A. S. Golub

Layered compounds assembled from molybdenum disulfide single-layers and alkylammonium cations

Abstract Intercalation compounds A x MoS 2 have been obtained by restacking aqueous MoS 2 dispersions in the presence of A-alkylammonium cations (A=R 4 N + or R(CH 3 ) 3 N + ). Varying the experimental conditions, the negative charge of the MoS 2 single-layers in the dispersions can be modified, which allows to control the content and packing geometry of the A guest layers in the resulting intercalation compounds. The value of the negative charge kept on the MoS 2 host layers of the intercalation compounds determines the degree of in-layer distortion of their Mo sublattice.

Phenanthroline intercalation into molybdenum disulfide

Abstract The interaction of MoS 2 single-layer dispersion with 1,10-phenanthroline has been studied over the pH range 0–11. Only protonated phenanthroline initiates flocculation of dispersion and formation of intercalation compounds. Two intercalated phases containing respectively 0.31–0.35 and 0.1 mol of phenanthroline per mol MoS 2 have been isolated. In the first one (interlayer spacing c = 14.92–15.56 A) the planar organic species are inclinated with respect to MoS 2 layers. In the second one ( c = 9.7 A) these moieties are oriented parallel to the layers.

From single-layer dispersions of molybdenum disulfide towards ternary metal sulfides: incorporating copper and silver into a MoS2 matrix

Abstract Interaction of MoS 2 single-layer dispersions with Cu(II) or Ag(I) salts results in formation of ternary metal sulfides. Upon this, reduction of Cu(II) to Cu(I) and reduction of part of Ag(I) to Ag(0) occur. The structural features of the compounds are discussed on the basis of XRD, electron diffraction, EXAFS and XPS data.

Nanocomposite materials consisting of alternating layers of molybdenum disulfide and cobalt or nickel hydroxides : Magnetic characterization

Abstract Magnetization measurements were performed from 5 to 300 K on nanocomposite compounds obtained by precipitation of MoS2 single-layer dispersion in the presence of Co2+ or Ni2+ ions. Ni(II) and high spin Co(II) were evidenced, both in octahedral oxygen surrounding. From similarity of their temperature magnetic behavior with that of lamellar references Ni(OH)2 and β-Co(OH)2 powders, it can be inferred that the nanocomposites contain 2D nickel or cobalt hydroxide species. The low temperature magnetic behavior is discussed on the basis of dimensionality and finite particle size effects.

Distortion of MoS2 host layers in intercalation compounds with various guest species: correlation with charge transfer

Abstract The MoS 2 host layers in various intercalation compounds freshly prepared from single-layer dispersions are substantially distorted compared to those in parent crystalline 2 H -MoS 2 . The coordination number for the Mo–Mo sphere ( d ∼3.2 A) obtained from Mo K-edge EXAFS data can be used as a convenient parameter to estimate qualitatively the degree of distortion, which is shown to correlate fairly with the residual negative charge kept by the host layers.

Solvent effects on the formation and absorption spectra of nanodisperse molybdenum disulfide

The optical absorption spectra of molybdenum disulfide prepared by monolayer dispersion of a crystalline precursor in a liquid medium were studied. On the whole, the three-dimensional structure of the crystalline analogue was reconstructed in disperse MoS2 dried to a powder state. A substantial fraction of the material transformed into a nanosized state during dispersion and was stabilized in the form of nanoparticles in various solvents. The stabilizing action of the solvents studied decreased in the series acetonitrile, ethanol > chloroform > water. The data on the optical absorption of MoS2 suspensions in various solvents were evidence of a broad particle-size distribution. Along with nanoscale particles, the samples contained larger particles responsible for long-wave absorption (>600 nm). The size of nanoparticles was estimated using an empirical correlation between the position of maximum A (the long-wave maximum of the first allowed absorption band) in the absorption spectrum and the size of particles (2R). This correlation was obtained using the literature data on monodisperse particles and mixtures of particles. The number of particles showed a tendency to increase as the concentration of disperse MoS2 in acetonitrile decreased.

Modification of molybdenum disulfide (2H-MoS2) and synthesis of its intercalation compounds

We have shown that powdered molybdenum disulfide prepared as a result of the exfoliation (singlelayer dispersion) of a crystalline precursor (2H-MoS2) and subsequent precipitation in an acid medium, is capable of forming intercalation compounds in reacting with salts of copper and tetramethylammonium, as well as diethylamine and triethylamine. We consider factors influencing the composition and type of the alternation of guest and host layers in the resulting layered compounds. Relationships between charge transfer to MoS2 layers and the extraordinary reactivity of its modified species are discussed.

Thermal transformations of nanocomposite material consisting of molybdenum disulfide and nickel hydroxide layers

Abstract The structure of Ni(OH)2/MoS2 nanocomposite material obtained via MoS2 single-layer dispersion and the products of its annealing in the 100–400°C temperature range were studied using X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The transformation of the initial MoS2 superlattice structure with Mo–Mo bonding to the usual structure with unique Mo–Mo distance was found to occur upon annealing. The decomposition of two-dimensional Ni(OH)2-like species in the interlayer space of MoS2 at 400°C leads to complete substitution of O by S in the Ni local environment.

Synthesis and Study of Self-Organization of Organo–Inorganic Nanostructures Based on Cationic Poly(meth)acrylates and Molybdenum Disulfide Single Layers

Poly(meth)acrylates of three types, namely, regular homopolymers containing side-chain tetraalkylammonium ionic groups with alkyl radicals of various lengths (C6 and C16), a copolymer with statistically distributed ionic and long-chain (C18) alkyl groups, and a block copolymer of the same composition in which alkylammonium and alkyl groups are located in separate blocks, are synthesized with the use of controlled radical polymerization processes. The interaction of the polymers with molybdenum disulfide singlelayer dispersions yields self-organized organic-inorganic nanocomposites containing up to 40% polymer. As evidenced by powder X-ray diffraction and high-resolution transmission electron microscopy structural studies of the composites, they possess a crystalline layered structure with interlayer distances depending on the composition and structure of the polymer. Structures with the most regular alternation of organic and inorganic layers are formed in the case of homopolymers. The orientation of their alkylammonium fragments relative to MoS2 layers depends on the length of the alkyl radical and corresponds to their parallel (C6) or perpendicular (C16) arrangement.

Mössbauer evidence for fast electron hopping between Fe(II) and Fe(III) in iron hydroxide/molybdenum disulfide lamellar nanocomposite

Abstract Nanocomposite compounds with iron hydroxide and molybdenum disulfide alternating layers have been studied using 57Fe Mossbauer spectroscopy. Evidence is given of the presence of two oxidation states for iron (Fe(II)/Fe(III)≈1.9). In the temperature range 60–160 K thermal evolution of the absorption areas obeys Debye’s model, with the lattice temperature ΘM equal to 275 and 320 K for Fe(II) and Fe(III), respectively. At higher temperature (T≥180 K), a new iron state is observed, which can be related to fast electron hopping between certain heterovalent iron ions. Tin-doping enhances this process which can already be detected at 140 K.