MoS2 Nanoflakes Research Articles

MoS2 nanoflakes integrated in a 3D carbon framework for high-performance sodium-ion batteries

Molybdenum disulfide (MoS2), employed for rechargeable sodium-ion batteries (SIBs) as an anode material, has attracted considerable attention attributing to its high Na+ intercalation capability. Nevertheless, MoS2 suffers from low conductivity and large volume expansion upon the discharging/charging. In this work, MoS2 nanoflakes were dispersed into a three-dimensional (3D) porous carbon framework by utilizing salt as hard template, obtaining a 3D porous MoS2/carbon composite. When employed as an anode material for SIBs, the composite shows large specific capacity, good rate capability and cycling stability. A large capacity of 361 mAh g−1 is achieved at 5.0 A g−1 and a capacity of 372 mAh g−1 is still well maintained at 0.5 A g−1 after 200 cycles. The 3D interconnected porous carbon framework is believed to improve the electrochemical performance through accelerating the transportation of electrons and ions, as well as suppressing the volume expansion upon the Na+ insertion and preventing the active materials aggregation.

Opening organic solvent pathways by molybdenum disulfide in mixed matrix membranes for molecular separation

2-dimensional (2D) materials such as molybdenum disulfide (MoS2) present tremendous opportunities in membrane-based, energy-efficient separation. However, the preparation methods of most current 2D membranes are filtration-based and difficult to scale up. This paper reports a fast and scalable approach to fabricate 2D material-based mixed matrix membranes for organic solvent nanofiltration. Via a simple 3-step layer-by-layer coating process, few-layered MoS2 nanoflakes are incorporated into the polyelectrolyte layer, and open the organic solvent pathways which are otherwise closed without MoS2. It is revealed that MoS2 can bridge the strong polyelectrolytes, lower the surface energy and maintain good stability in organic solvents, thereby creating interconnected channels for the selective passage of organic solvents while rejecting solutes. With a thin layer of < 50 nm, the mixed matrix membrane can achieve 92.9% rejection for Victoria blue B (VBB, MW 506.08) with an ethanol flux of 11.4 L m−2 h−1 bar−1.

Direct methanation with supported MoS2 nano-flakes: Relationship between structure and activity

Abstract With a rapid developing global economy and population growth, demand for natural gas is expected to outpace supply. Current state of the art methanation catalysts like nickel-based (Ni) catalysts are susceptible to poisoning by sulfuric compounds present in the syngas. MoS2 is one of the few methanation catalysts not affected by sulfuric impurities, allowing the use of syngas feedstocks from coal gasification for direct methanation before extensive clean-up of the syngas. Increasing the number of Mo active sites is challenging since they are mostly located at the edges while the basal planes are mostly inert. In this study, we report a method of producing MoS2 with a significant amount of exposed edges (nano-flakes) which resulted in highly active MoS2 catalysts. Effects of support, Mo precursors and synthesis techniques on the formation of nano-MoS2 structure and methanation activity have been investigated. MoS2 nano-flakes can be produced from a solvothermal method or thermolysis of a thiomolydate precursor. The resulting MoS2 catalysts were tested for direct methanation of CO with H2 to CO ratio of 1:1 and 3000 ppm of H2S under 3 MPa. X-ray absorption spectroscopy was also utilized to gain more insight into the structure of the catalysts.

Vertically aligned ultrathin MoSe2 nanoflakes grown on carbon cloth and its field emission behaviour

In this paper, MoSe2 nanoflakes on carbon cloth (MS-C) and MoSe2 powder (MS-P) were synthesized by facile hydrothermal route. The synthesized MoSe2 nanoflakes, owing to their high aspect ratio, are envisaged as potential candidates for field emitters. Accordingly, field emission (FE) characteristics of MoSe2 nanoflakes were investigated at the base pressure of 1 × 10-8 mbar. The FE properties were studied at three different anode-cathode separations (500, 1000 and 1500 μm). The observed values of turn-on and threshold fields are comparable to those exhibited by nanostructures and nano-composites of other TMDs. Moreover, the MS-C emitter showed competency to deliver very high emission current density of 5.372 mA/cm2 at an applied electric field of 8 V/μm. The MS-C emitter exhibited good emission stability at pre-set value of 100 μA and hardly any degradation in emission current was noticed over duration of 10 h. The use of carbon cloth as a substrate is two-fold advantageous, a substrate having very good electrical conductivity and mechanical flexibility. The observed results imply that the present synthesis protocol (carbon cloth as substrate and hydrothermal route) can be efficiently employed to fabricate flexible field emitters for practical applications in vacuum micro/nanoelectronic devices.

Edge-terminated few-layer MoS2 nanoflakes supported on TNAs@C with enhanced electrocatalysis activity for iodine reduction reaction

Construction of hierarchical structures composed of edge-terminated MoS2 with abundant active sites is challenging but yet desirable for many practical applications. Herein, the edge-terminated few-layer MoS2 nanoflakes are synthesized on carbon nanofilm–coated TiO2 nanorod arrays (TNAs@C) to form vertically aligned TNAs@C-MoS2 core-shell nanostructure. This TNAs@C-MoS2 nanomaterial exhibits a large number of MoS2 active sites and possesses fast electron transport ability. When evaluated as an electrocatalyst for the triiodide reduction in a dye-sensitized solar cell, the TNAs@C-MoS2 shows higher power conversion efficiency (7.98%) than that (7.16%) of Pt. This structure engineering synthesis offers a facile and general way of manipulating the relevant device structures and provides a promising approach for producing other transition-metal dichalcogenides materials with unique properties.

Chemical modification, field effect transistors and voltage-driven spin logic gates of tailored monolayer MoS2 nanoflakes

By using DFT method, we stitch monolayer MoS2 nanoflakes with different manners to tune the behaviors. The stability of these structures is identified by molecular dynamics simulations. The effect of chemical modification is also given and assessed by the calculated edge adsorption energy. It is found that the electronic structures can be manipulated from semiconducting to metallic properties by different edge modifications. The prototypes can also be constructed into three-terminal FET which owns smaller value of subthreshold swing S and the considerable transconductance G comparable to that of experiments. More importantly, we utilize the spin-transport properties to achieve a kind of voltage-driven spintronic logic gates. We control the spin transport with the electric field only and find the model can function in all base ‘AND’, ‘OR’, ‘NOT’ logic operations under specific combinations of the gate bias. The advantages of monolayer MoS2 nanoflakes are thus expected.

Reduced turn-on field through solution processed MoS2 nanoflakes anchored MWCNTs

Abstract An investigation of field emission on solution processed MWCNTs, MoS2 and MoS2 anchored MWCNTs thin films on low cost stainless steel substrates have been performed. Decorative morphology of MoS2 nanoflakes over MWCNTs interconnected high surface area nanonetwork supports the active path for the application of field emission. Drastic diminishing in turn-on field value has been obtained for MWCNTs/MoS2 nanocomposite compared to bare MWCNTs and MoS2. Hence, present investigation opens path for the development of low-temperature solution processed MWCNTs/MoS2 thin film in the field of nanoelectronics and the used process can be integrated for large scale.

Facial Synthesis of 1T Phase MoS2 Nanoflowers via Anion Exchange Method for Efficient Hydrogen Evolution

AbstractIn this work, a low cost and high yield method is proposed to synthesize 1T phase MoS2 nanoflowers (NFs) by means of anion exchange using MoO3 nanosheets as the exchange template. The synthesized MoS2 NFs are composed of ultrathin MoS2 nanoflakes with plenty of active edge sites, large specific surface area, and rich defects, as well as reduced intrinsic resistance. Therefore, they show enhanced hydrogen evolution reaction (HER) activity with an overpotential of 166 mV at 10 mA cm−2 and Tafel slope of 47 mV dec−1, better than those of previously reported MoS2‐based HER catalysts. A systematic study is carried out on the effects of mass loading and reaction temperature on its catalytic performance. It is shown that, with reaction temperature of 200 °C and mass loading of 0.43 mg cm−2, the obtained MoS2 NFs show the optimal HER activity. The present work provides a facile and cost‐effective way to synthesize 1T MoS2 NFs with advanced HER performances, indicating significant potential for larger‐scale production in practical industrial applications.

A facile layer-by-layer fabrication of three dimensional MoS2-rGO-CNTs with high performance for hydrogen evolution reaction

Molybdenum disulfide (MoS2), although considered as a promising transition metal dichalcogenides catalyst, owns low plane conductivity that limits its effective application. In this work, we grew monodispersed MoS2 nanoflakes on reduced graphene oxide (rGO), and then assembled the resulting MoS2-rGO with carbon nanotubes (CNTs) in a layer-by-layer manner to form the MoS2-rGO-CNTs composite. The CNTs spacing layer not only reduces the whole catalytic material's resistance by bridging different broken MoS2-rGO nanosheets, but also constructs a three-dimensional structure to prevent 2D MoS2-rGO nanosheets restacking and thus increases the active sites. Such three-dimensional MoS2-rGO-CNTs catalyst exhibited a low Tafel slope of 39 mV dec−1 and a high current density of 1200 mA cm−2 at −400 mV. Therefore, our study showed a cheap and simple method to combine three-dimensional hybrid material, facilitating the large-scale application of non-noble catalyst.

Three-dimension ivy-structured MoS2 nanoflakes-embedded nitrogen doped carbon nanofibers composite membrane as free-standing electrodes for Li/polysulfides batteries

Abstracts Three-dimension ivy-structured MoS2 nanoflakes @ nitrogen doped carbon nanofibers (MoS2@N-CNFs) composite membrane was designed by a combined electrospinning and hydrothermal technique. The MoS2@N-CNFs membrane is employed as a free-standing cathode for Li/polysulfides batteries. N-CNFs membrane with high electrical conductivity is used as a current collector to effectively reduce the internal resistance in the electrode and immobilize the dissolved lithium polysulfides with mesoporous N-CNFs with pyridine nitrogen. The MoS2 nanoflakes introduced into N-CNFs membrane offer a hierarchical composite structure, in which the MoS2 nanoflakes not only have chemical binding with the lithium polysulfides, but also promote fast redox reaction kinetics with high capacity and low voltage polarization. Meanwhile, the MoS2 nanoflakes have been demonstrated to show strong binding energy and be capable of anchoring polysulfides based on density functional theory calculations. As a result, with a high sulfur loading of 7.11 mg, the assembled cell with MoS2@N-CNFs + Li2S6 cathode demonstrates excellent electrochemical performances with a capacity decay rate of 0.08% per cycle over 250 cycles at 0.2C. Moreover, when the sulfur loading is further increased to 11.84 mg, a capacity decay rate of 0.25% per cycle over 100 cycles is achieved. Consequently, the method used in here provides a new insight to produce N-doped carbon nanofibers with metal sulfides/metal oxides nanoflakes composites as free-standing materials with the high sulfur loading for lithium-sulfur batteries.

Modulated electrochemical oxygen evolution catalyzed by MoS2 nanoflakes from atomic layer deposition

Electrochemical water splitting into H2 and O2 has attracted wide attention owing to the urgent need for clean and renewable energy sources. However, the scarcity and high-cost limit the large-scale application of noble metal catalysts such as IrO2 and RuO2. In this work, as a low-cost catalyst for the electrochemical O2 evolution reaction (OER), MoS2 nanoflakes were obtained by atomic layer deposition (ALD) using MoCl5 and H2S on carbon fiber paper surface. According to the results of electrochemical measurements, the MoS2 nanoflakes exhibit an excellent catalytic activity, and the activity can be modulated by controlling the density and the internal resistance of MoS2 nanoflakes. Moreover, the plasma treatment can further improve the activity of MoS2 nanoflakes, and the reason was discussed through the measurements of contact angle, electrochemical impedance spectroscopy, and electrochemically active surface area. The MoS2 nanoflakes obtained by ALD possess huge values for electrochemical OER as a catalyst.

Potential blockade of the human voltage-dependent anion channel by MoS2 nanoflakes.

Despite significant interest in molybdenum disulfide (MoS2) nanomaterials, particularly in biomedicine, their biological effects have been understudied. Here, we explored the effect of MoS2 nanoflakes on the ubiquitous mitochondrial porin voltage-dependent anion channel (VDAC1), using a combined computational and functional approach. All-atomic molecular dynamics simulations suggest that MoS2 nanoflakes make specific contact interactions with human VDAC1. We show that the initial contacts between hVDAC1 and the nanoflake are hydrophobic but are subsequently enhanced by a complex interplay of van der Waals (vdW), hydrophobic and electrostatic interactions in the equilibrium state. Moreover, the MoS2 nanoflake can insert into the lumen of the hVDAC1 pore. Free-energy calculations computed by the potential of mean force (PMF) verify that the blocked configuration of the MoS2-hVDAC1 complex is more energetically favorable than the non-blocked binding mode. Consistent with these predictions, we showed that MoS2 depolarizes the mitochondrial membrane potential (Ψm) and causes a decrease in the viability of mammalian tissue culture cells. These findings might shed new light on the potential biological effect of MoS2 nanomaterials.

Mott variable-range hopping transport in a MoS2 nanoflake

The transport characteristics of a disordered, multilayered MoS2 nanoflake in the insulator regime are studied by electrical and magnetotransport measurements. The MoS2 nanoflake is exfoliated from a bulk MoS2 crystal and the conductance G and magnetoresistance are measured in a four-probe setup over a wide range of temperatures. At high temperatures, we observe that ln G exhibits a −T−1 temperature dependence and the transport in the nanoflake dominantly arises from thermal activation. At low temperatures, where the transport in the nanoflake dominantly takes place via variable-range hopping (VRH) processes, we observe that ln G exhibits a −T−1/3 temperature dependence, an evidence for the two-dimensional (2D) Mott VRH transport. Furthermore, we observe that the measured low-field magnetoresistance of the nanoflake in the insulator regime exhibits a quadratic magnetic field dependence ∼ αB2 with α ∼ T−1, fully consistent with the 2D Mott VRH transport in the nanoflake.

Nanoceria decorated flower-like molybdenum sulphide nanoflakes: an efficient nanozyme for tumour selective ROS generation and photo thermal therapy.

We report nanoceria (NCeO2) decorated flower-like MoS2 nanoflakes as a nanozyme for cancer photothermal therapy (PTT). They exhibited enzyme-like activity for selectively killing tumor cells by ROS induction. The NCeO2 decoration significantly improved the photoconversion efficiencies (PCEs) of MoS2 nanoflakes when a NCeO2 concentration of ≤0.5 mg mL-1 was used for synthesis. The novel material demonstrated here showed high photostability and PCE, without any systemic toxicity for cancer PTT.

Binding low crystalline MoS2 nanoflakes on nitrogen-doped carbon nanotube: towards high-rate lithium and sodium storage

Low crystal MoS2 nanoflakes embedded on N-doping CNT has been prepared via alternating current and hydrothermal technique, demonstrating superior rate behavior for LIBs and SIBs.

A MoS₂ Nanoflakes-Based LC Wireless Passive Humidity Sensor.

In this study, an LC wireless passive humidity sensor based on MoS2 nanoflakes was proposed. The LC wireless passive humidity sensor was optimized by performing HFSS simulations and fabricated via a screen-printing technique. The MoS2 nanoflakes were characterized by laser scanning confocal microcopy, scanning electron microscope, and X-ray diffraction. The measurements show the sensor can operate stably for a long time with a hysteresis of 4% RH (relative humidity) in 10–95% RH. At low humidity environment (10–60% RH), the sensitivity of the as-prepared humidity sensor is 2.79 kHz/% RH, and a sensitivity of 76.04 kHz/% RH was realized in a high humidity environment (60–95% RH). In this regard, the sensing mechanism was discussed in the scope of proton transfer theory. The test results also indicate that the response time and recovery time of the prepared sensor are 10 s, 15 s, respectively and between 15~40 °C the sensitivity of sensor was not temperature-dependent in the range of 10~80% RH. In addition, the sensor shows less sensitivity to temperature in the 15–25 °C range at 90% RH. All of these experimental results show that the prepared LC wireless passive humidity sensor can stably monitor the rapidly changing humidity in a sealed and narrow environment for a long time.

Photocatalytic properties of MoS2 nanoflakes vertically assembled on reduced graphene oxide

Uniform two-dimensional MoS2 nanoflakes were vertically assembled on the surface of reduced graphene oxide (MoS2/rGO composite film) via a hydrothermal process. The structure, morphology and optical properties of MoS2/rGO composite were studied. It is demonstrated that photocatalytic activity of the composite films for the degradation of methylene blue in the visible light range is much higher than that of isolated MoS2 and rGO. This is associated with an efficient transfer and a rapid separation of photogenerated electrons and holes at the heterojunction between MoS2 nanoflakes and rGO film.

3D Nickel Scaffolded MoS2 Nanoflakes as Sodium Battery Anode with Improved Cycling Life and Rate Capability

AbstractWe report the design and fabrication of 3D nickel inverse opals scaffolded MoS2 nanoflakes (MoS2@Ni IO) by a combination of colloid spheres template, electrochemical deposition, and hydrothermal growth routes. The MoS2@Ni IO is further evaluated as sodium ion battery anode, which exhibits a high specific capacity (696.9 mAh/g of the second cycle), long cycling life stability (620.1 mAh/g after 200 cycles at 200 mA/g) and excellent rate capability. The excellent electrochemical performance of the electrode can be attributed to the unique 3D electrode design, in which the 3D ordered Ni scaffold shortens the ion diffusion paths, improves the electronic conductivity and mechanical stability, while the ultrathin MoS2 nanoflakes are involving in the Na+ insertion/extraction.

Resistive switching behaviors mediated by grain boundaries in one longitudinal Al/MoS2&PVP/ITO device

Nonvolatile memory devices based on 2D layered transition metal dichalcogenides have inspired tremendous amounts of research interests in recent years. In this work, resistive switching (RS) devices based on hybrid molybdenum disulphide and Polyvinylpyrrolidone (MoS2&PVP) is explored. One longitudinal Al/MoS2&PVP/ITO device exhibits three different modes of I-V characteristics, i.e. typical bipolar RS, asymmetrical bipolar RS and threshold switching (TS), which can be explained by the formation and rupture of conducting filaments (CFs) consisting of sulfur vacancy filaments in MoS2 nanoflakes and sulfur ions filaments in PVP. These CFs form from three different kinds of grain boundaries (GBs), intersecting-GB, bisecting-GB, and bridge-GB in which GBs attach one electrode, parallel to the two electrodes, and attach both electrodes, respectively, corresponding to the three modes of I-V characteristics. These three kinds of GBs coexist in one device and the CF forms randomly from one kind of them during sweeping loops. The mechanism was experimentally proved by our results of the increasing probability of typical bipolar RS in device with one layer of PVP thin film inserted into the interface of MoS2&PVP and ITO and other researchers’ results in all-surface MoS2 single-layer MoS2 devices.

MoS2 incorporated hybrid hole transport layer for high performance and stable perovskite solar cells

Two dimensional (2D) Transition Metal dichalcogenides have gained immense research attention in the recent years due to their superior opto-electronic properties and promising prospects in photonics and photovoltaic technologies. In this work, 2D Molybdenum disulphide (MoS2) nanoflakes were incorporated as hole transport layers (HTLs) in inverted (p-i-n) perovskite solar cells (PSCs). MoS2 nanoflakes were blended within the PEDOT:PSS layer together forming a hybrid HTL layer. The modified devices exhibited significant improvement in power conversion efficiency (PCE) and stability simultaneously. Compared to the control device, the efficiency enhancement of MoS2 incorporated devices was around 18.5%. The MoS2 nanoflake has improved the efficient charge extraction across the HTL layer reducing recombination at the interfaces, with a significantly lower electrode polarization and hysteresis. Impedance Spectroscopy (IS) analysis revealed that the MoS2 blended PEDOT:PSS HTL increased the recombination resistance by 50%. The modified HTL based devices also exhibited high device stability retaining more than 95% of the initial PCE even after 4 weeks.