Catalytic growth of bamboo-like boron nitride nanotubes using self-propagation high temperature synthesized porous precursor

The high-pure bamboo-like boron nitride (BN) nanotubes with high yield were synthesized via an effective chemical vapor deposition method by annealing porous precursor under NH₃ atmosphere at 1150 °C. The porous precursor was readily prepared by self-propagation high temperature synthesis (SHS) method. The as-synthesized BN nanotubes were characterized by SEM, TEM, HRTEM, XRD, Raman and FTIR spectroscopy. The results indicate these nanotubes have bamboo-like structures with an average diameter of about 90 nm and length of more than 10 μm. Nanotube content is estimated as approximately 90 wt.% according to the statistical analyses by SEM and TEM. Moreover, the reaction mechanism for the as-synthesized BN nanotubes is proposed.     

Characterization of nano-crystalline ZrO2 synthesized via reactive plasma processing

Nano-crystalline ZrO₂ powder has been synthesized via reactive plasma processing. The synthesized ZrO₂ powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and FTIR spectroscopy. The synthesized powder consists of a mixture of tetragonal and monoclinic phases of zirconia. Average crystallite size calculated from the XRD pattern shows that particles with crystallite size 20 nm or less than 20 nm are in tetragonal phase, whereas particles greater than 20 nm are in the monoclinic phase. TEM results show that particles have spherical morphology with maximum percentage of particles distributed in a narrow size from about 15 nm to 30 nm.     

Synthesis and characterization of carbon nanoribbons and single crystal iron filled carbon nanotubes

Carbon nanoribbons and single crystal iron filled multiwall carbon nanotubes (MWCNTs) have been synthesized by simple pyrolysis technique. SEM investigation shows that the material consist mainly carbon nanoribbons and carbon nanotubes (CNTs). X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), electron energy dispersive X-ray (EDX), transmission electron miscroscopy (TEM) and highresolution transmission electron miscroscopy (HRTEM) studies reveal carbon nanotubes are filled with α-Fe. Closer inspection of HRTEM images indicated that the bcc structure α-Fe nanowires are monocrystalline and Fe (1 1 0) plane is indeed perpendicular to the G (0 0 2) plane, whereas orientation of (0 0 2) lattice planes of carbon nanoribbon is perpendicular to the axis of growth. Magnetic properties studied by superconducting quantum interference device (SQUID) at 300 K and 10 K exhibited coercivity of 1037 Oe and 2023 Oe. The large coercitivity is strongly attributed to the small size monocrystalline single phase α-Fe, single domain nature of the encapsulated Fe crystal, magnetocrystalline shape anisotropy and ferromagnetic behaviour of localized states at the edges of the carbon nanoribbons.     

Nanococoon seeds for BN nanotube growth

A modification in the conventional arc-discharge method for synthesis of nanotubes is presented. By injecting pure nitrogen gas directly into the plasma we have greatly increased the amount of boron nitride nanotubes produced. Isolated nanotubes and bundles were characterized by TEM. The vast majority of the nanotubes were double-walled with outer diameter around 3 nm. The predominance of double-walled BN nanotubes is seen as a direct result of the distribution of the number of graphitic BN layers for the nanococoons, second major product of the synthesis. Detailed HRTEM examination of the ends of BN nanotubes indicates continuity between the graphitic BN layers that coat boron nanoparticles, that is nanococoon, and the nanotube. At the other end of the nanotubes a flat angular cap was observed. HRTEM images of nanotube ends give support to a root-based growth mechanism.     

Preparation of h-BN nano-tubes, -bamboos, and -fibers from borazine oligomer with alumina porous template

h-BN nano-tubes, -bamboos, and -fibers were prepared separately from borazine oligomers using an alumina porous template at different wetting times of 20 h, 40 h and 2 weeks at room temperature, respectively. The borazine oligomer in the template was transformed to the h-BN nano-materials by two-step heat-treatment at 600 and 1200 °C in flowing N₂. The FT-IR result confirmed the formation of BN. TEM and SEM images showed the formation of the nano-tubes in diameters 200-300 nm with thin walls about 10-20 nm thick, nano-bamboos 200-300 nm wide with knots at the separations of 0.5-1 μm, and the nano-fibers 15-20 μm long with fine crystallized BN particles. The mechanism for the formation of h-BN nano-tubes, -bamboos and -fibers is proposed.     

An effective precursor for growth of bubble-chain boron nitride nanotubes

Large amounts of bubble-chain boron nitride nanotubes were synthesised by annealing an effective precursor. The porous precursor was produced by self-propagation high-temperature synthesis method using Mg, B₂O₃, amorphous B and Fe₂O₃ as the starting materials, which played an important role in synthesis of BN nanotubes in large quantities. Samples were characterised by SEM, TEM, HRTEM, X-ray powder diffraction and Raman and Fourier transform infrared spectroscopy. The as-synthesised BN nanotubes revealed periodical bubble-chain structures, having diameters of range 20–200?nm?and an average length of more than 5?µm. The effects of temperature, time and the possible mechanism of the growth of the BN nanotubes were also discussed.     

Synthesis, characterization and optical properties of sheet-like ZnO

Sheet-like ZnO with regular hexagon shape and uniform diameter has been successfully synthesized through a two-step method without any metal catalyst. First, the sheet-like ZnO precursor was synthesized in a weak alkaline carbamide environment with stirring in a constant temperature water-bath by the homogeneous precipitation method, then sheet-like ZnO was obtained by calcining at 600 °C for 2 h. The structures and optical properties of sheet-like ZnO have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and UV-vis-NIR spectrophotometer. The results reveal that the product is highly crystalline with hexagonal wurtzite phase and has appearance of hexagon at (0 0 0 1) plane. The HRTEM images confirm that the individual sheet-like ZnO is single crystal. The PL spectrum exhibits a narrow ultraviolet emission at 397 nm and a broad visible emission centering at 502 nm. The band gap of sheet-like ZnO is about 3.15 eV.     

Structural,thermal and dielectric studies of polypyrrole nanotubes synthesized by reactive self degrade template method

In this work we investigate the structural, thermal and dielectric properties of polypyrrole nanotubes synthesized by in situ chemical oxidative polymerization method. Cetyl trimethylammonium bromide (CTAB) modified Methyl Orange (MO)-FeCl₃ reactive self degrade template is used to support the growth of PPy nanotubes. The diameter of the tubes decreased with increase in CTAB concentration and found to be 140–52 nm. The synthesized polypyrrole nanotubes are investigated by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), FTIR, UV–vis, conductivity measurements, TGA and impedance analysis. TGA analysis shows decrease in decomposition rate with decrease in tube diameter. The response of the charge carriers to the ac field is also carried out in the frequency range of 42 Hz–5 MHz. The shifting of peak towards higher frequency in imaginary modulus formalism with decrease in CTAB concentration suggests faster relaxation.     

Ni2+掺杂纤蛇纹石纳米管的制备与磁性研究

通过水热法制备了Ni2+掺杂纤蛇纹石纳米管.采用X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、傅里叶变换红外光谱(FTIR)和磁性测试等手段研究了合成样品的形貌、结构以及磁性与掺杂量的关系.结果表明:合成纳米管样品的内、外径分别为6～7nm和30～40nm;随Ni2+掺杂量的增加,...     

Large-scale synthesis of CuS hexaplates in mixed solvents using a solvothermal method

Large-scale covellite CuS hexaplates were successfully synthesized by the 200 °C solvothermal reactions of CuCl₂.2H₂O and (NH₄)₂S in C₂H₅OH-H₂O mixed solvents containing HCOOH as a pH stabilizer, including different amounts and molecular weights (MWs) of polyethylene glycol (PEG). By using XRD and SAED, CuS (hcp) was detected. XRD peaks of the product, synthesized in a solution containing 5 g PEG6000 and 1.5 ml HCOOH for 5 h, are in accordance with those of the simulation and database. The (110) peak shows the preferential growth, corresponding to the hexaplates, characterized using SEM, TEM and HRTEM. CuS hexaplates with the (100) and (010) lattice planes at an angle of 120° were detected on the flat surface, and the (002) lattice plane on the edge. UV-vis absorption edge was detected at 610 nm (2.03 eV), and the PL emission at 361 nm (3.43 eV). Phase and morphology formations were also explained according to the experimental results.     

Synthesis of boron nitride nanotubes employing mechanothermal process and its characterization

Multi-walled boron nitride (BN) nanotubes having cylindrical structure were synthesized employing the mechanothermal process. In this process hexagonal boron nitride powder (hBN) was first ball milled for 50–100 h using a high-energy ball mill and the ball-milled samples were annealed in N₂ atmosphere for about 10 h in the temperature range of 950–1300 °C. The BN nanotubes exhibited a well-crystallized hexagonal structure with about 25–40 nm in diameter and up to 1 μm length. These BN nanotubes were well characterized using various techniques, such as, XRD, SEM, TEM and Raman Spectroscopy.     

Fabrication, structural characterization and formation mechanism of multiferroic BiFeO3 nanotubes

Multiferroic BiFeO3 (BFO) nanotubes have been successfully fabricated by the modified sol-gel method within the nanochannels of porous anodic aluminum oxide (AAO) templates. The morphology, structure and composition of the nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), high resolution TEM, (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). Postannealed (650 degrees C for 1 h), BFO nanotubes were polycrystalline and X-ray diffraction study revealed that they are of the rhomohedrally distorted perovskite crystal structure. The results of SEM and TEM revealed that BFO nanotubes possessed a uniform length (up to 60 microm) and diameter (about 200 nm), which were controlled by the thickness and the pore diameter of the applied AAO template, respectively and the thickness of the wall of the BFO nanotube was about 15 nm. Y-junctions in the BFO nanotubes were observed. EDX analysis demonstrated that stoichiometric BiFeO3 was formed. HRTEM analysis confirmed that the obtained BFO nanotubes made up of nanoparticles (3-6 nm). The possible formation mechanism of BFO nanotubes was discussed.     

Synthesis of CeB6 thin films by physical vapor deposition and their field emission investigations

High quality CeB₆ thin films have been obtained through direct evaporation of raw micron-sized CeB₆ powders at a pressure of 70 Pa. The X-ray diffraction (XRD), Raman spectrum, scanning electron microscope (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and the field-emission equipment were used to characterize the morphology, structure, composition and FE properties of the samples. The XRD and Raman spectrum analysis results show the as-prepared product is cubic phase CeB₆. The TEM, SAED and HRTEM analysis reveal that the samples are mixtures of thin films (polycrystalline) and small crystals (single crystallines aligned preferentially in the [1 1 0] direction). Compared to oxide nanostructures, field-emission measurements show that the CeB₆ films have better FE performance with turn-on field and threshold field of 12.93 V/μm and 14.86 V/μm, respectively.     

Low temperature synthesis of h-BN nanoflakes

Boron nitride (BN) with flake-like morphology has been synthesized by reacting powder H₃BO₃, Mg and NH₄Cl in an autoclave at 600 °C for 10 h. X-ray diffraction (XRD) patterns show the sample has hexagonal phase with lattice parameters a = 2.506 and c = 6.692 Å. Transmission electron microscopy (TEM) and field emission scanning electron (FE-SEM) indicate the as-synthesized product is pure flake with a mean size of about 100 nm in thickness and 600 nm in width length. X-ray photoelectron spectra (XPS) give an average B/N atomic ratio of 0.98:1. Fourier transformation infrared spectroscopy (FTIR) has a strong B-N absorption at 1376 cm^− 1 and 814 cm^− 1.     

Preparation of silicon carbide nanowires via a rapid heating process

Silicon carbide (SiC) nanowires were fabricated in a large quantity by a rapid heating carbothermal reduction of a novel resorcinol-formaldehyde (RF)/SiO₂ hybrid aerogel in this study. SiC nanowires were grown at 1500 °C for 2 h in an argon atmosphere without any catalyst via vapor-solid (V-S) process. The β-SiC nanowires were characterized by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM) equipped with energy dispersive X-ray (EDX) facility, Fourier transformed infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The analysis results show that the aspect ratio of the SiC nanowires via the rapid heating process is much larger than that of the sample produced via gradual heating process. The SiC nanowires are single crystalline β-SiC phase with diameters of about 20-80 nm and lengths of about several tens of micrometers, growing along the [1 1 1] direction with a fringe spacing of 0.25 nm. The role of the interpenetrating network of RF/SiO₂ hybrid aerogel in the carbothermal reduction was discussed and the possible growth mechanism of the nanowires is analyzed.     

Synthesis and characterization of CuO nanowhiskers by a novel one-step, solid-state reaction in the presence of a nonionic surfactant

A novel and simple one-step, solid-state reaction in the presence of a nonionic surfactant, PEG 400, has been developed to synthesize CuO nanowhiskers with diameters of approximately 2-10 nm and lengths of more than 100 nm. The CuO nanowhiskers were characterized by XRD, TEM, HRTEM and XPS.     

Synthesis of monodisperse shuttle-like α-Fe2O3 nanorods via the EDA-assisted method

Monodisperse hematite shuttle-like nanorods were synthesized successfully by the ethylenediamine (EDA)-assisted method. The structure and morphology were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometer (EDS). XRD studies indicated that the as-prepared product was well-crystallized orthorhombic phase of α-Fe₂O₃. TEM and SEM images showed that the α-Fe₂O₃ nano-particles were of rod shape with an average length of 400 nm and diameter of about 80 nm in the middle part.     

Synthesis and characterization of nanocrystallined zirconia by hydrothermal method

Nano-size zirconia was prepared by hydrothermal method using commercial zirconia powder. XRD study showed that the nano-size zirconia has an appreciable amount of monoclinic phase. The nano-size zirconia obtained has average particle size in the range of 24-36 nm. The SEM of nano-sized zirconia showed diminutively different morphology than the commercial one. TEM micrographs shows well-dispersed monoclinic ZrO₂ nanoparticles. The UV-DRS absorption spectrum of alkali treated zirconia showed an absorption peak at 235 nm (5.3 eV). The FTIR spectrum showed the purity of treated zirconia.     

CuSn(OH)6 submicrospheres: Room-temperature synthesis and weak antiferromagnetic behavior

CuSn(OH)₆ submicrospheres with a diameter of 400-900 nm, which are composed of nanoparticles with a size of about 27.8 nm, have been successfully synthesized for the first time via a simple liquid approach at room temperature in 15 min. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the products. Standard magnetization measurements at low temperature reveal that the as-obtained CuSn(OH)₆ submicrospheres are antiferromagnetic and have a weak spin-Peierls transition at about 78 K.     

Formation of crystalline AlN nanotubes by a roll-up approach

In this study, aluminum nitride (h-AlN) nanotubes with high crystallinity and yield have been prepared by AlP and NaN₃ in a stainless steel autoclave at 350 °C. The samples were studied by powder X-ray diffraction pattern (XRD), transmission electron microscopy (TEM) and HRTEM in detail. The lengths of the AlN nanotubes are about 1 μm with most of the tube ends are open. The AlN nanotube preferentially grow along the [001] direction. The results demonstrate that the bending and roll-up of a thin layer to form tubular nanoscrolls is a thermally driven process. One-dimensional preferential growth was explained in terms of the crystallographic feature of hexagonal AlN.