Showing papers on "Molybdenum published in 2014"
TL;DR: In this article, the authors proposed a cost-effective molybdenum phosphide that exhibits high activity towards the hydrogen evolution reaction (HER) in both acid and alkaline media even in bulk form.
Abstract: Electrochemical production of hydrogen from water has been directed to the search for non-noble metal based and earth-abundant catalysts. In this work, we propose a novel cost-effective catalyst, molybdenum phosphide that exhibits high activity towards the hydrogen evolution reaction (HER) in both acid and alkaline media even in bulk form. Comparative analysis of Mo, Mo3P and MoP as catalysts for HER clearly indicates that phosphorization can potentially modify the properties of the metal and different degrees of phosphorization lead to distinct activities and stabilities. Theoretical calculations by density functional theory also show that a simple phosphorization of molybdenum to form MoP introduces a good ‘H delivery’ system which attains nearly zero binding to H at a certain H coverage. With the combination of experimental results and theoretical calculations, this work has enlightened a new way of exploring cost-effective catalysts for HER.
1,091 citations
TL;DR: The extraordinarily high activity and stability of this catalyst open up avenues to replace platinum in technologies relevant to renewable energies, such as proton exchange membrane (PEM) electrolyzers and solar photoelectrochemical (PEC) water-splitting cells.
Abstract: Introducing sulfur into the surface of molybdenum phosphide (MoP) produces a molybdenum phosphosulfide (MoP|S) catalyst with superb activity and stability for the hydrogen evolution reaction (HER) in acidic environments. The MoP|S catalyst reported herein exhibits one of the highest HER activities of any non-noble-metal electrocatalyst investigated in strong acid, while remaining perfectly stable in accelerated durability testing. Whereas mixed-metal alloy catalysts are well-known, MoP|S represents a more uncommon mixed-anion catalyst where synergistic effects between sulfur and phosphorus produce a high-surface-area electrode that is more active than those based on either the pure sulfide or the pure phosphide. The extraordinarily high activity and stability of this catalyst open up avenues to replace platinum in technologies relevant to renewable energies, such as proton exchange membrane (PEM) electrolyzers and solar photoelectrochemical (PEC) water-splitting cells.
876 citations
TL;DR: In this article, four phases of molybdenum carbide were synthesized and investigated for their electrocatalytic activity and stability for hydrogen evolution reaction in acidic solution.
Abstract: Molybdenum carbide has been proposed as a possible alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Previous studies were limited to only one phase, β-Mo2C with an Fe2N structure. Here, four phases of Mo-C were synthesized and investigated for their electrocatalytic activity and stability for HER in acidic solution. All four phases were synthesized from a unique amine-metal oxide composite material including γ-MoC with a WC type structure which was stabilized for the first time as a phase pure nanomaterial. X-ray photoelectron spectroscopy (XPS) and valence band studies were also used for the first time on γ-MoC. γ-MoC exhibits the second highest HER activity among all four phases of molybdenum carbide, and is exceedingly stable in acidic solution.
746 citations
TL;DR: This work reports a high-yield exfoliation process using lithium, potassium and sodium naphthalenide where an intermediate ternary Li(x)MX(n) crystalline phase (X=selenium, sulphur, and so on) is produced.
Abstract: Transition-metal dichalcogenides like molybdenum disulphide have attracted great interest as two-dimensional materials beyond graphene due to their unique electronic and optical properties. Solution-phase processes can be a viable method for producing printable single-layer chalcogenides. Molybdenum disulphide can be exfoliated into monolayer flakes using organolithium reduction chemistry; unfortunately, the method is hampered by low yield, submicron flake size and long lithiation time. Here we report a high-yield exfoliation process using lithium, potassium and sodium naphthalenide where an intermediate ternary Li(x)MX(n) crystalline phase (X=selenium, sulphur, and so on) is produced. Using a two-step expansion and intercalation method, we produce high-quality single-layer molybdenum disulphide sheets with unprecedentedly large flake size, that is up to 400 μm(2). Single-layer dichalcogenide inks prepared by this method may be directly inkjet-printed on a wide range of substrates.
659 citations
TL;DR: Molybdenum disulphide is identified as a promising cost-effective substitute for noble metal catalysts and shows superior carbon dioxide reduction performance compared with the noble metals with a high current density and low overpotential in an ionic liquid.
Abstract: Electrochemical reduction is one process to produce higher value chemicals from carbon dioxide, and it is typically catalysed by noble metals. Here, the authors demonstrate that molybdenum disulphide is also capable of efficiently catalysing the reaction in the presence of an ionic liquid.
616 citations
TL;DR: This work reports comprehensive studies on the pressure-dependent electronic, vibrational, optical and structural properties of multilayered molybdenum disulphide up to 35 GPa and reveals a structural lattice distortion followed by an electronic transition from a semiconducting to metallic state.
Abstract: Molybdenum disulphide is a layered transition metal dichalcogenide that has recently raised considerable interest due to its unique semiconducting and opto-electronic properties. Although several theoretical studies have suggested an electronic phase transition in molybdenum disulphide, there has been a lack of experimental evidence. Here we report comprehensive studies on the pressure-dependent electronic, vibrational, optical and structural properties of multilayered molybdenum disulphide up to 35 GPa. Our experimental results reveal a structural lattice distortion followed by an electronic transition from a semiconducting to metallic state at B19 GPa, which is confirmed by ab initio calculations. The metallization arises from the overlap of the valance and conduction bands owing to sulphur–sulphur interactions as the interlayer spacing reduces. The electronic transition affords modulation of the opto-electronic gain in molybdenum disulphide. This pressuretuned behaviour can enable the development of novel devices with multiple phenomena involving the strong coupling of the mechanical, electrical and optical properties of layered nanomaterials.
475 citations
TL;DR: A simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films, which demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production.
Abstract: Photoelectrochemical water splitting may be used to produce hydrogen using abundant solar energy. Here, the authors fabricate layered films of amorphous molybdenum sulphide on copper(I) oxide and demonstrate the catalytic activity and enhanced stability of these devices made from earth-abundant materials.
426 citations
TL;DR: Amorphous molybdenum phosphide (MoP) nanoparticles have been synthesized and characterized as electrocatalysts for the hydrogen evolution reaction (HER) in 0.50 M H2SO4 (pH 0.3).
Abstract: Amorphous molybdenum phosphide (MoP) nanoparticles have been synthesized and characterized as electrocatalysts for the hydrogen-evolution reaction (HER) in 0.50 M H2SO4 (pH 0.3). Amorphous MoP nanoparticles (having diameters of 4.2 ± 0.5 nm) formed upon heating Mo(CO)6 and trioctylphosphine in squalane at 320 °C, and the nanoparticles remained amorphous after heating at 450 °C in H2(5%)/Ar(95%) to remove the surface ligands. At mass loadings of 1 mg cm–2, MoP/Ti electrodes exhibited overpotentials of −90 and −105 mV (−110 and −140 mV without iR correction) at current densities of −10 and −20 mA cm–2, respectively. These HER overpotentials remained nearly constant over 500 cyclic voltammetric sweeps and 18 h of galvanostatic testing, indicating stability in acidic media under operating conditions. Amorphous MoP nanoparticles are therefore among the most active known molybdenum-based HER systems and are part of a growing family of active, acid-stable, non-noble-metal HER catalysts.
353 citations
TL;DR: X-ray diffraction, Raman spectroscopy, and electrical conductivity measurements of molybdenum disulfide MoS(2) are performed at pressures up to 81 GPa, which provide evidence for isostructural phase transition from 2H(c) to2H(a) modification through layer sliding previously predicted theoretically.
Abstract: X-ray diffraction, Raman spectroscopy, and electrical conductivity measurements of molybdenum disulfide MoS(2) are performed at pressures up to 81 GPa in diamond anvil cells. Above 20 GPa, we find discontinuous changes in Raman spectra and x-ray diffraction patterns which provide evidence for isostructural phase transition from 2H(c) to 2H(a) modification through layer sliding previously predicted theoretically. This first-order transition, which is completed around 40 GPa, is characterized by a collapse in the c-lattice parameter and volume and also by changes in interlayer bonding. After the phase transition completion, MoS(2) becomes metallic. The reversibility of the phase transition is identified from all these techniques.
225 citations
TL;DR: Molybdenum phosphide was adopted as a new electrocatalyst for the hydrogen evolution reaction for the first time, exhibiting an excellent electrocatalytic activity with a small Tafel slope of 60 mV dec(-1), which is amongst the most active, acid-stable, earth abundant HER Electrocatalysts reported to date.
212 citations
TL;DR: A method for synthesizing large-area and uniform molybdenum disulfide films, with control over the layer number, on insulating substrates using a gas phase sulfuric precursor (H2S) and a molyBdenum metal source is described.
Abstract: We describe a method for synthesizing large-area and uniform molybdenum disulfide films, with control over the layer number, on insulating substrates using a gas phase sulfuric precursor (H2S) and a molybdenum metal source. The metal layer thickness was varied to effectively control the number of layers (2 to 12) present in the synthesized film. The films were grown on wafer-scale Si/SiO2 or quartz substrates and displayed excellent uniformity and a high crystallinity over the entire area. Thin film transistors were prepared using these materials, and the performances of the devices were tested. The devices displayed an on/off current ratio of 105, a mobility of 0.12 cm2 V−1 s−1 (mean mobility value of 0.07 cm2 V−1 s−1), and reliable operation.
TL;DR: The effect of room temperature ultraviolet-ozone (UV-O3) exposure of MoS2 on the uniformity of subsequent atomic layer deposition of Al2O3 is investigated in this paper.
Abstract: The effect of room temperature ultraviolet-ozone (UV-O3) exposure of MoS2 on the uniformity of subsequent atomic layer deposition of Al2O3 is investigated. It is found that a UV-O3 pre-treatment removes adsorbed carbon contamination from the MoS2 surface and also functionalizes the MoS2 surface through the formation of a weak sulfur-oxygen bond without any evidence of molybdenum-sulfur bond disruption. This is supported by first principles density functional theory calculations which show that oxygen bonded to a surface sulfur atom while the sulfur is simultaneously back-bonded to three molybdenum atoms is a thermodynamically favorable configuration. The adsorbed oxygen increases the reactivity of MoS2 surface and provides nucleation sites for atomic layer deposition of Al2O3. The enhanced nucleation is found to be dependent on the thin film deposition temperature.
TL;DR: Molybdenum oxide nanoribbons as a model of photothermal materials can efficiently convert the 980 nm wavelength laser energy into heat energy, and this localized hyperthermia produces the effective thermal ablation of cancer cells, meaning a potential photothermal material.
Abstract: The molybdenum oxide nanosheets have shown strong localized surface plasmon resonance (LSPR) absorption in the near-infrared (NIR) region. However, the long alky chains of ligands made them hydrophobic and less biocompatible. To meet the requirements of molybdenum based nanomaterials for use as a future photothermal therapy, a simple hydrothermal route has been developed for hydrophilic molybdenum oxide nanospheres and nanoribbons using a molybdenum precursor and poly(ethylene glycol) (PEG). First, molybdenum oxide nanomaterials prepared in the presence of PEG exhibit strong localized surface plasmon resonance (LSPR) absorption in near-infrared (NIR) region, compared with that of no PEG. Second, elevation of synthetic temperature leads to a gradual transformation of molybdenum oxide nanospheres into nanoribbons, entailing the evolution of an intense LSPR absorption in the NIR region. Third, as-prepared molybdenum oxide nanomaterials coated with PEG possess a hydrophilic property and thus can be directly used for biological applications without additional post treatments. Moreover, molybdenum oxide nanoribbons as a model of photothermal materials can efficiently convert the 980 nm wavelength laser energy into heat energy, and this localized hyperthermia produces the effective thermal ablation of cancer cells, meaning a potential photothermal material.
TL;DR: In this paper, three kinds of molybdenum disulfides with distinguishable morphologies are prepared and used as counter electrode materials for dye-sensitized solar cells (DSSCs).
Abstract: Molybdenum disulfide attracts additional attention due to its layered structure which allows transformation into a two-dimensional morphology, like graphene. In this paper, three kinds of molybdenum disulfides with distinguishable morphologies, i.e. multilayers, a few layers and nanoparticles, are prepared and used as counter electrode materials for dye-sensitized solar cells (DSSCs). The characterization results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrate that the molybdenum disulfides have an obviously different edge area to basal-plane ratio, with the order: synthesized MoS2 nanoparticles (MoS2-NPs) > multilayered MoS2 (ML-MoS2) > few-layered MoS2 (FL-MoS2). It is interesting that the MoS2 counter electrodes show the same order as above in the energy conversion efficiency measurements of the corresponding DSSCs. Electrochemical impedance spectra (EIS) show that the MoS2-NPs electrode has the minimum charge-transfer resistance, while the FL-MoS2 electrode provides the maximum. Combined with the results from triiodine ion adsorption experiences and N2-adsorption measurements, it is proposed that the catalytically active sites of molybdenum disulfide lie on the edges of the typical layered material, but not on the basal planes. In addition, the transparency of the FL-MoS2 electrode is obviously higher than that of the other MoS2 and Pt electrodes.
TL;DR: In this article, a molybdenum carbide phase (Mo2C) with a hexagonal structure was formed using a novel synthetic method involving the reaction of a M2C precursor with the carbon residue originating from C3N4 under nitrogen at various temperatures.
Abstract: Molybdenum carbide nanocrystals (Mo2C) with sizes ranging from 3 to 20 nm were synthesized within a carbon matrix starting from a mesoporous graphitic carbon nitride (mpg-C3N4) template with confined pores. A molybdenum carbide phase (Mo2C) with a hexagonal structure was formed using a novel synthetic method involving the reaction of a molybdenum precursor with the carbon residue originating from C3N4 under nitrogen at various temperatures. The synthesized nanocomposites were characterized using powder X-ray diffraction (XRD), temperature-programmed reaction with mass spectroscopy (MS), CHN elemental analyses, thermogravimetric analyses (TGA), nitrogen sorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results indicated that the synthesized samples have different surface structures and compositions, which are accordingly expected to exhibit different electrocatalytic activities toward the hydrogen evolution reaction (HER). Electrochemical measurements demonstrated that the sample synthesized at 1323 K exhibited the highest and most stable HER current in acidic media, with an onset potential of −100 mV vs. RHE, among the samples prepared in this study. This result is attributed to the sufficiently small particle size (∼8 nm on average) and accordingly high surface area (308 m2 g−1), with less oxidized surface entrapped within the graphitized carbon matrix.
TL;DR: Evidence indicates that intracellular molybdate levels are tightly controlled by moly bdate transporters, in particular during plant development.
Abstract: In the form of molybdate the transition metal molybdenum is essential for plants as it is required by a number of enzymes that catalyze key reactions in nitrogen assimilation, purine degradation, phytohormone synthesis, and sulfite detoxification. However, molybdate itself is biologically inactive and needs to be complexed by a specific organic pterin in order to serve as a permanently bound prosthetic group, the molybdenum cofactor, for the socalled molybdo-enyzmes. While the synthesis of molybdenum cofactor has been intensively studied, only little is known about the uptake of molybdate by the roots, its transport to the shoot and its allocation and storage within the cell. Yet, recent evidence indicates that intracellular molybdate levels are tightly controlled by molybdate transporters, in particular during plant development. Moreover, a tight connection between molybdenum and iron metabolisms is presumed because (i) uptake mechanisms for molybdate and iron affect each other, (ii) most molybdo-enzymes do also require iron-containing redox groups such as iron-sulfur clusters or heme, (iii) molybdenum metabolism has recruited mechanisms typical for iron-sulfur cluster synthesis, and (iv) both molybdenum cofactor synthesis and extramitochondrial iron-sulfur proteins involve the function of a specific mitochondrial ABC-type transporter.
TL;DR: In this paper, thin films of molybdenum diselenide have been synthesized using a two-step wet-chemical method, in which excess sodium selenide was first added to a solution of ammonium heptamolydbate in aqueous sulfuric acid, resulting in the spontaneous formation of a black precipitate that contained MDEs, MoSe3, MoO3, and elemental selenium, and after the film had been drop cast onto a glassy carbon electrode, a reductive potential was applied to the precipitate
Abstract: The catalytically inactive components of a film have been converted, through an operando method of synthesis, to produce a catalyst for the reaction that the film is catalyzing. Specifically, thin films of molybdenum diselenide have been synthesized using a two-step wet-chemical method, in which excess sodium selenide was first added to a solution of ammonium heptamolydbate in aqueous sulfuric acid, resulting in the spontaneous formation of a black precipitate that contained molybdenum triselenide (MoSe3), molybdenum trioxide (MoO3), and elemental selenium. After purification and after the film had been drop cast onto a glassy carbon electrode, a reductive potential was applied to the precipitate-coated electrode. Hydrogen evolution occurred within the range of potentials applied to the electrode, but during the initial voltammetric cycle, an overpotential of ∼400 mV was required to drive the hydrogen-evolution reaction at a benchmark current density of −10 mA cm–2. The overpotential required to evolve hy...
TL;DR: In this paper, metal-doped molybdenum carbides were investigated as alternative catalysts for the steam reforming of methanol, and it was found that Pt doped carbide had the highest catalytic activity and selectivity among the prepared catalysts and reached 100% even at a temperature as low as 200°C.
TL;DR: The findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions and the face-centred cubic structure appears to be a well-defined metastable state.
Abstract: Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original -oriented body-centred cubic structure to a -oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into -oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.
TL;DR: The reaction of MoS(2) with Li is not as simple as with usual metal oxide based conversion reactions, but that the pathway of the conversion reaction changes after the first discharge process, and the non-reversibility of the converted material is supported.
Abstract: The lithium storage mechanism in molybdenum disulfide (MoS2) has been comprehensively investigated as the existing conversion-based storage mechanism is unable to explain the reason behind its high practical capacity, high polarization losses, and the change in the discharge profile after the 1st charge–discharge cycle. To resolve these issues and to gain a deeper understanding of MoS2-based Li-ion batteries, for the first time, we have studied the reaction mechanism of the MoS2 anode using various experimental techniques such as XRD, Raman spectroscopy, electrochemical impedance spectroscopy, XANES, and EXAFS, as well as ab initio density functional theory based calculations. On the basis of the results presented here, and in line with some experimental findings, we find that the reaction of MoS2 with Li is not as simple as with usual metal oxide based conversion reactions, but that the pathway of the conversion reaction changes after the first discharge process. In the first discharge process, lithiation is initiated by a limited intercalation process, followed by a conversion reaction that produces molybdenum nanoparticles (Mo) and lithium sulfide (Li2S). Whereas, unlike oxide-based conversion materials, MoS2 does not transverse back during the delithiation process. Indeed, instead of MoS2 formation, we identified the presence of polysulfur after the complete cycle. In consecutive cycles, polysulfur reacts with lithium and forms Li2S/Li2S2, and this Li–S reaction is found to be highly reversible in nature and the only source of the high practical capacity observed in this electrode. To validate our experimental findings, an atomic scale ab initio computational study was also carried out, which likewise suggests that Li first intercalates between the MoS2 layers but that after a certain concentration, it reacts with MoS2 to form Li2S. The calculations also support the non-reversibility of the conversion reaction, by showing that Mo + Li2S formation is energetically more favorable than the re-formation of MoS2 + Li.
TL;DR: In this article, a phase X molybdenum oxynitride (phase X) was developed from a partial nitridation strategy by heating bulk molydenum trioxide (MoO3) in a NH3 atmosphere.
Abstract: To obtain new anode materials with improved lithium storage properties, molybdenum oxynitride (phase X) was developed from a partial nitridation strategy by heating bulk molybdenum trioxide (MoO3) in a NH3 atmosphere. The elemental mapping shows homogeneous distribution of nitrogen and the nominal composition of the material was well characterized by X-ray photoelectron spectroscopy (XPS) in combination with elemental analysis. The material was evaluated as an anode material for lithium ion batteries for the first time. A reversible capacity of about 980 mA h g−1 was achieved at a current density of 50 mA g−1, showing significantly improved capability retention compared to bulk MoO3, which was due to its increased conductivity. Considering the ease of large-scale fabrication, molybdenum oxynitride should be very promising for lithium ion battery applications. The strategy may also be applied to other metal oxides to improve their performances in lithium ion batteries.
TL;DR: In situ quartz crystal microbalance (QCM) measurements reveal the self-limiting growth nature of the deposition that is further verified with ex situ spectroscopic ellipsometry and X-ray reflectivity (XRR) measurements.
Abstract: Molybdenum nitride (MoNx) thin films are deposited by atomic layer deposition (ALD) using molybdenum hexacarbonyl [Mo(CO)6] and ammonia [NH3] at varied temperatures. A relatively narrow ALD temperature window is observed. In situ quartz crystal microbalance (QCM) measurements reveal the self-limiting growth nature of the deposition that is further verified with ex situ spectroscopic ellipsometry and X-ray reflectivity (XRR) measurements. A saturated growth rate of 2 A/cycle at 170 °C is obtained. The deposition chemistry is studied by the in situ Fourier transform infrared spectroscopy (FTIR) that investigates the surface bound reactions during each half cycle. As deposited films are amorphous as observed from X-ray diffraction (XRD) and transmission electron microscopy electron diffraction (TEM ED) studies, which get converted to hexagonal-MoN upon annealing at 400 °C under NH3 atmosphere. As grown thin films are found to have notable potential as a carbon and binder free anode material in a Li ion batte...
TL;DR: In this paper, microstructural characteristics and electrochemical responses of four metastable beta Ti-Nb-Mo alloys for biomedical implantation were explored, and they were synthesized by the cold crucible levitation melting technique and compositions were selected to keep the molybdenum equivalency close to 12 wt% Mo eq.
TL;DR: A flow sheet on the recovery of vanadium from vanadium-bearing chloride solution containing high concentration of iron was proposed in this article, where an extractant of bis (2-ethylhexyl) phosphoric acid (D2EHPA) was used to extract vanadium.
TL;DR: In this paper, Softcontact transfer lamination of thin layers of the doped poly(3-hexylthiophene) on undoped polymer layers is used to create spatially-confined doped regions, which serve as hole-injection contacts on P3HT diodes.
Abstract: Poly(3-hexylthiophene) (P3HT) is p-doped by the new soluble dopant molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene] and investigated via photoemission spectroscopy and transport measurements. Soft-contact transfer lamination of thin layers of the doped P3HT on undoped polymer layers is used to create spatially-confined doped regions, which serve as hole-injection contacts on P3HT diodes. This strategy is then used to create efficient hole-collecting contacts on solution-processed inverted polymer solar cells.
TL;DR: This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli using a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine under ambient conditions.
Abstract: The NN bond of molecular dinitrogen bridging two molybdenum atoms in the pentamethylcyclopentadienyl molybdenum complexes that bear ferrocenyldiphosphine as an auxiliary ligand is homolytically cleaved under visible light irradiation at room temperature to afford two molar molybdenum nitride complexes. Conversely, the bridging molecular dinitrogen is reformed by the oxidation of the molybdenum nitride complex at room temperature. This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli using a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine under ambient conditions.
TL;DR: Two-dimensional (2D) molybdenum oxides at their various stoichiometries are promising candidates for generating plasmon resonances in visible light range and offer great opportunities for future sensing and optical applications.
Abstract: Two-dimensional (2D) molybdenum oxides at their various stoichiometries are promising candidates for generating plasmon resonances in visible light range. Herein, we demonstrate plasmonic 2D molybdenum oxide flakes for gas sensing applications, in which hydrogen (H2) is selected as a model gas. The 2D molybdenum oxide flakes are obtained using a grinding-assisted liquid exfoliation method and exposed to simulated sunlight to acquire its substoichiometric quasi-metallic form. After the exposure to H2 gas molecules, the quasi-metallic molybdenum oxide flakes are partially transformed into semiconducting states, thus gradually losing their plasmonic properties. The novel 2D plasmonic sensing platform is tested using different concentrations of H2 gas at various operating temperatures to comprehensively assess its sensing performance. The presented 2D plasmonic system offers great opportunities for future sensing and optical applications.
TL;DR: In this paper, a wide range of p- and m-substituted aromatic nitriles, including 3-trifluoromethylbenzonitrile, m-and p-disubstitized benzonitriles, and the aliphatic nitriniles cyclohexylcarbonitrile and benzylcyanide, were found to be hydrogenated at 140 °C and 60 bar H2 in THF with high yields.
Abstract: Low-valent molybdenum and tungsten amides M(NO)(CO)(PNP) {M = Mo, 1a; W, 1b; PNP = N(CH2CH2PiPr2)2} were found to be active catalysts for the hydrogenation of various nitriles to the corresponding imines, primary amines, and N-substituted imines with high selectivity for the latter type of product. A wide range of p- and m-substituted aromatic nitriles—p-methyl, p-methoxy, p-bromobenzonitriles; 3-trifluoromethylbenzonitrile, m- and p-disubstituted benzonitrile; the heterocyclic 2-thiophencarbonitrile; and the aliphatic nitriles cyclohexylcarbonitrile and benzylcyanide—could be hydrogenated at 140 °C and 60 bar H2 in THF with high yields. TOFs were found to be between 0.4 and 36 h–1.
Patent•
12 Mar 2014
TL;DR: Bis(alkylimido)-bis(alkylamido)molybdenum compounds, their synthesis, and their use for the deposition of molybDENum-containing films are disclosed in this article.
Abstract: Bis(alkylimido)-bis(alkylamido)molybdenum compounds, their synthesis, and their use for the deposition of molybdenum-containing films are disclosed.
TL;DR: Mechanistic studies by (1)H NMR spectroscopy show that upon two-electron reduction the Mo(CNR)2(bdt)2 complex dissociates the isocyanide ligands, followed by addition of acid to result in the formation of molecular hydrogen and the Mo-bdt-2 complex.
Abstract: Homogeneous light-driven systems employing molecular molybdenum catalysts for hydrogen production are described. The specific Mo complexes studied are six-coordinate bis(benzenedithiolate) derivatives having two additional isocyanide or phosphine ligands to complete the coordination sphere. Each of the complexes possesses a trigonal prismatic coordination geometry. The complexes were investigated as proton reduction catalysts in the presence of [Ru(bpy)3]2+, ascorbic acid, and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis occurs between the MoIV/MoIII and MoIII/MoII redox couples, around 1.0 V vs SCE. Mechanistic studies by 1H NMR spectroscopy show that upon two-electron reduction the Mo(CNR)2(bdt)2 complex dissociates the isocyanide ligands, followed by addition of acid to result in the formation of molecular hydrogen and the Mo(bdt)2 complex.