Promoted Photocharge Separation in 2D Lateral Epitaxial Heterostructure for Visible-Light-Driven CO2 Photoreduction

Article abstract of DOI:10.1002/adma.202004311

Photocarrier recombination remains a big barrier for the improvement of solar energy conversion efficiency. For 2D materials, construction of heterostructures represents an efficient strategy to promote photoexcited carrier separation via an internal electric field at the heterointerface. However, due to the difficulty in seeking two components with suitable crystal lattice mismatch, most of the current 2D heterostructures are vertical heterostructures and the exploration of 2D lateral heterostructures is scarce and limited. Here, lateral epitaxial heterostructures of BiOCl?@?Bi₂O₃ at the atomic level are fabricated via sonicating-assisted etching of Cl in BiOCl. This unique lateral heterostructure expedites photoexcited charge separation and transportation through the internal electric field induced by chemical bonding at the lateral interface. As a result, the lateral BiOCl?@?Bi₂O₃ heterostructure demonstrates superior CO₂ photoreduction properties with a CO yield rate of about 30?μmol g^?1 h^?1 under visible light illumination. The strategy to fabricate lateral epitaxial heterostructures in this work is expected to provide inspiration for preparing other 2D lateral heterostructures used in optoelectronic devices, energy conversion, and storage fields.

Full text of DOI:10.1002/adma.202004311

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Promoted Photocharge Separation in 2D Lateral
Epitaxial Heterostructure for Visible-Light-Driven CO2
Photoreduction
Li Wang,* Xue Zhao, Dongdong Lv, Chuangwei Liu, Weihong Lai, Chunyi Sun,*
Zhongmin Su, Xun Xu, Weichang Hao, Shi Xue Dou, and Yi Du*
solar-energy conversion process, not only
in solar cell but also in photocatalysis,
involves solar-light harvesting and photo-
excited charge carrier separation/transpor-
Photocarrier recombination remains a big barrier for the improvement
of solar energy conversion efficiency. For 2D materials, construction of
heterostructures represents an efficient strategy to promote photoexcited
carrier separation via an internal electric field at the heterointerface.
However, due to the difficulty in seeking two components with suitable
crystal lattice mismatch, most of the current 2D heterostructures are vertical
heterostructures and the exploration of 2D lateral heterostructures is scarce
and limited. Here, lateral epitaxial heterostructures of BiOCl@Bi O at the
[8,9]
tation.
Heterostructure, in which
materials with different properties are
integrated together, generally can harvest
wide solar light derived from multiple com-
ponents and possesses prominent photo-
excited charge separation/transportation
properties benefiting from internal elec-
2
3
atomic level are fabricated via sonicating-assisted etching of Cl in BiOCl. This
unique lateral heterostructure expedites photoexcited charge separation and
transportation through the internal electric field induced by chemical bonding
at the lateral interface. As a result, the lateral BiOCl@Bi O heterostructure
[10]
tric field formed at the heterointerface.
Hence, exploring suitable components to
construct heterostructure represents an
efficient and facile strategy to improve the
solar energy conversion efficiency.
2
3
demonstrates superior CO photoreduction properties with a CO yield
2
rate of about 30 µmol g−
1
−1
Nowadays, 2D materials have attracted
enormous research interest in optical elec-
tronic devices, catalysis, and solar-energy
conversion fields due to their high specific
h
under visible light illumination. The strategy
to fabricate lateral epitaxial heterostructures in this work is expected to
provide inspiration for preparing other 2D lateral heterostructures used in
optoelectronic devices, energy conversion, and storage fields.
[
11]
surface area,
large fraction of surface
[12]
exposed atoms, and excellent mechanical,
optical, and electronic properties.
[13,14]
Ben-
Solar energy is a green and renewable energy source.[1,2] It can
be converted into electricity via solar cell or be stored into chem-
efiting from layered structural properties, 2D materials are prone
to be constructed into heterostructures. Typically, 2D hetero-
structures include vertical heterostructures in which the layers of
ical forms via photocatalytic water splitting for H and photocat-
2
[3–7]
[15]
alytic CO reduction for CO, CH , etc.
As a result, employing
various 2D materials are stacked vertically, and lateral hetero-
2
4
solar energy is recognized as a promising strategy to meet
continuously increased worldwide energy demand. The typical
structures in which multiple 2D materials are seamlessly stitched
[16]
lateral.
Most of the current reported 2D heterostructures
Dr. L. Wang, Dr. W. Lai, Dr. X. Xu, Prof. S. X. Dou, Prof. Y. Du
Institute for Superconducting and Electronic Materials (ISEM)
Australian Institute for Innovative Materials (AIIM)
University of Wollongong
Wollongong, New South Wales 2500, Australia
E-mail: yi_du@uow.edu.au
Dr. L. Wang
Chair for Photonics and Optoelectronics
Nano-Institute Munich
X. Zhao, Prof. C. Sun, Prof. Z. Su
Department of Chemistry
Northeast Normal University
Changchun, Jilin 130024, P. R. China
E-mail: suncy009@nenu.edu.cn
Dr. D. Lv, Dr. X. Xu, Prof. W. Hao, Prof. Y. Du
BUAA-UOW Joint Research Centre and School of Physics
Beihang University
Beijing 100191, P. R. China
Ludwig-Maximilians-Universität München
Königinstr. 10, Munich 80539, Germany
E-mail: li.wang@lmu.de
Dr. C. Liu
Department of Energy Conversion and Storage
Technical University of Denmark
Lyngby 2800, Denmark
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adma.202004311.
©
2020 The Authors. Advanced Materials published by Wiley-VCH GmbH.
This is an open access article under the terms of the Creative Commons
Attribution License, which permits use, distribution and reproduction in
any medium, provided the original work is properly cited.
DOI: 10.1002/adma.202004311
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are vertical heterostructures, such as BiOI/Bi WO , Bi O Cl /
heterostructure, and thus facilitates their further application in
electronic devices, energy storage, and conversion fields.
As observed in our previous work, Ag nanoparticles are
prone to be loaded on the edge of BiOCl during the hydro-
thermal reaction under the perturbation of water with the
2
6
12 17
2
MoS . In vertical heterostructures, the internal electric field at
2
the heterointerface is originated from the van der Waals force
between interlayers.[
8,17–19]
As is known, the van der Waals force
is weaker than chemical bonding which exists at heterointer-
face in lateral heterostructures. Thus, the photoexcited charge
separation/transportation properties are proposed to be better in
lateral heterostructure. However, due to strict restrictions in lat-
tice mismatch and difficulties in selecting suitable components,
the construction of lateral heterostructures is strictly limited to
few species. Hence, exploring the possibilities of new 2D lateral
heterostructures is of great importance to promote the evolution
of materials and improve the solar-energy conversion efficiency.
Bismuth oxyhalides (BiOX, X = Cl, Br, I) represent a popular
species of 2D semiconductors due to their special sp hybridiza-
tion which results in photogenerated charge carriers with less
[
4]
content close to 10%. With the content of water continuously
increasing to be larger than 20%, the edge of BiOCl starts to
be etched into multiple layered thin nanosheets of Bi O by
2
3
the loaded Ag nanoparticles. Interestingly, the dimension of
the generated thin nanosheets increases with the content of
water increasing. The fabrication process and the proposed
formation mechanism of BiOCl@Bi O with lateral epitaxial
2
3
heterostructure are illustrated in Figure 1 and Figure S1, Sup-
porting Information. The SEM images of BiOCl-Ag-Bi O com-
2
3
posites with different content of water involved are displayed
in Figures S2–S7, Supporting Information. As demonstrated
in Figure S2, Supporting Information, Ag is loaded on the sur-
face of BiOCl when BiOCl is retreated with Ag nanoparticles
and pure ethanol via hydrothermal method, indicating that
[
4,19]
effective mass and superior mobility.
In the typical crystal
2
+
structure of BiOX, [Bi O ] layer is sandwiched between two
2
2
slabs of halogen ions by strong electrovalent bonds along the
highly active [001] direction, and the two neighboring slabs of
BiOCl–Bi O3 cannot be fabricated without the assistance of
2
[
20,21]
halogen ions are connected by van de Waals interactions.
Benefiting from this unique structure, Bi O , which is a typ-
water. To investigate the role of Ag in the fabrication process
of BiOCl–Bi O , BiOCl retreated with pure water via hydro-
2
3
2
3
ical visible-light sensitizer, has the inherent priority to be in
situ formed in BiOCl via removing halogen ions in the inter-
layer. In this work, BiOCl@Bi O with lateral epitaxial hetero-
thermal method is carried out. The SEM image in Figure S8,
Supporting Information, and the UV–vis diffuse reflectance
spectrum in Figure S9, Supporting Information, show that no
big difference appears on the morphology and composition of
BiOCl after retreated with pure water. It reveals that the only
water cannot induce the growth of BiOCl–Bi O . Transmission
2
3
structure is fabricated via etching the edged halogen ion of
BiOCl with the assistance of Ag and water molecule under
sonicating. It is proved that BiOCl@Bi O can not only take
2
3
2
3
the advantages of both BiOCl and Bi O in solar absorption
electron microscopy (TEM) image of the intermediate sample
prepared with Ag nanoparticles, ethanol, 20% water and BiOCl
via hydrothermal method is demonstrated in Figure S10, Sup-
porting Information, to further claim the role of Ag nanoparti-
cles. It can be observed that Ag nanoparticles, BiOCl, and Bi O
2
3
but also can delocalize the photoproduced charge carriers via
in-building driving force generated by lateral heterojunction.
As a result, the lateral heterogeneous BiOCl@Bi O possesses
2
3
great potential to be excellent photocatalyst, and its CO yield
2
3
rate for the CO photoreduction process under visible light irra-
diation is about 30 µmol g h . This facile method to prepare
lateral heterostructure paves way to fabricate other 2D lateral
exist simultaneously. Besides, Bi O nanosheets are formed at
2
2 3
−1
−1
the position where Ag nanoparticles are present. For the posi-
tion where there are no Ag nanoparticles, no Bi O nanosheets
2
3
Figure 1. Schematic illustration of the fabrication process of lateral heterogeneous BiOCl@Bi O .
2
3
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are present and BiOCl nanoplate keeps the original sharp edge.
It further confirms the role of Ag during the fabrication of
BiOCl@Bi O . Thus, it can be concluded that both water and
between edge part and middle part in the as-prepared particles.
By characterizing the atomic high-resolution TEM image on
the heterointerface, it can be observed in Figure 2c that there
is no big difference in the lattice fringe between the middle and
edge part of the as-prepared particle, revealing that the fabrica-
tion method in this work will not change the lattice assignment
at the heterointerface and thus perfect lateral epitaxial hetero-
structure can be generated. To further confirm the composition
of the middle and edge part of the as-prepared particle, the EDS
elemental mapping and EDS line profiles were carried out on
Bi, O, and Cl atoms, and the corresponding results are illus-
trated in Figure 2d–f. It is clear that Bi has a large distribution
both in the middle and the edge part, and O has a smaller dis-
tribution in the middle part and a large distribution in the edge
part. In contrast, Cl has a large distribution in the middle part
and a negligible distribution in the edge part. Combining with
XRD analysis, it can be concluded that the middle component
of the as-prepared particle is BiOCl and the edge component
is Bi O , suggesting that Cl in the edge part of BiOCl has been
2
3
Ag are indispensable components in fabricating 2D lateral het-
erogeneous BiOCl@Bi O . In this work, BiOCl@Bi O pre-
2
3
2
3
pared with 80% of water is selected to characterize its structure
and CO photoreduction performance.
2
X-ray diffraction (XRD) analysis was adopted to charac-
terize the composition of the as-prepared powders. As shown
in Figure 2a, the diffraction peaks in the XRD pattern can be
indexed to BiOCl and Bi O , indicating that the as-synthesized
2
3
materials mainly contain BiOCl and Bi O components. The
2
3
annular dark-field TEM in Figure 2b and low-resolution TEM
image of single particle in Figure S11, Supporting Information,
demonstrate that there is a clear brightness contrast between
the middle and edge part of the as-prepared particle. The top
view (Figure S12, Supporting Information) and cross-sectional
(Figure S13, Supporting Information) SEM images of the as-
prepared particles further confirm the existence of the interface
2
3
Figure 2. a) XRD pattern of the as-prepared BiOCl@Bi O . The standard patterns of BiOCl with JCPDS No. 82–0485 and Bi2O3 with JCPDS No.
2
3
4
5–1344 have also been displayed. b) The annular dark-field image of BiOCl@Bi O . c) The atomic high-resolution TEM image of BiOCl@Bi O for
2
3
2
3
the selected area marked with green box in (b). The boundary between BiOCl and Bi O are marked by red dashes. d–f) The EDS elemental mappings
2
3
and line profiles for Bi, O, and Cl, respectively.
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etched out with the assistance of water and noble metal particle
without distorting the lattice at the heterointerface. It reveals
that etching facilitates the growth of epitaxial heterostructure
via removing the elements between layers in the 2D layered
materials.
in the UV–vis diffuse reflectance spectrum of BiOCl@Bi O .
2
3
The one with the edge at about 370 nm is assigned to band-gap
absorption of BiOCl, and another one with the edge extended
to 613 nm belonged to Bi O . It is obvious that there is no
2
3
big difference on the band-gap absorption of BiOCl for pure
BiOCl and BiOCl@Bi O , indicating that the etching assisted
X-ray photoelectron spectroscopic (XPS) analysis was
employed to further study the chemical composition of the
as-prepared lateral heterostructure. As shown in Figure S14,
Supporting Information, there are three deconvolved peaks
in the high-resolution core-level XPS spectrum of O 1s for
BiOCl@Bi O , which is quite different from pure BiOCl which
2
3
growth of lateral heterostructure do not change much on the
original 2D materials. Potentiostatic electrochemical imped-
ance spectrum (PEIS) measurement is generally employed to
evaluate interface resistance and carrier mobility of semicon-
[
21]
ductors. As demonstrated in Figure 3b, the impedance radius
of BiOCl@Bi O is much smaller than that of BiOCl, revealing
2
3
only presents two deconvolved peaks in the XPS spectra.
The peak observed at 530.15 eV for BiOCl and 529.84 eV for
BiOCl@Bi O are assigned to the lattice oxygen.[22,23] Since
2
3
that the resistance for the charge transfer in BiOCl@Bi O
2
3
is lower than that in BiOCl. Thus, compared with BiOCl, the
photogenerated charge carriers in BiOCl@Bi O possess larger
2
3
Cl atom in the edge of BiOCl is etched out in BiOCl@Bi O ,
2
3
2
3
the concentration of the positive charges on Bi atom in
BiOCl@Bi O at the edge part is decreased. As a result, the
mobility, which facilitates the photocatalytic process.
Transient pump-proble absorption spectroscopy (TAS) is a
well-known technique in developing in-depth understanding
of photoexcited charge carrier dynamics and interfacial
2
3
electron screening effect for the related Bi-O bonding is
decreased,[
24,25]
which results in decreased bonding energy for
[
27–29]
lattice oxygen in BiOCl@Bi O . Similar phenomenon appears
charge transfer dynamics.
The TAS spectrum of BiOCl
2
3
in the bridging hydroxyls with XPS peak sited at 531.97 eV for
BiOCl and 530.61 eV for BiOCl@Bi O . Compared with BiOCl,
in Figure S15, Supporting Information, and TAS spectrum of
BiOCl@Bi O in Figure 3c show a featured bleaching peak at
2
3
2
3
XPS spectra of O 1s for BiOCl@Bi O presents another addi-
around 390 nm which is assigned to state-filling effect of the
2
3
[
30,31]
tional peak shoulder located at 533.52 eV which belongs to the
physisorbed water.[ This is attributed to the fact that the open
band edge of BiOCl.
Besides, a positive signal sited at
26]
about 380 nm is observed in BiOCl@Bi O and it is arising
2
3
metal sites caused by etching of interlayer Cl in BiOCl@Bi O3
from electroabsorptive effects of Bi O . The electron lifetime in
2 3
2
have strong interaction with the surrounding water.
BiOCl@Bi O probed by TAS kinetics (Figure 3d) is observed
2 3
Figure 3a shows the UV–vis diffuse reflectance spectra of
the as-prepared BiOCl and BiOCl@Bi O . It can be observed
to be a little longer than that in BiOCl. It reveals the existence
of charge-separation states in BiOCl@Bi O3 which is origi-
2
3
2
that BiOCl possesses a featured absorption band with the edge
at about 370 nm.[ In contrast, there are two absorption bands
nated from internal electric field induced by strong chemical
4]
[31]
bonding at the heterointerface.
To further confirm it, we
Figure 3. a) UV–vis diffuse reflectance spectra of BiOCl and BiOCl@Bi O . b) The PEIS spectra of BiOCl and BiOCl@Bi O . c) TAS spectra of
2
3
2
3
−
2
BiOCl@Bi O at indicated delay with the excitation pump of 350 nm and excitation power density of 6 µJ cm . d) TAS kinetics probed at around
2
3
3
90 nm for BiOCl and BiOCl@Bi O .
2 3
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Figure 4. a) Crystal structure of BiOCl viewed from the [001] direction with Bader charge analysis results marked. b) Crystal structure of BiOCl@Bi O
2
3
viewed from the [001] direction with Bader charge analysis results marked. c) Charge density distribution of BiOCl. d) Charge density distribution of
BiOCl@Bi O .
2
3
carried out DFT simulation on BiOCl and BiOCl@Bi O . As
signals with the intensities of 1:2:2:1 under simulated solar
2
3
shown in Figure 4a,b, the charge amount for the edge and
light, which is contributed to the appearance of DMPO-•OH
−
[23]
centre part in BiOCl@Bi O is about 1.69 eV, which is larger
adduct originated from the OH /H O oxidation by holes.
2
3
2
than that in BiOCl, indicating a stronger chemical bonding in
BiOCl@Bi O when Cl in the edge part is etched out. Similar
Compared with BiOCl, the ESR signals of BiOCl@Bi O is
2 3
stronger. As the square of signal intensity is approximately
2
3
[
35]
phenomenon can be observed in electron density distribution.
Figure 4c,d demonstrate that compared with BiOCl, the elec-
proportional to the number of free radicals,
more charge
carriers can be generated over BiOCl@Bi O3 under simu-
2
2+
tron density distribution of O in [Bi O ] slab of BiOCl@Bi O3
lated solar light illumination. Similar phenomenon can be
2
2
2
at the heterointerface is more prone to be directed to the edge
part. It suggests a stronger chemical bonding in BiOCl@Bi O ,
observed in Figure 5b, in which four ESR signals assigned to
−
DMPO-•O2 and related with the O reduction by electrons can
2
3
2
[
36]
this stronger chemical bonding induces the generation of
stronger internal electric field which contributes to better
photoexcited charge separation and charge transfer kinetics.
Benefiting from better charge separation and charge transfer
kinetics, BiOCl@Bi O is proposed to be able to generate more
be detected. Hence, it can be inferred that BiOCl@Bi O can
2 3
produce larger number of holes and electrons under simulated
solar light in the photocatalytic process. Figure 5c shows that
no ESR signals can be detected over pure BiOCl under vis-
ible light irradiation whereas four peaks of DMPO-•OH are
observed over BiOCl@Bi O in the same process. The inspec-
2
3
photoexcited charge carriers. Transient photocurrent response
is a direct way to check the amount of photoexctied charge car-
riers. With larger amount of photoexcited charge carriers, the
intensity of the photocurrent is higher. The results of transient
2
3
−
tion of DMPO-•O2 in Figure 5d demonstrates that both BiOCl
and BiOCl@Bi O cannot produce electrons under visible light
2
3
irradiation. Thus, it is obvious that the introduction of Bi O
2
3
photocurrent response over BiOCl@Bi O3 and BiOCl under
can facilitate BiOCl@Bi O to utilize the visible light to produce
2
2 3
simulated solar light are displayed in Figure S16, Supporting
Information. The current density of BiOCl@Bi O in each
holes. Since Ag nanoparticles are employed in assisting the
growth of BiOCl@Bi O , we compared the visible-light-driven
2
3
2
3
−2
light-on cycle is about −1.05 µA cm , which is 7 times that
oxygen active species of BiOCl@Bi O and BiOCl-Ag to further
2 3
of BiOCl. In contrast, for BiOCl@Bi O with vertical hetero-
check whether BiOCl@Bi O is influenced by the plasmonic
2 3
2
3
[32]
structure reported in reference, the current density is about
.70 µA cm which is less than 5 times that of pure BiOCl,
effect induced by residual Ag. The results are demonstrated in
Figure S17, Supporting Information. It is clear that the visible-
light-driven oxygen active species in BiOCl@Bi O and BiOCl-
−
2
0
indicating that lateral heterostructure is superior than ver-
tical heterostructure. Thus, it can be documented that strong
internal electric field at the lateral epitaxial heterojunction of
BiOCl@Bi O can help to facilitate more efficient photoexcited
2
3
Ag are completely different. The visible-light-driven oxygen
active species in BiOCl@Bi O are mainly •OH while those in
2
3
−
BiOCl-Ag are mainly •O , revealing that the plasmonic effect
2
3
2
charge separation and generate more photoinduced charge
carriers.
induced by few amounts of residual Ag has negligible influence
on BiOCl@Bi O , and the outstanding photocatalytic activity
2
3
The detection of molecular oxygen active species is another
effective way to check the species and amount of photoexcited
charge carriers. Generally, •OH is employed to evaluate posi-
tive charge carriers and •O2− is employed to evaluate negative
charge carriers. DMPO assisted ESR measurement can be
used to detect molecular oxygen active species.[33,34] As shown
in Figure 5a, both BiOCl and BiOCl@Bi O present four ESR
of BiOCl@Bi O is mainly originated from the construction of
lateral heterostructures.
2 3
CO photoreduction was carried out to further investigate
2
the role of the lateral heterojunction in the application of lat-
eral heterogeneous BiOCl@Bi O . As shown in Figure 6a, the
2
3
−1
−1
CO yield rate of BiOCl@Bi O is about 75 µmol g
h
under
2
3
simulated solar light while the CO yield rate of BiOCl is about
2
3
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Figure 5. a,b) ESR signals for DMPO-•OH (a) and DMPO-•O2− (b) over BiOCl and BiOCl@Bi O under simulated solar light irradiation for 4 min.
2
3
−
c,d) ESR signals for DMPO-•OH (c) and DMPO-•O2 (d) over BiOCl and BiOCl@Bi O under visible light (λ > 420 nm) irradiation for 4 min.
2
3
2 µmol g− h−1 under same conditions. With the irradiation of
1
outstanding charge separation and mobility properties. In addi-
tion, Bi O can utilize visible light. Due to these multiple advan-
5
visible light, nearly no CO is generated by BiOCl, indicating
2
3
that pure BiOCl cannot utilize visible light to reduce CO into
tages, the CO photoreduction properties of BiOCl@Bi O is
2
−
2
2
3
1
−1
fuel energy. In contrast, a CO yield rate of about 29 µmol g
h
enhanced in a large extent and the visible-light-driven CO yield
−
1
−1
can be observed over BiOCl@Bi O in the same process. The
rate is about 30 µmol g h . The method to fabricate lateral
heterostructure in this work can help to enrich the current
family of 2D heterogeneous materials, and thus will promote
the applications of these 2D materials in optical devices, energy
conversion, and storage fields.
2
3
rather larger CO yield over BiOCl@Bi O under visible light
2
3
benefits from the visible absorption of Bi O and the superior
2
3
charge separation driven by the intrinsic electric field induced
by the lateral heterojunction. The details of the CO photoreduc-
2
tion process is studied via inspecting the time-dependent CO
yield. Figure 6c shows that the yield of CO increases smoothly
with the increasing of irradiation time under visible light Experimental Section
illumination, and about 386 µmol g− can be generated over
1
Chemicals: Sodium chloride (NaCl, 99.5%), bismuth (III) nitrate
BiOCl@Bi O in 12 h. Figure 6d presents three cycling test of
2
3
pentahydrate (Bi(NO ) · 5H O, 99.999%), polyvinylpyrrolidone (PVP,
3
3
2
the CO photoreduction process under the irradiation of visible
2
Mw ≈ 40 000), silver nitrate (AgNO , 99.0%), and hydrazine hydrate
3
light. It can be observed that the CO yield rate in each test time
is stable and all the values are around 30 µmol g−1 h , indi-
cating that the photoreduction properties over BiOCl@Bi O
(NH NH · H O, 50–60%) were purchased from Sigma-Aldrich. Ethanol
2
2
2
−1
(C2H5OH, 100%) was purchased from Chem-Supply Pty. Ltd. All
chemicals were used as received without further purification.
2
3
1
3
Synthesis of BiOCl: First, 0.058 g NaCl were dissolved into 15 mL
distilled water containing 0.486 g Bi(NO ) · 5H O under vigorous
is stable. Isotope measurement with CO as the source was
2
3
3
2
carried out to check whether the yield of CO is originated from
stirring for 30 min. Second, the suspension was transferred to a 50 mL
Teflon-lined stainless-steel autoclave, and then heated at 170 °C for 16 h.
Finally, the products were washed with distilled water and ethanol, and
then dried at 80 °C for 24 h in air.
the photoreduction of CO instead of atmosphere or other
2
sources.[ Figure 6e demonstrates that the CO is the mainly
product in the photocatalytic process, revealing that the CO is
indeed generated by the photoreduction of CO2.
30]
13
Synthesis of Ag Nanosphere: 100 mg AgNO were added into
3
−
1
2
0 mL-glass vial containing 2 mL 10 mg mL PVP aqueous solution. After
In summary, the lateral heterogeneous BiOCl@Bi O3 2D
2
magnetic stirring for 5 min, 2 µL hydrazine hydrate solution was slowly
dropped into the above mixture. The reduction reaction was carried out
at room temperature for 2 min with continuous magnetic stirring. Then
the resulting products were collected via centrifugation and washed with
100% ethanol for several times. The final Ag nanoparticles with the size
material was prepared via etching with the assistance of noble-
metal nanoparticles and water under sonicating. Benefiting
from the strong intrinsic electric field induced by chemical
bonding at the lateral heterointerface, BiOCl@Bi O possesses
2
3
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Figure 6. a,b) CO yield rate of photoreduction of CO over BiOCl and BiOCl@Bi O under simulated solar light (a) and visible light (λ > 420 nm) (b).
2
2
3
c) Time-dependent photoreduction of CO2 over BiOCl@Bi O under visible-light irradiation. d) The cycling test of photoreduction of CO2 over
2
3
BiOCl@Bi O under the illumination of visible light. e) Isotope measurement for the CO photoreduction process over BiOCl@Bi O under visible
2
3
2
2
3
light irradiation.
selected by centrifugation at 3100 rpm for 2 min were redispersed into
A platinum foil, Ag/AgCl electrode and 0.5 ꢀ Na SO4 were selected
2
2
mL 100% ethanol.
Synthesis of BiOCl@Bi O : 10 mg BiOCl nanoplates were dispersed
as the counter electrode, reference electrode, and the electrolyte,
respectively. The working electrode was prepared by depositing the
as-synthesized powders on the glassy carbon electrode. 300 W Xe lamp
with the distance of 10 cm to the working electrode was employed as
the light source to test the photocurrent response. The PEIS was tested
in the frequency range of 100 mHz to 200 kHz, and the Mott–Schottky
measurements was carried out at the fixed frequency of 1 kHz.
A reaction cell, in which 3 mL distilled water was added and a quartz
fiber filter with 50 mg photocatalyst uniformly deposited was placed
and was adopted to characterize the photoreduction of CO2 under an
2
3
into 40 mL solvent containing 32 mL distilled water and 8 mL 100%
−
1
ethanol. Then 0.5 mL 5 mg mL Ag aqueous solution was dropped
into the above suspension under ultrasonication. After 5 min, the
mixture was transferred to a 50 mL Teflon-lined stainless-steel autoclave
and then heated at 100 °C for 1 h. The final product was collected and
washed with ethanol for several times, and then dried at 60 °C for 24 h.
Characterizations: The XRD pattern of the as-synthesized sample
was collected by GBC MMA X-ray powder diffractometer with Cu-Kα1
radiation (40 kV, 25 mA, λ = 0.15 418 nm). JEOL JSM-7500 was used to
obtain the scanning electron microscopy images, and the JEOL JEM-
atmospheric pressure of CO . The 300 W Xe lamp with 420 nm cut-off
2
filter was selected to simulate the visible light. A gas chromatography
equipped with a packed molecular sieve column (TDX-01 mesh) was
employed to detect the produced gas. The isotropic test was conducted
2
010 was used to acquire the typical TEM images. The high-resolution
TEM images and the EDS elemental mappings were conducted by
JEOL ARM-200F under the voltage of 200 kV. Shimadzu UV-3600 was
employed to characterize the UV–vis diffuse reflectance spectra. The
photoelectron spectroscopy station (Beamline 4W9B) with the resolution
of 0.05 eV was adopted to obtain the high-resolution X-ray photoelectron
spectroscopy spectrum. The detection of the active oxygen species was
carried out by the JES-FA200 ESR Spectrometer.
1
3
under same conditions with the above experiment except CO selected
2
as the carbon source. Gas chromatography–mass spectrometry was
used to carry out the detection of CO in the isotropic measurement.
Pump–probe TAS measurement was performed by adopting a
regenerative amplified Ti:sapphire laser system with the coherent
wavelength of 800 nm. The pump light was generated by employing
optical prametric amplifier to generate a laser pulse with the wavelength
VSP-300 electrochemical analyzer with standard three-electrode
set-up was used to conduct the photoelectrochemical characterization.
of 350 nm. The probe light was generated via employing a CaF window
2
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to attenuate the 800 nm output beam. The samples were dispersed into
water and then placed in 1 nm quarts cuvettes for measurement. The
absorption intensity of the samples in 1 nm quarts cuvettes should be
about 0.1 OD.
All theoretical simulations were carried by employing Vienna Ab
initio Simulation Package (VASP) with Perdew–Burke–Ernzehof as
the functional. The k-point mesh for the simulated samples is set as
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