Preparation and photocatalytic activity of Y-doped Bi2O3

Article abstract of DOI:10.1016/j.jallcom.2015.08.068

Y³⁺ doped Bi₂O₃ photocatalysts with enhanced photocatalytic activity were synthesized via thermal decomposition of molecular precursor at 500 °C and characterized by X-ray powder diffraction (XRD), Brunauer-Emmett-Teller surface area, field emission scanning electron microscopy (FE-SEM), energy dispersive analysis of X-rays (EDX), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), and photoluminescence spectra (PL). The XRD results indicated that the introduction of Y³⁺ ions can stabilize the phase of Bi₂O₃. The DRS results indicated that the doping of Y³⁺ increased the visible light absorption ability of Bi₂O₃ and red-shifts appeared when compared with pure Bi₂O₃. Their photocatalytic activities were evaluated through the photocatalytic degradation of methyl orange. The results showed that an appropriate concentration of yttrium dopant can enhance the photocatalytic performance of Bi₂O₃ due to the strong visible light absorption and the efficient inhibition of the recombination of photogenerated electron-hole pairs. The active species trapping experiments indicated ·O₂^- is the main active species in the photocatalytic reaction. Recycling experiments demonstrated that Y-doped Bi₂O₃ has strong photostability and recyclability and it will be a promising photocatalyst for the photodegradation of organic dyes in water.

Full text of DOI:10.1016/j.jallcom.2015.08.068

Journal of Alloys and Compounds 651 (2015) 135e142
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Preparation and photocatalytic activity of Y-doped Bi2O3
,
b
,
,
Xuemei Liu a, Hongquan Deng a *, Weilong Yao a, Qiying Jiang a c, Juan Shen a
a Department of Chemistry, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, Sichuan, China
b State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang,
621010, Sichuan, China
c Engineering Research Center of Biomass Materials, Ministry of Education, Southwest University of Science and Technology, Mianyang, 621010, Sichuan,
China
a r t i c l e i n f o
a b s t r a c t
Y3þ doped Bi2O3 photocatalysts with enhanced photocatalytic activity were synthesized via thermal
decomposition of molecular precursor at 500 ꢀC and characterized by X-ray powder diffraction (XRD),
BrunauereEmmetteTeller surface area, field emission scanning electron microscopy (FE-SEM), energy
dispersive analysis of X-rays (EDX), ultravioletevisible diffuse reflectance spectroscopy (UVevis DRS),
and photoluminescence spectra (PL). The XRD results indicated that the introduction of Y3þ ions can
stabilize the phase of Bi2O3. The DRS results indicated that the doping of Y3þ increased the visible light
absorption ability of Bi2O3 and red-shifts appeared when compared with pure Bi2O3. Their photocatalytic
activities were evaluated through the photocatalytic degradation of methyl orange. The results showed
that an appropriate concentration of yttrium dopant can enhance the photocatalytic performance of
Bi2O3 due to the strong visible light absorption and the efficient inhibition of the recombination of
Article history:
Received 17 June 2015
Received in revised form
27 July 2015
Accepted 9 August 2015
Available online 12 August 2015
Keywords:
Yttrium
Bismuth oxide
Molecular precursor method
Photocatalysis
ꢁ
photogenerated electronehole pairs. The active species trapping experiments indicated $O2 is the main
active species in the photocatalytic reaction. Recycling experiments demonstrated that Y-doped Bi2O3
has strong photostability and recyclability and it will be a promising photocatalyst for the photo-
degradation of organic dyes in water.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
five different polymorphs namely,
(tetragonal), -Bi2O3 (body centered cubic),
cubic), ε-Bi2O3 (orthorhombic) [22]. Among these polymorphs, only
-phase is stable at room temperature with band gap energy of
2.85 eV. While -Bi2O3 has the strongest absorption in the visible
light region because it has the narrowest band gap (Eg z 2.58 eV),
and has been demonstrated with better photocatalytic perfor-
mance than other phases under visible light irradiation [23e28].
a
-Bi2O3 (monoclinic),
b-Bi2O3
g
d-Bi2O3 (face centered
Semiconductor photocatalysis technology has attracted
considerable attention because of its application in solving envi-
ronment problems, such as air purification, soil remediation, and
wastewater treatment. A number of semiconductor metal oxides
such as TiO2 [1e3], Cu2O [4,5], SnO2 [6,7], ZnO [8e10], sulfides
[11,12], etc. have been intensively investigated. Bismuth trioxide,
known for nontoxic property, high refractive index, dielectric
permittivity, as well as good photoelectrical conductivity and
thermal properties, is widely used in various applications [13e18].
As a p-type semiconductor with the band gap energy range of
2e3.96 eV [19], Bi2O3 is an active photocatalyst and attracts great
interest owing to its strong oxidizing ability that can oxidize water
via direct generation of $O2ꢁ and ∙OH [20,21]. It exists generally, in
a
b
However, three main problems limit further applications of
in photocatalysis. First, -Bi2O3 is a metastable phase and is easily
transformed to -phase or to bismuth carbonate during the pho-
b-Bi2O3
b
a
tocatalytic reaction. Second, it has low quantum efficiency for the
fast recombination of the photogenerated electronehole pairs.
Finally, the valence band of b-Bi2O3 is relatively negative, and the
oxide-ability of the photogenerated holes in the valence band is
weak [29e31]. In order to enhance the stability and improve the
photocatalytic activity of b-Bi2O3, different approaches and some
nonmetal or metal atoms such as Ag, Fe, Au, Pb and C have been
introduced [32e38].
* Corresponding author. Department of Chemistry, School of Materials Science
and Engineering, Southwest University of Science and Technology, Mianyang,
621010, Sichuan, China.
Due to the special f and d electron orbital structure, and the
radius of rare earth ions is similar to Bi3þ, the rare earth elements
E-mail address: dhqsouthwest@163.com (H. Deng).
http://dx.doi.org/10.1016/j.jallcom.2015.08.068
0925-8388/© 2015 Elsevier B.V. All rights reserved.

136
X. Liu et al. / Journal of Alloys and Compounds 651 (2015) 135e142
and their oxides may be doped in Bi2O3 to improve light conversion
efficiency and stability [39e41], but the Y-induced influences on
the photocatalytic activities of Bi2O3 has rarely been reported.
Molecular precursors produce exceptionally homogeneous mate-
rials due to the intimate mixing of the metals at the molecular level
[42]. Further, the presence of bridging or chelating organic ligands
in molecular complexes has been shown successfully to arrest
unwanted metal segregation during oxide formation. In addition,
the loss of organic volatile material during calcination may impart
unusual or desirable structural features on the product material,
such as high surface area, low density, connected channels, or the
formation of metastable phases [43e45]. In this paper, pure Bi2O3
and doping Bi2O3 with yttrium were prepared by thermal decom-
position of molecular precursor with diethylenetriamine-
pentaacetate ligand. The effects of yttrium doping on the crystal-
line phase, optical property and photocatalytic performance were
studied and the optimization of the Y-doped Bi2O3 composites was
obtained. The enhanced mechanism was also discussed.
2.4. Photocatalytic experiments
The photocatalytic activities of pre-prepared samples were
evaluated by the degradation of 20 mg/L MO solution in a self-
designed quartz glass reactor. The pH value of MO solution was
adjusted to 4 with NaAc-HAc buffer solution. A 100 W tungsten
halogen lamp (365 nm) was used as light source. 100 mg prepared
sample was added into 100 mL above MO solution. Before light
irradiation, the mixture solution was stirred by air through a mini-
type pump to keep catalyst in fluidized state for half an hour in the
dark to ensure adsorption/desorption equilibrium at room tem-
perature. During the reaction, the MO solution was aerated by air
also through the mini-type pump to keep catalyst in fluidized state.
At given time intervals, about 5 mL of the suspension was with-
drawn and centrifuged to separate solid particles for analysis. The
concentration of aqueous MO was determined using a UVevis
spectrophotometer (Varian Cary 50) at 485 nm. The degradation
rate of MO was calculated as the following formula:
R% ¼ ðA0 ꢁ AtÞ=A0 ¼ ðC0 ꢁ CtÞ=C0
(1)
2. Experimental section
Where A0 and C0 are referring to the absorbance and the concen-
tration of MO solution before irradiation, respectively. At and Ct are
referring to the absorbance and the concentration of MO at the
irradiation time of t min.
2.1. Materials
Bi(NO3)3$5H2O, Y2O3, diethylenetriamine penlaacetic acid
(H5DTPA), methyl orange (MO), benzoquinone, isopropanol,
ammonium oxalate, nitric acid and NaAc-HAc buffer solution
(pH ¼ 4). All chemicals were of analytic grade and used without
treating further for purification.
2.5. Active species trapping experiments
In order to investigate the reactive species during the photo-
catalytic process, some sacrificial agents, such as benzoquinone
(BQ), isopropanol (IPA) and ammonium oxalate (AO) were used as
2.2. Preparation of Y-doped Bi2O3
ꢁ
the superoxide radical ð$O2 Þ scavenger, hydroxyl radical (ꢂOH)
scavenger and hole (hþ) scavenger, respectively [46,47]. The
method was similar to the former photocatalytic experiment with
the addition of 1 mmol of quencher in the presence of MO under
light irradiation for 60 min.
Y-doped Bi2O3 catalysts were prepared by the following
method. 0.006 mol DTPA was dissolved in 200 mL hot water (80 ꢀC)
and mixed with 0.006 mol Bi(NO3)3$5H2O. After being dissolved,
the solution was colorless and clear. At the same time, Y2O3 was
taken to dissolve in the dilute nitric acid to be Y(NO3)3 solution, and
added to the above solution with stirring. The molar ratios of Y/Bi
were 0%, 1%, 5%, 10% and 15%, respectively. The final colorless and
clear solution was kept in an oven at 80 ꢀC for 3 days to gain dry
precursor of BiYx(DTPA) (NO3)x$zH2O(x ¼ 0e0.15). And all prepared
precursors were calcined at 500 ꢀC for 1 h to obtain Y-doped Bi2O3,
named as Y0, Y1, Y5, Y10 and Y15, respectively. The color of samples
is from light yellow to orange-yellow with the increase of Y3þ
content.
3. Results and discussion
3.1. TG analysis
Fig. 1 shows TG curves of different molar ratios of Y-doped Bi2O3
precursors from room temperature to 550 ꢀC under flowing air
atmosphere. From Fig. 1, all precursors display
a similar
2.3. Characterization
Thermal analysis was conducted using a Q500 thermogravi-
metric analyzer (America TA) under the flow of air at the rate of
10 ꢀC/min. The crystal structure of the samples was characterized
by X-ray diffraction (XRD) on a Panalytical (Netherlands) X'Pert
PRO X-ray diffractometer (Cu Ka radiation,
l
¼ 0.15406 nm) in the
range from 3ꢀ to 80ꢀ with a step-size of 8ꢀ/min. The specific surface
area measurements were performed on a JW-BK112 static nitrogen
adsorption instrument (Beijing JWGB Sci. & Tech. Co., Ltd.). Field
emission scanning electron microscopy (FE-SEM) and energy
dispersive analysis of X-rays (EDX) were conducted using a UItra55
(Carl zeiss SMT Pte Ltd.). The diffuse reflectance spectrum (DRS)
was measured by a UVevis spectrometer equipped with an inte-
grating sphere within the range of 200e900 nm (UV-3900, Japan
Hitachi), BaSO4 as the reference standard. The optical property was
obtained by the photoluminescence (PL) measurement using F-
4600 fluorescence spectrometer (Japan Hitachi).
Fig. 1. TG curves of molecular precursors.

X. Liu et al. / Journal of Alloys and Compounds 651 (2015) 135e142
137
decomposition stages, corresponding to dehydration at about
Where D is the size of the crystallites, k ¼ 0.89,
l
¼ 0.154 nm, h(1/
150e200 ꢀC, pyrolysis of ligand at about 260e300 ꢀC and finally
leaving the oxide under 500 ꢀC. In order to ensure that each pre-
cursor was completely decomposed, the temperature for annealing
was 500 ꢀC.
2) ¼ peak width at half-height of strongest peak and
q corresponds
to the peak position. The size of samples is shown in Table 1. From
Table 1, the peak width at half-height of strongest peak is broader,
and the particle diameter is reduced with the increase of yttrium
dopant. It indicates the doping of Y3þ can inhibit growth of the
Bi2O3 particles.
3.2. Structural characterization
Table 2 shows the specific surface areas of all samples. It can be
seen the specific surface areas of Y5, Y10 and Y15 are obviously
larger than Y0 and Y1. The highest specific surface area is obtained
when Y doping molar ratio is 10%, then the specific surface area
drops at 15%. It is suggested that a low content of yttrium can in-
crease specific surface area of photocatalyst, while a large amount
of yttrium may lead to a drop in the specific surface area due to the
reunion of particles. A high specific surface area can provide more
reactive adsorption/desorption sites for photocatalytic reaction,
which is favorable for the enhancement of photocatalytic
performance.
The FE-SEM images of samples are shown in Fig. 3(a)e(f). It is
observed that all samples are irregular and large cluster.
The particle size of pure Bi2O3 and Y1 are larger obviously
than the other samples. And the Y5, Y10, Y15 are uniform
and disperse relatively, which is consistent with the observation
from XRD patterns and specific surface areas. The EDX
technique is used for confirming purity of the samples and
presence of the elements in the samples and the results are
shown in Fig. 4. For pure Bi2O3, the peaks are clearly related to O
and Bi elements. In the case of Y-doped Bi2O3 samples, the peaks
correspond to O, Bi and Y elements. Other peaks in the figure are
related to the elements applied for sputter coating of the samples
on the EDX stage. The EDX data of samples are also listed in Table
3. It can be observed that there is an increase in the Y content
indeed.
XRD patterns of different molar ratios of Bi2O3 doped with
yttrium are shown in Fig. 2. It can be seen that the diffraction peaks
of prepared samples were relatively sharp, which suggests all
samples were with high crystallinity. The number of diffraction
peaks gradually reduced with the increase of yttrium concentra-
tion. The main 2q peaks of Y0 and Y1 observed in the XRD patterns
at 25.75ꢀ, 26.91ꢀ, 27.38ꢀ, 28.01ꢀ, 33.254ꢀ and 46.32ꢀ are consistent
with monoclinic Bi2O3 (0 0 2), (111), (ꢁ1 2 1), (0 1 2), (2 0 0) and (2
2 1) lattice planes, which can be indexed to a-phase Bi2O3 (JCPDS
71-2274). And the main 2q peaks of Y5 and Y10 observed in the XRD
patterns at 27.97ꢀ, 31.77ꢀ, 32.72ꢀ, 46.26ꢀ, 54.26ꢀ and 55.52ꢀ are
consistent with tetragonal Bi2O3 (2 0 1), (0 0 2), (2 2 0), (2 2 2), (2
0 3) and (4 2 1) lattice planes, which can be indexed to
b
-phase
Bi2O3 (JCPDS 27-0050). Moreover, the main 2
q peaks of Y15
observed in the XRD pattern at 27.945ꢀ, 32.42ꢀ, 46.49ꢀ, 55.12ꢀ,
74.77ꢀ and 77.37ꢀ are consistent with cubic Bi2O3 (111), (2 0 0), (2 2
0), (3 11), (3 3 1) and (4 2 0) lattice planes, which can be indexed to
d-phase Bi2O3 (JCPDS 27-0052). No crystalline Y2O3 phase was
observed in all samples, the reason may contain two aspects. On the
one hand, the yttrium content is below the detection limit of XRD
instrument. On the other hand, it is assumed that the metal ions
were either interacted with the framework of Bi2O3 because of little
radius of Y3þ [d(Y3þ) ¼ 0.09 nm, d(Bi3þ) ¼ 0.103 nm] or dispersed
on the surface of Bi2O3 in an amorphous form. As known, the low-
temperature
while - and
would be easily transformed to
a
g
-Bi2O3 and the high-temperature
-Bi2O3 phases are high-temperature metastable and
-phase as the temperature cooled
d-Bi2O3 are stable,
b
3.3. UVevis DRS analysis
a
to room temperature, and all kinds of phases can be transformed
with the change of temperature, shown in Scheme 1. However, XRD
UVevis DRS of as-prepared samples are shown in Fig. 5. It can be
seen that all samples exhibit broad and strong absorption in the
region of 200e400 nm. At the same time, the absorption onset of Y-
doped Bi2O3 in the visible light range was larger red-shifts than that
of pure Bi2O3. The red-shifts could be attributed to the charge-
transfer transition between the d electrons of Y3þ and the con-
duction or valence band of Bi2O3. A larger red-shift might indicate
that the catalyst absorbs more photons and the photocatalytic ac-
tivity could be enhanced. The absorption edge was extend to longer
wavelength with increasing yttrium content and the direct band
results showed Y5 and Y10 were
b-phase. It indicates the incor-
poration of an appropriate concentration of yttrium dopant may
restrict the phase transition from
cooling after annealing.
b-phase to a-phase during the
The as-products size from the broadening of peaks was esti-
mated by the Scherrer's equation:
D ¼ kl=hð1=2Þcos q
(2)
gap of Eg was estimated according to the formula Eg ¼ 1240/
l,
shown in Table 4. The wavelength at the absorption edge, , was
l
determined as the intercept on the wavelength axis for a tangential
line drawn on the absorption spectra. From Table 4, the Eg of Y-
doped Bi2O3 were lower than that of pure Bi2O3, indicating that Y-
doped Bi2O3 has a potential ability for photocatalysis under visible
light irradiation.
3.4. PL analysis
It is well known that the photoluminescence (PL) spectra signals
of semiconductor materials result from the recombination of pho-
togenerated electronehole pairs. Generally, the lower PL intensity
suggested the lower the recombination rate of photogenerated
electronehole pairs, which leads to the higher photovoltaic effi-
ciency of the semiconductor materials [48]. Fig. 6 shows PL spectra
of samples with the excitation wavelength of 365 nm to investigate
the efficiency of charge carrier trapping, immigration, transferring,
and the fate of photogenerated electronehole pairs. It can be
Fig. 2. XRD patterns of Y-doped Bi2O3.

138
X. Liu et al. / Journal of Alloys and Compounds 651 (2015) 135e142
photocatalytic activity than a-phase. From the FE-SEM images, Y5
is more uniform and disperse, being more favorable for the ab-
sorption of organics and reaction with photogenerated carriers. At
the same time, the nanosized of Y5 means the carriers spread fast
from inner to surface of the catalyst, reducing the recombination
of photo-generated electrons and holes. Moreover, Y5 shows the
weakest photoluminescence intensity from PL, suggesting the
highest separation efficiency of eꢁ/hþ pairs and highest photo-
catalytic performance [49]. The reason about the enhanced effect
could be described as follows, dopant yttrium combined with
bismuth oxide forming a doping level at the bottom of the con-
duction band of bismuth oxide. And the doping level narrowed
band gap and extended absorption in the visible light region.
Meanwhile, the doping level could also be a capture center of
photo-generated electrons, prolonging the life of the photo-
generated hole, thus improving the quantum efficiency and the
photocatalytic activity of Bi2O3. But excessive compounds may
become a new recombination center of photo-generated carriers,
resulting in photocatalytic performance deterioration and there-
fore doped with 5%Y was the best.
Scheme 1. Transformation temperatures for
a-,
b-,
g
-,
d-, and ε-Bi2O3 [22].
Table 1
The effect of photocatalyst dose on the decoloration rate was
also studied. A set of experiments under the similar conditions
were carried out by changing the Y5 catalyst dose from 0.5 g/L to
1.5 g/L under light irradiation for 60 min. The result is shown in
Fig. 8. It can be seen that as the dose increased, the decoloration
rate fell after rising. When the dose was increased up to 1.0 g/L,
the decoloration rate reached the maximum value of 95.1%, owing
to maximum active surface sites available on the surface of pho-
tocatalyst. However, the decoloration rate decreased when the
dose exceeded 1.0 g/L, meaning that 1.0 g/L is the optimum pho-
tocatalyst dose. This could be attributed to the presence of excess
of substrate molecules hinder the photons reaching the active
sites.
Size of as-prepared samples.
Donate of Y3þ/%
The strongest peak 2
q
/
h (1/2)/ꢀ
D/nm
ꢀ
0
1
5
10
15
27.384
27.384
27.973
27.976
27.946
0.128
0.132
0.184
0.199
0.226
63
61
44
41
36
Table 2
Specific surface areas of photocatalysts.
Photocatalyst
Y0
Y1
Y5
4.30
Y10
Y15
SBET (m2/g)
2.48
2.75
5.76
5.72
To further investigate the photostability and recyclability of
the as-prepared Y-doped Bi2O3 photocatalyst, the Y5 sample was
collected, dried and reused in three successive photoreaction
experiments. Fig. 9 shows the results of the three successive runs
of the MO degradation in the presence of Y5 sample under light
irradiation. During these repeated experiments, the experimental
conditions, such as initial MO concentration and pH were kept
the same. From Fig. 9, it is found that the photocatalytic activity
of the Y5 maintained effective for dye degradation in 3 cycles of
operation, but the decoloration rate within 60 min decreased a
little. It is 95.1% removal of the MO for the first time, 92.7% for
the second time and 90.0% for the third time. The reason for the
decrease may be the slight loss of photocatalyst during the
centrifugal recycle process. The obtained results demonstrated
that Y5 has strong photostability and recyclability and it will be a
promising photocatalyst for the photodegradation of organic
dyes in water.
observed that the fluorescence intensity of pure Bi2O3 was stronger
than that of Y-doped Bi2O3 samples, which shows the recombina-
tion restraint of the eꢁ/hþ pairs resulting from the doping of Y3þ
ions. It may be attributed to the introduction of new defect sites so
that the photogenerated electrons can migrate to this site and thus
there recombination of photogenerated electrons and holes
reduced. Among them, the PL intensity of Y5 was weakest, meaning
it may be a more efficient photocatalyst compared with the others.
3.5. Photocatalytic activity analysis
Fig. 7(a) shows the photodegradation efficiency of MO solution
in the presence of prepared samples under light irradiation. From
Fig. 7(a), the decoloration rates for MO were 37.9%, 61.3%, 95.1%,
91.2% and 71.4% for Y0, Y1, Y5, Y10 and Y15 photocatalysts under
light irradiation for 60 min, respectively. While the decoloration
rate for MO solution was only 5% in the absence of catalyst, which
indicates prepared samples can accelerate the decoloration of MO.
Y5 sample exhibited the highest photocatalytic efficiency in the
degradation process, and the MO solution was nearly colorless
after 60 min irradiation in the presence of it. Fig. 7(b) shows the
absorption spectra of MO in the presence of Y5 along with the
increase of light irradiation time. From Fig. 7(b), the absorption
peaks belonging to C]C (275 nm) and NeN (485 nm) are dis-
appearing with the increase of irradiation time, indicating MO has
been changed to many little molecules. The results of photo-
catalytic degradation are consistent with the results of XRD, FE-
3.6. Photocatalytic activity mechanism
In order to better understand the photocatalytic mechanism,
the reactive species in the photocatalytic process were detected
through the trapping experiments. þThe scavengers used were BQ
ꢁ
ꢂ
for $O2 , IPA for OH, and AO for h . The more MO decoloration
efficiency is decreased by a scavenger, the more important role
the corresponding reactive species play in the photocatalytic
decoloration reaction. Effects of a series of scavengers on the MO
photocatalytic decoloration efficiency are shown in Fig. 10. The
decoloration rate of MO decreꢁases rapidly from 95.1% to 37.8%
after adding BQ, indicating $O2 is the main active species in the
photocatalytic reaction. It is also observed that the decoloration
efficiency of MO drops greatly in the presence of IPA, which
SEM and PL. From XRD results, Y5 is
b-phase with higher

X. Liu et al. / Journal of Alloys and Compounds 651 (2015) 135e142
139
Fig. 3. FE-SEM images of (a) and (b) pure Bi2O3, (c) Y1, (d) Y5, (e) Y10, (f) Y15.
Fig. 4. EDX spectra for (a) pure Bi2O3, (b) Y5, (c) Y10, (d) Y15.

140
X. Liu et al. / Journal of Alloys and Compounds 651 (2015) 135e142
Table 3
EDX data of pure Bi2O3, Y5, Y10 and Y15.
Element (atomic%)
Pure Bi2O3
Y5
75.14
23.57
1.29
Y10
68.75
28.69
2.56
Y15
65.31
29.83
4.86
O
Bi
Y
68.68
31.32
e
Totals
100
100
100
100
Fig. 5. UVevis DRS of the prepared Y-doped Bi2O3.
Table 4
Eg of prepared samples.
Donate of Y3þ/%
l/nm
Eg/eV
0
1
5
10
15
462
545
573
589
612
2.68
2.28
2.16
2.11
2.03
Fig. 7. (a) Photodegradation efficiency of MO over Y-doped Bi2O3. (b). Absorption
spectra of MO in the presence of Y5.
ꢂ
indicates that OH has effect on the degradation of MO. However,
the photocatalytic activity of Y5 decreases slightly with the
addition of AO, suggesting hþ has little effect on the decoloration
of MO.
Based on the effects of scavengers, a possible schematic illus-
tration for the photocatalytic degradation of MO with Y-doped
Bi2O3 is shown in Fig. 11. The photocatalytic reaction can be
described through the following equations:
Fig. 6. PL spectra of prepared Y-doped Bi2O3.
Fig. 8. Effect of photocatalyst dose on the decoloration rate.

X. Liu et al. / Journal of Alloys and Compounds 651 (2015) 135e142
141
Fig. 11. Mechanism of photocatalytic reaction on the surface of YeBi2O3 photocatalyst.
(Equation (3)). In heterogeneous photocatalytic system, the OHꢁ,
water molecules and organic pollutants which are adsorbed on the
surface of semiconductor particles can act as a photoexcited hole
capture agent (Equations (4) and (5)). ꢂOH is an active substance in
the photocatalytic oxidation reaction with almost no selectivity to
pollutants, and can oxide all kinds of organic pollutants, then make
them mineralized. Oxygen, which is adsorbed on the surface of
semiconductor particles, is the main capture agent of photoexcited
electrons. On the semiconductor surface, the electrons in the CB
react with the atmospheric O2 to yield $O2ꢁ (Equation (6)), and this
kind of material can also be another source of surface ꢂOH after the
protonation ꢁeffect (Equations (7)e(9)). These highly oxidizing
species ($O2 , ꢂOH, etc.) can oxide MO into simple molecules such
as CO2, H2O, etc (Equation (10)).
Fig. 9. Recycling experiments for the photodegradation of MO by Y5.
YeBi2O3 þ hv/eꢁ þ hþ
OHꢁ þ hþ/$OH
(3)
(4)
(5)
(6)
(7)
(8)
(9)
H2O þ hþ/$OH þ Hþ
ꢁ
O2 þ eꢁ/$O2
$O2ꢁ þ Hþ/HO2$
4. Conclusions
2HO2$/O2 þ H2O2
Nanosized Y-doped Bi2O3 photocatalysts were prepared through
thermal decomposition of molecular precursors. The introduction
of yttrium can stabilize the crystalline phase of Bi2O3, inhibit the
recombination of the eꢁ/hþ pairs, expand the visible light absorp-
tion range, and improve the photocatalytic performance of Bi2O3.
The decoloration rate of 20 mg/L MO solution is 95.1% under light
irradiation time of 60 min in the presence of 1 g/L Y5.
H2O2 þ $O2ꢁ/$OH þ OHꢁ þ O2
MO þ $OH þ $O2ꢁ/CO2 þ H2O þ other simple molecules
(10)
When the semiconductor YeBi2O3 is irradiated by light, the
photoexcited electrons can be transferred to the conduction band
(CB) from the valence band (VB) and whilst the holes form in the VB
Acknowledgments
We gratefully acknowledge that this work was supported by
National Natural Science Foundation of China (No. 21201142 and
No. 21301142), Sichuan Provincial Education Department (No.
14ZA0101), and National Training Program of Innovation and
Entrepreneurship for Undergraduates (2014106190081).
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