No abstract

In materials with low-dimensional structures, the instability of the weakly bonded layered slabs against folding, and the saturation of dangling bonds in finite layers, leads to the formation of a variety of nanostructures with spherical or cylindrical shapes. In analogy to nested carbon fullerenes [1] and nanotubes, [2] Tenne and co-workers [3,4] discovered related MQ 2 -based (M = early transition metal, Q = S, Se) concentric closed-shell materials, which laid the foundation for the entire field of nanostructures based on inorganic materials.[5] Substantial progress has been made in the application of MoS 2 and WS 2 nanoparticles as lubricants [6±9] and heterogeneous catalysts, [10,11] and MoS 2 nanotubes as electrochemical hydrogen-storage [12] and lithium-intercalation materials. [13,14] During the past few years a huge body of experimental evidence has been accumulated that suggests the phase diagram of the elements that form layered compounds includes new phases of hollow and closed nanostructures. Provided that the crystal growth is limited and the crystallites remain smaller than a critical size (ca. 100 nm), these nanostructures are the thermodynamically preferred phases. In other words, a key step in the preparation of nanostructured layered materials is the restricted growth of the newly formed two-dimensional (2D) crystallites. [15,16] Various strategies have been developed to prepare nanostructured metal chalcogenides, including sulfides and selenides, through different growth mechanisms. A characteristic feature of all closed-shell structures is that high reaction temperatures (> 800 C) or large activation energies are needed to overcome the activation barrier associated with the bending of the otherwise flat 2D layers.[ can provide large activation energies in a very short period, such as electron irradiation, [19] laser ablation, [20] microwave plasma, [21] arc discharge, [22] and pulsed-laser vaporization, [23,24] have been used to synthesize a variety of inorganic fullerene (IF)-like nanostructures. Schuffenhauer et al. [25] have synthesized nested fullerene-like NbS 2 by the reaction between NbCl 5 vapor and H 2 S gas at 400 C followed by further heat treatment at 550 C. Similarly, Coleman et al. [26] have synthesized ReS 2 fullerene-like nanoparticles by sulfidization of ReO 2 obtained from ReO 3 decomposition. As the above methods have to rely mostly on high temperatures and/or complicated processes they may not be optimally suited for the large-scale preparation of nanostructured metal chalcogenides with a minimum amount of side products. On the other hand, as the mechanical, physical, and catalytic properties of nanostructured chalcogenides strongly depend on their size and shape, it is desirable to devise synthetic procedures that enable significant control of the particle size and morphology. From an applications point of view, the focus on nanoparticle growth will be on high-purity, high-yield, and, therefore, low-cost products.In this contribution we report on the facile, large-scale s...

Softly, softly: VS2 nanotubes (see electron micrograph, layer separation 1.6 nm) are prepared from vanadium oxide nanotubes by a “chimie douce” process. The VS2 nanotubes are remarkably stable; the corresponding bulk compound is unstable unless it is intercalated with alkali‐metal atoms. The nanotubes reversibly intercalate copper with high capacity and thus could serve as precursors for conductors or contacts in electronic circuitry.

Inseparably interwoven are three independent polymeric diamond‐type U(P2S6)2 frameworks in the structure of the title compound (see picture). The linear P2S6 units act as molecular rods linking the pseudotetrahedral U4+ centers. U(P2S6)2 may be viewed as a coordination polymer which is formed from U/P/S melts by the solid‐state equivalent of the self‐assembly reactions in solution.

The synthesis of WS 2 onion-like nanoparticles by means of a high-temperature metal-organic chemical vapor deposition (MOCVD) process starting from W(CO) 6 and elemental sulfur is reported. The reaction can be carried out as a single-step reaction or in a two-step process where the intermediate products, amorphous WS 2 nanoparticles, formed through the high-temperature reaction of tungsten and sulfur in the initial phase of the reaction, are isolated and converted into onion-type WS 2 nanoparticles in a separate annealing step. Analysis of the reaction product using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) combined with energy dispersive X-ray spectroscopy (EDX) allowed to optimize the reaction in such a way that filled onion-like structures are formed in a one-step reaction, whereas hollow onion-like structures are obtained by the two-step procedure. A model could be devised that allows us to rationalize the different outcome of the reactions. The MOCVD approach therefore allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles.