Plasmonic Heterostructure TiO2-MCs/WO3?x-NWs with Continuous Photoelectron Injection Boosting Hot Electron for Methane Generation

Article abstract of DOI:10.1002/adfm.201808696

Nonmetallic plasmonic heterostructure TiO₂-mesocrystals/WO_3?x-nanowires (TiO₂-MCs/WO_3?x-NWs) are constructed by coupling mesoporous crystal TiO₂ and plasmonic WO_3?x through a solvothermal procedure. The continuous photoelectron injection from TiO₂ stabilizes the free carrier density and leads to strong surface plasmon resonance (SPR) of WO_3?x, resulting in strong light absorption in the visible and near-infrared region. Photocatalytic hydrogen generation of TiO₂-MCs/WO_3?x-NWs is attributed to plasmonic hot electrons excited on WO_3?x-NWs under visible light irradiation. However, utilization of injected photoelectrons on WO_3?x-NWs has low efficiency for hydrogen generation and a co-catalyst (Pt) is necessary. TiO₂-MCs/WO_3?x-NWs are used as co-catalyst free plasmonic photocatalysts for CO₂ reduction, which exhibit much higher activity (16.3 μmol g^?1 h^?1) and selectivity (83%) than TiO₂-MCs (3.5 μmol g^?1 h^?1, 42%) and WO_3?x-NWs (8.0 μmol g^?1 h^?1, 64%) for methane generation under UV–vis light irradiation. A photoluminescence study demonstrates the photoelectron injection from TiO₂ to WO_3?x, and the nonmetallic SPR of WO_3?x plays a great role in the highly selective methane generation during CO₂ photoreduction.

Full text of DOI:10.1002/adfm.201808696

FULL PAPER
Plasmonic Photocatalysis
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Plasmonic Heterostructure TiO -MCs/WO -NWs with
2
3−x
Continuous Photoelectron Injection Boosting Hot Electron
for Methane Generation
Zaizhu Lou,* Peng Zhang, Juan Li, Xianguang Yang, Baibiao Huang,* and Baojun Li*
utilization in plasmonic photocatalysis.
Nonmetallic plasmonic heterostructure TiO -mesocrystals/WO -nanowires
Recently, some low-cost nonmetallic mate-
rials (metal oxides/sulfides) exhibiting
SPR phenomenon attracted attentions as
2
3−x
(
TiO -MCs/WO -NWs) are constructed by coupling mesoporous crystal
2 3−x
TiO and plasmonic WO through a solvothermal procedure. The con-
2
3−x
potential substitutes of plasmonic noble
tinuous photoelectron injection from TiO stabilizes the free carrier density
[12,13]
2
metals.
The free carriers density on
and leads to strong surface plasmon resonance (SPR) of WO3 , resulting
−x
metal oxides/sulfides can be improved
through heavy-doping, similarly with SPR
of noble metals, the free carriers oscil-
late with incident light leading to strong
in strong light absorption in the visible and near-infrared region. Photo-
catalytic hydrogen generation of TiO -MCs/WO -NWs is attributed to
2
3−x
plasmonic hot electrons excited on WO3 -NWs under visible light irradia-
−x
[
14]
SPR.
However, most doped plasmonic
tion. However, utilization of injected photoelectrons on WO3 -NWs has low
−x
NPs exhibited SPR absorption in long
efficiency for hydrogen generation and a co-catalyst (Pt) is necessary.
wavelength region (>1500) resulting in
[
15]
TiO -MCs/WO -NWs are used as co-catalyst free plasmonic photocatalysts
low energy hot carriers for catalysis.
2
3−x
−
1
−1
for CO reduction, which exhibit much higher activity (16.3 µmol g h ) and
selectivity (83%) than TiO -MCs (3.5 µmol g h , 42%) and WO -NWs
8.0 µmol g h , 64%) for methane generation under UV–vis light irradia-
tion. A photoluminescence study demonstrates the photoelectron injection
from TiO to WO , and the nonmetallic SPR of WO plays a great role in
Among various nonmetallic plasmonic
NPs, self-doping semiconductors such as
2
−1
−1
2
3−x
[
16–18]
[19,20]
[21,22]
−
1
−1
WO3−x,
MoO3−x
and Cu2−xS
(
are much attractive for their facile syn-
thesis and strong SPR absorption in vis-
ible–near-infrared (NIR) region, which
have been applied to promote catalysis
and cancer therapy by plasmonic thermal
2
3−x
3−x
the highly selective methane generation during CO photoreduction.
2
[
23–27]
effect and sensitization.
Recently,
Cheng et al. reported nonmetallic plasmonic MoO3−x exhib-
iting plasmon-enhanced hydrogen generation from ammonia
1
. Introduction
[
28]
Plasmonic photocatalyst coupling noble metal nanoparticle
borane.
While, in strictly, hydrogen generation from
(
NPs) and semiconductors have been applied in various fields
ammonia decomposition do not give direct evidence to show
the energy transfer from solar light to chemicals. Then, Zhang
et al. reported photocatalytic hydrogen generation by plasmonic
hot electrons of heterostructural W O /g-C N under visible–
including water splitting,[
1–3]
6–11]
environmental treatment,
Surface plasmon resonance
SPR) is unique optical property which occurs on rare noble
[4,5]
and artificial photosynthesis.[
(
metals (Au, Ag, and Cu) under light irradiation; however, the
low-reserve and high-cost noble metals restrict their practical
18
49
3
4
[
29,30]
NIR light irradiation.
Therefore, nonmetallic plasmonic
NPs are promising SPR materials for photocatalysis.
Plasmonic hot electrons are very unique for catalysis. In
recently, Halas's group published work on Science to illustrate
the quantifying contributions of hot carriers and thermal effect
in plasmonic photocatalysis, and plasmon-induced hot car-
riers of Cu–Ru were demonstrated to act predominant effects
Prof. Z. Z. Lou, Dr. J. Li, Dr. X. G. Yang, Prof. B. J. Li
Institute of Nanophotonics
Jinan University
Guangzhou 511443, China
E-mail: zzlou@jnu.edu.cn; baojunli@jnu.edu.cn
on NH decomposition by reducing activation barrier of reac-
3
Dr. P. Zhang
[31]
tion. Similar to metals, plasmon-induced hot carriers from
Division of Environmental Science and Engineering
Pohang University of Science and Technology
Pohang 37673, Korea
nonmetallic WO3−x is expected to play great roles on promoting
catalytic reaction. For nonmetallic plasmonic NPs, the hot car-
riers generated on the surface can easily react with the absorbed
substances, while, their surface vacancies are unstable in
solvent. Aiming to stabilize the nonmetallic plasmonic photo-
catalysts, one strategy is to marry with semiconductors for con-
structing heterostructures, and photoelectrons injection from
semiconductor increases free carrier density and keeps SPR of
Prof. B. B. Huang
State Key Laboratory of Crystal Materials
Shandong University
Jinan 250100, China
E-mail: bbhuang@sdu.edu.cn
DOI: 10.1002/adfm.201808696
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nonmetallic NPs, which is preliminarily confirmed in our very
(PL) study to play a great role for stable SPR of WO3−x, and
recent work of CdS/WO
nanowires with stable plasmonic
plasmon-induced hot carrier leads to CH generation with effi-
ciency and high selectivity.
3−x
4
hydrogen generation.[ However, the construction of hetero-
structures with fast and continuous photoelectron injection
is still one great challenge. Band structures, carrier migration
ability, interface transfer, and electron storage capacity of semi-
conductors are all important for constructing stable nonmetallic
32]
2
. Results and Discussion
plasmonic materials. TiO is well known n-type semiconductor
Tungsten oxides (WO3−x) were synthesized by the simple one-
2
[33]
[16]
with high electron migration, and WO can store electrons
step solvothermal procedure,
and the morphologies are
3
as electrochromic materials.[
34,35]
Tungsten oxides with defects
are reported as photocatalysts for CO reduction, while, the
nanowires with the diameter of 5 nm and the length of 20 nm
aggregated to be bunches (Figure 1a and Figure S1, Supporting
Information). Crystal structure of as-prepared WO3−x-NWs
[36]
2
effect of their SPR on CO reduction is unclear and it is neces-
2
sary to be studied. The constructed TiO /WO heterostructure
is expected not only as one stable nonmetallic plasmonic photo-
catalysts with continuous photoelectrons injection, but also as
belongs to that of W O from X-ray diffraction (XRD) pattern
2
3−x
18 49
5+
(Figure S2, Supporting Information), and abundant W and
adsorbed oxygen species at the defect were detected by X-ray
photoelectron spectroscopy (XPS) (Figure S2, Supporting
Information), demonstrating the existence of oxygen vacancies
one potential strategy for efficient CO photoreduction.
2
In this work, nonmetallic plasmonic WO3−x nanowires
(
WO3−x-NWs) were loaded on the mesoporous crystal struc-
in the crystal structure. TiO -MCs (Figure 1b,c) were fabricated
2
[37]
ture TiO (TiO -MCs), by one-step solvothermal process, and
by following the reported methods,
showing microsize
2
2
the heterostructures (TiO -MCs/WO3−x-NWs) were obtained
plates and smooth surface. Selected area electron diffraction
(SAED) (Figure S3, Supporting Information) demonstrated
2
as plasmonic photocatalysts for hydrogen generation and CO2
reduction. Photocatalytic results show that the hot electrons gen-
eration on WO3−x-NWs have dominant role but low efficiency for
hydrogen generation under visible light irradiation. When TiO2-
MCs/WO3−x-NWs was used as co-catalyst free plasmonic photo-
catalyst for CO reduction, and their activity for CH generation
the single crystal structure of TiO -MCs. The heterostructures
2
(Figure 1d,e) coupled with TiO -MCs and WO3−x-NWs were syn-
2
thesized by in situ growth of WO3−x-NWs on TiO -MCs during
2
solvothermal process. Surface of TiO -MCs becomes rough after
2
WO3−x-NWs loaded, which is observed clearly on the edges of
microplates. From high resolution transmission electron micro-
scopy (HRTEM) image of Figure 1f, the lattice spacing of 0.380
and 0.189 nm correspond to (010) planes of W O and (200)
2
4
−
1
−1
(
16.3 µmol g h ) is fourfold and twofold higher than those of
−1
−1
−1 −1
TiO -MCs (3.5 µmol g h ) and WO3−x-NWs (8.0 µmol g h )
2
under solar light irradiation, respectively. Photoelectron injec-
18
49
tion of TiO -MCs was demonstrated by photoluminescence
planes of TiO , respectively, demonstrating the compositions
2
2
Figure 1. TEM images of WO3−x-NWs a), TiO -MCs b,c), WO -NWs/TiO -MCs-2 d,e), and HRTEM image of WO -NWs/TiO -MCs-2 f).
2
3−x
2
3−x
2
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test the photocatalytic performance of the
heterostructure TiO -MCs/WO3−x-NWs-2,
2
5
mg sample was mixed with 5 mL methanol
(10 vol%) aqueous solution in 15 mL reaction
chamber sealed with rubber stop. As shown
in Figure 3b, little hydrogen is detected for
TiO -MCs, attributing to its weak response to
2
visible light. Plasmon-induced hot electrons
−1
from WO3−x generated 27 µmol g hydrogen
in 30 min under visible light irradiation. In
the heterostructures, TiO -MCs act as photo-
2
electron injector to increase free carrier
density and stabilize SPR of WO3−x-NWs.
Before photocatalytic reaction, TiO -MCs/
2
WO3−x-NWs-2 firstly irradiated under UV
light for 30 min (preirradiation) to increase
the electron density of WO3−x. To keep same
experiment sets, 30 min preirradiation was
also done for TiO -MCs and WO
before
2
3−x
photocatalytic reaction. To our surprise, TiO -
2
MCs/WO3−x-NWs-2 generated 323 µmol g−
hydrogen in 30 min under visible light irra-
diation, which is 11-fold higher than that of
WO3−x-NWs. Effect of UV preirradiation on
plasmonic hydrogen generation was investi-
gated by varying irradiation time, as shown
in Figure S5 in the Supporting Information;
generated hydrogen (at 30 min) was meas-
ured to be 175, 267, and 323 µmol g− over
1
1
TiO -MCs/WO3−x-NWs-2 with 10, 20, and
Figure 2. STEM a) and HAADF STEM b) of TiO -MCs/WO3−x-NWs-2. Element mapping images
2
2
Ti: c), W: d), Ti-W overlap: e), and EDX spectra f) of TiO -MCs /WO3−x-NWs-2.
30 min preirradiation, respectively. It proves
that the photoelectrons injection from TiO2-
MCs plays a great role on hydrogen gen-
2
of heterostructures. XRD patterns and XPS spectrum further
confirmed the crystal structure and composition in the hetero-
structures (Figure S4, Supporting Information). Moreover, the
ratio between XPS bands of adsorbed oxygen species at the
eration of WO3−x-NWs. Four recycle reactions over TiO -MCs/
2
WO3−x-NWs-2 with 10 min preirradiation is repeated with 176,
−1
172, 171, and 180 µmol g hydrogen generation in 30 min
(Figure 3c), demonstrating their stable structure and activity
in photocatalysis. Under visible light irradiation, the hydrogen
generation rate is decreased as reaction time is prolonged
(Figure 3d), which is attributed to the decreased free carriers
density of WO3−x-NWs during photocatalysis.
[38]
defect (532.2 eV) and O–W (530.5 eV) in TiO /WO3−x is larger
2
than that in pure WO3−x, indicating the more oxygen vacancies
existence in the heterostructures. To analyze the structures of
TiO -MCs/WO3−x-NWs, measurements of scanning transmis-
2
sion electron microscope (STEM) and high-angle annular dark
field STEM (HAADF-STEM) (Figure 2a,b) were done to clearly
show that the growth of WO3−x nanowires is along the surface of
Photocatalytic activity of samples under UV–vis light irra-
diation were investigated as shown in Figure 4a. Compared
with TiO -MCs and TiO -MCs/WO3−x-NWs, WO3−x-NWs
2
2
TiO -MCs and some bunches exist due to the aggregation. The
show much weak efficiency for hydrogen generation. Within
2
existence and distribution of W and Ti elements are revealed by
element mapping images (Figure 2c–e) and energy dispersive
X-ray (EDX) spectra (Figure 2f). The molar ratio between WO3−x
30 min, 32 µmol hydrogen was generated over TiO -MCs,
2
which is threefold higher than 10 µmol hydrogen over TiO2-
MCs/WO3−x-NWs, indicating that the photoelectron injection
and TiO is calculated to be 1:10, and the sample is labeled as
decrease the activity of TiO -MCs for photocatalytic hydrogen
2
2
TiO -MCs/WO3−x-NWs-2.
generation. In order to investigate the photoelectron injection
2
With abundant existence of oxygen vacancies in WO3−x
nanowires, the free charges density is high enough to occur
process, TiO -MCs/WO3−x-NWs was kept in dark for over-
2
night to decrease the free charge density in WO3−x-NWs, and
hydrogen generation was monitored under UV–vis light irra-
diation. The hydrogen generation (Figure 4b) is slow from
0 to 20 min and then becomes fast from 20 to 30 min, finally
becomes stable after 30 min, proving the continuous photoelec-
in SPR, which has been demonstrated in theoretical mode-
ling calculations.[
39]
From diffuse reflection spectroscopy
(DRS) in Figure 3a, WO3−x nanowires have a strong absorp-
tion from 400 nm to NIR region. While, TiO -MCs have only
2
absorption in UV region. As-prepared TiO -MCs/WO3−x-NWs-2
tron injection from TiO -MCs to WO3−x-NWs. Consequently,
2
2
have a wide response region from UV–vis to NIR light, provi-
ding the possible to utilize of full-spectrum solar light. To
the photoelectrons injected from TiO to WO are used in low
efficiency for photocatalytic hydrogen generation.
2 3−x
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by varying the volumes of W(CO)6 solu-
tion during solvothermal procedure. Three
different samples labeled as TiO -MCs/
2
WO3−x-NWs-1, TiO -MCs/WO3−x-NWs-2,
2
and TiO -MCs/WO3−x-NWs-3 were obtained
2
as shown in scanning electron microscopy
(
SEM) images of Figure S7 in the Sup-
porting Information, and their molar ratio
between WO3−x and TiO was calculated by
2
EDX spectra as 0.5:10, 1:10, and 2:10, respec-
tively. Within 3 h, the product of methane
was measured to be 38, 49, and 34 µmol g−
for TiO -MCs/WO3−x-NWs-1, TiO -MCs/
1
2
2
WO3−x-NWs-2, and TiO -MCs/WO3−x-NWs-3,
2
respectively.(Figure 6a) And carbon monoxide
was detected to be 6.9, 7.3, and 6.3 µmol g−
for TiO -MCs/WO3−x-NWs-1, TiO -MCs/
1
2
2
WO3−x-NWs-2, and TiO -MCs/WO3−x-NWs-3,
2
respectively.(Figure 6b) On increasing of
WO3−x, more active sites and strong SPR
are positive for CO reduction. However, too
2
much loading will reduce the UV light absorp-
Figure 3. DRS a) of WO3−x-NWs, TiO -MCs, and TiO -MCs/WO3−x-NWs-2. Photocata-
2
2
tion of TiO resulting in decreased photoelec-
lytic hydrogen generation b) over TiO -MCs, WO -NWs, and TiO -MCs/WO3−x-NWs-2 as
2
2
3−x
2
trons injection. Consequently, TiO -MCs/
photocatalysts under visible light irradiation. Four times recycle reaction c) over TiO -MCs/
2
2
WO3−x-NWs-2 as photocatalysts with 10 min preirradiation. Photocatalytic hydrogen generation WO3−x-NWs-2 with strong SPR and photo-
d) of TiO -MCs/WO3−x-NWs-2 over reaction time. Co-catalyst: Pt (1 wt%). Light source: 200 W electron injection exhibited optimal activity
2
Xenon lamp (>420 nm).
−1
(
49 µmol g , CH ) for CO reduction,
4 2
which is fivefold high than that of TiO -MCs
(10 µmol g , CH ). For pure WO3−x-NWs, UV light irradiation
excited electron transfer from valence band to conduct band,
and the generated photoelectrons on conduct band increased
carrier density and SPR, leading to higher photocatalytic activity
(24 µmol g , CH ) of WO -NWs than TiO -MCs, but twofold
lower than TiO -MCs/WO3−x-NWs-2. Carbon monoxides and
methanol is intermediate product of CO reduction. TiO -MCs
2
−
1
The low hydrogen generation may, due to localized SPR of
WO3−x limiting the plasmon-induced hot carriers, transfer to
non-uniform loaded co-catalyst Pt NPs on surface. To prove that
injected photoelectrons have high efficiency for photocatalysis,
CO reduction over WO with co-catalyst free plasmonic photo-
4
−
1
2
3−x
4
3−x
2
catalysts was studied to evaluate the photocatalytic activity of
TiO -MCs/WO -NWs. 5 mg TiO -MCs/WO3−x-NWs-2 as photo-
2
2
3−x
2
2
2
catalysts was mixed with 0.2 mL water and plastered on cover
show highest activity than other samples in monoxide genera-
2
−1
glass (4.9 cm ), and then sealed in 100 mL reaction chamber for
tion (at 3 h, 13 µmol g , CO) and WO3 nanowires exhibited
−x
−
1
−1
−1
CO reduction. In 3 h, 49 µmol g methane and 7.3 µmol g
activity in methanol generation (at 3 h, 4.2 µmol g , methanol).
2
carbon monoxide were generated over TiO -MCs/WO3−x-NWs-2
Generation rate and selectivity of products were calculated as
shown in Figure 6c,d. For TiO -MCs, TiO -MCs/WO3−x-NWs-1,
2
as photocatalyst under UV–vis light irradiation, and to our sur-
prise, no methanol was detected.(Figure 5a) Small amount
of oxygen was detected during CO2 photoreduction. Under
2
2
TiO -MCs/WO -NWs-2, TiO -MCs/WO3−x-NWs-3, and
2
3−x
2
WO3−x-NWs, their methane generation rate is 3.5, 12.7, 16.3,
−
1
visible light irradiation, only 2.0 µmol g
methane and 1.1 µmol g− carbon monoxide
are generated, which are 24-fold and 6-fold
1
lower than those generated over TiO -MCs/
2
WO3−x-NWs-2 under UV–vis light irradia-
tion (Figure 5b). Under UV light irradiation,
−
1
−1
only 1.82 µmol g methanol, 1.44 µmol g
−1
carbon monoxides, and 1.25 µmol
g
methane are generated as shown in Figure
S6 in the Supporting Information. Without
SPR, tungsten oxides exhibited no activity on
[36]
photocatalytic CO reduction. Therefore, we
2
conclude that the plasmon-induced hot car-
riers play predominant role on CO reduction.
To support our conclusion, more experi-
ment sets were done. Different compositions
2
Figure 4. Hydrogen generation a) over WO3−x-NWs, TiO -MC, and TiO -MCs/WO3−x-NWs-2 as
2
2
photocatalysts under UV–vis light irradiation. Hydrogen generation of TiO -MCs/WO3−x-NWs-2
2
(
kept in dark for one day before irradiation) over reaction time under UV–vis light irradiation
of TiO -MCs/WO3−x-NWs were synthesized b). Co-catalyst: Pt (1 wt%). Light source: 200 W Xenon lamp.
2
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is decreased as shown in Figure 7b, and
the quenching efficiency (Figure S8, Sup-
porting Information) of PL1 and PL2
was calculated to be 22.5% and 30.6% for
TiO -MCs/WO3−x-NWs-1. No PL bands are
2
observed from WO3−x-NWs (Figure S9, Sup-
porting Information) because their photo-
electrons are trapped on the defects caused
by the abundant oxygen vacancies. As the
amount of WO3−x increases, the quenching
efficiency of PL1 and PL2 becomes 37.9%
and 39.2% for TiO -MCs/WO3−x-NWs-2,
2
Figure 5. Products of CO2 photoreduction over TiO -MCs/WO3−x-NWs-2 as photocatalyst
under UV–vis a) and visible b) light irradiation.
2
while, 40.7% and 42.5% for TiO -MCs/
2
WO3−x-NWs-2, respectively. PL quenching
of TiO -MCs demonstrates the charge
2
1
1.5, and 8.0 µmol g−1 h−1, respectively, and their selectivity is
transfer between TiO -MCs and WO3−x-NWs. Generation and
2
calculated to be 42%, 80%, 83%, 81.7%, and 64%, respectively;
While, their carbon monoxides generation rate is 3.7, 2.2, 2.4,
transfer of photoelectrons in heterostructure was illustrated
in the diagram (Figure 7c). Under UV light irradiation, elec-
.1, and 3.0 µmol g− h , respectively, and their selectivity is
1
−1
tron on valence band (VB) of TiO is excited and transfers to
2
4
2
4%, 14.4%, 12.4%, 14.9%, and 23.7%, respectively. Further-
the conduct band (CB). The photoelectron on CB (ECB) has a
more, some C2 compounds (ethane and ethene) were detected
direct irradiative decay to recombine with hole on VB (EVB
emitting one high energy photon as the PL1 band (around
450 nm). With the surface defect, photoelectron on CB (ECB
transfers (CT ) to surface defect energy level (E ), and then
recombines with hole on VB (EVB) to emit one low energy
photon as PL2 band (around 520 nm). For WO3−x-NWs,
abundant oxygen vacancies make free carriers on CB which
occur in oscillation with incident light to exhibit SPR pheno-
menon. The free electrons occupy low energy level of CB,
and electrons on VB are excited by short-wavelength light
)
−
1
−1
(
0.91 µmol g h ) over TiO -MCs/WO3−x-NWs-2 as photo-
2
catalysts. Only TiO -MCs and WO -NWs show generation of
methanol with rate of 0.74 and 1.3 µmol g h , and their selec-
tivity is 8.7% and 10%. Consequently, TiO -MCs/WO3−x-NWs-2
)
2
3−x
−1
−1
1
S
2
has optimal compositions to exhibit high activity and selectivity
in methane generation during CO photoreduction.
2
The photoelectron transfer between TiO2 and WO3−x
was investigated by the photoluminescence spectra which
were measured by microspectrophotometer. With excita-
tion of 365 nm light, two PL bands labeled as PL1 and PL2
and transfer to the lowest vacant energy level (E ) of CB,
V
are observed for pure TiO -MCs sample (Figure 7a). When
combined with WO3−x, the intensity of both PL1 and PL2
which limits UV light utilization. Under visible light irradia-
tion, the free electrons on CB of WO3−x are excited to be hot
electron on high energy level which has
more power to react with carbon dioxides.
When the hot electrons are removed, free
electron density is decreased resulting in
weak SPR, and which leads WO3−x to being
weak SPR and low activity in plasmonic
photocatalysis. In the obtained heterostruc-
tures, under UV–vis light irradiation, the
2
excited photoelectrons on TiO have charge
2
transfer (CT and CT ) to WO which has
2
3
3−x
been demonstrated by PL quenching study
Figure 7a,b). The continuous injection
(
of photoelectrons stabilizes the free car-
riers density on CB of WO3−x, meanwhile,
the photoelectrons rapidly fill in the vacant
energy level of CB after hot electrons are
generated, leading to longer life time of
the hot electrons to reduce carbon dioxides
for methane and carbon monoxide genera-
tion under UV–vis light irradiation. Con-
sequently, the synergetic effects of photo-
electron injection of TiO -MCs and non-
2
metallic SPR of WO3−x-NWs make hetero-
structure TiO -MCs/WO3−x-NWs with high
lysts: TiO -MCs, TiO -MCs/WO -NWs-1, TiO -MCs/WO -NWs-2, TiO -MCs/WO3−x-NWs-3, activity and selectivity on carbon dioxides
Figure 6. CH a), CO b), and their generation rate c), and selectivity d) over different photocata-
2
4
2
2
3−x
2
3−x
2
and WO3−x-NWs under UV–vis light irradiation. Light source: 200W Xenon lamp.
photoreduction.
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chemicals were used as purchased without any
further purification.
Synthesis of TiO -MCs: MCs were prepared
2
following the reported method. A mixed aqueous
solution of TiF , NH NO , NH F, and ultrapure
4
4
3
4
H O, with the molar ratio of 1:6.6:4:117 was
2
dropped on a silicon wafer dropwise to form a thin
layer. The precursor layer was annealed in air at
−
1
5
00 °C for 2 h with a ramping rate of 10 °C min .
The product was obtained after annealing at 500 °C
in oxygen atmosphere for another 8 h to remove
surface impurities.
Synthesis of TiO -MCs/WO -NWs: TiO -MCs/
2
3−x
2
WO3−x-NWs were synthesized by following the
previous work.[ In a typical procedure, 10 mg
16]
TiO -MCs were mixed with 30 mL ethanol, and then
2
−
1
2
mL W(CO) solution (2 g L ) was added. Then,
6
the solution was transferred to a 50 mL Teflon-
lined stainless steel autoclave, and heated up to
1
60 °C for 12 h. The produced sample TiO -MCs/
2
WO3−x-NWs-1 was separated from the solution by
centrifugation, washed with ethanol three times,
and dried in a vacuum oven. The TiO -MCs/
2
WO3−x-NWs-2 and TiO -MCs/WO3−x-NWs-3 were
2
synthesized following the above same experiment
set, with just the change of W(CO)6 solution
volumes with 4 and 6 mL, respectively, and the total
solution volume kept as same.
Figure 7. PL spectra a) and intensity b) of different samples: TiO -MCs, TiO -MCs/
Photocatalytic Hydrogen Generation:
5
5
mg
mL
2
2
WO3−x-NWs-1, TiO -MCs/WO -NWs-2, and TiO -MCs/WO3−x-NWs-3. Excitation wavelength:
TiO -MCs/WO3−x-NWs were dispersed in
2
3−x
2
2
3
65 nm. Mechanism diagram c) of photoelectron generation and transfer in TiO -MCs/ aqueous solution containing 10 vol% methanol using
2
WO3−x-NWs. EVB: valence band; ECB: conduct band; E : surface defect energy level; E : lowest
an ultrasonic bath, and then the mixture solution
was sealed in 15 mL reaction chamber. Subsequently,
TiO ; CT : charge transfer of photoelectron from E (TiO ) to E (WO ); CT : charge transfer the chamber was degassed with Argon for 30 min
S
V
vacant energy level on conduct band; CT : charge transfer of photoelectron from E to E on
1
CB
S
2
2
CB
2
V
3−x
3
of photoelectron from E (TiO ) to E (WO3−x).
to completely remove the dissolved oxygen and it
was ensured that the reactor was in an anaerobic
condition. Then, the tube was irradiated under visible
S
2
V
light (Asahi Spectra, LAX-C100) with magnetic stirring at room temperature.
A 420 nm, cut-off filter was used to remove UV light. Hydrogen evolution
was measured by using Shimadzu GC-2014A gas chromatograph with
thermal conductivity detector (TCD).
3
. Conclusion
In summary, to stabilize SPR of nonmetallic plasmonic WO3−x
heterostructure TiO -MCs/WO3−x-NWs were constructed by
coupling mesoporous crystal TiO -MCs and nonmetallic plas-
monic WO3−x nanowires through one-step solvothermal proce-
,
2
Photocatalytic Carbon Dioxides Reduction: 5 mg TiO -MCs/WO3−x-NWs
2
2
was mixed with 0.2 mL pure water and plastered on cover glass
2
(4.9 cm ), which promises the same irradiation area. The cover glass coated
dure. Continuous photoelectron injection from TiO to WO3−x
samples were putt on bottom of reaction chamber (100 mL), and the side
with samples coating was upside. The chamber was sealed with thick
quartz cover glass and degassed with pure carbon dioxide gas for 20 min.
The reaction was started under irradiation of UV–vis light (Perfectlight,
PLS-SXE300D). The generation of methane, carbon monoxide, and
methanol was measured by gas chromatography (Shimadzu, GC-2014A)
with one TCD and two flame ionization detector (FID). Other reaction
followed the same procedure under different light irradiation.
2
increases the free carrier density of WO3−x, leading to stable
SPR absorption and hot electron generation for plasmonic
photocatalysis, which was demonstrated by the PL study. Photo-
catalytic results illustrate the dominant role of hot electrons of
WO3−x for hydrogen generation under visible light irradiation.
Furthermore, TiO -MCs/WO3−x-NWs with absence of noble
2
Characterizations: The samples were characterized using XRD (Rigaku
Rint-2500, CuK source), SEM (JEOL JSM-6330FT), TEM (JEOL, 2100,
operated at 100 KV), and high-resolution TEM (JEM-3000F, operated
at 300 KV). UV–vis diffuse reflectance spectra were obtained on a JASO
V-570 UV–vis/NIR spectrophotometer. XPS was performed with a JEOL
JPS-9010 MC spectrometer. The adventitious carbon (C 1s located at
284.6 eV) was used as reference to binding energy. PL measurement
was carried by using UV–vis microspectrophotometer (CRAIC
TECHNOLOGIES, 20/30 PV) with 365 nm as excitation light.
metals as co-catalysts and SPR antenna are demonstrated to
be highly active plasmonic photocatalysts for carbon dioxide
reduction. The synergetic effects of photoelectron injection and
nonmetallic SPR induced plasmonic hot electrons contributes
to highly selective methane generation under UV–vis light
irradiation.
4
. Experimental Section
Materials: Titanium fluoride (TiF , >98.0%, Wako), ammonium nitrate
4 3 4
4
Supporting Information
(
NH NO , >98%, Sigma-Aldrich), ammonium fluoride (NH F, >98.0%,
Wako), tungsten hexacarbonyl (W(CO) , >97%, Sigma-Aldrich), ethanol
Supporting Information is available from the Wiley Online Library or
from the author.
6
(
>99.5%), methanol (>99.5%), and carbon dioxides (>99.999%). All
Adv. Funct. Mater. 2019, 1808696
1808696 (6 of 7)
© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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www.afm-journal.de
[
[
[
15] M. Kanehara, H. Koike, T. Yoshinaga, T. Teranishi, J. Am. Chem. Soc.
Acknowledgements
2
009, 131, 17736.
16] Z. Z. Lou, Q. Gu, L. Xu, Y. S. Liao, C. Xue, Chem. - Asian J. 2015,
0, 1291.
17] Z. Z. Lou, Q. Gu, Y. S. Liao, S. J. Yu, C. Xue, Appl. Catal., B 2016,
84, 258.
This work was supported by the National Natural Science Foundation of
China (No. 51872125, 21703083, and 11804120), Guangdong Natural
Science Funds for Distinguished Young Scholar (No. 2018B030306004), the
Natural Science Foundation of Guangdong Province (2017A030310463)
and the Project supported by GDUPS(2018).
1
1
[
[
18] S. Ishii, S. L. Shinde, T. Nagao, Adv. Opt. Mater. 2018, 7, 1800603.
19] Y. Kuwahara, Y. Yoshimura, K. Haematsu, H. Yamashita, J. Am.
Chem. Soc. 2018, 140, 9203.
[
[
[
[
20] H. F. Cheng, M. C. Wen, X. C. Ma, Y. Kuwahara, K. Mori, Y. Dai,
B. B. Huang, H. Yamashita, J. Am. Chem. Soc. 2016, 138, 9316.
21] X. L. Wang, Y. J. Ke, H. Y. Pan, K. Ma, Q. Q. Xiao, D. Q. Yin, G. Wu,
M. T. Swihart, ACS Catal. 2015, 5, 2534.
Conflict of Interest
The authors declare no conflict of interest.
22] R. Alam, M. Labine, C. J. Karwacki, P. V. Kamat, ACS Nano 2016, 10,
2
880.
Keywords
23] Z. F. Huang, J. J. Song, L. Pan, X. W. Zhang, L. Wang, J. J. Zou, Adv.
Mater. 2015, 27, 5309.
artificial photosynthesis, carbon dioxide reduction, nonmetallic SPR,
photocatalysis, plasmonic hot electron
[24] H. Zhu, Y. Wang, C. Chen, M. R. Ma, J. F. Zeng, S. Z. Li, Y. S. Xia,
M. Y. Gao, ACS Nano 2017, 11, 8273.
Received: December 6, 2018
Revised: December 31, 2018
Published online:
[25] L. Wen, L. Chen, S. M. Zheng, J. F. Zeng, G. X. Duan, Y. Wang,
G. L. Wang, Z. F. Chai, Z. Li, M. Y. Gao, Adv. Mater. 2016, 28,
5072.
[
26] M. Yan, G. L. Li, C. S. Guo, W. Guo, D. D. Ding, S. H. Zhang,
S. Q. Liu, Nanoscale 2016, 8, 17828.
[
27] K. P. Yuan, Q. Cao, H. L. Lu, M. Zhong, X. Z. Zheng, H. Y. Chen,
T. Wang, J. J. Delaunay, W. Luo, L. W. Zhang, Y. Y. Wang, Y. H. Deng,
S. J. Ding, D. W. Zhang, J. Mater. Chem. A 2017, 5, 14697.
[
[
[
[
1] S. Y. Wang, Y. Y. Gao, S. Miao, T. F. Liu, L. C. Mu, R. G. Li, F. T. Fan,
C. Li, J. Am. Chem. Soc. 2017, 139, 11771.
2] Z. Z. Lou, S. Kim, M. Fujitsuka, X. G. Yang, B. J. Li, T. Majima, Adv.
Funct. Mater. 2018, 28, 1706969.
[28] H. F. Cheng, T. Kamegawa, K. Mori, H. Yamashita, Angew. Chem.,
Int. Ed. 2014, 53, 2910.
[29] Z. Y. Zhang, X. Y. Jiang, B. K. Liu, L. J. Guo, N. Lu, L. Wang,
J. D. Huang, K. C. Liu, B. Dong, Adv. Mater. 2018, 30, 170522.
[30] Z. Y. Zhang, Y. Liu, Y. R. Fang, B. S. Cao, J. D. Huang, K. C. Liu,
B. Dong, Adv. Sci. 2018, 5, 1800748.
3] J. W. Hong, D. H. Wi, S. U. Lee, S. W. Han, J. Am. Chem. Soc. 2016,
138, 15766.
4] P. Wang, B. B. Huang, X. Y. Qin, X. Y. Zhang, Y. Dai, J. Y. Wei,
M. H. Whangbo, Angew. Chem., Int. Ed. 2008, 47, 7931.
[
[
5] N. N. Jiang, X. L. Zhuo, J. F. Wang, Chem. Rev. 2018, 118, 3054.
6] A. Manzi, T. Simon, C. Sonnleitner, M. Döblinger, R. Wyrwich,
O. Stern, J. K. Stolarczyk, J. Feldmann, J. Am. Chem. Soc. 2015, 137,
[31] L. N. Zhou, D. F. Swearer, C. Zhang, H. Robatjazi, H. Q. Zhao,
L. Henderson, L. L. Dong, P. Christopher, E. A. Carter,
P. Nordlander, N. J. Halas, Science 2018, 362, 69.
1
4007.
7] G. Kumari, X. Q. Zhang, D. Devasia, J. Heo, P. K. Jain, ACS Nano
018, 12, 8330.
[32] Z. Z. Lou, M. S. Zhu, X. G. Yang, Y. Zhang, M. H. Whangbo, B. J. Li,
B. B. Huang, Appl. Catal., B 2018, 226, 10.
[33] M. L. Sushko, K. M. Rosso, J. Liu, J. Phys. Chem. C 2010, 114,
20277.
[34] N. E. Mendieta-Reyes, A. K. Diaz-Garcia, R. Gomez, ACS Catal.
2018, 8, 1903.
[
2
[
8] S. J. Yu, A. J. Wilson, J. Heo, P. K. Jain, Nano Lett. 2018, 18, 2189.
9] C. Clavero, Nat. Photonics 2014, 8, 95.
10] T. Ding, J. Mertens, A. Lombardi, O. A. Scherman, J. J. Baumberg,
[
[
[
[
ACS Photonics 2017, 4, 1453.
11] Y. X. Wang, S. S. Wang, S. P. Zhang, O. A. Scherman, J. J. Baumberg,
T. Ding, H. X. Xu, Nano Res. 2018, 11, 6384.
12] G. Garcia, R. Buonsanti, E. L. Runnerstrom, R. J. Mendelsberg,
A. Llordes, A. Anders, T. J. Richardson, D. J. Milliron, Nano Lett.
[35] H. X. Gu, C. S. Guo, S. H. Zhang, L. H. Bi, T. C. Li, T. D. Sun,
S. Q. Liu, ACS Nano 2018, 12, 559.
[36] G. C. Xi, S. X. Ouyang, P. Li, J. H. Ye, Q. Ma, N. Su, H. Bai, C. Wang,
Angew. Chem. 2012, 124, 2445.
[37] O. Elbanna, M. Fujitsuka, T. Majima, ACS Appl. Mater. Interfaces
2017, 9, 34844.
2
011, 11, 4415.
[
13] R. Buonsanti, A. Llordes, S. Aloni, B. A. Helms, D. J. Milliron, Nano
Lett. 2011, 11, 4706.
14] J. M. Luther, P. K. Jain, T. Ewers, A. P. Alivisatos, Nat. Mater. 2011,
[38] N. Zhang, A. Jalil, D. X. Wu, S. M. Chen, Y. F. Liu, C. Gao, W. Ye,
Z. M. Qi, H. X. Ju, C. M. Wang, X. J. Wu, L. Song, J. F. Zhu,
Y. J. Xiong, J. Am. Chem. Soc. 2018, 140, 9434.
[
10, 361.
[39] K. Manthiram, A. P. Alivisatos, J. Am. Chem. Soc. 2012, 134, 3995.
Adv. Funct. Mater. 2019, 1808696
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