Reshef Tenne

High-Rate, Gas-Phase Growth of MoS2 Nested Inorganic Fullerenes and Nanotubes

The gas-phase reaction between MoO3-x and H2S in a reducing atmosphere at elevated temperatures (800� to 950�C) has been used to synthesize large quantities of an almost pure nested inorganic fullerene (IF) phase of MoS2. A uniform IF phase with a relatively narrow size distribution was obtained. The synthesis of IFs appears to require, in addition to careful control over the growth conditions, a specific turbulent flow regime. The x-ray spectra of the different samples show that, as the average size of the IF decreases, the van der Waals gap along the c axis increases, largely because of the strain involved in folding of the lamella. Large quantities of quite uniform nanotubes were obtained under modified preparation conditions.

Stress-induced fragmentation of multiwall carbon nanotubes in a polymer matrix

We report the observation of single nanotube fragmentation, under tensile stresses, using nanotube-containing thin polymeric films. Similar fragmentation tests with single fibers instead of nanotubes are routinely performed to study the fiber-matrix stress transfer ability in fiber composite materials, and thus the efficiency and quality of composite interfaces. The multiwall nanotube-matrix stress transfer efficiency is estimated to be at least one order of magnitude larger than in conventional fiber-based composites.

Hollow nanoparticles of WS2 as potential solid-state lubricants

Solid lubricants fill a special niche in reducing wear in situations where the use of liquid lubricants is either impractical or inadequate, such as in vacuum, space technology or automotive transport. Metal dichalcogenides MX2 (where M is, for instance, Mo or W and X is S or Se) are widely used as solid lubricants. These materials are characterized by a layered structure with weak (van der Waals) inter-layer forces that allow easy, low-strength shearing,. Within the past few years, hollow nanoparticles (HNs) of MX2 with structures similar to those of nested carbon fullerenes and nanotubes have been synthesized,. Here we show that these materials can act as effective solid lubricants: HN-WS2 outperforms the solid lubricants 2H-MoS2 and 2H-WS2 in every respect (friction, wear and lifetime of the lubricant) under varied test conditions. We attribute the outstanding performance of HN-WS2 to its chemical inertness and the hollow cage structure, which imparts elasticity and allows the particles to roll rather than to slide.

Mechanisms of ultra-low friction by hollow inorganic fullerene-like MoS2 nanoparticles

Abstract Inorganic Fullerene-like (IF)-MoS2 nanoparticles were tested under boundary lubrication and ultra-high vacuum (UHV) and were found to give an ultra-low friction coefficient in both cases compared to hexagonal (h)-MoS2 material. Previous works made by Rapoport et al. with IF-WS2 revealed that the benefit effect of the inorganic fullerene-like materials decreases at high loads and sliding velocities. Nevertheless, under the conditions used in our experiments using high contact pressure (maximum pressure above 1.1 GPa in oil and 400 MPa in high vacuum) and slow sliding velocities (1.7 mm/s in oil test and 1 mm/s in high vacuum), friction always decreases and stabilizes at about 0.04 for 800 cycles in both cases. Therefore, IF-MoS2 material appears to be a good candidate for use in various environments in regard to other MoS2 crystal structures. Wear mechanisms were investigated using both High Resolution TEM and surface analyses (XPS) on the wear tracks. Wear particles collected from the flat wear scar show several morphologies, suggesting at least two lubricating mechanisms. As spherical particles are found in the wear debris, rolling may be a possible event. However, flattened and unwrapped IF-MoS2 particles are often observed after friction. In this case, low friction is thought to be due either to sliding between IF-MoS2 external flattened planes or to slip between individual unwrapped MoS2 sheets.

Cage structures and nanotubes of NiCl 2

Nanoparticles of layered compounds form hollow cage structures of various types, including nanotubes. Here we study nanoparticles of the layered compound NiCl2, which can form cage structures, with different numbers of atomic layers, and nanotubes. Because Ni atoms in a layer are coupled ferromagnetically and the interlayer (IIc) coupling is antiferromagnetic, these structures may show different magnetic behaviour according to the parity of closed NiCl2layers in the nanoparticles.

Applications of WS2(MoS2) inorganic nanotubes and fullerene-like nanoparticles for solid lubrication and for structural nanocomposites

Nanoparticles of WS2 and MoS2 with a closed cage structure (fullerene-like) that are termed IF phases are synthesized in large amounts in a pure form. These nanoparticles were shown to play a favorable role as solid lubricants under severe conditions where fluids are unable to support the heavy load and are squeezed away from the contact area. Various tribological scenarios are presented for these superior solid lubricants, demonstrating the large scale potential for applications of these materials. The mechanism of action of these solid lubricants is briefly discussed. Various other potential applications of IF phases for nanocomposites with high impact resistance; in rechargeable batteries and in optical devices are discussed in short.

Inorganic fullerene-like material as additives to lubricants: structure–function relationship

Abstract Recently, inorganic fullerene-like (IF) supramolecules of metal dichalcogenide MX2 (M=Mo, W, etc.; X=S, Se), materials with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized. The main goal of the present work was to study the tribological properties of IF–WS2 in comparison to 2H–WS2 and MoS2 platelets over a wide range of loads and sliding velocities. The size and shape distributions of the nanoparticles were studied by transmission electron microscopy (TEM). The average size of the IF–WS2 particles was 120 nm, while that of 2H–WS2 and 2H–MoS2 was 0.5 μm and 4 μm. The chemical reactivity of the different powders in an oxygenated atmosphere was verified by heating the powders in ambient atmosphere. The friction experiments were performed in laboratory atmosphere (humidity ∼50%) using a ring-block tester. Complementary information on the state of wear of the powders in the lubricating fluid and on the metal surfaces of the specimens was obtained using a combination of TEM, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It has been established that IF–WS2 nanoparticles appear to have excellent tribological properties in definite loading range in comparison to typical metal dichalcogenides. The oxidation of the IF particles and the wear track was essentially less than with solid lubricants made of platelets of the same chemical compound (WS2). The main advantages of IF nanoparticles lie in their round shape and the absence of dangling bonds.

Passivation of recombination centers in n‐WSe2 yields high efficiency (>14%) photoelectrochemical cell

It is shown that careful photoetching of n‐WSe2 leads to a large improvement in its photoresponse. Conversion efficiencies in excess of 14% were obtained in polyiodide solution under simulated solar light. A significant red shift in the photocurrent spectrum is observed after photoetching as well as hexagonal etch pits which reduce the reflectivity of the surface.

Efficient electrochemical reduction of nitrate to ammonia using conductive diamond film electrodes

Diamond posseses many outstanding properties such as its chemical inertness, mechanical hardness and high thermal conductivity (about five times greater than copper). It is a good electrical insulator in nature but its resistivity can be controlled in the range lo-*-lo5 0 cm by doping. These redeeming properties render diamond suitable for many new applications [l-7]. Although many reports have appeared on the growth and applications of diamond, very few papers have been published dealing with its chemical [8] and electrochemical behavior 19,101. The use of semiconducting diamond films for electrochemical systems has been reported only recently. One of the most intriguing properties for electrochemical application is a very negative energetic position of the conduction band ( 4.4 V vs. SCE), which can be estimated’ from the flat band potential (+0.4 V vs. SCE), bandgap of 5.45 eV and the energy difference between the Fermi level and the top of the valence band (0.35 eV). In other words the conduction band electrons of diamond are located very close to the vacuum level [lo-121, leading to the possibility that diamond electrodes drive electrochemical and photoelectrochemical reactions requiring very negative potentials with a small rate of hydrogen generation. For example, nitrogen fixation, CO, reduction, and deposition of electronegative metals are reactions which could be suitably attempted with this material. Generation of ammonia from gaseous nitrogen (nitrogen fixation) remains one of the most elusive goals of modem electrochemistry [13]. This difficulty can be attributed to the highly negative redox potential of ammonia (2.85 V vs. SCE).

Biocompatible inorganic fullerene-like molybdenum disulfide nanoparticles produced by pulsed laser ablation in water.

We report on the synthesis of inorganic fullerene-like molybdenum disulfide (MoS(2)) nanoparticles by pulsed laser ablation (PLA) in water. The final products were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and resonance Raman spectroscopy, etc. Cell viability studies show that the as-prepared MoS(2) nanoparticles have good solubility and biocompatibility, which may show a great potential in various biomedical applications. It is shown that the technique of PLA in water also provides a green and convenient method to synthesize novel nanomaterials, especially for biocompatible nanomaterials.