Low-valent vanadium oxide nanostructures with controlled crystal structures and morphologies

Low-valent vanadium oxide nanostructures have been synthesized in large quantities using commercial V2O5 powder as the precursor by a facile reduction method. The crystal structures and morphologies of vanadium oxide nanostructures can be adjusted by altering the concentrations and types of reductants. VO2(B) nanostructures are fabricated using oxalic acid as the reductant. VO2(B) nanobelts with widths of 80-150 nm, thicknesses of 20-30 nm, and lengths up to several micrometers can evolve to olive-like nanostructures composed of nanosheets with thicknesses of several nanometers and lateral dimensions of several micrometers as the concentration of oxalic acid increases. H2V3O8 nanobelts with widths of 200-300 nm, thicknesses of 10-20 nm, and lengths up to several 10s of micrometers are obtained under the reduction of V2O5 powder with ethanol. The belt-shaped morphologies of H2V3O8 are not affected by the concentration of ethanol.     

Bulk synthesis of single-crystalline magnesium oxide nanotubes

Crystalline tubular magnesium oxide nanostructures were obtained through carbon-thermal evaporation of a MgO powder. Gallium oxide was added into the mixture of MgO and carbon. The reduction of gallium oxide by carbon resulted in gallium vapor at high temperatures. Condensed gallium droplets catalyzed the anisotropic growth of tubular MgO nanostructures in situ. The products were characterized by X-ray powder diffraction technique, scanning electron microscopy, and high-resolution microscopy. All the analyses indicated that the prepared tubular MgO nanostructures are, in fact, single crystals.     

多元醇法形貌可控制备氧化亚铜微纳米颗粒

以硝酸铜、乙酸铜、乙酰丙酮铜为原料,采用多元醇还原法合成制备了氧化亚铜立方体、微球、空心球、核壳结构等微纳米颗粒。 利用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)和紫外可见吸收光谱(UV-Vis)等测试手段对样品的物相、形貌、元素组分及吸光性能进行了表征。 同时考察了铜源、反应时间、和多元醇类型对氧化亚铜微纳米材料形貌的影响,对产物形成机理进行了初步的探讨。 对产物形成机理进行了初步的探讨。 采用简单低廉的多元醇合成法,可以控制合成不同相貌的氧化亚铜微纳米结构。 对制备形貌可控的氧化物具有一定的指导意义。     

P123-assisted hydrothermal synthesis and characterization of rectangular parallelepiped and hexagonal prism single-crystalline mgo with three-dimensional wormholelike mesopores

By adopting the strategy of dissolution-recrystallization under hydrothermal conditions (at 240 degrees C for 72 h) in the presence of a triblock copolymer (Pluronic P123), we fabricated nano- and microparticles of single-crystalline MgO of rectangular parallelepiped and hexagonal prism morphologies. The MgO crystallites display three-dimensional wormholelike mesopores and have a surface area as high as 298 m(2)/g even after calcination at 550 degrees C for 3 h.     

Facile Non‐enzymatic Lactic Acid Sensor Based on Cobalt Oxide Nanostructures

In this study, we have investigated the effect of counter anions on the morphology of cobalt oxide nanostructures. The nanostructures of cobalt oxide are prepared by a low temperature aqueous chemical growth method. The morphology of cobalt oxide nanostructure material was investigated by scanning electron microscopy and the crystalline structure was studied by powder X‐ray diffraction technique. The cobalt oxide nanostructures exhibit the nanowire, lump, bundle of the nanowire and flower‐like morphologies. The XRD study has revealed a cubic phase of cobalt oxide nanostructures. The electro‐catalytic properties of cobalt oxide nanostructures were explored through cyclic voltammetry and amperometric techniques by sensing of lactic acid in the alkaline media. The cobalt oxide nanostructures prepared from cobalt nitrate have shown a well‐resolved redox peak. The proposed mechanism for the non‐enzymatic lactic acid sensor is elucidated by considering the morphology and cyclic voltammetry response. The limit of detection for the sensor was found to be 0.006 mM and it exhibits a linear range from 0.05–3 mM of lactic acid as shown by cyclic voltammetry. The amperometric response has shown the excellent current‐concentration response and the linear range of sensor was found to be 0.1 mM to 5.5 mM. The lactic acid sensor is stable, selective and can be used for practical applications. This study provides an excellent alternative analytical tool for the determination of lactic acid.     

Systematic Synthesis of ZnO Nanostructures

In this study, we report a simple solution‐phase method to prepare ZnO nanostructures with controllable morphologies. By using oleylamine (OAm) and dodecanol (DDL) as solvents, zinc oxide nanocrystals with tunable sizes and diverse shapes (hexagonal pyramids, bulletlike, and pencil‐like shapes) have been obtained under mild conditions. At the same time, the introduction of presynthesized gold nanocrystals can also lead to the hybrid nanostructures of gold–zinc oxide hexagonal nanopyramids. In addition, the possible formation mechanism of the as‐prepared ZnO nanostructures has been investigated. Notably, the unique optical properties of the ZnO nanostructures with different sizes and shapes have also been discussed. We hope that this strategy will be a general and effective method for fabricating other metal oxide nanocrystals.     

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.     

The effect of solvent on the morphology of ZnO nanostructure assembly by dielectrophoresis and its device applications

Different zinc oxide nanostructured morphologies were grown on photolithographically patterned silicon/silicon dioxide substrates by dielectrophoresis technique using different solvents, such as water and ethanol, obtaining rod-like and net-like nanostructures, respectively. The formation of continuous nanostructures was confirmed by scanning electron microscopic, atomic force microscopic images, and electrical characterizations. The rod-like zinc oxide nanostructures were observed in the 10 μm gap between the fingers in the pattern, whereas net-like nanostructures were formed independently of microgap. A qualitative study about the mechanism for the assembly of zinc oxide continuous nanostructures was presented. Devices were electrically characterized, at room temperature, in controlled environment to measure the conductance behavior in ultraviolet and humidity environment. Devices based on zinc oxide nanostructures grown in ethanol medium show better responses under both ultraviolet and humidity, because of the net-like structure with high surface-to-volume ratio.     

Oriented attachment-based assembly of dendritic silver nanostructures at room temperature

How particles aggregate into an interesting dendritic structure has been the object of research for many years because of its importance in understanding physical processes involved and in designing novel materials. In this work, we for the first time describe an oriented attachment-based assembly mechanism for formation of different types of dendritic silver nanostructures at room temperature. It is found that the concentration of both AgNO(3) and p-aminoazobenzene (PA) molecules has a significant effect on the formation and growth of these novel nanostructures. Characterization by transmission electron microscopy (TEM) clearly shows that the dendritic silver nanostructures can be obtained through the preferential oriented growth along a crystallographically special direction. Interestingly, we observe that the oriented attachment at room temperature can also take place between relatively large single-crystalline silver particles with a diameter range from 20 to 60 nm, which may provide a new possibility for the design of novel metal nanostructures by using large metal nanoparticles as building blocks at room temperature. Moreover, a surface-enhanced Raman scattering (SERS) technique is used to investigate the role of PA molecules during the growth of the dendritic silver nanostructures.     

Synthesis and characterization of ultrathin WO3 nanodisks utilizing long-chain poly(ethylene glycol)

Metal oxide nanostructures hold great potential for photovoltaic (PV), photoelectrochemical (PEC), and photocatalytic applications. Whereas thin films of various materials of both nanoparticle and nanorod morphologies have been widely investigated, there have been few inquiries into nanodisk structures. Here, we report the synthesis of ultrathin WO3 nanodisks using a wet chemical route with poly(ethylene glycol) (PEG) as a surface modulator. The reported nanodisk structure is based on the interaction of the nonionic 10000 g/mol PEG molecules with tungsten oxoanion precursors. The WO3 nanostructures formed are dominated by very thin disks with dimensions on the nanometer to micrometer scale. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal the structures to have dimensions on the order of 350-1000 nm in length, 200-750 nm in width, and 7-18 nm in thickness and possessing textured single-crystalline features. A number of analytical techniques were used to characterize the WO3 nanodisks, including selected-area electron diffraction (SAED), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Raman scattering spectroscopy, UV-visible spectrophotometry, and cyclic voltammetry (CV). The growth of the WO3 nanodisks was inhibited in the [010] crystal direction, leading to ultrathin morphologies in the monoclinic crystal phase. The large flat surface area and high aspect ratio of the WO3 nanodisks are potentially useful in PEC cells for hydrogen production via direct water splitting, as has been demonstrated in a preliminary experiment with external bias.     

Low-temperature polymer-assisted synthesis of shape-tunable zinc oxide nanostructures dispersible in both aqueous and non-aqueous media

We report the shape-controlled synthesis of zinc oxide (ZnO) nanostructures by a poly(vinyl methyl ether) (PVME)-assisted alkaline hydrolysis of zinc acetate at low temperature (20 °C). In this method, ZnO nanostructures of various morphologies including dumbbells, lances and triangles have been successfully prepared via a simple variation of different reaction parameters such as polymer concentration, pH of the reaction mixture and precursor concentration. However, without PVME, ZnO of such structurally uniform morphologies were not formed; rather ZnO of a mixture of defined and undefined morphologies were obtained indicating PVME-assisted the growth of such regular shaped ZnO nanostructures. HRTEM analysis of lance- and triangle-shaped samples as well as SAED patterns of all kinds of samples (dumbbell, lance and triangle) revealed that the ZnO nanostrcutures are single crystalline in nature and might form through oriented growth. XRD analysis also revealed the formation of well crystalline ZnO with a hexagonal structure. FTIR spectroscopy and TGA analysis confirmed the adsorption of PVME on the surface of ZnO nanostructures. Being a solvent adaptable polymer, the adsorbed PVME makes these shaped ZnO nanostructures highly dispersible in both polar and non-polar organic solvents including water. The extent of dispersibility in different solvents was studied by spectroscopic and microscopic techniques. Such solvent adoptability of PVME-coated ZnO nanostructures increases its ease of applications in device fabrication as well as in biological systems.     

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.     

Cu_2O纳米阵列的铜阳极氧化法制备及其光催化杀菌性能研究

本文通过阳极氧化法直接在铜片上生长出纳米氧化亚铜阵列,所得到的样品通过扫描电子显微镜(SEM),紫外可见漫反射(UV-Vis diffuser reflectance),X-射线光电子能谱(XPS)等方法进行了表征,并研究了不同形貌氧化亚铜的杀菌效果.实验结果表明:反应过程中在阳极液中加入一定量的CTAB,有助于氧化亚铜的定向生长.通过控制反应条件(如电流密度,温度,和反应时间),可以得到不同形貌的氧化亚铜.随着电流密度的增大,氧化亚铜的形貌从网状,片状到棒状进行转化.所得到氧化亚铜的禁带宽度为1.95 eV.用所得样品进行杀菌实验,1 h内棒状氧化亚铜的杀菌率达到90.85%,而其它形貌的氧化亚铜杀菌率只有50%左右,与空铜片的杀菌率30%相比,所制得氧化亚铜具有较好的杀菌效果.     

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.     

Morphology-controlled synthesis of ZnO nanostructures by a simple round-to-round metal vapor deposition route

One-dimensional ZnO nanostructures with different morphologies have been successfully synthesized through a simple round-to-round metal vapor deposition route at 550 degrees C with a zinc powder covered indium film as the source material. The structures and morphologies of the products were characterized in detail by using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that the morphology of the products can be easily tuned from one experimental round to another. Possible growth mechanisms for the formation of one-dimensional ZnO nanostructures with different morphologies are discussed. Photoluminescence studies show that there are sharp UV emission and broad defect-related green emissions for the products obtained in all experimental rounds. Relative intensity of the UV emission to defect-related emissions gradually increased from one experimental round to another.     

Control of ZnO morphologies on carbon nanotube electrodes and electrocatalytic characteristics toward hydrazine

We controlled the morphologies of zinc oxide (ZnO) nanostructures on single-walled carbon nanotube electrodes by an electrochemical deposition method and investigated the dependence of the electrocatalytic characteristics toward hydrazine on the different morphologies. ZnO nanorods provided high electrocatalytic activity with unique electrochemical behaviours, associated with the H(+) ion generated by the electro-oxidation of hydrazine.     

Synthesis of Copper Oxide Hierarchical Nanostructures

The copper oxide (CuO) hierarchical nanostructures were synthesized by a simple hydrothermal reaction, using copper(II) acetylacetonate and NaOH as the reactants. The morphologies of CuO nanostructures are strongly influenced by the dosage of copper(II) acetylacetonate, alkali concentration and reaction temperature. The possible formation process was also discussed on the basis of time‐dependent experiments. This simple solution‐phase method may be useful for morphological synthesis of other oxides nanocrystals.     

金属氧化物纳米材料的电化学合成与形貌调控研究进展

金属氧化物纳米材料因其丰富的形貌、独特的性能、广泛的应用成为材料合成领域研究的热点.调控金属氧化物纳米材料的形貌对于调变其性能、拓展其应用空间具有重要意义.电化学方法由于操作简单易控、方法灵活多变,因此成为调控金属氧化物形貌的常用方法.本文综述了近年来我们在金属氧化物纳米材料的电化学合成与形貌调控方面已取得的研究结果;总结了不同金属氧化物在电化学过程中晶体生长机制和形貌调控的规律,为实现功能材料的定向合成奠定了基础.     

Hydrothermal synthesis of carbon nanotube/cobalt oxide core-shell one-dimensional nanocomposite and application as an anode material for lithium-ion batteries

Carbon nanotube/cobalt oxide core-shell one-dimensional nanostructures were prepared via a hydrothermal synthesis method, in which nanosize cobalt oxide crystals were homogeneously coated on the surface of carbon nanotubes. The morphologies and crystal structures of the as-prepared core-shell nanocomposites were analysed by X-ray diffraction, field emission gun scanning electron microscopy, and transmission electron microscopy. When applied as anodes in lithium-ion cells, carbon nanotube/cobalt oxide core-shell nanostructures exhibited an initial lithium storage capacity of 1250 mAh/g and a stable capacity of 530 mAh/g over 100 cycles. The good electrochemical performance could be attributed to the nanocrystalline cobalt oxide and the unique core-shell one-dimensional nanostructures.     

Fabrication and optical property of silicon oxide layer coated semiconductor gallium nitride nanowires

Quasi one-dimensional GaN-SiO(2) nanostructures, with a silicon oxide layer coated on semiconductor GaN nanowires, were successfully synthesized through as-synthesized SiO(2) nanoparticles-assisted reaction. The experimental results indicate that the nanostructure consists of single-crystalline wurtzite GaN nanowire core, an amorphous SiO(2) outer shell separated in the radial direction. These quasi one-dimensional nanowires have the diameters of a few tens of nanometers and lengths up to several hundreds of micrometers. The photoluminescence spectrum of the GaN-SiO(2) nanostructures consists of one broad blue-light emission peak at 480 nm and another weak UV emission peak at 345 nm. The novel method, which may results in high yield and high reproducibility, is demonstrated to be a unique technique for producing nanostructures with controlled morphology.