Internal Polarization Modulation in Bi2MoO6 for Photocatalytic Performance Enhancement under Visible-Light Illumination

Article abstract of DOI:10.1002/cssc.201800180

A built-in electric field from polarization inside polar photocatalysts could provide the driving force for photogenerated electrons and holes to move in opposite directions for better separation to improve their photocatalytic performance. The photocatalytic performance of a polar photocatalyst of Bi₂MoO₆ has been enhanced through the precise control of its structure to increase internal polarization. DFT calculations predicted that a shortened crystal lattice parameter b in Bi₂MoO₆ could induce larger internal polarization, which was achieved by the modulation of the pH of the reaction solution during a solvothermal synthetic process. A series of Bi₂MoO₆ samples were created with reaction solutions of pH≈1, 4, and 8; the crystal lattice parameter b was found to decrease gradually with increasing solution pH. Accordingly, these Bi₂MoO₆ samples demonstrated a gradually enhanced photocatalytic performance with decreasing crystal lattice parameter b, as demonstrated by the photocatalytic degradation of sulfamethoxazole/phenol and disinfection of Staphylococcus aureus bacteria under visible-light illumination due to improved photogenerated charge-carrier separation. This study demonstrates an innovative design strategy for materials to further enhance the photocatalytic performance of polar photocatalysts for a broad range of technical applications.

Full text of DOI:10.1002/cssc.201800180

Accepted Article
Title: Internal Polarization Modulation in Bi2MoO6 for Photocatalytic
Performance Enhancement under Visible Light Illumination
Authors: Yan Chen, Weiyi Yang, Shuang Gao, Linggang Zhu, Caixia
Sun, and Qi Li
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of the final Version of Record (VoR). This work is currently citable by
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To be cited as: ChemSusChem 10.1002/cssc.201800180
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ChemSusChem
10.1002/cssc.201800180
FULL PAPER
Internal Polarization Modulation in Bi MoO for Photocatalytic
2
6
Performance Enhancement under Visible Light Illumination
[
a,b,‡]
[a,‡]
[c]
[d]
[e,f]
[a, ]
Yan Chen,
Weiyi Yang,
Shuang Gao, Linggang Zhu, Caixia Sun,
and Qi Li *
Abstract: A built-in electric field from their internal polarization inside Introduction
polar photocatalysts could provide the driving force for
photogenerated electrons and holes to move in opposite directions
for better separation to improve their photocatalytic performance. In
this study, we enhanced the photocatalytic performance of a polar
Since the discovery of photocatalytic water splitting on the TiO
2
[
1]
photoanode in the 1972, semiconductor-based photocatalysis
has been attracting significant research attentions due to its
promising potentials in solar energy conversion and environment
photocatalyst of Bi
increase its internal polarization. DFT calculation predicted that a
shortened crystal lattice parameter b in Bi MoO could induce a
2 6
MoO by the precise control of its structure to
[
1-4]
remediation.
Despite the significant progresses achieved in
2
6
the past decades, the current research on photocatalysis still
could not meet the efficiency requirement for its industrial
applications in renewable/clean energy technologies and the
larger internal polarization, which was achieved by the modulation of
the reaction solution pH in its solvent-thermal synthesis process. A
series of Bi
pH of ~ 1, 4, and 8, respectively, and their crystal lattice parameter b
was found to decrease gradually with the increase of the solution pH. separation, and surface reactions, while the charge carrier
Accordingly, these Bi MoO samples demonstrated a gradually
separation is generally believed to be the most important factor
2
MoO
6
samples were created with the reaction solution
environment protections. The overall efficiency of
a
photocatalyst is determined by its light absorption, charge carrier
2
6
[
5,6]
enhanced photocatalytic performance with the decrease of their
crystal lattice parameter b as demonstrated by their photocatalytic
degradation of sulfamethoxazole/phenol and disinfection of
staphylococcus aureus bacteria under visible light illumination due to
the improved photogenerated charge carrier separation. This study
demonstrated a novel material design strategy to further enhance
the photocatalytic performance of polar photocatalysts for a broad
range of technical applications.
among them.
Thus, the enhancement of the charge carrier
separation efficiency is critical for the improvement of the overall
efficiency of a photocatalyst. Various approaches had been
developed for the enhancement of charge carrier separation
efficiency in photocatalysts, including doping with transition
[
7,8]
metals,
gap structures,
facet engineering.
forming composite photocatalysts with matched band
[
9-11]
[12-14]
noble metal modification,
and crystal
[
5,15-17]
Recently, the introduction of a built-in electric field inside polar
photocatalysts was proved effective for the improvement of their
photocatalytic performances because the internal electric filed
could provide the driving force for electrons and holes to move in
[
18]
opposite directions for their enhanced separation.
Most
[
a]
Prof. Q. Li, Dr. W. Yang, Y. Chen
Environment Functional Materials Division, Shenyang National
Laboratory for Materials Science
Institute of Metal Research, Chinese Academy of Sciences
Shenyang, Liaoning Province, 110016, P. R. China
E-mail: qili@imr.ac.cn (Q. Li)
research in polar photocatalysts is now focused on exploring
[
19]
polar semiconductors as novel photocatalysts, including GaN,
[
20,21]
[22,23]
[24]
[25]
[30]
ZnO,
Cu (OH)PO
and Bi Fe Ti
BaTiO
3
,
NaNbO
3
,
Sr
Na VO
2
(Ta,Nb)
2
O
7
,
,
[26]
[27]
[28]
[29]
2
4
,
BiOCl,
BiOF,
BiOIO
3
,
3
2
B
6
O
11
[31]
7
3
3
O
21
,
while fewer efforts had been made on the
[
[
b]
c]
Y. Chen
University of Chinese Academy of Sciences
Beijing 100049, P. R. China
Dr. S. Gao
Division of Energy and Environment
Graduate School at Shenzhen, Tsinghua University
Beijing 100049, P. R. China
modulation of their internal polarization through the precise
control of their structure to modulate their photocatalytic
performances.
Bi
2 6
MoO is one of the simplest members of the Aurivillius
2
+
family, which is composed by [Bi
2
O
2
]
layers sandwiched
The strong covalent bonding within
these layers and the weak interlayer van der Waals interaction
give rise to a highly anisotropic structure of Bi MoO . It had been
found that the internal electric field formed between the [Bi
2
-
[32]
[
[
d]
e]
Dr. L. Zhu
between MoO
slabs.
4
School of Materials Science and Engineering
Beihang University
Beijing 100049, P. R. China
2
6
2+
Dr. C. Sun
2 2
O ]
2
-
Key Laboratory of New Metallic Functional Materials and Advanced
Surface Engineering in Universities of Shandong
Qingdao Binhai University
and MoO
photogenerated charge carriers,
layers in Bi
MoO
could effectively separate
4
2
6
[32-36]
while the hybridization
between its O 2p and Bi 6s states could narrow its band gap to
Qingdao 266555, P. R. China
[f]
Dr. C. Sun
enable the absorption of visible light. Thus, it had drawn
School of Mechanical and Electronic Engineering
Qingdao Binhai University
Qingdao 266555, P. R. China
research attentions as an efficient visible-light-activated
[36-45]
photocatalyst for various applications.
More interestingly, its
[
‡]
layered structure with weak interlayer interaction could provide
the potential to be modulated, which could subsequently change
its internal polarization and open up an unexplored avenue to
These authors contributed equally to this work
Supporting information for this article is given via a link at the end of
the document.
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ChemSusChem
10.1002/cssc.201800180
FULL PAPER
further enhance the photocatalytic performance of a polar
photocatalyst.
Herein, we report the modulation of internal polarization in
apparent movements when the strain was applied on lattice b,
which should be attributed to the lower atomic density of
2
+
2-
[Bi
2
O ]
2
layers compared to MoO
4
layers. Thus, the atomic
Bi
2
MoO
6
by the precise control of its structure through both the
relaxation was mainly contributed by oxygen atoms near Bi. The
directions of the oxygen atom movements were shown in Figure
1a when the lattice parameter b was compressed, while their
movement directions would be reversed for a tensile strain (b
increased). Thus, the calculation results of dipole moment
variations with the change of lattice constant b suggested that
the lattice parameter b value should be decreased for the
theoretical and experimental approaches for the first time.
Theoretical calculation based on density function theory (DFT)
discovered that the internal polarization in Bi MoO could be
2 6
increased by shortening its crystal lattice parameter b.
Subsequently, a simple, one-pot template-free solvent-thermal
2 6
process was developed for the synthesis of Bi MoO
photocatalyst, and the addition of NaOH in the reaction solution
was found to be effective to shorten its crystal lattice parameter
increase of the polarity in Bi
photogenerated charge carriers, which provide the guidance in
2 6
MoO for a better separation of
b. With shortened crystal lattice parameter b, the Bi
2
MoO
6
the following synthesis of Bi
photocatalytic performance.
2 6
MoO photocatalysts for a better
photocatalyst demonstrated improved photogenerated charge
carrier separation efficiency due to its increased internal
polarization as demonstrated by the powder second-harmonic
generation (SHG) signal measurement, and subsequently
possessed a largely enhanced photocatalytic performance as
demonstrated in its photocatalytic degradation of organic
pollutants and disinfection of staphylococcus aureus bacteria
under visible light illumination.
Results and Discussion
Calculations of dipole moment variations with the change of
lattice constant b
Figure 1. (a) The schematic illustration of the crystal lattice structure of
Bi MoO (Note, dashed circles show oxygen atoms with significant movements
after the relaxation when the crystal lattice parameter b decreased). (b) The
calculated dipole moments of the system with different lattice parameter b
values before and after the relaxation, respectively (with the dipole moment of
The polarity of a polar photocatalyst is critical for its separation
of photogenerated charge carriers to enhance the photocatalytic
performance, which could be quantitatively described by its
2
6
dipole moment. With
a larger dipole moment, the polar
equilibrium state of Bi
2
MoO
6
(b=16.31 Å) as the reference).
photocatalyst has a higher polarity for a better separation of
photogenerated charge carriers. Figure 1a shows the schematic
illustration of the crystal lattice structure of Bi
2 6
MoO , and the
2-
Synthesis of Bi
lattice parameter b values
2
MoO
6
photocatalysts with a series of crystal
direction of dipole moment was along the b axis from MoO
4
2+
[33,46]
layer to [Bi
2
O ]
2
layer.
Thus, the change of lattice
parameter b should affect its dipole moment. Figure 1b shows
the calculated dipole moments of the system with different lattice
parameter b values. It was found that the dipole moment could
slightly increase with the increase of lattice parameter b value
when lattice a/c as well as the internal positions of the atoms
were fixed (before relaxation). This result could be easily
understood because in this case the distances between all
atoms were changed uniformly and the effective distance
between the centers of the positive charge and the negative
charge will increase/decrease with the increase/decrease of the
lattice parameter b value.
A solvent-thermal process was used for the synthesis of
Bi
2
6 2 5
MoO photocatalysts, in which C H OH and ethylene glycol
(
EG) served both as the reaction solvents and the complexing
[37]
agents to control the release of Bi(III).
It had been
demonstrated that hydroxyl groups in the reaction system could
largely affect the hydrolysis and condensation reactions for the
[
48-51]
synthesis of metal oxide nanoparticles,
and the reaction
solution pH could have an impact on the electrostatic
[
44]
interactions between reactants to modulate the crystal growth.
Thus, the addition of NaOH was adopted to vary the reaction
solution pH in our solvent-thermal synthesis of Bi MoO
2
6
However, to minimize the system energy, a relaxation will
happen in the crystal lattice with the change of lattice parameter
photocatalysts to examine its effect on the obtained samples.
When the reaction solution pH was over 8, it was found that
phases other than Bi MoO could occur. Thus, the highest
2 6
[
33,47]
b value.
Interestingly, an opposite trend was found after the
relaxation when the lattice a/c and the atomic positions were
free to relax. The dipole moment decreased with the increase of
the lattice parameter b value (see Figure 1b). To figure out its
origin, the atomic movements after the relaxation were studied.
It was found that the deformation was nonuniform inside the
deformed cell. Only oxygen atoms near Bi demonstrated
reaction solution pH was limited at 8. By the addition of proper
amounts of NaOH, the reaction solution pH was adjusted to 4
and 8 to obtain the BMO-4 and BMO-8 samples, respectively,
while the BMO-1 sample was synthesized without the addition of
0
NaOH in the reaction solution (pH ~1). It was found that 160 C
was the optimized solvent-thermal reaction temperature to
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10.1002/cssc.201800180
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obtain samples with better photocatalytic performances, while
the solvent-thermal reaction time was set at 20 h to avoid the
Characterization of Bi
crystal lattice parameter b values
2
MoO
6
photocatalyst with a series of
2 6
occurrence of other phases besides Bi MoO in the obtained
product due to incomplete reaction. The product yields of the
BMO-1, BMO-4 and BMO-8 samples were ~ 79%, 82%, and
Figure 3a to Figure 3c show the bright field TEM observations of
the BMO-1 sample, the BMO-4 sample, and the BMO-8 sample,
respectively, which demonstrated their nano-sized features. The
BMO-1 sample was composed of irregular nanoplates, the
BMO-4 sample was composed of thicker nanoblocks, while the
BMO-8 sample was composed of relatively large nanosheets
close to the rectangular shape. The insert image in Figure 3c
shows the selected area electron diffraction (SAED) pattern
obtained from the black circular area on the nanosheet in the
BMO-8 sample, which clearly demonstrated its single crystal
feature. Figure 3d shows the high resolution TEM (HRTEM)
image of the nanosheet in the BMO-8 sample marked by the
black rectangular in Figure 3c, and the insert images in Figure
3d show the fast Fourier transformation (FFT) pattern and the
magnified high resolution TEM image of the area marked by the
white rectangular in Figure 3d, respectively. From the TEM
analysis results, the basal plane of the nanosheet in the BMO-8
sample could be indexed as {010}, which was exactly
87%, respectively. Figure 2a shows the XRD patterns of all three
samples, which demonstrated that they had the same crystal
structure type and their diffraction peaks all belonged to the pure
Bi
towards the higher 2θ direction of their corresponding diffraction
peaks could be observed on these Bi MoO sample with the
increase of the reaction solution pH as demonstrated in Figure
b with their (131) peaks as an examples at a higher
2 6
MoO phase (JCPDS No. 21-0102). However, a slight shift
2
6
2
magnification. This observation clearly suggested that the
addition of NaOH in the reaction solution could affect the
crystallization and growth of Bi
From the XRD analysis data, the crystal lattice parameters of
these three Bi MoO samples were obtained as shown in Table
, which clearly demonstrated that their crystal lattice parameter
2 6
MoO in our synthesis approach.
2
6
1
b values gradually decreased from 16.3947 Å of the BMO-1
sample, to 16.2906 Å of the BMO-4 sample, and to 16.2415 Å of
the BMO-8 sample, respectively. Thus, a simple and robust
approach of the addition of NaOH in the reaction solution was
2 6
perpendicular to the b axis of Bi MoO (the dipole moment
direction). Two side faces of the nanosheet in the BMO-8
sample could be indexed as {100} plane and {001} plane,
respectively. BET analysis results demonstrated that the BET
2 6
found to be effective for the creation of Bi MoO photocatalysts
with shortened crystal lattice parameter b in our synthesis
process, which could increase its internal polarization and
subsequently enhance its photocatalytic performance as
demonstrated in relevant sections followed.
2
-1
specific surface area of the BMO-1 sample was ~ 46.52 m ·g ,
2
-1
that of the BMO-4 sample was ~ 34.79 m ·g , and that of the
2
-1
BMO-8 sample was ~ 15.77 m ·g . The isoelectric point (IEP)
values of the BMO-1, BMO-4, and BMO-8 samples were
determined at ~ 3.8, 4.7, and 5.0, respectively (see Figure S1 in
the supplementary information).
The chemical compositions and element valence states in
these Bi MoO photocatalyst samples were investigated by X-
2 6
ray photoelectron spectroscopy (XPS). Figure 4a shows their
XPS survey spectra, which demonstrated clearly the existence
of Bi, Mo, and O in all of them. Due to the widespread presence
of carbon in the environment, C 1s peak could also be observed
in their XPS survey spectra. Elemental analysis was conducted
on these samples, which demonstrated that the carbon contents
in the BMO-1, BMO-4, and BMO-8 samples were ~ 0.3000 wt%,
Figure 2. (a) The XRD patterns of the BMO-1 sample, the BMO-4 sample and
the BMO-8 sample. (b) The (131) peak of the BMO-8 sample at a higher
magnification, compared with that of the BMO-1 sample and that of the BMO-4
sample.
0.2436 wt%, and 0.2412 wt%, respectively. Such a low carbon
content should have minimum effect on their photocatalytic
performance. Figure 4b to 4d show their high resolution XPS
scans over Bi 4f, Mo 3d, and O 1s peaks, respectively, which
demonstrated that they had very similar XPS spectra for all the
three elements. For Bi 4f spectrum (Figure 4b), the two XPS
Table 1. The crystal lattice parameters of the Bi
2
MoO
6
photocatalyst
3
+
samples
peaks at 158.8 and 164.2 eV could be assigned to Bi 4f7/2 and
3
+
Bi 4f5/2, respectively. For Mo 3d spectrum (Figure 4c), the two
Sample
BMO-1
BMO-4
BMO-8
a (Å)
b (Å)
c (Å)
Vol (Å3)
498.23
494.30
488.71
6+
XPS peaks at 232.2 and 235.3 eV could be assigned to Mo
6
+
[38,50]
3d5/2 and Mo 3d3/2, respectively.
For O 1s spectrum
5.5330
5.5290
5.4900
16.3947
16.2906
16.2415
5.4924
5.4879
5.4810
(
Figure 4d), the wide and asymmetric peak could be fitted into
the combination of two peaks with the peak positions at 529.79
and 530.65 eV, which are related to Bi–O and Mo–O,
[52]
respectively.
This observation was in accordance with the
XRD and TEM analysis results, suggesting that the BMO-1
sample, the BMO-4 sample and the BMO-8 sample had the
same chemical composition as Bi MoO .
2 6
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ChemSusChem
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[
53,54]
Munk function.
Figure 5a shows their light absorbance
2
spectra compared with that of Degussa P25 TiO nanoparticles,
and the insert image in Figure 5a shows their band gap values
determined by the construction of Tauc Plots ((F(R)*hv)n vs. hv)
[
53]
from their light absorbance data.
Degussa P25 TiO
2
nanoparticles demonstrated a characteristic adsorption stopping
edge at ~ 400 nm, while all these BMO samples demonstrated a
strong light absorbance from the UV light region into the visible
light region, which was consistent with their yellow color
appearance. For all three BMO samples, their light absorbance
spectra had the steep shape with fundamental absorbance
stopping edges into the visible light region (~ 500 nm), which
indicated that its visible light absorption was arisen from the
[
37]
band-gap transition. Among them, the BMO-1 sample had the
best visible light absorbance, while the BMO-8 sample had the
lowest visible light absorbance. From their Tauc Plots, their band
gaps were determined at ~ 3.03 eV for Degussa P25 TiO
2
nanoparticles, ~ 2.74 eV for the BMO-1 sample, ~ 2.78 eV for
the BMO-4 sample, and ~ 2.85 eV for the BMO-8 sample,
respectively.
Mott−Schottky analysis was carried out to determine the
conduction band (CB) minimums of our samples. From the M-S
Plots (Figure 5b), the flat band potentials of our samples (vs.
Ag/AgCl) were determined at ~ -0.22 V (BMO-1), -0.27 V (BMO-
Figure 3. (a) to (c) The bright field TEM observations of the BMO-1 sample,
the BMO-4 sample, and the BMO-8 sample, respectively (Note, the insert
image in Figure 3c shows the selected area electron diffraction (SAED) pattern
obtained from the black circular area on the nanosheet in the BMO-8 sample).
(d) The high resolution TEM (HRTEM) image of the nanosheet in the BMO-8
sample marked by the black rectangular in Figure 3c (Note, the insert images
in Figure 3d show the fast Fourier transformation (FFT) pattern and the
magnified high resolution TEM image of the area marked by the white
rectangular in Figure 3d, respectively).
4), and -0.32 V (BMO-8), respectively. It is generally known that
E (Ag/AgCl) is 0.2224 V (vs. NHE, Normal Hydrogen Electrode),
and the bottom of the conduction band of an n-type
semiconductor is 0.2 V more negative than its flat band
[
55,56]
potential.
samples (vs. NHE) could be determined at ~ -0.20 V (BMO-1), -
.25 V (BMO-4), and -0.30 V (BMO-8), respectively. With the
Thus, the conduction band (CB) minimums of our
0
band gap values determined from their Tauc Plots, the valence
band (VB) maximums of our samples (vs. NHE) could be
determined at ~ 2.54 V (BMO-1), 2.53 V (BMO-4), and 2.55 V
(
BMO-8), respectively. Thus, their energy band structures could
be constructed as demonstrated in Figure 5c, which
demonstrated that their conduction band potentials were all
more negative than the one-electron reduction potential of O
−0.05 V vs NHE). VB-XPS measurements were also conducted
2
(
on our samples (see Figure S2 in the supplementary
information), which demonstrated that their relative positions of
VB maximum edges were very close. This observation was in
accordance with their energy band structures determined by
their Mott-Schottky Plots and Tauc Plots.
Figure 4. (a) XPS survey spectra of the BMO-8 sample, compared with that of
the BMO-1 sample and that of the BMO-4 sample. (b) to (d) The high
resolution XPS scans over Bi 4f, Mo 3d, and O 1s peaks of both samples,
respectively.
2 6
Polarity measurements of Bi MoO photocatalyst with a
series of crystal lattice parameter b values
To demonstrate the increase of polarity in Bi
2
MoO
6
by
decreasing the lattice
b experimentally, powder second-
2 6
Optical properties and energy band structures of Bi MoO
photocatalyst with a series of crystal lattice parameter b
values
harmonic generation (SHG) signals of our BMO samples
irradiated by a Nd:YAG laser (λ at 1064 nm) were measured,
and the results were shown in Figure 6a. The non-
centrosymmetric polar crystal structure of Bi
2
MoO
6
could
The optical properties of these three samples were examined by
measuring their UV-vis diffuse reflectance spectra, and their light
absorbance spectra could be approximated by the Kubelka-
generate a non-linear optical (NLO) property, and a larger NLO
[
57]
response could indicate a larger polarity.
Figure 6a clearly
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ChemSusChem
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FULL PAPER
demonstrated that the NLO response of our samples followed
the ranking of the BMO-1 sample < the BMO-4 sample < the
BMO-8 sample, although they had the same crystal structure
and chemical composition. This experimental result clearly
2 6
Photoelectrochemical (PEC) measurements of Bi MoO
photocatalysts with a series of crystal lattice parameter b
values
suggested that the polarity in Bi
decrease of the lattice b, which was in accordance with the DFT
calculation result.
2
MoO
6
increased with the
A better light absorbance, however, could not directly suggest a
better photocatalytic activity because photogenerated charge
carriers may be lost due to their recombination and could not
produce radicals. Thus, the detection of charge carriers that
transferred to the surface of the photocatalyst could provide a
more accurate estimation of its photocatalytic response. As a
powerful tool for investigating the photogenerated charge carrier
separation and transfer behavior, the photoelectrochemical
(
PEC) measurement were conducted on these three samples,
respectively, and the results were shown in Figure 6b and 6c.
Figure 6b compares the photocurrent responses of these
samples under illumination. Under applied potential between 0.2
V to 1.0 V versus Ag/AgCl, the dark current of all these three
samples remained a very low level. When the illumination was
on, they all exhibited obvious photocurrent densities. Although
the visible light absorbance of the BMO-1 sample was higher
than that of the BMO-4 sample and the visible light absorbance
of the BMO-4 sample was higher than that of the BMO-8 sample
(
see Figure 6a), their photocurrent densities obviously had the
opposite ranking. The photocurrent density of the BMO-8
sample was ~ 4 times as that of the BMO-1 sample, while the
photocurrent density of the BMO-4 sample was ~ 2 times as that
of the BMO-1 sample.
Figure 5. (a) The light absorbance of the BMO-8 sample, compared with that
of the BMO-1 sample, that of the BMO-4 sample, and that of Degussa P25
TiO nanoparticles (Note, the insert image in Figure 5a shows their band gap
2
values determined by the construction of Tauc Plots ((F(R)*hv)n vs. hv) from
their light absorbance data). (b) The Mott-Schottky Plots of the BMO-8 sample,
compared with that of the BMO-1 sample and that of the BMO-4 sample. (c)
The energy band structures of the BMO-1, BMO-4, and BMO-8 samples,
respectively.
Figure 6c compares the electrochemical impedance spectra
(EIS) of these samples under illumination, which clearly
demonstrated that the BMO-8 sample had the smallest diameter
of the Nyquist circular radius among them and the BMO-4
sample had a smaller diameter of the Nyquist circular radius
than the BMO-1 sample. The arc radius on the EIS Nyquist plot
could reveal reaction rate occurring at the surface of the
electrodes. A smaller arc radius indicated a more effective
separation of photogenerated carriers and faster interfacial
[
46]
charge transfer to the electron acceptor or donor.
understand the EIS measurement results, the EIS data were
fitted to the equivalent circuit as demonstrated in Figure 6c. R is
the series resistance which depends on the external circuit
dynamics, dl is the space charge capacitance in the
To better
s
C
semiconducting layer, and Rct is the charge-transfer resistance.
The Cdl values of the BMO-1, BMO-4, and the BMO-8 samples
were 3.87 μF, 9.271 μF, and 30.26 μF, respectively, while their
Rct values were 94.7 kΩ, 30.16 kΩ, and 10.6 kΩ, respectively. A
smaller Rct value and a larger Cdl value could suggest an
[
58,59]
improved charge transport characteristics.
Thus, the BMO-8
sample had the best charge transfer efficiency among these
samples.
Figure 6. (a) The second harmonic generation (SHG) responses of the BMO-1,
BMO-4, and BMO-8 samples, respectively. (b) The photocurrent responses of
the BMO-1, BMO-4, and BMO-8 samples under illumination in the applied
potential range between 0.2 V to 1.0 V versus Ag/AgCl, respectively. (c) The
electrochemical impedance spectra of the BMO-1, BMO-4, and BMO-8
samples under illumination, respectively (Note, the insert image in Figure 6c
shows the equivalent circuit used to fit the spectra). (d) The IPCE spectra of
the BMO-1, BMO-4, and BMO-8 samples, respectively.
Figure S3 in the supplementary information compares the
surface photovoltage (SPV) spectra of the BMO-1 sample and
the BMO-8 sample. It clearly demonstrated that the surface
photovoltage of the BMO-8 sample was much stronger than that
of the BMO-1 sample, which suggested that the BMO-8 sample
had a largely enhanced charge separation efficiency than that of
the BMO-1 sample. This observation was consistent with the
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ChemSusChem
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photocurrent responses and the electrochemical impedance
spectra of these samples.
These observations indicated that the photogenerated charge
BMO photocatalysts were negatively charged. Thus, its
adsorptions onto these BMO photocatalysts were not favored
due to the electrostatic repulsion between them, and the
adsorption effect was not obvious. Due to the co-existence of
2 6
carrier separation efficiencies of these Bi MoO photocatalysts
were different, which could be attributed to their different internal
polarizations from their different crystal lattice parameter b
values. With their gradually decreased crystal lattice parameter
anatase and rutile phases in P25 TiO
2
nanoparticle, it
demonstrated a moderate photocatalytic degradation effect on
SMX under visible light illumination. After 40 min treatment, the
residue SMX concentration was still ~ 90%. The BMO-1
demonstrated a better photocatalytic degradation effect on SMX
b
values, their photogenerated charge carrier separation
efficiencies increased as predicted by the DFT calculation
results of dipole moment variations with the change of crystal
lattice constant b and the SHG measurement results. Thus, a
better photocatalytic performance should be expected with the
ranking of the BMO-1 sample < the BMO-4 sample < the BMO-8
sample when their crystal lattice constant b gradually decreased.
2
under visible light illumination than P25 TiO nanoparticle. After
40 min treatment, the residue SMX concentration dropped to ~
70%. When its crystal lattice parameter b was shortened by the
increase of the reaction solution pH from ~ 1 to ~ 4, the BMO-4
sample demonstrated a better photocatalytic degradation effect
on SMX than the BMO-1 sample under visible light illumination.
After 40 min treatment, the residue SMX concentration dropped
to ~ 50%. As expected, the BMO-8 sample with the shortest
crystal lattice parameter b demonstrated the best photocatalytic
degradation effect on SMX under visible light illumination among
Incident photon to current efficiency (IPCE) spectra of
Bi MoO photocatalysts with a series of crystal lattice
2 6
parameter b values
2 6
these three Bi MoO photocatalysts. After 40 min treatment, the
The incident photon to current efficiency (IPCE) spectra
measurements were conducted on our BMO samples to provide
residue SMX concentration largely dropped to just ~ 25%.
A first-order exponential decay of SMX concentration was
a comparison of standard quantum efficiencies of these samples, observed for all these four photocatalysts, which could be fitted
and the result was shown in Figure 6d. As expected, the IPCE
values of these samples followed the ranking of the BMO-1
sample < the BMO-4 sample < the BMO-8 sample in the whole
visible light region, although their visible light adsorption
capabilities followed the ranking of the BMO-8 sample < the
BMO-4 sample < the BMO-1 sample. It is well known that IPCE
is mainly affected by the light harvesting efficiency, charge
to Eq. (1):
ꢀ ꢁꢂ ꢃ⁄ꢃ ꢅ ꢆ ꢇꢈꢉ
(1)
ꢄ
where C is the residue SMX concentration, t is the visible light
illumination time, and k is the decay rate constant that could be
used to compare the photocatalytic SMX degradation efficiency
of different samples. The decay rate constant k of the BMO-8
sample on SMX was determined at ~ 0.0502 min , which was ~
2.8 times, ~ 3.6 times, and ~ 13 times as that of the BMO-4
[
60,61]
separation and collection yields.
Thus, these results further
-1
suggested that the BMO-8 sample had an improved charge
separation and collection yield, which was in good agreement
with its polarity increase from the decrease of the lattice b and
subsequent better PEC measurement results. Thus, the BMO-8
sample should have the best photocatalytic performance among
these BMO samples.
-1
-1
sample (0.0178 min ), the BMO-1 sample (0.0140 min ), and
-1
P25 TiO
they had the same Bi
the photocatalytic SMX degradation performance ranking of
these Bi MoO samples followed the sequence as the BMO-8
2
nanoparticle (0.0038 min ), respectively. Although
2
MoO crystal structure and composition,
6
2
6
sample > the BMO-4 sample > the BMO-1 sample, opposite to
their visible light absorbance ranking and BET specific area
ranking. This observation was in accordance to their
photogenerated charge carrier separation efficiency ranking
result and IPCE ranking result, which could be attributed to their
gradually increased internal polarization as we shortened its
crystal lattice parameter b in the material design and synthesis.
The apparent quantum efficiency is an important parameter to
Photocatalytic degradation of SMX under visible light
illumination
2 6
The photocatalytic performances of these Bi MoO
photocatalysts with a series of crystal lattice parameter b values
were first demonstrated by their degradation of organic
pollutants under visible light illumination. As a widely used
veterinary medicine, SMX has been identified in surface water
due of its low biodegradability as an emerging pollutant, which
could cause environmental pollution and increase antibiotic
demonstrate the performance of
a
photocatalyst in
[
65-67]
heterogeneous photocatalysis,
Eq. (2):
which could be defined as
[
62-64]
resistance in human.
Unlike colorful organic dyes, SMX
does not absorb visible light, which could exclude the potential
photosensitization effect from organic dyes on the evaluation of
the photocatalytic activity under visible light illumination. Figure
ꢊ ꢆ ꢇꢂꢌ[ꢃ]⁄ꢌꢉꢅꢍꢂꢌ[ꢎꢏ]ꢐꢑꢒ⁄ꢌꢉꢅꢁ
(2)
ꢋ
where ꢌ[ꢃ]⁄ꢌꢉꢁis the change rate of the pollutant concentration,
and ꢌ[ꢎꢏ]ꢐꢑꢒ⁄ꢌꢉ is the total light illumination power striking the
sample. The apparent quantum efficiencies of these samples on
the photocatalytic degradation of SMX under visible light
illumination could be determined as Eq. (3):
7a summaries the residue SMX concentrations vs. treatment
time under visible light illumination by the P25 TiO nanoparticle,
2
the BMO-1 sample, the BMO-4 sample, and the BMO-8 sample,
respectively. At the solution pH of ~ 6.5, both SMX and these
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ꢓ ꢆ ꢕꢖ ꢗꢘꢙꢚꢍꢂꢛ[ꢜꢝ]ꢞꢟꢠ⁄ꢛꢡꢅꢁ
(3)
serve as a model organic pollutant for the evaluation of the
photocatalytic activity under visible light illumination. Figure 7b
ꢔ
ꢄ
which was dependent on the treatment time t. In our
photocatalytic organic degradation experimental setup,
ꢌ[ꢎꢏ]ꢐꢑꢒ⁄ꢌꢉ is a constant of 76.34 J/min. Thus, the initial
apparent quantum efficiencies (t→0) of the BMO-1 sample, the
BMO-4 sample, and the BMO-8 sample on the photocatalytic
degradation of SMX under visible light illumination could be
summaries the residue phenol concentrations (in C/C
treatment time under visible light illumination by the P25 TiO
0
form) vs.
2
nanoparticle, the BMO-1 sample, the BMO-4 sample, and the
BMO-8 sample, respectively. At the solution pH of ~ 6.5, both
phenol and these BMO photocatalysts were negatively charged.
Thus, its adsorptions onto these BMO photocatalysts were not
favored due to the electrostatic repulsion between them, and the
adsorption effect was not obvious. After 120 min treatment with
-3
-3
-
determined at ~ 4.58×10 ppm/J, 5.83×10 ppm/J, and 1.65×10
2
2
ppm/J, respectively, while that of P25 TiO nanoparticle was
-3
only ~ 1.24×10 ppm/J. After being normalized by their specific
surface areas to exclude the surface area factor in the
comparison, the initial apparent quantum efficiencies of these
BMO samples with the same surface area on the photocatalytic
degradation of SMX under visible light illumination could be
the P25 TiO
still ~ 90%. All the Bi
photocatalytic degradation performances on phenol than the
P25 TiO nanoparticle under visible light illumination. The BMO-
1 and BMO-4 samples demonstrated a better photocatalytic
degradation effect on phenol than P25 TiO nanoparticle. After
2
nanoparticle, the residue phenol concentration was
2
MoO photocatalysts demonstrated better
6
2
-
5
2
-4
2
determined at ~ 9.8×10 ppm·g/(J·m ), 1.67×10 ppm·g/(J·m ),
and 1.05×10
2
-3
2
ppm·g/(J·m ), respectively, which further
120 min treatment under visible light illumination, the residue
phenol concentration dropped to ~ 80% for the BMO-1 sample,
~ 70% for the BMO-4 sample, and ~ 60% for the BMO-8 sample,
respectively. A zero-order decay of phenol concentration was
observed for all these four photocatalysts, which could be fitted
to Eq. (4):
confirmed the largely enhanced photocatalytic degradation effect
on SMX by the BMO-8 sample with the enhanced internal
polarization from its shortened crystal lattice parameter b.
ꢃ⁄ꢃ ꢆ ꢇꢈꢉ
(4)
ꢄ
where C is the residue phenol concentration, t is the visible light
illumination time, and k is the decay rate constant that could be
used to compare the photocatalytic phenol degradation
efficiency of different samples. The decay rate constant k of the
-1
BMO-8 sample on phenol was determined at 0.0032 min ,
which was ~ 1.4 times, ~ 2.3 times and ~ 6 times as that of the
-
1
-1
BMO-4 sample (0.0023 min ), the BMO-1 sample (0.0014 min )
-1
2
and the P25 TiO nanoparticle (0.00053 min ), respectively. The
apparent quantum efficiencies of these samples on the
photocatalytic degradation of phenol under visible light
illumination could be determined as Eq. (5):
ꢊ ꢆ ꢈꢃ ꢍꢂꢌ[ꢎꢏ]ꢐꢑꢒ⁄ꢌꢉꢅ
(5)
ꢋ
ꢄ
which was independent on the treatment time t due to the zero
order decay behavior. Thus, the apparent quantum efficiencies
of the BMO-1 sample, the BMO-4 sample, and the BMO-8
sample on the photocatalytic degradation of phenol under visible
Figure 7. (a) The residue SMX concentrations vs. treatment time under visible
light illumination by the P25 TiO
sample, and the BMO-8 sample, respectively. (b) The residue phenol
concentrations (in C/C form) vs. treatment time under visible light illumination
by the P25 TiO nanoparticle, the BMO-1 sample, the BMO-4 sample, and the
2
nanoparticle, the BMO-1 sample, the BMO-4
0
-4
2
light illumination could be determined at ~ 1.83×10 ppm/J,
BMO-8 sample, respectively. (c) The survival ratio of S. aureus by the
treatment of the BMO-1 sample, the BMO-4 sample, and the BMO-8 sample
under visible light illumination, respectively, compared with that without the
presence of photocatalyst under visible light illumination.
-4
-4
3
.01×10 ppm/J, and 4.19×10 ppm/J, respectively, while that of
-5
2
P25 TiO nanoparticle was only ~ 6.94×10 ppm/J. After being
normalized by their specific surface areas to exclude the surface
area factor in the comparison, the initial apparent quantum
efficiencies of these BMO samples with the same surface area
on the photocatalytic degradation of phenol under visible light
Photocatalytic degradation of phenol under visible light
illumination
-5
2
illumination could be determined at ~ 4.83×10 ppm·g/(J·m ),
-5
2
-4
2
8.65×10
ppm·g/(J·m ),
and
2.66×10
ppm·g/(J·m ),
respectively, which further confirmed the largely enhanced
photocatalytic degradation effect on phenol by the BMO-8
sample with the enhanced internal polarization from its
shortened crystal lattice parameter b.
Phenol is one of the widely-distributed organic pollutants in
wastewater from industrial activities, which could cause
damages to both the environment and human beings due to its
[
68,69]
bio-recalcitrance and acute toxicity.
As a colorless organics,
phenol also does not absorb visible light, which could exclude
the potential photosensitization effect from organic dyes and
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Photocatalytic disinfection of staphylococcus aureus
bacteria under visible light illumination
1320 (cfu/mL)/J, respectively. After being normalized by their
specific surface areas to exclude the surface area factor in the
comparison, the initial apparent quantum efficiencies of these
samples with the same surface area on the photocatalytic
The superior photocatalytic performance of the BMO-8 sample
was further demonstrated by its photocatalytic disinfection of S.
aureus cells, which is a commonly found pathogenic coccus in
hospitals that could cause nonspecific infection and nosocomial
disinfection of S. aureus cells under visible light illumination
2
could be determined at
~
3.5 (cfu/mL)·g/(J·m ), 21
2
2
(cfu/mL)·g/(J·m ), and 58 (cfu/mL)·g/(J·m ), respectively, which
further confirmed the largely enhanced photocatalytic
disinfection effect on S. aureus cells by the BMO-8 sample with
the enhanced internal polarization from its shortened crystal
lattice parameter b.
[
70]
infection.
The photocatalytic disinfection experiment was
conducted by exposing the cells suspended in the buffer solution
with the photocatalyst under visible light illumination for varying
time intervals. Figure 7c shows the survival ratio of S. aureus by
the treatment of the BMO-1 sample, the BMO-4 sample, and the
BMO-8 sample under visible light illumination, respectively,
compared with that without the presence of photocatalyst under
visible light illumination. Without the presence of photocatalyst,
no obvious vitality loss was observed on S. aureus cells under
visible light illumination. The BMO-1 sample demonstrated a
moderate photocatalytic disinfection effect on S. aureus cells
under visible light illumination. After 120 min treatment, the
survival ratio of S. aureus cells dropped to ~ 85%. The BMO-4
sample demonstrated a better photocatalytic disinfection effect
on S. aureus cells than the BMO-1 sample under visible light
illumination. After 120 min treatment, the survival ratio of S.
aureus cells dropped to ~ 43%. As expected, the BMO-8 sample
demonstrated the best photocatalytic disinfection effect on S.
aureus cells under visible light illumination. The survival ratio of
S. aureus cells continuously decreased with the increase of the
treatment time. After 120 min treatment, the survival ratio of S.
aureus cells treated by the BMO-8 sample largely dropped to
less than 16%, which was more than 5 times lower than that
treated by the BMO-1 sample. A zero-order decay of the survival
Main reactive oxygen species for the photocatalytic activity
of Bi MoO photocatalyst with shortened crystal lattice
2 6
parameter b under visible light illumination
Under proper illumination, various reactive oxygen species
(ROSs) could be produced by photocatalysts, and the
determination of main ROSs involved in the photocatalytic
process is critical for the understanding of its working
mechanism. Thus, radical scavengers of Benzoquinone (P-BQ),
NaBrO
3
, isopropanol (IPA), and ammonium oxalate were used in
-
-
radical trapping experiments for superoxide (·O
2
), electrons (e ),
+
hydroxyl radicals (·OH), and holes (h ), respectively, to examine
if their existence could affect the photocatalytic degradation of
SMX by the BMO-8 sample. Figure 8 shows the residue SMX
concentrations vs. treatment time under visible light illumination
by the BMO-8 sample with different radical scavengers,
respectively. The results demonstrated that the addition of
3
NaBrO or IPA had no effect on the photocatalytic degradation of
ratio of S. aureus cells was observed, which could be fitted to Eq. SMX by the BMO-8 sample, while the addition of P-BQ or
(
6):
ammonium oxalate largely inhibited the photocatalytic
degradation of SMX by the BMO-8 sample. Thus, the dominant
ROSs involved in the photocatalytic SMX degradation by the
ꢢ ⁄ꢢ ꢆ ꢇꢈꢉ
(6)
ꢣ
ꢄ
-
+
BMO-8 sample were ·O
2
and h . This observation was
where N
0
and N
t
are the numbers of colony forming units at the
consistent with its energy band structure of the BMO-8 sample
(Figure 5c). Due to its more negative conduction band potential
initial and each following time interval, respectively, t is the
visible light illumination time, and k is the decay rate constant
that could be used to compare the photocatalytic efficiency of
different samples. The decay rate constant k of the BMO-8
sample on S. aureus cells was determined at 0.007 min , which
was ~ 1.25 times and ~ 5.6 times as that of the BMO-4 sample
than the one-electron reduction potential of O
electrons could readily react with O to produce ·O
photogenerated holes reacted directly with SMX.
2
, photogenerated
-
2
2
, while
-1
-1
-1
(
0.0056 min ) and the BMO-1 sample (0.00125 min ). The
apparent quantum efficiencies of these samples on the
photocatalytic disinfection of S. aureus cells under visible light
illumination could be determined as Eq. (7):
ꢊ ꢆ ꢈꢢ ꢍꢂꢌ[ꢎꢏ]ꢐꢑꢒ⁄ꢌꢉꢅ
(7)
ꢋ
ꢄ
which was also independent on the treatment time t due to the
zero order decay behavior. In our photocatalytic disinfection
experimental setup,ꢁꢌ[ꢎꢏ]ꢐꢑꢒ⁄ꢌꢉ is a constant of 53.01 J/min.
Thus, the apparent quantum efficiencies of the BMO-1 sample,
the BMO-4 sample, and the BMO-8 sample on the photocatalytic
disinfection of S. aureus cells under visible light illumination
could be determined at ~ 236 (cfu/mL)/J, 1056 (cfu/mL)/J, and
Figure 8. The residue SMX concentrations vs. treatment time under visible
light illumination by the BMO-8 sample with the presence of different radical
scavengers.
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The stability and reusability of Bi
shortened crystal lattice parameter b
2
MoO
6
photocatalyst with
under visible light illumination. This observation could be
attributed to its increased internal polarization with the decrease
of crystal lattice parameter b, which subsequently improved
photogenerated charge carrier separation efficiency as verified
in the photoelectrochemical measurement results. This study
demonstrated an unexplored strategy for the design and
synthesis of polar photocatalysts to enhance their photocatalytic
performance, which may have the potential for a broad range of
technical applications.
The stability and reusability of a photocatalyst is critical for its
potential applications in environmental remediation practice.
Figure 9a shows the photocatalytic degradation of SMX by the
BMO-8 sample under visible light illumination for five runs. After
each run, the photocatalyst was collected, washed, dried, and
then reused in the photocatalytic degradation of SMX for the
next run. In general, the BMO-8 sample demonstrated similar
photocatalytic degradation behavior on SMX under visible light
illumination for the five runs, and no obvious reduction of the
photocatalytic degradation efficiency was observed. Figure 9b
shows the XRD patterns of the BMO-8 sample before and after
the photocatalytic SMX degradation experiment for five runs,
respectively, which clearly demonstrated that the two XRD
patterns were identical. Figure S4 in the supplementary
information shows the TEM image of the BMO-8 sample after
the photocatalytic SMX degradation experiment for five runs,
which clearly demonstrated that its nanosheet morphology was
not changed. Thus, the recycle photocatalytic degradation
experiment, the XRD analysis results, and the TEM observations
suggested that the BMO-8 sample had a good stability and
reusability, which was beneficial for its potential applications.
Experimental Section
Calculation methods
All the calculations were performed in the framework of Density
Functional Theory as implemented in Vienna ab initio simulation package
[
71,72]
(
VASP).
generalized gradient approximation (GGA-PBE).
cutoff energy was set as 400 eV, and a k-point mesh of 9× 3× 9 was
Exchange-correlation potential was described by
[
46]
The plane-wave
[
73]
used for the unit cell. Van der Waals (vdW) interactions
were
considered in the structure optimization, leading to the lattice parameters
(
a = 5.52 Å, b = 16.31 Å, and c = 5.50 Å) in much better agreement with
[
34,47,74]
the experimental data than that in the absence of vdW corrections.
The structural optimization stopped when the forces on the atoms were
smaller than 0.01 eV/ Å. The effects of lattice parameter b on the dipole
moments of the system were evaluated by the following steps. A
tensile/compression strain was firstly applied in the b direction. Then, the
supercell including the internal positions of the atoms was allowed for a
full relaxation, and the dipole moments of the deformed structures were
calculated both before and after the relaxation.
Chemicals and materials
Ethylene glycol (EG, 98%, Aladdin Industrial Corporation Co. Ltd.,
Shanghai, P. R. China) and ethyl alcohol (EtOH, 99.7%, Beijing Yili Fine
Chemicals Co. Ltd., Beijing, P. R. China) were used as the solvents in
Figure 9. (a) The photocatalytic degradation of SMX by the BMO-8 sample
under visible light illumination for five runs. (b) The XRD patterns of the BMO-8
sample before and after the photocatalytic SMX degradation experiment for
five runs, respectively.
the
Na
Shanghai, P. R. China) and bismuth nitrate pentahydrate (Bi(NO
9%, Sinopharm Chemical Reagent Co., Ltd., Shanghai, P. R. China)
were used as the Mo and Bi sources in the synthesis of Bi MoO
respectively. Commercially available Degussa P25 TiO nanoparticles
Evonik Industries, Germany) were used for the comparison. Sodium
solvent-thermal
MoO ·2H O, 99%, Sinopharm Chemical Reagent Co., Ltd.,
·5H O,
process.
Sodium
molybdate
dihydrate
(
2
4
2
3
)
3
2
9
Conclusions
2
6
,
2
(
In summary, a novel approach was developed to enhance the
hydroxide (NaOH, 96%, Sinopharm Chemical Reagent Co., Ltd.,
Shanghai, P. R. China) was used to modulate the reaction solution pH.
Deionized (DI) water was obtained from a water purification system
photocatalytic performance of a polar photocatalyst of Bi
by the precise control of its structure to increase its internal
polarization. From the DFT calculation results, Bi MoO with a
2 6
MoO
2
6
(Sichuan Wortel Water Treatment Equipment Co., Ltd, Chengdu, P. R.
shortened crystal lattice parameter b could have a larger internal
polarization, which was beneficial for a better photogenerated
charge carrier separation efficiency to enhance its photocatalytic
performance. A simple and robust approach of the addition of
NaOH in the reaction solution was found to be effective for the
China) with resistivity higher than 18 MΩ·cm. Sulfamethoxazole (SMX,
98%, Aladdin Industrial Corporation Co. Ltd., Shanghai, P. R. China),
Phenol (C H O, 99.5%, Aladdin Industrial Corporation Co. Ltd., Shanghai,
6 6
P. R. China) were used as the target organic pollutants in photocatalytic
degradation experiments. All chemicals were of analytically pure grade
and used without further purification. Bnzoquinone (BQ, 98%, Sinopharm
Chemical Reagent Co., Ltd. Shanghai, P. R. China), sodium bromate
creation of Bi
parameter b in its solvent-thermal synthesis process. With the
decrease of crystal lattice parameter b, the Bi MoO
2 6
MoO photocatalyst with shortened crystal lattice
(
NaBrO
China), isopropanol (IPA, 99.7%, Sinopharm Chemical Reagent Co., Ltd.
Shanghai, P. R. China), and ammonium oxalate (C ·H O, 99.5%,
Sinopharm Chemical Reagent Co., Ltd., Shanghai, P. R. China) were
3
, 99.7%, Sinopharm Chemical Reagent Co., Ltd., Shanghai, P. R.
2
6
photocatalyst demonstrated a gradually enhanced photocatalytic
performance in both the photocatalytic degradation of organic
pollutants and disinfection of staphylococcus aureus bacteria
H N O
2 8 2 4
2
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ChemSusChem
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FULL PAPER
used as radical scavengers in the photocatalytic SMX degradation
experiments.
measured under illumination at 0 V versus Ag/AgCl electrode as the
reference electrode with the frequency range of 0.01 Hz to 50 Hz on the
CHI 660D electrochemical workstation. The incident photon to current
efficiency spectra (IPCE) measurements were conducted on our samples
by using a QEX10 solar cell quantum efficiency measurement system
(QEX10, PV Measurements, USA).
2 6
Synthesis of Bi MoO photocatalysts
In a typical process, 6 mmoL Bi(NO
3 3 2
) ·5H O (2.91 g) and 3 mmoL
Na MoO ·2H O (0.726 g) were dissolved in 10 mL ethylene glycol (EG)
2
4
2
Photocatalytic degradation of sulfamethoxazole (SMX) and
phenol under visible light illumination
under magnetic stirring, respectively, and they were then mixed together.
Proper amount of NaOH (0 g, 0.24 g, and 0.57 g, respectively) was
dissolved in 40 mL ethanol (0 M, 0.16 M, or 0.37 M, respectively), and it
was slowly added into the above mixture solution to adjust the solution
pH to ~ 1, 4, and 8, respectively. After being further stirred for 10 min, the
mixture solution was transferred into a 100 mL teflon-lined stainless steel
2 6
The photocatalytic activities of Bi MoO photocatalysts were evaluated
firstly by the degradation of model organic pollutants of sulfamethoxazole
(SMX) and phenol under visible light irradiation, respectively. In a typical
experiment, 50 mL of SMX solution (25 ppm) or 50 mL of phenol solution
(10 ppm) was added into a 100 mL beaker (radius at 3 cm), and 0.05 g of
photocatalyst sample was dispersed then dispersed into the organic
pollutant solution. A 300 W xenon lamp (PLS-SXE300, Beijing Perfect
Light Technology Co., Ltd., Beijing, P. R. China) was used as the light
source, which had two glass filters to provide zero light intensity below
0
autoclave. The solvent-thermal process was conducted at 160 C for 20 h,
and the autoclave was then cooled to room temperature naturally. After
the reaction, the precipitate was filtered, washed with ethanol several
0
times, and then dried at 80 C in air for 12 h to obtain the desired
2 6
Bi MoO photocatalyst. The samples were named as BMO-1, BMO-4,
and BMO-8, respectively, according to their different reaction solution pH
values.
400 nm and over 700 nm. The light intensity striking the solution was at
2
4
5 mW/cm as measured by a FZ-A optical radiometer (Photoelectric
Instrument Factory of Beijing Norman University, P. R. China). Prior to
irradiation, the suspension was kept in the dark under stirring for 30 min
to ensure the establishment of the adsorption/desorption equilibrium. At
given time intervals, 3 mL aliquots were collected from the suspension
2 6
Characterization of Bi MoO photocatalysts
and immediately centrifuged at 9700 rpm for
5 min to separate
The crystal structures of samples were obtained by X-ray diffraction
XRD) on D/MAX-2004 X-ray powder diffractometer (Rigaku
Corporation, Japan) with Cu Kα (λ=1.54178 Å) radiation at 56 kV and
photocatalysts, and the light absorption of the clear solution was
measured by the UV-2550 spectrophotometer. For the recycle
performance tests, the recovered photocatalysts after the SMX
degradation experiment were washed by de-ionized water and dried in a
vacuum oven for 10 h before being used for the next run. All analyses
were in triplicate.
(
a
0
182 mA. The scanning step width was 0.02 in 2 theta and the sampling
time was 4 s per step. The morphologies of samples were observed by
TEM observations conducted on a JEOL 2100 TEM (JEOL Ltd., Japan)
operated at 200 kV with the point-to-point resolution of 0.28 nm. TEM
samples were prepared by dispersing a thin film of these powder
samples on Cu grids. Brunauer-Emmett-Teller (BET) measurement was
2
conducted by N adsorption-desorption isotherm with an Autosorb-1
Photocatalytic disinfection of staphylococcus aureus (S.
aureus) bacteria under visible light illumination
Series Surface Area and Pore Size Analyzers (TriStar II 3020,
Micromeritics Instrument Corporation, USA). Isoelectric point (IEP)
values of these samples were measured on a Nano-ZS90 Zetasizer
(
Malvern, UK). X-ray photoelectron spectroscopy (XPS) measurements
Wild-type S. aureus (CMCC (B) 26003, China national standard material
were conducted on an ESCALAB 250 X-ray photoelectron spectrometer
network, P. R. China) were used for the photocatalytic disinfection
(
(
Thermo Fisher Scientific Inc., Waltham, USA.) with an Al K anode
1486.6 eV photon energy, 300 W). Elemental analysis was performed
experiments. After overnight culture, cells were diluted to a cell
7
suspension (ca.10 cfu/mL) in 0.9% NaCl solution prior to the use for
photocatalytic disinfection experiments. All solid or liquid materials had
on an EA: CHONS elemental analyser (Thermo Flash 2000, USA) to
determine the mass fractions of carbon in these samples. The UV-vis
spectra of samples were measured on a UV-2550 spectrophotometer
0
been autoclaved for 30 min at 121 C before use, and the same visible
light source was used as in the photocatalytic degradation experiments.
In the photocatalytic disinfection of S. aureus bacteria experiment, aliquot
of 10 mL S. aureus cell suspension was pipetted onto a sterile 50 × 10
mm petri dish with the photocatalytst sample, which was first spin coated
(Shimadzu Corporation, Japan). Mott−Schottky analysis was carried out
at a dc potential range from −0.6 V to +0.7 V vs Ag/AgCl electrode as the
reference electrode with the ac potential frequency of 2 kHz and an
amplitude of ac potential of 50 mV in the dark on a CHI 660D
electrochemical workstation (Shanghai Chenhua Instrument Ltd., P. R.
China). Powder second-harmonic generation (SHG) signals of these
at the bottom of the dish.
A fixed concentration of ~ 1.0 mg
photocatalyst/mL S. aureus suspension was used. At regular time
intervals, 100 μL of aliquots of the treated cell suspensions were
withdrawn in sequence. After appropriate dilutions in 0.9% NaCl solution,
aliquot of 100 μL was spread onto an agar medium plate and incubated
[
75]
BMO samples were measured according to the Kurtz–Perry method.
The measurements were performed with a Q-switched Nd:YAG laser at
the wavelength of 1064 nm using KDP as the reference sample. Since
the powder SHG efficiencies depended strongly on particle size,
polycrystalline samples were ground into the same particle size range.
Photoelectrochemical (PEC) measurements were conducted in
conventional three-electrode configuration in 0.2 M Na SO solution with
platinum as the counter electrode and Ag/AgCl electrode as the
0
at 37 C for 24 h. The number of viable cells in terms of colony-forming
units was counted. Analyses were in triplicate, and control runs were
carried out each time under the same experiment conditions except for
the nonexistence of photocatalysts.
a
2
4
[
76]
reference electrode on the CHI 660D electrochemical workstation.
Electrochemical impedance spectra (EIS) of these samples were
Acknowledgements
This article is protected by copyright. All rights reserved.

ChemSusChem
10.1002/cssc.201800180
FULL PAPER
This study was supported by the National Natural Science
Foundation of China (Grant No. 51672283 and 51602316), the
Basic Science Innovation Program of Shenyang National
Laboratory for Materials Science (Grant No. Y4N56R1161 and
Y5N56F2161), and the Natural Science Foundation of
Shandong Province, P. R. China (Grant No. ZR2017MEM017).
The authors would like to thank Prof. Dejun Wang and Mr. Linqi
Shi in College of Chemistry, Jilin University for the assistance on
the surface photovoltage spectrum measurements, and Miss X.
Hao, Dr. T. Yan, and Prof. N. Ye in Fujian Institute of Research
on the Structure of Matter, Chinese Academy of Sciences for the
assistance on SHG measurements.
[25] Z. Li, Y. Dai, X. Ma, Y. Zhu, B. Huang, Phys. Chem. Chem. Phys. 2014,
16, 3267-3273.
[
[
26] A. Kudo, H. Kato, S. Nakagawa, J. Phys. Chem. B. 2000, 104, 571-575.
27] J. Jiang, K. Zhao, X. Xiao, L. Zhang, J. Am. Chem. Soc. 2012, 134,
4473-4476.
[
28] S. Zou, F. Teng, C. Chang, Z. Liu, S. Wang, RSC Adv. 2015, 5, 88936-
88942.
[29] W. Wang, B. Huang, X. Ma, Z. Wang, X. Qin, X. Zhang, Y. Dai, Chem.
Eur. J. 2013, 19, 14777-14780.
[
[
[
[
30] X. Fan, K. Lai, L. Wang, H. Qiu, J. Yin, P. Zhao, S. Pan, J. Xua, C.
Wang, J. Mater. Chem. A. 2015, 3, 12179-12187.
31] X. Li, Z. Ju, F. Li, Y. Huang, Y. Xie, Z. Fu, R. J. Knized, Y. Lu, J. Mater.
Chem. A. 2014, 2, 13366-13372.
32] Y. S. Shimodaira, H. Kato, H. Kobayashi, A. Kudo, J. Phys. Chem. B.
2006, 110, 17790-17797.
33] L. Long, S. Wang, H. Chang, B. Zhao, B. Liu, Y. Zhou, W. Wei, X.
Wang, L. Huang, W. Huang, Small 2014, 10, 2791-2795.
34] L. Xie, J. F. Mab, G. Xua, Mater. Chem. Phys. 2008, 110, 197-200.
35] C. Kongmark, R. Coulter, S. Cristol, A. Rubbens, C. Pirovano, A.
Lӧfberg, G. Sankar, W. V. Beek, E. B. Richard, R. N. Vannier, Cryst.
Growth Des. 2012, 12, 5994-6003.
Keywords: Bi
2 6
MoO • polar photocatalysts • internal polarization
modulation • charge carrier separation • visible light
[
[
[
1]
A. Fujishima, K. Honda, Nature 1972, 238, 37-38.
[
[
2]
3]
H. Kisch, Angew. Chem. Int. Ed. 2013, 52, 812-847.
X. B. Chen, S. H. Shen, L. J. Guo, S. S. Mao, Chem. Rev. 2010, 110,
[
[
36] M. Long, W. M. Cai, H. Kisch, Chem. Phys. Lett. 2008, 461, 102-105.
37] G. H. Tian, Y. J. Chen, W. Zhou, K. Pan, Y. Z. Dong, C. G. Tian, H. G.
Fu, J. Mater. Chem. 2011, 21, 887-892.
6503-6570.
[
[
4]
5]
N. Severin, Habisreutinger, Schmidt-Mende, Lukas. K. Jacek,
Stolarczyk, Angew. Chem. Int. Ed. 2013, 52, 7372-7408.
G. Liu, H. G. Yang, J. Pan, Y. Q. Yang, G. Q. Lu, H. M. Cheng, Chem.
Rev. 2014, 114, 9559-9612.
[
[
[
[
[
[
[
[
[
[
38] Y. C. Hao, X. L. Dong, S. R. Zhai, X. Y. Wang, H. C. Ma, X. F. Zhang,
RSC Adv. 2016, 6, 35709-35718.
39] K. Jing, J. Xiong, N. Qin, Y. Song, L. Li, Y. Yu, S. Liang, L. Wu, Chem.
Commun. 2017, 53, 8604-8607.
[
[
6]
7]
R. Marschall, Adv. Funct. Mater. 2014, 24, 2421-2440.
A. D. Paola, G. Marcı`, L. Palmisano, M. Schiavello, K. Uosaki, S. Ikeda,
B. Ohtani, J. Phys. Chem. B. 2002, 106, 637-645.
40] Y. Zheng, T. Zhou, X. Zhao, W. K. Pang, H. Gao, S. Li, Z. Zhou, H. Liu,
Z. Guo, Adv. Mater. 2017, 29, 700396.
[
[
[
[
[
[
[
[
8]
9]
S. Senapati, K. Suneel, Srivastava, B. Shiv, Singh, Nanoscale 2012, 4,
41] L. N. Song, L. Chen, J. He, P. Chen, H. K. Zeng, C. T. Au, S. F. Yin,
Chem. Commun. 2017, 53, 6480-6483.
6
604-6612.
J. Fu, B. B. Chang, Y. L. Tian, F. N. Xi, X. P. Dong, J. Mater. Chem. A.
013, 1, 3083-3090.
10] Z. J. Sun, H. F. Zheng, J. S. Li, P. W Du, Energy Environ. Sci. 2015, 8,
668-2676.
42] J. S. Cai, J. Y. Huang and Y. K. Lai, J. Mater. Chem. A. 2017, 5, 16412-
2
16421.
43] S.N. Lou, J. Scott, A. Iwase, R. Amala and Y.H. Ng, J. Mater. Chem.
A. 2016, 4, 6964-6971.
2
11] G. R. Ran, G. P. Gao, F. T. Li, T. Y. Ma, A. J. Du, S. Z. Qiao, Nat.
Commun. 2017, 8, 13907.
44] D. Ma, J. Wu, M. C. Gao, Y. J. Xin and C. Chai, Chem. Eng. J. 2017,
316, 461-470.
12] L. Xu, F. Y. Zhang, X. Y. Song, Z. L. Yin, Y. X. Bu, J. Mater. Chem. A.
45] J. L. Lv, J. F. Zhang, J. Liu, Z. Li, K. Dai, and C. H. Liang, ACS
Sustainable Chem. Eng. 2018, 6, 696-706.
2015, 3, 5923-5933.
13] E. Elmalem, E. Aaron, Saunders, C. Ronny, S. Asaf, U. Banin, Adv.
Mater. 2008, 20, 4312-4317.
46] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77, 3865-
3868.
14] Y. F. Xu, C. Zhang, L. X. Zhang, X. H. Zhang, H. L. Yao, G. L. Shi,
Energy Environ. Sci. 2016, 9, 2410-2417.
47] B. Senthilkumar, R. K. Selvan, L. Vasylechko, M. Minakshi, Solid State
Sci. 2014, 35, 18-27.
15] D. Wu, B. Wang, W. Wang, T. C. An, G. Y. Li, T. W. Ng, H. Y. Yip, C. M.
Xiong, H. K. Lee, P. K. Wong, J. Mater. Chem. A. 2015, 3, 15148-
[
[
48] X. Wang, Y. D. Li, J. Am. Chem. Soc. 2002, 124, 2880-2881.
49] J. Zhu, S. H. Wang, Z. F. Bian, S. H. Xie, C. L. Cai, J. G. Wang, H. G.
Yang, H. X. Li, CrystEngComm 2010, 12, 2219-2224.
15155.
[
[
16] L. C. Mu, Y. Zhao, A. L. Li, S. Y. Wang, Z. L. Wang, J. X. Yang, Y.
Wang, T. F. Liu, R. T. Chen, J. Zhu, F. T. Fan, R. G. Li, C. Li, Energy
Environ. Sci. 2016, 9, 2463-2469.
[
[
50] J. Joo, B. Y. Chow, M. Prakash, S. Edward, J. Boyden, M. Jacobson,
Nat Mater. 2011, 10, 596-601.
51] L. N. Demianets, D. V. Kostomarov, I. P. Kuz’mina, S. V. Pushko,
Crystallography Reports 2002, 47, 86-98.
17] H. F. Li, H. T. Yu, X. Quan, S. Chen, H. M. Zhao, Adv. Funct. Mater.
2015, 25, 3074-3080.
[52] Y. S. Xu and W. D. Zhang, Dalton Trans. 2013, 42, 1094-101.
[53] J. Tauc, R. Grigorovici, A. Vancu, Phys. Stat. Sol. 1966, 15, 627-637.
[54] S. K. Loalka, C. A. Riggs, Appl. Spectrosc. 1995, 49, 1107-1110.
[55] Y. Matsumoto, J. Solid State Chem. 1996, 126, 227–234.
[56] H. S. Chen, Y. Qi, G. J. Liu, J. X. Yang, F. X. Zhang and C. Li, Chem.
Commun. 2014, 50, 14415-14417.
[
[
18] D. T. Steve-Dunn, J Mater Sci. 2009, 44, 5063-5079.
19] M. G. Kibria, R. M. Qiao, W. L. Yang, I. Boukahil, X. H. Kong, F. A.
Chowdhury, L. T. Michel, W. Ji, H. Guo, F. J. Himpsel, L. Vayssieres, Z.
T. Mi, Adv. Mater. 2016, 28, 8388-8397.
[
[
20] Z. Liu, X. D. Wen, X. L. Wu, Y. J. Gao, H. T. Chen, J. Zhu, P. K. Chu, J.
Am. Chem. Soc. 2009, 131, 9405-9412.
[
[
[
[
57] H. W. Huang, Y. He, X. W. Li, M. Li, C. Zeng, F. Dong, X. Du, T. R.
Zhang and Y. H. Zhang, J. Mater. Chem. A. 2015, 3, 24547-24556.
58] S. Cho, J. W. Jang, L. Li, J. Jian, H. Wang, J. L. MacManus-Driscoll,
Chem. Mater. 16, 28, 3017-3023.
21] X. W. Wang, L. C. Yin, G. Liu, L. Z. Wang, R. Saito, G. Q. Lu, H. M.
Cheng, Energy Environ. Sci. 2011, 4, 3976-3979.
[
[
22] Y. F. Cui, B. Joe, D. Steve, Chem. Mater. 2013, 25, 4215-4223.
23] R. Su, Y. Shen, L. Li, D. Zhang, G. Yang, C. Gao, Y. Yang, Small 2015,
59] W. J. Jo, J. W. Jang, K.J. Kong, H. J. Kang, J. Y. Kim, H. Jun, K. P. S.
Parmar, J. S. Lee, Angew. Chem., Int. Ed. 2012, 51, 3147−3151.
60] X. Y. Fan, K. R. Lai, L. C. Wang, H. S. Qiu, J. Yin, P. J. Zhao, S. L. Pan,
J. B. Xu and C. Y. Wang, J. Mater. Chem. A. 2015, 3, 12179–12187
11, 202-207.
[
24] L. Jiang, Y. Zhang, Y. Qiu, Z. Yi, RSC Adv. 2014, 4, 3165-3170.
This article is protected by copyright. All rights reserved.

ChemSusChem
10.1002/cssc.201800180
FULL PAPER
[
[
[
[
[
61] L. Q. Jiang, Y. H. Zhang, Y. Qiu and Z. G. Yi, RSC Adv. 2014, 4, 3165–
170
62] M. N. Abella´n, B. Bayarri, J. Gime´nez, J. Costa, Appl. Catal. B. 2007,
4, 233-241.
[69] Y. X. Liu, H. H. Dai, J. G. Deng, L. Zhang and C. T. Au, Nanoscale
2012, 4, 2317–2325.
3
[70] K. Shang, Z. Qiao, B. Sun, X. Z. Fan, S. Y. Ai,
J Solid State
7
Electrochem. 2013, 17, 1685-1691.
63] G. Alam, Trovo´, F. P. Raquel, Nogueira, A. Aguer, R. Amadeo, Water
Res. 2009, 43, 3922-3931.
[71] G. Kresse, J. Furthmüller, Phys. Rev. B. 1996, 54, 11169-11186.
[72] G. Kresse, J. Furthmuller, Comput. Mater. Sci. 1996, 6, 15-50.
[73] J. Klimeš, D. R. Bowler, A. Michaelides, Phys. Rev. B. 2011, 83,
195131.
64] Y. F. Su, G. B. Wang, D. T. Kuo, M. L. Chang, Y. H. Shih,
Appl. Catal., B. 2016, 186, 184-192.
65] M. R. Hoffmann, S. T. Martin, W.Y. Choi and D. W. Bahnemannt, Chem.
Rev. 1995, 95, 69-96.
[74] Z. Q. Li, X. T. Chen, Z. L. Xue, CrystEngComm. 2013, 15, 498-508.
[75] S. K. Kurtz and T. T. Perry, J. Appl. Phys. 1968, 39, 3798.
[76] E. Gao, W. Z. Wang, M. Shang and J. H. Xu, Phys. Chem. Chem. Phys.
2011, 13, 2887–2893
[
66] N. Serpone, A. Salinaro, Pure Appl. Chem. 1999, 71, 303-320.
67] M. Jillian Buriak, V. Prashant, Kamat, S. Kirk, Schanze, ACS Appl.
Mater. Interfaces. 2014, 6, 11815-11816.
[
[68] M. Long, W. M. Cai, J. Cai, B. X. Zhou, X. Y. Chai and Y. H. Wu, J.
Phys. Chem. B. 2006, 110, 20211-20216.
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Entry for the Table of Contents (Please choose one layout)
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[
a,b,‡]
[a,‡]
The crystal lattice parameter b of
Yan Chen,
Weiyi Yang, Shuang
[
c]
[d]
[e,f]
Bi
2
MoO
6
is modulated by adjusting the
Gao, Linggang Zhu, Caixia Sun,
[
a, ]
solution pH in its solvent-thermal
synthesis to control its internal
polarization. Both DFT calculation and
powder SHG signal measurement
and Qi Li
Page No. – Page No.
Internal Polarization Modulation in
*
2 6
show that Bi MoO with a shortened
Bi MoO for Photocatalytic
Performance Enhancement under
Visible Light Illumination
2
6
crystal lattice parameter b has a larger
internal polarization, beneficial for a
better photogenerated charge carrier
separation efficiency to enhance its
photocatalytic performance.
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