Synergistic Polarization Engineering on Bulk and Surface for Boosting CO2 Photoreduction

Article abstract of DOI:10.1002/anie.202106310

Sluggish charge kinetics and low CO₂ affinity seriously inhibit CO₂ photoreduction. Herein, the synchronous promotion of charge separation and CO₂ affinity of Bi₄Ti₃O₁₂ is realized by coupling corona poling and surface I-grafting. Corona poling enhances ferroelectric polarization of Bi₄Ti₃O₁₂ by aligning the domains direction, which profoundly promotes charge transfer along opposite directions across bulk. Surface I-grafting forms a surface local electric field for further separating charge carriers and provides abundant active sites to enhance CO₂ adsorption. The two modifications cooperatively further increase the ferroelectric polarization of Bi₄Ti₃O₁₂, which maximize the separation efficiency of photogenerated charges, resulting in an enhanced CO production rate of 15.1 μmol g^?1 h^?1 (nearly 9 times) with no sacrificial agents or cocatalysts. This work discloses that ferroelectric polarization and surface ion grafting can promote CO₂ photoreduction in a synergistic way.

Full text of DOI:10.1002/anie.202106310

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Synergistic Polarization Engineering on Bulk and Surface for
Boosting CO2 Photoreduction
Authors: Lizhen Liu, Hongwei Huang, Zhensheng Chen, Hongjian Yu,
Keyang Wang, Jindi Huang, Han Yu, and Yihe Zhang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202106310
Link to VoR: https://doi.org/10.1002/anie.202106310

Angewandte Chemie International Edition
10.1002/anie.202106310
RESEARCH ARTICLE
Synergistic Polarization Engineering on Bulk and Surface for
Boosting CO Photoreduction
2
[
a]
[a]
[a]
[a]
[b]
[c]
Lizhen Liu, Hongwei Huang,* Zhensheng Chen, Hongjian Yu, Keyang Wang, Jindi Huang,
[d]
[a]
Han Yu,* Yihe Zhang
[
a]
L. Z. Liu, Prof. H. W. Huang, Z. S. Chen, H. J. Yu, Prof. Y. H. Zhang
Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials
Science and Technology
China University of Geosciences, Beijing 100083, P. R. China
E-mail: hhw@cugb.edu.cn
[b]
[c]
[d]
K. Y. Wang
The department of mechanics and engineering science, college of civil engineering and mechanics
Lanzhou University, Lanzhou, Gansu 730000, P. R. China
J. D. Huang
Engineering Technology Research Center of Henan Province for Solar Catalysis, College of Chemistry and Pharmaceutical Engineering
Nanyang Normal University, Nanyang 473061, P. R. China
Prof. H. Yu
Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry
Tsinghua University, Beijing 100084, P. R. China
E-mail: hanyu0220@mail.tsinghua.edu.cn
Supporting information for this article is given via a link at the end of the document.
Abstract: Sluggish charge kinetics and low CO
inhibit CO photoreduction. Herein, the synchronous promotion of
charge separation and CO affinity of Bi Ti 12 is realized by
coupling corona poling and surface I-grafting. Corona poling
enhances ferroelectric polarization of Bi Ti 12 by aligning the
2
affinity seriously
structure of semiconductors for facilitating carrier separation and
[
5]
2
2
CO activation is essential.
2
4
3
O
Noncentrosymmetric (NCS) materials provide natural
advantages for the separation and transportation of electron-
hole pairs because the spontaneous polarization in NCS
materials offers an internal electric field for propelling the
4
3
O
domains direction, which profoundly promotes charge transfer along
opposite directions across bulk. Surface I-grafting forms a surface
local electric field for further separating charge carriers, and provides
[
6]
migration of electrons and holes along opposite direction. Our
group reported that the spontaneous polarization enhancement
abundant active sites to enhance CO
modifications cooperatively further increase the ferroelectric
polarization of Bi Ti 12, which maximize the separation efficiency of
photogenerated charges, resulting in an enhanced CO production
2
adsorption. Notably, the two
in BiOIO
or directional stacking along [001] direction results in the
facilitated separation of charge carriers, enabling BiOIO single
crystals efficient photocatalytic activity. In addition, BiFeO as a
multiferroic material shows strong ferroelectricity. It has been
reported that well-polarized BiFeO nanoparticles by facile
electrical poling show promoted charge separation with
3 3
induced by enhanced distortion of polar IO polyhedra
4
3
O
3
[7]
3
-
1
-1
rate of 15.1 µmol·g ·h (nearly 9 times) with no sacrificial agents or
cocatalysts. This work discloses that ferroelectric polarization and
3
2
surface ion grafting can promote CO photoreduction in a synergistic
[
8]
way.
prolonged lifetime compared to unpolarized BiFeO
3
.
It is also
MoO
demonstrated by our group that the ferroelectricity of Bi
2
6
can be elevated by constructing ultrathin nanosheet structure
and corona poling treatment, which largely increases the
ferroelectric polarization electric field for improving the charge
Introduction
[
9]
2
directional migration and CO photoreduction. Furthermore,
The development of industrialization leads to increasing energy
defect engineering holds a strong ability in enriching the
[
1]
crisis with the emission of surplus greenhouse gas. Converting
CO to highly-valued chemical fuels is considered as one of the
best solutions to relieve above problems.
photocatalytic CO reduction reaction (CO RR) with solar light
[10]
insufficient reactive sites on the surface of photocatalysts.
2
Yang et al. reported highly efficient and selective CO
is achieved for oxygen-deficient Bi MoO with CH selectivity up
to 96.7%, profiting from oxygen vacancies on the {001} surface
that offer more active sites to favor CO adsorption in a special
bidentate carbonate mode for transform the intermediate *CO
2
reduction
[
2]
Recently,
2
6
4
2
2
as energy input to produce chemical fuels attracts considerable
attention. However, the conversion efficiency is far from
satisfactory due to sluggish carriers kinetics and high CO
2
2
[11]
into CH
4
.
Recently, anchoring of halogen ions is recognized
[
3]
activation barriers. The previous studies point that the photo-
excited electrons and holes form, transfer and catalytically
consume in a time scale of several femtoseconds, hundreds of
picoseconds and from several nanoseconds to several
microseconds, respectively. However, the recombination of
electrons and holes is always much faster with a time scale from
several picoseconds to dozens of nanoseconds. Besides, the
surviving charges arrived at the catalytic sites still face the
as a promising strategy for enriching the surface active sites,
which are reported to considerably enhance the photocatalytic
CO
TiO .
2
2
reduction performance of g-C
Inspired by the above pioneering studies, combination of
3
N
4
, Bi
2 2 3
O (OH)(NO ) and
[12]
[
4]
ferroelectric polarization and halogen ion grafting should be a
worth-exploring tactic for boosting the separation of electron-
hole pairs in bulk and on the surface.
Herein, we firstly employ corona poling to enhance the
challenges of large difficulty in activating CO
easy recombination. Thus, engineering the bulk and surface
2
molecules and
ferroelectric polarization of Bi
4 3
Ti O12 (BTO) nanoflowers and
then graft I ions on the surface of BTO. Corona poling increases
1
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
−
the ferroelectricity of BTO by keeping the domain direction
uniform, which profoundly promotes separation and transfer of
charge carriers along opposite directions across the bulk.
Surface I-grafting not only remains vast surviving electrons to
participate catalytic reaction but also provides abundant active
CO
2
RR. Figure 1h shows that the I 3d5/2 and I 3d3/2 of I at
619.1 and 630.5 eV in BTO-P-I2 are detected, respectively,
[
16]
confirming the grafted-I ions. For obtaining further information,
+
[12b, 17]
XPS depth profiling technique was applied by Ar etching.
The intensity of I 3d peak gradually reduces with increasing the
sputtering time of Ar from 0 s to 200 s, and nearly disappears
s (Figure 1h). It
corroborates that the I ions are grafted on the surface Ti atoms
of BTO instead of doping into crystal lattice. In Raman spectra,
+
sites to enhance the affinity with CO
modifications collectively enhance
performance of BTO nanoflowers, which delivers the highest CO
2
molecules. The two
the photoreduction
when the etching time reaches 200
−1
−1
production rate of 15.1 μmolg h (nearly 9 times higher than
–
1
that of BTO). Theoretical calculations have been conducted to
the modes with the Raman shift lower than 200 cm are related
-1
elucidate the potential distribution and adsorption of CO
molecules.
2
to the motion of heavier atoms and the modes at 250-300 cm
[
18]
manifest the vibrational bands in [TiO
6
] octahedrons.
It
–
1
demonstrates that the modes at 117 and 272 cm apparently
shift to higher frequency (120 and 276 cm ) with I grafting, and
the intensity of these modes with higher frequencies decreases
–
1
Results and Discussion
−
with I grafting (Figure 1i). The above XPS and Raman results
disclosed that I ions are successfully grafted on the surface of
BTO improving surface physicochemical properties.
BTO is synthesized by a hydrothermal method at 180 °C for 20 h.
A series of I-grafted BTO samples is prepared by treating BTO
in KI solution with different concentrations, which are denoted as
BTO-IX (X=1, 2, 4, 8) corresponding to the KI concentrations of
0.01, 0.02, 0.04 and 0.08 M, respectively. BTO is poled by a
corona poling process to obtain the polarized BTO (BTO-P), and
then BTO-P-I2 is prepared by treating BTO-P in KI solution (0.02
M, Scheme S1, Supporting Information). X-ray diffraction
(
XRD) was conducted to analyze the crystalline phase. The
characteristic diffraction peaks of all samples conform well to the
BTO (PDF#72-1019), indicating the formation of pure BTO and
that the crystal phase of all samples has no change (Figure 1a;
[13]
Figure S1, Supporting Information).
Scanning electron
microscopy (SEM) images (Figure S2, Supporting
Information) show that all samples are composed of self-
[
14]
assembly
nanoflowers
constructed
by
nanoplates.
Transmission electron microscopy (TEM) and filtered high angle
annular dark field scanning transmission electron microscopy
(
HAADF-STEM) confirm the well-crystallized microstructure of
the as-obtained BTO-P-I2. The lattice spacings of the top facet
of BTO-P-I2 are 0.270 and 0.272 nm (Figure 1c), which
correspond well to the (020) and (200) crystal planes of BTO,
4 3
Figure 1. (a) XRD patterns of samples. (b) Crystal structure of Bi Ti O12. (c)
[
13b]
TEM and filtered HAADF-STEM image (inset). XPS spectra of (d) survey, (e)
Bi 4f, (f) Ti 2s, (g) O 1s, (i) Raman spectra of BTO, BTO-P, BTO-I2 and BTO-
respectively, indicating the dominantly exposed {001} facet.
The SEM elemental mapping indicates the uniform distribution of
Bi, Ti, and in BTO-P-I2 (Figure S3, Supporting
Information).
+
P-I2. (h) I 3d XPS spectra of BTO-P-I2 with Ar sputtering for different times.
O
I
The optical properties are investigated by UV–vis diffuse
reflectance spectra (DRS). The absorption edges of all BTO
series samples are located at around 450 nm (Figure S4,
Supporting Information). Due to I modification, BTO-I2 and
BTO-P-I2 shows slightly stronger photoabsorption than BTO and
BTO-P in the visible range. The band gaps of BTO, BTO-P,
BTO-I2 and BTO-P-I2 are determined to be 2.75, 2.79, 2.67 and
2.60 eV by the Kubelka-Munk equation, respectively (Figure S5,
Supporting Information). Mott-Schottky plots show that the
conduction band (CB) positions of BTO, TO-P, BTO-I2 and
BTO-P-I2 are approximately -1.46, -1.41, -1.51 and -1.50 eV vs.
NHE, respectively (Figure S6, Supporting Information). Their
2
X-ray photoelectron spectroscopy (XPS) is used to study the
surface states and chemical composition of all BTO series
samples. The Bi, Ti and O elements are observed in all BTO
series samples, but the I element only exists in BTO-I2 and
BTO-P-I2 (Figure 1d). The peaks centering at 158.9 and 164.2
3
+
eV in the samples are attributed to the Bi 4f7/2 and Bi 4f5/2 of Bi ,
[
15]
respectively (Figure 1e). The binding energy of Ti 2s in BTO
and BTO-P is located at 564.0 eV (Figure 1f), while that in BTO-
I2 and BTO-P-I2 shift to 564.6 eV, which may suggest the
grafting of I onto Ti atoms. For O 1s, the peaks at 529.6 and
531.4 in BTO and BTO-P correspond to the lattice O and O-H
band structures are favorable for photocatalytic CO RR (Figure
[19]
bonds, respectively (Figure 1g). In contrast, the binding energy
S7, Supporting Information).
of O-H bonds displays an obvious shift, and more notably a new
2
peak at 533.3 eV attributable to surface adsorbed H O is
2
The photocatalytic CO RR performance is investigated
under simulated solar irradiation in a gas-solid system without
the presence of cocatalysts or sacrificial agents. Firstly, the
observed for BTO-I2 and BTO-P-I2, which may be resulted from
the strong H bonding interaction between I and H atoms. This
phenomenon indicates that the I-grafting can enhance the
2
photocatalytic CO RR activity of pure BTO and BTO-IX (X=1, 2,
2
adsorption of H O on the surface of BTO, which will promote the
2
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
4, 8) is investigated to obtain the optimal I concentration. All the
samples demonstrate CO photoreduction property for producing
2
CO. It can be seen that the CO yield increases first and then
decreases with the I concentration, and BTO-I2 shows the
−
1
−1
largest CO evolution rate of 10.8 μmolg h , which is over 6
−
1
−1
times that of BTO (1.7 μmolg h ). The corona poling
treatment is also found to enhance the photocatalytic activity of
BTO; the BTO-P exhibits
μmolg h . Thus, the BTO-I2 sample is selected for corona
a CO production rate of 5.2
−
1
−1
poling treatment, and as expected, the BTO-P-I2 demonstrates
−
1
−1
the highest CO production rate of 15.1 μmolg h among all
the samples, ⁓9 times higher than that of the BTO (1.7
−
1
−1
μmolg h ) (Figure 2a, b and d; Figure S8, Supporting
Information), which also outperforms most of reported bismuth-
based photocatalysts (Table S1, Supporting Information). The
control experiments are carried out to clarify the origin of CO
Figure 2. (a–b) Time-dependence and (d) apparent rate of CO yields by the
photoreduction of CO over BTO, BTO-IX (X=1, 2, 4, 8), BTO-P and BTO-P-I2
2
samples under simulated solar light irradiation. (c) The corresponding rates
over BTO-P-I2 under different conditions for 4 h (inset of c): mass spectra for
13
CO
2
reduction of BTO-P-I2 with using CO
2
as the reacting gas). (e) In situ
FTIR spectra for CO
2
photoreduction on BTO-P-I2 for different time.
(
2
Figure 2c). No CO is produced in photocatalytic CO process
without catalysts or illumination, and a negligible amount of CO
is generated under Ar attributing to the organics attached on the
catalysts. To further clarify the carbon source in the reaction, the
To explore the origin of significantly promoted photoreduction
activity by ferroelectric polarization and surface I-grafting, the
separation and transportation behaviors of photoinduced
charges are surveyed. Surface photovoltage (SPV) spectra
demonstrate the stronger SPV signal intensities for BTO-P and
BTO-I2 than BTO in the range of 320-400 nm, indicating that
both the corona poling and surface I-grafting are capable of
elevating the charge separation efficiency. It is also confirmed by
the largest enhancement of SPV signal for BTO-P-I2,
uncovering the most boosted separation of electron-hole pairs
(Figure 3a). Figure 3b shows that BTO-P, BTO-I2 and BTO-P-
I2 all exhibit more intense transient photocurrent response than
BTO, and the highest current density obtained for BTO-P-I2
increases to ~3.5 times that of BTO. Here, silver nitrate as a fast
electron scavenger is added into electrolyte (0.1 M Na SO ) to
1
3
C isotopic detecting test is carried out (Figure 2c). When
CO (m/z = 45) is purged into the reactor, CO (m/z = 29) as
2
1
3
13
the only detectable reductive product is obtained, confirming that
the evolved CO originates from the photocatalytic CO RR
2
process over the synthesized catalysts. The cycling tests and
XRD patterns after photocatalytic reaction reveal that steady CO
production initiated on BTO-P-I2 maintains for four successive
cycles and the photocatalysts show high stability (Figure S9
and S10, Supporting Information). These results confirm the
photocatalytic reaction pathway of CO
2
conversion into CO
catalyzed by BTO-P-I2 with excellent activity and durability,
illuminating that the photoreduction activities of BTO are
enhanced by corona poling and surface I ions grafting.
2
4
survey the surface charge transfer efficiency (ηtrans) (Figure S12,
[
21]
Supporting Information). The ηtrans of BTO is determined to
be 21.8%. In contrast, the ηtrans of BTO-P-I2 increases to 27.8%,
disclosing that BTO-P-I2 possesses higher surface charge
transfer efficiency than BTO. The linear sweep voltammetry
In situ Fourier-transform infrared (FTIR) tests are conducted
Figure 2e; Figure S11, Supporting Information) to survey the
(
CO reduction mechanism. The peaks between 2310 and 2370
2
−
1
cm resulted by the adsorption of CO
decreases, while the characteristic absorption around 2017 cm
attributed to the stretching vibration of CO gradually increases
with the irradiation time, demonstrating that CO is gradually
2
molecules gradually
(
LSV) curves with different applied bias voltage also confirm the
−
1
most accelerated charge separation and migration efficiency of
BTO-P-I2 (Figure S13, Supporting Information), aligning well
with the above results. The photoexcited carriers transfer
dynamics are studied by time-resolved fluorescence decay
spectroscopy. The average lifetime increases from 69.4 ns for
BTO to 108.0 ns for BTO-P-I2, demonstrating the substantially
contribution of corona poling and surface I-grafting in inhibiting
the recombination of charge (Figure 3c), which is also identified
by the steady photoluminescence (PL) result (Figure S14,
Supporting Information). These results indicate that the charge
separation and surface charge transfer efficiencies are
substantially increased by the ferroelectric polarization and
2
converted into CO (Figure S11, Supporting Information).
Based on the in situ FTIR result, it can be concluded that the
catalytic process of CO molecules on the surface of BTO-P-I2
2
follows adsorption first and then dissociation, and conversion
into various immediate species featured by the peaks in the
−
1
−
−1
2−
range of 1250-1700 cm , such as CO
2
(1700 cm ), b-CO
3
−
1
2−
(
1650, 1621, 1365 and 1337 cm ), m-CO
3
(1460, 1510, 1540
−
1
−
−1
and 1560 cm ), HCO
3
(1425 and 1474 cm ), and carbonate
−
1
(
1318 cm ), and eventual transformation into CO upon
[
20]
illumination (Figure 2e).
surface I-grafting cooperatively. Besides, the CO
capacity is investigated, and it is found that the CO
2
adsorption
adsorption
2
of BTO-P-I2 is much stronger than that of BTO (Figure 3d). As
the corona poling shows slight effect on the adsorption ability of
BTO for CO
2 2
molecules, the enhanced CO adsorption of BTO-
P-I2 should be attributed to the I-grafting, consistent with the
[
9, 12b]
previous report.
3
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
Here Δɸ is determined to be 0.039 V for BTO, 0.060 V for BTO-
P, 0.086 V for BTO-I2 and 0.166 V for BTO-P-I2 (Figure 4c). It
confirms that both corona poling and I-grafting are capable of
promoting the separation of photogenerated charge. The largest
surface potential difference and Δɸ value of BTO-P-I2 favor the
formation of the most robust electric field for the rapid separation
and transfer photogenerated charges. It is worth to note that the
Δɸ difference between BTO and BTO-P-I2 is larger than the sum
of that between BTO and BTO-P and that between BTO and
BTO-I2, which implies a cooperative effect between corona
poling and I-grafting on increasing the effective photogenerated
charges.
For obtaining more in-depth information on this synergy,
electric hysteresis loops of the above four photocatalysts are
measured, as the polarization electric field is mainly contributed
[
24]
by Pr after the corona poling. As illustrated in Figure 4d, the
2
Figure 3. (a) Surface photovoltage (SPV) spectra and (b) the transient
photocurrent response of BTO, BTO-P, BTO-I2 and BTO-P-I2. (c)
Pr is 0.08, 0.21, 0.08 and 0.42 μC/cm for BTO, BTO-P, BTO-I2
and BTO-P-I2, respectively. It uncovers that corona poling
enables BTO to keep a larger Pr, while I-grafting does not
change the Pr of BTO. It is understandable that the grafted I ions
on the surface of BTO is difficult to affect the bulk ferroelectric
polarization intensity. Even though, it is worth noting that the
largest Pr is produced over BTO-P-I2 by combining corona
poling and surface grafting, demonstrating that the both
modifications synergistically increase the ferroelectricity of BTO.
In combination of the above KPFM results, it is concluded that
the surface potential decrease of BTO-P is resulted from the
bulk ferroelectric polarization, and that of BTO-I2 is attributed
from the I-grafting that construct a surface local electric field.
Namely, polarization from the bulk and surface of BTO
cooperatively contributes to the increase of surface potential,
which maximize the separation of photogenerated electrons and
holes. Besides, finite element method (FEM) is employed to
simulate the domains direction change inside the BTO to
disclose the corona poling process (Figure 4e, f). Generally, the
domains of a ferroelectric orient disorderly in the absence of
electric field. Under an external electric field, the domains
rearrange to keep a uniform orientation. It can be seen that the
disordered orientation of domains leads to chaotic internal
electric field without external electric field. However, the domain
orientation becomes highly uniform when applying an external
Fluorescence emission decay spectra and (d) CO
BTO and BTO-P-I2.
2
adsorption isotherms of
Bi
4 3
Ti O12 is a ferroelectric with a NCS space group of Aba2,
and its spontaneous polarization arose from the distortion of
[
22]
[
TiO
6
] octahedra can form a polarization electric field.
Under
external voltage, polarization electric field will be enhanced to
provide a strong driving force for the transfer of positive and
negative charges on the two ends of Bi Ti O12 crystals. Even the
4 3
external electric field is removed, there still exists strong
remnant polarization (Pr). To get an insight into the ferroelectric
property, BTO is characterized by piezoresponse force
microscope (PFM) and scanning Kelvin probe force microscopy
(
KPFM). The topographic, phase map and the corresponding
phase curves of Bi Ti 12 are shown in Figure S15; Figure S16,
4
3
O
Supporting Information. It can be seen that there are obvious
phase angle changes when applying a backward ramp voltage
loop, which is accompanied by the typical butterfly shape in the
displacement–voltage curve (Figure S17, Supporting
Information). The above PFM results indicated that BTO
displays strong spontaneous polarization, which is in
accordance with its crystal structure features.
-1
electric field of 10 kVcm , which provides a strong driving force
for triggering the separation of photogenerated electrons and
holes.
For more deeply understanding migration behaviors of the
photogenerated charges, the surface potential of the four
catalysts is recorded by KPFM in the conditions of dark and
under illumination. In dark, BTO-I2 and BTO-P-I2 show larger
surface potential difference than BTO, which demonstrates that
surface I-grafting allows BTO a stronger surface electric field
(
Figure 4a, c). With illumination, all samples exhibit a reduction
in surface potential in comparison with those in dark (Figure 4b,
c), which can be explained as that the photogenerated charge
migrate to the opposite sites of the catalysts driven by the
potential difference, thus decreasing the surface potential
[23]
because of charge screening effect. The difference of surface
potential between in dark and under illumination is defined as
follows:
Δɸ =surface potential(dark)-surface potential(illumination)
(1)
4
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
tremendous enhancement on photocatalytic CO
2
RR
performance of BTO-P-I2 compared to that of BTO-IX, BTO-P
and BTO.
Figure 4. (a-b) KPFM potential images in the dark (ax) and under illumination
(bx) (x=1-4), (c) surface potential curve along line in the inset of part was
measured in the dark and under illumination and (d) electric hysteresis loop
-
1
(
under 30 kVcm ) for BTO, BTO-P, BTO-I2, and BTO-P-I2, respectively. FEM
simulation for the potential distribution of BTO with the external electric field of
-
1
-1
(
e) 0 Vcm and (f) 10 kVcm .
Figure 5. (a-c) Charge difference of BTO-I (a), and CO
2
absorbed BTO (b)
and BTO-I (c) (charge accumulation is in yellow and depletion in blue). (d-e)
4 3
Density of states (DOS) of Bi Ti O12 with I-grafting.
To further understand the role of surface I-grafting, density
functional theory (DFT) calculations are carried out on BTO and
I-grafted BTO. The charge difference of I-grafted BTO and I-
grafted BTO with adsorbed CO models are calculated to
2
Conclusion
analyze the charge transfer behavior (Figure S18, Supporting
Information). It can be clearly seen that the charge
accumulation and depletion around I atom are enhanced which
indicates more efficient charge transfer and active surface
4 3
In summary, a polarized Bi Ti O12 photocatalyst with I-grafting is
synthesized by a hydrothermal method followed by corona
poling and I ion solution treatment. In comparison with pristine
Bi
4
Ti
3
O
12
,
4 3
the optimal polarized Bi Ti O12 with I-grafting
reactive sites (Figure 5a). Then, the affinities of CO
and I-grafted BTO have been analyzed. More intense charge
transfer is observed between CO and surrounding I atom, which
is conducive to the CO adsorption and activation (Figure 5b, c).
2
on BTO
demonstrates a nearly 9 times enhancement on photocatalytic
−
1
−1
CO
dramatically improved CO
profited from the cooperation of corona poling and I-grafting,
which enhances the ferroelectric polarization of Bi Ti
largely promoted bulk charge separation, surface charge
transfer and adsorption of CO molecules. The work may offer a
2
reduction with a CO evolution rate of 15.1 μmolg h . The
2
2
photoreduction performance is
2
The above theoretical data are in accordance with the
photo(electro)chemical and KPFM results, confirming that the
ferroelectric polarization and I-grafting promote the charge
separation in bulk and on the surface of BTO, thereby
4
3
O12 for
2
new inspiration of collaborative strategy for the rational design of
highly efficient photocatalysts.
2
substantially elevating the photocatalytic CO RR performance.
Furthermore, the electronic band composition is analyzed by
calculating the densities of states (DOS) of I-grafted BTO. The
top of valance band (VB) is mainly composed of O 2p orbitals,
and the bottom of CB primarily originates from the Ti 4s orbital Acknowledgements
Figure 5d). For further understanding carriers transfer path, the
DOS of selected O atoms (O3 from [Bi ] layer and O7 [TiO
(
2
O
2
6
]
This work was jointly supported by the National Natural Science
Foundation of China (No. 51972288 and 51672258), the
Fundamental Research Funds for the Central Universities
octahedron) is calculated (Figure 5e). It can be seen that O3
atom principally contributes to the bottom of CB and the orbits of
O7 atom are located at the top of VB, which illustrates that the
photogenerated holes will migrate to the [Bi
photogenerated electrons are transferred to the [Bi
(
2652018287).
2
O
2
] layers, while the
3 10
Ti O ]
2
2
Keywords: corona poling • ion grafting • CO reduction •
octahedral layers. Based on the above analysis, the
photocatalytic reaction mechanism is proposed. After corona
ferroelectric photocatalysts • Bi Ti
4
3 12
O
poling, the Pr of Bi
internal electric field to drive holes and electrons migrated to the
Bi ] layers and [Bi Ti 10] layers, respectively. Then, I-
4 3
Ti O12 is increased, which can provide strong
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RESEARCH ARTICLE
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6
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Angewandte Chemie International Edition
10.1002/anie.202106310
RESEARCH ARTICLE
Entry for the Table of Contents
Synergistic polarization engineering on bulk and surface of Bi
4
Ti
3
O12 is realized by coupling corona poling and surface I-grafting,
which strengthen ferroelectric polarization for facilitating the separation and transfer of photogenerated charge carriers and enrich the
reactive sites, largely improving the photocatalytic activity for reducing CO in CO.
2
7
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