CoFe2O4@TiO2 decorated reduced graphene oxide nanocomposite for photocatalytic degradation of chlorpyrifos

Article abstract of DOI:10.1016/j.molliq.2015.04.032

Chlorpyrifos is widely used to control pest insects in residential, agricultural, and commercial applications. Its common use has led to the release of chlorpyrifos into sediments, wastewater and water sources. The presence of chlorpyrifos in wastewaters and water sources may affect ecosystem and human health due to its chronicle toxicity to aquatic organisms. In this study, magnetic recoverable CoFe₂O₄@TiO₂ decorated reduced graphene oxide nanocomposite was prepared and used for investigating the photodegradation of chlorpyrifos. The nanocomposite was characterized by using transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. In photocatalytic degradation of chlorpyrifos experiments, the effect of operating variables such as initial chlorpyrifos concentration, catalyst dosage and contact time was also investigated. The photocatalytic degradation of chlorpyrifos followed the pseudo-first-order kinetic model. The results indicated that the nanocomposite exhibited a high efficient photocatalytic activity on the photodegradation of chlorpyrifos. The nanocomposite was separated from the solution by a magnet and reused after the photodegradation of chlorpyrifos. The recyclable of the nanocomposite is economically significant in the industry.

Full text of DOI:10.1016/j.molliq.2015.04.032

Journal of Molecular Liquids 208 (2015) 122–129
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
CoFe O @TiO decorated reduced graphene oxide nanocomposite for
2
4
2
photocatalytic degradation of chlorpyrifos
a,b,c,
d
d,
e
Vinod Kumar Gupta
⁎, Tanju Eren , Necip Atar ⁎⁎, Mehmet Lütfi Yola ,
f
g
Cemal Parlak , Hassan Karimi-Maleh
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
Center for Environment and Water, The Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia
Department of Applied Chemistry, University of Johannesburg, South Africa
Department of Chemical Engineering, Pamukkale University, Denizli, Turkey
Department of Metallurgical and Materials Engineering, Sinop University, Sinop, Turkey
Department of Physics, Dumlupinar University, Kütahya, Turkey
Department of Chemistry, Graduate University of Advanced Technology, Kerman, Iran
a
b
c
d
e
f
g
a r t i c l e i n f o
a b s t r a c t
Available online xxxx
Chlorpyrifos is widely used to control pest insects in residential, agricultural, and commercial applications. Its
common use has led to the release of chlorpyrifos into sediments, wastewater and water sources. The presence
of chlorpyrifos in wastewaters and water sources may affect ecosystem and human health due to its chronicle
Keywords:
Photocatalysis
Nanoparticles
Graphene oxide
Chlorpyrifos
2 4 2
toxicity to aquatic organisms. In this study, magnetic recoverable CoFe O @TiO decorated reduced graphene
oxide nanocomposite was prepared and used for investigating the photodegradation of chlorpyrifos. The nano-
composite was characterized by using transmission electron microscopy, X-ray photoelectron spectroscopy,
X-ray diffraction and scanning electron microscopy. In photocatalytic degradation of chlorpyrifos experiments,
the effect of operating variables such as initial chlorpyrifos concentration, catalyst dosage and contact time was
also investigated. The photocatalytic degradation of chlorpyrifos followed the pseudo-first-order kinetic
model. The results indicated that the nanocomposite exhibited a high efficient photocatalytic activity on the
photodegradation of chlorpyrifos. The nanocomposite was separated from the solution by a magnet and reused
after the photodegradation of chlorpyrifos. The recyclable of the nanocomposite is economically significant in the
industry.
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
is one of the most common pest control products due to its efficient
activity. Organophosphorus pesticides have powerful inhibitor effects
to reproductive cholinesterase [12,13], toxicity [14], cytotoxicity [15],
immunotoxicity [16] and genotoxicity [17]. The pesticide pollution in
the environment has encouraged the development and usage of new
treatment techniques for degradation and removal of pesticides in
water samples. Several studies have been reported for the treatment
of wastewater including adsorption [18,19], photocatalysis [20,21],
oxidation [22] membrane filtration [23], and biosorption [19,24].
Among these techniques, photocatalysis has emerged as a promising
wastewater treatment technology [25–28]. Because of the reusable
Because of the diversity of manufactured products, the wastewater
including pollutants has turned into a worldwide public health issue
1–3]. The agricultural and industrial wastewaters are one of the
significant sources of the pesticides which are organic contaminants
4]. The presence of pesticides in water is a threat to the general public
[
[
health due to their high toxicity [5,6]. The pesticides can be classified as
bactericides, herbicides, fungicides, insecticides etc. [5,7]. Some of the
common pesticides is chlorpyrifos (CP), cypermethrin, methamidophos,
atrazine, chlorothalonil etc. [8]. Due to their environmental threats and
the chronically toxic, existence of pesticides in water and wastewater
has increased public health issues [5,9]. Among these pesticides, CP is
an organophosphorus insecticide included in water sources [10,11]. CP
and self-regenerated properties, photocatalysts such as TiO
2 3
, WO ,
and ZnS have a wide range of use and major advantages than other
treatment materials [29–31].
Recently, magnetic and non-magnetic nanoparticles as photocatalysts
were prepared to use in photocatalysis studies [2,32,33]. A nanocom-
posite can be useful in separating nanoparticles from the suspension
by constructing them with magnetic nanoparticles. Iron and cobalt
oxides show magnificent photocatalytic and magnetic properties [33,
34]. In some of the reported studies, the homogeneous photocatalytic
⁎
Correspondence to: V.K. Gupta, Department of Chemistry, Indian Institute of
Technology Roorkee, Roorkee 247667, India.
⁎⁎
Corresponding author.
E-mail addresses: vinodfcy@gmail.com, vinodfcy@iitr.ac.in (V.K. Gupta),
necipatar@gmail.com (N. Atar).
http://dx.doi.org/10.1016/j.molliq.2015.04.032
0167-7322/© 2015 Elsevier B.V. All rights reserved.

V.K. Gupta et al. / Journal of Molecular Liquids 208 (2015) 122–129
123
Fig. 1. The chemical formula of chlorpyrifos.
degradation of organic contaminants in the presence of metal ions
performed a maximum rate of degradation [34,35]. The CoFe
2 4
O
magnetic nanoparticles have been used as photocatalysts for the
degradation of different environmental pollutants [36,37]. Graphene/
graphene oxide based nanomaterials have been considered as carbon
material due to its superior mechanical strength, low density, high
catalytic activity and high surface area properties [38–42].
2 4 2 2 4 2
Fig. 2. XRD patterns for (A) rGO, (B) CoFe O @TiO and (C) CoFe O @TiO /rGO.
of 15 mA was used for X-ray diffraction measurement of the samples
with a scanning speed of 2°2θ/min and a step size of 0.02° were used
to examine the samples in the range of 20–70°2θ. To examine the
In this study, synthesis of the CoFe
2
O
4
@TiO
2
nanoparticle decorated
@TiO /rGO)
reduced graphene oxide (rGO) nanocomposite (CoFe
2
O
4
2
was performed. The nanocomposite was characterized by using
transmission electron microscopy (TEM), X-ray photoelectron spectros-
copy (XPS), X-ray diffraction (XRD) and scanning electron microscopy
2 4
morphologies of CoFe O nanoparticles and rGO, TEM measurements
were performed on a JEOL 2100 HRTEM instrument (JEOL Ltd., Japan)
and SEM measurements were performed on a ZEISS EVO 50 analytic
microscope (Germany). A diffuse reflectance spectrum (DRS) of the
(
SEM). The photocatalytic activity was investigated in an aqueous
solution for the photocatalytic degradation of CP with UV irradiation.
2 4 2
CoFe O @TiO /rGO nanocomposite was monitored on a UV-2550
Shimadzu UV–vis spectrophotometer equipped with ISR-2200 DRS
2
. Materials and methods
accessory (UV-2550 Shimadzu, Japan). The BET surface areas of
the nanocomposites were measured by N
2
adsorption–desorption
2
.1. Materials
(Quantachrome Corporation, NOVA-2000, USA).
All the chemicals that were used in the experiments were reagent
grade including graphite powder (Sigma-Aldrich, USA), H
Aldrich, USA), H (Sigma-Aldrich, USA), KMnO (Sigma-Aldrich,
USA), K (Merck, USA), P (Merck, USA), NaOH (Sigma-Aldrich,
USA), Co(NO (Merck, Germany), Fe(NO (Merck, Germany), and
TiO (Sigma-Aldrich, USA). Fig. 1 shows the chemical structure of the
2
SO
4
(Sigma-
2 4 2
2.3. Preparation of the CoFe O @TiO nanoparticles
2
O
2
4
2 2
S
O
8
O
2 5
CoFe
Co(NO
2
O
4
nanoparticles were prepared by a co-precipitation method.
and Fe(NO solutions were prepared and mixed under
)
2
3 3
)
3
)
2
3
)
3
3
magnetic stirring for 10 min. The solution was then added drop wise
2
CP. All the experiments were done in aqueous media. Ultra pure quality
water with a resistance of 18.3 MΩ cm (Human Power 1 Scholar
purification system) was used in the preparation of the aqueous
into 20% NaOH and a dark brown suspension was obtained. The Co–Fe
+
precursor was kept under magnetic stirring for 15 min. 1 g of TiO
was calcined at 400 °C for 5 h. Then the calcined TiO was added to
2
2
solutions.
20% NaOH solution and magnetically stirred for 15 min. After the
Co–Fe precursor solution was added to the suspension, the new mixture
was stirred for 30 min in the dark at 90 °C for 3 h. The obtained residue
was filtered and washed with ultrapure water for several times and
dried at 100 °C overnight. The residue was calcined at 400 °C for 5 h
2
.2. Instrumentation
A Rigaku Miniflex X-ray diffractometer (Japan) using mono-
chromatic CuKα radiation operating at a voltage of 30 kV and current
2 4 2
to form CoFe O @TiO nanoparticles.
2 4 2
Scheme 1. Synthesis of CoFe O @TiO /rGO nanocomposite.

124
V.K. Gupta et al. / Journal of Molecular Liquids 208 (2015) 122–129
2 4 2
Fig. 3. (A) TEM, (B) SEM and (C) EDX analyses of CoFe O @TiO /rGO nanocomposite.
2
.4. Preparation of GO
2 4 2
the stoichiometric ratio of CoFe O @TiO was added under the atmo-
sphere. Then, the resulting suspension was refluxed at 95 °C in an oil
bath for 2 h. After all these treatments, the suspension was cooled to
room temperature. The residues were collected by ultracentrifugation
and washed with ultrapure water and ethanol. Then the centrifuged
GO was synthesized by a modified Hummers method [43]. 25 mL of
H SO (98%) was mixed with 5 g of K S O , 5 g of P O and 5 g of graphite
2 4 2 2 8 2 5
and kept in a flask at 80 °C for 6 h. The mixture was cooled to 20 °C and
diluted with 1 L of ultra pure water and left for 12 h. The pre-oxidized car-
bon material was filtered and washed with ultra pure water. The pre-
2 4 2
residues were dried at 60 °C for 12 h to obtain CoFe O @TiO /rGO nano-
composite as seen in Scheme 1.
treated graphite was diluted with 250 mL H
0 g KMnO was added in the suspension and cooled to 20 °C. After the
KMnO feeding was finished, the flask was heated to about 35 °C and
2 4
SO (98%) under 0 °C and
3
4
2.6. Photocatalytic degradation experiments
4
stirred under this temperature for 4 h and then diluted with 500 mL
ultra pure water in the ice bath. The last mixture was stirred for 2 h.
The mixture was diluted with 2 L ultra pure water. The suspension was
The solution in experiments was prepared with diluting a CP solu-
tion (60 mg L ). A batch system with a UV lamp (400 W, k =
−
1
250–570 nm) is used to perform the photocatalytic degradation of CP.
−
1
further treated with 40 mL of H
O
2 2
(30%). The color of the suspension
A 0.4 g L
2 4 2
of CoFe O @TiO /rGO nanocomposite solution and a
−
1
changed to brilliant yellow from brownish and the mixture was stirred
until the bubbling stopped. The synthesized GO was filtered and washed
with 0.1 M HCl and distilled water three times, respectively. The as-
prepared GO was dispersed into 200 mL water under mild ultrasound
yielding a yellow-brown suspension, then 4 mL hydrazine hydrate
5 mg L of CP solution were kept in a quartz reactor. During the exper-
iment, 2 mL of CP solution was taken out every 10 min and measured
with LC–MS. A Metler Toledo MA 235 pH meter is used to set the opti-
mum pH value of the solution by using NaOH solution. The kinetic stud-
ies were performed at 25 °C with a mixture of 75 mg of CoFe
2 4 2
O @TiO /
(
80 wt.%) was added and the solution was heated in an oil bath maintain-
rGO nanocomposite and 50 mL of CP solution with a concentration
−
1
ing at 100 °C under a water-cooled condenser for 24 h. After the reaction,
the prepared rGO product was collected by vacuum filtration.
range of 1.0 to 40 mg L
The effect of catalyst amount is investigated at 25 °C with 5 mg L of
CP solution and CoFe @TiO /rGO nanocomposite with a concentra-
tion range of 0.05 to 0.6 g L
at different times (10–60 min) at pH 5.8.
−
1
O
2 4
2
−
1
at different intervals (10–60 min) at
2
2 4 2
.5. Preparation CoFe O @TiO /rGO photocatalyst
pH 5.8. The linear regression equations are used to calculate the residual
CP concentration.
5
0 mg of rGO was dispersed into 50 mL of ultrapure water with
2 4 2
The reusability of CoFe O @TiO /rGO nanocomposite on the photo-
ultrasonication for 1 h to form a stable rGO suspension. Subsequently,
catalytic degradation of CP was investigated under similar circumstances.

V.K. Gupta et al. / Journal of Molecular Liquids 208 (2015) 122–129
125
2 4 2
Fig. 4. Survey and core level XPS spectra of CoFe O @TiO /rGO nanocomposite.
−
The catalyst was centrifuged at 12,000 rpm for 10 min and cleaned with
ethanol after every experiment to split it from the treated water.
Fig. 4. O1s peaks at around 524.2 eV corresponded to O2 of OH groups.
The C1s core-level spectrum was curve-fitted in Fig. 4. The peaks at
285.3, 286.4, 287.6 and 288.8 eV were assigned to C_C, C\\O, C_O
and O_C\\O, respectively. The Co peaks were detected with doublet
2 4 2
CoFe O @TiO /rGO nanocomposite was kept at 100 °C for about 2 h to
get dried for every eight experiments.
3/2
1/2
2
p
and 2p signals at 779.9 and 802.4 eV, respectively. This peaks
1/2
3/2
3
. Results and discussion
confirmed the presence of Co. Fe 2p and Fe 2p peaks appear at
18.3 and 722.1 eV, respectively, indicating the presence of Fe [21,44].
The Ti2p peaks for CoFe @TiO /rGO were detected with a doublet
7
3
2 4 2
.1. Characterization of CoFe O @TiO /rGO nanocomposite
2
O
4
2
Fig. 2 shows the X-ray diffraction patterns for rGO, CoFe
2 4 2
O @TiO
and CoFe @TiO /rGO, respectively. It confirms that the peaks in
2
O
4
2
Fig. 2A are attributed to (001) and (100) structures of rGO. The peaks
centered at 2θ = 25.1° and 40.8° corresponded to the anatase and rutile
phases of TiO
and 52.3° corresponded to CoFe
tense and sharp peaks at 2θ = 33.8° and 48.6° corresponded to rGO of
CoFe @TiO /rGO, respectively.
The TEM analysis of CoFe @TiO
fine dispersion of dark and light particles (CoFe
surface (rGO) as shown in Fig. 3A. The dark gray particles (CoFe
were dispersed on the surface of light gray particles (TiO ). Fig. 3B
shows the SEM image of the CoFe @TiO /rGO nanocomposite. It is
observed from the image that the CoFe @TiO nanoparticles have
uniformly dispersed on rGO sheets. Fig. 3B confirms the surface mor-
phology of the CoFe @TiO /rGO nanocomposite. Fig. 3C shows the
2
, respectively (Fig. 2B). The peaks centered at 2θ = 35.2°
2 4
O
@TiO , respectively. In Fig. 2C, the in-
2
O
2 4
2
O
2 4
2
/rGO nanocomposite confirms the
@TiO ) on stratified
O
2 4
2
2 4
O )
2
2
O
4
2
2
O
4
2
2
O
4
2
EDX data for the nanocatalyst CoFe
C, Fe, Ti, Co and O.
2 4 2
O @TiO /rGO and the presence of
XPS characterization was carried out as survey and narrow region
spectra to confirm that the formation of CoFe @TiO nanoparticles
on GO is shown in Fig. 4. The peak signals for C1s, Ti2p, O1s, Fe2p and
Co2p were examined in the survey spectrum of CoFe @TiO /rGO in
2
O
4
2
2
O
4
2
2 4 2
Fig. 5. DRS spectrum of CoFe O @TiO /rGO nanocomposite.

126
V.K. Gupta et al. / Journal of Molecular Liquids 208 (2015) 122–129
Fig. 6. LC–MS chromatogram of photocatalytic degradation of chlorpyrifos.
−
2
p3/2 and 2p1/2 signals at 462.6 and 467.7 eV, respectively [5]. The
increase the partition of e and h+ which enhances the producing of
−
XPS spectrum has proposed the formation of CoFe
nanocatalyst.
2
O
4
@TiO
2
/rGO
•O
2
and •OH radicals. Scheme 3 shows the possible mechanism of CP
degradation.
A series of experiments without the catalyst to prove the degrada-
2 4 2
Fig. 5 shows the DRS spectrum of CoFe O @TiO /rGO nanocompos-
ite. The DRS spectrum of GO was subtracted from that of CoFe
2
O
O
4
@
@
tion of CP was completed in the presence of UV–vis radiation. There
was no degradation without the photocatalyst (Fig. 7A). The reaction
kinetics of the photocatalysis was reclaimed using the first order kinetic
model as follows [5,21,45-60].
TiO
TiO
2
2
/rGO by using OriginPro8 software. In the spectra of CoFe
/GO, GO would work as a sensitizer and CoFe @TiO
2
4
2
O
4
2
would
work as a substrate in the hetero-junction, giving rise to the estimation
of the band-gap energy of CoFe @TiO /rGO. The band-gap value of
CoFe @TiO /rGO was calculated as 2.7 eV [5,21]. The BET surface
areas of rGO, CoFe /rGO, TiO /rGO, and CoFe @TiO /rGO were
found to be 140.2; 185.9; 210.2; and 305.3 m , respectively,
suggesting that the BET surface area of CoFe @TiO /rGO was
enhanced after the intercalation of CoFe @TiO
2
O
4
2
2
O
4
2
O
4
2
2
O
g
4
2
lnCt ¼ lnCo−kt
ð1Þ
2
2
−1
2
O
4
2
where C
o
and C
t
are the initial CP concentration and CP concentration at
/C ) versus t can be approximated as
O
2 4
2
.
t time, respectively. The plot of ln(C
t
o
straight lines (Fig. 7B), implying that the photodegradation of CP is
fitted as pseudo-first-order kinetics. The calculated rate constant and
the correlation coefficient under various conditions were given in
Table 2.
3
.2. Photocatalytic degradation and kinetics of CP
The CoFe @TiO /rGO nanocomposite is used for the photocatalyt-
O
2 4
2
ic degradation of CP under UV–vis irradiation. During the experiments
of photocatalytic degradation, LC–MS chromatography is used to detect
the produced materials as seen in Fig. 6. The retention times of main
products and structural characteristics are shown in Table 1. The prod-
ucts in Table 1 were identified in Fig. 6. The possible photochemical
The effect of catalyst amount at 5 mg/L CP concentration within the
range of 0.05 to 0.6 g/L catalyst is shown in Fig. 7A. The amount of
degraded CP increased with the amount of catalyst. The results show
that the photocatalytic degradation of CP by using CoFe O @TiO /rGO
2 4 2
nanocomposite substantially rises with the amount of increasing
catalyst up to 0.4 g/L. The degradation of CP was important after
2 4 2
mechanism was shown in Scheme 2. CoFe O @TiO nanoparticles
Table 1
t
LC–MS-EI retention times (R ) MS and structural characteristics of CP and its main degradation products.
Photodegradation products
R
t
(min)
Products
MS
Structures of products
2
MS
n
a
b
c
O,O-diethyl O-(3,5,6-trichloropyridin-2-yl) phosphorothioate
O-ethyl O-(3,5,6-trichloropyridin-2-yl) O-hydrogen phosphorothioate
O-(3,5,6-trichloropyridin-2-yl) O,O-dihydrogen phosphorothioate
18.32
13.21
11.41
350.57
322.51
294.43
348.91
320.82
292.84
d
e
O,O-dihydrogen phosphorothioite
2.43
97.08
96.93
Diethyl (3,5,6-trichloropyridin-2-yl) phosphate
17.54
334.49
332.90
f
Ethyl (3,5,6-trichloropyridin-2-yl) hydrogen phosphate
3,5,6-Trichloropyridin-2-yl dihydrogenphosphate
10.53
9.56
306.45
278.38
304.89
276.87
g
h
i
Dihydrogen phosphate
1.67
80.98
80.93
3,5,6-Trichloropyridin-2-ol
15.21
198.45
196.93

V.K. Gupta et al. / Journal of Molecular Liquids 208 (2015) 122–129
127
2 4 2
Scheme 2. Photochemical mechanism for the photodegradation of the chlorpyrifos by using CoFe O @TiO /rGO nanocomposite.
2 4 2
Scheme 3. Photocatalytic degradation pathways of chlorpyrifos by using CoFe O @TiO /rGO nanocomposite.
0
.4 g/L catalyst (Table 2). Hence, the number of available catalyst sites
The effect of initial concentration of CP on the degradation rate was
studied within the range of 1 to 40 mg/L at a catalyst amount of 0.4 g/L
(Fig. 8). The rates of photocatalytic degradation of CP showed an
increase and then a decrease with increased initial concentration of CP
causes a rise in the catalyst dosage. This situation results in an increase
of decomposed CP concentration. The experiments of photocatalysis
were performed at pH 5.8 due to the natural pH of CP solution.
Fig. 7. A) The effect of catalyst amount on the photocatalytic degradation of chlorpyrifos and B) the linear plot fitting of the pseudo-first-order kinetic model.

128
V.K. Gupta et al. / Journal of Molecular Liquids 208 (2015) 122–129
Table 2
2 4 2
Pseudo-first order kinetic model on the photodegradation of chlorpyrifos using CoFe O @TiO /rGO.
Initial concentration of chlorpyrifos (mg L−1)
Catalyst amount (g L−1
)
1
3
5
10
20
40
0.05
0.1
0.2
0.4
0.6
1.05 × 10−
0.965
2
2.90 × 10−2
0.990
3.26 × 10−2
0.994
2.19 × 10−2
0.995
1.98 × 10−2
0.994
9.80 × 10−3
0.996
1.07 × 10−2
0.997
1.19 × 10−2
0.994
2.26 × 10−2
0.995
2.60 × 10−2
0.990
2.85 × 10−2
0.994
k
r
2
removal experiments shows that the adsorptive and photocatalytic
property of CoFe @TiO /rGO nanocomposite is stable and practically
important.
O
2 4
2
4. Conclusion
In the present study, we have developed a basic, clean, fast, inexpen-
sive, stable, recyclable, eco-friendly and highly efficient photocatalyst.
The photocatalyst was characterized by TEM, SEM, XRD and XPS. The
2 4 2
photocatalytic degradation of CP by using CoFe O @TiO /rGO nanocom-
posite was substantially related on contact time (60 min), initial
−
1
−1
concentration of CP (5 mg L ) and amount of the catalyst (0.4 g L ).
The experimental data is fitted by performing the calculation of the pseu-
do-first-order kinetic model. The nanocomposite was separated easily
from the solution without filtering and then it was stabilized into solution
2 4 2
for the next cycle. The developed CoFe O @TiO /rGO nanocatalyst has
good reusability for the removal of CP from wastewater.
Fig. 8. The effect of initial chlorpyrifos concentration on the photocatalytic degradation.
References
[
[
[
1] N. Atar, A. Olgun, S. Wang, S. Liu, J. Chem. Eng. Data 56 (2011) 508.
2] V.K. Gupta, M.L. Yola, N. Atar, Sensors Actuators B Chem. 194 (2014) 79.
3] A. Alinsafi, F. Evenou, E.M. Abdulkarim, M.N. Pons, O. Zahraa, A. Benhammou, A.
Yaacoubi, A. Nejmeddine, Dyes Pigments 74 (2007) 439.
and the rate of the highest photocatalytic degradation was found at
5
mg/L of initial concentration of CP (Fig. 8 and Table 2).
[4] M. Neumann, R. Schulz, K. Schäfer, W. Müller, W. Mannheller, M. Liess, Water Res.
6 (2002) 835.
3
The nanocomposite was separated easily from the solution within
2 s by using a magnet without filtering and it was stabilized into
[
[
5] M.L. Yola, N. Atar, T. Eren, Sensors Actuators B Chem. 198 (2014) 70.
6] E. Eriksson, A. Baun, P.S. Mikkelsen, A. Ledin, Desalination 215 (2007) 187.
1
solution for the next cycle. A series of stability experiments were carried
out to investigate the reusability of the nanocomposite. The reusability
[7] C.S. Jacobsen, M.H. Hjelmsø, Curr. Opin. Biotechnol. 27 (2014) 15.
[
8] R.M. Whyatt, R. Garfinkel, L.A. Hoepner, D. Holmes, M. Borjas, M.K. Williams, A.
Reyes, V. Rauh, F.P. Perera, D.E. Camann, Environ. Health Perspect. 115 (2007) 383.
9] V.K. Gupta, T.A. Saleh, Environ. Sci. Pollut. Res. 20 (2013) 2828.
of CoFe
of CP from an aqueous solution was shown in Fig. 9. As seen from
Fig. 9, CoFe @TiO /rGO nanocomposite can be recycled and reused
eight times without much decline in stable removal efficiency. The
good reusability of CoFe @TiO /rGO nanocomposite in the cyclic
2 4 2
O @TiO /rGO nanocomposite for the photocatalytic removal
[
[10] C. Moschet, E.L.M. Vermeirssen, R. Seiz, H. Pfefferli, J. Hollender, Water Res. 66
2014) 411.
(
2
O
4
2
[
[
11] R. Schwartz, O. Lahav, A. Ostfeld, Water Res. 63 (2014) 271.
12] E. Testai, F.M. Buratti, E. Di Consiglio, Hayes' Handbook of Pesticide, Toxicology
(2010) 1505–1526.
2
O
4
2
2 4 2
Fig. 9. The reusability of CoFe O @TiO /rGO nanocomposite for the photocatalytic degradation of chlorpyrifos.

V.K. Gupta et al. / Journal of Molecular Liquids 208 (2015) 122–129
129
[
[
13] C. Pope, S. Karanth, J. Liu, Environ. Toxicol. Pharmacol. 19 (2005) 433.
14] B. Piña-Guzmán, M.J. Solís-Heredia, B. Quintanilla-Vega, Toxicol. Appl. Pharmacol.
[39] B.J. Sanghavi, S.M. Mobin, P. Mathur, G.K. Lahiri, A.K. Srivastava, Biosens. Bioelectron.
39 (2013) 124.
2
02 (2005) 189.
[40] B.J. Sanghavi, W. Varhue, J.L. Chávez, C.F. Chou, N.S. Swami, Anal. Chem. 86 (2014)
4120.
[41] P.K. Kalambate, B.J. Sanghavi, S.P. Karna, A.K. Srivastava, Sensors Actuators B Chem.
213 (2015) 285.
[42] B.J. Sanghavi, A.K. Srivastava, Electrochim. Acta 55 (2010) 8638.
[43] M.L. Yola, V.K. Gupta, T. Eren, A.E. Şen, N. Atar, Electrochim. Acta 120 (2014) 204.
[44] M.L. Yola, T. Eren, N. Atar, Biosens. Bioelectron. 60 (2014) 277.
[45] N. Atar, A. Olgun, Desalination 249 (2009) 109.
[46] V.K. Gupta, A.K. Jain, G. Maheshwari, Talanta 72 (4) (2007) 1469–1473.
[47] V.K. Gupta, M.R. Ganjali, P. Norouzi, H. Khani, A. Nayak, Shilpi Agarwal, Critical Re-
views in Analytical Chemistry 41 (2011) 282–313.
[
[
15] G. Giordano, Z. Afsharinejad, M. Guizzetti, A. Vitalone, T.J. Kavanagh, L.G. Costa,
Toxicol. Appl. Pharmacol. 219 (2007) 181.
16] M.I. Girón-Pérez, A. Santerre, F. Gonzalez-Jaime, J. Casas-Solis, M. Hernández-
Coronado, J. Peregrina-Sandoval, A. Takemura, G. Zaitseva, Fish Shellfish Immunol.
2
3 (2007) 760.
[
[
[
[
[
[
[
17] Ş. Çakir, R. Sarikaya, Food Chem. Toxicol. 43 (2005) 443.
18] V.K. Gupta, A. Nayak, S. Agarwal, I. Tyagi, J. Colloid Interface Sci. 417 (2014) 420.
19] N. Atar, A. Olgun, F. Çolak, Eng. Life Sci. 8 (2008) 499.
20] V.K. Gupta, G. Sharma, D. Pathania, N.C. Kothiyal, J. Ind. Eng. Chem. 21 (2015) 957.
21] M.L. Yola, T. Eren, N. Atar, Electrochim. Acta 125 (2014) 38.
22] N. Mohan, N. Balasubramanian, V. Subramanian, Chem. Eng. Technol. 24 (2001) 749.
23] A. Kaya, T. Kutlu, A. Hol, A. Surucu, H.K. Alpoguz, Desalin. Water Treat. 52 (2014)
[48] R.N. Goyal, V.K. Gupta, S. Chatterjee, Sens. Actuators B. Chemical 149 (2010)
252–258.
3
219.
[49] V.K. Gupta, A.K. Jain, Shiva Agarwal and G, Maheshwari, Talanta 71 (2007)
1964–1968.
[
[
[
24] F. Çolak, N. Atar, D. Yazicioĝlu, A. Olgun, Chem. Eng. J. 173 (2011) 422.
25] S. Liu, H. Sun, S. Liu, S. Wang, Chem. Eng. J. 214 (2013) 298.
26] Y. Yao, Y. Cai, F. Lu, J. Qin, F. Wei, C. Xu, S. Wang, Ind. Eng. Chem. Res. 53 (2014)
[50] R. Jain, V.K. Gupta, N. Jadon, K. Radhapyari, Analytical Biochemistry 407 (2010)
79–88.
1
7294.
[51] V.K. Gupta, A.K. Singh, S. Mehtab, B. Gupta, Anal. Chim. Acta 566 (2006) 5–10.
[52] R.N. Goyal, V.K. Gupta, S. Chatterjee, Electrochim. Acta 53 (2008) 5354–5360.
[53] V.K. Gupta, A.K. Singh, M. AL Khayat, Barkha Gupta, Anal. Chim. Acta 590 (2007)
81–90.
[54] V.K. Gupta, R. Prasad, R. Mangla, P. Kumar, Anal. Chim. Acta 420 (2000) 19–27.
[55] R.N. Goal, V.K. Gupta, S. Chatterjee, Talanta 76 (2008) 662–668.
[56] V.K. Gupta, S.K. Srivastava, D. Mohan and S. Sharma, Waste Management 17 (1998)
517–522.
[
[
[
[
[
[
27] Y. Yao, J. Qin, Y. Cai, F. Wei, F. Lu, S. Wang, Environ. Sci. Pollut. Res. 21 (2014) 7296.
28] Y. Yao, J. Qin, H. Chen, F. Wei, X. Liu, J. Wang, S. Wang, J. Hazard. Mater. 291 (2015) 28.
29] R. Saravanan, V.K. Gupta, E. Mosquera, F. Gracia, J. Mol. Liq. 198 (2014) 409.
30] R. Saravanan, V.K. Gupta, V. Narayanan, A. Stephen, J. Mol. Liq. 181 (2013) 133.
31] R. Velmurugan, M. Swaminathan, Sol. Energy Mater. Sol. Cells 95 (2011) 942.
32] A.M. Balu, B. Baruwati, E. Serrano, J. Cot, J. Garcia-Martinez, R.S. Varma, R. Luque,
Green Chem. 13 (2011) 2750.
[
[
[
33] V.K. Gupta, M.L. Yola, T. Eren, F. Kartal, M.O. Ça layan, N. Atar, J. Mol. Liq. 190 (2014) 133.
34] R. Liu, S. Li, X. Yu, G. Zhang, S. Zhang, J. Yao, L. Zhi, J. Mater. Chem. 22 (2012) 3319.
35] J. Madhavan, P. Maruthamuthu, S. Murugesan, M. Ashokkumar, Appl. Catal. A Gen.
[57] V.K. Gupta, Alok Mittal, Jyoti Mittal, J. Colloid Interface Sci. 342 (2010) 518–527.
[58] V.K. Gupta, Alok Mittal, Dipika Kaur Arti Malviya, Jyoti Mittal, J. Colloid Interface Sci.
337 (2009) 345–354.
3
68 (2009) 35.
[59] Alok Mittal, Arti Malviya, Jyoti Mittal, V.K. Gupta, J. Colloid Interface Sci. 340 (2009)
16–26.
[
36] J.C. Xu, P.H. Xin, Y.B. Han, P.F. Wang, H.X. Jin, D.F. Jin, X.L. Peng, B. Hong, J. Li, H.L. Ge,
Z.W. Zhu, X.Q. Wang, J. Alloys Compd. 617 (2014) 622.
[60] V.K. Gupta, Shilpi Agarwal, A. Tawfik, J. Saleh, J. Hazardous Mat. 185 (2011) 17.
[
[
37] L. Zhou, L. Ji, P.C. Ma, Y. Shao, H. Zhang, W. Gao, Y. Li, J. Hazard. Mater. 265 (2014) 104.
38] B.J. Sanghavi, S. Sitaula, M.H. Griep, S.P. Karna, M.F. Ali, N.S. Swami, Anal. Chem. 85
(2013) 8158.