Electrospun BiOCl/Bi2Ti2O7 Nanorod Heterostructures with Enhanced Solar Light Efficiency in the Photocatalytic Degradation of Tetracycline Hydrochloride

Article abstract of DOI:10.1002/cctc.201800100

Bismuth titanates (BTs) can be fabricated by electrospinning combined with calcination at different temperatures. BiOCl/Bi₂Ti₂O₇ nanorod heterostructures were obtained at 500 °C. They possess excellent photocatalytic efficiency and stability for tetracycline hydrochloride (TC-HCl) degradation under simulated solar light. The excellent catalytic activity is predominantly attributed to the heterostructure between BiOCl and Bi₂Ti₂O₇, which accelerates the separation of photogenerated carriers while the narrow band gap of Bi₂Ti₂O₇ enhances solar energy utilization. On the basis of energy band engineering, scavenger tests, and LC-HRMS analysis, a possible degradation pathway of TC-HCl and photocatalytic mechanism were proposed. Our work can predict a facile route for achieving high photocatalytic performance of Bi₂Ti₂O₇-based materials in the application of TC-HCl degradation.

Full text of DOI:10.1002/cctc.201800100

Accepted Article
Title: Electrospun BiOCl/Bi2Ti2O7 nanorod heterostructures with
enhanced solar light efficiency in photocatalytic degradation of
tetracycline hydrochloride
Authors: Yuxian Xu, Daifeng Lin, Xinping Liu, Yongjin Luo, Hun Xue,
Baoquan Huang, Qinghua Chen, and Qingrong Qian
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201800100
Link to VoR: http://dx.doi.org/10.1002/cctc.201800100
A Journal of
www.chemcatchem.org

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
Electrospun BiOCl/Bi2Ti2O7 nanorod heterostructures with
enhanced solar light efficiency in photocatalytic degradation of
tetracycline hydrochloride
Yuxian Xu, [a] Daifeng Lin, [a] Xinping Liu, [a] Yongjin Luo*, [a] Hun Xue, [a] Baoquan Huang, [a]
Qinghua Chen, [a,b] and Qingrong Qian* [a]
Abstract: Bismuth titanates (BTs) can be fabricated via
most of the semiconductor photocatalysts possess wide band
electrospinning combined with calcination at different temperatures. gaps and could only work under UV light irradiation (~4% of
BiOCl/Bi2Ti2O7 nanorod heterostructures were obtained at 500 oC. It solar energy).[6] Accordingly, it is necessary to search new and
possesses excellent photocatalytic efficiency and stability for
efficient visible-light-driven photocatalysts for TCs degradation.
tetracycline hydrochloride (TC-HCl) degradation under simulated Recently, Bi-based semiconductors, such as BiOX (X = Br，I)[7],
solar light. The excellent catalytic activity is predominantly attributed BixOyXz (X = Cl, I)[8], Bi2MO6 (M= W, Mo)[9], Bi2O2CO3
and
[10]
to the heterostructure between BiOCl and Bi2Ti2O7, which
bismuth titanate, as new promising visible light photocatalysis
accelerates the separation of photogenerated carriers while narrow candidates are particularly interesting. Among bismuth titanate,
band gap of Bi2Ti2O7 enhances solar energy utilization. On the basis Bi2Ti2O7, with a narrow band gap of 2.90 eV[11] and good
of energy band engineering, scavenger tests and
LC-HRMS
chemical stability[12]
semiconductor for visible light photocatalysis. However, the
,
is
a
very suitable candidate of
analysis, the possible degradation pathway of TC-HCl and
photocatalytic mechanism were proposed. Our work can predict a photocatalytic capability of Bi2Ti2O7 is not efficient enough to
facile route for achieving high photocatalytic performance of Bi2Ti2O7 meet the application requirement due to the low separation
based materials in the application of TC-HCl degradation.
efficiency of the photoexcited electron-hole pairs. To address
this issue, building heterojunction with a suitable semiconductor
is an effective strategy.[13] To date, Bi2Ti2O7 based heterojunction
[14]
photocatalysts,
such
as
Bi2Ti2O7/TiO2
and
Introduction
[15]
Bi2Ti2O7/Bi4Ti3O12
, have been studied to enhance the
photocatalytic efficiency for degradation of dye pollutants in
water treatment. Amongst the various Bi-based semiconductors,
BiOCl have attracted tremendous attention owing to its layered
structure. The {Cl-Bi-O-Bi-Cl} sheets structure benefits the
photogenerated electron–hole pairs separation and transport
process although it has a wide band gap.[16] Considering that the
valence band maximum (VBM) and conduction band minimum
(CBM) potentials of BiOCl are both more positive than those of
Bi2Ti2O7, the construction of BiOCl/Bi2Ti2O7 heterostructure is
feasible. Lately, K. V. Pham et.al prepared BiOCl/Bi2Ti2O7 by
hydrothermal method in combination with an annealing process,
and found BiOCl/Bi2Ti2O7 nanocomposite shows higher
photocatalytic activity than pure BiOCl and Bi2Ti2O7.[17] But that
BiOCl can be excited by visible light in above work is
Recently, antibiotic has been widely used as antibacterial
agents in human and veterinary medicine for treatment of
bacterial infection.[1] A survey research had indicated that total
production of all antibiotics in China was estimated to be 248000
tons, the total usage for the 36 chemicals was 92700 tons, and
estimated 53800 tons of them entered into the receiving
environment (46% received by water) following various
wastewater treatments in 2013.[2] Amongst the different
antibiotics, tetracycline antibiotics (TCs) are ranked second in
the production and usage of antibiotics worldwide and are
ranked first in China due to their low cost, ease of use and
relatively minor side effects.[3] However, tetracycline antibiotics
residues in the environment have adverse effects on organisms,
contamination of food and drinking water, and increased
bacterial resistance.[4] Unfortunately, most of the wastewater
treatment plants are not capable to remove TCs effectively.[5]
Therefore, it is imperative to develop alternative processes to
remove TCs from waters.
controversial to the wide band gap of BiOCl [12]
On the other hand, it has
.
been
reported
that 1D nanostructures, such as nanowires, nanotubes and
nanorods, are beneficial for charge transport.[18] To bring out the
superiority of the nanostructures, constructing 1D BiOCl/Bi2Ti2O7
nanostructures is meaningful. Electrospinning as a remarkably
simple and versatile technique for preparing well-
defined 1D nanostructured materials, has been widely used to
fabricate many catalysts.[19] Previously, we have successfully
Semiconductor
photocatalysis
offers
great
potential
opportunities to remove TCs from waters due to its high
efficiency, no secondary pollution and low cost. However, there
are still some problems, the major drawback of which is that
synthesized
a
series of 1D nanostructured oxide by
electrospinning technology, including LaOCl, TiO2 and
[a] Y. Xu, D. Lin, Prof. Dr. X. Liu, Prof. Dr. Y. Luo, Prof. Dr. H. Xue, Prof.
Dr.B. Huang, Prof. Dr. Q. Chen, Prof. Dr. Q. Qian
Environment Science and Engineering, Fujian Normal University,
Fujian
LaCoO3.[20]
In this work, we fabricated PVP/BiCl3/Ti(OiPr)4 composite
nanofibers via electrospinning first, and bismuth titanates (BTs)
with different phase can be obtained by tuning calcination
temperature. For example, calcination at 400 or 500 oC can
obtain heterostructured BiOCl/Bi2Ti2O7, while 600 or 700 oC
gives rise to Bi2Ti4O11/Bi2Ti2O7. The results of tetracycline
hydrochloride (TC-HCl) photodegradation show that a 500 oC
calcination of PVP/BiCl3/Ti(OiPr)4 composite nanofibers exhibit
the best photocatalytic activity, approximate 90% of TC-HCl can
Key Laboratory of Pollution Control
350007,
& Resource Reuse, Fuzhou
China
[b] Prof. Dr. Q. Chen
Fuqing Branch of Fujian Normal University, Fuqing, Fujian 350300,
China
E-mail: yongjinluo@fjnu.edu.cn (Y. Luo), qrqian@fjnu.edu.cn (Q. Qian)
Supporting information for this article is given via a link at the end of the
document.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
be removed within 2 h. Moreover, the possible degradation
pathway of TC-HCl and photocatalytic mechanism were study in
detail.
the respective (001), (101), (110), (102), (200) and (113) planes
of BiOCl (JCPDS no. 85-0861, marked with “  ”). Additional
peaks (14.8o, 28.7o, 34.7o, 38.0o and 49.9o) attributed to Bi2Ti2O7
(JCPDS no. 32-0118, marked with “♠”) can be found for BT-400.
o
With increasing temperature to 500 C, the XRD peaks intensity
of Bi2Ti2O7 become stronger as the amount of Bi2Ti2O7 increases.
Results and Discussion
o
o
Further raising the calcination temperature to 600 C or 700 C,
the diffraction peaks of Bi2Ti2O7 is retained, but BiOCl phase has
been replaced with Bi2Ti4O11 phase (JCPDS no. 15-0325,
marked with “●”). The results may cause by BiOCl gradually
decomposes to form Bi2O3 and BiCl3 gas with the increase of
temperature.[22]
The morphology of BTs is observed through SEM images.
Fig.1a shows the PVP/BiCl3/Ti(OiPr)4 composite nanofibers are
continuous and smooth with a diameter of approximate 20-100
o
nm. After calcination at 300 C, the composite nanofibers are still
smooth, but accompanied with some breakage and bend of
nanofibers (Fig.1b). As the temperature rises to 400 C (Fig.1c),
o
most nanofibers have been broken into nanorods. Further
increasing temperatures to 500-700 oC (Fig.1d-f), no obvious
change is observed expect that nanorods become thicker. The
textural properties (specific surface areas, pore volume and
average pore diameter) of BTs are summarized in Table 1. With
o
o
raising the calcination temperature from 300 C to 700 C, the
specific surface areas increase first and then decreases. BT-500
exhibits an apparent the largest surface area. The higher
surface area of BT-500 will probably adsorb more irradiation
photons and target pollutant and thus favors the photocatalytic
activity.[21]
Figure 2. XRD patterns of BTs: (a) BT-300, (b) BT-400, (c) BT-500, (d) BT-
600, (e) BT-700.
More detailed information regarding the chemical environment
of Bi, Ti and O in samples is ascertained using XPS. As
observed in Fig. 3A, the binding energies at positions around
159.3 and 164.6 eV can be attributed to Bi 4f7/2 and Bi 4f5/2,
respectively. The two peaks with a typical Bi 4f spin-orbit
splitting of 5.3 eV is characteristic of Bi3+.[23] With the increase in
the calcination temperature, these peaks of Bi 4f clearly shift
toward the low band energy, which plausibly caused by Bi-O-Cl
system transits to Bi-O-Ti system. As for Ti 2p element (Fig. 3B),
two peaks at 458.2 and 464.6 eV for BT-300 are assigned to Ti
2p1/2 and Ti 2p3/2, respectively, which is corresponding to Ti4+
in pure TiO2.[24] Combine with XRD analysis, BT-300 consists of
BiOCl and unchecked TiO2, which illustrates that Bi-O-Ti system
cannot be fabricated at low calcination temperature. For other
samples, the binding energy of Ti 2p has a slight shift toward the
high band energy, due to the decreasing electron density around
the Ti4+ in the forming Bi-O-Ti bands.[25] From the XRD and XPS
analysis, we can deduce that the phase transformation to
BiOCl/Bi2Ti2O7 form BiOCl/TiO2, and then transfers to
Bi2Ti4O11/Bi2Ti2O7.
Figure 1. SEM images of (a) PVP/BiCl3/Ti(OiPr)4 composite nanofibers; (b)
BT-300, (c) BT- 400, (d) BT-500, (e) BT-600, (f) BT-700.
Table 1. Textural properties and the values of OII /OI of samples
a
b
Sample
SBET
(m2/g)
Pore
volume
(cm3/g)
Average
pore
diameter
(nm)
OII/OI
K(h-1)c
a
a
BT-300
BT-400
BT-500
BT-600
BT-700
4
0.015
0.142
0.120
0.089
0.023
4.4
0.05
0.75
0.95
0.55
0.41
20
21
9
3.9
0.21
0.29
0.18
0.14
12.5
16.3
3.9
5
a Deduced from N2 adsorption–desorption curves.
b Deduced from XPS analysis.
The
O
1s spectrum region shows two peaks with
approximately binding energies of 531 eV and 530.0 eV (Fig.
c Deduced from the pseudo-first equation.
3C). Because the weight contents of C in BT-300 is 39.65%, the
The phase analysis of BTs is performed using XRD and is
reported in Fig.2. It is clearly that various diffraction peaks are
observed in different BTs. The diffraction peaks of BT-300 at
12.0o, 25.9o, 32.5o, 33.5o, 46.7o and 49.7o, are corresponding to
[26]
peaks of BT-300 should correspond to C=O bond
and the
lattice O of samples, respectively. However, increasing the
calcination temperature to 400-700 oC, the two peaks should
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
belong to surface-adsorbed hydroxyl groups(OII) and the lattice
O (OI). It has been generally accepted that O II species play an
important role in photocatalytic degradation. As seen in table1,
BT-500 shows the largest molar ratio of OII/OI than other
samples, indicating the more hydroxyl groups in BT-500 can
react with photogenerated holes and facilitate separation of
photogenerated charges.
Figure 4. (A) Degradation curves of TC-HCl, (B) apparent rate constants for
degradation of TC-HCl under solar light irradiation over BTs: (a) BT-300, (b)
BT-400, (c) BT-500, (d) BT-600, (e) BT-700, (f) Blank.
UV/vis diffuse reflectance spectra are measured to
characterize the optical bandgap and absorption capability of the
as-prepared photocatalysts. As seen in Fig. 5, BT-300 absorbs
light of all wavelengths, which could be due to the high C
contents and the color of sample is black. BT-400, BT-500, BT-
600 and BT-700 all exhibit an obvious spectra absorption in the
visible light region. The band gap energy can be obtained from
the plots of (Ahv)1/2 versus hv (in the inset of Fig. 5). The band
gap values for BT-400, BT-500, BT-600 and BT-700 are 2.58,
2.54, 2.68 and 2.78 eV, respectively. Meanwhile, the intensity of
absorption for BT-400 and BT-500 are higher than that for BT-
600 and BT-700 in 200-800 nm, which can be expected to the
better utilization of solar light for photocatalytic reaction.[30]
Figure 3. High-resolution XPS spectra of (A) Bi, (B) Ti, and (C) O for BTs: (a)
BT-300, (b) BT-400, (c) BT-500, (d) BT-600, (e) BT-700.
Photocatalytic performance is evaluated for degradation of
TC-HCl aqueous solution under simulated solar irradiation. As
seen in Fig.4A, the degradation efficiency of TC-HCl without
catalyst is approximately 6% after 2 h, suggesting that the TC-
HCl degradation is indeed induced by photocatalysis.[27] BT-300
shows poor photodegradation efficiency (~10%) after
illumination for
2
h. This may result from too much
carbonaceous residue in BT-300, occupying active sites and
reducing the utilization of the light.[28] In contrast, under the same
illumination time, the removal rates can be reached as high as
81% and 90% over BT-400 and BT-500, respectively. However,
the removal rate reduces to 68% for BT-600 and 57% for BT-
700. In addition, the pseudo-first-order model[29] is applied to
quantitatively compare the reaction kinetics of decomposition
rate of TC-HCl. The various rate constant (k) is depicted in the
form of columns of different colors (Fig. 4B) and shows in table 1.
It can be seen from the diagram that the catalytic efficiency of
BT-500 is 19.0 and 1.75 times higher than that of BT-300 and
BT-600, respectively. Therefore, BiOCl/Bi2Ti2O7 has better
photocatalytic activity than Bi2Ti4O11/Bi2Ti2O7, and more Bi2Ti2O7
content in BiOCl/Bi2Ti2O7 enhances the photocatalytic
performance. Moreover, as seen Table S1, the observed
photocatalytic performance of BT-500 is better than most of the
reported Bi2Ti2O7 based semiconductors.
Figure 5. UV-vis diffuse reflectance spectra of BTs: (a) BT-300, (b) BT-400, (c)
BT-500, (d) BT-600, (e) BT-700. The inset is band-gap evaluation from the plot
of (Ahv)1/2 versus hv.
The rapid recombination of photogenerated electron-hole
pairs is main drawback of Bi2Ti2O7 PL spectra are performed to
observe the separation rate of the photogenerated electron-hole
pairs. The lower PL intensity often reflect the higher separation
efficiency of the charge carriers.[31] The PL intensity of BTs is in
the order of BT-300 > BT-700 > BT-600 > BT-400 > BT-500 (Fig.
6A). To provide additional evidence, the transient photocurrent
responses of BTs electrodes are recorded for several on-off
cycles, and the results are shown in Fig. 6B. All samples exhibit
fast and reproducible transient photocurrent responses under
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
several on-off cycles of intermittent simulated solar irradiation.
The photocurrent density of BT-300, BT- 400, BT-500, BT-600
and BT-700 are about 0.049-0.040, 1.00-0.65, 1.15-0.66, 0.074-
0.066, 0.068-0.050 uA cm-2, respectively. It is notable that BT-
400 and BT-500 have
a better reproducible photocurrent
response. Therefore, BiOCl/Bi2Ti2O7 has higher separation
efficiency of the charge carriers than Bi2Ti4O11/Bi2Ti2O7.
Amongst BTs, BT-500 has the lowest PL intensity and the
highest photocurrent density. That is, BT-500 has the highest
separation efficiency of photogenerated electron-hole pairs and
greatly facilitate its photocatalytic activity.
Figure 7. (a) TEM images and (b) HRTEM images of BT-500.
In order to better understand the photocatalytic mechanism of
TC-HCl photodegradation over BT-500 under simulated solar
irradiation, the trapping experiments of active species involved in
34]
the photocatalytic reaction are investigated.[10,
In this study,
Benzoquinone (BQ)[35], ammonium oxalate (AO)[36] and dimethyl
sulfoxide (DMSO)[37] acting as the scavengers for superoxide
radicals (O2−•), holes (h+) and hydroxyl radicals (·OH) are
introduced into the photocatalytic process, respectively. From
Fig.8, it is clearly that N2 bubbling and excess BQ and AO show
little effects on the degradation of TC-HCl compared with no
−•
scavenger at the same conditions, suggesting that O2 and h+
Figure 6. (A) PL spectra and (B) Transient photocurrent response for BTs: (a)
BT-300, (b) BT-400, (c) BT-500, (d) BT-600, (e) BT-700.
have
a negligible effect on the TC-HCl photodegradation
mechanism. On the contrary, the decomposition rate of TC-HCl
decreases to 67% after the addition of DMSO. According to
these results, it can be clearly seen that •OH radicals are main
reactive species for BT-500 in the photodegradation process of
TC-HCl.
Compared with Bi2Ti2O7/Bi2Ti4O11, BiOCl/Bi2Ti2O7 could
effectively inhibit the electron-hole pair recombination which may
cause energy band engineering. According to the references,[12,
32]
the band gap of BiOCl, Bi2Ti2O7 and Bi2Ti4O11 is 3.40，2.90
and 3.24 eV, respectively. Then the equations [33]: EVB = X − Ee +
0.5Eg and ECB = EVB − Eg are applied to calculate the energy
band edges of single semiconductor, where Eg is the band gap
energy of semiconductor; EVB is valence band (VB) edge
potentials; ECB is conduction band (CB) edge potentials; X is the
electronegativity of semiconductor; Ee is the energy of free
electrons on hydrogen scale (~4.5 eV). Thus, ECB/EVB of BiOCl,
Bi2Ti2O7 and Bi2Ti4O11 are 0.18/3.58, -0.24/2.66 and -0.23/3.01
eV, respectively. The electrons cannot easily transfer from
Bi2Ti2O7 to Bi2Ti4O11, due to their close CBM potentials. On the
contrary, VBM and CBM potentials of BiOCl are both more
positive than those of Bi2Ti2O7. In that case, heterojunctions are
formed at the interface between BiOCl and Bi2Ti2O7, favoring
charge transfer and significantly inhibiting electron-hole
recombination rate.
The microstructural details of BT-500 are further characterized
by TEM and HRTEM observation as shown in Fig.7. TEM image
shows that BT-500 nanorods mainly consists of nanoparticles
(Fig. 7a). As seen in Fig. 7b, the interplanar spacing of 0.267
and 0.344 nm corresponds to the (102) and (101) plane of BiOCl,
while 0.298 and 0.236 nm corresponds to the respective (444)
and (662) plane of Bi2Ti2O7. The continuity of lattice fringes
between the interface of BiOCl and Bi2Ti2O7 can favor the
charge transfers between them.
Figure 8. Effects of scavengers on the degradation of TC-HCl over BT-500.
The intermediates formed on BT-500 during the photocatalytic
process is characterized by LC-HRMS. Fig. 9 shows the mass
spectra of TC-HCl before and after 2 h photocatalytic treatment.
The peak with m/z of 445 is regarded as the tetracycline
hydrochloride molecule. After simulated solar light irradiation,
the peak with m/z of 445 disappear, and a lot of extra peaks
(such as m/z = 481, 476, 437, 432, 393, 388, 349, 344, 327, 305,
283, 261, 217, 177, 133, 89) appear along with the degradation
of TC-HCl. The possible molecular structures of these products
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
are described in Table S2. Combining with these detection
results and references,[38] the degradation removal process
could be proposed as two main pathways (Fig. 10).
Figure 10. The removal pathway of TC-HCl over BT-500.
Figure 9. LC-HRMS spectra of TC-HCl, (A) before and (B) after
photocatalysis.
Based on the above results,
a possible photocatalytic
mechanism for BTs under simulated solar light is proposed in
Fig.11. Under simulated solar light irradiation, BiOCl and
Bi2Ti2O7 can be excited by UV and visible light, respectively,
generating the electrons and holes (Fig.11a). The electrons in
the conduction band (CB) of Bi2Ti2O7 shift to BiOCl due to the
CBM of Bi2Ti2O7 is more negative than that of BiOCl.
Simultaneously, the holes in the VB of BiOCl move to Bi2Ti2O7
due to the VBM of BiOCl is more positive than that of Bi2Ti2O7.
As a result, the photogenerated charge carriers are separated
efficiently, and the electron-hole recombination rate is
suppressed. However, since CB edges of Bi2Ti2O7 and Bi2Ti4O11
is very close, the photogenerated electrons transfer difficultly
from Bi2Ti2O7 to Bi2Ti4O11, resulting in an unsatisfied charge
separation (Fig.11b).
The first pathway is primary degradation by addition of
hydroxyl locating at C11a–C12 and C2-C3 double-bond of TC-HCl
with attack of the •OH radicals to generate the intermediate
with m/z 476, which is further fragmented to the product 2
(m/z 393) via deprivation of methyl from the tertiary amine and
amide group. Subsequently, •OH attacks C4 bond to cleave
benzene rings and eliminate methyl, forming product 4 (m/z 344).
Further degradation products (products 5-7, 14-16) with lower
molecular weight result from the elimination of hydroxyl, N-
methyl and cleavage of benzene rings. On the other hand, the
product 2 (m/z 393) can also be decomposed to the detected
product
3 with m/z 347 via cleavage of benzene rings,
elimination of methyl, and the addition of hydroxyl and
dehydration. The possible degradation pathways at this stage in
terms of molecular weight (MW) can be expressed as follows:
445→476→393→347;
Although the photogenerated electrons are transferred to the
−•
CB of BiOCl, which cannot react with O2 to produce O2
,
because the CBM potential of BiOCl (0.18 eV vs NHE) is more
−•
positive than E0(O2/O2
)
(−0.33 eV vs NHE).[39] The
393→344→327→283→217→177→134→88.
photogenerated holes on the VB of BiOCl could be easily
transferred to that of Bi2Ti2O7, which can react with surface-
adsorbed hydroxyl or H2O to produce •OH.[40] Then •OH directly
involves in the degradation of TC-HCl. In this way, the efficient
separation of photogenerated electron-hole pairs can be
achieved, and the photocatalytic activity is improved.
The second pathway, •OH radicals attack the C11a–C12 double-
bond of TC-HCl to add hydroxyl and remove methyl from the
tertiary amine, generating the m/z 432 (product 8). Then,
aromatic ring is attacked at C6a-C7 bond, in which gives rise to a
ketone group and a carboxylic group at the C6a and C7 positions,
respectively, yielding the product 9 with m/z 480. It is further
decomposed to simpler intermediates (products 10-16) detected
in the following reaction, such as the elimination of amide group,
hydroxyl group, amidogen, ketone group, carboxylic group and
methyl alcohol, and the substitution reaction by ring-opening
reaction is also involved in this process. The possible
degradation pathways at this stage are expressed as follows:
445→432→481→437→388→305→261→177→134→88.
Thus, it can be seen that TC-HCl has been gradually
disintegrated, and the relevant degradation intermediates are
produced and then decomposed. Finally, these substances can
convert into CO2, H2O and the other degradation products.
Figure 11. Photocatalytic mechanism scheme for the degradation of TC-HCl
over (a) BiOCl/Bi2Ti2O7, (b) Bi2Ti2O7/Bi2Ti4O11 under simulated solar light.
Besides excellent photocatalytic activity, photocatalysts also
should display great photocatalytic stability. The stability is a
very important factor for practical applications. In order to
evaluate the stability of prepared catalysts, BT-500 is selected
for the recycling test under simulated solar light, as shown in
Fig.12A. The result shows that there is no obvious reduction of
the photocatalytic degradation efficiency upon five recycling.
Furthermore, the XRD patterns of the fresh and used BT-500
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
clearly indicates that the structure of BT-500 has no change
(Fig.12B). SEM image in Fig.12C reveals that the morphology of
used BT-500 is still featured by nanorods. These results indicate
that the obtained BT-500 has good stability during the
photocatalytic process.
Experimental Section
Preparation
The bismuth titanates (BTs) were synthesized by an electrospinning
method, followed by furnace treatment. In a typical process, 1mmol
bismuth chloride (BiCl3) was firstly dissolved in the solution containing 20
mL N, N dimethylformamide and 5 mL acetic acid. Then 2 g PVP (Mw:
1300000, Aldrich) was added to the above solution under stirring for 4 h
to form homogenous solution, which is then mixed with 1 mmol tetrabutyl
titanate (Ti(OiPr)4) under continued stirring for another 2 h to form light
yellow precursor solution. The precursor solution was electrospun under
high voltage of 23 kV, and the distance between spinneret and collector
was fixed at 15 cm with a flow rate of 1 mL h-1. Finally, the collected
electrospun composite fibers were calcined in air at different
temperatures for 3 h with a heating rate of 2 °C min−1. For simplicity, the
samples obtained from different calcination temperatures (300-700 oC)
were denoted as BT-300, BT- 400, BT-500, BT-600 and BT-700,
respectively.
Characterization
The phase of the samples was determined on an X-ray diffraction
analyzer (XRD, D8 Advance, Bruker) using graphite monochromatized
Cu Kα radiation, the accelerating voltage and the applied current were 40
kV and 40 mA, respectively. The morphology of the samples was
analyzed on a field emission scanning electron microscope (FESEM,
JEOL, JSM-7500F). Transmission electron microscopy (TEM) and high-
resolution transmission electron microscopy (HRTEM) images were
obtained on a JEM-2100F transmission electron microscope with an
accelerating voltage of 200 kV. X-ray photoelectron spectroscopy (XPS)
was measured using a Thermo ESCALAB 250Xi XPS, and the C 1s peak
at 284.8 eV of the adventitious carbon was referenced to rectify the
binding energies. The UV-visible diffuse reflectance absorption features
were investigated on a UV-visible spectrophotometer (Cary 500 Scan
Spectrophotometers, Varian, USA). The specific surface areas were
analyzed by N2 gas adsorption-desorption at 77 K on a BELSORP-mini
surface area analyzer (BELSORP Co., Japan). Photoluminescence (PL)
spectra were recorded on RF-5301PC spectrophotometer using room
temperature photoluminescence with a 280 nm excitation wavelength.
The photoelectrochemical measurements of samples were investigated
by a CHI600E electrochemical workstation with a conventional three-
electrode process in a quartz cell. Samples were deposited on FTO
photoanode used as a working electrode, while Pt foil and Ag/AgCl
electrode served as counter electrode and reference electrode,
respectively. A 0.1 M Na2SO4 aqueous solution was employed as the
Figure 12. (A) Cycling runs in the photocatalytic degradation of TC-HCl under
simulated solar light illumination of BT-500; (B) XRD patterns of BT-500:
before photocatalysis and after cycling runs; (C) SEM image of used BT-500.
Conclusions
In this study, bismuth titanates with different phases can be
tuned by an electrospinning combined with calcination route.
After calcination at 400 °C, the smooth nanofibers of
PVP/BiCl3/Ti(OiPr)4 break into BiOCl/Bi2Ti2O7 nanorods. Further
increasing calcination temperatures to 600-700 °C, the phase of
Bi2Ti2O7/Bi2Ti4O11 is formed. The results of TC-HCl
photodegradation under simulated solar irradiation indicate that
BiOCl/Bi2Ti2O7 shows higher photocatalytic performance than
Bi2Ti2O7/Bi2Ti4O11. It is mainly thanks to the good match of
energy levels between BiOCl and Bi2Ti2O7 to form heterojunction
structure, accelerating the separation of photogenerated
electron-hole pairs. The enhanced charge separation efficiency
was confirmed by PL spectra and photoelectrochemical
measurements. The obtained BT-500 exhibits the excellent and
good stable photocatalytic performance. Scavenger tests
demonstrate that •OH plays the dominant role for the
photodegradation of TC-HCl. The possible degradation pathway
of TC-HCl over BT-500 was identified by LC-HRMS analysis. It
mainly consists of losing of amide group, hydroxyl group,
amidogen, carboxylic group, methyl etc. and cleavage of
benzene rings with the attack of •OH radicals. This work
provides new route for the construction of BiOCl/Bi2Ti2O7
nanorod heterostructures and offers pathway of TC-HCl into
photodegradation.
electrolyte. The working electrode was illuminated using
a Beijing
Perfectlight Co., PLS-SXE300C Xe lamp. The intermediates formed
during the degradation of TC-HCl were monitored by Liquid
chromatography-high resolution mass spectrometry (LC-HRMS, Agilent
6460 Triple Quad) with electrospray ionization (ESI) source and a EC-
C18 column (3.0× 50 mm; 2.7 um). The mixture of methanol-water (30:70,
v/v, 1‰ formic acid containing in water) was used as mobile phase with a
flow rate of 1 mL min−1
.
Photocatalytic activity test
The photocatalytic activities of BTs were evaluated by the
decomposition of 50 mg L-1 TC-HCl solution. Simulated solar
photocatalytic reactions were performed in a 100 mL Pyrex glass vessel
containing 100 mL TC-HCl aqueous solution and 100 mg catalyst. Before
the photocatalytic activity test, the suspension mixture was stirred in the
dark for 1 h to reach the adsorption/desorption equilibrium. Then the
suspension solution was irradiated by a 300 W Xe lamp (PLS-SXE300C,
Perfectlight, China). During irradiation, a 4 mL suspension was withdrawn
at 20 min intervals and centrifuged. The obtained supernatant was
analyzed on
a Shimadzu UV-1750 UV-vis spectrophotometer at a
wavelength of 364 nm.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
Acknowledgements
[17] K. V. Pham, V. H. Nguyen, D. P. Nguyen, D. B. Do, M. O. Le, H. H. Luc,
J. Electron. Mater. 2017.
[18] a) X. Zhang, V. Thavasi, S. G. Mhaisalkar, S. Ramakrishna, Nanoscale
2012, 4, 1707-1716.; b) J. Chen, H. B. Yang, J. Miao, H.-Y. Wang, B.
Liu, J. Am. Chem. Soc. 2014, 136, 15310-15318.
This work is supported by the National Science Foundation of
China (21407025), the National Science Foundation of Fujian
Province (2016J01047), and New Century Talent Project of
Fujian Province.
[19] L. Li, S. Peng, J. Wang, Y. L. Cheah, P. Teh, Y. Ko, C. Wong, M.
Srinivasan, ACS Appl. Mater. Interfaces 2012, 4, 6005-6012.
[20] a) Y. Xu, Z. Li, X. Liu, Y. Luo, Q. Qian, B. Huang, L. Xiao, Q. Chen, J
Mater Sci: Mater Electron 2017, 28, 8596-8600.; b) X. Liu, Y. Chen, C.
Cao, J. Xu, Q. Qian, Y. Luo, H. Xue, L. Xiao, Y. Chen, Q. Chen, New
New J. Chem. 2015, 39, 6944-6950.; c) Y. Luo, K. Wang, Y. Xu, X.
Wang, Q. Qian, Q. Chen, New J. Chem. 2015, 39, 1001-1005.
[21] U. G. Akpan, B. H. Hameed, J. Hazard. Mater. 2009, 170, 520-529.
[22] a) Y. Qi, W. Wu, L. Han, H. Qu, X. Han, A. Wang, J. Xu, J. Therm. Anal.
Calorim. 2016, 123, 1263-1271.; b) F. Gao, D. Zeng, Q. Huang, S. Tian,
C. Xie, Phys. Chem. Chem. Phys. 2012, 14, 10572-10578.
Keywords:
BiOCl/Bi2Ti2O7
•
heterostructure
•
solar
photocatalysis • photocatalytic mechanism • removal pathway
[1]
a) E. M. H. Wellington, A. B. A. Boxall, P. Cross, E. J. Feil, W. H. Gaze,
P. M. Hawkey, A. S. Johnson-Rollings, D. L. Jones, N. M. Lee, W.
Otten, C. M. Thomas, A. P. Williams, Lancet Infect. Dis. 2013, 13, 155-
165.; b) A. M. Hammerum, O. E. Heuer, Clin. Infect. Dis. 2009, 48,
916-921.; c) E. S. Elmolla, M. Chaudhuri, Desalination 2010, 252, 46-
52.; d) P. Huo, Y. Yan, S. Li, H. Li, W. Huang, Appl. Surf. Sci. 2010,
256, 3380-3385.
[23] L. Xu, Y. Wei, W. Guo, Y. Guo, Y. Guo, Appl. Surf. Sci. 2015, 332, 682-
693.
[24] S. K. Parayil, H. S. Kibombo, C.-M. Wu, R. Peng, J. Baltrusaitis, R. T.
Koodali, Int. J. Hydrogen Energy 2012, 37, 8257-8267.
[25] H. Zuo, J. Sun, K. Deng, R. Su, F. Wei, D. Wang, Chem. Eng. Technol.
2007, 30, 577-582.
[2]
[3]
Q. Zhang, G. Ying, C. Pan, Y. Liu, J. Zhao, Environ. Sci. Technol. 2015,
49, 6772-6782.
a) R. Daghrir, P. Drogui, Environ. Chem. Lett. 2013, 11, 209-227.; b) Q.
Chen, X. Guo, G. Hua, G. Li, R. Feng, X. Liu, Environ. Pollut. 2017, 220,
1301-1310.
[26] P. Zhang, C. Shao, Z. Zhang, M. Zhang, J. Mu, Z. Guo, Y. Liu,
Nanoscale 2011, 3, 2943-2949.
[4]
[5]
R. Gothwal, T. Shashidhar, CLEAN – Soil, Air, Water 2015, 43, 479-
489.
[27] N. Liang, M. Wang, L. Jin, S. Huang, W. Chen, M. Xu, Q. He, J. Zai, N.
Fang, X. Qian, ACS Appl. Mater. Interfaces 2014, 6, 11698-11705.
[28] G.-w. Cui, W.-l. Wang, M.-y. Ma, M. Zhang, X.-y. Xia, F.-y. Han, X.-f.
Shi, Y.-q. Zhao, Y.-B. Dong, B. Tang, Chem. Commun. 2013, 49, 6415-
6417.
A. Christou, A. Agüera, J. M. Bayona, E. Cytryn, V. Fotopoulos, D.
Lambropoulou, C. M. Manaia, C. Michael, M. Revitt, P. Schröder, D.
Fatta-Kassinos, Water Res. 2017, 123, 448-467.
[6]
[7]
[8]
Y. Wang, Q. Wang, X. Zhan, F. Wang, M. Safdar, J. He, Nanoscale
2013, 5, 8326-8339.
[29]
a) S.-F. Yang, C.-G. Niu, D.-W. Huang, H. Zhang, C. Liang, G.-M.
Zeng, Environ. Sci.: Nano 2017, 4, 585-595.; b) T. C. Machado, T. M.
Pizzolato, A. Arenzon, J. Segalin, M. A. Lansarin, Sci. Total Environ.
2015, 502, 571-577.
H. Huang, X. Han, X. Li, S. Wang, P. K. Chu, Y. Zhang, ACS Appl.
Mater. Interfaces 2015, 7, 482-492.
a) H. Huang, K. Xiao, Y. He, T. Zhang, F. Dong, X. Du, Y. Zhang, Appl.
Catal. B: Environ. 2016, 199, 75-86; b) H. Huang, K. Xiao, T. Zhang, F.
Dong, Y. Zhang, Appl. Catal. B: Environ. 2017, 203, 879-888. c) H.
Huang, S. Tu, C. Zeng, T. Zhang, A. H. Reshak, Y. Zhang, Angew.
Chem. Int. Ed. 2017, 129, 12022-12026.
[30] Y. Luo, Y. Xu, X. Liu, H. Xue, Q. Qian, Q. Chen, J. Mater. Sci. 2017, 52,
1265-1271.
[31] D. Mao, A. Yu, S. Ding, F. Wang, S. Yang, C. Sun, H. He, Y. Liu, K. Yu,
Appl. Surf. Sci. 2016, 389, 742-750.
[32] a) C. Tan, G. Zhu, M. Hojamberdiev, K. Okada, J. Liang, X. Luo, P. Liu,
Y. Liu, Appl. Catal. B: Environ. 2014, 152, 425-436.; b) T. Ghorai, D.
Dhak, S. Dalai, P. Pramanik, J. Alloys Compd. 2008, 463, 390-397.
[33] T. Yan, J. Tian, W. Guan, Z. Qiao, W. Li, J. You, B. Huang, Appl. Catal.
B: Environ. 2017, 202, 84-94.
[9]
L. Zhou, W. Wang, L. Zhang, J. Mol. Catal. A: Chem 2007, 268, 195-
200.
[10] H. Huang, X. Li, J. Wang, F. Dong, P. K. Chu, T. Zhang, Y. Zhang, ACS
Catal. 2015, 5, 4094-4103.
[11] Y. Fu, L. Peng, Q. Zeng, Y. Yang, H. Song, J. Shao, S. Liu, J. Gu,
Chem. Eng. J. 2015, 270, 631-640.
[34] H. Huang, S. Tu, C. Zeng, T. Zhang, A. H. Reshak, Y. Zhang, Angew.
Chem. Int. Ed. 2017, 129, 12022-12026.
[12] S. Gupta, V. Subramanian, ACS Appl. Mater. Interfaces 2014, 6,
18597-18608.
[35] a) X. Guo, Y. Chen, Z. Qin, J. Su, L. Guo, ChemCatChem, 2016, 8,
3780–3789.
[13] F. Niu, D. Chen, L. Qin, N. Zhang, J. Wang, Z. Chen, Y. Huang,
ChemCatChem 2015, 7, 3279-3289.
[36] D. Sun, J. Li, L. He, B. Zhao, T. Wang, R. Li, S. Yin, Z. Feng, T. Sato,
CrystEngComm 2014, 16, 7564-7574.
[14] a) D. Zhou, H. Yang, Y. Tu, Y. Tian, Y. Cai, Z. Hu, X. Zhu, Nanoscale
res. Lett. 2016, 11, 1-8.; b) Z. Zhang, C. Jiang, P. Du, Y. Wang, Ceram.
Int. 2015, 41, 3932-3939.; c) H. Liu, Y. Chen, G. Tian, Z. Ren, C. Tian,
H. Fu, Langmuir 2015, 31, 5962-5969.
[37] Y. Jiang, T.-P. Loh, Chem. Sci. 2014, 5, 4939-4943.
[38] a) Y. Du, Q. Hao, D. Chen, T. Chen, S. Hao, J. Yang, H. Ding, W. Yao,
J. Song, Catal. Today 2017.; b) B. Gao, S. Dong, J. Liu, L. Liu, Q. Feng,
N. Tan, T. Liu, L. Bo, L. Wang, Chem. Eng. J. 2016, 304, 826-840.; c)
X. Wang, J. Jia, Y. Wang, Chem. Eng. J. 2017, 315, 274-282.; d) V. M.
Mboula, V. Hequet, Y. Gru, R. Colin, Y. Andres, J. Hazard. Mater. 2012,
209, 355-364.
[15] a) H. Shi, H. Tan, W.-b. Zhu, Z. Sun, Y. Ma, E. Wang, J. Mater. Chem.
A 2015, 3, 6586-6591.; b) Y. Liu, G. Zhu, J. Peng, J. Gao, C. Wang, P.
Liu, J Mater Sci: Mater Electron 2017, 28, 2172-2182.
[16] a) H. Peng, C. K. Chan, S. Meister, X. F. Zhang, Y. Cui, Chem. Mater.
2008, 21, 247-252.; b) Y. Yu, C. Cao, H. Liu, P. Li, F. Wei, Y. Jiang, W.
Song, J. Mater. Chem. A 2014, 2, 1677-1681.
[39] Z. Zhao, W. Zhang, Y. Sun, J. Yu, Y. Zhang, H. Wang, F. Dong, Z. Wu,
J. Phys. Chem. C 2016, 120, 11889-11898.
[40] H. Huang, Y. He, X. Li, M. Li, C. Zeng, F. Dong, X. Du, T. Zhang, Y.
Zhang, J. Mater. Chem. A 2015, 3, 24547-24556.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800100
ChemCatChem
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Yuxian Xu, Daifeng Lin, Xinping Liu,
Yongjin Luo*, Hun Xue, Baoquan
Huang, Qinghua Chen, and Qingrong
Qian*
Page No. – Page No.
Title Electrospun BiOCl/Bi2Ti2O7
nanorod heterostructures with
enhanced solar light efficiency in
photocatalytic degradation of
tetracycline hydrochloride
This article is protected by copyright. All rights reserved.