From cobalt nitrate carbonate hydroxide hydrate nanowires to porous Co(3)O(4) nanorods for high performance lithium-ion battery electrodes

We have developed a simple approach for the large-scale synthesis of cobalt nitrate carbonate hydroxide hydrate (Co(CO(3))(0.35)(NO(3))(0.2)(OH)(1.1)·1.74H(2)O) nanowires via the hydrothermal process using sodium hydroxide and formaldehyde as mineralizers at 120?°C. The porous Co(3)O(4) nanorods 10-30?nm in diameter and hundreds of nanometres in length have been fabricated from the above-mentioned multicomponent nanowires by calcination at 400?°C. The morphology and structure of cobalt nitrate carbonate hydroxide hydrate nanowires and Co(3)O(4) nanorods have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD). Moreover, the porous Co(3)O(4) nanorods have been applied in the negative electrode materials for lithium ion batteries, which exhibit high electrochemical performance.     

Controlled synthesis of LaPO(4) and CePO(4) nanorods/nanowires

LaPO(4) and CePO(4) nanorods/nanowires with controlled aspect ratios have been successfully synthesized using a hydrothermal microemulsion method under mild conditions. It has been shown that the obtained LaPO(4) has a monoclinic structure, while CePO(4) exists in the hexagonal structure. Uniform nanorods/nanowires with diameters of 20-60?nm and lengths ranging from several hundreds of nanometres to several micrometres were obtained. The aspect ratios of the obtained 1D nanostructures can be fine-tuned by simply changing the [H(2)O ]/[surfactant] molar ratios. The possible growth mechanism of LaPO(4) and CePO(4) nanorods/nanowires was explored in detail.     

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.     

Synthesis of Tb(OH)(3) nanowire arrays via a facile template-assisted hydrothermal approach

Hexagonal wurtzite structure Tb(OH)(3) nanowires with a uniform diameter of about 70-80?nm and lengths of up to several micrometres have been synthesized on a large scale via a hydrothermal treatment based on the use of an anodic aluminium membrane as the template. Aligned Tb(OH)(3) nanowire arrays can be obtained by dissolving the template. Field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, x-ray diffraction, and photoluminescence (PL) spectra have been employed to characterize the as-prepared samples. The PL spectrum of Tb(OH)(3) under 350?nm excitation consists of four main peaks at 489.9, 543, 584 and 621?nm, among which that for the electric dipole transition (5)D(4) to (7)F(5) (at 543?nm) is the strongest. Furthermore, a preliminary suggestion for the mechanism of growth of the Tb(OH)(3) nanowires using the hydrothermal-template synthesis technique has been proposed.     

Effect of Oleic Acid and Oleylamine Surfactants on the Size of FePt Nanoparticles

FePt magnetic nanoparticles have been synthesized by superhydride reduction of FeCl₂ and Pt(acac)₂ at high temperature. Adding superhydride (LiBEt3H) to the phenyl ether solution of FeCl₂ and Pt(acac)₂ in the presence of oleic acid, oleylamine, and 1,2-hexadecanediol at 190?^°C, followed by refluxing at 245?^°C, led to monodisperse 3.5?nm FePt nanoparticles. The effect of oleylamine and oleic acid surfactants on the nucleation and growth of FePt nanoparticles were studied. The size of Pt was controlled by oleylamine surfactant in nucleation stage. To prevent sintering of the FePt nanoparticles, oleic acid surfactant was used in growth stage. The energy dispersive spectroscopy results revealed that the particle composition was first Fe₁₁Pt₈₉ in nucleation stage and after adding superhydride the composition changed to Fe₆₃Pt₃₇ in growth stage. The structural and magnetic measurements indicated that the L1₀ structure of FePt nanoparticles is formed after annealing and the coercivity of superlattice FePt nanoparticles increases to 7.5?kOe after heat treatments.     

Conversion of potassium titanate nanowires into titanium oxynitride nanotubes

Tunnel-structured potassium titanate with a K(3)Ti(8)O(17) phase was synthesized by direct oxidation of titanium powder mixed with KF(aq) in water vapor at 923 K. The reaction conditions were adjusted so that uniform single crystalline potassium titanate nanowires with [010] growth direction (length: 5-30 μm, diameter: 80-100 nm) were obtained. Nitridation of the nanowires by NH(3)(g) at 973-1073 K converted the titanate nanowires into rock-salt structured cubic phase single crystalline titanium oxynitride TiN(x)O(y) nanotubes (x = 0.88, y = 0.12, length = 1-10 μm, diameter = 150-250 nm, wall thickness = 30 - 50 nm) and nanorods (x = 0.5, y = 0.5, length = 1-5 μm, diameter = 100-200 nm) with rough surfaces and [200] growth direction. The overall conversion of the titanate nanowires into the nanotubes and the nanorods can be rationalized by Ostwald ripening mechanism. We fabricated an electrode by adhering TiN(x)O(y) nanotubes (0.2 mg) on a screen-printed carbon electrode (geometric area: 0.2 cm(2)). Electrochemical impedance spectroscopy demonstrated its charge transfer resistance to be 20Ω. The electrochemical surface area of the nanotubes on the electrode was characterized by cyclic voltammetry to be 0.32 cm(2). This property suggests that the TiN(x)O(y) nanostructures can be employed as potential electrode materials for electrochemical applications.     

One-step formation of core-shell sulfide-oxide nanorod arrays from a single precursor

Densely packed and well-aligned coaxial (core-shell) CdS-CdO and ZnS-ZnO nanorod arrays were prepared with a one-step, non-catalytic, template-free metalorganic chemical vapour deposition (MOCVD) process by using single-source molecular precursors Cd(O-EtXan)(2) and Zn(O-EtXan)(2), respectively (O-EtXan = S(2)COCH(2)CH(3)). Data from pyrolysis gas chromatography/mass spectrometry of the precursors revealed the sequence of formation, namely sulfide core first and oxide shell later, with the first formed sulfide nanorods serving as the template for subsequent in?situ oxide shell coating. The coaxial CdS-CdO and ZnS-ZnO nanorod arrays were formed at collection temperatures of 180 and 200?°C, respectively. At a slightly higher collection temperature of 250?°C, coaxial ZnS-ZnO nanowires were also obtained. The coaxial nanostructure was characterized and confirmed with high-resolution transmission electron microscopy. In a photoluminescence study, near band edge emissions at around 530?nm, a composite emission of the two near band edge emissions of 524?nm of CdS and 551?nm of CdO, were observed for the coaxial CdS-CdO nanorod sample, while defect-induced emissions at around 470?nm were observed for both coaxial ZnS-ZnO nanorod and nanowire samples. A more stable oxide shell not only protects the sulfide core but also provides possible surface passivation beneficial to enhanced photoluminescence. The present work demonstrates the feasibility of growth of coaxial one-dimensional nanostructures from single-source precursors that contain all the necessary constituent elements in one compound.     

Synthesis of ITO nanowires and nanorods with corundum structure by a co-precipitation-anneal method

Tin-doped indium oxide (ITO) nanowires and nanorods were synthesized by a co-precipitation-anneal process. Both the nanowires and the nanorods had nearly uniform diameter of ca. 60 nm. The nanowires had long and straight morphology with length up to several micrometers. Moreover, the products were the ITO with corundum structure.     

Formation and characterisation of CeO2 and Gd:CeO2 nanowires/rods for fuel cell applications

Ceria and gadolinium (Gd) doped ceria nanowires have been synthesised by hydrothermal technique with mild reaction conditions. The structure and morphology of as-prepared nanowires were studied by X-ray diffraction and field emission scanning electron microscopy (FE-SEM) techniques. The FE-SEM analysis revealed the formation of nanowires with an average diameter of 10–15 nm. Atomic force microscopy (AFM) analysis for the annealed samples confirms the existence of well defined nanorods of 120–150 nm diameter and 1–1.3 μm length. Fluorescence and diffuse reflectance spectroscopy techniques have been used to study the optical properties of the prepared nanowires. The observed red shift in the ultraviolet–visible absorption spectra confirmed the promoted electron–phonon interaction in CeO₂ and Gd:CeO₂ nanowires compared to bulk structures. The prepared nanowires/rods were thermally stable at up to 350?°C, as revealed by thermogravimetric analysis. The electrical properties were studied by cyclic voltammetry (CV) and impedance spectroscopy. The CV results demonstrated that Gd:CeO₂ exhibited a higher electro-oxidation than CeO₂ nanowires.     

Fabrication of GaN nanowires and nanorods catalyzed with tantalum

Single-crystalline GaN nanowires and nanorods have been fabricated through ammoniating Ga₂O₃ films catalyzed with tantalum (Ta) by RF magnetron sputtering, and microstructure, morphology and optical properties were investigated in particular. The results indicate that the nanowires have a hexagonal wurtzite structure with size about 50 nm in diameter and more than ten microns in length, however, the nanorods are rod-like structures with smooth surface and 100–300 nm in diameter. The growth direction of these nanostructures are perpendicular to the (100) crystal plane. The photoluminescence spectrum at room temperature exhibits a strong UV light emission band centered at 364 nm.     

Self-assembly of colloidal gamma-Fe2O3 and FePt nanoparticles on carbon nanotubes by dip-coating process

The chemically synthesized colloidal gamma-Fe2O3 and FePt nanoparticles (NPs), with the diameter of approximately 10 nm and approximately 4 nm, respectively, adsorbed and assembled on the surface of carbon nanotubes (CNTs) by dip-coating process, through van der Waals interaction between NP and CNT. Repeating the steps of dip-coating and removing the surfactants from NPs significantly increased the amount of NPs as forming multilayers on the CNT. In addition, the electrochemical activities of FePt/CNTs for methanol oxidation were investigated for the potential application as catalysts of direct methanol fuel cells.     

A facile solution-phase approach to the synthesis of luminescent europium methacrylate nanowires and their thermal conversion into europium oxide nanotubes

Novel one-dimensional (1D) nanostructures of rare earth complexes (europium methacrylate (Eu(MA)(3))) have been prepared from the precursor of irregularly shaped Eu(MA)(3) powder in ethanol solvent without the assistance of an added surfactant, catalyst, or template. These hexagonal-shaped complex nanowires have diameters of about 100-300?nm and lengths ranging from tens to hundreds of micrometers. Nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) studies and thermogravimetric analysis (TGA) show that the precursor powder and the resulting nanowires have identical compositions. Under UV light excitation, strong red fluorescence can be clearly seen throughout the whole wires. This good luminescence characteristic of the complex nanowires is further confirmed by the fluorescence spectrum where strong and narrow emission can be seen. These rare earth complex nanowires provide a useful source for 1D rare earth oxide materials, as the europium ions are distributed uniformly in the Eu(MA)(3) nanowires. Through calcination, the Eu(MA)(3) nanowires are successfully converted into Eu(2)O(3) nanotubes. X-ray investigation confirms that the Eu(2)O(3) nanotubes have a cubic body-centered structure. FTIR measurements and TGA analysis are used to follow the calcination process. A plausible mechanism responsible for the formation of Eu(2)O(3) nanotubes is presented.     

Shape control of PbS nanocrystals using multiple surfactants

A novel technique is presented for preparing PbS nanorods with all spatial dimensions comparable to the excitonic Bohr radius of PbS. The shape of the PbS nanocrystals is entirely controlled by using a combination of three different surfactants with different end functional groups. Oleylamine, oleic acid and trioctylphosphine are used to tune the shape of the PbS nanocrystals from cubic, stars, to rods and then to branched nanowires. The PbS nanorods have rock-salt structure with growth along the [220] direction.     

Microemulsion-based synthesis of porous zinc ferrite nanorods and its application in a room-temperature ethanol sensor

Porous zinc ferrite (ZnFe(2)O(4)) nanorods with a diameter of around 50?nm and a length of several micrometers have been synthesized by a microemulsion-based method in combination with calcination at 500?°C. The morphology and structure of the ZnFe(2)O(4) nanorods and its precursor (ZnFe(2)(C(2)O(4))(3) nanorods) were systematically characterized by x-ray powder diffraction, transmission electron microscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The formation mechanism for the porous ZnFe(2)O(4) nanorods is also discussed. Moreover, the porous ZnFe(2)O(4) nanorods were applied in a room-temperature ethanol sensor and exhibited much better sensing performance than ZnFe(2)O(4) nanoparticles.     

A comparative study on the NO2 gas sensing properties of ZnO thin films, nanowires and nanorods

ZnO thin films were fabricated using the spin coating method, ZnO nanowires by cathodically induced sol-gel deposition by the means of an anodic aluminum oxide (AAO) template, and ZnO nanorods with the hydrothermal technique. For thin film preparation, a clear, homogeneous and stable ZnO solution was prepared by the sol-gel method using zinc acetate (ZnAc) precursor which was then coated on a glass substrate with a spin coater. Vertically aligned ZnO nanowires which were approximately 65 nm in diameter and 10 μm in length were grown in an AAO template by applying a cathodic voltage in aqueous zinc nitrate solution at room temperature. For fabrication of the ZnO nanorods, the sol-gel ZnO solution was coated on glass substrate by spin coating as a seed layer. Then ZnO nanorods were grown in zinc nitrate and hexamthylenetetramine aqueous solution. The ZnO nanorods are approximately 30 nm in diameter and 500 nm in length. The ZnO thin film, ZnO nanowires and nanorods were characterized by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). The NO₂ gas sensing properties of ZnO thin films, nanowires and nanorods were investigated in a dark chamber at 200 °C in the concentration range of 100 ppb-10 ppm. It was found that the response times of both ZnO thin films and ZnO nanorods were approximately 30 s, and the sensor response was depended on shape and size of ZnO nanostructures and electrode configurations.     

Preparation of anisotropic transition metal phosphide nanocrystals: the case of nickel phosphide nanoplatelets, nanorods, and nanowires

We have synthesized anisotropic nickel phosphide nanocrystals, including triangular/hexagonal nanoplatelets, nanorods and nanowires, via a solution-phase synthetic method that uses nickel(II) acetylacetonate as a metal precursor and trioctylphosphine as a phosphorus source. Nickel phosphide nanoplatelets have been prepared from a one-pot reaction, and their dimensions in the length mostly vary from 20 to 50 nm, while their thicknesses are in a narrow range of 7-9 nm. Nickel phosphide nanorods with a width of approximately 6 nm and a typical length of 25-32 nm can be synthesized from either the one-pot reaction or the multi-injection approach, although the latter can generate nanorods with a much higher uniformity. A continuous injection approach has been used to synthesize nanowires that have a typical width of approximately 6 nm and a length ranging from tens of nanometers up to several hundred nanometers. Major factors that influence the growth of nickel phosphide nanocrystals have been investigated, and a multi-surfactant system is found to be essential for the formation of anisotropic nanostructure. Magnetic studies have revealed paramagnetic characteristics for all the synthesized samples.     

Perpendicularly self-oriented and shape-controlled L10-FePt nanorods directly synthesized by a temperature-modulated process

The synthesis and self-assembly of tetragonal phase-containing L1₀-Fe₅₅Pt₄₅ nanorods with high coercive field is described. The experimental procedure resulted in a tetragonal/cubic phase ratio close to 1:1 for the as-synthesized nanoparticles. Using different surfactant/solvent proportions in the process allowed control of particle morphology from nanospheres to nanowires. Monodisperse nanorods with lengths of 60 ± 5 nm and diameters of 2–3 nm were self-assembled in a perpendicular oriented array onto a substrate surface using hexadecylamine as organic spacer. Magnetic alignment and properties assigned, respectively, to the shape anisotropy and the tetragonal phase suggest that the self-assembled materials are a strong candidate to solve the problem of random magnetic alignment observed in FePt nanospheres leading to applications in ultrahigh magnetic recording (UHMR) systems capable of achieving a performance of the order of terabits/in².      

一步法制备L10相FePt纳米颗粒

以乙酰丙酮铁(Fe(acac)3)和氯铂酸(H2PtCl6.6H2O)分别作Fe源和Pt源,三缩四乙二醇(TEG)作溶剂和还原剂,聚乙烯基吡咯烷酮(PVP)作表面活性剂,通过多元醇还原法制备出单分散的FePt纳米颗粒。通过X射线衍射仪(XRD)及透射电子显微镜(TEM)分析表明,所制备的FePt纳米颗粒形状近似球形,分散性较好,平均颗粒粒径约为5.5nm。通过振动样品磁强计(VSM)分析显示所制备FePt纳米颗粒矫顽力为37.64kA/m,这意味着FePt纳米颗粒部分转变为面心四方相(L10相)。     

铬酸铅一维纳米材料的水热制备、表征及性能研究

利用水热法在不使用任何表面活性剂的情况下成功制备出了包括纳米棒、纳米线在内的铬酸铅一维纳米材料,通过改变反应温度可以很容易对铬酸铅一维纳米材料的长度和长径比进行调节。运用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和高分辨透射电镜(HRTEM)等对所得产物进行了系统的表征,同时对所制备的铬酸铅一维纳米材料的光学性质进行了研究分析。     

化学气相沉积法制备GaN纳米线和纳米棒

采用浸渍法在未抛光的硅衬底上涂抹一层NiCl2薄膜,通过化学气相沉积法(CVD)制备出高质量的GaN纳米线和纳米棒.X射线衍射(XRD)、傅立叶红外吸收光谱(FTIR)、选区电子衍射(SAED)和高分辨透射电子显微镜(HRTEM)的分析结果表明,采用此方法得到了六方纤锌矿结构的GaN单晶纳米线.通过扫描电镜(SEM)观察发现纳米线的形貌,纳米线的直径在50～200nm之间,纳米棒的直径在200～800nm之间.