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Abstract: General and simple methods for the syntheses of borides, carbides and nitrides are highly desirable, since those materials have unique physical properties and promising applications. Here, a series of boride (TiB2, ZrB2, NbB2, CeB6, PrB6, SmB6, EuB6, LaB6), carbide (SiC, TiC, NbC, WC) and nitride (TiN, BN, AlN, MgSiN2, VN) micro/nanocrystals were prepared from related oxides and amorphous boron/active carbon/NaN3 with the assistance of metallic Na and elemental S. In-situ temperature monitoring showed that the reaction temperature could increase quickly to ∼850°C, once the autoclave was heated to 100°C. Such a rapid temperature increase was attributed to the intense exothermic reaction between Na and S, which assisted the formation of borides, carbides and nitrides. The as-obtained products were characterized by XRD, SEM, TEM, and HRTEM techniques. Results in this report will greatly benefit the future extension of this approach to other compounds. [Copyright &y& Elsevier]

Abstract: Rare-earth hexaborides (RB6, R=Ce, Pr, Nd) nanocrystals were prepared by a facile solid state reaction in an autoclave. Single-crystalline RB6 nanocubes were fabricated at 500°C starting from B2O3, RCl3·6H2O and Mg powder. RB6 nanoflakes and nanoparticles could be obtained around 400°C using NaBH4 as boron resource. XRD patterns show that all of the hexaborides are cubic phase with high crystallinity and high purity and have lattice parameters that are consistent with nearly stoichiometric products. Raman spectra elucidate the active vibrational modes of the hexaborides. The TEM and FESEM images clearly show that the nanocubes have an average size of 200nm and nanoparticles of 30nm. Our experiment developed an efficient, simple and low-cost route to prepare RB6, which could be extended further to the preparation of other rare-earth metal hexaborides. [Copyright &y& Elsevier]

Abstract: Single-crystalline nanorods of β-MnO2, α-Mn2O3 and Mn3O4 were successfully synthesized via the heat-treatment of γ-MnOOH nanorods, which were prepared through a hydrothermal method in advance. The calcination process of γ-MnOOH nanorods was studied with the help of Thermogravimetric analysis and X-ray powder diffraction. When the calcinations were conducted in air from 250 to 1050°C, the precursor γ-MnOOH was first changed to β-MnO2, then to α-Mn2O3 and finally to Mn3O4. When calcined in N2 atmosphere, γ-MnOOH was directly converted into Mn3O4 at as low as 500°C. Transmission electron microscopy (TEM) and high-resolution TEM were also used to characterize the products. The obtained manganese oxides maintain the one-dimensional morphology similar to the precursor γ-MnOOH nanorods. Further experiments show that the as-prepared manganese oxide nanorods have catalytic effect on the oxidation and decomposition of the methylene blue (MB) dye with H2O2. [Copyright &y& Elsevier]

Nanocrystalline silicon carbide has been prepared via reacting magnesium silicide (Mg2Si) with carbon tetrachloride (CCl4) in an autoclave at 450–600°C. X-ray diffraction patterns of the products can be indexed as the cubic cell of SiC with the lattice constant, a=4.352 Å, in good agreement with a=4.349 Å (JCPDS card No. 75-0254). The transmission electron microscopy images show that the sample mainly consists of nanoparticles with an average size from 30 to 80 nm co-existing with a small fraction of nanorods and nanowires. Typically the nanorods range from 20 to 40 nm in diameter and the nanowires have diameters of 20 nm and lengths up to 10 μm. The Raman spectrum shows a characteristic sharp peak at 790 cm-1. X-ray photoelectron spectra (XPS) gives an atomic ratio of Si to C as 1.08:1.00 from the quantification of the peak intensities. Photoluminescence spectrum reveals that the SiC sample emits ultraviolet light of 328 nm. A possible mechanism and the influence of temperature on the formation of crystalline SiC are proposed. [Copyright &y& Elsevier]

VOx·nH2O (2.0⩽x⩽2.5) nanoribbons have been synthesized by direct hydrothermal processing of the aqueous solution of NH4VO3 and polyethylene glycol 400 (PEG-400) at pH 3.5–5.5. Techniques of XRD, SEM, TEM, HRTEM, ED, and XPS have been used to characterize the structure, morphology, and composition of the nanoribbons. The VOx·nH2O nanoribbons are up to ∼200 μm in length, 100–150 nm in width, 20–30 nm in thickness, and grow along the [010] direction. The ratios of V4+ to V5+ in the products can be readily controlled by carefully adjusting the periods of reaction time. PEG carries the roles of both transport and reducing agent. A coordination self-assembly mechanism was proposed to elucidate the formation of the VOx·nH2O nanoribbons. [Copyright &y& Elsevier]