Spontaneous polarization effect and photocatalytic activity of layered compound of bioio3

Article abstract of DOI:10.1021/acs.inorgchem.9b02328

Internal polarized electric field is found to be an effective and available strategy to separate photogenerated electron-hole pairs. By this method, the efficiency of photocatalytic reactions can be obviously enhanced. Here, the layered compound of BiOIO₃ with spontaneous polarization was synthesized by a simple hydrothermal method. Taking another bismuth compound BiOI as a counterpart, which has a similar layered structure, the spontaneous polarization effects of BiOIO₃ were analyzed and confirmed. The photocatalytic activity of BiOIO₃ and BiOI were evaluated by the degradation of methyl orange. Methyl orange was almost completely photocatalytically decomposed by BiOIO₃ and BiOI in 40 and 90 min, respectively. The separation and transfer behaviors of photogenerated electron-hole pairs were investigated by a series of photoelectrochemical characterizations. It is further proved the separation and transmission efficiency of BiOIO₃ are higher than those of BiOI. According to the results of density of theory calculations, the internal polarized electric field in BiOIO₃ is ascribed to the spatial asymmetry of the IO₃ group, which is estimated to 1.5 × 10¹⁰ V/m. Under the action of this internal polarized electric field, the photogenerated electrons and holes would transfer along opposite directions, i.e., photogenerated electrons and holes respectively gather at the Bi/I side and O side. Additionally, superoxide radicals (a￠O₂^-) and holes (h⁺) are produced during the degradation process, which are responsible for the high visible-light photocatalytic activity. Finally, the cyclic degradation test proves that its photocatalytic performance has long-term stability. Therefore, BiOIO₃ polar material can be used as one of the alternative materials for efficient photocatalytic reaction.

Full text of DOI:10.1021/acs.inorgchem.9b02328

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Spontaneous Polarization Effect and Photocatalytic Activity of
Layered Compound of BiOIO3
Xu-Dong Dong, Guo-Ying Yao, Qing-Lu Liu, Qing-Meng Zhao, and Zong-Yan Zhao*
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, P. R. China
ABSTRACT: Internal polarized electric field is found to be an effective and available strategy to separate photogenerated
electron−hole pairs. By this method, the efficiency of photocatalytic reactions can be obviously enhanced. Here, the layered
compound of BiOIO3 with spontaneous polarization was synthesized by a simple hydrothermal method. Taking another
bismuth compound BiOI as a counterpart, which has a similar layered structure, the spontaneous polarization effects of BiOIO3
were analyzed and confirmed. The photocatalytic activity of BiOIO3 and BiOI were evaluated by the degradation of methyl
orange. Methyl orange was almost completely photocatalytically decomposed by BiOIO3 and BiOI in 40 and 90 min,
respectively. The separation and transfer behaviors of photogenerated electron−hole pairs were investigated by a series of
photoelectrochemical characterizations. It is further proved the separation and transmission efficiency of BiOIO3 are higher than
those of BiOI. According to the results of density of theory calculations, the internal polarized electric field in BiOIO3 is
ascribed to the spatial asymmetry of the IO3 group, which is estimated to ∼1.5 × 1010 V/m. Under the action of this internal
polarized electric field, the photogenerated electrons and holes would transfer along opposite directions, i.e., photogenerated
−
electrons and holes respectively gather at the Bi/I side and O side. Additionally, superoxide radicals (•O2 ) and holes (h+) are
produced during the degradation process, which are responsible for the high visible-light photocatalytic activity. Finally, the
cyclic degradation test proves that its photocatalytic performance has long-term stability. Therefore, BiOIO3 polar material can
be used as one of the alternative materials for efficient photocatalytic reaction.
driving force to improve the separation rate of photogenerated
electron−hole pairs.2
1. INTRODUCTION
With the increasingly severe situation of energy shortage and
environmental deterioration, photocatalytic technology is one
of the promising strategies to solve the above two issues due to
its ability to produce hydrogen from water splitting and
photocatalytic decompose pollutants. However, traditional
photocatalysts (for example, TiO2, WO3, ZnO, and so on)
usually have a wide band gap and low quantum conversion
efficiency, which seriously restrict the further development and
practical application of photocatalytic technology. According
to current research reports, metal/nonmetal doping, dye/
narrowband semiconductor sensitization, plasma metal load-
ing, and novel visible/NIR-light-driven photocatalysts have
achieved broad spectral response, but their quantum
conversion efficiency needs to be further improved.1 Hence,
numerous efforts are concentrated on improving the quantum
efficiency of semiconductor photocatalytic materials. In recent
years, internal electric fields have become one of the hotspots
in the research field of photocatalytic materials as an internal
The origin of an internal electric field in photocatalytic
materials mainly includes polarization of ferroelectric materials,
semiconductor p-n heterojunction, polarized surface, lattice
distortion caused by doping, and spontaneous polarization
effect of polar materials. In 2004, Grosso et al. first proposed
the application potential of ferroelectric materials in photo-
catalysis.3 The spontaneous polarization of ferroelectric
materials produces a charged surface that drives carriers to
migrate in the opposite direction to separate photogenerated
electron−hole pairs. In the case of semiconductor p-n
heterojunctions, due to the difference in the Fermi energy
levels between the p-type and n-type semiconductors, charge
transfer occurs between the two and ultimately reaches
equilibrium. The redistribution of charge creates an internal
Received: August 2, 2019
© XXXX American Chemical Society
A
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electric field that points from the n-region space charge region
to the p-region space charge region, thereby facilitating the
separation of photogenerated carriers.4 Wang et al.5 studied
the transfer behavior of photogenerated electrons in ZnO/
Cu2O heterojunctions under the action of an electric field and
confirmed that the internal electric field between the two
interfaces can promote the separation and migration of
carriers. In regard to the heterojunction, due to the different
crystal structure and electronic structure of the two phases, the
positions of the conduction band and valence band are
different, and an internal electric field is formed at the interface
which can accelerate the separation of carriers. Li et al.6
reported that the surface heterojunction formed by α-Ga2O3
and β-Ga2O3 has good photocatalytic properties. The polarity
of the material surface depends on the surface atomic
composition and crystal structure, and the exposed polar
surface of the crystal can form an electric field, which in turn
affects the photocatalytic properties of the material. Yang et al.7
prepared NiO octahedron photocatalytic material with a polar
(111) surface and found that its catalytic degradation of dye
molecules is much more active than P25. The internal electric
field generated by the spontaneous polarization between the
polar (111) and (111) crystal faces will accelerate the
photogenerated charge separation, allowing the reduction
and oxidation reactions to proceed on the two crystal faces,
respectively. In addition, the doping and modification of
traditional photocatalysts can lead to lattice distortions in their
crystal structures and generate an internal electric field. Cai et
al.8 researched the I-doped anatase TiO2, and calculations
showed that the TiO6 octahedrons adjacent to iodine atoms
were so heavily distorted that the center of the gravity deviated
from the position of the Ti4+ ion, resulting in a dipole moment
of 1.39 D. Although the internal electric field generated by
these mechanisms can improve quantum efficiency to some
extent, there are still some shortcomings. For example,
although the interface electric field of the heterojunction can
promote the separation of photogenerated carriers, defects are
easily formed at the interface, and the interface electric field
has a narrower range and less strength. It does not effectively
improve the separation efficiency of photogenerated carriers.
Similarly, the internal electric field generated by doping and
modification causing lattice distortion is beneficial to the
separation of photogenerated carriers. However, due to the
introduction of impurity elements, defects are introduced
inside the semiconductor to become a recombination center of
photogenerated carriers, thereby reducing the separation
efficiency of photogenerated carriers.
significant photocatalytic activity. In these novel photo-
catalysts, owing to the stereochemically active of 6s2 lone
pair of Bi3+ ions, Bi-based polar materials show outstanding
spontaneous polarization effects.19
On the other hand, BiOI is considered as a new type of
photocatalyst, due to its unique layered crystal structure.20 Mi
et al.21 used a simple hydrothermal process to synthesize BiOI
nanosheets and found that the samples have strong photo-
catalytic activity for degrading rhodamine B, methyl orange
(MO), and phenol. However, the BiOI band gap is relatively
small, resulting in a high recombination rate of photogenerated
electron hole pairs. Recently, another polar photocatalytic
material, BiOIO3, which has the similar layered crystal
structure with BiOI as shown in Figure 1, was synthesized.22
Figure 1. Crystal structure models of (a) BiOI and (b) BiOIO3.
BiOIO3 also exhibits a layered structural topology composed of
(Bi2O2)2+ and (IO3)− layers, which is very similar to that of
BiOI. The only difference between them is that double I−
layers have become double (IO3)− layers in BiOIO3. The IO3
triangular pyramid structure is asymmetric. Thus, the centers
of positive charges and negative charges are not coinciding
together, resulting residual dipole distance stacking to give
BiOIO3 a large macro polarity.23 Wang et al.24 have reported
that the polarity of BiOIO3 can effectively inhibit the
recombination of electron−hole pairs. However, the relation-
ship between IO3 pyramid and macro polarity, and the intrinsic
mechanism of this polarity-enhanced photocatalytic perform-
ance in BiOIO3, has not been studied in depth. Hence, in this
study, BiOI will be used as a reference comparison, and the
combination of density functional theory (DFT) calculations
with experiments will allow us to systematically elaborate the
spontaneous polarization effects of BiOIO3 as an efficient
photocatalyst.
Polar materials have a noncentrosymmetric spatial structure,
in which positive and negative charge centers do not coincide,
resulting in spontaneous polarization.9 The advantages of the
internal polarized electric field generated by spontaneous
polarization present the following three aspects, namely, the
internal polarized electric field generated by spontaneous
polarization exists in the entire material and its range of action
is large; thus, the stronger the electric field strength is; the
fewer carrier recombination centers there are.10 Therefore, the
internal polarized electric field in polar material can more
effectively promote the separation of the photogenerated
carriers. Therefore, more and more scholars have explored
polar materials, internal field mechanisms, and their function-
alities. According to reports, Ag9(SiO4)2NO3,11 Ag6Si2O7,12
Bi2O2(OH)(NO3),13 Bi2O2[BO2(OH)],14 Bi2MoO6,15
Bi4V2O11,16 NaNbO3,17 BaNbO(IO3)5,18 and so on exhibit
2. EXPERIMENTAL SECTION
2.1. Preparation of Sample. All of the chemicals used in the
experiment were analytical grade reagents and were used without
further purification. BiOIO3 and BiOI samples are prepared by using a
simple hydrothermal process. Bi(NO3)3·5H2O and KIO3 were used as
the sources of Bi and IO3, which are environmentally friendly and
inexpensive. The BiOIO3 sample was synthesized as follows. First, 1
mmol of Bi (NO3)3·5H2O was dissolved in 40 mL of deionized water
to form a suspension after constant stirring. Then, 1 mmol of KIO3
was added into the suspension under vigorous stirring. The mixture
was transferred into 100 mL Teflon-lined stainless steel autoclaves.
The aqueous suspension was hydrothermally heated at a temperature
of 150 °C. After they were heated for 5 h, the samples naturally
B
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Figure 2. Power XRD patterns and results of Rietveld refinement of (a) BiOI and (b) BiOIO3 synthesized by a hydrothermal method.
cooled to room temperature. Afterward, all generated samples were
obtained by centrifuging them, filtering them, and rinsing them with
deionized water and ethanol for four times. Finally, the samples were
dried at 60 °C for 12 h. For comparison, BiOI was also prepared by
the same simple hydrothermal process, in which KI was used instead
of KIO3.
2.2. Characterization. The crystal structure and phase purity of
the samples was determined by X-ray diffraction (XRD, Bruker D8
Advance, Germany) using Cu Kα radiation, and the scanning range
was 10−100° (2θ). The BET specific surface area of the samples was
examined by the nitrogen adsorption−desorption (Micromeritics
ASAP 2460, USA) method. The morphologies and structures of as-
prepared samples were observed by scanning electron microscopy
(SEM, S-4800 Hitachi, Japan), and the diffuse reflectance absorption
spectra (DRAS) were obtained with a UV/vis spectrophotometer
(UV-3900H, Hitachi, Japan).
(Pt) electrode were used as the reference electrode and the counter
electrode, respectively. The sample film prepared on the FTO
conductive glass was the working electrode and was prepared by a
screen printing method. The printing slurry was prepared by mixing
and grinding a sample (0.1 g), ethyl cellulose, lauric acid and pinealol
according to the designed proportion. Subsequently, the obtained
slurry was subjected to screen printing on a 13 mm × 14 mm FTO
glass to form a film, which was placed in a muffle furnace and
quenched at 400 °C for 2 h. The measurements are carried under
simulated solar-light irradiation (Xe lamp, 300 W). The illuminated
surface area was 4 cm2, and the applied voltage was 0.2 V.
2.6. Computational Methods. All of the calculations were
performed by using DFT software package of QuantumATK, in which
the eigenfunctions of the Kohn−Sham Hamiltonian are expanded in a
linear combination of atomic orbitals (LCAO). The basis sets were
chose as psudopotential SG15. The exchange-correlation interaction
was treated by the meta-GGA method that is predefined by the
function of TB09LDA. The density mesh cutoff was set as 200
hartree, in which the occupation method was chose as Fermi−Direc
method with broadening of 25 meV. The Monkhorst−Pack scheme of
k-points grid sampling was set as 19 × 19 × 3. The energy tolerance
for self-consistent filed iteration was set as 0.0001 hartree in the
algorithm of PulayMixer. The optimizer method of LBFGS was
chosen for optimized geometry. Its convergence criteria were set as
0.05 eV/Å for force tolerance, 0.1 GPa for stress error tolerance, and
0.2 Å for maximum step size. During geometry optimization, the
lattice vectors, space group, and Bravais lattice type were freely
relaxed.
2.3. Photocatalytic Degradation Testing. The photocatalytic
activity of the BiOIO3 and BiOI samples was evaluated by
photocatalytic degradation of methyl orange (MO) under simulated
solar-light irradiation (Xe Lamp, 300 W). Next, 0.2 g of as-prepared
catalysts was stirred and dispersed in 200 mL of MO solutions (1 g/
L) in a quartz reactor. Prior to irradiation, the suspensions were
magnetically stirred in the darkness for 30 min to allow an
adsorption−desorption equilibrium. After that, 5 mL of the liquid
was sampled at every 10 min interval and then centrifuged to remove
solid catalyst. The concentration of MO was determined by recording
the characteristic absorption spectra on a UV−vis spectrophotometer.
The catalyst’s lifetime is an important parameter of the photo-
catalytic process, so it is essential to evaluate the stability of
photocatalyst for practical application. The recycling experiments on
BiOIO3 sample were carried out under the same reaction conditions.
After every 40 min of photocatalytic degradation, the separated
photocatalysts were washed with deionized water and then dried.
Next, 200 mL of MO solutions (1 g/L) were readded to the quartz
reactor; light was added, and the experiment was repeated four times.
2.4. Active Species Trapping Testing. For the purpose of
detecting the active substances that play crucial roles in the
photocatalytic process, radical trapping experiments have been carried
out. Ethylene diamine tetraacetic acid disodium salt (EDTA-2Na, 1
mmol), p-benzoquinone (BQ, 1 mmol), and isopropanol (IPA, 1
mmol) were introduced in the degradation system to capture holes
3. RESULTS AND DISCUSSION
3.1. Physical Characterization. The powder X-ray
powder diffraction (XRD) patterns of as-prepared BiOI and
BiOIO3 samples are shown in Figure 2. First of all, the
characteristic diffraction peaks of BiOI (Figure 2(a)) and
BiOIO3 (Figure 2(b)) accord well with the database of JCPDS
file 10-0445 and ICSD no. 262019, respectively, demonstrating
the pure phase of BiOI and BiOIO3. No other peaks are found,
suggesting the high purity and crystallinity of the samples. In
addition, the powder XRD patterns of as-prepared BiOI and
BiOIO3 samples were refined. In Figure 2, the red curve is the
experimental value, the blue curve is the analog value, and the
black curve is the difference between the two. It can be seen
the experimental values and the simulated values agree very
well. In addition, the lattice constant obtained from Rietveld
refinement is listed as the following. For BiOI, a = b = 4.0422
Å, c = 9.8113 Å; for BiOIO3, a = 5.6891 Å, b = 11.2521 Å, c =
−
(h+), superoxide radicals (•O2 ), and hydroxyl radicals (•OH),
respectively.25−27
2.5. Photoelectrochemical Testing. The transient photocurrent
response, EIS, cyclic voltammetry curves, and Mott−Schottky curves
were measured on an electrochemical system (ModuLab XM
PhotoEchem, Solartron Analytical, England) with 0.1 M Na2SO4
solution as the electrolyte. A saturated calomel electrode and platinum
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Figure 3. SEM images of (a) BiOI and (b) BiOIO3 synthesized by a hydrothermal method.
Figure 4. (a) UV−vis diffuse reflectance absorption spectra. (b) Band gaps of BiOI and BiOIO3 estimated by the Tauc plot method.
5.7861 Å. After crystal structural optimization in DFT
calculations, the lattice constant was obtained as follows. For
BiOI, a = b = 3.9915 (3.9738) Å, c = 9.1501 (9.3722) Å; for
BiOIO3, a = 5.6596 (5.5396) Å, b = 11.0502 (11.0793) Å, c =
5.7411 (5.6434) Å, in which the corresponding measured
values in the PDF card are provided in parentheses. By
comparing the above three groups of lattice constants, one can
find that they are very close. These results further demonstrate
that the synthesized BiOI and BiOIO3 samples are pure phases.
The particle size and morphology of BiOI and BiOIO3
products were observed by the field emission SEM. As shown
in Figure 3, both BiOI and BiOIO3 samples show clear lamellar
morphology, which is very similar to those of other (Bi2O2)2+
layer-containing compounds.28 This is the unique feature of
layered compounds, which have been reported previously in
the literature to easily synthesize similar morphologies. In the
case of the BiOI sample, the width is estimated to be ∼1.1 μm,
and the thickness is estimated to be ∼40 nm, as shown in
Figure 3(a). Compared with BiOI sample, the BiOIO3 sample
shows a more uniform and smaller size morphology. As shown
in Figure 3(b), the BiOIO3 sample presents a flake stack
morphology, which has an average width around ∼0.5 μm. It is
important that the thickness of the BiOIO3 sample is also
estimated to ∼40 nm. And, the specific surface area of the
pristine BiOI and BiOIO3 was measured, which was
determined to be 2.583 and 11.280 m2 g−1, respectively.
There is a certain difference in the specific surface area of BiOI
and BiOIO3, which may be due to their special interlayer
messy staggered stack structure. In the field of photocatalysis,
the nanoscale platelet-like morphology has the special
advantage of a shorter carrier diffusion distance, which enables
the carrier to reach the reactive site on the surface within its
lifetime.29 Furthermore, the thickness of the layered photo-
catalytic material is also an important factor affecting the
photocatalytic performance.30 In the present work, since
BiOIO3 and BiOI have the same morphology and longitudinal
size, it can be assumed that these factors should contribute the
same to their photocatalytic performances.
3.2. UV−Vis Light Absorption Properties. The UV−vis
diffuse reflectance absorption spectra (DRAS) of BiOI and
BiOIO3 are displayed in Figure 4(a). It shows that the
absorption edges of BiOI and BiOIO3 were located at
approximately 650 and 400 nm, respectively. This observation
clearly indicates that BiOI is a visible-light-driven photo-
catalyst, while BiOIO3 is a UV-light-driven photocatalyst. This
is a major obstacle to the development of BiOIO3-based
photocatalysts and a direction to be broken in the future. In
semiconductors, the square of the absorption coefficient (α) is
linear with photon energy for direct optical transitions in the
absorption edge region, whereas the square root of the
absorption coefficient is linear with photon energy for indirect
transitions.31 Data plots of (αhv)1/2 versus photon energy in
the absorption edge region for BiOI and BiOIO3 shown in
Figure 4(a) are nearly linear, indicating the absorption edge of
BiOI and BiOIO3 is caused by indirect transitions. Band gaps
of the two compounds are determined by optical absorption
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Figure 5. (a) Photocatalytic degradation rate, (b) decolorization efficiency, and (c) photocatalysis performance index of MO for BiOIO3 powder,
which are compared with BiOI and P25 powder. (d) Cycling runs in the photocatalytic degradation of MO in the presence of BiOIO3 samples.
Absorbance spectrum of MO solution in the presence of the as-prepared (e) BiOI, (f) BiOIO3, and (g) P25.
near the band edge by the following equation: α(hv) = A(hv −
Eg)n/2, where α, hv, A, and Eg are the optical absorption
coefficient, photonic energy, proportionality constant, and
band gap, respectively.32 In this equation, n determines the
type of the transition in a semiconductor (n = 1, direct
absorption; n = 4, indirect absorption). By applying n = 4, we
can determine the indirect band gap of BiOI and BiOIO3 from
the plot of (αhv)1/2 versus photon energy, as presented in the
Figure 4(b). By extrapolating the straight line to the x-axis in
this plot, we estimated the Eg of BiOI and BiOIO3 to 1.79 and
3.01 eV, respectively. Among them, the band gap value of
BiOIO3 is close to that of P25 (3.06 eV).
absorption range. The most fundamental reason for this is that
the interaction between atoms in the Bi2O4 layer has changed.
For the Bi2O4 layer in BiOI, the distances between Bi−Bi and
Bi−O are 3.968 and 2.331 Å, respectively. Compared with
BiOIO3, the distances between Bi−Bi and Bi−O in the Bi2O4
layer are 3.777 and 2.304 Å, respectively. Obviously, due to the
introduction of the IO3 pyramid, the bond length between the
atoms of the Bi2O4 layer in the BiOIO3 structure is shortened
and the interaction becomes stronger, such that the conduction
band moves up and the band gap becomes larger.
3.3. Photocatalytic Degradation Testing. The photo-
catalytic activities of BiOI and BiOIO3 samples were evaluated
by photocatalytic degradation of MO under UV−vis light
irradiation under refrigeration of condensed water to 10 °C.
However, the band gap of BiOIO3 is larger than the band
gap of BiOI, resulting in a large difference in the light
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Figure 6. Cyclic voltammetry curve of (a) BiOI and (b) BiOIO3 synthesized by a hydrothermal method.
Figure 7. Mott−Schottky curves of (a) BiOI and (b) BiOIO3 synthesized by a hydrothermal method.
The degradation efficiencies are defined as C/C0, in which C
and C0 represent the remnant and initial concentration of MO,
respectively. MO is quite stable, and its self-photolysis is
negligible. Figure 5(a)−5(c) illustrate the photocatalytic
performances [(a): photocatalytic degradation rate; (b):
decolorization efficiency; (c): photocatalysis performance
index] of BiOIO3 powder, which are compared with those of
BiOI and P25 powder. BiOIO3 shows superior photocatalytic
performance relative to BiOI in the degradation rate,
decolorization rate, and photolysis index. Even more surprising
is that BiOIO3 also has a better photocatalytic performance
than P25. At the same time, as discussed in the previous DRAS
measurements, the light absorption range of BiOIO3 is much
smaller than that of BiOI and almost the same as that of P25.
On the one hand, BiOIO3 and BiOI have a similar layered
crystal structure. BiOIO3 and P25 have identical spectral
response characteristics. On the other hand, the crystal
structure of BiOI and P25 determines that they have no
internal polarized electric field. Combining this evidence, the
excellent photocatalytic performance of BiOIO3 can be
preliminarily identified as its own internal polarized electric
field. To evaluate the stability of samples in the photocatalytic
reaction, BiOIO3 was reclaimed and re-examined for four extra
cycles as shown in Figure 5(d). BiOIO3 did not exhibit any
significant loss of activity. It implies that BiOIO3 has long-term
stability. The MO concentrations versus the reaction time and
absorbance curves for these photocatalysts are plotted in
Figure 5(e)−5(g) [(e): BiOI; (f): BiOIO3; (g): P25]. It shows
that MO was almost photocatalytically degraded by BiOI,
BiOIO3, and P25 in 90, 40, and 55 min, respectively. These
results demonstrate that BiOIO3 can be used as an efficient,
stable, and low-cost alternative photocatalyst.
3.4. Photoelectrochemical Properties and Photo-
catalytic Mechanism. To obtain insight into the uncommon
photocatalytic activity trend, the charge separation and transfer
behaviors were investigated by a string of photoelectrochemical
characterizations. First, the cyclic voltammetry trend of BiOI as
shown in Figure 6(a) and BiOIO3 as shown in Figure 6(b) are
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Figure 8. (a) Transient photocurrent responses, (b) Bode-phase spectra, and (c) EIS Nyquist plots of BiOIO3, BiOI, and P25.
very similar. The peak intensity of the reduction peak
(downward peak) is greater than the peak intensity of the
oxidation peak (upward peak), indicating that the two are
more susceptible to reduction, and both show good redox
ability. At the same time, the volt−ampere curve of the three
cycles showed only a slight change, indicating that the two
have good stability. This is consistent with the results of the
degradation MO cycle experiment in Figure 5(d).
photocatalytic activity. It is further proved that the internal
polarized electric field can enhance the charge separation and
transmission efficiency, so that the photocatalytic performance
of the polar material BiOIO3 is better than that of BiOI and
P25.
To speculate the photocatalytic mechanism, radical trapping
experiments are performed to capture the reactive species
generated in the degradation process. As shown in Figure 9,
In this article, the semiconductor types and flat-band
potentials of BiOI and BiOIO3 were determined by Mott−
Schottky (M-S) methods.33,34 It is well-known that the slope of
linear 1/C2 versus potential curves is positive for n-type
semiconductors and negative for p-type semiconductors.35,36
The slope of linear 1/C2-potential curves of BiOIO3 as shown
in Figure 7(a) and BiOI Figure 7(b) are separately positive and
negative, indicating that BiOI and BiOIO3 are p-type and n-
type semiconductors, respectively. By calculating the values of
the abscissa axis-intercept with extrapolation to 1/C2 = 0, the
flat potentials of BiOIO3 and BiOI are separately determined
to be −0.81 and 1.81 V, versus the saturated calomel electrode
(SCE), which is in good agreement with the reported values.37
They amount to −0.613 and 2.007 V, respectively, versus the
normal hydrogen electrode (NHE).
The transient photocurrent response can indicate the
generation and separation efficiency of photoexcited charge
carriers. As revealed by Figure 8(a), the two photoelectrodes
show a stable photocurrent response, and BiOIO3 produces a
current density of 0.025 μA/cm2 with the light on, which is 1.5
times that of BiOI (0.017 μA/cm2). Evidently, BiOIO3
possesses a much higher charge separation efficiency. Figure
8(b) displays the Bode-phase spectra, which can reflect the
lifetime of injected electrons that is highly correlated with the
frequency (f). According to the equation τ = 1/(2πf),38 the
lifetime of injected electrons in BiOIO3 (47.4 × 10−6 s) is
estimated to be approximately 1.9 times and 3.1 times higher
than that of BiOI (24.9 × 10−6 s) and P25 (15.5 × 10−6 s),
respectively. It can be seen that the injected electron lifetime of
BiOIO3 is much longer than that of BiOI and P25.
Furthermore, in order to detect the interfacial transfer
efficiency of the catalysts, electrochemical impedance spec-
troscopy (EIS) was measured. Figure 8(c) shows Nyquist EIS
plots of BiOIO3 and BiOI with irradiation of visible light. It is
clear that BiOIO3 has a smaller arc radius than BiOI, indicating
the higher charge mobility at the interface between BiOIO3
and the electrolyte. The EIS that is obtained by the Zview
software simulation equivalent circuit processing, as shown in
the inset of Figure 8(c), also verifies this result. Overall, the
results of multiple spectra indicate that charge separation and
transfer efficiencies play significant roles in the photocatalytic
reaction of BiOIO3, which makes BiOIO3 have higher
Figure 9. Photocatalytic degradation curve of MO over BiOIO3 alone
and with the addition of EDTA-2Na, IPA, and BQ.
the MO degradation rate was almost not influenced by the
addition of isopropyl alcohol (IPA, a scavenger of •OH),
excluding the effect of •OH. By contrast, both the p-
−
benzoquinone (BQ, a scavenger of •O2 ) and ethylene
diamine tetraacetic acid disodium salt (EDTA-2Na, a
scavenger of h+) have significant impediment in MO
degradation, revealing that •O2 and h+ are the critical active
−
species.
3.5. Electronic Structure of BiOI and BiOIO3. The
calculated electronic structures (i.e., band structure and density
of states) of BiOI and BiOIO3 are illustrated in Figure 10. First
of all, the obtained band gap values of BiOI as shown in Figure
10(a) and of BiOIO3 as shown in Figure 10(b) are 2.03 and
2.91 eV, respectively, which are very consistent with above
DRAS measurements and previous reports. So, the meta-GGA
functional within the LCAO method can overcome the well-
known underestimated band gap by GGA functional within the
plane wave method.39 In fact, there are little differences
between DRAS measurements and DFT calculations; the main
reasons can be ascribed to the following aspects: (1) the
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Figure 10. Band structures and total density of states of (a) BiOI and (b) BiOIO3. (c) The corresponding local density of states in BiOI and
BiOIO3.
defects are unavoidable in samples prepared by the chemical
solution method and (2) DFT calculations only consider the
properties of the ground state at absolute zero. As shown in
Figure 10(a), in the case of BiOI, the valence band maximum
(VBM) is located on the ZR line, while the conduction band
minimum (CBM) is located at Γ point. As shown in Figure
10(b), in the case of BiOIO3, the VBM is located on the YS
line, while the CBM is located at Y point. This result indicates
that both BiOI and BiOIO3 are the indirect band gap
semiconductors, which is confirmed above discussions about
Tacu plot method in Figure 4(b). The symmetry group of
BiOI is P4/nmm (no. 129), while the symmetry group of
BiOIO3 is Pca21 (no. 29). In other words, BiOI has higher
symmetry, so its band structure shows higher degeneracy and
dispersion.
Figure 11. Schematic diagram of the separation mechanism of
photogenerated electron−hole pairs and the estimated internal
polarized electric field in BiOIO3.
To clearly understand the contribution of atom and orbital
to the electronic states, the total and local density of states
(DOS) are also provide in Figure 10. As described in Figure
10(a) and Figure 10(c), it is found that the conduction band
(CB) of BiOI mostly consists of Bi6p states; the upper valence
band (VB) is mainly composed by I-5p states, and the lower
VB is mainly composed by O-2p states. In the whole range of
VB and CB of BiOI, there are slight hybridized states between
O-2p states and Bi6p or I-5p states. As described in Figure
10(b) and Figure 10(c), it is found that the lower CB of
BiOIO3 is mainly composed by I-5p states, and the upper CB
is mainly composed by Bi6p states; the VB mostly consists of
O-2p states. In the whole range of CB BiOIO3, there are
obvious hybridized states between O-2p states and Bi6p or I-
5p states. These results are consistent with previous literature
on BiOIO3.20,40 Although BiOI and BiOIO3 have similar
layered structures, their electronic structures show different
compositions. This is mainly due to the different interactions
between layers. In the case of BiOI, the Bi2O2 layers are
connected by the van der Waals interaction of I− ions; while in
the case of BiOIO3, the Bi2O2 layers are connected by the
bridging valence interaction of IO3− group. Furthermore, there
are three kinds of oxygen atoms in BiOIO3, i.e., the O1 atoms
form the Bi2O2 layers, the O2 atoms bridging the BiO6 and IO3
pyramids, and the O3/O4 atoms forming the terminal atoms
of IO3 pyramids, as shown in Figure 11.24 These three kinds of
oxygen atoms show different contributions of the composition
of VB. According to above analysis, the photogenerated holes
are mainly located on the O-2p states, while the photo-
generated electrons are mainly located on the Bi6p and I-5p
states.
intrinsic mechanism is further analyzed. The Bader method is
used to calculate the charge distribution, and the results are as
follows: +1.769 e at Bi atom, −0.506 e at I atom, and −1.263 e
at O atom in the case of BiOI and +2.168 e at Bi atom,
+2.567e at I atom, −1.340 e at O1 atom, −1.138 e at O2/O3
atom, and −1.120 e at O4 atom in the case of BiOIO3. First of
all, the I atom obtains electrons in BiOI, while the I atom
contributes electrons in BiOIO3. Second of all, the O atom
located at different sites will obtain different electrons in
BiOIO3. The asymmetry of spatial atom distribution and the
uneven charge distribution IO3 groups are the two key factors
for generating the internal polarized electric field in BiOIO3. In
previous works, the internal polarized electric field has often
been described by the dipole moment of polyhedron.41−43
Therefore, it is easy to estimate the internal polarized electric
field (∼1.5 × 1010 V/m) in BiOIO3, according to the
optimized geometrical configurations and charge distributions.
The calculation uses the following formula: E = σ/εr(0) (where
σ is the surface charge density, and εr(0) is the static dielectric
constant). The value of σ could be determined by the Mulliken
population analysis, and the value of εr(0) is determined by the
optical properties calculations. Although previous literature
reports have reported that BiOI also has internal polarized
electric fields, its internal polarized electric fields are arranged
alternating along the c-axis with equal magnitude and opposite
direction, and the final effective electric field is equal to zero.
On the opposite, the internal polarized electric fields in
BiOIO3 can be accumulated along the c-axis, due to the same
polarization direction of IO3 groups. In this part of the
theoretical calculations, the existence of a polar electric field in
BiOIO3 is confirmed and its origin is elucidated. Simulta-
neously, it fully reveal the root cause of the higher
In order to more clearly describe the separation and transfer
process of photogenerated electron−hole pairs in BiOIO3, the
H
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Article
photocatalytic performance of BiOIO3 in the above exper-
imental test results.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zzy@kmust.edu.cn.
ORCID
Zong-Yan Zhao: 0000-0001-8953-3150
Notes
The authors declare no competing financial interest.
The underlying mechanism of enhanced photocatalytic
performace of BiOIO3 is summarized in Figure 11. With the
internal polarized electric field in BiOIO3, the photogenerated
electrons on O atoms can be effectively transferred to Bi/I
atoms, while the photogenerated holes remain on O atoms.
Then, the separated electrons and holes will be fast transfer to
the surface of BiOIO3 sample along opposite directions.
Finally, the photo-oxidation would occur at the O sites on the
surface, and the photoreduction would occur at the Bi/I sites.
Therefore, the internal polarized electric field is the key factor
to enhance the photocatalytic performances of BiOIO3,
compared with BiOI and P25.
ACKNOWLEDGMENTS
■
The authors would like to acknowledge financial support from
the National Natural Science Foundation of China
(11964015) and the 18th Yunnan Province Young Academic
and Technical Leaders Reserve Talent Project (2015HB015).
4. CONCLUSIONS
REFERENCES
■
(1) Lou, Z.; Wang, P.; Huang, B.; Dai, Y.; Qin, X.; Zhang, X.; Wang,
Z.; Liu, Y. Enhancing Charge Separation in Photocatalysts with
Internal Polar Electric Fields. Chemphotochem 2017, 1 (5), 136−147.
(2) Ling, Z.; Yang, S.; Wang, W. Internal Electric Fields within the
Photocatalysts. Prog. Chem. 2016, 28 (4), 415−427.
In summary, a layered polar compound of BiOIO3 was
synthesized from Bi(NO3)3·5H2O and KIO3 by using a
hydrothermal method. The as-prepared BiOIO3 sample is a
pure phase and exhibits clear lamellar morphology. Combined
with optical measurements and DFT calculations, BiOIO3 is an
indirect gap semiconductor with a band gap of 2.91 eV. The
photocatalytic degradation testing indicates that BiOIO3 shows
excellent photocatalytic performance for methyl orange
degradation under UV−vis light irradiation, which is much
better than its counterpart of BiOI and P25. And, it also
presents long-term stability. Additionally, superoxide radicals
̀
(3) Grosso, D.; Boissiere, C.; Smarsly, B.; Brezesinski, T.; Pinna, N.;
Albouy, P. A.; Amenitsch, H.; Antonietti, M.; Sanchez, C. Periodically
ordered nanoscale islands and mesoporous films composed of
nanocrystalline multimetallic oxides. Nat. Mater. 2004, 3 (11),
787−92.
(4) Li, H.; Sang, Y.; Chang, S.; Huang, X.; Zhang, Y.; Yang, R.; Jiang,
H.; Liu, H.; Wang, Z. L. Enhanced Ferroelectric-Nanocrystal-Based
Hybrid Photocatalysis by Ultrasonic-Wave-Generated Piezophoto-
tronic Effect. Nano Lett. 2015, 15 (4), 2372−2379.
(•O2 ) and holes (h+) are produced during the degradation
−
process. The photoelectrochemical measurements demonstrate
that BiOIO3 has a higher separation rate of photogenerated
electron−hole pairs. The DFT calculations also prove that
there are internal polarized electric fields in BiOIO3 along the
c-axis, which is the root to the asymmetry of spatial atom
distribution and the uneven charge distribution IO3 groups.
The photogenerated electrons and holes were gathered mainly
on Bi/I and O atoms, respectively. Under the action of the
internal polarized electric field (∼1.5 × 1010 V/m), the
photogenerated electrons and holes could transfer along
opposite directions, which facilitates the separation rate of
photogenerated electron−hole pairs. Thus, the higher photo-
catalytic efficiency of BiOIO3 is caused by the internal
polarized electric field, in comparison with BiOI and P25.
It is worth noting that the large macroscopic polarity is
mainly attributed to the alignment of the lone-pair-containing
IO3 polyhedra. Therefore, further research on the polar groups,
such as doping, atomic substitution, etc., can be carried out in
subsequent work, thereby fully exerting the promoting effect of
the inner polar field on the photocatalytic performance. In
addition, the correspondence between the internal polar
electric field generated by the spontaneous polarization of
polar materials and the photocatalytic performance is worthy
of further investigation.
(5) Jiang, T.; Xie, T.; Zhang, Y.; Chen, L.; Peng, L.; Li, H.; Wang, D.
Photoinduced charge transfer in ZnO/Cu2O heterostructure films
studied by surface photovoltage technique. Phys. Chem. Chem. Phys.
2010, 12 (47), 15476.
(6) Wang, X.; Xu, Q.; Li, M.; Shen, S.; Wang, X.; Wang, Y.; Feng, Z.;
Shi, J.; Han, H.; Li, C. Photocatalytic overall water splitting promoted
by an α-β phase junction on Ga2O3. Angew. Chem., Int. Ed. 2012, 51
(52), 13089−13092.
(7) Zhao, W.; Guo, Y.; Wang, S.; He, H.; Sun, C.; Yang, S. A novel
ternary plasmonic photocatalyst: ultrathin g-C3N4 nanosheet hybrided
by Ag/AgVO3 nanoribbons with enhanced visible-light photocatalytic
performance. Appl. Catal., B 2015, 165, 335−343.
(8) Long, M.; Cai, W.; Wang, Z.; Liu, G. Correlation of electronic
structures and crystal structures with photocatalytic properties of
undoped, N-doped and I-doped TiO2. Chem. Phys. Lett. 2006, 420
(1), 71−76.
(9) Chen, F.; Huang, H.; Guo, L.; Zhang, Y.; Ma, T. The Role of
Polarization in Photocatalysis. Angew. Chem., Int. Ed. 2019, 58 (30),
10061−10073.
(10) Wang, Z.; Huang, B.; Dai, Y. Design and synthesis of highly
reactive photocatalysts. Materials China 2017, 36 (1), 7−16.
(11) Zhu, X.; Wang, Z.; Huang, B.; Wei, W.; Dai, Y.; Zhang, X.; Qin,
X. Synthesis of Ag9(SiO4)2NO3 through a reactive flux method and its
visible-light photocatalytic performances. APL Mater. 2015, 3 (10),
104413.
(12) Lou, Z.; Huang, B.; Wang, Z.; Ma, X.; Zhang, R.; Zhang, X.;
Qin, X.; Dai, Y.; Whangbo, M.-H. Ag6Si2O7: a silicate photocatalyst
for the visible region. Chem. Mater. 2014, 26 (13), 3873−3875.
(13) Huang, H.; He, Y.; Li, X.; Li, M.; Zeng, C.; Dong, F.; Du, X.;
Zhang, T.; Zhang, Y. Bi2O2(OH)(NO3) as a desirable [Bi2O2]2+
layered photocatalyst: strong intrinsic polarity, rational band structure
and {001} active facets co-beneficial for robust photooxidation
capability. J. Mater. Chem. A 2015, 3 (48), 24547−24556.
(14) Zhang, R.; Dai, Y.; Lou, Z.; Li, Z.; Wang, Z.; Yang, Y.; Qin, X.;
Zhang, X.; Huang, B. Layered photocatalyst Bi2O2[BO2(OH)]
nanosheets with internal polar field enhanced photocatalytic activity.
CrystEngComm 2014, 16 (23), 4931−4934.
ASSOCIATED CONTENT
■
Accession Codes
CCDC 1946651 and 1946712 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
I
DOI: 10.1021/acs.inorgchem.9b02328
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(15) Chen, Y.; Yang, W.; Gao, S.; Zhu, L.; Sun, C.; Li, Q. Internal
Polarization Modulation in Bi2MoO6 for Photocatalytic Performance
Enhancement under Visible-Light Illumination. ChemSusChem 2018,
11 (9), 1521−1532.
(16) Jiang, Z.; Liu, Y.; Li, M.; Jing, T.; Huang, B.; Zhang, X.; Qin, X.;
Dai, Y. One-Pot Solvothermal Synthesis of Bi4V2O11 as A New Solar
Water Oxidation Photocatalyst. Sci. Rep. 2016, 6, 22727.
(17) Jiang, L.; Zhang, Y.; Qiu, Y.; Yi, Z. Improved photocatalytic
activity by utilizing the internal electric field of polar semiconductors:
a case study of self-assembled NaNbO3 oriented nanostructures. RSC
Adv. 2014, 4 (7), 3165−3170.
(18) Sun, C. F.; Hu, C. L.; Xu, X.; Ling, J. B.; Hu, T.; Kong, F.;
Long, X. F.; Mao, J. G. BaNbO(IO3)5: A New Polar Material with a
Very Large SHG Response. J. Am. Chem. Soc. 2009, 131 (27), 9486−
7.
(19) Li, M.; Huang, H.; Yu, S.; Tian, N.; Zhang, Y. Facet, Junction
and Electric Field Engineering of Bismuth-Based Materials for
Photocatalysis. ChemCatChem 2018, 10 (20), 4477−4496.
(20) Zhao, Z. Y.; Dai, W. W. Structural, electronic, and optical
properties of Eu-doped BiOX (X = F, Cl, Br, I): a DFT+U study.
Inorg. Chem. 2014, 53 (24), 13001−13011.
(21) Mi, Y.; Zhou, M.; Wen, L.; Zhao, H.; Lei, Y. A highly efficient
visible-light driven photocatalyst: two dimensional square-like
bismuth oxyiodine nanosheets. Dalton Trans. 2014, 43 (25), 9549−
9556.
(22) Nguyen, S. D.; Yeon, J.; Kim, S. H.; Halasyamani, P. S.
BiO(IO3): a new polar iodate that exhibits an aurivillius-type
(Bi2O2)2+ layer and a large SHG response. J. Am. Chem. Soc. 2011,
133 (32), 12422−5.
(23) Huang, H.; Tu, S.; Zeng, C.; Zhang, T.; Reshak, A. H.; Zhang,
Y. Macroscopic Polarization Enhancement Promoting Photo- and
Piezoelectric-Induced Charge Separation and Molecular Oxygen
Activation. Angew. Chem., Int. Ed. 2017, 56 (39), 11860−11864.
(24) Wang, W.; Huang, B.; Ma, X.; Wang, Z.; Qin, X.; Zhang, X.;
Dai, Y.; Whangbo, M. H. Efficient separation of photogenerated
electron-hole pairs by the combination of a heterolayered structure
and internal polar field in pyroelectric BiOIO3 nanoplates. Chem. -
Eur. J. 2013, 19 (44), 14777−80.
(25) Huang, H.; Han, X.; Li, X.; Wang, S.; Chu, P. K.; Zhang, Y.
Fabrication of Multiple Heterojunctions with Tunable Visible-Light-
Active Photocatalytic Reactivity in BiOBr−BiOI Full-Range Compo-
sites Based on Microstructure Modulation and Band Structures. ACS
Appl. Mater. Interfaces 2015, 7 (1), 482−492.
(32) Cheng, H.; Huang, B.; Dai, Y.; Qin, X.; Zhang, X. One-Step
Synthesis of the Nanostructured AgI/BiOI Composites with Highly
Enhanced Visible-Light Photocatalytic Performances. Langmuir 2010,
26 (9), 6618−6624.
(33) He, Z. Q.; Wang, D.; Fang, H. Y.; Chen, J. M.; Song, S. Highly
efficient and stable Ag/AgIO3 particles for photocatalytic reduction of
CO2, under visible light. Nanoscale 2014, 6 (18), 10540.
(34) Huang, H.; He, Y.; Lin, Z.; Kang, L.; Zhang, Y. Two Novel Bi-
Based Borate Photocatalysts: Crystal Structure, Electronic Structure,
Photoelectrochemical Properties, and Photocatalytic Activity under
Simulated Solar Light Irradiation. J. Phys. Chem. C 2013, 117 (44),
22986−22994.
(35) He, Z. Q.; Wang, D.; Fang, H. Y.; Chen, J. M.; Song, S. Highly
efficient and stable Ag/AgIO3 particles for photocatalytic reduction of
CO2 under visible light. Nanoscale 2014, 6 (18), 10540.
(36) Lee, K.; Ruddy, D. A.; Dukovic, G.; Neale, N. R. Synthesis,
optical, and photocatalytic properties of cobalt mixed-metal spinel
oxides Co(Al1−xGax)2O4. J. Mater. Chem. A 2015, 3 (15), 8115−8122.
(37) Huang, H.; Xiao, K.; Liu, K.; Yu, S.; Zhang, Y. In Situ
Composition-Transforming Fabrication of BiOI/BiOIO3 Hetero-
structure: Semiconductor p−n Junction and Dominantly Exposed
Reactive Facets. Cryst. Growth Des. 2016, 16 (1), 221−228.
(38) Kern, R.; Sastrawan, R.; Ferber, J.; Stangl, R.; Luther, J.
Modeling and interpretation of electrical impedance spectra of dye
solar cells operated under open-circuit conditions. Electrochim. Acta
2002, 47 (26), 4213−4225.
̈
(39) Kresse, G.; Furthmuller, J. Efficiency of ab-initio total energy
calculations for metals and semiconductors using a plane-wave basis
set. Comput. Mater. Sci. 1996, 6 (1), 15−50.
(40) Huang, H.; He, Y.; He, R.; Jiang, X.; Lin, Z.; Zhang, Y.; Wang,
S. Novel Bi-Based Iodate Photocatalysts with High Photocatalytic
Activity. Inorg. Chem. Commun. 2014, 40, 215−219.
(41) Lu, J.; Zeng, X.; Liu, H.; Zhang, W.; Zhang, Y. Preparation and
Photoluminescence of (3C-ZnS)/(2H-ZnS) Superlattice in Mn-
doped ZnS Nanoribbons. J. Phys. Chem. C 2012, 116 (43), 23013−
23018.
(42) Ma, X.; Wu, Y.; Lu, Y.; Xu, J.; Wang, Y.; Zhu, Y. Effect of
Compensated Codoping on the Photoelectrochemical Properties of
Anatase TiO2 Photocatalyst. J. Phys. Chem. C 2011, 115 (34), 16963−
16969.
(43) Zhao, Z. Y.; Dai, W. W. Electronic Structure and Optical
Properties of BiOI Ultrathin Films for Photocatalytic Water Splitting.
Inorg. Chem. 2015, 54 (22), 10732−7.
(26) Huang, H.; Li, X.; Wang, J.; Dong, F.; Chu, P. K.; Zhang, T.;
Zhang, Y. Anionic Group Self-Doping as a Promising Strategy: Band-
Gap Engineering and Multi-Functional Applications of High-
Performance CO32−-Doped Bi2O2CO3. ACS Catal. 2015, 5 (7),
4094−4103.
(27) Huang, H.; Xiao, K.; He, Y.; Zhang, T.; Dong, F.; Du, X.;
Zhang, Y. In situ assembly of BiOI@Bi12O17Cl2 p−n junction: charge
induced unique front-lateral surfaces coupling heterostructure with
high exposure of BiOI {001} active facets for robust and nonselective
photocatalysis. Appl. Catal., B 2016, 199, 75−86.
(28) Hao, L.; Huang, H.; Guo, Y.; Zhang, Y. Multifunctional
Bi2O2(OH)(NO3) Nanosheets with {001} Active Exposing Facets:
Efficient Photocatalysis, Dye-Sensitization, and Piezoelectric-Catal-
ysis. ACS Sustainable Chem. Eng. 2018, 6 (2), 1848−1862.
(29) Liu, Y.; Mi, X.; Wang, J.; Li, M.; Fan, D.; Lu, H.; Chen, X. Two-
dimensional SnS2 nanosheets exfoliated from an inorganic−organic
hybrid with enhanced photocatalytic activity towards Cr(vi)
reduction. Inorg. Chem. Front. 2019, 6 (4), 948−954.
(30) Chen, F.; Huang, H.; Ye, L.; Zhang, T.; Zhang, Y.; Han, X.; Ma,
T. Thickness-Dependent Facet Junction Control of Layered BiOIO3
Single Crystals for Highly Efficient CO2 Photoreduction. Adv. Funct.
Mater. 2018, 28, 1804284.
(31) Zhang, K. L.; Liu, C. M.; Huang, F. Q.; Zheng, C.; Wang, W. D.
Study of the electronic structure and photocatalytic activity of the
BiOCl photocatalyst. Appl. Catal., B 2006, 68 (3), 125−129.
J
DOI: 10.1021/acs.inorgchem.9b02328
Inorg. Chem. XXXX, XXX, XXX−XXX