MoS2 Powder Research Articles

Rational synthesis of molybdenum disulfide nanoparticles decorated reduced graphene oxide hybrids and their application for high-performance NO2 sensing

In this work, we have reported a novel NO2 sensor using molybdenum disulfide nanoparticles (MoS2 NPs) decorated RGO (MoS2-RGO) hybrids as sensing materials, where MoS2-RGO hybrids were prepared by a two-step wet-chemical method. Firstly, MoS2 NPs prepared by modified liquid exfoliation method from bulky MoS2 powder. Then, MoS2-RGO hybrids were obtained by self-assembly of MoS2 NPs and GO nanosheets, followed by a facile hydrothermal treatment progress. The combined characterizations indicate that MoS2 NPs with the size of 3–5 nm are uniformly dispersed on RGO nanosheets. Most importantly, the sensor based on MoS2-RGO hybrids could detect NO2 at room temperature. To further improve sensing performances, especially response and recovery rate, sensing properties are further examined by increasing the operation temperature to 160 °C. It is notably seen that MoS2-RGO-based NO2 sensor not only shows improved sensitivity to NO2 compared to pure RGO-based sensor, but also exhibits fast response and recovery characteristics (response time and recovery time are 8 s and 20 s toward 3 ppm NO2). This work paves a new way for application of MoS2 and RGO in chemical sensors, providing an effective method for fabrication of NO2 sensors with high sensitivity and fast response/recovery rate.

Preparation, characterization and properties of MoS2 nanosheets via a microwave-assisted wet-chemical route

MoS2 nanosheets have been prepared by a rapid and simple microwave-assisted wet-chemical method using MoS2, LiOH·H2O and ethylene glycol as the raw materials. The structure and morphology of the obtained product have been characterized by X-Ray diffraction (XRD), Raman spectroscopy, Atomic force microscopy (AFM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The thickness of the MoS2 nanosheets is about 4.42nm. The MoS2 nanosheets after cold pressing have a low electrical conductivity and a high Seebeck coefficient of 690μV/K. The Seebeck coefficient is much higher than that (280μV/K) of raw MoS2 powders. In addition, the MoS2 nanosheets have enhanced capacitive performance compared with the raw MoS2 powders, too.

Experimental and numerical investigation of ultrasonically assisted micro-ring compression test

In this study, ultrasonically assisted ring compression test was used to study the frictional behavior of contacting surfaces. Samples of above- and sub-millimeter sizes were prepared using stainless steel 316. Two commonly used lubricants in micro-forming, i.e., MoS2 and graphite powder, were used to lubricate the ring surfaces. The effects of ram speed, die material, ultrasonic vibration amplitude, and specimen size on the friction coefficient and deformation load were studied. In addition, the contribution of material softening and friction reduction on the deformation load decrease was identified using the test data and finite element simulation. The general trend of increase in friction coefficient with miniaturization was observed in ultrasonically assisted micro-ring compression test. However, the percentage of increase in friction coefficient due to miniaturization reduced when ultrasonic vibrations were applied. The results also showed that both friction reduction and material softening phenomena contribute to the decrease of the deformation load; however, the contribution of friction reduction was more than that of material softening.

Reaction Mechanism and Synthesis of Ni3Al–MoS2 Matrix Self-Lubricating Composites Using Ni, Al, and MoS2 Powders

The reactions between MoS2 and several metallic powders, including Ni, Al, and Ni3Al, were studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The DSC results revealed that MoS2 started to react with Ni and Al at 630 and 560 °C, respectively, but did not react with Ni3Al even at 1200 °C. The XRD results indicated that the reaction products of MoS2 and Ni were a series of new sulfides and molybdenum compounds, including Ni3S2, Ni7S6, and Ni4Mo, and those of MoS2 and Al were Al2S3 and various aluminides. Additionally, the compositions of the products varied with the reaction temperature. Because these new sulfides did not possess self-lubricating properties, the consumption of MoS2 should be avoided. According to these reactions, a synthetic route for the Ni3Al/MoS2 composite using Ni, Al, and MoS2 composite powders was proposed and demonstrated. During the synthesis process, the composite powders were first compressed under a pressure of 180 MPa. The resulting green compacts were heated to 500 °C with a heating rate of 20 °C/min, and then to 530 °C with a heating rate of 1 °C/min. The holding time at 530 °C was 4 h. The phase composition and microstructure of the as-synthesized composite were studied by XRD and SEM. The results showed that MoS2 remained stable during the synthesis process. Friction and wear tests demonstrated that the composite exhibited good self-lubricating properties with a low friction coefficient of about 0.2 and a small wear rate of 1.04 × 10− 5 mm3 N− 1 m− 1.

Tailored MoS2 nanorods: a simple microwave assisted synthesis

We report here the synthesis of MoS2 nanostructures by a simple liquid phase exfoliation of MoS2 powder in organic solvents followed by microwave treatment. The probe sonication and the microwave treatment play an important role in rolling and curling of the MoS2 nanosheets to give rise to MoS2 spheres and rod/tube like-structures with diameter approximately 150–200 nm. The MoS2 nanorods formed in this fashion are hollow inside with a wall thickness of 15–20 nm and the length of the nanorods is found in the order of several micrometers. Synthesis of such tailored MoS2 nanorods by liquid phase exfoliation is not yet reported. Our observations suggest the 2H phase of bulk MoS2 remains preserved in the nanostructures with high crystalline quality.

Side‐Chain‐Directed Dispersion of MoS2 Nanosheets by V‐Shaped Polyaromatic Compounds

Bulk molybdenum disulfide (MoS2 ) itself is virtually insoluble in common organic solvents because of the tight stacks of multiple MoS2 nanosheets. Here we report that V-shaped polyaromatic compounds with non-ionic side chains can efficiently exfoliate and disperse the inorganic nanosheets. Simple grinding and sonication (less than total 1 h) of MoS2 powder with the V-shaped compounds gave rise to large MoS2 nanosheets highly dispersed in NMP through efficient host-guest S-π interactions. DLS and AFM analyses revealed that the lateral sizes (ca. 150-270 nm) and thicknesses (ca. 2-8 nm) of the products depend on the identity of the non-ionic side chains on the V-shaped dispersant.

Low power continuous-wave nonlinear optical effects in MoS2 nanosheets synthesized by simple bath ultrasonication

Here, we have unveiled low power continuous-wave nonlinear optical properties of a few layer (4-12L) Molybdenum disulfide (MoS2) dispersion in N, N-dimethylformamide (DMF) by using spatial self-phase modulation technique. The effective third-order nonlinear susceptibility of the monolayer has been estimated to be as high as ∼10−8 esu. Also a low power technique of syntheses of stable and a few-layer (4-12L) MoS2 dispersion in DMF has been demonstrated here by utilizing ultrasonication bath treatment combined with the natural gravitation sedimentation effect starting from the bulk MoS2 powder. The synthesized samples are exhibiting interesting linear optical absorption and photoluminescence (PL) after exfoliation to a few layer nanosheets (NSs) and the exciton binding energies have been determined from PL emission data in association with 2D hydrogenic Bohr-exciton model. The specific capacitances (Csp) of the electrode prepared with MoS2 NSs have been measured by electrochemical measurement and the highest value of Csp is 382 Fg−1 for 4L sample. The reported intensity driven change of Csp in the presence of light emitted from light emitting diodes of various colours is unprecedented. The demonstrated technique can be scaled up for large scale and easy synthesis of other 2D materials having applications in optoelectronics and energy devices.

Ultrafast Charge Dynamics in Dispersions of Monolayer MoS2 Nanosheets

Ultrafast charge dynamics in dispersions of MoS2 nanosheets in N-methyl-2-pyrrolidone are reported. Samples were prepared by the ultrasonication-assisted exfoliation of MoS2 powder, resulting in nanosheets that were predominantly monolayer and had an average sheet size of 32.4 ± 0.1 nm. These dispersions were characterized using absorption and photoluminescence spectroscopy, transient photoluminescence measurements, and atomic force microscopy before the ultrafast charge dynamics were studied via transient absorption spectroscopy. The transient absorption spectra exhibited bleach peaks and photoinduced absorption peaks in spectral regions corresponding to both the A and B excitons of MoS2. The growth and decay of the features in the B exciton region were determined largely by the dynamics of the exciton population, while the features in the A exciton region depend on the dynamics of both excitons and trions.

Cost-effective liquid-phase exfoliation of molybdenum disulfide by prefreezing and thermal-shock

In this work, we present a facile method without hazardous material for improving the liquid-phase exfoliation of MoS2 nanosheets by use of pre-freezing and thermal shock. The MoS2 bulk is easily exfoliated and functionalized by prefreezing and thermal shock of MoS2 powder in the ethanol solvent. Atomic force microscopy confirms that the approach can exfoliate MoS2 powder to nanosheets. UV–visible spectroscopy of the prepared samples shows that fingerprint excitonic peaks appear in the spectrums and they become sharper by repeating the process. Optical band gap from Tauc plot of UV–visible spectrum shows an increase in the band gap of exfoliated MoS2 up to 1.85eV and the surface energy of the exfoliated MoS2 is measured as 29.8mJ/m2. Annealing the prepared samples at temperatures up to 400°C decreases the contact angle of water droplet from 130° down to 2°. X-ray diffraction patterns and Fourier transform infrared spectroscopy confirm that exfoliated MoS2 is functionalized during the exfoliation process and molybdite is formed on the surface by crumpling and agglomerating nanosheets due to heating, which is mainly responsible for increasing the surface energy as well as superhydrophilicity of the samples at 400°C.

Preparation of MoS2‐graphene Hybrid Nanosheets and Simultaneously Electrochemical Determination of Levodopa and Uric Acid

AbstractMoS2 nanoflakes were prepared by exfoliating commercial MoS2 powders with the assistance of ultrasound and graphene foam was synthesized by chemical vapor deposition using nickel foam as the template. MoS2‐graphene hybrid nanosheets were developed through the combination of MoS2 nanoflakes and graphene nanosheets by ultrasonic dispersion. The hybrid nanosheets were sprayed onto the ITO coated glass, which acts as an electrode for the simultaneously electrochemical determination of levodopa and uric acid. The MoS2‐graphene hybrid nanosheets were characterized by scanning electron microscopy, X‐ray diffraction and Raman spectroscopy. The results show that the hybrid nanosheets are composed of MoS2 and graphene with a sheet‐like morphology. The sensitivity of the electrode for levodopa and uric acid is 0.36 μA μM−1 and 0.39 μA μM−1, respectively. The electrode also shows low limit of detection, good selectivity, reproducibility and stability. And it is potential for use in clinical research.

Surface modification of molybdenum disulfide (MoS2) fine powder

This work reports a novel method to chemically modify the surface of molybdenum disulfide (MoS2) powder that is used as the antigalling filler in the lubricants for thread-tubing in oil pipelines. The modification by way of coupling agents effectively reduces friction and improves the antiwear and antigalling properties. The effects of three coupling agents, including KH-570, polyvinylpyrrolidone and hexadecyl cetyltrimethylammonium bromide, on particle resistance to sedimentation, powder activation index and lipophilicity are compared in detail. KH-570 on the powder improves the lipophilicity and the dispersion stability of MoS2. The modified MoS2 exhibits a much improved activation index, more than twice the original MoS2 powder. The amount of DOP absorbed by modified MoS2 powder decreases significantly. The turbidity is much higher in the modified MoS2 powders, this is in good accordance with the findings from other tests – that is, the lipophilicity has improved. The lipophilicity of the modified MoS2 increases then decreases with the increased concentration of KH-570. Overall, KH-570 outperforms the rest and is further explored for optimisation and coupling mechanism.

MoS2 hollow microspheres used as a green lubricating additive for liquid paraffin

Molybdenum disulfide (MoS2) hollow microspheres were prepared via a hydrothermal method, which were characterized by XRD, SEM, TEM and UV–vis spectroscopy. The tribological performances of liquid paraffin (LP) mixtures containing these hollow microspheres and the following photo-catalytic degradation behaviors of LP promoted by the worn MoS2 powders were investigated. The results indicate that 0.50wt% of MoS2 hollow microspheres in LP can reduce the friction coefficient of the mixture remarkably, and the photo-catalytic degradation degree of LP also reaches a satisfactory level. MoS2 serves as both lubricating additives and photo catalysts at the different life stages, and related mechanisms have been discussed, which suggests potential values in the design of novel and sustainable lubricating systems.

Electrochemical Reduction of Molybdenium Compounds to Form Molybdenium Powder

Molybdenum (Mo) is a refractory metal and mostly used as an alloying agent in cast iron, steels and superalloys to enhance hardenability, strength, toughness and corrosion resistance. It also finds other uses either in the form of a pure metal or an element in, for example, lubricants and catalysts. Traditional metal production methods are not suitable for molybdenum because pure molybdenum has very high melting point and has a tendency to get oxidized at low temperatures. Hydrogen reduction of molybdenum oxide is a very common way for Mo production but, it has two stages during process. At the second stage, the reduction process needs very high temperatures, therefore, high energy consumption and special equipment requirement is essential. FFC Cambridge process [1] based on electrochemical reduction of solid compounds was considered as an alternative way to produce molybdenum at relatively low temperatures. Similar to reduction of WO3 [2], loss of molybdenum as molybdenum oxychloride from MoO3 in CaCl2 containing molten salts is inevitable [3]. MoS2 powder pressed and sintered at 400oC to form pellets were used as starting material for electrochemical formation of pure Mo in molten CaCl2-NaCl salt mixture under argon gas at 800oC. A constant voltage in the range 1 to 3.0V was applied between MoS2 cathode and graphite anode. When the process was terminated at a prescribed time, the cathode was removed from the molten salt, cooled in argon, washed with water in air to dissolve the solidified salt, and then dried at about 100oC in vacuum before further analysis employing XRD, SEM and EDS. [1] G.Z. Chen, D. J. Fray, T. W. Farthing, Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride, Nature, 407 (2000), 361-364. [2] M. Erdoğan, İ. Karakaya, Electrochemical Reduction of Tungsten Compounds to Produce Tungsten Powder, Metallurgical and Materials Transactions B, 41B (2010), 798-804. [3] W.T. Thompson, C.W. Bale, and A.D. Pelton: Facility for the Analysis of Chemical Thermodynamics (FACT), McGill University Montreal, Royal Military College of Canada in Kingston, E´cole Polytechnique, Montreal, Canada, 1985.

Deintercalation of Zero-Valent Metals from Two-Dimensional Layered Chalcogenides

A general solution-based approach to deintercalate zero-valent tin and copper from two-dimensional layered chalcogenides is presented using a one-step comproportionation reduction–oxidation reaction. The reaction is performed between the intercalated zero-valent metal and high oxidation state metal cations (Sn4+ and Cu2+) dissolved in acetone. This chemistry is shown to work for a variety of layered chalcogenides with differing morphologies and crystallinity. Copper and tin are deintercalated from powders of MoS2, MoSe2, NbSe2, and WS2 and crystalline nanoribbons of Bi2Se3, In2Se3, and GeS. This chemistry achieves a general route to remove zero-valent tin and copper from 2D layered chalcogenides.

Exfoliation of MoS2 and h-BN nanosheets by hydrolysis of LiBH4

Efficient preparation of two-dimensional materials is still a great challenge. These materials possess unique electrical, optical, and thermal properties. In this study, few-layer MoS2 nanosheets and nanoflakes were exfoliated by the hydrolysis reaction of LiBH4. First, the layered MoS2 powder materials were mixed with LiBH4 to obtain a homogeneous powder mixture, and then the mixture was heated above the melting point of LiBH4 under 300 °C and 4 MPa H2 for 2 h, during which the layered materials were curled by liquid LiBH4. In the subsequent hydrolysis of LiBH4, the layered materials were split into nanosheets by H2 gas generation. The obtained MoS2 nanosheets show almost uniform thickness of ~4 nm, with a width of 2–10 μm and a yield of more than 1.5 wt.%. The effectiveness of this method has also been verified by the preparation of few-layer h-BN. This work provides a new high-yield route to producing two-dimensional materials.

Three-dimensional MoS2/reduced graphene oxide aerogel as a macroscopic visible-light photocatalyst

Photocatalysis is regarded as an ideal technology for solving the urgent environmental and energy issues that we face today. Among the reported photocatalysts, molybdenum disulfide (MoS2) is very promising for applications in hydrogen production and pollutant photodegradation. However, its lack of active sites and the difficulty of recovering catalysts in powder form have hindered its wide application. Here, we report the successful preparation of a macroscopic visible-light responsive MoS2/reduced graphene oxide (MoS2/RGO) aerogel. The obtained MoS2/RGO aerogel exhibits enhanced photocatalytic activity towards hydrogen production and photoreduction of Cr(VI) in comparison with the MoS2 powder. In addition, the low density (56.1 mg/cm3) of the MoS2/RGO aerogel enables it to be used as an efficient adsorption material for organic pollutants. Our results demonstrate that this very promising multifunctional aerogel has potential applications in environmental remediation and clean energy production.

Microstructure, mechanical properties and tribological performance of CoCrFeNi high entropy alloy matrix self-lubricating composite

A CoCrFeNi high entropy alloy matrix self-lubricating composite was prepared by spark plasma sintering using a mixture of CoCrFeNi high entropy alloy powder, nickel-coated graphite powder and nickel-coated MoS2 powder. The composite consisted of four phases: face-centered cubic phase of the high entropy alloy, graphite, MoS2 and nickel. Graphite and MoS2 existed in the composite were mainly due to the nickel coatings onto the lubricants and the unique advantage of spark plasma sintering. The hardness, yield strength, compressive strength and fracture toughness of the composite were 271HV, 610MPa, 921MPa and 14.3MPa·m0.5, respectively. The good mechanical properties of the composite were mainly derived from the CoCrFeNi high entropy alloy matrix. The composite exhibited excellent tribological properties from room temperature to 800°C. From room temperature to medium temperatures, the reduction of friction coefficients and wear rates of the composite was attributed to the synergistic lubricating effect of graphite and MoS2. At high temperatures, it was found that various metal oxides formed on the composite surfaces played a key role in improving the tribological properties.

Liquid-exfoliated MoS2 nanosheets/graphene composites with high capacity and excellent cycle stability for lithium-ion batteries

Improving the rate capability and cycle stability of two-dimensional molybdenum disulfide (MoS2) still holds the key to its application in lithium-ion batteries (LIBs). Here we reported liquid-exfoliated MoS2 nanosheets/graphene composites (MoS2/Gra) towards the high capacity and excellent cycle stability for LIBs. The composites were assembled by pristine graphene and MoS2 nanosheets, which were prepared via the sonication-assisted liquid exfoliation of pristine graphite and MoS2 powders in aqueous surfactant solutions. The composites exhibited the reversible capacity as high as 1145mAhg−1 after 175 cycles at 100mAg−1 and excellent rate capability by retaining ∼88% of the capacity at 2000mAg−1. It is the first time that liquid-exfoliated MoS2/Gra composites show so excellent electrochemical performances and thus are fascinating for LIBs due to the facile, cost-effective and scalable liquid exfoliation route.

Sequential Solvent Exchange Method for Controlled Exfoliation of MoS2 Suitable for Phototransistor Fabrication.

In this study, flakes of molybdenum disulfide (MoS2) with controlled size and thickness are prepared through sequential solvent exchange method by sonication in dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) solvents. While NMP acts more effectively in reducing the thickness of flakes, DMF shows better potential in conserving the lateral size of nanosheets. The distribution of size and thickness of nanoflakes as a function of sonication time verifies that extended sonication results in dramatic drop of the dimension of the exfoliated flakes. This technique leads to the formation of few-layered MoS2 flakes without further drop of their lateral dimensions. It has been observed that by exposing the bulk MoS2 powders to oxygen plasma, the exfoliation process is accelerated without converting to 2H-MoS2 structures. Finally, a phototransistor has been fabricated based on few-layered MoS2 layers with a field effect mobility of ∼2.1 cm2 V-1 s-1 showing a high response to laser excitation of 532 nm wavelength.

A novel process to prepare MoSi2 by reaction between MoS2 and Si

In this study, a thermodynamic analysis of the reaction between MoS2 and Si was performed, which indicated that when the molar ratio of MoS2 to Si is 1:4, the final products were composed of SiS and MoSi2, without other solid phases, in the temperatures range of 0 °C–1700 °C. The reaction between MoS2 and Si powders with a MoS2/Si molar ratio of 1:4 was investigated in the range of 800 °C–1600 °C. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the phase composition and microstructure of the products, respectively. The content of sulfur in MoSi2 product was measured using an infrared carbon-sulfur analyzer. It was found that pure MoSi2 can be successfully synthesized in the temperature range of 1100 °C–1600 °C after reacting for 2 h with very little sulfur residual. Meanwhile, gaseous SiS was also generated and escaped from the MoSi2. It was also found that the reaction rate between MoS2 and Si was very slow at 800 °C and 900 °C. The microstructural analyses indicated that grain size of the MoSi2 product increased with increasing temperature.