Constructing ZIF-8 derived C-ZnS/ZnMoO4?MoS2 and C-ZnS/MoS2 nanocomposites using a simple one-pot strategy to enhance photocatalytic degradation activity

Article abstract of DOI:10.1039/c9ra06591a

Efficient C-ZnS/ZnMoO₄?MoS₂ and C-ZnS/MoS₂ nanocomposite photocatalysts, using ZIF-8 derived C-ZnO as a precursor were successfully synthesized using a simple one-pot procedure. This is the first application that involves transforming ZIF-8 into C-ZnMoO₄ for photocatalysis. The C-ZnS/ZnMoO₄?MoS₂ and C-ZnS/MoS₂ heterostructures were characterized by X-ray diffraction, UV-vis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, photocurrent measurements, scanning electron microscopy and transmission electron microscopy. The ZM2 sample of C-ZnS/ZnMoO₄?MoS₂ exhibited enhanced photocatalytic activity of about 2.9 times as high as that of ZIF-8 derived C-ZnO in the reduction of tetracycline hydrochloride, and also showed obvious photocatalytic activity 1.81 and 3.33 times as high as that of a ZM3 sample of C-ZnS/MoS₂ and ZIF-8 derived C-ZnO in the degradation of RhB, respectively. The improved photodegradation activity is a result of the heterogenous structure and the tighter contact between C-ZnS and C-ZnMoO₄ compared with the physical contact of general heterogenous photocatalysts. The C-ZnS/ZnMoO₄?MoS₂ heterostructure photocatalyst is expected to be a new type of nanomaterial for the degradation of pollutants from wastewater.

Full text of DOI:10.1039/c9ra06591a

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Constructing ZIF-8 derived C–ZnS/ZnMoO @MoS
4
2
and C–ZnS/MoS nanocomposites using a simple
2
Cite this: RSC Adv., 2019, 9, 35189
one-pot strategy to enhance photocatalytic
degradation activity†
Yi-Wei Cui, Hai-Huan Zhang and Shi-Yong Yu
*
Efficient C–ZnS/ZnMoO
ZnO as a precursor were successfully synthesized using a simple one-pot procedure. This is the first
application that involves transforming ZIF-8 into C–ZnMoO for photocatalysis. The C–ZnS/
ZnMoO @MoS and C–ZnS/MoS heterostructures were characterized by X-ray diffraction, UV-vis, X-ray
4 2 2
@MoS and C–ZnS/MoS nanocomposite photocatalysts, using ZIF-8 derived C–
4
4
2
2
photoelectron spectroscopy, electrochemical impedance spectroscopy, photocurrent measurements,
scanning electron microscopy and transmission electron microscopy. The ZM2 sample of C–ZnS/
ZnMoO
derived C–ZnO in the reduction of tetracycline hydrochloride, and also showed obvious photocatalytic
activity 1.81 and 3.33 times as high as that of a ZM3 sample of C–ZnS/MoS and ZIF-8 derived C–ZnO in
the degradation of RhB, respectively. The improved photodegradation activity is a result of the
heterogenous structure and the tighter contact between C–ZnS and C–ZnMoO compared with the
physical contact of general heterogenous photocatalysts. The C–ZnS/ZnMoO @MoS heterostructure
4 2
@MoS exhibited enhanced photocatalytic activity of about 2.9 times as high as that of ZIF-8
2
Received 22nd August 2019
Accepted 1st October 2019
4
4
2
DOI: 10.1039/c9ra06591a
photocatalyst is expected to be a new type of nanomaterial for the degradation of pollutants from
wastewater.
rsc.li/rsc-advances
frameworks to fabricate porous metal oxides as photocatalysts
has been a research hotspot in recent years.
Zeolite imidazolate frameworks (ZIFs) as a sub aggregation
1
. Introduction
14,15
Wastewater containing antibiotics has become a grave threat to
1,2
human health and the environment. Tetracycline hydrochlo- of MOFs are a kind of porous crystalline material in which
ride (TC-H) as the second most widely distributed antibiotic in imidazolate linkers are cross-linked to transition metal ions to
3,4
16–19
the world has been extensively produced and used. However, form 3D tetrahedral frameworks.
They have attracted
due to the unique characteristic properties of TC-H, only 10– extensive attention in various elds, such as heterogeneous
20–23
24
25
26–28
3
0% of TC-H can be metabolized by animals and human beings, catalysis,
photocatalysis, sensing, gas adsorption
and
and 70–90% is released into the water environment via drug delivery due to their high surface area and high crystal-
29
discharge of wastewater effluent and animal manure aer being linity as well as good chemical and thermal stability. However,
heavily used in the pharmaceutical industry, animal husbandry as photocatalysts, most ZIFs cannot be excited by visible light
and aquaculture, which causes serious water environmental because their band gaps are too wide to be excited: for example,
5,6
30
problems.
ZIF-8 has a band gap of 5.1 eV. For the purposes of dimin-
Among the treatments of tetracycline wastewater, photo- ishing their band gaps and broadening their application in
7
catalysis is a simple, dependable and environmentally-friendly photocatalysis, MOFs can be used as precursors to directly
technology compared to traditional techniques, such as prepare C-doped oxides and it has been proved that the
8
9
10
adsorption, microbial degradation or membrane separation.
Compared with conventional photocatalysts, such as TiO , C
or ZnO,
prepared C-doped materials can expand the response to visible
light and facilitate the absorption of visible light. Du et al.
2
3
N
4
1
1–13
using MOFs as “precursors” or self-sacricial prepared porous C–ZnO by calcining ZIF-8 directly in air and
they found that such ZnO showed improved photocatalytic
31
activity compared to ZIF-8 or pure ZnO. Feng et al. prepared N–
ZnO from the direct calcination of urea and a ZIF-8 mixture for
Inner Mongolia Key Laboratory of Mongolian Medicine Chemistry, Inner Mongolia Key
Laboratory of Coal Chemistry, School of Chemistry and Chemical Engineering, Inner
Mongolia University, Hohhot 010021, Inner Mongolia, China. E-mail: syyunano@ RhB degradation, and found that such a material can enhance
imu.edu.cn
the visible-light harvesting ability and achieve a photocatalytic
efficiency higher than that of ZIF-8 derived C–ZnO. However,
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra06591a
32
1
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ꢀ
reports about transforming ZIF-8 directly into heterojunctions to a 45 ml Teon-lined autoclave and maintained at 200 C for
are very scarce.
24 h in an oven. The resulting samples were collected by
Molybdenum disulde (MoS ) has been proven to be an centrifugation, and washed several times with deionized water
2
excellent co-catalyst in photocatalytic activity by providing more and ethyl alcohol. In order to synthesize materials with different
active sites and inhibiting the recombination rate of electron– ratios of ZnS, ZnMoO
4 2
and MoS , a series of samples were
hole pairs. Thomas et al. reported active edge sites for electro- prepared by adding different raw materials. In general, C-doped
3
3
chemical hydrogen production from MoS
and ZnMoO are both well-known photocatalysts, which have of CH
a wider band gap than MoS . Such a combination can facilitate 50 mg of C–ZnO, 0.12 g of CH
the separation of the electron–hole pairs by photoexcitation.
Inspired by this, herein, we have adopted a one-pot route in CH N S and 0.24 g of NH MoO named as ZM4. C–ZnS/MoS
2
2
.
By contrast, ZnS ZnS/ZnMoO
4
@MoS
2
was produced from 50 mg of C–ZnO, 0.12 g
MoO and named as ZM1; from
S and 0.48 g of NH MoO
named as ZM2; and from 25 mg of C-doped ZnO, 0.12 g of
4
4
N
2
S and 0.24 g of NH
4
4
2
4
N
2
4
4
34,35
4
2
4
4
which ZIF-8 derived C–ZnO was added to the raw materials for was prepared by adding 50 mg of C–ZnO, 0.24 g of CH N S and
4
2
the synthesis of MoS
ZnS/ZnMoO @MoS
MoS could be nally obtained. It is worth mentioning that,
because the C–ZnS and C–ZnMoO in the three-phase hetero- 2.3 Characterization of the photocatalysts
2
and a three-phase heterojunction of C– 0.48 g of NH
4 4
MoO and named as ZM3.
4
2
and a two-phase heterojunction of ZnS/
2
4
junction were directly produced together from ZIF-8 derived C–
ZnO in the same step, the contact between C–ZnS and C–
The crystallographic phase of the as-synthesized samples was
determined with a Panalytical X-Pert X-ray diffractometer (XRD)
ZnMoO will be tighter than the physical contact of general
ꢀ
4
with a scanning rate of 2.5 per min. The morphology and
heterojunction photocatalysts, and this can facilitate the sepa-
ration of the electron–hole pairs.
elemental compositions of the prepared photocatalysts were
observed by a scanning electron microscope (SEM) equipped
with an energy dispersive X-ray (EDX) spectrometer and trans-
mission electron microscopy (TEM, JEM-2010). X-ray photo-
electron spectroscopy (XPS) was performed on an ESCALAB250
instrument (Thermo VG Corp.) The UV-vis spectra were carried
2. Experimental section
2.1 Materials
Zinc nitrate hexahydrate [Zn(NO ) $6H O $ 99.0%], absolute out on a spectrometer (Shimadzu UV-3600). The photo-
3
2
2
methanol (EtOH $ 99.7%) and ethanol (EtOH $ 99.7%) were luminescence (PL) spectra of the samples were recorded on an
purchased from Sinopharm Chemical Reagents Co., Ltd. 2- Edinburgh Instruments FLS 920 spectrometer at an excitation
Methylimidazole [H-MeIM], thiourea (CH
molybdate [(NH Mo 24$4H O] were purchased from Aladdin
P. R. China). All chemicals were used without any further
purication.
4 2
N S) and ammonium wavelength of 350 nm.
4
)
6
7
O
2
(
2.4 Photocatalytic measurements
The photocatalytic activities of C–ZnS/ZnMoO @MoS and C–
4
2
2
8
.2 Preparation
.2.1 Preparation of zeolitic imidazolate framework-8 (ZIF-
). ZIF-8 was synthesized according to previously reported
ZnS/MoS were measured using the photodegradation of tetra-
2
cycline hydrochloride and RhB in an aqueous solution under
full spectrum light irradiation (320 nm < l < 780 nm) using
a 300 W xenon lamp. Typically, in the degradation process of
tetracycline hydrochloride: 15 mg of catalyst was dispersed in
2
36
studies. In a typical synthesis, 0.9852 g of 2-methylimidazole
was dissolved in 15 ml of methyl alcohol and 0.8925 g of zinc
nitrate hexahydrate [Zn(NO ) $6H O] was dissolved in 10 ml of
3 2 2
methyl alcohol. Aer that 2-methylimidazole and zinc nitrate
hexahydrate were mixed together and stirred at room temper-
ature for 24 h. The sample was collected by centrifugation and
ꢁ1
3
0 ml of tetracycline hydrochloride (15 mg l ); in the degra-
dation process of RhB: 25 mg of catalyst was dispersed in 50 ml
ꢁ1
of RhB (5 mg l ). The reactor was stirred in the dark for 20 min
before irradiation to ensure absorption–desorption equilib-
rium. During the process, the suspension was kept under stir-
ring to retain the homogeneity of the suspension.
washed several times with methyl alcohol and then dried at
ꢀ
50 C overnight.
2
.2.2 Preparation of ZIF-8 derived C doped ZnO (C–ZnO).
ZIF-8 derived C–ZnO was obtained directly by calcining ZIF-8
ꢀ
ꢀ
ꢁ1
2.5 Photoelectrochemical measurements
powders at 380 C for 2 h at a heating rate of 2 C min
.
2
.2.3 Preparation of ZIF-8 derived C-doped ZnS/ Photoelectrochemical analysis was carried out in a conventional
ZnMoO @MoS (C–ZnS/ZnMoO @MoS ) named as ZM1,2,4, three electrode cell. In the working cell, the fabricated electrode
and C-doped ZnS/MoS (C–ZnS/MoS ) named as ZM3. In (a platinum wire) and reference electrodes Ag/AgCl (saturated
typical preparation process of ZIF-8 derived C–ZnS/ KCl) were used. The photocatalyst powder was deposited on
ZnMoO @MoS , 50 mg of ZIF-8 derived C–ZnO powder was FTO (F doped tin oxide) glass by electrophoretic deposition.
4
2
4
2
2
2
a
4
2
added to 30 ml of deionized water and sonicated for 30 min to Electrochemical impedance spectroscopy (EIS) measurements
form a homogeneous dispersion. Then, 0.12 g of CH N S and were performed at frequencies from 0.1 Hz to 100 KHz and the
4
2
0
.48 g of NH
4
MoO
4
were added to the preceding solvent and applied voltage was the open circuit voltage. The electrolyte was
SO
aqueous solution (0.2 M, pH ¼ 7).
stirred for 2 h. Aer that, the obtained solution was transferred Na
2
4
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3. Results and discussion
3.1 Structural and morphological analysis
The crystal phases of the samples (ZIF-8 C–ZnO ZM) were rst
identied by X-ray diffraction and the results are shown in
Fig. 1.
As shown in Fig. 1a, the transition from ZIF-8 to C–ZnO can
be seen. The XRD pattern of ZIF-8 is consistent with the patterns
37
reported in the literature. Aer thermal annealing, the
diffraction peaks of ZIF-8 derived C–ZnO located at about
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Scheme 1 Synthetic procedure of ZIF-8 derived C–ZnS/ZnMoO @-
MoS and C–ZnS/MoS .
2 2
31.738 , 34.380 , 36.217 , 47.487 , 56.535 , 62.777 , 67.865 can
4
be indexed to the (100), (002), (101), (102), (110), (103) and (112)
diffraction planes of ZnO (JCPDS no. 01-076-0704), which
reects the successful transformation from ZIF-8 to ZnO.
The XRD patterns of the ZMs are shown in Fig. 1b. Six peaks
will also react with thiourea and ammonium molybdate to
generate C–ZnS/ZnMoO or C–ZnS. The differences in the
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
4
located at about 26.915 , 28.502 , 30.530 , 47.563 , 51.778 ,
5
ꢀ
products is because the amount of thiourea will affect the acid–
base properties of the solution and this may be the requirement
6.394 correspond to diffraction from the (100), (002), (101),
(110), (103) and (112) crystallographic planes of ZnS (JCPDS no.
for determining whether or not ZnMoO
the raw material in the preparation of C–ZnS/MoS
used in a larger amount than in the preparation of ZnS/
ZnMoO @MoS (ZM1, 2 and 4), the size of MoS in ZM3 was
4
can be formed. Since
0
0-036-1450) respectively in all samples. The peaks corre-
ꢀ
ꢀ
2
(ZM3) was
sponding to ZnMoO
4
4
can be observed at 24.302 , 36.620 ,
ꢀ
ꢀ
8.844 , 53.715 corresponding to the (110), (120), (022) and
4
2
2
(
ꢁ221) diffraction planes of ZnMoO
4
(JCPDS no. 00-016-0310) in
ꢀ
ꢀ
much larger than that in ZM2, eventually resulting in the
different morphologies of ZM2 and ZM3, as shown in Scheme 1.
The morphologies of the composites were investigated by
ZM1, 36.620 and 53.715 corresponding to the (120) and
ꢀ
(
ꢁ221) diffraction planes of ZnMoO in ZM2, and 36.620 cor-
4
responding to the (120) diffraction planes of ZnMoO in ZM4,
4
SEM and TEM. Pure ower-like MoS is shown in Fig. S1.† It
2
and no peaks corresponding to ZnMoO were observed in ZM3.
4
ꢀ
should be noted that pure MoS
2
exhibited a smaller diameter
@MoS , the reason
The peaks located at 33.4 corresponding to MoS
2
could be
than MoS in C–ZnS/MoS or C–ZnS/ZnMoO
2
2
4
2
observed in ZM3. Unfortunately, no diffraction peaks corre-
sponding to MoS could be discerned in the other XRD patterns,
being that, in the process of preparing the catalysts, the addi-
2
tion of C–ZnO will increase the pH of the solution. According to
which may be because of the low content of this material in the
three composites. Other than this, we also found that the main
37,38
research,
2
in the process of preparing ower-like MoS , an
ꢀ
ꢀ
increase in the pH of the solution will accelerate the growth of
diffraction peaks corresponding to MoS at 37.6 and 57.8 were
2
the diameter of the obtained MoS . The prepared ZIF-8 shown
2
almost coincident with the diffraction peaks corresponding to
ꢀ
ꢀ
in Fig. S2† has a uniform polyhedral morphology with a diam-
eter of 200–300 nm.
Aer hydrothermal treatment, the sphere-like ZM2 with
a rough surface covered with 200–300 nm particles shown in
Fig. 2a and b was proved by XRD (Fig. 1b) and XPS (Fig. 3)
ZnMoO at 36.620 and ZnS at 56.394 , which may also cause
4
the inconspicuous peaks of MoS
composites, except for ZM3 which did not contain the compo-
nent of ZnMoO . The presence of MoS and the composition of
2
in the XRD patterns of these
4
2
the catalysts will be further corroborated by SEM, TEM and XPS
images.
4
analysis to be ZIF-8 derived C–ZnS/ZnMoO . We also found that
C–ZnS/ZnMoO4 approximately retained the polyhedral
morphology of ZIF-8 (inset Fig. 1b). The morphologies of MoS2
cannot clearly be observed in the SEM images because the
The synthetic procedure for ZIF-8 derived C–ZnS/
ZnMoO @MoS2 and C–ZnS/MoS2 is shown in Scheme 1. As
4
shown in Scheme 1, ZIF-8 derived C–ZnO was mixed with the
surface of ZM2 is covered with nanoparticles of C–ZnS/ZnMoO
4
.
raw materials for the synthesis of MoS
2
. During the hydro-
However, because MoS is a exible kind of material, its nano-
2
thermal reaction, when the MoS is forming from the reaction
2
sheets can pass through the outer layer, which cannot be clearly
observed in the SEM images. As shown in Fig. 2c–e, a large
number of nanosheets can be found at the surface of ZM2 in the
TEM images, and the high-resolution TEM (HRTEM) images
of thiourea and ammonium molybdate, ZIF-8 derived C–ZnO
(Fig. 2c and e) show clear fringes with a lattice spacing of
0
.62 nm, which correspond to the (002) plane of MoS . In
2
addition, EDS analysis shows that selected areas of the ZM2
composites comprise Zn, S, Mo, C and O elements (inset
Fig. 2a).
It is worth mentioning that the carbon content can be
observed both in the EDS pattern of the ZM2 and ZM3 samples
(
inset Fig. 2a and f), but no diffraction peaks of carbon were
Fig. 1 XRD patterns of (a) ZIF-8 and ZIF-8 derived ZnO and (b) ZM1,
ZM2, ZM3 and ZM4.
found in the XRD patterns of any of the samples, which
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Fig. 3 The high resolution XPS spectra of (a) survey spectrum, (b) C 1s,
4 2
(c) Mo 3d (d) Zn 2p, (e) O 1s, (f) S 2p of (1) C–ZnS/ZnMoO @MoS (ZM2)
and (2) C–ZnS/MoS (ZM3).
2
Fig. 2 (a) and (b) SEM images and EDS pattern (inset (a)) of ZM2; (d)
TEM images of ZM2; (c) and (e) HRTEM images of ZM2; (f) and (g) SEM
images and EDS pattern (inset (f)) of ZM3; (h) and (i) TEM images of
ZM3; (j) HRTEM images of ZM3.
2
85.9 eV (Fig. 3b). The main peak at 284.6 eV can be assigned to
adventitious hydrocarbons and the peak at 285.9 eV can be
attributed to Zn–C bonds, which further proves that carbon was
doped into the lattice of ZnS/ZnMoO and ZnS into the C–ZnS/
4
ZnMoO @MoS and C–ZnS/MoS samples, respectively.
4
2
2
In Fig. 3c(1), the high resolution spectrum for Mo 3d of ZM2
could be divided into ve peaks: the binding energy at
indicates that the carbon was successfully doped into the lattice
39
of ZnS/ZnMoO and ZnS. This conclusion was also further
4
approximately 226.0 eV can be attributed to the S 2 s of MoS
and the binding energies of 232.53 and 235.5 eV correspond to
2
proved by XPS analysis (Fig. 3). Unlike the composition and
morphology of ZM2, the nanoparticles of ZM3 were proved by
XRD (Fig. 1b) and XPS (Fig. 3b) analysis to be ZIF-8 derived C–
ZnS, and the particles retained the polyhedral morphology of
6
+
the Mo 3d5/2 and Mo 3d3/2 of Mo , respectively. The Mo 3d5/2
peak reveals that Mo exists in the form of a hexavalent oxide.
Another two peaks at 228.3 and 231.5 eV are characteristic of the
2
ZIF-8 (inset Fig. 2g) loaded onto the ower-like MoS , as shown
4
+
Mo 3d5/2 and Mo 3d3/2 of Mo in MoS , which further proves
2
in Fig. 2f and g. The nanosheets on the surface of ZM3 can be
clearly observed in Fig. 2j and i. The HRTEM (Fig. 2j) images
also show fringes with a lattice spacing of 0.62 nm corre-
the existence of MoS
2
in the C–ZnS/ZnMoO
4 2
@MoS samples
(
3
Fig. 2c and e). In Fig. 3c(2), the high resolution spectrum of Mo
d of ZM3 can also be divided into ve peaks. Compared to ZM2
2
sponding to the (002) plane of MoS . The EDS analysis shows
in Fig. 3c(1), the main peaks of ZM3 are located at 228.7 and
the ZM3 to have Zn, S, Mo, C and O elements, in which the
existence of oxygen might be due to the presence of water
molecules absorbed on the surface of ZM3, which was further
conrmed by XPS (Fig. 3).
4
+
2
31.8 eV, characteristic of Mo 3d3/2 and Mo 3d5/2 of Mo , and
another two weaker peaks at about 232.75 and 235.35 eV were
6
+

tted as Mo , which might be due to the incomplete decom-
2
ꢁ
position of MoO4 , consistent with the XRD results shown in
Fig. 1b. The differences between the peak positions might due
to the difference in the compositions of the two samples,
resulting in a slight shi in the peak position.
3.2 XPS analysis
XPS analysis was carried out to further conrm the chemical
As displayed in Fig. 3d(1), two distinct peaks at 1021.7 and
composition and surface chemical state of ZM2 and ZM3
1
044.7 eV correspond to Zn 2p1/2 and Zn 2p3/2, and the slight
(
Fig. 3). The characteristic peaks of C, Mo, Zn, O and S elements
appear over the whole XPS survey spectrum of the two samples
Fig. 3a) which is consistent with the EDS results. The peaks of
the high-resolution spectrum of C 1s are located at 284.6 and
deviation is also due to the difference in the compositions of the
two samples. The characteristic binding energy of 530.1 eV of
ZM2 in Fig. 3e(1) for O 1s reveals that O is present in the metal
(
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oxide ZnMoO
4
in C–ZnS/ZnMoO
4
@MoS
2
, and the binding ZM1, ZM2 and ZM4 are three-phase catalysts composed of C–
energy at 531.5 eV can be attributed to the chemisorbed or ZnS, C–ZnMoO4 and MoS . The transfer of photogenerated
2
dissociated oxygen or OH species on C–ZnS/MoS . The two charge carriers in the three phases is equivalent to increasing
2
peaks at 162.8 and 161.7 eV correspond to the S 2p and S 2p3/2 the transfer distance of carriers and reducing the recombina-
1
/2
2
ꢁ
of S and the slight difference in the 2p3/2 peak of ZM3, which tion of the photogenerated electron–hole pairs. In addition, the
can be found in Fig. 3f(2), is also due to the different compo- reason for the differences in the photodegradation activity of
sitions of the two samples.
ZM1, ZM2 and ZM4 is the different ratios of C–ZnS, C–ZnMoO
and MoS , due to the different amounts of raw materials added
during their preparation.
The reaction kinetics of the TC-H degradation were further
studied according to the pseudo-rst-order kinetic model
shown eqn (1), and the results are shown in Fig. 4c
4
2
3.3 Photocatalytic activity
3.3.1 Photodegradation of TC-H. The absorption spectra of
TC-H degraded by ZM2 are shown in Fig. 4a. It was found that
the characteristic peak at 357 nm decreased rapidly under light
irradiation and became barely visible aer 60 min of irradia-
tion. When the irradiation time was further increased to 80 min,
the absorbance spectra barely changed. The absorption spectra
of TC-H solutions degraded by other samples are shown in
Fig. S3.† The photocatalytic degradation results of all the
samples (ZM1-4) are shown in Fig. 4b. As shown in Fig. 4b, ZIF-8
derived C–ZnO exhibits enhanced catalytic efficiency compared
to pure ZnO, which proves the superiority of C–ZnO prepared
from ZIF-8 as a precursor in terms of photocatalytic perfor-
mance compared with pure ZnO. All the ZM samples (ZM1,
ZM2, ZM3 and ZM4) showed higher photocatalytic efficiency
than ZIF-8 derived C–ZnO because of the heterojunction
ln(C /C ) ¼ kt
0
t
(1)
in which t is the reaction time, k is the rate constant, and C and
0
Ct are the concentrations of the TC-H solution at times 0 and t
respectively.
It should be noted that TC-H was completely degraded by
ZM2 in 80 minutes (Fig. 4a), so only the rst ve points were
taken to obtain the slope (eqn (1)). As shown in Fig. 4c, the rates
of TC-H photodegradation were 0.001, 0.003, 0.012, 0.016,
ꢁ
1
0
.004, and 0.010 min for pure ZnO, ZIF-8 derived C–ZnO,
ZM1, ZM2, ZM3 and ZM4, respectively. Thus, the ZM2 samples
showed excellent performance in the degradation of TC-H. In
Fig. 4d, the recycling tests reveal that C–ZnS/ZnMoO
4 2
@MoS
4 2
combination of C–ZnS, C–ZnMoO and MoS , and such
(
ZM2) can be used repeatedly at least three times and the
a structure can improve the photodegradation activity of these
photocatalysts. Among them, ZM2 exhibited the highest pho-
tocatalytic activity for the degradation of TC-H and the ratio C/
photocatalytic activity remains sufficiently stable without any
signicant deactivation.
3.3.2 Photodegradation of RhB. To further demonstrate
0
C decreased from 58% to 20% compared to ZIF-8 derived C–
their applications in the removal of organic dye from waste-
water, the photocatalytic activities of the obtained products
were evaluated by measuring the degradation of RhB under full
spectrum light irradiation. Fig. 5a indicates that ZM2 exhibits
the best photocatalytic performance with an efficiency of 100%
compared with the other photocatalysis for the degradation of
RhB aer irradiation for 120 min. As for the degradation of TC-
H, the catalytic efficiencies of ZM1, ZM2 and ZM4 were also
better than that of ZM3, and all the ZM (ZM1, ZM2, ZM3 and
ZM4) samples exhibited enhanced catalytic efficiency compared
to pure ZnO or ZIF-8 derived C–ZnO. As shown in Fig. 5b, the
rate constants of different samples are 0.015, 0.026, 0.007 and
ZnO. It is worth noting that the catalytic efficiency of ZM3 was
much lower than those of ZM1, ZM2 or ZM4, and only 60% of
TC-H could be degraded in 120 minutes under light irradiation.
2
Compared to ZM3, which is only composed of C–ZnS and MoS ,
ꢁ1
0.021 min for ZM1-4, respectively.
Fig. 4 (a) Absorption spectra of TC-H solution collected during the
photodegradation of ZM2; (b) the photodegradation efficiency of TC-
H (C/C
0
) as a function of irradiation time over ZM1, ZM2, ZM3, ZM4,
ZIF-8 derived C–ZnO and pure ZnO; (c) kinetic linear simulation Fig. 5 (a) Photodegradation efficiency of RhB (C/C
0
) as a function of
curves of TC-H degradation with different photocatalysts under full irradiation time over ZM1, ZM2, ZM3, ZM4, ZIF-8 derived C–ZnO and
spectrum light irradiation; (d) photocatalytic activities of ZM2 for TC-H pure ZnO; (b) kinetic linear simulation curves of RhB degradation with
degradation with three times of cycling use.
different photocatalysts under full spectrum light irradiation.
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In order to reveal the underlying reaction mechanism of the 3.5 Photoelectrochemical analysis
enhanced photocatalytic activity of ZM2, the radical and hole
As shown in Fig. 7a, a fast and steady photocurrent response
was detected for each light-on and light-off period over ZM2 and
ZM3. The ZM2 samples show a signicant enhancement in
photocurrent density compared with that of the ZM3 samples,
which further conrms the efficient transfer of photo-induced
electrons of ZM2.
Electrochemical Impedance Spectroscopy (EIS) measure-
ments were also carried out to gure out the interface charge
transport behavior of ZM2 and ZM3. As shown in Fig. 7b, the
radius of the arc on the EIS Nyquist plot reects the reactor rate
occurring at the electrode surface. The lower arc radius of ZM2
with respect to ZM3 demonstrates a faster interfacial transfer
and more effective separation of photo-induced pairs occurring
in the composites. These results are well consistent with the
above-mentioned photocurrent tests. Thus, the photocurrent
spectra and EIS Nyquist plots conrm the superior separation
efficiency of the photo-induced electrons and holes and efficient
charge transfer in ZM2, which are responsible for the enhanced
photocatalytic activity.
The separation efficiency of the charge carriers is also shown
in the photoluminescence (PL) analysis. As shown in Fig. S5,†
the main emission peak is observed at around 623 nm. The ZM3
sample exhibits a lower PL intensity than ZIF-8 derived C–ZnO,
and ZM2 shows the lowest emission peak among the C–ZnO,
ZM3 and ZM2 samples, which proves that the construction of
the heterojunction structure effectively inhibits photo-induced
electron–hole pair recombination and the separation rate of
the electron–hole pairs of ZM2 is better than that of ZM3, which
is consistent with the results of the photoelectrochemical
analysis.
generation during the process of photocatalytic degradation of
RhB over ZM2 was investigated by adding various scavengers. As
+
shown in Fig. S4,† ammonium oxalate (AO) was added as an h
ꢁ
scavenger, p-benzoquinone (PBQ) as an $O
2
scavenger and tert-
butanol (t-BuOH) as an $OH scavenger. It was found that there
was a dramatic decrease in the photocatalytic activity when PBQ
ꢁ
was added, indicating that $O
2
plays an important role in the
photocatalytic degradation process. In addition, the photo-
degradation rate of RhB was also suppressed when AO and t-
+
BuOH were added, suggesting that h and $OH participate in
the photodegradation process of RhB.
3.4 Optical analysis
Fig. 6 reveals the UV-vis diffuse reection spectra of pure ZnO,
ZIF-8 derived C–ZnO and ZM1-4. As shown in Fig. 6a, the main
absorption intensity of pure ZnO occurs at ca. 390 nm and the
edge of absorption is very low. In contrast to that, the absorp-
tion values of ZIF-8 derived C–ZnO extend into the visible light
region, which conrms that it can harvest visible light
effectively.
It is obvious that using ZIF-8 as a precursor to prepare
catalysts has more advantages compared to using pure ZnO as
2
a photocatalyst. Aer the introduction of MoS and trans-
formation of ZIF-8 derived C–ZnO to C–ZnS/ZnMoO and C–
4
ZnS, the absorption peaks of the ZM composite materials were
red shied and the light absorption was obviously enhanced
compared to that of ZIF-8 derived C–ZnO. The enhanced
absorption intensities of these materials are also consistent
with the colors of the catalyst powders (inset Fig. 6a) which will
be benecial for their photodegradation activities.
3.6 Possible mechanism
On the basis of the Kubelka–Munk equation, the band gap
energy of a semiconductor can be calculated using the following On the basis of the experimental results and previous studies,
formula eqn (2)
a possible mechanism for the enhanced photoactivity of TC-H and
RhB degradation can be proposed. As shown in Scheme 2a, under
the excitation of light, C–ZnS, C–ZnMoO and MoS will all be
2
(
ahv) ¼ (hm ꢁ E
g
)
(2)
4
2
ꢁ
excited at the same time, and the electrons (e ) in the valence band
VB) are easily photoexcited to the conduction band (CB), leaving
where h, m, Eg, and a denote Plank's constant, the frequency of
(
the light, the band gap energy, and the absorbance, respec-
+
41
holes (h ) in the VB. The difference between the CB and VB edge
potentials of these semiconductors
transfer from the CB of C–ZnMoO
40
tively. As shown in Fig. 6b, the E of ZIF-8 derived C–ZnO is
42,43
g
allows the electrons to rst
estimated to be 2.91 eV, the E of ZM2 to be 2.81 eV, and the Eg
of ZM3 to be 3.15 eV, which were all calculated based on the
above formula.
g
4
to the CB of C–ZnS; aer that,
all the electrons on the CB of C–ZnS will continue to transfer to the
Fig. 7 (a) Photocurrent spectra of as-synthesized samples under UV-
Fig. 6 (a) UV-vis diffuse reflection spectra (inset: photographs of ZM1- vis light irradiation; (b) EIS Nyquist plots of the samples under dark
2
4
) and (b) (ahv) vs. hv curves of different samples.
condition.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant No. 21661024), the Open Funds of
the State Key Laboratory of Rare Earth Resource Utilization
(Grant No. RERU2017009), the Natural Science Foundation of
Scheme 2 (a) Schematic illustration of the charge transfer in the C– Inner Mongolia (Grant No. 2018MS02004), the Projects of Inner
ZnS/ZnMoO
under full spectrum light irradiation.
4
@MoS
2
composites and (b) C–ZnS/MoS
2
composites Mongolia Scientic research (Grant No. NJZZ14003) and the
Student's Platform of Inner Mongolia University.
Notes and references
2
. During the process, the holes leaving the VB of C–ZnS
CB of MoS
rst move in the opposite direction to the electrons to the VB of C–
ZnMoO , which could result in effective electron–hole separation

K. Kummerer, J. Antimicrob. Chemother., 2003, 52, 5–7.
¨
1
4
2 M. Seifrtova, L. Novakova, C. Lino, A. Pena and P. Solich,
´
´
´
and the holes will nally transfer to the VB of MoS . It is harder for
2
Anal. Chim. Acta, 2009, 649, 158–179.
photogenerated electrons and holes to recombine in the indirect
band gap of the MoS nanosheets. Thus, the lives of photo-
2
generated electrons and holes are prolonged, which results in
enhanced photocatalytic activity. And, it should be noted that the
C-doping of the structure can improve the visible-light response,
which can also enhance the photocatalytic activity.
3
4
P. Shetty, Lancet Infect. Dis., 2002, 2, 704.
B. Luo, D. Xu, L. Di, G. Wu, M. Wu, W. Shi and C. Min, ACS
Appl. Mater. Interfaces, 2015, 7, 17061.
5
6
7
8
A. K. Sarmah, M. T. Meyer and A. B. Boxall, Chemosphere,
2006, 65, 725–759.
R. Daghrir and P. Drogui, Environ. Chem. Lett., 2013, 11, 209–
227.
X. Wang, Y. Zhang and S. Song, Angew. Chem., Int. Ed., 2016,
C–ZnS/MoS is a two-phase catalyst, so the transfer of elec-
2
trons and holes only occurs in two phases, which may decrease
the separation of the electron–hole pairs and increase the
recombination of the photo excitation pairs. Compared to C–ZnS/
55, 4542–4546.
J. Rivera-Utrilla, C. V. Gomez-Pacheco, M. Sanchez-Polo,
´
´
ZnMoO
consisting of C–ZnS, C–ZnMoO
between C–ZnS and C–ZnMoO will be closer and intersecting
compared to the physical contact of general heterojunction
photocatalysts, because they were prepared from ZIF-8 derived C–
ZnO at the same time using a direct one-pot route. The longer
transfer steps and closer contact of the catalyst can facilitate the
separation of electron–hole pairs through closer contact between
the different semiconductors and enhance the photocatalytic
4
@MoS
2
, C–ZnS/ZnMoO
4
@MoS
2
is a three-phase catalyst
´
˜
´
J. J. Lopez-Penalver and R. Ocampo-Perez, J. Environ.
4
and MoS
2
, so the contact
Manage., 2013, 131, 16–24.
K. Yang, Q. Yue, J. Kong, P. Zhao, Y. Gao, K. Fu and B. Gao,
Chem. Eng. J., 2016, 285, 319–330.
0 S. F. Pan, M. P. Zhu, J. P. Chen, Z. H. Yuan, L. B. Zhong and
Y. M. Zheng, Sep. Purif. Technol., 2015, 153, 76–83.
4
9
1
1
1 C. Reyes, J. Fernandez, J. Freer, M. A. Mondaca, C. Zaror,
S. Malato and H. D. Mansilla, J. Photochem. Photobiol., A,
´
2
008, 184, 141–146.
4 2
performance of C–ZnS/ZnMoO @MoS .
12 M. Yan, Y. Hua, F. Zhu, L. Sun, W. Gu and W. D. Shi, Appl.
Catal., B, 2017, 206, 531–537.
1
1
3 S. Liu, M. Lim and R. Amal, Chem. Eng. Sci., 2014, 3, 46–52.
4 K. Shen, L. Chen, J. Long, W. Zhong and Y. Li, ACS Catal.,
2015, 5, 150730103814009.
4
. Conclusion
In summary, a series of ZIF-8 derived C–ZnS/ZnMoO
and C–ZnS/MoS
efficient and facile one-pot strategy. The as-prepared ZIF-8
derived C–ZnS/ZnMoO @MoS and C–ZnS/MoS2 show 16 B. Li, H. M. Wen, W. Zhou and B. Chen, J. Phys. Chem. Lett.,
enhanced photocatalytic activity in the photocatalytic degrada-
2014, 5, 3468.
tion of TC-H and RhB compared to ZIF-8 derived C–ZnO or pure 17 K. Huang, Z. Dong, Q. Li and W. Jin, Chem. Commun., 2013,
ZnO. C–ZnS/ZnMoO @MoS also shows better photocatalytic
49, 10326–10328.
capability over C–ZnS/MoS . The enhanced photocatalytic 18 K. Tan, N. Nijem, P. Canepa, Q. Gong, J. Li, T. Thonhauser
capability is due to the C-doped structure and the hetero-
and Y. J. Chabal, Chem. Mater., 2016, 24, 3153–3167.
junction structure, which improve the visible-light response 19 F. G. Cirujano, A. Corma and F. X. Llabr ´e s i Xamena, Chem.
and facilitate the separation of photogenerated electron–hole
Eng. Sci., 2015, 124, 52–60.
pairs and reduce the recombination of photogenerated charge 20 A. Corma, H. Garc ´ı a and F. X. L. I. Xamena, Chem. Rev., 2010,
carriers. We believe that such novel ZIF-8 derived C–ZnS/
41, 4606–4655.
ZnMoO @MoS and C–ZnS/MoS heterojunction structures can 21 D. Farrusseng, S. Aguado and C. Pinel, Chem. Inf., 2010, 48,
4 2
@MoS
2
catalysts were successfully produced by an 15 J. Long, K. Shen, L. Chen and Y. Li, J. Mater. Chem. A, 2016, 4,
10254–10262.
4
2
4
2
2
4
2
2
potentially be developed into a new-type of photocatalyst.
7502–7513.
22 R. Jin, Y. Yang, Y. Xing, L. Chen, S. Song and R. Jin, ACS
Nano, 2014, 8(4), 3664–3670.
Conflicts of interest
23 N. M. Mahmoodi, J. Abdi, M. Oveisi, M. A. Asli and
M. Vossoughi, Mater. Res. Bull., 2018, 100, 357–366.
The authors declare no conict of interest.
This journal is © The Royal Society of Chemistry 2019
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View Article Online
RSC Advances
Paper
24 P. Hu, C. Chen and J. Song, Mater. Sci. Semicond. Process., 35 S. Y. Zhang, H. Liu, C. C. Sun, P. F. Liu, L. C. Li, Z. H. Yang,
2018, 77, 40–49.
X. Feng, F. W. Huo and X. H. Lu, J. Mater. Chem. A, 2015, 3,
25 Z. Z. Lu, R. Zhang, Y. Z. Li, Z. J. Guo and H. G. Zheng, J. Am.
Chem. Soc., 2011, 133, 4172–4174.
5294–5298.
36 J. Yao, M. He and H. Wang, CrystEngComm, 2015, 17, 4970–
26 J. Yao and H. Wang, Chem. Soc. Rev., 2014, 43, 4470–4493.
4976.
2
7 J. Yao, D. Dong, D. Li, L. He, G. Xu and H. Wang, Chem. 37 M. He, J. Yao, Q. Liu, K. Wang, F. Chen and H. Wang,
Commun., 2011, 47, 2559–2561. Microporous Mesoporous Mater., 2014, 184, 55–60.
8 T. G. Glover, G. W. Peterson and B. J. Schindler, Chem. Eng. 38 B. Liu, H. Shioyama, T. Akita and Q. Xu, J. Am. Chem. Soc.,
Sci., 2011, 66(2), 163–170. 2008, 130, 5390–5391.
9 P. Horcajada, T. Chalati, C. Serre, B. Gillet, C. Sebrie, 39 B. Lin, H. An, X. Yan, T. Zhang, J. Wei and G. Yang, Appl.
2
2
T. Baati, J. F. Eubank, D. Heurtaux, P. Clayette and
C. Kreuz, Nat. Mater., 2010, 9, 172–178.
0 G. S. Cl ´a udia, L. Ignacio, C. Avelino and G. Hermenegildo,
Catal., B, 2017, 210, 173–183.
40 D. Lin, H. Wu, R. Zhang, W. Zhang and W. Pan, J. Am. Ceram.
Soc., 2010, 93, 3384–3389.
3
3
3
3
3
Chem.–Eur. J., 2010, 16, 11133–11138.
1 Y. Du, R. Z. Chen, J. F. Yao and H. T. Wang, J. Alloys Compd.,
41 S. Yang, S. Xu, D. Chen and W. Shi, Appl. Catal., B, 2017, 204,
602–610.
42 J. Zhang, X. Mao, W. Xiao and Y. Zhuang, Chin. J. Catal.,
2017, 38, 2009–2020.
43 Y. Yang, Y. Zhang, Z. Fang, L. Zhang, Z. Zheng, Z. Wang,
W. Feng, S. Weng, S. Zhang and P. Liu, ACS Appl. Mater.
Interfaces, 2017, 9, 6950–6958.
2013, 551, 125–130.
2 Y. Feng, H. Lu, X. Gu, J. Qiu, M. Jia, C. Huang and J. Yao, J.
Phys. Chem. Solids, 2017, 102, 110–114.
3 C. Feng, J. Ma and H. Li, Mater. Res. Bull., 2009, 449, 1811–
1815.
4 B. Zhu, B. Lin, Y. Zhou, P. Sun, Q. Yao, Y. Chen and B. Gao, J.
Mater. Chem. A, 2013, 2, 3819–3827.
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