Synthesis of <Emphasis Type="Italic">γ</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires through a boehmite precursor route

Crystalline γ-Al₂O₃ nanowires with diameter, 20–40 nm, length above 600 nm and aspect ratio above 30 have been successfully synthesized by thermal decomposition of boehmite (γ-AlOOH) precursors obtained via hydrothermal route by using AlCl₃, NaOH and NH₃ as starting materials. Thermogravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED) and high resolution transmission electron microscope (HRTEM) were used to characterize the features of the as-made γ-Al₂O₃ nanowires and their γ-AlOOH precursors. The pH value of the solution and the mixed precipitant play important roles in the formation of γ-AlOOH nanowires. After calcination at 500°C for 2 h, the orthorhombic γ-AlOOH transforms to cubic γ-Al₂O₃ and retains nanowire morphology.     

Effect of hydrothermal duration on synthesis of WO<Subscript>3</Subscript> nanorods

Among different type of transition metal oxides, tungsten trioxide (WO₃) is a suitable candidate for electronic device fabrication due to its n-type property and wide band gap. Herein, one-dimensional tungsten trioxide (WO₃) nanorods were achieved from an aqueous solution of sodium tungstate dihydrate (Na₂WO₄·2H₂O) and sodium chloride (NaCl) in an acidic media by a time-optimized hydrothermal synthesis in autoclave at 180°C or different synthesis durations. For studying morphology and size of obtained powder, X-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscope (HRTEM) were applied. Finally, WO₃ nanorods of about 2–3 μm in length and 100–200 nm in diameter were obtained during 3 h hydrothermal process.     

Hydrothermal synthesis of calcium hydroxyapatite nanorods in the presence of PVP

Calcium hydroxyphosphate (Ca₁₀(PO₄)₆(OH)₂, HAP) nanorods have been successfully synthesized by a simple and mild hydrothermal treatment in the presence of polyvinylpyrrolidone (PVP). A complex of calcium nitrate (Ca(NO₃)₂) and Na₂HPO₄ was used to supply the calcium and phosphate ions during the reactions. The synthesis of pure HAP nanorods was under near neutral condition. The morphology and structure of the samples were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy analysis. The nanorods were uniform with diameter of 20–25 nm and length ranging from several hundreds of nanometers to several micrometers. The influence of different experiment conditions, i.e., the PVP concentration, molar ratio of Ca²⁺ to HPO₄ ²⁻, reaction time, and temperature, on the morphology of the nanorods was investigated. The formation mechanism of rod-like HAP and effects of PVP on the crystal nucleation and growth have also been discussed.     

Nanoparticles assembly of boehmite nanofibers without a surfactant

Self-assembly of aluminum hydrate particles into larger boehmite (γ-AlOOH) nanofibers was illustrated by a facile hydrothermal method without using any surfactants. The size and morphology of boehmite nanofibers could be controlled by adjusting the pH value of the reaction mixture. The resulting products were characterized by XRD (X-ray diffraction), FTIR (Fourier transform infrared spectra), SEM (scanning electron microscopy), and TEM (transmission electron microscopy). The specific surface area and pore-size distribution of the obtained product as determined by gas-sorption measurements show that the boehmite nanofibers possess high-surface area and porosity properties. A possible formation mechanism of nanofibers via a nanoparticle assembly procedure is proposed based on the experiments under the different conditions.     

A new route to synthesis of γ-alumina nanorods

γ-Alumina single-crystalline nanorods have been successfully synthesized by thermal decomposition of boehmite precursor which was prepared by solvothermally treating AlCl₃ ⁎ 6H₂O, NaOH, sodium dodecyl benzene sulfonate in water and dimethylbenzene mixed solvents. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Our experiments show that the surfactant plays an important role in the morphology and assembly of boehmite. Photoluminescence (PL) spectrum of the boehmite nanorods was also investigated.     

Synthesis of SrCrO<Subscript>4</Subscript> nanostructures by onion inner-coat template and their optical properties

This paper describes a bio-template method of the squama inner coat of onion for preparing the SrCrO₄ nanostructures including nanospheres, nanorods and dumbbell-shaped superstructure. The method is able to make SrCrO₄ nanoparticles with average diameters in the range of 90–170 nm, SrCrO₄ nanorods with length in the range 0·70–2 μm, width in the range of 80–180 nm, and SrCrO₄ dumbbell-shaped superstructure with length in the range 10–14 μm. The dumbbell-shaped superstructures are assembled by many SrCrO₄ nanowires with length in the range 10–14 μm and width in the range 30–50 nm. The products were characterized by transmission electron microscope, powder X-ray diffraction, UV-Vis spectroscopy and luminescence spectrophotometer. A possible formation mechanism was also proposed. In the preparation, the SrCrO₄ nanostructures were synthesized at room temperature without any surfactants. This new bio-template method will have potential applications in preparation of the nanoscale materials with different morphologies.     

Preparation and characterization of Co<Subscript>9</Subscript>S<Subscript>8</Subscript> nanocrystalline and nanorods

Hexagonal Co₉S₈ nanocrystal and nanorods were synthesized using cobalt chloride (CoCl₂·6H₂O), dimethyl sulfoxide (DMSO) and non-aqueous alcohol as the starting materials, and taking dimethyl sulfoxide as both sulfur source and strong infiltrator in nanorods preparation. The Co₉S₈ samples were characterized by X-ray diffraction (XRD), scanning tunneling microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and laser Raman spectrometer. The results show that the as-prepared Co₉S₈ nanocrystal with a size of 6 nm take on weak paramagnetism at room temperature. The lengths and diameters of the nanorods were about 4 μm and 200 nm, respectively. The reason for the relative lower synthesis temperature of nanorods was discussed and a ‘micro-autoclave reactor’ model was suggested as well.     

Growth and optical properties of ZnO nanorods by introducing ZnO sols prior to hydrothermal process

ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.     

水热合成勃姆石纳米棒及其改性复合膜

商用锂离子电池隔膜遭受高温时,会发生热收缩现象,通过涂覆无机颗粒对隔膜进行改性,可以有效地提高隔膜的热稳定性能,从而提高锂离子电池的安全性能,而勃姆石纳米棒具有耐热性好和弹性模量大等特点,适用于涂覆改性隔膜.本研究利用AlCl3和NaOH与NH4 OH混合沉淀剂,通过水热法制备了勃姆石纳米棒,并使用线棒涂布工艺制备了涂...     

Additive-free and time-saving microwave hydrothermal synthesis of hollow microspheres structured boehmite

In this study, by using Al₂(SO₄)₃ aqueous solution and urea as raw materials, hollow microspheres structured boehmite was successfully synthesized only after 30 min reaction time at 180 °C via an additive-free and time-saving microwave hydrothermal route. The final products were characterized by techniques of X-ray diffraction (XRD), transmission electronic microscope (TEM), scanning electron microscope (SEM) and Fourier transform infrared spectrometry (FTIR). To investigate its crystal form and morphology evolution process, samples subjected to different reaction durations were prepared and characterized. The pivotal influence factors on boehmite morphology, such as reaction temperature, dosage of urea and microwave power range were discussed based on the experiment facts.     

Low-temperature synthesis of CuS nanorods by simple wet chemical method

CuS nanorods of length 60–100 nm and 15 nm in diameter have been synthesized by simple wet chemical method at 105 °C using CuCl₂·2H₂O as Cu-precursor, CS₂ as S-source and ethylenediamine as the attacking reagent. The plausible reaction mechanism has been proposed and the effect of reaction temperature on morphology has been discussed. X-ray diffraction (XRD) pattern suggests the formation of hexagonal phase CuS. The morphology of the products has been studied by transmission electron microscope (TEM) analysis. A detailed optical study has also been done.     

Effect of ammoniating temperature on microstructure of one-dimensional GaN nanorods with Tb intermediate layer

GaN nanorods have been successfully synthesized on Si (111) substrates by magnetron sputtering through ammoniating Ga₂O₃/Tb thin films. The influence of ammonating temperatures on microstructure, morphology and light emitting properties of GaN nanorods was ananlyzed in detail using X-ray diffraction, X-ray photoelectron spectroscopy, FT-IR spectrophotometer, scanning electron microscopy, high- resolution transmission electron microscopy, and photoluminescence spectroscopy. The results demonstrate that the GaN nanorods are single crystalline and exhibit hexagonal wurtzite symmetry. The highest crystalline quality was achieved at 950 °C for 15 min with the size of 100–150 nm in diameter, which have an excellent light emitting properties. A small red-shift occurs due to band-gap change caused by the tensile stress.     

Synthesis and characterization of anatase and rutile TiO2 nanorods by template-assisted method

Well-aligned anatase and rutile TiO₂ nanorods and nanotubes with a diameter of about 80–130 nm have successfully been fabricated via sol-gel template method. The prepared samples were characterized by using thermogravimetric (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The XRD results indicated that the TiO₂ nanorods were crystallized in the anatase and rutile phases, after annealing at 400–800 °C for different periods of time from 0.2 to 10 h.     

Synthesis and characterization of silver molybdate nanowires, nanorods and multipods

Silver molybdate nanowires, nanorods and multipods like structures have been prepared by an organic free hydrothermal process using ammonium molybdate and silver nitrate solutions. The powder X-ray diffraction (PXRD) patterns reveal that the silver molybdate belongs to anorthic structure. The thickness, 200–500 nm, for silver molybdate nanorods/wires and 2–5 μm for microrods are identified from SEM images. UV-visible spectrum of silver molybdate nanorods/nanowires shows maximum absorbance at 408 nm. Photo-luminescence (PL) spectrum exhibits UV emission at 335 nm, violet emission at 408 nm and a weak green emission at 540 nm. The influence of hydrothermal synthesis conditions on silver molybdate nanowires, nanorods and multipods compositions were established.     

Microwave assisted hydrolysis of aluminium metal and preparation of high surface area <Emphasis Type="Italic">γ</Emphasis> Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powder

Phase pure boehmite particles were prepared by microwave assisted hydrolysis of aluminium sheets. These particles were calcined in air to produce γ Al₂O₃ particles with specific surface area of ~210 m²/g. The alumina particles were characterized by studying X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy. For comparison, the aluminium hydroxide particles were also prepared by normal hydrolysis of aluminium metal. Normal hydrolysis yielded a mixture of boehmite and bayerite particles whereas microwave assisted hydrolysis produced phase pure boehmite particles. The importance of using microwave radiation for the hydrolysis of aluminium metal is also manifested in a shorter reaction time.     

Phase formation in rapidly quenched Cu-based alloys

In the present investigation, we report the formation of γ-brass type phase in the rapidly quenched Cu₅₀Ga₃₀Mg₅Ti₁₅ and Cu₅₀Al₃₀Mg₅Ti₁₅ alloys. Rapid solidification of Cu₅₀Ga₃₀Mg₅Ti₁₅ alloy shows the formation of simple cubic γ-brass type phase (a = 0.863 nm), which on annealing at 1,023 K for 60 h transforms to disordered type γ-brass phase (a = 0.879 nm). It has been observed that intensity modulation of electron diffraction spots corresponding to simple cubic γ-brass phase is similar to the intensity modulation observed in the mirror orientation of icosahedral quasicrystalline phase. Contrary to the crystalline phase formation in Cu–Ga–Mg–Ti alloy, rapid solidification of Cu₅₀Al₃₀Mg₅Ti₁₅ shows the formation of amorphous and nanocrystalline bcc γ-brass type phase (a = 0.870 nm), which on annealing transforms to ordered γ-brass type phase (a = 0.872 nm). The structural and microstructural characterization was done through X-ray diffraction and transmission electron microscopy.     

A facile approach to synthesize silver nanorods capped with sodium tripolyphosphate

Silver nanorods have been successfully synthesized via a facile route using sodium tripolyphosphate (Na₅P₃O₁₀) as the capping agent. Silver nitrate and glucose served as the Ag⁺ source and green reducing agent in aqueous solution, respectively. The products were characterized by X-ray powder diffraction (XRD), UV–visible spectroscopy (UV–vis), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The results showed that the obtained silver nanorods are highly crystallized with an average diameter of 30 nm and lengths up to 400 nm. The linear structure of the capping agent and slow reaction rate are considered to be key factors in the control of particle morphology. The possible formation mechanism has been discussed based on the experimental results.     

Preparation of γ-alumina precursors for metal reinforcement

In the metal matrix composite field, both fine (<0.5 µm) and coarse, crystalline, calcined aluminas with narrow or broad particle size distributions, are being used as reinforcement phase. The effect was studied of the preparation method of fine boehmite (-AlOOH), precursor of the -Al₂O₃, on the product morphology. The material was produced by heating three kinds of hydrothermal precursors at different pH, and for 2 h at 200°C, using constant stirring. Under the conditions investigated (i.e., 0.12 mol/dm³ of Al(OH)₃ and only diluted NaOH and HNO₃ solutions used to adjust the pH of slurry), the pH of hydrothermal slurry influenced the product morphology; in contrast, the three different hydrothermal precursors, namely dry aluminum hydroxide gel, fresh aluminum hydroxide precipitate and gibbsite reagent powders, had only a little effect on the product morphology. The dehydration/transformation mechanism from Al(OH)₃ to -AlOOH is believed to be dissolution/reprecipitation rather than a direct dehydration.     

Synthesis of GaN nanorods by ammoniating Ga2O3 films on TiO2 (rutile) layer deposited on Si(111) substrates

GaN nanorods have been synthesized by ammoniating Ga₂O₃ films on a TiO₂ middle layer deposited on Si(111) substrates. The products were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM). The XRD analysis indicates that the crystallization of GaN film fabricated on TiO₂ middle layer is rather excellent. The FTIR, SEM and HRTEM demonstrate that these nanorods are hexagonal GaN and possess a rough morphology with a diameter ranging from 200 nm to 500 nm and a length less than 10 μm, the growth mechanism of crystalline GaN nanorods is discussed briefly.     

Synthesis of LiFePO<Subscript>4</Subscript>/C composite as a cathode material for lithium-ion battery by a novel two-step method

In this study, LiFePO₄/C is synthesized via a novel two-step method. The first step is the synthesis of nano-sized intermediate FePO₄ by a modified sol–gel method. A fast and full combustion procedure is involved to remove carbon and control the size of the intermediate particles. The second step is to prepare LiFePO₄/C by combining solid-state reaction with controllable carbon coating. This two-step method is facile to prepare nano-sized LiFePO₄ and easy to optimize the carbon content for surface coating. X-ray diffraction shows that the LiFePO₄/C composite possesses good crystallinity. Spherical morphology with a diameter of 30–150 nm is observed by scanning electron microscope and transmission electron microscope. Electrochemical measurements indicate that the LiFePO₄/C composite exhibits discharge capacities of 162, 144, 126, and 106 mAh g⁻¹ at 0.1, 1, 2, and 5C, respectively. No capacity fading is observed in 50 cycles.