Graphene oxide nanocomposite with Co and Fe doped LaCrO3 perovskite active under solar light irradiation for the enhanced degradation of crystal violet dye

Article abstract of DOI:10.1016/j.molliq.2020.114895

Pristine LaCrO₃ and Co, Fe co-doped La_1-xCo_xCr_1-yFe_yO₃ (x, y = 0.24) perovskite nanoparticles was prepared via micro-emulsion method and the La_1-xCo_xCr_1?yFeyO₃ composite was prepared with 5% reduced-graphene oxide (r-GO) by ultra-sonication process. The morphological, structural and thermal properties were investigated by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Raman Spectroscopy, Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The effect of Co, Fe doping and r-GO on the conductivity of the synthesized samples was investigated by current-voltage (I-V) analysis. The perovskite structure was orthorhombic with particle size in 21.24 to 31.58 nm range. Crystal violet (CV) dye was selected for evaluation of photocatalytic activity (PCA) of the prepared materials under visible light irradiation. La_1-xCo_xCr_1-yFe_yO₃/r-GO showed remarkably higher PCA as compared to pristine LaCrO₃ and La_1-xCo_xCr_1-yFe_yO₃. The r-GO composite furnished the CV dye degradation of 89.08% within 100 min irradiation under visible light at the light intensity in the range of 864.45–872.86 W/m². This valuable enhancement in PCA was due to the structural features of La_1-xCo_xCr_1-yFe_yO₃/r-GO nanocomposite. In view of promising PCA, the composite has potential for the catalytic degradation of dyes in effluents using sunlight irradiation.

Full text of DOI:10.1016/j.molliq.2020.114895

MOLLIQ-114895; No of Pages 12
Journal of Molecular Liquids xxx (2020) xxx
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Graphene oxide nanocomposite with Co and Fe doped LaCrO3 perovskite
active under solar light irradiation for the enhanced degradation of
crystal violet dye
b
c
d
e
Muhammad Aamir a, Ismat Bibi a, , Sadia Ata , Farzana Majid , Shagufta Kamal , Norah Alwadai ,
⁎
Misbah Sultan b, Shahid Iqbal a, Muhammad Aadil a, Munawar Iqbal f,
Department of Chemistry, the Islamia University of Bahawalpur, Bahawalpur, Pakistan
⁎
a
b
Institute of Chemistry, University of the Punjab, Lahore, Pakistan
Department of Physics, University of the Punjab, Lahore, Pakistan
c
d
Department of Applied Chemistry and Biochemistry, GC University, Faisalabad, Pakistan
Department of Physics, College of Sciences, Princess Nourah bint Abdulrahman University (PNU), Riyadh 11671, Saudi Arabia
Department of Chemistry, The University of Lahore, Lahore, Pakistan
e
f
a r t i c l e i n f o
a b s t r a c t
Article history:
Pristine LaCrO3 and Co, Fe co-doped La1-xCoxCr1-yFeyO3 (x, y = 0.24) perovskite nanoparticles was prepared via
micro-emulsion method and the La1-xCoxCr1−yFeyO3 composite was prepared with 5% reduced-graphene oxide
(r-GO) by ultra-sonication process. The morphological, structural and thermal properties were investigated by
Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Raman Spectroscopy, Thermogravimetric Analysis
(TGA) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The effect of Co, Fe doping and r-GO on
the conductivity of the synthesized samples was investigated by current-voltage (I-V) analysis. The perovskite
structure was orthorhombic with particle size in 21.24 to 31.58 nm range. Crystal violet (CV) dye was selected
for evaluation of photocatalytic activity (PCA) of the prepared materials under visible light irradiation. La1-x
CoxCr1-yFeyO3/r-GO showed remarkably higher PCA as compared to pristine LaCrO3 and La1-xCoxCr1-yFeyO3.
The r-GO composite furnished the CV dye degradation of 89.08% within 100 min irradiation under visible light
at the light intensity in the range of 864.45–872.86 W/m2. This valuable enhancement in PCA was due to the
structural features of La1-xCoxCr1-yFeyO3/r-GO nanocomposite. In view of promising PCA, the composite has po-
tential for the catalytic degradation of dyes in effluents using sunlight irradiation.
Received 4 September 2020
Received in revised form 9 November 2020
Accepted 25 November 2020
Available online xxxx
Keywords:
Perovskite nanoparticles
Graphene oxide
Micro-emulsion
Ultra-sonication
Electrical-conductivity
Crystal violet
Photocatalyst
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
of rare-earth ions with other rare-earth ion is the best way to enhance
the functional properties, which play a vital role to fabricate many
Nanotechnology deals with the fabrication of material at the nano-
scale that extends from 1 to 100 nm. The material having a size dimen-
sion in the nano-range exhibited ideal physicochemical properties as
compared to bulk [1,2]. Nanomaterials gained much attention due to
applications in diverse fields, i.e., medicine, agriculture, biotechnology,
transportation, food industry, national defense, information technology,
sensors, aerospace, packaging, textile, electronics and cosmetics [3–7].
Perovskite have general formula ABO3 type, are very useful materials
due to their unique structure and properties such as electric conductiv-
ity, dielectric, ferroelectric, anti-ferromagnetism, magnetic, thermo-
chemical, and catalytic. Furthermore, these characteristic properties
can be easily handled through the specific ratio of rare-earth ion A and
B (transition metal ion) in the perovskite oxides [8,9]. The substitution
new-generation devices [10,11]. ABO3 type mixed oxide perovskite
nanomaterial such as LaCrO3 [12], NiTiO3, BaZrO3, CoTiO3, LaMnO3,
LaNiO3, PbTiO3 and LaFeO3 [13] have been prepared using range of
methods with the aim of application in different fields and promising ef-
ficiency have been documented. LaCrO3-based perovskite oxides have
been potentially used in SOFCs as a ceramic interconnecting material
because of their high thermal, electrical and good phase stability
under both reducing and air atmosphere [14] and due to its high cata-
lytic activity, it is also used in catalytic combustion of methane [15].
In recent years, ABO3 type perovskite oxides have been extensively
used in heterogeneous catalysis because of their unique electronic prop-
erties [16]. However, one of main limitation of LaCrO3 is less specific sur-
face area, which cause a high deactivation based on the thermal
sintering impact. The LaCrO3 with higher surface area have efficient per-
formance in catalytic applications. The surface area and conductivity of
the LaCrO3 can be accelerated by substituting the divalent metal ions in
⁎
Corresponding author.
E-mail addresses: drismat@iub.edu.pk (I. Bibi), bosalvee@yahoo.com (M. Iqbal).
https://doi.org/10.1016/j.molliq.2020.114895
0167-7322/© 2020 Elsevier B.V. All rights reserved.
Please cite this article as: M. Aamir, I. Bibi, S. Ata, et al., Graphene oxide nanocomposite with Co and Fe doped LaCrO3 perovskite active under solar
light irradia..., Journal of Molecular Liquids, https://doi.org/10.1016/j.molliq.2020.114895

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
the ABO3 lattice. The Cr3+ ion sites on the surface of pristine LaCrO3 cre-
ates excellent adsorption conditions for atomic oxygen that blessed it
with more suitable and favorable characteristics toward best photocat-
alytic applications under UV and visible light irradiation [8,9]. Recently,
the foreign metal ions doping in the structure of NPs is a very useful way
to enhance the conductivity and PCA of the doped nanomaterials
[8,17,18]. Therefore, an attempt has been made to prepare the materials
for PCA with large improved surface area and chemical stability with
higher electron transportation capacity [1,2,19].
The rapid increase in population and industrialization affected the
quality of the environment. Excessive contamination of water bodies
with highly stable organic pollutants could be a serious threat to the liv-
ing organisms. The dyes are one of toxic pollutants that are discharged
into the wastewater resources from the textile, food, printing, and
leather industries [20–22]. The existence of organic dyes contaminants
in wastewater cause several severe health problems, inhibition in pho-
tosynthetic activity and put adverse effects on all types of aquatic life by
blocking the sunlight and disturbing the dissolved oxygen of water
[23,24]. Therefore, the degradation of organic dyes in wastewater
demands advanced treatment methods due to their extremely slow bio-
degradation and toxic nature. Photocatalytic based advanced technique
are efficient in the regard, which degrades the organic pollutants non-
selectively and converts the toxic pollutants in to end-products (harm-
less) like CO2 and H2O along with inorganic ions [1,2,25]. In comparison
to conventional methods for the treatment of wastewater [26–37], the
advanced oxidation process is highly efficient, which remove the pollut-
ants complete in water and wastewater by utilizing hydroxyl radicals
[1,2,25,38,39].
times to lower down pH up to 7. After washing particles were dried
completely in an oven at 100 °C and then dried particles were grounded
and calcined at 900 °C for 7 h. The systematic scheme for the synthesis of
LaCrO3 and La1-xCoxCr1-yFeyO3 nanoparticles is shown in Fig. 1.
2.3. Preparation of GO
The GO (graphene oxide) suspension was synthesized following
Hummer's method using graphite powder. In this process, conc.
H2SO4 (75 mL), NaNO3 (2 g), and graphite powder (2 g) were
mixed in a 200 mL for 40 min on a magnetic stirrer. The resulting
combination was kept in ice-bath and then, 10 g KMnO4 salt was
propped with continuous stirring. During this addition, the temper-
ature of the mixture was 18 °C. The obtained slurry was further
stirred on a magnetic stirrer for two days. Then, the mixture was di-
luted with pure water a greenish-black was appeared and its tem-
perature increases up to 80 °C and when temperature reached to
30 °C, H2O2 (33%) was added that resulted in a brilliant yellowish
mixture. Then resulting yellowish mixture was subjected to washing
several times by HCl and H2O2 mixture and later with pure water
until the pH reached 7. Finally, the drying was done at 25 °C and
then, it was dispersed in deionized water to get the GO [40].
2.4. Synthesis of r-GO
The GO was reduced chemically using liquid ammonia as exfoliating
and hydrazine as a reducing agent. Firstly, the GO was diluted with
water and it was sonicated for 3 h, and heating was done in a paraffin
oil bath up to 80 °C and added liquid ammonia and hydrazine in it. Fi-
nally, the mixture was heated and stirred until the greyish suspension
of r-GO was obtained [41]. A systematic scheme for the synthesis of
GO and its reduction into a r-GO is shown in step II of Fig. 1.
Based on above mentioned facts, the pristine LaCrO3, doped
La1-xCoxCr1-yFeyO3 perovskite-nanoparticles and La1-xCoxCr1-yFeyO3/
r-GO nanocomposite were prepared by micro-emulsion and ultra-
sonication routes and characterized by TGA, XRD, FT-IR, SEM, raman-
spectroscopy, EDX and UV–visible techniques. The PCA (under sunlight
irradiation) of La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO nano-
composite was compared with pristine LaCrO3.
2.5. Synthesis of La1-xCoxCr1-yFeyO3/r-GO composite
The La1-xCoxCr1-yFeyO3/r-GO composite was synthesized by the
ultra-sonication method. The La1-xCoxCr1-yFeyO3 (76 mg) was mixed
in 100 mL of r-GO aqueous solution (40 mg/L) and then, the resulting
material was sonicated for 50 min to obtain the highly dispersed mix-
ture and drying was done at 90 °C for 2 h to obtain the required
La1-xCoxCr1-yFeyO3/r-GO nanocomposite [42]. A systematic scheme for
the fabrication of La1-xCoxCr1-yFeyO3/r-GO nanocomposite is shown in
step III of Fig. 1.
2. Material and methods
2.1. Reagents and chemicals
The reagents and chemicals, i.e., lanthanum (III) nitrate hexahydrate
(≥ 99%), cobalt(III) nitrate hexahydrate (≥ 98%), chromium (III) nitrate
(≥ 98%), iron(III) nitrate (≥ 98%) were supplied by Sigma Aldrich (US).
The CTAB (cetyltrimethylammonium bromide) was purchased from
Bio basic Canada, INC.
2.6. Characterization
2.2. Synthesis of La1-xCoxCr1-yFeyO3
The LaCrO3 NPs, La1-xCoxCr1-yFeyO3 NPs and La1-xCoxCr1-yFeyO3-
r-GO nanocomposite were investigated by XRD analysis using
X-ray Diffractometer (Phillips, X- pert PRO 3040/60), having CuKα
as a source of radiation with λ = 1.542 Å in 2θ range of 20°-80°).
For morphological study, S-3400 SEM was employed. The Yyon
Atago/Bussan spectrometer (Via T- 6400 Triple-Jobin,) was
employed for Raman spectra recording (in the range of 100 cm−1
to 800 cm−1) were recorded. The FTIR (Tensor-27) was employed
to investigate the functionalities in the La1-xCoxCr1-yFeyO3 NPs and
La1-xCoxCr1-yFeyO3-r-GO nanocomposite. Furthermore, two probes
current-voltage (I-V) investigations, was done by Keithley-487
Picoammeter and a UV- visible spectrum was recorded using Dual-
beam Cary 60 spectrophotometer.
LaCrO3 and La1-xCoxCr1-yFeyO3 were fabricated via the micro-
emulsion approach. Briefly, to synthesize pristine LaCrO3 NPs the solu-
tion of La (NO3)3.6H2O and Cr(NO3)3.9H2O was prepared in 100 mL
deionized water by dissolving stoichiometric ratio, 4.33 g, and 4.00 g re-
spectively. Similarly, for the synthesis of La1-xCoxCr1-yFeyO3 NPs, 3.29 g
of La(NO3)3.6H2O, 0.70 g of Co(NO3)2.6H2O, 3.04 g of Cr(NO3)3.9H2O
and 0.96 g of Fe(NO3)3.9H2O were dissolved in 76 mL, 24 mL, 76 mL,
and 2 mL deionized water, respectively. After solution preparation, sam-
ple solutions were mixed and put on the hotplates keeping stirring and
heating on. When the temperature of the sample solutions reaches
50 °C, 100 mL (0.3 M) CTAB solution was added to both sample solu-
tions. After the successful addition of the CTAB solution, the heating
process was closed and then, 10 mL (0.3 M) NH4OH aqueous solution
was added to sample solutions after a constant interval of time
(10 min) till 2 h with continuous stirring. After the successful addition
of (0.3 M) NH4OH, sample solutions were subjected to continuous stir-
ring till 5 h, and nanoparticles have been appeared in this step. Then
washing of these nanoparticles was done via deionized water several
2.7. Photocatalytic activity
The PCA of the synthesized samples (LaCrO3 NPs, La1-xCoxCr1-yFeyO3
NPs and La1-xCoxCr1-yFeyO3-r-GO nanocomposite) was studied through
CV dye degradation under sunlight (Time: 11:00 am to 12:30 pm,
dated: 13-July 2020, Place: Bahawalpur, Pakistan). The intensity of
2

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
Fig. 1. Schematic flow sheet diagram for the formation of La1-xCoxCr1-yFeyO3 NPs (Step 1), r-GO (Step II), and their nanocomposite (Step III).
sunlight radiations was measured by Kipp & Zonen CMP-11 pyran-
ometer and it was found in the range of 864.45–872.86 W/m2. A 5 mg
of LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3-r-GO nanocom-
posite was mixed with 5 ppm CV dye solution (50 mL) and mixture
was subjected to continuous stirring for 30 min in dark and concentra-
tion of CV dye was noted before and after dark-reaction to determine
the of dye adsorbed and for the concentration determination of the
dye, 4 mL sample was taken at a specific time interval (15 min). After
that, the catalyst was separated by the centrifugation process, and
then obtained supernatant was further subjected to find out the absorp-
tion spectra of the CV dye at 672 nm. The CV dye degradation (%) was
computed by Eq. (1) [42,43].
Fig. 2. SEM images, (a) pristine LaCrO3 NPs, (b) doped La1-xCoxCr1-yFeyO3 NPs and (c) La1-xCoxCr1-yFeyO3/r-GO nanocomposite.
3

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
spectra of doped La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-y FeyO3/r-GO
nanocomposite (Fig. 3b and c) also shows the clear characteristic
peaks of La, Co, Cr, Fe, O and La, Co, Cr, Fe, C and O. Hence, the absence
of any other impurity/contamination peaks in all three EDX spectra
has confirmed the purity and successful synthesis of the desired
materials.
Ct
C0
Degradation ð%Þ ¼ 1−
ð1Þ
where, C0, and Ct are depicting the absorbance values of initial and dye
concentration at time “t”, respectively [44].
3. Results and discussion
3.3. Structural analysis
3.1. Surface morphology
The XRD responses of LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-y
FeyO3-r-GO nanocomposite is shown in Fig. 4a. The crystal structure
conformation was determined by taking XRD in 2θ range of 20 to 80°.
From the XRD data, it was noticed that the diffraction peaks of fabricated
nanoparticles appeared at 21.72°, 31.35°, 39.01°, 45.65°, 51.76°, 57.09°,
67.01°, 76.72°, which correspond to the miller indices values; (110),
(112), (022), (004), (114), (024), (224), (314), (044), respectively.
The diffraction patterns of La1-xCoxCr1-yFeyO3 nanoparticles reflects
pure perovskite phase and matched with JCPDS # 024–1016, all peaks
correspond to an orthorhombic structure with space group Pbnm with-
out any contaminated phase [46]. Lattice constants values were deter-
mined by ‘cell software’ and particle size was determined with the
help of Debye Scherrer equation Eq. (2). [47].
The morphological investigation of the LaCrO3, La1-xCoxCr1-yFeyO3
and La1-xCoxCr1-yFeyO3/r-GO nanocomposite were done using SEM
and responses, thus observed are depicted in Fig. 2. The pristine
LaCrO3 NPs show heterogeneous morphology with particle size range
82–87 nm as shown in Fig. 2a. While the SEM image of doped La1-x
CoxCr1-yFeyO3 nanoparticles (Fig. 2b) shows that the particles are
fused and formed agglomerates and it is noticed that, the particle size
decreases with doping and resultantly, agglomeration phenomenon
among particles was observed [45]. The average particle size of the
doped La1-xCoxCr1-yFeyO3 NPs was determined from the well-scattered
zones and it was 78.4 nm. While in the case of La1-xCoxCr1-yFeyO3/r-
GO nanocomposite (Fig. 2c), the particles are finely mixed with r-GO
and their agglomeration reduced slightly. The r-GO nano sheets due to
its excellent 2D nanostructure feature, it provides sufficient surfaces
for the loading of nanoparticles.
0:9 λ
D ¼
ð2Þ
βcosθ
where, ‘D’ is the average size for the particles, while ‘λ’ expresses the
wavelength (1.542 Å) of X-rays used. The ‘β’ represents the full-width
at half maxima while ‘θ’ expresses the Bragg's angle and 0.9 is the value
of constant K. The calculated crystallite size of La1-xCoxCr1-yFeyO3 by the
Scherrer equation was found to be 21.24 nm to 31.58 nm. Unit cell vol-
ume for the orthorhombic system was computed as per Eq. (3) [48]. The
X-ray density was measured using Eq. (4) [41].
3.2. Composition analysis
Fig. 3a, b, and c, shows the spectra of LaCrO3, doped La1-xCoxCr1-y
FeyO3 and La1-xCoxCr1-yFeyO3/r-GO nanocomposite, respectively for
EDX investigation. The EDX spectra of LaCrO3 (Fig. 3a) clearly show
the existence of very fine peaks of La, Cr, and O. Similarly, The EDX
Fig. 3. EDX spectra, (a) pristine LaCrO3 NPs, (b) doped La1-xCoxCr1-yFeyO3 NPs and (c) La1-xCoxCr1-yFeyO3/r-GO nanocomposite.
4

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
Fig. 4. (a) XRD pattern of fabricated NPs, (b) TGA curve of pristine LaCrO3 NPs, (c) Raman spectra, (d) FTIR spectra of pristine LaCrO3 and doped La1-xCoxCr1-yFeyO3 NPs.
where ‘m’ represents the mass of the pellet and ‘v’ express the volume of
the pellet. With the help of these two densities, the percentage of poros-
ity (P) was calculated using Eq. (6) [58].
Cell volume ¼ a ꢀ b ꢀ c
z:Mw
ð3Þ
ð4Þ
ρx−ray
¼
NA:
V
1−ρBulk
ρx−ray
Porosity ¼
ꢀ 100
ð6Þ
where, ‘z’ represents the number of atoms per unit cell, Mw expresses
the MW, NA represents the Avogadro's number and V expresses the vol-
ume of the unit cell. The obtained value of X-ray density for pristine
LaCrO3 was 6.35 g/cm3. From the above calculations it was concluded
that as we increase the x and y concentrations, the crystalline size of fab-
ricated nanoparticles also increases from 21.24 nm to 31.58 nm, this in-
crease in crystalline size by doping may be due to the larger ionic radii of
Co3+ ion (0.72 Å), Fe3+ ion (0.64 Å) against the ionic radii of Cr3+ ion
(0.62 Å), which confirmed the successful substitution of Cr and Fe
[49–53]. The cell volume of La1-xCoxCr1-yFeyO3 perovskite nanoparticles
was decreased by increasing Co3+ and Fe3+ions concentration. This de-
crease in cell volume is because of the smaller ionic radii of Co3+
(0.72 Å) ion as compare to the La3+ (1.03 Å) ion which also proved that
The percentage of porosity value of synthesized nanoparticles was
recorded in 42.04 to 51.81 nm range and a comparison among the crys-
tallographic parameter of pristine and doped samples is given in Table 1.
Table 1
Cell parameters, cell volume, crystallite size, X-ray density, bulk density and porosity for
pristine LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO nanocomposite.
Par parameters
Pristine LaCrO30.0.0
Doped La1-xCoxCr1-yFeyO3
Lattice-constant a/A°
Lattice-constant b/A°
Lattice-constant c/A°
Cell volume / A3°
Crystallite size/nm
X-ray density/gcm−3
Bulk density/gcm−3
Porosity (%) P (a.u)
5.558
6.267
8.000
278.65
21.24
5.60
5.764
5.565
7.883
252.86
31.58
6.17
successful substitution of La and Co [54–56]. The bulk density (ρbulk
)
was also determined using Eq. (5) [57].
3.047
45.58
2.993
51.49
m
v
ρBulk
¼
ð5Þ
5

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
3.4. Thermogravimetric analysis (TGA)
3.5. Raman scattering
The thermal transformation of the pristine LaCrO3 was done through
TGA. The obtained thermo-gram of the pristine LaCrO3 is shown in Fig. 4b.
According to a thermo-gram, weight loss takes place between two tem-
perature zones. The weight loss in the first temperature zone was noticed
between 34 and 200 °C, and in this zone, 1.43% weight loss was inv-
estigated, which is may be a result of the desorption of water contents.
While the second temperature zone was noticed between 200 and
600 °C and in this zone 11.90% weight loss takes place, which might
be due the formation of lanthanum oxide from Lanthanum hydroxide
breakdown with hydroxide and lanthanum oxide as an intermediate
product. The weight losses in both zones are expressed by the
Eqs. (7)–(8), respectively [59]. The observed weight loss (11.90%)
which is the result of decomposition of the precursors is closed to the the-
oretically determined weight loss (13.67%). The creation of LaCrO3 using
lanthanum and chromium oxide can be expressed in Eqs. (9)–(10).
Raman spectrum of pristine LaCrO3, La1-xCoxCr1-yFeyO3 and
La1-x CoxCr1-yFeyO3/r-GO nanocomposite was noted in 100 to
800 cm−1 range at ambient temperature and obtained peaks
were assigned to various Raman modes as shown in Fig. 4c. Out
of 8 Raman modes, in the current study, 5 modes were found at
132, 158, 432, 560, and 672 cm−1 that are assigned to Ag symme-
try, while other modes 195, 258, 536 cm−1 belong to Bg symmetry.
The bands noticed at Ag(1), Ag(2) and Bg(1) attributed to rare-
earth ions because of the greater atomic mass of R3+ ions also
known as vibrational modes. The Ag(5) mode allied with the tilting
of CrO6 octahedral and it shifted toward the high wavenumber re-
gion, which has been attributed to an rise in the tilt of CrO6 octahe-
dral due to reduction of R3+ radii. The modes Bg(2) and Bg(3),
which are due to the CrO6 octahedral (bending and rotation) and
shifting toward high wavenumber, which reveals distortion in the
orthorhombic structure. The fluctuation toward high wavenumber
are the result of anti-symmetric stretching vibrations of O-Cr-O
and this shifting also fluctuates as the R3+ ionic radii changes
[46,60]. Moreover, no inferior peak was found in the spectra
which confirmed the structure of fabricated nanoparticles in a sin-
gle phase and the width of the bands attributed to the grain-size of
the fabricated NPs [61].
LaðOHÞ3 ðsÞ þ heat ! LaOðOHÞ ðsÞ þ H2O ðgÞ
ð7Þ
ð8Þ
2LaOðOHÞ ðsÞ þ heat ! La2O3 ðsÞ þ H2O ðgÞ
6CrðOHÞ3 ðsÞ þ 1=2 O2 ðgÞ þ heat ! 2Cr3O4 ðsÞ þ 9H2O ðlÞ
3La2O3 ðsÞ þ 2Cr3O4 ðsÞ þ 1=2O2 ðgÞ þ heat ! 6LaCrO3 ðsÞ
ð9Þ
ð10Þ
Fig. 5. Nitrogen physisorption isotherms, (a) pristine LaCrO3, (b) La1-xCoxCr1-yFeyO3 NPs (c) La1-xCoxCr1-yFeyO3/r-GO nanocomposite.
6

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
3.6. FT-IR analysis
(Fig. 5a), La1-xCoxCr1-yFeyO3 (Fig. 5b), and La1-xCoxCr1-yFeyO3/r-GO
nanocomposite (Fig. 5c) were 88.4 m2/g, 91.32 m2/g and 168.6 m2/g, re-
spectively. The observed BET surface area of La1-xCoxCr1-yFeyO3/r-GO
nanocomposite (168.6 m2/g) was larger than the pristine LaCrO3 NPs
(88.4 m2/g) and doped La1-xCoxCr1-yFeyO3 (91.32 m2/g). The BET
specific surface area of pristine LaCrO3 (88.4 m2/g) and doped
La1-xCoxCr1-yFeyO3 (91.32 m2/g) are comparatively close to each other,
but less than the BET surface area of La1-xCoxCr1-yFeyO3/r-GO nano-
composite (168.6 m2/g), which is due to their agglomeration and stack-
ing effects. The higher BET surface area in the case of La1-xCoxCr1-yFeyO3/
r-GO nanocomposite (168.6 m2/g) can be described based on two facts.
Firstly, the 2D r-GO sheets itself provided an additional surface to the
La1-xCoxCr1-yFeyO3/r-GO nanocomposite. Secondly, the r-GO nano
sheets act as volume buffering agents and preclude the NPs from ag-
glomeration formation, which resultantly, enhanced the surface area.
The functional group was studied by FTIR analysis in 400 to
4000 cm−1 range and outcomes, thus observed are depicted in
Fig. 4d. A two intense bands in 400 cm−1 to 850 cm−1 range was ob-
served, which was due to the Cr\\O stretching and O\\Cr\\O defor-
mation, respectively. The band detected at 941 cm−1, reveals the
stretching of La\\O, Co\\O and Fe\\O bonds, another feature by the
increasing of x and y concentration slightly shift in the metal‑oxygen
stretching peak was noticed from 835 cm−1 to 1104 cm−1. This shift
may be due to the increasing bond strength and decreasing ionic
radii by the doping Co element. The bands observed between
1100 cm−1 to 1500 cm−1 may be attributed to the distortion in
water molecules. The large peak detected at 3605 cm−1 indicates
stretching of O\\H for an adsorbed water molecule, which is in the
agreement with reported studied [62–65].
3.7. BET analysis
3.8. Current-voltage (I-V) analysis
The BET technique was employed to investigate the surface area of
the fabricated samples. The N2 adsorption-desorption isotherm curves
of the LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO nano-
composite are depected in Fig. 5. The BET surface area of the LaCrO3
To study the effect of Co and Fe doping on the conductivity (σ), the
doped La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO nanocomposite
were tested via two-probe current-voltage measurements (I-V). For
this measurement, samples pellets (3 mg) were prepared with
Fig. 6. I-V profiles of LaCrO3, (b) La1-xCoxCr1-yFeyO3 NPs (c) La1-xCoxCr1-yFeyO3/r-GO nanocomposite.
7

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
2.27 mm (w) width and 7.85 mm (d) diameter. By using this, the area
(A) of the pellets was calculated as depicted in Eq. (11) [66].
I-V curves using Ohm's equation (V = IR). The determined σ
values of the LaCrO3, doped La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-y
FeyO3/r-GO nanocomposite are 2.17 × 10−2 Sm−1, 3.38 × 103
Sm−1 and 7.4 × 103 Sm−1, respectively. The observed results indi-
cate that the higher electrical conductivity (σ) value of the doped
La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO nanocomposite
that is referred to the reduction in the band gap, after r-GO addi-
tion and doping of Co, Fe ions. The UV–visible investigation also
confirmed the successful reduction in band gap of La1-xCoxCr1-y
FeyO3/r-GO nanocomposite that is due to r-GO addition and doping
of Co and Fe ions [40,67].
ꢀ ꢁ
2
d
2
A ¼ π
ð11Þ
The I-V profiles of the LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-y
FeyO3/r-GO are shown in Fig. 6. The I-V curve of the LaCrO3 (Fig. 6a) is
non-linear that reflects its non-ohmic and semi-conductive behavior.
While Co and Fe doped LaCrO3 exhibits an almost linear I-V curve
(Fig. 6b) with a better current-voltage response. Whereas, a straight I-
V curve of La1-xCoxCr1-yFeyO3/r-GO nanocomposite with an excellent
current-voltage output is shown in Fig. 6c. This excellent response is
the result of two factors, r-GO addition and doping of Co and Fe ions.
The electrical conductivity (σ) values for all prepared samples were de-
termined using Eq. (12).
3.9. Photocatalytic degradation of dye
The PCA of LaCrO3, doped La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-y
FeyO3/r-GO nanocomposite was investigated by degrading the CV
dye under visible light. The recorded UV–visible absorption spectra
of the dye are shown in Fig. 7(a-c). The degradation efficiency of
the pristine LaCrO3, doped La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-y
FeyO3/r-GO nanocomposite are explained in term of Ct/C₀ as
shown in Fig. 8a, where C₀ express the initial concentration of the
CV dye and Ct, express the concentration at a specific time interval.
w
RA
σ ¼
ð12Þ
where, A, R, and w are the area, resistance and width of the pel-
lets, respectively, the values of R (resistance) was determined from
Fig. 7. Absorption spectra of CV dye photo-degradation over, (a) pristine LaCrO3 (b) doped La 1-xCoxCr1-yFeyO3 and (c) La 1-xCoxCr1-yFeyO3/r-GO nanocomposite.
8

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
Table 2
From the UV–visible profiles, it is clear that La1-xCoxCr1-yFeyO3/r-
GO degrades the CV dye faster as compared to pristine LaCrO3
and doped La1-x CoxCr1-yFeyO3 and the % degradation of CV dye
was recorded to be 35.78, 55.27 and 89.08 (%) for pristine
LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO, respec-
tively (Fig. 8d). The high catalytic efficiency of the La1-xCoxCr1-y
FeyO3 (55.27%) as compared to pristine LaCrO3 (35.78%) is the
result of defects that are generated by doping [68]. Moreover,
the dopants act like trapping agents toward holes/electrons to
retard their recombination phenomenon. While in the case of
La1-xCoxCr1-yFeyO3/r-GO, the percentage of CV dye degradation
was 89.08%. It is due to the r-GO nano sheets that shielded the
La1-x CoxCr1-yFeyO3 agglomeration process and resultantly, surface
to volume ratio increases. Hence, La1-xCoxCr1-y FeyO3/r-GO due to
its larger surface area adsorbed a higher amount of CV dye and re-
sultantly, it degraded 89.08% of CV dye, which is a promising cata-
lytic efficiency [69]. The PCA of the LaCrO3, La1-xCoxCr1-yFeyO3 and
La1-x CoxCr1-yFeyO3/r-GO composite was studied through kinetics
of the CV dye photodegradation, which followed the first-order
kinetics [70].
The comparison of the PCA of the La1-xCoxCr1-yFeyO3/r-GO (for CV dye) with reported sim-
ilar studies.
Photo-catalysts
Dye Degradation (%) Time (min) Reference
CdS/CMS
CV
CV
CV
CV
CV
CV
CV
81.03
75
82
64
89
120
60
300
45
100
75
240
90
[74]
[75]
[76]
[77]
[78]
[79]
[80]
Fe3O4/ZnO/CRC
TiO2(B)/fullerene
Co3O4 NPs
TiO2/clinoptilolites
FB-HAp
77
68
S/RGO
La1-xCoxCr1-yFeyO3/r-GO CV
89.08
Present study
express the reaction time. A straight line is obtained (Fig. 8b) by plot –
ln Ct/Co vs. t and the value of ‘k’ in min−1 can be calculated through
the slope of the straight line [71]. The values of rate constant
(k) (Fig. 8c) for the degradation of CV dye by pristine LaCrO3, doped
La1-xCoxCr1-y FeyO3 and La1-xCoxCr1-yFeyO3/r-GO are 0.00311 min−1
,
0.00845 min−1 and 0.0195 min−1, respectively [72]. In-fact, faster deg-
radation of CV dye with La1-xCoxCr1-yFeyO3/r-GO is mainly due to the ex-
istence of effective charge separation in the La1-xCoxCr1-yFeyO3/r-GO
composite and it may also be due to the formation of heterojunction be-
tween the La1-xCoxCr1-yFeyO3 and r-GO. Moreover, the existence of the
r-GO in La1-xCoxCr1-yFeyO3/r-GO nanocomposite not only provides a
large surface area to facilitate the adsorption of CV dye, but also
−lnCt=C₀ ¼ kt
ð13Þ
where, C₀ and Ct are CV dye concentration at zero time and a specific in-
terval of time, respectively. ‘k’ express the rate constant, while ‘t’
Fig. 8. Degradation curves profiles of CV dye over pristine LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO, (a) The degradation-rate, (b) Linear-kinetic, (c) Rate-constant and
(d) percentage degradation of dye.
9

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
Fig. 9. (a) Photocatalytic degradation of CV over La1-xCoxCr1-yFeyO3/r-GO photo-catalyst alone and with different scavengers and (b) dye removal percentages in the presence of
scavengers.
suppresses the electron/holes recombination process [73]. In compari-
son of PCA of fabricated photo-catalyst closely relates with reported
studies (Table 2) and La1-xCoxCr1-yFeyO3/r-GO nanocomposite showed
significant PCA versus reported related catalysts.
La1−xCoxCr1−yFeyO3 þ Visible light
À
Á
! La1−xCoxCr1−yFeyO eCB þ hþ
ð14Þ
ꢀ
3
VB
À
Á
La1−xCoxCr FeyO eCB þ hþ
þ r−GO
ꢀ
1−y
3
VB
To confirm the species (OH• & •O2−) responsible for the
degradation of dye, isopropyl alcohol (IPA) and ascorbic acid
(Vit. C) were used for scavenging the OH• and •O2−, respectively,
by keeping all other experimental conditions constant. The scaven-
ger results are shown in Fig. 9a. The degradation efficiency of La1-x
CoxCr1-yFeyO3-r-GO composite over CV dye, which declined in case
of scavengers presence. Thus, the experimental results (Fig. 9b)
infer that OH• and •O−2 were the main species that were involved
in the degradation of CV dye. The proposed mechanism of photo-
catalyzed CV dye degradation is shown in reactions (Eqs. (14)–
(22)) and the photocatalytic degradation mechanism is shown in
Fig. 10.
À
Á
! La1−xCoxCr FeyO hþ
þ r−GO ðeÞ
ð15Þ
ð16Þ
ꢀ
1−y
3
VB
À
Á
La1−xCoxCr1−yFeyO3 hþ
þ H2O ! OH˙ þ Hþ
VB
−
ꢀ
E ðr−GOÞ þ O2 ! r−GO þ ˙O2
˙
ð17Þ
ð18Þ
ð19Þ
ð20Þ
−
−
˙O2 ˙ þ 2Hþ ! HO2 ˙ þ Hþ ! 2OH˙
−
−
˙O2 þ H2O ! ˙OOH þ HO2
2˙OOH ! O2 þ H2O2
Fig. 10. Photocatalytic proposed mechanism for dye degradation over La1-xCoxCr1-yFeyO3/r-GO photocatalyst.
10

M. Aamir, I. Bibi, S. Ata et al.
Journal of Molecular Liquids xxx (2020) xxx
−
H2O2 þ O2 ˙ ! OH˙ þ HO− þ ˙O2−
ð21Þ
ð22Þ
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OH˙=˙O2− þ CV dye ! Degraded products
4. Conclusion
Pristine LaCrO3, La1-xCoxCr1-yFeyO3 and La1-xCoxCr1-yFeyO3/r-GO
nanocomposite were successfully fabricated via micro-emulsion
and ultra-sonication method, respectively. The effect of Cr, Fe doping
on La1-xCoxCr1-yFeyO3, and La1-xCoxCr1-yFeyO3/r-GO nanocomposite
were studied, the electrical conductivity of the pristine LaCrO3 was in
the range of 2.17 × 10−2 Sm−1 to 7.4 × 103 Sm−1. Besides, the La1-x
CoxCr1-yFeyO3/r-GO nanocomposite exhibited excellent PCA for CV dye
degradation under visible light. The improved PCA of the La1-xCoxCr1-y
FeyO3/r-GO composite is due to the surface area, low band gap and
fast charge transportation character. In view of promising PCA of La1-x
CoxCr1-yFeyO3/r-GO nanocomposite, it could be employed as
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photocatalyst for the remediation of dyes in textile effluents.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgements
This research was funded by the Deanship of Scientific Research at
Princess Nourah bint Abdulrahman University through the Fast-track
Research Funding Program.
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