Novel 2D self-assembled arrays of SiOx nanowire bundles

Novel 2D ordered arrays formed by self-assembly of SiO_x nanowire bundles have been prepared on a silicon wafer via a facile metal-mediated gas-phase reaction. The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Two types of arrays were grown on a substrate surface by adjusting the preparation parameters. The findings suggest that the growth atmosphere, the flow rate of carrier gas and the relative placement of source and substrate are all responsible for the formation of these unique self-assembled structures. The intermolecular action is the internal driving force for the self-assembly. The formation mechanism of the arrays was proposed on the basis of the growing process.     

In2O3 nanowires for gas sensors: morphology and sensing characterisation

Thin and densely packed In₂O₃ nanowires have been synthesised on alumina substrates via transport and condensation method, starting from nanoparticles of indium or palladium as catalysts for the condensation process. Indium catalyst promoted wires growth according to vapour-solid (VS) mechanism, while palladium catalyst leads to wires formation based on vapour-liquid-solid (VLS) condensation. Electron microscopy and related diffraction analysis demonstrated that the wires are monocrystalline, with atomically sharp termination of the lateral sides, and are free from extended defects. The sensing properties of nanowires bundles have been tested to acetone using the flow through technique in the temperature range between 100 and 500 °C.     

Single crystal GaN nanowires

Single crystal gallium nitride nanowires have been obtained by heating gallium acetylacetonate in the presence of carbon nanotubes or activated carbon in NH3 vapor at 910 degrees C. GaN nanowires also were obtained when the reaction of gallium acetylacetonate with NH3 was carried out over catalytic Fe/Ni particles dispersed over silica. The former procedure with carbon nanotubes is preferable because it avoids the presence of metal particles in the nanowire bundles.     

A very simple and low cost route to Bi2S3 nanorods bundles and dandelion-like nanostructures

Bi₂S₃ nanorods bundles as well as three-dimensional dandelion-like nanostructures were synthesized in high yield at lower temperature (room temperature or ambient temperature of 15 °C) in a very simple system composed only of Bi(NO₃)₃, thioacetamide (TAA), hydrochloride acid and distilled water. It is the first report to obtain such nanostructures at such a low temperature and by such a simple method, and the reaction does not demand any additional energy such as heating or agitation. A splitting crystal growth and self-assemble mechanism should be responsible for the formation of these structures. This kind of novel Bi₂S₃ nanostructures may find potential applications in hydrogen storage, high-energy batteries, as well as luminescence and catalysis fields.     

Fabrication of bismuth oxide-tin oxide nanowires by direct thermal oxidation of Bi-Sn eutectic nanowires

Bismuth oxide-tin oxide (BiO_x-SnO_x) heterostructure nanowires with a diameter of 70 nm were fabricated by directly annealing Bi-Sn eutectic nanowires synthesized by the vacuum hydraulic pressure injection process. After removal of AAO (Anodic Aluminum Oxide) template with an etching solution, a spontaneous oxide was formed on nanowires to enclose the Bi-Sn eutectic alloys. While these nanowires went through the annealing process with the proper heating rate of 50 °C/min, the well-annealed oxide nanowires remain solid, straight and segmental. The results of cathodoluminescence (CL) spectrum and photoresponse proved that the products consisted of bismuth oxide and tin oxide. This fabrication methodology provides a simple way to produce one-dimensional oxide nanomaterials.     

Large-scale synthesis of single-crystal alpha manganese sesquioxide nanowires via solid-state reaction

Smooth single-crystal α-Mn₂O₃ nanowires have been fabricated using a one-step solid-state reaction method. X-ray diffraction patterns show that the nanowires have pure phase of α-Mn₂O₃. Transmission electron microscopy was employed to investigate the size and morphology of the products. The α-Mn₂O₃ nanowires exhibit mean diameter of 50 nm and length of 10 μm. Selected-area electron diffraction pattern demonstrates the single-crystal structure of the α-Mn₂O₃ nanowires, which are in good agreement with the X-ray diffraction results. The processes of the reactions and the phase transitions were also studied by using a simultaneous thermal gravimetric/differential thermal analyzer. It is found that the concentration of the precursor MnCO₃ is a crucial factor in the formation of the nanowires. This work provides the probability of the industrialization of fabricating smooth single-crystal α-Mn₂O₃ nanowires.     

Rapid microwave-assisted synthesis of hierarchical ZnO hollow spheres and their application in Cr(VI) removal

A rapid one-pot synthesis of hierarchical ZnO hollow spheres consisting of nanoparticles was realized by a facile microwave-assisted solvothermal method using ethanol as the solvent. According to the time-dependent observation of the formation process, a tentative mechanism based on ethyl acetate bubble-templating self-assembly of ZnO nanoparticles was proposed for the formation of the ZnO hollow spheres. Compared with the conventional heating, the microwave irradiation resulted in a significantly shortened reaction time (within 30?min) and considerably improved quality of the ZnO hollow spheres, such as narrower size distribution and more regular morphology, owing to the high heating rate and thus the accelerated reaction rate. It was shown that the microwave-assisted synthesis of ZnO nanostructures with tunable morphologies can be realized by judicious selection of appropriate solvents. The obtained ZnO hollow spheres exhibited an excellent adsorption capacity towards Cr(VI) ions in water because of their high surface area for adsorption and a good ability to preserve the accessible surface.     

Different morphologies of strontium carbonate in water/ethylene glycol and their photocatalytic activity

Three-dimensional SrCO₃ flower-like nanostructures self-assembly from nanocrystals have been successfully synthesized by solvothermal method at the temperature of 120?°C. In the presence of anionic surfactant sodium dodecyl sulfate, SrCO₃ is crystallized in different alcohols and aqueous solutions. X-ray diffraction (XRD) pattern reveals that needles and flakes flower-like SrCO₃ are orthorhombic phases. The product also has a high specific surface area of about 60.52 m² g^?1. Based on the nucleation and self-assembly process, a possible formation mechanism is proposed. The effects of SDS and alcohol on the product are also studied. Results suggest that –OH groups of alcohol play a key role in morphological controlling of SrCO₃. Moreover, the FCNS exhibits excellent photocatalytic activity for the photodegradation of RhB under visible light irradiation and the degradation rate approached to 90.32%.     

Synthesis of K6Ta10.8O30 nanowires by molten salt technique

The synthesis of single crystalline K₆Ta_10.8O₃₀ nanowires by molten salt method was reported for the first time. X-ray diffraction results indicated that the as-prepared products were pure phase K₆Ta_10.8O₃₀. Scanning electron microscopy and transmission electron microscopy results showed that the products consisted of wire-like nanostructures with 100-300 nm in diameter and several micrometers in length. High resolution electron microscopy and selected area electron diffraction results indicated that the K₆Ta_10.8O₃₀ nanowires were single crystalline with a growth direction of [0 0 1]. The ultraviolet-visible diffuse reflectance measurement showed that the band gap of the nanowires was about 4.1 eV. The effects of reaction temperature, time, and weight ratio of the precursor (mixture of K₂CO₃ and Ta₂O₅) to KCl salt on the morphology of the products were investigated.     

Synthesis and characterization of CeCO3OH one-dimensional quadrangular prisms by a simple method

Orthorhombic single-crystalline cerium carbonate hydroxide (CeCO₃OH) one-dimensional (1D) quadrangular prisms have been successfully synthesized by a facile sonochemical reaction between cerous nitrate and carbamide in the presence of surfactant polyvinyl alcohol (PVA). The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM). The as-synthesized CeCO₃OH have uniform lengths and good dispersion. These one-dimensional CeCO₃OH structures are quadrangular prisms with edge length of about 300 nm. The quadrangular prisms have well-resolved edges and their surfaces are very smooth. Interestingly, each end of the prism is cut along the diagonal of underside plane to form two chamfered planes. Furthermore, room-temperature photoluminescence of CeCO₃OH samples have also been investigated.     

Synthesis of GaN nanowires by CVD method: effect of reaction temperature

GaN nanowires are fabricated on Si substrates by ammoniating Ga₂O₃/NiCl₂ thin films using chemical vapour deposition method. The influence of reaction temperature on microstructure, morphology and optical properties of GaN nanowires is characterised by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrophotometer, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The results demonstrate that the GaN nanowires are single crystalline and exhibit hexagonal wurtzite symmetry. The best crystalline quality was achieved for an reaction temperature of 1150°C for 15?min. The growth process follows vapour–liquid–solid mechanism and Ni plays an important role as the nucleation point and as a catalyst.     

Redox reaction-assisted growth of ZnO nanowires on SnO2 thin films

ZnO nanowires were grown onto SnO₂ film coated on Si substrate using a vapor transport method. Zn vapor was found to play important roles in reducing SnO₂ and in being oxidized as a ZnO layer. The growth mechanism of ZnO nanowires was revealed to be a two-step process of Zn-SnO₂ redox reaction and Sn catalyzed V-L-S (vapor-liquid-solid) growth; initially, Zn vapor atoms arriving at the SnO₂ surface reduce the SnO₂ to Sn and O atoms and diffuse into the SnO₂ layer to form a ZnO layer. The reduced Sn atoms diffuse out of the SnO₂ layer and are agglomerated to form Sn liquid droplets. Then, the Sn droplets on the surface of ZnO layer serve as a catalyst for the catalytic V-L-S growth of ZnO nanowires.     

Ultraviolet photodetectors made from SnO2 nanowires

SnO₂ nanowires can be synthesized on alumina substrates and formed into an ultraviolet (UV) photodetector. The photoelectric current of the SnO₂ nanowires exhibited a rapid photo-response as a UV lamp was switched on and off. The ratio of UV-exposed current to dark current has been investigated. The SnO₂ nanowires were synthesized by a vapor-liquid-solid process at a temperature of 900 °C. It was found that the nanowires were around 70-100 nm in diameter and several hundred microns in length. High-resolution transmission electron microscopy (HRTEM) image indicated that the nanowires grew along the [200] axis as a single crystallinity. Cathodoluminescence (CL), thin-film X-ray diffractometry, and X-ray photoelectron spectroscopy (XPS) were used to characterize the as-synthesized nanowires.     

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Abstract

Silicon nitride (Si₃ N₄) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si₃ N₄ nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ～500 nm diameter and ～0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.     

Simple and rapid synthesis of α-Fe2O3 nanowires under ambient conditions

We propose a simple method for the efficient and rapid synthesis of one-dimensional hematite (α-Fe₂O₃) nanostructures based on electrical resistive heating of iron wire under ambient conditions. Typically, 1–5 μm long α-Fe₂O₃ nanowires were synthesized on a time scale of seconds at temperatures of around 700 ° ⊂. The morphology, structure, and mechanism of formation of the nanowires were studied by scanning and transmission electron microscopies, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman techniques. A nanowire growth mechanism based on diffusion of iron ions to the surface through grain boundaries and to the growing wire tip through stacking fault defects and due to surface diffusion is proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Synthesis of hexagonal prisms and hexagonal plates of Na2SiF6 microcrystals

Hexagonal Na₂SiF₆ prisms and hexagonal or dodecagonal Na₂SiF₆ plates were prepared using Na₂CO₃, SiO₂, and HF under microwave irradiation for the large-scale production of ice-analog materials. The morphology of the Na₂SiF₆ crystals changed from long thin hexagonal prisms to flat hexagonal or dodecagonal plates with pyramidal faces as the Na₂CO₃ concentration was increased. X-ray diffraction studies confirmed that the axes of the hexagonal Na₂SiF₆ prisms were aligned along the c axis. The microwave irradiation time played an important role in controlling the morphology and aspect ratio of the Na₂SiF₆ microcrystals. The mechanisms of formation of the various Na₂SiF₆ microcrystalline morphologies are discussed.     

Controlled synthesis and photocatalytic properties of porous hollow In2O3 microcubes with different sizes

Uniform single-crystalline In(OH)₃ hollow microcubes have been synthesized in large quantities via a hydrothermal reaction of InCl₃ with NaF and ethylene glycol (EG) at 140–220 °C for 12 h. Porous In₂O₃ hollow microcubes with a polycrystalline cubic structure can be obtained via calcining In(OH)₃ precursors at 400 °C for 2 h in air. Controlled Synthesis of In(OH)₃ and In₂O₃ hollow microcubes with the average edge lengths in the range of 2.0–4.7 μm can be achieved by changing the hydrothermal reaction temperature. The In(OH)₃ hollow microcubes were formed via an EG-assisted oriented attachment growth route using HF bubbles as the templates. Photocatalytic activities of the as-synthesized porous In₂O₃ hollow microcubes were studied at room temperature. The results indicated that the hollow In₂O₃ nanostructures display high photocatalytic activity in the photodegradation of rhodamine B and methyl orange.     

Template-free fabrication of SnO2 hollow spheres with photoluminescence from Sni

SnO₂ hollow spheres with interstitial Sn²⁺ defect were fabricated by the hydrothermal method without any surfactant or polymer, whose shell is constructed by two layers of tetragonal prism nanorod arrays. The growth mechanism of the hollow spheres was investigated and attributed to the nucleation and arrangement of SnO₂ tetragonal prism nanorods on the surface of the hydrothermal reaction formed NO bubbles in the aqueous solution. After illumination by 275 nm wavelength light, narrow peak emissions centered at about 587-626 nm have been found in the photoluminescence spectrum, which have been ascribed to the interstitial Sn²⁺ defect in the SnO₂ hollow spheres.     

Large-scale hydrothermal synthesis of WO3 nanowires in the presence of K2SO4

WO₃ nanowires were fabricated by a hydrothermal method in the presence of K₂SO₄. The nanowires exhibit a well crystallized one-dimensional structure with 10 nm in diameter and several microns in length. Effects of other alkali salts (KNO₃, NaNO₃ and Na₂SO₄) on the morphologies of WO₃ nanocrystals were also investigated. The important role of K₂SO₄ salt in the WO₃ nanowires synthesis has been demonstrated.     

Solid phase growth of tin oxide nanostructures

For the first time, single-crystalline SnO₂ nanostructures comprising of nanobelts, nanowires and nanosheets have been synthesised by solid phase crystal growth from tin oxide single crystals. The product was characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, selected area electron diffraction, and Raman spectroscopy. The procedure consisted of two stages. In the first stage, a mixture of SnO₂ polyhedral single crystals attached with graphite particles were produced by heating a mixture of SnCl₂ and graphite. Then, the SnO₂ single crystals were grown into nanobelts, nanowires and nanosheets by further heating. The role of graphite in the process is also discussed to be the surface reduction of SnO₂ into oxides with lower oxygen content which provide a driving force for surface diffusion and subsequent crystal growth of tin oxide into the one and two dimensional nanostructures. The results provide insights for both fundamental research as well as technological production of SnO₂ nanostructures.