MoS2 Nanostructures Research Articles

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.

Nanobelt and nanoplatelet structured molybdenum disulfide thin film as a saturable absorber under nanopulsed green laser excitation

Demonstration of saturable absorption (SA) in MoS2 thin films with varying NLO coefficients as a function of reaction time of hydrothermal method is made using the open aperture Z-scan technique. Under nanosecond pulsed laser excitation (532 ​nm, 9 ns, 10 HZ), saturable absorption occurred involving the overtone of electron - hole pair state and band edge state of MoS2. Further higher ground state cross-section than excited state cross-section favors SA process in MoS2 thin films. The strong saturable absorption behaviors of nanobelt like structured MoS2 film could be attributed to the coexistence of 1T and 2H crystal phases and lower dimension morphology that allows more photons to transit to the higher energy state. Earlier the fabrication of MoS2 thin film on a FTO substrate with a varying reaction time of the hydrothermal technique such as 24, 36, 48 and 60 ​h was made. Raman spectrum has two sets of characteristics vibration representing the metallic 1T – octahedral coordination Oh phase and the semiconducting 2H – trigonal prismatic D3h phase. XRD and Raman studies confirm the formation of mixed phases of MoS2 with 1T phase dominating over 2H phase in MoS2 thin films. Here the absorbance and band gap of the MoS2 thin film increased with increase in reaction time. The luminescence spectra exhibit prominent peaks at 594 ​nm and 621 ​nm resulting from a direct bandgap transition and they are mostly due to the VBM splitting at the K-point. All the films exhibit maximum absorbance in the UV region (291 ​nm) due to the excitonic features of MoS2 and notable absorbance in the visible region (680 ​nm) due to the overtones of MoS2 ‘s electron-hole pair. SEM images confirm that nanoplatelet and nanobelt structured MoS2 was formed with varying size with respect to reaction time. Furthermore, while the nanoplatelet structure faded, nanobelts were grown for a prolonged reaction time. Thus, MoS2 nanostructure coated thin film would be useful for the design of saturable absorbers for fabricating optical switches and mode locking devices.

Dual mode detection of a glucose molecule using MoS2/NiO electrode

In this article, we demonstrate detection of a glucose molecule present in an alkaline medium at very low concentration (8–10 µM) using commercially available carbon-based paper electrodes. For the effective detection of a glucose molecule the active area of a paper electrode was modified using hydrothermally synthesized NiO nano layers and the NiO nano layers decorated by MoS2 nanostructures. To grow MoS2 nanostructures on NiO nano layers pulsed laser deposition technique was used. The cyclic voltammetry measurements recorded using paper electrode (where active area is modified using NiO layers decorated with MoS2 nanostructures) showed presence of two distinct redox peaks. Appearance of redox peaks at different potentials indicates the oxidation of a glucose molecule via two different mechanisms. Based on the cyclic voltammetry results observed herewith and comparing it with our previously reported results, for the first time we propose the dual mode electrocatalytic activity that may occur on the surface of electrode materials.

Effect of sulfur precursors on hydrothermal growth of MoS2 nanostructures and its visible-light-driven photocatalytic activities

The molybdenum disulfide (MoS2) nanostructures such as nanosheets, nanoflowers, nanoparticles, and nanoflakes are promising candidate materials for environmental pollution control. In this work, the effect of sulfur precursors i.e. thioacetamide, thiourea, and elemental sulfur on the morphology of hydrothermally grown MoS2 material was studied followed by their visible-light-driven photocatalytic activities toward methyl orange (MO) dye degradation at ambient conditions. Interestingly under scanning electron microscope (SEM) images, the morphologies of synthesized materials were seen to consist of systematic nanosheets, aggregates, and agglomerates. Raman spectroscopy and XRD studies suggested that the grown materials were composed of primarily 1T-2H mixed phase of MoS2 along with a minor oxide phase of molybdenum. Moreover, photocatalytic MO dye degradation activities exhibited by thioacetamide-grown MoS2 nanostructures were found to be better than those of elemental sulfur and thiourea counterparts. The kinetic rates of degradation towards MO dye by materials synthesized with thioacetamide, elemental sulfur, and thiourea were found to be 0.00804 min−1, 0.00614 min−1, and 0.00531 min−1, respectively. The relatively better photocatalytic activities exhibited by thioacetamide-grown MoS2 material were attributed to its predominant nanosheet morphology and the presence of a greater amount of MoS2 contents. This work will be helpful for a better understanding of morphological control hydrothermal synthesis of MoS2-based materials and their subsequent organic dye degradation activities.

Synthesis of the Elusive Doublewall Nanotubes and Nanocones(Horns) of MoS2 via Focused Solar Ablation (Adv. Mater. Interfaces 3/2023)

Fundamentally Small MoS2 Nanostructures In article number 2201930 by Gilles Flamant, Jeffrey M. Gordon, Reshef Tenne, and co-workers, highly concentrated sunlight focused onto a mixture of MoS2 and MoO3 is used to generate previously elusive MoS2 nanostructures, most notably doublewall MoS2 nanotubes (shown) and nanocones (horns). The far from equilibrium conditions achieved in the high-temperature solar furnace (shown) create the special reactor conditions amenable to their synthesis. DFT calculations support the experimental findings.

Environmental gas sensing studies using flower-like MoS2 hybrid structure

Molybdenum disulfide (MoS2) is one of the most potent transition metal dichalcogenide (TMDc) material for gas sensing applications due to its various advantageous properties. It exhibits modest electron mobilities, reduced dimensionality, and favorable mechanical properties. The deposition of metal nanoparticles on nanostructured MoS2 leads to the modification in their sensing properties. By keeping in view, present work reports the fabrication of stable MoS2 nanoflowers (MNF) and their hybrids (Au-MoS2 nanoflowers). The hydrothermal approach was used to synthesize MNF nanostructures and in order to form the hybrid Au-MoS2 nanoflower (AuMNF) Au nanoparticle were deposited over MNF by an inert gas evaporation method. X-ray Diffraction and micro–Raman spectroscopy were used to study MNF and AuMNF hybrid structures. XRD found MoS2 1 T-2H mixed-phase. The peak shift and broadening in E1g, J3, and E3g modes for AuMNF hybrids was observed compared to MNF. The flower-like morphology of the pristine and hybrid nanostructures was confirmed via the Scanning electron microscopy (SEM) technique and transmission electron microscopy (TEM). Furthermore, the fabricated samples MNF and AuMNF hybrids were investigated for environmental gas sensing. According to the results of the gas sensing tests, the AuMNF hybrid provides the best sensing response. The gas sensing measurements revealed that the best sensing response is found from the AuMNF hybrid. This hybrid shows a response of 21.2 % in the presence of CO, which is 5.5 times higher than the response of pure MoS2. These findings contribute to a better interpretation of how the resistance of MoS2 nanostructures reacts towards CO gas exposure. These findings contribute to a better interpretation of how the resistance of MoS2 nanostructures reacts towards CO gas exposure.

Enhanced electrocatalytic hydrogen evolution from nitrogen plasma-tailored MoS2 nanostructures.

Two-dimensional (2D) layered transition metal dichalcogenides such as MoS2 have been viewed as the most favorable candidates for replacing noble metals in catalyzing the hydrogen evolution reaction in water splitting owing to their earth abundance, superb chemical stability, and appropriate Gibbs free energy. However, due to its low number of catalytic sites and basal catalytic inertia, the pristine MoS2 displayed intrinsically unsatisfactory HER catalytic activity. Here, the hydrogen evolution catalytic activities of nanostructured MoS2 powder before and after plasma modification with nitrogen doping were experimentally compared, and the influence of treatment parameters on the hydrogen evolution catalytic performance of MoS2 has been studied. The feasibility of regulating hydrogen evolution catalytic activity by nitrogen doping of MoS2 was verified based on density functional theory calculations. Our work demonstrates a more convenient and faster way to develop cheap and efficient MoS2-based catalysts for electrochemical hydrogen evolution reactions. Additionally, theoretical studies reveal that N-doped MoS2 exhibits strong hybridization between Mo-d and N-p states, causing magnetism to evolve, as confirmed by experiments.

An Efficient, Short Stimulus PANC-1 Cancer Cell Ablation and Electrothermal Therapy Driven by Hydrophobic Interactions.

Promising results in clinical studies have been demonstrated by the utilization of electrothermal agents (ETAs) in cancer therapy. However, a difficulty arises from the balance between facilitating the degradation of ETAs, and at the same time, increasing the electrothermal performance/stability required for highly efficient treatment. In this study, we controlled the thermal signature of the MoS2 by harnessing MoS2 nanostructures with M13 phage (MNM) via the structural assembling (hydrophobic interaction) phenomena and developed a combined PANC-1 cancer cell-MNM alternating current (AC)-stimulus framework for cancer cell ablation and electrothermal therapy. A percentage decrease in the cell viability of ~23% was achieved, as well as a degradation time of 2 weeks; a stimulus length of 100 μs was also achieved. Molecular dynamics (MD) simulations revealed the assembling kinetics in integrated M13 phage-cancer cell protein systems and the structural origin of the hydrophobic interaction-enabled increase in thermal conduction. This study not only introduced an 'ideal' agent that avoided the limitations of ETAs but also provided a proof-of-concept application of MoS2-based materials in efficacious cancer therapy.

Low-frequency vibration induced piezoelectric boost to photocatalytic hydrogen evolution through 2D-2D-stacked MoS2-carbon nitride

MoS2-carbon nitride heterostructures which are highly sensitive to low-frequency vibration are demonstrated to be the catalysts for piezo-photocatalytic hydrogen evolution reaction (HER). The configuration of MoS2 nanostructure on carbon nitride plays a crucial role in the piezo-photocatalytic HER activity of MoS2-carbon nitride heterostructure. With the cocatalyst of Pt NPs on the carbon nitride portion, 2D-2D stacked MoS2-carbon nitride catalyst exhibits considerably higher HER rate compared to the pristine carbon nitride and MoS2 nanoflower (NF)-carbon nitride catalysts under illumination coupling with the mechanical energy of vortex-induced shearing force. Experimental and calculation results indicate that the MoS2 nanosheets mainly perform as the piezopotential generator to induce an electric field in the carbon nitride counterpart. With the configuration of 2D-2D stacking, the light harvesting of carbon nitride in the heterostructure remains the same as the pristine one. Nevertheless, the recombination of photogenerated electron-hole pairs in the carbon nitride portion of the MoS2-carbon nitride heterostructure is inhibited due to the electric field induced by MoS2 nanosheet under low-frequency vortex vibration, resulting in the significantly boosted HER rate obtained from the 2D-2D stacked MoS2-carbon nitride heterostructure.

Enhancing energy storage capabilities of MoS2 nanoflowers through designing nanoarchitecture by controlling synthesis growth parameters

Among transition metal dichalcogenides, molybdenum disulfide (MoS2) is considered as the most cost-effective electrode material for energy storage applications such as supercapacitors and supercapatteries. The layered morphology, intrinsic high surface area and edge sites favour the enhanced energy storage performance of MoS2 nanostructures. Low-cost, solution based hydrothermal synthesis has been considered as the most attractive route for the growth of exotic MoS2 nanostructures for their potential applications in energy storage devices. Yet, the performance of an electrode in a supercapacitor is related to the structural aspects such as morphology, crystallinity and phase which in turn can be tailored suitably by altering the synthesis conditions. Here in, we report a detailed study on the role of synthesis parameters such as reaction time, temperature and precursor amount on the capacitive performance of MoS2 nanoflowers by one-step hydrothermal synthesis. The morphological and structural analysis of the samples were carried out using various characterization techniques including electron microscopy, X-ray diffraction, Raman, UV–Visible and X-ray photoelectron spectroscopy. Tuning the inter-layer spacing by altering the synthesis conditions of MoS2 nanoflowers resulted in the enhanced charge storage performance. A superior value of specific capacitance ~215 F/g with high power density of ~1 kW/kg with an energy density of ~30 Wh/kg, respectively, have been achieved for bare MoS2 nanoflowers, simply by tailoring the synthesis conditions.

In-Situ Assembly of MoS2 Nanostructures on EHD-Printed Microscale PVDF Fibrous Films for Potential Energy Storage Applications.

Three-dimensional (3D) printing has been widely utilized to fabricate free-standing electrodes in energy-related fields. In terms of fabrication, the two most challenging limitations of 3D printed electrodes are the poor printing resolution and simple structural dimension. Here we proposed a novel process to fabricate molybdenum disulfide-polyvinylidene fluoride (MoS2-PVDF) hierarchical electrodes for energy storage applications. The 20-layer microscale PVDF films with a stable fiber width of 8.3 ± 1.2 μm were fabricated by using electrohydrodynamic (EHD) printing. MoS2 nanostructures were synthesized and assembled on the microscale PVDF fibers by using hydrothermal crystal growth. The structural and material investigations were conducted to demonstrate the geometrical morphology and materials component of the composite structure. The electrochemical measurements indicated that the MoS2-PVDF electrodes exhibited the typical charge-discharge performance with a mass specific capacitance of 60.2 ± 4.5 F/g. The proposed method offers a facile and scalable approach for the fabrication of high-resolution electrodes, which might be further developed with enhanced specific capacitance in energy storage fields.

Deterministic Thermal Sculpting of Large‐Scale 2D Semiconductor Nanocircuits

Abstract2D transition metal dichalcogenide semiconductor (TMDs) nanocircuits are deterministically engineered over large‐scale substrates. This original additive nanolithography approach combines large‐area physical growth of 2D TMDs layer with high resolution thermal‐scanning probe lithography, to reshape the ultra‐thin semiconducting layers at the nanoscale level. The additive nanofabrication of few‐layer MoS2 nanostructures of controlled thickness, grown in the 2H‐semiconducting phase, is demonstrated as shown by their Raman vibrational fingerprints and by their optoelectronic response. The electronic signatures of the MoS2 nanostructures are locally identified by Kelvin probe force microscopy providing chemical and compositional contrast at the nanometer scale. Finally, the potential role of the 2D TMDs nanocircuits as building blocks of deterministic 2D semiconducting interconnections is demonstrated by high‐resolution local conductivity maps showing the competitive transport properties of these large‐area nanolayers. This work thus provides a powerful approach to scalable nanofabrication of 2D nano‐interconnects and van der Waals heterostructures, and to their integration in real‐world ultra‐compact electronic and photonic nanodevices.

Synthesis of the Elusive Doublewall Nanotubes and Nanocones(Horns) of MoS2 via Focused Solar Ablation

AbstractThe synthesis of fundamentally small MoS2 nanotubes and nanocones(horns) that have proven elusive in prior studies has been achieved via ablation of a precursor mixture of crystallites of MoS2 + MoO3 by highly concentrated solar radiation. The special far‐from‐equilibrium conditions achieved in the solar furnace prove conducive to the generation of these singular nanostructures. Extensive electron microscopy and characterization results (transmission electron microscopy (TEM), electron diffraction (ED), X‐ray diffraction (XRD), scanning TEM (STEM), and high angle annular dark field (HAADF)) reveal a range of nanoparticle shapes and sizes based on which reaction mechanisms are proposed. Molecular dynamics simulations indicate that the sizable thermal fluctuations intrinsically produced in the high‐temperature solar reactor soften the MoS2 nanostructures, yielding corrugated layers that favor nanostructures with only a few layers, in agreement with the experimental observations.

In Situ Assembly of Well-Defined MoS2 Slabs on Shape-Tailored Anatase TiO2 Nanostructures: Heterojunctions Role in Phenol Photodegradation

MoS2/TiO2-based nanostructures have attracted extensive attention due to their high performance in many fields, including photocatalysis. In this contribution, MoS2 nanostructures were prepared via an in situ bottom-up approach at the surface of shape-controlled TiO2 nanoparticles (TiO2 nanosheets and bipyramids). Furthermore, a multi-technique approach by combining electron microscopy and spectroscopic methods was employed. More in detail, the morphology/structure and vibrational/optical properties of MoS2 slabs on TiO2 anatase bipyramidal nanoparticles, mainly exposing {101} facets, and on TiO2 anatase nanosheets exposing both {001} and {101} facets, still covered by MoS2, were compared. It was shown that unlike other widely used methods, the bottom-up approach enabled the atomic-level growth of well-defined MoS2 slabs on TiO2 nanostructures, thus aiming to achieve the most effective chemical interactions. In this regard, two kinds of synergistic heterojunctions, namely, crystal face heterojunctions between anatase TiO2 coexposed {101} and {001} facets and semiconductor heterojunctions between MoS2 and anatase TiO2 nanostructures, were considered to play a role in enhancing the photocatalytic activity, together with a proper ratio of (101), (001) coexposed surfaces.

Study on Nickel-induced 1T/2H MoS2 nanostructures in realizing efficient electrocatalysts for hydrogen evolution reaction

• Rational design and successfully prepared Ni-induced 1T/2H MoS 2 . • Ni-induced 1T/2H MoS 2 exhibits efficient HER catalytic performance. • The Ni-ions are favorable for enhancing the HER performance. Two-dimensional (2D) molybdenum disulfide (MoS 2 ) catalysts have gained great attention in several applications due to their unique properties as well as their tunable electronic structures. Fabrication of cost-effective and highly efficient electrocatalysts is vital for water splitting. Herein, we have synthesized nickel (Ni) induced mixed-phase (1T/2H) MoS 2 by solvothermal method and have studied its characteristics to be used for hydrogen evolution reaction (HER). The doping of Ni in MoS 2 is aimed at increasing the efficiency of HER performance and it has been proved to be a highly effective HER catalyst in an acidic medium. Ni-doped (9%) MoS 2 achieved the lowest overpotential of 127 mV for the HER at 10 mA cm −2 and a Tafel slope of 86 mV dec -1 among the other concentrations of Ni-doping studied. This work demonstrates the constructive outcome of doping the catalyst for HER and provides a pragmatic way for obtaining earth-abundant electrocatalysts.