Ultrathin Molybdenum Disulfide Research Articles

Efficient activation of peroxymonosulfate by molybdenum disulfide cocatalysis of Co and N co-doped porous carbon for degrading perfluorooctanoic acid: Synergistic effect of Co and N by molybdenum and its mechanism

In this study, precursor ultrathin molybdenum disulfide nanosheets and ZIF-67 was selected to prepare Co and N co-doped porous carbon by the support of Mo (MoS2/Co@NPC) to activate peroxymonosulfate (PMS) for perfluorooctanoic acid (PFOA) degradation. The morphology, crystal form and composition of MoS2/Co@NPC are studied by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and other methods. In MoS2/Co@NPC/PMS process, PFOA was completely degraded in 180 min at pH 7, 0.3 g/L catalyst, 0.1 mM PMS and reaction temperature of 25 °C. The degradation efficiency was much higher than that in other systems. The oxidative species for PFOA degradation was studied using free radical quenching experiments and electron paramagnetic resonance (ESR) tests. SO−4 plays a major role in the degradation of PFOA, OH plays an auxiliary role, and 1O2 contributes the least. The effect of different types and positions of cobalt‑nitrogen and molybdenum atoms on the electrocatalytic activity was investigated by density functional theory (DFT) calculations. The co-doping of Co and N into carbon-based materials can synergistically enhance by Mo for the activation of PMS. The unsaturated S atoms on the surface of metal sulfides can trap protons to form H2S while exposing the reducing metal active site, which also accelerates the rate-limiting step of the Co3+/Co2+ conversion. The core-shell structure of Co@NPC doped with Mo has the characteristics of improving the electron transfer ability of carbon, promoting the mass transfer of reactants, and preventing cobalt metal agglomeration and metal dissolution. The degradation pathways of PFOA were investigated and three possible pathways were proposed. In addition to PFOA, MoS2/Co@NPC-800/PMS system can also remove contaminant in pharmaceutical wastewater, indicating that the process has potential application value in practical wastewater treatment.

Synthesis and tribological properties of the novel tubular MoS2/GR nanocomposite

This study used a simple one-step hydrothermal method to synthesize the MoS2/GR composites with a new morphology composed of graphene nanotubes and ultra-thin molybdenum disulfide with the help of sodium chloride. The composites were characterized by XRD, XPS, SEM, TEM, and a series of characterization methods. Meanwhile, the tribological properties of the composites were studied. The results show that the addition of 1% MoS2/GR composite nanotubes has excellent tribological properties. In addition, the structure and excellent tribological properties of MoS2-C- nanocomposite lubrication materials will be conducive to designing new nanomaterials with 2D/3D structures, enhancing the anti-friction and anti-wear properties, and expanding their practical applications in industrial and agricultural fields.

Assessing the Optical Properties of 2D MoS2 Nanosheets Synthesized Using Facile Two-Step Sequential Process

Among 2D Transition Metal Dichalcogenides (TMDs), ultrathin molybdenum disulfide (MoS2) nanosheets are well researched in terms of synthesis, characterization and applications owing to its unique properties in contrast to the bulk material. Here, 2D MoS2 suspensions are prepared via grinding-assisted liquid phase exfoliation. The processing parameters like initial concentration of MoS2 powder, grinding hours, solvent and high-power sonication are optimized for efficient and scalable production of MoS2 nanosheets. The suspensions are characterized for their optical and structural properties and are compared to analyze the effect of synthesis conditions on the properties of the obtained samples. The bandgap of the synthesized MoS2 lies above 2.0 eV in contrast with a bandgap of 1.57 eV for bulk sample. The difference between the peaks corresponding to in-plane and out-of-plane vibration modes is lower than bulk sample depicting the formation of mono to few-layered MoS2. It is found that grinding-assisted sonication in NMP solvent is the most efficient method to produce low-dimensional nanosheets. The well dispersed MoS2 nanoflakes can be blended with other nanomaterials to prepare hybrid dispersions and can thus be explored for optoelectronic applications.

Photo-/piezo-activated ultrathin molybdenum disulfide nanomedicine for synergistic tumor therapy.

Molybdenum disulfide (MoS2), as a transition metal dichalcogenide, has attracted tremendous attention owing to its remarkable electronic, physical, and chemical properties. In this study, based on the energy-converting nanomedicine, we report multifunctional two-dimensional (2D) MoS2 nanosheets with inherent plasmonic property and piezocatalytic activity for imaging-guided synergistic tumor therapy. MoS2 nanosheets display strong plasmon resonances in the near-infrared (NIR) region, especially in the second NIR biological window, possessing a notable light energy to heat effect under 1064 nm laser irradiation, which not only serves as a robust photothermal agent for cancer cell ablation but also acts as a contrast-enhanced agent for thermal imaging and photoacoustic imaging. Meanwhile, MoS2 nanosheets feature a remarkable piezotronic effect, exhibiting mechanical vibration energy to electricity under the stimulation of ultrasound-mediated microscopic pressure for reactive oxygen species generation to further kill cancer cells. The new function for old materials may open up the in-depth exploration of MoS2-based functional biomaterials in the future clinical application of imaging-guided photothermal and piezocatalytic synergetic treatment.

Design and Investigation of Double Gate Field Effect Transistor Based H2 Gas Sensor Using Ultra-Thin Molybdenum Disulfide

In this article, a low-power hydrogen (H2) gas sensor has been proposed using a two-dimensional (2D) material based Double Gate Field Effect Transistor (2D-FET). It is imperative to highlight that the conventional three-dimensional (3D) materials cannot be scaled down to an ultra-low dimension due to the presence of dangling bonds, surface roughness scattering etc. This creates a major challenge in developing low-dimensional sensors for next generation sensing and computing. In this context, we have developed an extensive simulation model, which articulates the physical phenomena behind a catalytic metal gate-based hydrogen gas sensor using a 2D-FET. A 5 nm thin Molybdenum disulfide (MoS2) film has been used as the channel material for the proposed 2D-FET based gas sensor. The sensor has been modelled by emphasizing on the catalytic metal (Palladium) gate approach, where the work function of the gate metal deposited on top of the channel region varies after the absorption of the hydrogen gas. Moreover, the Technology Computer Aided Design (TCAD) based gas sensor model has been developed by considering a change in the pressure of H2 gas as well. We have also highlighted the effect of Metal/MoS2 contact on sensor performance. In terms of the performance, a maximum threshold voltage (Vth) shift of 100 mV has been obtained against a gas pressure of 10−10 torr, whereas the maximum percentage of change in ION/IOFF is 100. Lastly, the authors have shown the thermal noise characteristics of the gas sensor.

Construction and tribological properties of 2D heterojunction of g-C3N4/MoS2 nanocomposites

2D/2D heterojunction of flower-like MoS2 nanosheets anchored on g-C3N4 was fabricated through a facile hybridization approach, and systematically investigated by various characterization methods (e.g. XRD, SEM, TEM and XPS analysis). Furthermore, tribological properties of g-C3N4/MoS2 composites containing with liquid paraffin were comparatively measured by UMT-2 multispecimen friction and wear tester, and various tribological variables including additive concentration, applied load and rotational speed were also investigated in details. Among all samples, 2%-g-C3N4/MoS2 composites exhibit the minimal friction coefficient (~0.08), and the anti-wear performance is improved obviously. The improvement of tribological properties of the base oil is due to the synergistic effect of g-C3N4 and ultra-thin molybdenum disulfide nanosheets. This study provides a new idea for the design of two-dimensional layered composites with enhanced tribological properties of lubricating oil and matrix.

Ultrathin, transparent, flexible, and dual-side white light-responsive two-dimensional molybdenum disulfide quantum disk light-emitting diodes

Ultrathin, transparent, and flexible devices with multifunctionalities are indispensable for emerging technologies. However, the related reports are very few, and the efficiency is rather limited owing to material restriction and complicated fabrication processes. In this work, a light-responsive white light-emitting diode (LED) with ultrathin, transparency, dual-side emission, and flexible characteristics based on graphene-insulator-semiconductor (GIS) structure is demonstrated. The GIS light-responsive white LED consists of highly luminescent histidine-doped two-dimensional molybdenum disulfide (MoS2) quantum disks, an Al2O3 insulating layer, and a graphene transparent electrode. By applying an external bias, it enables to generate white light emission with a high emission efficiency of around 9%. The underlying mechanism can be well understood by quantum tunneling. In addition, the GIS structure also shows good durability under a bending test of 200 cycles. Unlike conventional white LEDs, which always required multiple emissive layers, our GIS light-responsive LED is only based on a single emissive material of histidine-doped MoS2 quantum disks, which possess a broadband emission property and low toxicity. Therefore, with the superior multiple functionalities, our study shown here is very useful for the future development of next-generation optoelectronic devices.

Self-sustaining MoS2 nanomechanical oscillators and feedback cooling

We report on the experimental demonstration of self-sustaining feedback oscillators referenced to ultrathin molybdenum disulfide (MoS2) nanomechanical resonators vibrating in the ∼10 to 20 MHz range. Based on comprehensive open-loop characterization of MoS2 resonators with dynamic ranges up to 85 dB, self-sustaining oscillators are constructed by incorporating the MoS2 resonators into an optoelectronic feedback circuitry. The prototyped MoS2 self-sustaining oscillators generate stable radio frequency waveforms with frequency stability (measured in Allan deviation) down to ∼2 × 10−5 and phase noise mainly limited by electronic thermal noise. Beyond self-sustaining oscillations, we demonstrate feedback cooling of thermomechanical motion of a bilayer (2L) MoS2 resonator from 300 K to 255 K by tuning the phase in the feedback, suppressing or “squashing” the noise level of the system.

Covalent Pinning of Highly Dispersed Ultrathin Metallic-Phase Molybdenum Disulfide Nanosheets on the Inner Surface of Mesoporous Carbon Spheres for Durable and Rapid Sodium Storage.

Two-dimensional (2D) transition-metal dichalcogenide materials show potential for use in alkali metal ion batteries owing to their remarkable physical and chemical properties. Nevertheless, the electrochemical energy storage performance is still impaired by the tendency of aggregation, volume, and morphological change during the conversion reaction and poor intrinsic conductivity. Until now, ultrathin molybdenum disulfide nanosheets with a metallic-phase structure on the inner surface of mesoporous hollow carbon spheres (M-MoS2@HCS) have rarely been investigated as an anode for sodium-ion batteries. In this work, a novel M-MoS2@HCS anode was designed and synthesized by employing a template-assisted solvothermal reaction. Structural and chemical analyses indicate that the M-MoS2 nanosheets with a larger interlayer spacing compared to their semiconductor counterpart grow on the inner surface of HCS via covalent interactions. When used as the anode materials for Na+ storage, the M-MoS2@HCS anode presents durable and rapid sodium storage properties. The developed electrode shows a reversible capacity of 291.2 mAh g-1 at a high current density of 5 A g-1. After 100 cycles at 0.1 A g-1, the reversible capacity is 401.3 mAh g-1 with a capacity retention rate of 79%. After 2500 cycles at 1.0 A g-1, the electrode still delivers a reversible capacity of 320.1 mAh g-1 with a capacity retention rate of 75%. The excellent sodium storage capability of the MoS2@HCS electrode is explained by the special structural design, which reveals great potential to accelerate the practical applications of transition-metal dichalcogenide electrodes for sodium storage.

Synthesis of 1D-MoS2/graphene nanotubes aided with sodium chloride for reversible lithium storage

A novel negative material consisting of graphene nanotubes and ultrathin MoS2 is synthesized by a simple one-step hydrothermal method assisted with Sodium chloride. The MoS2/Graphene electrodes deliver a specific capacity of 1350 mAh g−1 under 0.1 A g−1 and high rate capability (retaining 85.5% capacity from 0.1 A g−1 to 0.8 A g−1). A high remarkable capacity of 820 mAh g−1 can still be recovered at 0.5 A g−1 after 500 cycles, and the average coulombic efficiency was as high as 99.98% during the additional 500 cycles. The excellent Li-ion storage performance of MoS2/Graphene nanotubes may be attributed to the ultra-thin MoS2 flakes and curled graphene nanotubes. This structural feature has a strong adsorption capacity for lithium ions, which can provide a broad space for ion storage. A large number of active sites dispersed in the layered molybdenum disulfide promote the kinetics of the electrochemical reaction, empowering the ultra-thin layered molybdenum disulfide to get a higher theoretical capacity. In addition, the existence of the tubular structure alleviates volume expansion and provides a way for the rapid movement of electrons and diffusion of Li+ during repeated cycles.

Carbon nanotubes-reinforced preparation of flat MoS2 nanomaterials: Co-enhancement of acoustic exfoliation efficiency and dye removal capacity

A novel and effective preparation technology was developed to prepare ultrathin molybdenum disulfide (MoS2) crystals with a high yield of the top-down exfoliation. Multidimensional carbon nanotubes (MWCNTs) were selected to be an assistant to enhance the effect of the traditional ultrasonic exfoliation efficiency. The rough and messy tubes strengthened the shear force in some parts during the acoustic treatment, which helped to weaken the van der Waals force between the MoS2 layers. Excitingly, this high-efficiency strategy can increase the dispersion concentration of nanosheets by 15 times compared to the traditional acoustic production, which represented the preparation yield was improved greatly. It is found that the addition of MWCNTs not only facilitated the exfoliation efficiency of bulk material but also indirectly improved the adsorption of malachite green (MG) in wastewater. With a maximum removal capacity of 87.80 mg g−1, the adsorption ability of the nanotubes-reinforced layered adsorbent was effectively strengthened. In addition, the performance of reproducibility, stability, functioning free radical types, and the adsorption models were systematically studied.

Thickness-Dependent Photocatalysis of Ultra-Thin MoS2 Film for Visible-Light-Driven CO2 Reduction

The thickness of transition metal dichalcogenides (TMDs) plays a key role in enhancing their photocatalytic CO2 reduction activity. However, the optimum thickness of the layered TMDs that is required to achieve sufficient light absorption and excellent crystallinity has still not been definitively determined. In this work, ultra-thin molybdenum disulfide films (MoS2TF) with 25 nm thickness presented remarkable photocatalytic activity, and the product yield increased by about 2.3 times. The photocatalytic mechanism corresponding to the TMDs’ thickness was also proposed. This work demonstrates that the thickness optimization of TMDs provides a cogent direction for the design of high-performance photocatalysts.

Ultrathin MoS2 nanosheet as co-catalyst coupling on graphitic g-C3N4 in suspension system for boosting photocatalytic activity under visible-light irradiation

In this study, ultrathin molybdenum disulfide (MoS2) nanosheets with thickness of 1.6–8.8 nm were obtained by liquid-phase exfoliating bulk MoS2. Then, they were employed as cocatalyst to build ultrathin MoS2/g-C3N4 heterojunction by self-assembly method. The degradation reaction of chlorimuron-methyl herbicide and tetracycline antibiotics under visible light was used to evaluate the photocatalytic properties of ultrathin MoS2/g-C3N4. The results showed that ultrathin MoS2/g-C3N4 composite exhibit superior photocatalytic performance. The MoS2/g-C3N4 composite with 15 wt% of ultrathin MoS2 nanosheet exhibited the highest degradation efficiency with 90.4% for chlorimuron-ethyl and 91.7% for tetracycline in 45 min under simulated sunlight, which was 8.8 times and 13.4 times than that of bare g-C3N4, respectively. The outstanding photocatalytic activity of ultrathin MoS2/g-C3N4 heterojunction thanks to the unique features of ultrathin MoS2 nanosheet that it harvesting the entire visible light, increasing the contact surface area with the support and shortened the electron and ion migration length, as well as more exposed edge sulfur atoms as redox centers. The radical scavenger experiments showed that •OH and •O2- plays a key role in the photocatalytic degradation process. This study provides a new idea for the design of high-activity a co-catalyst, that is, ultrathin MoS2 nanosheet has a significant influence on the photocatalytic performance of MoS2/g-C3N4 heterostructure photocatalyst.

A Current–Voltage Model for Double Schottky Barrier Devices

AbstractSchottky barriers (SBs) are often formed at the semiconductor/metal contacts and affect the electrical behavior of semiconductor devices. In particular, SBs are playing a major role in the investigation of the electrical properties of mono and 2D nanostructured materials, although their impact on the current–voltage characteristics is frequently neglected or misunderstood. In this work, a single equation is proposed to describe the current–voltage characteristics of two‐terminal semiconductor devices with Schottky contacts. The equation is applied to numerically simulate the electrical behavior for both ideal and nonideal SBs. The proposed model can be used to directly estimate the SB height and the ideality factor. It is applied to perfectly reproduce the experimental current–voltage characteristics of ultrathin molybdenum disulfide or tungsten diselenide nanosheets and tungsten disulfide nanotubes. The model constitutes a useful tool for the analysis and the extraction of relevant transport parameters in any two‐terminal device with Schottky contacts.

Broadband absorption enhancement with ultrathin MoS2 film in the visible regime* *Project supported by the National Natural Science Foundation of China (Grant No. 61405217), the Zhejiang Provincial Natural Science Foundation, China (Grant No. LY20F050001), the Anhui Polytechnic University Research Startup Foundation, China (Grant No. 2020YQQ042), and the Pre-research Project of Natural Science Foundation of Anhui Polytechnic University, China (Grant No.

The broadband absorption enhancement effect in ultrathin molybdenum disulfide (MoS2) films is investigated. It is achieved by inserting the MoS2 film between a dielectric film and a one-dimensional silver grating backed with a silver mirror. The broadband absorption enhancement in the visible region is achieved, which exhibits large integrated absorption and short-circuit current density for solar energy under normal incidence. The optical properties of the proposed absorber are found to be superior to those of a reference planar structure, which makes the proposed structure advantageous for practical photovoltaic application. Moreover, the integrated absorption and short-circuit current density can be maintained high for a wide range of incident angles. A qualitative understanding of such broadband absorption enhancement effect is examined by illustrating the electromagnetic field distribution at some selected wavelengths. The results pave the way for developing high-performance optoelectronic devices, such as solar cells, photodetectors, and modulators.

Ultrathin MoS2 nanosheets in situ grown on rich defective Ni0.96S as heterojunction bifunctional electrocatalysts for alkaline water electrolysis

Developing earth-abundant and highly active bifunctional electrocatalysts are critical to advance sustainable hydrogen production via alkaline water electrolysis but still challenging. Herein, heterojunction hybrid of ultrathin molybdenum disulfide (MoS2) nanosheets and non-stoichiometric nickel sulfide (Ni0.96S) is in situ prepared via a facile one-step hydrothermal strategy, followed by annealing at 400 °C for 1 h. Microstructural analysis shows that the hybrid is composed of intimate heterojunction interfaces between Ni0.96S and MoS2 with exposed active edges provided by ultrathin MoS2 nanosheets and rich defects provided by non-stoichiometric Ni0.96S nanocrystals. As expected, it is evaluated as bifunctional electrocatalysts to produce both hydrogen and oxygen via water electrolysis with a hydrogen evolution reaction (HER) overpotential of 104 mV at 10 mA cm−2 and an oxygen evolution reaction (OER) overpotential of 266 mV at 20 mA cm−2 under alkaline conditions, outperforming most current noble-metal-free electrocatalysts. This work provides a simple strategy toward the rational design of novel heterojunction electrocatalysts which would be a promising candidate for electrochemical overall water splitting.

Robust and efficient optical limiters based on molybdenum disulfide nanosheets embedded in solid-state heavy-metal oxide glasses

Simple and effective methods are needed to incorporate two-dimensional functional materials with distinctive nonlinear optical (NLO) response into appropriate solid-state matrices while maintaining inherent functionalities for practical applications in optoelectronic fields. Here, ultrathin molybdenum disulfide (MoS2) nanosheets and lead silicate (PbO-SiO2) gel glasses were chosen as a representative guest dopant and mother matrix, respectively. The MoS2 was introduced into the PbO-SiO2 binary gel glasses by a simple sol-gel wet chemical technique to obtain transparent and s three-dimensional monolithic bulk materials. The presence of MoS2 in the gel glasses and the formation of binary gel glasses were confirmed by various techniques. The NLO and optical limiting (OL) performances were investigated by both open-aperture (OA) and closed-aperture (CA) Z-scan techniques on nano- and picosecond timescales with the use of a laser operating at 532 nm. Our results demonstrate that the NLO effect of MoS2/PbO-SiO2 binary gel glasses was greater than that observed for MoS2/SiO2 unary gel glasses because of enhanced third order nonlinear susceptibility effects induced by the heavy metal. The OA and CA Z-scan patterns suggested that the NLO response of the MoS2/PbO-SiO2 gel glasses is mainly attributed to their nonlinear absorption and nonlinear refraction. Remarkably, the extracted OL thresholds of the MoS2/PbO-SiO2 gel glasses were 12.4 and 7.8 times as great as those recently reported in a MoS2 suspension at nanosecond timescale and MoS2/PMMA organic glass at the picosecond timescale, respectively. The present results demonstrate the feasibility and versatility of MoS2/PbO-SiO2 silica gel glasses, as a new class of highly efficient NLO and OL materials that can be applied in the field of nonlinear optics.

Preparation of ultrathin molybdenum disulfide dispersed on graphene via cobalt doping: A bifunctional catalyst for hydrogen and oxygen evolution reaction

The development of highly active and low-cost catalysts for hydrogen evolution reaction (HER) is significant for the development of clean and renewable energy research. Owing to the low H adsorption free energy, molybdenum disulfide (MoS2) is regarded as a promising candidate for HER, but it shows low activity for oxygen evolution reaction (OER). Herein, graphene-supported cobalt-doped ultrathin molybdenum disulfide (Co–MoS2/rGO) was synthesized via a one-pot hydrothermal method. The obtained hybrids modified electrode exhibits a high HER catalytic activity with a low overpotential of 147 mV at the current density of 10 mA cm−2, a small Tafel slope of 49.5 mV dec−1, as well as good electrochemical stability in acidic electrolyte. Meanwhile, the catalyst shows remarkable OER activity with a low overpotential of 347 mV at 10 mA cm−2. The superior activity is ascribed not only to the high conductivity originated from the reduced graphene, but also to the synergistic effect between MoS2 and cobalt.

Defect-Engineered Atomically Thin MoS2 Homogeneous Electronics for Logic Inverters.

Ultrathin molybdenum disulfide (MoS2 ) presents ideal properties for building next-generation atomically thin circuitry. However, it is difficult to construct logic units of MoS2 monolayer using traditional silicon-based doping schemes, such as atomic substitution and ion implantation, as they cause lattice disruption and doping instability. An accurate and feasible electronic structure modulation strategy from defect engineering is proposed to construct homogeneous electronics for MoS2 monolayer logic inverters. By utilizing the energy-matched electron induction of the solution process, numerous pure and lattice-stable monosulfur vacancies (Vmonos ) are introduced to modulate the electronic structure of monolayer MoS2 via a shallow trapping effect. The resulting modulation effectively reduces the electronic concentration of MoS2 and improves the work function by 100 meV. Under modulation of Vmonos , an atomically thin homogenous monolayer MoS2 logic inverter with a voltage gain of 4 is successfully constructed. A brand-new and practical design route of defect modulation for 2D-based circuit development is provided.

A GSH Functionalized Magnetic Ultra-thin 2D-MoS2 nanocomposite for HILIC-based enrichment of N-glycopeptides from urine exosome and serum proteins

Protein N-glycosylation plays crucial roles in many biological processes and has close association with the occurrence and development of various cancers. Therefore, it is necessary to analyze the abnormal changes of N-glycopeptides in complex biological samples for biomarker discovery. However, due to their low abundance and poor ionization, N-glycopeptides identification in complex samples by mass spectrometry (MS) is still a challenging task. In this work, a novel magnetic hydrophilic material was prepared by serial functionalization of ultra-thin two-dimensional molybdenum disulfide with Fe3O4 nanoparticles, gold nanowire and glutathione (MoS2–Fe3O4–Au/NWs-GSH) for efficient N-glycopeptides enrichment. The advantage of using the new nanocomposite is threefold. First, the introduction of magnetic Fe3O4 nanoparticles efficiently simplifies the enrichment process. Second, the gold nanowire modification enlarges the surface area of the nanocomposites to facilitate interaction with N-glycopeptides. Third, the employment of highly hydrophilic glutathione leads to specific HILIC-based retention of N-glycopeptides. Low femtomolar detection sensitivity and 1:1000 enrichment selectivity can be achieved using MoS2–Fe3O4–Au/NWs-GSH enrichment and bio-mass spectrometry analysis. Successful applications in human urine exosome and serum proteins were demonstrated by the enrichment and identification of 1250 and 489 N-glycopeptides, respectively. This remarkable data set of N-glycoproteome indicates the application potential of the novel nanocomposites for N-glycopeptides enrichment in complex biological samples and for related glycoproteome studies.