Morphology Of MoS2 Research Articles

Controlling the morphology of ultrathin MoS2/MoO2 nanosheets grown by chemical vapor deposition

The morphology of MoS2 plays an important role in its properties and applications, such as electronics and catalysis. Herein, the morphology of as-grown MoS2/MoO2 freestanding nanosheets and 2D MoS2, as synthesized by chemical vapor deposition using S and MoO3 powders as reactants, was studied by tuning the distances between the MoO3 source and the substrate and between the S and MoO3 powder sources. The distance between the MoO3 source and the substrate was deliberately reduced to obtain a sharp gradient of MoO3 precursor concentration on the growth substrate, and the position of S was changed to obtain various sulfur concentrations and initial reaction temperatures. As a result, morphology evolution, including 2D MoS2 and MoS2/MoO2 freestanding nanosheets was observed. A mechanism was proposed to explain the morphology transformation between horizontal 2D flakes and freestanding nanosheets. Based on this mechanism, synthesis methods to produce dense, ultrathin, large-sized MoS2 freestanding nanosheets were proposed. These results may be further generalized to create novel nanostructured devices.

Edge-Terminated MoS2 Nanoassembled Electrocatalyst via In Situ Hybridization with 3D Carbon Network.

Transition metal dichalcogenides, especially MoS2 , are considered as promising electrocatalysts for hydrogen evolution reaction (HER). Since the physicochemical properties of MoS2 and electrode morphology are highly sensitive factor for HER performance, designed synthesis is highly pursued. Here, an in situ method to prepare a 3D carbon/MoS2 hybrid catalyst, motivated by the graphene ribbon synthesis process, is reported. By rational design strategies, the hybrid electrocatalysts with cross-connected porous structure are obtained, and they show a high HER activity even comparable to the state-of-the-art MoS2 catalyst without appreciable activity loss in long-term operations. Based on various physicochemical techniques, it is demonstrated that the synthetic procedure can effectively guide the formation of active site and 3D structure with a distinctive feature; increased exposure of active sites by decreased domain size and intrinsically high activity through controlling the number of stacking layers. Moreover, the importance of structural properties of the MoS2 -based catalysts is verified by controlled experiments, validating the effectiveness of the designed synthesis approach.

Dependence of Morphology, Dispersion and Hydrodesulfurization Performance of Active Phases in NiMo/SBA‐15 on Loading Method

AbstractWith the aim of exploring the dependence of morphology, dispersion and hydrodesulfurization (HDS) activity of active phases over SBA‐15 on loading method, four NiMo/SBA‐15 catalysts have been prepared by two different Mo introduction strategies with varying MoO3 contents (13 and 19 wt.% in each approach, respectively). One of the approaches is the conventional incipient wetness impregnation (IM) and the other is a new‐proposed Mo‐based inorganic‐organic hybrid nanocrystals as the precursor with hydrothermal‐assisted (HA) loading method. The results show that metal species are severely aggregated at a high concentration by IM method, leading to the poorly distributed MoS2 slabs with large sizes and ultra‐high stacking layers. While in case of the HA approach, the organic molecules surrounding the Mo species can isolate Mo species effectively to prevent them from aggregation and greatly improve the dispersion of active phases, even at high MoO3 loadings. Therefore, the HDS activity is improved as increasing the amounts of MoO3 for the catalyst prepared with HA method because of the more active sites accessible to the reactants, however, HDS activity is decreased for the catalyst acquired by the IM method due to the serious metal aggregation. It is demonstrated that the HA method is favorable for the better dispersion of active phases over SBA‐15 with the help of organic molecules leading to the effective MoS2 morphology with remarkably enhanced catalytic activity, and such superiority of the HA approach is more prominent at high MoO3 loadings.

Hydrothermal synthesis and controlled growth of hierarchical 3D flower-like MoS2 nanospheres assisted with CTAB and their NO2 gas sensing properties

Hierarchical 3D flower-like MoS2 nanospheres with the diameter of about 300 nm were successfully synthesized via a facile hydrothermal process assisted with CTAB. And we found that CTAB played a vital role on the formation of MoS2 architectures. As the concentration of CTAB increasing, MoS2 nanopowders with sheet-like, flower-like, large size spherical morphologies were synthesized. And particle sizes of synthesized powders also increased. The optimum concentration of CTAB for the well-defined 3D hierarchical spherical morphology of MoS2 was 6 g/L. In addition, a feasible formation mechanism of the morphology evolution was put forward in detail on the basis of the experimental results. The gas–sensing properties of flower-like MoS2 nanospheres were tested. The result indicated that the sensor exhibited high response and selectivity towards NO2, which may be related to the open and well-defined structures and the abundant micro reaction rooms assembled by ultrathin nanosheets.

MoS2 nanosheets uniformly coated TiO2 nanowire arrays with enhanced electrochemical performances for lithium-ion batteries

Three-dimensional heterogeneous nanocomposites exhibit eminent cycling stability and rate capability as electrode materials for lithium-ion batteries. In this work, the composites of MoS2 nanosheets uniformly coated TiO2 nanowire arrays are fabricated by a glucose-assisted hydrothermal approach. The usage of glucose can be favorable to the uniform growth of MoS2 morphology. As anode materials for lithium ion batteries, the composites exhibit good specific capacity, cycling stability and rate capacity. The enhanced electrochemical properties are attributed to uniformity of composites since the uniform composites can effectively integrate the good cycling stability of TiO2 nanowire arrays and high capacity of MoS2 nanosheets. The gentle synthesis procedure and excellent electrochemical properties make TiO2 nanowire@MoS2 nanosheet arrays promising in high-performance lithium-ion batteries.

Metallic 1T Phase MoS2 Nanosheets for Supercapacitor Application

In the present study, a molybdenum disulfide MoS2 nanosheets (MoS2 NSs) were synthesized via a lithium intercalation and exfoliation method. The morphology and structure of the as-prepared MoS2 was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectrometer. The MoS2 NSs electrode exhibited higher specific capacitance (148 Fg-1 at 1 mVs-1 or 142 Fg-1 at 1 Ag-1) with excellent cycling stability, compared with bulk MoS2. The result shows that MoS2 is a promising electrode material for electrochemical supercapacitor.

MICROWAVE–ASSISTED SYNTHESIS OF MOLYBDENUM DISULFIDE (MoS2)

Molybdenum disulfide (MoS2) nanostructured has been synthesized by a facile and rapid microwave, in which ethylene glycol can act as an excellent susceptor of microwave irradiation. The structure and morphology of MoS2 were characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that nanometer scaled (< 100 nm) molybdenum disulfide with different morphologies can be successfully fabricated by microwave liquid–state method. Microwave irradiation can make localized heating that allows higher heating rates and shorter processing time. The low–cost synthesis procedure paves the way for the exploitation of the present product as electrode material in lithium ion batteries (LIBs).

Novel SiQDs–MoS2 heterostructures with increasing solar absorption for the photocatalytic degradation of malachite green

Novel heterostructures based on silicon quantum dots and molybdenum disulfide nanosheets (SiQDs–MoS2) were synthesized by a hydrothermal method, in which the introduced SiQDs play a determining role in manipulating the morphology, phase and band structure of MoS2. The resultant SiQDs–MoS2 is uniform flowerlike 3D microspheres assembled from petallike 2D MoS2 nanosheets anchored with 0D SiQDs, possessing abundant active sites. Besides, the primary MoS2 nanosheets consist of both semiconductive 2H and metallic 1T phases accompanied with intralayer mesopores and expanded interlayer spacing, endowing the resulting architectures with effective electron transfer. Significantly, the as-synthesized SiQDs–MoS2 exhibits intense full solar-spectrum absorption, indicating efficient solar energy harvesting. First-principles calculations simulate similar increased spectral absorption of monolayer MoS2 adhered with a Si cluster, suggesting the existence of new energy states associated with the integration of SiQDs and MoS2 nanosheets as evidenced by photoluminescence (PL) spectral analysis. As expected, the current SiQDs–MoS2 heterostructures demonstrate substantial photocatalytic activity even under visible and near-infrared (NIR) light on degradation of malachite green (MG). The type II electronic structure of SiQDs–MoS2 was proposed, enabling sufficient photogenerated electrons and holes for the photocatalytic reactions. This study may establish a new frontier on the rational design and feasible development of the hybrid structures with the desirable morphologies, phase compositions and band structures for the catalysis and beyond.

The High Surface Ratio Micro-MoS<sub>2</sub> Grain Composed of MoS<sub>2</sub> Nanosheet Prepared with One-Step Hydrothermal Synthesis

Micro molybdenum disulfide was prepared with one-step hydrothermal method; the influence of reactant concentration and temperature on the surface ratio of micro-MoS2 grain was investigated. Raman spectroscopy (Raman), X-ray diffraction (XRD), and Scanning electron microscopy (SEM) were used to characterize the structure, composition and morphology of MoS2. The results show that micro-MoS2 grains were synthesized with one-step hydrothermal synthesis, and the morphology of micro-MoS2 grains is like flower and sphere. The SEM figures indicate that the surface ratio of micro-MoS2 grains is different and also show that the surface ratio of micro-MoS2 grains can be improved by regulating reactant concentration and temperature. This research showed a method to improve the surface ratio of micro-MoS2 grains.

Impact of CTAB on morphology and electrochemical performance of MoS2 nanoflowers with improved lithium storage properties

The search for high capacity, low-cost electrode materials for lithium-ion batteries is a significant challenge in energy research. Among the numerous potential candidates, layered compounds such as MoS2 (Molybdenum Disulfide) have attracted increasing attention. A facile hydrothermal reduction process using hexadecyltrimethy ammonium bromide (CTAB) as surfactant was developed for the synthesis of lithium-ion battery anode material MoS2 nanoflowers. The impact of CTAB on morphology and electrochemical performance of MoS2 has been investigated. With the increase of CTAB content, MoS2 ultrathin nanosheets with high specific surface area and more active sites have been successfully synthesized. Electrochemical measurements demonstrated that MoS2 nanoflowers synthesized with 1% content of CTAB have better electrochemical performance than others as anode materials for Li-ion batteries, which yield a high discharge capacity of 1245 mAh g−1 at a current density of 50 mA g−1 and a stable capacity retention of 740 mAh g−1 until 100 electrochemical cycles.

Ultradispersed and Single-Layered MoS2 Nanoflakes Strongly Coupled with Graphene: An Optimized Structure with High Kinetics for the Hydrogen Evolution Reaction.

As one of the most promising Pt alternatives for cost-effective hydrogen production, molybdenum disulfide (MoS2), although has been studied extensively to improve its electrocatalytic activity, suffers from scarce active sites, low conductivity, and lack of interaction with substrates. To this end, we anchor ultradispersed and single-layered MoS2 nanoflakes on graphene sheets via a hybrid intermediate (MoOx-cysteine-graphene oxide), which not only confines the subsequent growth of MoS2 on the graphene surface but also ensures the intimate interaction between Mo species and graphene at the initial stage. Mo-O-C bond and a possible residual MoO3-x layer are proposed to comprise the interface bridging the two inherent incompatible phases, MoS2 and graphene. This strongly coupled structure together with the highly exposed MoS2 morphology accelerates the electron injection from graphene to the active sites of MoS2, and thus the hydrogen evolution reaction (HER) can achieve an overpotential of ∼275 mV at ∼-740 mA cm-2, and a Pt-like Tafel slope of ∼35 mV dec-1. Our results shed light on the indispensable role of interfacial interaction within semiconducting material-nanocarbon composites and provide a new insight into the actual activity of MoS2 toward the HER.

Controlled growth of MoS2 nanopetals on the silicon nanowire array using the chemical vapor deposition method

In order to get a physical/chemical insight into the formation of nanoscale semiconductor heterojunctions, MoS2 flakes are deposited on the silicon nanowire (SiNW) array by chemical vapor deposition (CVD). In this study, H2O2 treatment provides a favorable place where the formation of SiO bonds on the SiNW surfaces that play important roles (i.e., the nucleation centers, catalyst control centers or “seeds”) can dominate the growth of MoS2 on the SiNWs. Using this configuration, the effect of a change in the S/MoO3 mass ratio (MS/MMoO3) on the surface morphology of MoS2 is studied. It is shown that an increase in the value of MS/MMoO3 leads to the increased nucleation rate, increasing the size of MoS2 nanopetals. This study provides valuable scientific information for directly CVD-grown edge-oriented MoS2/SiNWs heterojunctions for various nanoscale applications, including hydrogen evolution reaction and electronic and optoelectronic devices.

Stability of two orientations of MoS2 on α-Al2O3(0001)

We have studied the morphology of MoS2 on α-Al2O3(0001) using first-principles calculations. We found that the binding energy between MoS2 and the OH-terminated α-Al2O3(0001) surface is weaker than that for the Al-terminated surface. The band gap reduction of MoS2 is also smaller on the OH-terminated surface than on the Al-terminated surface. The strong chemical interaction between MoS2 and α-Al2O3(0001) seems to result in the larger binding energy and the larger band gap reduction on the Al-terminated surface. Despite the different binding characteristics between the OH- and Al-terminated surfaces, the total energy difference between the two orientations of the MoS2 monolayer related by a 60° rotation is quite small for both surfaces, indicating that the two orientations of MoS2 exist with almost the same amount on the α-Al2O3(0001) regardless of the termination. This result suggests that it is essentially difficult to obtain large-scale MoS2 with a single domain on the α-Al2O3(0001) by chemical vapor deposition.

Fabrication of Porous MoS2 with Controllable Morphology and Specific Surface Area for Hydrodeoxygenation

SiO2 nanoparticles modified with aminopropyl-triethoxysilane (APTES) were used as hard templates for preparing porous MoS2. The method offers the advantages of simple steps, convenient operation, controllable pore size, and a specific surface area. Two morphologies of MoS2 were obtained by using thiourea and L-cysteine as sulfur sources, respectively. Porous MoS2 prepared by using thiourea had a smooth surface, whereas the surface of porous MoS2 prepared with L-cysteine had many burrs. The MoS2 nanomaterials with the respective morphologies were used to catalyze the hydrodeoxygenation (HDO) reaction. The activity of MoS2 prepared with L-cysteine was lower than that prepared with thiourea. Transmission electron microscopy and X-ray diffraction analyses showed that MoS2 had a large sheet-shaped structure and high crystallinity, leading to high reaction activity and high selectivity for cyclohexane. The reaction temperature also influenced the HDO significantly. The mechanism of hydrogenation of phenol was discussed.

Electron-spun 2D MoS2-decorated carbon nanofibers as pseudocapacitive electrode material into lithium ion battery

High lithium storage capacity and high conductivity of the LIB anode materials are extremely desirable for lithium-ion batteries (LIBs). Herein, the article demonstrated the method of embedding single or few layers 2D MoS2 into e-spun carbon nanofibers (MS-CNFs) to improve the electrochemical behavior of lithium anode materials. As demonstrated by various microscopic and spectroscopic analyses, MS-CNFs exhibited well-aligned morphology with uniform diameter of 330–360 nm. The roughness surface of MS-CNFs is favorable to shorten ion diffusion pathway and decrease the charge transfer resistance. Moreover, MS-CNFs hybrids exhibit a higher specific capacity of 1172 mAh g−1 with the good rate capability (97.3%) and cycle stability (86.4%) than pristine PAN based carbon nanofibers (p-CNFs) and 2D MoS2 due to the synergistic effect of pseudocapacitive material MoS2 and roughness morphology of CNFs. It is anticipated to exploit surface modification of MoS2 nanosheets and MoS2-based composites with high performances.

Morphologies controllable synthesis of MoS2 by hot-injection method: from quantum dots to nanosheets

Layered MoS2, which is treated as an alternative candidate of graphene, has attracted great attention due to its large intrinsic band gap and relatively high carrier mobility. It is relatively convenient and inexpensive to prepare MoS2 through chemical synthesis route. Herein, a novel solution-based hot-injection method is used to prepare MoS2. Controlling the reaction time leads to the variation of MoS2 morphologies, which present as quantum dots and nanosheets. Detail studies are carried out to investigate the formation mechanism of MoS2. The results indicate that the formation of layered MoS2 nanosheets follows a bottom-up process, which includes three steps in the order of quantum dots, small pieces and large area nanosheets.

Free-Standing Two Dimensional MoS2 nanosheet/Acitvated Carbon Clothes Composite for High Performance of Supercapacitor

Two dimensional (2D) MoS2 nanosheet has been successfully grown on Activated Carbon Clothes (ACC) by facile method, microwave-assisted hydrothermal at a shorter time. We have investigated the growth mechanism at different time reactions and their performance as electrode material of supercapacitor. Scanning electron microscopy (SEM) confirmed that time reaction controls the morphology and growth orientation of MoS2. On the other hand, it was found from the X-Ray Photoelectron Spectroscopy (XPS) that the additional phase which is MoO3 was formed during the reaction. This phase contributed to the performance by giving an additional pseudocapacitance. Furthermore, the intimate contact between MoS2 and ACC favor for fast electron transport during the charge and discharge. As a result, MoS2/ACC composite shows an excellent performance with specific capacitance of 230 F g-1 at a scan rate of 5 mV s-1 in 1M H2SO4 and high energy density of 79.9 W h kg-1 at high power density of 1044 W kg-1. Noteworthy, by growing MoS2 on ACC, the specific capacitance of MoS2 is 913.7 F g-1 which is the highest that ever been reported. Furthermore, this free-standing material is a promising material for a flexible supercapacitor. Keywords: MoS2, microwave-assisted hydrothermal, supercapacitor, energy density.

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.

Anisotropic MoS2 Nanosheets Grown on Self-Organized Nanopatterned Substrates.

Manipulating the anisotropy in 2D nanosheets is a promising way to tune or trigger functional properties at the nanoscale. Here, a novel approach is presented to introduce a one-directional anisotropy in MoS2 nanosheets via chemical vapor deposition (CVD) onto rippled patterns prepared on ion-sputtered SiO2 /Si substrates. The optoelectronic properties of MoS2 are dramatically affected by the rippled MoS2 morphology both at the macro- and the nanoscale. In particular, strongly anisotropic phonon modes are observed depending on the polarization orientation with respect to the ripple axis. Moreover, the rippled morphology induces localization of strain and charge doping at the nanoscale, thus causing substantial redshifts of the phonon mode frequencies and a topography-dependent modulation of the MoS2 workfunction, respectively. This study paves the way to a controllable tuning of the anisotropy via substrate pattern engineering in CVD-grown 2D nanosheets.

Highly selective hydrodesulfurization of gasoline on unsupported Co-Mo sulfide catalysts: Effect of MoS2 morphology

To remove sulfur-containing molecules from gasoline via hydrodesulfurization (HDS) while minimizing olefin hydrogenation is quite difficult. In this work, we report that an unsupported Co-Mo catalyst can achieve high HDS activity with low activity in olefin hydrogenation. The HDS selectivity of the Co-Mo catalyst is fourfold that of CoMo/γ-Al2O3 for both model gasoline and full-range FCC gasoline. For Co-Mo sulfide catalysts, we found that the MoS2 slab morphologies such as curvature, stacking number and slab length were important factors influencing the catalytic performance. Co-Mo catalyst with longer slab length and higher stacking number of MoS2 exhibited higher HDS selectivity. Nevertheless, it was found that the slab length showed much more influence on HDS selectivity than the stacking number. Furthermore, the curved MoS2 could facilitate the olefin isomerization. Present work provides a new way to develop a highly selective HDS catalyst by controlling the MoS2 morphology.