ZnO Nanorod Bundles Research Articles

Tower-Like ZnO Nanorod Bundles Grown on Freestanding Diamond Wafers for Electron Field Emission Improvement

Tower-like ZnO nanorod (ZNR) bundles were grown on freestanding diamond (FSD) wafers by a low-temperature hydrothermal method without any catalysts, and the corresponding electron field emission property was investigated. The structural characterizations disclosed that these tower-like bundles were composed of single crystalline ZNRs with hexagonal wurtzite structure. They grew perpendicularly to each crystal planes of the diamond grains. Different hydrothermal reaction times (e.g., 1.5, 3, 6, 8 h) were carried out to investigate the morphology features of ZNRs grown on the growth surface of FSD wafers. The ZNR bundles with a growth time of 6 h showed the highest crystallinity and aspect ratio. Such ZNR bundles/FSD hybrid exhibited a high emission current density of 0.2 mA at an applied field of 11.8 V/μm and a reduced turn-on field of 6.8 V/μm. The field enhancement factor β was calculated to be ~4979 based on the Fowler-Nordheim theory. The geometry and structure of polycrystalline diamond were responsible for the formation of ZNR bundles and the high β-value.

Highly selective detection of saturated vapors of abused drugs by ZnO nanorod bundles gas sensor

It is very necessary to quickly and selectively detect the abused drugs in real time, because of their bad influence on the central nervous system. So ZnO nanorod bundles were prepared by simple hydrothermal reaction combined with calcination in this paper, which were assembled into thick film gas sensor to detect three analogs of drugs. Such ZnO nanorod bundles gas sensor exhibited not only good gas response and selectivity, but also good reproducibility and stability to the saturated vapors of three kinds of drugs (C10H15NO, C9H13NO, C8H9NO2) at 252 °C. The excellent gas response can be ascribed to its rough surface and the large number of holes formed by nanorod bundles accumulation, which are conducive to diffusion, adsorption and desorption of gas molecules on ZnO nanorods. The reaction mechanism was further analyzed and discussed by XPS.

ZnO/Si hetero-structured nanotrees fabricated by all-solution process

ZnO/Si hetero-structured nanotrees have been fabricated by an all-solution-based hydrothermal process. First, urchin-shaped ZnO nanostructures were grown on ZnO-island seed layers by selective growth of ZnO nanorod bundles. In the hydrothermal solution, NH4OH supplied OH- source for ZnO growth to maintain the urchin-shaped ZnO nanostructures and etched the exposed Si surfaces simultaneously. The urchin-shaped ZnO nanostructures acted as a mask for undercut etching of the exposed Si surfaces. The Si {111} surfaces with the lowest surface energy were exposed and formed pyramid-shaped stems for the nanotrees during the etching. The final ZnO/Si hetero-structured nanotrees consisted of ZnO nanorod branches and pyramidal Si stems.

Microwave absorption properties of polyaniline-Fe3O4/ZnO-polyester nanocomposite: Preparation and optimization

New nanocomposites have been successfully prepared based on polyester resin, including various metal oxides (ZnO nanorod bundles, Fe3O4 nanoparticles, and nano Fe3O4/ZnO) and Polyaniline (PANI) synthesized with different dopants. The microwave absorption properties of nanocomposites were investigated in X-band range. The Taguchi experimental design was used to study the effects of the type of metal oxide and that of PANI (doped with various acids) and the weight percent of metal oxide in PANI and that of filler (metal oxide and PANI) in polyester matrix on the microwave absorption properties with the absorber thickness of only 2mm. The weight percent of metal oxide in PANI was found to be the most significant parameter, accounting for 45.611% of the total contribution of the four selected parameters. Fe3O4/ZnO as inorganic oxide, PTSA as dopant of PANI, 25wt.% for inorganic oxide in PANI, and filler in the polyester matrix were selected as optimum conditions by Taguchi method. The sample prepared in optimal conditions had reflection loss of less than −10dB (absorption >90%) and covering a frequency range of 8.4–11.6GHz.

Photocatalytic performance of ZnO nanomaterials for self sensitized degradation of malachite green dye under solar light

ZnO nanomaterials of different morphologies are synthesized by different methodologies. These semiconductor photocatalysts are potentially explored for self-sensitized photodegradation of malachite green (MG) dye in water in a batch reactor. The effects of various parameters like initial dye concentration, catalyst loading, solution pH, light source on degradation efficiency was also investigated. The experimental results showed substantial reduction of COD, besides removal of colour. The photodegradation of MG dye followed the pseudo first order kinetics of Langmuir–Hinshelwood model. The hydrothermally synthesized flower shaped homocentric pencil like ZnO nanorod bundles exhibit excellent photocatalytic activity under solar light. A comparative study of photodegradation efficiency among ZnO nanoparticles, ZnO nanoparticles (hydrothermal) and flower shaped homocentric pencil like ZnO nanorod bundles were also performed. Semiconductor photocatalysis often leads to partial or complete mineralization of organic pollutants. The CO2 gas evolved due to mineralization of MG was determined using Warburg manometric method under solar light. The possible mechanism of photodegradation under both solar and UV light were also proposed.

Flower shaped homocentric pencil like ZnO nanorod bundles: synthesis, characterisation and study of their photocatalytic activity

Flower shaped homocentric pencil like ZnO nanorod bundles are synthesized by a hydrothermal method. The PXRD pattern corresponds to the typical wurtzite structures of ZnO, which exhibits excellent activity as a photocatalyst for the degradation of malachite green under solar light irradiation.

Growth of three-dimensional ZnO nanorods by electrochemical method for quantum dots-sensitized solar cells

There-dimensional (3D) superstructure was expected to fabricate high performance photoelectrodes of quantum dot-sensitized solar cells (QDSCs). In this paper, the ZnO 3D superstructure with multi-layer structure (3D ZnO nanorods) was grown on ITO glass by a novel electrochemical method at low temperature (60–90 °C). The 3D ZnO nanorods were composed of close-packed ZnO nanorod bundles with wide dimension distribution ranging from hundreds of nanometers to several micrometers. The effects of some important parameters, such as concentration of Zn(NO 3) 2, deposition temperature and concentration of ZnO nanoparticles (served as growth seeds for ZnO nanorods), on the morphology of 3D ZnO nanorods were also studied by scanning electron microscopy. Once being applied in QDSCs, the 3D ZnO nanorods showed more superior photoelectrochemical performance to ZnO nanorod array. The conversion efficiency of 1.42% achieved by the QDSC based on 3D ZnO nanorods was a very promising value for the QDSCs based on ZnO electrodes.

Mechanism Study of ZnO Nanorod-Bundle Sensors for H2S Gas Sensing

This work reports the H2S gas-sensing properties of ZnO nanorod bundles and an investigation of their gas sensing mechanism. A one-dimensional ZnO nanostructure was synthesized using the hydrothermal method; scanning electron microscopy (SEM); and X-ray diffraction (XRD) spectra confirmed that the structures were crystalline ZnO of hexagonal structure. A furnace-type gas sensing system was used to characterize the nanorod bundles’ sensing properties in air containing dilute H2S gas (50 ppm) at sensing temperatures Ts ≤ 500 °C. The response of ZnO nanorod-bundle sensors to H2S gas increased with Ts; this trend may be due to chemical reaction of nanorods with gas molecules. X-ray photoelectron spectroscopy results indicated that the sensing mechanism of the ZnO nanorod-bundle sensor was explained by both the well-known surface reaction between H2S and adsorbed oxygen on ZnO, and the formation of zinc−sulfur bonding in ZnO nanorods, which becomes a dominant sensing mechanism at high Ts above 300 °C.

Synthesis of Zinc Glycerolate Microstacks from a ZnO Nanorod Sacrificial Template

AbstractWe synthesized zinc glycerolate (ZnGly) microstacks bytreating ZnO with glycerol at 100 °C under reflux. We observed that the morphology of the ZnO source has a pronounced effect on the appearance of the ZnGly product. In the absence of structure‐directing effects the product ZnGly is obtained as a random heap of hexagonal prisms with an average diameter and thickness of ca. 2.5 μm and ca. 350 nm, respectively. However, bundles of nanorod‐shaped ZnO obtained by the thermal decomposition of zinc oxalate nanorods could readily be transformed into 2–4 μm long zinc glycerolate microstacks in which 6–12 hexagonal prisms are aligned face‐to‐face. We present evidence that the ZnGly plates in the microstacks are bound together by forces strong enough to withstand mechanical deformation exercised by a contacting AFM tip. The ZnGly microstacks appear to emerge from the ZnO nanorod bundles in an approx. 1:1 ratio in the reactive template synthesis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis and Ethanol Sensing Properties of Self-Assembled Monocrystalline ZnO Nanorod Bundles by Poly(ethylene glycol)-Assisted Hydrothermal Process

The flowerlike ZnO nanorod bundles, consisting of closely packed nanorods with diameter of ∼90 nm, have been successfully synthesized by a poly(ethylene glycol) (PEG)-assisted hydrothermal route at low temperature (80 °C). The results characterized from FESEM, TEM, and SAED demonstrate that the nanorod structures are single crystals and formed from self-assembled nanoparticles. Further investigation of the formation mechanism reveals that the PEG-assisted hydrothermal process is vital to the formation of the complex nanostructures. The sensors based on the ZnO nanostructures exhibit excellent ethanol-sensing properties at reduced working temperature (250 °C), which could still respond to 1 ppm ethanol. The sensitivity of the sensor to 100 ppm ethanol is about 154.3 with the response time of 12 s. The enhancement in sensing properties of the present ZnO sensor may be attributed to the peculiar ZnO nanostructures.

Self-assembly of ZnO Nanorod Bundles into Flowerlike Architectures by a Simple Hydrothermal Route

The self-assembly of ZnO nanorod bundles into interesting flowerlike architectures were achieved via a simple hydrothermal route.The as-prepared samples were characterized by X-ray powder diffraction(XRD),scanning electron microscope(SEM),and high-resolution transmission electron microscope(HRTEM).The composed ZnO nanorods,as self-assembly building blocks,are single crystals nature with the c-axis growth crystallographic direction.And most of them have diameters of 500nm and lengths of 6.0μm.The results indicate that commercial ammonia(28%) plays an important role in the formation of the flowerlike architectures in the present of ethylenediamine.When pH value is about 10 adjusted by the addition of ammonia,self-assembly of ZnO nanorod bundles into flowerlike architectures are obtained.With the further increase of the content of ammonia,self-assembly of ZnO nanorods into different flowerlike architectures are synthesized.A possible growth mechanism of the flowerlike ZnO architectures is proposed.

Electrochemical synthesis of orientation-ordered ZnO nanorod bundles

The high density and orientation-ordered ZnO nanorod bundles with wurtzite structures were prepared on Cu substrates by electrochemical deposition in solution of ZnCl 2 + tartaric acid at a temperature of 90 °C. This approach is a unique and size controlled synthetic method for the large-scale preparation of ZnO nanorod bundles. Cyclic voltammogram measured in solution of the mixture of ZnCl 2 and tartaric acid shows a restraining role of tartaric acid for the electro-reduction of Zn(II). The formation mechanism of ZnO on the surface of the cathode can be explained that the high temperature (⩾90 °C) promotes the corrosion of electrodeposited Zn via reacting with H 2O and O 2 to form the stable passive phase of ZnO. The compositions of the nanorod bundles can be entirely ZnO or Zn and ZnO composites determined by the temperature and deposition rate. The photoluminescence (PL) properties indicate that these ZnO deposits are highly crystallized and of excellent optical quality.

LOW TEMPERATURE SYNTHESIS OF Fe-DOPED ZnO NANOROD BUNDLES IN AQUEOUS SOLUTION

Pure and Fe -doped ZnO nanorod bundles were synthesized in aqueous solution at low temperature, in which inexpensive reagents such as Zn ( NO 3)2, NaOH and Fe ( NO 3)3 were used as precursors. The composition of the final product can be roughly tuned by the precursor ratio used. Energy dispersive X-ray spectroscopy confirms the successful incorporation of Fe element into ZnO nanorods, and X-ray diffraction reveals that ZnO nanorod bundles have a pure hexagonal wurtzite-phase structure. UV–vis spectroscopy show that the spectrum shifts to longer wavelength with increasing iron doping.

Crystal orientation-ordered ZnO nanorod bundles on hexagonal heads of ZnO microcones: epitaxial growth and self-attraction

We demonstrate a preferential nucleation, epitaxial growth, and self-attraction of crystal orientation-ordered ZnO nanorod bundles on (0001) plane of single-crystal ZnO microcones.

Hexagonally packed zinc oxide nanorod bundles on hydrotalcite sheets

A hexagonal-shaped, hydrotalcite-like [Zn(II)(1−x)Al(III)x(OH)2)]·mH2O interface that is very effective in promoting the self-assembly of ZnO nanorods has been developed on aluminium-coated substrates in alkaline hydrothermal conditions. The growth of the hydrotalcite interface is due to the reaction between zinc and aluminium ions and it provides a surface of low interfacial energy for the heterogeneous growth of ZnO nanorods at supersaturation levels that do not sustain homogeneous nucleation. The ZnO nanorods self-assemble to form a tightly packed “nail-on-bed” hexagonal structure on the hydrotalcite template. The size of the nanorods can be controlled by controlling the pH of the solution. Delamination of the thin hydrotalcite template at high temperatures produces sheets of ZnO nanorod bundles. Oriented growth of ZnO nanorods can be achieved on a wide range of substrates mediated by the thin hydrotalcite-precoated interface. Stable electron field emission characteristics can be obtained from the ZnO nanorods at a turn-on voltage of 2.73 V µm−1.