Noreen, Javed Iqbal, Aqsa Arshad, Rani Faryal, Ata-ur-Rahman, Rozina
Khattak
PII:
S0022-4596(19)30155-0
https://doi.org/10.1016/j.jssc.2019.03.045
YJSSC 20694
DOI:
Reference:
To appear in: Journal of Solid State Chemistry
Received Date: 12 January 2019
Revised Date: 28 February 2019
Accepted Date: 23 March 2019
Please cite this article as: H. Noreen, J. Iqbal, A. Arshad, R. Faryal, Ata-ur-Rahman, R. Khattak,
Sunlight induced catalytic degradation of bromophenol blue and antibacterial performance of graphene
nanoplatelets/polypyrrole nanocomposites, Journal of Solid State Chemistry (2019), doi: https://
doi.org/10.1016/j.jssc.2019.03.045.
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ACCEPTED MANUSCRIPT
Sunlight induced catalytic degradation of bromophenol blue and antibacterial
performance of graphene nanoplatelets/polypyrrole nanocomposites
1
,2,3
*3
4
5
1
Hamsa Noreen , Javed Iqbal , Aqsa Arshad , Rani Faryal , Ata-ur-Rahman , Rozina
Khattak
3
1
Institute of Chemical Sciences, University of Peshawar, Peshawar,
Khyber Pakhtunkhwa, Pakistan
2
Department of Chemistry, Shaheed Benazir Bhutto Women University Peshawar, Khyber
Pakhtunkhwa, Pakistan
3
Department of Physics, Quaid-i-Azam University, Islamabad, Pakistan
4
Department of Physics, International Islamic University, Islamabad, Pakistan
5
Department of Microbiology, Quaid-i-Azam University, Islamabad, Pakistan
*Corresponding authors
Dr. Javed Iqbal Saggu
Tel: +92-51 9064-2112. Email: javed.saggu@qau.edu.pk
1

ACCEPTED MANUSCRIPT
Abstract
Graphene-polymer nanocomposites are innovative materials that have attracted much attention due
to their novel features. Herein, we report photocatalytic and antibacterial properties of GNP-PPy
nanocomposites. The formation of nanocomposites was confirmed by various characterization
techniques. The assembly of GNPs and PPy NPs with optimized GNP content amazingly increased
the photocatalytic degradation of bromophenol blue (BPB) up to 93% under solar light irradiation
in 120 min. The antibacterial assay revealed that 50% GNPs-PPy nanocomposite showed a best
(32.43%) inhibition of growth against a Gram negative bacteria E. coli. The GNP-PPy
nanocomposites can possibly be utilized as multifunctional material for wastewater treatment and
as antimicrobial agent.
Keywords: Ploymers, graphene nanocomposites, wastewater treatment, bacterial growth
inhibition
Graphical Abstract
2

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1
. Introduction
The development of novel polymers nanocomposites has opened new dimension for their
numerous application in all the fields of science and technology. The use of fillers in the form of
inorganic nanomaterials provides additional choice for improvement of physical and chemical
[
1– 8]
properties of polymers
. Graphene nanoplatelets (GNPs) are an attractive filler for polymers
and exhibit wonderful properties for different applications i.e., electronic industries, automotive,
[
9]
construction, photocatalyst and aerospace . Some other commonly used nanofillers are graphene,
[
10]
clay, nanotubes, alumina, silver and gold . Among these, GNPs are new class of derivatives of
2
graphene family, that are sp -hybridized carbon with few stacked atomic layers. This material can
introduce extraordinary thermal and mechanical strength to polymer nanocomposites and polymer
matrix composites, which makes it a superior candidate for many applications like energy storage
[
11-16]
and conversion, fuel cells, sensors
. The exciting characteristic features of GNPs have opened
new dimensions for assembling a variety of inorganic and organic nanoscale units with them, to
tailor the combined properties in a novel fashion for the accomplishment of modern scientific
[
17]
requirements in all the fields of science and technology
.
It has been observed that polymer/GNPs nanocomposites exhibit good properties and performance
even at lesser loadings, when compared with conventional micron-scale fillers (like carbon fibers
or glass) based polymer composites. One of the advantage is lower component weight. Additional
advantage is choice of multi-functionalization that enables the polymer to find variety of
[
18, 19]
applications
. However, a major drawback is that only few conducting polymers are stable
enough to be incorporated in practical applications under normal processing conditions. Among
them, the most promising are polypyrrole, polyaniline and polythiophene as they possess
3

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reasonable air stabilities, high conductivities, sensors, environment remediation and photo catalytic
[
20]
properties etc.
.
Polypyrrole (PPy) has been studied as one of the best conducting electroactive polymer owing to
[
21]
its intrinsic characteristics i.e., redox-active nature and high electrical conductivity . It has co-
planar ( -stacked) structure which make it superior contestant for catalysts support, non-ferrous
π
and ferrous metals protector from corrosion, absorption of electromagnetic radiation, sensing of
gases, electrode materials in supercapacitors and generation of thermoelectricity at low-
temperature. Furthermore, it can also be used in different biomedical applications like tissue
engineering, wound-infection cure, biosensing, imaging, drug delivery, diagnosis, nanocarrier
development, photothermal therapy, cancer therapy, photodynamic therapy, tissue engineering
[
22-30]
and gene transfection
.
The ecological problems caused by enormous use of dyes, organic wastes, pesticides and heavy
metals in seas and rivers on global scale have opened new prospects for the initiation of
[
31]
fundamental and applied research on the environmental protection . Photocatalysis is one of the
potential approach to achieve degradation of organic dyes to CO , H O and other non-hazardous
2
2
inorganic compounds without generating secondary pollution. Different organics dyes like
bromophenol blue (BPB), methyl orange (MO) and methylene blue (MB) are commonly utilized in
a range of textile industries. They cause severe ecological hazards and result in mutagenic and
[
32, 33]
carcinogenic effects to the environment and aquatic organisms
. To tackle this, the
decolorization of toxic organic dyes, to detoxify water is a solution that can be achieved by
[
34, 35]
synthesizing an effective catalyst that can promptly trigger the disintegration of pollutants
.
GNPs offer an attractive choice to prepare graphene-based nanomaterials for photocatalysis.
Previous work show that the nanocomposites composed of graphene and photoactive materials can
4

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effectively improve the photocatalytic degradation by enhancing the transfer and separation of
[36]
photo-generated charges, which is imperative for photocatalytic reactions
. It has also been
reported that the inclusion of the amazing visible and solar-light absorption capabilities of organic
photosensitizers with the charge transfer properties of graphene-based nanomaterials leads towards
[
37]
the cutting-edge performance of materials for water remediation
.
In this work, we have used GNPs as nanofillers for polypyrrole (PPy) to improve optical,
structural, and electrical properties for photodegradation of organic pollutants. Herein, we report
the synthesis of pristine PPy NPs and GNP-PPy nanocomposites. To the best of our knowledge,
the photodegradation of bromophenol blue (BPB) dye using PPy NPs and GNP-PPy
nanocomposites as photocatalyst has not been reported so far. For the first time, these
nanocomposites have been used as photocatalysts to decolorize BPB under solar light irradiation.
BPB dye has been selected as modal noxious waste for photocatalytic degradation due to its
presence in wastewaters of industries. Moreover, we also present a first study on GNPs loading
dependent antimicrobial activity of GNP-PPy nanocomposites.
2
2
. Materials and Methods
.1 Materials
3 2
Pyrrole (98%, Sigma Aldrich), ferric chloride hexahydrate (FeCl .6H O, 98%, Sigma Aldrich),
polyvinyl alcohol (PVA, 87-90% hydrolyzed, molecular weight 85000-124000, Alfa Aesar) and
graphene nanoplatelets (99.9%, KNano) have been used as received without further purification.
Distilled water has been used for the synthesis of PPy NPs and its nanocomposites.
5

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2
.2 Preparation of PPy NPs
Uniform pristine PPy NPs were synthesized using a mixture of FeCl -PVA with pyrrole monomer
3
o
in aqueous solution. Briefly, 1.50 g PVA was dissolved in deionized water for 20 min at 60 C.
After cooling to room temperature, FeCl .6H O (1.2434 g) was introduced to the PVA solution, as
3
2
a result the water-soluble polymer cation system changed to a viscous orange form. After one
3
hour, the monomer pyrrole was added to the FeCl -PVA mixture and the polymerization
o
proceeded at 5 C.
Polymerization process starts instantaneously when pyrrole was combined with the oxidizing
agent. After some time, the solution changed its color to black and then it was stirred for four
hours. As the polymerization reaction completed, the synthesized PPy NPs were separated from
the dispersion solution by centrifugation (4000 rpm, 40 min). The materials were washed three
times with distilled water to eliminate contaminations. The PPy NPs were resuspended in distilled
[
37]
water by ultrasonication
.
2
.3 Synthesis of GNPs-PPy Nanocomposites
The GNPs-PPy nanocomposites were synthesized using an in situ chemical oxidative
polymerization method. GNPs with different weight percent i.e., from 10 to 50% were sonicated
for 30 min. After sonication, pyrrole (1.67 g) was added to each selected wt. % of the GNPs
suspensions. Later, the suspensions were stirred for one hour. Similarly, three different solutions
3 2
were prepared in the separate flasks by adding 15.5 g FeCl .6H O and 1.74 g PVA in deionized
water. The reaction mixtures were added into the solutions of GNPs-PPy (10–50 wt %) and were
stirred for 4 h to start the polymerization. GNPs-PPy nanocomposites in black powder form were
obtained by centrifugation and washing with deionized water was carried out to eliminate
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3
impurities like un-reacted pyrrole, free PVA and FeCl . Finally, prepared nanocomposites were
o
dried in a vacuum oven for 24 h at 60 C.
2
.4 Characterizations
Different characterization techniques were used to confirm the sample formation. X-ray
diffractometer (JDX-3532, JEOL), UV-vis-NIR spectrophotometer (PerkinElmer Lambda 1050),
scanning electron microscope (JSM-5910, JEOL) and Fourier transform infrared
spectrophotometer (PerkinElmer Spectrum 2) were used to characterize pristine PPy NPs and
GNPs-PPy nanocomposites.
2
.5 Photocatalytic Activity
The photodegradation of bromophenol blue (BPB) under solar light irradiation was carried out to
reveal the photocatalytic effect of the pristine PPy NPs and GNPs-PPy nanocomposites (10%, 30%
and 50%). A UV-vis spectrophotometer was used to record the absorbance profiles of used
pollutant. To suggest a cheap solution to clean the dye contaminated water, all the experiments
were conducted in direct sunlight. All the photocatalytic experiments were performed from
o
1
0:00 am to 2.00 pm, on a sunny day, with a temperature 37 C in Peshawar (Pakistan)
(
34.0087° North latitude, 71.4878° E). The amount of catalyst used was 0.05 gm. and initial
volume of water was 100 ml that was taken to perform experiments. All experiments were
performed in Pyrex containers with internal diameter 8.5 cm. A 20-ppm aqueous solution of BPB
was used in all experiments. Prior to irradiation, the solutions in presence of photocatalysts were
magnetically stirred for 120 min in the dark to assure the establishment of adsorption/desorption
equilibrium.
7

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Figure 1 A schematic presentation of the photocatalytic experiment
After exposure to sunlight, a 2 mL of solution was taken out at regular intervals and centrifuged to
eliminate photocatalysts. The collected solution was centrifuged at 4000 rpm for 5 min to remove
the photocatalyst from solution. The absorbance of all the collected samples was recorded using
UV–vis spectrophotometer.
2
.6 Antimicrobial Assay
The antibacterial activity of pristine PPy NPs and GNPs-PPy nanocomposites (10%, 30% and
0%) against two bacterial stains E. coli and S. aureus were tested by agar well diffusion method.
5
The pristine PPy NPs and GNPs-PPy nanocomposites (10%, 30% and 50%), with a known
concentration of sterile water, were mixed and sonicated for 30 min. The selected bacterial strains
were first grown in LB (Luria-Bertani) broth. A 10
µl aliquot of the each of bacterial strain was
then taken and added to 8 ml of fresh LB broth with 0.7% agar and was poured over a 90 mm petri
dish that contains 25 ml of 1.5% agar in LB broth. After the top agar got hardened, a 20 µl aliquot
8

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of the test sample was filtered on a 0.22 µm Millipore filter and was dropped onto the surface of
o
the top agar. It was then allowed to be completely dried before being incubated overnight at 37 C.
If the sample examined had antimicrobial activity, a clear zone would be formed on the surface of
[
38]
the top agar representing inhibition of bacterial growth.
The diameter of this zone would
present the extent to which the bacteria have been killed. The inhibition of growth was measured
as zone of inhibition (ZOI) in mm.
3
3
. Results and Discussion
.1 Surface and Morphology
The morphology and size of pristine PPy NPs were studied by SEM as shown in Fig. 2(a). The
image clearly indicates that PPy consists of exclusively spherical nanoparticles with narrow
particle size distribution and the average size is about 50 nm. The morphology of GNPs-PPy
nanocomposites having 10%, 30%, and 50% GNPs respectively is shown in Fig. 2(b)–(d).
These images indicate the bi-phase nature of the nanocomposites.
9

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Fig. 2 SEM images of (a) pristine PPy NPs, (b) 10% GNPs-PPy nanocomposite, (c)
30% GNPs-PPy nanocomposite, and (d) 50% GNPs-PPy nanocomposite
During the polymerization of pyrrole monomer GNP strongly influenced the architecture of PPy
NPs. This is evident from Fig. 2(b)-(d). The biphase nature of the prepared material is also clearly
visible. The SEM images indicate the successful formation of nanocomposites.
3
.2 Vibrational Analysis
IR spectra of pristine PPy NPs and GNPs-PPy nanocomposites (10%, 30% and 50%) are shown in
-
Fig. 3. The spectrum (a) is that of pristine PPy NPs and shows that a band that appears at 1180 cm
1
can be attributed to the S=O aromatic ring-doped state of polypyrrole, while the stretching
-1
vibration regions that appear at 1305 and 1548 cm represent the C-N and C=C characteristic
vibration of pristine PPy NPs respectively. These bands are also observed in (b), (c), and (d)
curves that belong to GNPs-PPy nanocomposites (i.e., 10% GNPs-PPy nanocomposite, 30% GNP-
-1
-1
PPy nanocomposite and 50% GNPs-PPy nanocomposite). The band at 1534 cm and 1035 cm
corresponds to the bipolaran structures of PPy in the GNPs-PPy nanocomposites, representing that
the polymerization occurred during the loading of graphene. Furthermore, some bands show slight
shifts, which can be assigned to the incorporation of pristine PPy nanoparticles on the surface of
1
0

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GNPs in the GNPs-PPy nanocomposites. All the bands shown in Fig. 2 agree with the FTIR
[
39]
spectra of pristine PPy NPs as given in previous work . These results indicate the successful
synthesis of GNPs-PPy nanocomposites.
Fig. 3 FTIR analysis of (a) pristine PPy NPs, (b) 10% GNPs-PPy nanocomposite,
(c) 30% GNPs-PPy nanocomposite and (d) 50% GNPs-PPy nanocomposite
3
.3 Optical Properties
The absorbance spectra of aqueous suspensions of pristine PPy NPs and GNPs-PPy
nanocomposites (10%, 30% and 50%) was recorded from 200 nm-900 nm on UV-vis
spectrophotometer. The results are displayed in Fig. 4(a). Neat PPy NPs show an absorbance peak
at 357 nm in the whole visible light region, that corresponds to the
π–π* (HOMO–LUMO)
[
40]
transition of the PPy NPs . However, GNPs-PPy nanocomposites (10%, 30% and 50%) show
significantly different spectra as compared to neat PPy NPs. That may be due to introduction of
GNPs to PPy NPs. It is demonstrated in literature that the energy of aromatic C=C bonds (π- π*) of
1
1

ACCEPTED MANUSCRIPT
GNPs is considerably changed by adding PPy NPs which is because of the intensification of
[
41, 42]
conjugated
π-bond caused by the
π-
π
stacking between GNP and PPy NPs
.
Fig. 4(a) UV-Vis-NiR analysis of (a) pristine PPy NPs, 10% GNP-PPy nanocomposite, 30%
GNP-PPy nanocomposite and 50%GNP-PPy nanocomposite, (b) Tauc’s plot for calculation of
bandgap energies of PPy and graphene PPy nanocomposites.
g
Moreover, E , the energy bandgap is the energy variation between the valence band and the
conduction band, characterizes the spectroscopic and chemical properties of material and it also
explains different kinds of reactions in conjugated system. Conduction band is the well-known
lowest unoccupied molecular orbital, LUMO (
which the electron is always in free motion in the lattice system, while the valence band is the
highest occupied molecular orbital, HOMO ( donor) and the last filled energy level for molecules
The E of pristine PPy NPs and GNPs-PPy nanocomposites (10%, 30% and 50%) is obtained
π acceptor) and is the first unfilled energy level in
π
[
43]
.
g
[
44]
by using Tauc’s relation
correlation with the reported values
direct band gap energy i.e. to 1.85 eV, 1.69 eV and 1.63 eV for 10% GNP-PPy nanocomposite,
0% GNP-PPy nanocomposite and 50% GNP-PPy nanocomposite respectively (Figure 4). The
narrowing of band gap energy mainly arises because of the chemical interaction of GNPs and PPy
. E obtained for pristine PPy NPs is 2.38 eV which is in good
g
[
45,46]
, whereas addition of GNP has slightly minimized the
3
1
2

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NPs in the synthesized nanocomposites. The good photodegradation and decrease in absorbance of
BPB with time can be correlated with the decreased optical bandgap energy. The low bandgap
makes the fast photoexcitation of electrons possible. This would make the photocatalyst to
photodegrade the adsorbed dye quickly. The low band gap of GNP-PPy nanocomposites has
[
47,49]
indicated its potential use as an effective photocatalyst in outdoor sunlight conditions
.
3
.4 Photocatalytic Activity
Photocatalytic degradation of textile industrial dye bromophenol blue (BPB) is investigated using
the pristine PPy NPs and GNPs-PPy nanocomposites (10%, 30% and 50%). Pristine PPy NPs and
GNsP-PPy nanocomposites have been stirred in dark for 120 min to achieve the adsorption-
desorption equilibrium. After the exposure of prepared samples to sunlight, the UV-visible
absorption spectra for BPB in the presence of photocatalysts were again recorded and their spectra
are shown in Fig. 5 (a)-(d).
1
3

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Fig. 5 Photocatalytic degradation of under solar light irradiation of (a) pristine PPy NPs, (b)10%
GNPs-PPy nanocomposite, (c) 30% GNPs-PPy nanocomposite, and (d) 50% GNPs-PPy
nanocomposite
The % degradation is estimated with the help of following equation,
%
Degradation efficiency = (1 – C
is the concentration at different time intervals, C is the initial concentration of aqueous
solution of BPB. C and C are estimated using the Beer Lambert’s law. The absorbance of BPB
t o
/C ) x100
Where C
t
o
o
t
shows a decreasing trend with increase in irradiation time.
The graphene content in the nanocomposites highly affects the photodegradation rates. Among all
the samples 50% GNPs-PPy nanocomposite exhibited best photocatalytic action. PPy
nanoparticles, 10% and 30% GNP-PPy nanocomposites didn’t show good catalytic efficiencies.
However, it is observed that, an increase quantity of GNPs used in the nanocomposites,
significantly affects the photodegradation of pollutants. A higher amount results in the superior
photocatalytic degradation.
The results showed that 93% BPB was degraded in 120 min when 50% GNP-PPy photocatalyst
was used. This superior performance of nanocomposite is due to the synergistic properties of PPy
NPs and GNPs. The results show that effective charge transfer between PPy NPs and GNPs can
1
4

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improve the photocatalytic activity. A strong interfacial contact between PPy and GNPs is vital in
this case.
3
.4.1 Kinetic Study
The kinetics of the photocatalytic reactions are presented in Fig. 6(a) and (b). A pseudo first order
kinetics were used to fit the data, that obeyed the following equation.
ln(C /C ) = kt
o
t
Where Co and C are the concentrations of BPB at time t = 0 and other times respectively, and
k
is
t
the apparent rate constant of reaction. The apparent rate constant increases significantly for 50%
-1
-1
-
GNPs-PPy nanocomposite i.e., 0.02 min , whereas it is 0.0007 min for neat PPy NPs, 0.001 min
1
-1
for 10% PPy-GNPs nanocomposite, and 0.0056 min for 30% PPy-GNPs nanocomposite.
These results recommend 50% PPy-GNPs nanocomposite for an efficient and quick photocatalytic
degradation of BPB.
Fig. 6 (a) Variation in concentration of BPB in presence of different samples, (b) the pseudo first
order reaction kinetics of different samples
1
5

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Concluding, results indicated that 50% GNPs-PPy nanocomposite is one of the best photocatalyst
under solar light illumination and BPB can be removed up to 93% in 120 min with a greater
apparent rate constant.
3
.4.2 Mechanism of ROS Generation and Dye Degradation
·
- ·
Reactive oxygen species ( O , OH) are remarkably responsible for photocatalytic degradation of
2
dyes of semiconductor materials. The GNPs-PPy nanocomposites can possibly degrade the dye by
releasing the ROS, which highlights the symbiotic role of PPy NPs and GNPs for the degradation
of dye. The photocatalytic degradation has three main steps. First is the adsorption of contaminants
on the surface of photocatalyst, second is the absorption of light by photocatalyst, and third is the
charge transfer reactions that generate ROS to decompose the contaminants. It was further
highlighted in previous works that carbonaceous compounds show amazing absorption efficacy
[
50]
[51]
,
therefore, these are the promising candidates for different environmental applications
.
Mostly industrial dyes and other relevant noxious wastes have the capability to produce
π-π
stacking with graphene due to their aromatic nature. Therefore, adsorption facilitates the
enhancement in concentration of contaminants on surface of catalyst. This aspect significantly
[
52]
contributes towards photocatalytic degradation
.
A mechanism for the photo-degradation of BPB is proposed in Fig. 7. The dye molecules are
adsorbed on the surface of PPy-GNPs nanocomposite. After exposure to the solar light, the
excitation of electrons from HUMO of PPy occurs. These electrons are excited to LUMO of PPy
NPs. As the graphene based nanomaterials exhibit wonderful electrical conductivity, therefore, the
adjacent GNPs network ultimately accepts these electrons and large number of holes remain
unoccupied. GNPs maintain the continuous flow of charge carriers, that eventually hinders the
1
6

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recombination of e-h pairs. The large number of electrons and holes cause the formation of
•
reactive oxygen species (ROS), specially generates OH radicals by the reaction of holes in the
HUMO with chemisorbed water which successively attacks BPB. Finally, it produces numerous
intermediates by the oxidation of adsorbed dye which are then converted into H
2 2
O and CO . The
photodegradation of BPB is elucidated in following reaction.
+
-
GNP-PPy +
h
ν → PPy (
h
) + GNP (e )
+
–
The generated
h
on the PPy NPs surface reacts with water or OH to form
•
OH, while the
.
-
-
produced e reacts with O
2
and forms superoxides ( O
2
).
GNP
Polypyrrole NPs
1
7

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Fig. 7 Schematic illustration of Pristine PPy NPs and GNP-PPy nanocomposites
3
.6 Antimicrobial Activity
The prepared materials i.e., pristine PPy NPs and GNP-PPy nanocomposites (10%, 30% and 50%)
were explored against infectious bacteria i.e., Escherichia coli E. coli) and Staphylococcus aureus
S. aureus) as shown in Fig. 8. Results show that 50% GNP-PPy nanocomposite exhibited
(
(
maximum zone of inhibition against E. coli with zone diameter of 12 mm as compared to the 10%
GNP-PPy nanocomposite and 30% GNP-PPy NPs nanocomposite (Fig. 8 and 9), while the pristine
PPy NPs and all GNPs-PPy nanocomposites were inactive against S. aureus as presented by zone
of inhibitions. Various mechanisms have been suggested in literature to demonstrate the growth
inhibitory property of graphene based nanocomposites. It has been suggested that the oxidative
stress is the basic reason of cellular damages. This stress can be caused by presence of
nanocomposites. A similar study has also reported that oxidative stress can be created due to other
[
53]
carbon nanomaterials e.g., fullerene and CNTs
.
Fig. 8 Antibacterial assay using prepared materials (a) ZOI using different samples and (b) %
growth inhibition of E. coli using pristine PPy NPs and GNPs-PPy nanocomposites
1
8

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Furthermore, few recent studies asserted that cell membrane undergoes charge imbalance, which
results in collapsing of membrane. GNPs-PPy nanocomposites showed selective cytotoxicity. This
is due to the difference in charge nature of cell membranes of E. coli and S. aureus. The negatively
charged bacterial cell membranes strongly interact with the excellent electron acceptors graphene
and their nanocomposites which results in the flow of electrons from bacterial membrane to the
GNPs. As a result, a conductive network encompasses the bacterial cell membranes. Consequently,
[
54]
it causes the oxidative stress in the bacterial cell membrane, inducing the microbial cell death
.
Fig. 9 Zone of inhibition of pristine PPy NPs and GNPs-PPy nanocomposites against
(a) E. coli and (b) S. aureus
Conclusively, it can be established on the similar grounds that the antibacterial activity of GNPs-
PPy nanocomposites is the synergistic effect of oxidative stress induced by GNPs and PPy on
bacterial cell wall because of flow of negative charge from the membrane to GNPs.
Since, E. coli are dangerous because of their presence in intestine, contaminated food and drinking
[
55]
water , therefore, the development of cost effective, easy processable and efficient antimicrobial
materials to inhibit the growth of pathogenic bacteria is the need of the day. In this regard, 50%
1
9

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GNP-PPy nanocomposite is a promising antibacterial agent that can inhibit the infectious bacterial
growth.
4
. Conclusions
A simple method has been described in this work to synthesize GNPs-PPy nanocomposites.
Morphological studies reveal that the PPy NPs have been successfully anchored on graphene
nanoplatelets. The photocatalysis shows that the assembly of GNPs and PPy NPs amazingly
increased the photocatalytic degradation of BPB up to 93% under solar light irradiation in 120 min.
Interestingly, 50% GNPs-PPy nanocomposite demonstrated 32.43% growth inhibition of E. coli, as
revealed by antibacterial assay. Therefore, 50% GNPs-PPy nanocomposite can be utilized as an
interesting multifunctional material for cleaning contaminated water and bacterial growth
inhibition.
Acknowledgments
This research is funded by the Higher Education Commission of Pakistan (HEC) NRPU (Grant
No.: 20-4861/R&D/HEC/14) to Dr. Javed Iqbal at Quaid-i-Azam University, Islamabad.
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HIGHLIGHTS
•
•
Graphene/PPy nanocomposite with different compositions have been prepared.
Photocatalytic activity of prepared materials has been investigated. The materials are
sunlight active and show good photocatalytic activity.
•
The materials also show moderate antibacterial activity.