Showing papers on "Molybdenum published in 2013"
TL;DR: In this paper, single-crystal islands and polycrystals containing tilt and mirror twin grain boundaries are characterized, and the influence of the grain boundaries on the material properties of molybdenum disulphide is assessed.
Abstract: Despite recent progress in the synthesis and characterization of molybdenum disulphide, little is yet known about its microstructure. Using refined chemical vapour deposition synthesis, high-quality crystals of monolayer molybdenum disulphide have now been grown. Single-crystal islands and polycrystals containing tilt and mirror twin grain boundaries are characterized, and the influence of the grain boundaries on the material properties of molybdenum disulphide is assessed.
1,911 citations
TL;DR: The controlled vapour phase synthesis of molybdenum disulphide atomic layers is reported and a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers is elucidated.
Abstract: Single-layered molybdenum disulphide with a direct bandgap is a promising two-dimensional material that goes beyond graphene for the next generation of nanoelectronics. Here, we report the controlled vapour phase synthesis of molybdenum disulphide atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers. Furthermore, a nucleation-controlled strategy is established to systematically promote the formation of large-area, single- and few-layered films. Using high-resolution electron microscopy imaging, the atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain boundary formation are evaluated. Grain boundaries consisting of 5- and 7- member rings are directly observed with atomic resolution, and their energy landscape is investigated via first-principles calculations. The uniformity in thickness, large grain sizes, and excellent electrical performance signify the high quality and scalable synthesis of the molybdenum disulphide atomic layers.
1,645 citations
TL;DR: This study provides direct evidence that sulphur vacancies exist in molybdenum disulphide, and introduces localized donor states inside the bandgap, suggesting that the low-carrier-density transport is dominated by hopping via these localized gap states.
Abstract: Molybdenum disulphide is a novel two-dimensional semiconductor with potential applications in electronic and optoelectronic devices. However, the nature of charge transport in back-gated devices still remains elusive as they show much lower mobility than theoretical calculations and native n-type doping. Here we report a study of transport in few-layer molybdenum disulphide, together with transmission electron microscopy and density functional theory. We provide direct evidence that sulphur vacancies exist in molybdenum disulphide, introducing localized donor states inside the bandgap. Under low carrier densities, the transport exhibits nearest-neighbour hopping at high temperatures and variable-range hopping at low temperatures, which can be well explained under Mott formalism. We suggest that the low-carrier-density transport is dominated by hopping via these localized gap states. Our study reveals the important role of short-range surface defects in tailoring the properties and device applications of molybdenum disulphide.
948 citations
TL;DR: A two-step solid-state reaction for preparing cobalt molybdenum nitride with a nanoscale morphology has been used to produce a highly active and stable electrocatalyst for the hydrogen evolution reaction (HER) under acidic conditions that achieves an iR-corrected current density.
Abstract: A two-step solid-state reaction for preparing cobalt molybdenum nitride with a nanoscale morphology has been used to produce a highly active and stable electrocatalyst for the hydrogen evolution reaction (HER) under acidic conditions that achieves an iR-corrected current density of 10 mA cm–2 at −0.20 V vs RHE at low catalyst loadings of 0.24 mg/cm2 in rotating disk experiments under a H2 atmosphere. Neutron powder diffraction and pair distribution function (PDF) studies have been used to overcome the insensitivity of X-ray diffraction data to different transition-metal nitride structural polytypes and show that this cobalt molybdenum nitride crystallizes in space group P63/mmc with lattice parameters of a = 2.85176(2) A and c = 10.9862(3) A and a formula of Co0.6Mo1.4N2. This space group results from the four-layered stacking sequence of a mixed close-packed structure with alternating layers of transition metals in octahedral and trigonal prismatic coordination and is a structure type for which HER activ...
828 citations
TL;DR: A nanostructuring strategy is reported that achieves Mo alloys with yield strength over 800 MPa and tensile elongation as large as ~40% at room temperature and a general pathway for manufacturing dispersion-strengthened materials with both high strength and ductility.
Abstract: The high-temperature stability and mechanical properties of refractory molybdenum alloys are highly desirable for a wide range of critical applications. However, a long-standing problem for these alloys is that they suffer from low ductility and limited formability. Here we report a nanostructuring strategy that achieves Mo alloys with yield strength over 800 MPa and tensile elongation as large as ~ 40% at room temperature. The processing route involves a molecular-level liquid-liquid mixing/doping technique that leads to an optimal microstructure of submicrometre grains with nanometric oxide particles uniformly distributed in the grain interior. Our approach can be readily adapted to large-scale industrial production of ductile Mo alloys that can be extensively processed and shaped at low temperatures. The architecture engineered into such multicomponent alloys offers a general pathway for manufacturing dispersion-strengthened materials with both high strength and ductility.
728 citations
TL;DR: Using a simple integration scheme, it is found that the electrical conductivity of MoS2 films is highly sensitive to NH3 adsorption, consistent with n-type semiconducting behavior.
Abstract: High-performance sensors based on molybdenum disulfide (MoS2 ) grown by sulfurization of sputtered molybdenum layers are presented. Using a simple integration scheme, it is found that the electrical conductivity of MoS2 films is highly sensitive to NH3 adsorption, consistent with n-type semiconducting behavior. A sensitivity of 300 ppb at room temperature is achieved, showing the high potential of 2D transition metal-dichalcogenides for sensing.
434 citations
TL;DR: A simple one-step method is reported to synthesize low-temperature solution-processed transition metal oxides (TMOs) of molybdenum oxide and vanadium oxide with oxygen vacancies for a good hole-transport layer (HTL).
Abstract: A simple one-step method is reported to synthesize low-temperature solution-processed transition metal oxides (TMOs) of molybdenum oxide and vanadium oxide with oxygen vacancies for a good hole-transport layer (HTL). The oxygen vacancy plays an essential role for TMOs when they are employed as HTLs: TMO films with excess oxygen are highly undesirable for their application in organic electronics.
273 citations
TL;DR: Electrochemical impedance spectroscopy is used to identify a slow electron transport process in hydrogen evolution catalysed by amorphous molybdenum sulphides on glassy carbon.
267 citations
TL;DR: The transition element molybdenum needs to be complexed by a special cofactor to gain catalytic activity and is bound to a unique pterin, thus forming the Moco cofactor, which is the active compound at the catalytic site of all molyBdenum-containing enzymes in nature, except bacterial moly bdenum nitrogenase.
206 citations
TL;DR: In this paper, molybdenum and tungsten promoted SnO2 solid acids (wet-impregnation) and pure SnO 2 (fusion method) were prepared.
168 citations
TL;DR: Higher reducibility at loadings close to the monolayer measured by temperature-programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions.
Abstract: Highly dispersed molybdenum oxide supported on mesoporous silica SBA-15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2–2.5 Mo atoms nm−2). X-ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO4 units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature-programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O-K-edge at high Mo loadings are explained by distorted MoO4 complexes. Limited availability of anchor silanol groups at high loadings forces the MoO4 groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity.
TL;DR: In this paper, a review mainly discusses the application of oxido-peroxido Molybdenum(VI) complexes as catalysts or mediators in homogeneous or heterogeneous catalytic systems for oxidations of olefins, sulfides, alcohols, alkanes, and amines toward the synthesis of a variety of organic compounds.
TL;DR: Sputtering of MoS2 films of single-layer thickness by low-energy argon ions selectively reduces the sulfur content of the material without significant depletion of molybdenum.
Abstract: Sputtering of MoS2 films of single-layer thickness by low-energy argon ions selectively reduces the sulfur content of the material without significant depletion of molybdenum. X-ray photoelectron spectroscopy shows little modification of the Mo 3d states during this process, suggesting the absence of significant reorganization or damage to the overall structure of the MoS2 film. Accompanying ab initio molecular dynamics simulations find clusters of sulfur vacancies in the top plane of single-layer MoS2 to be structurally stable. Measurements of the photoluminescence at temperatures between 175 and 300 K show quenching of almost 80% for an ~10% decrease in sulfur content.
TL;DR: A solution-based preparation route for 7.5% efficient thin-film solar cells with a kesterite-type Cu2ZnSn(S,Se)4 absorber is reported that allows low carbon residues after a rapid selenization step as discussed by the authors.
TL;DR: In this article, Pd supported on tungsten carbide and molybdenum carbide was evaluated for hydrogen evolution reaction (HER) electrocatalysts to minimize capital costs associated with large-scale hydrogen production from water electrolysis.
TL;DR: In this article, the stacking fault energies (SFE) from the chemical compositions of austenitic stainless steels were measured for 54 laboratory-melted heats and 2 commercial heats, and the results were checked against those of a first-principle, atomistic approach.
Abstract: In order to establish more reliable formulae for calculating stacking fault energies (SFE) from the chemical compositions of austenitic stainless steels, SFE values were measured for 54 laboratory-melted heats and 2 commercial heats The results were checked against those of a first-principle, atomistic calculation approach More than ~20,000 data points for the width and angle of the Burgers vectors were determined from dark-field images of isolated extended dislocations in 56 heats of austenitic stainless steel using weak electron beams with g-3g diffraction conditions Based on these numerous observations and on fundamental thermodynamic analyses, it is concluded that the SFE values for austenitic stainless steels are changed not only by chemical composition but also by heat treatment In this paper, new formulae for calculating SFE values from the chemical compositions in three different heat treatment conditions have been proposed for austenitic stainless steels within given limited chemical composition ranges In these formulae, the SFE values are calculated from the nickel, chromium, molybdenum, silicon, manganese, nitrogen, and carbon contents for the each heat treatment condition The three heat treatment conditions studied were water cooling after solution heat treating (SHTWC), furnace cooling after solution heat treating, and aging after SHTWC
TL;DR: In this article, the interphase precipitation of carbides has been studied in two microalloyed steels containing Ti and Nb, but only one of which contains molybdenum.
Abstract: The interphase precipitation of carbides has been studied in two microalloyed steels containing Ti and Nb, but only one of which contains molybdenum. The precipitates obtained are, therefore, (Ti,Nb)C and (Ti,Nb,Mo)C respectively. It is found that molybdenum significantly reduces the size of the carbide precipitates and also strongly retards their coarsening behaviour during subsequent heat treatment. This is because it enhances the nucleation rate by reducing the interfacial energy, but it is not thermodynamically favoured within the (Ti,Nb,Mo)C, so the later stages of growth involve its partitioning into the matrix, thus explaining the reduction in coarsening rate relative to the molybdenum free steel.
TL;DR: This study combined a waste input-output material flow model and physical unit input- Output analysis to perform a simultaneous MFA for nickel, chromium, and molybdenum in the Japanese economy in 2000, indicating the importance of recovery of these elements in recycling policies for end-of-life (EoL) vehicles and constructions.
Abstract: Steel is not elemental iron but rather a group of iron-based alloys containing many elements, especially chromium, nickel, and molybdenum. Steel recycling is expected to promote efficient resource use. However, open-loop recycling of steel could result in quality loss of nickel and molybdenum and/or material loss of chromium. Knowledge about alloying element substance flow is needed to avoid such losses. Material flow analyses (MFAs) indicate the importance of steel recycling to recovery of alloying elements. Flows of nickel, chromium, and molybdenum are interconnected, but MFAs have paid little attention to the interconnected flow of materials/substances in supply chains. This study combined a waste input–output material flow model and physical unit input–output analysis to perform a simultaneous MFA for nickel, chromium, and molybdenum in the Japanese economy in 2000. Results indicated the importance of recovery of these elements in recycling policies for end-of-life (EoL) vehicles and constructions. Im...
TL;DR: This paper deals with the development of a process for the recovery of metals such as Mo, V, Ni, Al from spent hydroprocessing catalyst which may otherwise cause a nuisance if dumped untreated.
TL;DR: In this paper, a facile one-pot synthesis of a tri-component gold nanoparticle/molybdenum cluster/graphene oxide (AuNPs@Mo-GO) nanohybrid composite was reported.
Abstract: The paper reports on a facile one-pot synthesis of a tri-component gold nanoparticle/molybdenum cluster/graphene oxide (AuNPs@Mo–GO) nanohybrid composite. The synthetic methodology consists on direct UV irradiation of an aqueous solution containing graphene oxide (GO), Na 2 [Mo 6 Br 8 (N 3 ) 6 ], HAuCl 4 ·3H 2 O and isopropanol at room temperature in air using a UV fiber lamp. The composite material exhibits very high photocatalytic activity for the degradation of rhodamine B under visible light irradation. The resulting nanohybrid material was characterized using Raman spectroscopy, UV–vis spectrometry, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).
TL;DR: In this paper, the authors investigate the trapping behaviors of hydrogen in molybdenum (Mo) and tungsten (W) using a first-principles method with a zero point energy correction as well as the molecular dynamics (MD) method.
TL;DR: Calculated calculations suggest that the nitrogen will be favored at the surface compared to hydrogen even at potentials of -0.8 V and the Faradaic losses due to HER should be low.
Abstract: Theoretical investigations of electrochemical production of ammonia at ambient temperature and pressure on nitrogen covered molybdenum nanoparticles are presented. Density functional theory calculations are used in combination with the computational hydrogen electrode approach to calculate the free energy profile for electrochemical protonation of N2 and N adatoms on cuboctahedral Mo13 nanoparticles. Pathways for electrochemical ammonia production via direct protonation of N adatoms and N2 admolecules with an onset potential as low as −0.5 V and generally lower than −0.8 V on both a nitrogen covered or a clean Mo nanoparticle. Calculations presented here show that nitrogen dissociation at either nitrogen vacancies on a nitrogen covered molybdenum particle or at a clean molybdenum particle is unlikely to occur under ambient conditions due to very high activation barriers of 1.8 eV. The calculations suggest that the nitrogen will be favored at the surface compared to hydrogen even at potentials of −0.8 V and the Faradaic losses due to HER should be low.
TL;DR: In this article, the Ni-based alloys Incoloy 800, Inconel 825, Incoroy 625, and Hastelloy C-276 were analyzed by using scanning electron microscopy, X-ray diffraction, and Xray photoelectron spectroscopy.
Abstract: The Ni-based alloys Incoloy 800, Incoloy 825, Inconel 625, and Hastelloy C-276 exposed to subcritical water (350 °C, 25 MPa) and supercritical water (450 °C, 25 MPa) with high concentrations of chloride and oxygen were analyzed by using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. There is a strong synergistic effect between salt and oxygen, leading to severe corrosion. The selective dissolution of nickel is the severest of all alloying elements, and a stable oxide in oxidizing condition is formed by chromium. Molybdenum improves the resistance to pitting corrosion when chromium is present. Without molybdenum, Incoloy 800 exhibits the severest pitting corrosion of the test alloys under subcritical condition. Inconel 625 and Hastelloy C-276 exhibit good corrosion resistance under the condition of oxygen and salt existing. NiO, NiCr2O4, and Cr2O3 are the three main components of oxide films on Ni-based alloys. The possible corrosion mechanisms of Ni-based alloys are...
TL;DR: In this paper, single-crystalline mesoporous molybdenum nitride nanowires (meso-Mo3N2-NWs) were obtained by topotactic reaction using single-Crystal Stochastic MolyBdenum oxide (SMEO) nanowire.
Abstract: We report single-crystalline mesoporous molybdenum nitride nanowires (meso-Mo3N2-NWs) prepared by topotactic reaction using single-crystalline molybdenum oxide nanowires. The single-crystalline nature of meso-Mo3N2-NWs was clearly observed by field-emission transmission electron microscopy. The meso-Mo3N2-NWs exhibited mesoporous structure with ∼45 m2/g in specific surface area and ∼4.6 nm in average pore size confirmed by a nitrogen sorption measurement. Due to high specific surface area and mesoporous structure, meso-Mo3N2-NWs showed much higher specific capacitance and excellent charging–discharging performance as compared with Mo3N2 prepared using conventional nitridation process.
TL;DR: The recent progress in the research area of M-cluster assembly is reviewed, with an emphasis on the work that provides useful insights into the mechanistic details of this process.
TL;DR: The isolation of a novel molybdate-reducing Gram positive bacterium tentatively identified as Bacillus sp.rzi from a metal-contaminated soil is reported, and the characteristics of this bacterium make it an ideal tool for bioremediation ofmolybdenum pollution.
Abstract: Molybdenum is very toxic to agricultural animals. Mo-reducing bacterium can be used to immobilize soluble molybdenum to insoluble forms, reducing its toxicity in the process. In this work the isolation of a novel molybdate-reducing Gram positive bacterium tentatively identified as Bacillus sp. strain A.rzi from a metal-contaminated soil is reported. The cellular reduction of molybdate to molybdenum blue occurred optimally at 4 mM phosphate, using 1% (w/v) glucose, 50 mM molybdate, between 28 and 30 °C and at pH 7.3. The spectrum of the Mo-blue product showed a maximum peak at 865 nm and a shoulder at 700 nm. Inhibitors of bacterial electron transport system (ETS) such as rotenone, sodium azide, antimycin A, and potassium cyanide could not inhibit the molybdenum-reducing activity. At 0.1 mM, mercury, copper, cadmium, arsenic, lead, chromium, cobalt, and zinc showed strong inhibition on molybdate reduction by crude enzyme. The best model that fitted the experimental data well was Luong followed by Haldane and Monod. The calculated value for Luong's constants p max, K(s), S(m), and n was 5.88 μmole Mo-blue hr(-1), 70.36 mM, 108.22 mM, and 0.74, respectively. The characteristics of this bacterium make it an ideal tool for bioremediation of molybdenum pollution.
TL;DR: Although formation of NO from nitrite or formation of xanthine from urate by XOR is chemically feasible, it is not yet clear whether these reactions have any physiological significance since the reactions are catalyzed at a slow rate even under anaerobic conditions.
Abstract: Xanthine oxidoreductase (XOR), a complex flavoprotein, catalyzes the metabolic reactions leading from hypoxanthine to xanthine and from xanthine to urate, and both reactions take place at the molybdenum cofactor. The enzyme is a target of drugs for therapy of gout or hyperuricemia. We review the chemical nature and reaction mechanisms of the molybdenum cofactor of XOR, focusing on molybdenum-dependent reactions of actual or potential medical importance, including nitric oxide (NO) synthesis. It is now generally accepted that XOR transfers the water-exchangeable -OH ligand of the molybdenum atom to the substrate. The hydroxyl group at OH-Mo(IV) can be replaced by urate, oxipurinol and FYX-051 derivatives and the structures of these complexes have been determined by xray crystallography under anaerobic conditions. Although formation of NO from nitrite or formation of xanthine from urate by XOR ischemically feasible, it is not yet clear whether these reactions have any physiological significance since the reactions are catalyzed at a slow rate even under anaerobic conditions.
TL;DR: In this paper, a systematic investigation of the kinetics of propene oxidation to acrolein over Bi 1− x /3 V 1−x Mo x O 4 was conducted.
TL;DR: In this article, the molybdenum bis(dinitrogen) complexes cis and trans were obtained for the catalytic conversion of N 2 to ammonia, where the tetraphos ligand 1,1,1-tris(diphenylphosphinomethyl)ethane (tdppme) and the bidentate coligands dppm (bis(diphos) and dmpm (dimethylphosphino)methane) were investigated.
TL;DR: In this article, the salicylidene 2-picoloyl hydrazone ligand (H2sal-phz) was prepared by reaction of picoloyls hydrazine with Salicylaldehyde, and the new compounds were characterized by 1H NMR and IR spectroscopies.