Exfoliation Of MoS2 Research Articles

Synergistic effect of Bi-doped exfoliated MoS2 nanosheets on their bactericidal and dye degradation potential.

Nanosheets incorporated with biological reducing agents are widely used to minimize the toxic effects of chemicals. Biologically amalgamated metal oxide nanomaterials have crucial importance in nanotechnology. In this study, bare and bismuth (Bi)-doped molybdenum disulfide (MoS2) nanosheets were synthesized via a hydrothermal method. Different Bi weight ratios of 2.5, 5, 7.5 and 10% were incorporated in a fixed amount of MoS2 to evaluate its catalytic and antimicrobial activities. Doped nanosheets were characterized using XRD, FTIR and UV-vis spectroscopy, FESEM, HRTEM, Raman, PL, DSC/TGA, EDX, XRF and XPS analysis. The XRD spectra confirmed that the doped nanosheets exhibit a hexagonal structure and their crystallite size increases gradually upon doping. The morphology and interlayer d-spacing of doped MoS2 were determined by FESEM and HRTEM. The presence of functional groups in the doped nanosheets was confirmed using FTIR, PL and Raman analysis. The absorption intensity increased and the corresponding measured band gap energy decreased with doping. The thermal stability and weight loss behaviour of the prepared samples were studied using DSC/TGA. The doped MoS2 nanosheets showed a higher catalytic potential compared to undoped MoS2. The doped Bi nanosheets exhibited higher antimicrobial activity against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) at different concentrations of Bi (0.075 and 0.1), showing a tendency to counter the emerging drug resistance against pathogenic bacterial diseases. Consequently, significant inhibition zones were recorded against (MDR) S. aureus ranging from 2.25 to 3.3 mm and 3.25 to 5.05 mm at low and high concentrations of doped-Bi nanosheets and against Gram-negative E. coli ranging from 1 to 1.45 mm at high concentrations. In conclusion, the Bi-doped MoS2 nanocomposite has exhibited significant potential for use in industrial dye degradation applications. Its antibacterial properties can also mitigate health risks associated with the presence of several well-known pathogens in the environment.

Exfoliated MoS2@C nanosheets as anode for sodium/potassium storage

Due to high theoretical capacity (670 mA h g−1), MoS2 can become a good application for energy storage. It is reported that the layer spacing of MoS2 can be exfoliated, which improves Na+/K+ insertion/extraction and promotes electron diffusion and ion transport. So, we obtained exfoliated MoS2 nanosheets with the modification of a carbon layer, in order to form exfoliated MoS2@C nanosheets. With the analysis of XRD and TEM, it was found that the larger interlayer spacing was obtained. As the anodes for sodium ion batteries (SIBs), the exfoliated MoS2 nanosheet electrode showed a high capacity (641 mA h g−1 at 50 mA g−1) and maintained a capacity of 214 mA h g−1 at 1000 mA g−1 after 400 cycles. Moreover, it was discussed as anode for potassium ion batteries (KIBs). It can be found that the electrode had 241 mA h g−1 at 100 mA g−1 after 20 cycles.

Photoelectrochemical determination of the activity of histone acetyltransferase and inhibitor screening by using MoS2 nanosheets.

The enzyme histone acetyltransferase (HAT) catalyzes the acetylation of a substrate peptide, and acetyl coenzyme A is converted to coenzyme A (CoA). A photoelectrochemical method is described for thedetermination of the HAT activity by using exfoliated MoS2 nanosheets, phos-tag-biotin, and β-galactosidase (β-Gal) based signal amplification. The MoS2 nanosheets are employed as the photoactive material, graphene nanosheets as electron transfer promoter, gold nanoparticles as recognition and capture reagent for CoA, and phos-tag-biotin as the reagent to link CoA and β-Gal. The enzyme β-Gal catalyzes the hydrolysis of substrate O-galactosyl-4-aminophenol to generate free 4-aminophenol which is a photoelectrochemical electron donor. The photocurrent increases with the activity of HAT. Under optimal conditions, the response is linear in the 0.3 to 100nM activity range, and the detection limit is 0.14nM (at S/N= 3). The assay was applied to HAT inhibitor screening, specifically for the inhibitors C646 and anacardic acid. The IC50 values are 0.28 and 39μM, respectively. The method is deemed to be a promising tool for epigenetic research and HAT-targeted cancer drug discovery. Graphical abstract Histone acetyltransferase was detected using asensitive photoelectrochemical method using MoS2 nanosheets as photoactive material.

Hierarchical ZnS@C@MoS2 core-shell nanostructures as efficient hydrogen evolution electrocatalyst for alkaline water electrolysis

Low-cost and highly efficient electrocatalysts are critical to advance the hydrogen production industry via water electrolysis in alkaline media. Molybdenum disulfide (MoS2) nanosheets as earth-abundant electrocatalyst became a star material due to its unique graphene-like layered structure favoring electron transfer for hydrogen evolution catalysis. However, its electrocatalytic activities greatly hindered by the poor conductivity and the fewer exposure of catalytically active edged sites. Herein, hierarchical ZnS@C@MoS2 core-shell nanostructures were designed by using a bottom-up strategy combined with a simple selective etching. The coexistence of semiconductor ZnS and defective porous carbonaceous shell as the core not only enhanced the electrical conductivity, but also separated and loaded the exfoliated MoS2 nanosheets which effectively proliferated the exposed catalytically active edge sites (Mo and S sites). Upon optimal conditions, hierarchical ZnS@C@MoS2 core-shell nanostructures gave an overpotential of 118 mV at 10 mA/cm2 with a Tafel slope value of 55.4 mV/dec and better cycling stability after 500 cycles during the alkaline HER process, superior to pristine MoS2.

A low‐cost and efficient pathway for preparation of 2D MoN nanosheets via Na2CO3‐assisted nitridation of MoS2 with NH3

AbstractIn this paper, an efficient and low‐cost method was developed for producing isolated 2D MoN nanosheets via Na2CO3‐assisted nitridation and exfoliation of natural 2H‐MoS2 by NH3 at 700‐800°C. It was found that, in the presence of Na2CO3, the nitridation of MoS2 with NH3 was a topochemical transformation. After heat treatment the mixture of MoS2 and Na2CO3 in NH3 at 700‐800°C, layered MoN with intercalated Na2S was obtained. Na2CO3 can dramatically promote the topochemical nitridation and exfoliation of MoS2 in NH3. At 750°C, the time for complete nitridation of (commercial) MoS2 can be shortened to 2 hours, which is much shorter than 40 hours in the case without the addition of Na2CO3 as reported in the previous literature. After acid‐washing, the intercalated Na2S was removed, and the generated H2S promoted the further separation of the MoN nanosheets. Finally, dispersed high crystalline 2D MoN nanosheets with thickness of a few nanometers were successfully produced. This method may be also applicable for the production of other 2D nitrides or carbides by nitridation or carbonization of various transition metal dichalcogenides (TMDs) with the assistance of sulfur‐fixed agent.

Highly Efficient Hydrogen Evolution from Seawater by Biofunctionalized Exfoliated MoS2 Quantum Dot Aerogel Electrocatalysts That Is Superior to Pt.

As a source of clean and sustainable energy, reliable hydrogen production requires highly efficient and stable electrocatalysts. In recent years, molybdenum disulfide (MoS2) has been demonstrated as a promising electrocatalyst for hydrogen evolution reactions (HERs). Here, we demonstrate that a three-dimensional (3D) MoS2 quantum dot (MoS2QD) aerogel is an efficient cathode electrocatalyst that can be used to enhance the HER in acid, neutral, and alkaline (e.g., real seawater) environments. In studying the effects of the exfoliated MoS2 dimension for the HER, we found that the biofunctionalized exfoliated MoS2QD shows much higher cathodic density, a more lower energy input, and a lower Tafel slope for the HER than the larger size of the chlorophyll-assisted exfoliated MoS2, highlighting the importance of the size of the MoS2 aerogel support for accelerating the HER performance. Moreover, the electrocatalytic activity of MoS2QD-aerogel is superior to that of Pt in neutral conditions. In real seawater, the MoS2QD-aerogel sample exhibits stable HER performance after consecutive scanning for 150 cycles, while the HER activity of the Pt dramatically decreases after 50 cycles. These results showed for the first time how the 3D MoS2 configuration in MoS2 aerogel can be used to effectively produce hydrogen for clean energy applications.

Exfoliated Molybdenum Disulfide Encapsulated in a Metal Organic Framework for Enhanced Photocatalytic Hydrogen Evolution

An exfoliated MoS2 encapsulated into metal-organic frameworks (MOFs) was fabricated as a promising noble-metal-free photocatalyst for hydrogen production under visible light irradiation. The as-synthesized samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) surface analysis. It is well known that bulk MoS2 is unsuitable for photocatalysis due to its inadequate reduction and oxidation capabilities. However, exfoliated MoS2 exhibits a direct band gap of 2.8 eV due to quantum confinement, which enables it to possess suitable band positions and retain a good visible-light absorption ability. As a result, it is considered to be an encouraging candidate for photocatalytic applications. Encapsulating exfoliated MoS2 into MOF demonstrates an improved visible light absorption ability compared to pure MOF, and the highest hydrogen production rate that the encapsulated exfoliated MoS2 could reach was 68.4 μmol h-1g-1, which was much higher than that of pure MOF. With a suitable band structure and improved light-harvesting ability, exfoliated MoS2@MOF could be a potential photocatalyst for hydrogen production.

Liquid Phase Exfoliation of MoS2 Nano-sheets and Observation of Resistive Switching Memory in MoS2 Nano-sheets-PVDF-HFP Composite Films

Abstract To realise the true and versatile application potentials of 2-D materials like MoS2, the preparation of mono-layer or few layer nano-sheets holds the key. In the present study, we report the successful exfoliation of bulk MoS2 into few layer nano-sheets by adopting a two-step process of grinding and then two hours of ultrasonication by using a probe sonicator. The yield of exfoliation was 32 mg/10 ml and the exfoliated MoS2 was very stable without any re-stacking for more than one month. Further, the exfoliated MoS2 nano-sheets are added to Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to prepare the nanocomposite thin films. Two-terminal devices are prepared with ITO and aluminium as bottom and top electrodes, respectively on a plastic substrate. Its electrical properties are investigated to observe the electrical bistability. Nanocomposite based devices showed bipolar resistive switching memory. For composite film with 1wt.% of MoS2, resistance switching is observed with SET and RESET voltages at 2.74 V and -0.9 V respectively. Resistance ratio of the order of 104 is achieved between the ON and OFF states.

Nanofibers with MoS2 nanosheets encapsulated in carbon as a binder-free anode for superior lithium storage

One-dimensional MoS2/carbon nanofibers (MoS2-CNFs) were synthesized by electrospinning using exfoliated MoS2 nanosheets and polyacrylonitrile as the precursors. The exfoliated MoS2 nanosheets about 150 nm across were encapsulated in carbon, and the free-standing MoS2/CNF film was easily cut into a flexible tablet that could be directly used as a binder-free anode for lithium storage. The MoS2/CNFs showed a high reversible capacity of 700 mAh g−1 at 100 mA g−1 after 50 cycles, a high rate capacity of 450 mAh g−1 at 1000 mA g−1 after 200 cycles and good cycling stability.

Molecular Simulation of MoS2 Exfoliation

A wide variety of two-dimensional layered materials are synthesized by liquid-phase exfoliation. Here we examine exfoliation of MoS2 into nanosheets in a mixture of water and isopropanol (IPA) containing cavitation bubbles. Using force fields optimized with experimental data on interfacial energies between MoS2 and the solvent, multimillion-atom molecular dynamics simulations are performed in conjunction with experiments to examine shock-induced collapse of cavitation bubbles and the resulting exfoliation of MoS2. The collapse of cavitation bubbles generates high-speed nanojets and shock waves in the solvent. Large shear stresses due to the nanojet impact on MoS2 surfaces initiate exfoliation, and shock waves reflected from MoS2 surfaces enhance exfoliation. Structural correlations in the solvent indicate that shock induces an ice VII like motif in the first solvation shell of water.

Highly enhanced hydrogen sensing properties of sericin-induced exfoliated MoS2 nanosheets at room temperature

Herein, we report a simple and inexpensive strategy for the scaling-up of highly stabilized MoS2 nanosheets using a bio-waste sericin-assisted liquid phase exfoliation (LPE) method. MoS2 nanosheets (NSs) was also prepared under the same conditions but without sericin for comparison. The as-prepared samples were then identified as MoS2 NSs and sericin-MoS2 NSs. Each sample was drop casted on Si/SiO2 substrates then fabricated with interdigitated electrodes prior to studying their H2 sensing properties. The as-fabricated sericin-MoS2 NSs exhibited better H2 sensing properties at room temperature compared to those of the MoS2 NSs. An outstanding sensor response of 49% was reached at low ppm with an ultra-fast response time (10 s) and recovery time (6 s). This exceptional H2 sensing performance was influenced by the adsorptive coating of sericin on the edges of the MoS2 NSs. The coating of sericin protein forms an electron depletion layer which can interact with metals (Mo and S) through their functional groups (NH2, COOH, OH and SH). Furthermore, such an interaction leads to a reduction of the electron depletion layer of exfoliated MoS2, and thereby enhances the H2 sensitivity, stability and response/recovery time. We expect that the present strategy of sericin-MoS2 combination will satisfy the demand for exfoliated MoS2 based high performance H2 sensors to-date.

Laser-assisted tunable optical nonlinearity in liquid-phase exfoliated MoS2 dispersion

The paper aims to explain the effect of laser irradiation on the nonlinear optical (NLO) response of MoS2 nanosheets. MoS2-layered nanostructures were prepared by liquid-phase exfoliation (LPE) in deionized (DI) water. The characterization of MoS2 dispersion proves the formation of 2-3-layered 2H-MoS2 nanosheets with less than 100 nm lateral dimension. The NLO response of prepared dispersion was explored using the Z-scan technique with 532 nm continuous wave (CW) laser beam at 30, 50, 70 mW powers. The main finding of this research is that the nonlinear refractive index (n2) of MoS2 dispersion is a laser-assisted tunable quantity. It has been shown that the nonlinear refractive index of MoS2 nanosheets is altered up to 48% of its initial value only by 1-h laser irradiation with 30 mW power.

A facile and clean process for exfoliating MoS2 nanosheets assisted by a surface active agent in aqueous solution

A facile, efficient and environmentally friendly process to exfoliate MoS2 is essentially critical to apply the obtained mono- and few-layer nanosheets in various electronic devices and sensors. Here we report a liquid phase exfoliation method for exfoliation of MoS2, which employs a surfactant of sodium dodecyl benzene sulfonate (SDBS) in water. The nonpolar benzene rings in SDBS can firmly bind to the MoS2 layer, facilitating the effective exfoliation of nanosheets in aqueous solution. It is found that the exfoliation efficiency and thickness of MoS2 nanosheets are related to the concentration of SDBS, and the mechanism was investigated. Defect free mono- and few-layer MoS2 nanosheets are obtained by controlling the amount of SDBS in solution, which exhibit stable dispersion in water over months, and it renders them as having great potential for solution-based device fabrication.

Scalable Exfoliation of Bulk MoS₂ to Single- and Few-Layers Using Toroidal Taylor Vortices.

The production of a large amount of high-quality transition metal dichalcogenides is critical for their use in industrial applications. Here, we demonstrate the scalable exfoliation of bulk molybdenum disulfide (MoS2) powders into single- or few-layer nanosheets using the Taylor-Couette flow. The toroidal Taylor vortices generated in the Taylor-Couette flow provide efficient mixing and high shear stresses on the surfaces of materials, resulting in a more efficient exfoliation of the layered materials. The bulk MoS2 powders dispersed in N-methyl-2-pyrrolidone (NMP) were exfoliated with the Taylor-Couette flow by varying the process parameters, including the initial concentration of MoS2 in the NMP, rotation speed of the reactor, reaction time, and temperature. With a batch process at an optimal condition, half of the exfoliated MoS2 nanosheets were thinner than ~3 nm, corresponding to single to ~4 layers. The spectroscopic and microscopic analysis revealed that the exfoliated MoS2 nanosheets contained the same quality as the bulk powders without any contamination or modification. Furthermore, the continuous exfoliation of MoS2 was demonstrated by the Taylor-Couette flow reactor, which produced an exfoliated MoS2 solution with a concentration of ~0.102 mg/mL. This technique is a promising way for the scalable production of single- or few-layer MoS2 nanosheets without using hazardous intercalation materials.

Hydrophobic and Electronic Properties of the E‐MoS2 Nanosheets Induced by FAS for the CO2 Electroreduction to Syngas with a Wide Range of CO/H2 Ratios

AbstractThe electrochemical CO2 reduction reaction (CO2RR) to produce CO and H2 (syngas) is a promising method for clean energy, but challenges remain, such as controlling the CO/H2 ratios required for the syngas yield. Herein, hydrophobic exfoliated MoS2 (H‐E‐MoS2) nanosheets are fabricated from bulk MoS2 by a cost‐effective ball‐milling method, followed by decoration with fluorosilane (FAS). H‐E‐MoS2 is a cost‐effective electrocatalyst capable of directly reducing CO2 and H2O for tuneable syngas production with a wide range of CO/H2 ratios (from 1:2 to 4:1). In addition, H‐E‐MoS2 shows a high current density, 61 mA cm−2 at −1.1 V, and the highest CO FE of 81.2% at −0.9 V, which are higher than those of unmodified MoS2. According to density functional theory calculations, FAS decoration on the surface of MoS2 electrode can change the electronic properties of the edge Mo atom, which facilitates the rate‐limiting CO‐desorption step, thus promoting CO2RR. Moreover, the hydrophobic surface of H‐E‐MoS2 depressed the H2 evolution reaction and created abundant three‐phase contact points that provided sufficient CO2. The hydrophobization of the electrode may provide an effective strategy for easily tuning the CO/H2 ratio of syngas in a large range for the direct electroreduction CO2 to syngas with an optimized CO/H2 ratio.

Understanding Surfactant Stabilization of MoS2 Nanosheets in Aqueous Dispersions from Zeta Potential Measurements and Molecular Dynamics Simulations

The sonication-assisted exfoliation of MoS2 in aqueous media in the presence of ionic surfactants to give stable dispersions is an attractive procedure for obtaining single or few-layered nanosheet...

Anchoring of ZnO nanoparticles on exfoliated MoS2 nanosheets for enhanced photocatalytic decolorization of methyl red dye

In this work, a facile method has been employed for the decoration of ultrafine ZnO nanoparticles over the exfoliated MoS2 nanosheets (ZnO-MoS2 composite) for the decolorization of methyl red dye under solar light irradiation. Further, the exfoliation of MoS2 nanosheets from bulk MoS2 powder and synthesis of pure ZnO nanoparticles was also demonstrated. Then, the prepared different photocatalyst materials have been characterized using various analytical techniques. The formation of ZnO and exfoliation of MoS2 in the composite has been evidently confirmed by XRD, FT-IR and Raman spectroscopic analysis. HR-TEM analysis clearly revealed the formation of ultrafine ZnO nanoparticles that are anchored on the exfoliated MoS2 nanosheets. In addition, the size of ZnO nanoparticles in the composite was significantly reduced compared to bare ZnO nanoparticles since the presence of MoS2 nanosheets which hinders the growth of ZnO nanoparticles. Due to the synergistic interaction between ZnO nanoparticles and exfoliated MoS2 nanosheets, the prepared composite exhibits superior photocatalytic activity towards the decolorization of methyl red dye up to 89% after 60 min irradiation time compared to pure ZnO nanoparticles (69%) and exfoliated MoS2 nanosheets (55%).

Room Temperature Formation of Carbon Onions via Ultrasonic Agitation of MoS₂ in Isopropanol.

Ultrasonic agitation is a proven method for breaking down layered materials such as MoS2 into single or few layer nanoparticles. In this experiment, MoS2 powder is sonicated in isopropanol for an extended period of time in an attempt to create particles of the smallest possible size. As expected, the process yielded a significant quantity of nanoscale MoS2 in the form of finite layer sheets with lateral dimensions as small as a few tens of nanometers. Although no evidence was found to indicate a larger the longer sonication times resulted in a significant increase in yield of single layer MoS2, the increased sonication did result in the formation of several types of carbon allotropes in addition to the sheets of MoS2. These carbon structures appear to originate from the breakdown of the isopropanol and consist of finite layer graphite platelets as well as a large number of multi-walled fullerenes, also known as carbon onions. Both the finite layer graphite and MoS2 nanoplatelets were both found to be heavily decorated with carbon onions. However, isolated clusters of carbon onions could also be found. Our results show that liquid exfoliation of MoS2 is not only useful for forming finite layer MoS2, but also creating carbon onions at room temperature as well.

Solution processable mixed-solvent exfoliated MoS2 nanosheets for efficient and robust organic light-emitting diodes

We demonstrate the use of solution-processed molybdenum trioxide (MoO3) nanoparticle-decorated molybdenum disulfide (MoS2) nanosheets (MoS2/MoO3) as hole injection layer (HIL) in organic lighting diodes (OLEDs). The device performance is shown to be significantly improved by the introduction of such MoS2/MoO3 HIL without any post-ultraviolet-ozone treatment, and is shown to better the performance of devices fabricated using conventional poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and MoO3 nanoparticle HILs. The MoS2/MoO3 nanosheets form a compact film, as smooth as PEDOT:PSS films and smoother than MoO3 nanoparticle films, when simply spin-coated on indium tin oxide substrates. The improvement in device efficiency can be attributed to the smooth surface of the nanostructured MoS2/MoO3 HIL and the excellent conductivity characteristics of the two-dimensional (2D) layered material (MoS2), which facilitate carrier transport in the device and reduce the sheet resistance. Moreover, the long-term stability of OLED devices that use such MoS2/MoO3 layers is shown to be improved dramatically compared with hygroscopic and acidic PEDOT:PSS-based devices.

Single-Molecule MoS2–Polymer Interaction and Efficient Aqueous Exfoliation of MoS2 into Single Layer

Single molecule force spectroscopy (SMFS) was utilized to study single-molecule interactions between synthesized polymers and MoS2 surfaces that provide the guidance to determine candidate polymers for efficient aqueous exfoliation of bulk MoS2 into single-layer nanosheets. The technique allowed the direct quantification of the adhesion force of single polymer molecules with both basal and edge surfaces of MoS2. Compared with two studied neutral polymers, highly water-soluble cationic poly(vinylbenzyl trimethyl ammonium chloride) (PVBTA) was shown to be more promising for MoS2 exfoliation as a result of strong single-molecule interactions with both basal and edge surfaces of MoS2. In 1 mM NaCl solution of pH around 5.5, the measured single-molecule adhesion forces on basal and edge surfaces were around 59 and 51 pN, respectively. Such strong adhesion force led to high performance of PVBTA in exfoliating MoS2 bulk material into single-layer sheets. Compared with reported approaches in the literatures, an o...