Studies of the photocatalytic and electrochemical performance of the Fe2O3/TiO2 heteronanostructure

Article abstract of DOI:10.1007/s13738-020-01993-0

The α-Fe₂O₃/TiO₂ nanostructure material, synthesized on FTO (fluorine-doped tin oxide) substrate using the hydrothermal method at 180?°C for 5?h, exhibits an enhanced performance in the photocatalytic degradation of an organic dye. The optical band gap was found to decrease compared to the TiO₂ one. The photocatalytic performances of the as-prepared heterojunction were evaluated with the degradation of methylene blue (MB) in an aqueous medium. The results revealed that the photocatalytic activity of the Fe₂O₃/TiO₂/FTO was much higher than that of the pure TiO₂. In addition, the photocurrent of the Fe₂O₃/TiO₂/FTO heterojunction was remarkably higher than that of the bare TiO₂ electrode. The obtained results indicate that the heterojunction formed between Fe₂O₃ and TiO₂significantly improved the separation efficiency of the photo-generated electron–hole pairs. The electrochemical properties of the as-synthesized nanocomposite materials (α-Fe₂O₃/TiO₂) were also evaluated with cyclic voltammetry for 1000 cycles. This nanocomposite exhibited an enhanced specific discharge capacity compared to the Fe₂O₃ nanomaterial. The as-produced material proved to have an impressive performance as a high-capacity anode for Na⁺-ion batteries.

Full text of DOI:10.1007/s13738-020-01993-0

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-020-01993-0
ORIGINAL PAPER
Studies of the photocatalytic and electrochemical performance
of the Fe2O3/TiO2 heteronanostructure
Abdelhak Othmani2 · Salah Kouass1 · Thamer Khalf3 · Sabrine Bourchada4 · Fathi Touati3 · Hassouna Dhaouadi3
Received: 25 March 2020 / Accepted: 29 June 2020
© Iranian Chemical Society 2020
Abstract
The α-Fe2O3/TiO2 nanostructure material, synthesized on FTO (fuorine-doped tin oxide) substrate using the hydrothermal
method at 180 °C for 5 h, exhibits an enhanced performance in the photocatalytic degradation of an organic dye. The optical
band gap was found to decrease compared to the TiO2 one. The photocatalytic performances of the as-prepared heterojunc-
tion were evaluated with the degradation of methylene blue (MB) in an aqueous medium. The results revealed that the pho-
tocatalytic activity of the Fe2O3/TiO2/FTO was much higher than that of the pure TiO2. In addition, the photocurrent of the
Fe2O3/TiO2/FTO heterojunction was remarkably higher than that of the bare TiO2 electrode. The obtained results indicate that
the heterojunction formed between Fe2O3 and TiO2signifcantly improved the separation efciency of the photo-generated
electron–hole pairs. The electrochemical properties of the as-synthesized nanocomposite materials (α-Fe2O3/TiO2) were also
evaluated with cyclic voltammetry for 1000 cycles. This nanocomposite exhibited an enhanced specifc discharge capacity
compared to the Fe2O3 nanomaterial. The as-produced material proved to have an impressive performance as a high-capacity
anode for Na+-ion batteries.
Keywords Nanocomposite · Heterojunction · Photocatalytic properties · Electrochemical properties
Introduction
of various photocatalysts such as: TiO2 [4], Au/ZnO [5],
C3N3S3 [6] and MoS2 [7]. Titanium dioxide (TiO2) is one of
the most commonly used photocatalysts given its efciency
in pollutant degradation in waste water, and also because
of its inexpensiveness, strong oxidizing power, hard-soluble
and long-term photostability [4]. However, its wide band
gap requires excitation with ultraviolet (UV) light, which
is only equivalent to 5–10% of the sunlight reaching the
surface of the earth. This limits its development and prac-
tical applications. Hence, enhancing photoactivity perfor-
mance under UV or visible light irradiation is necessary.
Several approaches, including metal and non-metal ion
doping and sensitization with organic and inorganic dyes,
have been developed to tune the band structure and broaden
the light response toward the long wavelength region [8].
TiO2coupled with other semiconductor transition metal
oxides to form heterojunction materials is another way of
extending the optical response range of TiO2 and improv-
ing the quantum efciency. This system can be expected to
achieve high photocatalytic activity. Among these oxides,
Fe2O3 presents a gap at around 2.0 eV [9, 10]. Fe2O3 seems
to be compatible with TiO2 and possesses a high solar-light
harvesting capability that is larger than that of TiO2. Indeed,
Green energy sources have been extensively investigated
in an attempt to replace fossil fuels, which have inherent
pollution problems, and given the limited availability of
resources [1]. In particular, the photocatalytic conversion
of solar energy into chemical energy or into hydrocarbon
fuels has been of great signifcance in environmental con-
servation and energy utilization [2, 3]. Over the last few
decades, much attention has been paid to the production
* Salah Kouass
koissa2000@yahoo.fr
1
Laboratoire des Matériaux Utiles, INRAP Sidi-Thabet,
2020 Tunis, Tunisia
2
Faculté des Sciences de Bizerte, LR01 ES15, Laboratoire
de Physique des Matériaux: Structure et Propriétés,
Université de Carthage, Faculté des Sciences de Bizerte,
7021 Zarzouna, Bizerte, Tunisia
3
Laboratoire Matériaux, Traitement et Analyses, INRAP,
Technopole Sidi-Thabet, Ariana Tunis, Tunisia
4
Laboratoire de Chimie des Matériaux, Faculté des Sciences
de Bizerte, 7021 Zarzouna, Bizerte, Tunisia
Vol.:(0123456789)
1 3

Journal of the Iranian Chemical Society
Yanqing Cong et al.proved that Fe2O3nanoparticles present a
stronger photo-response under visible light irradiation in the
nanostructured Fe2O3/TiO2nanotube electrodes [11]. Fe2O3/
TiO2nanocomposites exhibited an excellent photocatalytic
activity under visible light and were applied as photocata-
lysts in the degradation of oxytetracycline [12].
5 h. The obtained sample was washed several times with
distilled water and dried at 100 °C for 15 min. The obtained
product was annealed for 1 h at 400 °C.
Preparation of the Fe2O3nanoparticles
It is known that the TiO2 material shows a good structural
stability, stable voltage output and a long lifespan [13–15]
but its low electronic conductivity and its relatively low the-
oretical capacity (335 mAh g−1) limit its application as an
electrode material. Therefore, many eforts have been made
to develop the specifc discharge capacity of TiO2as elec-
trode material by using transition metal oxides. Among vari-
ous transition metal oxides, hematite (α-Fe2O3) has attracted
attention due to its very low cost and its theoretically high
capacity (1007 mAh g−1) [16]. Based on the synergy
between the two metallic oxides, TiO2and Fe2O3, we have
produced Fe2O3/TiO2 nanocomposite and heterojunction
flm via the hydrothermal process. The electrochemical and
photocatalytic properties of these materials were studied.
The Fe2O3 nanomaterial was prepared by dissolving 0.81 g
(3 × 10−3mol) of FeCl3.6H2O (97%, Sigma Aldrich) in
50 mL of aqueous solution under stirring for 30 min. Then,
an amount of NaOH (> 97% Carlo-ERBA) was added
(2.10−2mol). The as-prepared solution was put into a 100 mL
Tefon-lined autoclave which was placed in an oven at a tem-
perature of 180 °C for 10 h. The obtained sample was rinsed
with distilled water before being placed to dry for 15 min at
100 °C. Then it was annealed at 500 °C for 3 h.
Preparation of the Fe2O3/TiO2 nanocomposite
Firstly, the hydrochloric acid aqueous solution was mixed
with the titanium isopropoxide Ti(C3H7O)4 under vigorous
stirring for 1 h. Then an excess of NaOH (> 97% Carlo-
ERBA) 2 g=0.05 mol) was added. After 2 h of stirring, an
amount of FeCl3.6H2O was added and the pH was adjusted
to 10. The mixture was poured into an autoclave located in
an oven at a temperature of 180 °C for 10 h. After hydrother-
mal treatment, the sample was taken out of the autoclave and
rinsed with distilled water before being placed in an oven to
dry for 15 min at 100 °C. The obtained product was annealed
for 3 h at 500 °C.
Experimental
Characterization techniques
The structure of the as-prepared samples was characterized
by X-ray difraction (XRD), using a Bruker D8-Advance dif-
fractometer with CuKα1 radiation (k=1.54056 A) with θ–2θ
scans between 10° and 70°. The morphology of the samples
was determined using an FEI Quanta 200 environmental
SEM. TEM images were recorded on a JEOL-100-CX-
II electron microscope operating at 200 kV. The optical
properties were recorded using UV–vis difuse refectance
spectroscopy with a Perkin-Elmer Lambda 950 spectropho-
tometer at wavelengths ranging from 250 to 800 nm. Photo-
luminescence spectra were obtained using a Perkin-Elmer
(LS-50B) luminescence spectrometer with pulsed Xe-lamp
excitation at room temperature.
Preparation of the Fe2O3/TiO2/FTO heterojunction
The TiO2 flm was synthesized directly on transparent fu-
orine-doped tin oxide (FTO) conducting glass substrates as
described elsewhere for other metal oxide heterojunctions
on FTO substrates [17–19] (Figure 1).
•
TiO2 thin flms
The TiO2 flm was readily prepared by dissolving tita-
Preparation methods
nium isopropoxide Ti(C3H7O)4(97%, Sigma Aldrich) in an
aqueous solution of hydrochloric acid under stirring for 1h30
min. This method allows the TiO2nanorod synthesis directly
on the fuorine-doped tin oxide substrates (FTO). The result-
ing solution was transferred into an autoclave and the FTO
glass was immersed therein. The autoclave was sealed and
maintained at 180 °C for 5 h. After hydrothermal treatment,
the sample was washed several times with distilled water
and then dried at 100 °C for 15 min. Then, the sample was
annealed for 1 h at 400 °C.
Preparation of the TiO2nanoparticles
The TiO2 nanoparticles were prepared by dissolving tita-
nium isopropoxide Ti(C3H7O)4 (97%, Sigma Aldrich)
in an aqueous solution of hydrochloric acid (37%, Sigma
Aldrich) under stirring for 1 h 30 min. When homogeneity
was reached, 2 g (0.05 mol) of NaOH (>97% Carlo-ERBA)
were added to ensure the formation of the preferred hydrox-
ide and the pH was adjusted to 10. The mixture was then
stirred for 30 min. The resulting mixture was transferred in
an autoclave that was sealed and maintained at 180 °C for
•
Fe2O3/TiO2/FTO heterojunction
1 3

Journal of the Iranian Chemical Society
The substrate (TiO2/FTO), which had already been pre-
pared, was immersed in an autoclave containing a sodium
hydroxide aqueous solution mixed with FeCl3.6H2O (97%,
Sigma Aldrich). This autoclave was placed in an oven at a
temperature of 180 °C for 10 h. After hydrothermal treat-
ment, the sample was taken out of the autoclave and rinsed
with distilled water before being placed in an oven to dry
for 15 min at 100 °C. After this, the sample was annealed
for 3 h at 500 °C.
a 0.1 M Na2SO4 solution and was prepared with deionized
water, which was free from air by applying a continuous fow
of argon gas through the cell. The Ag/AgCl electrode in the
same electrolyte solution was used as the reference electrode
and a Pt wire was used as counter electrode. The working
electrodes were prepared as follows: a mixture of the active
material, carboxymethyl cellulose (CMC), used as a binder,
and acetylene black as the conductive agent in a weight ratio of
80:15:5. The active material was used to coat the nickel foam
and act as a working electrode (0.7 cm×0.7 cm). The coated
electrode was then dried at 100 °C overnight.
The structure of the as-prepared samples was characterized
by X-ray difraction (XRD), using a Bruker D8-Advance dif-
fractometer with CuKa1 radiation (k=1.54056 A°) with θ–2θ
scans between 10° and 70°. Their morphology was determined
using an FEI Quanta 200 environmental SEM. TEM images
were recorded on a JEOL-100-CX-II electron microscope
operating at 200 kV and a scanning electron microscope
(SEM, ZEISS Ultra 40, operating at 2.5 kV). The optical prop-
erties were recorded using UV–vis difuse refectance spec-
troscopy with a Perkin-Elmer Lambda 950 spectrophotometer
at wavelengths ranging from 250 to 800 nm. Photolumines-
cence spectra were obtained using a Perkin-Elmer (LS-50B)
luminescence spectrometer with pulsed Xe-lamp excitation at
room temperature.
Results and discussion
Structural characterization
In order to optimize the synthesis temperature for obtain-
ing the pure hematite Fe2O3 phase, several experiments
were carried out. The X-ray difractograms of the as-syn-
thesized samples at 100, 150 and 180 °C during 6 h under
hydrothermal conditions are shown in Fig. 2a. Indeed,
below 180 °C, a mixture of phases was obtained with the
presence of the Fe2O3 phase. The optimum hematite Fe2O3
synthesis conditions are 180 °C for 6 h.
Photocatalytic degradation
The XRD patterns of Fe2O3, TiO2and the Fe2O3/TiO-
2composites are shown in Fig. 2b. The analysis of the dia-
gram corresponding to TiO2 shows that the layer crystal-
lizes following the anatase phase characterized by three
hkl orientations (101), (004) and (200), respectively,
located at 2θ = 26.1°, 38.7° and 48°. The identifcation
of these diferent lines is in good agreement with the card
(JCPDS No. 88-1175). It can be seen that the two lines,
(101) and (200), are, respectively, located in the vicinity
of 26.1° and 48° and are the most intense peaks that can
be observed. This result clearly indicates the growth of
TiO2nanorods oriented along the c directional axis [001].
This has also been confrmed by Meidan Ye et al. [21].
The Fe2O3XRD difractogram is characterized by the
two most intense peaks, respectively, at 34.4° and 37.8°
that correspond to the two planes (104) and (110). The
rhombohedral structure of the iron oxide is well confrmed
by the card (JCPDS 33-0664).
For better results and to recover the photocatalyst, the FTO
was used as a substrate. This method allowed us to elaborate
the TiO2nanorods directly on the FTO substrates without mak-
ing a bufer layer due to a small mesh mismatch between the
FTO and the TiO2phase [20]. Then, an aqueous solution of
FeCl3.6H2O was poured into an autoclave and the TiO2/FTO
substrate, which had already been prepared, was immersed.
The remaining steps, previously described for a hydrothermal
treatment, were followed.
At room temperature, a thin flm layer of photocatalyst
(2 cm×2 cm) was immersed in 20 mL of methylene blue (MB)
aqueous solution (3 mg/L). The solution was stirred in the dark
for 30 min to reach adsorption equilibrium on the catalyst’s
surface. The purpose of stirring is to homogenize the catalyst’s
distribution and to dissolve the oxygen necessary for oxidation.
After 30 min of adsorption, and before lighting the visible light
lamp, sampling was carried out corresponding to t=0 min.
The solution was continuously maintained under stirring, was
then irradiated and samples were taken at regular times.
The analysis of the Fe2O3/TiO2difractogram indicates
the formation of the TiO2 anatase phase in the presence of
the Fe2O3rhombohedral structure confrmed by the pres-
ence of its characteristic peak at 2θ=35.72°. This result is
in agreement with the literature and clearly shows that the
Fe2O3nanoparticles crystallize in the rhombohedral system
(space group R-3c) [22].
Electrochemical study
The electrochemical measurements were conducted at room
temperature with a potentiostat/galvanostat system using a
conventional three-electrode cell. The electrolyte consisted of
The Fe2O3/TiO2/FTOXRD patterns are shown in
Fig. 2c. The analysis of the diagram corresponding to
TiO2 shows that the layer crystallizes following the rutile
1 3

Journal of the Iranian Chemical Society
Fig. 1 Schematic illustration of the formation of the Fe2O3/TiO2 heterostructure through a two-step process on FTO substrate: hydrothermal
growth of TiO2nanorod cores, followed by the deposition of the Fe2O3 shell
phase characterized by the four orientations (101), (002),
(301) and (110), respectively, located at 2θ = 36.1°, 62.7°,
69° and 70°. The identifcation of these diferent lines is
in good agreement with the card (JCPDS No. 88-1175).
The presence of Fe2O3 is confrmed by the presence of the
characteristic peaks centered on 2θ=35.72° corresponding
to the hkl crystallographic plane (110). The FTO substrate
is characterized by the three intense peaks, respectively,
located at 2θ = 26°, 46° and 51°.
singly coordinated surface hydroxyl groups are present [23].
The (001) basal plane and the side planes could be efec-
tively controlled, since these planes adsorb a large amount
of OH− ions. The superior adsorption of OH− on the planes
parallel to the basal planes induces the anisotropic growth
of the hematite via the (001) plane, which contributes to the
formation of the hexagonal thin platelets.
The Fe2O3/TiO2 nanocomposite presents a spherical
shape (Fig. 3b). The spherical core-shell nanocrystals could
originate from isotropic growth in diferent directions.
The SEM image of the Fe2O3/TiO2/FTO heterojunction is
shown in Fig. 3c. The images reveal Fe2O3 and TiO2 nano-
platelets. These nanoplatelets are arranged in such a way
that they give rise to pillars in the form of rods which are
almost uniformly distributed over the entire surface of the
FTO substrate.
Morphological characterizations
Figure 3 shows the SEM micrographs of the Fe2O3, Fe2O3/
TiO2 nanocomposite and Fe2O3/TiO2/FTO heterojunction
synthesized under hydrothermal conditions.
The results show that the Fe2O3has a platelet shape with
truncated sides as seen in Fig. 3a. The size of the as-obtained
particles under hydrothermal conditions is smaller than
1 µm. The uniform and monodisperse hexagonal platelets
could be due to the excess NaOH(OH−) in the solution. The
OH− amount could afect the anisotropic growth rates of
the diferent crystallographic planes through the specifc
adsorption of these anions. Thus, some planes grow very
fast, while others are slow-growing planes. However, the
growth rate of a given plane is mainly governed by the
intrinsic crystal structure and the experimental conditions.
The structural characteristics of the hematite, Fe2O3, make
the hydroxyl group interactions with the various hematite
crystal faces quite diferent. For the (001) plane, surface
hydroxyl functions are all doubly coordinated, whereas for
other commonly occurring planes on the surface of hematite
crystals, such as the (100), (110), (012) and (104) planes,
The detailed structures of Fe2O3 and the Fe2O3/TiO2
nanocomposite were recorded using TEM. As shown in
Fig. 4a, the Fe2O3nanorods are well dispersed with an aver-
age diameter of 50 nm. The HRTEM image in Fig. 4c pre-
sents the lattice spacing of 3.75 Å corresponding to the (012)
plane.
The magnified high-resolution TEM image (Fig. 4b)
reveals the presence of the Fe2O3nanorod covering the TiO2
nanoparticle surface. Lattice fringes in the HRTEM image
(Fig. 4d) of the binary hybrid nanocomposite Fe2O3/TiO2
could be attributed to a lattice spacing of 2.35 Å nm and 2.37
Å nm corresponding to the (103) plane of TiO2,while the
lattice spacing of 2.52Å nm could be indexed to the (110)
plane of Fe2O3.
1 3

Journal of the Iranian Chemical Society
Fig. 2 a DRX spectra of materials obtained at diferent temperatures: 100 °C, 150°C and 180 °C. b XRD patterns of Fe2O3, TiO2 and the
(Fe2O3/TiO2) nanocomposites. c XRD patterns of Fe2O3,TiO2 and FTO and the (Fe2O3/TiO2/FTO) heterojunction
predominant oxidation states of Fe, O and Ti are + 3, − 2
X‑ray photoelectron spectroscopy (XPS)
and +4, respectively.
To determine the valence states of the as-prepared mate-
rial, the Fe2O3/TiO2nanocomposite, the XPS test was car-
ried out. Figure 5 shows the detected peaks of Ti2p, Fe2p,
O1s and C1s. The binding energies of the Ti 2P1/2 and Ti
2P3/2 core levels are observed at approximately 458.5 and
464.5 eV in Fig. 5a, confrming the Ti (+IV) state in the
anatase TiO2 [24]. The spectrum of Fe 2p is formed by
two distinct peaks at around 711 eV and 724 eV (Fig. 5b),
which, respectively, correspond to the Fe 2p3/2 and Fe 2p1/2
in α-Fe2O3 [24, 25]. The core-level XPS spectrum of O1s
is shown in Fig. 5c, where the peak observed at 530 eV
is attributed to the O2− forming the two coupled oxides,
Fe2O3 and TiO2 [26]. In the C1s spectrum (Fig. 5d),
the peak at around 285 eV originates from adventitious
carbon [24]. In summary, the XPS results show that the
UV–vis difuse refectance spectroscopy
Figure 6a, b shows the UV–vis difuse refectance spectra of
pure Fe2O3, pure TiO2 and the Fe2O3/TiO2/FTO heterojunc-
tion. The compounds’ absorption peaks appear, respectively,
at 322 nm, 382 nm and 413 nm. A red shift of the UV–vis
refectance spectra of the Fe2O3/TiO2 composite nanopar-
ticles was observed when compared with the spectrum of
anatase TiO2 nanoparticles. The Fe2O3/TiO2 composite nan-
oparticles’ red shift could be attributed to the contribution of
each of the oxide components, Fe2O3 and TiO2 [20]. Hence,
Fe2O3 as the carrier of TiO2 extends the photoresponse range
of the composite semiconductor. As seen in Fig. 6b, the TiO2
spectrum shows a broad band between 650 and 850 nm. The
origin of this visible band could be attributed to the impurity
1 3

Journal of the Iranian Chemical Society
Fig. 3 SEM images of a pure
Fe2O3, b the Fe2O3/TiO2nano-
composite and c the Fe2O3/
TiO2/FTO heterojunction
Fig. 4 TEM image of: a Fe2O3;
b Fe2O3/TiO2; HRTEM image
of: c Fe2O3/TiO2; d Fe2O3/TiO2
1 3

Journal of the Iranian Chemical Society
Fig. 5 XPS core level spectra
of a Ti 2p, b Fe 2p, c O 1s and
d C 1s for the TiO2@Fe2O3
nanocomposite
levels within the TiO2 nanoparticle band gaps. These impuri-
ties are present in the as-prepared materials in weak amounts
meaning they could not be detected with XRD.
Generally, introducing an appropriate amount of transi-
tion metal oxide in the TiO2 matrix is a promising alter-
native frequently used to manipulate the band gap of the
as-obtained nanocomposite. The photocatalyst is essentially
based on the band gap (Eg) values. The weakness of this
parameter could be used to harvest most of the visible light,
and thus the electrons could be excited and injected into the
conduction band of TiO2, leading to the improvement in
the electron–hole pair separation. As indicated in Table 1,
the higher degradation activity of the nanocomposite sam-
ples (Fe2O3/TiO2, CdO/ZnO, ZnO/TiO2, Bi2O3/TiO2 and
CdS/TiO2 [28–33]) is correlated with its lower band gap
and strong adsorption in the visible region. In our case, the
The optical band gap (Eg) for pure Fe2O3, TiO2 and the
Fe2O3/TiO2 composite can be determined by extrapolating
the absorption edge using the model proposed by Tauc in
(
)
the following equation [27]: (ꢀhꢁ)2 = A hꢁ − Eg . Fig-
ure 6c, d shows the plot of (ꢀhꢁ)2 versus hꢀ. The estimate
of the gap energy value of TiO2 alone is Eg1 =3.1 eV, that
of Fe2O3 is Eg2 =1.93 eV and that of the Fe2O3/TiO2 junc-
tion is Eg3 =2.6 eV. Fe2O3clearly has the role of increasing
the intensity of the refux bands and shifting them to higher
wavelengths compared to TiO2.
Table 1 Comparison of the band gap energy (Eg) with the literature
Nanocomposite
type (A/B)
λMax (nm)
Semiconductor
type (A)
Energy gap
Organic molecule degradation
Reference
Eg (eV) of heterostructure materials pollutant
Fe2O3/TiO2
Fe2O3/TiO2
Fe2O3/TiO2
Fe2O3/TiO2
CdO/ZnO
ZnO/TiO2
Bi2O3/TiO2
CdS/TiO2
413
539
325
325
307.0
420
300
420
p-type
p-type
p-type
p-type
n-type
n-type
p-type
p-type
2.6
2.3
3.26
2.38
2.5
2.9
2.7
2.8
MB
Present work
[28]
[29]
[30]
[31]
[28]
[32]
[33]
Penta-Chloro-Phenol PCP
Orange II
Bisphenol A.
Remazol Brilliant Orange 3R
Penta-Chloro-Phenol PCP
Rhodamine B
Methyl orange
1 3

Journal of the Iranian Chemical Society
synthesized Fe2O3/TiO2 heterojunction presents a moderate
band gap (Eg =2.6 eV) compared to the other nanocomposite
samples. Consequently, the separation efciency of photo-
generated electron–hole pairs in the Fe2O3/TiO2 heterojunc-
tion could be improved, leading to the improvement in the
photocatalytic activity.
Figure 7b depicts linear sweep voltammograms (LSV)
of the Fe2O3/TiO2 and TiO2 samples. As shown in Fig. 8a,
the photocurrent density of photoanodes under illumination
increases after coupling TiO2 with α-Fe2O3. The Fe2O3/TiO2
heterostructure exhibits the largest photocurrent density of
0.25 mA.cm−2, which is almost twice the value of the bare
TiO2 sample. The Fe2O3/TiO2 sample maintains a photo-
current density of about 0.25 mA.cm−2, which is compara-
ble to that observed in the amperometric studies (Fig. 7a).
The photocurrent observed demonstrates that the interfacial
charge transfer between Fe2O3 and TiO2exists in this nano-
composite. The electron transfer could be further testifed
and quantifed by this characterization.
Photoluminescence measurement
To understand the mechanism of the improved photocata-
lytic results of the Fe2O3/TiO2/FTO heterojunction, infor-
mation such as the efciency of the charge carrier recom-
bination, migration and transfer, molecular adsorption and
surface reactions should be investigated. Photoluminescence
(PL) represents a non-destructive and high-sensitivity tool to
study the optical and electronic structure properties of semi-
conductor materials, particularly in the feld of photocataly-
sis. Figure 7b depicts the photoluminescence (PL) spectra of
the Fe2O3/TiO2/FTO heterojunction and TiO2flm. It is obvi-
ous that the PL emission intensity of Fe2O3/TiO2 is lower
than that of TiO2, implying that the coupling of TiO2 and
Fe2O3 can efectively inhibit the recombination of the photo-
generated electron–hole pairs. Meanwhile, the weaker PL
intensity of Fe2O3/TiO2compared to that of TiO2 indicates
that the charger recombination rate between photo-generated
holes and electrons has been signifcantly reduced. When the
recombination rate decreases, more photo-generated charge
carriers can participate in the photochemical transformation,
resulting in the enhancement of the photocatalytic activity
[34].
Mott–Schottky analysis
Mott–Schottky experiments were carried out using the pure
TiO2 and Fe2O3/TiO2/FTO electrodes (Fig. 8a). Both sam-
ples show a positive slope in the Mott-Schottky plots, indi-
cating that they are n-type semiconductors with electrons
as the main carriers. The fat band potential (EFB) is deter-
mined by taking the (x) intercept of a linear ft to the Mott-
Schottky plot, 1/C2, as a function of the applied potential
(E) [35]. The fat band positions (FB) of TiO2 and Fe2O3/
TiO2are − 0.45 V and − 0.55 V versus Ag/AgCl, respec-
tively. It should be noted that the EFB of the Fe2O3/TiO2pho-
toanode exhibits a positive shift in comparison with that of
the pure TiO2 electrode. Combined with the Eg calculated
from the DRS spectra, the optical band gaps of TiO2 and
Fe2O3/TiO2are 3.1 and 2.6 eV, respectively. According to
the formula Eg =EVB−ECB, the valence band positions (EVB
)
Photocurrent measurement
of TiO2 and Fe2O3/TiO2 are 2.65 and 2.05 V versus Ag/
AgCl, respectively. Figure 8b shows a slight negative shift
of the fat band, which means that the association of Fe2O3
and TiO2raised the Fermi level of the α-Fe2O3 flm and the
electron redox.
Figure 7a shows the photocurrent responses of the as-pre-
pared samples under periodic irradiation of visible light at
the bias potential of 0 V (vs. Ag/AgCl). It is clearly seen that
after several on–of cycles of irradiation, all the samples pre-
sent a good reproducibility and stability. Indeed, the photo-
current rapidly increases when the light is turned “on” and it
immediately decreases to zero when the light is turned “of”.
The pure TiO2 electrode shows a weak photocurrent den-
sity under visible light, which is related to the weak per-
centage of UV rays in sunlight. The photocurrent density
of the Fe2O3@TiO2/FTO heterojunction electrode is greatly
increased compared to the pure TiO2 electrode in the same
conditions. As is shown in Fig. 7, the maximum photocur-
rent density of the Fe2O3@TiO2/FTO heterojunction elec-
trode reached 0.25 mA cm−2, which is almost double the
amount of the pure TiO2 electrode, revealing the efcient
photo-induced charge transfer between Fe2O3 and TiO2.
Combined with the PL result, the superior charge transfer
and recombination inhibition in the Fe2O3@TiO2/FTO elec-
trode is responsible for the intensive photocatalytic activity.
Photocatalytic ability
The photocatalytic activity of the Fe2O3/TiO2/FTO hetero-
junction was evaluated by monitoring the degradation of MB
in an aqueous solution under visible light irradiation. The
UV-spectra of MB during the photodegradation process are
shown in Fig. 9a. As shown in Fig. 7, the absorption spec-
trum of MB without a catalyst is characterized by a broad
peak centered at 670 nm. The peak intensity as well as the
broadness observed in Fig. 9b indicates that the pure TiO2
sample exhibited relatively low photocatalytic ability for
MB photodegradation. Figure 7shows that the mixed Fe2O3/
TiO2/FTO heterojunction exhibits excellent photocatalytic
activity compared to pure TiO2. As shown in Fig. 9, the
MB absorbance at around 650 nm decreases and there is
almost no shift in the peak maximum. This proves that MB
1 3

Journal of the Iranian Chemical Society
Fig. 6 a, b UV–vis difuse
refectance spectra of pure
Fe2O3, pure TiO2and the
Fe2O3/TiO2 nanocomposite.
c, d Change of [F(R)hν]2 with
energy (hν) for pure TiO2, pure
Fe2O3and the Fe2O3/TiO2nano-
composite
Fig. 7 a UV–vis spectra of
MB during the photocatalytic
process over TiO2 and the
Fe2O3/TiO2/FTO heterojunc-
tion. b The photoluminescence
spectra of the Fe2O3/TiO2/FTO
heterojunction and TiO2excited
at 350 nm
was degraded via the destruction of the conjugated structure.
These results could be explained by the inability of the TiO2
sample to absorb under visible irradiation since its gap is
located in the UV region. This could be attributed to the
reduction in the distance between the valence band (VB) and
the conduction band (CB) after the addition of Fe2O3 which
promotes a rapid transfer of electrons between bands after
excitation. In comparison, the Fe2O3/TiO2/FTO heterojunc-
tion exhibits better photocatalytic degradation the TiO2 flm.
The photocatalytic activity degradation reaction depends
on factors, such as the phase structure, particle size, crystal-
linity, light absorption capacity and electron/hole recombi-
nation rate [36].
represents the absorbance after t (min) and C0 represents
the initial absorbance. The efciencies were found to be 22%
and 52% for the TiO2 flm and the Fe2O3/TiO2/FTO hetero-
junction, respectively.
Based on the UV–vis results, the hematite α-Fe2O3could
be considered as a promising candidate for visible light
absorption due to its abundance, the appropriate energy
gap, and its good stability in many electrolytes. However,
its photocatalytic activity still remains low because of the
inefcient charge separation that results from its intrinsic
ultra-short excited state life-time. Moreover, the increased
photocatalytic responses of the heterostructured Fe2O3/
TiO2/FTO compared to bare hematite are mainly due to
an enhanced separation of photo-generated charge carriers
that inhibit electron–hole pair recombination and enhance
The photocatalytic degradation efciency [37] has been
calculated using the formula [1 − (Ct/C0)]*100 where Ct
1 3

Journal of the Iranian Chemical Society
Fig. 8 a Transient photocurrent vs. irradiation time for pure TiO2 and
Fe2O3/TiO2 heterojunction samples in a 0.1 M NaOH solution under
visible light irradiation. b Linear sweep voltammetry curves of pure
TiO2 and Fe2O3@TiO2 heterojunction samples in a 0.1 M NaOH
solution with scan rate 10 mV.s−1under visible light irradiation
interfacial charge transfer reactions. The high photocata-
lytic activity of the Fe2O3/TiO2/FTO heterojunction could
be due to the active species involved in the photocatalytic
reaction:hydroxyl radicals (OH∙) and superoxide anion radi-
and the lifetimes of the electrons/holes are prolonged. The
conduction electrons can be captured by the adsorbed O2
−
on the catalyst surface to form the superoxide anion (O2 )
and hydroxylradicals (∙OH). The accumulated holes in
−
−
cals (∙O2 ), under visible light irradiation. The hydroxyl rad-
Fe2O3VBwill react with (OH−) to produce reactive (∙O2 )
−
icals (OH∙) and the superoxide anion radicals (∙O2 ) play an
and (∙OH). The resulting(•OH) will activate the MB organic
pollutants’ degradation as a powerful oxidant [39].In addi-
tion, the photo-generated hole(h+) in Fe2O3 may also decom-
pose the MB organic pollutants.
important role in the photocatalytic processes. Under visible
light irradiation, TiO2 shows no photo-electronic response,
whereas Fe2O3 is excited and yields photo-generated elec-
trons (e−) from the valence band (VB) to its conduction band
(CB), leaving a hole (h+) behind.
The reactions taking place during the whole process
could be described as follows:
Fe2O3
+ hν
→ Fe2O3
+
Fe2O3
(e−CB
Fe2O3
Fe2O3
CO2
(1)
Photocatalytic mechanism
(h+VB
)
)
Fe2O3(e−CB
)
+ O2(ads)
+ TiO2
+ MB
→
*O2−(ads)
+
+
+
(2)
(3)
H2O (4)
The heterogeneous photocatalysis mechanism has been dis-
cussed extensively in the literature [38]. In the current study,
the photoactivity mechanism of the Fe2O3/TiO2 thin flm
could be described as follows: when the system is irradiated
with visible light, the Fe2O3 electrons at the valence band are
excited and jump to the conduction band, leaving a hole (h+)
behind. As a result, electron (e−)/hole (h+) pairs form. Then,
the excited state electrons produced by Fe2O3 can be injected
into the conduction band (CB) of the coupled TiO2 due to
the existence of electric felds between the two materials. At
the same time, the photo-generated holes (h+) of TiO2 can
quickly transfer to the VB of Fe2O3. The photo-generated
electrons of Fe2O3 quickly transfer to the CB of TiO2 and
Fe2O3 (h+VB
)
→ TiO2(h+)
→ H2O
*O2−(ads)
(h+)
(h+VB (Fe2O3)
)
+ OH-(ads)
+ MB
→
*OH(ads)
→ H2O
(5)
H2O (6)
*OH(ads)
+
CO2
−
Based on our results, it should be noted that *OH, *O2 ,
and the holes (h+) played a vital role and enhanced the pho-
tocatalytic reaction. The possible mechanisms proposed for
MB photocatalytic degradation over the Fe2O3/TiO2 cata-
lyst and its corresponding individual catalytic system are
shown in Fig. 10. Under visible light irradiation, both Fe2O3
and TiO2 could generate e−/h+ pairs. However, the charge
recombination is dominant in TiO2 (Fig. 10a), leading to a
low generation of active species and, as a consequence, to
poor photocatalytic degradation. On the contrary, the charge
recombination process in Fe2O3 is not as efective as that in
TiO2 (Fig. 10b), therefore, the electron in the conduction
band (CB) could further react with molecular oxygen (O2)
to form *O2− and/or *OH. At the same time, the positive hole
−
the electrons react with dissolved (O2) to form (∙O2 ) and
•
further produce OH. On the other hand, the holes gener-
ated on the VB of Fe2O3 can easily transfer to that of TiO2
inducing an efective charge separation and transfer. Then
the positive charge hole (h+) on Fe2O3 surfaces reacts with
H2O to generate OH.
Through this process, the recombination of photo-gen-
erated electrons and holes is inhibited to a certain extent
1 3

Journal of the Iranian Chemical Society
and/or OH− to produce *OH. Although many types of active
species could be generated, the results clearly reveal that the
valence band hole (h+)is the main active species in the Fe2O3
system. Upon coupling Fe2O3 with TiO2, an efcient e−/h+
charge transfer between the two materials and an enhanced
visible light absorption ability due to the presence of TiO2
would greatly increase the formation of these active spe-
cies (Fig. 9c), leading to an improved photocatalytic activ-
ity. Although the photo-generated*O2− and OH also help
*
degrade the MB dye, the main degradation mechanism is
found to occur via direct oxidation through the holes.
Figure 11 shows the band gap structure and the possi-
ble charge carrier transfer between Fe2O3 and TiO2 under
visible light radiation. Before the contact between the two
semiconductors (Fig. 9a), the conduction band (CB) of TiO2
lies over the CB of α-Fe2O3. The valence band (VB) and
CB edges of Fe2O3 and TiO2 are determined using two for-
mulas EVB =χ −Ee+0.5 Eg and ECB =EVB −Eg. [40–42],
where Eg, Ee and χ represent the band gap energy of the
semiconductor, the energy of free electrons (about 4.5 eV)
and the electronegativity of the semiconductor, respectively.
The χ values for TiO2 and Fe2O3 are 5.83 eV and 5.88 eV,
respectively [43]. After substituting χ into the equation, the
EVB of TiO2 and Fe2O3 are found to be 2.93 eV and 2.35 eV,
respectively. Therefore, the CB potentials of TiO2 and Fe2O3
were calculated to be (−0.27 eV) and (0.4 eV), respectively.
After coupling TiO2 with Fe2O3 to form the p-n heterojunc-
tion, the Fermi level of Fe2O3 was dragged upwards, while
the Fermi level of TiO2 was dragged downwards, until they
were at the same level and reached equilibrium [29, 44].
Fig. 9 a Mott-Schottky plots of the TiO2 and Fe2O3/TiO2electrodes
measured in a0.1 M NaOH electrolyte (frequency 1000 Hz). b Sche-
matic diagram of the band confguration and fat band of TiO2 and the
Fe2O3/TiO2/FTO heterostructure under visible light irradiation
(h+)in the valence band (VB) could either directly oxidize
the organic dye or react with an adsorbed water molecule
Fig. 10 Proposed photocatalytic processes for the a TiO2, b Fe2O3 and c Fe2O3/TiO2/FTO systems
1 3

Journal of the Iranian Chemical Society
Fig. 11 Schematic illustration
of the MB degradation mecha-
nism under visible light irradia-
tion on the surface of the Fe2O3/
TiO2/FTO heterojunction
penetration of ions into the material’s pores due to the fast
potential change at a high scan rate.
Electrochemical performances
Efect of scan rate
At the same scan rate, the current intensity of the Fe2O3/
TiO2coupled system is greater than that observed in the
Fe2O3 nanomaterials. This indicates the enhanced capaci-
tance of the Fe2O3/TiO2 nanocomposite.
To examine the electrochemical performance of the Fe2O3
and Fe2O3/TiO2 nanostructures as potential electrode mate-
rial for supercapacitors, cyclic voltammetry (CV) tests were
performed in a three-electrode cell with Na2SO4 aqueous
electrolyte at various scan rates from 100 to 500 mVs−1(vs.
Hg/HgO) (shown in Fig. 12a-b). The CV curves of Fe2O3
and the Fe2O3/TiO2 electrodes don’t show cathodic and
anodic peaks, suggesting an ideal capacitive behavior. At a
high scan rate, broader curves are obtained than at a lower
scan rate, where nearly rectangular shaped curves are seen.
In addition, it was found that as the scan rate increases from
100 to 500 mVs−1, the current intensity gradually increases
indicating that the electron transport is faster.
Cycling stability
Cycling stability is another critical factor in evaluating the
electrochemical properties of supercapacitors. Figure 13a,
b gives the current response as a function of the potential
applied to the working electrode, recorded at 100 mV/s in
a potential range between −0.8 V and −0.4 V. In this fg-
ure, the voltammograms represent the superposition of 1000
cycles of the Fe2O3/TiO2 nanocomposite in the Na+-system.
Therefore, the Fe2O3/TiO2 nanocomposite shows electro-
chemical and structural stability during redox cycling.
The specifc capacitance (C, F.g−1), of the electrode was
calculated from the CV curves, according to the following
equation [45–47]:
Figure 10a, b shows the CV curves of the Fe2O3 and
α-Fe2O3/TiO2 electrodes obtained in a 1 M solution of
Na2SO4 electrolyte under a series of scan rates increasing
from 100 to 500 mVs−1. In both cases, with the increase in
the scan rate, the shapes of the CV curves basically remain
the same, indicating the good and fast charge–discharge
property of the Fe2O3 and α-Fe2O3/TiO2 electrodes. The
shape of the CV curves is quasi-rectangular without any
redox peaks, indicating their capacitive behavior. It can
be seen from Fig. 10 that the area under the CV curves
increases as the scan rate increases. The distortion of the
curves in high scan rates could be the result of the increased
electrode resistance.
ꢀ I(V)d(V)
C =
(1)
mꢀΔV
The variation of the specifc capacity values of the Fe2O3
and Fe2O3/TiO2nanocomposites with cycle number at ambi-
ent temperature is shown in Fig. 10.
The Fe2O3 nanomaterial electrode that presents the spe-
cifc capacity values decreasing from 43 F.g−1 to 35 F.g−1
after 1000 cycles retains a stability of 81%. This drop may
be associated with the loss of active electrode material dur-
ing charging [48, 49]. However, as observed in Fig. 14, the
TiO2/Fe2O3 nanocomposite electrode exhibited noticeable
improvement compared to the Fe2O3one. The initial spe-
cifc capacity value of the Fe2O3/TiO2 nano-hybrid electrode
As seen in Fig. 12c, both curves show similar specifc
capacitance trends, where the specifc capacitance values
decrease with increasing scan rate. This could be associated
with the difusion rate of electrolyte ions, since at lower scan
rates the electrolyte ions have sufcient time to penetrate the
pores of the material, while the higher scan rates limit the
1 3

Journal of the Iranian Chemical Society
Fig. 12 Typical cyclic voltammograms of the samples recorded in an electrolyte solution of Na2SO4at diferent scanning speeds for a Fe2O3 and
b the Fe2O3/TiO2 nanocomposite, c Specifc capacitance of the α-Fe2O3 and α-Fe2O3/TiO2 electrodes at various scan rates
Fig. 13 Cyclic voltammograms of a Fe2O3, b Fe2O3/TiO2at a scanning speed of ν=100 mV/s
1 3

Journal of the Iranian Chemical Society
behavior of the Fe2O3/TiO2 nanocomposite was evaluated
using the degradation of methylene blue (MB) under sun-
light irradiation for pollution prevention. The results proved
that the Fe2O3/TiO2 heterojunction has a higher removal
efciency of MB and stronger photo-response under visible
light irradiation. Compared to both pure TiO2 and Fe2O3,
the Fe2O3/TiO2photocatalyst had enhanced photocatalytic
abilities. These abilities of the Fe2O3/TiO2 heterojunction
can be ascribed to the synergetic efects between the TiO2
with active facets and the Fe2O3. This unique heterostruc-
ture improved the electron–hole separation efciencies and
enhanced the visible light response. Based on our results,
*
*
−
it should be noted that OH, O2 and the holes h+played
a vital role and enhanced the photocatalytic reaction. This
work shows that combining the heterojunction with mor-
phology engineering is a promising way to produce ef-
cient photocatalysts. During the cyclo-voltammetry study,
the Fe2O3/TiO2 nanocomposite showed electrochemical
and structural stability. Fe2O3/TiO2 exhibits excellent elec-
trochemical properties and could have applications in the
development of high-power anode materials for Li and Na-
ion batteries.
Fig. 14 Variation of the specifc capacity of Fe2O3and Fe2O3/TiO2af-
ter 1000 cycles
was found to be around 90 F.g−1. A sharp initial loss was
observed in the frst 200 cycles, beyond which the electrode
was found to be stable. In spite of this loss, the specifc
capacitance of Fe2O3/TiO2 at longer cycles presented a
smooth decrease at around 82 F g−1. This smooth decrease
in the cyclic performance of the Fe2O3/TiO2 electrodes could
be attributed to the low electrical conductivity and the iron
oxide aggregation during the charging/discharging process.
The Fe2O3/TiO2 nanocomposite has a specifc capacity of
82 F g−1 and shows a higher capacitance (almost 2.5 times
higher) than Fe2O3. Such an improvement in the electro-
chemical performance could be explained by:
References
1. T.N. Veziroglu, S. Sahin, 21 st century’s energy: hydrogen energy
system. Energy Convers. Manag. 49, 1820–1831 (2008)
2. K. Nakata, T. Ochiai, T. Murakami, A. Fujishima, Electrochim.
Acta 84, 103–111 (2012)
3. J. Zhao, B. Liu, L. Meng, S. He, R. Yuan, Y. Hou, Z. Ding, H. Lin,
Z. Zhang, X. Wang, J. Long, Plasmonic control of solar-driven
CO2 conversion at the metal/ZnO interfaces. Applied Catalysis B:
Environmental 256, 117823 (2019)
(1) The particle size: Due to their small size, Na+ ions have
a shorter path length difusion, which could facilitate
the electrolyte penetration by providing a large reaction
surface area and more active sites for electrochemical
reactions, which facilitates fast charge transport access.
(2) The synergistic efect between the two components
would lead to a fast ion/electron transfer and enhanced
fexibility, which could heavily improve the transport
characteristics during energy storage.
4. J. Long, H. Chang, G. Quan, X. Jie, L. Fan, S. Wang, Y. Zhou,
W. Wei, L. Huang, X. Wang, P. Liu, W. Huang, Gold-plasmon
enhanced solar-to-hydrogen conversion on the 001 facets of
anatase TiO2nanosheets. Energ. & Environ. Sci. 7, 973–977
(2014)
5. L. Meng, Z. Chen, Z. Ma, S. He, Y. Hou, H.-H. Li, R. Yuan, X.-H.
Huang, X. Wang, X. Wang, J. Long, Gold Plasmon-Induced Pho-
tocatalytic Dehydrogenative Coupling of Methane to Ethane on
Polar Oxide Surfaces. Energ. & Environ. Sci. 11, 294–298 (2018)
6. X. Jie, L. Luo, G. Xiao, Z. Zhang, H. Lin, X. Wang, J. Long,
Layered C3N3S3 polymer/graphene hybrids as metal-free catalysts
for selective photocatalytic oxidation of benzylic alcohols under
visible light. ACS Catal. 4, 3302–3306 (2014)
(3) The TiO2 structure is characterized by the combination
of a sufcient intercalation capacity with a good cyclic
stability due to the low volume expansion (<4%) [50,
51].
7. C.C. Wang, Y. Zhan, Z.Y. Wang, ChemistrySelect 3, 1713–1718
(2018)
8. H. Zhang, L. Ma, J. Ming, B. Liu, Y. Zhao, Y. Hou, Z. Ding, X.
Chao, Z. Zhang, J. Long, Amorphous Ta2OxNy-enwrapped TiO2
rutile nanorods for enhanced solar photoelectrochemical water
splitting. Appl. Catal. B: Environ. 243, 481–489 (2019)
9. R.L. Spray, K.J. McDonald, K.S. Choi, Enhancing photoresponse
of nanoparticulate alpha-Fe2O3 electrodes by surface composition
tuning. J. Phys. Chem. C 115(8), 3497–3506 (2011)
Conclusion
TiO2, Fe2O3 hematite nanoparticles and Fe2O3/TiO2 nano-
composites were synthesized via a simple hydrothermal pro-
cess. The efect of temperature and reaction time on the mor-
phology of the products was investigated. The photocatalytic
10. A. Umar, M. Abaker, M. Faisal, S.W. Hwang, S. Baskoutas, S.A.
Al-Sayari, High-yield synthesis of well-crystalline alpha-Fe2O3
1 3

Journal of the Iranian Chemical Society
nanoparticles: structural, optical and photocatalytic properties. J.
Nanosci. Nanotechnol. 11(4), 3474–3480 (2011)
30. C. Wei, Z. Maojin, R. Xiaosai, M. Andrew, Synthesis and photo-
catalytic activity of monolithic Fe2O3/TiO2. S. Afr. J. Chem. 70,
127–131 (2017)
11. Y. Cong, Z. Li, Z. Yi, W. Qi, X. Qian, Synthesis of α-Fe2O3/TiO2
nanotube arrays for photoelectro-Fenton degradation of phenol.
Chem. Engin. J. 191, 356–363 (2012)
31. M.R. Mohammed, M.A. Abdullah, E.Y. Tamer, M.M. Hadi,
Photocatalytic degradation of remazol brilliant orange 3R using
wet-chemically prepared CdO-ZnO nanofbers for environmental
remediation. Mater. Express. 6, 137–148 (2016)
12. L. Rong, J. Yuefa, W. Jun, Z. Qiang, Photocatalytic Degradation
and Pathway of Oxytetracycline in Aqueous Solution by Fe2O3/
TiO2 Nanopowders. RSC Adv. 51, 1–9 (2015)
32. W. Liugang, Z. Junying, L. Chunzhi, Z. Hailing, W. Wenwen, W.
Tianmin, Synthesis, characterization and photocatalytic activity of
TiO2 flm/Bi2O3 microgrid heterojunction. J. Mater. Sci. Technol.
27, 59–63 (2011)
13. Y. Zhang, Y. Tang, W. Li, X. Chen, Nanostructured TiO2-based
Anode Materials for High-performance Rechargeable Lithium ion
Batteries. Chem. NanoMat. 2, 764–775 (2016)
14. H. Ren et al., Multishelled TiO2 hollow microspheres as anodes
with superior reversible capacity for lithium ion batteries. Nano
Lett. 14, 6679–6684 (2014)
33. Z. Panpan, L. Zhanggao, X. Yu, F. Jing, X. Jiangwei, Studies on
facile synthesis and properties of mesoporous CdS/TiO2 com-
posite for photocatalysis applications. J. Alloys. Compd. 692,
170–177 (2017)
15. Y. Ren et al., Nanoparticulate TiO2 (B): an anode for lithium-ion
batteries. Angew. Chem. Int. Ed. 51, 2164–2167 (2012)
16. L. Zhang, H.B. Wu, X.W.D. Lou, Iron-oxide-based advanced
anode materials for lithium–ion batteries. Adv. Energy. Mater. 4,
1300958 (2014)
34. S.D. Deldkar, H.M. Yadav, S.N. Achary, S.S. Meena, S.H. Pawar,
Structural refnement and photocatalytic activity of Fe-doped
anatase TiO2 nanoparticles. Appl. Surf. Sci. 263, 536–545 (2012)
35. Z. Chen, H.N. Dinh, E. Miller, Photoelectrochemical water split-
ting (Springer, New York, 2013), pp. 49–61
17. T. Jiajia, H. Meiling, Z. Miao, C. Xiaoshuang, S. Zhaoqi, Efects
of growth substrate on the morphologies of TiO2 hierarchical
nanoarrays and their optical and photocatalytic properties. J.
Mater. Sci.: Mater. Electron. 27, 2103–2107 (2016)
36. L. Yin, Y. Xia, Core-shell structured α-Fe2O3@TiO2 nanocom-
posites with improved photocatalytic activity in visible light
region. Phys. Chem. Chem. Phys. 42, 1–7 (2013)
18. N. Zlatko, K. Demie, L. Leonardo, W. Tianlong, A.B. Ryan, D.O.
Samuel, L.G. Pedro, M.R. Quentin, F.L.E. Richard, M. Sara, K.L.
Vlado, Origin of reduced magnetization and domain formation in
small magnetite nanoparticles. Sci. Rep. 7, 5291 (2017)
19. T. Jiajia, Y. Guang, C. Yunlang, Z. Miao, L. Jianguo, S. Shiwei,
H. Gang, J. Xishun, C. Xiaoshuang, S. Zhaoqi, Enhanced opti-
cal and photocatalytic properties of Ag quantum dots-sensitized
nanostructured TiO2/ZnOheterojunctions. J. Alloys Compd. 688,
605–612 (2016)
37. G.L. Jian, B.G. Wan, H. Kai, B.Z. Jian, M.M. Fan, P.S. Xue, Q.S.
Zhao, Efect of annealing temperature on photocatalytic activ-
ity of ZnO thin flms prepared by sol–gel method. Superlattice.
Microstruct. 50, 98–106 (2011)
38. J. Aslam, M.R. Mohammed, F. Mohammed, B.K. Sher, Studies
on photocatalytic degradation of acridine orange and chloroform
sensing using as-grown antimony oxide. Microstruct. Mater. Sci.
Appl. 2, 676–683 (2011)
39. L.P. Zhu, N.C. Bing, D.D. Yang, Y. Yang, G.H. Liao, L.J. Wang,
Synthesis and photocatalytic properties of core–shell structured
α-Fe2O3@SnO2shuttle-like nanocomposites. Cryst. Eng. Com-
mun. 13, 4486–4490 (2011)
20. D. Lee, Y. Rho, F. Allen, A. Minor, S.H. Ko, C. Grigoropoulos,
Synthesis of hierarchical TiO2 nanowires with densely-packed and
omnidirectional branches. Nanoscale (2013)
21. Y. Meidan, L. Hsiang-Yu, L. Changjian, L. Zhiqun, Hierarchical
rutile TiO2 fower cluster-based high efciency dye-sensitized
solar cells via direct hydrothermal growth on conducting sub-
strates. Small 9, 312–321 (2013)
40. X. Zhang, L. Zhang, T. Xie, D. Wang, Low-temperature synthe-
sis and high visible-light-induced photocatalytic activity of BiOI/
TiO2 heterostructures. J. Phys. Chem. C 113, 7371–7378 (2009)
41. X. Lin, J. Xing, W. Wang, Z. Shan, F. Xu, F. Huang, Photocata-
lytic activities of heterojunction semiconductors Bi2O3/BaTiO3:
a strategy for the design of efcient combined photocatalysts. J.
Phys. Chem. C 111, 18288–18293 (2007)
22. G.C. Hyun, S. Jieun, S.K. Hyun, S. Woonsup, B.Y. Kyung, S.K.
Young, Facile preparation of Fe2O3 thin flm with photoelectro-
chemical properties. Chem. Commun. 47, 2441–2443 (2011)
23. T. Wen-Feng, Y. Ya-Ting, W. Ming-Xia, L. Fan, K.K. Luuk, Shape
evolution synthesis of monodisperse spherical, ellipsoidal, and
elongated hematite (α-Fe2O3) nanoparticles using ascorbic acid.
Cryst. Growth Des. 14, 157–164 (2014)
42. M.A. Butler, D.S. Ginley, Prediction of fatband potentials at sem-
iconductor-electrolyte interfaces from atomic electronegativities.
J. Electrochem. Soc. 125, 228–232 (1978)
43. M.A. Butler, D.S. Ginley, Prediction of fatband potentials at sem-
iconductor-electrolyte interfaces from atomic electronegativities.
J. Electrochem. Soc. 125(2), 228–232 (1978)
24. H. Xia et al., Hierarchical TiO2-B nanowire@α-Fe2O3nanothorn
core-branch arrays as superior electrodes for lithium-ion microbat-
teries. Nano Res 7, 1797–1808 (2014)
44. M. Niu, F. Huang, L. Cui, P. Huang, Y. Yu, Y. Wang, Hydro-
thermal synthesis, structural characteristics, and enhanced pho-
tocatalysis of SnO2/α-Fe2O3 semiconductor nanoheterostructures.
ACS Nano 4, 681–688 (2010)
25. J. Luo et al., Rationally designed hierarchical TiO2@Fe2O3 hol-
low nanostructures for improved lithium ion storage. Adv. Energy
Mater. 3, 737–743 (2013)
26. T. Yamashita, P. Hayes, Analysis of xps spectra of Fe2+ and Fe3+
ions in oxide materials. Appl. Surf. Sci. 254, 2441–2449 (2008)
27. J. Tauc, R. Grigorovici, A. Vancu, Optical properties and elec-
tronic structure of amorphous germanium. Phys. Stat. Sol. 15,
627–637 (1966)
45. Y. Zhao, Y. Meng, P. Jiang, Carbon@MnO2 core-shell nano-
spheres for fexible high-performance supercapacitor electrode
materials. J. Power Sources 259, 219–226 (2014)
46. S.S. Shinde, G.S. Gunda, D.P. Dubal, S.B. Jambure, C.D.
Lokhande, Morphological modulation of polypyrrole thin flms
through oxidizing agents and their concurrent efect on superca-
pacitor performance. Electrochim. Acta 119, 1–10 (2014)
47. D. Qu, H. Shi, Studies of activated carbons used in double-layer
capacitors. J. Power Sources 74, 99–107 (1998)
28. S. Yang, X. Quan, X. Li, Y. Liu, S. Chen, G. Chen, Preparation,
characterization and photoelectrocatalytic properties of nanocrys-
talline Fe2O3/TiO2, ZnO/TiO2and Fe2O3/ZnO/TiO2 composite
flm electrodes toward pentachlorophenol degradation. Phys.
Chem. Chem. Phys. 6, 659–664 (2004)
48. B. Babakhani, D.G. Ivey, Anodic deposition of manganese oxide
electrodes with rod-like structures for application as electrochemi-
cal capacitors. J. Power Sources 195, 2110–2117 (2010)
29. P. Linlin, X. Tengfeng, L. Yongchun, F. Haimei, W. Dejun, Syn-
thesis, photoelectric properties and photocatalytic activity of the
Fe2O3/TiO2 heterogeneous photocatalysts. Phys. Chem. Chem.
Phys. 12, 8033–8041 (2010)
1 3

Journal of the Iranian Chemical Society
49. B.S. Singu, K.R. Yoon, Porous manganese oxide nanospheres for
pseudocapacitor applications. J. Alloys. Compd. 695, 771–778
(2017)
51. R. Kirchgeorg, M. Kallert, N. Liu, R. Hahn, M.S. Killian, P.
Schmuki, Key factors for an improved lithium ion storage capac-
ity of anodic TiO2 nanotubes. Electrochimica Acta. 198, 56–65
(2016)
50. Y. Zhou, L. Cao, F. Zhang, B. He, H. Li, Lithium insertion into
TiO2 nanotube prepared by the hydrothermal process. J. Electro-
chem. Soc. A 150, 1246 (2003)
1 3