MoS2 Nanostructures Research Articles

MOCVD Growth of Hierarchical Nanostructured MoS2: Implications for Reactive States as the Large-Area Film

Large-area hierarchical grown transition metal dichalcogenide (TMD) nanostructures as out-of-plane directional layered TMD nanocrystals on a substrate could be considerably useful in electrochemical applications because of the high density of edge states. In this study, layered MoS2 nanocrystals less than 50 nm in diameter were synthesized by overlapping with each other as vertical growth in the form of a film with an area of 10 mm × 40 μm using metal–organic chemical vapor deposition (MOCVD) for the lateral growth of TMDs. Notably, in the spatial distribution, a singular point where the vertical growth is promoted was found through optical dark-field data and spatially resolved micro-Raman spectroscopy. The accelerated vertical growth region distinguished by the singular point is due to the layer-dependent dielectric constant of MoS2, which affects the surface energy and changes the conditions of vapor-phase deposition. In addition, with these phenomena, we discuss a way for expanding the hierarchical vertically grown MoS2 region on a substrate through analytical methods based on hydromechanics.

Electronic and Magnetic Properties of Transition Metal‐Doped MoS2 Monolayer: First‐Principles Calculations

Density functional theory in the framework of generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof to investigate the effects of some selected transition metal (TM) and rare‐earth metal (RE) dopants on the electronic and magnetic properties of a 2D molybdenum disulfide (MoS2) monolayer is reported. The results demonstrate that it is energetically stable to incorporate Ni and Cu in MoS2 structure under Mo‐rich conditions. The pristine MoS2 monolayer has a calculated direct bandgap of 1.70 eV and experiences significant reduction in the gap due to the defects. There is observed induced magnetic behavior due to the tight binding effect originating from the localized dopants and the nearest‐neighbor Mo atoms, with magnetic moments ranging between 0.82 and 3.00 μB. Some of the dopants result in spin polarization which is useful for engineering spin filter devices on magnetic MoS2 nanostructures.

Cost-Effective and Highly Efficient Manganese-Doped MoS2 Nanosheets as Visible-Light-Driven Photocatalysts for Wastewater Treatment.

One of the main objectives in wastewater treatment and sustainable energy production is to find photocatalysts that are favorably efficient and cost-effective. Transition-metal dichalcogenides (TMDs) are promising photocatalytic materials; out of all, MoS2 is extensively studied as a cocatalyst in the TMD library due to its exceptional photocatalytic activity for the degradation of organic dyes due to its distinctive morphology, adequate optical absorption, and rich active sites. However, sulfur ions on the active edges facilitate the catalytic activity of MoS2. On the basal planes, sulfur ions are catalytically inactive. Injecting metal atoms into the MoS2 lattice is a handy approach for triggering the surface of the basal planes and enriching catalytically active sites. Effective band gap engineering, sulfur edges, and improved optical absorption of Mn-doped MoS2 nanostructures are promising for improving their charge separation and photostimulated dye degradation activity. The percentage of dye degradation of MB under visible-light irradiations was found to be 89.87 and 100% for pristine and 20% Mn-doped MoS2 in 150 and 90 min, respectively. However, the degradation of MB dye was increased when the doping concentration in MoS2 increased from 5 to 20%. The kinetic study showed that the first-order kinetic model described the photodegradation mechanism well. After four cycles, the 20% Mn-doped MoS2 catalysts maintained comparable catalytic efficacy, indicating its excellent stability. The results demonstrated that the Mn-doped MoS2 nanostructures exhibit exceptional visible-light-driven photocatalytic activity and could perform well as a catalyst for industrial wastewater treatment.

Factors affecting photocatalytic degradation of methyl red by MoS2 nanostructures prepared by hydrothermal technique

Factors affecting photocatalytic degradation of methyl red by MoS2 nanostructures prepared by hydrothermal technique

Modulating MoS2 nanostructure by vanadium incorporation for high-efficiency hydrogen evolution reaction

In this work, we reported a facile approach to fabricate molybdenum sulfide (MoS2) electrocatalyst with the introduction of vanadium(V) for improved catalytic performance. The morphology of prepared samples can be characterizated by SEM observation. The XRD and XPS spectra further reveal that the proper amount of vanadium introduction can effectively prompt the increase of crystallinity and formation of edge-terminated structure in MoS2 nanostructure. The experimental results display that the morphology of MoS2 can be modulated by various amounts of V incorporation. The conductivity of prepared samples is increased by incorporating a certain amount of graphene. MoS2 nanostructure with 20% V incorporation shows excellent catalytic performance, and the corresponding mechanism is also discussed. The electrochemical performance of 20%V-MoS2 can be further improved by the introduction of appropriate graphene. Compared with pure MoS2 samples, 20%V-MoS2/Graphene7.5 shows a small resistance and excellent cycling stability in the acidic electrolyte, as well as the overpotential at 10 mA decreases from 213 mV to 168 mV.

Superlubricity of Titanium Alloy Enabled by MoS2 Flakes and a-C:H Film

Titanium alloys are often used in engineering fields including aerospace, cryogenic technologies, and weaponry due to their remarkable qualities. However, several issues including a high coefficient of friction, weak wear resistance, and low hardness hinder their widespread usage. Despite several efforts to enhance their tribology, achieving ultra-low friction on titanium alloy surfaces remains a challenging problem in materials science. Here, we report on the superlubricity of a MoS2 + a-C:H (Mo-a films) composite film, prepared by magnetron sputtering and spraying to lubricate titanium alloy surfaces. Robust superlubricity was achieved by the Mo-a composite films with a coefficient of friction (COF) below 0.007 in a helium environment. Compared to the reference titanium alloy substrates, the introduction of Mo-a composite film reduced the friction coefficient to roughly 1%, and the a-C:H film reduced wear by three orders of magnitude. High-resolution characterizations indicate that this enhanced tribology can be attributed to the formation of transfer film, which is enriched with nanostructured graphene sheets and MoS2 nanoscrolls, and is formed due to shear stress-induced structural transformation of a-C:H films and MoS2 nanosheets. This transfer film transitioned the initial high-resistance steel-to-a-C:H contact to super low-resistance steel-to-transfer film contact, thus achieving superlubricity and a remarkable wear reduction. This work outlines a pathway to solving the poor wear resistance and high friction coefficient problem of titanium alloy surfaces, which can be an important guideline for applications of titanium alloys in mechanical engineering.

High‐performance flexible supercapacitor based on morphology tuned polypyrrole/molybdenum disulfide nanocomposites

AbstractPolypyrrole (PPy) is the most studied material among the conducting polymers for high‐performance supercapacitors. However, due to morphology collapse, polypyrrole exhibits poor cycling ability and lower charge storage capacity, limiting its real‐world applications. To address these issues herein, the binary nanocomposites of PPy with MoS2 (molybdenum disulfide) NSs (nanostructures) in two different morphologies, that is, cenosphere (PPyC) and nanotubes (PPyNTs), have been prepared through in situ polymerization technique. The electrochemical performances of PPyC/MoS2 and PPyNTs/MoS2 nanocomposite are compared to define the most favorable morphology when PPy nanostructures are utilized as the electrode materials for creating flexible supercapacitors. The rational design of PPyNTs/MoS2 nanocomposite consisting of dense wrapping of PPyNTs on MoS2 leads to high specific capacitance (Csp) up to 481 F/g at 0.5 A/g. After 2000 charge‐discharge cycles, a decline of 5.6% in the specific capacitance of PPyNTs/MoS2 nanocomposite was observed, primarily attributed to the presence of chemically active sites on MoS2 nanosheets. This led to a strong alignment with the nitrogen group of pyrrole rings in the polymer chain to form a robust interconnected framework between tubular PPy and sheet‐like MoS2. This outstanding performance of PPyNTs/MoS2 nanocomposite resulted in designing futuristic flexible supercapacitors.

Synergistic effects of 1T-2H MoS2 nanoflowers modified with Ag3PO4 nanoclusters for highly efficient electrochemical activity

The development of highly efficient binary heterostructures with enhanced electrocatalytic activities is vital for reducing the energy consumed by the hydrogen evolution reaction (HER). Herein, we successfully design and synthesize an eco-friendly Ag3PO4/1T-2H MoS2 heterostructure to catalyze the HER process. Micromorphology and microstructure studies show that the Ag3PO4 nanoclusters are well dispersed with abundant catalytically active sites on the surface of the 1T-2H MoS2 nanoflowers. X-ray photoelectron spectroscopy confirms the stable oxidation state and electronic interactions in the 2 wt% Ag3PO4/1T-2H MoS2 nanostructure. Benefitting from the strong electronic interactions and advantages of abundant heterogeneous interfaces and catalytically active sites, the 2 wt% Ag3PO4/1T-2H MoS2 heterostructure delivers excellent and durable electrochemical HER activity in alkaline solution, with a low overpotential of 149 mV for the HER at 10 mA cm−2, in clear improvement over 1T-2H MoS2. The enhanced electrocatalytic activity is ascribed to the abundant catalytically active sites, rapid charge transport, and Ag3PO4/1T-2H MoS2 synergism. This study provides a novel strategy for exploring and synthesizing low-cost binary electrocatalysts that enhance the electrochemical HER performance in energy-conversion applications.

MoS2 Quantum Dots Alter Macrophage Plasticity and Induce Mitophagy to Attenuate Endothelial Barrier Dysfunctions

Molybdenum disulfide (MoS2), as a member of transition metal dichalcogenides (TMDs), presents enormous potential in biomedical applications due to its unique chemical–physical properties, photo-electronic properties, and biocompatibility. MoS2 nanostructures have recently been shown to be multifunctional nanotheranostic agents for neuroprotection and maintenance of endothelial homeostasis. However, whether ultrasmall MoS2 quantum dots (QD) participate in preventing the impairment of the endothelial barrier elicited by pro-inflammatory stimuli and the associated underlying mechanisms remain elusive yet. Herein, we set out to explore the protective effects of MoS2 QD on inflammatory endothelial barrier dysfunction and macrophage plasticity. We revealed an inhibitory effect of MoS2 QD on endothelial barrier impairment and monocyte–endothelial cell interactions, including monocyte adhesion and transmigration, and this might be associated with a reduced activation of focal adhesion kinase (FAK). Importantly, using an in vitro macrophage polarization system, we revealed that MoS2 QD altered macrophage plasticity via inhibiting M1-macrophage polarization, and the reduction in nuclear factor-κB (NF-κB) activation and promotion of mitophagy by MoS2 QD was involved in preventing M1 macrophage polarization. Taken together, these findings suggested potential therapeutic applications of MoS2-based bioactive nanoagents to attenuate inflammatory endothelial barrier dysfunctions that are provoked by macrophage-mediated endothelial activation.

Active sites rich manganese doped MoS2 nanostructures with enhanced photodegradation of methylene blue dye

Pure and manganese (Mn) doped molybdenum disulphide (MoS2) was synthesized by the facile hydrothermal approach. The incorporation of Mn2+ ions without affecting the MoS2 crystal structure was verified from the XRD spectrum. The FESEM images revealed flower like hierarchical nanostructures with an increased surface area for 3% Mn doping. RAMAN and XPS analysis indicated edge terminated active sites for doped sample. A photocatalytic degradation of 97% is obtained for 3% Mn doped sample for methylene blue in 55 min. The edge terminated structures comprising rich active sites along with increased surface area is accounted to the enhanced photocatalytic activity. To the best of our knowledge, this is the first report of Mn doped MoS2 as an efficient photocatalyst for the degradation of methylene blue.

Defect-Engineered 3D Nanostructured MoS2 for Detection of Ammonia Gas at Room Temperature

Recent studies on nanostructured MoS2 show promising performance in the detection of reducing gases like ammonia (NH3). However, this material in the pristine form possesses limitations in terms of response, recovery, and repeatability over a long duration of time. Several attempts have been made to overcome these shortcomings by modifying it chemically to make a hybrid form or direct doping with other atoms. In this work, we demonstrate that suitable defect engineering of 3D nanostructured MoS2 induced by a low energy ion beam can lead to a significantly improved performance of sensing NH3 compared to the as-prepared one. Significant decreases in response and recovery times have been demonstrated at room temperature for the modified MoS2 compared to its pristine form, which shows its best response only at a higher temperature of about 200 °C. A 3D nanoflower-like structure of MoS2 was synthesized hydrothermally, which was coated on substrates, and then irradiated with 5 keV argon ions at different doses. While the ion beam-induced morphological modifications are observed via electron microscopic study, the surface defects are apparent in X-ray diffraction, Raman scattering, and X-ray spectroscopic studies. The ion beam-modified MoS2 shows a higher electrical conductivity and water-repelling nature compared to the pristine one, which are complementary properties for better sensing performance. While Monte Carlo-based 3D ion-solid interaction simulation was used to support the morphological modifications and defect developments after ion irradiation, the sensing mechanism and change in conductivity were successfully explained using density functional theory-based simulations.

Morphologically controlled photodetector performance of molybdenum disulfide nanostructures

The objective of this work is to control the morphology of molybdenum disulfide nanostructures using hydrothermal technique for improving the visible-light photodetector performance. The morphology comprises nanosheets with dimensions and packing density that are dependent on the synthesis temperature. As the synthesis temperature increases from 170 to 210 °C, the dimensional change of nanosheets is accompanied by increased packing density, as confirmed from scanning and transmission electron microscopy images. The dark current increases from 0.9 to 1.18 μA while the bright current increases from 78.57 to 112.59 μA as synthesis temperature increases from 170 to 210 °C. In addition, there is an improvement in all other parameters such as sensitivity, responsivity and detectivity of the photodetector with increase in synthesis temperature. The MoS2 based photodetectors revealed an ultrahigh sensitivity and responsivity of 95% and 11.25 mA/W, very high detectivity of 0.11 × 1011 Jones and fast rise-time and fall-time of around 0.5 and 0.7 ms respectively. X-ray diffraction and x-ray photoelectron spectroscopy studies reveal that there is no change either in the crystallographic texture or stoichiometry of the samples with change in morphology. It is, thus concluded that improved photodetector performance is entirely morphological in origin. The present work represents a facile method based on morphological control to improve the visible light photodetector performance of MoS2 nanostructures.

Neodymium doping MoS2 nanostructures with remarkable surface-enhanced Raman scattering activity

In recent years, the study of surface-enhanced Raman scattering (SERS) substrate on semiconductors has greatly broadened the application of SERS technology in different fields. Developing new practical semiconductor SERS substrates materials is still important work. Here, different concentrations of Nd-doped MoS2 were synthesized by a simple hydrothermal method. Compared with pure MoS2, doping Nd successfully enhanced the SERS signal. The Enhancement factor (EF) of the 2 at% Nd-doped MoS2 is up to ∼1.29 × 106 due to the energy level transition and charge transfer effect. High sensitivity SERS detection of bilirubin, dipterex, and bisphenol A (BPA) was realized, and the lowest detection concentration was 10−8 M. Moreover, 2 at% Nd doped MoS2 as SERS substrate can realize high sensitivity SERS detection of bilirubin, dipterex and bisphenol A (BPA), and the limit of detection (LOD) is 10−8 M, 10−9 M, and 10−9 M, respectively. Furthermore, 2 at% Nd-doped MoS2 SERS substrate has high uniformity and excellent reproducibility, which is beneficial for practical applications. This work not only provides an efficient technique to get sensitive, stable, and low-cost SERS substrates but also advantageous for many application scenarios.

Fabrication of sodium and MoS2 incorporated NiO and carbon nanostructures for advanced supercapacitor application

Transition metal oxides and carbonaceous nanocomposites have triggered enormous interest in the application of high-performance supercapacitors due to the outstanding electrical conductivity and superior theoretical capacitance. In this study, we prepared highly porous nanostructured NiO/C yolk-shell nanocomposites via a simple calcination of nickel-based metal-organic frameworks. The porosity and electrochemical property were further enhanced by incorporating sodium and hierarchical MoS2 nanostructures via a facile hydrothermal method. It was found that the as-synthesized Na-doped MoS2@NiO/C nanocomposites with hierarchical porosity exhibited superior electrochemical performance. Particularly, the delivered electrochemical capacitance of NiO/C yolk-shell structure was 1779.50 F g−1 in an aqueous electrolyte (2 M KOH), and a superior specific capacitance of 2540.63 F g−1 was acquired after the incorporation of sodium and 2D layered MoS2 into the nanocomposite. When a symmetrical supercapacitor was fabricated, a remarkable energy density of 36.93 Wh kg−1 was recorded in an environmental-friendly aqueous-based electrolyte. More significantly, the outstanding delivered capacitance retention and coulombic efficiency were 111.92 % and 97.6 %, respectively after 4000 continuous GCD cycles. Hence, the Na-doped MoS2@NiO/C with hierarchical porous nanostructures and extraordinary electrochemical performance was explicitly demonstrated in this study and can be utilized as electrode active materials in realizing high-performance supercapacitors.

Photocatalytic and Antimicrobial Performance Evaluation of Reusable MoS2 Nanoflowers under Visible Light

2D semiconductor material, Molybdenum Disulfide (MoS2), with unique properties similar to that of graphene, is considered as a potential candidate for photocatalytic and antimicrobial applications. In the current work, MoS2 was prepared by a simple hydrothermal method using sodium molybdate and thiourea as precursors. The calculated band gap values of MoS2 grown at 200 °C and 180 °C were 2.1 eV and 1.98 eV, respectively. Flower like morphology was observed from FESEM analysis. Multi layered structure of MoS2 was confirmed from the difference the peak value obtained for A1g and E1 2g vibrational modes observed from Raman spectra. The reusability of the synthesized MoS2 was analyzed against MB dye degradation. The pristine MoS2 removed ∼98% of the dye molecules from the water under the minimum wattage (20 W) of visible light in 180 min. The catalyst retained good stability even after the third degradation, confirming the reusability of MoS2. The disk diffusion method was used to evaluate the antimicrobial activity of the grown MoS2 nanostructures. The gram-positive and gram-negative bacteria used in present study were Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli and Bacillus serius. Investigation of the antibacterial activity of MoS2 against these four different pathogens was carried out in detail and the resistance function was measured.

Phase manipulation of two-dimensional MoS2 nanostructures

Phase manipulation of two-dimensional MoS2 nanostructures

Resolution of MoS2 Nanosheets-Induced Pulmonary Inflammation Driven by Nanoscale Intracellular Transformation and Extracellular-Vesicle Shuttles.

Pulmonary exposure to some engineered nanomaterials can cause chronic lesions as a result of unresolved inflammation. Among 2D nanomaterials and graphene, MoS2 has received tremendous attention in optoelectronics and nanomedicine. Here an integrated approach is proposed to follow up the transformation of MoS2 nanosheets at the nanoscale and assessstheir impact on lung inflammation status over 1 month after a single inhalation in mice. Analysis of immune cells, alveolar macrophages, extracellular vesicles, and cytokine profiling in bronchoalveolar lavage fluid (BALF) shows that MoS2 nanosheets induced initiation of lung inflammation. However, the inflammation is rapidly resolved despite the persistence of various biotransformed molybdenum-based nanostructures in the alveolar macrophages and the extracellular vesicles forup to 1 month. Using in situ liquid phase transmission electron microscopy experiments, the dynamics of MoS2 nanosheets transformation triggered by reactive oxygen species could be evidenced. Three main transformation mechanisms are observed directly at the nanoscale level: 1) scrolling of the dispersed sheets leading to the formation of nanoscrolls and folded patches, 2) etching releasing soluble MoO4 - , and 3) oxidation generating oxidized sheet fragments. Extracellular vesicles released in BALF are also identified as a potential shuttle of MoS2 nanostructures and their degradation products and more importantly as mediators of inflammation resolution.

A novel two-step route to unidirectional growth of multilayer MoS2 nanoribbons

Alkali-assisted chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) has been shown to promote the growth of large single crystals of TMD monolayers. The morphology control of TMDs is a key parameter for the scalable synthesis of versatile layered materials. This work demonstrates that the alkali-assisted synthesis provides a route toward fabricating highly crystalline MoS2 nanoribbons. Our proposed method involves a vapour-liquid–solid phase reaction between MoOx(2 < x < 3) precursors grown by Pulsed Laser Deposition (PLD) and metal alkali halide (i.e., NaF). The growth process evolves via the emergence of the Na–Mo–O liquid phase, which mediates the formation of MoS2 multilayer nanoribbons in a sulfur-rich environment. Moreover, the as-grown MoS2 nanoribbons are surrounded by mono- and multilayer triangles of MoS2 and exhibit a preferential alignment defined by both MoS2 crystal symmetry and the underlying Al2O3 substrate. In addition, we observe a significant built-in strain in the as-grown MoS2 nanostructures, which increase in magnitude from the multilayer nanoribbons to the triangular monolayers, and which can be effectively released upon transfer onto another substrate. The growth method developed here can enable flexibility in designing nanoelectronic devices based on TMDs with tunable dimensions.

Layer Dependence of Thermally Induced Quantum Confinement and Higher Order Phonon Scattering for Thermal Transport in CVD-Grown Triangular MoS2

Heat dissipation and electron–phonon interaction hindering the charge carrier mobility are serious constraints for the fabrication of various integrated electronic and optoelectronic devices based on two-dimensional (2D) materials. In this paper, we examine the quantum confinement and phonon anharmonicity of different-layered MoS2, synthesized via the chemical vapor deposition technique. We explore the contribution of spin–orbit and interlayer couplings both theoretically (first-principles density functional theory) and experimentally (Raman and photoluminescence spectroscopies). Further, we demonstrate the thermally driven layer-dependent bandgap tunability in (1L, 3L, and 5L) triangular MoS2 grown over the SiO2/Si substrate. We have also scrutinized their phonon confinement behavior and thermal response in a low-temperature regime (80–300 K) using the optothermal Raman spectroscopy technique. A semiquantitative model comprising the volume and temperature effect provides insights into the nonlinear temperature-dependent phonon anharmonicity, revealing that the contribution of higher order (three) phonon scattering reduces with increasing layer numbers in MoS2. We further measure the interfacial thermal conductance (g) and thermal conductivity (ks) of synthesized MoS2, and the obtained values of g (and ks) are observed to increase (and decrease) with increasing layer number. Our study will advance the understanding of anharmonic behavior of phonons in different-layered MoS2 nanostructures for designing MoS2-based next-generation devices for various applications.

Modulating the HER-overpotential at the interface of nanostructured MoS2 synthesized via hydrothermal route: An in-situ mass-spectroscopy approach

Hydrogen evolution reaction (HER) using a new exfoliated in-situ and amine-functionalized MoS2 prepared via a hydrothermal method, assisted with sonication treatment, is reported. Techniques such as XRD, RAMAN, FTIR, XPS, N2-physisorption and HRTEM, confirmed the production of different MoS2 samples. Depending on the material, the overpotential for HER was modified; this was also observed for selected samples concerning the acid solution (HNO3, H2SO4, HCl, and HClO4), as demonstrated using linear sweep voltammetry and Tafel approach. The faradic current observed was in the order IHCLO4 > IHCl > IH2SO4 > IHNO3; whereas the charge-transfer resistance (ohms) was RHNO3 (29816) > RH2SO4 (311.5) > RHCl (167.7) > RHCLO4 (167.7). It was found (using DEMS) that protons (m/z = 1) modulated the generation of hydrogen (m/z = 2) at H2SO4, HCl, and HClO4 solutions; conversely, at HNO3 electrolyte, the reduction of NO3− to nitrogen was activated, delaying HER-kinetic.