In-situ fabrication of 0D/2D NiO/Bi12O17Cl2 heterojunction towards high-efficiency degrading 2, 4-dichlorophenol and mechanism insight

Article abstract of DOI:10.1016/j.jphotochem.2019.112102

2, 4-dichlorophenol (2, 4-DCP) as a persistent pollutant is frequently detected in water environments, complete eradication of trace which in water is an important task. Hence, a 0D/2D NiO/Bi₁₂O₁₇Cl₂ heterojunction was achieved by in-situ fabrication of NiO nanodots on Bi₁₂O₁₇Cl₂ nanosheets, which obviously improved the physical, optical and photoelectrochemical properties. The photocatalytic degradation activity of 0D/2D NiO/Bi₁₂O₁₇Cl₂ heterojunction was boosted dramatically, which originated from the improved transfer and separation efficiency of charge carriers owing to the formation of Z-scheme heterostructure between NiO and Bi₁₂O₁₇Cl₂. The possible photocatalytic reaction mechanism including migration behaviors of charge carriers, generation of reactive species and degradation intermediate products were revealed in depth. This work provides the valuable experiences for designing and fabricating otherwise 0D/2D heterojunction photocatalysts in the application of environmental treating fields.

Full text of DOI:10.1016/j.jphotochem.2019.112102

Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
In-situ fabrication of 0D/2D NiO/Bi O Cl heterojunction towards high-
1
2
17
2
efficiency degrading 2, 4-dichlorophenol and mechanism insight
a
b
a
c
a
a
a
Ning Song , Jiaming Li , Chunmei Li , Pengjie Zhou , Enhui Jiang , Xiaoxu Zhang , Chunbo Liu ,
a
a
b,⁎
a,b,⁎
Zhichen Wu , Hang Zheng , Guangbo Che , Hongjun Dong
Institute of Green Chemistry and Chemical Technology, School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, 212013, PR China
Key Laboratory of Preparation and Application of Environmental Friendly Materials, Ministry of Education, Jilin Normal University, Changchun, 130103, PR China
School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang, 212005, PR China
a
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
, 4-DCP
NiO/Bi12
D/2D heterojunction
Photocatalytic degradation
Reaction mechanism
2, 4-dichlorophenol (2, 4-DCP) as a persistent pollutant is frequently detected in water environments, complete
eradication of trace which in water is an important task. Hence, a 0D/2D NiO/Bi12O17Cl2 heterojunction was
2
O17Cl
2
achieved by in-situ fabrication of NiO nanodots on Bi12
physical, optical and photoelectrochemical properties. The photocatalytic degradation activity of 0D/2D NiO/
Bi12 17Cl heterojunction was boosted dramatically, which originated from the improved transfer and separa-
tion efficiency of charge carriers owing to the formation of Z-scheme heterostructure between NiO and
Bi12 17Cl . The possible photocatalytic reaction mechanism including migration behaviors of charge carriers,
2
O17Cl nanosheets, which obviously improved the
0
O
2
O
2
generation of reactive species and degradation intermediate products were revealed in depth. This work provides
the valuable experiences for designing and fabricating otherwise 0D/2D heterojunction photocatalysts in the
application of environmental treating fields.
1. Introduction
2
Bismuth oxychloride (Bi12O17Cl ), as an important semiconductor
material, has been attracted broadly attention because of its unique
open crystalline structure, appropriate band structure and high che-
Recently, the efficient development of industry brings convenience
to human, but the environmental problems are increasingly prominent
in the meanwhile [1–8]. 2, 4-dichlorophenol (2, 4-DCP) as one of the
most important persistent pollutants has been widely released in in-
dustry, agriculture, medicine and planting. In recent years, 2, 4-DCP is
frequently detected in a wide range of environmental samples, parti-
cularly in treated wastewater and even drinking water, which may
cause some pathological symptoms and changes for human endocrine
systems. Nevertheless, the complete elimination of trace 2, 4-DCP in
water cannot be easily achieved by the natural environment itself or
sewage treatment plants. As a result, it is urgent to explore an effective
method to eliminate 2, 4-DCP in water environment. Recently, there are
several methods to remove 2, 4-DCP in water, such as electrochemistry
mical stability [27–37]. Moreover, Bi12
related oxide layered structure consists of [Bi12
O
17Cl
2
has a sillen-aurivillius-
17] layers between two
O
slabs of [Cl] ions with an internal static electric field perpendicular to
each layer, which is in favor of the transfer and separation of photo-
generated charge carriers [34,38,39]. Meanwhile, the intrinsic polar-
izabilities induced by the synergy of Bi 6s2 lone electron pairs with
vacant Bi 6p orbits can facilitate the migration and mobility of photo-
generated electrons. However, the rapid recombination of electron-hole
pairs is still a significant restriction for photocatalytic performance of
2
Bi12O17Cl , which needs to be improved via the rational martial design
and fabrication strategies.
Nickel oxide (NiO) is one of the most widely used catalyst that have
been caught the focus due to their excellent physical and chemical
properties, which usually was investigated in some important applica-
tion fields including catalysis, gas sensing, battery cathodes, magnetic
materials, electrochromic films, chemical sensors, photovoltaic devices,
[
17], precipitation [18], adsorption [19], photocatalysis [20], etc.
Among them, photocatalysis has been proved to be a promising tech-
nology to completely degrade 2, 4-DCP owing to its high-efficiency,
eco-friendly and using renewable solar energy, etc. advantages.
[
21–26]. However, it still is a significant and challenging work to ex-
etc. [40]. In consequence, if NiO combines with Bi12
2
O17Cl to construct
plore high-efficiency photocatalysts.
the heterostructure, it may facilitate the separation and migration of
⁎
Corresponding authors at: Key Laboratory of Preparation and Application of Environmental Friendly Materials, Ministry of Education, Jilin Normal University,
Changchun, 130103, PR China.
E-mail address: donghongjun6698@aliyun.com (H. Dong).
https://doi.org/10.1016/j.jphotochem.2019.112102
Received 15 August 2019; Received in revised form 12 September 2019; Accepted 21 September 2019
Available online 23 September 2019
1010-6030/ © 2019 Elsevier B.V. All rights reserved.

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
charge carriers, thus improving the photocatalytic performance.
In this work, therefore, a zero-dimensional/two-dimensional (0D/
liquid chromatography-mass spectrometry (HPLC-MS) system was used
to test the structure of the intermediates.
2
D) NiO/Bi12
of NiO nanodots on the surface of Bi12
hydrothermal process followed by simple calcination. The powerful
interface interaction between NiO nanodots and Bi12 17Cl nanosheets
O
17Cl
2
heterojunction was obtained by in-situ fabrication
O
17Cl nanosheets in a facile
2
2.4. Photocatalytic activity experiments
O
2
2, 4-DCP was used as the target molecules to evaluate the photo-
catalytic degradation activity of samples. 50 mg sample was dispersed
obviously improves the physical, optical and photoelectrochemical
properties. The formed Z-scheme heterostructure distinctly enhances
the transfer and separation efficiency of charge carriers, thus dramati-
cally boosting the photocatalytic degradation performance for re-
moving 2, 4-DCP in water. Moreover, the possible photocatalytic re-
action mechanism is discussed in detail, including the separation and
migration behaviors of charge carriers, generation of active species,
intermediate products of degrading 2, 4-DCP and so on.
−1
in 100 mL 2, 4-DCP solution (20 mg L ) under the constant stirring.
After ultrasonic treatment of 10 min, the solution was stirred for 30 min
in the dark to make the adsorption-desorption equilibrium between 2,
4-DCP and sample [41]. Afterwards, a 250 W Xenon lamp covered with
a UV filter (λ > 420 nm) was used as light source. The specimen was
pipetted from the suspension with 30 min intervals in the solution. The
concentration of centrifugally separated supernatant was determined
by an UV–vis spectrophotometer (Shimadzu, USA) at 286 nm which is
the characteristic absorption wavelength of 2, 4-DCP.
2. Experimental section
2.1. Materials
2.5. Photoelectrochemical measurements
BiCl
3
(≥98.0%, AR), C
6
H
12
O
6
(AR), NaOH (≥96.0%), CH
4
N
2
O
The photocurrent and electrochemical impedance spectra were
measured by using a standard three-electrode system. The as-prepared
samples, saturated Ag/AgCl and Pt plate electrode are served as the
working electrodes, reference electrode and counter electrode, respec-
(
≥99.0%, AR), C
2
H
6
O (≥99.7%, AR)and NiCl
2
•6H O (≥98.0%, AR)
2
all were purchased from Sinopharm Chemical Reagents Co., LTD and
used without any further purification.
−
1
2 4 3 6
tively. The Na SO and K Fe(CN) aqueous solution (0.5 mol L ) as
2
.2. Preparation process
electrolytes can be applied to measure photocurrents and electro-
chemical impedance spectra (EIS), respectively. The working electrode
was prepared by the following method: 0.05 g of the sample was dis-
solved in 1 mL mix solution consisted of 0.01 g PVP, 0.03 mL oleic acid
and 3 ml ethanol. Afterwards, the dispersion mixture was spun onto
1.0 × 1.0 cm FTO substrates as working electrode. The light source was
the same as the photocatalytic measurement experiments.
4
mmol BiCl , 20 ml C H OH, 24 mmol NaOH and 20 ml deionized
3
2 5
water were stirred to form a homogeneous solution, and then trans-
ferred into 50 mL Teflon autoclaves and heated in an oven at 120 ℃ for
6
h. The produced yellow precipitate was washed by distilled water and
ethanol absolute for several times. After dried at 60 ℃ for 12 h,
Bi12 17Cl nanosheet was obtained.
O
2
NiO is prepared by a facile hydrothermal process followed by simple
calcination. Typically, the mixed materials with 1 : 12 : 29 ratios of
3. Results and discussion
NiCl
2
•6H
2
O : CO(NH
2
)
2
: C
6
H
12
O
6
were added in 70 ml deionized water,
The structure and phase composition of samples are analyzed by
stirred for 30 min, transferred into 100 mL Teflon autoclaves, and he-
ated in an oven at 160 ℃ for 20 h. The produced gray precipitate was
washed by distilled water and ethanol absolute for several times, dried
2
XRD. From XRD of Bi12O17Cl sample in Fig. 1a, the characteristic peaks
at 26.4°, 29.2°, 30.4°, 32.9°, 35.7°, 45.5°, 47.2°, 54.9° and 56.4° origi-
nate from (1 1 5), (1 1 7), (0 0 12), (2 0 0), (0 0 14), (2 0 12), (2 2 0), (3
at 60 ℃ for 12 h. Furthermore, the NiO/Bi12
tained by adding 0.3 g Bi12 17Cl at the preparation process of NiO. The
different mass ratios (1%, 3%, 5%, 7% and 9%) of NiO in NiO/
Bi12 17Cl sample were controlled and abbreviated as NiO/Bi12 17Cl
, NiO/Bi12 17Cl -2, NiO/Bi12 17Cl -3, NiO/Bi12 17Cl -4 and NiO/
Bi12 17Cl -5, respectively.
O
17Cl
2
samples were ob-
1 5) and (3 1 7) lattice planes of monoclinic Bi12
0760). In comparison, the relative diffraction intensity at 29.2° is sig-
nificantly improved in XRD of NiO/Bi12 17Cl -4 sample, which may
result from the modification effect of NiO on the surface of Bi12 17Cl
nanosheets. No diffraction peaks of NiO phase are observed which
probably due to its relative low contents in NiO/Bi12 17Cl -4 sample.
Meanwhile, Raman spectrum of Bi12 17Cl in Fig. 1b show that the
intense bands are centered at 96 cm 1, 130 cm
2
O17Cl (JCPDS No. 36-
O
2
O
2
O
2
O
2
-
O
2
1
O
2
O
2
O
2
O
2
O
2
O
2
−
−1
−1
2.3. Characterizations
,
165 cm
,
−
1
−1
−1
−1
3
95 cm , 472 cm
strong peaks at 96 cm and 130 cm are assigned to A1g external Bi-
and 600 cm . Among them, the distinctive
−
1
The scanning electronic microscopy (SEM) was used to identify the
−
1
morphology of as-prepared samples by JSM-7001 F. Raman spectra
were performed on HORIBA HR 800 Laser Confocal Raman
Microspectroscopy (Japan). The powder X-ray diffraction (XRD) pat-
terns of samples were obtained on a D/MAX-2500 diffractometer
Cl stretching mode; the band at 165 cm
g
is attributed to the E ex-
−
1
ternal Bi-Cl stretching mode; the intense band at 472 cm is produced
by the B1g motion of oxygen atoms [32,42]. Although vibration mode of
NiO is not detected owing to the relative contents, the signal peaks of
(
Rigaku, Japan) using a Cu Kα radiation source (λ = 1.54178 Å). The
Bi12
O
17Cl
2
are distinctly increased, which may result from surface
17Cl nanosheets.
transmission electron microscopy (TEM) and high-resolution transmis-
sion electron microscopy (HRTEM) were used to characterize the mi-
cromorphology and microstructure of samples by JEM-2100 (HR). The
X-ray photoelectron spectroscopy (XPS) was obtained by Thermo
ESCALAB 250X (America) electron spectrometer using 150 W Al Kα
radiations. The UV–vis diffuse reflectance spectra (DRS) were obtained
by a UV–vis-NIR spectrophotometer (Cary 8454 Agilent, inc) with the
scanning range of 200 nm −700 nm. Total organic carbon (TOC) was
determined by multiple N/C 2100 TOC analyzer (Analytik Jena AG,
Germany). The specific surface area and pore diameter distribution of
the samples were measured on a nitrogen adsorption BET method (3H-
decoration effect of NiO on Bi12
In order to further confirm the morphology and microstructure of
samples, SEM, TEM and HRTEM characterizations were carried out. As
shown in Fig. 2a–b, the SEM images of Bi12
nosheet structure with a clean and smooth surface. By contrast, the SEM
image of NiO/Bi12 17Cl -4 sample in Fig. 2c shows the plenty of NiO
nanodots are modified on Bi12 17Cl nanosheets. In addition, the na-
nosheet structure with smooth surface is also observed in TEM image of
O
2
2
O17Cl ample show a na-
O
2
O
2
Bi12
Bi12
O
O
17Cl
17Cl
2
sample (Fig. 2d). Similarly, the TEM image of NiO/
-4 sample further displays NiO nanodots are evenly dis-
2
tributed on Bi12
image of NiO/Bi12
lattice spacing of 0.259 nm corresponds to the (220) lattice planes of
O
17Cl
2
nanosheets (Fig. 2e). Furthermore, the HRTEM
2
000PS1). The electron spinning resonance (ESR) analysis was carried
O
17Cl
2
-4 sample is displayed in Fig. 2f, where the
out by the Bruker EPR JES-FA200 spectrometer. High performance
2

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
2 2
Fig. 1. XRD patterns (a) and Raman spectra (b) of Bi12O17Cl and NiO/Bi12O17Cl -4 samples.
Bi12
Bi12
Bi12
O
O
O
17Cl
17Cl
17Cl
2
2
2
phase and NiO nanodots are firmly anchored on the
nanosheets. In addition, EDX elemental mappings of NiO/
-4 sample in Fig. 2g–k exhibit Bi, O, Cl and Ni elements are
which attributed to Bi-O bonds and surficial hydroxyl groups (Bi-O-H),
respectively [44,45]. From Cl 2p XPS spectrum of Bi12 17Cl in Fig. 3c,
the binding energy peaks located at 199.5 eV and 197.9 eV are referred
O
2
−
1
−1
distributed throughout samples, implying the formation of NiO/
Bi12
Bi12
The chemical compositions and elemental valence states of samples
were investigated by XPS. Bi 4f XPS spectrum of Bi12 17Cl sample in
Fig. 3a shows the two characteristic peaks at 164.0 eV and 158.7 eV,
to Cl
similar shift phenomena are also observed in O 2 P and Cl 2 P XPS
spectra of NiO/Bi12 17Cl -4 sample, further indicating the intense in-
teraction existed inside NiO/Bi12 17Cl heterojunction. In term of Ni 2p
XPS spectrum of NiO/Bi12 17Cl -4 sample in Fig. 3d, there are two
2p1/2 and Cl
2p3/2 states [46]. It is worth noting that the
O
O
17Cl
17Cl
2
hybridization. The above results indicate that 0D/2D NiO/
heterojuction is fabricated.
2
O
2
O
2
O
2
O
2
predominant peaks at 855.4 eV and 873.9 eV, corresponding to Ni 2p3/2
and Ni 2p1/2 states, while the peaks centered at 860.8 eV and 879.9 eV
represented the shake-up satellite peak resulting from the presence of
3
+
3+
which are assigned to Bi
43]. Compared to Bi12 17Cl
spectrum of NiO/Bi12 17Cl -4 sample shift 0.3 eV to high energy di-
rection, respectively, which indicates the strong coupling effect be-
tween Bi12 17Cl and NiO. In addition, O 2p XPS spectrum of
Bi12 17Cl in Fig. 3b presents two peaks at 530.9 eV and 529.3 eV,
4f5/2 and Bi
4f7/2 states, respectively
[
O
2
, these two binding energy peaks in XPS
2+
O
2
Ni
cations. [47,48].
The photocatalytic activity of samples was determined by de-
gradation of 2, 4-DCP under the visible light irradiation. As shown in
Fig. 4a, the NiO/Bi12 17Cl samples exhibit the better degradation
O
2
O
2
O
2
Fig. 2. SEM images of Bi12
O
17Cl
2
(a, b) and NiO/Bi12
O17Cl
2 2 2
-4 (c) samples, TEM images of Bi12O17Cl (d) and NiO/Bi12O17Cl -4 (e) samples, HRTEM image (f) and
EDX elemental mappings (g–k) of NiO/Bi12
O
17Cl -4 sample.
2
3

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
2 2
Fig. 3. XPS spectra of Bi12O17Cl and NiO/Bi12O17Cl -4 samples.
0 2
Fig. 4. Dynamic curves (a) and plots of ln(C /C) versus time (b) of 2, 4-DCP over different samples, TOC removal rate of 2, 4-DCP over Bi12O17Cl and NiO/
Bi12O17Cl -4 samples within 180 min (c) and absorbance variations of 2, 4-DCP solution within 180 min (d).
2
4

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
activity than Bi12
over the NiO/Bi12
degradation reactions are in great agreement with the quasi-first-order
kinetic feature [49–51]. The rate constant of 2, 4-DCP degradation over
O
O
17Cl
17Cl
2
. The optimal degradation rate reaches to 89.3%
-4 sample. In addition, Fig. 4b shows that all
that of Bi12
Bi12 17Cl and NiO/Bi12
ture centered about 35 nm, which may result from the stacking of
O
17Cl
2
. From Fig. 7b, the pore diameter distributions of
2
O
2
O
17Cl -4 samples exhibit the mesoporous fea-
2
Bi12
O
17Cl
2
nanosheets. Meanwhile, the NiO/Bi12
O
17Cl
2
-4 sample pos-
−1
2 −1
NiO/Bi12
than that of NiO (0.0036 min ) and Bi12
spectively. Furthermore, Fig. 4c shows the TOC removal rates of 2, 4-
DCP within 180 min over Bi12 17Cl and NiO/Bi12 17Cl -4 samples. It
O
17Cl
2
-4 sample (0.0116 min ) is about 3.2 and 3.7 times
sesses a relatively low specific surface area (8.49 m g ) compared
with Bi12O17Cl (11.6 m g ), The results suggest that the boosted
2
−
1
−1
2 −1
O
17Cl
2
(0.0031 min ), re-
photocatalytic activity has little to do with specific surface area, pore
diameter and absorptivity, and indirectly indicate that the improved
transfer and separation efficiency of photogenerated charge carriers is
main influence factor on the photocatalytic activity.
O
2
O
2
is obvious that the mineralization rate of the latter (79.4%) is much
higher than that of the former (39.1%). Moreover, the absorbance of 2,
4
-DCP solution is distinctly decrease with prolonging reaction time,
further suggesting that it may be decomposed into small molecules/
ions, CO and H O [52]. The results indicate that the fabrication of 0D/
D NiO/Bi12 17Cl heterojunction enhances the photocatalytic de-
The capture tests are investigated in detail to detect the generated
active species during the degradation reaction. As can be seen from
Fig. 8 a–b, the degradation reactions of 2, 4-DCP are all obviously re-
strained when tetraacetic acid ethylenediamine disodium (EDTA-2Na),
2
2
2
O
2
gradation activity dramatically.
ascorbic acid (VC) and isopropyl (IPA) are used as trapping reagents to
capture h+, •O
−
and •OH in the photocatalytic reaction process, and
In order to evaluate photostability and recyclability of 0D/2D NiO/
2
Bi12
4
4
O
17Cl
-DCP were performed. As shown in Fig. 8a, the degradation rates of 2,
-DCP over NiO/Bi12 17Cl sample have no obvious reduction after six
2
heterojunction, the recycling degradation experiments of 2,
the degradation rates of 2, 4-DCP are 10.6%, 5.0% and 82.2%, re-
spectively, which indicate h+ and •O
influence of •OH is negligible. Moreover, •O
NiO/Bi12 17Cl -4 sample are detected by ESR technology. From Fig. 8c,
the intensity of DMPO-•O
far stronger than that over Bi12
−
are major active species and the
2
−
O
2
2
and •OH generated on
successive photocatalytic reactions, which demonstrate the 0D/2D
NiO/Bi12 17Cl heterojunction possesses the outstanding stability and
reusability. It is further confirmed by XRD of NiO/Bi12 17Cl -4 sample
before and after photocatalytic reaction. XRD pattern of NiO/
Bi12 17Cl -4 sample in Fig. 5b displays that the characteristic diffrac-
tion peaks has almost no variation after six consecutive cycle reactions,
which further proves that it has the superior stability.
The transfer and separation efficiency of photogenerated electron-
hole pairs of samples can be investigated by transient photocurrent
O
2
−
O
2
2
produced over NiO/Bi12
O
17Cl
, which indicates that the for-
heterojunction immensely promotes
2
-4 sample is
O
2
O17Cl
2
mation of 0D/2D NiO/Bi12
O
17Cl
2
−
O
2
the production of •O
2
active species. Meanwhile, no detecting char-
17Cl and NiO/Bi12 17Cl -4
acteristic signals of DMPO-•OH over Bi12
O
2
O
2
sample (Fig. 8d), it suggests that •OH cannot be generated in the de-
gradation process.
The UV–vis DRS is used to analyze the light absorption property of
responses. As displayed in Fig. 6a, the Bi12
samples both show the stable photocurrent responses under the visible
light irradiation [53]. The photocurrent response of NiO/Bi12 17Cl -4
sample is far higher than that of Bi12 17Cl , indicating that the mod-
ification effect of NiO nanodots on Bi12 17Cl nanosheets significantly
promotes the transfer and separation efficiency of charge carriers.
Furthermore, the electrochemical impedance spectroscopy (EIS) is an
effective to reveal the interface transfer efficiency of charge carriers
O
17Cl
2
and NiO/Bi12
O
17Cl
2
-4
samples. As presented in Fig. 9a, the Bi12
sample displays the superior visible light absorption ability. Meanwhile,
2 2
O17Cl and NiO/Bi12O17Cl -4
n/2
2
O
2
according to the Tauc formula (αhυ) = A(hυ−E
versus hυ (n = 1) is executed based on the direct band gap character-
istic of Bi12 17Cl and NiO [35,47]. As shown in the Fig. 9b, the band
gap values (E ) of Bi12 17Cl and NiO are estimated to be 2.87 eV and
3.29 eV, respectively. It is noteworthy that Bi12 17Cl and NiO samples
g
)
, the plots of (αhυ)
O
O
2
2
O
2
g
O
2
O
2
all form midgap levels of 2.62 eV and 2.30 eV due to the defects created
in the preparation process possibly [55], which avails the visible light
[
54]. In Fig. 6b, the smaller arc radius is observed on NiO/Bi12
sample, implying that it has the higher charge mobility and separation
ability of charge cariers than Bi12 17Cl . Therefore, the transfer and
separation efficiency of photogenerated electron-holes are distinctly
improved by the fabrication of 0D/2D NiO/Bi12 17Cl heterojunction,
2
O17Cl -4
response. Additionally, the bandgap and midgap of Bi12
changes after modification of a spot of NiO. Moreover, to further
identify the energy band position, the flat band potentials of Bi12 17Cl
and NiO samples were carried out. The positive slopes of Mott-Schottky
curves (Fig. 9c-d) imply the Bi12 17Cl and NiO samples are n-type
2
O17Cl have no
O
2
O
2
O
2
resulting in the enhanced photocatalytic activity for degrading 2, 4-
DCP.
O
2
semiconductors, and their flat band potentials are -0.73 V and 0.25 V
Fig. 7a displays the
Bi12 17Cl and NiO/Bi12 17Cl
loops at the range of 0.8–1.0 (P/P
adsorbing capacity of NiO/Bi12 17Cl
N
2
adsorption-desorption isotherms of
-4 sample, where they possess hysteresis
) in accordance with type H3 and the
-4 sample is slightly decrease than
(vs. Ag/AgCl), respectively. So, the conduction band (CB) potentials of
Bi12O17Cl and NiO sample are approximately -0.53 eV and 0.45 eV; the
2
valence band (VB) potential are calculated to be 2.34 eV and 3.74 eV; as
well as the intermediate levels are -0.28 eV and 1.44 eV (vs. NHE),
O
2
O
2
0
O
2
Fig. 5. Cycle degradation dynamic curves of 2, 4-DCP over NiO/Bi12
O
17Cl
2
2
-4 sample (a), XRD patterns of NiO/Bi12O17Cl -4 sample before and after six cycle
reactions.
5

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
2 2
Fig. 6. Transient photocurrent responses (a) and EIS Nyquist plots (b) of Bi12O17Cl and NiO/Bi12O17Cl -4 samples.
respectively [55–60].
and Bi12
with holes generation on their VB, respectively. Then, photogenerated
electrons on CB of NiO and holes on VB of Bi12 17Cl recombine rapidly
at their interfaces, which can tremendously improve the transfer and
separation efficiency of charge carriers. Afterwards, the plenty of
2
O17Cl preferentially migrate to the intermediate levels along
Moreover, HPLC-MS technology was used to analyze the inter-
mediates in the degradation of 2, 4-DCP over NiO/Bi12
61]. According to the detected specific charge in mass spectra
Fig. 10), the possible reasonable degradation pathway of 2, 4-DCP is
proposed (Fig. 11). We know that the ortho- or para- Cl of 2, 4-DCP are
O
17Cl
2
-4 sample
O
2
[
(
photogenerated electrons accumulated on Bi12
molecules dissolved in water to produce •O
mained on NiO and •O - will directly oxidize 2, 4-DCP to small mole-
cules/ions, CO and H O.
O
17Cl
2 2
react with the O
−
−
2
easily replaced by •O
2
through addition reaction. Therefore, •O
2
-. Finally, the holes re-
firstly attacks and removals ortho-Cl is considered to produce para-
chlorophenol superoxide radicals (m/z = 159, B) and transform into 4-
chloro-catechol (m/z = 143.5, C) [62]. With prolonging to reaction
time, 4-chloro-catechol is further oxidized to 2-hydroxyphenol (m/
z = 109, D). Finally, accompanied by ring-opening reaction of 2-hy-
droxyphenol, maleic acid (m/z = 115, E) and oxalic acid (m/z = 89, F)
2
2
2
4. Conclusions
are produced, which are mineralized into CO
tion going on.
Based on the aforementioned experimental results, the photo-
catalytic reaction mechanism of 2, 4-DCP over 0D/2D NiO/Bi12 17Cl
heterojunction is proposed (Fig. 12). UV–vis DRS reveals that the
midgaps are created within the band gap of NiO and Bi12 17Cl , which
2
and H
2
O with the reac-
In conclusion, a 0D/2D NiO/Bi12
thesized in a facile hydrothermal process followed by simple calcina-
tion. The in-situ decoration of NiO nanodots on Bi12 17Cl nanosheets
implies the formation of compact heterostructure, which is in favor of
transfer and separation of charge carriers. The photocatalytic de-
2
O17Cl heterojunction was syn-
O
2
O
2
O
2
gradation performance of 2, 4-DCP over 0D/2D NiO/Bi12
2
O17Cl het-
are 1.44 eV and -0.28 eV, respectively, suggesting that electrons on VB
preferentially transfer to the intermediate levels under the visible light
erojunction was significantly higher than those of single NiO and
Bi12
Bi12
O
O
17Cl
17Cl
2
under the visible light irradiation. The optimal NiO/
-4 sample shows the highest degradation rate of 2.4-DCP
irradiation. The electrons on the intermediate level of Bi12
O
17Cl
instead of NiO
- with -0.046 eV [63]. The
are 3.74 eV and 2.34 eV, respec-
tively, which implies that the holes on the VB of NiO rather than
Bi12 17Cl can oxidize H O to form •OH owning to the standard redox
potential of H O/•OH with 2.7 eV [23]. As a result, after NiO nanodots
decorate on Bi12 17Cl nanosheets, Z-scheme heterojunction should be
constructed between them. Therefore, when 0D/2D NiO/Bi12 17Cl
heterojunction is exposed to the visible light, the electrons on VB of NiO
2
can
2
−
oxidize the O
due to the standard redox potential of O
VB potential of NiO and Bi12 17Cl
2
molecules in the solution to generate •O
2
reaching up to 89.29% within 180 min, and the corresponding reaction
−
1
2
/•O
2
rate constant (0.0116 min ) was 3.2 and 3.7 times higher than that of
−
1
−1
O
2
single NiO (0.0036 min ) and Bi12
O
17Cl
2
sample (0.0031 min ). The
- and holes are main
photocatalytic reaction mechanism reveals the •O
2
O
2
2
active species and the possible degradation process of 2, 4-DCP is also
discussed. The enhanced photocatalytic performance derives from the
formation of Z-scheme heterostructure between NiO and Bi12O17Cl .
2
2
O
2
O
2
Fig. 7. N
2
2 2
adsorption-desorption isotherms (a) and pore diameter distributions (b) of Bi12O17Cl and NiO/Bi12O17Cl -4 sample.
6

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
Fig. 8. Degradation dynamic curves (a) and degradation rates (b) of 2, 4-DCP over NiO/Bi12
O
17Cl
2
-4 sample when adding different trapping reagents, ESR spectra of
−
DMPO-•O
2
2
(c) and DMPO-•OH (d) over NiO/Bi12O17Cl -4 sample.
Fig. 9. Normalized UV–vis DRS (a) and plots of (ahυ)1/2 versus (hυ) (b) of Bi12
O
2 2
17Cl and NiO samples, Mott-Schottky plots of Bi12O17Cl (c) and NiO (d) samples.
7

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
2
Fig. 10. Mass spectra of 2, 4-DCP over NiO/Bi12O17Cl -4 sample at 0 min (a), 90 min (b) and 180 min (c), respectively.
Declaration of Competing Interest
Acknowledgments
None.
This work was supported by the NSFC-Shanxi Coal Based Low
Carbon Joint Fund (U1810117), National Natural Science Foundation
of China (21606114, 21546006, 21878131), Postdoctoral Science
Foundation of China (2017M611712, 2017M611717), Jilin province
2
Fig. 11. Possible intermediate products at the degradation process of 2, 4-DCP over NiO/Bi12O17Cl -4 sample.
8

N. Song, et al.
Journal of Photochemistry & Photobiology A: Chemistry 386 (2020) 112102
2
Fig. 12. Possible photocatalytic degradation mechanism of 2, 4-DCP over 0D/2D NiO/Bi12O17Cl heterojunction.
science and technology innovation center construction project
20180623042TC) and Scientific Research Foundation for Senior Talent
of Jiangsu University (17JDG020).
2 3 4
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