Hydrothermal synthesis of B-doped Bi2MoO6 and its high photocatalytic performance for the degradation of Rhodamine B

Article abstract of DOI:10.1016/j.jpcs.2017.10.019

B-doped Bi₂MoO₆ photocatalysts have been synthesized by a hydrothermal method using HBO₃ as the doping source and the effect of B doping content on Bi₂MoO₆ structure and performance was studied. The samples were characterized with XPS, XRD, SEM, BET, UV–Vis DRS, and PL. The photocatalytic activity was evaluated by photocatalytic degradation of Rhodamine B (RhB) under visible light (λ ≥ 420 nm). The results show that all samples are orthorhombic structure. Doping Bi₂MoO₆ with B increases the amount of Bi⁵⁺ and oxygen vacancies, which led to stronger absorption in visible light region and lower band gap energy of the B-doped Bi₂MoO₆ but had little impact on morphology. B doping significantly improves the photocatalytic activity of Bi₂MoO₆ and the highest photocatalytic degradation rate is 89% when the initial molar ratio of B to Bi is 0.01.

Full text of DOI:10.1016/j.jpcs.2017.10.019

Accepted Manuscript
Hydrothermal synthesis of B-doped Bi MoO and its high photocatalytic performance
2
6
for the degradation of Rhodamine B
Min Wang, Jin Han, Pengyao Guo, Mingzhi Sun, Yu Zhang, Zhu Tong, Meiyan You,
Chunmei Lv
PII:
S0022-3697(17)30762-X
10.1016/j.jpcs.2017.10.019
PCS 8249
DOI:
Reference:
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 1 May 2017
Revised Date: 29 July 2017
Accepted Date: 12 October 2017
Please cite this article as: M. Wang, J. Han, P. Guo, M. Sun, Y. Zhang, Z. Tong, M. You, C. Lv,
Hydrothermal synthesis of B-doped Bi MoO and its high photocatalytic performance for the
2
6
degradation of Rhodamine B, Journal of Physics and Chemistry of Solids (2017), doi: 10.1016/
j.jpcs.2017.10.019.
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ACCEPTED MANUSCRIPT
Hydrothermal synthesis of B-doped Bi MoO and its high
2
6
photocatalytic performance for the degradation of Rhodamine B
*1
1
2
2
1
1
1
Min Wang , Jin Han , Pengyao Guo , Mingzhi Sun , Yu Zhang , Zhu Tong , Meiyan You ,
1
Chunmei Lv
1
. School of Mechanical Engineering and Automation, Northeastern University, Shenyang
10189, China
1
2
. School of Resources and Civil Engineering, Northeastern University, Shenyang 110189,
China ‘’
*
Corresponding author:
Tel.: +86 -24-83679926
Fax: +86 -24-83679926
E-mail: wangmin@me.neu.edu.cn
1

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ABSTRACT: B-doped Bi MoO photocatalysts have been synthesized by a
2
6
hydrothermal method using HBO as the doping source and the effect of B doping
3
content on Bi MoO structure and performance was studied. The samples were
2
6
characterized with XPS, XRD, SEM, BET, UV-Vis DRS, and PL. The photocatalytic
activity was evaluated by photocatalytic degradation of Rhodamine B (RhB) under
visible light (λ≥420 nm). The results show that all samples are orthorhombic structure.
5
+
Doping Bi MoO with B increases the amount of Bi and oxygen vacancies, which
2
6
led to stronger absorption in visible light region and lower band gap energy of the
B-doped Bi MoO but had little impact on morphology. B doping significantly
2
6
improves the photocatalytic activity of Bi MoO and the highest photocatalytic
2
6
degradation rate is 89% when the initial molar ratio of B to Bi is 0.01.
Key words: Bi MoO ꢀB-dopedꢀ hydrothermal methodꢀRhodamine Bꢀvisible-light
2
6
photoactivity
1
. Introduction
In recent years, semiconductor photocatalytic material has attracted great attention
due to its wide application in solar energy conversion, degradation of pollutants and
photo-induced splitting of water [1-2].The bismuth-based compounds, such as Bi O ,
2
3
Bi WO , BiVO , Bi MoO , BiOX (X=Cl, Br or I) and Bi GeO have been developed
2
6
4
2
6
12
20
as visible-light-induced photocatalyst [3-9]. Among them, Bi MoO has been
2
6
demonstrated to exhibit distinguished properties, such as gas sensitive, ion conductive,
luminescence, dielectric nature and catalytic properties [10, 11]. Bi MoO withnarrow
2
6
2

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band gap (2.5~2.8 eV) is a layered Aurivillius-type phase constructing of alternating
2
+
2+
(
Bi O ) layers and perovskite (MoO ) slaps [12-14]. However, the photocatalytic
2 2 4
activity of pure Bi MoO is still not sufficiently strong due to the rapid recombination
2
6
rate of photoinduced electron-hole pairs [15, 16]. To solve this problem, some
strategies have been applied to improve the photocatalytic activity of Bi MoO ,
2
6
including composite, metal ion doping or surface exposure and so on [18-23].
Recently, boron doping photocatalyst has been extensively carried out to improve
the photocatalytic performance. Li et al [24] synthesized a series of B-doped TiO2
particles by a hydrothermal method. The enhanced photocatalytic performance of
B-doped TiO due to a synergetic effect, which included a new chemical bond like
2
Ti-O-B, increased specific surface area and lower band gap energy. Yu et al [25]
prepared B-doped ZnO on PET-ITO flexible substrate. The B atoms can change the
formation of ZnO microspheres. The B atoms prefer to occupy the octahedral
interstice positions as the interstitial atoms, which lead to the decrease of band gap.
The B-ZnO/PET-ITO shows significantly more enhanced efficiency of photocatalytic
activities than that of pure ZnO. Bessegato et al [26] proposed that boron atom can
doped into the TiO structure, forming a possible chemical environment like
2
Ti-O-B-O-Ti that would result in enhanced absorption at the visible light region and
higher photocatalytic activity. Wang et al [27] prepared the B-doped BiVO through
4
citric acid complex method. The boron ion doped into BiVO lattice and the B-doped
4
BiVO samples show a red shift of the absorption edge and higher photocatalytic
4
degradation for methyl orange under visible light.
3

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So far B-doped Bi MoO prepared by a hydrothermal method has not been
2
6
reported in detail. In this work, we synthesized the B-doped Bi MoO samples by a
2
6
hydrothermal method using HBO as the doping source and characterized them with
3
XPS, XRD, SEM, BET, UV-vis DRS and PL. The effect of doping content on
photocatalytic activity of Bi MoO was investigated through the photocatalytic
2
6
degradation of RhB under visible light. The catalytic mechanism is also discussed on
the basis of the results of characterization and activity testing.
2
2
Experimental
.1. Synthesis of photocatalysts
All chemicals (Shanghai Chemical Co. Ltd, analytical grade) were used as
received without further purification.
In a typical synthesis process, 0.01 mol of Bi(NO ) ·5H O was dissolved in 50
3
3
2
mL of HNO (3mol/L), thus forming solution A. 5/7 mmol of (NH ) Mo O ·4H O
3
4 6
7
24
2
was dissolved in 50ml of NaOH (2mol/L), generating solution B. Then solution A was
slowly added into solution B under continual magnetic stirring. The pH value of the
mixtures was adjusted to 7 using 2mol/L of NaOH solution. And a given amount of
HBO was added into the mixtures. After 30 mintunes, the catalyst precursors were
3
transferred into the autoclave with teflon liner for a hydrothermal treatment. The
precursors were heated at 160 ℃ for 16 h and then naturally cooled to room
temperature. The yellow precipitates were isolated by vacuum filtration and washed
with absolute ethanol and distilled water for several times, and finally dried in at 80℃
for 12 h. For reference, the pure Bi MoO was also prepared by the similar method.
2
6
4

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For convenience, the sample was identified as xB-BMO, where x symbolized the
initial molar ratio of B to Bi (x=0, 0.004, 0.008, 0.01, 0.012 and 0.016, respectively).
2
.2. Characterization of the prepared catalysts
The surface composition and binding energy of elements were characterized by
X-ray photoelectron spectroscopy (XPS) equipped with Mg Ka excitation
MULTILAB2000, VG, Britain). The C 1s peak at Eb=285.0 eV was used for a
(
correction of the absolute binding energy. The crystal structures of catalysts were
analyzed by X-ray diffraction (XRD) with Cu Kα radiation (D/max-RB, Rigaku,
Japan). The accelerating voltage, the applied current and scanning range were 40 kV,
4
0 mA and 10ꢁ~ 80ꢁ, respectively. The morphology of all samples were observed by
scanning electron microscope (SEM) with an accelerating voltage of 20 kv (S-3400N,
Hitachi, Japan). The BET surface areas of photocatalysts were acquired from low
temperature nitrogen adsorption-desorption on a specific surface area analyzer
(F-Sorb 3400, Gold App, China). UV-vis diffuse reflectance spectra (UV-vis DRS)
were obtained on UV-vis spectro photometer using BaSO as a reference (U-3010,
4
Hitachi, Japan). The photoluminescence (PL) spectra were investigated on an F-2700
fluorescence spectrophotometer (Hitachi, Japan) at room temperature.
2
.4. Evaluation of photocatalytic activity and photostability of the catalysts
The photocatalytic activity of the catalysts was evaluated by the photocatalytic
degradation of RhB under visible light. A 250 W halogen lamp equipped with a 420
nm cutoff filter was used as the visible light source, which was placed at 14 cm from
the reactor. The details are as follows: 0.02g of catalyst was added into 100 mL of
5

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RhB (5 mg/L). Then the suspension was stirred in dark for 30 min to achieve an
adsorption/desorption equilibrium and the initial adsorption rates of RhB over all
samples are shown in Figure S. At every 10 minutes, 5ml of suspension centrifuged
and filtered through a millipore filter to separate catalyst particles. The concentration
of RhB was determined by the absorbance at 554 nm measured by 721 UV-vis
spectrophotometer. To study the stability and reusability of the photocatalyst, cyclic
degradation tests were carried out. After each cycle of degradation, the catalyst was
◦
separated by filtration and washed thoroughly with distilled water, dried at 60 C for
1
3
3
0 h and reused to the next cycle.
. Results and discussion
.1. XPS analysis
The overall XPS spectra of the BMO and 0.01 B-BMO samples are presented in
Fig.1(a). Eight peaks corresponding to Bi 5d, Bi 4f, Bi 4d , Bi4d , Bi 4p, Mo 4p, O
5
/2
3/2
1
s and C 1s are observed for both BMO and 0.01 B-BMO. The B 1s peak appears for
the 0.01 B-BMO. The existence of C 1s peek is attributed to the pollution of organic
materials used for calibration.
The B 1s high resolution XPS spectra were analyzed in order to investigate the
doped B chemical states in the catalyst. As shown in Fig. 1 (b), the asymmetric peak
can be decomposed into two peaks at Eb=189.3 and 188.5 eV. The standard binding
energies for B 1s in B O , H BO (B-O bond) and MoB (Mo-B bond) are 193.6 eV,
2
3
3
3
2
1
93.0 eV and 188.4 eV, respectively [28]. The binding energy at 189.3 eV is lower
than that of B O (193.6 eV), H BO (193.0 eV) and is higher than that of MoB
2
3
3
3
2
6

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(188.4 eV). Obviously, the B atoms are not bonded by means of a B-O bond. The
peak at Eb=188.5 eV is assigned to MoB and the B atoms are bonded by means of a
2
B-Mo-B bond. So, it can be concluded that the B may be weave into the Bi MoO
2
6
lattice and replaced some Bi atoms to form B-Mo-B.
In Fig.1 (c), two sets of Bi 4f spin-orbit doublet components are observed,
including Bi 4f5/2 and Bi 4f . The Bi 4f spectra can be decomposed into four peeks at
7/2
Eb=159.0, 159.7, 164.4 and 165.0 eV for BMO and Eb=158.9, 159.5, 164.2 and 164.8
eV for 0.01 B-BMO. The peeks at 159.0, 164.4, 158.9 and 164.2 eV are assigned to
3
+
the Bi species and the peeks at 159.7, 165.0, 159.5 and 164.8 eV are assigned to the
5
+
Bi species [25]. Furthermore, it indicated that B doping had no effect on the
chemical state of bismuth.
From Fig.1 (d), the Mo 3d XPS spectra of BMO consists of two symmetrical
peaks at Eb=232.4 and 235.6 eV, which correspond to Mo 3d5/2 and Mo 3d3/2,
respectively. The Mo 3d XPS spectra of 0.01 B-BMO also consists of two
symmetrical peaks at Eb=232.3 and 235.5 eV, corresponding to Mo 3d5/2 and Mo 3d3/2,
6
+
respectively. All peaks are characteristic of the Mo species [29].
The O 1s XPS spectra of the BMO and 0.01 B-BMO samples are showed in Fig.1
(e). As for the O 1s XPS spectra, the asymmetric peek can be decomposed into two
peaks at Eb=529.8 and 530.5 eV for BMO and Eb=529.7 and 530.4 eV for 0.01
B-BMO, and these peeks are assigned to the surface lattice oxygen (O ) and the
latt
adsorbed oxygen (O ) species, respectively[30].
ads
The surface compositions of the BMO and 0.01 B-BMO samples estimated by the
7

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XPS spectra are summarized in Table 1. The Bi/Mo molar ratios are closed to 2.0,
indicating that the BMO and 0.01 B-BMO samples are well-proportioned. The surface
5
+
3+
Bi /Bi and O /O molar ratios increase after boron doping, which may be
ads latt
contributed to improve the photocatalytic activity.
3
.2. XRD analysis
XRD was carried out to investigate the effect of B doping on the crystalline phase
and structure of Bi MoO . Fig.2 shows the XRD diffraction patterns of the BMOand
2
6
B-BMO samples. It has been found that the diffraction peaks of all samples can be
perfectly indexed as orthorhombic Bi MoO (JCPDS cards No.77-1246). Furthermore,
2
6
no characteristic peaks other than orthorhombic Bi MoO are observed, indicating that
2
6
boron doping did not change the crystal type of Bi MoO . This may be attributed to
2
6
the low B doping content in the B-BMO samples, which is beyond the detection limit
of XRD technique. In addition, the intensity of XRD patterns decreases with an
increase of doping content, which reveal that B doping can lead to a reduction in the
crystallization of Bi MoO . The (131) diffraction peek was designated to calculate the
2
6
average crystallite sizes of all samples based on Scherrer equation and the results are
listed in Table 2. To further study the effect of B doping on the crystal structure of
Bi MoO , the lattice parameters of the samples were calculated using Bragg’s law
2
6
2
2
2
2
2
2
(
2dsinθ=λ) and the formula ((l/d )=(h +k /a )+(l /c )), which is applicable to
orthorhombic systems, and the results are summarized in Table 2. As shown in Table 2,
the crystallite sizes and the lattice parameters of the B-BMO samples decrease with
increasing doping content, it can be deduced that B doping may result in a slight
8

ACCEPTED MANUSCRIPT
3
+
lattice distortion in the structure of Bi MoO . For one thing, the radius of B (27 pm)
2
6
2
-
3+
is smaller than that of O (140 pm) [24]. From the XPS results, the B is likely to
2
-
dope into the the interstitial Bi MoO structure to replace O and thus lead to smaller
2
6
cell volume. For another thing, the XPS results show that B doping caused an increase
5
+
3+
5+
of the Bi /Bi molar ratio and more Bi is found in the B-BMO lattice than BMO.
The B-BMO has smaller crystallite sizes and crystal lattice volumes due to the radius
5
+
3+
of Bi (76 pm) is smaller than that of Bi (103pm) [31].
3
.3. Scanning electron microscopy (SEM) and BET specific surface area
Fig. 3 shows the morphologies of the BMO and xB-BMO serials samples. A
sheet structure can be observed for all samples, and the nanosheets are not uniform in
size. There is a little difference in the morphologies and sheet shapes of the samples
with B doping content increasing.But it is obvious that the sizes of the nanosheets
decrease as B doping content increasing, which means that the dopant content led to
the bigger sheet being crushed to smaller sheet. Fig.3 h and j are TEM images with
higher-magnification of BMO and 0.01 B-BMO. By measuring the lattice fringes, the
resolved interplanar distances are about 0.315(Fig. 3h), and 0.275nm (Fig. 3j), which
corresponds to the (131) plane and the (002) plane of Bi MoO .
2
6
The BET specific surface areas of the samples were measured with low
temperature nitrogen adsorption-desorption method and the results are shown in Table
2
. The specific areas of the samples slightly increase with doping contents increasing,
which indicates that B doping has little impact on increasing the specific surface area.
3
.4 UV-Vis diffuse reflectance spectra (DRS)
9

ACCEPTED MANUSCRIPT
The absorbance properties of the BMO and xB-BMO samples were characterized
by means of UV-Vis diffuse reflectance spectroscopy (UV-vis DRS). As shown in Fig.
4
, all samples exhibit strong absorption in the UV and visible light regions. The steep
shape of the spectra implies that the visible light adsorption is owing to the bandgap
transition. B doping causes a red shift in the Bi MoO absorption edge, which may be
2
6
due to the mixture of B 1s and O 2p orbitals. B doping would be impurity level in the
band gap of Bi MoO . The existence of impurity states can enhance the absorption
2
6
and narrow the bandgap. Therefore, the absorption is strengthened in the visible light
region with B doping. It is generally accepted that the photocatalytic activity of the
catalyst is influenced by the photoabsorption ability. Thus, B doping can provide the
prerequisites for improving the photocatalytic activity. The band gap energy (Eg)
2
n
values of all samples were calculated with the formula of (ahv) =A(hv-Eg) , where a
is the absorption coefficient, hv is the photon energy, A is a constant (A=1) and Eg is
the band gap energy[29]. In the above formula, n is a constant and it is dependent on
the type of semiconductor material. In case of Bi MoO , the value of n is 1 for direct
2
6
band gap. The band gap energy of the BMO, 0.004 B-BMO, 0.008 B-BMO, 0.01
B-BMO, 0.012 B-BMO and 0.016 B-BMO are 2.69, 2.67, 2.62, 2.54, 2.59 and 2.61
eV, respectively. The band gap of the B-BMO is lower than that of the BMO. The
band gap of B doped BMO samples decrease as doping content increase when the
initial molar ratio of B to Bi is less than 0.01, whereas the band gap increase with
doping content increase when the initial molar ratio of B to Bi is more than 0.01. The
band gap of 0.01 B-BMO is the smallest.
1
0

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3
.5. Effect and mechanism discussion of doping on the photocatalytic activity of
Bi MoO6
2
The photocatalytic activity of all prepared catalysts was evaluated by measuring
the degradation of RhB solution under visible light irradiation. Fig. 5 (A) shows the
relative concentration of RhB (C/C ) for different times of all samples. The rate of
0
RhB degradation during direct visible light illumination is only 2% in the absence of
photocatalyst. It can be deduced that RhB is undegradable of itself at visible light
conditions. The rate of RhB degradation is 4% by the H O process because of the
2
2
production of some oxidizing agents when 0.1ml of H O (10%) was added to the
2
2
solution. The rate of RhB degradation for the BMO, 0.004 B-BMO, 0.008 B-BMO,
.01 B-BMO, 0.012 B-BMO and 0.016 B-BMO are 55, 66, 79, 89, 73 and 63%,
0
respectively. The photocatalytic activity increase as doping content increase when the
initial molar ratio of B to Bi is less than 0.01, whereas the photocatalytic activity
decrease at greater initial molar ratios of B to Bi. The highest photocatalytic
degradation rate of RhB is 89% when the initial molar ratio of B to Bi is 0.01. B
doping significantly improve the photocatalytic activity of Bi MoO .
2
6
From Fig. 5 (B), the photocatalytic degradation of RhB follows first order
kinetics, which is confirmed by the linear transforms of -ln (C/C ) ~ t (C and C are
0
0
RhB concentration after degradation and initial concentration, respectively). The
apparent rate constant acquired from various catalysts with different boron doping
content are listed in Fig. 5 (B). The larger the apparent rate constant, the faster the
photocatalytic reaction rate will be. Consequently, at given experiment conditions, the
11

ACCEPTED MANUSCRIPT
photocatalytic activity of the samples decrease in order of 0.01B-BMO > 0.008
B-BMO > 0.012 B-BMO > 0.004 B-BMO > 0.016 B-BMO > BMO.
Generally, the photoluminescence (PL) spectra of the semiconductor materials are
used to reflect the recombination efficiency of photogenerated electron-hole pairs
stimulated under light illumination. The stronger PL intensity usually means that the
photo-induced electron-hole pairs are prone to recombine and the lifetime of the
photogenerated electrons are short, thus photocatalytic performance is enhanced [31].
Fig.6A shows the PL spectra of as-prepared samples under excitation of 325 nm. All
the samples possess prominent PL peaks centering at approx. 513 nm at room
temperature. It shows that the relative intensity of the emission spectra of pure
Bi MoO is the greatest, which means that electrons and holes of Bi MoO are easy to
2
6
2
6
recombine. The relative intensities of the xB-Bi MoO samples are lower than that of
2
6
pure Bi MoO , indicating that B doping could suppress the recombination of electrons
2
6
and holes. Interestingly, the intensities of PL spectra changes with the B doping
content. The intensity of the peaks of 0.01B-BMO sample is the lowest compared
the other B doping Bi MoO samples.The PL intensity decreased in the sequence of
2
6
BMO< 0.016 B-BMO < 0.004 B-BMO < 0.012B-BMO <0.008B-BMO <0.01B-BMO,
which was coincide with the photocatalytic performance of the as prepared
photocatalysts.
To clarify the main actives species in the photocatalytic degradation preocess, the
radicals trapping experiments were carried out over the 0.01B-BMO.Herein, the
isopropanol(IPA) was used for hydroxyl radical (•OH) scavenger, 1,4-benzoquinone
1
2

ACCEPTED MANUSCRIPT
2
-
(
BQ) for superoxide radical (•O ) scavenger, and ammonium oxalate (AO) for hole
+
(
h ) scavenger. As shown in Fig. 6B, the photocatalytic activity of 0.01B-BMO
decreases slightly after IPA addition, but reduces greatly with the addition of BQ
only about 68% after 50 min) and AO (about 33% after 60 min).Therefore, it is well
(
2
−
+
recognized that the •O radicals plays an important role, h a secondary role in the
photodegradation process and the few •OH radicals just participate the photocatalytic
reaction.
Based on the above characterization and photocatalytic performance results, a
possible mechanism for the highest photocatalytic activity of the 0.01B-BMO is
proposed as following. Firstly, an acidic surface produces in the xB-BMO because of
B doping; the 0.01B-BMO may easily adsorb polarized organic reactants and thus
3
+
enhance the photocatalytic decomposition [24, 27]. Secondly, B is electron deficient
and it may create a shallow trap for electrons to extend the lifetime of photoinduced
electron/hole pairs, and improve the photocatalytic activity of the catalysts. Thirdly, B
doping can increase the amount of oxygen vacancies compared with that of the BMO
on the basis of the XPS results. The oxygen vacancies may act as electron trapping
centers, hence significantly boosting the separation of photogenerated electrons and
holes. Thus, more active species would be produced over 0.01B-BMO photocatalyst
5
+
[
32]. Besides, more Bi appeared in 0.01B-BMO, which can effectively departed
electrons on the conduction through capturing the elctrons. As a result, more electrons
and holes would be promoted and participate in the photocatalytic process, which
leads to a higher photodegradation rate for RhB. On the other hand, due to the B
1
3

ACCEPTED MANUSCRIPT
doping species, the band gap of Bi MoO is reduced to some extent as shown in Fig.4
2
6
and Table 2. The photoresponse enhancement will improve the utilization of light
energy for 0.01B-BMO photocatalysts compared to pure Bi MoO , thus resulting in
2
6
higher photocatalytic activity.The mechanism can be determined by the following
equations:
-
+
Bi MoO + hv → e + h
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
2
6
5
+
-
3+
Bi +2e → Bi
+
+
H O + h → •OH + H
2
-
-
H O + e → •OH + OH
2
2
-
+
OH +h → •OH
-
O + e → O •-
2
2
+
O •- + H → •OOH
2
•
OOH/•OH + RhB → degradationproducts → … → CO +H O
2 2
-
+
The Bi MoO catalysts absorb visible light to generate e /h pairs due to their
2
6
-
5+
suitable band gap (Eq. (1)). The photoinduced e can easily be trapped by Bi (Eq.
-
+
+
(
2)), thus effectively inhibiting recombination of e /h pairs. The photoinduced h are
+
subsequently hunted by H O molecules to yield ꢂOH and H species (Eq. (3)). The
2
-
-
photoinduced e activate H O molecules into ꢂOH and OH species (Eq. (4)). Thenꢃ
2
2
-
+
OH capture the photoinduced h to produce •OH. (Eq.(5)). Meanwhile, the
-
photoinduced e are scavenged by the adsorbed oxygen molecules to yield O •- first
2
(Eq. (6)), then on protonation yields ꢂOOH radicals (Eq. (7)). The •OOH/•OH
radicals eventually decompose RhB to carbon dioxide and water (Eq. (8)). Therefore,
1
4

ACCEPTED MANUSCRIPT
5
+
it can be concluded that the increased amount of Bi and O species after boron
ads
doping contributes to direct or indirect generation of •OOH/•OH species, which
promote the photocatalytic degradation of RhB. In addition, the 0.01B-BMO showed
stronger absorption in visible light region and lower band gap energy, which would
-
+
increase the amounts of photogenerated e /h pairs participating in the photocatalytic
reaction. Above all, it can be concluded that the improved photocatalytic activity of
the B-BMO dues to a synergetic effect, which includes the enhancement of surface
acidy, more oxygen vacancies, stronger visible light absorption and lower band gap
energy.
In addition, it is generally accepted that the phase structure, morphology, specific
surface areas have a significantly role in the photocatalytic activity of photocatalyst
[
33]. In the present work, the samples possessed similar orthorhombic phase structure,
so the phase structure is not the main reason for higher photocatalytic acitivity of
.01B-BMO. Also, the results of SEM and BET specific surface areas have no
0
obvious difference, so, the morphology and specific surface areas would not promoted
remarkably the photocatalytic activity.
However, when the molar ratio of B to Bi is more than 0.01, the photocatalytic
activity decrease significantly, which may be owing to the decreased absorption from
excessive amounts of B-doping.
3
.6. Evaluation of photostability
The stability and recyclability are important criteria for a practical and economic
perspective. To investigate the stability and recyclability of 0.01B-BMO photocatalyst,
1
5

ACCEPTED MANUSCRIPT
the repeatability test of the photocatalytic degradation of RhB was carried out for four
cycles under the same experimental conditions. After each run, the photocatalyst was
◦
collected by simple infiltration and dried in the oven 60 C for 12 h before reused. The
degradation rates for RhB over each run are shown in Fig.7 (A). It shows that after
four additional cycles of photodegradation, 0.01B-BMO does not exhibit loss of
activity and the photodegradation rate of RhB still reached to be 85%, indicating
that 0.01B-BMO photocatalyst is very stable. XRD were used to further characterize
the crystal structure of 0.01B-BMO after four cycled photodegradation of RhB. As
shown in Fig. 7(B), the XRD pattern of 0.01B-BMO after four successive cycles
exhibits the similar diffraction peaks as-synthesized 0.01B-BMO. These recycling
results show that the 0.01B-BMO photocatalyst has excellent stability and reusability
in activity, which favor a long time application in the photocatalytic removal rate of
pollutants.
4
. Conclusions
The B-doped Bi MoO photocatalysts were successfully synthesized by a
2
6
hydrothermal method using HBO as the doping source and the effect of doping
3
content on preparation of Bi MoO crystallite was studied. Based on XRD and XPS
2
6
analyses, B doping significantly improve the ability of the compounds to form a
orthorhombic Bi MoO structure. The B atom may have doped into the interstitial
2
6
Bi MoO structure and replaced the O atom to form B-Mo-B and B-Bi-O bonds,
2
6
5
+
which contribute to the appearance of more Bi and oxygen vacancies. In addition,
the B-doped Bi MoO photocatalysts show stronger absorption in visible light region
2
6
1
6

ACCEPTED MANUSCRIPT
and lower band gap energy compare with those of the pure Bi MoO . These facts are
2
6
the main reasons that the appropriate B doping content can effectively improve the
photocatalytic activity of Bi MoO . The highest photocatalytic activity is obtained
2
6
when the initial molar ratio of B to Bi is 0.01 and the degradation rate of 5 mg/LRhB
within 50 min is 89%.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of
China for Youth (21207093), by Liaoning Excellent Talents in University
ꢄLJQ2014023).
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Table Captions
Table 1 Surface compositions of the BMO and 0.01 B-BMO samples
Table 2 Some selected properties of samples
Figure Captions
Fig.1 overall spectra (a), B 1s (b), Bi 4f (c), Mo 3d (d) and O 1s (e) XPS spectra of the
BMO and 0.01 B-BMO
Fig. 2 XRD patterns of the samples for (a) BMO; (b) 0.004 B-BMO; (c) 0.008
B-BMO; (d) 0.01 B-BMO; (e) 0.012 B-BMO; (f) 0.016 B-BMO
Fig. 3 SEM images of (a) BMO; (b) 0.004 B-BMO; (c) 0.008 B-BMO; (d) 0.01
B-BMO; (e) 0.012 B-BMO; (f) 0.016 B-BMO; TEM of (g) BMO and (I) 0.01BMO;
HRTEM of (h) BMO and (J) 0.01BMO;
Fig. 4 UV-Vis DRS spectra of (a) BMO; (b) 0.004 B-BMO; (c) 0.008 B-BMO; (d)
2
2

ACCEPTED MANUSCRIPT
0
.01 B-BMO; (e) 0.012 B-BMO; (f) 0.016 B-BMO
Fig.5 (A) RhB degradation under visible light irradiation in the presence of the
samples; (B) -ln(C/C ) as a function of irradiation time on the catalysts for (a) only
0
dye; (b) without photocatalyst; (c) BMO; (d) 0.004 B-BMO; (e) 0.008 B-BMO; (f)
0
.01 B-BMO; (e) 0.012 B-BMO;(f) 0.016 B-BMO
Fig.6 (A) Photoluminescence spectra of the samples. The excitation wavelength is
25 nm; (B) Repeated photocatalytic degradation of RhB over as synthesized 0.01
B-BMO under visible light irradiation, (C) XRD patterns of cycling 0.01 B-BMO
3
2
3

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Table 1
samples
Surface composition (molar ratio)
5
+
3+
Bi/Mo
2.23
Bi /Bi
0.53
O /O
ads
latt
BMO
0.39
0.63
0
.01 B-BMO
2.38
0.77
Table 2
Samples
Crystal lattice parameters
D
S
Band gap
energy
BET
2
-1
/
nm
/m ·g
/eV
3
a/nm
b/nm
c/nm
v/nm
BMO
0.54925 1.62178 0.54977 0.48971
52.42
52.13
52.01
51.87
51.63
50.59
4.21
4.36
4.59
4.72
4.86
5.03
2.69
2.67
2.62
2.54
2.59
2.61
0
.004 B-BMO 0.54962 1.62127 0.54928 0.48945
.008 B-BMO 0.54947 1.62137 0.54925 0.48932
0
0
.01 B-BMO
0.54949 1.62150 0.54906 0.48921
0
.012 B-BMO 0.54932 1.62078 0.54909 0.48887
.016 B-BMO 0.54926 1.62022 0.54901 0.48858
0

ACCEPTED MANUSCRIPT
(
a)
0.01B-BMO
BMO
0
200
400
600
800
1000 1200
Binding energy/eV
158.9
(c) Bi 4f
(
b) B 1s
1
64.2
1
59.5
1
88.5
164.8
1
89.3
0.01B-BMO
1
59.0
1
64.4
1
59.7
1
65.0
BMO
156
158
160
162
164
166
168
1
87
188
189
190
Binding energy/eV
Binding Energy/eV
232.3
529.7
(
d) Mo 3d
(e) O 1s
235.5
530.4
0.01B-BMO
232.4
0
.01B-BMO
5
29.8
2
35.6
5
30.5
BMO
BMO
230
232
234
236
238
528
530
Binding Energy/eV
532
Binging Energy/eV
Fig. 1

ACCEPTED MANUSCRIPT
(
f)
e)
d)
(
(
(c)
(
b)
(
a)
JCDS No.77-1246
60 70 80
1
0
20
30
40
50
2θ/(°)
Fig.2

ACCEPTED MANUSCRIPT
g
h
DD = =0 0. 3. 31 15 5n nmm
I
J
D=0.275 nm
Fig. 3

ACCEPTED MANUSCRIPT
(
a)
2
1
1
0
0
0
.0
.6
.2
.8
.4
f
e
d
c
b
a
.0
3
00
400
500
600
f
Wavelength/nm
(b)
1
20
00
1
e
8
6
4
2
0
0
0
0
0
d
c
b
a
2
.0
2.4
2.8
3.2
hv/eV
3.6
4.0
Fig.4

ACCEPTED MANUSCRIPT
(
A)
1.0
0.8
0.6
0.4
0.2
0.0
a
b
c
d
e
f
g
h
0
10
20
30
40
50
Irradiation time/min
(B)
2.8
2.4
2.0
1.6
1.2
0.8
0.4
0.0
a. k:0.00035 R:0.9982
b. k:0.00085 R:0.9949
c. k:0.0156 R:0.9950
d. k:0.0217 R:0.9952
e. k:0.0311 R:0.9999
f. k:0.0450 R:0.9983
g. k:0.0258 R:0.9965
h. k:0.0198 R:0.9924
-
10
0
10
20
30
40
50
Irradiation time/min
Fig.5