Insight into facet-dependent photocatalytic H2O2production on BiOCl nanosheets

Article abstract of DOI:10.1039/d0nj05506a

Hydrogen peroxide is an important high-energy product widely used in various fields. Highly efficient semiconductor photocatalysts, especially those that can produce H₂O₂both from water oxidation and O₂reduction, are eagerly desired. In this work, BiOCl nanosheets with preferentially exposed (001) and (010) facets were synthesizedviaa simple hydrothermal method. The facet-dependent photocatalytic H₂O₂generation activities of these BiOCl nanosheets were assessed. The hydrogen peroxide evolution rate of BiOCl(001) is about 2-fold higher than that of BiOCl(010), which is assigned to the higher separation efficiency of photogenerated charge carriers. Interestingly, both the EPR study and active species trapping experiments demonstrate that the generation of H₂O₂on the BiOCl(001) photocatalyst mostly originates from sequential two step single-electron O₂reduction, while there are two pathways for photocatalytic H₂O₂production on BiOCl(010), from both oxygen reduction and water oxidation. This work offers a new strategy to pursue highly efficient semiconductor photocatalysts with two pathways for H₂O₂production from both water oxidation and O₂reduction.

Full text of DOI:10.1039/d0nj05506a

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Insight into facet-dependent photocatalytic H O
2
2
production on BiOCl nanosheets
Cite this: New J. Chem., 2021,
45, 3335
Yating Xu, Hanping Fu, Ling Zhao, Lishan Jian, Qingshuang Liang * and
Xiufeng Xiao*
Hydrogen peroxide is an important high-energy product widely used in various fields. Highly efficient
semiconductor photocatalysts, especially those that can produce H both from water oxidation and
reduction, are eagerly desired. In this work, BiOCl nanosheets with preferentially exposed (001) and
010) facets were synthesized via a simple hydrothermal method. The facet-dependent photocatalytic
generation activities of these BiOCl nanosheets were assessed. The hydrogen peroxide evolution
2 2
O
O
2
(
2 2
H O
rate of BiOCl(001) is about 2-fold higher than that of BiOCl(010), which is assigned to the higher
separation efficiency of photogenerated charge carriers. Interestingly, both the EPR study and active
Received 11th November 2020,
Accepted 8th January 2021
species trapping experiments demonstrate that the generation of H
mostly originates from sequential two step single-electron O reduction, while there are two pathways
for photocatalytic H production on BiOCl(010), from both oxygen reduction and water oxidation.
This work offers a new strategy to pursue highly efficient semiconductor photocatalysts with two
pathways for H production from both water oxidation and O reduction.
2 2
O on the BiOCl(001) photocatalyst
2
2 2
O
DOI: 10.1039/d0nj05506a
rsc.li/njc
O
2 2
2
photocatalysts, especially those that can produce H O2 from
2
Introduction
2
both water oxidation and O reduction, are eagerly needed.
2 2
Hydrogen peroxide (H O ) is an important high-energy product
As photocatalytic reactions take place on the surfaces of
widely used in various fields, acting as both an oxidant and semiconductors, the surface properties of photocatalysts are
reductant in chemical synthesis, environmental cleaning, fuel crucial in determining the photocatalytic activity. The surface
1
–4
cells and the medical field. At present, many methods have atom arrangement and coordination intrinsically determine
been developed to produce H O on a large scale, including the adsorption of reactant molecules and desorption of product
2
2
5
anthraquinone oxidation, direct synthesis from H and O and molecules, and the surface transfer between the reactant mole-
2
2
6
,7
oxidation of alcohols. However, these methods cannot be cules and photoexcited charges. The facet-dependent reactivity
1
4–19
considered ideal approaches because of the high energy of many photocatalysts has been reported.
demand, and undesirable by-products, and the mixture of H exposed (101) facets has exhibited selective photocatalytic
and O may create a potential explosion hazard. Therefore, an degradation of methylene orange (MO) in a methylene blue
efficient, energy-saving and environmentally friendly method to (MB) and methyl orange (MO) mixed solution, whereas TiO
produce H is highly desired. The conversion of solar energy with exposed (111) and (001) facets exhibits photocatalytic
2
TiO with
2
2
2
2 2
O
2
0
to chemical fuel is a fascinating approach. Recently, researchers selectivity for MB. Reduction and oxidation cocatalysts could
have found that H O can be produced through semiconductor selectively deposit on the (110) and (010) facets of BiVO4,
2
2
3
,8–10
photocatalytic processes from O2 and water.
photocatalysts, TiO and modified TiO could function as effec- photoelectrocatalytic water oxidation reactions. Facet engineering
tive photocatalysts for H generation under UV light.
free polymeric semiconductors based on graphitic carbon nitride photocatalysts.
As typical resulting in much higher activity in both photocatalytic and
21
2
2
9
,11
2
O
2
Metal- offers an exciting direction to pursue highly active new generation
22–25
have been found to generate H
O
2 2
by O
Despite the fact that many semiconductor systems transition band gap to reduce the recombination probability of
have been and are still being explored for H O generation, they the excited electron and the hole, has been explored as a promising
2
reduction under visible
BiOCl,
which has a layered structure and an indirect-
1
2,13
light.
2
2
still suffer from low efficiency. Highly efficient semiconductor photocatalyst in various clean energy and environmental technolo-
2
6–28
29,30
gies, such as water-splitting,
treatment.
N fixation
and waste water
Recent studies have revealed that different facets
of BiOCl crystals exhibited distinct photocatalytic activities. For
2
31–33
Fujian Provincial Key Laboratory of Advanced Materials Oriented Chemical
Engineering, College of Chemistry and Material Science, Fujian Normal University,
Fuzhou, Fujian 350007, China. E-mail: lqs671@163.com, xfxiao@fjnu.edu.cn
34
instance, Zhang et al. found that due to the cooperative effect
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between the surface atomic structure and suitable internal electric Synthesis of BiOCl(001) nanosheets
fields, BiOCl nanosheets with exposed (001) facets exhibited higher
The product was obtained by the same method without adding
NaOH solution, which was denoted as BiOCl(001).
activity for direct semiconductor photoexcitation pollutant degrada-
35
tion under UV-light irradiation. Xiong et al. reported that the
valence band edge of (110) is more negative than that of (001),
suggesting that BiOCl nanosheets with exposed (110) facets possess
a higher oxidation potential. It is demonstrated that BiOCl(001)
presents higher efficiency in charge separation and higher charge
Characterization
Transmission electron microscopy (TEM) and high-resolution
transmission electron microscopy (HRTEM) images of the sam-
ples were taken with a JSM-6700F microscope with a 200 kV
accelerating voltage. X-ray powder diffraction (XRD) measure-
ments were recorded on a Bruker D8 ADVANCE with Cu-Ka
radiation (l = 0.1518 nm). X-ray photoelectron spectroscopy
36
carrier density. Yet Liu et al. reported that due to the fact that the
010) surface consists of more terminal bismuth atoms and more
(
surface complexes are formed, BiOCl nanosheets exposing (010)
facets exhibit higher activity for photodegradation of 2-naphthol.
Nevertheless, in previous studies, BiOCl is mainly investigated
for photocatalytic degradation of pollutants and research
(XPS) was carried out with a Thermo ESCALab 250 analyzer
operating in constant analyzer energy mode. UV-vis diffuse reflec-
tance spectroscopy (DRS) was carried out on a Lambda 750 nm
spectrophotometer equipped with an integrating sphere attach-
ment. The electrochemical analysis was carried out on a Zennium
Pro electrochemical workstation (Zahner, Germany) with a stan-
dard three-electrode cell. Electron paramagnetic resonance (EPR)
measurements were carried out on a Bruker A300 spectrometer to
capture the intermediate radicals. The active radical species were
trapped by adding 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a
spin-trapping reagent. Typically, the experiments for superoxide
radicals and hydroxyl radicals were conducted in water or chro-
matographic purity methanol solution and 5% HCOOH solution
containing DMPO within a container, respectively. The detection
about exploring high H
is rare. A study of the facet-dependent catalytic activity of
generation on BiOCl nanosheets has not yet been
carried out.
In this work, BiOCl nanosheets with preferentially exposed
001) and (010) facets were synthesized via a simple hydro-
thermal method. The facet-dependent photocatalytic H O
2 2
O generation on BiOCl nanosheets
2 2
H O
(
2
2
generation activities of these BiOCl nanosheets were assessed.
The dominant reactive species involved in the facet-dependent
photocatalysis were also identified. The reaction mechanisms
2 2
of H O evolution on the BiOCl(001) and BiOCl(010) samples
were investigated and it is found that there are two pathways
for photocatalytic H O production on BiOCl(010) from both
ꢀ
À
ꢀ
of O2 and OH was in the air and in an anaerobic environment,
respectively. Then the solutions were processed in the dark and
under light irradiation (300 W xenon lamp) with stirring for
2
2
oxygen reduction and water oxidation.
10 min. After the irradiation, the resulting solution was subjected
to analysis at room temperature in a sealed capillary tube.
Experimental section
Photocatalytic activity tests
Chemicals
The photocatalytic activity was evaluated by the generation of
2 2
H O . The light source was chosen as a 300 W xenon lamp.
Bismuth nitrate pentahydrate (Bi(NO
KCl), sodium hydroxide (NaOH), formate acid (98%), ethanol
75%), P-benzoquinone (PBQ) and tert-butyl alcohol (TBA) were
purchased from Aladdin Industrial Corporation. Deionized water
was used throughout this study. All chemicals were used as
received without further purification.
3
)
3
Á5H
2
O), potassium chloride
Typically, 50 mg of catalyst powder was added into 40 mL
aqueous solution containing 5% HCOOH solution in a con-
tainer with an ice-water bath outside. The reaction solution was
stirred in the dark for 30 min before photoirradiation. During
the photocatalysis process, 2 mL of the suspension was taken
from the container every 10 min, and then centrifuged to
(
(
remove the photocatalysts. The concentration of H
2 2
O was
Preparation of photocatalysts
determined by the titanium sulfate spectrophotometric
3
7
method. Typically, 2 mL of the suspension taken from the
glass container was centrifuged to remove the photocatalysts.
Then 2 mL of titanium sulfate was added and reacted for the
Synthesis of BiOCl(010) nanosheets. The BiOCl nanosheets
3
4
were prepared via a facile hydrothermal process as reported.
Typically, Bi(NO O (1 mmol) and KCl (1 mmol) were
Á5H
3
)
3
2
4
+
measurement (H O + Ti - H TiO ). When the solution
2
2
2
4
dissolved in distilled water (15 mL) with constant stirring at
room temperature. NaOH solution was then dropwise added
into the mixed solution, followed by stirring for 30 min, which
was to adjust the pH value to about 6.0. Afterwards, the mixture
was transferred to a Teflon-lined stainless autoclave and heated
at 160 1C for 24 h, and then cooled to room temperature. The
precipitates were collected by centrifugation and washed with
ethanol and deionized water repeatedly. Finally, the product
became yellow, the absorbance of the reaction product at
4
H
00 nm was measured to calculate the concentration of
3
8
2
O
2
.
According to the standard curves of H
2 2
O , the amount
of H
2
O
2
in the solution can be calculated: abs = 0.287C + 0.068.
Results and discussion
was dried at 60 1C in air. The obtained powder was denoted as The BiOCl nanosheets with different exposed facets were pre-
BiOCl(010).
pared by a hydrothermal method. Fig. 1a–h display the
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different morphology and microstructure of the BiOCl(001) and
BiOCl(010) nanosheets. As shown in Fig. 1a, the BiOCl(001)
nanosheets are composed of a dimetric sheet-shaped morphol-
ogy and smooth surface with a width of around 0.5–1 mm.
Fig. 1b shows that the BiOCl(010) nanosheets exhibit a well-
defined truncated square morphology, and the width of the
BiOCl(010) sample is about 1–2.5 mm. The TEM images in
Fig. 1c and d further confirm the morphology of the as-prepared
nanosheets. In Fig. 1g, the corresponding selected-area electron
diffraction (SAED) pattern indicated BiOCl(001) nanosheets with a
single-crystalline characteristic. The angle labeled in the SAED
pattern is 451, which is in agreement with the theoretical value of
the angle between the (110) and (200) planes, matching well with
34
the [001] zone axis diffraction pattern of BiOCl. Fig. 1e shows the
HR-TEM image of the BiOCl(001) sample. The interplanar lattice
spacing of 0.275 nm is assigned to the (110) atomic plane, indexed
to the [001] zone axis diffraction pattern of BiOCl. The SAED
pattern and the HR-TEM both confirm that the BiOCl(001) sample
preferentially exposes the (001) plane. Similar characterizations of for BiOCl(001) and BiOCl(010), respectively. This difference in
the BiOCl(010) sample were carried out and the preferentially the intensity ratios reveals the different crystallization orienta-
exposed orientation of [010] is identified. Fig. 1f shows clear lattice tions of the BiOCl(001) and BiOCl(010) samples, which is
fringes of 0.194 nm and 0.267 nm, corresponding to the (200) and consistent with the HR-TEM and SAED results.
Fig. 2 XRD patterns of the BiOCl(001) and BiOCl(010) samples.
3
4
(102) atomic planes, respectively. The corresponding SAED pattern
The surface chemical state and composition of the BiOCl(001)
of the BiOCl(010) sample is shown in Fig. 1h, and the (002) and BiOCl(010) samples were analyzed by XPS. Fig. 3a–d display
and (102) planes are observed with an interfacial angle of 43.41, the full XPS survey spectra and the Bi 4f, O 1s and Cl 2p XPS
matching well with those of the [010] zone axis of BiOCl.
spectra of the BiOCl(001) and BiOCl(010) samples. As shown in
XRD was employed to further determine the crystallographic the survey spectra (Fig. 3a), bismuth, chlorine, and oxygen
phase of the samples. The XRD patterns of BiOCl(001) and species are observed in both samples. For the Bi 4f region, the
BiOCl(010) are shown in Fig. 2. All diffraction peaks of BiOCl peaks observed at 164.2 and 158.8 eV are assigned to the spin
could be indexed to the standard JCPDS: 06-0249, and no orbit splitting photoelectrons of Bi (4f5/2) and Bi (4f7/2) in BiOCl,
3
3
diffraction peaks of other impurities were observed, indicating respectively. Both the Bi 4f5/2 and 4f7/2 states can be observed in
high purity of the BiOCl samples. It can be seen that the (001) BiOCl(001) and BiOCl(010), indicating the same chemical state
peak is the most intense one among all of the peaks of the of Bi atoms in these two samples.
BiOCl(001) sample, indicating that the as-prepared nanosheets
Since the BiOCl nanosheets were covered with different
are covered with dominant (001) facets. In addition, the inten- dominant facets, their facet-dependent photocatalytic H
O
2 2
sity proportions of the (002) and (200) peaks are 2.404 and 1.233 production performances were tested to be compared. The
Fig. 1 Electron microscope images of BiOCl(001) and BiOCl(010): (a and b) SEM, (c and d) TEM, (e and f) HR-TEM, and (g and h) SAED.
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Fig. 3 (a) Full XPS survey spectrum of BiOCl. High-resolution XPS spectra of (b) Bi 4f, (c) O 1S, and (d) Cl 2p for the BiOCl(001) and BiOCl(010) samples.
photocatalytic H
measured in HCOOH solution. Fig. 4 shows the change of the
concentration with the irradiation time. It can be seen
that the concentration of H O gradually increases with con-
2 2
O production of the BiOCl samples was
2 2
H O
2
2
tinued irradiation in both suspensions. After 120 min of
À1
irradiation, about 7.1 and 3.3 mmol L of H
2
O
2
can be rapidly
generated over the BiOCl(001) and BiOCl(010) suspensions,
respectively. In the same irradiation time, the amount of
H
2
O
2
generation in the BiOCl(001) suspension is obviously
higher than that in the BiOCl(010) suspension. The amount
of H generation in the BiOCl(001) suspension is about 2-fold
2 2
O
higher than that of the BiOCl(010) sample after 2 h of irradia-
tion. This clearly shows that the as-prepared BiOCl(001) sample
exhibits higher photocatalytic H
the BiOCl(010) sample.
2 2
O production activity than
2 2
Fig. 4 The concentration of H O as the irradiation time-dependent
2 2
Generally, H O is produced through oxygen reduction and change over the BiOCl(001) and BiOCl(010) samples under light irradiation.
water oxidation, which occurs through three ways: (1) direct one-
À
ꢀ
À
2
) to H
electron reduction of O
reduction of O to H
2
(O
2
+ e = O
2
O
2
; (2) multi-electron
ꢀ
À
) and (3) hole- process. As shown in Fig. 5, no signals of DMPO-O2
+
À
2
2
O
2
(O
ꢀ
2
+ 2H + 2e = H
2
O
2
and
ꢀ
À
+
37
ꢀ
oxidized- OH (OH + h = OH) to generate H O . To uncover the DMPO- OH are observed in the dark. Meanwhile, with light irradia-
facet-dependent photocatalytic H O production over BiOCl tion, characteristic signals of DMPO-O2 can be observed on both
2
2
ꢀ
À
2
2
2 2
nanosheets, the reaction mechanisms of H O evolution on the of the BiOCl(001) and BiOCl(010) samples (Fig. 5a), indicating that
BiOCl(001) and BiOCl(010) samples were investigated, respectively. both of the BiOCl(001) and BiOCl(010) photocatalysts could generate
ꢀ
À
EPR study with DMPO as the spin-trapping agent was employed to O2
during the photocatalytic process. Therefore, both of the
measure the production of active radicals during the photocatalytic BiOCl(001) and BiOCl(010) photocatalysts could generate H O2
2
3338 | New J. Chem., 2021, 45, 3335À3342
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Fig. 5 EPR spectra of active oxygen radicals and hydroxyl radicals generated during BOC(001) and BOC(010) photocatalysis.
through oxygen reduction by a sequential two step single-electron are observed in BiOCl(001), indicating that the generation of H O
2
2
ꢀ
À
mechanism. Meanwhile, Fig. 5b shows the characteristic peak of on BiOCl(001) is almost all from O2 , the sequential two step
DMPO- OH in the BiOCl(010) samples, indicating that some of the single-electron mechanism. Therefore, there are two pathways to
ꢀ
generation of H
2
O
2
in BiOCl(010) originated from hole-oxidized- produce H
2
O
2
on the BiOCl(010) photocatalyst, while the generation
ꢀ
ꢀ
OH. On the contrary, no obvious DMPO- OH characteristic peaks of H
2
O
2
on BiOCl(001) is mainly by the one-electron reduction of O
2
.
2 2
Fig. 6 The influence of scavengers PBQ and TBA on the photocatalytic H O production using the BiOCl(001) and BiOCl(010) samples.
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p-benzoquinone (PBQ) and tert-butyl alcohol (TBA) were used to
ꢀ
À
ꢀ
eliminate O
and b, the H O generation gradually decreases with the PBQ
2
and OH radicals, respectively. As seen in Fig. 6a
2
2
concentration increasing. The generation of H O is scarcely
2
2
observed on the BiOCl(001) photocatalyst when the concentration
of PBQ is 5 mM. However, when the concentration of PBQ is
5
mM, the generation of H
photocatalyst. Meanwhile, comparing the BiOCl(001) photocata-
lyst, the decrease of H generation on the BiOCl(010) sample is
2 2
O still exists on the BiOCl(010)
2 2
O
more obvious with adding the scavenger TBA (as shown in Fig. 6c
and d). These results confirm that the generation of H O on the
2
2
BiOCl(001) photocatalyst mostly originates from sequential two
step single-electron O reduction, while the photocatalytic H O
2 2
2
production on BiOCl(010) can be both from oxygen reduction and
water oxidation.
Fig. 7 Transient photocurrent responses of the BiOCl(001) and BiOCl(010)
samples.
2 2
To clarify the facet-dependent photocatalytic H O produc-
tion efficiency of BiOCl nanosheets, an optical absorption
performance study and electrochemical analysis were con-
To further verify the reaction mechanisms of H O evolution ducted. Fig. 8a shows the UV-vis DRS of the as-prepared BiOCl
2
2
on the BiOCl(001) and BiOCl(010) samples, a series of active samples. It can be observed that BiOCl(001) and BiOCl(010)
species trapping experiments were conducted. The scavengers almost have the same light absorption, with similar absorbance
1/2
Fig. 8 Band structure between the BiOCl(001) and BiOCl(010) samples. (a) UV-vis absorption spectra and plots of (ahv) versus energy (hv) for the
BiOCl(001) and BiOCl(010) samples. (b) Mott–Schottky plot of the BiOCl(001) and BiOCl(010) samples. (c) Valence-band XPS spectra of the BiOCl(001)
and BiOCl(010) samples. (d) Schematic illustration of the band structure of the BiOCl(001) and BiOCl(010) samples.
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edges at about 370 nm. The transient photocurrent response of
the as-prepared BiOCl photocatalysts was tested to explore the
separation efficiency of photogenerated charge carriers. As
shown in Fig. 7, the photocurrent of the BiOCl(001) photo-
catalyst shows a higher current density than that of the
BiOCl(010) photocatalyst. The enhanced photocurrent of the
BiOCl(001) photocatalyst indicates the enhanced separation of
electrons and holes, then improving the photocatalytic perfor-
mance. These results demonstrate that the higher photo-
Conclusions
In summary, BiOCl nanosheets with preferentially exposed
001) and (010) facets were synthesized. The as-prepared BiOCl
(
nanosheets show facet-dependent photocatalytic properties for
hydrogen peroxide generation. The hydrogen peroxide evolu-
tion rate of BiOCl(001) is about two times higher than that
of BiOCl(010), which is assigned to the higher separation effi-
ciency of photogenerated charge carriers. Interestingly, the EPR
study, active species trapping experiments and corresponding
electronic structure analysis all demonstrate that the generation
catalytic
H
2
O
2
production efficiency of the as-prepared
BiOCl(001) sample benefits from the higher separation efficiency
of photogenerated charge carriers.
of H
sequential two step single-electron O
photocatalytic H production on BiOCl(010) is through two
O
2 2
on the BiOCl(001) photocatalyst mostly originates from
2
reduction, while the
To gain further insight on the facet-dependent photo-
2 2
O
catalytic H
ponding electronic structures of the as-prepared BiOCl samples
were investigated. The corresponding band gap energies (E
were estimated to be approximately 3.22 eV from DRS spectra
Fig. 8a). Valence-band XPS was used for measuring the valence
2 2
O production over BiOCl nanosheets, the corres-
pathways from both oxygen reduction and water oxidation. This
work offers a new strategy to pursue highly efficient semi-
conductor photocatalysts with two pathways for H O produc-
g
)
2
2
tion from both water oxidation and O reduction.
(
2
band position (VB) of the BiOCl(001) and BiOCl(010) nano-
sheets and Mott–Schottky plots were obtained to estimate the
flat-band potentials (Femi level). The flat-band potentials of the Conflicts of interest
BiOCl(001) and BiOCl(010) samples were measured at 0.09 V
and 0.4 V vs. NHE, respectively (Fig. 8b). As shown in Fig. 8c, the
There are no conflicts to declare.
valence band (VB) positions of BiOCl(001) and BiOCl(010) were
estimated as 1.94 V and 2.19 V vs. NHE, respectively. According
3
9
Acknowledgements
to the formula EVB = ECB + E
g
,
the ECB values of BiOCl(001) and
BiOCl(010) are calculated to be À1.28 and À1.03 V vs. NHE,
respectively. Combined with these results, the energy band
structures of the BiOCl(001) and BiOCl(010) samples are
described in Fig. 8d. As shown in Fig. 8d, since the reduction
This work is supported by the National Natural Science Foundation
of China (Grant 21805037), Fujian Province Nature Science Founda-
tion (Grants 2016Y0025, 2017J01685, 2019J01021009, 2020J02033)
and Fuzhou Science and Technology Project (2017-G-61, 2018-G-90).
ꢀ
À
potential of O
2
/O
2
is À0.33 V, the photogenerated electrons in
the CB of both BiOCl(001) and BiOCl(010) have sufficient
ꢀ
À
potential to reduce O
to H . Meanwhile, for the photogenerated holes, because the
VB potential of BiOCl(010) is more positive than the reduction
2
to O
2
, which can be further reduced
Notes and references
2 2
O
1 L. Pi, J. Cai, L. Xiong, J. Cui, H. Hua, D. Tang and X. Mao,
Chem. Eng. J., 2019, 123420.
2 G. Zuo, S. Liu, L. Wang, H. Song, P. Zong, W. Hou, B. Li,
Z. Guo, X. Meng, Y. Du, T. Wang and V. A. L. Roy,
Catal. Commun., 2019, 123, 69–72.
3 Y. Fu, C. a. Liu, M. Zhang, C. Zhu, H. Li, H. Wang, Y. Song,
H. Huang, Y. Liu and Z. Kang, Adv. Energy Mater., 2018,
8, 1802525.
À
ꢀ
potential of OH / OH, the photogenerated holes in the
À
ꢀ
BiOCl(010) photocatalysts could oxidize OH to OH, which
might further combine with each other to form H . There-
fore, the above results demonstrate that the generation of H
on the BiOCl(001) photocatalyst mostly originates from sequen-
tial two step single-electron O reduction, while the photocata-
lytic H production on BiOCl(010) is through two pathways
2 2
O
2 2
O
2
2 2
O
from both oxygen reduction and water oxidation. The involved
reactions are shown as follows:
4 B. O. Burek, D. W. Bahnemann and J. Z. Bloh, ACS Catal.,
2018, 9, 25–37.
5
S. Yang, A. Verdaguer-Casadevall, L. Arnarson, L. Silvioli,
+
À
BiOCl(001) + visible light - h + e
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
ˇ
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3342 | New J. Chem., 2021, 45, 3335À3342
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