Bulk MoS2 Research Articles

Molybdenum oxide and sulfide active sites for isobutane dehydrogenation with methanol as a probe molecule

Molybdenum oxides and sulfides are alternative catalysts for several reactions, including alkane dehydrogenation. Correlations have been developed between reactivity and structure, but it is difficult to compare different catalysts without determining numbers of active sites. Here, methanol temperature programmed surface reaction (TPSR) is applied to bulk MoS2 and a series of supported molybdenum oxides and sulfides used for isobutane dehydrogenation. Rates and deactivation behavior are similar between supported molybdenum oxides and sulfides. Coking increases with loading and correlates well with the fraction of Mo-based CO2-forming sites from methanol TPSR. Normalizing isobutane dehydrogenation rates by formaldehyde-forming sites unifies rates over oxide and sulfide materials. These measurements confirm earlier hypotheses that MoS2 and higher loadings of oxides and sulfides are intrinsically fast catalysts, but they have few active sites and are prone to coking. In general, methanol TPSR is proposed as an accessible route to count sites on both supported oxides and sulfides.

Ternary molybdenum sulfo-selenides alloy DS-MoSSe anode for high performance metal-ion batteries from first principles calculations

The development of multivalent metal-ion (Mg ion and Al ion) batteries with performance comparable to Li-ion batteries is hindered by the lack of suitable electrode materials. In this work, state-of-the-art first principle calculations reveal that a 2D double sandwich MoSSe (Ds-MoSSe), a novel electrode material, has a higher Mg and Al ion diffusion rate compared with bulk MoS2. Theoretical results show that the bimetallic control strategy makes the metal atoms prefer to be adsorbed in the Ds-MoSSe owing to the strong binding energy. We assess the influence of the interlayer spacing on electronic, adsorption and ion migration properties. And we find the charge transfer from the intercalated metal ions to the Ds-MoSSe and the interactions between the ionic and covalent bonding between the Ds-MoSSe and the intercalated metal ions. What’s more, micromechanical properties of the Ds-MoSSe are also assessed based on its mechanical performance parameters. Expanding the interlayer spacing improves the Young's modulus and ductility of the Ds-MoSSe, allowing it to withstand a larger structural change in the ion intercalation process. Our results suggest that the Ds-MoSSe is a promising electrode material and the study of the Ds-MoSSe with various interlayer distances opens a new direction of exploring electrodes for high-performance multivalent metal-ion batteries.

Evidence of Charging and Storage at the MoS2/Si Interface

Non-volatile memory chips are important in devices for data storage, where demand kept increasing and the demand of large capacity of storage grew with the development in technology. Flash memory is one of the non-volatile memory devices that has a simple structure that is based on CMOS basic structure. Flash memory was introduced by Toshiba in 1984, which is an electrically erasable/programable non-volatile memory device [1]. Due to the development new technology the demand for size scale down of the memory structure was high, at which the size was kept on being reduced. At sizes less than 65nm flash memory started to show different problem including charge loss and the stress-induced leakage current, due to the tunnelling oxide thickness reduction. [2,3]. The structure of the flash memory has been developed to overcome the issues due to size reduction by introducing nanoparticles to the floating gate, which showed huge development. This development made researchers explore different nanoparticles including 2D materials. 2D materials has distinctive electrical, optical, chemical, and mechanical properties that makes them interesting to be implemented in new technology [4]. One of the interesting 2D materials is Molybdenum disulfide (MoS2). MoS2 have a multitude of features such as high strength, flexibility and has better quantum yield than bulk MoS2 [5]. 2D films of MoS2 can be widely used in various devices for their electronic, optical, and catalytic properties [6]. In this work MoS2 nanoflakes were bonded to silicon to study the charge transport at the interface.The initial bulk MoS2 was in crystal form, which was used to prepare the MoS2 nanoflakes. The preparation procedure for the MoS2 flakes was by using mechanical exfoliation technique. Nitto SPV224 PVC tape had been used to exfoliate bulk MoS2, where part of the bulk MoS2 crystal is placed on the sticky part of the tape. The tape is then folded on the MoS2 piece with the tape surrounding the crystal on the top and bottom. The tape is then separated from each other, which results in exfoliation of the MoS2 into flakes. The more the steps are repeated of this process, the thinner the flakes are. The flakes on the tape were transferred to a p-Si wafer on a hot plate at 50C and bonded to create the MoS2/Si interface.The achieved MoS2 nanoflakes on p-Si wafer sample had been imaged using AFM topography and conductivity measurements. The AFM images were collected to identify the distribution of the flakes. AFM images showed clear flakes on the p-Si wafer at which they were distributed randomly over the surface. The thickness of single monolayer flakes measured was 0.65nm and two monolayer flakes were 1.3 nm. Furthermore, conductive AFM was employed to obtain the IV curve over the flake and obtain their electrical properties, where forward and reverses scanning was done showing a hysteresis loop. The hysteresis observed showed a voltage window gap of around ∆Vth=0.5 V. This indicates electron tunneling and charge storage at the MoS2/Si interface or in the MoS2. Finally, the results, highlight the potential use of 2D MoS2 flakes in future no power memory devices.

P-109 Nanoflakes of molybdenum disulfide functionalized with catechins modulate the sperm capacitation resulting in an improvement of the IVF outcomes in a swine in vitro model

Abstract Study question Are there any potential effects derived from the exposure of spermatozoa to MoS2/catechins nanoflakes during the process of capacitation? Summary answer The spermatozoa exposure to MoS2/catechin nanoflakes do not induce toxicity on spermatozoa and modulate sperm capacitation in a swine in vitro model. What is known already Molybdenum disulfide (MoS2)is a 2D graphene-like material widely used in a pletora of applications, such as energy storage, catalysts, sensors, lubricants and friction reducers. The unique features of this nanomaterial suggest interesting applications in the biomedical field. To date, there are no data regarding the potential effects of MoS2 nanoflakes on the reproductive field. Study design, size, duration To evaluate the potential effects derived from the interaction between the sperm cells and this material, spermatozoa were exposed to MoS2/Catechins nanoflakes at 10, 1, 0.1 ppm, using catechins as control, during capacitation. Different sperm capacitation events were studied, mainly related to their physic-chemical properties (membrane) and biochemical pathways (intracellular signaling), and then IVF experiments were performed with MoS2/catechins and catechins (0.1 ppm). Ten independent experiments were carried out between November 2020 and November 2021. Participants/materials, setting, methods The sonochemical exfoliation of bulk MoS2 in water-soluble MoS2 nanoflakes was obtained with a flavonoid, catechin (CT), that acts as stabilizing agent remaining anchored onto the surface of the MoS2 sheets. Sperm cells from different animals were included in this study. To evaluate the parameters exposed, different techniques were used: fluorescence microscopy, flow cytometry, western blot and in vitro fertilization assay. Main results and the role of chance No significant differences were found in terms of sperm membrane modifications (acrosome damage and membrane disorder) and sperm biochemical pathways (PKA activity, tyrosine phosphorylation patterns, intracellular calcium concentration and mitochondrial activity) between the groups of study compared to the control group. From the results arise that MoS2/CT nanoflakes do not induce any negative effect on the parameters evaluated related to sperm capacitation. Moreover, the addition of MoS2/CT nanoflakes and CT alone at a specific concentration (0.1 ppm) has demonstrated to increase the spermatozoa fertilizing ability in an IVF assay by increasing the number of fertilized oocytes with respect to the control group. Limitations, reasons for caution Despite the promising results in terms of IVF outcomes, further studies are needed to investigate the nature of the interaction between spermatozoa and the MoS2, as well as the potential effects on embryonic development. Wider implications of the findings Our findings open new interesting perspectives regarding the use of 2D graphene-like materials obtained using natural/bio compounds, to implement new strategies to manage sperm capacitation. Trial registration number not applicable

Polarity independent resistive switching in MoS2 nanosheets and PEO-based nanocomposite films

Here, we report the exfoliation of bulk MoS2 (molybdenum disulfide) into few-layer nanosheets and then prepared nanocomposite films (MoS2-PEO) with poly(ethylene oxide) as the host. We observed nonpolar or polarity independent bistable resistive switching memory in two-terminal devices with indium tin oxide and aluminum (Al) as bottom and top electrodes, respectively. In both bipolar and unipolar operations, it is observed that the biasing direction controls the current conduction mechanism. When the positive bias is applied at the top Al electrode, the low resistance state (LRS) conduction is ohmic type. But in the opposite biasing condition, LRS conduction is space charge controlled. The current–voltage characteristics of bipolar and unipolar switching are distinctly different in terms of their RESET process. In bipolar, the RESET process is very sharp, whereas in unipolar operation it is staggered and step-wise.

Steep-slope Schottky diode with cold metal source

Today's circuit technology requires low-power transistors and diodes to extend Moore's law. While research has been focused on reducing power consumption of transistors, low-power diodes have not been widely studied. Here, we report a low-power, thus steep-slope Schottky diode, with a “cold metal” source. The Schottky barrier between metal electrode and bulk MoS2 enabled the diode behavior, and the steep-slope diode IV curve originated from the change in the density of states of a graphite (cold metal) source with a bias voltage. The MoS2 Schottky diode with a cold metal exhibits an ideality factor (η) < 1 for more than four decades of drain current with a sizable rectifying ratio (108). The realization of a steep-slope Schottky diode paves the way to the improvement in low-power circuit technology.

ReS2 vs MoS2: Viable electrodes for batteries and capacitors

Presented is an electrochemical study on a relatively new member of TMDC: ReS2. A systematic study has been done wherein pure ReS2′s viability, as a component in both faradaic and capacitive storage devices, has been found to be superior to the oft-cited conventional TMDC: MoS2. When evaluated as anode for Li-ion batteries, ReS2 showed higher storage capacity as well as better cycling stability. For supercapacitor applications, bulk ReS2 electrode was found to hold two times higher charge than bulk MoS2. Post exfoliation, ReS2 values were augmented by ca. 630% compared to unexfoliated samples. Detailed analysis revealed that several structural variations between ReS2 and MoS2 lead to the superior performance observed. In ReS2, there exists a weaker interlayer coupling, an intrinsic structural anisotropy due to presence of Re-Re interaction, and improved conductivity is prevalent due to interaction between Re chains that cumulatively improve electrochemical performance of ReS2. These attributes provide for robustness of ReS2 under prolonged electrochemical activity and this provides impetus for its use as a more viable alternative for a successful energy storage material.

Employing Poly(4‐Vinylpyridine) as the Dielectrics for Enhanced Molybdenum Disulfide Field‐Effect Transistors

Herein, field‐effect transistors (FET) based on multilayer molybdenum disulfide (MoS2) nanoflakes are fabricated by employing poly(4‐vinylpyridine) (PVP) as the modified layer of typical inorganic dielectric (SiO2). The MoS2 nanoflakes are directly exfoliated from bulk MoS2 and transferred onto the PVP surface instead of bare SiO2 substrate that renders the enlarged nanoflake size. Taking advantage of the high surface energy and low surface roughness of PVP surface, the enhanced interaction between PVP and MoS2 bulk crystal may be achieved that is responsible for the large‐size MoS2 nanoflakes (≈2.5 × 105 μm2). Importantly, MoS2 FETs based on the double‐gate insulators consisting of PVP and SiO2 exhibit improved device performances. The on‐state current presents a fivefold increase and the field‐effect mobility is improved from 4.75 to 167.79 cm2 Vs−1, which are attributed to the PVP surface with low charge‐trap states and the lowered Schottky Barrier height (ΦSB). The current studies will effectively push the applications of MoS2 nanoflakes in flexible electronics.

Construction of carbon nanotubes bridged MoS2/ZnO Z-scheme nanohybrid towards enhanced visible light driven photocatalytic water disinfection and antibacterial activity

We fabricated carbon nanotubes (CNTs) bridged MoS2/ZnO nanohybrids from the hydrothermal process for the heterostructure photocatalysts. The nanohybrids were effectively operated as visible light action for the photocatalytic of organic compounds and heavy metal reduction. The results exhibit that the great photocatalytic efficiency from nanohybrids for the 94.5% of tetracycline (TC) degradation after 60 min of irradiation. Enhanced environmental pollutants removal was due to inhibition in recombination of photogenerated electron-hole pairs. The nanohybrids also displayed better photocatalytic performance and reduction capacity (Cr (VI) ions removal), about 10–15 folds as greater than that of bulk MoS2, and ZnO photocatalysts. The nanohybrid showing a wonderful photocatalytic antibacterial capability of 99.9% towards E. coli after 5 min and supplying a favourable environmentally friendly for water disinfection. Based on this studies, we believe that a promising candidate nanohybrids for the photocatalytic of various water contaminants under visible light activity.

Enhancing the catalytic activity of bulk MoS2 towards hydrogen evolution reaction by the formation of MoS2-MoO3-Re2O7 heterostructure

Two-dimensional transition metal dichalcogenides (TMD) are promising cost-effective catalysts for electrochemical/photoelectrochemical hydrogen evolution reactions (HER). One of the strategies to enhance the inherent HER activity of a catalyst is to form heterostructures. Herein, a facile thermal treatment method is reported for the synthesis of a novel heterostructure catalyst, Molybdenum disulphide-Molybdenum trioxide-Rhenium oxide (MoS2-MoO3-Re2O7), for HER. MoS2-MoO3-Re2O7 composite is prepared using bulk MoS2, which is otherwise known as a weak HER catalyst. Electrochemical and photoelectrochemical studies substantiate the enhanced catalytic activity of the MoS2-MoO3-Re2O7 composite than the MoS2 bulk towards HER. The Mott-Schottky analysis suggests the formation of p-n heterojunction, which offers large interfacial contact and facilitates easier charge separation and transfer of photogenerated charge carriers resulting in an improved photoelectrocatalytic activity. The catalyst exhibits excellent stability, confirmed by the repeated cycles of reaction.

Bound states in the continuum in all-van der Waals photonic crystals: a route enabling electromagnetically induced transparency.

Recent studies have demonstrated that multilayer transition metal dichalcogenides can serve as promising building blocks for creating new kinds of resonant optical nanostructures due to their very high refractive indices. However, most of such studies have focused on excitonic regimes of light-material interaction, while there are few on the low-loss region below the bandgap. Here, we conceptually propose all-van der Waals photonic crystals made of electronically bulk MoS2 and h-BN, designed to operate in the telecom wavelengths. And we demonstrate that, due to extremely low absorption loss and destructive interaction between symmetry-protected and resonance-trapped bound states in the continuum, high-quality factor transmission peaks associated with electromagnetically induced transparency (EIT) are observed, thus rendering our proposed structures highly useful for applications like slow light and optical sensing. Furthermore, EIT-like effects are demonstrated in well-engineered MoS2 nanostructures with broken symmetry. We argue that this work is not only of significance for light harvesting in nanostructured van der Waals materials, but provides also a simple path of constructing classical analogues of EIT using dielectric photonic crystals.

Exploring the Effects of the Interaction of Carbon and MoS2 Catalyst on CO2 Hydrogenation to Methanol.

Hydrogenation of CO2 to form methanol utilizing green hydrogen is a promising route to realizing carbon neutrality. However, the development of catalyst with high activity and selectivity to methanol from the CO2 hydrogenation is still a challenge due to the chemical inertness of CO2 and its characteristics of multi-path conversion. Herein, a series of highly active carbon-confining molybdenum sulfide (MoS2@C) catalysts were prepared by the in-situ pyrolysis method. In comparison with the bulk MoS2 and MoS2/C, the stronger interaction between MoS2 and the carbon layer was clearly generated. Under the optimized reaction conditions, MoS2@C showed better catalytic performance and long-term stability. The MoS2@C catalyst could sustain around 32.4% conversion of CO2 with 94.8% selectivity of MeOH for at least 150 h.

Impedimetric detection of miRNA biomarkers using paper-based electrodes modified with bulk crystals or nanosheets of molybdenum disulfide

Paper-based electrodes modified with molybdenum disulfide (MoS2) in the form of bulk crystals or exfoliated nanosheets were developed and used as a biosensing platform for the impedimetric detection of miRNAs (miRNA-155 and miRNA-21) related to early diagnosis of lung cancer. For this purpose, MoS2 crystals or nanosheets were used for the modification of the working electrode area of paper-based platform for the first time in this study. The proposed assay offers sensitive and selective detection of microRNAs by electrochemical impedance spectroscopy (EIS) technique. The entire assay, both the electrode modification and the miRNA detection being completed in 30min and a single sample droplet (5μL) was enough to cover working electrode area which enabled analysis in low sample volumes. The limits of detection (LOD) for miRNA-21 and miRNA-155 were calculated both in buffer and fetal bovine serum media. It is found that the LOD is varying between 1 and 200ng/mL. In comparison to nanosheets, a larger electroactive surface area was obtained with bulk MoS2 resulting in lower LOD values on miRNA detection. The paper-based electrodes showed high specificity towards their target sequences. Moreover, they effectively discriminated single base mismatched non-target sequences. The advantages of these MoS2 paper based electrodes include high sensitivity, and low-cost provide great potential for improved monitoring of miRNA biomarkers even in artificial serum media.

Structural reorientation and compaction of porous MoS2 coatings during wear testing

Industrial upscaling frequently results in a different coating microstructure than the laboratory prototypes presented in the literature. Here, we investigate the wear behavior of physical vapor deposited (PVD) MoS2 coatings: A dense, nanocrystalline MoS2 coating, and a porous, prismatic-textured MoS2 coating. Transmission electron microscopy (TEM) investigations before and after wear testing evidence a crystallographic reorientation towards a basal texture in both samples. A basal texture is usually desirable due to its low-friction properties. This favorable reorientation is associated to a tribological compaction of the porous specimens. Following running-in, sliding under high contact pressure ultimately leads to a wear rate as small as for an ideal grown bulk MoS2 single crystal grown by chemical vapor deposition (CVD). This suggests that the imperfections of industrial grade MoS2 coatings can be remediated by a suitable pretreatment.

SLM-processed MoS2/Mo2S3 nanocomposite for energy conversion/storage applications

MoS2-based nanocomposites have been widely processed by a variety of conventional and 3D printing techniques. In this study, selective laser melting (SLM) has for the first time successfully been employed to tune the crystallographic structure of bulk MoS2 to a 2H/1T phase and to distribute Mo2S3 nanoparticles in-situ in MoS2/Mo2S3 nanocomposites used in electrochemical energy conversion/storage systems (EECSS). The remarkable results promote further research on and elucidate the applicability of laser-based powder bed processing of 2D nanomaterials for a wide range of functional structures within, e.g., EECSS, aerospace, and possibly high-temperature solid-state EECSS even in space.

Ionic Liquid Crystals Confining Ultrathin MoS2 Nanosheets: A High-Concentration and Stable Aqueous Dispersion

To realize the application potential of molybdenum disulfide (MoS2) in aqueous environments, scalable and efficient methods for the preparation of high-concentration and stable dispersions need to be developed. In this paper, ultrathin MoS2 successfully was synthesized using an in situ-exfoliated bulk MoS2 method in water using ionic liquid crystals (ILCs) as green exfoliating/dispersing agents. The ILCs containing hydrophobic cations and hydrophilic anions not only help to exfoliate bulk MoS2 into ultrathin MoS2 nanosheets but also prevent the re-agglomeration of the ultrathin MoS2 nanosheets in water. MoS2 nanosheets were confined by the ILCs through π–π and C–H···π interactions, preventing direct contact of MoS2 with water. The ILC–MoS2 dispersion exhibited remarkable dispersion stability exceeding 8 months at room temperature. Moreover, the ILC–MoS2 dispersion has been successfully proven to be an excellent water-based lubricant, where the ILCs form a lubricant film on the friction surface through electrostatic interactions and MoS2 increases the load-bearing capacity of the lubricant film due to its high modulus, resulting in an 84.9% reduction in the coefficient of friction compared to pure water. The method is expected to provide a new idea for the preparation and application of MoS2.

High Performance Semiconducting Nanosheets via a Scalable Powder-Based Electrochemical Exfoliation Technique.

The liquid-phase exfoliation of semiconducting transition metal dichalcogenide (TMD) powders into 2D nanosheets represents a promising route toward the scalable production of ultrathin high-performance optoelectronic devices. However, the harsh conditions required negatively affect the semiconducting properties, leading to poor device performance. Herein we demonstrate a gentle exfoliation method employing standard bulk MoS2 powder (pressed into pellets) together with the electrochemical intercalation of a quaternary alkyl ammonium. The resulting nanosheets are produced in high yield (32%) and consist primarily of mono-, bi-, triatomic layers with large lateral dimensions (>1 μm), while retaining the semiconducting polymorph. Exceptional optoelectronic performance of nanosheet thin-films is observed, such as enhanced photoluminescence, charge carrier mobility (up to 0.2 cm2 V-1 s-1 in a multisheet device), and photon-to-current efficiency while maintaining high transparency (>80%). Specifically, as a photoanode for iodide oxidation, an internal quantum efficiency up to 90% (at +0.3 V vs Pt) is achieved (compared to only 12% for MoS2 nanosheets produced via ultrasonication). Further using a combination of fluorescence microscopy and high-resolution scanning transmission electron microscopy (STEM), we show that our gently exfoliated nanosheets possess a defect density (2.33 × 1013 cm-2) comparable to monolayer MoS2 prepared by vacuum-based techniques and at least three times less than ultrasonicated MoS2 nanoflakes. Finally, we expand this method toward other TMDs (WS2, WSe2) to demonstrate its versatility toward high-performance and fully scalable van der Waals heterojunction devices.

Exfoliation of MoS2 Nanosheets Enabled by a Redox-Potential-Matched Chemical Lithiation Reaction.

Ion intercalation assisted exfoliation is the oldest and most popular method for the scalable synthesis of molybdenum disulfide (MoS2) nanosheets. The commonly used organolithium reagents for Li+ intercalation are n-butyllithium (n-BuLi) and naphthalenide lithium (Nap-Li); however, the highly pyrophoric nature of n-BuLi and the overly reducing power of Nap-Li hinder their extensive application. Here, a novel organolithium reagent, pyrene lithium (Py-Li), which has intrinsic safe properties and a well-matched redox potential, is reported for the intercalation and exfoliation of MoS2. The redox potential of Py-Li (0.86 V vs Li+/Li) is located just between the intercalation (1.13 V) and decomposition (0.55 V) potentials of bulk MoS2, thus allowing precise Li+ intercalation to form a lamellar LiMoS2 compound without undesirable structural damage. The lithiation reaction can be accomplished within 1 h at room temperature and the exfoliated nanosheets are almost single layer. This method also offers the advantages of low cost, high repeatability, and ease in realizing large-scale production.

Study of Exfoliated Molybdenum Disulfide (MoS2)

In this study, We demonstrate mono and few layers MoS2 samples on the SiO2 (270nm)/Si substrate from bulk MoS2 crystal by micromechanical exfoliation technique. We also report that the Raman and PL intensity can be thermally modulated by annealing 1L, 2L and 7LMoS2 in a vacuum or air. We have systematically studied Atomic Force Microscopy, Raman and PL properties of mono and few layer MoS2 on the SiO2 (270nm)/Si substrate. First, we find that the number of layer values dependent the Raman and PL emission. First, Raman intensity area ratio of the MoS2 E12g, Ag1 and 2LA modes to that area of the Si substrate increased linear with increasing number of layers MoS2. Second, Normalized PL intensity area of the (A) peak decreased linear with increasing number of layers MoS2. The value of those graphs is a method to understand the number of layers the exfoliated MoS2. Third we found that some effects of the few layers MoS2after thermal annealed (vacuum and air 3000C for 40 min).

A simple two-step strategy to synthesize defect-rich MoS2 nanocrystals for enhanced electrochemical hydrogen evolution

MoS2 based materials are considered the most reliable alternative catalysts for the hydrogen evolution reaction (HER), where engineering of active sites has emerged as an acceptable approach to tune their HER activity. In this approach, the dispersion of bulk MoS2 in the aqueous phase was increased with a surfactant (sodium dodecyl sulfate), which reduced the exfoliation time and enhanced the exfoliation ability to produce layered MoS2 nanosheets. During the hydrothermal treatment, the nanosheets were further scissored into small nanocrystals. Nanocrystals have attractive properties with stable dispersion and high-water solubility. Our method provides a scalable, eco-friendly, easy, and low-cost strategy for designing other HER catalysts. Such ultra-small MoS2 nanocrystals with rich Mo vacancies were used as catalysts for HER, which showed excellent electrocatalytic activity with a low overpotential (95 mV) and small Tafel slope (41 mV/dec) in 0.5M H2SO4 electrolyte. The design and synthesis of the HER catalyst in this work presents a promising path for preparing active and stable electrocatalysts to replace costly metal-based catalysts for hydrogen production.