Interfacial synergy of Pd sites and defective BiOBr for promoting the solar-driven selective oxidation of toluene

Article abstract of DOI:10.1039/d0ta05733a

Metal-modified semiconductors are being deemed as one of the most promising photocatalysts for various applications. Although great efforts have been devoted to developing a variety of metal-modified semiconductor photocatalysts, the exact functions of their interfaces in governing photocatalytic processes still remain elusive. Herein, the interfacial synergy of metal sites and defective semiconductor with oxygen vacancies (V_Os) was investigated toward the photocatalytic selective oxidation of toluene, by taking the Pd/BiOBr photocatalyst as an example. The presence of Pd induces the generation of more V_Os on the BiOBr surface due to the electronic interaction at the Pd-BiOBr interface. The coexistence of the Pd and V_Osites on BiOBr enables the favorable adsorption of O₂and toluene molecules. The Pd-BiOBr interface governs the charge separation and prompts the activation of O₂and toluene, leading to 1.5 times the activity of BiOBr-V_Ofor the photocatalytic selective oxidation of toluene to benzaldehyde with a high selectivity (>99%). Moreover, the typical influencing factors, such as the illumination intensity and toluene concentration, were optimized to improve the photocatalytic efficiency. The active species and intermediates in the photocatalytic reaction were identified by a series of controlled experiments, as well asin situESR measurements. Therefore, both experimental and theoretical results provide the direct evidence to understand the key roles of the interfacial Pd and V_Osites in enhancing photocatalysis toward the selective oxidation of toluene.

Full text of DOI:10.1039/d0ta05733a

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Page 1 of 42
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Interfacial Synergy of Pd Sites and Defective BiOBr for
Promoting Solar-Driven Selective Oxidation of Toluene
#
,a
#,a
a
a
b,*
a,*
Xiaoli Li , Ting Wang , Xueqin Tao , Ganhua Qiu , Can Li , Benxia Li
a
Department of Chemistry, School of Science, Zhejiang Sci-Tech University, Hangzhou 310018,
China
b Institute of optoelectronic materials and devices, College of optical and electronic technology,
China Jiliang University, Hangzhou 310018, China
*
Corresponding author. Prof. Benxia Li, Email: libx@mail.ustc.edu.cn; Prof. Can Li, Email:
Canli@cjlu.edu.cn
#
X. L. Li and T. Wang contributed equally to this work.
1

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ABSTRACT: Metal-modified semiconductors are being deemed as one kind of the
most promising photocatalysts for various applications. Although great efforts have
been devoted to developing a variety of metal-modified semiconductor photocatalysts,
the exact functions of their interfaces in governing photocatalytic processes still
remain elusive. Herein, the interfacial synergy of metal sites and defective
semiconductor with oxygen vacancies (V s) is investigated toward the photocatalytic
O
selective oxidation of toluene, by taking the Pd/BiOBr photocatalyst as an example.
The presence of Pd induces to generate more V s on BiOBr surface due to the
O
electronic interaction at Pd-BiOBr interface. The coexistence of Pd and V sites on
O
BiOBr enables the favorable adsorption of O and toluene molecules. The Pd-BiOBr
2
interface governs the charge separation and prompts the activation of O and toluene,
2
leading to a 1.5-times activity of BiOBr-V for photocatalytic selective oxidation of
O
toluene to benzaldehyde with a high selectivity (> 99%). Moreover, the typical
influencing factors, such as illumination intensity and toluene concentration, are
optimized to improve the photocatalytic efficiency. The active species and
intermediates in the photocatalytic reaction are identified by a series of controlled
experiments as well as in situ ESR measurements. Therefore, both
experimental and theoretical results provide the direct evidence to understand the key
roles of interfacial Pd and V sites in enhancing the photocatalysis toward selective
O
oxidation of toluene.
Keywords: metal-semiconductor interface; oxygen vacancy; synergetic effect;
photocatalysis; selective oxidation.
2

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Introduction
3
The selective transformation of sp C−H bonds in alkanes or aromatics for the
production of value-added products has been always an attractive issue of great
1
significance for both the studies in lab and the chemical productions. Especially, the
selective oxidation of the organic pollutant toluene to valuable benzaldehyde under
mild and eco-friendly conditions is one of the most desirable reactions for fine
chemicals and pharmaceuticals production.2,3 The conversion of toluene to
benzaldehyde in the present industrial processes is achieved mainly by chlorination of
4
toluene and subsequent hydrolysis, which is usually plagued by harsh reaction
conditions, toxic acidic waste generation, and lower selectivity of benzaldehyde.
Recently, the selective oxidation of toluene via the heterogeneous photocatalysis
using molecular oxygen as an oxidant is attracting intensive interest,5-8 because of its
distinct advantages for solar energy utilization and high selectivity to the target
products. Notwithstanding, the photocatalytic selective oxidation of toluene with O2
to benzaldehyde is still a more challenging task, in comparison with the selective
oxidation of active and expensive alcohol substrates,9-11 due to the high bond
3
dissociation energy of C(sp )−H bonds and the low adsorbability of toluene
molecules.12,13 Therefore, it is continuously desired to develop heterogeneous
photocatalysts with high activity for the selective oxidation of toluene to
benzaldehyde.
In photocatalytic reactions, the photoexcited electrons and holes are separated to
drive reduction and oxidation, respectively. Engineering the adjacent active sites for
3

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the respective reactions driven by electrons and holes could accelerate the reduction
1
4
and oxidation occurring in series. The photocatalytic selective oxidation of toluene
to benzaldehyde using O as an oxidant generally involves the electron-driven
2
3
reduction of O molecules and the hole-driven oxidation of C(sp )−H bonds in toluene,
2
where the reactive oxygen species (ROSs) generated from O reduction can react
2
rapidly with the hole-activated toluene intermediate to produce benzaldehyde.5,15,16
Engineering the adjacent active sites for activating O and toluene will be
2
certainly of much help in accelerating the selective oxidation of toluene. Constructing
the metal−oxide interfaces provides a new opportunity to tune different active sites
and enable their synergetic effects based on the interfacial interaction.17-19 Depositing
metal nanoparticles (NPs) on oxide semiconductor is an effective strategy to improve
the photocatalytic activity, because the metal NPs can not only act as electron traps to
2
0
facilitate the interfacial charge separation and transfer, but also offer the active sites
for the adsorption and activation of substrate molecules.21,22 In such heterostructure
photocatalysts, the rational construction of heterogenous interfaces plays a critical
role in determining the charge transfer efficiency and consequent reaction activity.23,24
The metal-oxide interfacial interaction can induce the generation of a high
concentration of oxygen vacancies (V s) at the interface, forming the adjacent
O
2
5-27
metal-V dual active sites to promote synergistically the photocatalytic reactions.
O
Moreover, the introduction of V defects can further modulate the energy band
O
structure and surface active sites to enhance the light absorption, charge mobility, and
catalytic activity of the photocatalysts.28-30 Therefore, constructing the metal-oxide
4

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interfaces can achieve synchronously the multiple purposes of tuning energy band
structure, inhibiting the electron-hole recombination and engineering active sites of
photocatalysts. These advantages inspire that creating a metal/oxide photocatalyst
with metal-V dual active sites at the interface holds great promise to enhance the
O
efficiency of photocatalytic selective oxidation of toluene.
To confirm the above-mentioned opinions, bismuth oxybromide (BiOBr) was
selected as a model of oxide semiconductor due to its suitable energy band levels,
2
+
–
unique layered structure with alternatively arranged [Bi O ] slabs and double Br
2
2
slabs, as well as the special {001} facets being inclined to generate V s under mild
O
conditions.31,32 Besides, Pd NPs have been recognized as versatile catalysts in various
organic oxidation reactions, because of their outstanding capability for O activation
2
1
− 33,34
to produce ROSs ( O and •O ).
Although a few previous investigations on the
2
2
preparation of Pd/BiOBr photocatalysts and their applications in degradation of
organic pollutants have been reported,35-38 the exact functions and synergetic effects
of different active sites at Pd-BiOBr interface for promoting the photocatalytic
selective oxidation were seldom studied. This work focuses on constructing the
Pd/BiOBr photocatalyst with metal-V dual active sites and revealing their synergy
O
for photocatalytic selective oxidation of toluene to produce benzaldehyde. It is found
that the Pd-BiOBr interfacial interaction not only stabilizes the small Pd NPs but also
induces more V s on BiOBr surface. Both experimental results and theoretical
O
calculations indicate that the hole-driven toluene oxidation at the Pd-BiOBr interface
is easier to occur than that directly on the BiOBr surface without Pd NPs. Meanwhile,
5

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the electrons trapped on Pd sites expedite the O activation to afford sufficient ROSs.
2
The coexistence of Pd and V sites at Pd-BiOBr interface obviously improves the
O
efficiency of photocatalytic selective oxidation of toluene to benzaldehyde.
Experimental
Chemicals
Bismuth nitrate pentahydrate (Bi(NO ) ·5H O), polyvinylpyrrolidone (PVP-K30),
3
3
2
potassium bromide (KBr), ammonium tetrachloropalladate ((NH ) PdCl ), ethylene
4
2
4
glycol (EG), mannitol, ammonium oxalate (AO), benzoquinone (BQ), isopropanol
IPA), potassium persulfate (K S O ), β-carotene, catalase (≥ 200000 unit/g),
superoxide dismutase (SOD, ≥ 1400 units/mg), 3,3’,5,5’-tetramethylbenzidine
(
2
2
8
(
TMB), 5,5-dimethyl-pyrroline-N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine
TEMP) were purchased from Aladdin Biochemical Technology Co. Ltd. Toluene,
(
p-chlorotoluene, p-bromotoluene, p-methyltoluene and p-methoxytoluene were
purchased from Shanghai Macklin Biochemical Co. Ltd. All chemical regents were
used without further purification.
Synthesis of BiOBr nanostructures
The nanosheet-assembled BiOBr nanostructures were synthesized by a solvothermal
process. Typically, 1 mmol Bi(NO ) ∙5H O and 1 mmol KBr were dissolved in 30 mL
3
3
2
ethylene glycol in sequence to form a transparent solution. Then 0.2 g PVP and 0.05 g
mannitol were dissolved in the solution. After 20 min stirring, the solution was
transferred into a 50 mL solvothermal autoclave which was sealed and kept at 160 °C
6

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for 8 h. After the reaction, the precipitate was collected by centrifugation, washed
with deionized water and ethanol consecutively, and dried at 60 °C.
Preparation of Pd/BiOBr photocatalysts
The Pd/BiOBr photocatalysts were prepared by photodeposition of Pd NPs on the
nanosheets-assembled BiOBr nanostructures. Typically, 20 mg BiOBr sample was
dispersed in 10 ml deionized water by ultrasonic, and a certain volume of
(
NH ) PdCl aqueous solution (0.01 M) was injected into the BiOBr suspension. After
4 2 4
stirred for 30 min in dark, the suspension was exposed to a LED irradiation ( = 365
2
nm, optical power density = 2.04 mW/cm ) for 10 min with continuously stirring. The
final product was obtained by centrifugation, washing and drying in sequence.
Characterization
X-ray diffraction (XRD) analysis was performed on Shimadzu XRD-6000
diffractometer using a monochromatic Cu K radiation with a scan rate of 5°/min.
Scanning electron microscope (SEM) images were recorded by a Zeiss Ultra 55
instrument with a 20 kV accelerating voltage. Transmission electron microscope
(TEM) and high resolution TEM (HRTEM) images were taken on a Hitachi S4800
instrument. The specific surface areas and pore size distributions of the samples were
calculated by Brunauer-Emmet-Teller (BET) and Barrett-Joyner-Halenda (BJH)
models, respectively, on the basis of N adsorption/desorption process performed on a
2
Micromeritics ASAP 2020 instrument. X-ray photoelectron spectra (XPS) were
detected by a thermal SCIENTIFIC ESCALAB 250Xi X-ray photoelectron
spectrometer, and the binding energies were calibrated internally by the C 1s at 284.8
7

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eV. UV–vis diffuse reflectance spectra (DRS) were recorded on a UV–vis
spectrometer (UV-2600, Shimadzu, Japan) with BaSO as the reference sample. The
4
photoluminescence (PL) properties of the samples were analyzed by Edinburgh
FL/FS900 spectrophotometer using the excitation of 250 nm wavelength.
Time-resolved fluorescence decay spectra were acquired according to the
time-dependent single photon counting method on the Edinburgh FS5 fluorescence
spectrometer. The electron spin resonance (ESR) measurements were performed at
room temperature on a Bruker model JEOL JES-FA200 spectrometer, with using the
same quartz capillary tubes for all the sample testing. The photoelectrochemical
properties of the materials were tested by a three-electrode system referring to our
previous report.39
Photocatalytic tests
The photocatalytic reactions were performed under the irradiation of Xe lamp
(PLS-SXE300, Beijing Perfectlight Technology Co. Ltd.). For a typical reaction, 5 mg
photocatalyst, 0.05 mmol toluene and 2 mL acetonitrile were mixed in a transparent
quartz test tube which has a diameter of 1.5 cm and a length of 12 cm. After the
reaction suspension was bubbled with O for 30 min, the test tube was sealed by a
2
balloon full of O (~1 atm) and then exposed to the irradiation. After 5 h of
2
irradiation, the reaction solution was collected, centrifuged, and filtered through a
syringe filter to remove photocatalyst particles. The filtrate was analyzed by a gas
chromatograph (GC-2014C, Shimadzu) with a KB1701 capillary column and using
bromobenzene as the internal standard, to determine the content of each product. The
8

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conversion of toluene and the selectivity for producing benzaldehyde were calculated
by Eqs. (1)-(2):
∑
푐표푛푡푒푛푡 (푚푚표푙) 표푓 푒푎푐ℎ 푝푟표푑푢푐푡 푎푛푎푙푦푧푒푑 푏푦 퐺퐶
퐶표푛푣푒푟푠푖표푛 (%) =
푆푒푙푒푐푡푖푣푖푡푦 (%) =
× 100%
(1)
(2)
푠푢푏푠푡푟푎푡 (푚푚표푙)
푐표푛푡푒푛푡 표푓 푐표푟푟푒푠푝표푛푑푖푛푔 푝푟표푑푢푐푡 (푚푚표푙)
푐표푛푡푒푛푡 (푚푚표푙) 표푓 푒푎푐ℎ 푝푟표푑푢푐푡
× 100%
∑
Identification of photocatalytic reactive species
The reactive species produced in the photocatalytic selective oxidation of toluene,
1
2-
such as carbon radical, O and ∙O , were detected by ESR spectroscopy, in which
2
2
-
1
DMPO was used to trap ∙O and carbon radicals and TEMP was used to trap O . In
2
addition, the reactive species were also identified by a series of controlled
experiments with adding various scavengers into the photocatalytic reaction
suspension to scavenge the corresponding reactive species. For example, ammonium
oxalate, benzoquinone, isopropanol, K S O and BHT were used as scavengers to trap
2
2
8
+
2-
-
holes (h ), ∙O , hydroxyl radical (∙OH), electrons (e ) and carbon radicals,
respectively. TEMPO can scavenge almost all of the radicals.
Theoretical calculations
The surfaces of BiOBr-Vo (001) with and without Pd cluster were built, respectively,
where the vacuum space along the z direction was set to be 20 Å. Then the O and
2
C H CH molecules were adsorbed on the surfaces, respectively. The three atomic
6
5
3
layers at bottom were fixed and the three atomic layers at top were relaxed adequately
for all systems. The first principles calculations in the framework of density
functional theory (DFT) were carried out based on the Cambridge Sequential Total
Energy Package known as CASTEP. The exchange–correlation functional under the
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generalized gradient approximation (GGA) with norm-conserving pseudopotentials
and Perdew–Burke–Ernzerhof (PBE) functional was adopted to describe the electron–
electron interaction. An energy cutoff of 750 eV was used and a k-point sampling set
-1
of 551 was tested to be converged. A force tolerance of 0.01 eV∙Å , energy
-7
-4
tolerance of 5.010 eV per atom and maximum displacement of 5.010 Å were
considered. The adsorption energy of O and C H CH molecules were calculated by
2
6
5
3
4
0
Eq.(3), where E , E and E denote the energy of adsorbed system, clear surface,
*
A
*
A
and adsorbate (A = O or C H CH ), respectively.
2
6
5
3
∆
E = E – E – E
A
(3)
A
*A
*
Results and discussion
Compositions and structures of BiOBr and Pd/BiOBr photocatalysts
The Pd/BiOBr heterostructure photocatalyst was prepared via a two-step process
shown in Fig. 1a, where the BiOBr flower-like nanostructures were synthesized
through a solvothermal reaction and then modified by Pd NPs via LED-light induced
deposition. In the synthesis, the addition of mannitol has distinct influence on the
sizes and surface structures of BiOBr nanostructures, because the polyhydroxyl
characteristics of mannitol makes it a good multi-dentate ligand strongly interacting
3
+
41,42
with Bi ions.
The BiOBr flower-like spheres synthesized with mannitol have the
relatively more uniform diameters of ~ 600 nm and the nanosheets for building the
flower-like spheres show the less average thickness about 15 nm (Fig. S1a), compared
with the BiOBr(no mannitol) sample synthesized in the absence of mannitol (Fig.
S1b). XRD patterns (Fig. S1c) of both the BiOBr samples are well matched with that
1
0

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of tetragonal BiOBr (JCPDS No. 9-393), while the XRD peaks of BiOBr sample are
obviously wider than those of BiOBr(no mannitol), confirming the smaller crystalline
size of BiOBr sample. Moreover, ESR spectra (Fig. S1d) indicate that the addition of
mannitol in the synthesis can induce the generation of more V defects in BiOBr.
O
Therefore, the BiOBr flower-like nanostructures synthesized in the presence of
mannitol are used to prepare the Pd/BiOBr photocatalysts. After photodepositing Pd
NPs, the crystalline phase of BiOBr remains unchanged in the Pd(x)/BiOBr samples
with various theoretical Pd contents (x) (Fig. 1b and Fig. S2), whereas the diffraction
peaks of Pd are unobservable due to the small sizes and high dispersity of Pd NPs. Fig.
1
c-f display SEM and TEM images of the Pd/BiOBr sample with a theoretical Pd
content of 1.0 wt% which was optimized to possess the best photocatalytic activity,
and the Pd/BiOBr sample mentioned below is this sample unless otherwise specified.
The Pd/BiOBr heterostructures maintain well the flower-like morphology of BiOBr
nanostructures. HRTEM image (Fig. 1d) of Pd/BiOBr sample presents two sets of
lattice structures, and the interplanar spacings of 2.74 and 2.25 Ǻ are corresponding to
those of (110) plane in tetragonal BiOBr and (111) plane in cubic Pd, respectively.
The sizes of Pd NPs in the Pd/BiOBr sample are estimated according to TEM
observation (Fig. 1e), which indicates that the Pd NPs with a small average size of
~4.0 nm are highly dispersed on the nanosheets of BiOBr nanostructures. Moreover,
the uniform distribution of Pd element in the Pd/BiOBr sample is further confirmed
by SEM-associated EDX element mapping (Fig. 1f and g). These results demonstrate
that the small Pd NPs have been evenly anchored on the nanosheets of BiOBr
1
1

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nanostructures. The surface structures of BiOBr and Pd/BiOBr samples are
determined by BET and BJH models, respectively, on the basis of N2
adsorption/desorption process (Fig. S3). Both the samples exhibit the similar
adsorption/desorption isotherms and pore size distribution profiles. The BET specific
2
-1
surface areas of BiOBr and Pd/BiOBr are 13.7 and 11.5 m ∙g , respectively, and their
average pore sizes are 29.9 and 28.3 nm (Table S1), indicating that Pd loading has
little influence on the surface area and pore size distribution of BiOBr nanostructures.
XPS spectra (Fig. 2a-e) provide further information about the surface element
compositions and their chemical states of BiOBr before and after loading Pd NPs.
Both the XPS survey spectra (Fig. 2a) show notable signals of Bi, O, Br, and C
elements, whereas the signal of Pd is hardly observed in the survey spectrum of
Pd/BiOBr sample due to the low Pd content. The high-resolution Pd 3d spectrum (Fig.
2
b) of Pd/BiOBr sample can be fitted with two doublets of Pd 3d5/2 and Pd 3d3/2 from
spin-orbit splitting. The predominant doublet at 335.5-340.5 eV is characteristic of
0
metallic Pd , and the other doublet with lower intensity at higher binding energies of
2
+ 43
3
37.0-342.5 eV is corresponding to the oxidized state of Pd . The presence of a
little Pd2+ can be ascribed to the electron transfer from surface Pd atoms to the
4
4
chemisorbed oxygen. The XPS peaks of Bi 4f (Fig. 2c) and Br 3d (Fig. 2d) in both
BiOBr and Pd/BiOBr samples are assigned to Bi3+ cations and Br anions,
respectively,45 whereas the peaks of Pd/BiOBr sample shift towards the higher
binding energies with respect to the ones of BiOBr sample, suggesting that the
electron transfer occurs from BiOBr to Pd at Pd-BiOBr interface due to a large
-
1
2

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difference in the work functions of Pd (5.11 eV) and BiOBr (2.93 eV).44,46,47 The O 1s
spectra (Fig. 2e) of both BiOBr and Pd/BiOBr samples are fitted with three peaks at
5
29.8/530.1, 531.2/531.5, and 531.9/532.2 eV, respectively, corresponding to the
3
0
lattice oxygen of BiOBr, the adsorbed oxygen at V sites and the hydroxyl groups.
O
The binding energies of O 1s in Pd/BiOBr sample also present positive shifts in
comparison with BiOBr sample, which can also be ascribed to the intimate interfacial
4
8
integration and interaction between Pd and BiOBr in forming heterostructures. The
adsorbed oxygen species at V sites in Pd/BiOBr sample account for a higher
O
proportion (30.5%) of the O 1s peak, compared with that (24.4%) for BiOBr sample,
suggesting a higher V concentration induced by Pd loading. In ESR spectra (Fig. 2f),
O
the characteristic V signal with a g factor of 2.0 is observed for both BiOBr and
O
Pd/BiOBr samples. Moreover, the higher signal intensity indicates the increase in VO
concentration of Pd/BiOBr sample compared with that of pure BiOBr, meaning that
Pd NPs induces the generation of more V defects in BiOBr due to the interfacial
O
interaction between Pd and BiOBr. The interfacial interaction stabilizes small Pd NPs
and V s, which will be beneficial to the excitation, migration and separation of
O
photogenerated electrons and holes.
Photoabsorption and photoexcited charge separation
The photoabsorption of BiOBr and Pd/BiOBr samples are analyzed by UV-vis DRS
spectroscopy, and the Kubelka-Munk transformed absorption spectra are shown in Fig.
3
a. The BiOBr sample shows a strong absorption in UV region (  400 nm) and a
4
9
weak tailing absorption in visible region due to the presence of surface defects. For
1
3

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Pd/BiOBr sample, the optical absorption in visible region is enhanced by introducing
Pd NPs, and the absorption edge of BiOBr shifts a little to longer wavelength. The
room-temperature steady-state photoluminescence (PL) spectra of both BiOBr and
Pd/BiOBr samples are employed to evaluate the photoexcited electron-hole separation
efficiencies in the photocatalysts (Fig. 3b). Under an excitation wavelength of 250
nm, BiOBr sample shows a very strong emission band around 390 nm derived from
the indirect radiative recombination of photoexcited electrons and holes.50 In
comparison, the Pd/BiOBr heterostructures exhibit a remarkably quenched
fluorescence emission, suggesting that the recombination of photoexcited charge
carries is suppressed in the Pd/BiOBr sample. The time-resolved photoluminescence
(TRPL) analysis is further used to determine the photoexcited charge carrier dynamics
of BiOBr and Pd/BiOBr samples. Both the TRPL decay curves (Fig. 3c) can be fitted
by the following biexponential function:
I  A exp(t / )  A exp(t / )
(4)
(t)
1
1
2
2
where τ and A denote the fluorescent lifetime and its weighing factor,
i
i
respectively.51,52 The average fluorescent lifetimes (τ ) of BiOBr and Pd/BiOBr are
m
0
.84 and 0.58 ns (Table S2), respectively. In the present case, the electron transfer
from BiOBr to Pd NPs guarantees the efficient separation of photoexcited electrons
and holes, thus shortening the fluorescent lifetime of Pd/BiOBr heterostructures.51,52
To further demonstrate the photoexcited charge separation efficiencies and electron
transfer abilities of BiOBr and Pd/BiOBr photocatalysts, their photocurrent responses
and electrochemical impedance spectroscopy (EIS) Nyquist plots were measured
1
4

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under the Xe lamp irradiation. The higher photocurrent intensity (Fig. 3d) of
Pd/BiOBr suggests the more efficient separation of photoexcited holes and
5
3
electrons. The EIS Nyquist plot (Fig. 3e) of Pd/BiOBr shows a smaller arc radius
than that of BiOBr sample, indicating that the introduction of Pd NPs can promote the
5
4
charge transfer. Fig. 3f shows the Mott−Schottky (M-S) plots of the BiOBr and
Pd/BiOBr photoelectrodes, where the positive slopes of the linear regions indicate the
characteristic of n-type semiconductor for BiOBr nanostructures before and after
loading Pd NPs.55,56 Moreover, the slopes of the linear regions is inversely
proportional to the charge carrier density (N ) of the photoelectrode.57,58 The declined
D
slope in the M–S plot of Pd/BiOBr sample, compared with that of BiOBr sample,
reveals the higher charge carrier density in Pd/BiOBr.
DFT calculations were further performed to elucidate the electronic interaction at
Pd–BiOBr interface. The optimized structures of BiOBr-V (001) without and with
O
Pd cluster are shown in Fig. S4. The BiOBr-V (001) surface was built by cutting the
O
crystal lattice along (001) plane with Bi atomic layer as the terminated surface, with
one V site being introduced. The introduction of V site leads to local distortion of
O
O
BiOBr (001) surface. The BiOBr-V (001) with Pd cluster was built by anchoring a
O
Pd cluster on the BiOBr-V (001) surface. Fig. 4a shows the partial density of states
1
2
O
(PDOS) of two systems. The conduction band (CB) of BiOBr-VO (001) is
predominated by Bi 6p orbitals, while the valence band (VB) is mainly occupied by
Br 4p orbitals hybridized with the low-density O 2p state.31,59 In contrast, for
BiOBr-V (001) with Pd cluster, Pd 4d electron state contributes significantly to
O
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enhancing the charge density above the valence band maximum (VBM) of BiOBr,
which is greatly beneficial to the generation and migration of photoinduced electrons.
The charge density difference (Fig. 4b) of BiOBr-V (001) with Pd cluster provides
O
further insight into the charge density variation of the Pd-BiOBr interface, indicating
that the Pd sites at the interface are the electron accumulation area. This confirms the
obvious electronic interaction at the Pd-BiOBr interface and electrons are trapped by
the interfacial Pd sites. At the Pd-BiOBr interface, electrons transfer from BiOBr to
Pd for aligning the Fermi levels, due to the larger work function (5.11 eV) of Pd than
that (2.93 eV) of BiOBr,46,47 forming the Schottky barrier at the interface (Fig. 4c).60
The Schottky barrier can prevent the recombination of photoinduced electron–hole
pairs. The interfacial electron transfer from BiOBr to Pd leaves positive charges on
BiOBr, which has been verified by XPS spectra described above where the electronic
binding energies of BiOBr in Pd/BiOBr sample shift positively, compared with those
of BiOBr without Pd NPs. In consequence, the electrons are trapped by the Pd sites in
the vicinity of the interface; meanwhile the holes migrate toward the interface around
the Pd NPs for the charge balance, as shown in Fig. 4d. The resultant
charge-separated states at the Pd-BiOBr interface (electrons in Pd sites and holes in
BiOBr) are highly conducive to the subsequent chemical transformations consisting of
reduction and oxidation steps.
Photocatalytic performance for selective oxidation of toluene
Based on all the analysis results above, the unique interface of Pd/BiOBr
heterostructures predicts its superior photocatalysis for selective oxidation of toluene
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with O as an oxidant (Fig. 5a). The photocatalytic performance of BiOBr and
2
Pd/BiOBr with different Pd loadings was screened by the selective oxidation of
toluene (0.05 mmol toluene in 2 mL acetonitrile) under UV-vis irradiation with an
−
2
optical power density of 200 mW∙cm . As shown in Fig. 5b and Table S3, these
photocatalysts exhibit high selectivity (> 99%) for producing benzaldehyde from
toluene oxidation. The BiOBr nanostructures without Pd NPs show the mediocre
photocatalytic activity with a toluene conversion rate of 317.8 μmol∙gcat-1∙h . After
loading Pd NPs, the selective oxidation of toluene is further improved. When the
Pd(x)/BiOBr samples with different Pd mass fractions (x wt.%) are used as
photocatalysts, the toluene conversion rate presents a peak-like variation with the Pd
loading contents and achieves a maximum value of 476.8 μmol∙gcat-1∙h over the
Pd(1.0)/BiOBr photocatalyst. The Pd(1.5)/BiOBr and Pd(2.0)/BiOBr samples exhibit
the gradually depressed photocatalytic activities, which can be ascribed to the
formation of larger Pd NPs (Fig. S5) with the reduced active sites. The results indicate
that the dispersion of Pd NPs have an obvious effect on the photocatalytic selective
oxidation of toluene. In addition, the BiOBr(water) sample consisting of large
nanosheets (Fig. S6) is synthesized by a hydrothermal process in the absence of any
organic additive. The Pd/BiOBr(water) and Pd/BiOBr(no mannitol) samples with
each theoretical Pd content of 1.0 wt% are also prepared by the same photodeposition
process as that for the preparation of Pd/BiOBr photocatalyst. By comparison,
the activities of various photocatalysts in an increasing order are: BiOBr(water) <
BiOBr(no mannitol) < Pd/BiOBr(water) ≈ BiOBr < Pd/BiOBr(no mannitol) <
-1
-1
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Pd/BiOBr, as shown in Fig. S7 and Table S3. The results indicate that the critical
factors influencing the photocatalytic activities toward selective oxidation of toluene
are Pd loading as well as the V concentration in BiOBr nanostructures. The
O
flower-like nanostructures of BiOBr synthesized by the solvothermal process with
mannitol have the highest V concentration, compared with BiOBr(water) and
O
BiOBr(no mannitol). As a result, the Pd/BiOBr photocatalyst exhibits the best
photocatalytic performance due to the synergy of Pd and V sites at the interface of
O
Pd/BiOBr photocatalyst. Furthermore, as shown in Fig. 5c, the Au/BiOBr
photocatalyst exhibits a lower toluene conversion (331.9 μmol∙gcat-1 ∙h ) than that
from the Pd/BiOBr photocatalyst (476.8 μmol∙gcat-1∙h ), confirming the favorable
function of Pd NPs in improving the photocatalytic activity toward selective oxidation
of toluene to benzaldehyde. This should be attributed to the fact that oxygen
-1
-1
6
1
molecules are more easily activated on the surface of Pd NPs than Au ones. The
calcinations of BiOBr and Pd/BiOBr samples at 350 °C in air lead to the remarkable
drops in their photocatalytic activities because V s in the samples can be filled by
O
oxygen from air during the calcination process, which further testify that the
integration of well-dispersive Pd sites and abundant V s in Pd/BiOBr heterostructures
O
is crucial for promoting the photocatalytic selective oxidation of toluene. The
temperature of the photocatalytic suspension with Pd/BiOBr is measured to be 45 ℃
after being exposed to the irradiation for 5 h. Whereas, the toluene conversion cannot
occur over the Pd/BiOBr catalyst at 45 ℃ in dark even after heating for 5 h (Fig. 5c),
excluding the thermal effect on the photocatalytic selective oxidation of toluene over
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Pd/BiOBr under the present conditions. In addition, the toluene conversion hardly
proceeds when the photocatalytic reaction is performed in high purity N atmosphere,
2
confirming the necessity of O in photocatalytic selective oxidation of toluene.
2
The light intensity, which influences the photoexcitation of photocatalyst, also
affects the photocatalytic efficiency of toluene oxidation. The performance of the
optimal Pd/BiOBr photocatalyst is further probed under the UV-visible light with
varied optical power densities, as shown in Fig. 5d and Table S4. The conversion rate
of toluene to benzaldehyde is enhanced from 333.8 to 476.8 μmol·gcat-1·h as the
-1
−
2
optical power density of irradiation increases from 100 to 200 mW∙cm . The stronger
irradiation induces the generation of more electrons and holes, enhancing the
photocatalytic efficiency of selective toluene oxidation. However, the photocatalytic
conversion of toluene over Pd/BiOBr declines when the optical power density is
−
2
further increased to 300 mW∙cm . It has been reported that the plasmonic effect of Pd
nanocrystals could generate a reverse flow of electrons from Pd to the CB of adjacent
semiconductor under strong illumination, which could lower the electron density of
3
3
Pd surface in opposition to the function of the Schottky junction. Therefore, the
transfer of electrons from BiOBr to Pd dominates when the irradiation is relatively
−
2
weak (< 200 mW∙cm ), where the charge densities on Pd and BiOBr increase with
the enhancive incident illumination, thus enhancing the photocatalytic efficiency;
whereas, the efficiency is lowered by the plasmonic effect of Pd NPs under the
−
2
stronger illumination (> 200 mW∙cm ). Fig. 5e and Table S5 show the effect of the
toluene dosage on its oxidation conversion rate over the Pd/BiOBr photocatalyst. The
1
9

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higher toluene loading in the photocatalytic system increases the possibility of toluene
adsorption on the active sites of photocatalyst, resulting in a higher conversion rate of
toluene. When 9.4 mmol of toluene is added initially, the conversion rate achieves as
high as 6022.5 μmol·gcat−1·h−1.
Subsequently, the Pd/BiOBr photocatalyst was further used toward the selective
oxidation of several toluene derivatives with different substituents under the same
-2
conditions (UV−visible irradiation of 200 mW∙cm , 0.05 mol toluene in 2 mL
acetonitrile). The results (Fig. 6a and Table S6) indicate that the selective oxidation of
toluene derivatives into the aromatic aldehydes can also achieve the relatively high
conversion rates (320.6−549.5μmol·gcat-1·h ) and excellent selectivity ( > 99%) over
the Pd/BiOBr photocatalyst. The substrates with electron-donating para substituents
-1
(
−CH , −OCH ) exhibit higher reactivity than the ones with electron-withdrawing
3 3
para substituents (−F, −Cl), because the electron-donating groups on benzene ring
+
3
6,62,63
facilitate the h -driven C(sp )−H oxidation.
The recyclability of the Pd/BiOBr
photocatalyst was examined by the selective oxidation of toluene with 5 h irradiation
for each cycle (Fig. 6b and Table S7). After five photocatalytic cycles, only a slight
decrease in the toluene conversion rate is observed. Both the excellent activity and the
high selectivity are well maintained after 25 h of the photocatalytic reaction. XRD,
TEM and XPS analyses on the recycled Pd/BiOBr photocatalyst (Figs. 6c-f)
demonstrate that the crystalline phase, microstructures and valence states of typical
elements in the recycled Pd/BiOBr photocatalyst remain unchanged, verifying the
high stability of Pd/BiOBr photocatalyst for a long-term photocatalytic reaction.
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Insight into the photocatalytic mechanism
To acquire more insight into the photocatalytic mechanism of selective toluene
oxidation on the Pd/BiOBr photocatalyst, the contributions of various active species
to this reaction were investigated by the controlled experiments carried out in the
presence of the radical scavengers. As displayed in Fig. 7a, the addition of
isopropanol (IPA) acting as a hydroxyl radical (•OH) scavenger results in only a slight
decrease in the toluene conversion rate, indicating that •OH radical is scarcely
involved in the oxidation of toluene. In contrast, the conversion rate of toluene was
+
extremely reduced by adding ammonium oxalate (AO) for eliminating holes (h ) or
butylated hydroxytoluene (BHT) for clearing off carbon-centered radicals which are
generated usually from the hole-activated organic substrates.5,64 In addition, the
-
addition of p-benzoquinone (p-BQ) for clearing off superoxide radical (•O ) also
2
causes a remarkable declination in the conversion rate of toluene, suggesting the
considerable contribution of •O2- in this reaction. When tetra-methylpiperidine
N-oxide (TEMPO) is introduced to quench all the radicals in the reaction system, the
toluene oxidation is almost completely suppressed, which confirms that the
photocatalytic selective oxidation of toluene undergoes a radical-initiated reaction
pathway.16,65 These results demonstrate that h , carbon-centered and •O radicals
+
-
2
dominate the photocatalytic process over Pd/BiOBr catalyst for selective oxidation of
toluene. The active radicals generated in the photocatalytic reaction of toluene
oxidation over BiOBr and Pd/BiOBr photocatalysts are further identified and
compared by in situ ESR detection (Fig. 7b), respectively. The ESR signal is hardly
2
1

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observed in the reaction solution with whether BiOBr or Pd/BiOBr in dark. Under the
irradiation, distinct peaks emerge in both the reaction systems, where the sextet peaks
(
★) are assigned to DMPO-carbon-centered radicals and the quartet peaks () belong
-
64,66
to DMPO-•O species.
Obviously, the signals of active radicals generated from
2
Pd/BiOBr photocatalyst is more conspicuous than those from BiOBr, confirming the
enhanced photocatalysis of Pd/BiOBr.
The activation of molecular oxygen usually plays a crucial role in the selective
6
7
oxidation of organics with O as an oxidant. The ROSs stemmed from O activation,
2
2
−
1
generally including superoxide radical (∙O ) and singlet oxygen ( O ), can react
2
2
rapidly with the pre-adsorbed organic molecules or the organic intermediates to
accomplish the oxidation reactions.68,69 Therefore, the photocatalytic O activation
2
ability of Pd/BiOBr catalyst and the photogenerated ROSs were probed by TMB
oxidation, on the basis of monitoring the absorbance evolution at 370 nm of TMB
solution along the irradiation time (Figs. S8-10 and Fig. 7c).70-72 The time-dependent
absorption intensity of 370 nm peak from TMB solution without scavenger (Fig. S8
and Fig. 7c) indicates the superior O activation ability of Pd/BiOBr than that of pure
2
BiOBr. In addition, a series of controlled experiments in regard to TMB oxidation
were performed by adding various scavengers in the solution, such as superoxide
1
dismutase (SOD, quenching ∙O ), carotene (quenching O ) mannitol (quenching ∙OH),
2
2
and catalase (quenching H O ), respectively (Fig. 7c and Figs. S9-10), which can
2
2
further distinguish the photoinduced ROSs involved in TMB oxidation. For BiOBr,
TMB oxidation is mainly depressed by SOD but little affected by other scavengers,
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−
reflecting that ∙O radical is the major ROS generated from BiOBr. For Pd/BiOBr,
2
TMB oxidation can be remarkably suppressed by adding SOD or carotene, suggesting
that both ∙O2− and O coexist as the major ROSs. Furthermore, the in situ ESR
1
2
detection with using TEMP as a radical-trapping agent provides more direct evidence
1
for the photogeneration of O during photocatalytic toluene oxidation. As shown in
2
Fig.
7d,
the
1:1:1
triplet
signal
is
characteristic
of
1
2
,2,6,6-Tetramethylpiperidine-N-oxyl (TEMPO), indicating the generation of O . In
2
a sharp contrast, the triple-signal intensity is remarkably enhanced in the presence of
1
Pd/BiOBr, suggesting the abundence of O yield. According to the above results, the
2
Pd/BiOBr photocatalyst possesses the higher ability for activating toluene and O2
molecules, thus producing more carbon-centered radical and ROSs (∙O2− and O ),
1
2
which contribute together to promoting the selective oxidation of toluene to
benzaldehyde.
DFT calculations are performed to further reveal the active sites for substrate
activation on the photocatalysts. The optimized configurations and adsorption
energies of O and toluene adsorbed onto V in BiOBr-V surface and different Pd
2
O
O
sites in Pd/BiOBr-V surface are displayed in Fig. 8 and Table S8. By contrast, the
O
Pd/BiOBr-V surface shows stronger interactions with O and toluene molecules. In
O
2
the Pd/BiOBr-V surface, the interfacial Pd site (labeled as Site 1) affords the most
O
negative adsorption energy of -4.72 eV for toluene, due to the electron donation effect
of the aryl ring in toluene to the Pd surface through the -bond interaction.44,73 This
preferential adsorption configuration of toluene on the interfacial Pd site can keep the
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+
+
methyl group close to the h -rich BiOBr surface, thus beneficial to the h -driven
3
activation of C(sp )-H bonds. Moreover, the Pd sites show much stronger chemical
interactions with O than that of the BiOBr-V surface, where O molecules can be
2
O
2
adsorbed onto either interfacial or top Pd sites of Pd/BiOBr-V . As demonstrated
O
−
1
above, both ∙O and O are produced predominately in the photocatalytic reaction
2
2
system with Pd/BiOBr. It is reasonable to consider that the two adsorption modes of
O on interfacial Pd site and top Pd site exist simultaneously, which induce the
2
−
1
simultaneous generation of ∙O and O through the transfer of electron and energy,
2
2
3
3
−
respectively. As a typical charge carrier process, the photocatalytic ∙O generation
2
is generally determined by the concentration and transfer of surface free electrons.71
The interfacial Pd site with higher electron density, as illustrated in Fig. 4d, is able to
−
highly activate O to •O via electron transfer. Besides, Pd NPs can also promote the
2
2
1
33,69,74
generation of O by inducing the spin-flip process in O molecules.
The
2
2
calculated results prove that the presence of Pd NPs enables the strong chemical
adsorption of toluene and O molecules on the photocatalyst, ensuring the efficient
2
electron exchange and energy transfer between reactants and Pd/BiOBr photocatalyst.
Based on the experimental and calculation studies above, the photocatalytic
mechanism of the selective toluene oxidation to benzaldehyde over the Pd/BiOBr
photocatalyst is illustrated in Fig. 9. Upon the photo-excitation, the electrons and
holes are generated and separated as the above descriptions, where the electrons are
located at the interfacial Pd sites and the holes gather in the vicinity of the Pd NPs for
−
the charge balance. The chemisorbed O molecules are activated to generate ∙O and
2
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1
O at different Pd sites through the transfer of electron and energy, respectively.
2
3
Meanwhile, the C(sp )-H bond of toluene are oxidized by holes to produce the benzyl
radical. Subsequently, the generated ROSs (∙O2− and O ) react with the activated
1
2
5
,75
benzyl intermediates, to produce benzaldehyde and H O.
The Pd/BiOBr
2
photocatalyst has been proved to possess a great superiority in the generation and
separation of photoinduced electrons and holes due to the Schottky barrier at
Pd-BiOBr interface, which facilitates the electron-driven activation of molecular O2
3
and the hole-driven activation of C(sp )-H bonds in toluene. Moreover, the Pd NPs
and defective BiOBr surface provide more active sites for the catalytic reactions,
synergistically improving the reactivity and selectivity of photocatalytic selective
oxidation of toluene to benzaldehyde.
Conclusions
The Pd/BiOBr photocatalyst, prepared by photodepositing Pd NPs on the V -rich
O
BiOBr flower-like nanostructures, is taken as a model to study the synergetic effect of
metal site and defective semiconductor at the interface for promoting the
photocatalytic selective oxidation of toluene. The anchoring of Pd NPs can induce the
generation of more V s on BiOBr surface owing to the electronic interaction between
O
Pd and BiOBr, while the interfacial interaction stabilizes small Pd NPs and abundant
V s. DFT calculations indicate that the presence of both Pd NPs and V on BiOBr
O
O
surface enables the favorable adsorption of O and toluene. Furthermore, the
2
separated charge carriers at the Pd-BiOBr interface greatly promote the
3
electron-driven activation of O molecules and the hole-driven activation of C(sp )-H
2
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bonds in toluene, respectively. Both the experimental results and theoretical
calculations substantiate that the toluene oxidation at the Pd–BiOBr interface is easier
to occur than that directly on BiOBr surface, and the electrons gathered on Pd sites
−
1
expedite the O activation to afford sufficient ROSs (∙O and O ). The photocatalytic
2
2
2
efficiency is optimized to achieve a considerable toluene conversion rate of 6022.5
μmol·gcat-1·h . The active species and intermediates in the photocatalytic reaction are
identified by a series of controlled experiments as well as in situ ESR measurements.
-1
Therefore, the synergetic effect of Pd NPs and V defects at the interface of Pd/BiOBr
O
photocatalyst improves the performance toward photocatalytic selective oxidation of
toluene to benzaldehyde. This study offers insight into the interfacial synergy of metal
sites and V -rich oxide semiconductors for promoting photocatalytic selective
O
oxidation reactions and is expected to guide future structural design and modulation
of photocatalysts.
Conflicts of interest
There are no conflicts to declare.
Acknowledgments
This work was supported by the National Natural Science Foundation of China
(
21471004), the Natural Science Foundation of Zhejiang Province of China
LY19B010005 and LY18E020007), the Fundamental Research Funds of Zhejiang
(
Sci-Tech University (2020Y003) and the Science Foundation of Zhejiang Sci-Tech
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University (17062002-Y).
Notes and references
1
2
C. Coperet, Chem. Rev., 2010, 110, 656-680.
L. Kesavan, R. Tiruvalam, M. H. A. Rahim, M. I. bin Saiman, D. I. Enache, R. L.
Jenkins, N. Dimitratos, J. A. Lopez-Sanchez, S. H. Taylor, D. W. Knight, C. J.
Kiely and G. J. Hutchings, Science, 2011, 331, 195-199.
3
4
5
D. D. Mal, S. Khilari and D. Pradhan, Green Chem., 2018, 20, 2279-2289.
J. A. B. Satrio and L. K. Doraiswamy, Chem. Eng. J., 2001, 82, 43-56.
X. Cao, Z. Chen, R. Lin, W. C. Cheong, S. Liu, J. Zhang, Q. Peng, C. Chen, T.
Han, X. Tong, Y. Wang, R. Shen, W. Zhu, D. Wang and Y. Li, Nat. Catal., 2018,
1
, 704-710.
6
7
8
9
1
L. N. Song, F. Ding, Y. K. Yang, D. Ding, L. Chen, C. T. Au and S. F. Yin, ACS
Sustain. Chem. Eng., 2018, 6, 17044-17050.
J. He, L. Chen, D. Ding, Y. K. Yang, C. T. Au and S. F. Yin, Appl. Catal. B:
Environ., 2018, 233, 243-249.
W. Yang, B. Ling, B. Hu, H. Yin, J. Mao and P. J. Walsh, Angew. Chem. Int. Ed.,
2
020, 59, 161-166.
B. Li, L. Shao, R. Wang, X. Dong, F. Zhao, P. Gao and Z. Li, J. Mater. Chem. A,
018, 6, 6344-6355.
2
0 L. Chen, J. Tang, L. N. Song, P. Chen, J. He, C. T. Au and S. F. Yin, Appl. Catal.
B: Environ., 2019, 242, 379-388.
2
7

Journal of Materials Chemistry A
Page 28 of 42
View Article Online
DOI: 10.1039/D0TA05733A
1
1
1
1
1 X. Yang, S. Zhang, H. Tao, X. Yan, Y. Tan, Y. Zhang, S. Gao and R. Cao, J.
Mater. Chem. A, 2020, 8, 6854-6862.
2 H. Sterckx, B.Morel and B. U. W. Maes, Angew. Chem. Int. Ed., 2019, 58,
7
946-7970.
3 Y. Dai, C. Poidevin, C. Ochoa-Hernández, A. A. Auer and H. Tüysüz, Angew.
Chem. Int. Ed., 2020, 59, 5788-5796.
4 Y. Zhou, Z. Zhang, Z. Fang, M. Qiu, L. Ling, J. Long, L. Chen, Y. Tong, W. Su,
Y. Zhang, J. C. S. Wu, J. M. Basset, X. Wang and G. Yu, Proc. Natl. Acad. Sci.
U. S. A., 2019, 116, 10232-10237.
1
1
1
1
1
5 L. N. Song, L. Chen, J. He, P. Chen, H. K. Zeng, C. T. Au and S. F. Yin, Chem.
Commun., 2017, 53, 6480-6483.
6 F. Liu, C. X. Xiao, L. H. Meng, L. Chen, Q. Zhang, J. B. Liu, S. Shen, J. K. Guo,
C. T. Au and S. F. Yin, ACS Sustain. Chem. Eng., 2020, 8, 1302-1310.
7 X. Li, G. Liu, D. Xu, X. Hong and S. C. Edman Tsang, J. Mater. Chem. A, 2019,
7
, 23878-23885.
8 T. Gan, X. Chu, H. Qi, W. Zhang, Y. Zou, W. Yan and G. Liu, Appl. Catal. B:
Environ., 2019, 257, 117943.
9 W. Huang, Q. Liu, Z. Zhou, Y. Li, Y. Ling, Y. Wang, Y. Tu, B. Wang, X. Zhou,
D. Deng, B. Yang, Y. Yang, Z. Liu, X. Bao and F. Yang, Nat. Commun., 2020,
1
1, 2312.
2
0 H. Song, X. Meng, S. Wang, W. Zhou, X. Wang, T. Kako and J. Ye, J. Am.
Chem. Soc., 2019, 141, 20507-20515.
2
8

Page 29 of 42
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/D0TA05733A
2
2
1 L. Y. Lin, S. Kavadiya, X. He, W. N. Wang, B. B. Karakocak, Y. C. Lin, M. Y.
Berezin and P. Biswas, Chem. Eng. J., 2020, 389, 123450.
2 S. Wu, X. Tan, J. Lei, H. Chen, L. Wang and J. Zhang, J. Am. Chem. Soc., 2019,
1
41, 6592-6600.
2
2
3 Z. Zhang and J. T. Yates, Chem. Rev., 2012, 112, 5520-5551.
4 S. Mo, Q. Zhang, M. Zhang, Q. Zhang, J. Li, M. Fu, J. Wu, P. Chen and D. Ye,
Nanoscale Horiz., 2019, 4, 1425-1433.
2
2
2
5 M. Wang, M. Shen, X. Jin, J. Tian, M. Li, Y. Zhou, L. Zhang, Y. Li and J. Shi,
ACS Catal., 2019, 9, 4573-4581.
6 M. Xiao, L. Zhang, B. Luo, M. Lyu, Z. Wang, H. Huang, S. Wang, A. Du and L.
Wang, Angew. Chem. Int. Ed., 2020, 59, 7230-7234.
7 Y. Chen, S. Ji, W. Sun, Y. Lei, Q. Wang, A. Li, W. Chen, G. Zhou, Z. Zhang, Y.
Wang, L. Zheng, Q. Zhang, L. Gu, X. Han, D. Wang and Y. Li, Angew. Chem.
Int. Ed., 2020, 59, 1295-1301.
2
2
3
8 D. Cui, L. Wang, K. Xu, L. Ren, L. Wang, Y. Yu, Y. Du and W. Hao, J. Mater.
Chem. A, 2018, 6, 2193-2199.
9 X. Tong, X. Cao, T. Han, W. C. Cheong, R. Lin, Z. Chen, D. Wang, C. Chen, Q.
Peng and Y. Li, Nano Res., 2019, 12, 1625-1630.
0 H. Wang, D. Yong, S. Chen, S. Jiang, X. Zhang, W. Shao, Q. Zhang, W. Yan, B.
Pan and Y. Xie, J. Am. Chem. Soc., 2018, 140, 1760-1766.
3
3
1 H. Li, J. Shang, Z. Ai and L. Zhang, J. Am. Chem. Soc., 2015, 137, 6393-6399.
2 J. Wu, X. Li, W. Shi, P. Ling, Y. Sun, X. Jiao, S. Gao, L. Liang, J. Xu, W. Yan,
2
9