Structural and catalytic properties of ZnO and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanostructures loaded with metal nanoparticles

Nanostructured zinc oxide (ZnO) nanobelts and aluminum oxide (Al₂O₃) nanoribbons have been grown successfully from the vapor phase. XRD results confirmed the purity and the high quality of the formed crystalline materials. TEM images showed that ZnO nanostructures grew in the commonly known tetrapod structure with nanobelts separated from the tetrapods with an average width range of 10–30 nm and a length of about 500 nm. Al₂O₃ nanostructures grew in the form of nanoribbons with an average width range of 20–30 nm and a length of up to 1 μm. The catalytic oxidation of CO gas into CO₂ gas over the synthesized nanostructures is also reported. Higher catalytic activity was observed for Pd nanoparticles loaded on the ZnO nanobelts (100% conversion at 270 °C) and Al₂O₃ nanoribbons (100% conversion at 250 °C). The catalytic activity increased in the order Cu < Co < Au < Pd for the metal-loaded nanostructures. The preparation methods could be applied for the synthesis of novel nanostructures of various materials with novel properties resulting from the different shapes and morphologies.     

Electrical and photocatalytic properties of Na2Ti6O13 nanobelts prepared by molten salt synthesis

Single-crystalline Na₂Ti₆O₁₃ nanobelts were prepared on large-scale by molten salt synthesis at 825 °C for 3 h. The obtained nanobelts have typical width of less than 200 nm and thickness of 10-30 nm, and length up to 10 μm. The growth direction of the nanobelts was determined to be along [0 1 0]. Electrical transport property of an individual nanobelt was measured at room temperature and ambient atmosphere, and results showed that the nanobelts are semiconductor. Na₂Ti₆O₁₃ nanobelts exhibited good photocatalytic efficiency for the degradation of RhB under UV irradiation.     

Hydrothermal synthesis of ZnO nanobelts and gas sensitivity property

The ZnO nanobelts were synthesized by a hydrothermal method. The XRD spectrum indicates that the sample is wurtzite (hexagonal) structured ZnO with lattice constants of , . SEM and TEM images show the nanobelts to have lengths of 10-20 μm, widths of 50-500 nm, thicknesses of about 30-60 nm, and growth direction of [0001]. Gas sensitivity experiments on ZnO nanobelts were carried out under different temperatures. The results indicated high sensitivities with an operating temperature of only 220 ^°C for the oxidative gas O₂, and 305 ^°C for the gas N₂. The mechanism of gas sensitive effects is analyzed in detail.     

Synthesis of homogeneous bunched lead molybdate nanobelts in large scale via vertical SLM system at room temperature

Large scale and homogeneous bunched lead molybdate nanobelts were synthesized via a vertically supported liquid membrane system in the presence of ethylenediamine at room temperature. The typical bunched nanobelts were of length of ca. 300–500 μm, the width of ca. 230–280 nm and the thickness of ca. 90–110 nm. The X-ray diffraction patterns showed that all the obtained PbMoO₄ crystals belonged to tetragonal structure. Scanning electron microscopy images revealed that the positioning of the two compartments in the SLM system, modifier additive and reacting time, highly affect the morphologies and sizes of PbMoO₄ crystals. Room-temperature emission spectra of PbMoO₄ were investigated and the relative photoluminescence intensity of 400 nm was intensified in PbMoO₄ nanobelts. A possible growth mechanism is proposed. PACS 81.07.-b; 87.15.-Mi; 78.67-n     

Growth and optical properties of ultra-long single-crystalline α-Si3N4 nanobelts

Ultra-long single-crystalline -Si₃N₄ nanobelts were synthesized by catalyst-assisted crystallization of polymer-derived amorphous silicon carbonitride (SiCN). The obtained nanobelts were characterized using X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and selected-area electron diffraction. The results revealed that the -Si₃N₄ nanobelts are 20 to 40 nm in thickness, 400–600 nm in width and a few hundreds of micrometers to several millimeters in length, and grow along either the [011] or the [100] direction. Intense visible photoluminescence was observed over a spectrum ranging from 1.65 to 3.01 eV, which can be attributed to defects in the -Si₃N₄ structure. PACS 81.07.-b; 78.67.-n; 81.05.Je     

Hydrothermal synthesis of mesoporous Co3O4 nanobelts by means of a compound precursor

In the present work, high surface area mesoporous cobalt oxide (Co₃O₄) nanobelts have been synthesized by thermal treatment of cobalt hydroxide carbonate (CHC) precursors. CHC nanobelts were prepared by a facile hydrothermal method. Control experiments with variations in reaction time, solvent and different cobalt source revealed that temperature and sulfates are key factors in determining the formation of CHC nanobelts. Scanning electron microscopy and transmission electron microscopy images showed that the Co₃O₄ nanobelts consisted of mesoporous nanobelts with the average width of 40 nm. Brunauer–Emmett–Teller (BET) gas adsorption measurement further indicated that the products presented a rather large surface area (172.09 m² g^?1).     

Spinel-type ZnSb<Subscript>2</Subscript>O<Subscript>4</Subscript> nanowires and nanobelts synthesized by an indirect thermal evaporation

Uniform zinc antimoniate (ZnSb₂O₄) nanowires and nanobelts with a spinel structure were synthesized by an indirect thermal evaporation method in air. The as-synthesized ZnSb₂O₄ nanowires and nanobelts are single crystalline, usually several tens of microns in length. The diameter of the nanowires is about 20 nm; the thickness and the width of the nanobelts are about 15 nm and 60 nm, respectively. Most of the nanowires and nanobelts grow along the [001] direction. A possible formation mechanism is also proposed to account for the growth of these ZnSb₂O₄ nanobelts and nanowires. PACS 61.46.+w; 81.07.-b     

Growth of β-Ga2O3 nanobelts on Ir-coated substrates

We demonstrate the production of gallium oxide (Ga₂O₃) nanobelts on iridium (Ir)-coated substrates by thermal evaporation of GaN powders. Scanning electron microscopy revealed that the product consisted of nanobelts with widths in the range of 100–700 nm and thicknesses less than 1/5 of the widths. X-ray diffraction and high-resolution transmission electron microscopy indicated that the nanobelts have the single-crystalline monoclinic structure of Ga₂O₃. The photoluminescence spectrum under excitation at 325 nm showed a broad band with a prominent emission peak around 433 nm.PACS 81.07.-b     

Synthesis, structure, and photoluminescence of Zn2SnO4 single-crystal nanobelts and nanorings

A large quantity of single-crystal Zn₂SnO₄ (ZTO) nanobelts is synthesized by using a thermal evaporation method. The lengths of the nanobelts are up to several hundreds of micrometers, and the average width and thickness are about 400 and 30 nm, respectively. Some ring-like nanobelts, called nanorings here, are also observed. The nanobelts are characterized in detail with scanning electron microscope, X-ray powder diffraction, transmission electron microscope, high-resolution transmission electron microscope and selected area electron diffraction. Possible growth mechanisms for the ZTO nanobelts and nanorings are proposed. In addition, the photoluminescence spectrum (PL) of the nanobelts at room temperature shows a stable broad blue-green emission around the 400-600 nm wavelengths with a maximum center at 490 nm. The strong PL emission of the nanobelts may find potential applications in nano-scale optoelectronic devices.     

Optical properties of pyridine funtionalized TbF<Subscript>3</Subscript> nanoparticles

The preparation of pyridine functionalized TbF₃ nanoparticles are described in this report. Synthesized nanoparticles were characterized using the TEM, UV/Vis, FTIR and photoluminescence spectroscopy. TEM micrograph reveals the nanorod shaped, uniform in size with a particles size in the range of 20–30 nm. FTIR spectrum shown characteristic absorption bands of pyridine and a small intensity band at 411 cm⁻¹ corresponding metal nitrogen ν(Tb–N) bonding. Uv-vis spectrum shown the characteristic absorption transitions of Tb³⁺ ion. A strong emission transition at 540 nm (⁵D₄ → ⁷F₅) was observed on excite by visible light at 414 nm.     

Characterization and photoluminescence studies of Eu<Superscript>2+</Superscript>-doped BaSO<Subscript>4</Subscript> phosphor prepared by the recrystallization method

Eu doped BaSO₄ was prepared by the recrystallization method and characterization of the material was done by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. From the XRD pattern of Eu doped BaSO₄ compound, it was found that the prominent phase formed was BaSO₄ and traces of other phases were very weak and the result of FTIR spectrum of BaSO₄:Eu shows that the sulfur-oxygen stretch was found at around 1100 cm⁻¹. The room-temperature PL spectra of the Eu doped BaSO₄ sample showed one peak centered at 374 nm, which is the characteristic emission of Eu²⁺ ion. This emission band at 374 nm corresponds to the 4f⁶ 5d→4f⁷ (⁸S_7/2) transitions of Eu²⁺ ions. The excitation spectrum taken at the wavelength 374 nm extends over a wide range of wavelengths from 220–350 nm with a strong peak at around 260 nm. Furthermore, the present sample shows good crystal quality and high photoluminescence sensitivity. Hence our results suggest possible potential applications of Eu doped BaSO₄ phosphor in optoelectronic devices.     

Synthesis and characterization of novel nano-size polyreactive yellow 107

The reactive yellow 107 was polymerized by chemical oxidation method using potassium persulfate. The polymer was characterized by UV-VIS and Fourier transform infrared spectroscopy (FTIR) spectral studies. The peaks at 2,922 and 2,852 cm⁻¹ in the FTIR spectrum of polyreactive yellow 107 are assigned to the symmetric and asymmetric stretching vibrations of CH₂. The peak observed at 1,583 cm⁻¹ for polyreactive yellow 107 may be assigned to the stretching vibration of C=O, N=N, and C=C, 1,347 cm⁻¹ stretching vibration of C–N. The stretching vibrations of sulfone and sulfonic acid of S=O groups show a strong broad peak at 1,091 and 1,051 cm⁻¹. The conductivity of the polymer was determined to be 5.57 × 10⁻⁵ S cm⁻¹. The solubility of the chemically polymerized powder was ascertained and polyreactive yellow 107 showed good solubility in N,N-dimethyl formamide and dimethyl sulfoxide. The X-ray diffraction studies revealed the formation of nano-sized (84 nm) crystalline polymer. Using X-ray diffraction, behavior strain and dislocation density was also calculated. Scanning electron microscope analysis showed uniform crystalline nature of the polymer (200 nm). The thermogravimetric analysis, differential thermal analysis, and differential scanning calorimetry studies revealed good thermal stability of the polymer.     

Bicrystalline indium oxide nanobelts

Indium oxide (In₂O₃) nanobelts were synthesized by a chemical vapor deposition using thermal oxidation of In at 1000 °C. The nanobelts exhibited a unique bicrystalline structure that consisted of two single-crystalline cubic In₂O₃ nanobelts each having a different growth direction that often split along the twin boundary that exists at the centerline. The width of split nanobelts was 200–500 nm and the thickness was about 1/10 of the width. The growth direction of the bicrystals was [310]/[611] or [310]/[411]. X-ray diffraction and photoluminescence were measured to characterize the crystalline nature of the nanobelts. PACS 61.64.+w; 61.50.-f; 68.90.+g     

Growth of single-crystal ZnS nanobelts through a low-temperature thermochemistry route and their optical properties

ZnS nanobelts have been synthesized on a large scale using a simple thermochemistry method where the sources were Zn and ammonium polysulphide. The nanobelts had a uniform single-crystal hexagonal wurtzite structure with width ranging from 50 to 150 nm and length up to several tens of micrometers. The growth of ZnS nanobelts is controlled by vapor-solid (VS) crystal growth mechanism. Photoluminescence (PL) measurement shows that the nanobelts have a strong blue emission at about 450 nm and a green light emission at 530 nm. PACS 73.61.Ga; 78.55.Et; 81.15.Gh; 68.37.Hk; 68.37.Lp     

Hydrothermal synthesis of single crystal MoO3 nanobelts and their electrochemical properties as cathode electrode materials for rechargeable lithium batteries

Orthorhombic phase MoO₃ (α-MoO₃) nanobelts with uniform diameter are successfully prepared through a hydrothermal synthesis route at a low temperature (180 °C) in the presence of cetyltrimethylammonium bromide (CTAB) using saturated solution of ammonium molybdate tetrahydrate (AHM) as well as nitrate as raw materials, and are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The CTAB plays a key role in the formation of α-MoO₃ nanobelts and the aspect ratio of nanobelts significantly varies with quality of CTAB. The nanobelts with rectangular cross-sections have single crystalline orthorhombic phase structure, preferentially grow in [001] direction. Raman shifts of the α-MoO₃ nanobelts are fully consistent with that of flaky structure; however, intensity ratio of peaks 818.3 cm^?1 and 991.2 cm^?1 of α-MoO₃ nanobelts remarkably changes comparing with that of lamellar MoO₃. Electrochemical properties of α-MoO₃ single crystal nanobelts synthesized as cathode electrode materials for rechargeable lithium batteries are also measured. It indicates that the α-MoO₃ nanobelts exhibit a better performance than MoO₃ micro flakes.     

Structure and optical properties of tungsten oxide nanomaterials prepared by a modified plasma arc gas condensation technique

With the use of a modified plasma arc gas condensation technique and control of the processing parameters, namely, plasma current and chamber pressure, we synthesized tungsten oxide nanomaterials with aspect ratios ranging from 1.1 (for equiaxed particles with the length and width of 48 nm and 44 nm, respectively) to 12.7 (for rods with the length and width of 266 nm and 21 nm, respectively). The plasma current and chamber pressure, respectively, ranged from 70 to 90 A and from 200 to 600 Torr. We then characterized the tungsten oxide nanomaterials by means of X-ray diffraction, high-resolution transmission electron microscope, UV–visible spectroscope, and photoluminescence (PL) spectroscope. Experimental results show that equiaxed tungsten oxide nanoparticles were produced at a relatively low plasma current of 70 A, whereas nanorods were produced when plasma currents or chamber pressures were increased. All of the as-prepared tungsten oxide nanomaterials exhibited a WO_2.8 phase. Compared to the nanoparticles, the nanorods exhibited unique properties, such as a redshift in the UV–visible spectrum, a blue emission in PL spectrum, and a good performance in field emission. With respect to the field emission, the turn-on voltage for WO_2.8 nanorods was found to be as low as 1.7 V/μm.     

Microwave-induced solid-state synthesis of TiO<Subscript>2</Subscript>(B) nanobelts with enhanced lithium-storage properties

A fast and economical route based on an efficient microwave-induced solid-state process has been developed to synthesize metastable TiO₂(B) nanobelts with widths of 30–100 nm and lengths up to a few micrometers on a large scale. This new method reduces the synthesis time for the preparation of TiO₂(B) nanobelts to less than half an hour, allowing the screening of a wide range of reaction conditions for optimizing and scaling up the production and facilitating the formation of metastable phase TiO₂(B). The as-formed TiO₂(B) nanobelts exhibit enhanced lithium-storage performances, compared with the TiO₂(B) product obtained by the conventional heating. This study provides a new way for large-scale industrial production of high-quality metastable TiO₂(B) nanostructures. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy.     

Study of the bending modulus of individual silicon nitride nanobelts via atomic force microscopy

Analysis of the bending modulus of individual silicon nitride nanobelts in elastic regime is reported here. The nanobelts have the size between 200∼800 nm in width, and thickness 20∼50 nm. Atomic force microscopy was used to image and to perform measurements of force versus bending displacement on individual nanobelts suspending over strips. The bending modulus E_b is deduced by comparison of the measured force curves on the substrate and on the suspending nanobelts. It is shown that the elastic modulus of the silicon nitride nanobelts is about 570 GPa, which is much larger than that of bulk and film of the silicon nitride material. The larger elastic modulus is ascribed to the fact there are less structural defects in the silicon nitride nanobelts. PACS 81.70.Bt; 81.40.Lm; 61.80.+g     

Fabrication of MgO nanobelts using a halide source and their structural characterization

MgO nanobelts have been fabricated by chemical vapor deposition using MgCl₃ as starting material. The products consist of a large quantity of belt-like nanostructures with typical lengths in the range of several tens to several hundreds of micrometers; some of them even have lengths on the order of a millimeter. The typical thickness and width-to-thickness ratio of the MgO nanobelts are in the range of 20 to 100 nm and about 5 to 10, respectively. The size and morphology of the MgO nanobelts were measured by transmission electron microscopy. Investigations of X-ray diffraction patterns and using high-resolution transmission electron microscopy indicate that the nanobelts have a cubic structure and are single-crystalline. Received: 23 August 2001 / Accepted: 27 August 2001 / Published online: 2 October 2001     

Synthesis of High Quality CdS Nanorods by Solvothermal Process and their Photoluminescence

Large-scale cadmium sulfide (CdS) nanorods with high quality were successfully synthesized by solvothermal method using ethylenediamine (en) aqueous as solvent. The as-obtained product was investigated by X-ray diffractometer (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FE-SEM), ultraviolet–visible (UV–Vis) spectrum and photoluminescence (PL) spectrum. The length and width of the CdS nanorods were in the range of 1–2 μm, 30–40 nm, respectively. XRD analysis revealed that the crystal structure of the product was hexagonal phase. Photoluminescence measurement showed that the nanobelts have two main emission bands around 470 and 560 nm, which should come from the higher-level transition and the intrinsic transition, respectively.