Layered MoS2 Nanosheets Research Articles

Thermoelectric performance of Cu-doped MoS2 layered nanosheets for low grade waste heat recovery

Transition Metal Dichalcogenides (TMDCs) are the potential thermoelectric materials due to their high thermal stability as well as tunable electronic and phonon transport properties. In this work, we investigate theeffect of copper doping in thermoelectric properties of layered MoS2 nanosheets. X-ray Diffraction analysis and HRTEM micrographs show the reduction in interatomic spacing which confirms the interaction of copper ions with MoS2 lattice. Downshift in X-ray Photoelectron Spectroscopy (XPS) of Cu doped samples proves the shift of Fermi energy near to the valence band and it results in the enhancement of electrical conductivity of Cu doped MoS2 samples from 0.75 Sm−1 to 14.20 Sm−1 (for 7.5 wt% Cu doped sample). Thus, obtained maximum power factor of 0.313 µWcm−1K−2 for 7.5 wt% Cu doped MoS2 at 420 K.

Facile synthesis of Co-doped MoS2/TiO2 composite as an enhanced photocatalyst for hydrogen evolution

MoS2/TiO2 composite was prepared through a simple solvothermal route by combining the layered MoS2 and TiO2 nanosheets. Then, when preparing MoS2/TiO2 composite, cobalt acetate was added to prepared Co-doped MoS2/TiO2 photocatalyst. The experimental results show that the photocatalytic activity of the Co-doped MoS2/TiO2 composite is significantly improved compared with that of the undoped MoS2/TiO2 composite in the aspect of photocatalytic hydrogen production from water. The enhanced activity should be mainly ascribed to the more exposed active sites and broadened absorption region due to the doping of Co ions.

Stretchable MoS2 Electromechanical Sensors with Ultrahigh Sensitivity and Large Detection Range for Skin-on Monitoring.

Although two-dimensional (2D) layered molybdenum disulfide (MoS2) has widespread electrical applications in catalysis, energy storage, display, and photodetection, very few reports are available to achieve MoS2 for electromechanical sensing. Here, we report a novel solution-processed MoS2 strain sensor by constructing nanojunctions between layered MoS2 nanosheets and high-conductivity silver nanofibers (AgNFs) inside an elastic film. Benefiting from the outstanding lubrication property of layered MoS2 nanosheets, these nanojunctions can be easily separated by strains, giving rise to excellent electromechanical response. The resulting MoS2 strain sensor for the first time exhibits ultrahigh sensitivity with a gauge factor of 3,300 in a large detection range over 10%. The pronounced strain-sensing ability, combined with fast response speed and good operational stability, enables the MoS2 sensor for real-time and skin-on monitorings of various physiological signals such as finger movements, pulse, and breath. Our results may pave the way to extend 2D materials in novel applications such as soft robotics and human-machine interfaces.

Interlayered MoS2/rGO thin film for efficient lithium storage produced by electrospray deposition and far-infrared reduction

Three-dimensional (3D) interlayered composites offer many advantages for energy storage owing to their fast charge transfer kinetics. In this study, the interlayered molybdenum disulfide (MoS2)/graphene (rGO) composites were prepared by electrospray deposition and far-infrared reduction (FIR) processes from single layer MoS2 and graphene nanosheets. Such hierarchical layer-by-layer assembling thin film structure is formed by the driving force of electrostatic interactions between MoS2 and graphene oxide (GO) via the electrospray process. Subsequently, a simple and efficient FIR irradiation (~5 min) process was carried out to reduce the as-prepared MoS2/GO thin film in ambient air using a commercial convection oven. The electro-spraying and FIR reduction processes will jointly help to prevent surface migration and agglomeration of MoS2 and graphene nanosheets, enable efficient electron transfer between the rGO and MoS2 nanosheets, and realize fast lithium storage. As expected, the binder-free MoS2/rGO thin film electrode delivers an outstanding specific capacity (1242.7 mAh g−1 at 0.1 A g−1), high-rate capability (533.7 and 361.6 mAh g−1 at 2.0 and 5.0 A g−1, respectively) and long cycle-life (99.6% capacity retention after 1000 cycles at 2.0 A g−1). More interestingly, the simple economic and efficient strategy for fabricating interlayered MoS2/rGO composites containing electrode can be extended to other electrode materials for energy storage.

Ultra small few layer MoS2 embedded into three-dimensional macro-micro-mesoporous carbon as a high performance lithium ion batteries anode with superior lithium storage capacity

Molybdenum disulfide (MoS2) exhibits additional reversible capacity beyond their theoretical value is promising candidates for electrodes of lithium ion batteries (LIBs). However, the sluggish kinetics, low conductivity and self-aggregating of MoS2 nanosheets hinder the practical application. Herein, ultra small few layer MoS2 combined with carbon hybrids of macro-micro-mesoporous structure (MoS2/MmC) is prepared via a simple and scalable liquid-solid-gas three-phase interface self-assembly process. When employed as anode for lithium ion batteries, such a clever structure possesses superior performance: exhibits discharge capacity of 938 mAh g−1 at current density of 200 mA g−1 following 100 cycles, and reveals reversible capacity of 843 mAh g−1 at current density of 2 A g−1 after 1000 cycles. The excellent performance is attributed to the rational design of electrode structure: ultra small few layer MoS2 nanosheets offer abundant active sites, while the 3D porous architectures are in favor of enhancing the mass-transportation and alleviating the volume expansion. These structural features greatly enhance surface reaction kinetics and facilitate the charge transport. Furthermore, Ex-situ XRD, FESEM are used to confirm the phase transformation of MoS2/MmC and verify the structure stability during the cycling. It is believed that our work opens up a new possible route for the industrial production of MoS2 based anode materials.

New Insights into the Triton X‐100 Induced Chemical Exfoliation of MoS2 to Derive Highly Luminescent Nanosheets

AbstractThe exfoliation of two dimensional (2D) transition metal dichalcogenides (TMDs) into mono‐ or few‐layers without compromising their semiconductor properties has momentous interest for both point of view; fundamental studies and further implementation in practical applications. Herein, we reported a novel and inexpensive approach for high yield nanosheets from bulk MoS2 to few layers of strong luminescent MoS2 nanosheets using Triton X‐100 as a surfactant with tailoring the bulk band gap 1.2 eV to 1.79 eV of few layers of nanosheets after chemical exfoliation process, which can be easily scaled‐up in large quantity. The microstructural results reveal that the exfoliated nanosheets have thickness in the range of few layers and lateral dimension in the range of few hundred nanometers. Our findings may offer a new innovative one setup chemical exfoliation process to design a few layer of MoS2 nanosheets without suppressing luminescent properties, which is highly desirable for the next generation optoelectronic devices.

Highly active free-standing and flexible MoS2/rGO sandwich-structured films for supercapacitor applications

Highly active free-standing and flexible MoS2/rGO nanofilms is mass-produced via ball-milling the bulk layered materials and further hydrazine-reducing process. In the well assembled structure, the loose few layered MoS2 nanosheets and rGO make the composites with enhanced active reaction sites. The synergetic effect between MoS2 nanosheets and rGO could also improve the electronic conductivity and flexibility of the obtained electrode films. The flexible MoS2/rGO nanofilms films are fabricated as symmetric supercapacitor, which deliver a specific capacitance of 365 F g−1 at current density of 0.5 A g−1 and exhibits a high energy density of 89.0 Wh·kg−1 at the power density of 16.7 kW kg−1.

Template-assisted synthesized MoS2/polyaniline hollow microsphere electrode for high performance supercapacitors

Herein we report a template-assisted method to synthesize molybdenum disulfide/polyaniline (MoS2/PANI) hollow microspheres with excellent electrochemical performances for supercapacitors applications. The hollow MoS2 microspheres are assembled by layered MoS2 nanosheets, which provide substantial ion channels and large surface area for electrolyte ion transport. PANI is grown on the surface of the hollow MoS2 microspheres by oxidative polymerization with different mass. The MoS2/PANI-1:2 hollow microspheres electrode possesses the maximum specific capacitance of 364 F/g at a scan rate of 5 mV/s. In addition, the specific capacitance achieves 299 F/g with a current density of 10 A/g and 84.3% of the specific capacitance is retained after 8000 cycles at 10 A/g. The energy density can be as high as 32 Wh/kg at a power density of 320 W/kg. Even at a very high power density of 8320 W/kg, the energy density still maintains 23.1 Wh/kg, showing a large power density range for supercapacitor applications. We assemble a symmetric supercapacitor by using two identical MoS2/PANI microspheres electrodes, and it shows high specific capacitances of 231, 139 F/g at 0.2 and 0.5 A/g, respectively. Our results suggest that the MoS2/PANI hollow microspheres electrode have good cycle stability and significant potential for supercapacitor applications.

2D MoS2 grown on biomass-based hollow carbon fibers for energy storage

2D MoS2 sheets have been extensively served as the anode materials for lithium and sodium ion batteries (LIBs, SIBs) due to its high theoretical capacity. However, its low electrical conductivity and large volume change during cycles impair the rate performance and lifespan of the electrodes. Herein, few layer MoS2 nanosheets vertically grown on biomass-based hollow carbon fibers (BHCFs) derived from palm silk are prepared via a facile hydrothermal method. The density functional theory (DFT) calculations verify an optimized structure of MoS2 vertically grown on BHCF surface and the strong interaction between the S edges of MoS2 and the carbon surface. The few layer nanosheets structure and the enhanced conductivity of MoS2 by biomass derived hollow BHCF ameliorate the diffusion of both Li and Na ions and electrons, as well as the electrode reaction kinetics. Deservedly, the MoS2@BHCF electrodes display excellent lithium and sodium storage performance, especially remarkable high-rate capabilities in LIBs. The higher reversible capacity in LIBs than in SIBs reflects the better kinetics of MoS2@BHCF in LIBs, owing to a much lower energy barrier of Li atoms diffusing through MoS2 crystals than the Na counterparts.

Development of an effective electrochemical platform for highly sensitive DNA detection using MoS2 - polyaniline nanocomposites

Molybdenum disulfide (MoS2) and its associated nanocomposites are widely explored in different applications like capacitance, batteries, sensing etc. However, the nanosheet formation of MoS2 exhibits excellent properties for DNA adsorption without any further surface or probe DNA modification which makes it a suitable matrix for the less explored DNA sensing application. In this present work, an ultrasensitive electrochemical DNA biosensor, based on few layered MoS2 nanosheets blended with conducting polymer, polyaniline is constructed as a sensing platform and used as a DNA sensing probe via differential pulse voltammetric technique. The sensor works well even at concentrations as low as 10−15 M of target DNA without labeling or any use of amplifiers. The sensing performances show highly satisfactory results in case of serum samples and in presence of other interferrants. In addition, the sensor can successfully recognize any positional mismatch in a known concentration of targeted DNA which can lead to a DNA mismatch senor in near future. The detection method described here expands the application of MoS2 in the biosensor field with a viable alternative for easy, cost effective electrochemical DNA detection technique with mismatch identification capability.

Well-patterned Au nanodots on MoS2/TiO2 hybrids for enhanced hydrogen evolution activity

It was realized that two-dimensional layered MoS2 holds great promise as a replacement for Pt-based catalysts for hydrogen evolution reaction (HER) owing to its optimal affinity to H2. However, the synthesis and assembly of MoS2 with remarkably effective HER is still a challenge. In this work, we fabricated layered MoS2 nanosheets (NSs) on highly ordered TiO2 nanotube arrays to form MoS2/TiO2 heterostructures. The disordered MoS2 NSs expose more active sites with better HER performance. The Au deposition results in nicely patterned nanodots (NDs) on in-plane MoS2 NSs which further improves the catalytic activity due to the increased conductivity, fast electron transport and efficient charge separation. In the end, the energy required to initialize HER decreases distinctly by 170 mV and the exchange current density is as high as 71.6 μA/cm2. The Tafel slop of 72 mV/dec suggests a Volmer–Heyrovsky mechanism. Furthermore, our results demonstrate the feasibility of using Au NDs decoration to map the in-plane atomic-level defect patterns on MoS2 NSs.

A comparison of temperature dependent photoluminescence and photo-catalytic properties of different MoS2 nanostructures

Here, a comparison of optical absorption, photoluminescence (PL) emission and catalytic properties of hydrothermally synthesized MoS2 nanoplatelets (MNPs), a few-layer MoS2 nanosheets (MNSs), and MoS2 nanorods (MNRs) have been done, which is rarely available in the literature. The formation of MNSs has been confirmed by transmission electron microscopy, field emission scanning electron microscopy, and Raman spectra analyses. In UV–Vis absorption and PL emission spectra of colloidal aqueous dispersions of the samples, ‘A’ and ‘B’ excitonic peaks having energy separation of ∼219 meV are clearly observed. The ‘D’ excitonic band-gap at 0 K of MNSs has been calculated to be 3.21 eV from the temperature-dependent PL emission studies. A thermodynamic approach has been employed to understand the adsorption of methylene blue (MB) dye onto MNPs, MNRs, and MNSs at various temperatures and it is revealed that the adsorption process is spontaneous, endothermic, and physisorption in nature. The equilibrium adsorption capacities of the samples are found out to be 7.75, 7.67, and 10.17 mg/g, respectively of MNPs, MNRs, and MNSs at room temperature. It is found that MNSs, having large specific surface area and a large number of active sites, exhibit a relatively higher photo-catalytic activity than those of MNPs and MNRs. In case of MNSs, the obtained value of hydrogen evolution reaction (HER) onset overpotential of −49 mV (vs. reversible hydrogen electrode) which is much smaller than those of MNPs and MNRs. The relatively lower Tafel slope of 38 mV/dec of MNSs suggests that these can act as the best electrocatalyst amongst MNSs, MNPs, and MNRs. Thus, it has been revealed that a few layered 2D MoS2 nanosheets are the best candidate for degradation of hazardous organic dye and HER activity in compared to MoS2 nanoplatelets and nanorods.

Active-defective activated carbon/MoS2 composites for supercapacitor and hydrogen evolution reactions

Low-cost, earth-abundant, clean and high stability material are of undivided interest for energy storage and conversion. The present work involves the investigation of one such material, activated carbon (AC), that is derived from abundantly available biomass – Tendu leaves. The work also addresses hydrothermal synthesis of 2-D MoS2 layers and composites with AC, for supercapacitors and hydrogen evolution reaction (HER). AC derived from Tendu leaves showed micro and mesopore structure with high specific surface area (SSA) of 1509 m2 g−1. Layered MoS2 nanosheets sheets, showed a biphasic system namely, 1-T and 2-H. Different ratios of AC and MoS2 nanocomposites are prepared. And the best ratio composites tested for symmetric and hybrid supercapacitor electrodes and HER. Symmetric supercapacitor and hybrid supercapacitors exhibited good cycle stability and show higher specific capacitance of 261 F g−1 and 193 F g−1 respectively, at a scan rate of 2 mV s−1. Defective sites were created on AC for electrochemical HER. The defects were created through, hydrothermal N doping followed by high-temperature dedoping of the N-doped AC. The defective activated carbon (DAC) showed a reduction in SSA of 1300 m2 g−1. The nanocomposites of DAC/MoS2 were then tested for HER. The nanocomposites exhibited enhanced catalytic activity owing to better hydrogen evolution with lesser Tafel slope of −84 mVdec−1.

Novel branched sulfonated polyimide/molybdenum disulfide nanosheets composite membrane for vanadium redox flow battery application

A novel branched sulfonated polyimide/molybdenum disulfide nanosheets (bSPI/MoS2-ns) composite membrane was fabricated for vanadium redox flow battery (VRFB) application. Scanning probe microscope (SPM) and field emission-scanning electron microscope (FE-SEM) images verify the successful exfoliation of monolayer and a few layers of MoS2 nanosheets. X-ray diffraction (XRD), attenuated total reflection-fourier transform infrared spectrometer (ATR-FTIR) and FE-SEM results demonstrate that bSPI, bSPI/MoS2-ns and bSPI/MoS2 nanopowders (bSPI/MoS2-np) membranes are successfully prepared. Both thermogravimetric analysis/differential thermogravimetry (TGA/DTG) and ex-situ chemical stability testing results confirm bSPI/MoS2-ns membrane has improved thermal and chemical stabilities in contrast with pristine bSPI membrane. The bSPI/MoS2-ns membrane owns high proton conductivity (5.04 × 10−2 S cm−1) and extremely low vanadium ion permeability (0.65 × 10−7 cm2 min−1), leading to its highest proton selectivity (7.75 × 105 S min cm−3) among all the membranes tested. Besides, during 500 times cycle charge–discharge test, the coulombic efficiency, energy efficiency and discharge capacity retention of VRFB using bSPI/MoS2-ns membrane are higher than or comparable to those of VRFB using Nafion 117 membrane. And the surfacial morphological integrity of bSPI/MoS2-ns membrane maintains better than reported pristine bSPI membrane after long-time VRFB usage. Above results indicate that the as-prepared bSPI/MoS2-ns membrane has great potential for VRFB application.

Smart Hybridization of Au Coupled CdS Nanorods with Few Layered MoS2 Nanosheets for High Performance Photocatalytic Hydrogen Evolution Reaction

Fabrication of core–shell heteronanostructures with excellent optical properties and light induced charge separation effects have recently emerged as promising materials for solar to hydrogen conversion. Here, one-dimensional CdS–Au/MoS2 hierarchical core/shell heteronanostructures (CSHNSs) have been successfully synthesized by a facile two-step hydrothermal method. Such heteronanostructures exhibit high efficiency and excellent stability toward hydrogen production. The introduction of Au nanoparticles on to CdS nanorods not only made a Schottky junction with strong plasmonic absorption enhancement but also directed the growth of few layered MoS2 nanosheets as a hierarchical protective shell around the CdS nanorods. These CdS–Au/MoS2 hybrid structures possess a large number of edge sites in the MoS2 layers which are active sites for hydrogen evolution reaction. As a result, the CdS–Au/MoS2 CSHNSs exhibit outstanding hydrogen evolution performance which is 7 times that of pure CdS nanorods. Also these CdS–...

Ultrathin layered MoS2 nanosheets with rich active sites for enhanced visible light photocatalytic activity.

Edge-rich active sites of ultrathin layered molybdenum disulphide (MoS2) nanosheets were synthesized by a hydrothermal method. The effect of pH on the formation of MoS2 nanosheets and their photocatalytic response have been investigated. Structural and elemental analysis confirm the presence of S–Mo–S in the composition. Morphological analysis confirms the presence of ultrathin layered nanosheets with a sheet thickness of 10–28 nm at pH 1. The interplanar spacing of MoS2 layers is in good agreement with the X-ray diffraction and high-resolution transmission electron microscopy results. A comparative study of the photocatalytic performance for the degradation of methylene blue (MB) and rhodamine B (RhB) by ultrathin layered MoS2 under visible light irradiation was performed. The photocatalytic activity of the edge-rich ultrathin layered nanosheets showed a fast response time of 36 min with the degradation rate of 95.3% of MB and 41.1% of RhB. The photocatalytic degradation of MB was superior to that of RhB because of the excellent adsorption of MB than that of RhB. Photogenerated superoxide radicals were the key active species for the decomposition of organic compounds present in water, as evidenced by scavenger studies.

Facile Synthesis of MoSx and MoSx‐rGO Composite: Excellent Electrocatalyst for Hydrogen Evolution Reaction

AbstractIn this work, one pot synthetic methodology was developed, wherein simple purging of H2S gas into a solution/dispersion of polyoxometalates in the absence as well as presence of reduced graphene oxide (rGO) at room temperature resulted in the formation of MoSx and MoSx‐rGO composites. Powder XRD, TEM, EDS elemental analysis, TGA, and XPS study reveal that as prepared samples mainly consist of nanocrystalline MoS3 particles whereas annealed samples mainly contain few layers of MoS2 nanosheets. Annealed samples exhibit better electrocatalytic activity towards hydrogen evolution reaction (HER) as compared to the as‐prepared samples. Among all the annealed samples, MoS2‐rGO nanocomposite exhibits superior catalytic activity for HER with lower onset overpotential and higher current density, as compared to other conventional MoS2. The Tafel slope of 41.7 mV/decade for MoS2‐rGO nanocomposite signifies that MoS2 catalyzed HER follows the Volmer‐Heyrovsky mechanism wherein, electrochemical desorption of hydrogen is the rate‐limiting step. Moreover, the integration of few layers of MoS2 and rGO enable remarkable long‐term electrochemical stability and showing negligible change in the current density even after 3000 cycles.

Large-scale production of defect-free MoS2 nanosheets via pyrene-assisted liquid exfoliation

Two dimensional (2D) layered MoS2 nanosheets are gaining increasing attention due to their attractive properties associated with myriads potential applications. However, large-scale production of high-quality MoS2 nanosheets in a simple manner remains a big challenge. Herein, we present a facile approach for scalable production of defect-free MoS2 nanosheets by direct ultrasonication exfoliation of bulk MoS2 crystals in ethanol in the presence of pyrene. Our findings indicate that the pyrene can not only serve as an exfoliating agent to significantly accelerate the exfoliation process but also endow the resulted MoS2 nanosheets with excellent solution dispersibility and stability. The obtained MoS2 nanosheets are highly crystalline and exhibit superior electrical properties as compared with the bulk MoS2. In addition, the MoS2 nanosheets can also be employed as nanofillers to enhance the mechanical properties of polymers. Moreover, this method can also be extended to exfoliation of other 2D layered transition metal dichalcogenide as demonstrated by the exfoliation of bulk WS2 crystals in this study. This work thus brings more opportunities for the investigation and applications of 2D layered inorganic nanosheets.

Fabrication and enhanced photocatalytic properties of novel 3D MoS2/Na0.9Mg0.45Ti3.55O8 heterostructures

A novel three-dimensional (3D) nanocomposite based on Na0.9Mg0.45Ti3.55O8 (NMTO) nanoplates and few layered MoS2 nanosheets was fabricated via a facile two-step hydrothermal process. The few-layer MoS2 nanosheets were uniformly loaded on NMTO nanoplates to form a 3D hierarchical structure. The as-obtained MoS2/NMTO composites exhibit superior photocatalytic activities for stably photodegradating methylene blue (MB) and methyl orange (MO) in comparison with pure MoS2 nanoflowers and pure NMTO nanoplates. Importantly, the MoS2/NMTO heterostructure with 30wt% of MoS2 shows the highest performance in photocatalytic degradation of dye molecules. The formation of 3D hierarchical heterostructure between few-layer MoS2 nanosheets and NMTO nanoplate favors the separation of photoinduced electron-hole pairs and contributes to the enhanced photocatalytic properties.

Assembled graphene nanotubes decorated by hierarchical MoS2 structures: Enhanced lithium storage and in situ TEM lithiation study

Molybdenum disulfide (MoS2) has received considerable interest for electrochemical energy storage and conversion. In this work, we demonstrate a material on synthesis of a unique hierarchical hollow structure by growing layered MoS2 nanosheets on assembled graphene nanotubes via a template-sacrificed approach (named as graphene@MoS2 nanotubes). As a proof of concept, the graphene@MoS2 nanotubes as the anode materials of lithium-ion batteries exhibit excellent cycling performance at 400mAg−1 up to 120 cycles without considerable capacity loss (830mAhg−1, with 96.5% capacity retention) and high rate behavior (502mAhg−1 at 2000mAg−1), which is far beyond than that of the pure MoS2 nanosheets and even graphene@MoS2 nanosheets composites. Furthermore, combined with in-situ TEM lithiation experiments, we find a novel conversion reaction mechanism of MoS2 anodes that Li ions induce structural destruction in c-direction following a dynamic layer-by-layer dissociation with Mo/Li2S composites left, rather than well-known multistep reaction in bulk phase. The first-principles computations verify that the surfacial relaxation of Li2S to form an anti-fluorite structure on higher electric conductive LixMoS2 surface is the primarily thermodynamic driving force for activating the above-mentioned reaction. These results are envisaged to be helpful for designing durable conversion-type MoS2 anodes by surface engineering, and the hierarchical tubular feature further points out a new protocol for graphene based hybrid anode for enhanced lithium-ion batteries.