Synthesis of γ-Fe2O3-CdS nanocomposites with enhanced photocatalytic activity by thermal decomposition approach

Article abstract of DOI:10.1166/jnn.2016.12902

γ-Fe₂O₃-CdS nanocomposites have been prepared by a single step thermal decomposition method which involves thermal decomposition of iron acetylacetonate, cadmium acetate and thiourea in diphenyl ether at 200 ^°C. The nanocomposites were characterized by powder X-ray diffraction, IR spectroscopy, atomic absorption spectroscopy, thermal gravimetric analysis, energy dispersive X-ray analysis, transmission electron microscopy, surface area measurements, diffuse reflectance spectroscopy, photoluminescence spectroscopy and magnetic measurements. The effect of varying concentration of iron acetylacetonate, cadmium acetate and thiourea during synthesis of the nanocomposites on the crystal phases, microstructure and properties of the nanocomposites was investigated. The XRD results confirm the presence of CdS nanocrystals (1.2 to 2.9 nm) in the γ-Fe₂O₃-CdS nanocomposites and the nanocomposites exhibit superparamagnetic behaviour at room temperature. The nanocomposites show good absorption in visible region (1.8 eV to 2.5 eV) and they exhibit visible-light-driven photocatalytic degradation of congo red in an aqueous solution with good stability.

Full text of DOI:10.1166/jnn.2016.12902

Article
Journal of
Nanoscience and Nanotechnology
Vol. 16, 9072–9084, 2016
Copyright © 2016 American Scientific Publishers
All rights reserved
www.aspbs.com/jnn
Printed in the United States of America
Synthesis of ꢀ-Fe2O3–CdS Nanocomposites with
Enhanced Photocatalytic Activity by Thermal
Decomposition Approach
Sudheer Kumar Yadav and P. Jeevanandam∗
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
ꢀ-Fe2O3–CdS nanocomposites have been prepared by a single step thermal decomposition method
which involves thermal decomposition of iron acetylacetonate, cadmium acetate and thiourea in
diphenyl ether at 200 ꢀC. The nanocomposites were characterized by powder X-ray diffraction,
IR spectroscopy, atomic absorption spectroscopy, thermal gravimetric analysis, energy dispersive
X-ray analysis, transmission electron microscopy, surface area measurements, diffuse reflectance
spectroscopy, photoluminescence spectroscopy and magnetic measurements. The effect of vary-
ing concentration of iron acetylacetonate, cadmium acetate and thiourea during synthesis of the
nanocomposites on the crystal phases, microstructure and properties of the nanocomposites was
investigated. The XRD results confirm the presence of CdS nanocrystals (1.2 to 2.9 nm) in the
ꢀ-Fe2O3–CdS nanocomposites and the nanocomposites exhibit superparamagnetic behaviour at
Delivered by Ingenta to: State University of New York at Binghamton
room temperature. The nanocomposites show good absorption in visible region (1.8 eV to 2.5 eV)
IP: 46.161.63.44 On: Wed, 08 Mar 2017 08:33:28
and they exhibit visible-light-driven photocatalytic degradation of congo red in an aqueous solution
Copyright: American Scientific Publishers
with good stability.
Keywords: Nanoparticles, ꢀ-Fe2O3–CdS
Nanocomposites,
Thermal
Decomposition,
Photocatalytic Activity.
1. INTRODUCTION
chemical stability, iron oxide nanoparticles have been
extensively investigated for a wide variety of applications
such as catalysis, water treatment, sensors, magnetic mate-
rials, pigments, drug delivery and lithium ion batteries.14–20
With low band gap (about 2.0 to 2.2 eV), ꢁ-Fe2O3 absorbs
in the visible region and it is one of the most promis-
ing photocatalysts in this region.21 However, the photo-
induced electron–hole pairs in ꢁ-Fe2O3 easily recombine
which inhibits its application as an efficient photocatalyst.
To overcome this drawback, composites of ꢁ-Fe2O3 with
Nanocomposites have been intensively investigated due
to their diverse applications.1–4 Metal oxide-metal sul-
fide nanocomposites are of current technological interest
due to their wide applications in solar energy conver-
sion, optoelectronic devices, and photocatalysis.5 Metal
sulfide semiconductor nanocrystals such as CdS, ZnS, CuS
and PbS have been coupled with metal oxide semicon-
ductors such as TiO2, SnO2, ZnO and Fe2O3 to extend
their photo response to visible region. The coupling facil-
itates charge separation by accumulating electrons and
holes in separate particles.6 Some of the recently reported
metal oxide-metal sulfide nanocomposites that are useful
for the photocatalytic degradation of organic dye pollu-
tants include CdS–TiO2, Fe3O4–ZnS, CuS–ZnO, Fe2O3–
CdS and PbS–TiO2.7–11
22
other semiconductors such as CdS, SnO2,20 and TiO2
have been prepared. CdS is a semiconductor with a direct
band gap of 2.42 eV and regarded as one of the most
important photocatalysts in the visible region. However,
CdS is susceptible to photo corrosion in aqueous media
due to which it is not preferred for applications in envi-
ronmental remediation.23 In recent times, attempts have
been made to prepare CdS based nanocomposites.10 CdS
is coupled with another semiconductor with lower but
closely lying conduction band and appropriate valence
band. Charge separation occurs at the interface of the two
Synthesis of iron oxide based semiconductor nanocom-
posites is of immense interest.12ꢀ13 Because of their low
cost, easy production, environmental friendliness and good
∗Author to whom correspondence should be addressed.
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1533-4880/2016/16/9072/013
doi:10.1166/jnn.2016.12902

Yadav and Jeevanandam
Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Table I. Designation of various ꢁ-Fe2O3–CdS nanocomposites pre-
semiconductors and the photo generated carriers interact
with the reactants efficiently at the interface.24 CdS–Fe2O3
heterojunctions are good photocatalysts for the degradation
of hazardous organic dyes such as methylene blue, and
congo red, photocatalytic reduction of Cr(VI) and hydro-
gen production.25–28
pared using different synthetic conditions.
Sample
code
Fe(acac)3
(mmol)
Cd(ac)2
(mmol)
Thiourea
(mmol)
Thermal decomposition
time (min)
Fe2O3
CdS
FC1
FC2
FC3
FC4
FC5
FC6
1
–
1
1
1ꢃ25
1
–
1
0ꢃ1
0ꢃ25
1
0ꢃ1
0ꢃ25
1
–
1
0ꢃ1
0ꢃ25
1
0ꢃ1
0ꢃ25
1
35
35
35
35
35
70
70
70
Fe2O3–CdS nanocomposites with different morpholo-
gies such as CdS nanowires decorated with Fe2O3
nanoparticles have been prepared by a solvothermal
method.10 Wang et al. have synthesized CdS nanowires
decorated with Fe3O4 microspheres by the same method.25
Shi et al. have grown CdS nanoparticles on single crys-
talline ꢂ-Fe2O3 nanorods by hydrothermal and solution
routes.29 Wu et al. have synthesized CdS urchin-like
micro-spheres decorated with hematite/magnetite nanopar-
ticles by the solvothermal method.30 Zhang et al.
have synthesized hierarchical ꢂ-Fe2O3/CdS microflow-
ers with ꢂ-Fe2O3 core and CdS shell through chem-
ical bath deposition.27 Preethi et al. have synthesized
Fe2O3@CdS@ZnS core–shell nanoparticles by a multi-
step solution route.28 Chen et al. have deposited CdS
1
1ꢃ25
or 70 min. Then, 30 mL methanol was added to the con-
tents to get the precipitate. The precipitates obtained were
centrifuged, washed with methanol and dried overnight
under vacuum to obtain the ꢁ-Fe2O3–CdS nanocomposite
powders. For comparison purpose, pure CdS and Fe2O3
nanoparticles were also prepared using the similar syn-
thetic procedure.
The analysis of crystal phases of all the nanocompos-
ites was carried out by powder X-ray diffraction using
a Bruker AXS D8-Advance X-ray diffractometer with
Cu-Kꢂ radiation (ꢄ = 1.5406 Å) with a scan speed,
0.2ꢀ/min. A Thermo Nicolet Nexus (FT-IR) spectrome-
ter was used for recording IR spectra of the nanocom-
posites using KBr pellets. Thermo gravimetric analysis
nanoparticles on Fe2O3 nanorods via
a three step
hydrothermal method.31 Kwon et al. have synthesized
hetero-structured nanocrystals of ꢁ-Fe2O3 and CdS by
airless thermal decomposition of Fe(CO)5 in octyl ether
in the presence of oleic acid.32 Liu et al. have synthe-
sized Zn1−xCdxS/ꢁ-Fe2O3 nanocomposites (x = 0 to 1)
by a solution combustion method.33 Most of the reported
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(TGA) was carried out on an EXSTAR TG/DTA 6300
IP: 46.161.63.44 On: Wed, 08 Mar 2017 08:33:28
instrument under air (flow rate = 200 mL/min) from 25
to 1000 ꢀC with a heating rate of 10 ꢀC min−1. The
elemental analysis of the ꢁ-Fe2O3–CdS nanocomposites
was carried out using a field emission scanning elec-
tron microscope (Carl Zeiss ULTRA plus) operating at
an accelerating voltage of 15 kV coupled with an energy
dispersive X-ray analysis (EDXA) facility. The cadmium
content in the nanocomposites and in the supernatant solu-
tions after photocatalytic experiments was analyzed using
a Perkin–Elmer AAnalyst 800 atomic absorption spec-
trometry (AAS) instrument. For the AAS measurements,
all the composites of known amount were digested in
HCl and then, Cd2+ solutions were prepared in volu-
metric flasks and then analyzed. Transmission electron
micrographs and selected area electron diffraction pat-
terns of the nanocomposites were recorded using a FEI
TECHNAI G2 electron microscope operating at 200 kV.
For the TEM measurements, the sample powders were
dispersed in ethanol with the help of a sonicator and
a drop each from the dispersions was allowed to dry
in air on carbon coated copper grids. For the study of
optical properties of the ꢁ-Fe2O3–CdS nanocomposites,
a Shimadzu UV-2450 UV-visible spectrophotometer was
used along with a diffuse reflectance accessory and BaSO4
was used as the reference. Photoluminescence spectra
were recorded using a HORIBA Fluoromax-4 spectroflu-
orophotometer (ꢄexcitation = 360 nm). The emission spectra
were recorded at room temperature for the suspensions
methods for the preparation of Fe O –CdS nanocompos-
ites consist of multi-steps with long reaction time and the
2 Copyright: American Scientific Publishers
3
methods often require expensive reagents. In the present
study, ꢁ-Fe2O3–CdS nanocomposites were synthesized by
a single step thermal decomposition of cadmium acetate,
thiourea and iron acetylacetonate in diphenyl ether at about
200 ꢀC for 35 min. The ꢁ-Fe2O3–CdS nanocomposites
were characterized by different techniques and their optical
and magnetic properties were studied. The nanocomposites
were then explored as catalysts for photocatalytic degra-
dation of congo red, a toxic dye, in an aqueous solution.
2. EXPERIMENTAL DETAILS
The chemicals used were cadmium acetate (Hime-
dia), thiourea (Rankem), iron acetylacetonate (ACROS),
diphenyl ether (Aldrich) and congo red (SRL). All the
chemicals were used as received. Millipore® water was
used for the preparation of the solutions. The ꢁ-Fe2O3–
CdS nanocomposites were synthesized by the thermal
decomposition method and more details are as follows.
Six different nanocomposites (Table I) were prepared
by varying the concentration of cadmium acetate, thiourea
and iron acetylacetonate and also by varying the thermal
decomposition time. The reagents (iron acetylacetonate,
cadmium acetate and thiourea) were added to 10 mL of
diphenyl ether (boiling point = 257 ꢀC) in a round bot-
ꢀ
tom flask and refluxed in air at about 200 C for 35 min
J. Nanosci. Nanotechnol. 16, 9072–9084, 2016
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Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Yadav and Jeevanandam
prepared by dispersing about 5 mg each of ꢁ-Fe2O3–CdS
Fe2O3
* CdS
nanocomposite powders in about 5 mL water by soni-
cation for 10 minutes. Surface area of the nanocompos-
ites was measured using a NOVA 2200e (Quantachrome)
instrument by BET method using nitrogen physisorption
at 77 K. Prior to the analysis, the samples were degassed
at about 100 ꢀC for about 2 h. Magnetic measurements
(M–H curves at 300 K and 5 K) of pure Fe2O3 nanopar-
ticles and the ꢁ-Fe2O3–CdS nanocomposites were carried
out on a 3 Tesla cryogen free mini Vibrating Sample
Magnetometer with a pulse cryocooler (CRYOGENICS
Ltd., UK).
CdS
FC1 (1:0.1:0.1)
FC2 (1:0.25:0.25)
FC3 (1.25:1:1)
FC4 (1:0.1:0.1)
FC5 (1:0.25:0.25)
FC6 (1.25:1:1)
*
*
*
*
*
*
*
*
Congo red (sodium salt of benzidine diazo-bis-1-
naphthyl amine-4-sulphonic acid) is an azo dye which
is often used as a coloring agent in textile and paper
10
20
30
40
50
60
70
80
90
industries.34 Congo red can cause serious environmental
hazards and endanger human life due to its toxic, muta-
genic and carcinogenic nature.35 Hence, it is necessary
to develop efficient and economical methods to remove
congo red from the waste water. Semiconductors based
photocatalysis is considered as one of the most promising
methods for waste water treatment. This is because of the
strong destructive power of semiconductors to mineralize
toxic pollutants into CO2 and H2O. In the present study,
photocatalytic activity of the ꢁ-Fe2O3–CdS nanocompos-
ites was tested using aqueous solution of congo red under
sunlight irradiation. About 50 mg of each nanocomposite
powders was dispersed in 50 mL of congo red solution
(concentration = 50 mg L−1ꢅ. The suspension was soni-
cated for about 10 minutes and kept in dark for 10 minutes
to reach adsorption–desorption equilibrium. Afterwards,
the suspension was irradiated in sunlight at room tem-
perature for various time intervals (0 to 60 minutes).
Aliquots were taken from the suspension every 5 minutes
and the photocatalyst powder was separated by centrifu-
gation. The concentration of congo red in the supernatant
solutions was determined by measuring the absorbance at
495 nm using a UV-visible spectrophotometer (Shimadzu
UV-2450); congo red shows an intense absorption band at
495 nm and two other bands at 236 and 341 nm.17 Pure
CdS and ꢁ-Fe2O3 nanoparticles were also tested as the
photocatalysts to compare their photocatalytic activity with
that of the ꢁ-Fe2O3–CdS nanocomposites.
2θ (Degrees)
Figure 1. XRD patterns of pure Fe2O3, CdS nanoparticles and
ꢁ-Fe2O3–CdS nanocomposites (FC1–FC6).
(SAED) results discussed later. Pure CdS nanoparticles
and all the ꢁ-Fe2O3–CdS nanocomposites show peaks at
2ꢆ values of 24.8ꢀ, 26.53ꢀ, 28.2ꢀ, 36.28ꢀ, 43.9ꢀ, 47.9ꢀ,
51.9ꢀ and 70.8ꢀ corresponding to (100), (002), (101),
(102), (110), (103), (112) and (211) reflections of wurtzite
CdS (JCPDS no. 41-1049). The crystallite size of CdS in
the nanocomposites calculated using Debye-Scherrer for-
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mula, varies from 1.2 to 2.9 nm while the crystallite size
IP: 46.161.63.44 On: Wed, 08 Mar 2017 08:33:28
of pure CdS nanoparticles is about 5.7 nm. In general,
Copyright: American Scientific Publishers
the crystallite size of CdS in the nanocomposites increases
with an increase in the concentration of cadmium acetate
and thiourea used during their synthesis.
The IR spectra of pure Fe2O3, CdS nanoparticles and
all the nanocomposites are shown in Figure 2. All the
samples show bands near 3400 cm−1 and 1630 cm−1
attributed to O–H stretching and bending, respectively,
due to physisorbed water molecules.37 The IR bands in
FC6
FC5
FC4
FC3
FC2
FC1
3. RESULTS AND DISCUSSION
The X-ray diffraction (XRD) patterns of pure Fe2O3,
CdS nanoparticles and all the ꢁ-Fe2O3–CdS nanocompos-
ites (FC1–FC6) are shown in Figure 1. Pure iron oxide
nanoparticles do not show any feature in the XRD pattern.
Since the thermal decomposition of iron acetylacetonate
was carried out in the presence of air and under refluxing
conditions in diphenyl ether, the product obtained is pro-
posed to be ꢁ-Fe2O3.36 Further evidence for the presence
of ꢁ-Fe2O3 comes from transmission electron microscopy
(TEM) measurement and selected area electron diffraction
Fe2O3
CdS
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm–1
)
Figure 2. IR spectra of pure Fe2O3, CdS nanoparticles and ꢁ-Fe2O3–
CdS nanocomposites (FC1–FC6).
9074
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Yadav and Jeevanandam
Table II. EDX analysis data for the ꢁ-Fe2O3–CdS nanocomposites.
Cd
Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
S
Fe
O
Nanocomposite
FC1
Wt%
At%
Wt%
At%
Wt%
At%
Wt%
At%
Comment
Uniform
11ꢃ1
11ꢃ8
11ꢃ0
6ꢃ0
2ꢃ7
2ꢃ6
9ꢃ0
5ꢃ3
8ꢃ9
8ꢃ3
4ꢃ2
7ꢃ6
39ꢃ9
39ꢃ8
38ꢃ8
15ꢃ7
16ꢃ0
15ꢃ0
37ꢃ9
47ꢃ9
41ꢃ2
69ꢃ8
77ꢃ0
70ꢃ6
FC2
FC3
FC4
FC5
FC6
60ꢃ7
60ꢃ2
60ꢃ5
27ꢃ1
31ꢃ4
31ꢃ1
23ꢃ6
24ꢃ8
24ꢃ2
36ꢃ9
43ꢃ2
43ꢃ8
5ꢃ9
5ꢃ6
6ꢃ1
5ꢃ3
6ꢃ6
6ꢃ2
9ꢃ7
5ꢃ4
5ꢃ8
30ꢃ6
18ꢃ8
17ꢃ8
Uniform
Uniform
70ꢃ9
71ꢃ6
71ꢃ9
34ꢃ7
40ꢃ4
39ꢃ5
14ꢃ9
18ꢃ5
18ꢃ9
25ꢃ6
35ꢃ6
36ꢃ0
2ꢃ6
2ꢃ2
2ꢃ4
3ꢃ6
2ꢃ5
2ꢃ6
10ꢃ5
5ꢃ5
5ꢃ7
35ꢃ9
21ꢃ4
21ꢃ9
9ꢃ3
14ꢃ1
15ꢃ5
3ꢃ5
1ꢃ3
5ꢃ8
4ꢃ8
3ꢃ8
11ꢃ5
6ꢃ3
4ꢃ3
14ꢃ8
71ꢃ9
69ꢃ9
69ꢃ6
53ꢃ8
54ꢃ8
45ꢃ8
23ꢃ9
22ꢃ1
12ꢃ7
36ꢃ4
49ꢃ5
33ꢃ6
Non-uniform
Uniform
45ꢃ8
46ꢃ1
46ꢃ2
16ꢃ6
31ꢃ2
18ꢃ2
16ꢃ2
21ꢃ2
16ꢃ2
20ꢃ8
36ꢃ7
21ꢃ4
17ꢃ0
18ꢃ9
17ꢃ7
14ꢃ8
18ꢃ9
13ꢃ5
18ꢃ5
6ꢃ7
17ꢃ7
47ꢃ7
23ꢃ2
46ꢃ9
28ꢃ7
28ꢃ8
28ꢃ6
11ꢃ2
11ꢃ1
12ꢃ8
14ꢃ1
14ꢃ2
14ꢃ7
19ꢃ3
19ꢃ2
18ꢃ2
44ꢃ8
43ꢃ8
45ꢃ7
35ꢃ9
34ꢃ2
34ꢃ1
12ꢃ4
13ꢃ2
13ꢃ2
34ꢃ1
35ꢃ4
35ꢃ7
Uniform
the 3000–2500 cm−1 range in the nanocomposites are
attributed to C–H stretching. The IR bands in the range
2000–2500 cm−1 are attributed to CO2 present in the
chamber of IR spectrometer during the spectral mea-
surement and the band at 1049 cm−1 is attributed to
C–O–C stretching.38 The band at 1421 cm−1 is attributed
acetylacetonate, methanol etc.) from the nanocomposites.
The nanocomposites FC1, FC2, FC3, FC4, FC5 and FC6
exhibited % wt loss of 30.8, 18.4, 6.6, 45.5, 6.7 and
3.9, respectively. The nanocomposites FC1 and FC4 show
more weight loss compared to the other nanocomposites
and this is attributed to the presence of more organic moi-
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to the stretching vibration of COO . These bands sug-
eties and some undecomposed precursors (e.g., iron acety-
lacetonate) in these nanocomposites.
Copyright: American Scientific Publishers
gest the presence of organic content adsorbed on the sur-
face of the nanocomposites.39ꢀ40 The band at 503 cm−1
is attributed to Cd–S stretching41 and the IR bands at
about 553 and 480 cm−1 are attributed to the character-
istic vibrations of ꢁ-Fe2O3.21 TGA measurements were
carried out for pure ꢁ-Fe2O3, CdS and the nanocompos-
ites (FC1–FC6). Pure iron oxide showed a weight loss of
23.1% and pure CdS showed a weight loss of 12.2% in
Table II shows the energy dispersive X-ray (EDX) anal-
ysis results on the ꢁ-Fe2O3–CdS nanocomposites. The
nanocomposites FC1, FC2, FC3, FC5 and FC6 show fairly
uniform elemental distribution and nanocomposite FC4
exhibits non-uniform elemental distribution. The particle
size and morphology of the ꢁ-Fe2O3–CdS nanocompos-
ites were investigated by transmission electron microscopy
(TEM) analysis. The TEM images for pure ꢁ-Fe2O3 and
CdS nanoparticles are shown in Figure 3. The TEM
ꢀ
ꢀ
the range 25 C to 400 C. The weight loss is attributed
to the removal of organic molecules (e.g., diphenyl ether,
Figure 3. TEM images and SAED patterns of (a) pure Fe2O3 and (b) CdS nanoparticles.
J. Nanosci. Nanotechnol. 16, 9072–9084, 2016
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Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Yadav and Jeevanandam
image of Fe2O3 (Fig. 3(a)) shows that the nanoparti-
cles are very small (∼2 nm) and they are agglomerated.
The selected area electron diffraction (SAED) pattern of
ꢁ-Fe2O3 nanoparticles (inset of Fig. 3(a)) shows rings
that are attributed to (311), (410), (511) and (440) planes
of ꢁ-Fe2O3 (JCPDS no. 39-1346). The TEM image
of CdS nanoparticles (Fig. 3(b)) shows agglomerated
nanoparticles with no particular shape. The inset of
Figure 3(b) shows the SAED pattern of CdS nanopar-
ticles and the observed rings are attributed to (103),
(100), (110) and (300) planes of polycrystalline hexago-
nal CdS. Figure 4 shows the TEM images of ꢁ-Fe2O3–
CdS nanocomposites FC1, FC2, FC3, FC5 and FC6. The
images reveal that small nanoparticles are agglomerated
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Copyright: American Scientific Publishers
Figure 4. TEM images and SAED patterns of ꢁ-Fe2O3–CdS nanocomposites; (a) FC1, (b) FC2, (c) FC3, (d) FC5 and (e) FC6.
9076
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Yadav and Jeevanandam
Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Delivered by Ingenta to: State University of New York at Binghamton
IP: 46.161.63.44 On: Wed, 08 Mar 2017 08:33:28
Copyright: American Scientific Publishers
Figure 5. HRTEM images of ꢁ-Fe2O3–CdS nanocomposites; (a) FC1, (b) FC2 and (c) FC3.
Figure 5(c) corresponds to (210), (211) and (311) planes
of ꢁ-Fe2O3, respectively.
The diffuse reflectance spectra (DRS) of pure ꢁ-Fe2O3,
CdS nanoparticles and the ꢁ-Fe2O3–CdS nanocomposites
to produce particles with close to spherical morphol-
ogy. The SAED pattern of nanocomposite FC1 (inset of
Fig. 4(a)) shows rings attributed to (311) and (440) planes
of ꢁ-Fe2O3. The SAED patterns of nanocomposites FC2
and FC3 (insets of Figs. 4(b and c)) show rings that are
attributed to (103), (100), (101) planes of polycrystalline
hexagonal CdS and (311), (440) planes of ꢁ-Fe2O3. The
SAED patterns of nanocomposites FC5 and FC6 (insets of
Figs. 4(d and e)) show rings that are attributed to (103),
(100), (101) planes of polycrystalline hexagonal CdS and
(311), (511), (440) planes of ꢁ-Fe2O3.
Fe2O3
Nanocomposites FC4, FC5 and FC6 were prepared in
order to understand the effect of thermal decomposition
time on the morphology of final products. It was found
from electron microscopy studies that there is not much
difference in the morphology of nanocomposites when
the thermal decomposition time is increased from 35 to
70 minutes. The high resolution TEM images (HRTEM) of
nanocomposites FC1, FC2 and FC3 are shown in Figure 5.
The observed interplanar spacing of 0.35 nm in nanocom-
posites FC1, FC2 and FC3 corresponds to (100) plane
of hexagonal CdS. The interplanar spacing of 0.37 nm
in Figure 5(a), 0.34 nm in Figure 5(b) and 0.25 nm in
CdS
FC1
FC2
FC3
FC4
FC5
FC6
300
400
500
600
700
Wavelength (nm)
Figure 6. DRS spectra of ꢁ-Fe2O3, CdS nanoparticles and the
ꢁ-Fe2O3–CdS nanocomposites (FC1–FC6).
J. Nanosci. Nanotechnol. 16, 9072–9084, 2016
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Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Yadav and Jeevanandam
CdS
Fe2O3
1.9 eV
2.45 eV
1.6
1.6
1.6
1.8
2.0
2.2
hν (eV)
2.4
2.6
2.8
3.0
1.6
1.8
2.0
2.2
hν (eV)
2.4
2.6
2.8
3.0
FC1
FC2
1.8 eV
2.1 eV
2.4
1.8
2.0
2.2
hν (eV)
2.4
2.6
2.8
3.0
1.6
1.8
2.0
2.2
hν (eV)
2.6
2.8
3.0
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FC3
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Copyright: American Scientific Publishers
2.45 eV
2.2 eV
2.4
1.8
2.0
2.2
2.4
2.6
2.8
3.0
1.6
1.8
2.0
2.2
2.6
2.8
3.0
hν (eV)
hν (eV)
FC5
FC6
2.1 eV
2.35 eV
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
hν (eV)
hν (eV)
Figure 7. Tauc plots of pure ꢁ-Fe2O3, CdS nanoparticles and the ꢁ-Fe2O3–CdS nanocomposites (FC1–FC6).
9078
J. Nanosci. Nanotechnol. 16, 9072–9084, 2016

Yadav and Jeevanandam
Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
estimated by plotting (ꢂhꢇꢅ2 versus hꢇ (Tauc plots) using
1.2
529 nm
560 nm
504 nm
510 nm
Fe2O3
the relation:
CdS
ꢂhꢇ = Aꢈhꢇ −Egꢅ1/2
1.0
0.8
0.6
0.4
0.2
0.0
475 nm
465 nm
FC1
FC2
Where ꢂ is the absorption coefficient, hꢇ is the pho-
ton energy, Eg the optical band gap and A is a constant.
FC3
FC4
From the Tauc plots (Fig. 7), Eg was estimated by extrap-
FC5
olating a straight line from the absorption curve to the
FC6
X-axis. Pure ꢁ-Fe2O3 and CdS nanoparticles have band
gap of 1.9 eV and 2.45 eV, respectively. The nanocom-
posites FC1, FC2, FC3, FC4 and FC6 show band gap
absorption at about 1.8 eV, 2.1 eV, 2.45 eV, 2.2 eV, and
2.35 eV, respectively. Nanocomposite FC5 possesses the
same band gap as that of FC2 (2.1 eV). In general, the
400
450
500
550
600
650
700
band gap of nanocomposites increases with an increase in
the concentration of CdS (FC1 to FC3). Figure 8 shows the
photoluminescence spectra of pure ꢁ-Fe2O3, CdS nanopar-
ticles and the ꢁ-Fe2O3–CdS nanocomposites (FC1–FC6).
The spectra for the nanocomposites were normalized with
respect to the amount of CdS present in the nanocompos-
ites, as determined by the atomic absorption spectroscopy
(AAS) analysis. Pure ꢁ-Fe2O3 shows a small emission
hump at 470 nm which is attributed to the presence of
Wavelength (nm)
Figure 8. Photoluminescence spectra of pure ꢁ-Fe2O3, CdS nanoparti-
cles and the ꢁ-Fe2O3–CdS nanocomposites (FC1–FC6).
(FC1–FC6) are shown in Figure 6. The ꢁ-Fe2O3–CdS
nanocomposites exhibit optical absorption in the vis-
ible region. The optical band gap of ꢁ-Fe2O3, CdS
nanoparticles and the ꢁ-Fe2O3–CdS nanocomposites was
Fe2O3
8
FC1(1:0.1:0.1)
MH–300K
4
MH–300K
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MH–
w
Y5Kork at Binghamton
MH–5K
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4
Mar 2017 08:33:28
2
0
Copyright: American Scientific Publishers
2
0
–2
–4
–6
–8
–2
–4
–3
–2
–1
0
1
2
3
–3
–2
–1
0
1
2
3
Magnetic field (T)
Magnetic field (T)
FC2 (1:0.25:0.25)
0.8
0.4
MH–300K
MH–5K
0.0
–0.4
–0.8
–3
–2
–1
0
1
2
3
Magnetic field (T)
Figure 9. Typical M–H curves for pure ꢁ-Fe2O3 nanoparticles and ꢁ-Fe2O3–CdS nanocomposites (FC1 and FC2) at 300 K and 5 K.
J. Nanosci. Nanotechnol. 16, 9072–9084, 2016
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Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Yadav and Jeevanandam
oxygen vacancies, defects and other structural impurities.42
Pure CdS nanoparticles show band edge emission at about
529 nm with a broad shoulder at 560 nm attributed to
Cd2+ and S2− vacancies.43 Nanocomposites FC1 and FC5
show band edge emission due to CdS at about 510 nm
and nanocomposites FC3 and FC6 show band edge emis-
sion at about 475 nm. Nanocomposite FC2 shows band
edge emission due to CdS at 465 nm and nanocomposite
FC4 shows band edge emission due to CdS at 504 nm
and a broad shoulder at 560 nm attributed to vacancies.
There is a blue shift of the CdS band edge emission
in the ꢁ-Fe2O3–CdS nanocomposites compared to pure
CdS nanoparticles. The blue shift is attributed to quan-
tum size effect due to decrease in the particle size of
CdS in the nanocomposites. The blue shift is more in
the case of nanocomposites FC2 and FC3 as compared
to that in FC1 and FC5 in spite of the larger crystal-
lite size of CdS and this is attributed to the presence
of defects.27ꢀ43 The ꢁ-Fe2O3–CdS nanocomposites con-
tain CdS content (from AAS analysis) of 0.93%, 26.3%,
60.3%, 7.2%, 25.9% and 10.9% for FC1, FC2, FC3, FC4,
FC5 and FC6, respectively. In general, the PL intensity of
the ꢁ-Fe2O3–CdS nanocomposites decreases as compared
to pure CdS nanoparticles which is attributed to an efficient
charge separation in the nanocomposites.10ꢀ27 Nanocom-
posite FC3 exhibits the highest PL emission intensity
among the nanocomposites. The nanocomposites FC2 and
FC5 exhibit less emission intensity compared to FC3 due
to decrease in the CdS content. The nanocomposites FC1,
FC4 and FC6 have less CdS content and thus show lower
emission intensity compared to the other nanocomposites
(FC2, FC3 and FC5). The presence of a broad emission
band at 475 nm in the nanocomposite FC6 is attributed
to the transfer of excited electrons from the conduction
band of CdS to the empty surface oxygen vacancies on the
surface of iron oxide. Although nanocomposites FC1 and
FC4 contain appreciable amount of iron oxide, they pos-
sess less amount of CdS compared to FC6 (see Table II).
The decrease in emission intensity at 475 nm in nanocom-
posite FC6 compared to FC1 and FC4 is attributed
3.0
(a)
3.0
(b)
CR(50 mg L–1
Fe2O3
)
FC5
0
2.5
2.0
1.5
1.0
0.5
0.0
2.5
2.0
CdS
FC1
FC2
FC3
FC5
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1.5
FC6
Copyright: American Scientific Publishers
1.0
0.5
0.0
60 min
700
200
300
400
500
600
700
800
200
300
400
500
600
800
Wavelength (nm)
Wavelength (nm)
(c)
1.0
Fe2O3
CdS
FC5
0.8
0.6
0.4
0.2
0.0
0
10
20
30
Time (min)
40
50
60
Figure 10. (a) UV-visible spectra indicating photocatalytic degradation of congo red in an aqueous solution (time = 30 min) using pure ꢁ-Fe2O3,
CdS nanoparticles and the ꢁ-Fe2O3–CdS nanocomposites as the catalysts, (b) kinetics of photocatalytic degradation of congo red using ꢁ-Fe2O3–
CdS nanocomposite FC5 and (c) comparison of photocatalytic degradation of congo red with pure ꢁ-Fe2O3, CdS nanoparticles and ꢁ-Fe2O3–CdS
nanocomposite FC5.
9080
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Yadav and Jeevanandam
Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
to the presence of smaller amount of CdS in these
nanocomposites.
moments across the anisotropy barrier.44ꢀ45 Nanocompos-
ite FC1 shows higher coercivity (0.05 T) compared to
pure iron oxide nanoparticles which is attributed to larger
particle size of iron oxide in the nanocomposite which
increases the anisotropic energy in the single domain.39 On
the other hand, nanocomposite FC2 exhibits lower coerciv-
ity (0.033 T) compared to nanocomposite FC1 due to the
formation of particles in multi-domain size range.46 The
remanent magnetization (Mrꢅ for the nanocomposite FC1
(1.65 emu/g) is higher compared to that of pure ꢁ-Fe2O3
nanoparticles. Nanocomposite FC2 shows decrease in the
remanent magnetization (0.23 emu/g) compared to that of
pure iron oxide nanoparticles. At room temperature, the Ms
values for the nanocomposites FC1 (4.4 emu/g) and FC2
(0.65 emu/g) are higher compared to that of pure ꢁ-Fe2O3
nanoparticles. In general, the ꢁ-Fe2O3–CdS nanocompos-
ites show lower saturation magnetization values com-
pared to that of bulk ꢁ-Fe2O3 (Ms = 76 emu/g). This is
attributed to the presence of disordered or canted spins
Typical field dependent magnetization (M–H) plots
for pure iron oxide nanoparticles and the ꢁ-Fe2O3–CdS
nanocomposites with uniform elemental distribution (FC1
and FC2) at 300 K and 5 K are shown in Figure 9. Pure
ꢁ-Fe2O3 nanoparticles show superparamagnetic behaviour
at 300 K, while at 5 K, weak ferromagnetic behaviour is
observed with Mr and Hc values of 0.32 emu/g and 0.03 T,
respectively. At 300 K, the magnetization of ꢁ-Fe2O3
nanoparticles saturates with a Ms value of 0.61 emu/g
while at 5 K, the magnetization does not saturate at a
maximum field of 3 Tesla. The ꢁ-Fe2O3–CdS nanocom-
posites FC1 and FC2 show superparamagnetic behaviour
at 300 K, weak ferromagnetic behaviour at 5 K and satu-
ration of magnetization is not observed in these nanocom-
posites at 5 K. Pure iron oxide nanoparticles and all the
nanocomposites show coercivity at 5 K but not at 300 K
and this is attributed to thermal fluctuation of the blocked
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Scheme 1. Proposed mechanism of photodegradation of congo red.
J. Nanosci. Nanotechnol. 16, 9072–9084, 2016
9081

Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Yadav and Jeevanandam
on the surface of nanocomposites and superparamagnetic
relaxation.47
the presence of ꢁ-Fe2O3–CdS nanocomposites as the cata-
lyst. Based on the literature,26ꢀ27ꢀ30 the mechanism of pho-
todegradation is described as follows (Scheme 2):
The photocatalytic activity of the ꢁ-Fe2O3–CdS
nanocomposites was examined by studying the degradation
of congo red in an aqueous solution under sunlight irra-
diation. Figure 10(a) shows the UV-visible spectral results
on the photodegradation of congo red by pure ꢁ-Fe2O3,
CdS nanoparticles and all the nanocomposites (FC1–FC6).
It can be seen from Figure 10(a) that nanocomposite
FC5 shows maximum photodegradation compared to pure
Fe2O3, CdS nanoparticles and all the other nanocom-
posites. It is proposed that when the amount of CdS
in the nanocomposites is too low (e.g., FC1), an effi-
cient interfacial electron transfer from CdS to ꢁ-Fe2O3
does not occur. Also, too much CdS on the surface of
ꢁ-Fe2O3 (e.g., nanocomposite FC6) will block irradiation
of Fe2O3 and nanocomposite FC5 contains optimum con-
centration of CdS and it exhibits the maximum degrada-
tion. The BET surface area values for the ꢁ-Fe2O3–CdS
nanocomposites FC1, FC2, FC3, FC4, FC5 and FC6 are
29.8 m2/g, 52 m2/g, 59.8 m2/g, 30.7 m2/g, 66.1 m2/g and
65.2 m2/g, respectively. The ꢁ-Fe2O3–CdS nanocompos-
ite FC5 possesses higher surface area than that of pure
ꢁ-Fe2O3 (51.1 m2/g), CdS nanoparticles (58.9 m2/g) and
all the other nanocomposites. Thus, due to optimum con-
centration of CdS and high surface area, nanocomposite
FC5 shows better photocatalytic activity compared to pure
hꢇ
CdS–Fe2O3 →CdSꢈe− +h+ꢅ+Fe2O3ꢈe− +h+ꢅ
CdSꢈe− +h+ꢅ+Fe2O3ꢈe− +h+ꢅ → CdSꢈh+ꢅ+Fe2O3ꢈe−ꢅ
e− +O2 → Oꢁ2−
2e− +O2 +2H+ → H2O2
H2O2 +Oꢁ2−→OHꢁ +OH− +O2
On sunlight irradiation, electrons in the valence bands
of CdS and ꢁ-Fe2O3 are excited to their respective con-
duction bands. The electrons on the CB of CdS are trans-
ferred to that of ꢁ-Fe2O3 while the photo generated holes
on the VB of ꢁ-Fe2O3 are transferred to that of CdS.49
The photogenerated electron–hole pairs migrate easily to
the surface and are separated efficiently at the interface of
(a)
Fe2O3 (0.009 min–1
CdS (0.024 min–1
FC5 (0.035 min–1
)
3.0
2.5
2.0
)
)
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ꢁ-Fe2O3, CdS nanoparticles and other nanocomposites.
1.5
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Figure 10(b) shows the kinetics of photo degradation
Copyright: American Scientific Publishers
of congo red using ꢁ-Fe2O3–CdS nanocomposite FC5 as
1.0
0.5
0.0
the catalyst. It can be seen that the absorbance at 495 nm
decreases with time, and it almost approaches zero within
60 min. On the other hand, pure Fe2O3 and CdS nanopar-
ticles are unable to complete the degradation of congo red
even after 60 minutes of irradiation (Fig. 10(c)). Accord-
ing to the reported literature34ꢀ35ꢀ48 the mechanism for the
photo degradation of congo red involves cleavage of C–S
bond, aromatic ring opening, cleavage of –N N– dou-
ble bond and cleavage of various C–N and C–C bonds in
addition to decarboxylation. Scheme 1 shows the possible
species formed during the degradation of congo red in
0
10
20
30
40
50
60
Time (min)
(b)
Fe2O3 (0.006 mg–1 min–1
CdS (0.022 mg–1 min–1
FC5 (0.088 mg–1 min–1
)
6
5
4
3
2
1
0
)
)
0
10
20
30
Time (min)
40
50
60
Figure 11. Kinetics plots using (a) pseudo first order and (b) pseudo
second order kinetic models for photo degradation of congo red. Symbols
are experimental values and solid lines are the fits using the two kinetic
models.
Scheme 2. Band alignment and photo-induced electron transfer in
ꢁ-Fe2O3–CdS nanocomposites.
9082
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Yadav and Jeevanandam
Synthesis of ꢁ-Fe2O3–CdS Nanocomposites with Enhanced Photocatalytic Activity
Table III. Estimated pseudo first order and second-order kinetic parameters for the photocatalytic degradation of congo red in an aqueous solution
using pure ꢁ-Fe2O3, CdS nanoparticles and ꢁ-Fe2O3–CdS nanocomposite (FC5) as the catalysts.
Pseudo first-order kinetics
)
Pseudo second-order kinetics
k2 (mg−1 min−1
Catalyst
k1 (min−1
R2
)
R2
ꢁ-Fe2O3
CdS
Nanocomposite (FC5)
0ꢃ009
0ꢃ024
0ꢃ035
0ꢃ52
0ꢃ89
0ꢃ71
0ꢃ006
0ꢃ022
0ꢃ088
0ꢃ93
0ꢃ97
0ꢃ98
the nanocomposites with low recombination.50 The trans-
ferred electrons are trapped by the adsorbed surface oxy-
gen molecules to give Oꢁ2− and H2O2 to form active species
(OHꢂ radicals) which attack chromophore of the congo red
leading to its degradation.26ꢀ51 The pseudo-first-order and
pseudo-second-order kinetics models were applied to study
the kinetics of congo red photodegradation by pure Fe2O3,
CdS nanoparticles and ꢁ-Fe2O3–CdS nanocomposite FC5
(Eqs. (1) and (2)).52
decreased from 93% to 85% after three cycles. From
atomic absorption spectroscopy studies, after the photo-
catalytic experiments, on the supernatant solutions, it was
found that no detectable amount of cadmium is leaching
into the solution. These studies prove that the ꢁ-Fe2O3–
CdS nanocomposites can be used to purify water.
4. CONCLUSION
ꢁ-Fe2O3–CdS nanocomposites were successfully prepared
by a simple and facile thermal decomposition approach.
The nanocomposites were characterized using different
analytical techniques. XRD results confirm the presence
of CdS nanocrystals (1.2 to 2.9 nm) in the nanocom-
posites and TEM results indicate formation of agglomer-
ated sphere-like particles in the nanocomposites. Diffuse
reflectance spectral studies of ꢁ-Fe2O3–CdS nanocom-
posites indicate absorbance in the visible region (1.8 to
Pseudo first order kinetics model:
ꢀ
ꢁ
Co
C
ln
= k1t
(1)
(2)
Pseudo second order kinetics model:
1
ꢉCꢊ
1
ꢉCoꢊ
= k2t +
Where Co and C represent the concentration of congo
red at t = 0 and at any time t. k1 and k2 are pseudo-
first order and pseudo-second order rate constants, respec-
tively. Figures 11(a and b) show the fitting of kinetics
data for the photodegradation of congo red using pure
Fe2O3, CdS nanoparticles and ꢁ-Fe2O3–CdS nanocompos-
ite FC5 as the catalyst. The kinetic parameters obtained
by linear regression using the two kinetic models are
summarized in Table III. The higher correlation coeffi-
cient values (R2ꢅ indicate a better fitting of the kinetic
data using the pseudo-second-order kinetics model rather
than the pseudo-first-order one. The value of second
order rate constant of photodegradation of congo red
degradation using ꢁ-Fe2O3–CdS nanocomposite FC5 is
0.088 mg−1 min−1 which is higher than the values
for pure ꢁ-Fe2O3 (0.006 mg−1 min−1ꢅ and pure CdS
(0.022 mg−1 min−1ꢅ. The enhanced photocatalytic activ-
ity of the ꢁ-Fe2O3–CdS nanocomposites is attributed to an
efficient charge separation at the CdS–Fe2O3 interface.
The ability to recycle a photocatalyst is very impor-
tant. To investigate the reusability ꢁ-Fe2O3–CdS nanocom-
posites, the photocatalytic degradation experiment was
repeated four times using the same catalyst (FC5) again
and again. The concentration of congo red was kept con-
stant (50 mg L−1ꢅ with 60 minutes as the irradiation time.
The photocatalyst was recovered in each cycle from the
sun light irradiated solutions by centrifugation followed
by subsequent washing with double distilled water three
times and the recovered catalyst was reused for the catal-
ysis. The degradation efficiency of nanocomposite FC5
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2.5 eV) and the nanocomposites show blue shift of band
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edge emission compared to pure CdS due to quantum size
Copyright: American Scientific Publishers
effect. The ꢁ-Fe2O3–CdS nanocomposites exhibit super-
paramagnetic behavior at room temperature and they are
promising catalysts for the photodegradation of congo red
in an aqueous solution with good recyclability.
Acknowledgments: The award of Senior Research Fel-
lowship (SRF) to Mr. Sudheer Kumar Yadav by the
University Grants Commission, Government of India, is
gratefully acknowledged. The authors are thankful to the
Institute Instrumentation Centre, Indian Institute of Tech-
nology Roorkee for providing the XRD, FE-SEM and
TEM facilities.
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Yadav and Jeevanandam
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Received: 26 September 2015. Accepted: 7 November 2015.
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