Growth and optical properties of large-scale MoS2 films with different thickness

The synthesis of large-scale molybdenum disulfide (MoS₂) with high quality is highly desirable for the promising applications in flexible optoelectronic devices. Here, we report a feasible one-step chemical vapor deposition (CVD) synthesis of continuous MoS₂ films with different layer-number via adjusting the growth temperature in the range of 740–800 °C. Influences of the annealing treatments at diverse temperature ranging from 300 to 500 °C on Raman and PL spectra of the monolayer MoS₂ film grown at 780 °C are reported. PL characterization shows that the PL emission of film annealed at 400 °C exhibits highest intensity with a blue-shift in comparison to that of the pristine film grown at 780 °C. The PL fluctuation of the MoS₂ film annealed at 400 °C is mainly originated from the high crystalline quality and strain-release. This study sheds a light on growth and performance optimization of the large-area two-dimensional transition metal dichalcogenides films.     

A Review of Molybdenum Catalysts for Synthesis Gas Conversion to Alcohols: Catalysts,Mechanisms and Kinetics

Recent literature on synthesis gas conversion to higher alcohols over Mo-based catalysts is reviewed. Density functional theory calculations show that Mo-CO adsorption is weakened by C, P, or S ligands and this facilitates CO dissociation, either directly on Mo₂C, or by H-assisted dissociation on MoS₂, Mo₂C, and MoP. Consequently, Mo-based catalysts have high hydrocarbon selectivity unless they are promoted with alkali metals and/or Group VIII metals. Promoted MoS₂ and MoP have alcohol selectivities of ～80 C atom % (CO₂-free basis) at typical operating conditions (5–8 MPa, H₂/CO = 2–1, 537–603 K), whereas on promoted Mo₂C, alcohol selectivities are ～60%. The kinetics of the synthesis gas conversion reactions over Mo-based catalysts have mostly been described by empirical power law models and the alcohol and hydrocarbon product distributions are consistent with a CO insertion mechanism for chain growth.     

P-doped MoS2/Ni2P/Ti3C2Tx heterostructures for efficient hydrogen evolution reaction in alkaline media

By combining the advantages of doping to change the electronic structure of molybdenum disulfide (MoS₂), transition metal phosphides, and MXene, we proposed the idea of designing and preparing a new type of composite material, P-doped MoS₂/Ni₂P/Ti₃C₂T_x heterostructures (denoted as P@MNTC), to serve as the hydrogen evolution reaction (HER) catalyst of electrochemical water splitting. The as-prepared P@MNTC heterostructures show a significant HER activity with an overpotential of 120 mV at 10 mA cm^–2 in alkaline electrolyte, with decreasing 105 and 125 mV compared with those of MoS₂ and MXene, respectively. The density functional theory indicates that the P doping and synergy effect of Ti₃C₂T_x can enhance the activation of MoS₂ and thus promote dissociation and absorption of H₂O during HER process. This strategy provides a promising way to develop high-efficiency MoS₂- and Ti₃C₂T_x-based composite catalysts for alkaline HER.     

High temperature friction and wear behavior of MoS<Subscript>2</Subscript>/Nb coating in ambient air

MoS₂ coatings are well-known for their solid lubricant properties and used as self-lubricants in vacuum and inert gas environments, and such coatings are not used in atmospheric conditions because of their deteriorating tribology. The tribological performance of MoS₂ solid lubricant coatings in the different atmospheres has been improved by the codeposition of a small amount of another metal. In this study, the tribological behavior of MoS₂/Nb coatings was investigated in ambient air at temperatures up to 500°C by using high-temperature pin-on-disc tribo testers and alumina balls as counterfaces. MoS₂/Nb coatings were deposited on silicon wafers and AISI 52100 steel substrate by closed-field unbalanced magnetron sputtering. The structural analyses of the coatings were performed using X-ray diffraction and scanning electron microscopy techniques. The hardness was measured using a microhardness tester.     

Enhanced thermoelectric properties of 2H–MoS2 thin film by tuning post sulfurization temperature

Two-dimensional transition metal dichalcogenide semiconductors (TMDCs) like MoS₂ are becoming more popular as thermoelectric materials because they are abundant, nontoxic, and have good performance. In the study, the MoS₂ thin films have prepared by the sputtering and post-sulfurization process at various temperatures 450 °C, 550 °C, 650 °C, and 750 °C. The XRD data exhibits the formation of the 2H phase of MoS₂ thin film with (002), (004), and (006) planes. The Raman spectroscopy has confirmed the 2H–MoS₂ thin films with 2LA (M), A_1g, E_2g, and E_g vibrational modes. The SEM images have shown the thin MoS₂ flakes. The Seebeck and electrical conductivity data indicated an enhancement in Seebeck coefficient and electrical conductivity from 20 to 31 μV/^°C and 26–53 S/m, respectively, as the post sulfurization temperature increased from 450 °C to 750 °C. The enhancement of the Seebeck coefficient and electrical conductivity have been linked to the perfection of the 2H phase of MoS₂ film. The improved crystal structure has increased carrier mobility, leading to a high power factor of the 5.09 μWm^?1C^?2.     

The possible use of alkali metal modified NbMCM-41 in the synthesis of 1,4-dihydropyridine intermediates

In this work we have prepared the catalysts containing all alkali metals (from Li to Cs) supported on mesoporous niobosilicate molecular sieve, NbMCM-41, and for comparison also loaded on silicate MCM-41. The materials were characterised by N₂ adsorption, XRD, and test reactions (acetonylacetone cyclisation and Knoevenagel condensation). It has been found that niobium located in the mesoporous material plays a role of structural promoter which prevents the solid from the disordering caused by the treatment with alkali metal solution. Moreover, it changes the catalytic properties of basic centres generated by alkali metal loading in relation to those observed for alkali metals supported on silicate MCM-41. Rb/NbMCM-41 has been proposed as active and selective catalyst in the condensation of benzaldehyde and different substituted benzaldehydes with ethyl acetoacetate towards the synthesis of intermediates in the preparation of some dihydropyridines.     

Electrochemical energy storage applications of carbon nanotube supported heterogeneous metal sulfide electrodes

Electrochemical system centered on hierarchically carbon-based metal sulphide assemblies are of great fame for competent supercapacitors. Herein, the synthesis of a hierarchical CNT anchored MoS₂–Bi₂S₃ nanocomposite is reported. Attractively, a vertically grown Bi₂S₃ nanorods supported on MoS₂ nanosheets with carbon framework acts as a highly effective electrode in alkaline electrolyte. More interestingly, this hierarchical structure and synergetic upshot of CNT and composites provide excess coverage of active sites with improved conductivity and stability. Advancing from the physical and compositional properties of nanocomposites, the specific capacitance of MoS₂–Bi₂S₃@CNT composites is measured to be 1338 F/g at 10 mV/s, columbic efficiency of 99.5% over 10000 cycles and long-term stability (60% retention at 0.5 A g^?1 over 2000 cycles and 34.6% up to 10000 cycles). The success of this MoS₂–Bi₂S₃@CNT composite may be attributed to the structural advantages, admirable cyclic stability, and better capacitance retention for supercapacitor applications.     

Hydrothermal Syntheses and Catalytic Properties of Dispersed Molybdenum Sulfides

Reactions of ammonium thiomolybdate under mild hydrothermal conditions were studied, and the range of conditions leading to the dispersed MoS₂ product has been determined. The morphology and the catalytic properties of the hydrothermal MoS₂ preparations have been compared with those of reference MoS₂ produced from the thermal decomposition of thiosalts. It has been shown that the length of the slabs and their stacking number of the crystallites of hydrothermal MoS₂ preparations differ considerably from those in the reference sulfides. The morphological differences strongly influence the hydrogenation to hydrodesulfurization activity ratio in these systems.     

Hydroxy Sulfonated Fatty Acid Esters as Surface Active Agents III: Kinetics of the Synthesis

Kinetics of synthesis of a new type of surface active agents having the general formula RCOOCH₂CHOHCH₂SO₃M, where M is an alkali metal or other basic radical, have been studied. Synthesis of hydroxy sulfonated fatty acid esters of oleic and lauric acids by the reaction of molar proportion of sodium chlorohydroxy propane sulfonate with fatty acid soap (formed in situ) was found to be a pseudo-first order reaction. The energy of activation was calculated from Arrhenius equation as 25.7 kcal/mole. Paper chromatographic method has also been used for kinetic studies.     

Prediction of a highly sensitive molecule sensor for SOx detection based on TiO2/MoS2 nanocomposites: a DFT study

First principles calculations within density functional theory have been carried out to investigate the adsorptions of SO_x (x?=?1, 2) molecules on TiO₂/MoS₂ nanocomposites in order to fully discover the gas sensing capabilities of TiO₂/MoS₂ composite systems. The van der Waals interactions were included to obtain the most stable geometrical structures of TiO₂/MoS₂ nanocomposites with adsorbed SO_x molecules. SO_x molecules preferentially interact with the doped nitrogen and fivefold coordinated titanium sites of the TiO₂ anatase nanoparticles because of their higher activities in comparison with the other sites. The results presented include structural parameters such as bond lengths and bond angles and energetics of the systems such as adsorption energies. The variation of electronic structures are discussed in view of the density of states and molecular orbitals of the SO_x molecules adsorbed on the nanocomposites. The results show that the adsorption of the SO_x molecule on the N-doped TiO₂/MoS₂ nanocomposite is energetically more favorable than the adsorption on the undoped one, implying that the nitrogen doping helps to strengthen the interaction of SO_x molecules with TiO₂/MoS₂ nanocomposites. These calculated results thus provide a theoretical basis for the potential applications of TiO₂/MoS₂ nanocomposites in the removal and sensing of harmful SO_x molecules.     

Application of nanocatalytic systems for deep processing of coal and heavy petroleum feedstock

The specific features of the catalysis of deep processing (hydrogenation and gasification) of coal and hydroconversion of heavy petroleum feedstock are considered. It has been shown that it is reasonable to use new catalyst forms and catalyst introduction methods for the processing of these raw materials in view of their specific composition and properties (large size of molecules, thermal instability, and the presence of inorganic compounds in the feedstock). In particular, a dispersion of nanosized spherical particles of MoS₂ in a liquid hydrocarbon medium is an effective catalyst for the coal hydrogenation and heavy-oil hydrocon-version processes. Gaseous alkali metal hydroxides have been proposed for the gasification of solid fuels. The mechanisms of the formation of catalyst systems and some of their properties are discussed.     

Enhancement of mechanical and tribological properties in ring‐opening metathesis polymerization functionalized molybdenum disulfide/polydicyclopentadiene nanocomposites

This study focuses on the possibility of improving performance properties of polydicyclopentadiene (PDCPD) nanocomposites for engineering applications using nanoparticles. In this article, molybdenum disulfide/polydicyclopentadiene (MoS₂/PDCPD) nanocomposites have been prepared by in situ ring‐opening metathesis polymerization using reaction injecting molding (RIM) process. To enhance the interfacial adhesion between the fillers and PDCPD matrix, the surface modified MoS₂ nanoparticles hybridized with dialkyldithiophosphate (PyDDP) were successfully prepared by in situ surface grafting method. The effect of low MoS₂ loadings (<3 wt %) on the mechanical and tribological behaviors of PDCPD was evaluated. The results indicated that the friction coefficient of the MoS₂/PDCPD nanocomposites was obviously decreased and the wear resistance of nanocomposites was greatly improved by the addition of PyDDP‐hybridized MoS₂ nanoparticles; meanwhile, the mechanical properties were also enhanced. The MoS₂/PDCPD nanocomposites filled with 1 wt % PyDDP‐hybridized MoS₂ exhibited the best mechanical and anti‐wear properties. The friction coefficient was shown to decrease by more than 40% compared to pure PDCPD by incorporating just 1 wt % hybridized MoS₂ nanoparticles, and modest increase in modulus and strength was also observed. The reinforcing and wear‐resistant mechanisms of MoS₂/PDCPD nanocomposites were investigated and discussed by scanning electron microscopy. The well interfacial compatibility between the particle/matrix interfaces played an important role for the improved mechanical and tribological properties of MoS₂/PDCPD nanocomposites in very low MoS₂ loadings. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Nickel and manganese co-modified K/MoS2 catalyst: high performance for higher alcohols synthesis from CO hydrogenation

Mn and Ni co-modified K/MoS₂ catalyst for higher alcohols synthesis from syngas was prepared by co-precipitation, and its performance in CO hydrogenation was tested. The results indicated a synergistic effect between Mn and Ni on co-modified K/MoS₂ catalyst, which led to high performance for higher alcohols synthesis.     

Relevant photovoltaic effect in N-doped CQDs/MoS2 (0D/2D) quantum dimensional heterostructure

In this work, a novel kind of solar cell based on the N-CQDs/MoS₂ (0D/2D) quantum dimensional heterostructure has been fabricated using a two-dimensional (2D) MoS₂ ultrathin layer and zero-dimensional (0D) Nitrogen-doped carbon quantum dots (N-CQDs). The combination of N-CQDs and MoS₂ offers good optical and electrical characteristics. The current-voltage (I–V) characteristics of the quantum dimensional heterostructure have been recorded in the dark and under the illumination of solar radiations. A significant current rectification ratio has been observed in dark I–V characteristics. Furthermore, a remarkable shift of ?13.49 mA in the I–V curve is observed on the exposure to solar radiation. The fabricated quantum dimensional heterostructure exhibits a significant power conversion efficiency (η) of 4.06% and an open-circuit voltage of 0.83 V. The external quantum efficiency (EQE) spectra support the recorded photovoltaic performance of the heterostructure. The aforementioned results could be ascribed to the effective separation of photogenerated electron-hole pairs at the junction contact. The N-CQDs serve as an electron blocking layer, preventing additional carrier recombination at the metal electrode. Our findings show that N-CQDs/MoS₂ heterostructure has a great potential in futuristic low-cost, non-toxic, and highly efficient solar cells for next-generation energy harvesting applications.     

On methanethiol synthesis from H2S‐containing syngas over K2MoS4/SiO2 catalysts promoted with transition metal oxides

The catalysts K₂MoS₄/SiO₂ promoted with transition metal oxides Fe₂O₃, CoO, NiO and MnO₂ were prepared and used to catalyze the synthesis of methanethiol from H₂Scontaining syngas. The results of activity assay show that the catalysts promoted with Fe₂O₃, CoO and NiO can remarkably increase the hour space yield of methanethiol. Nevertheless, MnO₂ was found to have a disadvantageous effect on the selectivity of methanethiol. The results of XRD and XPS characterization indicate that the addition of the transition metal oxides promoters is in favor of the formation of a Mo–S–K active phase and also retards the decomposition of K₂MoS₄ to MoS₂, thereby suppressing both the deep reduction of Mo species and the formation of (S–S)² species, which are reflected by the increment of the concentration ratios of both Mo⁶⁺/Mo⁴⁺ and S²/(S–S)².     

Edge defect-assisted synthesis of chemical vapor deposited bilayer molybdenum disulfide

The synthesis of two-dimensional molybdenum disulfide (MoS₂) has invoked much research interest in recent years. In this work, chemical vapor deposition (CVD) was employed to grow a novel molybdenum disulfide. The synthesis reaction was operated in an inert gas environment, with the sulfur precursor placed in the upstream zone of a double zone tube furnace, and the molybdenum trioxide (MoO₃) precursor placed in a small tube in the downstream zone. A piece of glass was used as the substrate, which was placed beside the small tube. We intentionally built a high concentration of molybdenum precursor above the substrate. The specific morphology hinged highly on the concentration of molybdenum. Abundant molybdenum atoms adsorbed on the edges of the bottom MoS₂ and formed defects, which promoted the nucleation of the top layer MoS₂ and preferentially grew from the edges. This result provides an innovative method to controllably synthesize novel bilayer molybdenum disulfide by a one-step method of chemical vapor deposition.     

Liquid-Phase Exfoliation and Functionalization of MoS2 Nanosheets for Effective Antibacterial Application

A lysozyme (Lys)-assisted liquid-phase exfoliation technique was designed to synthesize MoS₂ nanosheets (MoS₂-Lys NSs). As a novel nanozyme antibacterial agent with high peroxidase-like catalyst activity, MoS₂-Lys NSs showed good antibacterial efficacy against both Gram-negative ampicillin-resistant Escherichia coli (Amp^r E. coli) and Gram-positive Bacillus subtilis. A possible antibacterial mechanism is also proposed. This work provides an effective antibacterial strategy based on the MoS₂-Lys NSs antibacterial agent.     

MoS2 nanosheet/ZnO nanowire hybrid nanostructures for photoelectrochemical water splitting

As an efficient cocatalyst, the 2D MoS₂ is thought to be a promising substitute to noble metals in the hydrogen evolution reaction (HER). In the past few years, single and few‐layer MoS₂ nanosheets have attracted a wide range of concerns for HERs. In this paper, single crystalline ZnO nanowires and MoS₂ nanosheets are fabricated to form MoS₂ nanosheet/ZnO nanowire hybrid nanostructure to enhance the hydrogen photogeneration. The results show that the hybridization of ZnO with moderate MoS₂ loading could enhance the PEC activity by producing more electrons and holes and reducing their recombination. The synthesis of MoS₂/ZnO composites proposed an effective way to build low cost and highly active HER catalysts. Moreover, the study on MoS₂/ZnO composites sheds light to the deep insight into the mechanism of photoelectrocatalytic HERs.     

Novel strategy for molybdenum disulfide nanosheets grown on titanate nanotubes for enhancing the flame retardancy and smoke suppression of epoxy resin

A novel hybrid consisting of a molybdenum disulfide (MoS₂) coating on a titanium dioxide nanotube (TNT) surface (MoS₂–TNT) was synthesized by a hydrothermal method. The MoS₂, TNTs, and MoS₂–TNT hybrid were incorporated into epoxy resin (EP) to study their effects on its thermal performance and flame retardancy. Thermogravimetric analysis results show that the char yield at 700 °C of EP–MoS₂–TNTs was obviously increased compared with that of the EP–MoS₂ or EP–TNTs; this indicated that MoS₂–TNTs had a good carbonization effect. The limiting oxygen index, cone calorimetry, and smoke density tests showed that MoS₂–TNTs effectively improved the flame retardancy and smoke suppression of EP. This was attributed to the physical barrier effect of MoS₂ and the adsorption of TNTs. Moreover, the flame retardancy and smoke suppression of the EP–MoS₂–TNTs were better than those of the EP–MoS₂ or EP–TNTs alone with the same amount of addition; this indicated that there was a synergistic effect between MoS₂ and TNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46064.     

Some properties of styrene‐based ionomers. I

Some properties of styrene‐based ionomers containing alkali metal salts of acrylic acid or methacrylic acid have been investigated. A study has been conducted to examine the influence of the acidic content and nature (acrylic or methacrylic) and the nature of the alkali metal salt on the glass transition temperature, density, melt index and activation energy of a flow of the styrene‐based ionomers. The present studies have indicated that the temperature of glass transition (T_g) of sodium ionomers increases as the sodium content rises and the region of the glass transition broadens. The T_g's of the styrene‐acrylic acid (S‐AA) ionomers do not depend on the nature of the alkali metal introduced into the copolymer. The density of films rises with the content of acid or salt introduced to the polystyrene chain. The melt index of the investigated ionomers depends on the amount and type of the introduced acid and salt as well as on the molecular weight of the initial copolymer. The energy of activation of the flow is independent of the polymer molecular weight; however, the energy of activation of flow of the ionomers increases with larger ionic radii of the introduced alkali metal. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 55–62, 2003