As-prepared MoS2 Research Articles

Synthesis of Layered MoS2 with Enlarged d-Spacing and Its Carbon Composite By Substrate-Induced-Coagulation Coating Method As Anode Materials for Lithium-Ion Batteries

2D layer structured molybdenum disulfide (MoS2) has been considered as an alternative next generation anode material over graphite, hard carbon and metal alloys, because MoS2 is structurally analogous to graphite (0.335nm) and has the interlayer d-spacing of 0.615nm while exhibiting two or three times the specific capacity of graphite. We will show how electrochemically active molybdenum disulfide (MoS2) with extended interlayer d-spacing was successfully prepared by the solvothermal synthesis method in an ethylene glycol-based mixed solvent at 200oC for 24h under an inert gas atmosphere. Then the prepared MoS2 samples were thermally annealed at various temperatures (300oC, 500oC, 800oC) to remove ethylene glycol from between the MoS2 nanosheets and to tune the d-spacing distance. The main redox reaction is described as Li2S ↔ 2Li+ + S + 2e-, and it suggests that the electrical conductivity of the MoS2 electrode must be enhanced by impregnation with carbonaceous materials to counteract the insulating properties of the sulfur. Therefore, the as-prepared MoS2 powders were surface- modified with nano-carbons (e.g. graphite and graphene) by the substrate-induced coagulation coating process and subsequent annealing at 600oC for 5h under the argon gas environment. The surface-modified carbon-MoS2 composite had a lithium diffusion coefficient (DLi: 1.08x10-6 cm2/s) during charging and discharging as compared to the as-prepared MoS2 (DLi: 4.14x10-7 cm2/s); the cell with the modified MoS2also exhibited higher capacity with a good capacity retention. The carbon-modified MoS2 electrode showed an initial capacity of 1150mAh/g and an average specific capacity of around 900 mAh/g, comparing favorably to the as-prepared MoS2 (700mAh/g). The carbon-MoS2 composite showed a higher capacity with good capacity retention and higher rate capability. The cells were electrochemically characterized by cyclic voltammetry, rate capability measurements, electrochemical impedance spectroscopy, lithium ion diffusion coefficient (DLi) measurement, differential capacity measurements, and in-situ electrochemical XRD measurement. In particular, the volumetric dilatation of the electrode materials during repeated cycles was monitored by in-situ electrochemical dilatometry. It was observed that the dilatations occur during charging /discharging, which corresponds to lithium inter-/deintercalation reactions at redox potentials of reduction at 1.1 V and oxidation at 1.6 V, 2.2V, respectively. The improved electrochemical properties of MoS2 tuned by the enlargement of the d-spacing and by the surface modification make it possible for MoS2to be used as a promising anode material for lithium-ion batteries.

Scalable Patterning of MoS2 Nanoribbons by Micromolding in Capillaries.

In this study, we report a facile approach to prepare dense arrays of MoS2 nanoribbons by combining procedures of micromolding in capillaries (MIMIC) and thermolysis of thiosalts ((NH4)2MoS4) as the printing ink. The obtained MoS2 nanoribbons had a thickness reaching as low as 3.9 nm, a width ranging from 157 to 465 nm, and a length up to 2 cm. MoS2 nanoribbons with an extremely high aspect ratio (length/width) of ∼7.4 × 10(8) were achieved. The MoS2 pattern can be printed on versatile substrates, such as SiO2/Si, sapphire, Au film, FTO/glass, and graphene-coated glass. The degree of crystallinity of the as-prepared MoS2 was discovered to be adjustable by varying the temperature through postannealing. The high-temperature thermolysis (1000 °C) results in high-quality conductive samples, and field-effect transistors based on the patterned MoS2 nanoribbons were demonstrated and characterized, where the carrier mobility was comparable to that of thin-film MoS2. In contrast, the low-temperature-treated samples (170 °C) result in a unique nanocrystalline MoSx structure (x ≈ 2.5), where the abundant and exposed edge sites were obtained from highly dense arrays of nanoribbon structures by this MIMIC patterning method. The patterned MoSx was revealed to have superior electrocatalytic efficiency (an overpotential of ∼211 mV at 10 mA/cm(2) and a Tafel slope of 43 mV/dec) in the hydrogen evolution reaction (HER) when compared to the thin-film MoS2. The report introduces a new concept for rapidly fabricating cost-effective and high-density MoS2/MoSx nanostructures on versatile substrates, which may pave the way for potential applications in nanoelectronics/optoelectronics and frontier energy materials.

Hydrothermal preparation of MoS2/TiO2/Si nanowires composite with enhanced photocatalytic performance under visible light

In this paper, we report on a simple, low cost and environmentally friendly method for the synthesis of 3D hierarchical molybdenum disulfide (MoS2) nano-sheets on TiO2 coated Si nanowires (SiNW). The synthetic method has several advantages such as low temperature, short reaction time and does not require any additives or surfactants. Characterization of the obtained composite material was performed by using scanning electron microscopy (SEM), Raman spectroscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) patterns and high resolution transmission electron microscopy (HR-TEM). The photocatalytic activity of the as-prepared MoS2 nanosheets was investigated for the degradation of Rhodamine B (RhB) under visible light irradiation. We found that MoS2/TiO2/SiNW interface exhibited stable and good catalytic activity as compared to other MoS2-based photocatalytic materials. The photocatalytic mechanism is believed to occur through photocatalytic and photosensitization processes.

Hierarchical 3D flower-like MoS2 spheres: Post-thermal treatment in vacuum and their NO2 sensing properties

Hierarchical 3D flower-like MoS2 spheres were first synthesized by a facile hydrothermal process. Afterwards, MoS2 spheres were annealed in vacuum under an Ar atmosphere to prevent MoS2 partial oxidation in the MoO3 form. As-prepared MoS2 samples were characterized by XRD, EDS, SEM, TEM and BET. SEM images showed that the flower-like spheres were about 1–2µm in diameter and built up with MoS2 thin sheets. Moreover, there were many mesoporous structures consisting of nanosheets on the surface of the MoS2 spheres. The resulting NO2 gas sensor displayed a high sensitivity, good reproducibility and selectivity. A possible NO2 gas sensing mechanism of MoS2 spheres was preliminarily proposed.

As-prepared MoS2 quantum dot as a facile fluorescent probe for long-term tracing of live cells

Recently, the newly emerged two-dimensional nanomaterials, layered transition metal dichalcogenide (e.g. MoS2) nanosheets, have drawn tremendous attentions due to their extraordinary electronic and optical properties, and MoS2 quantum dots (MoS2 QDs) with lateral sizes less than 10 nm have been found to be highly luminescent. In the present study, a facile approach for large-scale preparation of MoS2 QDs by Na intercalation reaction without using any toxic organic reagents is proposed. MoS2 QDs were carefully characterized by various techniques including transmission electron microscopy, atomic force microscopy, dynamic light scattering, spectroscopy, in vitro cytotoxicology, and capillary electrophoresis. The as-prepared MoS2 QDs were strongly fluorescent, highly photo-stable, low in cytotoxicity, and readily reactive to thiols. These inherent properties of MoS2 QDs make them excellent fluorescent probes for long-term live cell tracing. The results of live cells imaging indicated that MoS2 QD stained cells remained highly fluorescent after long-term culture, and could be easily traced from other co-cultured cell lines.

Efficient exfoliation of bulk MoS2 to nanosheets by mixed-solvent refluxing method

In this work, we reported a versatile and environmental-friendly mixed-solvent refluxing method to prepare MoS2 nanosheets with few layers by exfoliation of bulk MoS2 for the first time. The optimal synthetic conditions, including refluxing temperature, time and the volume ration of ethanol/water, were investigated according to the results of photocatalytic H2 evolution from water splitting. The results show that the optimal conditions involve refluxing in 30% ethanol/water solution at 80 °C for 3 h. And the as-prepared MoS2 nanosheets show much better photocatalytic properties than bulk MoS2. The rate of photocatalytic H2 evolution is 176.7 μmol g−1 h−1 over the MoS2 nanosheets synthesized under the optimal conditions, whereas the rate of H2 production is only 21.8 μmol g−1 h−1 over the bulk MoS2. In addition, some characterization studies demonstrate the MoS2 nanosheets have been successfully prepared by using the mixed-solvent refluxing method. The present work opens a new avenue to obtain two-dimensional nanosheets with single or few layers, such as the layered transition metal dichalcogenides.

Synthesis of Highly Uniform Molybdenum-Glycerate Spheres and Their Conversion into Hierarchical MoS2 Hollow Nanospheres for Lithium-Ion Batteries.

Highly uniform Mo-glycerate solid spheres are synthesized for the first time through a solvothermal process. The size of these Mo-glycerate spheres can be easily controlled in the range of 400-1000 nm by varying the water content in the mixed solvent. As a precursor, these Mo-glycerate solid spheres can be converted into hierarchical MoS2 hollow nanospheres through a subsequent sulfidation reaction. Owing to the unique ultrathin subunits and hollow interior, the as-prepared MoS2 hollow nanospheres exhibit appealing performance as the anode material for lithium-ion batteries. Impressively, these hierarchical structures deliver a high capacity of about 1100 mAh g(-1) at 0.5 A g(-1) with good rate retention and long cycle life.

Multi-layered mesh-like MoS2 hierarchical nanostructure fabricated on Ti foil: An efficient noble metal-free photocatalyst for visible-light-driven H2 evolution from water

In the present work, multi-layered mesh-like MoS2 hierarchical nanostructure was fabricated on a Ti foil in a hydrothermal process. Meanwhile, photocatalytic H2 evolution from water over the as-prepared MoS2 hierarchical nanostructure was investigated under visible irradiation. The results indicate that the as-prepared MoS2 hierarchical nanostructure consists of the vertically grown few-layers MoS2 nanosheets. And this three-dimensional mesh-like MoS2 hierarchical nanostructure possesses high photocatalytic activity for visible-light-driven H2 evolution from water. A rate of H2 evolution of approximately 240μmolg−1h−1 was achieved under optimal conditions. Furthermore, the photocatalytic mechanism was preliminarily discussed.

Constructing a MoS₂ QDs/CdS Core/Shell Flowerlike Nanosphere Hierarchical Heterostructure for the Enhanced Stability and Photocatalytic Activity.

MoS2 quantum dots (QDs)/CdS core/shell nanospheres with a hierarchical heterostructure have been prepared by a simple microwave hydrothermal method. The as-prepared samples are characterized by XRD, TEM, SEM, UV-VIS diffuse reflectance spectra (DRS) and N2-sorption in detail. The photocatalytic activities of the samples are evaluated by water splitting into hydrogen. Results show that the as-prepared MoS2 QDs/CdS core/shell nanospheres with a diameter of about 300 nm are composed of the shell of CdS nanorods and the core of MoS2 QDs. For the photocatalytic reaction, the samples exhibit a high stability of the photocatalytic activity and a much higher hydrogen evolution rate than the pure CdS, the composite prepared by a physical mixture, and the Pt-loaded CdS sample. In addition, the stability of CdS has also been greatly enhanced. The effect of the reaction time on the formations of nanospheres, the photoelectric properties and the photocatalytic activities of the samples has been investigated. Finally, a possible photocatalytic reaction process has also been proposed.

Pulsed erbium-doped fiber laser by a few-layer molybdenum disulfide saturable absorber: from Q-switching to mode-locking

Abstract. Wedemonstrated a pulsederbium-doped fiber laser (EDFL)based on a few-layer molybdenum disul-fide saturableabsorber(MoS 2 -SA). The MoS 2 -SA wasfabricated intoa film structure by evaporatingthe mixtureof MoS 2 nanosheets and polyvinyl alcohol. The Raman spectra and nonlinear optical characteristics were mea-sured to confirm the quality of the as-prepared MoS 2 -SA. By inserting the MoS 2 -SA into an EDFL, the pulsedoperation from the stable Q-switched to mode-locking regime could be achieved by simply increasing the pumppower level. The Q-switched pulse duration and repetition rate could vary from 5.18 to 3.53 μsand from 72.74to86.39 kHz, respectively. The maximum pulse energy was 74.93 nJ. After the achievement of Q-switched oper-ation, the ultrashort mode-locking pulse was obtained by further increasing the pump power. The results furtherdemonstrate the excellent saturable absorption ability of the few-layer MoS 2 at telecommunication waveband. ©2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.55.8.081308]

One-step fabrication of large-area ultrathin MoS2 nanofilms with high catalytic activity for photovoltaic devices.

Here we report a facile one-step solution-phase process to directly grow ultrathin MoS2 nanofilms on a transparent conductive glass as a novel high-performance counter electrode for dye-sensitized solar cells. After an appropriate reaction time, the entire surface of the conductive glass substrate was uniformly covered by ultrathin MoS2 nanofilms with a thickness of only several stacked layers. Electrochemical impedance spectroscopy and cyclic voltammetry reveal that the MoS2 nanofilms possess excellent catalytic activity towards tri-iodide reduction. When used in dye-sensitized solar cells, the MoS2 nanofilms show an impressive energy conversion efficiency of 8.3%, which is higher than that of a Pt-based electrode and very promising to be a desirable alternative counter electrode. Considering their ultrathin thickness, superior catalytic activity, simple preparation process and low cost, the as-prepared MoS2 nanofilms with high photovoltaic performance are expected to be widely employed in dye-sensitized solar cells.

Measurement of Ultrafast Excitonic Dynamics of Few-Layer MoS2 Using State-Selective Coherent Multidimensional Spectroscopy.

We report the first coherent multidimensional spectroscopy study of a MoS2 film. A four-layer sample of MoS2 was synthesized on a silica substrate by a simplified sulfidation reaction and characterized by absorption and Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. State-selective coherent multidimensional spectroscopy (CMDS) on the as-prepared MoS2 film resolved the dynamics of a series of diagonal and cross-peak features involving the spin-orbit split A and B excitonic states and continuum states. The spectra are characterized by striped features that are similar to those observed in CMDS studies of quantum wells where the continuum states contribute strongly to the initial excitation of both the diagonal and cross-peak features, while the A and B excitonic states contributed strongly to the final output signal. The strong contribution from the continuum states to the initial excitation shows that the continuum states are coupled to the A and B excitonic states and that fast intraband relaxation is occurring on a sub-70 fs time scale. A comparison of the CMDS excitation signal and the absorption spectrum shows that the relative importance of the continuum states is determined primarily by their absorption strength. Diagonal and cross-peak features decay with a 680 fs time constant characteristic of exciton recombination and/or trapping. The short time dynamics are complicated by coherent and partially coherent pathways that become important when the excitation pulses are temporally overlapped. In this region, the coherent dynamics create diagonal features involving both the excitonic states and continuum states, while the partially coherent pathways contribute to cross-peak features.

Luminescent monolayer MoS2 quantum dots produced by multi-exfoliation based on lithium intercalation

An effective multi-exfoliation method based on lithium (Li) intercalation has been demonstrated for preparing monolayer molybdenum disulfide (MoS2) quantum dots (QDs). The cutting mechanism of MoS2 QDs may involve the complete breakup around the defects and edges during the reaction of LixMoS2 with water and its following ultrasonication process. The multiply exfoliation make the MoS2 fragile and easier to break up. After the third exfoliation, a large number of monolayer MoS2 QDs is formed. The as-prepared MoS2 QDs show photoluminescence (PL) inactive due to the existence of 1T phase. After heating treatment, the PL intensity excited at 300nm is enhanced by five times. The MoS2 QDs solution has an excitation-dependent luminescence emission which shifts to longer wavelengths when the excitation wavelength changes from 280nm to 370nm. The optical properties are explored based on the quantum confinement and edge effect.

Effect of Polymer Addition on the Structure and Hydrogen Evolution Reaction Property of Nanoflower-Like Molybdenum Disulfide

Nano-structured molybdenum disulfide (MoS2) catalysts have been extensively developed for the hydrogen evolution reaction (HER). Herein, a novel hydrothermal intercalation approach is employed to fabricate nanoflower-like 2H–MoS2 with the incorporation of three polymers, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyethylenimine (PEI). The as-prepared MoS2 specimens were characterized by techniques of scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), together with Raman and Fourier transform infrared spectroscopy (FTIR). The HER properties of these lamellar nanoflower-like composites were evaluated using electrochemical tests of linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The existent polymer enlarges the interlayer spacing of the lamellar MoS2, and reduces its stacked thickness. The lamellar MoS2 samples exhibit a promoting activity in HER at low additions of these three polymers (0.04 g/g MoS2 for PVA and PEI, and 0.08 g/g MoS2 for PVP). This can be attributed to the fact that the expanded interlayer of MoS2 can offer abundant exposed active sites for HER. Conversely, high additions of the polymers exert an obvious interference in the HER activity of the lamellar MoS2. Compared with the samples of MoS2/PVP–0.08 and MoS2/PEI–0.04, the MoS2/PVA–0.04 composite exhibits excellent activity in HER, in terms of higher current density and lower onset potential.

Improved dehydrogenation performance of LiBH4 by 3D hierarchical flower-like MoS2 spheres additives

In this work, 3D hierarchical flower-like MoS2 spheres are successfully fabricated via a hydrothermal method followed by a heat treatment. The obtained product is composed of few-layered MoS2 nanosheets with enlarged interlayer distance (ca. 0.66 nm) of the (002) plane. Meanwhile, the hydrogen storage properties of the as-prepared MoS2 ball milled with LiBH4 are systematically investigated. The results of temperature programmed desorption (TPD) and isothermal measurement suggest that the LiBH4–MoS2 (as-prepared) mixture exhibits favorable dehydrogenation properties in both lowering the hydrogen release temperature and improving kinetics of hydrogen release rate. LiBH4–MoS2 (as-prepared) sample (the preparation mass ratio is 1:1) starts to release hydrogen at 171 °C, and roughly 5.6 wt% hydrogen is released within 1 h when isothermally heated to 320 °C, which presents superior dehydrogenation performance compared to that of the bulk LiBH4. The excellent dehydrogenation performance of the LiBH4–MoS2 (as-prepared) mixture may be attributed to the high active site density and enlarged interlayer distance of the MoS2 nanosheets, 3D architectures and hierarchical structures.

Thin-layered MoS2/polyaniline nanocomposite for highly sensitive electrochemical detection of chloramphenicol

Abstract In this study, we synthesized molybdenum disulfide/polyaniline (MoS 2 /PANI) nanocomposite via in situ polymerization of aniline in the presence of thin-layered MoS 2 . The as-prepared MoS 2 /PANI nanocomposite obtained an improved electrochemical performance due to the physisorption interaction between aromatic aniline and the basal plane of MoS 2 . Furthermore, we constructed a new kind of electrochemical sensor based on MoS 2 /PANI nanocomposite for the detection of chloramphenicol, which showed an excellent performance. The sensor has a high sensitivity and wide detection range from 1 × 10 −7 mol/L to 1 × 10 −4 mol/L, with a low detection limit of 6.9 × 10 −8 mol/L.

Synthesis of fungus-like MoS2 nanosheets with ultrafast adsorption capacities toward organic dyes

Fungus-like molybdenum disulfide (MoS2) nanosheets with a thickness of a few nanometers have been successfully synthesized via one-pot hydrothermal method. The as-prepared MoS2 nanosheets with a high surface area of 106.989 m2 g−1 exhibited excellent wastewater treatment performance with high removal capacities toward organic dyes. In addition, the fungus-like MoS2 nanosheets can absorb Congo red completely within 2 min. Successful access to high quality fungus-like MoS2 nanosheets will make it possible for their potential application in catalysis and other fields.

Ball-milling MoS2/carbon black hybrid material for catalyzing hydrogen evolution reaction in acidic medium

Replacing platinum for catalyzing hydrogen evolution reaction (HER) in acidic medium remains great challenges. Herein, we prepared few-layered MoS2 by ball milling as an efficient catalyst for HER in acidic medium. The activity of as-prepared MoS2 had a strong dependence on the ball milling time. Furthermore, Ketjen Black EC 300J was added into the ball-milled MoS2 followed by a second ball milling, and the resultant MoS2/carbon black hybrid material showed a much higher HER activity than MoS2 and carbon black alone. The enhanced activity of the MoS2/carbon black hybrid material was attributed to the increased abundance of catalytic edge sites of MoS2 and excellent electrical coupling to the underlying carbon network.

Synthesis of MoS2 multi-wall nanotubes using wet chemical method with H2O2 as growth promoter

This paper reports the synthesis of MoS2 multi-wall nanotubes (MWNTs) using a wet chemical method assisted by H2O2 solvent as a growth promoter for the first time. The influence of the calcination temperature on the morphology of the nanotubes is discussed. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the as-prepared MoS2 MWNTs. The powder XRD measurement indicated a hexagonal phase of the MoS2 MWNTs. The addition of H2O2 solvent influenced the growth, and the mean length of the nanotubes was 100–300nm with diameter of 20–30nm. The synthetic conditions for optimization of the MoS2 MWNTs are also discussed. The calculated band gap energy is 2.57eV. The MoS2 MWNTs exhibit higher photocatalytic activity for the degradation of Rhodamine B (RhB) under UV light irradiation for 60min. The highest photocatalytic activity was obtained with the sample containing 0.5wt% MoS2 MWNTs, with which more than 98% of the RhB was degraded within 60min.

Highly transparent ultrathin metal sulfide films as efficient counter electrodes for bifacial dye-sensitized solar cells

Highly transparent metal sulfides (Ni3S4, MoS2) are directly deposited on fluorine doped tin oxide (FTO) substrates as effective Pt-free counter electrodes (CEs) for novel bifacial dye-sensitized solar cells (DSSCs). The blocky-like Ni3S4 and petal-shaped MoS2 nanoparticles (NPs) possess large surface area, which provides amount of active site to contact with electrolyte. The films not only show high transmittance at visible wavelengths, but also exhibit prominent electrocataltytic activity and outstanding metallic conductivity in iodine/iodide based bifacial DSSCs. Under front-side irradiation (100mW/cm2), the bifacial DSSC based on the transparent Ni3S4 or MoS2 CE presents remarkable photovoltaic conversion efficiency (Eff=6.56%, 6.11%, respectively), closing to that of conventional Pt CE (Eff=6.83%). Moreover, by appending an ordinary mirror as a photo reflector to achieve both-side illumination, the bifacial DSSC using the transparent Ni3S4 or MoS2 sample as CE obtained higher short-circuit current density (Jsc) and more attractive power conversion efficiency (PCE) (Eff=7.06%, 6.65%, respectively). It indicates that the as-prepared transparent Ni3S4 and MoS2 CEs are promising potential candidates to explore low-cost and high-efficiency bifacial DSSCs.