Low-temperature catalytic preparation of multi-wall MoS2 nanotubes
ABSTRACT In the catalytic reduction atmosphere of H2+CH4+C4H4S, the ball-milled precursor (NH4)2MoS4 is heated to 300°C for decomposition. The as-synthesized product is characterized by XRD, SEM, HRTEM, EDX, and BET. The results
show that multi-wall MoS2 nanotubes are obtained. The length of the nanotubes is around 3–5 μm. The diameters of the nanotubes are homogeneous, with
an inner diameter of ∼15 nm, an outer diameter of ∼30 nm, and an interlayer (002) d-spacing of 0.63 nm. This catalytic thermal reaction occurring at low temperatures is important for the large-scale preparation
of similar transition-metal disulfide nanotubes.
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ABSTRACT: Changes in the hydrologic characters of the Tarim River Basin of Xinjiang Province during the past 50 years were studied to identify the key factors responsible for these changes. Observed hydrologic and socio-economic data provided the basis for this study. The impact of human activities on the decrease in the streamflow and changes in total dissolved solids (TDS) in the watercourse and groundwater of the mainstream were analyzed using the Mann–Kendall test, regression and principal component analysis. The results showed that during the past 50 years the streamflow in the headwater streams has increased slightly while the streamflow in the mainstream has decreased significantly. Human activities along the mainstream are the primary reason for the decreased streamflow, with the impact of human activities on the decrease in the streamflow of the mainstream being 65.61, 74.73 and 77.62% in the 1970s, 1980s and 1990s, respectively. The key factor that affected the TDS of the watercourse was the decreasing streamflow, which was caused by anthropological activities. However, the TDS of the groundwater was found to be affected significantly by groundwater depth. The degeneration of ecosystems in the lower reaches of the Tarim River was directly related with anthropogenic activities.Environmental Geology 01/2009; 57(2):435-445. · 1.13 Impact Factor
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ABSTRACT: Flowerlike MoS2 nanoparticles have been successfully synthesized through a mild solvothermal reaction with the aid of ethanol aqueous solution, and the samples have been characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and low temperature nitrogen adsorption-desorption. The nanometer flower MoS2 is composed of ultrathin nanosheets of approximately 10 nanometers in thickness. The influence of the reaction temperature and the reaction time on the formation of the flowerlike MoS2 nanoparticles were evaluated. The optimal experimental conditions were determined as follows: the molar ratio of 1:1 between ethanol and water, the reaction temperature of 190°C, and the reaction time of 24 h.Frontiers of Chemistry in China 4(2):173-176.
Vol. 46 No. 2
SCIENCE IN CHINA (Series B)
Low-temperature catalytic preparation of multi-wall MoS2
CHEN Jun (陈 军)1, LI Suolong (李锁龙)1, GAO Feng (高 峰)1,
XU Qiang (徐 强)2 & Koji Tanaka2
1. Institute of New Energy Material Chemistry, Nankai University, Tianjin 300071, China;
2. National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan
Correspondence should be addressed to Chen Jun (email: firstname.lastname@example.org)
Received September 2, 2002
Abstract In the catalytic reduction atmosphere of H2+CH4+C4H4S, the ball-milled precursor
(NH4)2MoS4 is heated to 300°C for decomposition. The as-synthesized product is characterized by
XRD, SEM, TEM, HRTEM, EDX, and BET. The results show that multi-wall MoS2 nanotubes are
obtained. The length of the nanotubes is around 3—5 μm. The diameters of the nanotubes are
homogeneous, with an inner diameter of ∼15 nm, an outer diameter of ∼30 nm, and an interlayer
(002) d-spacing of 0.63 nm. This catalytic thermal reaction occurring at low temperatures is impor-
tant for the large-scale preparation of similar transition-metal disulfide nanotubes.
Keywords: MoS2, nanotubes, catalytic thermal decomposition, specific surface area.
Since the first report on inorganic fullerene-like WS2 polyhedra and nanotubes by Tenne et
al. in 1992, this kind of nanostructural materials have become extensive research topics owing to
their unique electronic structures. WS2 and MoS2 nanomaterials have shown potential applications
in the fields of scanning probe microscopy, solid-state lubrication, heterogeneous catalysis,
and electrochemical hydrogen storage. Up to now, a great deal of progress has been achieved in
the studies of MS2 (M = W or Mo) nanomaterials. The main methods for their syntheses involve
high-temperature thermal reactions (800—1300℃, such as gas-solid reaction[6—9], chemical trans-
port, electron radiation, in-situ heating) and low-temperature solution routes (for example,
template preparation and solution chemistry). The high-temperature thermal reactions are
relatively easy to produce nanotubes; however, they need to provide more energy, and furthermore,
the reaction conditions should be controlled exactly during the complicated steps. As a compari-
son, the low-temperature solution routes are indeed to proceed at lower temperatures, but the
products are generally nanorods or/and nanofibers, resulting in seldom obtaining nanotubes.
Obviously, these works have serious effects on the property measurement and practical application
of MS2 nanotubes. Thus, the large-scale preparation of high-purity MS2 nanotubes at low tem-
peratures is of great importance.
In this paper, the precursor (NH4)2MoS4, which was controlled by high-energy ball-milling
technique, was heated in the catalytic reduction atmosphere of H2+CH4+C4H4S, and the resulting
sample was analyzed by XRD, SEM, TEM/HRTEM, and BET. The result shows that multi-wall
192 SCIENCE IN CHINA (Series B) Vol. 46
MoS2 nanotubes are achieved through the present preparation technique.
The mixture of 5 g (NH4)2MoS4 (supplied by Aldrich Ltd. with 99.9% purity) and 25 g
stainless steel balls of 6 mm in diameter was sealed in the stainless steel vial. The container was
vacuumed and then filled with Ar through a connection valve. After repeating for several times,
hydrogen of 0.2 MPa was introduced into the vial. The ball milling was carried out in a QM-ISP2
apparatus at a speed of 600 r/min for 1 h.
An alumina plate, on which the ball-milled (NH4)2MoS4 powder was homogeneously loaded,
was put in a furnace as described previously in ref. . In this paper, the reaction atmosphere and
the gas-flow rate can be adjusted by mass-flow valves and pressure gauges. To have a high-yield
and high-purity MoS2 nanotubes, we tried large experimental improvements, and the optimized
conditions were concluded with a total gas flow rate of 120 mL/min (volume ratio of H2︰CH4
︰C4H4S = 18︰1︰1), a heating temperature of 300℃, and a total heating time of 30 min. Under
these conditions, we can achieve an optimal yield of 5 g MoS2 nanotubes per day. The off-gases
were diverted through a three-way valve to a sample loop for gas chromatograph analysis (GL
Science, GC353B) or to a dimethylformamide solvent and then to a ZnSO4 solution before they
were vented into the atmosphere. The gas chromatograph analysis shows that C4H4S is taking the
role of catalyst.
After cooling to room temperature, the solid products on the alumina substrate were divided
into 4 parts, respectively, for the observation of XRD (Rigaku INT-2000, 40 kV/150 mA); SEM
(JEOL JSM-5600, 15 kV); TEM and HRTEM (JEOL JEM 3000F, 300 kV); and BET adsorp-
tion-desorption (Shimadzu-Micromeritics ASAP-2010).
2 Results and discussion
Fig. 1 shows the XRD patterns of polycrystalline MoS2 powder and ball-milled (NH4)2MoS4
before and after the thermal reaction. Comparison of the two diffraction peaks in fig. 1(a) and (b)
shows that their features look different. In the XRD pattern of fig. 1(a) for the sample before the
thermal reaction, the characteristic peak at 2θ = 17.2° indicates that the phase is orthorhombic
structure (ICDD-JCPDS Card No. 48-1662). The peak broadening is owing to the very fine grain
size and defects produced during the high-energy ball-milling process. However, the diffraction
peaks corresponding to (NH4)2MoS4 in the XRD pattern in fig. 1(b) for the as-synthesized product
disappear, and new peaks appear with relatively strong intensities. The XRD pattern in fig. 1(b)
coincides well with that of polycrystalline MoS2 in fig. 1(c) (ICDD-JCPDS Card No. 39-1492).
Further analysis confirms that the sample after the thermal reaction is characteristic of a hexagonal
structure (P63/mmc) with the lattice parameters of a = 0.31665 nm and c = 1.2367 nm.
Fig. 2 shows the SEM image of the as-synthesized MoS2. From which, it can be seen that a
large amount of nanotube filaments is homogeneously distributed over large areas. The length of
these nanotube filaments can reach 3—5 μm and the diameter is in the range of 30—50 nm.
No. 2 LOW-TEMPERATURE CATALYTIC PREPARATION 193
Fig. 2. SEM image of the as-synthesized MoS2 nanotubes.
Fig. 1. XRD patterns of ball-milled (NH4)2MoS4 before (a)
and after low-temperature catalytic thermal reaction (b) and
polycrystalline MoS2 (c).
Fig. 3 shows typical TEM and HRTEM images of the MoS2 nanotubes. The TEM image in
fig. 3(a) confirms that the product consists of long nanofibers. The HRTEM image in fig. 3(b)
shows that the nanofibers are nanotubes with an inner diameter of ∼15 nm, an outer diameter of
∼30 nm, and an interlayer (002) d-spacing of 0.63 nm (corresponding to the value of c/2). In addi-
tion, the topological layers are stacked together with regular directions, suggesting the existence of
defects in the nanotubes (fig. 3(c)). The chemical composition of the nanotube was analyzed by
EDX, giving an atomic Mo/S ratio of 1︰2. Therefore, on the basis of the above analyses, we con-
clude that the product after the thermal decomposition is multi-wall MoS2 nanotubes.
In the synthesis of MoS2 nanotubes, we need to consider the comprehensive parameters such
as the reaction temperature, the precursor and the catalyst. Using the high-temperature thermal
reaction is indeed to prepare nanomaterials, however, the product is not so pure, possibly owing
to the fast nucleation. As a comparison, the low-temperature liquid reaction uses organic solvents,
resulting in a complicated process. Moreover, this route normally produces nanorods or/and nano-
fibers, meaning the difficult obtaining of nanotubes. Introducing catalysts during the reaction
takes important roles in the preparation of nanotubes. Remskar et al. reported the synthesis of
single-wall MoS2 nanotubes using a novel type of catalyzed transport reaction at 800°C, in which
C60 was used as a growth promoter. In this study, we adopt a combined method that considers the
solution chemistry and gas-solid reaction, the ball-milling technique, and the catalyst of C4H4S.
After adjusting the thermal decomposition conditions, we can control the nanotube growth of
S-Mo-S layer in order, prevent the conglomeration of Mo and S atoms at the nanotube tips, and
thus obtain the synthesis of open-ended nanotubes in a large scale. The equation involved during
the thermal reaction is
194 SCIENCE IN CHINA (Series B) Vol. 46
Fig. 3. TEM (a) and HRTEM ((b) and (c)) of the as-synthesized MoS2 nanotubes.
(NH4)2MoS4 + H2 → MoS2 + 2NH3 + 2H2S (1)
Fig. 4 shows the N2 adsorption-desorption
and the pore size distribution curves of the as-
synthesized MoS2 nanotubes. The specific sur-
face areas are 12.8 m2/g, while the pore size
shows a narrow distribution around 2.0 nm.
These data offer possibilities for gas adsorption
storage and related adsorption theory on
high-purity MoS2 nanotubes. Further study will
be reported in the near future.
In summary, this paper describes the method
for the preparation of multi-wall MoS2 nanotubes
by low-temperature thermal decomposing of
ball-milled (NH4)2MoS4 in H2+CH4+C4H4S at-
Fig. 4. Curves for N2 adsorption-desorption and pore size
distribution (inset) of MoS2 nanotubes.
No. 2 LOW-TEMPERATURE CATALYTIC PREPARATION 195
mosphere. The structure, morphology, and N2 adsorption-desorption of the synthesized MoS2
nanotubes are also characterized. The results show that multi-wall MoS2 nanotubes can be pre-
pared with a large scale through the present route, which can be extended to the synthesis of MX2
(M = Mo, W; X = S, Se, Te) nanotubes. This kind of nanotubes that have two-element composi-
tion, cylindrical layered structure, and relatively high specific surface area, may lead to new solu-
tions toward energy-storage and energy-conversion nanomaterials.
Acknowledgements The authors thank Prof. Nobuhiro Kuriyama and Prof. Tetsuo Sakai in National Institute of AIST
Kansai Center (Japan), Prof. Li Yadong in Chemistry Department of Tsinghua University and Prof. Yuan Huatang in Department
of Material Chemistry of Nankai University for their help and discussion. This work was supported by the Scientific Research
Foundation for the Returned Overseas Chinese Scholars from the Ministry of Education of China (Grant No. 2002247) and the
Specially Appointed Professorial Award from Nankai University (Grant No. 20010907).
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