Shape-controllable Synthesis of Ultrafine ZnO Powders of Different Morphologies

By employing zinc acetate and sodium hydroxide as raw materials, ultrafine ZnO powders with different morphologies were successfully synthesized through hydrothermal method. The influences of the reaction temperature, the OH-/Zn2+ mol ratio and the reaction time on the morphologies of the ZnO powders were discussed. The reaction conditions were obtained, under which the ZnO of flower-like particles, micro-rods and flake particles was synthesized, respectively. The crystal structures and morphologies of those ZnO particles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ZnO with flower-like structures was composed of lots of micro-rods with hexagon morphology. The XRD patterns indicated that the ZnO powders were hexagonal wurtzite structures with high purity. Finally, the growth mechanism of the ZnO particles was discussed.     

Facile Synthesis of SnO2 Nanotube Arrays by Using ZnO Nanorod Arrays as Sacrificial Templates

SnO2 nanotube arrays have been synthesized by means of a simple and low-cost method. The ZnO nanorod arrays prepared by aqueous chemical growth method were used as templates. By liquid phase deposition, SnO2 nanotubes were obtained with proper deposition time. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were used to characterize the morphologies and structures of the products, and the formation mechanism was discussed according to the experimental results.     

Microwave Synthesis of Cuprous Oxide Micro-/Nanocrystals with Different Morphologies and Photocatalytic Activities

Cuprous oxide micro-/nanocrystals were synthesized by using a simple liquid phase reduction process under microwave irradiation.Copper sulfate was used as the starting materials and macromolecule surfactants served as the templates.The morphologies phase and optical properties of them are characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM) and ultraviolet-visible diffuse reflection absorptive spectra (UV-vis/DRS),respectively.The crystals had four different shapes,namely spheres,strips,octahedrons,and dandelions.The photocatalytic behavior of the cuprous oxide particles were investigated by monitoring the degradation of rhodamine B.In spite of the different morphologies,all of the cuprous oxide micro-/nanocrystals exhibited photocatalytic activities under visible light irradiation in the following order:dandelions,strips,spheres,and octahedral crystals.The photocatalytic degradation rates of rhodamine B are 56.37%,55.68%,51.83% and 46.16%,respectively.The morphology affects significantly the photocatalytic performance.     

Catalytic Graphitization of Phenolic Resin

The catalytic graphitization of thermal plastic phenolic-formaldehyde resin with the aid of ferric nitrate(FN) was studied in detail.The morphologies and structural features of the products including onion-like carbon nanoparticles and bamboo-shaped carbon nanotubes were investigated by transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM),X-ray diffraction and Raman spectroscopy measurements.It was found that with the changes of loading content of FN and residence time at 1000 ℃,the products exhibited various morphologies.The TEM images showed that bamboo-shaped carbon nanotube consisted of tens of bamboo sticks and onion-like carbon nanoparticle was made up of quasi-spherically concentrically closed carbon nanocages.     

Characterization of Ga-doped ZnO Nanorods Synthesized via Microemulsion Method

Gallium-doped ZnO (GZO) nanorods were synthesized by microemulsion method with different types of surfactants. The phase and morphology of the above nanorods were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). SEM observations show that the ZnO nanorods have diameters around 70-200 nm and lengths up to several micrometers. The room temperature photoluminescence (PL) spectrum of GZO nanorods exhibited a sharp and strong ultraviolet bandgap at 383 nm and a relatively weaker emission associated with the defect level. Resistivity of GZO nanorods synthesized with sodium lauryl sulfate (SLS) and sodium benzene sulfonate (SBS) surfactants showed 2.84Ωm and 14.2Ωm, respectively.     

Synthesis of Al-doped ZnO Nanorods via Microemulsion Method and Their Application as a CO Gas Sensor

Aluminum doped ZnO(AZO) nanorods were synthesized by microemulsion method with different types of surfactants.The phase and the morphology of the above nanorods were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD).SEM observations showed that the ZnO nanorods had diameters around about 50—200 nm and lengths up to several micrometers.The CO gas sensing properties of the AZO nanorods were tested at operating temperatures of 200,300,350 and 400 ℃.It was found that AZO nanorods based sensor exhibited the highest sensitivity to CO at 350℃.     

A Simple Method to Synthesize Multi-branched Carbon Fibers Using Cupric Chloride Aqueous Solution as Catalyst Precursor

Carbon fibers with multi-branched structures were synthesized by chemical vapor deposition method using cupric chloride as catalyst precursor and acetylene as carbon source at different reaction temperatures. Effects of water vapor and reaction temperature on the growth mode of carbon fibers were investigated. Experimental results demonstrate that initial reaction conditions and temperature are key factors for the formation of different carbon materials. Carbon fibers with typical multi-branched structures can be obtained at 450 ℃ when cupric chloride solution was used as catalyst precursor. X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy are used to characterize carbon materials, and the growth mechanisms of multi-branched carbon fibers were discussed.     

Evaluation of Pitting Behavior on Solution Treated Duplex Stainless Steel UNS S31803

The pitting corrosion resistance of duplex stainless steels UNS S31803 annealed at different temperatures ranging from 1050 ℃ to 1200 ℃ for 24 h has been investigated by means of potentiostatic critical pitting temperature(CPT).The microstructural evolution and pit morphologies of the specimens were studied through optical microscopy and scanning electron microscopy.The potentiostatic CPT measurements show that the CPT was elevated with the annealing temperature increased from 1050 ℃ to 1150 ℃ and decreased as the temperature further increased to 1200 ℃.The specimens annealed at 1150 ℃ exhibited the highest CPTand the best pitting corrosion resistance.The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases.The results were explained by the variation of pitting resistance equivalent number(PREN) of ferrite and austenite phases as the annealing temperature was varied.     

Effects of Annealing Temperature on Cu-Doped ZnO Nanosheets

The synthesis of Cu-doped ZnO nanosheets at room temperature was reported in our previous paper. The effects of annealing temperature on Cu-doped ZnO nanosheets were studied in this paper. Cu-doped ZnO nanosheets were annealed at 200-500℃ in air. The annealed specimens were characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The results show that Cu concentration in Cu-doped ZnO nanosheets reduced with increasing annealing temperature. When annealing temperature was lower than Zn melting point （410℃）, the morphologies of the Cu-doped ZnO nanosheets remained nearly the same as that before annealing. However, when the annealing temperature was over Zn melting point, Cu-doped ZnO nanosheets changed to nanowires, wormlike nanosheets or did not change. The change of Cu concentration in Cu-doped ZnO nanosheets is explained by oxidation thermodynamics. A physical model is suggested to explain the morphology changes of Cu-doped ZnO nanosheets, based on the existence of Cu-rich layer beneath Cu-doped ZnO nanosheets.     

Growth of Variable Aspect Ratio ZnO Nanorods by Solochemical Processing

In this work,variable aspect ratio(length divided by diameter) zinc oxide nanorods were synthesized through a simple solochemical method by reacting a Zn~(2+) precursor with sodium hydroxide at low reaction temperatures.The analysis of the X-ray diffraction data indicated that the samples had hexagonal wurtzite structure and nanometric size crystallites.The transmission electron microscopy(TEM) images of the products prepared at60 and 80 ℃ exhibited rod-like architecture,showing that the reaction temperature did not affect the ZnO morphology.The average aspect ratio of the ZnO nanorods decreased from 3.4 to 2.4 when the reaction temperature was raised from 60 to 80 ℃.The samples presented a blue shift in the excitonic absorption compared to ZnO bulk that increased alongside with reaction temperature.In addition,this research investigated the results obtained by varying the concentration of zinc chloride solution.At the same temperature,it could be verified that when the zinc concentration was increased,the diameter of the ZnO nanorods also slightly increased,and much shorter nanorods were achieved,especially in the reactions performed at 50 and 70 ℃.Finally,the growth mechanism of the ZnO nanostructures was proposed based on the results obtained by changing the zinc precursor concentration and reaction temperature.     

Morphological control of flower-like ZnO nanostructures

Flower-like ZnO nanostructures composed of different building blocks, such as hexagonal pyramids, hexagonal prisms, and cones, have been synthesized on a large scale by a simple hydrothermal method in the absence of surfactants or organic solvents. The effects of the concentration of NaOH, reaction temperature, and reaction time on the morphologies of the resulting products have been investigated. The morphologies and the crystal structures of flower-like ZnO nanostructures were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM).     

ZnO纳米材料制备及其场发射性能的研究

采用水热法制备形貌和尺寸各异的纳米ZnO材料。用X射线衍射分析仪(XRD)和扫描电子显微镜(SEM)测试产物结构和表面形貌,分析影响纳米ZnO材料生长的因素,探讨纳米ZnO的生长机理。研究了各种形貌ZnO阵列的场致发射特性。实验结果表明,在各种ZnO纳米结构中,纳米管的场致发射性能最好,其最大电流密度可达到0.2mA/cm2,开启场强2.5V/μm,为寻求良好场发射性能的ZnO纳米材料提供了一个可行的途径。     

Synthesis of different architectures like stars, multipods, ellipsoids and spikes of zinc oxide by surfactantless precipitation

Zinc oxide with different morphologies like stars, multipods, ellipsoids and spikes was synthesized using zinc nitrate and sodium hydroxide in the absence of surfactants. Seed mediation was found to be essential for the formation of ZnO nanospikes. Synthesized ZnO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), UV-visible diffuse reflectance spectroscopy (UV-vis-DRS) and energy dispersive analysis by X-rays (EDAX) techniques. The predominant c-axis growth of hexagonal lattice was observed in ZnO anisotropic particles. TEM analysis revealed the formation of two types of ZnO ellipsoid particles. Concentration of the reactants was found to have a role in controlling the morphology of the resulting ZnO. Mechanism of formation of varying morphologies of ZnO particles has been proposed.     

Morphological syntheses of ZnO nanostructures under microwave irradiation

ZnO nanostructures with flower-, rod-, and flake-like morphologies have been controllably synthesized using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single-source precursor through a facile and fast microwave-assisted method. The morphologies of ZnO nanostructures can be systematically adjusted by using various surfactants. The ZnO products are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. The results show that all ZnO nanostructures are of single-crystalline nature with hexagonal wurtzite structure. The possible formation mechanism for these ZnO nanostructures is proposed and their photoluminescence properties are also investigated.     

Microwave synthesis and characterization of ZnO with various morphologies

ZnO micro- and nanostructures with a variety of morphologies have been synthesized using Zn(NO₃)₂·6H₂O and pyridine by a microwave-assisted aqueous solution method at 90 °C for 10 min. The pyridine has a significant influence on the morphology of ZnO. Various morphologies of ZnO (hexagonal columns, linked hexagonal needles, hollow structures, and hexagonal nanorings) were obtained by adjusting the concentration of pyridine. The effect of the type of other alkaline additive (aniline and triethanolamine) on the morphology of ZnO was also investigated. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM).     

Synthesis, characterization and optical properties of star-like ZnO nanostructures

Star-like ZnO nanostructures were synthesized in bulk quantity by thermal evaporation method. The morphologies and structure of ZnO nanostructures were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results demonstrated that the as-synthesized products consisted of star-like ZnO nanostructure with hexagonal wurtzite phase. The legs of the star-like nanostructures were preferentially grown up along the [0001] direction. A vapor-solid (VS) growth mechanism was proposed to explain the formation of the star-like structures. Photoluminescence spectrum exhibited a narrow ultraviolet emission at around 380 nm and a broad green emission around 491 nm. Raman spectrum of the ZnO nanostructures was also discussed.     

Controlled morphology of ZnO nanostructures by adjusting the zinc foil heating temperature in an air-filled box furnace

By heating zinc foil in an air-filled box furnace, one-dimensional ZnO nanorods, two-dimensional ZnO nanoplates and three-dimensional ZnO nanotetrapods were prepared by adjusting the temperature in the furnace in the ranges of 500–600, 650–750 and 800–900 °C, respectively. The morphologies, structures and emissions of the synthesized ZnO nanostructures were investigated by scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, selected area electron diffraction and photoluminescence spectroscopy. Mechanisms on the control of the morphology and photoluminescence were discussed in terms of the crystal growth habits combined with the temperature-dependent diffusions of zinc and oxygen atoms in the ZnO lattices.     

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.     

Anionic surfactant-assisted hydrothermal synthesis of high-aspect-ratio ZnO nanowires and their photoluminescence property

ZnO nanowires with high-aspect-ratio of up to ca. 600 were synthesized in a quaternary reverse microemulsion containing sodium dodecyl sulfate (SDS) / water / heptane / n-hexane via a hydrothermal method. SDS, as an anionic surfactant, plays an important role in the formation of morphologies. Subsequently, we studied lots of key influencing factors including the molar ratio (w) value of NaOH to Zn(OAc)₂, the reaction temperature, and the instance without the quaternary reverse microemulsion. The selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) reveal the single-crystal nature of the ZnO nanowires. The morphologies and crystalline structure of the as-obtained products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD), respectively. Through this route, we can obtain a mass of products and the method is both convenient and reproducible. Finally, we measured the photoluminescence (PL) spectra and found that the ZnO nanowires exhibited green-orange emission at 525 nm and short ultraviolet emission at 380 nm and the ZnO nanomaterials with different aspect ratio (length to diameter) (L / D) showed PL intensity disciplinary change. Aiming at this phenomenon, we propose a reasonable mechanism to explain the PL spectra of the ZnO nanomaterials in detail.     

Synthesis and Characterization of Transition Metals Doped ZnO Nanorods

Different morphologies of undoped and transition metals(Mn,Co and Ni) doped one-dimensional(1D) ZnO nanocrystals were successfully synthesized by chemical method in an air atmosphere using polyvinylpyrrolidone(PVP) as a surfactant.The structure and optical properties were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),thermal gravimetric analysis(TGA),ultraviolet visible(UV-vis) absorption spectra and photoluminescence(PL) spectra.The doped ZnO nanorods exhibited a blue-shifted band gap and enhanced ultraviolet(UV) emission.In addition defect related emission was observed for the doped ZnO.