Synthesized Molybdenum Disulfide Research Articles

Two-Dimensional MoS2 nanosheets as cocatalyst to augment the nanocatalytic tumor therapy

As an appealing modality of tumor nanocatalytic therapeutics, Fenton chemistry has been extensively employed to combat cancer through the generation of highly cytotoxic reactive oxygen species (ROS). For iron-triggered catalytic Fenton chemistry, the therapeutic consequence was largely dependent on the available catalytically active ferrous species. In this work, hydrothermally synthesized molybdenum disulfide (MoS2-PEG) nanosheets were served as Fenton cocatalyst to enhance the Fenton kinetics as contributed by ultrasmall gallic acid (GA)-coordinated Fe nanoparticles (GA-Fe NPs) in tumor destruction. The tetravalent Mo4+ species of MoS2-PEG cocatalysts could efficiently transfer Fe3+ species into Fe2+ species by the reduction process, regenerating the catalytically active Fe2+ species and restoring the catalytic activity of GA-Fe nanocatalysts during the Fenton-based tumor therapeutics. Based on systematic in vitro and in vivo investigations of cocatalyst-augmented Fenton nanotherapeutics against 4-T1 tumor cells/xenografts, we have demonstrated a proof-of-concept enhanced nanocatalytic tumor-therapeutic modality by MoS2-PEG/GA-Fe nanocatalyst/cocatalyst hybridized system, which offers an explicit cocatalytic strategy to improve the therapeutic efficacy during nanocatalytic tumor therapy.

Dependence of reaction time in hydrothermal synthesis of MoS2 quantum dots: An investigation using optical tools and fractal analysis

The article discusses the novel fractal nature of hydrothermally synthesized Molybdenum Disulfide (MoS2) Quantum Dots (QDs), where the key parameter controlling the process is the 'reaction time’. This parameter is adjusted from 7 to 30 h, including five intermediate values, while keeping all other synthesis conditions constant. The study employs various structural, morphological, and optical techniques, including X-ray diffraction (XRD), X-ray photoelectron Spectroscopy (XPS), High-Resolution Transmission Electron Microscopy (HRTEM) equipped with Selected Area Electron Diffraction (SAED), Scanning Transmission Electron Microscopy (STEM), UV–Vis, and photoluminescence (PL) spectroscopy to track the evolution of MoS2 samples with changing reaction times. The average size of the QDs exhibits a trend of increase followed by a decrease with longer reaction times. This trend is also compared with band gap calculations. STEM images indicate that shorter reaction times lead to the formation of MoS2 sheets, while extended reaction times cause these sheets to fragment into MoS2 QDs. The concept of “compactness” in the system is explored and analyzed using fractal analysis, a statistical tool. The observations from PL, absorption, and STEM align with the time-evolved fractal dimensional analysis, demonstrating the synthesis dynamics.

Determination of Thallium in Tea with Preconcentration by Microwave-Assisted Synthesized Molybdenum Disulfide Nanoparticles and Flame Atomic Absorption Spectrometry (FAAS) Analysis

A simple, quick and environmentally friendly microwave-assisted synthesis method was developed to produce MoS2 nanoparticles (MoS2NP) for the preconcentration of thallium. The characteristics of the synthesized MoS2NP were validated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The determination of thallium was achieved with MoS2NP based preconcentration and a flame atomic absorption spectrophotometer (MoS2NP-PM-FAAS). A detection limit of 14.6 µg/kg was achieved for thallium using the optimum conditions by the MoS2-PM-FAAS method. The developed method provided an improvement in the detection power of the FAAS system by approximately 20-fold. The applicability of the method was validated with tea samples through spike recovery experiments.

An investigation on tribological properties of advanced microwave synthesized molybdenum disulfide as anti-friction additives in commercially available lubricating oils

The frictional stress between opposing contact surfaces will damage the mechanical parts of a machine. An appropriate lubricant can significantly reduce this. Blending nanoadditives with base oil is claimed to be an effective technique to increase the anti-friction qualities of lubricants using nanotechnology. Advanced microwave synthesized molybdenum disulfide (MoS2) anti-friction nanoadditive was employed in various lubricating oils namely fully synthetic, semi-synthetic, mineral, and hydraulic oil to formulate the nanolubricant. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), and a physical stability observation test were used to study the nanoadditives (MoS2) physicochemical characteristics. The tribological analysis of the MoS2 nanolubricant was measured using the four-ball tribotester. The coefficient of friction (COF) and average wear scar diameter (WSD) of the anti-friction additives were analyzed. The experimental results revealed improvements in COF and WSD in the range of 7.47–15.81% and 6.57–16.07% after the addition of MoS2 nanoparticles in the various lubricating oils. This study discovered that engine oil with advanced microwave-synthesized MoS2 nanoparticles has a significantly lower COF and WSD than engine oil that is not added with the anti-friction additives.

Hydrothermally grown MoS2-flowers as low cost counter electrode material for dye sensitized solar cell and electrode modifier for electrochemical sensing of 4-chlorophenol

In present scenario, energy crisis and environmental pollution are the two major concerns which need immediate attention. Design and fabrication of bi-functional materials to deal with the above concerns are the major challenges for scientific community. Herein, we reported the bi-functional properties of the hydrothermally synthesized molybdenum disulfide (MoS2)-flowers to deal with energy and environmental issues related applications. MoS2-flowers were used as counter electrode material for the fabrication of dye-sensitized solar cells (DSSCs). Fabricated DSSCs showed power conversion efficiency (PCE) of 5.7% and open circuit voltage (Voc) of 0.76 V. Furthermore, MoS2-flowers was used as electrode modifier for the construction of 4-chlororhenol (4-CP). This modified MoS2-flowers based working electrode exhibited reasonable performance in terms of limit of detection and selectivity. A low detection limit of 0.39 µM with sensitivity of 11.47 µA/µMcm2 was achieved. MoS2-flowers demonstrated reasonable performance for DSSCs and 4-CP sensing applications.

Thermal Diffusivity Measurement of MoS2 & MoS2-GO Nano-Composite By Photoacoustic Spectroscopy

Photoacoustic spectrometer (PAS) is a significant technique to measure the thermal diffusivity of any material. When modulated light interact with solid sample which is covered by aluminium or other metal plate, first the light is absorbed by the sample and then thermal energy emitted due to non-radiative decay. Thereafter, acoustic wave produced due to different temperature which maintain by an optical chopper. The medium inside the cavity expands or retract according to the chopper frequency. So, the generated pressure fluctuation inside it measures by using a sensitive condenser microphone which fitted inside the cavity by a narrow path. Here the authors successfully synthesized molybdenum disulfide (MoS2) and its nanocomposite with graphene oxide (MoS2-GO) by simple hydrothermal method. The XRD and FESEM data confirm the phase and morphological structures of the synthesized material. The thermal diffusivity of MoS2 and MoS2-GO nanocomposite are obtained 10.94 mm2/s and 14.72 mm2/s respectively.

Fabrication of MoS2/rGO/AgNWs on PET substrate for flexible electrochromic devices

Emergence of stretchable and flexible optoelectronic devices has motivated scientific community to develop novel transparent conductive electrodes (TCE) as an alternative to indium tin oxide (ITO) substrates. Recently, flexible electrochromic devices (ECDs) have drawn enormous attention because of their flexible nature and potential for next-generation smart windows application. The TCE should have high electrical conductivity, smooth surface, high transparency, and mechanical flexibility. Silver nanowires (AgNWs) have been used as electrode material for the development of flexible TCE for ECDs or smart windows applications. In present work, we have synthesized molybdenum disulfide (MoS2) flowers decorated reduced graphene (rGO) composite via hydrothermal method. Further, flexible TCE (MoS2/rGO/AgNWs) was developed on polyethylene terephthalate (PET) substrate for the construction of flexible ECDs. The MoS2/rGO composite was employed as passivation layer to reduce the oxidation of AgNWs during electrochemical reactions. The use passivation layer (MoS2/rGO) hindered the direct contact between AgNWs and electrolyte which may improve the stability of the AgNWs based ECDs. The fabricated flexible ECDs exhibited good coloration efficiency of 50 cm2/C with stability up to 450 cycles.

Tribological analysis of advanced microwave synthesized Molybdenum disulfide (MoS2) as anti-friction additives in diesel engine oil for military vehicles

One of the most important method to reduce friction and wear is lubrication which is important in the automotive industry for energy efficiency, environmental conservation, and carbon reduction. Additionally, incorporating nanoparticles into engine oil lubricants can significantly increase their performance, particularly in terms of tribological properties. Advanced microwave synthesized Molybdenum disulfide (MoS2) anti-friction additive in SAE 20 W50 diesel engine oil was employed to formulate the nanolubricant. Fourier-transform infrared spectroscopy (FTIR) and a physical stability observation test was used to study the nano additives' physicochemical qualities (MoS2). The tribological performance of the MoS2 nanolubricant was measured using the four-ball tribotester. The Coefficient of Friction (COF) and average Wear Scar Diameter (WSD) of the anti-friction additives were analysed through tribological investigations of the wear rate and scar of the worn-out surface on ball bearings. MoS2 based nanolubricant improves COF and WSD by 10.25 % and 10.6 % respectively, as a contrast to the engine oil revealed from the tribological analysis. The current study discovered that the engine oil with advanced microwave synthesized nanoparticles have a significantly lower COF and WSD than engine oil which is not added with the anti-friction additives.

A simple hydrothermal one-step synthesis of 3D-MoS2/rGO for the construction of sensitive enzyme-free hydrogen peroxide sensor

Hydrogen peroxide (H2O2) is an important intermediate in biological and environmental systems, which is widely used in pharmaceutical, environmental protection, fuel cell and other fields. It is also the most important signal conducting molecule, second messenger and growth factor in Reactive Oxygen Species (ROS). The increase of intracellular H2O2 level is closely related to cancer and neurodegenerative diseases. Therefore, the detection of H2O2 is an important goal of clinical research. Herein, we synthesized molybdenum disulfide (MoS2) with a lattice spacing of 0.62 nm using a simple method, maintaining the excellent characteristics of MoS2 itself, and performing sensitive detection of H2O2. In this work, we use graphene oxide as the precursor, and use one-step hydrothermal method to synthesize three-dimensional molybdenum disulfide/reduced graphene oxide composite (MoS2/rGO). Graphene not only provides a support structure for the growth of MoS2, but also forms large number of pores in it. These channels greatly increase the specific surface area of the MoS2/rGO composite and provide a sufficient reaction environment for the reaction of H2O2 on the composite. Its greatly improves the sensitivity of the MoS2/rGO enzyme-free sensor. We have calculated that the enzyme-free sensor composed of this electrode has a good linear dependence on the H2O2 concentration in the range of 2 μM to 23.18 mM, and the detection limit is 0.19 μM. The enzyme-free sensor with simple preparation method is expected to be greatly developed in the clinical application of hydrogen peroxide sensor.

Two-dimensional electronic transport and surface electron accumulation in MoS2

Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors. Van der Waals crystals are expected to have an inert surface because of the absence of dangling bonds. However, here we show that the surface of high-quality synthesized molybdenum disulfide (MoS2) is a major n-doping source. The surface electron concentration of MoS2 is nearly four orders of magnitude higher than that of its inner bulk. Substantial thickness-dependent conductivity in MoS2 nanoflakes was observed. The transfer length method suggested the current transport in MoS2 following a two-dimensional behavior rather than the conventional three-dimensional mode. Scanning tunneling microscopy and angle-resolved photoemission spectroscopy measurements confirmed the presence of surface electron accumulation in this layered material. Notably, the in situ-cleaved surface exhibited a nearly intrinsic state without electron accumulation.

Quick colorimetric determination of choline in milk and serum based on the use ofMoS2 nanosheets as a highly active enzyme mimetic.

The authors have synthesized molybdenum disulfide nanosheets (MoS2 nanosheets) by using a bottom-up hydrothermal method. The nanosheets display strong catalytic (enzyme mimetic) activity in catalyzing the oxidation of peroxidase substrate of 3,3',5,5'-tetramethylbenzidine (TMB) in presence of H2O2 to produce a blue product. The peroxidase mimicking properties ofMoS2nanosheets depend on temperature, H2O2 concentration and pH value. A choline assay was worked out where choline was oxidized by choline oxidase in presence of oxygen to produce H2O2 which is colorimetrically detected, best at 652nm. The method works in the 1 to180 μM choline concentration range with a 0.4 μMdetection limit. Color changes may also be detected visually. The assay is simple, highly sensitive, selective and rapid. It was applied in the determination of choline in (spiked) milk and serum. Graphical abstract Basic principle of intrinsic peroxidase-like activity of MoS2 nanosheets, applied to design a rapid and selective colorimetric assay for choline detection based on the tetramethylbenzidine (TMB) color reaction.

Growing and Etching MoS₂ on Carbon Nanotube Film for Enhanced Electrochemical Performance.

In this work we directly synthesized molybdenum disulfide (MoS2) nanosheets on carbon nanotube film (MoS2@CNT) via a two-step chemical vapor deposition method (CVD). By etching the obtained MoS2@CNT into 10% wt HNO3, the morphology of MoS2 decorated on CNT bundles was modulated, resulting in more catalytic active MoS2 edges being exposed for significantly enhanced electrochemical performance. Our results revealed that an 8 h acid etching sample exhibited the best performance for the oxygen evolution reaction, i.e., the current density reached 10 mA/cm2 under 375 mV over-potential, and the tafel slope was as low as 94 mV/dec. The enhanced behavior was mainly originated from the more catalytic sites in MoS2 induced by the acid etching treatment and the higher conductivity from the supporting CNT films. Our study provides a new route to produce two-dimensional layers on CNT films with tunable morphology, and thus may open a window for exploring its promising applications in the fields of catalytic-, electronic-, and electrochemical-related fields.

Bandgap modulation of MoS2 monolayer by thermal annealing and quick cooling.

We developed a non-mechanical straining method to simultaneously modulate the bandgap and photoluminescence (PL) quantum efficiency of a synthesized molybdenum disulfide (MoS2) monolayer on SiO2, by vacuum annealing and subsequent quick cooling in ethanol. Influences of the thermal treatments at different temperatures from 100 °C to 600 °C on the PL and Raman spectra of the MoS2 monolayers are reported. A maximum PL peak intensity, twice that of the untreated counterparts under the same measurement conditions, was observed at the treating temperature of 200 °C. At the same time, approximately permanent tensile strains were induced, due to the quick cooling from high temperatures, which led to a red-shift of the direct optical bandgap. Modulation of the bandgap was achieved by changing the treating temperatures; nearly linear PL and Raman frequency shifts of ∼3.82 meV per 100 °C and ∼-0.28 cm-1/100 °C for A exciton photoluminescence and Raman E12g mode frequency were observed, respectively. The proposed thermal modulation promises a wide range of applications in functional 2D nanodevices and semiconductors. To our knowledge, our findings constitute the first demonstration of thermal engineering by combinational manipulation of annealing and quick cooling of the 2D transition-metal dichalcogenides.

High‐resolution transmission electron microscopy of hexagonal and rhombohedral molybdenum disulfide crystals

Natural (molybdenite) and synthesized molybdenum disulfide crystals have been studied by high-resolution transmission electron microscopy. The image simulation demonstrates that the [0001] and [0110] HRTEM images of hexagonal and rhombohedral MoS2 crystals hardly disclose their stacking sequences, and that the [2110] images can distinguish the Mo and S columns along the incident electron beam and enable one to determine not only the crystal structure but also the fault structure. Observed [0001] images of cleaved molybdenite and synthesized MoS2 crystals, however, reveal the strain field around partial dislocations limiting an extended dislocation. A cross-sectional image of a single molecular (S-Mo-S) layer cleaved from molybdenite has been observed. Synthesized MoS2 flakes which were prepared by grinding have been found to be rhombohedral crystals containing many stacking faults caused by glides between S/S layers.

Cross-Sectional Observations of Layer Structures and Stacking Faults in Natural and Synthesized Molybdenum Disulfide Crystals by High-Resolution Transmission Electron Microscopy

Cross sections of the (0001) layers in natural (molybdenite) and synthesized molybdenum disulfide crystals have been observed by high-resolution transmission electron microscopy. The image simulation for hexagonal and rhombohedral MoS 2 crystals which are perfect and contain various types of stacking faults shows that the Mo and S columns along the incident electron beam can be distinguished in the [2110] images and hence the stacking sequence of Mo and S layers can be determined. The layer structures and the formation mechanisms of the stacking faults which have been found in natural and synthesized molybdenum disulfide flakes are presented

Lubricating properties of molybdenum and tungsten disulfides

1. A study was made of the influence of temperature and environment on the coefficients of friction of natural MoS2 and synthesized MoS2 and WS2. 2. The maximum temperatures at which the materials investigated are capable of effective operation in various gaseous media have been determined. 3. It has been established that the coefficient of friction of synthesized molybdenum disulfide is slightly higher than that of the natural disulfide under all test conditions. The coefficient of friction of tungsten disulfide is higher than that of natural or synthesized molybdenum disulfide under all test conditions with the exception of tests in an air atmosphere. 4. An attempt has been made to explain the changes in the coefficients of friction of the materials investigated in terms of the physicochemical processes occurring in the friction zone when experimental conditions are altered.