High-pressure syntheses of TaS3, NbS3, TaSe3, and NbSe3 with NbSe3-type crystal structure

Transition metal trichalcogenides TaSe₃, TaS₃, NbSe₃ and NbS₃ were prepared under the reaction conditions of 2 GPa, 700°C, 30 min. NbSe₃ is exactly the same as that obtained in the usual sealed-tube method. The other products are modifications of each usual phase. They have crystal structures very similar to that of NbSe₃. The lattice parameters are a = 10.02Å, b = 3.48 Å, c = 15.56 Å, β = 109.6° for TaSe₃, a = 9.52 Å, b = 3.35 Å, c = 14.92 Å, β = 110.0° for TaS₃, and a = 9.68 Å, b = 3.37 Å, c = 14.83 Å, β = 109.9° for NbS₃. In spite of the similarity in their crystal structures, these high-pressure phases show a variety of electrical transport properties. TaSe₃ is a superconductor having T_c at 1.9 K. TaS₃ is a semiconductor with two transitions at 200 and 250 K. NbS₃ is a semiconductor with E_a = 180 MeV.     

A Facile and Universal Top‐Down Method for Preparation of Monodisperse Transition‐Metal Dichalcogenide Nanodots

Despite unique properties of layered transition‐metal dichalcogenide (TMD) nanosheets, there is still lack of a facile and general strategy for the preparation of TMD nanodots (NDs). Reported herein is the preparation of a series of TMD NDs, including TMD quantum dots (e.g. MoS₂, WS₂, ReS₂, TaS₂, MoSe₂ and WSe₂) and NbSe₂ NDs, from their bulk crystals by using a combination of grinding and sonication techniques. These NDs could be easily separated from the N‐methyl‐2‐pyrrolidone when post‐treated with n‐hexane and then chloroform. All the TMD NDs with sizes of less than 10 nm show a narrow size distribution with high dispersity in solution. As a proof‐of‐concept application, memory devices using TMD NDs, for example, MoSe₂, WS₂, or NbSe₂, mixed with polyvinylpyrrolidone as active layers, have been fabricated, which exhibit a nonvolatile write‐once‐read‐many behavior. These high‐quality TMD NDs should have various applications in optoelectronics, solar cells, catalysis, and biomedicine.     

Facile synthesis of ternary AgInS2 nanowires and their self-assembly of fingerprint-like nanostructures

Nanowires (NWs) and self-assemble nanostructures made of chalcogenide semiconductor nanocrystals (NCs) are of great interests to the fundamental studies and practical applications. In this study, we reported a seeded-mediated growth of AgInS₂ NWs and their intriguing self-assembly nanostructures with fingerprint-like shape. The key to the formation and self-assembly of AgInS₂ NWs was the presence of In-S species that was a type of molecular metal chalcogenide complexes, serving as specific inorganic ligands for the growth of NWs and cross-linker molecules for the self-assembly of fingerprint-like nanostructures. Systematic studies were carried out to investigate the reaction factors, including the thermodynamics, amount and type of In precursors, and 1-dodecanethiol usage, to the success of the desired products.     

Highly Stable Passively Q-Switched Erbium-Doped All-Fiber Laser Based on Niobium Diselenide Saturable Absorber

A saturable absorber (SA) based on niobium diselenide (NbSe₂), which is a layered transition metal dichalcogenide (TMD) in the VB group, is fabricated by the optically driven deposition method, and the related nonlinear optical properties are characterized. The modulation depth, saturable intensity, and nonsaturable loss of the as-prepared NbSe₂ nanosheet-based SA are measured to be 16.2%, 0.76 MW/cm², and 14%, respectively. By using the as-fabricated NbSe₂ SA, a highly stable, passively Q-switched, erbium-doped, all-fiber laser is realized. The obtained shortest pulse width is 1.49 μs, with a pulse energy of 48.33 nJ at a center wavelength of 1560.38 nm. As far as we know, this is the shortest pulse duration ever obtained by an NbSe₂ SA in a Q-switched fiber laser.     

Towards Syntheses and Structures of Heterometallic Clusters Containing Tantalum-tetrachalcogenato Building Blocks

An approach to tackle the synthesis of mixed-transition metal tantalum chalcogenide clusters is described. The synthesis of 1/_∞[Li₃(TaSe₄)(MeCN)₄]_∞ (1) will in future allow the construction of Ta–Se-transition metal clusters. The potential of this route was demonstrated by the synthesis of the mixed-metal Ta–S–Fe and Ta–S–Cu complexes (Et₄N)₃[Fe₂(SPh)₄(TaS₄)] (2) and [Cu₃(TaS₄)(PPh₃)₄] (3). Dedicated to Professor Günter Schmid on the occasion of his 70th birthday.     

Incoherent neutron spectra of HxTaS2, a nonstoichiometric covalent tantalum hydrosulfide

Inelastic neutron spectra show the presence of a fundamental hydrogen vibration at 712 and 744 cm^?1 in H_0.1TaS₂ and H_0.5TaS₂, respectively. This permits the structural deduction that H_xTaS₂ is a non-stoichiometric covalent metal hydrosulfide. In H_0.5TaS₂ another low-intensity band in the spectrum may be interpreted as suggesting the presence of a small concentration of SH^? anions. An X-ray diffraction pattern taken after the neutron experiments reveals partial decomposition to TaS₂ and the presence of satellites to the (00l) reflections show the decomposition to be a process involving considerable long-range order.     

Experimente und Überlegungen zum Chemischen Transport von TaS2 mit Schwefel. Die Gasmolekel TaS5

Experiments and Conclusions on the Chemical Transport of TaS₂ with Sulfur. The Gas Molecule TaS₅ The transport rate was determined experimentally in cylindrical ampouls for the unexpected transport of TaS₂ with sulfur which proceeds to the high or low temperature zone depending on temperature and pressure. The transport must obviously be due to the existence of an unknown gaseous polysulfide TaS_x. The gas transport which is governed essentially by thermal convection was evalueted by NaCl/S_x. On this base the transport rate of TaS₂ was transformed into the pressure difference ΔP(TaS_x) = P(TaS_x)T₂ – P(TaS_x)T₁. These experimental data were compared to the calculated values ΔP′(TaS_x) = Δλ(TaS₂) × 0.5 [ΣP₁(S₁) + ΣP₂(S₁)]; λ corresponds to the solubility of TaS₂ in the gas phase (based on the sulfur content). In this way we found that the transport proceeds via TaS_5,g less likely via TaS_6,g: The change in transport direction in the temperature gradient originates from the transition endothermic/exothermic reaction with increasing temperature. Although the TaS₅ pressure is small, it is sufficient for the transport of considerable amounts of TaS₂ due to the multiplicative character of the transport process.     

One‐dimensional Nanomaterial Electrocatalysts for CO2 Fixation

Electroreduction of CO₂ into valuable molecules or fuels is a sustainable pathway for CO₂ reduction as well as energy storage. However, the premature development stage of electrocatalysts with high activity, selectivity, and durability still remains a significant bottleneck that hinders this field. One‐dimensional (1D) nanomaterials, including nanorods, nanotubes, nanoribbons, nanowires, and nanofibers, are generally considered as high‐activity and stable electromaterials, due to their unique uniform structures, orientated electronic and mass transport, and rigid tolerance to stress variation. During the past several years, 1D nanomaterials and nanostructures have been extensively studied due to their potentials in serving as CO₂ electroreduction catalysts. In this minireview, recent studies and advances in 1D nanomaterials for CO₂ eletroreduction are summarized, from the viewpoints of both computational and experimental aspects. Based on the composition, the 1D nanomaterials are studied in four categories, including metals, transition‐metal oxides/nitrides, transition‐metal chalcogenides, and carbon‐based materials. Different parameters in tuning 1D materials are also summarized and discussed, such as the crystal facets, grain boundaries, heteroatoms doping, additives and the electrochemical tuning effects. Finally, the challenges and prospects in this direction will be discussed.     

Hydrothermal Synthesis and Properties of Controlled α‐Fe2O3 Nanostructures in HEPES Solution

A facile, template‐free, and environmentally friendly hydrothermal strategy was explored for the controllable synthesis of α‐Fe₂O₃ nanostructures in HEPES solution (HEPES=2‐[4‐(2‐hydroxyethyl)‐1‐piperazinyl]ethanesulfonic acid). The effects of experimental parameters including HEPES/FeCl₃ molar ratio, pH value, reaction temperature, and reaction time on the formation of α‐Fe₂O₃ nanostructures have been investigated systematically. Based on the observations of the products, the function of HEPES in the reaction is discussed. The different α‐Fe₂O₃ nanostructures possess different optical, magnetic properties, and photocatalytic activities, depending on the shape and size of the sample. In addition, a novel and facile approach was developed for the synthesis of Au/α‐Fe₂O₃ and Ag/α‐Fe₂O₃ nanocomposites in HEPES buffer solution; this verified the dual function of HEPES both as reductant and stabilizer. This work provides a new strategy for the controllable synthesis of transition metal oxide nanostructures and metal‐supported nanocomposites, and gives a strong evidence of the relationship between the property and morphology/size of nanomaterials.     

Tailoring Transition‐Metal Hydroxides and Oxides by Photon‐Induced Reactions

Controlled synthesis of transition‐metal hydroxides and oxides with earth‐abundant elements have attracted significant interest because of their wide applications, for example as battery electrode materials or electrocatalysts for fuel generation. Here, we report the tuning of the structure of transition‐metal hydroxides and oxides by controlling chemical reactions using an unfocused laser to irradiate the precursor solution. A Nd:YAG laser with wavelengths of 532 nm or 1064 nm was used. The Ni²⁺, Mn²⁺, and Co²⁺ ion‐containing aqueous solution undergoes photo‐induced reactions and produces hollow metal‐oxide nanospheres (Ni_0.18Mn_0.45Co_0.37O_x) or core–shell metal hydroxide nanoflowers ([Ni_0.15Mn_0.15Co_0.7(OH)₂](NO₃)_0.2?H₂O), depending on the laser wavelengths. We propose two reaction pathways, either by photo‐induced redox reaction or hydrolysis reaction, which are responsible for the formation of distinct nanostructures. The study of photon‐induced materials growth shines light on the rational design of complex nanostructures with advanced functionalities.     

Synthesis of Inorganic Structural Isomers By Diffusion‐Constrained Self‐Assembly of Designed Precursors: A Novel Type of Isomerism

The structure of precursors is used to control the formation of six possible structural isomers that contain four structural units of PbSe and four structural units of NbSe₂: [(PbSe)_1.14]₄[NbSe₂]₄, [(PbSe)_1.14]₃[NbSe₂]₃[(PbSe)_1.14]₁[NbSe₂]₁, [(PbSe)_1.14]₃[NbSe₂]₂[(PbSe)_1.14]₁[NbSe₂]₂, [(PbSe)_1.14]₂[NbSe₂]₃[(PbSe)_1.14]₂[NbSe₂]₁, [(PbSe)_1.14]₂[NbSe₂]₂[(PbSe)_1.14]₁[NbSe₂]₁[(PbSe)_1.14]₁[NbSe₂]₁, [(PbSe)_1.14]₂[NbSe₂]₁[(PbSe)_1.14]₁[NbSe₂]₂[(PbSe)_1.14]₁[NbSe₂]₁. The electrical properties of these compounds vary with the nanoarchitecture. For each pair of constituents, over 20 000 new compounds, each with a specific nanoarchitecture, are possible with the number of structural units equal to 10 or less. This provides opportunities to systematically correlate structure with properties and hence optimize performance.     

Structure cristalline et propriétés physiques électriques et magnétiques des phases M0.50NbSe2 (M = Ti,V, Cr)

The structure of M_0.50NbSe₂ (M = Ti, V, Cr) phases is reported. A detailed crystal structure analysis has been performed on Cr_0.50NbSe₂. Large single crystals were grown by chemical transport reaction with bromine as the transport agent. Electrical and magnetic properties have been measured in the 4.2–300°K range. Susceptibilities of both Cr_0.50NbSe₂ and Ti_0.50NbSe₂ follow the Curie-Weiss law. At low temperature (T < 53°K) an antiferromagnetic ordering is observed for Cr_0.50NbSe₂. V_0.50NbSe₂ exhibits a temperature-independent paramagnetism. Transport properties of M_0.50NbSe₂ phases are consistent with their metallic behavior and show several transitions at low temperature. The physical properties are discussed along with the reported crystal structure.     

Studies of the system TaS2−xSex

Single crystal and powder samples of the system TaS_2?xSe_x have been prepared and studied. The range of solubility was found to extend from x = 0 to x = 2.0. X-Ray analysis has shown that mixed anion samples exhibit a series of hexagonal layered polymorphs similar to those found in TaS₂ and TaSe₂, with the a and c lattice parameters increasing monotonically from TaS₂ to TaSe₂. Electrical transport properties were measured on single crystals and found to be similar to the end compositions. Organic molecules such as pyridine and collidine were found to intercalate TaS_2?xSe_x for x ≦ 1.4, and superconducting transition temperatures were measured for both intercalated and unintercalated samples. The highest T_c obtained was 4.1 K in the 4H(c) phase of the sample TaS_1.6Se_0.4.     

A Solution‐based Method for Synthesizing Pyrite‐type Ferrous Metal Sulfide Microspheres with Efficient OER Activity

Simple and stable synthesis of transition metal sulfides and clarification of their growth mechanisms are of great importance for developing catalysts, metal‐air batteries and other technologies. In this work, we developed a one‐step facile hydrothermal approach to successfully synthesize NiS₂ microspheres. By changing the experimental parameters, the reason that affects the formation of nanostructured spheres is investigated and discussed in detail, and the formation mechanism of microspheres is proposed innovatively. Furthermore, electrochemical testing results show that the 7 h‐NiS₂ catalyst exhibits a remarkable oxygen evolution reaction (OER) activity with an overpotential of 311 mV at 10 mA cm^?2 in 1.0 M KOH, superior to precious metal RuO₂. The NiS₂ catalyst also exhibits a robust durability. This work will contributes to the rational design and the understanding of growth mechanism of transition metal chalcogenide electrocatalysts for diverse energy conversion technologies.     

Facile Synthesis of Three‐Dimensional Pt‐TiO2 Nano‐networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

Three‐dimensional (3D) porous metal and metal oxide nanostructures have received considerable interest because organization of inorganic materials into 3D nanomaterials holds extraordinary properties such as low density, high porosity, and high surface area. Supramolecular self‐assembled peptide nanostructures were exploited as an organic template for catalytic 3D Pt‐TiO₂ nano‐network fabrication. A 3D peptide nanofiber aerogel was conformally coated with TiO₂ by atomic layer deposition (ALD) with angstrom‐level thickness precision. The 3D peptide‐TiO₂ nano‐network was further decorated with highly monodisperse Pt nanoparticles by using ozone‐assisted ALD. The 3D TiO₂ nano‐network decorated with Pt nanoparticles shows superior catalytic activity in hydrolysis of ammonia–borane, generating three equivalents of H₂.     

Chemischer Transport fester Lösungen. 23 [1] Der Chemische Transport von Mischphasen im System MoS2/MoSe2, MoS2/NbS2, MoSe2/NbSe2 und NbS2/NbSe2

Chemical Vapor Transport of Solid Solutions. 23 Chemical Vapor Transport of Mixed Phases in the System MoS₂/MoSe₂, MoS₂/NbS₂, MoSe₂/NbSe₂ and NbS₂/NbSe₂ X‐ray powder investigations have shown that MoS₂/MoSe₂, MoS₂/NbS₂, MoSe₂/NbSe₂ and NbS₂/NbSe₂ form mixed crystals without a miscibility gap. The mixed crystals can be prepared by heating the Elements for some days in the presence of small amounts of iodine as well as by chemical vapour transport. In the systems NbS₂/NbSe₂ and MoS₂/MoSe₂ the vapor transport occurs congruently, in the systems NbS₂/MoS₂ and NbSe₂/MoSe₂ however a strong enrichment of Niobium has been observed during the transport process. Mass spectrometric investigations and thermochemical calculations have shown that the transport occurs via NbI₄(g) and MoI₃(g).     

Hydrogen Treatment for Superparamagnetic VO2 Nanowires with Large Room‐Temperature Magnetoresistance

One‐dimensional (1D) transition metal oxide (TMO) nanostructures are actively pursued in spintronic devices owing to their nontrivial d electron magnetism and confined electron transport pathways. However, for TMOs, the realization of 1D structures with long‐range magnetic order to achieve a sensitive magnetoelectric response near room temperature has been a longstanding challenge. Herein, we exploit a chemical hydric effect to regulate the spin structure of 1D V–V atomic chains in monoclinic VO₂ nanowires. Hydrogen treatment introduced V³⁺ (3d²) ions into the 1D zigzag V–V chains, triggering the formation of ferromagnetically coupled V³⁺–V⁴⁺ dimers to produce 1D superparamagnetic chains and achieve large room‐temperature negative magnetoresistance (?23.9 %, 300 K, 0.5 T). This approach offers new opportunities to regulate the spin structure of 1D nanostructures to control the intrinsic magnetoelectric properties of spintronic materials.     

Probing the Electronic Effect of Carbon Nanotubes in Catalysis: NH3 Synthesis with Ru Nanoparticles

Carbon nanotubes (CNTs) have been shown to modify some properties of nanomaterials and to modify chemical reactions confined inside their channels, which are formed by curved graphene layers. Here we studied ammonia synthesis over Ru as a probe reaction to understand the effect of the electron structure of CNTs on the confined metal particles and their catalytic activity. The catalyst with Ru nanoparticles dispersed almost exclusively on the exterior nanotube surface exhibits a higher activity than the CNT‐confined Ru, although both have a similar metal particle size. Characterization with TEM, N₂ physisorption, H₂ chemisorption, temperature‐programmed reduction, CO adsorption microcalorimetry, and first‐principles calculations suggests that the outside Ru exhibits a higher electron density than the inside Ru. As a result, the dissociative adsorption of N₂, which is an electrophilic process and the rate‐determining step of ammonia synthesis, is more facile over the outside Ru than that over the inside one.     

Phase‐Controlled Synthesis of Transition‐Metal Phosphide Nanowires by Ullmann‐Type Reactions

Transition‐metal phosphide nanowires were facilely synthesized by Ullmann‐type reactions between transition metals and triphenylphosphine in vacuum‐sealed tubes at 350–400 °C. The phase (stoichiometry) of the phosphide products is controllable by tuning the metal/PPh₃ molar ratio and concentration, reaction temperature and time, and heating rate. Six classes of iron, cobalt, and nickel phosphide (Fe₂P, FeP, Co₂P, CoP, Ni₂P, and NiP₂) nanostructures were prepared to demonstrate the general applicability of this new method. The resulting phosphide nanostructures exhibit interesting phase‐ and composition‐dependent magnetic properties, and magnetic measurements suggested that the Co₂P nanowires with anti‐PbCl₂ structure show a ferromagnetic–paramagnetic transition at 6 K, while the MnP‐structured CoP nanowires are paramagnetic with Curie–Weiss behavior. Moreover, GC‐MS analyses of organic byproducts of the reaction revealed that thermally generated phenyl radicals promoted the formation of transition‐metal phosphides under synthetic conditions. Our work offers a general method for preparing one‐dimensional nanoscale transition‐metal phosphides that are promising for magnetic and electronic applications.     

Synthesis of Metal-Oxide/Carbon-Fiber Heterostructures and Their Properties for Organic Dye Removal and High-Temperature CO<Subscript>2</Subscript> Adsorption

One-dimensional metal-oxide/carbon-fiber (MO/CF) heterostructures were prepared by a facile two-step method using the natural cotton as a carbon source the low-cost commercial metal salts as precursors. The metal oxide nanostructures were first grown on the cotton fibers by a solution chemical deposition, and the metal-oxide/cotton heterostructures were then calcined and carbonized in nitrogen atmosphere. Three typical MO/CF heterostructures of TiO₂/CF, ZnO/CF, and Fe₂O₃/CF were prepared and characterized. The loading amount of the metal oxide nanostructures on carbon fibers can be tuned by controlling the concentration of metal salt in the chemical deposition process. Finally, the performance of the as-obtained MO/CF heterostructures for organic dye removal from water was tested by the photocatalytic degradation under a simulated sunlight, and their properties of high-temperature CO₂ adsorption were predicted by the temperature programmed desorption. The present study would provide a desirable strategy for the synthesis of MO/CF heterostructures for various applications.