Synthesis of Bi2O3@BiOI@UiO-66 composites with enhanced photocatalytic activity under visible light

Article abstract of DOI:10.1016/j.cplett.2021.138354

Bi₂O₃ is a photocatalyst with excellent performance; however, its applications are limited due to its wide bandgap. In this paper, by adding BiOI and the metal–organic framework UiO-66, a Bi₂O₃@BiOI@UiO-66 composite material is obtained with high adsorption capacity, in which the bandgap of Bi₂O₃ is reduced, the recombination of photogenerated electrons and holes is prevented, the photocatalytic efficiency and stability are improved. In visible light degradation experiments, Bi₂O₃@BiOI@UiO-66 has obvious degradation effects on Rhodamine B and tetracycline, which are 22.2 and 1.04 times that of pure Bi₂O₃, respectively. Bi₂O₃@BiOI@UiO-66 demonstrats its potential as photocatalytic degradation material.

Full text of DOI:10.1016/j.cplett.2021.138354

Chemical Physics Letters 768 (2021) 138354
Contents lists available at ScienceDirect
Chemical Physics Letters
journal homepage: www.elsevier.com/locate/cplett
Research paper
Synthesis of Bi2O3@BiOI@UiO-66 composites with enhanced
photocatalytic activity under visible light
Jijun Tanga, Tang Zhanga, Zhengzhou Duana, Chuwen Lia, Chunfeng Menga, Yamei Zhanga,
,*,*
Qiyuan Zhangb, Dongmei Houb, Qinyun Xvb, Yu Zhub
a School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, PR China
b Taizhou University, College of Pharmacy and Chemistry & Chemical Engineering, Jiangsu Key Laboratory of Chiral Pharmaceuticals Biomanufacturing, Taizhou
225300, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bi2O3 is a photocatalyst with excellent performance; however, its applications are limited due to its wide
bandgap. In this paper, by adding BiOI and the metal–organic framework UiO-66, a Bi2O3@BiOI@UiO-66
composite material is obtained with high adsorption capacity, in which the bandgap of Bi2O3 is reduced, the
recombination of photogenerated electrons and holes is prevented, the photocatalytic efficiency and stability are
improved. In visible light degradation experiments, Bi2O3@BiOI@UiO-66 has obvious degradation effects on
Rhodamine B and tetracycline, which are 22.2 and 1.04 times that of pure Bi2O3, respectively. Bi2O3@-
BiOI@UiO-66 demonstrats its potential as photocatalytic degradation material.
Bi-based compounds
UiO-66
Composite material
Photocatalysis degradation
Persistence organic pollutions
1. Introduction
framework (MOF) materials has proved effective to solve this problem
[16]. MOFs are a class of crystalline porous materials with periodic
With the development of social industrialisation, persistent organic
pollutions (POPs) are increasingly contaminating water resources [1,2].
In this context, photocatalytic technologies have been receiving
considerable attention because they can efficiently degrade POPs to
harmless molecules such as H2O and CO2 on the basis of the redox ability
of the photocatalyst upon light irradiation [3]. Bi2O3 is a promising
candidate in this regard due to its high electrochemical stability and
high redox reversibility [4,5]. However, the wide application of pure
Bi2O3 is still constrained due to its wide bandgap. BiOX (X = Cl, Br and I)
semiconductors having a layered inner structure can accelerate the
separation efficiency of photogenerated carriers for high photocatalytic
activity because of the built-in electric field; therefore, they have
emerged as new efficient and environmental-friendly photocatalytic
materials [6]. In particular, BiOI has a narrow bandgap (1.63–2.20 eV)
[7] that provides it with excellent photocatalytic performance under
visible light irradiation. In fact, the combination of BiOI with Bi2O3 can
effectively reduce the bandgap of the latter, facilitating the generation of
electrons under visible light [8–13]. However, photogenerated electrons
and holes can be easily recombined, resulting in a decrease in photo-
catalytic efficiency [14,15].
network structures formed by the self-assembly of inorganic metal
centres (metal ions or metal clusters) and bridged organic ligands,
affording a specific surface area that increases the contact area and
improves the photocatalytic efficiency [17]. As an example of MOF,
thermally and chemically stable UiO-66 has been applied in various
fields including liquid separation, adsorption and catalysis [18,19]. The
addition of UiO-66 to composite materials improves the transfer
pathway of photogenerated electron and holes, thereby reducing the
recombination of electrons and valence band holes. Therefore, the cat-
alytic efficiency is improved in composites containing porous UiO-66
[20–26].
Following this line of thought, we were interested in evaluating the
effect of the addition of UiO-66 on the photocatalytic activity of the
Bi2O3@BiOI systems. In this paper, Bi2O3@BiOI binary composite ma-
terials and Bi2O3@BiOI@UiO-66 ternary composite materials were
synthesised by an improved solvothermal method. The optimal sub-
strate ratio in the composites was determined, and the porous structure
of the MOF material was found to improve the photocatalytic efficiency
of the binary system, providing a method for the degradation of organic
dyes.
The combination of semiconductor materials and metal–organic
* Corresponding authors.
E-mail addresses: 471596844@qq.com (J. Tang), zhuyu@tzu.edu.cn (Y. Zhu).
https://doi.org/10.1016/j.cplett.2021.138354
Received 11 October 2020; Received in revised form 11 January 2021; Accepted 14 January 2021
Available online 23 January 2021
0009-2614/© 2021 Elsevier B.V. All rights reserved.

J. Tang et al.
Chemical Physics Letters 768 (2021) 138354
2. Experimental
tetracycline (TC) by the prepared samples (Bi2O3@BiOI and Bi2O3@-
BiOI@UiO-66) was studied under visible light irradiation. A 250 W Xe
lamp (λ ≥ 420 nm) with an ultraviolet cut-off filter was used as the
visible light source. The photocatalyst (20 mg) was dispersed in a 100
mL aqueous solution of RhB (10 mg/L) and stirred in the dark for 30 min
to form an adsorption–desorption system. After centrifuging the sus-
pension to remove the catalyst from the aqueous solution, the absor-
bance of RhB or TC was analysed by a 759 UV–vis spectrophotometer.
Benzoquinone (BQ), sodium oxalate (Na2C2O4) and isopropanol (IPA)
were used as a superoxide anion (⋅Oꢀ2 ) scavenger, a hole (h) scavenger
and a hydroxyl radical scavenger (⋅OH) respectively.
2.1. Synthesis of Bi2O3
As reported in a previous work [27], Bi2O3 was synthesised using
Bi2O2CO3 as a precursor. First, 11.64 g of Bi(NO3)3⋅5H2O was dissolved
in 60 mL of HNO3 aqueous solution (1 mol/L). To this mixture, 240 mL
of Na2CO3 aqueous solution (0.6 mol/L) was slowly added with constant
stirring, resulting in the formation of a large amount of a white pre-
cipitate. The suspension was further stirred for 15 min and left to stand
at 60 ◦C for 12 h. Finally, the precipitate was collected, washed several
times with deionised water and dried at 60 ◦C for 6 h to form the
Bi2O2CO3 precursor. Bi2O3 was obtained by annealing the as-prepared
Bi2O2CO3 at 350 ◦C for 30 min.
3. Results and discussion
3.1. Morphology and structure
2.2. Synthesis of UiO-66
The crystal structure and phase composition of the samples were
determined by powder XRD (Fig. 1). The major characteristic peaks of
the Bi2O3 sample at around 2θ = 28.01◦, 33.25◦ and 46.37◦ could be
Following a reported procedure [28], 0.233 g of ZrCl4 and 0.166 g of
H2BDC were dissolved in 50 mL of DMF with stirring for 30 min and then
reacted at 120 ◦C for 24 h in a hydrothermal reaction vessel. The
resulting product was washed and dried at 80 ◦C for 12 h.
readily indexed to monoclinic α-Bi2O3 according to the standard card
JCPDS NO. 71–2274 and were ascribed to the (ꢀ 121), (ꢀ 202) and
(041) lattice planes, respectively [29]. The four major peaks of BiOI at
2θ = 29.7◦, 31.7◦ and 55.2◦ were assigned to the (102), (110) and
(212) planes, illustrating that the synthesised BiOI has a tetragonal
phase (JCPDS NO. 10-0445) [30]. The patterns of the Bi2O3@BiOI
composites show all the peaks of BiOI but not those of Bi2O3. This may
be due to the overlapping of the BiOI peaks at 46.37◦ and 55.2◦ with the
Bi2O3 peaks having weak intensity of diffraction. The characteristic
peaks of UiO-66 located at 2θ = 7–9◦ are in line with previous reports,
suggesting that UiO-66 crystals were successfully synthesized [17,31].
In the Bi2O3@BiOI@UiO-66 sample, the peaks at 7◦ and 9◦ are much
smaller than those of pure UiO-66, which may be because Bi2O3@BiOI
covers the crystal plane of UiO-66 during the formation of the
composite.
2.3. Synthesis of Bi2O3@BiOI
Different ratios of Bi2O3 and 1 mmol of Bi(NO3)3⋅5H2O were added
to a solution containing 1 g of KI in ethylene glycol, mixed thoroughly,
placed in a hydrothermal reaction kettle and reacted at 110 ◦C for 24 h.
After cooling to room temperature, the mixture was washed with water
and ethanol, then dried at 80 ◦C.
2.4. Synthesis of Bi2O3@BiOI@UiO-66
UiO-66, Bi2O3 and 1 mmol of Bi(NO3)3⋅5H2O were added to a solu-
tion containing 1 g of KI in ethylene glycol (2.5 mL), mixed thoroughly
and placed in a hydrothermal reaction kettle. The reaction was con-
ducted at 110 ◦C for 24 h. Then, the mixture was cooled to room tem-
perature, washed with water and ethanol and dried at 80 ◦C.
The morphology of the substrates Bi2O3, BiOI and UiO-66 (Fig. 2)
and the Bi2O3@BiOI and Bi2O3@BiOI@UiO-66 composites (Fig. 3) was
characterised using SEM. As can be seen in Fig. 2a, Bi2O3 displays a
hollow rod-like structure with a particle size of 20–30 µm and an inner
pore diameter of 5 µm. BiOI is a cluster of flower-shaped aggregates with
a diameter of about 2 µm (Fig. 2b). Fig. 2c shows the octahedral crystal
structure of UiO-66 with a diameter of 600 nm. As can be extracted from
the SEM images of the composites (Fig. 3), the top smaller rod-shaped
load material is Bi2O3, which is relatively evenly distributed on BiOI
(Fig. 3a–c). Fig. 3d shows that the regular holes of UiO-66 are loaded
2.5. Characterisation
X-ray diffraction (XRD) data were collected on a Shimadzu XRD-
6000 instrument. Scanning electron microscopy (SEM) was performed
on a Japan Electronics JSM-6480 microscope to observe the morphology
of the photocatalysts. Fourier transform infrared (FTIR) spectra were
obtained using an Agilent spectrometer in a frequency range of
4500–450 cmꢀ 1. The absorption spectra were recorded on a Hitachi
U4100 UV spectrometer. N2 physisorption measurement was performed
at 77 K on a BELSORP-mini II instrument; each sample was degassed in
vacuo at 200 ◦C for 3 h. The specific surface area was determined ac-
cording to the Brunauer-Emmett-Teller (BET) equation. Fluorescent
spectra were obtained on a FS5 spectrofluorometer. The transient photo-
current measurements were performed using an Electrochemical
Workstation (Chenhua 660E, China), equipped with three-electrodes
involving ITO electrode covered with samples, Pt and Ag/AgCl elec-
trodes. For the single working electrode, 5 mg of the sample was
Bi2O3
Bi2O3:BiOI=1:1
Bi2O3:BiOI=1:2
Bi2O3:BiOI=2:1
Bi2O3:BiOI:UiO-66=1:1:1
UiO-66
PDF#71-2274
dispersed in 10
μ
L nafion and then added 0.1 mL anhydrous ethanol to
make a homogeneous solution. Then, 40
μL of above solution was
dropped on ITO conducting glass. The 0.5 M Na2SO4 aqueous solution
was used as the electrolyte and exposed by Xe lamp (300 W, λ > 420
nm). The impedance test is performed in the frequency range of 0.1
Hz–10 kHz, an amplitude of 0.005 V, a Quiet time of 2 s, and an initial
potential of 0.071 V.
10
20
30
40
50
60
70
80
2.6. Photocatalytic activity test
Fig. 1. X-ray diffraction spectra of Bi2O3@BiOI and Bi2O3@BiOI@UiO-66
The photocatalytic degradation of Rhodamine
B
(RhB) and
prepared with different substrate ratios.
2

J. Tang et al.
Chemical Physics Letters 768 (2021) 138354
Fig. 2. Scanning electron microscopy images of (a) Bi2O3, (b) BiOI and (c) UiO-66.
Fig. 3. Scanning electron microscopy images of (a), (b), (c) the Bi2O3@BiOI binary composite at three different substrate ratios (1:1, 1:2, 2:1), and (d) the
Bi2O3@BiOI@UiO-66 ternary composite.
with flower-like and rod-shaped substances, which confirms that Bi2O3
and BiOI were successfully loaded onto UiO-66.
the pore size of pure UiO-66 (2.232 nm) is smaller than that of the
composite (3.206 nm). However, the specific surface area of the com-
Infrared spectroscopy verified the each peak of UiO-66 and com-
posite materials. (Fig. S1) The sharp peak observed at 530 cmꢀ 1 can be
assigned to the typical stretching modes of Bi–O [17,31]. The presence
of Bi2O3 was confirmed by the band at 423 cmꢀ 1, which is attributable to
the symmetrical stretching vibration of the Bi–O bond of Bi2O3 species
[32,33]. The peak at 744 cmꢀ 1 likely originates from the O–Zr–O vi-
bration of UiO-66, and small peaks located in the range 700–1200 cmꢀ 1
stem from the vibration of aromatic rings. The presence of three strong
peaks at 1392, 1590 and 1670 cmꢀ 1 attributed to carboxyl groups of the
ligands is in accord with previous reports [34–36].
posite material is still much larger than that of Bi2O3 (8.149 m2 gꢀ 1
)
[37,38]. This result demonstrates that the addition of UiO-66 improves
the specific surface area of the final product compared with the Bi2O3
substrate.
The as-prepared Bi2O3, BiOI and composite materials were shown in
the UV–vis diffuse reflectance spectra (Fig. S2). According to the
Kubelka–Munk curve and the fitting of the spectrum, the forbidden
bandwidth of Bi2O3 is 2.7 eV, whereas those of Bi2O3@BiOI and
Bi2O3@BiOI@UiO-66 are 1.89 and 1.94 eV, respectively (Fig. S2b, S2c).
Due to this reduction of the bandgap in the composites, electrons are
more easily excited into photogenerated electrons in solution to
participate in the photocatalytic reaction, which improves the photo-
catalytic degradation efficiency of the material.
BET was used to characterise the specific surface area and pores of
UiO-66 [30] and the composite materials [17]. The specific surface area
of UiO-66 is about 794.69 m2 gꢀ 1, whereas that of the Bi2O3@BiOI
@UiO-66 composite is 51.14 m2 gꢀ 1 (Table S1 and Fig. 4). In addition,
To further confirm the effective charge separation in the materials,
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J. Tang et al.
Chemical Physics Letters 768 (2021) 138354
adsorption effect, whereas that of Bi2O3@BiOI was basically the same as
that of Bi2O3. Due to the large specific surface area of UiO-66, the
Bi2O3@BiOI@UiO-66 composite can absorb more RhB molecules than
the binary composite. The degradation rate of Bi2O3@BiOI@UiO-66
reached an astonishing 89.9% when exposed to visible light (Fig. 6a).
After first-order kinetics fitting, the k value of Bi2O3@BiOI@UIO-66 was
found to be the largest (k = 0.03437 minꢀ 1), and those of the other
materials followed the order Bi2O3 > 0.5Bi2O3@BiOI > 2Bi2O3@BiOI >
1Bi2O3@BiOI (Fig. 6b). Due to the narrow bandgap of BiOI, Bi2O3 not
only produces photogenerated electrons more easily upon visible light
irradiation but also improves their mobility [40]. The recombination of
photogenerated electrons and holes in Bi2O3@BiOI is hindered by add-
ing UiO-66, and Bi2O3@BiOI@UiO-66 has high adsorptivity. This results
in multiple reaction centres on the surface of the material, thereby
improving the photocatalytic efficiency.
400
UiO-66
Bi2O3@BiOI@UiO-66
300
200
100
0
TC has also been selected as a pollutant to study the photocatalytic
activities of these materials. In dark, the adsorption capacity of
Bi2O3@BiOI@UiO-66 increased to a certain extent via composited with
UiO-66 compared with Bi2O3, BiOI and Bi2O3@BiOI. The degradation
rate of TC by Bi2O3@BiOI@UiO-66 was 63.6% when exposed to visible
light, and the degradation rate of Bi2O3 turned out to be 60.1% (Fig. 6c).
The k value of Bi2O3@BiOI@UiO-66 was still the largest (k = 0.00974
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure(P/Po)
Fig.4. N2 adsorption and desorption isotherms.
minꢀ 1), and those of the other samples followed the order Bi2O3
>
the samples were measured by fluorescence spectroscopy with an exci-
tation wavelength of 530 nm. An emission peak is observed around 648
nm, which originates from the recombination of photogenerated elec-
trons and valence band holes (Fig. 5). The peak intensity of Bi2O3 is five
times that of Bi2O3@BiOI and Bi2O3@BiOI@UiO-66. The lower emission
intensity for the composites indicates that they are more conducive to
charge separation, thereby inhibiting the recombination of electro-
n–hole pairs [39].
2Bi2O3@BiOI > 1Bi2O3@BiOI > 0.5Bi2O3@BiOI (Fig. 6d). The high
degradation rate of Bi2O3 may be due to the large adsorption of TC in the
dark.
Besides, the adsorption also acts as an important part for the
pollutant removing. UiO-66 has a specific surface area of 794.69 m2⋅gꢀ 1
,
which can improve the adsorption performance of semiconductors. In
photocatalytic process, Bi2O3@BiOI@UiO-66 can enrich pollutants with
low concentration around or on UiO-66 due to the good adsorption ca-
pacity. Compared with Bi2O3, Bi2O3@BiOI, Bi2O3@BiOI@UiO-66
exhibited the best adsorption effect on the two pollutants. Because of the
different sizes of pollutants, the adsorption to TC with 37% in dark is a
little larger than that to RhB which owns a larger size with 23%.
Photogenerated holes, ⋅OH, ⋅O–2 are important active substances for
photodegradation. The degradation of organic matter is dominated by
free radical redox reactions. In the degradation of RhB, the addition of
isopropanol has the greatest impact on photodegradation, which proves
that the degradation of RhB is dominated by ⋅OH (Fig. 7a). Besides,
benzoquinone has the greatest impact on the photodegradation of TC,
indicating⋅O–2 the primary factor in the photodegradation of TC (Fig. 7b).
Furthermore, EPR was measured here to distinguish the free radicals
with DMPO as the scavenger [41,42]. A characteristic quartet signal for
DMPO-⋅O–2 and ⋅OH with an intensity ratio of approximately 1:1:1:1 is
observed in Figs. 8 and 9, confirming the generation of ⋅O–2 and ⋅OH over
the Bi2O3@BiOI@UiO-66 catalyst under visible light irradiation.
The photocatalytic degradation of RhB by Bi2O3@BiOI@UiO-66 was
compared in different pH (Fig. S3a, S3b) and solutions containing
different ions (Fig. S3c, S3d). It is basically unaffected in acidic solutions
and the photocatalytic performance of the sample on RhB also varies
slightly with good stability in solutions with different ions. The photo-
catalytic degradation of tetracycline by Bi2O3@BiOI@UiO-66 was also
compared in different pH (Fig. S4a, S4b) and solutions containing
different ions (Fig. S4c, S4d). It is found that the photocatalytic per-
formance of the sample has a certain downward trend in different pH
and different ions, but the photocatalytic efficiency can still be main-
tained. The degradation of the RhB has been carried out five runs to test
the stability (Fig. S5). The degradation ratio is decreasing from 88.9% to
83.9%, which is only about 5% loss in RhB degradation (Fig. S5). Be-
sides, Bi2O3@BiOI@UiO-66 was tested by XRD to confirm the stability
before and after photocatalysis. The peaks remain unchanged, which
shows that Bi2O3@BiOI@UiO-66 can still maintain the complete struc-
ture after photocatalysis with no changes in components (Fig. S6).
To study the carriers transfer process and separation process in
photocatalysts, the photoelectrochemical analyses were performed.
3.2. Photocatalytic performance
We evaluated the catalytic degradation ability of pure Bi2O3 and the
Bi2O3@BiOI and Bi2O3@BiOI@UiO-66 samples using RhB and TC as
pollutants under visible light irradiation. The experiment was repeated
three times to get the variance and shown on the chart. (Fig. 6) The
following first-order kinetic formula was used to fit the experimental
data: ln (C0/C) = kt, where C0 and C are the concentrations of pollutants
in the solution at times 0 and t, respectively, and k is the photocatalytic
rate constant.
First, the photocatalytic performance of the Bi2O3@BiOI and
Bi2O3@BiOI@UiO-66 composites in the degradation of RhB was
assessed. In the dark, Bi2O3@BiOI@UiO-66 exhibited the best RhB
Fig. 5. Emission fluorescence spectra of Bi2O3 and the binary and ternary
composite materials.
4

J. Tang et al.
Chemical Physics Letters 768 (2021) 138354
1.0
0.8
0.6
0.4
0.2
0.0
2.5
2.0
1.5
1.0
0.5
0.0
a
k=0.00243min-1
b
Blank
Bi2O3
k=0.00152min-1
k=0.00147min-1
k=0.00242min-1
k=0.00188min-1
Bi2O3:BiOI=1:1
Bi2O3:BiOI=1:2
Bi2O3:BiOI=2:1
-1
Bi O @BiOI@UiO-66
k=0.03546min
2
3
Blank
Bi2O3
Bi2O3:BiOI=1:1
Bi2O3:BiOI=1:2
Bi2O3:BiOI=2:1
Bi2O3@BiOI@UiO-66
0
20
40
60
-20
0
20
40
60
Time(min)
Irradiation time(min)
1.0
c
k=0.00132min-1
k=0.002min-1
d
Blank
Bi2O3
0.8
k=0.00315min-1
k=0.00321min-1
k=0.00336min-1
Bi2O3:BiOI=1:1
Bi2O3:BiOI=1:2
Bi2O3:BiOI=2:1
0.8
0.6
0.4
0.6
0.4
0.2
0.0
Bi2O3@BiOI@UiO-66 k=0.01103min-1
Blank
Bi2O3
Bi2O3:BiOI=1:1
Bi2O3:BiOI=1:2
Bi2O3:BiOI=2:1
Bi2O3@BiOI@UiO-66
-20
0
20
40
60
0
20
40
60
Time(min)
Irradiation time(min)
Fig. 6. (a) and (b) Degradation efficiency and fitting rate constant of RhB (10 mg/L) by different samples; (c) and (d) Degradation efficiency and fitting rate constant
of TC (10 mg/L) by different samples.
1.0
1.0
b
a
0.8
0.6
0.4
0.8
0.6
Blank
Blank
Isopropyl alcohol
Sodium oxalate
Benzoquinone
Isopropyl alcohol
Sodium oxalate
Benzoquinone
-20
0
20
40
60
-20
0
20
40
60
Time(min)
Time(min)
Fig. 7. Photocatalytic degradation rate of RhB (a) and TC (b) in different inhibitors.
Compared with Bi2O3, BiOI and Bi2O3@BiOI, Bi2O3@BiOI@UiO-66
displays the strong photo current response, revealing the efficient photo-
induced charge transfer between Bi2O3, BiOI and UiO-66 (Fig. 10). The
superior charge transfer and recombination inhibition in Bi2O3@-
BiOI@UiO-66 is responsible for the intensive photocatalytic activity
[43]. To further confirm above results, EIS Nyquist plot for monomer
and composite materials has been used to study the course of charge
separation and transfer. Fig. 11 displays the Nyquist impedance plots of
monomer and composite materials. The resistance Rct value of each
sample is BiOI(16.23 Ω) > Bi2O3(16.13 Ω) > Bi2O3@BiOI(14.97 Ω) >
5

J. Tang et al.
Chemical Physics Letters 768 (2021) 138354
8
4
-
O2 dark
Bi2O3
-
BiOI
Bi2O3@BiOI
O2 light 5 min
-
O2 light 10 min
Bi2O3@BiOI@UiO-66
0
0
100
200
300
400
500
Magnetic field(G)
-4
0
5
10
15
20
25
Fig. 8. EPR spectra in methanol dispersion for DMPO-⋅O–2.
Z' /Ohm
Fig. 11. Nyquist plots in the 0.5 M Na2SO4 solution, 0.01 Hz to 10 kHz fre-
quency range, Initial potential 0.071 V, 0.005 V amplitude, 2 sec quiet time 0.5
M Na2SO4 for the electrodes.
·OH dark
·OH light 5 min
·OH light 10 min
Bi2O3@BiOI@UiO-66(13.42 Ω), while the capacitance C is BiOI(0.94 C)
> Bi2O3@BiOI(0.90 C) > Bi2O3(0.89 C) > Bi2O3@BiOI@UiO-66(0.93
C).(Fig. S7) What’s more, the |Z| value of different samples does not
change greatly with the increase of frequency, which proves the stability
of the samples to the circuit signal. Compared with Bi2O3, the phase
angle changes are concentrated in the low frequency region, which
proves that the material’s response to the circuit is mainly in the low
frequency region and the capacitive reactance arc is smaller than Bi2O3.
This reflects that Bi2O3@BiOI@UiO-66 is more polarized larger, higher
current discharge capability is better. It is found that Bi2O3@BiOI@UiO-
66 displays a low arc radius in comparison to other samples, suggesting
that Bi2O3@BiOI@UiO-66 owns strong migration and separation of
photo-generated charge carrier.
0
100
200
300
400
500
From the photocatalytic experiments, it can be extracted that the
interaction between BiOI, Bi2O3 and UiO-66 is responsible for the effi-
cient generation and separation of carriers under visible light excitation
(Fig. 12). For a semiconductor, at the point of zero charges, the band
positions can be calculated by the following empirical formula:
Magnetic field(G)
Fig. 9. EPR spectra in methanol dispersion for DMPO-⋅OH.
EVB = X ꢀ Ee + 0.5Eg
Bi2O3
18
15
12
9
BiOI
Bi2O3@BiOI
ECB = EVB ꢀ Eg
Bi2O3@BiOI@UiO-66
6
3
0
0
40
80
120
160
Time (s)
Fig. 10. Photocurrent response graph of monomer, binary composite and
ternary composite (electrolyte composition: 0.5 M Na2SO4, electrode area: 1
cm2, optical power: 300 W).
Fig. 12. Energy band structure and charge separation map of materials, and
possible ways of photodegradation of pollutants.
6

J. Tang et al.
Chemical Physics Letters 768 (2021) 138354
hollow microspheres with improved photocatalytic performance, Inorg. Chem. 51
(2012) 6245–6250.
where EVB and ECB are the valence band (VB) and conduction band edge
potentials, respectively, and X is the electronegativity of the semi-
conductor, which is the geometric mean of the electronegativity of the
constituent atoms [44]. BiOI, with a narrow bandgap energy of 1.86 eV,
could be easily excited by visible light (λ > 400 nm, energy less than
3.10 eV), inducing the generation of electrons and holes. After
Bi2O3@BiOI@UiO-66 is irradiated with visible light, because BiOI has
the lowest conduction band, electrons are excited on BiOI to form photo-
induced carriers, which are then transferred from BiOI to Bi2O3 and UiO-
66 and released [45].
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4. Conclusion
In this paper, a solvent method was used to synthesise Bi2O3@BiOI
and Bi2O3@BiOI@UiO-66 composites with different substrate ratios as
photocatalysts to degrade RhB and TC under visible light irradiation.
The degradation rate of Bi2O3@BiOI@UiO-66 for RhB and TC is six and
three times that of the Bi2O3@BiOI system, respectively. The results
show that addition of UiO-66 increases significantly the adsorption ca-
pacity of the sample, accelerates the charge separation and reduces the
electron–hole recombination during the photocatalytic process. In
addition, Bi2O3@BiOI@UiO-66 shows good stability. Therefore, the
high efficiency and stability of the Bi2O3@BiOI@UiO-66 composite
renders it a good candidate material for photocatalytic applications.
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CRediT authorship contribution statement
[15] J. Zhang, W. Zhang, L. Wei, L. Pu, J. Liu, H. Liu, Y. Li, J. Fan, T. Ding, Z. Guo,
Alternating multilayer structural epoxy composite coating for corrosion protection
of steel, Macromol. Mater. Eng. 304 (2019) 1900374.
Jijun Tang: Supervision, Writing - original draft, Data curation.
Tang Zhang: Investigation, Writing - original draft, Software. Zhengz-
hou Duan: Software. Chuwen Li: Formal analysis. Chunfeng Meng:
Resources. Yamei Zhang: Resources. Qiyuan Zhang: Methodology.
Dongmei Hou: Investigation. Qinyun Xv: Investigation. Yu Zhu: Su-
pervision, Project administration, Writing - review & editing.
[16] W. Zhan, L. Sun, X. Han, Recent progress on engineering highly efficient porous
semiconductor photocatalysts derived from metal–organic frameworks, Nano
Micro Lett. 11 (2019) 5–32.
[17] X. Zhang, Y. Yang, W. Huang, Y. Yang, Y. Wang, C. He, N. Liu, M. Wu, L. Tang, g-
C3N4/UiO-66 nanohybrids with enhanced photocatalytic activities for the
oxidation of dye under visible light irradiation, Mater. Res. Bull. 99 (2018)
349–358.
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photoelectrochemical performance of Mo-doped BiVO4, J. Phys. Chem. C 116
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Declaration of Competing Interest
[19] Y. Yuan, L. Yin, S. Cao, G. Xu, C. Li, C. Xue, Improving photocatalytic hydrogen
production of metal-organic framework UiO-66 octahedrons by dye-sensitization,
Appl. Catal. B-Environ. 168 (2015) 572–576.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[20] Y. Li, X. Shang, C. Li, X. Huang, J. Zheng, Novel p-n junction UiO-66/BiOI
photocatalysts with efficient visible-light-induced photocatalytic activity, Water
Sci. Technol. 77 (2018) 1441–1448.
[21] R. Peng, C.-M. Wu, J. Baltrusaitis, N.M. Dimitrijevic, T. Rajh, R.T. Koodali, Ultra-
stable CdS incorporated Ti-MCM-48 mesoporous materials for efficient
photocatalytic decomposition of water under visible light illumination, Chem.
Commun. 49 (2013) 3221–3223.
Acknowledgement
Y.Z. acknowledges support from the Natural Science Foundation of
Jiangsu Province (BK20190245), Nature Science Research in Colleges
and Universities in Jiangsu Province (17KJB150037), Research Foun-
dation for Talented Scholars of Taizhou University (QD2016006), and
the Science and Technology Support Program (Social Development) of
Taizhou (SSF20190047).
[22] L. Shen, S. Liang, W. Wu, R. Liang, L. Wu, CdS-decorated UiO–66(NH2)
nanocomposites fabricated by a facile photodeposition process: an efficient and
stable visible-light-driven photocatalyst for selective oxidation of alcohols,
J. Mater. Chem. A 1 (2013) 11473–11482.
[23] J. He, Z. Yan, J. Wang, J. Xie, L. Jiang, Y. Shi, F. Yuan, F. Yu, Y. Sun, Significantly
enhanced photocatalytic hydrogen evolution under visible light over CdS
embedded on metal-organic frameworks, Chem. Commun. 49 (2013) 6761–6763.
[24] E.Q. Procopio, S. Rojas, N.M. Padial, S. Galli, N. Masciocchi, F. Linares, D. Miguel,
J.E. Oltra, J.A. Navarro, E. Barea, Study of the incorporation and release of the
non-conventional half-sandwich ruthenium(II) metallodrug RAPTA-C on a robust
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Appendix A. Supplementary material
[25] Z. Hasan, M. Tong, B.K. Jung, I. Ahmed, C. Zhong, S.H. Jhung, Adsorption of
pyridine over amino-functionalized metal-organic frameworks: attraction via
hydrogen bonding versus base-base repulsion, J. Phys. Chem. C 118 (2014)
21049–21056.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.cplett.2021.138354.
[26] W.-W. Zhan, Q. Kuang, J.-Z. Zhou, X.-J. Kong, Z.-X. Xie, L.-S. Zheng,
Semiconductor@Metal-organic framework core-shell heterostructures: a case of
ZnO@ZIF-8 nanorods with selective photoelectrochemical response, J. Am. Chem.
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8