Two-dimensional MoS2 Nanosheets Research Articles

Facile and Cost-Efficient Synthesis of Quasi-0D/2D ZnO/MoS2 Nanocomposites for Highly Enhanced Visible-Light-Driven Photocatalytic Degradation of Organic Pollutants and Antibiotics.

Nanoscale transition-metal dichalcogenide materials showed promising potential for visible-light responsive photocatalysis. Here, we report our investigations on the synthesis of heterodimensional nanostructures of two-dimensional (2D) ultrathin MoS2 nanosheets interspersed with ZnO nanoparticles by using a facile two-step method consisting of sonication-aided exfoliation technique followed by a wet chemical process. The photocatalytic activity of the nanocomposites was examined by studying the degradation of different organic dye pollutants and tetracycline, a common antibiotic, under visible-light irradiation. It is found that within 30 min more than 90 % of the model organic dye was photodegraded by the optimized quasi-0D/2D hybrid nanomaterial. The reaction rate of pollutant degradation is about five and eight times higher than those of the pristine MoS2 naonosheets and P25 photocatalysts, respectively. The outstanding photocatalytic activity of the heterodimensional hybrids can be attributed to a few beneficial features from the synergetic effects. Most importantly, the intimate junction between ZnO and MoS2 facilitates the separation of photogenerated carriers, leading to the enhancement of photocatalytic efficiency. A tentative photocatalytic degradation mechanism was proposed and tested. Overall, the present work provides valuable insights for the exploration of cost-effective nanoscale heterodimensional hybrids constructed from atomically thin layered materials.

Toward the use of CVD-grown MoS2 nanosheets as field-emission source.

Densely populated edge-terminated vertically aligned two-dimensional MoS2 nanosheets (NSs) with thicknesses ranging from 5 to 20 nm were directly synthesized on Mo films deposited on SiO2 by sulfurization. The quality of the obtained NSs was analyzed by scanning electron and transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy. The as-grown NSs were then successfully transferred to the substrates using a wet chemical etching method. The transferred NSs sample showed excellent field-emission properties. A low turn-on field of 3.1 V/μm at a current density of 10 µA/cm2 was measured. The low turn-on field is attributed to the morphology of the NSs exhibiting vertically aligned sheets of MoS2 with sharp and exposed edges. Our findings show that the fabricated MoS2 NSs could have a great potential as robust high-performance electron-emitter material for various applications such as microelectronics and nanoelectronics, flat-panel displays and electron-microscopy emitter tips.

Hierarchical photocatalyst of In2S3 on exfoliated MoS2 nanosheets for enhanced visible-light-driven Aza-Henry reaction

Exploration of appropriate photocatalysts for visible-light-driven organic synthesis is of great importance. Here we design and construct a two-dimensional hierarchical In2S3/MoS2 composite as an excellent and reusable photocatalyst for Aza-Henry reaction. The dahlia-flower-like In2S3 nanostructures are homogeneously grown on both sides of the two-dimensional MoS2 nanosheets via a hydrothermal reaction. The as-prepared two-dimensional hierarchical In2S3/MoS2 composite exhibits higher photocatalytic performance than pure In2S3. The hierarchical heterostructure can enhance the light absorption in the visible region, facilitate the separation of the photo-induced electron–hole pairs, offer rich active sites for photoredox reactions and promote the generation and migration of the O2‐ and h+. Profiting from these compositional and structural features, the two-dimensional hierarchical In2S3/MoS2 composite shows remarkably enhanced photocatalytic performance and good stability.

Detection of chikungunya virus DNA using two-dimensional MoS2 nanosheets based disposable biosensor

Development of platforms for a reliable, rapid, sensitive and selective detection of chikungunya virus (CHIGV) is the need of the hour in developing countries. To the best of our knowledge, there are no reports available for the electrochemical detection of CHIGVDNA. Therefore, we aim at developing a biosensor based on molybdenum disulphide nanosheets (MoS2 NSs) for the point-of-care diagnosis of CHIGV. Briefly, MoS2 NSs were synthesized by chemical route and characterized using scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, Raman spectroscopy and X-Ray Diffraction. MoS2 NSs were then subjected to physical adsorption onto the screen printed gold electrodes (SPGEs) and then employed for the detection of CHIGV DNA using electrochemical voltammetric techniques. Herein, the role of MoS2 NSs is to provide biocompatibility to the biological recognition element on the surface of the screen printed electrodes. The detection strategy employed herein is the ability of methylene blue to interact differentially with the guanine bases of the single and double-stranded DNA which leads to change in the magnitude of the voltammetric signal. The proposed genosensor exhibited a wide linear range of 0.1 nM to 100 µM towards the chikungunya virus DNA.

Templated synthesis of plate-like MoS2 nanosheets assisted with HNTs and their tribological performance in oil

Two-dimensional MoS2 nanosheets were synthesized by using halloysite nanotubes (HNTs) as template under the hydrothermal synthesis. The structure and morphology of the as-synthesized MoS2 nanosheets were determined by a series of characterizations. The results showed that the as-synthesized MoS2 nanosheets were of the plate-like structure with about five layers, and the basal spacing was about 0.63 nm. It was demonstrated that HNTs played a crucial template role in the formation of the plate-like MoS2 nanosheets. The formation mechanism was proposed. Furthermore, the tribological performance of the as-prepared MoS2 nanosheets in oil was intensively examined on the ball-on-ball wear tester. The testing results verified that the as-prepared MoS2 nanosheets as additive could significantly improve the friction performance of oil, which exhibited the good antifriction, antiwear, and load-carrying properties.

Design of superior ethanol gas sensor based on indium oxide/molybdenum disulfide nanocomposite via hydrothermal route

This paper demonstrates an ethanol gas sensor based on indium oxide/molybdenum disulfide (In2O3/MoS2) nanocomposite via hydrothermal route. The microstructure and micromorphology of In2O3/MoS2 nanocomposite were fully characterized by various analytical techniques. The gas-sensing properties of the In2O3/MoS2 composite were investigated upon exposure to different concentrations of ethanol gas from 1 ppm to 50 ppm at the optimum temperature, and compared with the pristine In2O3 sensors. Owing to the supporting substrate of specific two-dimensional MoS2 nanosheets, the sensor based on In2O3/MoS2 composite exhibit superior gas sensing performance towards ethanol, which outstripped that of pure In2O3 sensor and have potential applications in the detection of ethanol vapors.

Novel “203” type of heterostructured MoS2-Fe3O4-C ternary nanohybrid: Synthesis, and enhanced microwave absorption properties

It is widely recognized that constructing multiple interface structures to enhance interface polarization is very good for the attenuation of electromagnetic (EM) wave. Here, a novel “203” type of heterostructured nanohybrid consisting of two-dimensional (2D) MoS2 nanosheets, zero-dimensional (0D) Fe3O4 nanoparticles and three-dimensional (3D) carbon layers was elaborately designed and successfully synthesized by a two-step method: Fe3O4 nanoparticles were deposited onto the surface of few-layer MoS2 nanosheets by a hydrothermal method, followed by the carbonation process by a chemical vapor deposition method. Compared to that of “20” type MoS2-Fe3O4, the as-prepared heterostructured “203” type MoS2-Fe3O4-C ternary nanohybrid exhibited remarkably enhanced EM and microwave absorption properties. And the minimum reflection loss (RL) value of the obtained MoS2-Fe3O4-C ternary nanohybrid could reach −53.03 dB at 14.4 GHz with a matching thickness of 7.86 mm. Moreover, the excellent EM wave absorption property of the as-prepared ternary nanohybrid was proved to be attributed to the quarter-wavelength matching model. Therefore, a simple and effective route was proposed to produce MoS2-based mixed-dimensional van der Waals heterostructure, which provided a new platform for the designing and production of high performance microwave absorption materials.

A reliable and highly efficient exfoliation method for water-dispersible MoS2 nanosheet

Since the pioneering work on exfoliated single-layer graphene, layered inorganic nanosheet materials have been widely explored due to their unusual properties with potential applications in energy devices and optical electronics. Among these layered inorganic nanosheets, two-dimensional thin MoS2nanosheets show extraordinary properties such as the presence of a direct bandgap, magnetism, superconductivity and ferroelectricity. Over the past few years, solution-processed exfoliation methods of layered materials have been extensively studied; most of the exfoliation processes employ organic solvents or use surfactants as well as other functionalization agents. Although pure water is considered as an ideal solvent, however, it is generally believed stable dispersions of water could not be achieved due to poor solubility MoS2 in water. Thus, there are very limited studies for developing of water based MoS2 dispersions. Here we introduce a facile, green and reliable exfoliation method for producing water-dispersible MoS2 nanosheet without surfactant. Pure water was used as a solvent and this exfoliation process was achieved by thinning the bulk MoS2 by mechanical force between sandpapers and dispersing it through probe sonication in water. The exfoliated single or few-layered MoS2 nanosheets were characterized by TEM and SEM images. The lateral dimensions of the nanosheets were around 500 nm to 5 µm, the same range as obtained in the organic solvents as reported. Zeta potential measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. Overall, it is concluded that with this exfoliation strategy, water can be used as a useful dispersible solvent for MoS2 nanosheets. Although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable.

Metallic MoS2 nanosheets: multifunctional electrocatalyst for the ORR, OER and Li-O2 batteries.

Lithium-oxygen batteries (LOBs) possess the highest theoretical specific density among all types of lithium batteries, making them ideal candidates to replace the current Li ion batteries for next-generation electric vehicle applications. However, designing highly active catalysts with high electronic conductivities to kinetically accelerate the sluggish oxygen reduction/evolution reactions (ORR/OER) is still a big challenge. This work was dedicated to developing two-dimensional (2D) trigonal phase MoS2 (1T-MoS2) nanosheets as a highly active electrocatalyst for LOBs for the first time. Metallic 1T-MoS2 prepared via in situ liquid-redox intercalation and exfoliation was hybridized with functionalized carbon nanotubes (CNTs) to form freestanding, binder-free oxygen electrodes. The 1T-MoS2/CNT electrode exhibited excellent electrochemical performances with a high reversible capacity of 500 mA h g-1 at a current density of 200 mA g-1 for more than 100 cycles owing to the catalytically active surfaces of 1T-MoS2 accessible by Li+ ions and O2. Density functional theory (DFT) calculations identified the catalytically active basal planes in 1T-MoS2 during the ORR as well as the initial ORR path during LOB cycles. The results based on the rotational ring disk electrode (RRDE) experiments also supported the findings from the DFT calculations, where the 1T-MoS2 basal planes are active for both the ORR and OER, not the semiconducting hexagonal MoS2 (2H-MoS2) whose edges are only electrocatalytically active. This study sheds light on the use of metallic 1T-MoS2 as a multifunctional oxygen electrocatalyst for LOB applications with enhanced ORR and OER activities.

Anion Engineering on Free-Standing Two-Dimensional MoS2 Nanosheets toward Hydrogen Evolution.

On the basis of theoretical predictions, nitrogen was designed and incorporated into free-standing two-dimensional MoS2 nanosheets. Both the amount of electrochemical active sites on the surface and its intrinsic conductivity could be significantly increased as a result of anion engineering, which can extremely improve the electrocatalytic kinetics toward hydrogen evolution.

Petal-like MoS2 Nanosheets Space-Confined in Hollow Mesoporous Carbon Spheres for Enhanced Lithium Storage Performance.

An innovative approach for efficient synthesis of petal-like molybdenum disulfide nanosheets inside hollow mesoporous carbon spheres (HMCSs), the yolk-shell structured MoS2@C, has been developed. HMCSs effectively control and confine in situ growth of MoS2 nanosheets and significantly improve the conductivity and structural stability of the hybrid material. The yolk-shell structured MoS2@C is proven to achieve high reversible capacity (993 mA h g-1 at 1 A g-1 after 200 cycles), superior rate capability (595 mA h g-1 at a current density of 10 A g-1), and excellent cycle performance (962 mA h g-1 at 1 A g-1 after 1000 cycles and 624 mA h g-1 at 5 A g-1 after 400 cycles) when evaluated as an anode material for lithium-ion batteries. This superior performance is attributed to the yolk-shell structure with conductive mesoporous carbon as the shell and the stack of two-dimensional MoS2 nanosheets as the yolk.

Ionic strength induced electrodeposition of two-dimensional layered MoS2 nanosheets

A new redox-free electrochemical approach for driving the deposition of two-dimensional (2D) layered MoS2 nanosheets is described. First, poly(acylic acid) (PAA) functionalized layered MoS2 nanosheets (PAA-MoS2) is prepared to form a stable aqueous PAA-MoS2 dispersion, which is subsequently used for the electrochemical deposition. In contrast to previous electrodeposition methods of MoS2, which involve the redox of molecular precursors of Mo and S, herein we introduce an electrochemical approach for the deposition of 2D layered MoS2 nanosheets directly from their nanometric building blocks, namely from their aqueous dispersion. This “nano to nano” approach is based on altering the ionic strength at the vicinity of the electrode surface by applying a potential. Specifically, the electrogeneration of Cu2+ ions, cause the PAA-MoS2 nanosheets in the dispersion to aggregate and deposit on the copper electrode. Scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy analysis show clearly that the deposited layered MoS2 maintains its original structure. Furthermore, the electrodeposited PAA-MoS2 nanosheets on copper show excellent catalytic activity for the hydrogen evolution reaction with low overpotential. Hence, we believe that these findings could lead to a generic approach for the formation of thin films or patterns of 2D nanomaterials.

Electrical transport properties of two-dimensional MoS2 nanosheets synthesized by novel method

In this work, we have reported the electrical transport properties of two-dimensional molybdenum disulfide (MoS2) nanosheets prepared by supercritical fluid method. Drop-casting technique has been used to make MoS2 thinfilm. The surface morphology and crystallinity of as-prepared MoS2 are studied using TEM, AFM, Raman and X-ray diffraction analyses. The observation of non-linear current-voltage (I-V) characteristics has been analyzed with different current conduction mechanisms such as Schottky barrier (SB), space-charge limited conduction, Fowler-Nordheim tunneling, and Poole-Frenkel conduction. Clear symmetricity in I-V curves confirms that charge-transport is not influenced by SB. However, all other transport mechanisms are to be found responsible for the non-linearity. The charge carrier mobility of the device is determined as ~1530cm2/Vs which is the highest value among supercritical fluid processed MoS2 to-date. The presence of bulk counterpart in MoS2 is accountable for such anomalous transport behavior and it is supported by Raman mapping analysis, evidently. Overall, our results demonstrate the understanding of the fundamental charge transport mechanisms in MoS2 thinfilm that can be the essential factors in development of various MoS2 based electronic devices and their applications.

Multidimensional Thin Film Hybrid Electrodes with MoS2 Multilayer for Electrocatalytic Hydrogen Evolution Reaction.

Hybrid electrodes are widely used in various energy storage and conversion devices. However, conventional fabrication methods like simple mixing allow only limited control over the internal electrode structure, and it is often difficult to elucidate the structure-property relationship among the electrode components. Taking advantage of the versatile layer-by-layer (LbL) assembly method, herein we report the preparation of electrocatalytic thin film electrodes for hydrogen evolution reaction (HER), highlighting the importance of nanoscale composition in multidimensional hybrid electrodes. The fabrication utilized the electrostatic interaction between the two components: catalytically active two-dimensional MoS2 nanosheets and conductive, one-dimensional multiwalled carbon nanotube (MWNT) support. The electrocatalytic activity was found to be highly tunable by adjusting the thickness of the electrode, suggesting structural dependence of electron transfer and mass transport between the electrolyte and electrode, which is otherwise difficult to investigate in electrodes fabricated by simple conventional methods. Furthermore, the detailed mechanism of HER on the hybrid electrode was also investigated, revealing the fine balance between the catalytic activity of MoS2 and conductivity of MWNT. We anticipate that this unique approach will offer new insights into the nanoscale control of electrode architecture and the development of novel electroactive catalysts.

Application of two-dimensional MoS2 nanosheets in the property improvement of polyimide matrix: Mechanical and thermal aspects

Two dimensional (2D) MoS2 nanosheets are firstly exfoliated by high shear mixing technique and then incorporated into PAA precursors to form the MoS2/PI nanocomposite films, and the preparation can be accomplished via in-situ polymerization, tape casting and thermalimidization processes. As a result, the mechanical and thermal properties of the prepared MoS2/PI nanocomposite films are significantly enhanced by incorporation of a small amount of MoS2 nanosheets without any surface modification. Especially, 43% and 47% increases in tensile strength and Young’smodulus can be respectively achieved upon adding certainsmall amountof MoS2 (0.75wt% or so). Meanwhile, the glass transition temperature (Tg) can be effectively improved by 11°C by taking advantages of unique superior thermal stability of MoS2 nanosheets. This desirablefabrication of MoS2/PI nanocomposite films is expectedto offer a new avenue on the development of high strength PI-based nanocomposites with comprehensive performances.

Construction of unique two-dimensional MoS2-TiO2 hybrid nanojunctions: MoS2 as a promising cost-effective cocatalyst toward improved photocatalytic reduction of CO2 to methanol.

Two-dimensional MoS2 nanosheets were in situ grown on TiO2 nanosheets to form two-dimensional (2D) hybrid nanojunctions, with which MoS2 nanosheets compactly contact with TiO2 to increase the interfacial area. MoS2 was identified as a promising cost-effective substitute for noble metal cocatalysts such as Pt, Au, and Ag, and shows superior activity and selectivity for reducing CO2 to CH3OH in aqueous solution to these metal cocatalysts under UV-vis light irradiation. The photo-luminescence (PL) spectra and transient time-resolved PL decay measurements reveal that the fast electron transfer from TiO2 to MoS2 can minimize charge recombination losses to improve the conversion efficiency of photoreduction. It reveals that Mo-terminated edges of MoS2 nanosheets possess the metallic character and a high d-electron density, and the Mo cation sites may benefit the stabilization of CHxOy intermediates via electrostatic attraction to enhance the CH3OH formation from the reduction of CO2 in aqueous solution.

Understanding the high-electrocatalytic performance of two-dimensional MoS2 nanosheets and their composite materials

This review describes recent advances in two-dimensional MoS2 nanosheets and their composite materials for understanding their high-electrocatalytic performance in HER and ORR.

A simple electrochemical route to metallic phase trilayer MoS2: evaluation as electrocatalysts and supercapacitors

The development of a simple, scalable and reproducible technique for the synthesis of two-dimensional metallic phase MoS2nanosheets is of paramount importance in the field of catalysis and energy storage devices.

Constructing Two-, Zero-, and One-Dimensional Integrated Nanostructures: an Effective Strategy for High Microwave Absorption Performance.

A novel "201" nanostructure composite consisting of two-dimensional MoS2 nanosheets, zero-dimensional Ni nanoparticles and one-dimensional carbon nanotubes (CNTs) was prepared successfully by a two-step method: Ni nanopaticles were deposited onto the surface of few-layer MoS2 nanosheets by a wet chemical method, followed by chemical vapor deposition growth of CNTs through the catalysis of Ni nanoparticles. The as-prepared 201-MoS2-Ni-CNTs composites exhibit remarkably enhanced microwave absorption performance compared to Ni-MoS2 or Ni-CNTs. The minimum reflection loss (RL) value of 201-MoS2-Ni-CNTs/wax composites with filler loading ratio of 30 wt % reached -50.08 dB at the thickness of 2.4 mm. The maximum effective microwave absorption bandwidth (RL< -10 dB) of 6.04 GHz was obtained at the thickness of 2.1 mm. The excellent absorption ability originates from appropriate impedance matching ratio, strong dielectric loss and large surface area, which are attributed to the "201" nanostructure. In addition, this method could be extended to other low-dimensional materials, proving to be an efficient and promising strategy for high microwave absorption performance.

Highly Sensitive and Selective Aptamer-Based Fluorescence Detection of a Malarial Biomarker Using Single-Layer MoS2 Nanosheets

We demonstrate a highly selective and sensitive aptamer-based “capture-release” fluorescence detection of a malarial biomarker, i.e., Plasmodium lactose dehydrogenase (pLDH) protein, using single-layer two-dimensional MoS2 nanosheets. The detection of the target pLDH protein utilizing the aptamer-nanosheet sensing platform is rapid and can be easily completed within 10 min. In addition, the developed biomolecular sensor is capable of detecting the target malarial biomarker in homogeneous protein solutions as well as in heterogeneous mixtures of proteins. We anticipate that the ultrathin MoS2 nanosheet-based biosensor will facilitate the further development of biomolecular nanosensors for the detection of a wide range of biomarkers for malaria and other diseases.