Tubular ZnO Research Articles

Fabrication of polycrystalline tubular ZnO via a modified ultrasonically assisted two-steppolyol process and characterization of the nanotubes

An ultrasonically assisted two-step polyol process was established to fabricatepolycrystalline ZnO nanotubes. Thus one-dimensional (1D) precursors were prepared froman ethylene glycol (EG) solution containing 0.3 M of zinc acetate in the presence ofultrasonic irradiation. The ZnO nanotubes were obtained by calcination of the precursorsat proper temperatures. The precursors and polycrystalline ZnO nanotubes obtained atvarious calcination temperatures were characterized by means of scanning electronmicroscopy (SEM), Fourier transformation infrared spectrometry (FTIR), x-ray diffraction(XRD, together with temperature-resolved XRD), and transmission electron microscopy(TEM). It was found that the precursors were extremely sensitive to atmosphericmoisture and instantly transformed to layered hydroxide zinc acetate (LHS-Zn)after being exposed to air, accompanied by the erosion and deformation of theone-dimensional structure. After being calcined at proper temperatures, the precursorswere completely transformed into polycrystalline tubular ZnO, and the sizes of theresulting ZnO nanocrystallites increased with increasing calcination temperature,implying that polycrystalline tubular ZnO of desired sizes could be fabricatedusing the present method by properly controlling the calcination temperature.However, the tubular structures were destroyed at a calcination temperature of400 °C and above, owing to the growth of polycrystalline ZnO. Moreover, the presentmethod could be used to synthesize other tubular metal oxides, and tubular ZnOmight find promising applications in gas-sensitive sensors and catalysis as well.

Terahertz Response of Bulk and Nanostructured ZnO

We present experimental characterization of far-infrared optical and dielectric prop- erties of single-crystal ZnO and nanostructured ZnO of difierent morphologies by terahertz time- domain spectroscopy. Frequency dependent complex dielectric function, power absorption, and refractive index of single-crystal, nanowire, tetrapod, tubular, and prismlike ZnO structures are experimentally measured in the terahertz regime, respectively. The experimental results are analyzed and well flt with dielectric theories and efiective medium models.

Terahertz Dielectric Properties and Low-Frequency Phonon Resonances of ZnO Nanostructures

Far-infrared optical and dielectric properties of nanostructured ZnO of different morphologies are characterized by terahertz time-domain spectroscopy. Frequency-dependent complex dielectric function, power absorption, and refractive index are experimentally measured in the terahertz regime. The results are analyzed and well fit with dielectric theories combined with effective medium models. Different ZnO nanostructure morphologies exhibit different characteristics due to diverse resonance mechanisms dominated by either free electrons or phonons. The dielectric function of tubular and prismlike ZnO structures exhibits the Drude-like behavior, while it is dominated by the low-frequency phonon resonances for nanowires. Additionally, the overall low-frequency phonon resonances of these nanostructures are measured by Raman scattering spectroscopy, showing good consistency with those of bulk wurtzite single-crystal ZnO.

A two-step hydrothermally grown ZnO microtube array for CO gas sensing

Tubular ZnO microstructure arrays were fabricated on a large scale by a two-step hydrothermal method. The porous ZnO tubular structures were then used to construct a gas sensor for CO detection. The microtube array gas sensor showed sensitive response to different concentration of CO with an optimum temperature of 250 °C. Because of the large surface to volume ratio, the sensitivity of the microtube arrays was about twice of that of the ZnO rods. Our results indicate that this simple two-step method for fabrication of large-scale tubular microstructure arrays can be potentially used in gas sensor applications with improved performance.

Tetrapod-shaped ZnO microtubes synthesized from Zn/C mixtures

We report for the first time the growth of tetrapod-shaped ZnO microtubes synthesized via a simple method. The tetrapod-shaped ZnO microtubes were synthesized from mixtures of high-purity Zn powder and activated carbon in a crucible at 930–940 °C in air without the presence of any catalyst. The ZnO microtubes were found to be grown on the arrays of ZnO microcrystals, which were horizontally grown from the inner walls of crucibles. Optical and scanning electron microscopy were utilized to observe the morphologies of the tetrapod-shaped ZnO microtubes, and X-ray diffraction was employed to study the crystal structure. The microtubes were found to be hexagonally shaped with well-defined side faces. A growth model was proposed to explain the formation of the tubular ZnO microcrystals.

Organic Molecule-Assisted Hydrothermal Self-Assembly of Size-Controlled Tubular ZnO Nanostructures

Tubular ZnO nanostructures have been synthesized by hydrothermal self-assembly of zinc ions at the interface of organic molecules and solution. The morphologies and structures of the products were ...

Electroless deposition of aligned ZnO taper-tubes in a strong acidic medium

In this communication, we report the hexagonal ZnO taper-tubes prepared through an electroless deposition method in an acidic medium based on a modified galvanic replacement reaction. Inspection of SEM images of ZnO suggests a one-step, acetic acid in situ crystallization/etching mechanism for producing tubular ZnO arrays. During electroless deposition reaction, the formation process may be rationalized by considering that the etching of ZnO with acetic acid starts from six sites located at the six corners of the top surface of ZnO truncated taper, resulting in a gradual widening of the open holes and tubular ZnO. The present electroless deposition strategy is versatile and with a potential to be developed into a more practical method.

Synthesis and Characterization of Hexagonal Tubular ZnO

Synthesis and Characterization of Hexagonal Tubular ZnO

Fabrication of tubular ZnO by vesicle–template fusion

Zinc oxide microtubes were synthesized by hydrothermal method. The cooperation activities of surfactant cetyltrimethylammonium bromide (CTAB) and bidentate ethylenediamine ligand were found to be appropriate for the formation of final tubes. The morphologies and structures of the samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A possible vesicle-template elongating fusion mechanism was proposed and discussed.

Growth mechanism of tubular ZnO formed in aqueous solution

Tubular ZnO microstructural arrays were fabricated by a hydrothermal decompositionmethod. The dependence of the morphologies on the growth time and temperature wasinvestigated in detail. An experiment was carried out to determine the mechanism oftubular ZnO formation. Our results showed that ZnO microtubes originated from an ageingprocess from ZnO microrods at a lower temperature (compared to the temperature whenhydrothermal deposition of ZnO microrods was dominant) due to the preferential chemicaldissolution of the metastable Zn-rich (0001) polar surfaces. A growth model was proposedbased on the coexistence of hydrothermal deposition and dissolution of ZnO in thefabrication process.

Raman spectra of single micrometer-sized tubular ZnO

Micrometer-sized tubular ZnO crystal was fabricated by a hydrothermal method, and was characterized by scanning electron microscopy (SEM). Back-scattering micro-Raman spectrum was applied to investigate the vibrational modes of the microtubes with the comparison to that of ZnO powder. Raman scattering in a single micrometer-sized tubular ZnO was also recorded with different polarization configurations consequently. Most of the observed vibrational modes were assigned on the basis of group theoretical analysis. Besides the typical Raman-active modes assigned to ZnO, a new mode with Raman shift of 860 cm −1 was observed which has not been reported in previous relative researches yet. In addition to this, the Raman signal of E 1T mode at 410 cm −1 increased dramatically and become asymmetric in some cases.

Bell-mouthed single-crystalline tubular ZnO prepared by a soft solution method

Faceted single-crystalline ZnO tubes were synthesized by a simple soft solution method at 65 ° C. These tubes are of several micrometers in length and several hundred nanometers in diameter, with bell-mouths on each end. Structural characterizations using electron spectroscopy revealed that these hexagonal ZnO tubes were along [0 0 0 1] direction and side-enclosed by { 01 1 ¯ 0 } facets. The growth of ZnO in hydrothermal condition and the formation of this unusual bell-mouthed structure were discussed on the basis of the observation of ring-shaped nano-crystallites upon decreasing the time for growth.

A New Method for the Preparation of Metal Nanowires by the Nebulized Spray Pyrolysis of Precursors

A new method based on nebulized spray pyrolysis is applied to the preparation of metal (zinc, cadmium, cobalt, and lead) nanowires. The resulting nanowires are single- crystalline. The oxidation of metal nanowires yields one-dimensional oxidic nanostructures. In the case of zinc metal, tubular ZnO is obtained.

Fabrication and microstructure analysis on zinc oxide nanotubes

Well crystallized aligned zinc oxide nanoscale tubular structures have been fabricated viavapour phase growth on large area substrates. The ZnO nanotubes have regular polyhedralshapes, hollow cores with diameters of 30–100 nm, lengths over a few tens of micrometresand wall thicknesses of 4–10 nm. In morphology, the nanotubes were either straight ortwisted with several straight parts. The microstructure of the tubular material wasinvestigated in detail by using high-resolution transmission electron microscopy (HRTEM),Z-contrastimaging and compositional line profile analysis. The chemical composition ofindividual tubular structures was found to be stoichiometric ZnO using selected areaenergy dispersive x-ray spectroscopy and electron energy loss spectroscopy. X-raydiffraction (XRD) and selected area electron diffraction results indicated thatthe ZnO nanotubes had wurtzite crystal structure. XRD analysis and HRTEMinvestigations indicated the ZnO nanotubes were grown along the [001] direction.The growth of the tubular ZnO nanostructures was found to be closely relatedto the hexagonal nature of the ZnO crystal and the peculiar growth conditionsused.

Growth and optical properties of single-crystal tubular ZnO whiskers

The growth of single-crystal tubular ZnO whiskers was achieved via a process of first reduction and following oxidation of ZnS powders. The products were characterized using x-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The whiskers are tubular single crystals with the [001] growth crystallographic direction, and most have outer diameters of ∼400 nm, lengths of up to 15 μm, and wall thickness range of 100–150 nm. Room-temperature photoluminescence spectrum of the whiskers reveals a strong and sharp UV emission band at 381 nm and a weak and broad green emission band at 583 nm. Possible growth mechanism of the ZnO whiskers was briefly discussed.

A simple route towards tubular ZnO.

Thermal treatment of Zn(NH3)(4)2+ precursor in ethanol solvent led to the formation of the tubular ZnO which exhibited strong ultraviolet photoluminescence around 385 nm at room temperature; TEM images showed the hollow tubules with approximately 450 nm in diameter and approximately 4 microns in length were built up by ZnO polycrystals.

Preparation and Photoactive Characterization of Tube-shaped Al-doped ZnO Ceramics.

ABSTRUCT:Tubular Al-doped ZnO particles were prepared by homogeneous precipitation in the mixed solutions of Al(NO3)2, Zn(NO3)2, sodium dodecyl sulfate (SDS) surfactant and urea. At the molar ratio of Metal ions(Mt) : SDS : urea : H2O is 1 : 2 : 20 : 60, tubular products formed by heating at 80°C for 12 h. Plate like ZnO particles were obtained at Mt : SDS : urea : H2O = 1 : 2 : 10 : 60 or 1 : 1 : 20 : 60. The diameter of typical ZnO tube is ca.100 nm, and the length of tube is about 600nm (aspect ratio = 6). The relative surface area of tubular Al-doped ZnO is ca. 40.2 m2/g. The photo-decomposition rate of NO3- ions using tubular Al-doped ZnO particles was higher than standard TiO2 photo-catalysts (P-25) by irradiation >290nm light in 10mM KNO3-10vol%EtOH solutions at 30°C. The obtained materials showed DC conductive properties as compacted substrate by sintered at 400°C.