Novel perovskite nanocatalyst (BiFeO3) for the photodegradation of rhodamine B/tartrazine and swift reduction of nitro compounds

Article abstract of DOI:10.1007/s13738-019-01710-6

Design and synthesis of visible light respondent photocatalyst with high separation efficiency is of great importance due to its application in practical point of view. In this presentation, novel perovskite-structured BiFeO₃ nanoparticles have been successfully synthesized by simple, cost-effective and eco-friendly technique. The BiFeO₃ nanoparticles were prepared by using different chelating agents (sucrose, citric acid, tartaric acid and urea) and under different range of calcination temperature (150–850?°C). Different characterization techniques such as FT-IR, XRD, VSM, BET, TEM and UV–Vis spectroscopy have been used for its structure evaluation. Further, by using this catalyst, a green approach has been developed for the removal of harmful organic compounds from the industrial waste. The catalytic activity was assessed by the catalytic degradation of industrial waste dyes such as rhodamine B and tartrazine (first time by perovskite-structured material) in aqueous media under sunlight irradiation and reduction of various nitro compounds to corresponding amines (in s) by using NaBH₄ in green solvent water at room temperature. Effect of all types of BiFeO₃ nanoparticles on catalytic degradation and reduction was investigated. BiFeO₃ nanoparticles prepared by sucrose as chelating agent and calcinated at 650° were selected as a better catalyst on the basis of its performance in degradation and reduction experiment. Thus, the present approach provides a promising way to prepare noble catalyst for extensive applications in degradation/reduction of organic pollutants. The examination of degraded products of dye has been carried out by using FT-IR; mass spectroscopy and UV–Vis spectroscopy and confirmation of reduction of nitrocompounds with UV–Vis spectroscopy.

Full text of DOI:10.1007/s13738-019-01710-6

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01710-6
ORIGINAL PAPER
Novel perovskite nanocatalyst (BiFeO ) for the photodegradation
3
of rhodamine B/tartrazine and swift reduction of nitro compounds
Harminder Singh · Jaspreet Kaur Rajput1
1
Received: 29 January 2019 / Accepted: 6 June 2019
©
Iranian Chemical Society 2019
Abstract
Design and synthesis of visible light respondent photocatalyst with high separation eꢀciency is of great importance due to its
application in practical point of view. In this presentation, novel perovskite-structured BiFeO nanoparticles have been suc-
3
cessfully synthesized by simple, cost-eꢁective and eco-friendly technique. The BiFeO nanoparticles were prepared by using
3
diꢁerent chelating agents (sucrose, citric acid, tartaric acid and urea) and under diꢁerent range of calcination temperature
(
150–850 °C). Diꢁerent characterization techniques such as FT-IR, XRD, VSM, BET, TEM and UV–Vis spectroscopy have
been used for its structure evaluation. Further, by using this catalyst, a green approach has been developed for the removal
of harmful organic compounds from the industrial waste. The catalytic activity was assessed by the catalytic degradation
of industrial waste dyes such as rhodamine B and tartrazine (ꢂrst time by perovskite-structured material) in aqueous media
under sunlight irradiation and reduction of various nitro compounds to corresponding amines (in s) by using NaBH in
4
green solvent water at room temperature. Eꢁect of all types of BiFeO nanoparticles on catalytic degradation and reduction
3
was investigated. BiFeO nanoparticles prepared by sucrose as chelating agent and calcinated at 650° were selected as a
3
better catalyst on the basis of its performance in degradation and reduction experiment. Thus, the present approach provides
a promising way to prepare noble catalyst for extensive applications in degradation/reduction of organic pollutants. The
examination of degraded products of dye has been carried out by using FT-IR; mass spectroscopy and UV–Vis spectroscopy
and conꢂrmation of reduction of nitrocompounds with UV–Vis spectroscopy.
Keywords RhB · Tartrazine · Degradation · Reduction · Photocatalyst · BiFeO3
Introduction
they display high toxicity, slow biodegradation, low decol-
oration [2], prospective mutagenic and carcinogenic eꢁects
[4]. Even a very small concentration of the dyes in eꢃuents
coming out from industries is highly visible and undesirable.
The colored part reduces the transparency, which reduces
the penetration of light, and results in the obstruction of the
photosynthesis and responsible for the destruction of large
number of water living organisms. Rhodamine B is a basic
dye of xanthene class, extensively used as colorant in textiles
and food stuꢁs. It is extremely soluble in water and organic
solvents and is well known as water tracer ꢄuorescent. Due
to its terrible heath eꢁects such as irritation of skin, eyes
and respiratory track, it is declared as harmful to human and
animal life. Further its neurotoxicity, carcinogenicity, devel-
opment toxicity, chronic toxicity, and reproductive toxicity
have proven experimentally for both humans and animals
[5, 6]. Tartrazine is an azo dye also known as FD&C Yellow
No. 5, widely used in food coloring, cosmetics, drugs, etc.,
and present in maximum amount in industrial eꢃuents cause
Environmental pollution is the area of great concern of
twenty-ꢂrst century. Waste coming out from textile and dye
industries is very hazardous to living bodies on earth [1].
Nearly, 1–20% of dyes are released as textile eꢃuents of the
total world production of dyes during dyeing process [2].
Various organic dyes which are water soluble are used in
various industries, and their degraded products represent a
series of environmental issue [3] for human beings because
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-019-01710-6) contains
supplementary material, which is available to authorized users.
*
Harminder Singh
Harmindersingh87@gmail.com
1
Department of Chemistry, Dr. B R Ambedkar National
Institute of Technology, Jalandhar, Punjab 144011, India
Vol.:(0
1
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Journal of the Iranian Chemical Society
various health issues for humans such as allergic reactions
among hypersensitive persons. It causes headaches, hives,
insomnia, asthma attack, thyroid cancer and lupus [7, 8].
Therefore, the elimination of organic dyes from environment
attracted much interest in the past decades.
agents, numerous catalysts [16–20] and methodologies [21]
are available for this transformation but all of them have
limitations such as prolonged reaction time, high H pres-
2
sure, use of organic solvents, reduced recyclability and high
temperature. So the development of proꢂcient and consistent
technique is highly desirable for the reduction of ANCs (aro-
Various methods like physical (adsorption, ultra ꢂltration,
coagulation and ion exchange) and biological (bacteria and
yeasts) have been reported in the literature so far, for the
elimination of colored eꢃuents coming out with industrial
and textile waste. These methods are not successful complete
for the conversion of contaminants into less harmful and
useful products [9, 10]. Moreover, they do not cause the
complete degradation and also unable to stop their move-
ment from one phase to another. These methods do not work
well due to high stability and resistance to chemical and
biological degradation of dyes. So, more convenient method
is still in demand which overcomes these problems for the
waste water treatment [11].
matic nitro compounds). Among reducing agents, NaBH is
4
of high important, since it is milder, selective and thermally
stable chemical hydride [20]. It represents the best economi-
cal option for the reduction reactions at normal conditions
of temperature and pressure.
Perovskite-structured BiFeO nanoparticles have got
3
much attention due to its high chemical and thermal stabil-
ity, potential electronic and magnetic applications [12]. In
addition, narrow bang-gap energy (2.1 eV) and photovoltic
eꢁects show their tendency to act as photocatalyst under vis-
ible light for degradation of harmful industrial compounds
[22]. All these observations make them a promising photo-
catalyst by utilizing solar energy for puriꢂcation of waste
water [12].
Nowadays, photocatalysis is proven to be more conveni-
ent, simple and eco-friendly way for the degradation of
harmful dyes due to the use of oxygen as oxidant, low-
temperature oxidation of organic compounds and complete
The present work aims to provide a new-generation
hybrid system with high catalytic eꢀciency and stability.
mineralization. TiO is reported to degrade many organic
Here we reported the potentiality of the BiFeO nanopar-
2
3
dyes under UV irradiation. However, its large band gap
ticles as heterogeneous photocatalyst that has been investi-
gated for the degradation of RhB and tartrazine (ꢂrst time
ever) in aqueous media under sunlight irradiation and for the
reduction of ANCs (aromatic nitro compounds) in aqueous
media at room temperature. In addition to excellent cata-
lytic activity of the as-prepared catalyst, it could be easily
recovered from the reaction medium by using an external
magnet and reused up to ꢂve times without considerable loss
in activity, indicative of its potential application in chemical
industries.
(
~ 3.2 eV) restricts its application as photocatalyst in vis-
ible light [12]. The sunlight consists of less than 4% of
UV light and more than 50% of the visible light. Hence,
the development of non-titania catalyst with high catalytic
activity in visible region with narrow band gap is highly
desirable [2].
Due to the environmental conditions of India, the sunlight
is abundantly available throughout the year. So the harmful
dyes can be degraded easily using natural sources of light
by using photocatalyst [5]. The photodegradation of tartra-
zine and rhodamine B has been carried out under sunlight
by using BiFeO as an eꢀcient and cost-eꢁective catalyst.
Experimental section
3
Aromatic nitro compounds are used in various indus-
tries for the formation of fungicides, rubber, insecticides
and synthetic dyes [13, 14]. Their solubility and stability
in aqueous media make it a serious issue of environmental
pollution, referred as the main pollutant coming out from
chemical, drug industries and agriculture waste. Its serious
inhalation causes nausea, drowsiness, headaches, cyanosis
and eye irritation [15]. So its quick degradation is required.
The simple and cost-eꢁective method is to convert them in
Materials
Bismuth nitrate (pentahydrate), ferric nitrate (extra pure,
nonahydrate), tartaric acid (extra pure), sucrose (extra
pure), citric acid (pure) and urea were purchased from Loba
Chemie. Nitric acid (70%) was supplied by Merck. 4-nitro-
phenol, 2-nitrophenol, 2, 4-dinitrophenol, 4-nitroaniline,
2-nitroaniline and 2,4-dinitroaniline were supplied by Avra
synthesis. All these were used as such without any further
puriꢂcation.
aromatic amines through reduction by using NaBH as a
4
reducing agent. Thus, its reduction to amino compounds is
of high importance [16]. Because aromatic amines are the
important starting materials or intermediates or precursors
for the formation of the pigments, pharmaceuticals products,
herbicides, polymers, dye stuꢁs, surfactants, agricultural
chemical [17, 18] and used as a photographic developer,
lubricating and anticorrosion agent [16]. Various reducing
Methods
The crystal structure of prepared magnetic nanoparticles
catalyst was investigated by X-ray diꢁraction (XRD) using
a Panlytical XPERTPRO (NPD) X-ray diꢁractometer with
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Journal of the Iranian Chemical Society
Cu Kα radiation (λ = 0.154 nm), in the 2θ range 10°–80°.
sonicated for 10 min. Then two solutions were mixed and
again sonicated for 15 min. Addition of 5 mmol of chelat-
ing agent (sucrose, citric acid, tartaric acid and urea) was
carried out to the mixture followed by stirring for 30 min to
enable complete dissolution. The contents were then heated
on a hot plate at 100 °C for 30 min. Heating resulted in
evaporation, auto-ignition followed by evaporation of large
quantities of gases, leaving behind black powder. The black
powder so obtained was then calcinated separately at diꢁer-
ent temperatures such as 150 °C, 450 °C, 550 °C, 650 °C,
750 °C and 850 °C.
Fourier transform IR (FT-IR) spectroscopy was carried out
−
1
by using Agilent Cary 600 in the range 400–4000 cm .
The morphology was studied using transmission electron
microscopy (TEM). The sample was prepared by disper-
sion of nanoparticles in ethanol, which were deposited on a
carbon-coated Cu grid, and after drying, analysis was per-
formed using a Hitachi S7500 instrument. The magnetic
properties were measured using a vibrating sample mag-
netometer (VSM, Princeton Applied Research model 155)
at room temperature with a maximum magnetic ꢂeld range
of + 1 T to − 1 T. Light intensity is measured by digital
lux meter of HTC™ of model LX-101A. A photocatalytic
chamber containing Hg lamp of power 15 W was used as a
source of artiꢂcial UV irradiation, and the distance of dye
solution (when stagnant) was set as 50 cm from the lamp.
Ultra-sonic cleaner (sonication) of JSGW model number
Sunlight irradiation
In order to estimate the photocatalytic activity of as-syn-
thesized catalyst by auto-combustion route, two diꢁerent
dyes RhB and tartrazine were taken. A typical experiment
constitutes 10 ml of 10 ppm of dye solution and 10 mg of
catalyst taken in a round-bottom ꢄask. Before exposing to
irradiation, the reaction suspension was magnetically stirred
at 800 rpm for 30 min in dark to establish adsorption equilib-
rium between the catalyst and the dye solution. Afterward,
the suspension was put under sunlight for appropriate time
for complete degradation. The experiments were carried out
under direct solar radiation in consecutive sunny days in
July, 2017 from 11.30 am to 2.30 pm with an average light
intensity 80,000–90,000 Lux. All experiments were carried
out under temperature range from 30 to 39 °C (Scheme 1).
1
2
236/2, of 33± 3 kHz frequency with internal dimensions
28×140×100 mm was used. Surface area and pore char-
acteristics were characterized using Quanta Chrome Nova-
1
000 surface analyzer instrument under liquid nitrogen
temperature with vacuum degassing at 110 °C for 3 h. The
speciꢂc surface area was calculated using the BET equation.
Mass spectroscopy was carried out by using XEVO G2-XS
QTOF instrument. ChemDraw ultra 8.0 was used for draw-
ing chemical structures.
Synthesis of BiFeO nanoparticles
3
BiFeO nanoparticles were synthesized using Bi
Reduction of 4‑nitrophenol (NP)
3
(
NO ) ·5H O and Fe(NO ) ·9H O as precursors.
3
3
2
3 3
2
Bi(NO ) ·5H O (2.5 mmol) and Fe(NO ) ·9H O
In typical experiment, 5 ml of 4NP (0.1 mmol) was taken;
3
3
2
3 3
2
(
2.5 mmol) were dissolved in 5 ml of distilled water and
then freshly prepared 12.5 ml of NaBH (0.53 mmol) was
4
1
0 ml of 3 M HNO , respectively. These solutions were
added. To the mixture, 25 mg amount of BiFeO was added
3
3
Scheme 1 Photocatalytic deg-
radation of RhB or tartrazine by
BiFeO nanoparticles
3
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Journal of the Iranian Chemical Society
and the mixture was stirred at 800 rpm at room tempera-
ture for appropriate time intervals. The reduction of nitro
group to amino group was estimated by elimination of yel-
low color. The time for decolorization was determined. The
reduction phenomena were further investigated by using
UV–Vis spectroscopy.
acid and urea and further their eꢁects on degradation and
reduction experiment were carried out.
Characterization of the as‑prepared catalyst
FT‑IR
To conꢂrm the removal of organic phase impurities and for-
Results and discussion
mation of pure form of BiFeO nanoparticles prepared by
3
sucrose as chelating agent with increase in calcination tem-
perature, FT-IR analysis was carried out as shown in Fig. 1.
In case of calcination temperature 150 °C, a broad peak near
The purpose of adding the chelating agent is to control the
size, agglomeration and surface morphology of the nano-
particles. The decomposition of the metal precursor (act-
ing as oxidizer) carried out at normal temperature by using
organic fuel (acting as reducing agent) with providing lit-
tle external heat. During the redox reaction high chemical
energy is released which causes the highest level molecular
mixing of the components. Sometimes more thermal treat-
ment is needed to remove the organic impurity left in the
sample during the course of the reaction. So the selection
of chelating agent signiꢂcantly aꢁects the properties of the
nanoparticles [23–25]. In our case, we have used four dif-
ferent chelating agents such as sucrose, citric acid, tartaric
−
1
3000–3400 cm was attributed to the stretching mode of
OH of water molecule as the sample might consist of some
moisture on its surface and several others peaks observed at
−
1
−1
−1
1060 cm , 1139 cm and 1165 cm were came out from
the result of stretching mode of C–OH and C–O–C bond,
respectively. With increase in temperature, i.e., 450 °C and
550 °C, the elimination of such above-mentioned peaks goes
on decreasing and FT-IR pattern of sample calcination at
highest temperature, i.e., 650 °C was totally free of such
kinds of impurity peaks. Further the formation of new peaks
of stretching mode of Bi–O, Fe–O and O–Fe–O bonds of
Fig. 1 Comparison study of FT-IR spectra of BiFeO calcinated at a 150 °C, b 450 °C, c 550 °C and d 650 °C
3
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Journal of the Iranian Chemical Society
−
1
−1
−1
FeO at 819 cm , 522 cm and 437 cm , respectively
main peaks of BiFeO nanoparticles started appearing along
6
3
[
26, 27], was increased with increase in calcination tem-
with other secondary phases of Bi Fe O and Bi Fe O at
2
4
9
36 24 57
perature, i.e., sharpness of formation of such peaks increased
with from 150 to 650 °C, showing the degree of crystallin-
ity increased with increase in calcination temperature [28].
So, calcination temperature 650 °C was optimized tempera-
ture which was free from all impurity peaks and consists of
sharp purity peaks. Therefore, it was considered to be the
2θ=25.75°, 30.33°, 48.41° and 49.30° and 24.64°, 30.31°,
33.28°, 42.07°, 43.43°, 54.29°, 55.55°, respectively. The dif-
ference in oxygen aꢀnity of Fe and Bi ion was responsible
for the generation of secondary impurity phases. Further,
as we increased the calcination temperature to 550 °C and
650 °C, the sharpening of main diꢁraction peaks increased
and intensity of secondary impurity phases decreased. In
case of sample calcinated at 650 °C, miller indices, i.e.,
ꢂnal calcination temperature to obtain pure form of BiFeO
3
nanoparticles.
(
012), (104), (110), (006), (202), (024), (116), (122), (214),
XRD
(018) and (300) were found corresponding to the main dif-
fraction peaks 22.5, 31.78, 32.0, 38.96, 39.09, 46.05, 51.47,
For the detection of formation of pure form of BiFeO
51.73, 55.54, 55.59 and 55.87° of BiFeO nanoparticles,
3
3
nanoparticles using sucrose as chelating agent, XRD analy-
sis of samples calcinated at various temperatures has been
explored as depicted in Fig. 2. The material looks like an
amorphous in nature with no characteristic peak observed
at initial calcination temperature 150 °C. Then we increased
the calcination temperature to 450 °C, 550 °C and 650 °C
which were accordingly with the JCPDS Card no. 86-1518
[29]. So from above discussion calcination temperature
650 °C, showing that more is the calcination temperature
more will be the sharpening of main diꢁraction peaks with
more will be the elimination of impurity phases [30, 31].
Now to check whether 650 °C temperature was the ꢂnal
to obtain the pure form of BiFeO nanoparticles. In case of
calcination temperature for obtaining pure form of BiFeO
3
3
calcination temperature 450 °C, it has been observed that
nanoparticles, we also extend our study on more calcination
Fig. 2 XRD analysis of BiFeO calcinated at a 150 °C, b 450 °C, c 550 °C, d 650 °C, e 750 °C and f 850 °C
3
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Journal of the Iranian Chemical Society
temperatures such as 750 °C and 850 °C. In case of 750 °C,
impurity phases such as Bi O , Bi Fe O , Bi Fe O [32]
bond and bond angles of Fe–O–Fe, Fe–O–Fe bonds [36,
37]. The low value of Ms at 150 °C was attributed to the
little bit formation of Fe–O and O–Fe–O bonds, and higher
value of Ms of calcination temperature 450 °C as compared
to calcination temperature 150 °C was due to the complete
appearance of the formation of Fe–O and O–Fe–O bonds
[25] as also explained by FT-IR and XRD analysis earlier.
2
3
3
4
9
2
4
4
and Bi Fe O [33] were found at 2θ=14.79° and 32.99°,
3
6
24 57
respectively. On further increasing the calcination tempera-
ture to 850 °C, the sample lost its main diꢁraction peaks with
more impurity phases at 2θ = 14.79, 28.99, 29.81, 33.80,
4
7.27 and 49.49° for Bi O , Bi Fe O [32] and Bi Fe O
2 3 3 4 9 2 4 4
[
33], respectively. So 650 °C temperature was the optimized
So as pure form of BiFeO nanoparticles was obtained at
3
calcinated temperature for obtaining pure form of BiFeO
calcination temperature 650 °C as explained by XRD earlier
and exhibiting 0.4 emu/g of saturation magnetization (Ms)
by VSM, proved it as a potential material to be used as mag-
netically separable in numerous applications [38].
3
nanoparticles. Further using Scherrer’s formula D = kλ/β
cosθ, where λ is the wavelength, β is the corrected diꢁrac-
tion line full-width at half maximum, k is a constant (having
a value of 0.94) and is Bragg’s angle, average particle size
was calculated for calcination temperature 150 °C, 450 °C,
TEM
5
5
50 °C and 650 °C and was found to be approximately
.74 nm, 11.79 nm, 69.3 nm and 70.01 nm, respectively.
Study of particle size and morphology was explored by TEM
The increase in particles size with increasing calcination
temperature was due to the formation of cluster, particles
collision [34] and sharpening of main diꢁraction peaks [35].
analysis. The TEM analysis of BiFeO nanoparticles using
3
sucrose as chelating agent at calcination temperature 150 °C
and 650 °C has been done as exposed in Fig. 4. Grain par-
ticle size exhibited by this analysis was found to be large as
compared to the average particle size by XRD analysis. The
reason behind is that some grain contains sub-grains which
were separated by low-angle grain boundaries [39].
VSM
Investigation regarding magnetic property of as-synthesized
samples, i.e., BiFeO nanoparticles using sucrose as chelat-
3
ing agent at diꢁerent ranges of calcination temperature over
a magnetic ꢂeld ± 1T was carried out as demonstrated in
Fig. 3. The value of saturation magnetization (Ms) of sam-
ple calcinated at temperature 150 °C, 450 °C, 550 °C and
BET
The surface area of BiFeO nanoparticles using sucrose
3
as chelating agent at different calcination temperature,
6
50 °C was found to be 0.6 emu/g, 5.6 emu/g, 2.5 emu/g
i.e., 150 °C, 450 °C, 550 °C and 650 °C was found to be
2
2
2
2
and 0.4 emu/g, respectively. The main reason of showing
6.4 m /g, 2.1 m /g, 1.8 m /g and 1.6 m /g, respectively. The
decrease in surface area with increase in calcination tem-
perature was attributed to the increase in particle size; results
were in good agreement as explained by XRD and TEM
analysis earlier [40].
magnetic properties by BiFeO nanoparticles was due to
3
3
+
the existence of Fe ions and excess of oxygen vacancies
[
32]. The decrease in Ms value from 450 °C to 650 °C is
that some grains are unable to contribute in magnetization
because they do not possess spontaneous magnetic moment
at higher temperature and increase in bond length of Bi–Fe
UV–Vis analysis
UV–Vis analysis of as-synthesized samples using sucrose as
a chelating agent prepared at diꢁerent calcination tempera-
ture, i.e., 150 °C, 450 °C, 550 °C and 650 °C, was carried
out as shown in Fig. 5. The nanoparticles showed a strong
absorption in visible light, which is related to the band gap
energy of the photocatalyst. Tauc’s equation was used for the
ꢀ
ꢁ
n
estimation of band gap, (ꢀhꢁ) = B hꢁ − E . Where α, h, ν,
g
g
E and B are the absorption coeꢀcient, Plank constant, light
frequency, band gap energy and a constant, respectively. For
BiFeO , n=2, which indicates the direct band gap. The band
3
gap energy was calculated by extrapolating the linear por-
2
tion of (ꢀhꢁ) vs hꢁ to the point α = 0. The value of band
gap observed using above formula was found to be 2.35 eV,
2
1
.21 eV, 2.12 eV and 2.04 eV for the sample prepared at
50 °C, 450 °C, 550 °C and 650 °C, respectively. The basic
Fig. 3 VSM of BiFeO nanoparticles calcinated at a 150 °C, b
3
4
50 °C, c 550 °C, and d 650 °C
reason for the change in band gap at nanoscale is that when
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Journal of the Iranian Chemical Society
Fig. 4 TEM analysis of BiFeO
3
calcinated at a 150 °C and b
6
50 °C
Fig. 5 UV–Vis spectra of BiFeO calcinated at a 150 °C, b 450 °C, c 550 °C, and d 650 °C
3
the size of particle reaches to nanoscale, number of overlap-
ping of orbitals decreases and thickness of band becomes
thinner. These will result into the increase in energy band
gap between the valence and conduction band. This behav-
ior of band gap is in good agreement with the previous
reports for perovskite type nanomaterials [41]. Moreover,
band gap also depends on the particle size of nanoparti-
cles. As in our case average particles size increased with
increase in calcination temperature, i.e., 5.74 nm, 11.79 nm,
69.3 nm and 70.01 nm observed for BiFeO nanoparticles
3
prepared at 150 °C, 450 °C, 550 °C and 650 °C, respec-
tively, as discussed earlier by XRD analysis. The reason
behind the decrease in band gap with increase in average
particle size is the “quantum size eꢁect” which leads to
increase in Eg values with decrease in average particle size
nanoparticles [42, 43]. So BiFeO nanoparticles prepared
3
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Journal of the Iranian Chemical Society
at calcination temperature 650 °C exhibited least value of
band gap energy, i.e., 2.04 eV which is in agreement with
the previous literature [22, 44]. This proves that as-prepared
catalyst is appropriate for acting as photocatalyst for the deg-
radation of harmful compounds in the range of visible light.
It has been observed that there is slightly a redshift in the
absorption edges, i.e., 292.92 nm, 290.98 nm, 288.15 nm
and 286.20 nm for the sample calcinated at 150 °C, 450 °C,
Eꢀect of BiFeO prepared by diꢀerent chelating agents
at calcination temperature of 150 °C
3
To ꢂnd out the better chelating agent (i.e. sucrose, tartaric
acid, urea and citric acid) for the synthesis of BiFeO nano-
3
particles and their eꢁects on the degradation of dyes were
checked. Eꢁect of BiFeO prepared by these diꢁerent chelat-
3
ing agents and calcinated at initial temperature, i.e., 150 °C
5
50 °C and 650 °C, respectively. This observation demon-
and on percentage degradation of RhB and tartrazine was
strated that redshift with increasing calcination temperature
is an indicative of decrease in band gap with increase in
crystalline size (as shown in Fig. 5). These results are in well
agreement with the previous reports [45].
explored. Study was also carried out by BiFeO prepared
3
without using any chelating agent. Data as illustrated in
Table 1 (Entry 1–5) demonstrate that better results were
given by BiFeO prepared by using sucrose as a chelating
3
agent.
Eꢀect of BiFeO prepared by diꢀerent chelating agents
at calcination temperature of 650 °C
Catalytic activity
3
Photocatalytic activity
Further we also continue our investigation on the diꢁerent
types of catalyst prepared at calcination temperature 650 °C.
The same reaction conditions were used for the degradation
of RhB and tartrazine as given above. The eꢁect on % degra-
dation was investigated by all types of catalysts prepared by
diꢁerent chelating agents as shown in Table 1 (Entry 6–10).
From above discussion, it was clear that better results were
given by the catalysts when prepared at 650 °C as compared
to prepared at 150 °C. This shows that as we increased the
The catalytic activity of as-synthesized BiFeO nanopar-
3
ticles has been evaluated for photocatalytic degradation of
RhB and tartrazine in aqueous media. No additives have
been added in the reaction of both dyes. Various param-
eters such as eꢁect of BiFeO prepared by diꢁerent chelat-
3
ing agents at calcination temperature of 150 °C, eꢁect of
BiFeO prepared by diꢁerent chelating agents at calcination
3
temperature of 650 °C, eꢁect of pH, eꢁect of diꢁerent cal-
cination temperature, dose of catalytic amount, optimiza-
tion of reaction condition, optimization of dye solution (ml),
optimization of dye concentration (ppm), optimization of
time and recyclability were investigated. The degradation
eꢀciency was evaluated by using the formula:
calcination temperature, the purity of the BiFeO nanopar-
3
ticles enhanced and band gap decreases (as shown in Fig. 5)
which was responsible for fast degradation process. These
results were in good agreement as demonstrated by XRD
analysis. Further, observation shows that best catalyst for
ꢀ
ꢁ
degradation was BiFeO nanoparticles prepared by chelating
3
%
Degradation = C − C ∕C × 100
0
(1)
t
o
agent sucrose. It shows better catalytic activity among all the
catalysts prepared at calcination temperature of 650 °C(citric
acid, tartaric acid and urea as chelating agent). The reason
for better catalytic activity was due to the value of band
where C is the initial concentration of RhB and tartrazine
o
and C is the concentration at time t.
t
Table 1 Eꢁect on %
Entry Catalyst Chelating agent Calcination Temp. Amount (mg) % Degrada- % Degradation
tion (RhB) (Tartrazine)
degradation by catalyst prepared
at 150°C
1
2
3
4
5
6
7
8
9
1
BiFeO3
BiFeO3
BiFeO3
BiFeO3
BiFeO3
BiFeO3
BiFeO3
BiFeO3
BiFeO3
BiFeO3
–
150 °C
150 °C
150 °C
150 °C
150 °C
650 °C
650 °C
650 °C
650 °C
650 °C
10
10
10
10
10
10
10
10
10
10
0.33
70.36
0.60
7.01
3.23
14.86
82.45
68.14
68.90
71.37
24.37
42.13
24.84
33.89
25.15
25.47
70.44
53.14
61.16
65.40
Sucrose
Citric acid
Tartaric acid
Urea
–
Sucrose
Citric acid
Tartaric acid
Urea
0
Reaction conditions: 10 ml (10 ppm dye sol), pH(RhB; 6.84, tartrazine; 7.2) (30 min stirring in dark,
0 min stirring under sunlight)
6
1
3

Journal of the Iranian Chemical Society
gap energy which plays an important role in the degradation
process. It has been found that the values of band gap ener-
as-synthesized catalyst at diꢁerent range of pH. The pH
factor aꢁects the surface charge properties of the catalyst
and the formation of ionic species in the solution [2]. So it
is the one of the most signiꢂcant parameters which inꢄu-
ences the % degradation of dyes. For this purpose, dye
solution of RhB and tartrazine were prepared at diꢁerent
pH, i.e., 0.5, 1, 2, 4, 6, 8, 10 and 12. The pH values of dye
solution were adjusted by using HCl and NaOH solution
of 1 N each as demonstrated in Table 2 and Fig. 6. Further
gies for BiFeO nanoparticles prepared by using diꢁerent
3
chelating agent citric acid, tartaric acid, urea and sucrose
were found to be 2.25 eV, 2,20 eV, 2.17 eV and 2.04 eV
with % degradation of RhB (68.14%, 68.90%, 71.37%
and 82.45%) and tartrazine (53.14%, 61.16%, 65.40% and
7
0.44%), respectively. So it was observed that the value of
percentage degradation of both dyes increased with decrease
in the band gap. The reason for increase in photocatalytic
activity with decrease in band gap was attributed to the pro-
duction of inter-band or heterojunction which decreases the
the point of zero charge of as-synthesized BiFeO nano-
3
particles was calculated by using pH drift method [47]
and found to be 7.006. In case of RhB (cationic dye), the
catalyst shows maximum degradation eꢀcacy (99.62%)
in acidic medium, i.e., at pH 1. The reason behind the
higher % degradation in acidic medium was due to the
fact that when pH < 4, there was a shifting of carboxylic
group of RhB to the acidic form. Because of the equi-
librium, the existence of carboxylic ions in the medium
adsorbed on the surface and then the equilibrium shifted
to balance the adsorbed species. This process continues
to whole degradation. With lower % degradation at higher
pH equal or greater than 4, there was a formation of zwit-
terion of RhB because of the ionization of carboxylic acid
group. Force of attraction between the carboxyl and the
xanthenes causes the demerization of zwitterion of RhB
in water. This brings the increase in the size of molecule
and decrease in density of charge due to the interaction
between the two monomers which further inhibited the
removal [2]. In case of tartrazine (anionic dye) maximum
degradation eꢀcacy (95.40%) in alkaline medium, i.e., at
pH 8 was observed. Rate of degradation in basic medium
was higher than in acidic medium. The reason behind it
might be more availability of hydroxyl ion which generates
electron–hole recombination [16, 46]. So, ꢂnally BiFeO
3
prepared by sucrose as chelating agent with calcination at
6
50 °C was the optimized catalyst for the reaction.
Optimization of pH
Since the industrial waste consists of wide range of pH
values, so it is necessary to check the catalytic activity of
Table 2 Eꢁect of pH on % degradationa
Entry
pH
Amount (mg)
% Degrada-
tion (RhB)
% Degrada-
tion (tartra-
zine)
1
2
3
4
5
6
7
8
0.5
1
2
4
6
8
10
12
10
10
10
10
10
10
10
10
85.71
99.62
72.21
19.42
15.54
15.10
14.46
3.90
39.76
52.03
62.95
48.83
43.43
95.40
4.20
1.4
·
more number of OH radicals, responsible for degradation
Reaction conditions: 10 ml (10 ppm dye sol), BiFeO (10 mg),
process [48].
3
3
0 min stirring in dark, 60 min stirring under sunlight
Fig. 6 Variation of % degrada-
tion with pH, reaction condi-
tions: 10 ml (10 ppm dye sol),
BiFeO (10 mg), 30 min stirring
3
in dark, 60 min stirring under
sunlight
1
3

Journal of the Iranian Chemical Society
Eꢀect of calcination temperature
It was found that % degradation of both dyes ꢂrst increases
and shows maximum eꢀciency at 10 mg/10 ml of dye solu-
tion beyond which it shows reduction. The increase in %
degradation with increasing catalytic amount may be attrib-
uted due to increase in catalytic active site available on the
catalyst surface for the reaction, which in turn increased the
hydroxyl and superoxide radicals that were essential for the
photocatalysis process [49]. The reduction in % degradation
with increasing the catalytic amount beyond 10 mg/10 ml
dye solution is due to the scattering of light and decrease
in penetration of light through the dye solution. Further,
deactivation of the active molecules by the collision with
the ground state molecules causes the decrease in the eꢀ-
ciency of the catalytic activity of the catalyst, which results
in reduction in % degradation of dyes [50, 51] as shown in
Fig. 8. So from above, it was observed that 10 mg amount
of the catalyst is the appropriate amount which shows maxi-
mum degradation, i.e., 99.62% and 95.40% for RhB and tar-
trazine dyes, respectively.
After deciding the better BiFeO among diꢁerent chelating
3
agents, i.e., BiFeO prepared by sucrose as chelating agent
3
with calcination at 650 °C, eꢁect of pH, i.e., 1 for RhB and
8
for tartrazine of 10 ppm of dye solution, next, we elabo-
rated our study on the BiFeO prepared by using sucrose as
3
chelating agent and calcinated at diꢁerent ranges of tem-
perature such as 150 °C, 450 °C, 550 °C, 650 °C, 750 °C
and 850 °C. RhB dye showed % degradation of 95.03, 98.75,
9
9.50, 99.62, 99.00, 87.45, and tartrazine showed % degra-
dation of 4.97, 5.42, 74.88, 95.40, 68.77, 62.21 by BiFeO
3
nanoparticles prepared at 150 °C, 450 °C, 550 °C, 650 °C,
50 °C and 850 °C, respectively. Here we observed that as
we increased the calcination temperature, i.e., from 150 to
7
6
50 °C, % degradation of both dyes increased, but further
increasing temperature from 750 to 850 °C, % degradation
in both cases decreased. The main reason for this observa-
tion is that as we increased the calcination temperature, the
purity BiFeO nanoparticles increased and maximum purity
3
is obtained at 650 °C. Further at higher temperature, i.e., at
7
50 °C and 850 °C, the purity decreases by the formation of
new impurity phases as it was also cleared by XRD study.
So, BiFeO nanoparticles prepared at calcination tempera-
3
ture 650 °C show maximum catalytic activity for the degra-
dation of both dyes as depicted in Fig. 7.
Dose of catalyst
Experiments were carried out by using diꢁerent amounts of
the catalyst, i.e., 0, 2, 4, 6, 8, 10 and 12 mg keeping concen-
tration of both dyes 10 ppm, dye solution 10 ml each, pH
(
1 for RhB, 8 for tartrazine) under sunlight, and values of
%
degradation were found to be 36.14, 59.13, 72.04, 79.13,
Fig. 8 Eꢁect of dose of catalyst on % degradation, Reaction condi-
9
1
8.26, 99.62 and 98.54 for RhB and 2.48, 10.40, 19.00,
9.23, 21.94, 95.40 and 19.00 for tartrazine, respectively.
tions: 10 ml (10 ppm dye sol), pH (1 for RhB, 8 for tartrazine),
BiFeO (mg), 30 min stirring in dark, 60 min stirring under sunlight
3
Fig. 7 Eꢁect of calcination
temperature on % degradation, a
RhB, b tartrazine, reaction con-
ditions: 10 ml (10 ppm dye sol),
pH (1 for RhB, 8 for tartrazine),
BiFeO (10 mg), 30 min stirring
3
in dark, 60 min stirring under
sunlight
1
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Journal of the Iranian Chemical Society
Eꢀect of concentration of dye
Eꢀect of amount of dye solution
The eꢁect concentration of dyes RhB and tartrazine was
studied by changing the concentration, i.e., 10, 15 and
After optimization of the concentration of dye, i.e., 10 ppm,
our next step was to investigate the eꢁect of diꢁerent amount
(ml) of dye solution. For this investigation, diꢁerent amount
of dye solution 10 ml, 20 ml, 30 ml, 40 ml and 50 ml of pH
2
0 ppm, keeping the BiFeO (10 mg/10 ml) constant.
3
The % degradation of RhB and tartrazine was found to
be decreased with increase in dye concentration. Since
the availability of the catalytic active sites for the reac-
tion is critical for the degradation to take place. Number
of factors is responsible for decrease in % degradation of
dyes. As we increased the dye concentration, more and
more number of molecules of dye gets adsorbed on the
surface of catalyst and requirement of reactive species
(1 for RhB, 8 for tartrazine) was taken by ꢂxing BiFeO
3
nanoparticles (10 mg) and under sunlight. The % degrada-
tion was decreased as we increased the amount of dye solu-
tion (ml). The % degradation for RhB observed were 99.62,
80.99, 78.88, 77.51, 59.13 and for tartrazine, 95.40, 4.75,
0.8, 0.7, 0.008 for 10 ml, 20 ml, 30 ml, 40 ml and 50 ml,
respectively. As we increased the amount of dye solution,
more number of molecules of dye gets adsorbed on the sur-
face of catalyst which in turn decreases the availability of
active sites of the catalyst for the reaction and results into
decrease in the % degradation of the dyes [5, 54]. It was
found that maximum eꢀciency was shown by catalyst in
10 ml of both dye solutions as illustrated in Fig. 10. So,
ꢂnally 10 ml amount was selected as optimized amount for
both dye solutions.
·
·
−
(
OH and O ) for the degradation of dye also increases.
2
Since at a particular light intensity, catalytic amount and
irradiation time, the formation of reactive species is also
constant (which is responsible for dye degradation) [52,
5
3]. As we increase the dye concentration by keeping the
catalytic amount constant, this causes the decrease in the
active sites of the catalyst. Further increase the dye con-
centration, the color of the solution becomes more intense,
which results in decrease in the path length of the entering
photons into the solution. And only fewer photons reach
the surface of catalyst for the formation of hydroxyl and
superoxide radical gets decreased [50, 51]. RhB shows %
degradation of 99.62, 83.23, 56.55, and tartrazine shows %
degradation of 95.40, 12.03, 1.05 at 10 ppm, 15 ppm and
Optimization of reaction condition
The photodegradation of RhB and tartrazine was also carried
out under diꢁerent reaction conditions to ꢂnd out the appropri-
ate condition to do the experiment. For this purpose, the reac-
tion was carried out using optimum conditions, i.e., amount of
2
0 ppm dye concentration, respectively. Our observation
is in good agreement with the reported literature as shown
in Fig. 9. So, 10 ppm dye concentration was found to be
optimized amount to carry out the reaction.
catalyst of BiFeO nanoparticles (10 mg), concentration of dye
3
solution (10 ppm), amount of dye solution (10 ml) and pH (1
for RhB, 8 for tartrazine) under sunlight (SL), ultra-sonication
(
US) and ultra-violet (UV) as shown in Fig. 11. Better results
were found under sunlight irradiation. Although only 5% opti-
mum energy of sunlight is for photodegradation of industrial
Fig. 10 Eꢁect of amount of dye solution on % degradation, reaction
Fig. 9 Eꢁect of dye concentration on % degradation, reaction condi-
conditions: ml (10 ppm dye sol), pH (1 for RhB, 8 for tartrazine),
tions: 10 ml (ppm dye sol), pH (1 for RhB, 8 for tartrazine), BiFeO
BiFeO (10 mg), 30 min stirring in dark, 60 min stirring under sun-
3
3
(
10 mg), 30 min stirring in dark, 60 min stirring under sunlight
light
1
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Journal of the Iranian Chemical Society
light for the degradation of organic compounds in aqueous
media [31, 55]. So reaction under sunlight irradiation was the
appropriate reaction condition to do the experiment.
Eꢀect of stirring time on degradation
After analysis of numerous factors, further we investigated
the eꢁect of stirring time on the photoassisted degradation
of RhB and tartrazine. Figure 12 depicts that photodegrada-
tion of both dyes using optimized conditions as a function
of stirring time under solar light irradiations. The intensity
of main absorption peak (557 nm for RhB and 425 nm for
tartrazine) decreased with irradiation time which indicates the
decrease in the concentration of dye, thus dye being gradually
degraded. The results demonstrated that the high activity of
the as-prepared catalyst caused the degradation of RhB and
tartrazine dyes [11].
Fig. 11 Eꢁect of diꢁerent reaction conditions on % degradation, reac-
tion conditions: 10 ml (10 ppm dye sol), pH (1 for RhB, 8 for tartra-
zine), BiFeO (10 mg), 30 min stirring in dark, 60 min stirring (under
3
Sunlight SL, Ultra-sonication (US) and Ultra-violet (UV))
pollutants, it is safe and cost-eꢁective. Both UV light source
and Ultra-sonication are costly and dangerous to health [5],
which renders our catalytic systems environmental friendly as
the ultimate source of energy is sun. The high activity in sun-
light as compared to UV source clearly indicates that perovs-
kite structure materials exhibit better catalytic activity under
visible light due to its narrow band gap energies (2.04 eV) [2]
as in our case. The results are in great agreement previous ꢂnd-
Kinetic study of photodegradation
Photocatalytic degradation rate of most organic compounds
follows pseudo-ꢂrst-order kinetics. Photodegradation rate
of organic compounds on the surface of semiconductor is
described by the Langmuir–Hinshelwood model [56].
krKC
dC
dt
R =
=
(
2)
1 + KC
ings that BiFeO nanoparticles can eꢁectively utilize visible
3
Fig. 12 Eꢁect of stirring time on % degradation, reaction conditions: 10 ml (10 ppm dye sol), pH (1 for RhB, 8 for tartrazine), BiFeO (10 mg),
3
3
0 min stirring in dark, (0–60 min) stirring under sunlight
1
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Journal of the Iranian Chemical Society
where k =reaction rate constant, K=adsorption coeꢀcient
Table 3 Kinetic data of both dyes using BiFeO nanoparticles as pho-
r
3
tocatalyst
of the reaction, C=reactant concentration.
S. No.
Dye
K (min−1
)
t1/2 (min)
The eꢁect of light intensity is also included in k , and K
r
expresses the equilibrium constant for adsorption–desorp-
tion phenomenon on interface between surface monolayer
and bulk solution. Integration of (Eq. 1) gives the following
equation.
1
2
Rh B
Tartrazine
0.37
0.05
1.86
13.07
ꢀ
ꢁ
ꢀ
ꢁ
ln C ∕C + K C − C = k Kt
0
(3)
0
r
Adsorption vs photodegradation
When the initial concentration C is small, (Eq. 3)
0
becomes (Eq. 4), which reveals a pseudo-ꢂrst-order reac-
The decolorization of dye solution may be due to either
adsorption of dye on the surface of the catalyst or adsorp-
tion of dye followed by its degradation by photoexcited elec-
trons. Thus, to establish the phenomenon responsible for
decolorization of dye and stability of the catalyst, the FT-IR
spectra of the catalyst before and after use (in both cases of
dyes) were recorded in Fig. 15. The above conꢂrmation is
veriꢂed by Fig. 15 which shows that decolorization of dye is
resulting from its photodegradation because if only adsorp-
tion had been occurring, the FT-IR of catalyst taken after
the photocatalytic reaction should have shown peaks due
to the presence of dye also. But the spectra of fresh catalyst
and after use have come out to be identical and also, there is
not even a single peak indicating the presence of dye on the
surface of catalyst, thus conꢂrming the process of photodeg-
radation of dye and also showed the stability of the catalyst
after being reused.
tion kinetics.
ꢀ
ꢁ
ln C ∕C = k Kt = kt
(4)
For pseudo-first order reaction half life t 0.693/k,
0
r
1
/2=
where k is the pseudo-ꢂrst-order reaction rate constant in
−
1
min . Figure 13 shows the plot of ln (C /C) versus time of
0
two dyes.
Rate constant (k) in each case, i.e., rhodamine and tartra-
zine, is calculated from the slopes of the respective curves
[
57, 58] as in Fig. 13. The value of rate constant and half life
time t is tabulated in Table 3.
1
/2
Stability and reusability of the catalyst
The estimation of stability and reusability of the as-synthe-
sized catalyst is an important parameter for practical point
of view for further application. For the determination of this,
photodegradation experiment was repeated for ꢂve cycles.
In case of each cycle, the catalyst was separated from the
reaction mixture by using an external magnet. Then the col-
lected sample was used in consecutive cycles for degrada-
tion as shown in Fig. 14. The minor change in performance
of catalyst with each cycle might be due to the reduction in
catalytic active sites [59].
Further XRD of the catalyst after use (in both cases
of dyes) was carried out as shown in Fig. 16. It has been
observed that the XRD of the catalyst after used in both
cases of dyes consist of the same main diꢁraction peaks
as appeared in the catalyst before use. This shows that the
structure of the catalyst did not change or we can say that the
catalyst showed its stability after being used.
Fig. 14 Recyclability of the as-prepared catalyst BiFeO , Reaction
3
conditions: 10 ml (10 ppm dye sol), pH (1 for RhB, 8 for tartrazine),
Fig. 13 Plot of photodegradation rate of rhodamine B and tartrazine
BiFeO (10 mg), 30 min stirring in dark, 60 min stirring under sun-
3
on BiFeO w.r.t. irradiation time under sunlight
light
3
1
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Journal of the Iranian Chemical Society
energy equal or greater than band gap causes the promo-
−
tion of electrons (e ) from the valance band (VB) to con-
duction band (CB) of the photocatalyst leaving behind
+
photogenerated hole (h ). Both species undergo redox
reaction with the adsorbed species on the surface of the
catalyst. Generation of hydroxyl ion and superoxide ion
+
was done by the reaction of h with the surface bound
−
water and reaction of e with oxygen, respectively, as
illustrated in Scheme 2 [49];
·
+
The generation of active species such as OH, h and
·
−
O
was also veriꢂed experimentally. The veriꢂcation of
2
·
+
hydroxyl radical ( OH), holes (h ) and superoxide radical
·
−
(
O ) was carried out by using 2-propanol(IPA), disodium
2
EDTA, and 1,4-benzoquinone(BQ) as scavengers [60]. In the
absence of scavengers, the degradation of RhB and tartrazine
was found to be 99.62% and 95.40% in 60 min, respectively.
But when IPA, EDTA and BQ were added, the degradation
of RhB was decreased to 81.5%, 39.07%, 16.03%, respec-
tively, and for tartrazine decreased to 70.02%, 43.59%,
30.51%, respectively. This conꢂrmed that the scavengers
consumed the active species generated during photocatalysis
Fig. 15 FTIR of the catalyst a Before use, b after use in case of RhB,
c after use in case of tartrazine
Further the color of the catalyst before and after use was
also checked in both cases. It has been observed that there
was no change in color observed as depicted in Fig. 17. This
study demonstrated that RhB and tartrazine dyes degraded
completely because there were no RhB and tartrazine dyes
found on the surface of as-synthesized catalyst.
+
·
caused by BiFeO nanoparticles. Since h and OH play an
3
+
important role in the photocatalytic reaction, here h acted
·
·
more OH in both cases. In photocatalytic system OH and
·
−
−
+
O
2
are produced by the reaction of e and h with the
2
O and H O [60, 61]. Further the degradation extent was
2
Mechanism
reduced with addition of BQ in both cases conꢂrmed that
·
−
O
was formed and consumed in the reaction [62, 63]. The
2
·
·
−
The proposed mechanism of the photodegradation of the
dyes was also investigated. Under the sunlight irradiation,
generation of OH was also caused by O by the series of
2
chemical reaction. So we can say that the degradation pro-
·
+
excitation of BiFeO nanoparticles starts; the photon of
cess was caused the OH and h .
3
Fig. 16 XRD of the catalyst
after used in repeating cycles
a in case of RhB, b in case of
tartrazine
1
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Journal of the Iranian Chemical Society
atoms, E is the energy of free electrons of the hydrogen
C
scale (4.5 eV) and E is the band gap value [64]. It has been
g
−
·
observed that redox potential of OH/ OH is 1.99 Ev which
is less positive than E (2.79 eV) of BiFeO nanoparticles.
VB
3
This observation also conꢂrmed the presence and responsi-
·
bility of OH for degradation process [65].
FT‑IR and mass analysis of products
after degradation
FT‑IR
The surface modiꢂcation analysis of RhB dye before and
after degradation has been explored. It has been observed
that RhB dye solution before degradation shows an absorp-
−
1
tion band near 3272 cm was attributed to the stretching
vibration of –COOH bonds and peaks related to –C=C–,
−
1
–
1
C=O, Ar–N–, –C–O–C–, –C–H and –C=N at 1488 cm ,
−
1
−1
−1
−1
−1
Fig. 17 Color of the catalyst a Before use, b after use in case of RhB,
c after use in case of tartrazine
418 cm , 1134 cm , 1008 cm , 983 cm and 487 cm
of aromatic ring system, respectively. When dye has under-
gone degradation after 60 min, the blueshift of –COOH
bond was observed which results from the change in conju-
gate structure of RhB and intensity of peak corresponding
above-mentioned groups totally disappeared indicates that
large conjugated chromophore structure was totally damaged
yielding smaller organic molecules as well as Ar–N(C H )
Further the values of E (conduction band potential)
CB
and E (valence band potential) were calculated by using
VB
formula and were found to be 2.79 eV and 0.75 eV, respec-
tively, as shown in Scheme 3;
2
5 2
ECB = X − E − 1∕2E
C
g
bond and the ether bond (–C–O–C–) in rhodamine B had
been broken [66] as exposed in Fig. 18. In case of tartrazine
before degradation the stretching vibration peak of chromo-
EVB = ECB + Eg,
−
1
where X is the absolute electronegativity denoted by geo-
phore (–N=N–) was found at 1557 cm . After degradation
this peak was not found. This clearly indicate that azo group
metric mean of absolute electreonegativity of the constituent
Scheme 2 Mechanism of deg-
radation of dyes
1
3

Journal of the Iranian Chemical Society
−
spectrum of RhB before degradation because Cl ion dis-
sociates when it was dissolved in water Fig. 20a. In mass
spectrum of RhB after degradation no peak corresponding
to molecular ion was found which indicated that dye was
degraded. The other peaks were observed corresponding to
the degraded products of the dye. The m/z peaks obtained
at 415 nm, 387 nm, 359 nm, 244 nm, 230 nm, 166 nm and
188 nm were attributed to the fragmented ions and were well
matched with earlier reports [68–70] as depicted in Fig. 20b.
Addition to these peaks, numerous peaks of insigniꢂcant
intensity were also present in the spectrum which indicated
that most of the RhB molecules have been mineralized. In
case of tartrazine molecular ion peak found at m/z=534 in
mass spectrum of dye before degradation was not found in
mass spectrum of dye after degradation at same position,
conꢂrmed that tartrazine has undergone degradation as
shown in Fig. 21. The m/z values of fragmented ions were
observed at 240 nm, 172 nm and 157 nm which were in
accordance with the degradation pathways reported in the
literature [71, 72]. Further the structure of fragmented ions
is free from –N=N– group, showing that dye has been bro-
ken into small ions or fragments. This observation is also in
well agreement with the FT-IR analysis of tartrazine shown
in Fig. 18b before. So from above discussion, it is clear that
dye after degradation broken into small ions or intermediates
which are lesser harmful than the respective dyes.
Scheme 3 Z-scheme diagram for BiFeO nanoparticles system
3
(
–N=N–) was degraded from the sample. This observation
further concluded that mechanism of discoloring of tartra-
zine occurred through degradation instead of adsorption [7,
6
7] as shown in Fig. 19.
Mass analysis
RhB has formula C H ClN O , in aqueous phase; it
2
8
31
2
3
showed a molecular ion peak m/z at 443.16, in mass
Fig. 18 Comparison study of
FT-IR of RhB a Before degra-
dation, and b after degradation
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Journal of the Iranian Chemical Society
Fig. 19 Comparison study of
FT-IR of tartrazine a Before
degradation, and b after degra-
dation
Reduction of nitro compounds
which conꢂrms the successful formation of 4-aminophenol
(
AP) product as shown in Fig. 22.
Due the various applications of 4-aminophenol, the reduc-
tion of 4-nitrophenol to 4-aminophenol is considered as
the benchmark system for the investigation of the catalytic
activity of nanoparticles. Thus, the superior catalytic per-
The reduction experiment was performed by taking 5 ml
of 4-nitrophenol (NP) (0.1 mmol), freshly prepared 12.5 ml
of NaBH (0.25 mmol) with 10 mg amount of BiFeO nano-
4
3
particles prepared by diꢁerent chelating agents (W without, S
sucrose, C citric acid, T tartaric acid and U urea) calcinated
at 650 °C. The mixture was stirred with appropriate time
as shown in Fig. 21. The color of the mixture was initially
light yellow; during reaction, it became bright yellow due
to the formation of 4-nitrophenolate ion and ꢂnally became
black color of 4 aminophenol. The better results were given
formance of the as-designed catalyst BiFeO nanoparti-
3
cles was thus estimated in the reduction of 4-nitrophenol
(
(
NP) to 4-aminophenol (AP) by using sodium borohydride
NaBH ) as a reducing agent or as hydrogen donor in aque-
4
ous media which is easily available and ecologically safe
solvent. Various parameters such as type of catalyst as
it was prepared by four diꢁerent chelating agents, eꢁect
of calcination temperature, amount of catalyst, amount of
by BiFeO nanoparticles prepared by sucrose as a chelat-
3
ing agent on basis of least time, i.e., 6 m:13 s taken for the
conversion as compared to others as illustrated in Fig. 23.
For the optimization of reaction condition, the reaction
was tried at room temperature, under reꢄuxing and soni-
NaBH , concentration of 4-nitrophenol and diꢁerent reac-
4
tion conditions were applied on reduction experiments. In
UV–Vis spectra, 4-nitrophenol (NP) showed a peak near
3
17 nm, with the addition of the freshly prepared NaBH
cation, by using ꢂxed amount of catalyst (10 mg, BiFeO
4
3
solution, a peak near 400 nm arised due to the formation
of 4-nitrophenolate ion. This changed the color of the mix-
ture from light yellow to bright yellow. When the catalyst
was added to the reaction mixture, the intensity of the peak
at 400 nm decreased and a fresh peak at 300 nm appeared
nanoparticles prepared by sucrose as chelating agent and
calcinated at 650 °C), NaBH (0.25 mmol) and 4-nitrophenol
4
(NP) (0.1 mmol). The time taken for the reduction experi-
ment was found to be 6.13 min, 8.43 min and 9.39 min for
room temperature, reꢄuxing and sonication, respectively,
as shown in Fig. 24. The ꢂndings conꢂrm that reaction
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Journal of the Iranian Chemical Society
Fig. 20 Comparison study of mass spectroscopy of RhB a Before degradation, and b after degradation
complete fast at room temperature condition, which is cost-
eꢁective, energy eꢀcient and green method according to
environmental point of view.
As we increased the catalytic amount from 10 to 25 mg,
the conversion time decreased. The main reason is that as
we increased the catalytic amount, the number of catalytic
active sites increased which enhanced the reaction rate by
decreasing time or we can say that due to proportional incre-
ment in number of catalytic active of the catalyst, activity of
catalyst was increased [18]. However, no further improve-
ment in conversion times was observed with increasing
the amount, i.e., 30 mg. The more time taken in the initial
amount could be due to more time taken for the diꢁusion
of reactant to the catalytic surface, may be due oxidized
surface and decreases in dissolved oxygen in solution [73].
These ꢂndings conꢂrms that 25 mg load of catalyst was the
optimized dose completing the conversion within 82 s as
depicted in Table 4 (Entry 1-5).
After examining the best catalyst and reaction condition,
our next aim was to evaluate the eꢁect of calcination tem-
perature on the reduction experiment. For this purpose, the
reaction was tried under identical conditions of the substrate
as discussed in earlier with BiFeO prepared by sucrose as
3
chelating agent and calcinated at 150 °C, 450 °C, 550 °C,
6
50 °C, 750 °C and 850 °C temperature, respectively.
Among the all as-prepared catalysts, this conversion was
better exhibited in least time by BiFeO prepared at 650 °C
3
as shown in Fig. 25. This could be due to the highest purity
was exhibited by BiFeO at this temperature. This observa-
3
tion was in good agreement with the previous results dem-
onstrated by XRD analysis earlier.
In order to check, the applicability of as-prepared catalyst
To optimized the better dose of catalyst, diꢁerent amounts
and use of NaBH in reduction experiment. Firstly, reac-
4
of BiFeO nanoparticles such as 10 mg, 15 mg, 20 mg,
tion was tried without catalyst in the presence of NaBH ;
3
4
2
5 mg and 30 mg were explored on reduction experiment.
conversion was not observed even for a long time due to the
1
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Journal of the Iranian Chemical Society
Fig. 21 Comparison study of
mass spectroscopy of tartrazine
a Before degradation, and b
after degradation
Fig. 23 Optimization of type of catalyst
−
electron relay system between the donor BH to accepter
4
Fig. 22 UV-Vis spectra of reduction of 4-NP to 4-AP
4
-nitrophenol (NP) [59]. This conꢂrms catalyst and reducing
agent NaBH are essential for the eꢁective reduction of the
4
−
repulsion between the 4-nitrophenol (NP) and BH4 ions.
Secondly the reaction was also tried in the presence of cata-
substrate [74] as demonstrated in Table 4 (Entry 4 and 6-7).
After ꢂnding the optimized load of catalyst, next study
lyst without NaBH ; conversion did not occur at all. Thirdly
includes the use of diꢁerent quantity of NaBH . Diꢁer-
4
4
reaction was tried with both using catalyst and NaBH- ; con-
ent quantities of NaBH , like 0.25 mmol, 0.53 mmol and
4
4
version completes in seconds because catalyst facilitates the
1.0 mmol had been tested by using the optimized amount
1
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Journal of the Iranian Chemical Society
−
quantity of NaBH , because of increase in BH concentra-
4
4
tion [75]. This demonstrates that 0.53 mmol of NaBH was
4
the suꢀcient amount to carry out the conversion.
Further various quantities of 4-nitrophenol (NP) like
0
.1 mmol, 0.5 mmol and 1.0 mmol were investigated by
using optimized amount of catalyst (25 mg) and NaBH
4
(
0.53 mmol). The reaction was completed in 24 s, 138 s and
4
46 s of 0.1 mmol, 0.5 mmol and 1.0 mmol for 4-nitrophenol
(
NP), respectively, as shown in Table 4 (Entry 8,10 and 11).
Further recyclability of the as-synthesized catalyst
was demonstrated as shown in Fig. 26. The catalyst was
recycled up to five cycles in the reduction experiment. It
has been observed that there was no considerable loss in
activity of the catalyst after being reused. This observa-
tion further confirmed the stability of the catalyst after
recyclability.
Fig. 24 optimization of reaction condition
Fig. 25 Optimization of calcination temperature
of catalyst, i.e., 25 mg and ꢂxed concentration of 4-nitro-
phenol (NP) (0.1 mmol). The reduction experiment was
completed in 82 s, 24 s and 133 s for 0.25 mmol, 0.53 mmol
and 1.0 mmol amount of NaBH , respectively, as in Table 4
4
(
Entry 4, 8 and 9). The reaction rate increases with increasing
Fig. 26 Recyclability of BiFO nanoparticles in reduction experiment
3
Table 4 Optimization of various
Entry
BiFeO (mg)
NaBH (mmol)
4-nitrophenol(NP) (mmol) Time
a
3
4
reaction conditions
1
2
3
4
5
6
7
8
9
10
15
20
25
30
25
–
25
25
25
25
0.25
0.25
0.25
0.25
0.25
–
0.25
0.53
1.0
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.5
1.0
6.13 min
5.19 min
5.14 min
82 s
6.02 min
No reaction
No reaction
24 s
133 s
138 s
446 s
10
1
0.53
0.53
1
Reaction conditions: BiFeO nanoparticles (mg) prepared by chelating agent Sucrose and calcinated at
3
6
8
50 °C, 12.5 ml of NaBH (mmol), 5 ml of 4-nitrophenol (NP) (mmol), RT room temperature, stirring at
4
00 rpm
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Journal of the Iranian Chemical Society
Table 5 Reduction of various nitro compounds with BiFeO nanoparticles
3
S.
Reactant
Product
Time
(sec)
24
Conversion Variation in color
No
(%)
1
.
OH
OH
100
NO2
OH
NH2
OH
2
.
33.03
100
100
NO2
NH2
3
.
OH
OH
6
NO2
NH2
NO2
NH2
4
5
.
.
NH
2
NH
2
20
33
100
100
NO2
NH2
NH
NH
2
2
NO2
NH2
6
.
NH
2
NH
2
58
100
NO2
NH2
NO2
NH2
o
Reaction conditions: BiFeO nanoparticles (25 mg) prepared by chelating agent Sucrose and calcinated at 650 C), 12.5 ml of NaBH
3
4
(
0.53 mmol), 5 ml of 4-nitrocompound (0.1 mmol), RT room temperature, stirring at 800 rpm
1
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Journal of the Iranian Chemical Society
reaction H gas was produced, the reaction could be based
2
NaBH
4
2
H O
NH
2
on catalytic hydrogenation concept for the reduction of nitro
group with NaBH ; (2) the eꢁect of BiFeO nanoparticles
H
2
4
3
NH
2
H
H
R
could be due to the presence of Lewis acidic sites on the sur-
H
H
face of the catalyst and hydride transformation from NaBH ;
4
R
(3) solubility of NaBH in water followed by hydrolysis of
4
H
the obtained amino-borane intermediates could be promoted
BiFeO
3
H
NO
2
the rate of reaction (Scheme 4).
-
H
2
O
After establishing, the catalytic system for the degrada-
tion of dye (RhB and tartrazine) and reduction of 4-nitro-
compounds. Further we compared catalytic activity of
as-prepared catalyst in both processes with the reported
catalysts in the literature as illustrated in Table 6. I has been
found that our developed method is much greener than oth-
ers in case of cost-eꢁective, simplicity, room temperature,
use of water as medium and use of natural source of light,
i.e., sunlight, which is abundantly available on earth. This
proved the superiority of our present work.
R
NO
2
H
NHOHH
NO
H
H
H
H
H
H
-H O
2
2
-H O
R
R
R
H
H
H
H
Scheme 4 Catalytic hydrogenation mechanism of nitro reduction
Based on the above observations, we explored the
potential of this catalytic system, further the reduction
of various nitro compounds was studied under optimized
reaction condition, and the consequences are summarized
in Table 5 and UV–Vis spectroscopy study in Fig. S1-S5
Conclusion
To sum up, we prepared perovskite-structured BiFeO nano-
3
(
supplementary data). The reduction of aromatic nitro
particles by using diꢁerent chelating agents (sucrose, citric
acid, tartaric acid and urea) using auto-combustion route fol-
lowed by calcination at diꢁerent range of temperature, i.e.,
150–850 °C. The selection of the better catalyst was carried
out on the basis of their performance both in degradation and
compounds basically depends upon mainly two factors:
(
1) formation of intermediate (nitrophenolate ion) (2) and
their reactivity. The formation of intermediate depends
upon the acidic strength of aromatic nitro compounds
where NaBH is a base. The order of acidic strength of
in reduction experiment. BiFeO nanoparticles prepared by
4
3
nitrophenolate ion was found in the literature, i.e., 2,4-
DNP > 4-NP > 2-NP [74]. Therefore, the reduction rate
follows the same order (entry 1-3, Table 5). Further it
has been observed that the reduction rate of 2,4-DNP was
large as compared to aromatic nitroamines (entry 4-6,
Table 5). The reason for this depends upon the electron
donating power of amine group, i.e., decrease in electron-
egativity of nitrogen in aromatic amines as compared to
oxygen of the hydroxyl group of aromatic nitrophenols
and thus nitrophemolate ion [9].
using sucrose as chelating agent and calcinated at 650 °C
have demonstrated a numerous promises in the terms of high
activity, selectivity, chemical stability, recyclability, reus-
ability, cost-eꢁective, eco-friendly, degradation of organic
contaminants and synthesis of ꢂne chemicals. On the basis
of their eꢀcient photocatalytic activity, perovskite-struc-
tured BiFeO showed potentials for use in environmental
3
puriꢂcation of organic pollutants under natural sunlight and
reduction of ANCs (aromatic nitro compounds) in aqueous
medium at room temperature under stirring conditions and
extend the scope of the photocatalyst in practical applica-
tions. Therefore, it would be the promising catalyst for the
waste water treatment and chemical synthesis of important
organic compounds.
Mechanism of nitro reduction
Proposed mechanism of the reduction experiment proceeds
through the following steps [17]: (1) during the course of the
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Journal of the Iranian Chemical Society
Table 6 Comparison Table of catalytic activity
Compound (process)
Catalytic system (Rex. condition)
Time
References
[76]
OH
Pd nanoparticles supported on reduced graphene oxide
120 min
(
NaBH , EtOH-H O, r.t)
4 2
NO2
4
-NP
(
reduction)
Np-Ag–Al (NaBH , H O, r.t)
105 min
1 min
[77]
[17]
4
2
NiFe O @Cu NPs(NaBH , EtOH-H O, reꢄux)
2
4
4
2
IO@NiNPs(NaBH , H O, r.t)
10 min
16 min
24 min
105 min
24 s
[19]
[78]
[79]
[77]
This work
[80]
4
2
Nano-LaFeO (KOH, (CH ) CHOH, MWI)
3
3 2
Ag PO /CoFe O (NaBH , r.t)
3
4
2
4
4
np-Ag (NaBH , EtOH-H O, reꢄux)
4
2
BiFeO nanoparticles (NaBH , H O, r.t)
3
4
2
3
H C
CH
3
ZnO nanoparticles (UV illumination)
70 min
H
3
C
N
O
N
CH
3
COOH
RhB(degradation)
H Ti O nanotubes(UV irradiation)
630 min
60 min
117 min
[81]
This work
[82]
2
3
7
BiFeO nanoparticles (Sunlight irradiation)
3
NaOOC
TiO suspension (500 W superhigh pressure mercury)
2
N
N
N
N
NaO
3
S
3
SO Na
OH
Tartrazine
degradation)
(
CuO (150 W Tungsten halogen lamp)
240 min
60 min
[83]
This work
BiFeO nanoparticles (Sunlight irradiation)
3
Acknowledgements We are thankful to IIT Ropar for Mass spectros-
copy, CIL IIT Roorkee for VSM, BIT Bengaluru for BET, SAIF, Panjab
University Chandigarh for TEM, Department of Chemistry NIT Jaland-
har for FT-IR and UV–Vis spectroscopy. One of the authors (H.S) is
thankful to UGC for providing the research fellowship. We would like
to thank Miss Priya Arora and Miss Jigyasa Badhan for their valuable
suggestions in the manuscript writing.
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