Applied Surface Science 605 (2022) 154751
Contents lists available at ScienceDirect
Applied Surface Science
journal homepage: www.elsevier.com/locate/apsusc
Full Length Article
(1T/2H)-MoS2/CoFe2O4 heterojunctions with a unique grape bunch
structure for photocatalysis of organic dyes driven by visible light
Kai Dou a, Yukai Lu a, Rongchen Wang a, Haopeng Cao a, Chao Yao a, Jialong Liu a, *,
Natalia Tsidaeva c, Wei Wang a, b, *
a
b
c
Department of Physics and Electronics, School of Mathematics and Physics, Beijing University of Chemical Technology, Beijing 100029, China
Beijing Key Laboratory of Environmentally Harmful Chemical Analysis, Beijing University of Chemical Technology, Beijing 100029, China
Scientific center “Magnetic Structures”, North Caucasus Mining and Metallurgical Institute, State Technological University, Vladikavkaz 362021, Russia
A R T I C L E I N F O
A B S T R A C T
Keywords:
Heterojunction
Photocatalysis
Dyes
Recycle
MoS2
The formation of heterostructures is an effective way to tune the band structure and photocatalytic property.
Herein, an efficient (1T/2H)-MoS2/CoFe2O4 heterojunction was prepared via a facile green hydrothermal
method and performed well in the photocatalytic removal of organic dyes. By varying the molar ratio of MoS2
versus CoFe2O4, the photogenerated electron-hole separation can be enhanced in the heterojunction. The MoS2/
CoFe2O4 composite with a 2:1 M ratio of MoS2 to CoFe2O4 (MC-2) shows the best photocatalytic performance,
where 91.9 % of methyl blue (MB) is degraded within 60 min and its apparent rate constant is 5.94 and 25.43
times higher than those of pure MoS2 and CoFe2O4. In addition, MC-2 maintains high photocatalytic performance
even in an aqueous environment similar to wastewater, where some different inorganic ions (e.g., NO–3, CO2–
3 and
SO2–
4 ) are present. Further, the remarkable ferromagnetic property of MC-2 at room temperature ensures that the
composites were easy to be separated from the wastewater. Meanwhile, the as-synthesized composites exhibit
good reusability. A possible mechanism for photodegradation of MB is proposed for (1T/2H)-MoS2/CoFe2O4
heterojunction by the analyses of the energy bands and the trapping experiments of active species.
1. Introduction
Water pollution, especially toxic and carcinogenic organic dyes, is a
serious and widespread environmental problem for decades. To date,
various physical, chemical and biological approaches have been raised
to address water contamination, including adsorption, photocatalysis,
filtration, anion exchange, chemical flocculation and biodegradation
[1–7]. Among all the technologies, visible-light-driven photocatalysis
has attracted much more attention in the degradation of pollutants due
to its good economic efficiency, high performance and environmental
friendliness [8–11].
Recently, layered transition metal sulfides have been extensively
studied in the field of photocatalysis due to the appropriate band gap
and specific multiphase structure [12,13]. Particularly, as a represen­
tative of the family, MoS2 has been studied a lot in energy storage and
photocatalysis owing to its good carrier transfer ability, narrow band
gap and chemical stability [14–17]. Besides, it is known that different
phase structures of MoS2 can greatly affect its photocatalytic activity
[18,19]. The semiconductor phase 2H-MoS2 typically has a narrow band
gap and is able to utilize most regions of visible light [20,21]. But the
poor electrical conductivity and severe internal strict electron-hole
recombination problem hamper its practical application [22–24]. The
other intrinsic phase, i.e., the metallic phase 1 T-MoS2 has high electrical
conductivity and an improved catalytically active basal plane [25,26],
which facilitate carrier motion and create more active sites [27,28]. But
the 1 T phase only plays the role of electron acceptor as other metal
catalysts. In this regard, combining two different phases to form 1T/2HMoS2 is an optimal approach to improve photocatalytic performance.
However, the instantaneous complexation of photogenerated carriers
and slow carrier motion capability are the shortcomings of MoS2.
Constructing heterojunction with other semiconductors is critical to
addressing these issues and enhancing the catalytic performance of
MoS2. Spinel ferrite CoFe2O4 with moderate saturation magnetization,
appropriate coercivity and physicochemical stability has been
frequently investigated as a promising candidate to form heterojunction
in recent years. For example, Ag3PO4/CoFe2O4 [29] and CoFe2O4/
* Corresponding authors at: Department of Physics and Electronics, School of Mathematics and Physics, Beijing University of Chemical Technology, Beijing
100029, China.
E-mail addresses: jialongliu@buct.edu.cn (J. Liu), wangwei@mail.buct.edu.cn (W. Wang).
https://doi.org/10.1016/j.apsusc.2022.154751
Received 11 July 2022; Received in revised form 29 August 2022; Accepted 30 August 2022
Available online 5 September 2022
0169-4332/© 2022 Elsevier B.V. All rights reserved.
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Ag2O/Ag2CO3 [30] have been fabricated for visible-light-driven pho­
tocatalysis, which can both increase their photocatalytic activity and
allow easy recovery from the reaction solution by magnetic separation
[31,32].
Herein, a simple and environmentally friendly strategy was devel­
oped to synthesize (1T/2H)-MoS2/CoFe2O4 heterojunctions with
tunable composition ratios. The characterization of the microstructure,
chemical state and optical properties of the as-prepared samples was
carried out. Then, the photocatalytic performance of (1T/2H)-MoS2/
CoFe2O4 heterojunctions with different constituents for the degradation
of methyl blue (MB) dyes were rationally evaluated. The as-prepared
products can be separated with a magnet. Finally, the corresponding
photocatalytic mechanism was suggested by the discussion on the en­
ergy bands and the trapping experiments of active species.
2.3. Synthesis of MoS2/CoFe2O4 composites
Scheme 1 describes the whole synthetic process of (1T/2H)-MoS2/
CoFe2O4 composites. CoFe2O4 nanospheres were coupled with MoS2
nanosheets by a simple hydrothermal method. In the first step, 0.484 g
Na2MoO4⋅2H2O and 0.608 g thiourea were dispersed in 50 ml of a mixed
solution consisting of water and ethanol (1:1), and the solution was kept
under ultrasound for 1 h. Then, 0.234 g of CoFe2O4 powder was
dispersed into the resulting solution and ultrasonic for 1 h. Next, 0.3 g
CTAB was dispersed into the solution after the previous ultrasound and
stirred for 2 h. After that, the mixed solution was poured into the
autoclave and placed in an oven set at 200 ◦ C for 4 24 h, then cooled
naturally. The prepared samples were then washed three times with DI
water and ethanol. Finally, the (1T/2H)-MoS2/CoFe2O4 composites can
be obtained after drying at 60 ◦ C. By changing the initial Mo/Co molar
ratio from 1:1, 2:1 to 4:1, the as-prepared products were named MC-1,
MC-2 and MC-4 respectively. For comparison, pure MoS2 samples
were prepared without the addition of CoFe2O4.
2. Experimental section
2.1. Materials
2.4. Characterization
The reagents are all of the analytical grade and are applied with no
further purification. Ferric chloride hexahydrate (FeCl3⋅6H2O, ≥99 %),
Ethylene glycol (EG, (CH2OH)2, ≥99 %), Cobalt chloride hexahydrate
(CoCl2⋅6H2O, ≥99 %), Diethylene glycol (DEG, C4H10O3, ≥99 %),
molybdate dihydrate (Na2MoO4⋅2H2O, ≥99 %), Thiourea (CH4N2S,
≥99 %), CTAB (C19H42BrN, ≥99 %), Sodium carbonate (Na2CO3, ≥99
%), Sodium nitrate (NaNO3, ≥99 %), Sodium sulfate (Na2SO4, ≥99 %),
Triethanolamine (TEOA, ≥99 %), p-Benzoquinone (BQ, ≥99 %), Iso­
propanol (IPA, ≥99 %) were purchased from Sinopharm Chemical Re­
agent Co., Ltd. China. The solutions were freshly prepared using
deionized water.
The crystal structure, morphology, components and elemental
mapping of the as-prepared samples were characterized by X-ray
diffraction (XRD, Rigaku D/max X-ray diffractometer, Cu Kα), scanning
electron microscopy (SEM, Hitachi S4700) equipped with energy
dispersive spectroscopy and transmission electron microscopy (TEM,
FEI Tecnai G2). X-ray photoelectron spectroscopy (XPS) was performed
in a VG ESCALAB 220 IXL photoelectron spectrometer employing Al Kα
radiation (10 KeV/150 W) and a concentric hemispherical electron en­
ergy analyzer. The electron pass energy was fixed at 40 eV for all scans.
The as-prepared samples were attached to the sample stub with a
double-sided carbon tape. The analysis chamber was operating at a
vacuum of 5 × 10− 9 mbar [33]. The optical properties were analyzed by
UV–vis diffusive reflectance spectra on a spectrophotometer (Shimadzu,
UV-2501PC) and photoluminescence (PL) spectra (Hitachi F-7000
Fluorescence Spectrophotometer with an excitation wavelength of 380
nm). Photodegradation intermediates of MB were detected by liquid
chromatography coupled with tandem mass spectrometer (LC-MS,
ACQUITY UPLC/XEVO-G2-S QTOF) with model of ACQUITY UPLC BEH
C18 (2.1 mm × 100 mm, 1.7 μm). The mobile phase was consisting of
1:1 (v/v) of 0.1 % formic acid solution and methanol at a flow rate of 0.3
ml/min and the injected volume were 1 µl. The MS source conditions
were as follows: capillary voltage of 2.5 kV; cone voltage of 25 V; ion
source temperature of 120 ◦ C; heated capillary temperature of 450 ◦ C;
ESI anion mode.
2.2. Synthesis of CoFe2O4 nanospheres
CoFe2O4 nanospheres were prepared by the solvothermal method.
First, solvent X was obtained by mixing 10 ml of DEG with 30 ml of EG.
In the second step, 0.238 g CoCl2⋅6H2O and 0.54 g FeCl3⋅6H2O were
dissolved in solvent X to form solution Y while 1.64 g CH3COONa⋅3H2O
was dissolved in solvent A to obtain solution Z. Solution Y and solution Z
were under ultrasound for 1 h. Then, while stirring, solution Z was
slowly poured into solution Y, and continued stirring after the solution
changed to orange for 2 h. Thirdly, pour the mixed solution into a 100 ml
Teflon-lined autoclave and put it into an oven to heat up to 200 ◦ C for 4
h. The prepared samples were then washed three times with DI water
and ethanol after they had cooled naturally to room temperature. At last,
the sample was dried at 60 ◦ C for 12 h to obtain a yellow–brown powder.
Scheme 1. Schematic illustration for the preparation of CoFe2O4/MoS2 heterojunction.
2
K. Dou et al.
Applied Surface Science 605 (2022) 154751
2.5. Measurement of photocatalytic activity
The photocatalytic performance of the materials was assessed via
degradation experiments on organic dyes. For the test, 30 mg of the
sample was dispersed into 100 ml of MB solution (40 mg⋅L-1). The so­
lution was kept in the dark and shaken vigorously in a water bath shaker
for 30 min to reach adsorption–desorption equilibrium Afterwards, the
solution was illuminated by visible light (provided by a 300 W xenon
lamp (PLS-SXE-300 W) with a 420 nm cut-off filter) at room temperature
for 60 min. In this procedure, 4 ml of suspension was withdrawn at every
specified time intervention (10 min) and the supernatant was extracted
by centrifugation and analyzed by UV–vis spectrometer (UV-2501PC).
Thus, the peak intensity (absorbance) at 664 nm (for MB) was recorded
and studied at different reaction times. The pH value of the solution was
adjusted with 1 M HCl or NaOH.
2.6. Measurement of photoelectrochemical activity
The photoelectrochemical properties for the as-synthesized com­
posites were measured with a typical three-electrode system on an
electrochemical workstation (CHI 660E). Pt plates (1 × 1 cm2) and Ag/
AgCl electrodes were used as counter and reference electrodes, respec­
tively. To prepare the working electrode, 10 mg of the sample was dis­
solved with a Nafion/ethanol/water (50 µl/50 µl/100 µl) ink mixture,
sonicated for 10 min and then dropped onto FTO (1 × 2 cm2) glass and
dried in an oven. Na2SO4 solution (0.5 M pH = 6.1) was used as the
electrolyte. The flat-band potential of the working electrode was tested
at 1000 and 2000 Hz using the Mott-Schottky (MS) method,
respectively.
Fig. 1. XRD patterns of pure MoS2, CoFe2O4, MC-1, MC-2 and MC-4 samples.
2 samples are characterized by SEM and depicted in Fig. 2. It can be
clearly seen that the CoFe2O4 sample is composed of nanospheres with a
diameter of 50–100 nm (Fig. 2a), while MoS2 is assembled from nano­
sheets and has the shape of an irregular flower with the size of 2–3 µm
(Fig. 2b). For the MoS2/CoFe2O4 composites, MC-1 sample is demon­
strated in Fig. S1a, where the CoFe2O4 particles are excessively
agglomerated on the MoS2 surface, and the MoS2 nanosheets can be
barely observed around CoFe2O4. Such structure restricts light from
reaching MoS2, which is not conducive to enhancing photocatalytic
activity. In contrast, there are few CoFe2O4 nanoparticles distributed on
the surface of MoS2 in MC-4 sample (Fig. S1b). leading to few hetero­
geneous interfaces for enhancing the photocatalytic performance.
Therefore, MC-2 sample with a moderate amount of CoFe2O4 distributed
on the surface of MoS2 nanosheets has the best configuration of the
interfacial structure (Fig. 2 c and d), which greatly facilitate the light
utilization at the heterogeneous interface.
The crystal structures of pure CoFe2O4, MoS2 and MC-2 are investi­
gated by TEM. Pure CoFe2O4 appears as nanospheres with diameter of
50–100 nm (Fig. 3a), in good agreement with the morphology observed
in the SEM above. Fig. 3b clearly demonstrates that MoS2 is composed of
thin nanosheets. As demonstrated in Fig. 3c, the lamellar structure
similar to MoS2 is clearly present at the edge of MC-2 sample, but it is
difficult to clearly observe the CoFe2O4 nanospheres due to particle
agglomeration. The HRTEM images in Fig. 3d show lattice stripes with a
spacing of 0.298 nm and 0.621 nm, which pairs correspond to the (2 2 0)
plane of CoFe2O4 and the (0 0 2) plane of MoS2, respectively. The
CoFe2O4 particles are closely attached around the MoS2 nanosheets and
form heterojunctions at the interface [38,39]. Similar results can be
observed in the other two cases in Fig. S2. Apparently, the heteroge­
neous structure can effectively enhance the carrier transfer efficiency
and thus improve the photocatalytic activity of the MoS2/CoFe2O4
composites. Furthermore, Fig. 4 presents the elemental mappings of MC2 sample, where Mo, S, Fe, Co and O elements are uniformly distributed,
confirming the successful coupling of (1T/2H)-MoS2 and CoFe2O4.
XPS was used to analyze the chemical valence and elemental
composition of pure MoS2, pure CoFe2O4 and representative MC-2
sample. As demonstrated in Fig. S3 and S4, the elemental composi­
tions and valence states of pure MoS2 and CoFe2O4 are as-expected with
no doubt. The appearance of O peak in pure MoS2 may be attributed to
chemisorbed oxygen. The full survey spectra shown in Fig. 5a further
verify the co-presence of Fe, Co, O, Mo and S elements in MC-2 sample.
The XPS spectrum of Co 2p is given in Fig. 5b, where the peaks at 803.1
and 794.7 eV are attributed to Co 2p1/2 and the peaks at 787.6 and
779.2 eV are attributed to Co 2p3/2, respectively [40]. Similarly, as
2.7. Point of zero charge (pzc)
To study the surface electrical properties of MC-2 sample, the point
of zero charge (pzc) was determined by a solid addition method. Briefly,
the pH value of the solution was adjusted from 2.0 to 10.0 by hydro­
chloric acid and sodium hydroxide solutions, and 20 mg of photocatalyst
was added to 5 ml of 0.1 M KCl solutions with different initial pH (pHi)
values. Further, the mixed solutions were shaken at room temperature
for 24 h. Herein, the final pH value (pHf) was determined by a pH meter.
The, the curve of ΔpH (pHi-pHf) versus pHi can be obtained, where the
point of zero charge (pzc) is the point at ΔpH = 0 in the curve.
3. Results and discussions
3.1. Characterization
Fig. 1 exhibits the XRD patterns of the synthesized pure MoS2,
CoFe2O4 and (1T/2H)-MoS2/CoFe2O4 composites. For the pure CoFe2O4
sample, distinct diffraction peaks are verified at 18.3◦ , 30.2◦ , 35.6◦ ,
43.3◦ , 57.2◦ , and 62.7◦ , which respectively correspond to the (1 1 1),
(2 2 0), (3 1 1), (4 0 0), (5 1 1), and (4 4 0) planes of face-centered cubic
CoFe2O4 marked on the orange curve (JCPDS No. 22–1086) [34–36].
The diffraction peaks at 14.9◦ , 32.6◦ , and 58.9◦ for pure MoS2 sample
can be attributed to the (0 0 2), (1 0 0) and (1 1 0) planes of hexagonal
MoS2 (JCPDS No. 37–1492) [37], which is the semiconducting phase
2H-MoS2. In addition to the three diffraction peaks mentioned above,
the peak appeared at 7.4◦ can be ascribed to the (0 0 1) plane of the
metallic phase 1 T-MoS2 [25], indicating that the as-prepared MoS2 is a
mixed phase (1T/2H-MoS2). For all the as-prepared MoS2/CoFe2O4
composites, the characteristic peaks of CoFe2O4 could be clearly detec­
ted. But due to the poor crystallinity of MoS2, it is difficult to distinguish
its diffraction peaks in MC-1 with low MoS2 content. With the increase of
MoS2 content, the (0 0 1) and (1 0 0) planes of MoS2 are clearly observed
in MC-4. The above analysis indicates that the (1 T/2H)-MoS2/CoFe2O4
composites were prepared successfully.
The morphologies of the pure MoS2, CoFe2O4 and representative MC3
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Fig. 2. SEM images of different samples: (a) pure CoFe2O4, (b) pure MoS2, (c, d) MC-2.
shown in Fig. 5c, the peaks at 725.1and 711.4 eV are attributed to Fe
2p1/2 and Fe 2p3/2, respectively [41]. Compared to pure CoFe2O4, the
positions of the Co and Fe characteristic peaks are shifted, which is the
evidence for the formation of the heterojunction between MoS2 and
CoFe2O4 as well as the variation of binding energy [42]. Three peaks of
530.0, 531.7 and 533.2 eV can be detected in the high-resolution O 1 s
spectrum in Fig. 5d, which can be ascribed to the oxygen from CoFe2O4,
H2O molecules and some residual oxygen-containing Mo materials,
respectively. The resolved Mo 3d peaks of MC-2 composite located at
228.5, 229.1, 231.7, and 232.3 eV are attributed to 1T-Mo 3d5/2, 2H-Mo
3d5/2, 1T-Mo 3d3/2 and 2H-Mo 3d3/2, respectively, as shown in Fig. 5e
[43]. This indicates that the coexistence of metal and semiconductor
phases in the MoS2 of MC-2 samples results in both good light absorption
and excellent charge transfer efficiency of MC-2. In addition, the two
weak peaks (233.1 and 235.6 eV) of Mo6+ appear due to the inevitable
slight oxidation during the synthetic experiment [29,30]. Similarly, S 2p
peaks can be resolved as four peaks as demonstrated in Fig. 5f. The two
peaks located at 162.0 and 163.2 eV can be attributed to 2H-S 2p3/2 and
2H-S 2p1/2 of MoS2, while the two peaks located at 162.6 eV and 161.4
eV can be attributed to 1T-S 2p3/2 and 1T-S 2p1/2 of MoS2, respectively
[44]. The XPS results demonstrate the successful preparation of (1T/
2H)-MoS2/CoFe2O4 heterojunction, which agrees with the analytical
conclusion of XRD.
For photocatalysts, the numerous mesoporous catalysts could pro­
vide abundant active sites. The nitrogen adsorption–desorption iso­
therms for CoFe2O4, MoS2, and MC-2 samples are measured and shown
in Fig. 6a (specific values in Table 1). The curve of CoFe2O4 conforms to
the basic characteristics of II-type isotherms, indicating that CoFe2O4 is
a non-porous material. Differently, the data of MoS2 and MC-2 samples
obey IV-type isotherms and prove their mesoporous characteristics [45].
Meanwhile, the average pore size of MC-2 composites slightly decreases
compared to MoS2 (Fig. 6b). Moreover, the specific surface areas of
CoFe2O4, MoS2 and MC-2 samples are calculated to be 70.4909, 8.5053,
and 13.6504 m2/g, respectively. Apparently, the average pore size of
MC-2 samples decreases after the coupling of MoS2 with CoFe2O4, but
the number of pores increases, which gives MC-2 a larger specific surface
area than that of MoS2. The increased pore size and enlarged specific
surface area provide more active sites for MC-2 to better adsorb and
attack pollutants and enhance its photocatalytic performance [46].
For the evaluation of light absorption properties of heterostructure
photocatalysts, diffuse reflection spectrum (DRS) is applied. As
demonstrated in Fig. 7a, pure CoFe2O4 displays an absorption band edge
near 650 nm, proving its excellent visible light absorption capability,
while pure MoS2 exhibits complete absorption properties in the entire
spectral range. As to MC-2 sample, it has an intense light absorbance
from UV to visible light region. Its absorbance remains higher than that
of pure CoFe2O4 with increasing wavelength, although there exists a
slight decrease. Further, the energy band gap of the materials can be
calculated from the classical Tauc method:
)
(
(1)
(αhυ)m = K hυ − Eg
where α is the absorption coefficient, K is a constant, h is the Planck’s
constant, υ is the photon frequency, Eg is the optical band gap and m is a
constant depending on whether the semiconductor type is a direct
bandgap semiconductor (m = 2) or an indirect bandgap semiconductor
(m = 1/2). Eg can be determined from the (αhυ)2–hυ plot in Fig. 7b, c,
d and the results are presented in Table 2. Notably, after compounding
with CoFe2O4 the bandgap of MC-2 is effectively adjusted from 1.98 to
1.45 eV, which implies that compounding CoFe2O4 with MoS2 can make
the electrons-and-holes pair easier to produce, accelerate carrier transfer
and improve light collection efficiency.
It is well known that the PL spectra are related to the recombination
effect of photogenerated electron-hole pairs. As shown in Fig. 8, pure
CoFe2O4 has an intense emission peak near 405 nm owing to its high
4
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Fig. 3. TEM images of sample: (a) pure CoFe2O4, (b) pure MoS2 (c) MC-2 samples. (d) HRTEM of MC-2.
recombination efficiency of the photogenerated electron-hole pairs. In
contrast, the characteristic peak of MC-2 sample is lower than that of
CoFe2O4 with MoS2, indicating that the formation of heterojunctions
dramatically suppresses the recombination of photogenerated carriers,
thus greatly strengthening its photocatalytic performance.
pairs and the opacity is also increased, leading to a decrease in photo­
catalytic activity [17,47]. Moreover, Fig. 9b demonstrates the kinetic
curves for all the as-synthesized samples, which are calculated by the
Langmuir-Hinshelwood model (-ln(C/C0) = kt, k is the apparent rate
constant) The specific values are presented in Table 3. After comparing
the fitted data of all the samples, the k value of MC-2 (0.02823 min− 1) is
the highest. It is 5.94 and 25.43 times higher than those of MoS2
(0.00475 min− 1) and CoFe2O4 (0.00111 min− 1), respectively. Therefore,
MC-2 sample is the best heterojunction for photocatalytic degradation of
MB. In addition, total organic carbon (TOC) was analyzed after the
photocatalytic degradation experiments. As shown in Fig. S6, the TOC
removal efficiency of MB by MC-2 sample under visible light irradiation
reaches 62.71 % and 77.19 % after photodegradation of 60 and 90 min.
This indicates that MC-2 can not only decolorize dye molecules, but also
completely convert them into small molecules such as carbon dioxide
and water.
It is well known that the pH of the solution is an important parameter
affecting the degradation rate during the photodegradation process. To
investigate the effect of pH on the photodegradation of MB by MC-2, we
conducted degradation experiments under different pH conditions
(Fig. 9c). It can be seen that the degradation rate of MB by MC-2 sample
remains above 90 % under alkaline conditions and the best catalytic
performance appears at pH = 8 (94.8 %), but the degradation rate de­
creases significantly under acidic conditions. Considering that pH has
effect on the electrostatic force between MB dye and the catalyst during
the catalytic process, the solid addition method was used to measure the
point of zero charge (pzc) for MC-2 sample and the value is 2.48 [48].
3.2. Photocatalytic activities
The photocatalytic activities of the as-synthesized samples were
studied by the degradation of MB with irradiation of visible light. Fig. S5
demonstrates the variation of absorption peak during the degradation of
MB by MC-2 sample. The intensity of the characteristic peak for MB
(664 nm) decreases continuously with time, which indicates that MB is
successfully degraded in the photocatalytic reaction. The real-time
concentration C of the MB solution during the photocatalytic process
can be obtained by the Lambert-Beer equation, where C0 is used as the
initial concentration. As shown in Fig. 9a, MoS2 has a small photo­
catalytic property while CoFe2O4 can only degrade a small amount of
MB. All the MoS2/CoFe2O4 composites show higher degradation rates of
MB than pure MoS2 and CoFe2O4 after 60 min, indicating that the for­
mation of (1T/2H)-MoS2/CoFe2O4 heterojunction successfully enhances
its photocatalytic performance. MC-2 sample performs best when the
molar ratio of MoS2 to CoFe2O4 is 2:1, which can remove 91.9 % MB in
only 60 min. Generally, as the proportion of MoS2 in the composites
increases, the photodegradation efficiency of MoS2/CoFe2O4 composites
firstly increases and then decreases. This effect is because excess MoS2
becomes the recombination center of photogenerated electron-hole
5
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Fig. 4. Elemental mappings of MC-2 sample.
Therefore, when the pH value is greater than 2.48, the surface of MC-2
sample is negatively charged, and positively charged conversely [48]. At
pH = 7–10, the negatively charged surface of MC-2 sample can strongly
adsorb the positively charged cationic MB dye molecules, resulting in a
good degradation rate. However, at pH = 2, the positively charged
surface of MC-2 sample repels the MB dye molecules, leading to a
decrease in the degradation rate [49].
There are many kinds of ions in wastewater other than the organic
dyes, which have an impact on the degradation efficiency. From the
application point of view, there is a need to study the effect of various
ions on the catalytic performance of the catalyst. Herein, three kinds of
typical ions (NaNO3, Na2SO4, and Na2CO3) were respectively added into
the MB solution for the photocatalytic degradation of MB in MC-2
sample. The introduction of NO–3 and SO24 shows a slightly negative
effect on the photocatalytic reaction in the first 40 min, since NO–3/SO24
ions would occupy the active sites instead of the organic dyes [50]. But
the final degradation efficiency in 60 min is almost the same. However,
when CO2–
3 is introduced, MC-2 exhibits an enhanced adsorption per­
formance on MB and almost completely removes the dye from the so­
lution within 30 min of dark treatment. Since the hydrolysis of CO2–
3
produces a certain amount of OH–/HCO–3 and leads to an increase in the
pH, more negative charges are generated on the surface of MC-2 sample,
which facilitates the enhanced adsorption of cationic dye like MB [51].
Therefore, it is easy to see that (1T/2H)-MoS2/CoFe2O4 composites can
maintain high performance even in an aqueous solution similar to actual
wastewater.
The stability and reusability of photocatalysts are important factors
that need consideration in practical applications. Four cycles of repeated
MB degradation experiments were conducted to evaluate the stability of
MC-2 sample within the same experimental conditions. During each
cycle, the catalyst was recovered by magnetic separation for the next
experiment (Fig. 10c). As shown in Fig. 10b, it can be seen that the
degradation rate of MC-2 sample to MB reached 91.9 %, 88.6 %, 87.5 %
and 77.2 % in four cycles, respectively. MC-2 sample maintains an
excellent degradation efficiency for the first three cycles, indicating that
the (1T/2H)-MoS2/CoFe2O4 composites are well reusable for degrading
organic pollutants. The abrupt decrease of the fourth cycle may be the
result of inevitable sample loss during the experiment. To further illus­
trate the stability of MC-2, XRD patterns of the samples were presented
after cyclic degradation experiments (Fig. S7). It can be seen that there is
no significant change in the XRD profile of MC-2 before and after use,
indicating that it is always structurally stable during the degradation
process. Therefore, as a synthetic (1T/2H)-MoS2/CoFe2O4 hetero­
junction catalyst with good stability and easy recovery, it has great
potential for practical applications in wastewater treatment.
In order to analyze the intermediates and possible degradation
pathways in the degradation of MB by MC-2 samples, LC-MS tests were
performed. As shown in Fig. S8, the peaks at different positions in the MS
spectra indicated various intermediates produced after degradation of
MB for 30 min. Based on the LC-MS results and literatures an MB
degradation pathway is proposed as described in Scheme 2 [52–53]. The
strong N-CH3 bond of MB dye is firstly broken down to form demethy­
lated intermediates, and eventually these intermediates are completely
mineralized to carbon dioxide and water [54–55].
3.3. Possible mechanism of photocatalytic reaction process
The detection of major active species during catalytic degradation of
MB by trapping experiments is essential to analyze the mechanism of the
as-synthesized samples. Herein, the scavengers including benzoquinone
(BQ), isopropanol (IPA) and triethanolamine (TEOA) were used to
remove ⋅O–2, ⋅OH and h+ in the degradation of MB with MC-2 sample,
respectively [56]. As depicted in Fig. 11, the efficiency to degrade MB
without the presence of scavengers in the solution was 91.9 %. After
adding the scavengers, the degradation efficiency of MB drops to 68.8 %
(IPA), 51.2 (TEOA), and 56.2 % (BQ), and the corresponding apparent
rate constants also decrease in different degrees. Thus, h+, ⋅O–2 and ⋅OH
play a synergistic role in the photocatalytic degradation of MB by MC-2
sample [57].
The heterojunction interface is known to be important for improving
the efficiency of photogenerated electron-hole pair separation and
enhancing photocatalytic activity. The band edge position of the com­
posite has a significant effect on the transfer pathway of photogenerated
carriers at the heterojunction interface. To identify the band edge po
6
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Fig. 5. XPS spectra of MC-2 sample: (a) Survey scan, (b) Co 2p, (c) Fe 2p, (d) O 1 s, (e) Mo 3d, (f) S 2p.
sitions of the synthesized samples, the electrochemical Mott-Schottky
(MS) method was applied. As shown in Fig. 12, the slopes of the
tangent lines of both MoS2 and CoFe2O4 are positive, proving that both
are n-type semiconductors. Further, the flat band potential of the sample
can be obtained from the intercept of the tangent line of the MS curve on
the x-axis. Therefore, the flat-band potentials of MoS2 and CoFe2O4 can
be calculated as − 1.04 and − 0.64 (vs Ag/AgCl), respectively. The ob­
tained flat-band potentials are approximated as their conduction band
potentials (CB) [58]. According to Eqs. (2), (3) and (4), the CB and
valence band (VB) of MoS2 and CoFe2O4 are calculated to be − 0.48,
0.77, − 0.08 and 1.9 eV, respectively.
EAg/AgCl = ERHE − 0.0591pH − 0.197
(2)
ENHE = ERHE − 0.0591pH
(3)
EVB = ECB + Eg
(4)
According to the above experimental results and trapping experi­
mental analysis, Scheme 3 meticulously elaborates the mechanism of
photocatalytic degradation of MB by (1T/2H)-MoS2/CoFe2O4 hetero­
junction, in which the charge separation and transfer can be visually
understood. Through photoexcitation, electrons from VB2H− MoS2 and
VBCoFe2 O4 will leap into CB2H− MoS2 and CBCoFe2 O4 , respectively (Eqs. 5–6).
The electrons from CB2H− MoS2 are quickly shifted to 1T-MoS2 due to its
unique metallic properties and strong electrical conductivity, which
makes it an excellent electron acceptor. Since the ECB of 2H-MoS2 is
more negative than that of CoFe2O4, the electrons then migrate from 1TMoS2 to CBCoFe2 O4 (Eq. (7)). In consequence, 1T-MoS2 becomes a channel
for electron transfer between 2H-MoS2 and CoFe2O4, allowing rapid
transfer of electrons. In addition, most of the holes migrate from
VBCoFe2 O4 to VB2H− MoS2 , which is the result of the more positive EVB of
7
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Fig. 6. (a) Nitrogen adsorption–desorption isotherm of CoFe2O4, MoS2, MC-2; (b) Pore size distribution of MoS2 and MC-2.
CoFe2O4 (0.28 eV vs NHE) is more positive than the standard potential
of O2/⋅O–2, the electrons transferred to CBCoFe2 O4 cannot produce ⋅O–2 from
O2 molecules by photoreduction. However, the ECB of CoFe2O4 (0.28 eV
vs NHE) is sufficiently negative that O2 can be reduced to H2O2 (0.695
eV vs NHE) by electrons on the ECB. Afterwards, H2O2 and e- react with
each other to produce ⋅OH radicals (Eqs. 8–9) to degrade organic pol­
lutants into small molecules [21]. Furthermore, the photoinduced holes
on VB2H− MoS2 and VBCoFe2 O4 are not sufficient to oxidize adsorbed H2O to
Table 1
Surface area, pore volume and pore size parameters for CoFe2O4, MoS2 and MC2 samples.
Samples
Surface area (m2/g)
pore volume (cm3/g)
Pore size (nm)
CoFe2O4
MoS2
MC-2
70.4909
8.5053
13.6504
0.016
0.037
0.046
22.367
27.135
12.628
CoFe2O4 compared to 2H-MoS2. As a result, a type II heterojunction is
confirmed between MoS2 and CoFe2O4. Electrons on CB2H− MoS2 can
induce O2 molecules to produce ⋅O–2 because the ECB of 2H-MoS2 (-0.48
eV vs NHE) is more negative than the standard potential of O2/⋅O–2
(-0.33 eV vs NHE) (Eq. (10)) [59]. Unfortunately, since the ECB of
Table 2
Band gaps of MoS2, MC-2, CoFe2O4, respectively.
Eg (eV)
MoS2
MC-2
CoFe2O4
1.25
1.45
1.98
Fig. 7. (a) UV–vis absorption spectra and the band gap energy of different samples: (b) CoFe2O4, (c) MoS2, (d) MC-2.
8
K. Dou et al.
Applied Surface Science 605 (2022) 154751
excellent visible light adsorption capability leads to the enhanced pho­
tocatalytic activity of (1T/2H)-MoS2/CoFe2O4 heterojunction.
Fig. 8. The PL spectra of pure MoS2, CoFe2O4 and MC-2 sample.
2H − MoS2 + hv→2H − MoS2 (h+ + e− )
(5)
CoFe2 O4 + hv→CoFe2 O4 (h+ + e− )
(6)
CoFe2 O4 (h+ )→2H − MoS2 (h+ )
(7)
2H − MoS2 (e− )→1T − MoS2 (e− )→CoFe2 O4 (e− )
(8)
CoFe2 O4 (e− ) + H + + O2 →H2 O2
(9)
(e− ) + H2 O2 + hv→⋅OH + OH −
(10)
2H − MoS2 (e− ) + O2 →⋅O−2
(11)
⋅OH + ⋅O−2 + h+ + MB→CO2 + H2 O + Othersmallmolecules
(12)
Table 3
Summary of kinetic data for the photocatalytic degradation of MB by the assynthesized samples under visible light.
⋅OH radicals, because both the EVB of MoS2 (0.77 eV vs NHE) and
CoFe2O4 (1.9 eV vs NHE) are more negative than the standard potential
of ⋅OH /OH– (1.99 eV vs NHE) [60]. Even so, the holes at VB2H− MoS2 and
VBCoFe2 O4 can be directly involved in the degradation of organic pollut­
ants. Hence, in this work, h+, ⋅O–2 and ⋅OH work together to degrade MB
(Eq. (11)) as what the trapping experiments reveal. Consequently, the
combination of superior photogenerated carrier mobility and the
No.
Photocatalyst
Degradation efficiency (%)
Rate constant k (min− 1)
1
2
3
4
5
MoS2
CoFe2O4
MC-1
MC-2
MC-4
32.5
6
72.8
91.9
82.9
4.75 × 10-3
1.11 × 10-3
9.59 × 10-3
2.823 × 10-2
1.308 × 10-2
Fig. 9. Photocatalytic degradation experiment of MB for different catalysts: (a) Photocatalytic degradation curves, (b) plot of -ln(C/ C0) vs time, (c) Photocatalytic
efficiency of sample MC-2 for the degradation of MB at different pH values, (d) The zero charge point of sample MC-2.
9
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Fig. 10. (a) Effect of coexisting ions on MB degradation by MC-2. (b) Photocatalytic degradation curves for cyclic experiments.
Scheme 2. Degradation pathway of MB measured by LC-MS for MC-2 sample.
Fig. 11. (a) Photocatalytic degradation of MB by MC-2 sample with different scavengers, (b) a histogram for the degradation rates of MB with different scavengers,
(c) apparent rate constant for Photocatalytic degradation of MB by MC-2 sample with different scavengers.
10
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Fig. 12. Mott–Schottky plots of (a) MoS2 and (b) CoFe2O4.
Scheme 3. Mechanism of the MoS2/CoFe2O4 heterojunction during the photocatalytic degradation of MB with visible light.
original draft. Yukai Lu: Visualization, Conceptualization, Methodol­
ogy, Writing – original draft. Rongchen Wang: Visualization, Formal
analysis, Investigation. Haopeng Cao: Visualization, Formal analysis,
Investigation. Chao Yao: Visualization, Formal analysis, Investigation.
Jialong Liu: Visualization, Project administration, Writing – review &
editing. Natalia Tsidaeva: Visualization, Project administration,
Funding acquisition, Writing – review & editing. Wei Wang: Visuali­
zation, Conceptualization, Methodology, Supervision, Project adminis­
tration, Funding acquisition, Writing – review & editing.
4. Conclusions
In conclusion, (1T/2H)-MoS2/CoFe2O4 composites were prepared
successfully by a simple hydrothermal method and the formation of
heterojunction was verified. MC-2 sample with the molar ratio of MoS2
to CoFe2O4 as 2:1 shows the highest photodegradation efficiency (91.9
%) for MB dyes. The enhancement can be attributed to two reasons.
First, the II-scheme heterojunction restrains the recombination of pho­
togenerated electron-hole pairs. Second, 1T-MoS2 facilitates the carrier
motion between CoFe2O4 and 2H-MoS2. The trapping experiments
demonstrated that h+, ⋅O–2 and ⋅OH work together in the photo­
degradation process. Moreover, cycling experiments show that the (1T/
2H)-MoS2/CoFe2O4 composites have good stability and reusability,
which can be recovered by magnetic separation. Overall, a new route is
provided in this work to design and synthesize the (1T/2H)-MoS2/
CoFe2O4 heterojunctions for photocatalytic degradation of organic dyes
in wastewater.
Declaration of Competing Interest
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.
Data availability
No data was used for the research described in the article.
CRediT authorship contribution statement
Kai Dou: Visualization, Conceptualization, Methodology, Writing –
11
K. Dou et al.
Applied Surface Science 605 (2022) 154751
Acknowledgements
[19] G. Eda, H. Yamaguchi, D. Voiry, T. Fujita, M. Chen, M. Chhowalla,
photoluminescence from chemically exfoliated MoS2, Nano Lett. 11 (12) (2011)
5111–5116.
[20] W.C. Peng, X.Y. Li, Synthesis of MoS2/g-C3N4 as a solar light-responsive
photocatalyst for organic degradation, Catal. Commun. 49 (2014) 63–67.
[21] S. Kumar, V. Sharma, K. Bhattacharyya, V. Krishnan, N-doped ZnO-MoS2 binary
heterojunctions: the dual role of 2D MoS2 in the enhancement of photostability and
photocatalytic activity under visible light irradiation for tetracycline degradation,
Mater. Chem. Front. 1 (2017) 1093–1106.
[22] J. Xie, H. Zhang, S. Li, R. Wang, X.u. Sun, M. Zhou, J. Zhou, X.W.D. Lou, Y.i. Xie,
Defect-rich MoS2 ultrathin nanosheets with additional active edge sites for
enhanced electrocatalytic hydrogen evolution, Adv. Mater. 25 (40) (2013)
5807–5813.
[23] J. Xie, J. Zhang, S. Li, F. Grote, X. Zhang, H. Zhang, R. Wang, Y. Lei, B. Pan, Y.i. Xie,
Controllable disorder engineering in oxygen-incorporated MoS2 ultrathin
nanosheets for efficient hydrogen evolution, J. Am. Chem. Soc. 135 (47) (2013)
17881–17888.
[24] S. Guo, X. Li, J. Zhu, T. Tong, B. Wei, Au NPs@MoS2 sub-micrometer sphere-ZnO
nanorod hybrid structures for efficient photocatalytic hydrogen evolution with
excellent stability, Small 12 (41) (2016) 5692–5701.
[25] M. Acerce, D. Voiry, M. Chhowalla, Metallic 1T phase MoS2 nanosheets as
supercapacitor electrode materials, Nat. Nanotechnol. 10 (4) (2015) 313–318.
[26] S. Bai, L. Wang, X. Chen, J. Du, Y. Xiong, Chemically exfoliated metallic MoS2
nanosheets: a promising supporting co-catalyst for enhancing the photocatalytic
performance of TiO2 nanocrystals, Nano Res. 8 (2015) 175–183.
[27] Y. Pi, Z. Li, D. Xu, J. Liu, Y. Li, F. Zhang, G. Zhang, W. Peng, X. Fan, 1T-Phase MoS2
nanosheets on tio2 nanorod arrays: 3d photoanode with extraordinary catalytic
performance, ACS Sustain. Chem. Eng. 5 (6) (2017) 5175–5182.
[28] K. Chang, X. Hai, H. Pang, H. Zhang, L.i. Shi, G. Liu, H. Liu, G. Zhao, M.u. Li, J. Ye,
Targeted synthesis of 2H- and 1T-Phase MoS2 monolayers for catalytic hydrogen
evolution, Adv. Mater. 28 (45) (2016) 10033–10041.
[29] Z. Liu, H. Feng, S. Xue, P. Xie, L. Li, X. Hou, J. Gong, X. Wei, J. Huang, D. Wu, The
triple-component Ag3PO4-CoFe2O4-GO synthesis and visible light photocatalytic
performance, Appl. Surf. Sci. 458 (2018) 880–892.
[30] A. Šutka, N. Döbelin, U. Joost, K. Smits, V. Kisand, M. Maiorov, K. Kooser, M. Kook,
R.F. Duarte, T. Käämbre, Facile synthesis of magnetically separable CoFe2O4/
Ag2O/Ag2CO3 nanoheterostructures with high photocatalytic performance under
visible light and enhanced stability against photodegradation, J. Environ. Chem.
Eng. 5 (4) (2017) 3455–3462.
[31] M. Shekofteh-Gohari, A. Habibi-Yangjeh, M. Abitorabi, A. Rouhi, Magnetically
separable nanocomposites based on ZnO and their applications in photocatalytic
processes: a review, Crit. Rev. Environ. Sci. Technol. 48 (10-12) (2018) 806–857.
[32] M. Mousavi, A. Habibi-Yangjeh, S.R. Pouran, Review on magnetically separable
graphitic carbon nitride-based nanocomposites as promising visible-light-driven
photocatalysts, J. Mater. Sci. Mater. Electron. 29 (3) (2018) 1719–1747.
[33] A. Chandekar, S.K. Sengupta, J.E. Whitten, Thermal stability of thiol and silane
monolayers: A comparative study, Appl. Surf. Sci. 256 (9) (2010) 2742–2749.
[34] Y.K. Lu, B.Y. Ren, S.C. Chang, W.B. Mi, J. He, W. Wang, Achieving effective control
of the photocatalytic performance for CoFe2O4/MoS2 heterojunction via exerting
external magnetic fields, Mater. Lett. 260 (2020), 126979.
[35] M.R. Li, C. Song, Y. Wu, M. Wang, Z.P. Pan, Y. Sun, L. Meng, S.G. Han, L.J. Xu,
L. Gan, Novel Z-scheme visible-light photocatalyst based on CoFe2O4/BiOBr/
Graphene composites for organic dye degradation and Cr(VI) reduction, Appl. Surf.
Sci. 478 (2019) 744–753.
[36] T. Muthukumaran, J. Philip, Synthesis of water dispersible phosphate capped
CoFe2O4 nanoparticles and its applications in efficient organic dye removal,
Colloids Surf. A Physicochem. Eng. Asp. 610 (2021), 125755.
[37] H. Sun, M. Nie, Z.H. Xue, J. Luo, Y. Tang, Q. Li, L.M. Teng, T. Gao, K.R. Xu, Study
on the simple synthesis and hydrogen evolution reaction of nanosized ZnO coated
MoS2, Mater. Chem. Phys. 262 (2021), 124279.
[38] X.Y. Wang, Y.K. Lu, T. Zhu, S.C. Chang, W. Wang, CoFe2O4/N-doped reduced
graphene oxide aerogels for high-performance microwave absorption, Chem. Eng.
J. 388 (2020), 124317.
[39] X. Wang, T. Zhu, S. Chang, Y. Lu, W. Mi, W. Wang, 3D nest-like architecture of
core-shell CoFe2O4@1T/2H-MoS2 composites with tunable microwave absorption
performance, ACS Appl. Mater. Inter. 12 (9) (2020) 11252–11264.
[40] A.M. Badizi, H. Maleki, One-step combustion synthesis of SiO2-CoFe2O4
nanocomposites and characterization for structural, thermal, optical and magnetic
properties, Mater. Sci. Semicond. Process. 124 (2021), 105594.
[41] Y. Cao, N. Farouk, N. Mortezaei, A.V. Yumashev, M.N. Akhtar, A. Arabmarkadeh,
Investigation on microwave absorption characteristics of ternary MWCNTs/
CoFe2O4/FeCo nanocomposite coated with conductive PEDOT-Polyaniline Copolymers, Ceram. Int. 47 (9) (2021) 12244–12251.
[42] S.N. Nguyen, T.K. Truong, S.-J. You, Y.-F. Wang, T.M. Cao, V.V. Pham,
Investigation on photocatalytic removal of NO under visible light over Cr-Doped
ZnO nanoparticles, ACS Omega. 4 (7) (2019) 12853–12859.
[43] L. Tian, R. Wu, HaiYang Liu, Synthesis of Au-nanoparticle-loaded 1T@2H-MoS2
nanosheets with high photocatalytic performance, J. Mater. Sci. 54 (13) (2019)
9656–9665.
[44] J.C. Yang, M.P. Zhu, X.G. Duan, S.B. Wang, B.L. Yuan, M.L. Fu, The mechanistic
difference of 1T–2H MoS2 homojunctions in persulfates activation: Structuredependent oxidation pathways, Appl. Catal. B: Environ. 297 (2021), 120460.
[45] X.Y. Wang, J. Liao, R.X. Du, G.H. Wang, N. Tsidaeva, W. Wang, Achieving superbroad effective absorption bandwidth with low filler loading for graphene
aerogels/raspberry-like CoFe2O4 clusters by N doping, J. Colloid Interface Sci. 590
(2021) 186–198.
This work was supported by the National Natural Science Foundation
of China (No. 52071009, 12011530067 and 11774020), the Beijing
Natural Science Foundation (No. 2172045), the long-term subsidy
mechanism from the Ministry of Finance and the Ministry of Education
of PRC for Beijing University of Chemical Technology as well as the
Fundamental Research Funds for the Central Universities (No. ZY2211),
the financial support of the Russian Foundation for Basic Research and
the National Natural Science Foundation of China in the framework of
the scientific project (No. 20-52-53038).
Appendix A. Supplementary material
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.apsusc.2022.154751.
References:
[1] M. Peydayesh, M.K. Suter, S. Bolisetty, S. Boulos, S. Handschin, L. Nystrom,
R. Mezzenga, Amyloid fibrils aerogel for sustainable removal of organic
contaminants from Water, Adv. Mater. 32 (2020), 190732.
[2] R. Du, H. Cao, G. Wang, K. Dou, N. Tsidaeva, W. Wang, PVP modified rGO/
CoFe2O4 magnetic adsorbents with a unique sandwich structure and superior
adsorption performance for anionic and cationic dyes, Sep. Purif. Technol. 286
(2022), 120484.
[3] X.R. Zhao, W. Wang, Y.J. Zhang, S.Z. Wu, F. Li, J.P. Liu, Synthesis and
characterization of gadolinium doped cobalt ferrite nanoparticles with enhanced
adsorption capability for Congo Red, Chem. Eng. J. 250 (2014) 164–174.
[4] W. Wang, K. Cai, X.F. Wu, X.H. Shao, X.J. Yang, A novel poly(mphenylenediamine)/reduced graphene oxide/nickel ferrite magnetic adsorbent
with excellent removal ability of dyes and Cr(VI), J. Alloy. Compd. 722 (2017)
532–543.
[5] S. Chang, Q. Zhang, Y. Lu, S. Wu, W. Wang, High-efficiency and selective
adsorption of organic pollutants by magnetic CoFe2O4/graphene oxide adsorbents:
Experimental and molecular dynamics simulation study, Sep. Purif. Technol. 238
(2020) 116400.
[6] G. Wang, K. Dou, H. Cao, R. Du, J. Liu, N. Tsidaeva, W. Wang, Designing Z-scheme
CdS/WS2 heterojunctions with enhanced photocatalytic degradation of organic
dyes and photoreduction of Cr(VI): Experiments, DFT calculations and mechanism,
Sep. Purif. Technol. 291 (2022) 120976.
[7] X.F. Wu, Z. Ding, W. Wang, N.N. Song, S. Khaimanov, N. Tsidaeva, Effect of
polyacrylic acid addition on structure, magnetic and adsorption properties of
manganese ferrite nanoparticles, Powder. Technol. 295 (2016) 59–68.
[8] S.Z. Liu, S.B. Wang, Y. Jiang, Z.Q. Zhao, G.Y. Jiang, Z.Y. Sun, Synthesis of Fe2O3
loaded porous g-C3N4 photocatalyst for photocatalytic reduction of dinitrogen to
ammonia, Chem. Eng. J. 373 (2019) 572–579.
[9] X. Li, H.P. Jiang, C.C. Ma, Z. Zhu, X.H. Song, H.Q. Wang, P.W. Huo, X.Y. Li, Local
surface plasma resonance effect enhanced Z-scheme ZnO/Au/g-C3N4 film
photocatalyst for reduction of CO2 to CO, Appl. Catal. B: Environ. 283 (2021),
119638.
[10] Y. Li, D. Zhang, J. Fan, Q. Xiang, Highly crystalline carbon nitride hollow spheres
with enhanced photocatalytic performance, Chin. J. Catal. 42 (4) (2021) 627–636.
[11] H.R. Sun, F. Guo, J.J. Pan, W. Huang, K. Wang, W.L. Shi, One-pot thermal
polymerization route to prepare N-deficient modified g-C3N4 for the degradation of
tetracycline by the synergistic effect of photocatalysis and persulfate-based
advanced oxidation process, Chem. Eng. J. 406 (2021), 126844.
[12] X. Zhang, C.L. Shao, X.H. Li, F.J. Miao, K.X. Wang, N. Luand, Y.C. Liu, 3D MoS2
nanosheet/TiO2 nanofiber heterostructures with enhanced photocatalytic activity
under UV irradiation, J. Alloy. Compd. 686 (2016) 137–144.
[13] B. Hinnemann, P.G. Moses, J. Bonde, K.P. Jørgensen, J.H. Nielsen, S. Horch,
I. Chorkendorffand, J.K. Nørskov, Biomimetic hydrogen evolution: MoS2
nanoparticles as catalyst for hydrogen evolution, J. Am. Chem. Soc. 127 (2005)
5308–5309.
[14] S.H. Choi, Y.N. Ko, J.-K. Lee, Y.C. Kang, 3D MoS2-Graphene Microspheres
consisting of multiple nanospheres with superior sodium ion storage properties,
Adv. Funct. Mater. 25 (12) (2015) 1780–1788.
[15] H. Li, W. Leachman, J. Kershaw, Fabrication and surface characterization of
photopatterned encapsulated micromagnets for microrobotics and microfluidics
applications, Appl. Surf. Sci. 386 (2016) 364–370.
[16] G. Li, D.u. Zhang, Q. Qiao, Y. Yu, D. Peterson, A. Zafar, R. Kumar, S. Curtarolo,
F. Hunte, S. Shannon, Y. Zhu, W. Yang, L. Cao, All the catalytic active sites of MoS2
for hydrogen evolution, J. Am. Chem. Soc. 138 (51) (2016) 16632–16638.
[17] W. Zhou, Z. Yin, Y. Du, X. Huang, Z. Zeng, Z. Fan, H. Liu, J. Wang, H. Zhang,
Synthesis of few-layer MoS2 nanosheet-coated TiO2 nanobelt heterostructures for
enhanced photocatalytic activities, Small 9 (1) (2013) 140–147.
[18] M.A. Lukowski, A.S. Daniel, F. Meng, A. Forticaux, L. Li, S. Jin, Enhanced hydrogen
evolution catalysis from chemically exfoliated metallic MoS2 nanosheets, J. Am.
Chem. Soc. 135 (28) (2013) 10274–10277.
12
K. Dou et al.
Applied Surface Science 605 (2022) 154751
[46] P. Aghasiloo, M. Yousefzadeh, M. Latifi, R. Jose, Highly porous TiO2 nanofibers by
humid-electrospinning with enhanced photocatalytic properties, J. Alloys Compd.
790 (2019) 257–265.
[47] Y. Min, G. He, Q. Xu, Y. Chen, Dual-functional MoS2 sheet-modified CdS branchlike heterostructures with enhanced photostability and phtocatalytic activity,
J. Mater. Chem. A 2 (2014) 2578–2584.
[48] R.X.D.H.P. Cao, G.H. Wang, K. Dou, N. Tsidaeva, W. Wang, PVP modified rGO/
CoFe2O4 magnetic adsorbents with a unique sandwich structure and superior
adsorption performance for anionic and cationic dyes, Sep. Purif. Technol. 286
(2022), 120484.
[49] J. Chen, J. Wei, H. Zhang, X. Wang, L.S. Fu, T.H. Yang, Construction of CuCdBMOF/GO composites based on phosphonate and their boosted visible-light
photocatalytic degradation, Appl. Surf. Sci. 594 (2022), 153493.
[50] C.D. Qi, X.T. Liu, J. Ma, C.Y. Lin, X.W. Li, H.J. Zhang, Activation of
peroxymonosulfate by base: Implications for the degradation of organic pollutants,
Chemosphere 151 (2016) 280–288.
[51] H.B. Yu, J.H. Huang, L.B. Jiang, Y.H. Shi, K.X. Yi, W. Zhang, J. Zhang, H.Y. Chen,
X.Z. Yuan, Enhanced photocatalytic tetracycline degradation using N-CQDs/OVBiOBr composites: Unraveling the complementary effects between N-CQDs and
oxygen vacancy, Chem. Eng. J. 402 (2020), 126187.
[52] S.T.T. Le, W. Khanitchaidecha, A. Nakaruk, Photocatalytic reactor for organic
compound removal using photocatalytic mechanism, Bull. Mater. Sci. 39 (2)
(2016) 569–572.
[53] H. Abbas, R.A. Nasr, A. Khalaf, A. Al Bawab, T.S. Jamil, Photocatalytic degradation
of methylene blue dye by fluorite type Fe2Zr2-xWxO7 system under visible light
irradiation, Ecotoxicol. Environ. Saf. 196 (2020), 110518.
[54] B. Kaushik, S. Yadav, P. Ranan, K. Solanki, D. Rawat, R.K. Sharma, Precisely
engineered type II ZnO-CuS based heterostructure: A visible light driven
photocatalyst for efficient mineralization of organic dyes, Appl. Surf. Sci. 590
(2022), 153053.
[55] J. Rashid, S. Saleem, S.U. Awan, A. Iqbal, R. Kumar, M.A. Barakat, M. Arshad,
M. Zaheer, M. Rafique, M. Awad, Stabilized fabrication of anatase-TiO2/FeS2
(pyrite) semiconductor composite nanocrystals for enhanced solar light-mediated
photocataly-tic degradation of methylene blue, RSC Adv. 8 (22) (2018)
11935–11945.
[56] B.Y. Ren, W. Shen, L. Li, S.Z. Wu, W. Wang, 3D CoFe2O4 nanorod/flower-like MoS2
nanosheet heterojunctions as recyclable visible light-driven photocatalysts for the
degradation of organic dyes, Appl. Surf. Sci. 447 (2018) 711–723.
[57] P.T. Liu, Y.G. Liu, W.C. Ye, J. Ma, D.Q. Gao, Flower-like N-doped MoS2 for
photocatalytic degradation of RhB by visible light irradiation, Nanotechnol. 27
(2016) 225–403.
[58] C. Yang, Q. Li, Y. Xia, K.L. Lv, M. Li, Enhanced visible-light photocatalytic CO2
reduction performance of ZnIn2S4 microspheres by using CeO2 as cocatalyst, Appl.
Surf. Sci. 464 (2019) 388–395.
[59] Q. Zhang, Y.D. Wang, X.M. Zhu, X. Liu, H.X. Li, 1T and 2H mixed phase MoS2
nanobelts coupled with Ti3+ self-doped TiO2 nanosheets for enhanced
photocatalytic degradation of RhB under visible light, Appl. Surf. Sci. 556 (2021),
149768.
[60] S. Zhang, J. Li, M. Zeng, G. Zhao, J. Xu, W. Hu, X. Wang, In situ synthesis of watersoluble magnetic graphitic carbon nitride photocatalyst and its synergistic catalytic
performance, ACS Appl. Mater. Inter. 5 (23) (2013) 12735–12743.
13