Preparation and characterization of molybdenum disulphide catalysts

Molybdenum disulphide has been prepared by atmospheric-pressure hydrogen reduction of molybdenum trisulphide in the temperature range 400–750 °C for 4 h and characterized. Chemical analysis of the product confirmed the S to Mo ratio 2.00 as desired for MoS₂, consistent with its thermogravimetric analysis data in an air atmosphere. MoS₂ prepared under these reducing conditions possessed a hexagonal structure with n-type diamagnetic semiconducting behaviour and a lower surface area. The catalytic activity of the MoS₂ was studied for liquid-phase hydrogenation of nitrobenzene. X-ray studies on MoS₃ when reduced at 750 °C for 48 h indicated that MoS₂ so formed is unstable, resulting in the formation of its over-reduced products Mo₂S₃ and Mo.     

Electrosynthesis of the molybdenum disulphide thin films and characterization

Thin films of molybdenum disulphide have been prepared by electrodeposition from an aqueous bath by using molybdenum trioxide and sodium thiosulphate as Mo⁺ ion and S⁻² ion sources, respectively. The films deposited onto stainless steel and fluorine doped tin oxide (FTO) glass substrates were adherent to the substrate. X-ray diffraction studies show that films are polycrystalline. SEM shows films are continuos and uniform. Optical absorption gives a bandgap energy of 1.7 eV.     

Synthesis and characterization of tungsten disulphide films grown by pulsed-laser deposition

The synthesis and characterization of tungsten disulphide (WS₂) films grown on 440C stainless steel substrates using the 248 nm line from a KrF excimer laser are reported. Film properties could be adjusted by controlling substrate temperature and by laser or thermal anneals. X-ray photoelectron spectroscopy, glancing angle XRD, Raman spectroscopy and high-resolution scanning electron microscopy were used to evaluate film chemistry, crystallinity and morphology. Films grown at room temperature were amorphous, near stoichiometric, and had a multiplicity of chemical states. Local order and bonding were improved most dramatically through post-deposition laser anneals. Crystallite size could be increased by raising the substrate temperature during deposition and, to a lesser degree, by post-deposition thermal anneals. Local disorder was observed within the larger crystallites compared to those that were laser annealed. Crystallinity was induced in amorphous films by mechanical rubbing at room temperature under conditions where frictional heating was negligible. The degree of control over film properties provided by PLD demonstrates its value for growing/designing tribological coatings.     

Chemical bath deposition of MoS2 thin film using ammonium tetrathiomolybdate as a single source for molybdenum and sulphur

Molybdenum disulphide, MoS₂, thin films have been deposited by chemical bath deposition method on glass and quartz substrate using ammonium tetrathiomolybdate as a single source precursor for Mo and S and subjected to vacuum heat treatment at different temperatures. X-ray diffraction of as-deposited film indicated its amorphous character and showed the development of poorly crystalline MoS₂ thin film on increasing annealing temperature. The film has been characterized by energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, scanning electron micrograph and the optical properties also have been studied.     

Synthesis and characterization of nanolamellar tungsten and molybdenum disulfides

Tungsten and molybdenum disulfides were produced in direct self-sustained combustion in argon between elementary sulfur and metal (W, Mo) nanopowders prepared by electrical explosion of wires. The results of XRD analysis show that the main phases of the synthesized nanopowders are hexagonal WS₂ and MoS₂. According to SEM and TEM observations, they are agglomerated nanolamellar particles of thickness 40–150 nm and width 100–3000 nm.     

Preparation and isochronal sintering behaviour of molybdenum disulphide compound

The low-dimensional solid 2H-MoS₂ has been prepared by the high-temperature solid state reaction technique. Different techniques such as positron annihilation, X-ray diffraction, microhardness and scanning electron microscopy have been used to study the isochronal sintering behaviour of this compound from room temperature to 700 ° C. In the positron annihilation experiments, an anomaly was observed in the temperature region 400 to 500 ° C. The presence and reduction of stacking fault defects, changes in the void size, breaking-up of grains and transcrystalline fractures during sintering were also investigated.     

Synthesis and characterization of molybdenum disulfide micro-sized solid spheres

Mono-dispersed molybdenum disulfide solid spheres with the diameter of 0.5–2 μm have been successfully synthesized by a solvothermal method with a homemade quaternary ammonium salt of 2-undecyl-1-dithioureido-ethyl-imidazoline (SUDEI) as surfactant. The obtained solid spheres are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The influences of reaction conditions are discussed while a mechanism is proposed to explain the formation of the peculiar morphology.     

Synthesis and characterization of high surface area molybdenum nitride

The synthesis of high surface area γ-Mo₂N materials using the nitridation of oxide precursors MoO₃, H₂MoO₅, and H₂MoO₅·H₂O with ammonia at 650°C is described. H₂MoO₅ and its hydrated form were obtained from the reaction of MoO₃ and diluted H₂O₂. The materials were characterized by means of X-ray powder diffraction, thermal analysis and nitrogen physisorption. Directly after the preparation, the nitride materials were subjected to different processing conditions: (1) contact to air, (2) inert gas or (3) treated with 1% O₂(g)/N₂(g) gas mixture (Passivation). The synthesis and passivation conditions critically affect the specific surface area of the final product. By means of XRD a minor quantity of MoO₂ was detected in most of the products. The highest specific surface area of the nitrides was 158.4 m²/g for γ-Mo₂N materials using H₂MoO₅·H₂O as the precursor. The high specific surface area corresponds to an average particle diameter of 4 nm, assuming a cubic morphology of the nanocrystals (d_p = 6/ρS_BET, ρ = 9.5 g/cc). The nitrogen physisorption isotherms of γ-Mo₂N are of type IV, but pore sizes and diameters differ significantly depending on the synthesis conditions due to different defect structures of the intermediates generated in the course of the topotactic transformation of the oxides to nitrides.     

Synthesis and characterization of indium intercalation compounds of molybdenum sulphoselenide

The synthesis, structure and properties of indium-intercalated compounds of molybdenum sulphoselenide, In_1/3MoS_xSe_2–x (0x 2) compounds were investigated. X-ray analysis shows that all these compounds possess layer-type structure with hexagonal symmetry. Studies of room-temperature magnetic susceptibility, thermoelectric power experiments and two-probe conductivity measurements in the temperature range 25–350 °C, confirmed that these are diamagnetic semiconductors with In_1/3MoS₂, In_1/3MoS_1.5Se_0.5 and In_1/3MoS_xSe_2–x (0x1.5) exhibiting n- and p-type conductivity, respectively. These results have been explained on the basis of existing band models. Thermal stability behaviour of these compounds in an air atmosphere and X-ray analysis of the oxidized product were also studied.     

Synthesis and characterization of intercalation compounds between lamellar molybdenum trioxide and amines

Compounds were obtained by the intercalation reaction of the amines 3-aminopyridine, piperazine and octyldiamine in molybdenum trioxide. The X-ray diffraction patterns show an increase in the interlamellar distance as compared with the pure lattice. It is observed the formation of different phases in the intercalated material. The infrared spectra reveal the interactions between the guest molecules and the trioxide lattice, by means of the observed displacements. The thermogravimetric curves for the compounds are present in the stages of losses of water and amines and also the oxide sublimation.     

Characterization of viscoelastic properties of molybdenum disulphide filled polyamide by indentation

In this paper, the creep behavior of molybdenum disulphide (MoS₂) filled polyamide 66 composite was investigated through sharp indentation at room temperature. Two types of indentation creep test, the 3-step indentation test, and the 5-step indentation test were considered in order to explore whether the measured creep response is mainly viscoelastic or includes a significant contribution from the plastic deformation developed during the loading phase. The experimental indentation creep data were analyzed within an analytical framework based on the hereditary integral operator for the ramp creep and a viscoelastic–plastic (VEP) model in order to determine the indentation creep compliance function including the short- and long-time modulus. The equivalent shear modulus calculated from the creep compliance function was compared to the indentation plane strain modulus derived from the initial slope of the unloading curve in order to investigate the validity of the Oliver and Pharr method.     

Synthesis and characterization of antibacterial polyurethane coatings from quaternary ammonium salts functionalized soybean oil based polyols

In this study, a simple and versatile synthetic approach was developed to prepare bactericidal polyurethane coatings. For this purpose, introduction of both quaternary ammonium salts (QASs), with well-known antibacterial activity, and reactive hydroxyl groups on to the backbone of soybean oil was considered. Epoxidized soybean oil was reacted with diethylamine and the intermediate tertiary amine containing polyol was reacted with two different alkylating agents, methyl iodide and benzyl chloride, to produce MQAP and BQAP, respectively. These functional polyols were reacted with different diisocyanate monomers to prepare polyurethane coatings. Depending on the structure of monomers used for the preparation of polyurethane coatings, initial modulus, tensile strength and elongation at break of samples were in the ranges of 122–339 MPa, 4.6–12.4 MPa and 8.4–46%, respectively. Polyurethane coatings based on isophorone diisocyanate showed proper mechanical properties and adhesion strength (0.41 MPa) for coating application. Study of fibroblast cells interaction with prepared polyurethanes showed promising cells viability in the range of 78-108%. Meanwhile, MQAP based samples with higher concentration of QASs showed better adhesion strength, surface hydrophilicity and antibacterial activity (about 95% bacterial reduction). Therefore, these materials can find applications as bactericidal coating for biomedical devices and implants.     

A new hydrothermal route for synthesis of molybdenum disulphide nanorods and related nanostructures

A simple approach to prepare nanorods of Molybdenum Disulphide (MoS2) using hydrothermal method by reacting aqueous solutions of (NH4)6Mo7O24.4H20, C2H4NS and Na2S2O4 at 190 degrees C for 24 h is described. The hydrothermal product has been subsequently subjected to the thermal treatment in nitrogen atmosphere at 675 degrees C for 6 h and characterized. X-ray diffraction (XRD) of the hydrothermal product indicated the formation of MoS2 relatively with much lower crystallinity compared to when it thermally treated. Energy dispersive analysis (EDX) was done to know the chemical composition of the product. TEM showed onset growth of MoS2 nanorods within the hydrothermal products itself and in thermally treated products it was prominent with the diameter of the nanorods ranging between 10-20 nm. Photoluminescence spectra MoS2 nanorods shows an intense absorbance at around 429 nm. TGA of the MoS2 nanorods in air and nitrogen atmosphere has also been studied. The extent of formation of MoS2 from the precursors obtained at 190 degrees C for duration of 12, 18, and 24 h and annealed at 675 degrees C for 6 h under nitrogen atmosphere is also demonstrated based on XRD data.     

含季铵荷电基团的有机-无机杂化介孔材料的合成与表征

以十二烷基硫酸钠(SDS)为模板剂,正硅酸乙酯(TEOS)和N-三甲氧基硅丙基-N,N,N-三甲基氯化铵(TSPMNC)为硅源,以NaOH为催化剂,合成出带有季铵荷正电基团的有序介孔材料(QAS)。采用XRD,TGA、BET、SEM,XPS、TEM、FT-IR等手段对产品结构进行了表征和分析。结果表明,产品具有较为均一的六方介孔结构,孔径约为3.5nm,产品中季铵荷电基团的含量约为1.41mmol/g。     

In-situ electron microscopy study of the reactivity of molybdenum disulphide in various gaseous environments

The interaction of single crystal molybdenum disulphide with various gases has been followed dynamically usingin situ scanning transmission electron microscopy. It is found that in the presence of oxygen attack takes place preferentially at edges and point defects on the basal plane. I1 appears that the reaction proceeds by two pathways, conversion to MoO₂ predominates at low temperatures (690 K) end formation of MoO₃ becoming significant at jigher temperatures (800 K), with intermediate metastable oxides playing some role. Reduction of molybdenum disulphide in hydrogen is a relatively sluggish reaction and attack occurs exclusively at the edge regions of crystals resulting in the formation of metallic molybdenum as major product with e minor amount of Mo₂S₃.     

Synthesis of ammonium aluminum oxalate from Bayer aluminum hydroxide

The synthesis of ammonium aluminum oxalate was performed using Bayer aluminum hydroxide as a raw material. For this aim, Bayer aluminum hydroxide of 99.7% purity was dissolved in oxalic acid to produce an aqueous aluminum solution. As a result, it was found that a mixing ratio of ethanol to Al solution exceeding 2:1 and a pH adjusted to greater than 8.0 should be employed in the synthesis of ammonium aluminum oxalate. From the chemical analysis of ammonium aluminum oxalate prepared in this work, the NH₄, Al and C content were found to be 14.5, 7.18 and 17.4%, respectively which are very close to the theoretical values of (NH₄)₃Al(C₂O₄)₃3H₂O.