Sonocatalytic activity of LuFeO3 crystallites synthesized via a hydrothermal route

Article abstract of DOI:10.1016/S1872-2067(15)60941-X

LuFeO₃ crystallites of different sizes and morphologies were synthesized via a hydrothermal route. The sonocatalytic properties of the as-synthesized samples were investigated by degrading various organic dyes, including acid orange 7 (AO7), rh

Full text of DOI:10.1016/S1872-2067(15)60941-X

Chinese Journal of Catalysis 36 (2015) 1987–1994
ava i l a b l e a t w w w. s c i e n c ed i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e /c h n j c
Article
Sonocatalytic activity of LuFeO3 crystallites synthesized via a
hydrothermal route
Ming Zhou, Hua Yang *, Tao Xian, Yang Yang, Yunchuan Zhang
School of Science, Lanzhou University of Technology, Lanzhou 730050, Gansu, China
A R T I C L E I N F O
A B S T R A C T
Article history:
LuFeO3 crystallites of different sizes and morphologies were synthesized via a hydrothermal route.
The sonocatalytic properties of the as‐synthesized samples were investigated by degrading various
organic dyes, including acid orange 7 (AO7), rhodamine B (RhB), methyl orange (MO), and meth‐
ylene blue (MB), under ultrasonic irradiation, revealing that they exhibit excellent sonocatalytic
activity toward the degradation of these dyes. Particularly, the synthesized bar‐like particles with
lengths of ~3 μm and widths of ~1 μm have the highest sonocatalytic activity, and the degradation
percentage of AO7 reaches 89% after 30 min of sonocatalysis. The effects of inorganic anions such
as Cl−, NO3 , SO42−, PO43−, and HCO3 on the sonocatalysis efficiency were investigated. Hydroxyl
radicals (•OH) detected by fluorimetry using terephthalic acid as a probe molecule were found to be
produced over the ultrasonic‐irradiated LuFeO3 particles. The addition of ethanol, which acts as a
•OH scavenger, leads to quenching of •OH radicals and a simultaneous decrease in the dye degrada‐
tion. This suggests that •OH is the dominant active species responsible for the dye degradation.
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 6 May 2015
Accepted 22 June 2015
Published 20 November 2015
Keywords:
Lutetium orthoferrite
Hydrothermal synthesis
Sonocatalytic activity
Hydroxyl radical
Inorganic anion
Degradation of organic dyes
−
−
Published by Elsevier B.V. All rights reserved.
1. Introduction
dye degradation is expected to be greatly enhanced by adding
semiconductor catalyst into the ultrasonic‐irradiated dye
Ultrasonic waves propagating in liquid can generate acous‐
tic cavitation, which involves the processes of nucleation,
growth, and implosion of cavitation bubbles. The violent implo‐
sion of cavitation bubbles results in the production of local high
temperatures and pressures (i.e., hot spots) [1], during which
the emission of light (i.e., sonoluminescences) is simultaneous‐
ly brought about [2]. Under these local high‐temperature and
pressure conditions, water molecules can, to some extent, be
thermally dissociated into hydroxyl radicals (•OH) [3]. The •OH
is a powerful oxidant that can attack organic pollutants, such as
dyes, to make them decompose [4]. However, the degradation
efficiency of dyes is extremely low because of the generation of
a limited number of •OH under bare ultrasonic irradiation. The
wastewater. Various semiconductors have been studied as
sonocatalysts in recent years, such as TiO2 and TiO2‐based
composites [5,6], ZnO [7], Ag3PO4 [8], AgPO3 [9], AgBr [10],
MnO2/CeO2 [11], and Sr(OH)2·8H2O [12]. Semiconductor‐based
sonocatalysis can be understood in a similar way to semicon‐
ductor‐based photocatalysis [13]. In a sonocatalytic system,
electrons are excited from the valence band (VB) of the semi‐
conductor to its conduction band (CB) by hot spots and/or
sonoluminescences, thus creating electron‐hole pairs. The
sono‐excited electrons and holes migrate to the catalyst parti‐
cle surface and participate in redox reactions to produce active
•
species like OH radicals, which are responsible for the degra‐
dation of dye molecules. Compared with photocatalytic tech‐
* Corresponding author. Tel: +86‐931‐2973783; Fax: +86‐931‐2976040; E‐mail: hyang@lut.cn
This work was supported by the National Natural Science Foundation of China (51262018), the Fundamental Research Funds for Universities of
Gansu Province (056003), and the Hongliu Outstanding Talents Foundation of Lanzhou University of Technology (J201205).
DOI: 10.1016/S1872‐2067(15)60941‐X | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 11, November 2015

1988
Ming Zhou et al. / Chinese Journal of Catalysis 36 (2015) 1987–1994
nology, the semiconductor‐based sonocatalysis offers an ad‐
vantage in degrading nontransparent and highly concentrated
dye wastewater because an ultrasonic wave has a strong pene‐
trating ability for any water medium [14].
The phase purity and structure of the as‐prepared LuFeO3
samples were investigated by powder X‐ray diffraction (XRD)
with Cu Kα radiation (λ = 0.15406 nm). The size and morpholo‐
gy of the as‐prepared LuFeO3 particles were investigated by
field emission scanning electron microscopy (SEM) operated at
5 kV. The ultraviolet‐visible (UV‐vis) diffuse reflectance spec‐
trum of the samples was measured using a UV‐visible spectro‐
photometer with an integrating sphere attachment.
LuFeO3 is a member of the rare‐earth orthoferrite family
and has been extensively studied because of its interesting
magnetic structure, large dielectric constant, and multiferroic
property [15–19]. LuFeO3 is also an important semiconductor
with a bandgap energy of ~2.14 eV [20,21], which makes it a
potential sonocatalyst [22]. Generally, the sonocatalytic activity
of a semiconductor highly depends upon its crystal size and
morphology. Hence, it is important to investigate the sonocata‐
lytic activity of LuFeO3 with different sizes and morphologies of
crystals, and their sonocatalytic mechanism. However, to date
there has been little work on the hydrothermal synthesis of
LuFeO3 and their sonocatalytic activity or mechanism. Among
various nanomaterial preparation techniques, the hydrother‐
mal route offers an advantage in controlling the product size
and morphology.
In this work, we synthesized LuFeO3 crystallites via a hy‐
drothermal route as described in Ref. [21], where the particle
size/morphology was tailored by varying the NaOH concentra‐
tion. The sonocatalytic activity of prepared samples was evalu‐
ated by the degradation of various organic dyes, including acid
orange 7 (AO7), rhodamine B (RhB), methyl orange (MO), and
methylene blue (MB), under ultrasonic irradiation. The sono‐
catalytic mechanism involved was systematically investigated
and discussed.
2.3. Sonocatalytic performance evaluation
The sonocatalytic performance of the LuFeO3 particles was
evaluated by the degradation of organic dyes AO7, RhB, MO,
and MB under ultrasonic irradiation. The ultrasonic source was
a commercial ultrasonic clearing machine (BK‐240), operating
at an ultrasonic frequency of 60 kHz and output power of 240
W. The dye was dissolved in distilled water to make a dye solu‐
tion (5 mg/L). The LuFeO3 catalyst (0.08 g) was added to 20 mL
of the dye solution, which was loaded in a glass beaker with an
inner diameter of 32 mm and height of 75 mm. Before each
sonocatalytic experiment, the mixture was magnetically stirred
for 30 min in the dark to establish absorption‐desorption equi‐
librium of the dye molecules on the catalyst particles, and then
submitted to ultrasonic irradiation. During the sonocatalytic
process, the ultrasonic bath temperature was maintained at 40
°C by circulating water through it. At a given time interval, 2 mL
of the reaction solution was pipetted out and centrifuged at
4000 r/min for 10 min to remove the catalyst. The upper clear
solution was then used for examination of the dye concentra‐
tion, which was determined by measuring the absorbance of
the solution at a fixed wavelength (λAO7 = 484 nm, λRhB = 554
nm, λMO = 464 nm, and λMB = 665 nm) using a UV‐vis spectro‐
photometer. The degradation percentage is defined as (C0 −
Ct)/C0 × 100%, where C0 and Ct are the dye concentrations be‐
fore and after ultrasonic irradiation for time t, respectively.
2. Experimental
2.1. Catalyst preparation
LuFeO3 crystallites were synthesized via a hydrothermal
route as described elsewhere [21]. All raw materials and rea‐
gents were of analytical grade and used without further purifi‐
cation. H2LuN3O10 (1 mmol) and Fe(NO3)3∙9H2O (1 mmol) were
dissolved in 30 mL of distilled water. Then, 50 mL of NaOH
solution with different concentrations was added dropwise
into the mixture solution under magnetic stirring until all the
metal ions were completely precipitated. The solution gradual‐
ly turned into a dark‐brown suspension. To make it mix homo‐
geneously, the suspension was ultrasonically treated for 8 min
and subsequently stirred vigorously for 30 min. The final mix‐
ture was transferred and sealed in a 100‐mL Teflon‐lined
stainless steel autoclave and submitted to hydrothermal treat‐
ment at 200 °C for 24 h. After the reaction was completed, the
autoclave was naturally cooled down to room temperature. The
precipitates were collected and washed alternately with dis‐
tilled water and absolute ethanol four times, and then dried in a
thermostat drying oven at 80 °C for 10 h to obtain the final
LuFeO3 products. By varying the NaOH concentration to 0.625,
2.5, and 5 mol/L (final concentration in autoclave), three
LuFeO3 samples with different particle sizes and morphologies
were prepared, and were termed as S1, S2, and S3, respectively.
−
The effects of inorganic anions Cl−, NO3 , SO42−, PO43−, and
−
HCO3 on the sonocatalysis efficiency were investigated by
separately adding NaCl, NaNO3, Na2SO4, Na3PO4, and NaHCO3 in
5 mmol/L to the reaction solution. Ethanol as a •OH scavenger
was also added to the reaction solution to investigate its effect
on the sonocatalytic degradation of the dye.
2.4. Hydroxyl radical analysis
Photoluminescence (PL) spectroscopy was used to examine
•
the OH radicals formed over the ultrasonic‐irradiated LuFeO3
catalyst using terephthalic acid (TPA) as a probe molecule. TPA
tends to react with •OH to produce 2‐hydroxyterephthalic acid
(TAOH), which is a highly fluorescent compound [23]. The PL
intensity of TAOH at around 429 nm is in proportion to the
amount of produced •OH radicals. Hence, we can obtain infor‐
mation on the •OH radicals by detecting the PL intensity of the
reacted solution. TPA was dissolved in NaOH solution (1.0
mmol/L) to make a 0.25 mmol/L TPA solution. The catalyst
(0.08 g) was added to 20 mL of the TPA solution. After being
magnetically stirred for 30 min in the dark, the mixed solution
was ultrasonically irradiated. The reacted solution (2 mL) was
2.2. Sample characterization

Ming Zhou et al. / Chinese Journal of Catalysis 36 (2015) 1987–1994
1989
S1
S2
S3
0.6
0.4
0.2
0.0
-0.2
-0.4
40

(3)
(2)
(1)
S1
30
S3
S2
20
400 600 800
10
Wavelength (nm)
0
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
200
300
400
500
600
700
800
2/(o)
Wavelength (nm)
Fig. 1. XRD patterns of LuFeO3 samples prepared at different NaOH
concentrations. (1) S1 (0.625 mol/L); (2) S2 (2.5 mol/L); (3) S3 (5
mol/L).
Fig. 3. UV‐vis diffuse reflectance spectra of LuFeO3 samples synthesized
at different NaOH concentrations. The inset shows the corresponding
first derivative spectra.
pipetted out at a given reaction time interval, and then centri‐
fuged at 4000 r/min for 10 min to remove the catalyst. The
upper clear solution in the centrifuge tube was used for the PL
measurements with a fluorescence spectrophotometer with an
excitation wavelength of 315 nm. Ethanol in different volume
fractions was added to the reaction solution to investigate its
effect on the •OH yield.
mol/L, the bar‐like particles become longer and broader and
have an average size of ~7 μm in length and ~2.5 μm in width.
By further increasing the NaOH concentration up to 5 mol/L,
the resulting particles become cube‐like with an average size of
~2 μm. Among these samples, the one prepared at CNaOH
=
0.625 mol/L has the smallest particle size. In addition, the
higher‐magnification images in Fig. 2 reveal that the particles
prepared in all cases are made up of small grains.
3. Results and discussion
3.3. Optical properties
3.1. XRD results
Figure 3 shows the UV‐vis diffuse reflectance spectra of the
LuFeO3 samples. The inset in Fig. 3 shows the corresponding
first derivative spectra, where the peak wavelengths are char‐
acterized as the absorption peaks of the samples. It is found
that the samples exhibit a similar optical absorption property.
The absorption peak at 579 nm is suggested to be attributed to
the electron transition from the valence to conduction band,
from which the bandgap energy, Eg, of the samples is 2.14 eV.
Figure 1 shows the XRD patterns of LuFeO3 samples pre‐
pared with different NaOH concentrations. It is seen that all of
the reflection peaks can be indexed to the LuFeO3 phase with
orthorhombic space group (PDF 47‐0071), and no traces of
second phases are observed.
3.2. SEM analysis
Figure 2 shows SEM images of the as‐prepared LuFeO3
samples, revealing that the size and morphology of the LuFeO3
particles are highly dependent on the NaOH concentration. It
shows that the sample prepared at CNaOH = 0.625 mol/L mainly
consists of bar‐like particles with lengths of ~3 μm and widths
of ~1 μm. When the NaOH concentration is increased to 2.5
3.4. Sonocatalytic activity of different LuFeO3 samples
Figure 4 shows the sonocatalytic degradation of AO7 over
LuFeO3 samples as a function of ultrasonic time (t), along with
the blank experimental result. It is seen that AO7 appears to be
stable under ultrasonic irradiation without catalyst, and its
Fig. 2. SEM images of LuFeO3 particles synthesized at different NaOH concentrations. (a) S1; (b) S2; (c) S3.

1990
Ming Zhou et al. / Chinese Journal of Catalysis 36 (2015) 1987–1994
MO, and MB over the LuFeO3 particles (S1) as a function of ul‐
1.0
0.8
0.6
0.4
0.2
0.0
trasonic time (t). The ultrasonic degradation of the four dyes
without catalyst is also shown in Fig. 5, revealing that they ap‐
pear to be stable under bare ultrasonic irradiation, and the
highest degradation, observed for MB, is only 8% after 30 min
of exposure to ultrasonic irradiation. In the absence of ultra‐
sonic irradiation, these dyes show moderate adsorption of
8%–13% onto LuFeO3 particles. Under the sonocatalysis over
LuFeO3 particles, all of the dyes undergo remarkable degrada‐
tion. After 30 min of sonocatalysis, the degradation percentages
of AO7, RhB, MO, and MB are about 89%, 82%, 73%, and 67%,
respectively. Numerous factors are expected to collectively
contribute to the differences between the degradation rates of
the dyes, such as the molecular structure of the dye and the dye
adsorption property on the catalyst particles.
Adsorption
Sonocatalysis
S1
S2
S3
Blank
-30
-20
-10
0
10
20
30
Time (min)
Fig. 4. Sonocatalytic degradation of AO7 over different LuFeO3 samples
as a function of ultrasonic time, along with the blank experimental
result.
3.6. Effect of inorganic anions on the sonocatalytic efficiency
−
Because inorganic anions such as Cl−, NO3 , SO42−, PO43−, and
degradation percentage is only 4% after 30 min of ultrasoni‐
cation. In the absence of ultrasonic irradiation, LuFeO3 samples
show moderate adsorption of 8%–11% toward AO7. However,
upon ultrasonic irradiation in the presence of the LuFeO3 sam‐
ples, the degradation of AO7 increases substantially with in‐
creasing irradiation time, implying that the samples exhibit
excellent sonocatalytic activity. After irradiation for 30 min, the
AO7 degradation percentage reaches 89%, 75%, and 86% over
the S1, S2, and S3 samples, respectively. Among the three sam‐
ples, S1 shows the highest sonocatalytic activity, which can be
ascribed to its relatively small particle size. Generally, the re‐
combination opportunity of the sonogenerated electron‐hole
pairs in the volume is expected to be reduced in small‐sized
particles, and the charge carriers can effectively migrate to the
particle surface [24]. Furthermore, small‐sized particles have a
large surface area and thus can provide abundant surface active
sites for the sonocatalytic reaction.
−
HCO3 commonly exist in dye wastewaters, their influence on
the sonocatalytic efficiency should be taken into consideration
for practical wastewater treatment. Figure 6 shows the effect of
inorganic anions on the sonocatalytic degradation of AO7 over
LuFeO3 particles (S1), where all the inorganic anions were
added in a concentration of 5 mmol/L. It indicates that the ad‐
dition of Cl− anion has a negligible effect on the sonocatalytic
degradation of AO7. However, inhibition of the sonocatalytic
efficiency is observed when adding NO3 , SO42−, PO43−, and
HCO3 to the reaction solution. One possible reason for this is
−
−
that these inorganic anions can react with the sonogenerated
•
•
•
•
holes and/or OH radicals to produce NO3, SO4, H2PO4, and
•HCO3 [25,26], which have an oxidation potential lower than
•
that of OH radicals. Moreover, the addition of the inorganic
anions leads to a slight decrease in the AO7 adsorption onto
LuFeO3 particles due to their competitive adsorption against
AO7 (Fig. 6), and this could also influence the sonocatalytic
degradation of the dye. Although the inorganic anions have an
inhibitive effect on the dye degradation, the sonocatalytic effi‐
ciency still maintains relatively high. After 30 min sonocatalytic
reaction, the degradation percentage of AO7 reaches about
3.5. Sonocatalytic degradation of different dyes
Figure 5 shows the sonocatalytic degradation of AO7, RhB,
1.0
1.0
0.8
0.8
AO7
RhB
MO
MB
Blank AO7
Blank RhB
Blank MO
Blank MB
0.6
Normal
0.6
Cl–
–
NO3
0.4
0.2
0.0
2–
0.4
0.2
0.0
SO4
PO4
3–
–
HCO3
-30
-20
-10
0
10
20
30
-30
-20
-10
0
10
20
30
Time (min)
Time (min)
Fig. 5. Sonocatalytic degradation of AO7, RhB, MO and MB over LuFeO3
particles (S1) as a function of ultrasonic time (t), along with the corre‐
sponding blank experiment results.
Fig. 6. Effect of Cl−, NO3 , SO42−, PO43−, and HCO3 on the sonocatalytic
degradation of AO7 over LuFeO3 particles (S1).
−
−

Ming Zhou et al. / Chinese Journal of Catalysis 36 (2015) 1987–1994
1991
−
2−
88%, 74%, 57%, 62%, and 64% when adding Cl−, NO3 , SO4
,
1.0
0.8
0.6
0.4
0.2
0.0
PO43−, and HCO3 , respectively. This result reveals that LuFeO3
can be used as a promising sonocatalyst for practical
wastewater treatment.
−
1st
2nd
3rd
4th
3.7. Effect of ethanol on the sonocatalytic efficiency
It is noted that ethanol can be used as the scavenger of •OH
radicals generated in the sonocatalytic process [27]. By inves‐
tigating the effect of ethanol on the sonocatalytic efficiency, we
can clarify the role of •OH radicals in the dye degradation reac‐
tion. Figure 7 shows the effect of ethanol on the sonocatalytic
degradation of AO7 over LuFeO3 particles (S1). It shows that
the degradation rate of the dye decreases with the increase of
ethanol content. When 2% ethanol is added, only 7% of the dye
is degraded after 30 min of sonocatalysis. This result implies
that the sonocatalytic active species is quenched by ethanol,
and hence •OH radicals are suggested to play an important role
in the sonocatalysis. Moreover, the addition of ethanol leads to
a slight decrease in the AO7 adsorption, which is possibly due
to the competitive adsorption of ethanol against AO7 onto the
catalyst.
0
10 20 30 40 50 60 70 80 90 100 110 120
Time (min)
Fig. 8. Four sonocatalytic degradation cycles of AO7 using LuFeO3 par‐
ticles (S1).
the dye is observed to be degraded after 30 min of sonocataly‐
sis for the fourth sonocatalytic cycle.
3.9. Detection of •OH radicals
Figure 9 gives the PL spectra of the TPA solution after reac‐
tion for 30 min over the ultrasonic‐irradiated LuFeO3 particles
(S1) without ethanol, adding 2% ethanol, and the blank ex‐
periment results. The inset shows the locally enlarged PL spec‐
tra. It is observed that in the presence of LuFeO3 particles, the
ultrasonic‐irradiated TPA reaction solution shows a strong PL
signal at around 429 nm, but this is absent for the fresh TPA
solution without irradiation. This implies the production of •OH
radicals over the ultrasonic‐irradiated LuFeO3 particles. When
adding an amount of ethanol to the TPA solution, the PL signal
disappears, indicating quenching of the •OH radicals caused by
ethanol. This result is consistent with the fact that the introduc‐
tion of ethanol results in a drastic decrease in the sonocatalytic
degradation of the dye, and hence •OH radicals are suggested to
be the dominant active species in causing the dye degradation.
In addition, a weak PL signal is visible for the ultrason‐
ic‐irradiated TPA solution without catalyst. This indicates the
production of a small amount of •OH radicals under bare ultra‐
3.8. Sonocatalytic reusability of LuFeO3 particles
The sonocatalytic reusability of LuFeO3 particles (based on
S1) was examined by the recycling sonocatalytic experiment.
After the first cycle of sonocatalysis was completed, the catalyst
was collected by centrifugation, washed with distilled water,
and dried at 60 °C for 10 h. The recovered catalyst was then
introduced to a fresh AO7 solution for the next cycle of the
sonocatalytic experiment under the same conditions. This pro‐
cess was repeated three times. Figure 8 shows the time‐de‐
pendent sonocatalytic degradation of AO7 over LuFeO3 parti‐
cles during the four sonocatalytic cycles. It is seen that the son‐
ocatalytic efficiency undergoes a slight decrease for cycled
sonocatalytic degradation of the dye. One possible reason for
the decreased sonocatalytic efficiency could be a slight loss of
catalyst during the catalyst recycling process. Despite this, the
catalyst still maintains a high sonocatalytic activity, and 65% of
Blank-unirradiated
Blank-irradiated
LuFeO3
LuFeO3+ethanol
30
20
10
0
1.0
700
600
500
400
300
200
100
0
0.8
0
0.005%
0.01%
0.05%
0.1%
0.5%
1%
0.6
0.4
0.2
0.0
350 400 450 500
Wavelength (nm)
2%
350
400
450
500
550
600
-30
-20
-10
0
10
20
30
Wavelength (nm)
Time (min)
Fig. 9. PL spectra of the TPA solution after reaction for 30 min over the
ultrasonic‐irradiated LuFeO3 particles without ethanol and adding 2%
ethanol, along with the blank experiment results.
Fig. 7. Effect of ethanol content (volume fraction) on the sonocatalytic
degradation of AO7 over LuFeO3 particles (S1).

1992
Ming Zhou et al. / Chinese Journal of Catalysis 36 (2015) 1987–1994
sonic irradiation, which come from the thermal dissociation of
water molecules by the local high temperature and pressure
[3]. However, the amount of OH radicals produced without
4. Conclusions
•
Bar‐ and cube‐like LuFeO3 particles were synthesized via a
hydrothermal route. The as‐synthesized particles exhibit good
sonocatalytic activity toward the degradation of AO7, RhB, MO,
and MB under ultrasonic irradiation. The highest sonocatalytic
activity is observed for the bar‐like particles with lengths of ~3
μm and widths of ~1 μm, where the degradation percentage of
AO7 reaches 89% after sonocatalysis for 30 min. The inorganic
catalyst is negligible compared with the amount produced over
the ultrasonic‐irradiated LuFeO3 particles.
3.10. Possible reaction mechanism
The sonocatalysis is initiated by exciting LuFeO3 through
hot spots and/or sonoluminescences, during which electrons
are excited from the valence band of LuFeO3 to its conduction
band, thus creating electron‐hole (eCB−‐hVB+) pairs (Eq. (1)). The
sonogenerated electrons and holes migrate to the LuFeO3 par‐
ticle surface and participate in a series of redox reactions to
produce active species. Based on the experimental results and
analysis, •OH radicals are suggested to be the main active spe‐
cies responsible for the dye degradation over the ultrason‐
ic‐irradiated LuFeO3 particles. It is well known that the redox
reaction to produce active species is highly dependent on the
CB and VB edge potentials of the semiconductor. According to
the Refs. [28–30], the CB and VB edge potentials of LuFeO3 are
calculated to be −0.08 and +2.06 V versus normal hydrogen
electrode (NHE), respectively. Figure 10 schematically shows
the band potentials of LuFeO3 and its sonocatalytic mechanism
toward the dye degradation. The redox potentials of H2O/•OH
and OH−/•OH are +2.72 and +1.89 V versus NHE [31], which are
positive and negative to the VB potential of LuFeO3, respective‐
ly. From a thermodynamic point of view, the sonogenerated
hVB+ can react with OH− (but cannot with H2O) to produce •OH
radicals (Eq. (2)). The redox potential of O2/H2O2 is +0.695 V
[32], which is positive relative to the CB potential of LuFeO3,
indicating that •OH radicals can also be produced through Eqs.
anions Cl−, NO3 , SO42−, PO43−, and HCO3− have an inhibitive ef‐
−
fect on the sonocatalytic degradation of the dye, but the catalyst
maintains a high sonocatalytic activity. The addition of ethanol
•
leads to substantial suppression of the dye degradation. OH
radicals are found to be produced over the ultrasonic‐irradiat‐
ed LuFeO3 particles and are quenched with the addition of
ethanol. Based on the experimental results, it is suggested that
•OH radicals are the primary active species in the sonocatalysis.
LuFeO3 particles also exhibit good sonocatalytic reusability.
References
[1] Leong T, Ashokkumar M, Kentish S. Acoust Aust, 2011, 39(2): 54
[2] Xu H X, Eddingsaas N C, Suslick K S. J Am Chem Soc, 2009, 131:
6060
[3] Juretic H, Montalbo‐Lomboy M, Van Leeuwen J, Cooper W J, Gre‐
well D. Ultrason Sonochem, 2015, 22: 600
[4] Antonopoulou M, Evgenidou E, Lambropoulou D, Konstantinou I.
Water Res, 2014, 53: 215
[5] Chave T, Navarro N M, Pochon P, Perkas N, Gedanken A, Nikitenko
S I. Catal Today, 2015, 241: 55
[6] Zhu L, Jo S B, Ye S, Ullah K, Oh W C. Chin J Catal, 2014, 35: 1825
[7] Khataee A, Soltani R D C, Karimi A, Joo S W. Ultrason Sonochem,
2015, 23: 219
[8] Zhang S N, Tian H F, Zhang S J, Wu X Q, Song L M, Ye J Y, Wei Q W. J
Am Ceram Soc, 2013, 96: 3536
[9] He P Z, Song L M, Wu X Q, Tian H F, Wei Q W, Ye J Y, Zhang L G, Cui
Y Y, Wang Y B. Ultrason Sonochem, 2014, 21: 136
[10] Wu Y, Song L M, Zhang S J, Wu X Q, Zhang S N, Tian H F, Ye J Y.
Catal Commun, 2013, 37: 14
[11] Zhao H, Zhang G M, Zhang Q L. Ultrason Sonochem, 2014, 21: 991
[12] Song L M, Li Y M, He P Z, Zhang S J, Wu X Q, Fang S, Shan J J, Sun D
L. Ultrason Sonochem, 2014, 21: 1318
•
(3) and (4). OH radicals attack the double bonds of dissolved
dye molecules, thus destroying the dyes (Eq. (5)).
+
LuFeO3 + US
hVB+ + OH−
2eCB− + O2 + 2H+ → H2O2
eCB− + H2O2
→ LuFeO3 (eCB− + hVB
→ OH
)
(1)
(2)
(3)
(4)
(5)
•
•
→ OH + OH−
•OH + dye
→ degradation products
[13] Zhang K, Oh W C. Bull Korean Chem Soc, 2010, 31: 1589
[14] Wang J, Guo B D, Zhang X D, Zhang Z H, Han J T, Wu J. Ultrason
Sonochem, 2005, 12: 331
[15] White R L. J Appl Phys, 1969, 40: 1061
[16] Zhu W K, Pi L, Tan S, Zhang Y H. Appl Phys Lett, 2012, 100:
052407
[17] Zhang L, Chen X M. Solid State Commun, 2009, 149: 1317
[18] Wang W B, Zhao J, Wang W B, Gai Z, Balke N, Chi M F, Lee H N, Tian
W, Zhu L Y, Cheng X M, Keavney D J, Yi J Y, Ward T Z, Snijders P C,
Christen H M, Wu W D, Shen J, Xu X S. Phys Rev Lett, 2013, 110:
237601
[19] Chowdhury U, Goswami S, Bhattacharya D, Ghosh J, Basu S, Neogi
S. Appl Phys Lett, 2014, 105: 052911
[20] Adams D J, Amadon B. Phys Rev B, 2009, 79: 115114
[21] Zhou M, Yang H, Xian T, Ma J Y, Zhang H M, Feng W J, Wei Z Q, Jiang
J L. J Alloys Compd, 2014, 617: 855
Dye
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Products
-
O2+H
H2O2 OH
Sudden collapse of
the cavitation bubbles
e- e- e- e-
O /
O
 = -0.13
2
ECB = -0.08
US
O /H O = 0.695
2
2 2
Hot spots
Sonoluminescence
-
OH / ·OH = +1.89
= +2.06
h+ h+ h+ h+
E
VB
OH
-
OH
H O/ ·OH = +2.72
2
Products
Dye
LuFeO3 catalyst
[22] Zhou M, Yang H, Xian T, Li R S, Zhang H M, Wang X X. J Hazard
Mater, 2015, 289: 149
Fig. 10. Schematic illustration of the sonocatalytic mechanism of
LuFeO3 particles toward the dye degradation.

Ming Zhou et al. / Chinese Journal of Catalysis 36 (2015) 1987–1994
1993
Graphical Abstract
Chin. J. Catal., 2015, 36: 1987–1994 doi: 10.1016/S1872‐2067(15)60941‐X
Dye
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Sonocatalytic activity of LuFeO3 crystallites synthesized via a
hydrothermal route
Products
-
O2+H
H O2 OH
2
Ming Zhou, Hua Yang*, Tao Xian, Yang Yang, Yunchuan Zhang
Lanzhou University of Technology
Sudden collapse of
the cavitation bubbles
e- e- e- e-
O
2
/

O
 = -0.13
ECB = -0.08
US
O /H O = 0.695
2
2 2
Hot spots
Sonoluminescence
-
OH / ·OH = +1.89
= +2.06
h+ h+ h+ h+
E
VB
OH
-
OH
H O/ ·OH = +2.72
2
LuFeO3 crystallites of different sizes and morphologies were synthe‐
sized via a hydrothermal route. The sonocatalytic property and
mechanism of the as‐synthesized samples were investigated by de‐
grading organic dyes under ultrasonic irradiation.
Products
Dye
LuFeO3 catalyst
[23] Ishibashi K I, Fujishima A, Watanabe T, Hashimoto K. J Photochem
Photobiol A, 2000, 134: 139
[29] Andersen T, Haugen H K, Hotop H. J Phys Chem Ref Data, 1999, 28:
1511
[24] Wang S F, Yang H, Xian T, Liu X Q. Catal Commun, 2011, 12: 625
[25] Wang K, Zhang J Y, Lou L P, Yang S Y, Chen Y X. J Photochem Photo‐
biol A, 2004, 165: 201
[30] Davis V T, Thompson J S. J Phys B, 2001, 34: L433
[31] Tachikawa T, Fujitsuka M, Majima T. J Phys Chem C, 2007, 111:
5259
[26] Burns R A, Crittenden J C, Hand D W, Selzer V H, Sutter L L, Salman
S R. J Environ Eng, 1999, 125: 77
[32] Jiang H Y, Cheng K, Lin J. Phys Chem Chem Phys, 2012, 14: 12114
[27] Xian T, Yang H, Di L J, Chen X F, Dai J F. J Sol‐Gel Sci Technol, 2013,
66: 324
[28] Morrison S R. Electrochemistry at Semiconductor and Oxidized
Metal Electrodes. New York: Plenum Press, 1980. 72
Page numbers refer to the contents in the print version, which include
both the English version and extended Chinese abstract of the paper. The
online version only has the English version. The pages with the extended
Chinese abstract are only available in the print version.