Synthesis of variable-aspect-ratio, single-crystalline ZnO nanostructures

Variable-aspect-ratio (length/diameter), one-dimensional (1-D) ZnO nanostructures (nanorods and nanowires) were prepared in alcohol/water solution by reacting a Zn2+ precursor with an organic weak base, tetramethylammonium hydroxide (Me4NOH). The effect of the experimental parameters (temperature, base concentration, reaction time, and water content) on nucleation, growth, and the final morphology of the ZnO nanostructures was investigated. The low-temperature syntheses (75-150 degrees C) yielded aspect ratios of the 1-D ZnO nanostructures that depended on the water content. The individual ZnO nanorods and nanowires were determined to be perfect, single crystals with their c axes as the primary growth direction.     

Growth mechanism of penniform BaWO4 nanostructures in catanionic reverse micelles involving polymers

The formation of penniform BaWO4 nanostructures made of nanowires or nanobelts under the direction of a block copolymer in catanionic reverse micelles has been studied in detail. On the basis of the experimental results obtained from the BaWO4 crystallization in aqueous polymer solutions and careful transmission electron microscopy (TEM) observations of BaWO4 nanostructures formed in reverse micelles containing polymers, a detailed two-stage growth mechanism has been proposed for the formation of the penniform nanostructures in reverse micelles, which involves the polymer-controlled shaft formation (Stage 1) and the mixed surfactants-controlled barb growth (Stage 2). During Stage 1, poly(ethylene glycol)-block-poly(methacrylic acid) (PEG-b-PMAA) induced the formation of c-axis-oriented shuttle-like nanocrystals and the subsequent oriented attachment of these shuttle-like nanocrystals resulted in the formation of [100]-oriented shafts with many parallel [001]-oriented pricks. During Stage 2, [001]-oriented nanowires or nanobelts grew gradually from the pricks into barbs, leading to the formation of well-defined penniform BaWO4 nanostructures with the barb morphology essentially determined by the mixing ratio r of the anionic to cationic surfactants (i.e., nanowires were formed at r=1 while nanobelts were formed at r deviating from 1). The current understanding of the growth mechanism of penniform BaWO4 nanostructures in catanionic reverse micelles involving polymers may be potentially applied for designing a new synthesis system for the controlled synthesis of other hierarchical 1D nanostructures with desired architectures.     

Fabrication of ZnO nanorods in ionic liquids and their photoluminescent properties

A novel and simple approach is reported to fabricate uniform single-crystal ZnO nanorods in ionic liq-uids. The as-obtained ZnO nanorods have been characterized by XRD,TEM,HRTEM,SAED,XPS,EDXA,PL and UV-vis absorption spectra. The rod diameters of the nanostructures can be controlled by tuning the amount of sodium hydroxide in the synthesis. Photoluminescence results show that the nanos-tructural ZnO exhibits better optical properties than bulk ZnO does and interestingly,the smaller the rod diameters are,the better optical property 1D nanostructural ZnO exhibits. The possible growth mechanism of ZnO nanorods is also investigated.     

Fabrication of 3D rotor-like ZnO nanostructure from 1D ZnO nanorods and their morphology dependent photoluminescence property

A facile and eco-friendly sonochemical route to fabricate well-defined dentritic (rotor-like) ZnO nanostructures from 1D ZnO nanorods without alloying elements, templates and surfactants has been reported. Phase and structural analysis has been carried out by X-ray diffraction (XRD) and Fourier Transform Infra-Red (FTIR) spectroscopy, showed the formation of hexagonal wurtzite structure of ZnO. Scanning electron microscopic (SEM) study showed the formation of rotor-like ZnO nanostructure having a central core which is surrounded by side branches nanocones. Transmission electron microscopic (TEM) study showed that these nanocones grow along [0001] direction on the six {01–10} planes of central core ZnO nanorods. A plausible formation mechanism of rotor-like ZnO nanostructures was studied by SEM which indicates that the size and morphology of side branches can be controlled by adjusting the concentration of OH^? ions and time duration of growth. The photoluminescence (PL) spectrum of the synthesized rotor-like ZnO nanostructures exhibited a weak ultraviolet emission at 400 nm and a strong green emission at 532 nm recorded at room temperature. The influence of morphology on the origin of green emission was discussed in detail. The results suggested a positive relationship among polar plane, oxygen vacancy and green emission.     

Straight and thin ZnO nanorods: hectogram-scale synthesis at low temperature and cathodoluminescence

A novel seed-assisted chemical reaction at 95 degrees C has been employed to synthesize uniform, straight, thin, and single-crystalline ZnO nanorods on a hectogram scale. The molar ratio of ZnO seed and zinc source plays a critical role in the preparation of thin ZnO nanorods. At a low molar ratio of ZnO seed and zinc source, javelin-like ZnO nanorods consisting of thin ZnO nanorods with a diameter of 100 nm and thick ZnO nanorods with a diameter of 200 nm have been obtained. In contrast, straight ZnO nanorods with a diameter of about 20 nm have been prepared. Dispersants such as poly(vinyl alcohol) act spatial obstructors to control the length of ZnO nanorods. The morphology, structure, and optical property of the ZnO nanostructures prepared under different conditions have been characterized by transmission electron microscopy, field emission scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and cathodoluminescence. The formation mechanisms for the synthesized nanostructures with different morphologies have been phenomenologically presented.     

Factors Affecting Laser-Excited Photoluminescence from ZnO Nanostructures

The role of defects on laser-excited photoluminescence of various ZnO nanostructures has been investigated. The study shows that defects present in ZnO nanostructures, specially Zn-related defects play a crucial role in determining the laser-excited photoluminescence intensity (LEI). ZnO nanoparticles as well as nanorods (NR) annealed in oxygen atmosphere exhibit remarkable enhancement in LEI. A similar enhancement is also shown by Al-doped ZnO NR.     

Room temperature solution synthesis of monodispersed single-crystalline ZnO nanorods and derived hierarchical nanostructures

In this work, we report a room temperature wet-chemical approach to synthesize highly regulated, monodispersed ZnO nanorods and derived hierarchical nanostructures. In particular, ZnO has been prepared into single-crystalline conical or prismatic nanorods, and various hierarchical structures such as hexagonally branched, reversed umbrella-type, and cactus-like ZnO nanostructures comprising individual c-oriented nanorods. Depending on the synthetic conditions used, the diameter of nanorods can be controlled with a size down to 10-30 nm, while the aspect ratio can be controlled up to 50-100. Various preparative parameters, such as initial reactant concentrations, solvents, ligands, surfactants, precursor salts, and reaction time, have been systematically examined. Due to slow reactions at room temperature, excellent crystallinity and high morphological yield (100% in most cases) have been achieved via tuning the synthetic parameters. Our photoluminescence and UV measurements also confirm the attained crystal perfection and size uniformity.     

两种形貌GdPO_4纳米粒子的制备和光学性质研究

以Gd2O3、H3PO4为原料,聚乙二醇(PEG)为结构导向剂,通过改变沉淀剂NaOH的用量,制备了棒状、丝状的GdPO4纳米粒子,用X射线衍射仪(XRD)、X射线能量扩散光谱仪(EDS)、透射电子显微镜(TEM)、X射线光电子能谱仪(XPS)、富里叶变换红外光谱仪(FT-IR)对样品进行表征,研究了样品的激光拉曼散射光谱(Raman)、光致发光(PL)性质。结果表明,两种不同形貌的GdPO4纳米粒子具有不同的光学活性,PEG的浓度以及它和Gd3+、H+的配位作用对棒状GdPO4纳米粒子的形成有重要的影响。     

Templateless assembly of molecularly aligned conductive polymer nanowires: a new approach for oriented nanostructures

Although oriented carbon nanotubes, oriented nanowires of metals, semiconductors and oxides have attracted wide attention, there have been few reports on oriented polymer nanostructures such as nanowires. In this paper we report the assembly of large arrays of oriented nanowires containing molecularly aligned conducting polymers (polyaniline) without using a porous membrane template to support the polymer. The uniform oriented nanowires were prepared through controlled nucleation and growth during a stepwise electrochemical deposition process in which a large number of nuclei were first deposited on the substrate using a large current density. After the initial nucleation, the current density was reduced stepwise in order to grow the oriented nanowires from the nucleation sites created in the first step. The usefulness of these new polymer structures is demonstrated with a chemical sensor device for H(2)O(2), the detection of which is widely investigated for biosensors. Finally, we demonstrated that controlled nucleation and growth is a general approach and has potential for growing oriented nanostructures of other materials.     

Fast synthesis of ZnO nanostructures by laser-induced decomposition of zinc acetylacetonate

A CO2 laser (lambda = 10.6 microm) was used to heat a solution of water and alcohol saturated by Zn(AcAc)2 on a fused quartz substrate in open air. After only a few seconds of irradiation, various zinc oxide (ZnO) nanostructures including nanorods and nanowires are formed near the center of the irradiated zone, surrounded by a porous thin film of ZnO nanoparticles. The type of structures produced and their localization on the substrate can be varied by selecting adequate irradiation time and laser power ranges. The deposits have been analyzed using SEM, TEM, EDS, XRD, and Raman spectroscopy, revealing that the nanorods (aspect ratio ~6) and nanowires (aspect ratio ~94) are single-crystalline structures which grow along the c axis of wurtzite ZnO. The nanoparticles are also single-crystalline and have an average diameter of 16 nm. A qualitative model for nanostructure growth is proposed, based on previous studies of aqueous solution and hydrothermal processing.     

Customized morphologies of self-condensed multisegment polymer nanowires

The direct formation of multisegment nanowires consisting of polymer domains by ion beam irradiation is investigated. Cross-linking reactions in the ion tracks result in localized gelation, giving isolated nanowires on substrates. It is demonstrated that the morphology of the final nanostructure is customized by appropriate selection of the ion fluence, combination of polymers, and the solvent employed for development. Octopus-like nanostructures consisting of a tangled hydrophilic polymer core and splayed hydrophobic polymer segments are successfully produced as an example of the process. The present technique provides universal feasibility for the formation of nanostructures based on "any" polymer materials in which radiation induces cross-linking reactions.     

Microsphere organization of nanorods directed by PEG linear polymer

We demonstrate the sphere organization of ZnO, Bi2S3, MnO2, and La(OH)3 nanorods directed by PEG linear polymer. Our study shows that zinc, bismuth, manganese, or lanthanum species added to PEG solutions, in which PEG molecules are well dissolved in a coil state, convert the polymer coils to aggregate structures, which further aggregate into micrometer-sized M(n+)-PEG globules. The concentration of metallic species is higher in the globules than in bulk solutions. The surfaces of the globules act as soft templates for the initial nucleation and thereafter the growth of the nanorods. Finally, echinus-type assemblies of single-crystalline nanorods form by the metallic species hydrolyzing or reacting with deposition agents. This approach opens the possibility of using polymers as soft templates to control the organization of nano building units into designed structures.     

Room-temperature surface-erosion route to ZnO nanorod arrays and urchin-like assemblies

A solution surface-erosion route was successfully employed to produce one-dimensional (1D) ZnO nanostructures. ZnO nanorod arrays and three-dimensional urchin-like assemblies could be selectively obtained with different manipulations. In this process, zinc foil was introduced to an organic solution system and acted both as a reactant and substrate to support the 1D nanostructures obtained. This method, without any template, apparatus, surfactants, or additional heterogenous substrates, has greatly simplified the preparation of oriented 1D ZnO nanostructures. In particular, this simple route could be carried out at room temperature over a period as short as several minutes, thus it could be conveniently transferred to industrial applications. The possible formation mechanism, erosion process, and influence factors were also investigated.     

导电聚合物的纳米结构及其在生物医学领域的应用

由于表面效应、小尺寸效应和量子效应,使纳米结构的导电聚合物材料与传统聚合物材料相比,显示出更优越的性能。基于神经组织对电场和电刺激敏感性,使得导电聚合物纳米材料在生物医学应用方面很有前景。本文综述了纳米结构的导电聚合物的合成方法,及其在生物医学领域的应用。合成方法主要关注于硬模板法、软模板法和无模板自组装法,以及这些方法中导电聚合物纳米结构的形成机理。总结了具有纳米结构的导电聚合物,如纳米颗粒、纳米纤维和纳米管等作为神经电极涂层材料和生物传感器等方面的应用。     

A general precipitation strategy for large-scale synthesis of molybdate nanostructures

A general precipitation strategy has been developed for the large-scale synthesis of molybdate nanostructures, and a series of molybdate nanostructures such as Fe(2)(MoO(4))(3) nanoparticles, ZnMoO(4) nanoplates, MnMoO(4) nanorods and CoMoO(4) nanowires have been successfully prepared.     

Zinc oxide nanostructures: morphology derivation and evolution

Zinc oxide nanostructures of various types, including nanobelts, nanoplatelets, nanowires, and nanorods, have been synthesized via well-developed routes by many research groups. However, so far, the underlying mechanism for the morphology derivation and evolution of the nanostructures has not been elucidated in depth. In this article, we report the systematic investigation of the morphology evolution characteristics of ZnO nanostructures from dense rods to dense nanoplatelets, nanoplatelet flowers, dense nanobelt flowers, and nanowire flowers in an evaporation-physical transport-condensation approach. Through the use of crystal growth theory, the determining factors for the formation of different nanostructural morphologies were found to be gas-phase supersaturation and the surface energy of the growing surface planes. Other experimental parameters such as the temperature at the source and the substrate, the temperature difference and the distance between the source and the substrate, the heating rate of the furnace, the gas flow rate, the ceramic tube diameter, and the starting material are all correlated with supersaturation and impose an effect on the morphology evolution. This finding may have an important impact on the qualitative understanding of the morphology evolution of nanostructures and the achieving of desired nanostructures controllably.     

Enhanced ultraviolet emission from ZnS-coated ZnO nanowires fabricated by self-assembling method

A simple chemical route for ZnS-coated ZnO nanowires with preferential (002) orientation is reported. Sodium sulfide and zinc nitrate were employed to supply S and Zn atoms at 60 degrees C to form ZnS-coated ZnO nanowires structures. Electron diffraction measurement shows that the ZnO/ZnS core-shell nanostructure is single crystalline. Interesting features are found in the photoluminescence (PL) spectra of ZnS-coated ZnO nanostructures. After coating, the UV emission of nanorods is dramatically enhanced at the expense of the green emission. The core/shell structure with higher band gap shell material and reduced surface states should be responsible for this PL enhancement.     

ZnO/CuO hetero-hierarchical nanotrees array: hydrothermal preparation and self-cleaning properties

ZnO/CuO heterohierarchical nanotrees array has been prepared via a simple hydrothermal approach combined with thermal oxidation method on Cu substrates. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometer(XRD) are employed to characterize and analyze the as-synthesized samples. The results demonstrate that the secondary growth of ZnO nanorods enclose with CuO nanowires, leading to the formation of ZnO/CuO heterohierarchical nanotrees array. The hierarchical nanostructures have isotropic crystal symmetry and they have no 6-fold (or 4-fold or 2-fold) symmetry as general epitaxial growth. Enlightened by the similarity with microstructure of lotus, the wettability of ZnO/CuO heterohierarchical nanotrees array has been investigated. It is revealed that as-prepared ZnO/CuO nanotrees array after silanization present remarkable superhydrophobic performance, which is attributed to the trapped air and hierarchical roughness. Furthermore, their wettability could be manipulated by the morphologies of hierarchical ZnO nanorods. At the optimal condition, the greatest static angle of water droplet on the obtained heterohierarchical nanotrees array could reach almost 170°, and this substrate could be used as self-cleaning surface.     

Facile controlled synthesis of MnO2 nanostructures of novel shapes and their application in batteries

In this paper, MnO2 nanomaterials of different crystallographic types and crystal morphologies have been selectively synthesized via a facile hydrothermal route and electrochemically investigated as the cathode active materials of primary and rechargeable batteries. Beta-MnO2 nano/microstructures, including one-dimensional (1-D) nanowires, nanorods, and nanoneedles, as well as 2-D hexagramlike and dendritelike hierarchical forms, were obtained by simple hydrothermal decomposition of an Mn(NO3)2 solution under controlled reaction conditions. Alpha- and gamma-MnO2 nanowires and nanorods were also prepared on the basis of previous literature. The as-synthesized samples were characterized by instrumental analyses such as XRD, SEM, TEM, and HRTEM. Furthermore, the obtained 1-D alpha- and gamma-MnO2 nanostructures were found to exhibit favorable discharge performance in both primary alkaline Zn-MnO2 cells and rechargeable Li-MnO2 cells, showing their potential applications in high-energy batteries.     

Solvent‐Annealing‐Induced Nanowetting in Templates: Towards Tailored Polymer Nanostructures

We study the solvent‐annealing‐induced nanowetting in templates using porous anodic aluminum oxide membranes. The morphology of polystyrene and poly(methyl methacrylate) nanostructures can be controlled, depending on whether the swollen polymers are in the partial or complete wetting regimes, which are characterized by the spreading coefficient. When the swollen polymers are in the partial wetting regime, polymers wet the nanopores by capillary action, resulting in the formation of polymer nanorods. When the swollen polymers are in the complete wetting regime, polymers form wetting layers in the nanopores, resulting in the formation of polymer nanotubes. The solubility parameters of polymers and solvents are also used to predict the wetting behavior of swollen polymers in cylindrical geometry.