Materials Letters 258 (2020) 126821
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Materials Letters
journal homepage: www.elsevier.com/locate/mlblue
Facile fabrication of hierarchical MoS2 architecture with efficient polar/
nonpolar liquid separation and desirable corrosion resistance
Ting Li a, Fuchao Yang a,⇑, Jing Fu a
a
Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062, People’s Republic of China
a r t i c l e
i n f o
Article history:
Received 19 September 2019
Received in revised form 13 October 2019
Accepted 14 October 2019
Available online 15 October 2019
Keywords:
Hydrophobicity
Molybdenum disulfide
Interfaces
Microstructure
Functional
Polar/nonpolar liquid separation
a b s t r a c t
The molybdenum disulfide (MoS2) coated hydrophobic surfaces have been considered as a competitive
candidate to separate polar/nonpolar liquid mixture for water remediation. In this study, a high
hydrophobic MoS2 coated melamine-formaldehyde (MF) sponge is presented by cetyltrimethyl ammonium bromide (CTAB)-assisted hydrothermal process. It shows efficient polar/nonpolar liquid separation
and desirable corrosion resistance. Several instruments have tested out the high hydrophobic of flowerlike MoS2 nanospheres, while different levels of acid and alkali are used to simulate corrosive
environment to test the as-prepared sponge’s corrosion resistance. The influence of different addition
of surfactants on this sponge’s wettability has also been discussed. Besides, the MoS2 sponge exhibits
excellent absorption capacity for a wide range of nonpolar solvents up to dozens of times of its own
weight.
Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction
The biomimetic hierarchical material has attracted enormous
attention for its inherent advantages like large superficial area,
anti-corrosive and high sieving efficiency [1–2]. Certainly, the
desirable performance of anti-corrosive and sieving efficiency are
also attributed to its surface chemistry. The molybdenum disulfide
(MoS2) with special stratified structure has been extensively
researched in recent years [3–6]. Wang et al. [3] obtained largearea monolayer WS2 and MoS2 films on SiO2/Si substrates by thermal reduction and sulfurization of WO3 and MO3 films. Li et al. [6]
synthesized MoS2 nanosheets via a solvent thermal reaction in N,
N-dimethylformamide (DMF) and explored the hydrogen evolution
reaction activity over a large range of surface S vacancy. MoS2
nanosheets prepared via a lithium intercalation method were
reported by Ries et al [2] and these MoS2 membranes demonstrate
outstanding rejection for micropollutants and NaCl.
These pioneers’ work offers new solutions or improves the
existing solutions to water remediation and the pollutants, which
are primarily caused by the oil spills and toxic organics leakages
[3,7]. But these approaches need complicated synthesis procedures, strict conditions or expansive cost [1]. The use of MoS2
remains strongly hampered by the difficulty in controlling hierar-
⇑ Corresponding author.
E-mail address: yfc@hubu.edu.cn (F. Yang).
https://doi.org/10.1016/j.matlet.2019.126821
0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
chical architecture by a facile preparation [8]. This study presents
a facile, convenient and inexpensive cetyltrimethyl ammonium
bromide (CTAB)-assisted hydrothermal method to fabricate a
hydrophobic MoS2 coated melamine-formaldehyde (MF) sponge
with efficient polar/nonpolar liquid separation and desirable corrosion resistance.
2. Material and methods
Briefly, the Na2MoO42H2O (9 mmol, CAS: 10102–40-6, 99.0%,
Sinopharm group chemical reagent Co. LTD) and CS(NH2)2
(30 mmol, CAS: 62–56-6, 99.0%, Sinopharm group chemical
reagent Co. LTD) were dissolved in 50 ml deionized water under
stirring. Then the CTAB (0.5 mmol, CAS:57-09-0, 99.0%, Sinopharm group chemical reagent Co. LTD) was added in the solution
stirring for ten minutes. The mixture was sealed in a 100 ml teflonlined stainless-steel autoclave and put in the DHG-9070 oven for
24 h at 180 °C. After naturally cooling to room temperature, the
precipitate was centrifuged at 10,000 r/min for 10 min with three
times. Then, it was dried in vacuum for 10 h at 60 °C. Besides,
the MF sponges obtained from local store were cut into small size.
After using ultrasonic dispersion (0.25 g MoS2 in 100 ml ethanol) to
distribute the particles on the sponge homogeneously, the final
samples were obtained. Contact angle (CA, Shanghai Zhongchen
Digtal Technology Apparatus Co., Ltd), X-ray diffraction (XRD, Bruker D8 Advance), X-ray photoelectron spectroscopy (XPS, Thermo
Scientific ESCALAB 250Xi) and scanning electron microscope
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T. Li et al. / Materials Letters 258 (2020) 126821
(SEM, sigma 500, Carl Zeiss, Germany) were adopted to assess the
properties of the newly formulated samples.
3. Results and discussion
The morphologies of the MoS2 on a silicon (Fig. 1a) and sponges
(Fig. 1b–f) are investigated by SEM. Its morphology changes little
on different substrates. The macro-porous network of the sponge
can adsorb oil rapidly (Fig. 1b) [9]. In Fig. 1d, MoS2 particles are
attached to the coarse part of sponge and the coatings do not
change the original structure of sponge. Fig. 1f shows that the
flower-like microspheres consist of abundant randomly assembled
bent nanosheets, and the diameters of the microspheres are in a
random distribution, ranging from 1 to 4 lm. This hierarchical
structure of MoS2 is the main reason for high hydrophobicity of
the modified sponge surface [10].
As shown in Fig. 2(a), the MoS2 sample has been indexed by
XRD and the diffraction peaks of (0 0 2), (1 0 0), (1 0 3), (1 1 0)
planes are located at 16.20°, 32.52°, 41.08°, 57.45°, respectively
[8,11]. Compared with standard cards (JCPDS card No. 37-1492),
the positions of four peaks are basically identical, which exactly
confirm the sample as hexagonal MoS2 [9]. Besides, the chemical
environment of Mo and S elements in MoS2 are investigated by
XPS analysis. For the XPS spectrum of Mo 3d scan (Fig. 2c), the
Mo signals derive from Mo 3d3/2 peak at 231.8 eV, Mo 3d5/2 peak
at 227.7 eV, indicating the characteristic Mo4+ oxidation state. It
is noticeable that the peak at 225.3 eV, assigned to S 2 s in
Fig. 2c, indicates the successful incorporation of S element in
MoS2. Moreover, the S 2p spectrum is split into two peaks for S
2p3/2 and S 2p1/2 of divalent sulfide at 161.3 eV and 162.3 eV,
respectively (Fig. 2d) [5].
Furthermore, as shown in Fig. 3a, the MoS2 coating can be used
to several substrates and the water droplets on these surfaces
show quasi-spheres. When the water drops on the coated glass,
poly-porous sponge, soft hydrophobic fabric, normal fabric substrates, the CAs are 143.0° ± 2.1°, 134.1° ± 2.9°, 128.1° ± 2.3°,
137.2° ± 2.5°, respectively. Besides, the original glass, poly-porous
sponge, soft hydrophobic fabric, normal fabric substrates surface
shows an initial CA of about 68.0° ± 2.3°, 100.1° ± 2.6°,
120.0° ± 2.5°, 0°, which suggests that the MoS2 coating enhances
different substrates’ hydrophobicity. For the polar water droplets,
the as-prepared sponge surface shows high hydrophobicity; while
the oil, a nonpolar substance, can permeate the sponge smoothly
[12]. Fig. 3b shows the processes of absorbing two nonpolar model
pollutants, 1,2-dichloroethane and cyclohexane. As for Fig. 3c,
these two images show the adhesive feature from modified sponge
surface. The Fig. 3d shows CAs of water drops with three kinds of
pH, simulating acid atmosphere (pH = 3 with CA = 133.1° ± 2.3°),
weak alkali atmosphere (pH = 9 with CA = 137.0° ± 2.0°) and alkali
atmosphere (pH = 12 with CA = 123.2° ± 3.0°). Even when the
water droplets are alkali or acid, the CAs are relatively high. It
means that the MoS2 coated sponge has certain resistance to acid
and alkali, and it keep hydrophobic even surrounded by corrosive
atmosphere.
Besides, the water and two nonpolar organics (1,2dichloroethane and cyclohexane) have been chosen as the representative for polar/nonpolar materials to verify the MoS2 coated
sponge as an effective absorbent [3]. Then the prepared MoS2
sponges are used to test its absorption capacity for these two
nonpolar organics with three cycles, as shown in Fig. 4a and b.
The sample can averagely absorb the 1,2-dichloroethane with
65.8 times and cyclohexane with 26.3 times (average value,
See Table S1, SI) of its own weight. Weber et al. [13] report that
BN nanotubes absorb up to 110 times their own weight in pump
oil and Wu et al. [14] argue that their prepared PU@Fe3O4@SiO2@FP sponge can absorb up to 27.5 times their own weight
in 1,2-dichlorobenzene and 20 times in n-hexane (more comparison, Table S2, SI). Besides, Fig. 4c has shown the relationship
between water contact angles and different addition of surfactants CTAB. As surfactants consist of polar hydrophilic group
and non-polar hydrophobic group, it would change the interface
state and thus the apparent contact angles are influenced. When
the adding surfactants’ concentrations are 0.2 mmol/L, 0.4 mmol/
L, 0.8 mmol/L, 4.0 mmol/L, and 8.0 mmol/L, the CAs become
144.7° ± 1.9°,
133.7° ± 2.2°,
130.0° ± 2.5°,
131.9° ± 2.8°,
127.0° ± 2.6°, respectively. That’s means the low concentration
surfactant is added, it changes the interface state sharply; but
the concentration reaches a special value of 0.8 mmol/L, its
effect was not obvious even several times of surfactants were
added.
Fig. 1. SEM image of MoS2 particles under different magnifications on (a) silicon wafer; (b–f) MF sponge.
T. Li et al. / Materials Letters 258 (2020) 126821
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Fig. 2. (a) XRD pattern of MoS2 sponge; (b) XPS spectrum of MoS2 sponge and MF sponge; High-resolution XPS spectra of (c) Mo 3d and (d) S 2p.
Fig. 3. (a) Photograph of water droplets (dyed with methyl blue in a3) as quasi-spheres on (a1) hard surface: glass; (a2) multirole surface: sponge; (a3) soft surface:
hydrophobic fabric; (a4) rough surface: normal fabric; (b) Snapshots of removal process of 1,2-dichloroethane/cyclohexane (dyed with Sudan III) by as-prepared sponges; (c)
process before and after water drops on the sponge; (d) different pH water droplets of MoS2 sponge.
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T. Li et al. / Materials Letters 258 (2020) 126821
Fig. 4. Absorption capability of the as-prepared sponge for (a) 1,2-dichloroethane; (b) cyclohexane; (c) water contact angles with different addition of surfactant CTAB.
4. Conclusions
In conclusion, the hydrothermal process assisted with CTAB has
been used to fabricate a high hydrophobic MoS2 coated MF sponge.
The hexagonal MoS2 shows high hydrophobic for several substrates with CAs of 128.0°
143.0°. Its flower-like microspheres
with 1–4 lm diameter consist of abundant nanosheets. The water
droplets containing different concertation of surfactants
(0.2 mmol/L, 0.4 mmol/L, 0.8 mmol/L, 4.0 mmol/L, and 8.0 mmol/
L) are used to measure the CAs of the MoS2 coated sponge
(144.7° ± 1.9°,
133.7° ± 2.2°,
130.0° ± 2.5°,
131.9° ± 2.8°,
127.0° ± 2.6°). Besides this sponge shows good absorption performance to 1,2-dichloroethane and cyclohexane (absorbing 65.8
and 26.3 times of its own weight) and excellent inertness to corrosive environments. In a nut shell, a facile, convenient and inexpensive method has been used to fabricate MoS2 coated sponge with
high hydrophobicity, which is a great potential candidate for water
remediation.
Conflict of interest
All authors have no conflicts of interest.
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.
Acknowledgement
This work is financially supported by the NSFC (No. 51705138).
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.matlet.2019.126821.
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