High-yield self-assembly of flower-like ZnO nanostructures

High-yield three-dimensional (3D) flower-like nanostructures self-assembled from 1 D ZnO nanorods and nanotubes are experimentally demonstrated. The Zn and O terminated crystal planes of ZnO nanorods results in positively and negatively charged top (001) and bottom (00-1) surfaces, respectively. The nanorods self-assembled into 3D nanostructures via the electrostatic interaction between the crystal planes with opposite charges. Moreover, on the basis of the different stability of polar and nonpolar planes in wurtzite-type ZnO, the nanorods based 3D nanostructures transformed into nanotubes based ones spontaneously. This provides a new approach to prepare multi-dimensional materials without the necessity to employ any external intervention.     

Hydrothermal controllable synthesis to convert ZnO hexagonal nanotubes to hexagonal nanorods and their photocatalytic application

Zinc oxide (ZnO) thick films were analyzed by high-resolution X-ray diffraction (HR-XRD), field emission scanning electron microscopy, and photoluminescence (PL) spectroscopy at room temperature. The films were grown on glass substrates using different molar concentrations of aqueous solution (0.02, 0.04, and 0.06 M) via a simple hydrothermal method. This method uses glass bottles with rubber caps as reactor vessels (100 mL) and, thus, is classified as a green chemistry technique. Hexahedral zinc nitrate (Zn (NO₃)₂·6H₂O), hexamethylenetetramine (C₆H₁₂N₄), and deionized water were used as starting materials and were reacted in the presence of heat. HR-XRD measurements confirmed that the diffraction peaks of the polycrystalline structure films can be assigned to the hexagonal-shaped wurtzite ZnO. In addition, the PL spectra show that the integrated intensity decreases with the increase in ZnO content. The SEM images also revealed the existence of hexagonal ZnO nanotubes in the 0.02 M sample, and these nanotubes are gradually converted into hexagonal nanorods with the increase in ZnO content. Moreover, the photocatalytic activity of both nanostructures was measured based on the degradation of methyl blue (MB) by using ultraviolet light (λ = 366 nm). Results showed that the ZnO nanotubes degraded MB more effectively than the nanorods.     

Controllable synthesis of ZnO with various morphologies by hydrothermal method

ZnO microstructures with various morphologies have been controllably synthesized by hydrothermal route using different precipitant and zinc source in liquid solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the ZnO2, Zn(OH)2 and ZnO structures to understand the role of precipitant and precursors in the growth of various morphologies. The nucleation and growth process can regulate by changing the precipitant. When H2O2 was used as precipitant, ZnO particles with a rather uniform particle size of -500 nm and a rather rough surface was obtained. While, ZnO synthesized in this polyvinyl pyrrolidone (PVP) solution has the same granular morphology with particle size of 300-1000 nm. In contrast, ZnO sunflower and polyhedron aggregates composed of several smaller polyhedron were formed, when ammonium hydroxide and NH4HCO3 was applied, respectively. Meanwhile, precursors play an important role in the determination of the morphology of ZnO. Sunflower and dumbbell like ZnO composed of nanosheets were obtained, when different centrifugal component of Zn(OH)2 suspension was applied as zinc source. In contrast, sunflower and dumbbell like ZnO composed of nanorods and ZnO rods were obtained, when different centrifugal components of ZnO2 suspension were used as zinc sources. The growth mechanism of ZnO nanostructures fabricated by the hydrothermal process using different zinc sources was tentatively investigated.     

Synthesis of zinc oxide nanotetrapods and nanorods by thermal evaporation without catalysis

ZnO nanotetrapods and nanorods have been synthesized by a simple thermal evaporation of Zn powder (300 mesh, 99.99% purity) under simultaneous flow of oxygen and argon gases in two-zone furnace in two different temperature regions. These ZnO nanostructures have hexagonal structure, which grow along the [001] direction in the form of nanotetrapods (diameter approximately 60-150 nm, length approximately 1-4 microm) and nanorods (diameter approximately 30-60 nm, length approximately 2-5 microm). The morphologies of these ZnO nanostructures have been investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been found that growth parameters like temperature, gas flow rate etc., control the diameter of the nanotetrapods and nanorods. These novel structures of ZnO nanorods and nanotetrapods may be attractive for optical and other nanodevices.     

Synthesis of neodymium hydroxide nanotubes and nanorods by soft chemical process

A facile soft chemical approach using cetyltrimethylammonium bromide (CTAB) as template is successfully designed for synthesis of neodymium hydroxide nanotubes. These nanotubes have an average outer diameter around 20 nm, inner diameter around 2 nm, and length ranging from 100 to 120 nm, high BET surface area of 495.71 m(2) g(-1). We also find that neodymium hydroxide nanorods would be obtained when CTAB absented in reaction system. The Nd(OH)3 nanorods might act as precursors that are converted into Nd2O3 nanorods through dehydration at 550 degrees C. The nanorods could exhibit upconversion emission characteristic under excitation of 591 nm at room temperature.     

Rapid growth of nanotubes and nanorods of würtzite ZnO through microwave-irradiation of a metalorganic complex of zinc and a surfactant in solution

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal würtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140–160 nm and a wall of thickness, 40–50 nm. The length of nanorods and nanotubes varies in the narrow range of 500–600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.     

两步法实现ZnO纳米结构的集成及光学性质研究

通过简单的两步热蒸发方法成功地实现了ZnO纳米管和纳米棒的集成.SEM结果表明,大量的纳米线以层层生长的机理从约200℃低温Si基片表面生长出来.EDS和XRD结果进一步表明第一步所制备的样品主要是由大量Zn和少量Zn的氧化物组成.第二步所制备样品的SEM和TME图像证实了在高温下以第一步所制备的样品作为第二步的基片,可实现纳米管和纳米棒的集成.TEM图像表明,纳米管的表面所生长的纳米棒是单晶的.通过改变工作气压,可调控纳米管表面纳米棒的尺寸和形貌,实现ZnO纳米结构可控生长.室温光致发光谱表明,样品的光学性质可通过可控的形貌来调制.     

Controllable synthesis of flower- and rod-like ZnO nanostructures by simply tuning the ratio of sodium hydroxide to zinc acetate

A controlled synthesis of flower-?and rod-like ZnO nanostructures in a hydrothermal phase has been realized in the absence of an additional template. The well-defined morphologies are obtained by simply tuning the ratio of sodium hydroxide to zinc acetate in a narrow range. The products are characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The growth mechanism is suggested to be that the supersaturation of the precursor Zn(OH)(4)(2-) results in various nucleation habits, which induce the ZnO nanostructures with different morphologies.     

Ultrathin ZnO nanostructures synthesized by thermal oxidation of hexagonal Zn micro/nanostructures

Ultrathin (<5 nm) ZnO nanobelts, as well as porous nanotubes/nanosheets were successfully synthesized via a very simple process: thermal oxidation of hexagonal Zn micro/nanostructures in a tube furnace in 50 sccm N2 flow. The ZnO nanobelt clusters were largely grown from the (0001) end surface of the Zn nanoprisms at 300 degrees C. The porous nanotubes and nanosheets were formed on the downstream substrate by 370-400 degrees C thermal oxidation of Zn films in low pressure. These structures are related to the anisotropic oxidation of Zn and differences of melting point between Zn and ZnO. We propose that the ultrathin nanobelts were formed in a vapor-liquid-solid process while the ultrathin nanotubes and nanosheets were formed via a vapor-solid-resublimation process. The structure of the nanostructures was characterized by transmission electron microscopy. The ultrathin mesoporous nanotubes and nanosheets have been found to possess rich surface defects. These structures may have potential applications in gas sensors, catalysts and hydrogen storage due to their large specific surface area.     

Growth parameter dependent structural and optical properties of ZnO nanostructures on Si substrate by a two-zone thermal CVD

We investigated the effect of growth parameters on the structural and optical properties of the ZnO nanostructures (NSs) grown on Au-coated Si substrate by a two-zone thermal chemical vapor deposition. The morphologies of ZnO NSs were controlled by various growth parameters, such as growth temperature, O2 flow rate, and working pressure, for different thicknesses of Au layer. The nanorod-like ZnO NSs were formed at 915 degrees C and the growth of two-dimensional structures, i.e., nanosheets, was enhanced with the increase of growth temperature up to 965 degrees C. It was found that the low working pressure contributed to improvement in vertical alignment and uniformity of ZnO NSs. The Zn/O atomic % ratio, which plays a key role in the growth mechanism of ZnO NSs, was changed by the growth parameters. The Zn/O atomic % ratio was increased with increasing the growth temperature, while it was decreased with increasing the working pressure. Under proper O2 flow rate, the ZnO nanorods with good crystallinity were fabricated with a Zn/O atomic % ratio of -0.9. For various growth parameters, the photoluminescence emission was slightly shifted with the ultraviolet emission related to the near band edge transition.     

Growth and photocatalytic properties of one-dimensional ZnO nanostructures prepared by thermal evaporation

Aligned ZnO nanorods and nanotubes were grown on the silicon substrates by thermal evaporation of high pure zinc powders without any other metal catalyst. The morphology evolution of ZnO nanostructures with prolonged growth time suggested that the growth of the ZnO nanorods and nanotubes follows the vapor–liquid–solid mechanism. ZnO nanoneedle and nanoparticle films were also synthesized by the same way, and their photocatalytic performances were tested for the degradation of organic dye methylene blue. The ZnO nanoneedle films exhibited very high photocatalytic activities. The decomposition kinetics of the organic pollutant was discussed. Moreover, it is found that the ZnO nanoneedle films showed very stable photocatalytic activity.     

表面活性剂辅助水热合成氧化锌纳米棒

以碱式碳酸锌为前驱体, 十六烷基三甲基溴化铵为表面活性剂, 在乙醇-水体系中水热反应制备了直径在10nm以下的氧化锌纳米棒. 用XRD、TEM、SAED等分析手段对制备的粉体进行了表征, 并对粉体的室温光致发光性能进行了测试. 结果表明, 合成的氧化锌纳米棒结晶良好, 沿[001]方向生长, 具有良好的近紫外发光性能. 同时对氧化锌纳米棒的生长机制进行了探讨.     

Photo-initiated growth of zinc oxide (ZnO) nanorods

A photo-initiated process via femtosecond pulse-induced heterogeneous nucleation in zinc ammine complex (Zn(NH₃)₄²⁺)-based aqueous solution without catalyst and surfactant, followed by hydrothermal treatments for crystal growth into zinc oxide (ZnO) nanorods, was investigated. Flat-top hexagonal ZnO nanorods with smooth planes of diameter ≥ 100 nm and length ≤ 1 μm were grown with laser irradiation, compared to porous rod-like structures without irradiation. The flat-top planes indicate slow growth rate, due to the intermediate step of Zn(NH₃)₄²⁺ decomposition to Zn(OH)₄²⁻, before dehydration to ZnO. Prolonged hydrothermal treatment produced nanotubes and lateral splits due to OH⁻ erosion of the crystal faces. XRD analysis showed a hexagonal crystal structure while photoluminescence study indicated a peak at about 380 nm.     

表面活性剂对纳米氧化锌形貌和发光性能的影响

以二水合乙酸锌和氢氧化钠为原料,分别以表面活性剂十六烷基三甲基溴化铵(CTAB)和聚乙烯吡咯烷酮(PVP)为结构导向剂,采用简单的水热法制备了不同形貌的纳米氧化锌。研究了两种表面活性剂对纳米氧化锌形貌和光致发光性能的影响,并探讨了表面活性剂的作用机理。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和室温光致发光光谱(PL)等测试方法对样品的结构、形貌和发光性能进行了表征。结果表明:添加了表面活性剂后,样品形貌和尺寸都更加均匀,紫外发射峰强度相对增加。     

Fabrication of single-crystal ZnO nanorods and ZnS nanotubes through a simple ultrasonic chemical solution method

A simple and rapid method has been developed for the preparation of rod-like ZnO nanocrystals via ultrasonic irradiation. The as-synthesized ZnO nanocrystals were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods had an average diameter of 15-70 nm that varied from the ultrasonic operation mode. The results showed that Zn powder played an important role in the synthesis of ZnO nanorods. Through adding a sulfur source in the reaction system, ZnO/ZnS nanocables and ZnS nanotubes could be obtained with continuous ultrasonic irradiation. The formation mechanism of ZnS nanotubes could be attributed to the Kirkendall effect.     

一维氧化锌的水热合成及其气敏性能的研究

Zn(NO₃)₂为原料,CTAB为形貌控制剂, 采用水热合成技术制备了一维氧化锌粉体. 采用X射线衍射(XRD)、透射电镜(TEM)、扫描电镜(SEM)等测试技术对产物的相组成和微观形态进行了表征和分析, 结果表明一维氧化锌属于六方晶系, 分散性好, 纯度高, 直径～200nm, 长度～5μm. 用该粉体制成烧结型旁热式气敏元件, 测试其气敏性能. 结果表明, 在170℃左右对10ppm的三甲胺、甲醇等还原性气体有很好的响应. 文中对一维材料的气敏机理也进行了讨论.     

Optical and bio-sensing characteristics of ZnO nanotubes grown by hydrothermal method

ZnO nanostructures were fabricated on copper substrates by hydrothermal method at an optimized growth temperature of -95 degrees C. Structural properties were investigated by field emission scanning electron and transmission electron microscopy. Distinct morphologies were found to be formed at different growth times. The formation of nanotubes mainly involved the initial nucleation followed by the growth of nanorods at 95 degrees C, and then with the increase of dissolution time at room temperature, the preferential chemical dissolution of the metastable Zn-rich [0001] polar surfaces resulted in removing the atoms from the surfaces, thus leading to the thinning of the wall of the nanostructures. Completely hollow ZnO nanotubes could be obtained at a high dissolution time. The room temperature photoluminescence and optical absorption properties of ZnO nanotubes have been studied as a function of dissolution time. The efficacy of ZnO nanotubes for glucose sensing applications has been studied.     

Solvothermal preparation and gas sensing properties of ZnO whiskers

ZnO whiskers were prepared by a solvothermal process with Zn(OH)4(2-), cetyltrimethylammonium bromide (CTAB), n-amyl alcohol and n-hexane at 140 degrees C. The influence of preparation condition on the morphology of the resultant sample was investigated through change zinc salts, co-surfactants, surfactants, reaction temperature, and reaction time. Experimental results revealed that the morphology of as-obtained ZnO was affected strongly by the zinc salts and surfactants. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction (ED). Results showed that ZnO whiskers had the diameters of 100-500 nm, the lengths of several microm, and grown along orientation of [0001]. The gas sensitivities of the as-prepared ZnO whiskers were detected. The results revealed that the ZnO whiskers had excellent potential application for gas sensor.     

Effect of Fe doping concentration on optical and magnetic properties of ZnO nanorods

Herein, a facile low temperature, aqueous solution-based chemical method has been demonstrated for large-scale fabrication of Fe doped ZnO nanorods (ZnO:Fe) with a series percentage of Fe dopant. Interestingly, the SEM results reveal a uniform well dispersed synthesis of ZnO:Fe nanorods throughout the substrate. The x-ray diffraction result suggests that Fe substitutes Zn in the ZnO matrix and rules out the formation of any secondary phase. Selected area electron diffraction investigation verifies the single crystal, hexagonal wurtzite structure of the ZnO:Fe nanorods. Energy dispersive spectroscopy data confirm Fe doping of the ZnO nanorods with a concentration ranging from 0.9 to 2.2 at.%. The photoluminescence spectrum reveals a continuous suppression of defect related broad-band emission (I(D)/I(UV) = 1-0.11) by increasing the concentration of the dopant ion, which produces the quenching of surface defects present in the nanostructures. An enhancement in ferromagnetism (M = 0.15 × 10?2-0.24 × 10?1 emu g?1 at 2000 Oe) is found in doped ZnO nanorods.     

Sol-gel assisted ZnO nanorod array template to synthesize TiO(2) nanotube arrays

A TiO(2) nanotube array with a large surface area is fabricated on a glass substrate using a ZnO nanorod array and sol-gel process, and the structural characteristics of the TiO(2) nanotube array are investigated. The well-aligned ZnO nanorod array, which is deposited on ZnO seed layer coated glass substrates by the wet-chemical route, is used as a template to synthesize TiO(2)/ZnO composite nanostructures through the sol-gel process. Then, by selectively removing the ZnO template, a TiO(2) nanotube with contours of the ZnO nanorods is fabricated on the ZnO seed layer coated glass. The resultant TiO(2) nanotubes are 1.5?μm long and 100-120?nm in inner diameter, with a wall thickness of ～10?nm. In addition, by adjusting the experimental parameters, such as the dip-coating cycle number or heating rate, porous TiO(2) thick films can also be obtained.