Probing the interfacial interaction between monolayer molybdenum disulfide and Au nanoclusters

Coupling of plasmonic metal nanostructures on two‐dimensional materials represents one promising approach to improve their optoelectronic device performance. In this article, we systematically investigated the interfacial interactions between Au nanoclusters and monolayer molybdenum disulfide (MoS₂) and the effect of Au decoration on the electrical transport and optical properties of MoS₂, through the combination of in situ MoS₂ field‐effect transistor device evaluation and in situ ultraviolet photoelectron spectroscopy and X‐ray photoelectron spectroscopy measurements. The in situ X‐ray photoelectron spectroscopy/ultraviolet photoelectron spectroscopy experiments revealed a weak interfacial coupling between Au nanoclusters and monolayer MoS₂. The absence of strong charge transfer between Au nanoclusters and MoS₂ was further confirmed by the photoluminescence and Raman measurements. It was also found that the electron charge‐carrier concentration in monolayer MoS₂ weakly depended on the coverage of Au nanoclusters. Copyright © 2017 John Wiley & Sons, Ltd.     

Synthesis and nanostructural characterization of new layered compounds based on molybdenum disulfide and organic dyes

Preparation of new MoS₂ layered compounds, in which organic dyes (rhodamine 6G, oxazine 1, and thionine) were used as the guest components, was successfully realized in two reaction systems differing by the nature of molybdenum disulfide. In one system, MoS₂ was used in the form of single-layer dispersion in aqueous media; in the other system, it was taken in the form of nanodispersed powdered material, res-MoS₂, obtained by exfoliation-restacking procedure and suspended in non-aqueous solvent. Structures of prepared compounds are discussed on the basis of their compositions, X-ray diffraction and high-resolution transmission electron microscopy data. The hybrid compounds formed in single-layer dispersions were found to contain the MoS₂ layers, each of which alternate with dye layer, whereas, in the case of res-MoS₂ the same as well as the other sequences of organic and inorganic layers are formed depending on the reaction conditions. The vicinity of different-thickness domains was revealed within the guest layers of rhodamine and oxazine. It results from different packings of organic molecules and sufficient flexibility of molybdenum disulfide layers.     

Nanocomposites composed of layered molybdenum disulfide and graphene for highly sensitive amperometric determination of methyl parathion

The authors describe an inexpensive electrode for the sensitive amperometric determination of the pesticide methyl parathion. A glassy carbon electrode was modified with a nanocomposite consisting of molybdenum disulfide nanosheets (MoS2) and graphene that was prepared via a hydrothermal process. Its morphology, elemental composition, diffraction, impedance and voltammetric characteristics were studied. The modified electrode displays excellent electrocatalytic ability towards methyl parathion, and the reduction peak current, measured typically at ?0.60 V (vs. Ag/AgCl) is related to the concentration of methyl parathion. The effect of concentration, scan rate and solution pH value were optimized. The calibration plot is linear in the 10 nM to 1.9 mM concentration range, with a 3.2 nM detection limit (at a signal-to-noise ratio of 3). The electrode is selective, stable, adequately repeatable and reproducible. The method was successfully applied to the determination of methyl parathion in spiked samples of homogenized apple, kiwi, tomato and cabbage.

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Graphical Abstract A reliable and robust methyl parathion sensor has been developed using heterostructured MoS₂/graphene. The linear range is 10 nM–1.9 nM and detection limit is 3.2 (±0.8) nM. The method was successful in real sample determination of spiked methyl parathion in food samples such as apple, kiwi, tomato and cabbage.

     

Colloidal dispersions of molybdenum disulfide with a narrow particle size distribution

Colloidal dispersions of MoS₂ in DMF were obtained, and a procedure for the preparation of the fraction of particles with the size distribution 1.5 times narrower than that in the original dispersion was developed. It was shown that for the gradual centrifugation of dispersions with an increase in the acceleration from 126g to 2016g the average thickness of nanosheets decreased from 35 to 8 nm and the average lateral sizes decreased from 250 nm to a constant value of 160 nm. A linear dependence of the absorbance of the dispersions on the concentration of MoS₂ was established.     

The formation of intercalation compounds of MoS2 with cations of alkali metals and alkylammonium from monolayer dispersion of molybdenum disulfide

Ion-exchange interaction of the monolayer aqueous dispersion obtained by hydration of crystalline LiMoS₂ with Li, Na, K salts and alkyiammoniiim halides is studied. Intercalation compounds of MoS₂ with hydrated inorganic cations as well as hitherto unattainable intercalation compounds of MoS₂ with alkylammonium cations are shown to be formed under these conditions. The composition and structure of these compounds are investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 672–674, April, 1993.     

层状复合金属氢氧化物：主客体结构研究进展

近年来, 基于层状复合金属氢氧化物（layered double hydroxides, 简称LDHs）的主客体插层化学在功能材料的构筑和应用方面得到了学术界和产业界的广泛关注. 本文从LDHs材料的层板主体及层间客体的结构、层间客体种类、层板堆积模式等角度总结了LDHs层状结构及主-客体、客-客体相互作用的最新研究进展.     

Atomic absorption spectrometry of tellurium with electrothermal atomization in a molybdenum microtube

Hydrogen, added to argon purge gas, is necessary to protect the molybdenum microtube atomizer from oxidation, but it increases the atomization temperature and decreases the maximum absorbance of tellurium. A mixture of thiourea and copper removes the interfering effects of diverse elements and counteracts the effect of hydrogen. Tellurium (20–200 ppm) in copper can be determined after extraction as a chloride complex.     

Tungsten and molybdenum nitrosyl cations in fluorosulfonic acid

The tungsten and molybdenum hexacarbonyls, M(CO)(6) (M = W, Mo), dissolve in fluorosulfonic acid, HSO(3)F, to generate the tungsten and molybdenum carbonyl cations, [M(CO)(4)](2+)(solv), which are transformed, by exposure to an NO atmosphere, into the tungsten and molybdenum carbonyldinitrosyl cations, [M(CO)(NO)(2)](2+)(solv), respectively. These complexes have been characterized by NMR ((183)W, (13)C, and (15)N), IR, and Raman spectroscopy, and they are the first well-characterized metal nitrosyl cations in strong acids or superacids although the spectroscopic techniques do not address the number or coordination mode of the solvent molecules. Their formation suggests that strong acids and superacids can hopefully be used to generate a number of metal nitrosyl cations as they have been successfully used for preparing a series of metal carbonyl cations.     

Atomic absorption spectrometry of tin with electro-thermal atomization in a molybdenum microtube

The atomic absorption spectrometry of tin with atomization in a molybdenum microtube is described. The addition of hydrogen to the argon purge gas improves the efficiency of atomization of tin; measurements are best done at 224.61 nm. Phosphoric acid lowers the atomization temperature of tin, and depresses the interferences from diverse elements. Tin in canned foods (fruit juices and drinks) can be determined by direct atomization after dilution with phosphoric acid. Prior extraction is necessary for analysis of geological materials.     

Formation of nanooctahedra in molybdenum disulfide and molybdenum diselenide using pulsed laser vaporization

Pulsed laser vaporization has been used to produce nanooctahedra of MoS2 and MoSe2. The nanooctahedra primarily form in two- or three-layer nested octahedra, although nesting up to five layers has been observed. Tilting the TEM sample stage and mapping how the images of single particles transformed provided the evidence to verify their octahedral geometry. Analysis of 30 two- and three-layered octahedra showed that their outer edge lengths clustered at approximately 3.8 nm and approximately 5.1 nm, respectively. This discreet sizing and the high symmetry of these closed nanooctahedra represent the closest inorganic analogy yet to the carbon fullerenes. The geometrical implications for forming octahedra from these layered compounds are investigated by considering different atomic arrangements assuming either trigonal prismatic or octahedral coordination around the Mo atom and yields two possible configurations for the actual structure of the nanooctahedra. A preliminary survey of pulsed laser vaporization of other layered metal chalcogenides shows that these dichalcogenides differ in their tendency to form small closed layered fullerene-like structures. These materials can be ranked from highest tendency to lowest as follows: NbSe2, WS2, WSe2, SnS2, TaS2, GaS, ReS2, and MoTe2.     

A microporous structure of a thin film made of an ion-exchangeable layered compound

A thin film made of an ion-exchangeable layered compound, K₄Nb₆O₁₇, was prepared by a novel method. Fine particles of K₄Nb₆O₁₇ obtained by wet-grinding of the powder were coated on a substrate and calcined. Recrystallization of the fine particles at 1073 K was confirmed by XRD and SEM, and very flat and large crystals with the b-axis perpendicular to the substrate surface were obtained. The obtained thin film had a layered structure and an ion-exchange property similar to that of K₄Nb₆O₁₇ powder. The adsorption of CO was investigated for the thin film calcined at 1073 K by IR spectroscopy. The initially IR-inactive H⁺ species were suggested to be transformed into OH groups as a result of CO adsorption at the interlayer space.     

A novel one-dimensional supramolecular inclusion compound linked by hydrogen bonding interaction

Crystal structure analysis shows the cucurbit[6]uril host and its tetrahydrofuran (THF) guest in the Pmn2₁ crystal lattice. The crystal data and refinement parameter for the title compound are: a = 14.027(3), b = 11.807(3), c = 16.760(4) Å, V = 2774.7(9) ų. For Z = 2 and Mw = 1529.52, the calculate density Dcal = 1.825 g/cm³. Hydrogen bonding interaction assembled the adjacent {[La(H₂O)₆Cl](C₄H₈O@C₃₆H₃₆N₂₄O₁₂)}²⁺ cations into a novel one-dimensional superamolecular chain.     

Electronic structure and metal-metal interaction in edge- and face-sharing bioctahedral compounds of molybdenum

Ab initio configuration interaction calculations have been performed for the title compounds to study the nature of the metal-metal interaction. By analyzing the energy diagrams and the CI wave functions, it can be shown that the metal-metal interaction in such compounds has a dual nature, namely, formation of some direct metal-metal bonds and antiferromagnetic coupling of remaining electron pairs. Experimental observations of the magnetic behavior of the compounds can be explained satisfactorily by the calculated energy diagrams which include low-lying magnetic excited states as the result of the weak exchange coupling. © 1996 John Wiley & Sons, Inc.     

Electronic structure,Fermi surface,and chemical bonding in new layered oxyselenide: HgCuSeO

A full-potential FLAPW-GGA method is used to study for the first time the electronic structure of new layered HgCuSeO oxyselenide with a tetragonal structure. The band structure, density of electron states, Fermi surface, and effective atomic charges are obtained and analyzed; the coefficients of low-temperature heat capacity and paramagnetic Pauli susceptibility are estimated. It is shown that the new layered HgCuSeO phase can be characterized as non-magnetic ionic metal.     

Synthesis,crystal structure and chemical bonding of the novel compound IrGa2

The crystal structure of the novel constant composition compound IrGa₂ was determined from X-ray single-crystal diffraction data. The compound crystallizes in the space group Cmcm with the lattice parameters a=3.9021(3) Å, b=12.9925(8) Å and c=10.8808(7) Å. Its structure represents a new type with the Pearson symbol oC36. Analysis of the electron localization function (ELF) showed that the d electrons of both iridium atoms in IrGa₂ are involved in the bonding and that the two crystallographically independent iridium atoms have different bonding character.     

Hydrogen-hydrogen bonding: a stabilizing interaction in molecules and crystals

Bond paths linking two bonded hydrogen atoms that bear identical or similar charges are found between the ortho-hydrogen atoms in planar biphenyl, between the hydrogen atoms bonded to the C1-C4 carbon atoms in phenanthrene and other angular polybenzenoids, and between the methyl hydrogen atoms in the cyclobutadiene, tetrahedrane and indacene molecules corseted with tertiary-tetra-butyl groups. It is shown that each such H-H interaction, rather than denoting the presence of "nonbonded steric repulsions", makes a stabilizing contribution of up to 10 kcal mol(-1) to the energy of the molecule in which it occurs. The quantum theory of atoms in molecules-the physics of an open system-demonstrates that while the approach of two bonded hydrogen atoms to a separation less than the sum of their van der Waals radii does result in an increase in the repulsive contributions to their energies, these changes are dominated by an increase in the magnitude of the attractive interaction of the protons with the electron density distribution, and the net result is a stabilizing change in the energy. The surface virial that determines the contribution to the total energy decrease resulting from the formation of the H-H interatomic surface is shown to account for the resulting stability. It is pointed out that H-H interactions must be ubiquitous, their stabilization energies contributing to the sublimation energies of hydrocarbon molecular crystals, as well as solid hydrogen. H-H bonding is shown to be distinct from "dihydrogen bonding", a form of hydrogen bonding with a hydridic hydrogen in the role of the base atom.     

Energetics and bonding in aluminosilicate rings with alkali metal and alkaline-Earth metal charge-compensating cations

The stabilizing effect of alkali and alkaline-earth metal ions on the oxygen donors of four- and six-membered faujausite-like rings has been calculated in terms of Kohn-Sham core-level (O1s) energy shifts with respect to these same complexes without cations. The results confirm and complement earlier investigations by Vayssilov and co-workers where Na(+) and K(+) were the only complexing cations. The oxygen donor centers in six-membered rings are stabilized by -3.6 ± 0.4, -3.9 ± 0.5, -7.3 ± 0.1, and -7.6 ± 0.2 eV by K(+), Na(+), Ca(2+), and Mg(2+) adions, respectively. The energy shifts are even greater for four-membered rings where the stabilization effects attain -3.7 ± 0.1, -4.1 ± 0.1, -8.1 ± 0.1, and -9.0 ± 0.1 eV, respectively. These effects are also observed on the low-lying σ-bonding and antibonding molecular orbitals (MOs) of the oxygen framework, but in a less systematic fashion. Clear relationships with the core-level shifts are found when the effects of alkali metal complexation are evaluated through electron localization/delocalization indices, which are defined in terms of the whole wave function and not just of the individual orbitals. Complexation with cations not only involves a small but significant electron sharing of the cation with the oxygen atoms in the ring but also enhances electron exchange among oxygen atoms while reducing that between the O atoms and the Si or Al atoms bonded to them. Such changes slightly increase from Na to K and from Mg to Ca, whereas they are significantly enhanced for alkaline-earth metals relative to alkali metals. With respect to Al-free complexes, Si/Al substitution and cation charge compensation generally enhance electron delocalization among the O atoms, except between those that are linked through an Al atom, and cause either an increased or a decreased Si-O ionicity (smaller/higher electron exchange) depending on the position of O in the chain relative to the Al atom(s). The generally increased electron delocalization among O atoms in the ring is induced by significant electron transfer from the adsorbed metal to the atoms in the ring. This same transfer establishes an electric field that leads to a noticeable change in the ring-atom core-level energies. The observed shifts are larger for the oxygen atoms because, being negatively charged, they are more easily polarizable than Al and Si. The enhanced electron delocalization among O atoms upon cation complexation is also manifest in Pauling's double-bond nature of the bent σ-bonding MO between nonadjacent oxygen centers in O-based ring structures.