Hydrothermal synthesis of BiOBr/FeWO4 composite photocatalysts and their photocatalytic degradation of doxycycline

Article abstract of DOI:10.1016/j.jallcom.2017.10.092

Novel BiOBr/FeWO₄ composite photocatalysts were fabricated using the solvothermal method to degrade doxycycline under visible light irradiation. The crystalline structures, morphology, chemical composition, chemical bonding, energy band gap and

Full text of DOI:10.1016/j.jallcom.2017.10.092

Accepted Manuscript
Hydrothermal synthesis of BiOBr/FeWO composite photocatalysts and their
4
photocatalytic degradation of doxycycline
Jiacong Gao, Yu Gao, Zhenying Sui, Zhibo Dong, Siyu Wang, Donglei Zou
PII:
S0925-8388(17)33526-0
10.1016/j.jallcom.2017.10.092
JALCOM 43489
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 22 June 2017
Revised Date: 11 October 2017
Accepted Date: 12 October 2017
Please cite this article as: J. Gao, Y. Gao, Z. Sui, Z. Dong, S. Wang, D. Zou, Hydrothermal synthesis of
BiOBr/FeWO composite photocatalysts and their photocatalytic degradation of doxycycline, Journal of
4
Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.10.092.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Hydrothermal synthesis of BiOBr/FeWO composite photocatalysts
4
and their photocatalytic degradation of doxycycline
Jiacong Gao, Yu Gao, Zhenying Sui, Zhibo Dong, Siyu Wang, Donglei
Zou*
Key Laboratory of Groundwater Resources and Environment, Ministry of Education,
Jilin University, Changchun 130021, China
E-mail
ꢀ Zoudl@jlu.edu.cn
ABSTRACT
Novel BiOBr/FeWO composite photocatalysts were fabricated using the
4
solvothermal method to degrade doxycycline under visible light irradiation. The
crystalline structures, morphology, chemical composition, chemical bonding,
energy band gap and photocatalytic properties of the samples were characterized
by XRD, SEM, TEM, EDS, XPS, FT-IR and UV-Vis DRS. The BiOBr/FeWO4
composite photocatalysts with different molar mass ratios exhibited higher
photocatalytic degradation efficiency of doxycycline than pure BiOBr and
FeWO , and the best photocatalytic degradation performance of 90% in 1 h was
4
found for BiOBr/FeWO (4:1). XPS and FT-IR analyses revealed the elemental
4
composition, corresponding hybrid orbitals and possible chemical bonds. The
DRS results indicated that FeWO enhanced the light response range of BiOBr.
4
-
The generation of O and holes was promoted by inhibiting the recombination of
2
photogenerated carriers, which could lead to the higher photocatalytic activity.
Keywords: BiOBr; FeWO4; doxycycline; photocatalytic; degradation;
photogenerated carriers
1
. Introduction
Antibiotics abuse is a serious problem in our country and globally [1]. Doxycycline
is a well-known tetracycline antibiotic that can inhibit upper respiratory tract infections,
tonsillitis, biliary tract infections and other diseases caused by gram-positive bacteria
and gram-negative bacilli [2,3]. However, excessive use of antibiotics can accelerate
1

ACCEPTED MANUSCRIPT
the spread of drug-resistant bacteria, reduce human immunity and pose a threat to the
environment [4-6]. Doxycycline has been detected in ground water and surface water,
and the degradation of tetracycline by traditional wastewater treatment plants is not
satisfactory [7,8]. Increasing attention has focused on the pollution of doxycycline, and
finding a solution for the doxycycline pollution is the most pressing need in this field
[
9-11].
In recent years, photocatalytic technology has shown a good ability to degrade
antibiotics [12,13]. Bismuth-based photocatalysts have attracted extensive attention due
to their unique bedded structures and high visible-light response properties [14].
Bismuth-based photocatalysts such as BiOBr [15], Bi WO [16], Bi O [17], BiVO [18]
2
6
2
3
4
3
+
2
and Bi S [19] have attracted great attention because their Bi ions have a full 6s
2
3
electron configuration and because these Bi-containing compounds have small band
gaps. The direct-gap semiconductor characteristics and the effective control of the
separation of photogenerated carriers are also attractive for applications and have drawn
attention to Bi-based photocatalysts. However, the high electron-hole pair
recombination rate and low photocatalytic performance limit the development of BiOBr
[
20-22]. Addressing these shortcomings, some researchers have found that the
photocatalytic activity can be improved by using composite semiconductors, noble
metal sedimentation, ion doping and photosensitization, and other approaches [23-25].
Up-conversion phosphors/BiOBr composites show good responsive photocatalysis
under visible, UV and near infrared (NIR) lights because the close integration of up-
conversion phosphors and BiOBr strengthens the effective energy transfer. The (Yb,
Tm)-NaYF /BiOBr and (Yb, Er)-NaYF /BiOBr composites show good quantum
4
4
removal efficiencies of NO, reaching 2.52 and 1.92%, respectively, under NIR light
[
26]. In particular, the creation of composites with different semiconductors to construct
2

ACCEPTED MANUSCRIPT
heterojunctions has become a popular research topic. For example, a BiOBr/CeO p-n
2
heterojunction was successfully prepared to investigate the degradation efficiency for
rhodamine B, methylene blue and phenol under visible light, and it was shown that
BiOBr/CeO exhibits superior photocatalytic activity, which was attributed to the
2
effective carriers separation [27]. The BiOBr Cl1-x (0 ꢁ x ꢁ 1) nanoflakes were
x
synthesized by a microwave-assisted synthesis method, and they exhibited high
photocatalytic activity for degrading rhodamine B (RHB), Natural Red 4 (N-Red) and
pentachlorophenol (PCP).
The photocatalytic degradation mechanism of both direct and indirect photocatalytic
pathways can be affected by the BiOBr Cl1-x (0 ꢁ x ꢁ 1) photocatalyst [28].
x
Ag/AgBr/BiOBr microplates were shown to degrade 74% of levofloxacin in 90 min,
-
+
and the high catalytic efficiency may be attributed to the reduced e /h recombination
29].
FeWO is one of the most important components of tungsten ore. FeWO is a
[
4
4
semiconductor with a band gap of approximately 1.8 eV, showing a wide range of light
response and playing an important role in magnetic materials and humidity sensitive
transmission, especially in photocatalysts [30-32]. For example, FeWO nanoparticles
4
were decorated on the surface of WS nanotubes, and the growth mechanism and
2
magnetic behaviour of the hybrid nanostructures were measured by XRD, electron
microscopy and other techniques. The orientation and position of hybrid nanostructures
can be changed by using non-viscous solvents, such as ethanol [33].
FeWO @ZnWO /ZnO was prepared using a two-step hydrothermal method, and it
4
4
showing higher photocatalytic activity in the photocatalytic degradation of methylene
blue, rhodamine B and phenol than pure FeWO and ZnWO /ZnO substrate. Hydroxyl
4
4
radicals (•OH) play a major role in this process [34]. The nitrogen-doped RGO-
3

ACCEPTED MANUSCRIPT
FeWO /Fe O (NRGO-FeWO /Fe O ) ternary composite photocatalyst was used to
4
3
4
4
3
4
degrade methylene blue dye and 4-nitrophenol (4-NP) and still showed excellent
efficiency and stability after 10 consecutive cycles [35]. However, FeWO exhibits a
4
-
+
high e / h recombination rate that limits its application in photocatalysis [36]. In this
work, BiOBr and BiOBr/FeWO microspheres were successfully prepared. The
4
prepared BiOBr/FeWO photocatalysts showed a greater range of light response
4
compared to pure BiOBr. We used various characterization techniques to analyse the
crystal structures, morphology characteristics, elemental composition, chemical bonding
and photocatalytic mechanism. The BiOBr/FeWO photocatalysts were successfully
4
fabricated to examine the role they play in pollutant degradation, and their effect on the
separation of electron-hole pairs was discussed.
2
. Experiment
2
.1 Synthesis of BiOBr/FeWO photocatalysts
4
Pure BiOBr was prepared by the solvothermal method. First, 4 mmol
Bi(NO ) ·5H O and 6 mmol [C16Mim]Br were each dissolved in 80 ml of ethylene
3
3
2
glycol monomethyl ether. Then, the two solutions were mixed, stirred and transferred to
a 200-ml Teflon steel autoclave with a filling volume of 80% at 160°C﹤for 12 h. The
autoclave was cooled to room temperature, and the prepared solution was centrifuged
and washed 3 times with ethanol and deionized water. Finally, the samples were dried at
6
0°C for 12 h.
FeWO was prepared by the hydrothermal method. First, 2 mmol FeCl ·6H O and 2
4
3
2
mmol Na WO ·2H O were each dissolved in 80 ml of distilled water. Then, the two
2
4
2
solutions were mixed, and 4 mmol of L-cysteine was added into the solution evenly and
4

ACCEPTED MANUSCRIPT
transferred to a 200-ml Teflon steel autoclave at 170°C for 24 h. The samples were
washed 3 times with ethanol and deionized water and dried at 60°C for 12 h.
The BiOBr/FeWO composite photocatalysts with different molar mass ratios were
4
synthesized by the solvothermal method. The 4 mmol of FeWO prepared as described
4
above was dispersed in 40 ml of ethylene glycol monomethyl ether. Then, 4 mmol
Bi(NO ) ·5H O (BiOBr/FeWO molar mass ratios were set as 1:1, 2:1, 4:1 and 8:1) and
3
3
2
4
6
mmol [C16Mim]Br were dissolved in 70 ml of ethylene glycol monomethyl ether.
The three solutions were mixed and poured into a 200-ml Teflon steel autoclave at
60°C for 12 h. When the reactor was cooled, the photocatalysts were washed 3 times
with ethanol and deionized water and dried at 60°C for 12 h.
1
2
.2 Characterization of photocatalysts
The crystal structures of the photocatalysts were evaluated by X-ray diffraction
(XRD, D/MAX 2500PC, CuKα, Rigaku Co, Tokyo, Japan) operating at 40 kV and 100
mA in the range of 2θ = 0-80°. The morphology characteristics of the photocatalysts
were examined by scanning electron microscopy (SEM, S-4800, Hitachi, Japan).
Transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and
selected area electron diffraction (SAED) images were observed using an F20
transmission electron microscope (FEI Company, USA). Energy dispersive X-ray
spectroscopy (EDS) and mapping of the BiOBr/FeWO (4:1) samples were performed
4
using a Thermo NORAN 7 instrument. The X-ray photoelectron spectra (XPS) of the
composite photocatalysts were collected using a Kratos AXIS-ULTRA DLD. The
chemical bonds and functional groups of the samples were determined using Fourier
-1
transform infrared (FT-IR) spectroscopy (Nexus 870 FT-IR) in the 4000–400 cm range.
UV-Vis diffuse reflectance spectra (DRS) of the samples were examined using a
5

ACCEPTED MANUSCRIPT
Shimadzu UV-Vis 2450 spectrophotometer with BaSO used as the reference.
4
2
.3 Photocatalytic experiments
The photocatalytic instrument used in this experiment was Lightcube 2.3 (Beijing
PerfectLight, China), and the light source was a 300 W Xenon lamp with a 400-nm
cutoff filter. To investigate the photocatalytic activity, 0.1 g of pure BiOBr, FeWO , and
4
the different molar mass ratios of BiOBr/FeWO were correspondingly added to 100 ml
4
of doxycycline. All samples reached absorption–desorption equilibrium with
doxycycline wastewater in the dark for 30 min. The absorption peak of doxycycline was
observed at 274 nm using a UV-2450 UV-Vis spectrophotometer. After the reaction, a
5
-ml suspension was centrifuged using a high-speed centrifuge at 2000 rpm for 5 min to
analyse the photocatalytic activity [37,38]. The photodegradation efficiency and kinetic
equation of doxycycline were calculated as follows:
Η = (C -C)/C ×100%
(1)
(2)
0
0
ln(C /C) = kt
0
where C is the initial concentration of doxycycline, C is the concentration of
0
doxycycline at some time and k is the apparent reaction rate constant.
3
. Results and discussion
3
.1 Crystal structures of BiOBr/FeWO4
The XRD patterns of BiOBr, FeWO and BiOBr/FeWO at different molar ratios are
4
4
shown in Fig. 1. The prepared BiOBr and FeWO exhibited a series of distinct
4
diffraction peaks, which were indexed to pure phase BiOBr (JCPDS card no. 73-2061)
and pure phase FeWO (JCPDS card no. 85-1354), respectively. The sharpest
4
6

ACCEPTED MANUSCRIPT
diffraction peak was located at 2θ = 32.3
°
and can be indexed to the (110) plane of
tetragonal BiOBr preferential growth. BiOBr/FeWO photocatalysts with different
4
molar mass ratios showed the characteristic diffraction peaks attributed to the (110),
(200), and (212) planes of tetragonal BiOBr and the characteristic diffraction peaks
—
—
attributed to the (100), (111), and (221) planes of monoclinic FeWO . The crystallite
4
sizes of BiOBr, FeWO and BiOBr/FeWO with different molar mass ratios were
4
4
calculated by Scherrer’s equation as shown in Table 1. The results confirmed that when
the molar ratio of BiOBr/FeWO was 1:1, 2:1, 4:1 and 8:1, the crystallite size of the
4
photocatalysts decreased to 13.6 nm, 13.0 nm, 12.2 nm and 12.9 nm, respectively. The
crystallite size shifts were thought to facilitate the transfer of charge carriers. For the
BiOBr/FeWO samples, the intensities of the corresponding diffraction peaks of BiOBr
4
did not show significant changes and no other impurity characteristic peaks appeared.
This finding confirms that the BiOBr/FeWO samples are only composed of BiOBr and
4
FeWO4 phases. Thus, BiOBr/FeWO composite photocatalysts were prepared
4
successfully.
Table 1
Calculated crystallite sizes of photocatalysts with different molar mass
ratios (BiOBr/FeWO 1:1, BiOBr/FeWO 2:1, BiOBr/FeWO 4:1, BiOBr/FeWO 8:1
4
4
4
4
and BiOBr, FeWO4).
Sample
BiOBr
Crystallite size (200)/nm
14.7 nm
BiOBr/FeWO (1:1)
13.6 nm
4
BiOBr/FeWO (2:1)
13.0 nm
4
BiOBr/FeWO (4:1)
12.2 nm
4
7

ACCEPTED MANUSCRIPT
BiOBr/FeWO (8:1)
12.9 nm
10.9 nm
4
FeWO4
3
.2 Morphology characteristics of BiOBr/FeWO4
The morphology and microstructures of BiOBr and BiOBr/FeWO4 were
characterized by SEM, TEM, HRTEM and EDS. SEM images of BiOBr and
BiOBr/FeWO samples are shown in Figs. 2(a)-(e). It can be seen from Figs. 2(a)-(b)
4
that the morphology of pure BiOBr was composed completely of microspheres and that
the size of the BiOBr microspheres varied from 1 to 2 ꢀm. The BiOBr microsphere
structures consisted of numerous nanosheets with a diameter of approximately 18 nm,
as shown in Fig. 2(c). The BiOBr/FeWO had the same microsphere structures as those
4
observed in pure BiOBr in Figs. 2(d)-(e). The difference between these two samples
was that FeWO nanoparticles were distributed on the surface of BiOBr, as also shown
4
in the TEM image presented in Fig. 2(f). Fig. 3(a) presents the corresponding HRTEM
image of BiOBr/FeWO (4:1), and the lattice spacings with two different directions
4
were calculated to be 0.306 nm and 0.387 nm, corresponding to the (012) planes of
BiOBr and the (200) planes of FeWO , respectively. Fig. 3(b) shows the SAED image
4
of BiOBr/FeWO (4:1). Here, the bright red ring in the picture corresponds to the (006),
4
(020), and (011) crystal planes of the tetragonal BiOBr, and the bright yellow ring
—
corresponds to the (110), (210), and (111) crystal planes of the monoclinic FeWO . This
4
result is consistent with the XRD results shown in Fig. 1. Based on the EDS image in
Fig. 4(a) and the EDS mapping image in Fig. 4(b), Bi, Br, Fe, O and W elements were
uniformly distributed in the BiOBr/FeWO (4:1) composites, and the element contents
4
were very close to the theoretical values, indicating that BiOBr and FeWO were
4
8

ACCEPTED MANUSCRIPT
closely related to each other.
3
.3 XPS analysis
XPS was used to investigate the surface composition and chemical states, and the
XPS spectra of BiOBr, FeWO , BiOBr/FeWO (4:1) are shown in Figs. 5(a)-(g). The
4
4
XPS spectra of BiOBr, FeWO and BiOBr/FeWO (4:1) samples in Fig. 5(a) indicated
4
4
that Bi, O and Br were present on the BiOBr surface, that Fe, W and O were on the
FeWO surface, and that BiOBr/FeWO (4:1) composite photocatalysts were composed
4
4
of Bi, O, Br, Fe, W and C. Fig. 5(b) shows two strong peaks at 163.9 eV and 158.5 eV
3
+
attributed to Bi 4f and Bi 4f , respectively, corresponding to the Bi in tetragonal
5/2
7/2
BiOBr and BiOBr/FeWO (4:1). Fig. 5(c) displays the double peaks located at 68.5 eV
4
and 67.6 eV, corresponding to Br 3d3/2 and Br 3d , respectively. This result confirms
5/2
-
the presence of Br in tetragonal BiOBr and BiOBr/FeWO (4:1). The two peaks at the
4
binding energies of 712.3 eV and 710.6 eV could be related to Fe 2p1/2 and Fe2p3/2,
2
+
respectively, confirming that Fe
was included in monoclinic FeWO and
4
BiOBr/FeWO (4:1) in Fig. 5(d). The obvious W 4f binding energy peaks in Fig. 5(e) at
4
3
6.4 eV and 34.2 eV are related to W 4f and W 4f in FeWO and BiOBr/FeWO
5/2 7/2 4 4
(4:1) samples. In Fig. 5(f), the O 1s peaks are located at 535.5 eV, 534.2 eV, 532.9 eV
2
-
and 531.6 eV, and were assigned to the O , O-H, Bi-O, and Fe-O bonds, respectively.
The C 1s spectrum in Fig. 5(g) can be fitted into four peaks at 288.3 eV, 286.7 eV, 286
eV and 284.5 eV, corresponding to O-C=O, C=O, C-H and C-C bonds, respectively.
The four C 1s peaks could be ascribed to the (C H O ), (C H NO S) and ([C16Mim]Br)
3
8
2
3
7
2
reagents. In Figs. 5(b)-(g), all peaks showed slight changes to higher binding energies or
lower binding energies when BiOBr was combined with FeWO . These binding energy
4
shifts in the spectra could be attributed to the presence of strong interactions between
9

ACCEPTED MANUSCRIPT
BiOBr and FeWO that could facilitate charge transfer and reduce hole-electron
4
recombination.
3
.4 FT-IR analysis
FTIR spectra in the range of 4000–400 cm were recorded for BiOBr, FeWO and
-1
4
BiOBr/FeWO (4:1) and are shown in Fig. 6. BiOBr/FeWO (4:1) shows the
4
4
-1
-1
-1
-1
-1
-1
characteristic peaks at 2918 cm , 2849 cm , 1650 cm , 1465 cm , 1160 cm , 731 cm
-1
-1
-1
and 514 cm of pure BiOBr and the characteristic peaks at 1602 cm , 826 cm , and
-1
6
94 cm of monoclinic FeWO , which is in agreement with the XRD and XPS results.
4
-1
-1
The peaks at 2918 cm and 2849 cm were ascribed to C-H bond stretching [39], the
-1
-1
peaks at 1650 cm and 1602 cm were attributed to the C=C bond stretching [40], the
-1
-1
peak at 1465 cm was attributed to the C-N bond stretching [41], the peak at 1160 cm
-1
-1
was ascribed to C-C bond stretching [42], and the peaks at 731 cm and 514 cm were
2
4
-
ascribed to stretching vibrations of the Bi-O bonds [43]. FeWO exhibited WO
4
-1
-1
stretching for the peaks located at 826 cm and 694 cm . When BiOBr/FeWO (4:1)
4
was synthesized with BiOBr and FeWO , the peaks showed a slight shift, indicating that
4
the FeWO crystal particles were successfully observed on the BiOBr surface.
4
3
.5 UV–Vis DRS and band gap analysis
The UV–Vis absorption spectrum was investigated to analyse the light absorption
abilities of BiOBr, FeWO and BiOBr/FeWO at different molar ratios, and the obtained
4
4
results are displayed in Fig. 7(a). As expected, BiOBr merely responded to visible light,
and its optical absorption edge is located at approximately 430 nm. However, FeWO4
displayed light absorption over nearly the entire visible range. When BiOBr and FeWO4
are mixed with different molar mass ratios (1:1, 2:1, 4:1, 8:1), it was found that the
absorption edge had a clear redshift compared with pure BiOBr. This result illustrates
1
0

ACCEPTED MANUSCRIPT
that BiOBr/FeWO at different molar ratios can be excited, thereby generating more
4
charge carries under visible light irradiation.
The band gaps of the as-prepared samples were calculated by an approximation
method as shown in Fig. 7(b), and the band gaps of BiOBr, BiOBr/FeWO (1:1),
4
BiOBr/FeWO (2:1), BiOBr/FeWO (4:1) and BiOBr/FeWO (8:1) were found to be
4
4
4
2
.90 eV, 2.73 eV, 2.63 eV, 2.46 eV and 2.57 eV, respectively. FeWO shows an equal
4
absorbance over the whole spectrum; thus no meaningful band gap can be determined.
The band gap of BiOBr/FeWO with different molar ratios decreased after the
4
introduction of FeWO into BiOBr. The valence band (VB) and conduction band (CB)
4
edge positions of BiOBr and FeWO can be calculated according to the following
4
empirical equations:
e
E = X-E +0.5E
(3)
(4)
VB
g
E = E -E
g
CB
VB
where EVB and ECB are the VB and CB edge potentials, respectively, X is the
Mulliken electronegativity of a semiconductor oxide, which is the geometric mean of
e
the electronegativities of the constituent atoms, and the X value for BiOBr is 6.45 eV. E
is the energy of free electrons on the hydrogen scale (approximately 4.5 eV), and E is
g
the band-gap energy of BiOBr. The calculated EVB and ECB values for BiOBr are
approximately 3.40 eV and 0.50 eV, respectively.
3
.6 Photocatalytic activity
The photocatalytic degradation of doxycycline was investigated for photocatalysts
with different molar mass ratios (BiOBr/FeWO 1:1, BiOBr/FeWO 2:1, BiOBr/FeWO
4
4
4
4
:1, BiOBr/FeWO 8:1 and BiOBr, FeWO ) under visible-light illumination (λ> 420
4
4
1
1

ACCEPTED MANUSCRIPT
nm), and the removal rates of doxycycline were calculated and are summarized in Fig.
8
(a). After 30 min of dark irradiation, all the samples exhibited low absorbability in
doxycycline. FeWO exhibited a weak doxycycline photodegradation rate of 10.2%
4
under a 60-min visible light irradiation, and pure BiOBr showed a rate of 66.2% under a
6
0-min visible light irradiation. The photodegradation of BiOBr/FeWO with different
4
molar mass ratios (1:1, 2:1, 4:1, 8:1) reached 73.3%, 76.8%, 90.4% and 80.5% under a
0-min irradiation, respectively. The BiOBr/FeWO (4:1) composite photocatalysts
6
4
demonstrated superior photocatalytic activities in doxycycline degradation owing to the
suppression of the recombination of photogenerated electron–hole pairs. As shown in
Fig. 8(b), the degradation pathways of all the samples followed the pseudo-first-order
kinetic model.
-1
-1
-1
-1
The rate constants k were 0.0194 min , 0.0017 min ,0.0219 min , 0.0245 min ,
-1
-1
0
.0375 min and 0.0269 min for BiOBr, FeWO , BiOBr/FeWO (1:1), BiOBr/FeWO
4 4 4
(
2:1), BiOBr/FeWO (4:1) and BiOBr/FeWO (8:1), respectively. With the increase of
4 4
the BiOBr content, the photocatalytic activity of the BiOBr/FeWO composites reached
4
-1
the maximum at 0.0375 min until the BiOBr/FeWO molar mass ratio of 4:1, which
4
was found to be approximately 1.9 times higher than that of pure BiOBr, 1.7 times
higher than that of BiOBr/FeWO (1:1), 1.5 times higher than that of BiOBr/FeWO
4
4
(
2:1) and 1.4 times higher than that of BiOBr/FeWO (8:1). These results are attributed
4
to the fact that an excess of BiOBr may induce agglomeration, reduce the interfacial
region of heterojunctions, and act as composite centres to attract photogenerated
electrons and photogenerated holes. Thus, an excess of BiOBr can restrain the
photocatalytic activity of the composites. Under the same conditions, BiOBr/FeWO4
(4:1) was reused four times to degrade doxycycline, as shown in Fig. 8(c). It can be seen
1
2

ACCEPTED MANUSCRIPT
that even after 4 repeated tests, BiOBr/FeWO (4:1) composite photocatalysts still
4
showed excellent photocatalytic activity, stability and recyclability.
3
.7 Photocatalytic mechanism
Based on the above studies, we proposed the energy band structure, as shown in Fig.
, to explain the photocatalytic mechanism of BiOBr/FeWO4 (4:1). For the
9
photocatalytic reaction of BiOBr only under visible light irradiation, the electrons in the
BiOBr valence band moved from the VB to the CB, leaving holes in the VB. When
BiOBr was combined with FeWO , the photogenerated excited electrons in the CB of
4
FeWO transferred to the CB of BiOBr because the CB of FeWO (0.81 eV) was higher
4
4
than the CB of BiOBr (0.53 eV). Meanwhile, the photogenerated holes in the VB of
BiOBr transferred to the VB of FeWO because the VB of BiOBr (3.38 eV) was higher
4
than the VB of FeWO (2.64 eV). This process showed the effective separation of
4
photogenerated electron-hole pairs, which resulted in the change of the electric field at
-
the heterojunction. The transferred electrons could combine with O to generate O .
2
2
-
+
Both O and h are strong oxidants that can perform doxycycline degradation to form
2
H O and CO . Therefore, BiOBr/FeWO composites improved the charge separation
2
2
4
efficiency, and the degradation of doxycycline showed a high photocatalytic activity.
4
. Conclusions
In summary, BiOBr/FeWO composite photocatalysts were first successfully
4
synthesized using the solvothermal method. The BiOBr/FeWO samples with different
4
molar mass ratios all demonstrated excellent photocatalytic abilities. BiOBr/FeWO4
(4:1) degraded 90.4% of doxycycline in less than 1 h and exhibited superior
photocatalytic capability and excellent stability after four repeated cycles. The DRS
results indicated that FeWO enhanced the light response range of BiOBr and
4
1
3

ACCEPTED MANUSCRIPT
accelerated the separation of the carriers photogenerated under visible light. The
successfully fabricated BiOBr/FeWO photocatalysts may have great potential
4
applications for the treatment of organic waste and pharmaceutical wastewater.
Acknowledgements
The authors are grateful for the financial support from the Natural Science
Foundation and the Technology Department of Jilin province, China (20150101093C)
and the Technology Department Key Research of Jilin province, China
(20140204038SF).
References
[
1]. T. Van den Meersche, E. Van Pamel, C. Van Poucke, L. Herman, M. Heyndrickx,
G. Rasschaert, E. Daeseleire, Development, validation and application of an ultra
high performance liquid chromatographic-tandem mass spectrometric method for
the simultaneous detection and quantification of five different classes of veterinary
antibiotics in swine manure, J. Chromatogr. A. 1429 (2016) 248-257.
[
[
[
[
2]. T. Phaechamud, N. Chanyaboonsub, O. Setthajindalert, Doxycycline hyclate-loaded
bleached shellac in situ forming microparticle for intraperiodontal pocket local
delivery, Eur. J. Pharm. Sci. 93 (2016) 360-370.
3]. S. Zhang, H. L. Song, X. L. Yang, S. Huang, Z. Q. Dai, H. Li, Y. Y. Zhang,
Dynamics of antibiotic resistance genes in microbial fuel cell-coupled constructed
wetlands treating antibiotic-polluted water, Chemosphere. 178 (2017) 548-555.
4]. A. Di Cesare, E. M. Eckert, M. Rogora, G. Corno, Rainfall increases the abundance
of antibiotic resistance genes within a riverine microbial community, Environ.
Pollut. 226 (2017) 473-478.
5]. R. R. Jha, N. Singh, R. Kumari, D. K. Patel, Ultrasound-assisted emulsification
microextraction based on a solidified floating organic droplet for the rapid
determination of 19 antibiotics as environmental pollutants in hospital drainage and
Gomti river water, J. Sep. Sci. 40 (2017) 2694-2702.
[
[
[
6]. H. Lin, J. Zhang, H. Chen, J. Wang, W. Sun, X. Zhang, Y. Yang, Q. Wang, J. Ma,
Effect of temperature on sulfonamide antibiotics degradation, and on antibiotic
resistance determinants and hosts in animal manures, Sci. Total Environ. 607-608
(
2017) 725-732.
7]. S. Naeimi, H. Faghihian, Application of novel metal organic framework, MIL-
3(Fe) and its magnetic hybrid: For removal of pharmaceutical pollutant,
doxycycline from aqueous solutions, Environ. Toxicol. Pharmacol. 53 (2017) 121-
32.
5
1
8]. S. Liu, W. H. Xu, Y. G. Liu, X. F. Tan, G. M. Zeng, X. Li, J. Liang, Z. Zhou, Z. L.
Yan, X. X. Cai, Facile synthesis of Cu(II) impregnated biochar with enhanced
1
4

ACCEPTED MANUSCRIPT
adsorption activity for the removal of doxycycline hydrochloride from water, Sci.
Total Environ. 592 (2017) 546-553.
[
[
9]. E. Adamek, W. Baran, A. Sobczak, Photocatalytic degradation of veterinary
antibiotics: Biodegradability and antimicrobial activity of intermediates, Process
Saf. Environ. Prot. 103 (2016) 1-9.
10]. N. Pronina, D. Klauson, T. Rudenko, K. Kunnis-Beres, I. Kamenev, S. Kamenev,
A. Moiseev, J. Deubener, M. Krichevskaya, Elimination of persistent emerging
micropollutants in a suspended-bed photocatalytic reactor: influence of operating
conditions and combination with aerobic biological treatment, Photochem.
Photobiol. Sci. 15 (2016) 1492-1502.
[
[
11]. J. Liu, D. Zhou, Z. Xu, S. Zheng, Adsorptive removal of pharmaceutical
antibiotics from aqueous solution by porous covalent triazine frameworks, Environ.
Pollut. 226 (2017) 379-384.
12]. M. Yan, Y. Hua, F. Zhu, W. Gu, J. Jiang, H. Shen, W. Shi, Fabrication of nitrogen
doped graphene quantum dots-BiOI/MnNb O p-n junction photocatalysts with
2
6
enhanced visible light efficiency in photocatalytic degradation of antibiotics, Appl.
Catal. B: Environ. 202 (2017) 518-527.
[
13]. M. Brigante, M. Avena, Biotemplated synthesis of mesoporous silica for
2+
doxycycline removal. Effect of pH, temperature, ionic strength and Ca
concentration on the adsorption behaviour, Micropor. Mesopor. Mat. 225 (2016)
34-542.
5
[
[
14]. W. Li, Y. Zhang, Y. Bu, Z. Chen, One-pot synthesis of the BiVO /BiOBr
4
heterojunction composite for enhanced photocatalytic performance, J. Alloys
Compd. 680 (2016) 677-684.
15]. J. Di, J. Xia, M. Ji, B. Wang, S. Yin, Q. Zhang, Z. Chen, H. Li, Advanced
photocatalytic performance of graphene-like BN modified BiOBr flower-like
materials for the removal of pollutants and mechanism insight, Appl. Catal. B:
Environ. 183 (2016) 254-262.
[
[
16]. C. Li, G. Chen, J. Sun, J. Rao, Z. Han, Y. Hu, W. Xing, C. Zhang, Doping effect
of phosphate in Bi WO and universal improved photocatalytic activity for
2
6
removing various pollutants in water, Appl. Catal. B: Environ. 188 (2016) 39-47.
17]. Y. Bao, T. T. Lim, Z. Zhong, R. Wang, X. Hu, Acetic acid-assisted fabrication of
hierarchical flower-like Bi O for photocatalytic degradation of sulfamethoxazole
2
3
and rhodamine B under solar irradiation, J. Colloid Interface Sci. 505 (2017) 489-
99.
4
[
18]. L. Jinhai, M. Han, Y. Guo, F. Wang, L. Meng, D. Mao, S. Ding, C. Sun,
Hydrothermal synthesis of novel flower-like BiVO /Bi Ti O with superior
4
2
2
7
photocatalytic activity toward tetracycline removal, Appl. Catal. A: Gen. 524 (2016)
05-114.
1
[
[
[
19]. F.-X. Liang, C.-W. Ge, T.-F. Zhang, W.-J. Xie, D.-Y. Zhang, Y.-F. Zou, K.
Zheng, L.-B. Luo, Plasmonic hollow gold nanoparticles induced high-performance
Bi S nanoribbon photodetector, Nanophotonics. 6 (2017) 494-501.
2
3
20]. L. Guang, W. Fei, Z. Xuejun, Hydrothermal synthesis of m-BiVO and m-
4
BiVO /BiOBr with various facets and morphologies and their photocatalytic
4
performance under visible light, J. Alloys Compd. 697 (2017) 417-426.
21]. D. Wu, S. Yue, W. Wang, T. An, G. Li, H. Y. Yip, H. Zhao, P. K. Wong, Boron
doped BiOBr nanosheets with enhanced photocatalytic inactivation of Escherichia
coli, Appl. Catal. B: Environ. 192 (2016) 35-45.
1
5

ACCEPTED MANUSCRIPT
[
[
[
[
22]. X. Jia, J. Cao, H. Lin, M. Zhang, X. Guo, S. Chen, Transforming type-I to type-II
heterostructure photocatalyst via energy band engineering: A case study of I-
BiOCl/I-BiOBr, Appl. Catal. B: Environ. 204 (2017) 505-514.
23]. C. Guo, S. Gao, J. Lv, S. Hou, Y. Zhang, J. Xu, Assessing the photocatalytic
transformation of norfloxacin by BiOBr/iron oxides hybrid photocatalyst: Kinetics,
intermediates, and influencing factors, Appl. Catal. B: Environ. 205 (2017) 68-77.
24]. T. Kanagaraj, S. Thiripuranthagan, Photocatalytic activities of novel SrTiO3-
BiOBr heterojunction catalysts towards the degradation of reactive dyes, Appl.
Catal. B: Environ. 207 (2017) 218-232.
25]. S. Chen, R. Yan, X. Zhang, K. Hu, Z. Li, M. Humayun, Y. Qu, L. Jing,
Photogenerated electron modulation to dominantly induce efficient 2,4-
dichlorophenol degradation on BiOBr nanoplates with different phosphate
modification, Appl. Catal. B: Environ. 209 (2017) 320-328.
[
26]. X. Wu, K. Zhang, G. Zhang, S. Yin, Facile preparation of BiOX (X = Cl, Br, I)
nanoparticles and up-conversion phosphors/BiOBr composites for efficient
degradation of NO gas: Oxygen vacancy effect and near infrared light responsive
mechanism, Chem. Eng. J. 325 (2017) 59-70.
[
[
[
[
27]. X.-J. Wen, C. Zhang, C.-G. Niu, L. Zhang, G.-M. Zeng, X.-G. Zhang, Highly
enhanced visible light photocatalytic activity of CeO through fabricating a novel
2
p–n junction BiOBr/CeO , Catal. Commun. 90 (2017) 51-55.
2
28]. K. Bijanzad, A. Tadjarodi, M. Moghaddasi Khiavi, O. Akhavan, Microwave-
assisted synthesis of bismuth oxybromochloride nanoflakes for visible light
photodegradation of pollutants, Phys. B: Condens. Matter. 475 (2015) 14-20.
29]. G. Gupta, A. Kaur, A. S. K. Sinha, S. K. Kansal, Photocatalytic degradation of
levofloxacin in aqueous phase using Ag/AgBr/BiOBr microplates under visible
light, Mater. Res. Bull. 88 (2017) 148-155.
30]. N. Goubard-Bretesché, O. Crosnier, G. Buvat, F. Favier, T. Brousse,
Electrochemical study of aqueous asymmetric FeWO /MnO supercapacitor, J.
4
2
Power Sources. 326 (2016) 695-701.
[
[
31]. K. Hoang, Polaron formation, native defects, and electronic conduction in metal
tungstates, Phys. Rev. mater., https://doi.org/10.1103/PhysRevMaterials.1.024603.
32]. X. Y. Qiu, H. W. Huang, Y. D. Gao, Effects of surface properties of (010), (001)
and (100) of MnWO and FeWO on absorption of collector, Appl. Surf. Sci. 367
4
4
(2016) 354-361.
[
[
33]. A. Sedova, G. Leitus, Y. Feldman, T. Bendikov, R. Popovitz-Biro, S. Khodorov,
H. Dodiuk, S. Kenig, R. Tenne, Synthesis of magnetic FeWO nanoparticles and
4
their decoration of WS nanotubes surface, J. Mater. Sci. 52 (2017) 6376-6387.
2
34]. F. Wang, W. Li, S. Gu, H. Li, X. Liu, M. Wang, Fabrication of
FeWO @ZnWO /ZnO Heterojunction Photocatalyst: Synergistic Effect of
4
4
ZnWO /ZnO and FeWO @ZnWO /ZnO Heterojunction Structure on the
4
4
4
Enhancement of Visible-Light Photocatalytic Activity, ACS Sustain. Chem. Eng. 4
2016) 6288-6298.
(
[
[
35]. M. M. J. Sadiq, U. S. Shenoy, D. K. Bhat, Enhanced photocatalytic performance
of N-doped RGO-FeWO /Fe O ternary nanocomposite in environmental
applications, Mat. Today. Chem. 4 (2017) 133-141.
36]. Z. Chen, H. Ma, J. Xia, J. Zeng, J. Di, S. Yin, L. Xu, H. Li, Ionic liquid-induced
4
3
4
strategy for FeWO microspheres with advanced visible light photocatalysis,
4
Ceram. Int. 42 (2016) 8997-9003.
1
6

ACCEPTED MANUSCRIPT
[
[
[
37]. Y. Bai, T. Chen, P. Wang, L. Wang, L. Ye, X. Shi, W. Bai, Size-dependent role of
gold in g-C N /BiOBr/Au system for photocatalytic CO reduction and dye
3
4
2
degradation, Sol. Energy Mater. Sol. Cells. 157 (2016) 406-414.
38]. J. Xia, M. Ji, W. Li, J. Di, H. Xu, M. He, Q. Zhang, H. Li, Synthesis of erbium
ions doped BiOBr via a reactive ionic liquid with improved photocatalytic activity,
Colloids Surf. A: Physicochem. Eng. Aspects. 489 (2016) 343-350.
39]. B. Priya, P. Raizada, N. Singh, P. Thakur, P. Singh, Adsorptional photocatalytic
mineralization of oxytetracycline and ampicillin antibiotics using Bi O /BiOCl
2
3
supported on graphene sand composite and chitosan, J. Colloid Interface Sci. 479
2016) 271-283.
(
[
[
40]. X. Hao, J. Gong, L. Ren, D. Zhang, X. Xiao, Y. Jiang, F. Zhang, Z. Tong,
Preparation of polyaniline modified BiOBr with enhanced photocatalytic activities,
Funct. Mater. Lett. 10 (2017) 1750040.
41]. P. Singh, B. Priya, P. Shandilya, P. Raizada, N. Singh, B. Pare, S. B. Jonnalagadda,
Photocatalytic mineralization of antibiotics using 60%WO /BiOCl stacked to
3
graphene
sand
composite
and
chitosan,
Arab.
J.
Chem.,
http://dx.doi.org/10.1016/j.arabjc.2016.08.005.
[
[
42]. F. Nekouei, S. Nekouei, Comparative evaluation of BiOCl–NPls–AC composite
performance for methylene blue dye removal from solution in the presence/absence
of UV irradiation: Kinetic and isotherm studies, J. Alloys Compd. 701 (2017) 950-
9
66.
43]. Z. Liu, H. Wang, G. Pan, J. Niu, P. Feng, Facile synthesis, structure and enhanced
photocatalytic activity of novel BiOBr/Bi(C O )OH composite photocatalysts, J.
2
4
Colloid Interface Sci. 486 (2017) 8-15.
1
7

ACCEPTED MANUSCRIPT
Fig. 1 XRD patterns of BiOBr, FeWO and BiOBr/ FeWO composites.
4
4
1
8

ACCEPTED MANUSCRIPT
Fig. 2 SEM images of BiOBr (a-c) and BiOBr/FeWO (4:1) (d-e); TEM image of
4
BiOBr/FeWO (4:1) (f).
4
1
9

ACCEPTED MANUSCRIPT
Fig. 3 HRTEM image of BiOBr/FeWO (4:1) (a) and SAED image of BiOBr/FeWO
4
4
(4:1) (b).
2
0

ACCEPTED MANUSCRIPT
Fig. 4 EDS image of BiOBr/FeWO (4:1) (a) and EDS mapping image of
4
BiOBr/FeWO (4:1) (b).
4
2
1

ACCEPTED MANUSCRIPT
Fig. 5 XPS spectra of pure BiOBr, FeWO and BiOBr/FeWO (4:1).Survey spectrum
4
4
(a), Bi 4f (b), Br 3d (c), Fe 2p (d), W 4f (e), O 1s (f), C 1s (g).
2
2

ACCEPTED MANUSCRIPT
Fig. 6 FT-IR spectra of pure BiOBr, FeWO , and BiOBr/FeWO (4:1) samples.
4
4
2
3

ACCEPTED MANUSCRIPT
Fig. 7 (a) UV–Vis absorption spectra and (b) band gap energies of BiOBr, FeWO , and
4
BiOBr/FeWO (4:1) samples.
4
2
4

ACCEPTED MANUSCRIPT
Fig. 8 (a) Photocatalytic activities, (b) kinetics of photocatalytic degradation and (c)
results of cycling experiments.
2
5

ACCEPTED MANUSCRIPT
Fig. 9 Schematic diagram of the photocatalytic mechanism under visible light over
BiOBr/FeWO4
2
6

ACCEPTED MANUSCRIPT
The microsphere structures BiOBr/FeWO were successfully fabricated.
4
The addition of FeWO reduced the band gap energy of BiOBr.
4
BiOBr/FeWO exhibited superior photodegradation in doxycycline.
4
BiOBr/FeWO promoted the separation of electron-hole pairs.
4