Preparation of a Bi2WO6 catalyst and its catalytic performance in an alpha alkylation reaction under visible light irradiation

Article abstract of DOI:10.1016/j.mcat.2019.01.018

In this study, different types of Bi₂WO₆ catalysts were synthesized by a hydrothermal method using Bi(NO₃)₃?5H₂O and Na₂WO₄?2H₂O as precursors, and various characterization methods, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Brunauer-Emmett-Teller (BET) specific surface area measurements, and photoluminescence (PL) analysis, were used to characterize the morphologies, structures, and valence states of the catalysts. Then, the catalysts were used to catalyze the alpha alkylation reaction of benzyl alcohol and acetophenone to obtain 1,3-diphenyl-1-propenone under visible light irradiation, and the photocatalytic reaction conditions were optimized. To expand the applicable range of alpha alkylation, the influence of different alcohols and different ketone derivatives on the photocatalytic reaction was determined. In addition, the effects of the wavelength and intensity of the light used were also important, and the recyclability of the catalyst and active species (such as superoxide radicals (^[rad]O₂^?), holes (h⁺) and electrons (e^?)) produced during the reaction were tested.

Full text of DOI:10.1016/j.mcat.2019.01.018

MolecularCatalysis466(2019)157–166
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Preparation of a Bi2WO6 catalyst and its catalytic performance in an alpha
alkylation reaction under visible light irradiation
Xiaoling Liu, Haiying Li, Jingjing Ma, Xiujuan Yu, Yan Wang, Jingyi Li⁎
College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot, Inner Mongolia, 010021, People’s Republic of China
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, different types of Bi2WO6 catalysts were synthesized by a hydrothermal method using Bi
(NO3)3•5H2O and Na2WO4•2H2O as precursors, and various characterization methods, such as X-ray diffraction
(XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron
microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Brunauer-Emmett-Teller (BET) spe-
cific surface area measurements, and photoluminescence (PL) analysis, were used to characterize the
morphologies, structures, and valence states of the catalysts. Then, the catalysts were used to catalyze the alpha
alkylation reaction of benzyl alcohol and acetophenone to obtain 1,3-diphenyl-1-propenone under visible light
irradiation, and the photocatalytic reaction conditions were optimized. To expand the applicable range of alpha
alkylation, the influence of different alcohols and different ketone derivatives on the photocatalytic reaction was
determined. In addition, the effects of the wavelength and intensity of the light used were also important, and
Bi2WO6
Alpha alkylation reaction
Benzyl alcohol
Acetophenone
Visible light irradiation
%
the recyclability of the catalyst and active species (such as superoxide radicals ( O2−), holes (h+) and electrons
(e−)) produced during the reaction were tested.
1. Introduction
method and applied it to photocatalytic reduction of Cr(VI) [17]. Wang
et al. synthesized Bi2WO6 using the solvothermal method and used it to
The formation of C－C bonds is of fundamental importance in or-
ganic synthesis. Because alcohol is a green chemical reagent, it is
widely used in various common applications. At present, the alpha al-
kylation of alcohols and ketones is an emerging reaction scheme.
Compared with conventional methods, this method has the advantages
of low toxicity and reduced alkali consumption [1]. In this paper, with
Bi2WO6 as a catalyst, 1,3-diphenyl-1-propenone was formed by the
alpha alkylation of benzyl alcohol and acetophenone.
degrade rhodamine B(RhB) with C3N4 under visible light irradiation
[18]. Although Bi2WO6 has many advantages, it still has certain lim-
itations in the field of photocatalysis. For example, Bi2WO6 has a large
probability of recombination of photogenerated electrons and holes and
exhibits absorption in a limited photoreaction region [19,20]. There-
fore, a series of methods have been used to expand the photocatalytic
activity of Bi2WO6. For example, it can be doped with precious metals
(Ag [21], Pt [22], etc.). A portion of Bi2WO6 can be reduced with
NaBH4 to form a Bi/Bi2WO6 system [23,24]. It can be coupled with
other semiconductors, such as TiO2 [25–30], CeO2 [31], BiVO4 [32],
and BiOX (X-Cl, Br, I) [33,34]. These methods contribute to the se-
paration of photogenerated electrons and holes, thereby enhancing the
photocatalytic activity of Bi2WO6. In this paper, the preparation con-
ditions of Bi2WO6 were changed to improve the photocatalytic activity.
Different methods for preparing Bi2WO6, the different pH values of the
solution [23], and the different temperatures used for hydrothermal
treatment are discussed. The results showed that the photocatalytic
activity was best when Bi2WO6 was prepared using the nitric acid
method with a pH value of 4–5 and hydrothermal treatment at 130 °C.
Bi2WO6 is one of the simplest members of the Aurivillius family of
compounds. It is a narrow-bandgap semiconductor (2.6–2.8 eV) that
can capture visible light in the range of 420–470 nm [2]. Its crystal
structure shows overlapping (Bi2O2)2+ and (WO4)2− layers [3,4]. Due
to its unique physical and chemical properties and thermal stability,
Bi2WO6 is widely used in organic pollution degradation [5,6], selective
oxidation [7,8] and photocatalytic reduction [9,10]. Bi2WO6 is con-
sidered to be an ideal photocatalyst. It is synthesized by many methods,
such as the hydrothermal method [11,12], solvothermal method
[13,14], and sol-gel method [15]. According to previous reports, Yu
et al. synthesized Bi2WO6 using a hydrothermal method and then ap-
plied it as a catalyst to degrade phenol in solution under visible light
conditions [16]. Xu et al. synthesized Bi2WO6 using a hydrothermal
⁎ Corresponding author.
E-mail address: lijingyicn@163.com (J. Li).
https://doi.org/10.1016/j.mcat.2019.01.018
Received 25 October 2018; Received in revised form 7 January 2019; Accepted 16 January 2019
2468-8231/©2019ElsevierB.V.Allrightsreserved.

X. Liu et al.
MolecularCatalysis466(2019)157–166
2. Materials and methods
an accelerating voltage of 200 kV, which was used to generate an X-ray
energy spectrum. The light absorption range of the catalyst was mea-
sured using a Hitachi U-390 solid ultraviolet-visible diffusion resonance
spectrometer (UV–vis DRS) with a scanning wavelength of 200–800 nm.
The specific surface size and pore size distribution of the catalyst were
measured by a Quantachrome specific surface and microporous ana-
lyzer (BET), and N2 was used as the analytical gas. The fluorescence
emission spectrum of the catalyst was determined using an Edinburgh
Instruments FLS920 fluorescence spectrometer (PL) with a pulsed
xenon lamp (450 W) that possessed an excitation wavelength of 325 nm
and a wavelength range of 450–650 nm. The conversion rate of the
reactants and the selectivity of the product were analyzed by gas
chromatography (GC-2014C), the reactants and the product were
identified by comparison with standard samples, and GC–MS analysis
was performed with a Trace DSQ II gas chromatograph-mass spectro-
meter.
2.1. Preparation of Bi2WO6 using the nitric acid method
Pure Bi2WO6 was obtained using
a traditional hydrothermal
method. At room temperature, 2 mmol of Bi(NO3)3•5H2O was dissolved
in 50 ml of 1 mmol of nitric acid and stirred with a magnetic stirrer for
10 min to completely dissolve. Simultaneously, 1 mmol of
Na2WO4•2H2O was dissolved in 40 ml of deionized water and stirred
constantly until completely dissolved. Then, the aqueous Na2WO4 so-
lution was slowly added dropwise into the solution of Bi(NO3)3. The pH
value of the mixed liquor was adjusted to 4–5, 7–8, or 9–10 (depending
on the experiment) with a certain concentration of NaOH solution.
Then, the pH-adjusted mixed liquor was transferred to a 100 ml auto-
clave; heated at 130, 100, or 160 °C (depending on the experiment) for
24 h; naturally cooled to room temperature; and washed with deionized
water and absolute ethanol several times. After drying for 24 h at 60 °C,
the catalyst was obtained by thorough grinding [24].
3. Results and discussion
2.2. Preparation of Bi2WO6 using the ethylene glycol method
3.1. X-ray diffraction (XRD) analysis
Pure Bi2WO6 was obtained using
a traditional hydrothermal
As shown in Fig. 1, the positions of the Bi2WO6 diffraction peaks for
catalysts prepared under different conditions were essentially the same,
but the intensity changed. The 2θ values were 28.4, 32.9, 47.2, 56.0,
58.6, 69.0, 76.1, and 78.5°, corresponding to the (131), (200), (202),
(331), (262), (410), (103), and (204) planes of Bi2WO6, respectively.
The standard card was JCPDS #73-1126. The diffraction peak was
slightly shifted, and the intensity was low (Fig. 1g). These results might
be due to the change in the crystal structure of Bi2WO6. This structure
was more conducive to the photocatalytic reaction. The diffraction peak
of the catalyst after five cycles corresponded to the standard card, and
there was no difference in intensity before and after five cycles. This
lack of difference was probably because the crystal form of Bi2WO6 was
retained [37].
method. At room temperature, 2 mmol of Bi(NO3)3•5H2O and 1 mmol of
Na2WO4•2H2O were simultaneously dissolved in 50 ml of ethylene
glycol. After stirring until these compounds were completely dissolved,
the pH of the mixture was adjusted to 4–5 with a certain concentration
of NaOH solution. Then, the pH-adjusted mixture was transferred to a
100 ml autoclave; heated at 180 °C for 24 h; cooled naturally to room
temperature; and washed repeatedly with deionized water and absolute
ethanol. After being dried for 24 h at 102 °C, the catalyst was obtained
by sufficient grinding [35].
2.3. Preparation of Bi2WO6 using the acetic acid method
Pure Bi2WO6 was obtained using
a traditional hydrothermal
method. At room temperature, 2 mmol of Bi(NO3)3•5H2O was dissolved
in 50 ml of acetic acid and stirred for 10 min using a magnetic stirrer
until completely dissolved. Simultaneously, 1 mmol of Na2WO4•2H2O
was dissolved in 40 ml of deionized water and stirred constantly until
completely dissolved. Then, the aqueous solution of Na2WO4 was added
dropwise into the solution of Bi(NO3)3 under magnetic stirring, and the
pH of the mixture was adjusted to 4–5 with a certain concentration of
NaOH solution. Then, the pH-adjusted mixture was transferred to a
100 ml autoclave; hydrothermally treated at 200 °C for 24 h; and
naturally cooled to room temperature. Finally, the precipitate was
washed with deionized water and absolute ethanol several times and
dried at 60 °C for 24 h. After sufficient grinding, the catalyst was ob-
tained [36].
3.2. X-ray photoelectron spectroscopy (XPS) analysis
XPS was used to study the chemical composition and chemical va-
lence state of the catalyst. Bi2WO6 (nitric acid method, pH = 4–5,
130 °C) was composed mainly of Bi, W, O, and C (Fig. 2a). As shown in
Fig. 2b, there were two peaks at binding energies of 159.0 and
164.4 eV. The 159.0 eV peak might be attributed to Bi 4f7/2, and the
intensity was higher than that of the other peak. The 164.4 eV peak
2.4. Characterization method
The phase structure of the catalyst was characterized using a
RIGAKU D/MAX-2500 X-ray powder diffraction (XRD) instrument with
a tube voltage of 40 kV, a tube current of 100 mA, and copper as a metal
target (λ = 1.5405 Å). The scanning range of the sample was 5–80°, the
scanning speed was 1°/min, and the step length was 0.05°. The surface
components of the catalyst and the chemical valence state of the ele-
ments were measured by X-ray photoelectron spectroscopy (XPS) by
using a Thermo-Fisher ESCLAB-250Xi system, and the Al anode target
of both the monochromated X-ray source (beam spot diameter of
200–900 μm) and the double anode X-ray source (Mg anode target was
1253.6 eV) was 1486.6 eV. The morphology of the catalyst was ob-
served using a Hitachi model S-4800 scanning electron microscope
(SEM) with an accelerating voltage of 10 kV. The internal structure of
the catalyst and the interplanar spacing were measured using an FEI
Tecnai F20 field emission transmission electron microscope (TEM) with
Fig. 1. XRD patterns of the different catalysts. (a) Bi2WO6 (nitric acid method,
pH = 4–5, 160 °C), (b) Bi2WO6 (acetic acid method, pH = 4–5, 200 °C), (c)
Bi2WO6 (ethylene glycol method, pH = 4–5, 180 °C), (d) Bi2WO6 (nitric acid
method, pH = 7–8, 160 °C), (e) Bi2WO6 (nitric acid method, pH = 9–10,
160 °C), (f) Bi2WO6 (nitric acid method, pH = 4–5, 100 °C), (g) Bi2WO6 (nitric
acid method, pH = 4–5, 130 °C), and (h) recycled Bi2WO6 (nitric acid method,
pH = 4–5, 130 °C).
158

X. Liu et al.
MolecularCatalysis466(2019)157–166
Fig. 2. XPS spectra of Bi2WO6 (nitric acid method, pH = 4–5, 130 °C): (a) full spectrum, (b) Bi 4f, (c) W 4f, and (d) O 1 s.
might be attributed to Bi 4f5/2, and the intensity was relatively lower.
There were two peaks attributed to W 4f7/2 and W 4f5/2, and their
binding energies were 35.3 and 37.4 eV, respectively (Fig. 2c). The O
1 s XPS spectra in Fig. 2d indicates that O 1s of Bi2WO6 (nitric acid
method, pH = 4–5, 130 °C) could be further separated into three peaks
with binding energies of 533.2, 532.1 and 530.1 eV, which are labeled
as O1, O2, and O3, respectively. O1 represents the adsorbed oxygen in
the form of hydrated OH species on the surface. O2 represents [WO4]2−
layers of Bi2WO6. O3 represents crystal lattice oxygen of [Bi2O2]2+
[24].
(Fig. 3a) had a microsphere structure composed of nanosheets, and the
film was thick, while Bi2WO6 prepared using the nitric acid method had
a flower-like microsphere structure assembled from many thin sheets
(Fig. 3b). The thin and densely packed sheets explained the good
photocatalytic properties of Bi2WO6 prepared using the nitric acid
method. A comparison of the different pH levels of the Bi2WO6 solution
is shown in Fig. 3b and c. These figures show that with increasing pH,
the structures of the flower-like microspheres were destroyed. A com-
parison of the different preparation temperatures of Bi2WO6 is shown in
Fig. 3b, d, e and f. The preparation temperature of Bi2WO6 did not
change the morphology of Bi2WO6 substantially, but the nanosheets
were densely distributed at 100 °C and were narrowly, uniformly, and
hierarchically distributed at 130 °C. The three-dimensional structure
increased the contact area between the catalyst and the reactants,
providing a large number of active sites. Therefore, the catalyst re-
activity was increased. After five cycles, the petal structure was de-
stroyed, and the catalyst became irregular (Fig. 3g). As shown in
Fig. 3h, there were three elements—Bi, W, and O—which proved that
Bi2WO6 had been successfully synthesized [39].
As shown in Figure S1a, the Bi 4f peaks of Bi2WO6 (nitric acid
method, pH = 4 to 5, 100 °C) and Bi2WO6 (acetic acid method, pH = 4
to 5, 200 °C) were slightly shifted. As shown in Figure S1b, the W 4f
peaks of Bi2WO6 (nitric acid method, pH = 4 to 5, 100 °C), Bi2WO6
(nitric acid method, pH = 4 to 5, 160 °C) and Bi2WO6 (acetic acid
method, pH = 4 to 5, 200 °C) were all shifted, which might be due to
the change in the chemical environment of Bi and W [38]. As shown in
Figure S1c, the characteristic peak intensities of O1 and O2 of Bi2WO6
were very low compared with those of Bi2WO6 (nitric acid method,
pH = 4 to 5, 130 °C), indicating that O1 and O2 played an important
role. Combined with the results of XRD, SEM, TEM, and PL, these re-
sults fully demonstrated that the photocatalytic performance of Bi2WO6
(nitric acid method, pH = 4 to 5, 130 °C) was the best. As shown in
Figures S2a and b, the peaks shifted toward smaller binding energy, and
the intensities were significantly reduced, indicating that the chemical
environment of Bi and W had been changed after five cycles [16]. As
shown in Figure S2c, O3 was significantly reduced, which indicated
that the lattice oxygen of [Bi2O2]2+ played a major role. It can be seen
from the recyclability test that the decrease in O3 intensity led to a
decrease in the conversion rate of the reactants.
3.4. Transmission Electron microscope (TEM) analysis
To explore the internal structure of the different catalysts more
closely, TEM images of the different catalysts (i.e., different preparation
methods, pH values and hydrothermal temperatures) are shown in
Fig. 4. A comparison of the different preparation temperatures of
Bi2WO6 is shown in Figs. 4a–d. Bi2WO6 was composed of irregular
nanosheets at 100 °C (Fig. 4a). Bi2WO6 consisted of a number of ordered
nanosheets with a clear sheet structure at 130 °C (Fig. 4b and c), which
was in agreement with the SEM results. The HRTEM image of Bi2WO6 at
130 °C showed two lattice fringes at approximately 0.272 and 0.315 nm
(Fig. 4c). These two different fringe spacings represented the (200) and
(131) crystal surfaces of Bi2WO6, respectively. This phenomenon in-
dicated that Bi2WO6 had good crystallinity [40]. Bi2WO6 prepared at
160 °C was composed of nanosheets and was scattered (Fig. 4d). A
3.3. Scanning Electron microscope (SEM) analysis
A comparison of the different preparation methods of Bi2WO6 is
shown in Figs. 3a and b. Bi2WO6 prepared using the acetic acid method
159

X. Liu et al.
MolecularCatalysis466(2019)157–166
Fig. 3. SEM images of the as-prepared samples: (a) Bi2WO6 (acetic acid method, pH = 4–5, 200 °C), (b) Bi2WO6 (nitric acid method, pH = 4–5, 160 °C), (c) Bi2WO6
(nitric acid method, pH = 9–10, 160 °C), (d) Bi2WO6 (nitric acid method, pH = 4–5, 100 °C), (e, f) Bi2WO6 (nitric acid method, pH = 4–5, 130 °C), (g) recycled
Bi2WO6 (nitric acid method, pH = 4–5, 130 °C), and (h) the corresponding EDX spectra of Bi2WO6 (nitric acid method, pH = 4–5, 130 °C).
comparison of the different pH values of Bi2WO6 is shown in Fig. 4d and
e. When the pH value was 9–10, the nanostructure of Bi2WO6 was in-
finitely extended, showing a large lamellar structure (Fig. 4e). Finally,
after five cycles, the nanoplates were thick and irregular (Fig. 4f). A
stacking phenomenon occurred, which might lead to a decrease in
photoactivity. The lattice spacing of approximately 0.272 nm (Fig. 4g),
which represented the (200) crystal plane of Bi2WO6, was consistent
with the XRD results. As shown in Fig. 4h, the atomic ratios of Bi and W
were 12.52% and 7.14%, respectively, which were lower than the
theoretical values, indicating that Bi2WO6 was damaged after five cy-
cles.
3.6. Brunauer-Emmett-Teller (BET) analysis
The adsorption-desorption curves of Bi2WO6 prepared by different
preparation methods were similar, and the pore size distribution of
Bi2WO6 prepared using the nitric acid method was larger than those of
Bi2WO6 prepared using the other two methods. The pores were wider
with a size of 300 nm (Figure S3a). In addition, the specific surface area
was calculated to be 49.3 m2 g−1 (Table 1), which was consistent with
the above results. The pore size distributions of Bi2WO6 prepared at
different pH values differed substantially (Figure S3b). The pore dia-
meter was larger when the pH value was 4–5. The specific surface area
at pH values of 4–5 was approximately 49.3 m2 g−1 (Table 1), which
was larger than that at pH values of 7–8 and 9–10. These results showed
that the catalyst had a larger specific surface area that provided more
surface active sites for the adsorption of active substances and reactant
molecules [42], which explains why Bi2WO6 prepared at a pH value of
4–5 using the nitric acid method was more favorable for the occurrence
of alpha alkylation of alcohols and ketones. As shown in Figure S3c, the
pore size was the smallest at 130 °C, and the intensity of the adsorption-
desorption curve was also the smallest. The specific surface area in-
itially decreased and then increased with increasing hydrothermal
temperature (Table 1). The minimum specific surface area of Bi2WO6
prepared at 130 °C was 42.6 m2 g−1. This might be because when the
temperature was 100 or 160 °C, the nanosheets composed of Bi2WO6
were densely distributed. The specific surface area increased, which
was consistent with the SEM image. The microspheres composed of
nanosheets prepared at 100 and 160 °C were tightly packed. When
prepared at 130 °C, the nanosheets were looser and more conducive to
photocatalytic activity.
3.5. UV–vis diffuse reflectance spectroscopy (DRS) analysis
As shown in Fig. 5a, Bi2WO6 obtained using the nitric acid, ethylene
glycol, and acetic acid methods had absorption edges at approximately
445, 466, and 466 nm, respectively, indicating that Bi2WO6 absorbed in
the visible region. The light absorption and the band gap of the semi-
conductor follow the equation αhυ=A(hυ-Eg)n/2, where h, υ, A, α, and
Eg represent Planck’s constant, the frequency, a constant, the diffusion
absorption coefficient, and the band gap energy, respectively [41].
Bi2WO6 has an n value of 1. The Eg values of the three catalysts were
approximately 2.79, 2.66, and 2.66 eV (Fig. 5b). As shown in Fig. 5c,
different pH values had little effect on the preparation of Bi2WO6,
which absorbed in the visible light region, and the absorption was
redshifted as the pH value increased. Bi2WO6 had better catalytic per-
formance when Eg was approximately 2.79 eV (Fig. 5d), which was
consistent with the literature value. As shown in Fig. 5e, there was a
significant redshift at 130 °C, the absorption was in the range of
460–600 nm, and the band gap energy was 2.66 eV (Fig. 5f).
160

X. Liu et al.
MolecularCatalysis466(2019)157–166
Fig. 4. TEM images of the as-prepared samples: (a) Bi2WO6 (nitric acid method, pH = 4–5, 100 °C), (b, c) Bi2WO6 (nitric acid method, pH = 4–5, 130 °C), (d) Bi2WO6
(nitric acid method, pH = 4–5, 160 °C), (e) Bi2WO6 (nitric acid method, pH = 9–10, 160 °C), (f, g) recycled Bi2WO6 (nitric acid method, pH = 4–5, 130 °C), and (h)
the corresponding EDX spectra of the recycled Bi2WO6 (nitric acid method, pH = 4–5, 130 °C).
3.7. Photoluminescence (PL) analysis
phenomenon indicated that the recombination efficiency of the elec-
trons and holes was the lowest when the catalyst was prepared using
the nitric acid method at a pH value of 4–5 and a temperature 130 °C,
and this result was consistent with that of the photocatalytic organic
synthesis experiment [41].
The photoluminescence spectrum in the range of 450–650 nm is
shown in Fig. 6. When the excitation wavelength was 325 nm, changing
the preparation conditions (i.e., different preparation methods, pH va-
lues and hydrothermal temperatures) of the catalysts did not affect the
position of the emission peak, which was located at a similar position of
approximately 485 nm for each catalyst. However, the peak intensities
of the different catalysts were different (Fig. 6a–c). The emission in-
tensity of Bi2WO6 obtained via the nitric acid method was the lowest
(Fig. 6a), and the emission intensities of Bi2WO6 obtained at a pH value
of 4–5 and a temperature of 130 °C were the lowest (Fig. 6b and c). This
3.8. Catalyst activity test
3.8.1. Alkylation of alcohols and ketones
The equation for the alpha alkylation reaction of benzyl alcohol and
acetophenone to form 1,3-diphenyl-1-propenone is as follows:
161

X. Liu et al.
MolecularCatalysis466(2019)157–166
Fig. 5. UV–vis DRS patterns of the different catalysts with (a, b) different preparation methods, (c, d) different pH values, and (e, f) different hydrothermal
temperatures.
This experiment was performed under visible light irradiation with
Table 1
a 400–800 nm filter, an air atmosphere for 24 h, a light source intensity
of 2.0 × 10−2 W•cm−2, and a reaction temperature of 30
3 °C. In
Specific surface area of the different catalysts (different preparation
methods, pH values and hydrothermal temperatures).
the selective formation of 1,3-diphenyl-1-propenone by benzyl alcohol
and acetophenone, the light-dark contrast method was used. The dark
reaction was wrapped with a sheet of aluminum foil. After the end of
the reaction, the conversion rate of the reactants and the selectivity of
the product were analyzed by gas chromatography (GC-2014C). As seen
in Table S1, the conversion rate of the reactants under visible light ir-
radiation was greater than that in the dark. Most of the conversion rates
of the reactants in the dark were 0, indicating that the reaction was not
a thermal reaction but a photoreaction [43].
Variable Sample BET surface area (m2 g−1
)
Preparation method
Cat1 49.3
Cat2 19.0
Cat3 3.9
pH value
Cat1 49.3
Cat4 11.6
Cat5 5.2
Hydrothermal temperature
Cat6 76.3
Cat7 42.6
Cat1 49.3
Initially, when investigating the effect of the different solvents on
the reaction, 1 mmol of benzyl alcohol and 1 mmol of acetophenone
were selected as reactants. Six milliliters of different solvents (Table S1,
entries 1–14), 0.6 mmol of CH3ONa, and 50 mg of Bi2WO6 (nitric acid
method, pH = 4–5, 160 °C) were added to the reaction system. With
increasing solvent polarity, the conversion rate of the reactants initially
increased and then decreased. This might be because the higher the
solvent polarity was, the lower the stability of the catalyst was [44]. In
n-heptane, the conversion rate was up to 12.2%, possibly due to the
Reaction conditions: Cat1: Bi2WO6 (nitric acid method, pH = 4–5,
160 °C); Cat2: Bi2WO6 (ethylene glycol method, pH = 4–5, 180 °C);
Cat3: Bi2WO6 (acetic acid method, pH = 4–5, 200 °C); Cat4: Bi2WO6
(nitric acid method, pH = 7–8, 160 °C); Cat5: Bi2WO6 (nitric acid
method, pH = 9–10, 160 °C); Cat6: Bi2WO6 (nitric acid method,
pH = 4–5, 100 °C); and Cat7: Bi2WO6 (nitric acid method, pH = 4–5,
130 °C).
162

X. Liu et al.
MolecularCatalysis466(2019)157–166
Fig. 6. Photoluminescence spectra of the different catalysts with (a) different preparation methods, (b) different pH values, and (c) different hydrothermal tem-
peratures.
acid method was more favorable for the alpha alkylation of alcohols
and ketones (Table 2, entries 1–7). When the pH value was 4–5, the
conversion rate of the reactants was the highest (26.3%) (Table 2, en-
tries 1, 4, and 5). This phenomenon might be caused by excessive hy-
drogenation [23]. With the increase in hydrothermal temperature, the
conversion rate initially increased and then decreased. When the hy-
drothermal temperature reached 130 °C, the conversion rate (30.4%)
was the highest (Table 2, entries 1, 6, and 7). This phenomenon might
be because there were more active sites with an increased hydrothermal
temperature within a certain temperature range, but if the hydro-
thermal temperature was too high, the reactivity of the catalyst would
decrease [46].
Table 2
Alpha alkylation of benzyl alcohol and acetophenone using different catalysts.a.
Entry
Catalyst
Under visible light
In the dark
Conv.
(%)b
Sel.
Conv.
(%)b
Sel.
(%)b
(%)b
1
2
3
4
5
6
7
Cat1
Cat2
Cat3
Cat4
Cat5
Cat6
Cat7
26.3
13.9
2.5
> 99
> 99
> 99
> 99
> 99
> 99
> 99
0.21
0.3
0.3
0.26
0.25
0
> 99
> 99
> 99
> 99
> 99
0
21.3
6.7
24.9
30.4
0
0
Based on the above discussion, n-heptane was used as the solvent
(6 mL), Bi2WO6 (nitric acid method, pH = 4–5, 130 °C) was used as the
catalyst, LiOH was used as the base, and benzyl alcohol and acet-
ophenone were used as the reactants. Then, the effects of the amount of
catalyst, base, and reactants on the alpha alkylation of benzyl alcohol
and acetophenone were investigated (Table S2, entries 1–5). This might
be because when the amount of catalyst exceeded a certain limit, an
excessive amount of particles occupied the photosensitive portion, re-
sulting in a decreased light absorption ability and a decreased conver-
sion rate [23].
a
Reaction conditions: visible light irradiation with a 400–800 nm filter, an
air atmosphere for 24 h, a light source intensity of 2.0 × 10−2 W•cm−2, a re-
action temperature of 30
3 °C, 6 ml of n-heptane as solvent, 1 mmol of
benzyl alcohol, 1 mmol of acetophenone, 0.6 mmol of LiOH as the base, and
50 mg of catalyst. Cat1: Bi2WO6 (nitric acid method, pH = 4–5, 160 °C); Cat2:
Bi2WO6 (ethylene glycol method, pH = 4–5, 180 °C); Cat3: Bi2WO6 (acetic acid
method, pH = 4–5, 200 °C); Cat4: Bi2WO6 (nitric acid method, pH = 7–8,
160 °C); Cat5: Bi2WO6 (nitric acid method, pH = 9–10, 160 °C); Cat6: Bi2WO6
(nitric acid method, pH = 4–5, 100 °C); and Cat7: Bi2WO6 (nitric acid method,
pH = 4–5, 130 °C).
b
The conversion rate was 0 without the base, and when the alkali
content gradually increased from 0.2 to 1.0 mmol, the conversion rate
also gradually increased. However, the conversion rate would even-
tually decrease if the amount of base continued to increase. When the
alkali content was 1.0 mmol, the conversion rate was at the uppermost
limit (44.4%) (Table S2, entries 4 and 8–17). This might be because
when the amount of alkali was too high, shielding because of excessive
particles occurred. This caused the light dispersion and the light path in
the system to be blocked, and the conversion rate was reduced [47].
Under visible light irradiation, when the amount of acetophenone
was controlled at 1 mmol, the conversion rate initially increased and
then decreased with an increase in benzyl alcohol. The selectivity did
The conversion rate and selectivity were analyzed using gas chromato-
graphy.
stronger affinity of acetophenone for n-heptane [23]. Therefore, n-
heptane was used in subsequent experiments.
In the alpha alkylation of alcohols and ketones, the role of the base
was important (Table S1, entries 5 and 15–20). We could see that a high
conversion rate (26.3%) was obtained using LiOH, which might be
because this reaction was very sensitive to LiOH [45]. However, low
conversion rates were obtained for Na2CO3 and K2CO3 (Table S1, en-
tries 18 and 19). In the investigation of the effect of the different cat-
alysts on the reaction, we found that Bi2WO6 prepared using the nitric
163

X. Liu et al.
MolecularCatalysis466(2019)157–166
Table 3
Alpha alkylation of different alcohols and different ketones.a.
Entry
Alcohol
Ketone
Under visible light
In the dark
Conv.
(%)b
Sel.
Conv. (%)b
Sel.
(%)b
(%)b
1
2
Acetophenone
Acetophenone
8.4
0.2
85.5
0
0
0
0
> 99
3
4
Acetophenone
Acetophenone
0.6
38.4
85.5
> 99
0
0
0
0
5
6
7
Acetophenone
Acetophenone
Acetophenone
1.8
0.7
0.9
17.3
0
0
0
0
0
0
> 99
> 99
8
9
Acetophenone
52.6
1.0
> 99
> 99
0
0
0
0
Benzyl alcohol
Benzyl alcohol
10
11
29.3
> 99
0
0
Benzyl alcohol
Benzyl alcohol
23.0
6.7
> 99
> 99
0
0
0
0
12
a
Reaction conditions: visible light irradiation with a 400–800 nm filter, an air atmosphere for 24 h, a light source intensity of 2.0 × 10−2 W•cm−2, a reaction
temperature of 30
3 °C, 6 ml of n-heptane as the solvent, 1.0 mmol of LiOH as the base, 75 mg of Bi2WO6 (nitric acid method, pH = 4–5, 130 °C) as the catalyst,
4 mmol of alcohol and 1 mmol of ketone.
b
The conversion rate and selectivity were analyzed using gas chromatography.
not change significantly, and the conversion rate and selectivity were 0
in the dark (Table S2, entries 12 and 18–22). This finding might be
because within a certain range, increasing the amount of benzyl alcohol
would be more beneficial to removal of hydrogen, which could com-
pletely oxidize benzyl alcohol to benzaldehyde. Therefore, the con-
version rate of benzaldehyde and acetophenone to 1,3-diphenyl-1-
propenone would increase [1,48]. When the amount of benzyl alcohol
was controlled at 1 mmol, an increased amount of acetophenone caused
the conversion rate to gradually decrease, whereas the selectivity re-
mained basically unchanged (Table S2, entries 12 and 23–25). This
phenomenon might be due to the larger amount of acetophenone,
which would occupy a larger active site, causing benzyl alcohol to be
insufficiently oxidized to benzaldehyde; thus, the amount of 1,3-di-
phenyl-1-propenone was reduced [1,48]. In general, when the amount
of benzyl alcohol was 4 mmol and the amount of acetophenone was
1 mmol, the conversion rate (52.2%) was the highest, and the se-
lectivity at that point was 98.6%. Therefore, when the ratio of benzyl
alcohol to acetophenone was 4:1, the photocatalytic reaction was more
favorable.
those under visible light irradiation. When a saturated fatty alcohol was
attached to the benzene ring, the conversion rate was low, and the
conversion rate of attaching a linear saturated fatty alcohol was higher
than that of attaching a saturated fatty alcohol with a branched chain
(Table 3, entries 1 and 2). The conversion rates for saturated fatty al-
cohols and unsaturated fatty alcohols were very similar (Table 3, en-
tries 3 and 6). The higher the number of carbon atoms in the alcohol
chain was, the higher the corresponding conversion rate was (Table 3,
entries 5 and 6). For the same number of carbon atoms, the conversion
rate for secondary alcohols was higher than that for primary alcohols
(Table 3, entries 4 and 5), which is relevant to the formation of 1,3-
diphenyl-1-propenone. Surprisingly, the conversion rate (52.6%) of the
reactant with -NO2 was extremely high, higher than that of the reactant
with -Cl, and the selectivity was almost the same (Table 3, entries 7 and
8). This might be because the electron absorption ability of -NO2 was
stronger than that of -Cl, and the alcohol with a strong electron ab-
sorption ability was more favorable for the reaction. Many ketone de-
rivatives have also been explored (Table 3, entries 9–12). The conver-
sion rate of reactants containing an electron-donating group (−CH3)
reached 29.3% (Table 3, entries 9 and 10), which might be because the
benzene ring could be activated when the electron-donating group was
attached. Surprisingly, the conversion rate (23.0%) of the aromatic
ketone was much higher than that of the aliphatic ketone (6.7%)
(Table 3, entries 11 and 12).
In the investigation of the effect of different atmospheres on this
reaction (Table S2, entries 4, 6, and 7), the conversion rate (3.1%) was
quite low in an atmosphere of Ar. Under atmospheres of air and oxygen,
the conversion rate changed little under visible light irradiation, but
oxygen promoted the occurrence of dark reactions. Therefore, air was
selected as the best reaction atmosphere [43].
To extend the generality of the alpha alkylation of benzyl alcohol
and acetophenone, this paper explored the effect of eight different al-
cohols and four different ketone derivatives on the alpha alkylation
reaction (Table 3), and the conversion rates in the dark were lower than
3.9. The influence of wavelength and light intensity on the reaction
To explore the influence of different wavelengths and light in-
tensities on the alpha alkylation reaction of benzyl alcohol and
164

X. Liu et al.
MolecularCatalysis466(2019)157–166
Fig. 7. Effects of different wavelengths on the alpha alkylation of benzyl al-
cohol and acetophenone.
Fig. 10. Active species capture experiment of Bi2WO6 (nitric acid method,
pH = 4–5, 130 °C).
conducive to the occurrence of the reaction [49].
3.10. Catalyst recycling ability test
To explore the stability of the catalyst, the influence of the cycling
experiment on the catalyst was studied (Fig. 9). The same conditions
were chosen for the cycling experiment (400–800 nm filter, air atmo-
sphere for 24 h, a light source intensity of 2.0 × 10−2 W•cm−2, a re-
action temperature of 30
3 °C, 6 ml of n-heptane, 4 mmol of benzyl
alcohol, 1 mmol of acetophenone, 1.0 mmol LiOH as the base, and
75 mg of Bi2WO6 (nitric acid method, pH = 4–5, 130 °C) as the catalyst.
During the four cycles of the Bi2WO6 catalyst (nitric acid method,
pH = 4–5, 130 °C), the conversion rate was almost the same (Fig. 9). In
the fifth cycle, the conversion rate decreased. However, the activity was
still high, and the selectivity remained basically unchanged during the
five cycles. This result might be due to the photocatalytic stability and
thermal stability of the catalyst [8,50].
Fig. 8. Effects of different light intensities on the alpha alkylation of benzyl
alcohol and acetophenone.
acetophenone, this study selected the aforementioned optimal experi-
mental conditions and explored six different wavelengths and light
intensities to study their effect on this reaction. The experimental data
are shown in Figs. 7 and 8. The broader the wavelength range was, the
higher the conversion rate was. When the wavelength range was
400–800 nm, the conversion rate (52.2%) was the highest. When the
wavelength range was 450–800 nm, the conversion rate was greatly
reduced (Fig. 7).
3.11. Active species test
To explore the active species of the Bi2WO6 catalyst (nitric acid
method, pH = 4–5, 130 °C) produced during the reaction, the optimal
conditions were selected (i.e., 1 mmol of benzyl alcohol, and the other
conditions were the same as 3.10), and 5 mmol of one of five capture
agents was added to each solution. Ethylene-diamine-tetraacetic-acid
(EDTA) acted as a scavenger for holes (h+). Tertiary butanol (t-BuOH)
and isopropyl alcohol (IPA) acted as scavengers for hydroxyl radicals
(•OH). 1,4-Benzoquinone (BQ) acted as a scavenger for superoxide ra-
dicals (•O2−), and carbon tetrachloride (CCl4) acted as a scavenger for
electrons (e−). The results of the active species experiment are shown
in Fig. 10. The conversion rate was reduced when 1,4-benzoquinone
(BQ), ethylene-diamine-tetraacetic-acid (EDTA), and carbon tetra-
chloride (CCl4) were added, thus demonstrating that the superoxide
As shown in Fig. 8, the conversion rate also gradually increased with
increasing light intensity. When the light intensity was 0.0211 W•cm−2
,
the conversion rate was 63.0%, which indicated that a higher light
intensity could produce more photoexcited electrons, resulting in a
higher conversion rate; thus,
a higher light intensity was more
radicals ( O2−), holes (h+), and electrons (e−) were active species
%
[16].
4. Conclusions
In summary, upon adding a 400–800 nm filter, Bi2WO6 prepared
using the nitric acid method (pH = 4–5, with a hydrothermal tem-
perature of 130 °C) was more favorable for the alpha alkylation reaction
of benzyl alcohol and acetophenone under visible light irradiation.
Bi2WO6 was stable after five cycles. Furthermore, active species capture
%
experiments demonstrated the main role of O2−, h+, and e− in the
Fig. 9. Recyclability test of the alpha alkylation of benzyl alcohol and acet-
ophenone.
alpha alkylation reaction.
165

X. Liu et al.
MolecularCatalysis466(2019)157–166
Acknowledgments
[22] M. Qamar, Rami B. Elsayed, Khalid R. Alhooshani, Muhammad I. Ahmed,
DetlefW. Bahnemann, ACS Appl. Mater. Interfaces 7 (2015) 1257–1269, https://
doi.org/10.1021/am507428r.
This work was financially supported by the National Natural Science
Foundation of China (NSFC, Nos. 20567002, and Nos. 21067007), the
Natural Science Fund of Inner Mongolia (2010MS0203 and
2014MS0201), the 2013 Annual Grassland Talents Project of Inner
Mongolia Autonomous Region, and the 2013 Annual Inner Mongolia
Talent Development Fund.
[23] R. Molinari, C. Lavorato, P. Argurio, Chem. Eng. J. 274 (2015) 307–316, https://
doi.org/10.1016/j.cej.2015.03.120.
[24] Y.K. Huang, S.F. Kang, Y. Yang, H.F. Qin, Z.J. Ni, S.J. Yang, X. Li, Appl. Catal. B 196
(2016) 89–99, https://doi.org/10.1016/j.apcatb.2016.05.022.
[25] A. Ziarati, A. Badiei, R. Luque, Appl. Catal. B 240 (2019) 72–78, https://doi.org/10.
1016/j.apcatb.2018.08.058.
[26] A. Ziarati, A. Badiei, R. Luque, Appl. Catal. B 238 (2018) 177–183, https://doi.org/
10.1016/j.apcatb.2018.07.020.
[27] A. Ziarati, A. Badiei, R. Luque, W.Y. Ouyang, J. Mater. Chem. A Mater. Energy
Sustain. 6 (2018) 8962–8968, https://doi.org/10.1039/c8ta02012d.
[28] L. Yuan, B. Weng, J.C. Colmenares, Y.G. Sun, Y.J. Xu, Small. 13 (2017) 1702253, ,
https://doi.org/10.1002/smll.201702253.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2019.01.018.
[29] Z. Wang, X.J. Lang, Appl. Catal. B 224 (2018) 404–409, https://doi.org/10.1016/j.
apcatb.2017.10.002.
[30] M. Zhang, Q.G. Shang, Y.Q. Wan, Q.R. Cheng, G.Y. Liao, Z.Q. Pan, Appl. Catal. B
241 (2019) 149–158, https://doi.org/10.1016/j.apcatb.2018.09.036.
[31] Z.L. Lv, H. Zhou, H. Liu, B.H. Liu, M.F. Liang, H. Guo, Chem. Eng. J. 330 (2017)
1297–1305, https://doi.org/10.1016/j.cej.2017.08.074.
References
[1] Q. Xu, J.H. Chen, H.W. Tian, X.Q. Yuan, S.Y. Li, C.K. Zhou, J.P. Liu, Angew. Chem.
Int. Ed. 53 (2014) 225–229, https://doi.org/10.1002/anie.201308642.
[2] J. Cheng, S.X. Shi, T.T. Tang, S.Q. Tian, W.J. Yang, D.W. Zeng, J. Alloys. Compd.
643 (2015) 159–166, https://doi.org/10.1016/j.jallcom.2015.03.119.
[3] R.Y. Wu, H.B. Song, N. Luo, G.J. Ji, J. Colloid Interface Sci. 524 (2018) 350–359,
https://doi.org/10.1016/j.jcis.2018.03.031.
[32] P. Ju, P. Wang, B. Li, H. Fan, S.Y. Ai, D. Zhang, Y. Wang, Chem. Eng. J. 236 (2014)
430–437, https://doi.org/10.1016/j.cej.2013.10.001.
[33] W. Zhao, Aj. Wang, Y. Wang, C.C. Lv, W.H. Zhu, S.P. Dou, Q. Wang, Q. Zhong, J.
Alloys. Compd. 726 (2017) 164–172, https://doi.org/10.1016/j.jallcom.2017.07.
268.
[34] Y.H. Xiang, P. Ju, Y. Wang, Y. Sun, D. Zhang, J.Q. Yu, Chem. Eng. J. 288 (2016)
264–275, https://doi.org/10.1016/j.cej.2015.11.103.
[4] F. Wang, K. Cao, Y. Wu, K.H. Zhang, Y. Zhou, Appl. Surf. Sci. 360 (2016)
1075–1079, https://doi.org/10.1016/j.apsusc.2015.11.061.
[35] Z.S. Seddigi, M.A. Gondal, S.G. Rashid, M.A. Abdulaziz, S.A. Ahmed, J. Mol. Catal.
A Chem. 420 (2016) 167–177, https://doi.org/10.1016/j.molcata.2016.04.026.
[36] Z.M. Cui, H. Yang, B. Wang, R.S. Li, X.X. Wang, Nanoscale Res. Lett. 11 (2016) 190,
https://doi.org/10.1186/s11671-016-1413-x.
[5] W. Guo, K. Fan, J.J. Zhang, C.J. Xu, Appl. Surf. Sci. 447 (2018) 125–134, https://
doi.org/10.1016/j.apsusc.2018.03.080.
[6] F.J. Zhang, S. Zou, T.Y. Wang, Y.X. Shi, P. Liu, Photochem. Photobiol. 93 (2017)
1154–1164, https://doi.org/10.1111/php.12747.
[37] R. Zhang, G. Li, Y. Zhang, Photochem. Photobiol. Sci. 16 (2017) 996–1002, https://
doi.org/10.1039/c7pp00073a.
[7] B.X. Li, L.Z. Shao, R.S. Wang, X.P. Dong, F.G. Zhao, P. Gao, Z.Q. Li, J. Mater. Chem.
A Mater. Energy Sustain. 6 (2018) 6344–6355, https://doi.org/10.1039/
c8ta00449h.
[38] D.H. Liu, J.F. Huang, X.W. Tao, D. Wang, RSC Adv. 5 (2015) 66464–66470, https://
doi.org/10.1039/c5ra11381d.
[8] P. Zhang, Y. Liu, B.Z. Tian, Y.S. Luo, J.L. Zhang, Catal. Today 281 (2017) 181–188,
https://doi.org/10.1016/j.cattod.2016.05.042.
[39] S.J. Li, S.W. Hu, W. Jiang, Y. Liu, J.S. Liu, Z.H. Wang, J. Colloid Interface Sci. 501
(2017) 156–163, https://doi.org/10.1016/j.jcis.2017.04.057.
[40] M. Niederberger, M.H. Bartl, G.D. Stucky, Chem. Mater. 14 (2002) 4364–4370,
https://doi.org/10.1021/cm021203k.
[9] L.B. Xiao, R.B. Lin, J. Wang, C. Cui, J.Y. Wang, Z.Q. Li, J. Colloid Interface Sci. 523
(2018) 151–158, https://doi.org/10.1016/j.jcis.2018.03.064.
[10] G.P. Zhang, D.Y. Chen, N.J. Li, Q.F. Xu, H. Li, J.H. He, J.M. Lu, Appl. Catal. B 232
(2018) 164–174, https://doi.org/10.1016/j.apcatb.2018.03.017.
[11] X.F. Qian, D.T. Yue, Z.Y. Tian, M. Reng, Y. Zhu, M. Kan, T.Y. Zhang, Appl. Catal. B
193 (2016) 16–21, https://doi.org/10.1016/j.apcatb.2016.04.009.
[12] Y.Y. Wang, W.J. Jiang, W.J. Luo, X.J. Chen, Y.F. Zhu, Appl. Catal. B 237 (2018)
633–640, https://doi.org/10.1016/j.apcatb.2018.06.013.
[41] B. Chong, L. Chen, W.T. Wang, D.Z. Han, L. Wang, L.J. Feng, Q. Li, C.H. Li, Mater.
Lett. 204 (2017) 149–153, https://doi.org/10.1016/j.matlet.2017.06.033.
[42] J. Tian, X.L. Hu, N. Wei, Y.L. Zhou, X.H. Xu, H.Z. Cui, H. Liu, Sol. Energy Mater. Sol.
Cells 151 (2016) 7–13, https://doi.org/10.1016/j.solmat.2016.02.017.
[43] P. Zhang, P.Y. Wu, S.Y. Bao, Z. Wang, B.Z. Tian, J.L. Zhang, Chem. Eng. J. 306
(2016) 1151–1161, https://doi.org/10.1016/j.cej.2016.08.015.
[44] S. Schünemann, M.V. Gastel, H. Tüysüz, ChemSusChem. 11 (2018) 2057–2061,
https://doi.org/10.1002/cssc.201800679.
[13] F. Yang, X.M. Zhu, J.Z. Fang, D.D. Chen, W.H. Feng, Z.Q. Fang, Ceram. Int. 44
(2018) 6918–6925, https://doi.org/10.1016/j.ceramint.2018.01.119.
[14] Y. He, L. Li, W.G. Fan, C.X. Zhang, M.K.H. Leung, J. Alloys. Compd. 732 (2018)
593–602, https://doi.org/10.1016/j.jallcom.2017.10.153.
[45] T. Song, J.E. Park, Y.K. Chung, J. Org. Chem. 83 (2018) 4197–4203, https://doi.
org/10.1021/acs.joc.8b00197.
[15] C.F. Sun, Y.B. Wang, Q. Su, Chem. Phys. Lett. 702 (2018) 49–56, https://doi.org/
10.1016/j.cplett.2018.04.052.
[46] E.I. Cedillo-González, R. Riccò, S. Costacurta, C. Siligardi, P. Falcaro, Appl. Surf. Sci.
435 (2018) 769–775, https://doi.org/10.1016/j.apsusc.2017.11.078.
[47] J.W. Che, M.J. Hao, W.Z. Yi, H. Kobayashi, Y.H. Zhou, L.P. Xiao, J. Fan, Chin. J.
Catal. 38 (2017) 1870–1879, https://doi.org/10.1016/S1872-2067(17)62904-8.
[48] S. Solmi, E. Rozhko, A. Malmusi, T. Tabanelli, S. Albonetti, F. Basile, S. Agnoli,
F. Cavani, Appl. Catal. A Gen. 557 (2018) 89–98, https://doi.org/10.1016/j.apcata.
2018.03.019.
[16] S.X. Yu, Y.H. Zhang, M. Li, X. Du, H.W. Huang, Appl. Surf. Sci. 391 (2017) 491–498,
https://doi.org/10.1016/j.apsusc.2016.07.028.
[17] F. Xu, H.M. Chen, C.Y. Xu, D.P. Wu, Z.Y. Gao, Q. Zhang, K. Jiang, J. Colloid
Interface Sci. 525 (2018) 97–106, https://doi.org/10.1016/j.jcis.2018.04.057.
[18] M. Wang, M.H. Fang, C. Tang, L.N. Zhang, Z.H. Huang, Y.G. Liu, X.W. Wu, J. Mater.
Res. 31 (2016) 713–720, https://doi.org/10.1557/jmr.2016.72.
[49] Y.M. Huang, Z. Liu, G.P. Gao, Q. Xiao, W. Martens, A.J. Du, S. Sarina, C. Guo,
H.Y. Zhu, Catal. Sci. Technol. 8 (2018) 726–734, https://doi.org/10.1039/
c7cy02291c.
[19] J.J. Wang, L. Tang, G.M. Zeng, Y.N. Liu, Y.Y. Zhou, Y.C. Deng, J.J. Wang, B. Peng,
ACS Sust. Chem. Eng. 5 (2017) 1062–1072, https://doi.org/10.1021/
acssuschemeng.6b02351.
[50] H.W. Huang, R.R. Cao, S.X. Yu, K. Xu, W.C. Hao, Y.G. Wang, F. Dong, T.R. Zhang,
Y.H. Zhang, Appl. Catal. B 219 (2017) 526–537, https://doi.org/10.1016/j.apcatb.
2017.07.084.
[20] Y.Y. Zhao, Y.B. Wang, E.Z. Liu, J. Fan, X.Y. Hu, Appl. Surf. Sci. 436 (2018) 854–864,
https://doi.org/10.1016/j.apsusc.2017.12.064.
[21] X.P. Xiao, J.H. Wei, Y. Yang, R. Xiong, C.X. Pan, J. Shi, ACS Sust. Chem. Eng. 4
(2016) 3017–3023, https://doi.org/10.1021/acssuschemeng.5b01701.
166