Novel Z-scheme heterogeneous photo-Fenton-like g-C3N4/FeOCl for the pollutants degradation under visible light irradiation

Article abstract of DOI:10.1016/j.jphotochem.2019.112343

Effective electron-hole separation efficiency is an important factor for enhanced photocatalytic activity. In this work, the Z-scheme heterogeneous photo-Fenton-like (HPF-like) g-C₃N₄/FeOCl catalysts were synthesized successfully by calcination method. The composites were applied for the photo-Fenton (PF) degradation of water pollutants with the assistance of H₂O₂. During this process, the color-less antibiotic tetracycline and dye rhodamine B were used as the target pollutants. Compared with pure FeOCl material, the Z-scheme g-C₃N₄/FeOCl composites reveal a higher PF catalytic activity under the irradiation of visible light. According to the experimental results, the enhanced catalytic activity of g-C₃N₄/FeOCl material was attributed to the formation of Z-scheme between g-C₃N₄ and FeOCl, which could promote the separation efficiency of electron-hole pairs induced by hybridization. Moreover, with the addition of g-C₃N₄, the increased specific surface area would further promoted the decomposition of H₂O₂ to form more ^[rad]OH. The results of radical trapping experiments and ESR confirmed the hydroxyl radical was the main active group in this process, indicating the Z-scheme was generated between g-C₃N₄ and FeOCl. Therefore, a possible mechanism of this HPF-like g-C₃N₄/FeOCl material was presented. This work may promote the development and application of FeOCl-based materials in the field of PF-like water pollutants treatment.

Full text of DOI:10.1016/j.jphotochem.2019.112343

Journal Pre-proof
Novel Z-scheme heterogeneous photo-Fenton-like g-C3N4/FeOCl for the
pollutants degradation under visible light irradiation
Junze Zhao (Investigation) (Writing - original draft) (Writing - review
and editing), Mengxia Ji (Validation) (Writing - review and editing),
Jun Di (Visualization) (Validation), Yi Zhang (Data curation),
Minqiang He (Methodology), Huaming Li (Resources) (Supervision),
Jiexiang Xia (Conceptualization) (Project administration)
PII:
S1010-6030(19)31514-X
DOI:
https://doi.org/10.1016/j.jphotochem.2019.112343
JPC 112343
Reference:
To appear in:
Journal of Photochemistry & Photobiology, A: Chemistry
Received Date:
Revised Date:
Accepted Date:
4 September 2019
21 December 2019
24 December 2019
Please cite this article as: Zhao J, Ji M, Di J, Zhang Y, He M, Li H, Xia J, Novel Z-scheme
heterogeneous photo-Fenton-like g-C3N4/FeOCl for the pollutants degradation under visible
light irradiation, Journal of Photochemistry and amp; Photobiology, A: Chemistry (2019),
doi: https://doi.org/10.1016/j.jphotochem.2019.112343

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Novel Z-scheme heterogeneous photo-Fenton-like g-C3N4/FeOCl for
the pollutants degradation under visible light irradiation
Junze Zhao1, Mengxia Ji1, Jun Di1, Yi Zhang1, Minqiang He1, Huaming Li1, Jiexiang
Xia1,*
1School of Chemistry and Chemical Engineering, Institute for Energy Research,
Jiangsu University, 301 Xuefu Road, Zhenjiang, 212013, P. R. China
*Corresponding author: Tel.:+86-511-88791108; Fax: +86-511-88791108;
E-mail address: xjx@ujs.edu.cn
Graphical abstract

Highlight
 The Z-scheme photo-fenton-like g-C3N4/FeOCl has been synthesized
successfully.
 Z-scheme built in g-C3N4/FeOCl efficiently accelerated the charge transfer.
 RhB and TC were effectively degraded by g-C3N4/FeOCl via a
photo-Fenton process.
 OH was the main role in the degradation process in the presence of H2O2.
Abstract
Effective electron-hole separation efficiency is an important factor for enhanced
photocatalytic activity of the catalyst. In this work, the Z-scheme heterogeneous
photo-Fenton-like (HPF-like) g-C3N4/FeOCl catalysts were synthesized successfully
by calcination method. The composites were applied for the photo-Fenton (PF)
degradation of water pollutants with the assistance of H2O2. During this process, the
color-less antibiotic tetracycline and dye rhodamine B were used as the target
pollutants. Compared with pure FeOCl material, the Z-scheme g-C3N4/FeOCl
composites reveal a higher PF catalytic activity under the irradiation of visible light.
According to the experimental results, the enhanced catalytic activity of
g-C3N4/FeOCl material was attributed to the formation of Z-scheme between g-C3N4
and FeOCl, which could promote the separation efficiency of electron-hole pairs
induced by hybridization. Moreover, with the addition of g-C3N4, the increased
specific surface area would further promoted the decomposition of H2O2 to form more
•OH. The results of radical trapping experiments and ESR confirmed the hydroxyl
radical was the main active group in this process, indicating the Z-scheme was
generated between g-C3N4 and FeOCl. Therefore, a possible mechanism of this
HPF-like g-C3N4/FeOCl material was presented. This work may promote the
development and application of FeOCl-based materials in the field of PF-like water
pollutants treatment.

Key words: FeOCl; g-C3N4; Photo-Fenton-like; Photocatalyst; Z-scheme
1. Introduction
As one of the important advanced oxidation processes, the Fenton reactivity has
got more focus in the field of water pollutant degradation [1-4]. During the Fenton
reaction, the hydroxyl radical (•OH) plays an important role in the degradation of
pollutants and the H2O2 is the source of •OH [4, 5]. In order to generate the •OH, the
homogeneous Fenton method normally choose the Fe2+ - H2O2 system [6]. However,
the pH of the homogeneous Fenton reaction needs to be kept within the acidic range
(pH = 2-4) [7]. Besides, the large rate of Fe3+ would be accumulated in the final
effluent [7]. To solve these drawbacks, the heterogeneous Fenton catalyst system,
especially iron-based heterogeneous Fenton catalysts [8-10], were reported as
promising alternatives and widely applied with a normal pH [9, 10]. However, the
further studies confirmed that the activity of heterogeneous Fenton-H2O2 system was
unsatisfactory due to their low decomposition efficiency of H2O2 and high cost of time.
[11,12]. To solve these problems, the recent researches are focus on the introduction
of the external energy (UV, visible light) into the heterogeneous Fenton system due to
the photo-induced electrons from the catalyst could react with H2O2 to generate more
•OH radicals or promote the reduction of Fe3+ into Fe2+ [13-15]. Therefore, the
HPF-like iron-based catalysts can be used as promising materials for water pollution
treatment [7, 13].
Recently, the iron oxychloride (FeOCl) arouses great concern as a functional
material in the fields of aquatic-organic-contaminants treatment and energy storage
[16-19]. The FeOCl shows two dimensional layer structure with the weak van der
Waals bonds supported [20-22]. In 2013, Han’s group firstly reported the FeOCl
material was used as a heterogeneous Fenton-like catalyst to treat water pollutants
[23]. In order to improve the Fenton catalytic activity of FeOCl, the same group
reported FeOCl/SiO2 and FeOCl/SBA-15 composites were further reported to confirm
the FeOCl materials with increased specific surface area materials could realize

higher reactive kinetics of the whole catalytic system due to more exposed active sites
[24, 25]. Recently, the FeOCl material shows potential applications in the field of
HPF-like catalyst [26-28]. As a semiconductor, recent research indicated that the
FeOCl could be activated by the visible light irradiation [26]. However, affected by
the narrow band gap of the pure FeOCl material, the PF activity was still limited by
its high recombination efficiency of electron-hole pairs [27]. To improve this
phenomenon, it was valid to compound the FeOCl material with other co-catalysts
such as FeOCl/iron hydroxide and FeOCl/GO [27, 28]. Therefore, with the assistance
of H2O2 and the irradiation of visible light, these composites could degrade the
pollutant in the water effectively [27, 28].
Based on the previous researches, the two dimensional (2D) materials with the
suitable band structure have been focused in the field of photocatalysis due to their
large specific surface area can provide more active sides [29, 30]. As a 2D layered
material, the graphitic carbon nitride (g-C3N4) has been known as a functional
photocatalytic material for a long time due to its wide response of the visible light,
large surface area and befitting band-gap (about 2.7 eV) [31]. The recent researches
also verified that the photo-induced electron of g-C3N4 could decompose the H2O2 in
water and to form the •OH, which indicated that the g-C3N4 could be used as a
promising HPF-like catalyst [32-34]. However, the low separation rate of
electron-hole pairs still limited the photocatalytic activity of g-C3N4 material [35-37].
Recently, the Z-scheme g-C3N4-based materials attracted more attentions due to its
remarkable photo-exited charge transfer efficiency and electron-hole pair separation
efficiency [38-40]. Previous literatures mainly concentrated on the construction of
g-C3N4-based Z-scheme heterogeneous photocatalysts which exhibited the increasing
photocatalytic activity such as g-C3N4/WO3 [41], MoS2/g-C3N4 [42] and g-C3N4/BiOI
[43]. However, engineering the g-C3N4-based Z-scheme structure into HPF-like
materials was reported rarely [44]. Inspired by the above discussion, a hypothesis can
be put forward. Considering the less negative VB position of the g-C3N4 and more
positive CB position of the FeOCl, it may be possible to construct a Z-scheme
structure between g-C3N4 and FeOCl to promote the photogenerated charge transfer

between the two materials, thus the composite may exhibit excellent redox ability.
Besides, more electron may gathered on the CB of g-C3N4 to active H2O2 to generate
more •OH.
Herein, the Z-scheme g-C3N4/FeOCl was synthesized by calcination method.
The PF catalytic, photocatalytic and Fenton catalytic activities were measured to
evaluate the different pollutant degradation efficiencies of pure FeOCl and
g-C3N4/FeOCl composite. Based on the results of catalytic activity, electrochemical
measurements and radical trapping experiments, the g-C3N4/FeOCl showed the
improved PF activity than pure FeOCl due to its enhanced photogenerated charge
transfer efficiency and specific surface area. As the result, the •OH was the main
radical group during the PF degradation and the possible mechanism of
g-C3N4/FeOCl was proposed.
2. Experimental Section
In this work, all the reagents were analytical grade and no purification is required
before used.
2.1 The synthesis of g-C3N4 materials
The synthesis method of g-C3N4 was based on the literature [45]. 2 g
o
dicyandiamide was put into the crucible and calcined at 350 C for 2 hours in a tube
furnace. Then the temperature was raised to 600 oC in 90 minutes and kept for another
2 hours. This process was kept in a N2 atmosphere. After cool down to the room
temperature, the yellow g-C3N4 powder was obtained.
2.2 The synthesis of g-C3N4/FeOCl and pure FeOCl materials
According to the previous reports of literature [46], the pure FeOCl material was
synthesized by the calcined method. 2 g FeCl3·6H2O powder was heated at 220 oC for
4 hours in air. After cool down to the room temperature by natural, the obtained dark
purple powder was FeOCl material.
The g-C3N4/FeOCl materials were synthesized by the similar method with pure
FeOCl material. The as-prepared g-C3N4 and FeCl3·6H2O powder were mixed by the
different mass ratios of 1:20, 1:10, 1:5 and 3:10, respectively. Then the mixtures were

milled and calcined at 220 oC for 4 hours, the powders was obtained and cool down to
the room temperature. The as-prepared powders were named as g-C3N4/FeOCl-5,
g-C3N4/FeOCl-10, g-C3N4/FeOCl-20 and g-C3N4/FeOCl-30, respectively.
2.3 Characterization
The crystalline structures of the g-C3N4/FeOCl composites, pure FeOCl and
g-C3N4 were characterized by a Shimadzu XRD-6000 X-ray diffraction (XRD) with
monochromatized Cu Kα (λ=1.5418 Å) radiation, the scanning speed was 7° min-1
from 10° to 80°. To qualitative analysis the elemental composition of each material,
the X-ray photo-electron spectrometer (XPS, ESCA Lab MKII) was applied by using
the Mg Kα radiation. To characterize the morphologies of photocatalysts, the scanning
electron microscope (SEM) and transmission electron microscopy (TEM) were
operated by the JEOL JSM-7001F (JEOL, Japan) and JEOL JEM-2100 (JEOL, Japan),
respectively. The UV-vis diffuse reflectance spectroscopy (DRS) was investigated on
a Shimadzu UV-2450 spectrophotometer. The TriStar II 3020 surface area and
porosity analyzer (Micromeritics Instrument Corporarion, USA) was applied to
analyze the specific surface area of g-C3N4/FeOCl composites, pure FeOCl and
g-C3N4 materials at 77 K. All the electrochemistry experiments were operated at a
performed on a CHI 660B electrochemical system (Chenhua Instrument Company).
2.4 PF catalytic and photocatalytic activities test
The PF catalytic, Fenton catalytic and photocatalytic activities of pure FeOCl
and g-C3N4/FeOCl materials were tested at the same condition, the target pollutant
was rhodamine B (RhB). During the PF activity research, 20 mg as-prepared materials
were poured into 100 ml RhB solution with the concentration of 10 mg/l, the reaction
temperature was kept at 30 oC. After the solution stirred for 30 minutes in dark to
achieve the adsorption-desorption equilibrium, 200 μl H2O2 was injected into the
solution. Then a 300 W Xe arc lamp with a 400 nm cutoff filter was used as the
source of visible light. During this process, about 3 ml solution was carried out per 20
min and centrifuged. Then the supernatants were analyzed by an UV-vis
spectrophotometer (Shimadzu, UV-2450) at the absorbance wavelength of 553 nm.
The photocatalytic and the Fenton catalytic activity experiments were carried out in

the similar condition with PF activity experiment. However no H2O2 would introduce
into the photocatalytic degradation and no visible light would irradiate during the
Fenton degradation.
Besides, the 50 mg/l color-less antibiotic pollutant tetracycline (TC) was also
used as the target pollutant to investigate PF catalytic activity of g-C3N4/FeOCl
materials. The dosage of catalysts was 10 mg for the degradation of TC and the
absorbance wavelength of TC was 356 nm.
3. Results and discussion
3.1 Analysis of materials qualitative
The crystalline and phase structures of g-C3N4/FeOCl, pure FeOCl and g-C3N4
were identified by powder x-ray diffraction (XRD) patterns. As shown in Figure 1, all
the diffraction peaks of pure FeOCl could be matched with the standard card of
FeOCl (JCPDS card No.24-1005). The diffraction pattern of g-C3N4 was
corresponded to the literature [45]. It was obviously that the peaks of g-C3N4/FeOCl
composites included both g-C3N4 and FeOCl. Among the XRD analysis, there were
no other impurities peaks could be found and further indicated the high purity of the
g-C3N4/FeOCl composites, FeOCl and g-C3N4 materials. Besides, the XRD pattern of
g-C3N4/FeOCl-30 material showed unclearly peaks of FeOCl means the surface of
FeOCl might be wrapped by the excess g-C3N4.
To investigate the surface chemical states and chemical composition of FeOCl
and g-C3N4/FeOCl composites, the X-ray photoelectron spectroscopy (XPS) spectra
were employed. All the XPS results have been corrected by the 284.6 eV of C 1s. The
Figure 2a showed the main elements of the pure FeOCl and g-C3N4/FeOCl-20
composite materials, the spectra could recognize Fe, O, Cl elements in FeOCl
material and g-C3N4/FeOCl-20 composite obviously, while the C and N elements in
g-C3N4/FeOCl-20 composite could also be observed clearly. The Figure 2b was the
Fe 2p3 spectra of two materials, the peaks at about 711.4 and 725.4 eV belonged to
the Fe 2p3/2 and Fe 2p1/2 of Fe3+ in the FeOCl [47]. The Figure 2c showed O 1s

spectra in FeOCl and g-C3N4/FeOCl composites, in which the peaks of FeOCl were
similar with g-C3N4/FeOCl composites from 528 to 534 eV. Moreover, the O in
g-C3N4/FeOCl materials could be mainly split into three peaks. The peak at 530.6 eV
could be matched with the Fe-O in the FeOCl lattice while the 532.7 and 531.7 eV
was ascribed to the H2O molecules and hydroxyl groups on the surface, respectively
[21, 27]. Figure 2d showed the spectra of Cl 2p which showed two obvious peaks at
about 199.8 and 198.6 eV associated with Cl– in the pure FeOCl and g-C3N4/FeOCl
composites [48]. The Figure 2e and Figure 2f showed the N and C elements in the
g-C3N4/FeOCl composites. In Figure 2e, the peaks at 397.7, 398.8 and 399.7 eV were
attributed to N element in Fe-N, C-N=C and tertiary N (N-(C)3), respectively [49, 50].
The results prove that there is an interaction between FeOCl and g-C3N4. On the other
hand, the peaks at 288.4 and 284.6 eV observed in Figure 2f were attributed to
defect-containing sp2-bonded carbon (N–C=N) and carbon (C–C and C=C),
respectively [49].
The scanning electron microscope (SEM) and transmission electron microscopy
(TEM) were employed to investigate the morphologies of g-C3N4, FeOCl and
g-C3N4/FeOCl-20 materials. The SEM (Figure S1a) and TEM (Figure S1c) images
exhibited that the morphology of g-C3N4 was bulk-like structure. As shown in Figure
S1b and Figure S1d, the SEM and TEM results of pure FeOCl indicated the pure
FeOCl was irregular ribbon-like sheet structure, the width of ribbons were about 100
nm to 2 μm. The Figure S1e showed the SEM image of g-C3N4/FeOCl-20 composite.
The as-prepared material was revealed as the accumulation of sheet-like structure. To
further recognize the morphology and structure of g-C3N4/FeOCl composite, the TEM
was further employed. As shown in Figure 3a, it can be observed that the irregular
ribbon-like sheet materials stacked on the g-C3N4 material obviously. The
high-resolution TEM was carried out to reveal the arrangement of FeOCl and g-C3N4
materials and the result was shown in Figure 3b. It can be observed distinctly that the
coexistence of FeOCl and g-C3N4 materials, and the spacing of lattice stripes was
confirmed to be 0.253 nm, which could be matched with the (0 2 1) plane of FeOCl
crystal (JCPDS card No.24-1005). Therefore, it could further prove the tight contact

between g-C3N4 and FeOCl.
To further identify the chemical composition of the g-C3N4/FeOCl-20 composite,
the energy dispersive spectrometer (EDS) spectrum was measured and the result was
shown at Figure S2. The C, N, Fe, O and Cl elements could be observed in the
g-C3N4/FeOCl-20 composite. Besides, basic on the results of weight percentages of
the elements, the C and N elements account for about 30.72 wt% of total mass while
the Fe, O and Cl were accounted for 69.28 wt% in as-prepared g-C3N4/FeOCl-20
composite. This result was fully close to the theoretical mass ratio of g-C3N4 and
FeOCl in g-C3N4/FeOCl-20 (about 1:2). Therefore, it could further confirm the
component of g-C3N4/FeOCl-20. The Figure S3 showed the mapping images of each
element, the C, N, Fe, O and Cl elements was distributed on the g-C3N4/FeOCl-20
material evenly.
3.2 PF catalytic, photocatalytic and Fenton catalytic activities
The PF catalytic activity of as-prepared material was evaluated by the
degradation of RhB under the visible light irradiation. As shown in Figure. S4c, the
adsorption-desorption equilibrium was realized between the catalysts and RhB after
adsorbing for 30 min in the dark. As shown in Figure 4a, the FeOCl degraded about
60% RhB in 60 min with the irradiation of visible light and the addition of H2O2.
However, with the introduced of the g-C3N4, the degradation activity of
g-C3N4/FeOCl composites revealed a growing tendency. Among it, the
g-C3N4/FeOCl-20 composite exhibited the best catalytic activity and about 90 % RhB
pollutant was removed after the visible light irradiation for 60 min. While the g-C3N4
dose was 30 wt%, the catalytic activity was decreased. The Figure 4b showed the
degradation kinetics of the RhB by FeOCl and g-C3N4/FeOCl composites. Based on
the pseudo-first-order kinetics plot, the spectra was following the equation of
−ln(C/C0) = kt while k, C and C0 were the reaction rate constant, concentration of
RhB at irradiation time and the initial concentration of RhB, respectively. The rate
constant of g-C3N4/FeOCl-20 material was higher than the other materials, which
could be assumed that the g-C3N4/FeOCl-20 composite shows the best PF catalytic
activity.

To explore the function of visible light and H2O2 in this system, the
photocatalytic and Fenton catalytic degradation efficiency of pure FeOCl and
g-C3N4/FeOCl towards RhB were also measured and the results were shown in
Figure 4c. Without the addition of H2O2, the photocatalytic degradation efficiency of
pure FeOCl and g-C3N4/FeOCl-20 composite were only reached about 9% and 25%
during the same light irradiation time, respectively. Without the irradiation of the
visible light, the Fenton catalytic activities of pure FeOCl and g-C3N4/FeOCl-20
composite were only 25% and 56%, respectively. Therefore, the PF activities of each
material were higher than that of photocatalytic and Fenton activities. These results
indicated the H2O2 and visible light played important roles in the process of RhB
degradation simultaneously.
To further investigate the PF catalytic activity of g-C3N4/FeOCl composite,
several experiments were carried out including the (1) Self-degradation of RhB; (2)
The photo-degradation of RhB with H2O2 (200 μl); (3) The RhB PF catalytic
degradation by g-C3N4 (20 mg/l) and H2O2 (200 μl); (4) The PF experiment of
mixture powder which was mechanical mixed by FeOCl and g-C3N4 (the mass rate
was 2:1, which was the same with the g-C3N4/FeOCl-20 composite). The four results
are exhibited in Figure 4d, The PF catalytic activity of the g-C3N4/FeOCl-20 was
shown as the contrast. The experiments of (1), (2) and (3) could be confirmed that the
catalytic activity of RhB self-degradation and H2O2 photo-degradation were poor. The
PF catalytic activity of g-C3N4 by adding H2O2 was also unsatisfactory which
indicated the RhB could not be degraded efficiently in the water with the presence of
H2O2 and g-C3N4 only. Compared with the g-C3N4/FeOCl-20 composite, the
experiment (4) showed a lower catalytic activity, indicating the construction of
junction between g-C3N4 and FeOCl could promote the catalytic activity of the
g-C3N4/FeOCl-20. The cycle stability of PF degradation of RhB by g-C3N4/FeOCl-20
was measured and shown in Figure S4a. After five cycles of RhB degradation
experiments, 74% of RhB pollutant could still be degraded by the g-C3N4/FeOCl-20
composite, indicating the high stability of as-prepared catalyst.
To investigate the degradation activity of other color-less pollutant by

g-C3N4/FeOCl composites, TC was chosen as the target pollutant. The Figure S4d
indicated the adsorption-desorption equilibrium was released between catalysts and
TC after 30 min. As shown in Figure S4b, the as-prepared g-C3N4/FeOCl exhibited
the apparently enhanced PF-catalytic activity and g-C3N4/FeOCl-20 composite
showed the highest PF catalytic activity, about 90% TC was degraded after 20 min
light irradiation. As the result, the g-C3N4/FeOCl-20 composite could degrade both
dye and color-less antibiotics efficiently.
3.3 Catalytic mechanism analysis
In order to investigate the enhanced catalyst activity of g-C3N4/FeOCl-20, the
DRS was employed to exhibit the light absorption capacity of g-C3N4/FeOCl
materials, FeOCl, and g-C3N4 and the results were shown in Figure 5a. It can be
observed that the wavelength of pure FeOCl and g-C3N4 materials absorbance were
shown at about 820 nm and 480 nm which all belonged to the range of visible light (>
420 nm). However, when the g-C3N4 material was introduced, a slightly blue shift
was observed for the g-C3N4/FeOCl (about 763 nm) which indicating the visible light
adsorption of composites was decreased. Besides, according to the DRS result of
FeOCl, the band-gap (Eg) of pure FeOCl material was 1.77 eV which was shown at
Figure S5. The Eg of g-C3N4 was 2.67 eV in the previous literature [31].
The BET specific surface area images of pure FeOCl and g-C3N4/FeOCl-20
composite were shown in Figure 5b. As the results, the BET specific surface area of
pure FeOCl was 0.49 m2/g, while the surface area of g-C3N4/FeOCl-20 material could
reach to 25.08 m2/g. The introduction of g-C3N4 could increase the specific surface
area of the material obviously and lead to more exposed reaction sites of
g-C3N4/FeOCl-20 for adsorbing massive pollutant molecules, thus improving a higher
dark-Fenton activity than pure FeOCl.
It is reported that the electrochemical methods were useful to study the
interfacial charge transition in the composite [51-53]. To investigate the relationship
between charge transfer efficiency and enhanced PF catalytic activity of
g-C3N4/FeOCl-20, the electrochemical impedance spectroscopy (EIS) of pure FeOCl,
g-C3N4 and g-C3N4/FeOCl-20 composite were measured and shown in Figure 5c. In

the EIS spectra, the radius of Nyquist arc of g-C3N4/FeOCl-20 composite was smaller
than that of g-C3N4 and FeOCl materials, which indicated the lower resistance for
charge transfer efficiency in g-C3N4/FeOCl-20 composite. Figure 5d showed the
photocurrent spectra of and g-C3N4/FeOCl, FeOCl and g-C3N4 materials. During this
process, the materials were irradiated by the Xe lamp light for 20 seconds, and then
the light was switched off for other 20 seconds. It could be observed that the
photocurrent of g-C3N4/FeOCl materials was higher than that of pure FeOCl and
g-C3N4, indicating the enhanced separation efficiency of photogenerated electron-hole
pairs under the visible light irradiation compared with FeOCl and g-C3N4. These
might lead to the higher PF catalytic activity of g-C3N4/FeOCl-20 during this process.
The radicals trapping experiments of g-C3N4/FeOCl-20 composite were carried
out to investigate the main active groups in this PF degradation process. As is shown
in Figure 6a, the tertiary butanol (TBA), EDTA-2Na and Ar gas were used as the
−
inhibitor of hole (h+), •OH and superoxide radical (•O2 ), respectively [54-56]. The
degradation activity was reduced obviously while the TBA was added which indicated
the •OH was the main active species of g-C3N4/FeOCl-20 with the irradiation of
visible light and the existence of H2O2. After the addition of EDTA-2NA, the
inhibitory catalytic activity also could be observed, which indicating the h+ also
played the indispensable role in this process. However, the PF catalytic activity
-
decreased slightly after the addition of Ar gas, means the •O2 was not the main
radical group during the PF degradation by g-C3N4/FeOCl material. Based on the
−
results of radical trapping, the •OH, h+ and •O2 were all generated and the •OH
played the main role during the PF process.
To further investigate the PF catalytic mechanism of g-C3N4/FeOCl-20
composite, the active species of g-C3N4/FeOCl composite were further measured by
the electron spin resonance (ESR). As comparison, the active species of pure FeOCl
were also revealed. During the experiments, the solvent was distilled water and no
H2O2 was added. The Figure 6b and Figure 6c were the spectra of DMPO-•OH and
−
DMPO-•O2 , respectively. While the light was irradiated on the pure FeOCl, The
−
signal of •OH could be found obviously while the signal of •O2 could not be

−
observed. However, the g-C3N4/FeOCl composite could form both •OH and •O2 with
the irradiation of visible light at the same time. These results were consistent with that
−
of the radicals trapping experiments and further proved the •OH and •O2 were all
generated in this g-C3N4/FeOCl composite system during the photocatalytic and PF
degradation process.
To confirm the valence band (VB) potential of the pure FeOCl material, the VB
spectrum was measured and the result was about 2.54 V as shown in Figure S6.
According to the VB spectra and DRS band-gap calculation, the potential of CB was
−
ECB = EVB − Eg = 0.78 V. Base on the previous researches, the E0 (O2/•O2 ) was
−0.046 V (vs. NHE) and the E0 (•OH/OH−) was 2.38 V (vs. NHE) [29, 30]. Due to the
VB of FeOCl was more positive than E0 (•OH/OH−), the high energy h+ of FeOCl
could oxidize OH- to yield •OH under the irradiation of the visible light. However,
−
because of the CB of FeOCl was more positive than E0 (O2/•O2 ), the pure FeOCl
−
could not reduced the O2 by electron (e-) to generate •O2 . These analyses were
consistent with the results of ESR.
According to the previous report [31], the CB and VB positions of the g-C3N4
were -1.17 V and 1.57 V, respectively. Therefore, the band gaps of g-C3N4 and FeOCl
were overlapped. If the conventional heterojunction was formed between FeOCl and
g-C3N4 materials (as shown in Figure S7), the electron would generated on the CB of
g-C3N4, then transferred and gathered on CB of FeOCl, the h+ would transfer from
VB of FeOCl to VB of g-C3N4 simultaneously with the visible light irradiation.
−
However, due to the CB of FeOCl was more positive than E0 (O2/•O2 ) and the VB of
g-C3N4 was more negative than E0 (•OH/OH−), the as-prepared g-C3N4/FeOCl was
−
impossible to generated the •O2 and •OH only by the photocatalytic reaction. Herein,
the mechanism of this g-C3N4/FeOCl composite system was not obeyed the
conventional heterojunction mode.
Based on the above discussion and the previous literatures [44, 57], the PF-like
mechanism of g-C3N4/FeOCl composite system could be analyzed as a Z-scheme
heterostructure and the schematic was shown in Figure 6 (d). While the visible light
irradiated on the materials, the electrons on the VB of the g-C3N4 and FeOCl

transferred to the CB, respectively. Due to the Z-scheme heterostructure was
constructed between g-C3N4 and FeOCl, the electron transferred from the CB of
FeOCl to the VB of the g-C3N4 and combined with h+. Then the electron gathered on
the CB of the g-C3N4 and transformed the H2O2 into the •OH. During this process, the
H2O2 was served as the electron acceptor which further successfully limited the
recombination of holes and electrons. On the other hand, on the surface of the FeOCl
material, the Fe3+ transformed into the Fe2+ with the existence of H2O2 and the
irradiation of visible light; the Fe2+ was easily reacted with H2O2 to generated the •OH
for removing the organic pollutant in water. Due to the CB of the g-C3N4 was more
−
negative than E0(O2/•O2 ) and the VB of the FeOCl was more positive than
E0(•OH/OH−), the electron which gathered on the CB of the g-C3N4 would also reduce
−
O2 to form the •O2 and the h+ on the VB of the FeOCl could oxide the OH− into the
•OH at the same time. This possible mechanism was consisting with the results of
radical trapping experiments and ESR.
Generally, compared with pure FeOCl at the same condition, the g-C3N4
successfully increased the separation efficiencies of the electron-hole pairs by the
Z-scheme heterostructure under the visible light irradiation. Moreover, the improved
charge transfer efficiency promoted more Fe3+ transform into Fe2+ during this process.
Therefore, more photo-generated electron and Fe3+/Fe2+ could join the Fenton reaction
with H2O2 in the solution to generate •OH. Besides the •OH also could be formed
from the OH− in water reacting with photo-generated h+. Therefore the PF degradation
activity of this Z-scheme g-C3N4/FeOCl was greatly enhanced after the introduction
of g-C3N4 and the •OH was the main radical group in this system.
4. Conclusion
In this work, the Z-scheme PF-like g-C3N4/FeOCl material was firstly
synthesized successfully which realized the complementation between photocatalytic
and Fenton technology. With the addition of H2O2 and the visible light irradiation, the
g-C3N4/FeOCl materials revealed excellent catalytic activities for the degradation of

RhB and TC. Among FeOCl and g-C3N4/FeOCl samples, the g-C3N4/FeOCl-20
composite exhibited the optimal catalytic activity. In this system, the introduced
g-C3N4 material increased the specific surface area of the g-C3N4/FeOCl composites
and effectively decreased the recombination of electron-hole pairs by the construction
of Z-scheme heterostructure. Thus, compared with pure FeOCl, the g-C3N4/FeOCl
composites could adsorb more reactants and generate more radical groups during the
PF-like degradation of pollutants. Inspired by this work, it revealed the synthesis of
FeOCl-based composites showed a highly potential application prospect in the field of
water pollution treatment by the PF-degradation process, even can be extended to
photo/electro Fenton catalytic field.
Author Statement
Junze Zhao: Investigation, Writing - Original Draft, Writing - Review & Editing
Mengxia Ji: Validation, Writing - Review & Editing
Jun Di: Visualization, Validation
Yi Zhang: Data Curation
Mingqiang He: Methodology
Huaming Li: Resources, Supervision
Jiexiang Xia: Conceptualization, Project administration
Acknowledgements
This work was financially supported by the National Natural Science Foundation of
China (No. 21576123, 21676128, 21476098), and Postgraduate Research & Practice
Innovation Program of Jiangsu Province (KYCX17_1792).

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Figure Caption:
Figure 1. The XRD patterns of pure FeOCl, g-C3N4 and g-C3N4/FeOCl composites.
Figure 2. The XPS spectra of pure FeOCl and g-C3N4/FeOCl-20 composite. (a) the full spectra of
FeOCl and g-C3N4/FeOCl-20 composite; the high resolution spectra of (b) Fe element, (c) O
element, (d) Cl element, (e) N element and (f) C element in g-C3N4/FeOCl-20 composite.
Figure 3. The (a) TEM and (b) HR-TEM images of g-C3N4/FeOCl-20 composite.
Figure 4. (a) The PF catalytic activities of pure FeOCl and g-C3N4/FeOCl composites by the
degradation of RhB; (b) the degradation kinetics of the RhB by FeOCl and g-C3N4/FeOCl
composites; (c) the photocatalytic, Fenton catalytic and PF catalytic activities of FeOCl and
g-C3N4/FeOCl composites by the degradation of RhB; (d) The degradation efficiency of RhB by
self-degradation, the pure H2O2, the g-C3N4+H2O2 and the mechanical mixture of FeOCl and
g-C3N4 under the visible light.
Figure 5. (a) The DRS of the g-C3N4, FeOCl and g-C3N4/FeOCl composite; (b) the N2 adsorption
isotherm of FeOCl and g-C3N4/FeOCl-20 composite materials (c) The EIS spectra of the g-C3N4,
FeOCl and g-C3N4/FeOCl-20 composite materials; (d) the photocurrent spectra of g-C3N4, FeOCl
and g-C3N4/FeOCl-20 composite.
Figure 6. (a) The radicals tripping experiments of g-C3N4/FeOCl-20 composite; The ESR spectra
of pure FeOCl and g-C3N4/FeOCl-20 composite by DMPO: (b) hydroxyl radical spectra at dark
and light on conductions, (c) the superoxide radical spectra at dark and light on conductions; (d)
the PF-like degradation mechanism of g-C3N4/FeOCl composite under the visible light irradiation.

g-C3N4
g-C3N4/FeOCl-30
g-C3N4/FeOCl-20
g-C3N4/FeOCl-10
g-C3N4/FeOCl-5
FeOCl
FeOCl: JCPDS card No.24-1005
10
20
30
40
50
60
70
80
2-Theta (degree)
Figure 1

b
a
Fe 2p3
Survey
FeOCl
FeOCl
g-C3N4/FeOCl-20
g-C3N4/FeOCl-20
740 735 730 725 720 715 710 705
1200 1000 800
600
400
200
0
Binding Energy (eV)
Binding Energy (eV)
c
d
Cl 2p
O 1s
Fe-O
O-H
H2O
FeOCl
FeOCl
O-H
Fe-O
g-C3N4/FeOCl-20
H2O
g-C3N4/FeOCl-20
210 208 206 204 202 200 198 196 194 192
542 540 538 536 534 532 530 528 526 524
Binding Energy (eV)
Binding Energy (eV)
e
C 1s
f
N 1s
C-N=C
C-N=C
N-(C)3
g-C3N4/FeOCl-20
C-C
g-C3N4/FeOCl-20
Fe-N
296 294 292 290 288 286 284 282 280 278
410 408 406 404 402 400 398 396 394
Binding Energy (eV)
Binding Energy (eV)
Figure 2

a
b
g-C3N4
g-C3N4
0.253 nm (0 2 1)
FeOCl
5 nm
0.5 μm
Figure 3
2.5
2.0
1.5
1.0
0.5
0.0
1.1
a
FeOCl
b
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
FeOCl
g-C3N4/FeOCl-5
g-C3N4/FeOCl-10
g-C3N4/FeOCl-20
g-C3N4/FeOCl-30
g-C3N4/FeOCl-5
g-C3N4/FeOCl-10
g-C3N4/FeOCl-20
g-C3N4/FeOCl-30
0
10
20
30
40
50
60
0
10
20
30
40
50
60
Time (h)
Time (min)
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
d
c
Photocatalytic
Fenton
Photo-Fenton
self-degradation of RhB
H2O2
g-C3N4 + H2O2
mechanical mixing powder + H2O2
g-C3N4/FeOCl-20 + H2O2
0
0
5
0
1
-
l
2
-
3
-
l
-
l
l
l
0
10
20
30
40
50
60
OC
OC
Fe
OC
Fe
/
4
OC
Fe
OC
Fe
4
Fe
/
/
4
/
N
4
N
3
N
3
N
3
C
-
g
C
3
-
C
Time (h)
C
g
-
-
g
g
Figure 4

120
100
80
60
40
20
0
b
a
FeOCl
g-C3N4/FeOCl-20
g-C3N4
g-C3N4/FeOCl-5
g-C3N4/FeOCl-10
g-C3N4/FeOCl-20
g-C3N4/FeOCl-30
FeOCl
200
300
400
500
600
700
800
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/Po)
Wavelength (nm)
120
50
0.10
0.08
0.06
0.04
0.02
0.00
FeOCl
g-C3N4/FeOCl-20
c
g-C3N4
FeOCl
g-C3N4/FeOCl-20
c
d
FeOCl
g-C3N4/FeOCl-20
100
40
g-C3N4
80
30
60
20
40
10
20
0
0
50
40
100
60
150
80
200
100
250
120
300
140
350
160
400
180
0
50
100
150
200
250
Time (s)
Z' (ohm)
Z' (ohm)
Figure 5

Figure 6