ZnO Hollow Microspheres Research Articles

Preparation of Hollow ZnO Microspheres Using Poly(methyl methacrylate) as a Template with Supercritical CO2-Ethanol Solution

Hollow ZnO microspheres were prepared using poly(methyl methacrylate) (PMMA) as a template with the assistance of supercritical CO2-ethanol solution. A precursor solution of zinc nitrate (Zn(NO3)2·6H2O) was dissolved in supercritical CO2/ethanol mixtures and was impregnated on the surface of the PMMA template. After the removal of the PMMA template by calcination in air, hollow ZnO microspheres were obtained. The products were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), nitrogen adsorption−desorption experiments, and scanning electronic microscopy (SEM). Furthermore, the effects of experimental conditions, such as the concentration of precursor, calcination temperature, impregnation media, and operating temperature during the depressurization process, on the particle morphology were investigated.

Synthesis of hollow ZnO microspheres and its novel UV absorption

In present study, hollow ZnO microspheres with interior diameter of about 10 μm were synthesized by a facile solution method using PMMA microspheres as template. The hollow microspheres are built by layers of nanoparticles with high crystallinity. The shell thicknesses are found to be about 100 nm. Based on the experimental results of XRD, SEM, TEM and XPS measurements, a possible formation mechanism for the hollow ZnO microspheres was discussed. As-synthesized hollow ZnO microspheres exhibit novel absorption band in the region of ultraviolet. Band gap of the hollow ZnO microsphere was calculated to be 3.53 based on its UV–visible absorption spectrum.

Microstructural Study of Assorted ZnO Nanostructures: Nanocombs, Nanocones and Microspheres

We report the microstructural study of ZnO nanostructures: nanocombs, nanocones and microspheres, synthesized using a simple thermal evaporation technique. While nanocombs require the presence of a catalyst, nanocones and hollow ZnO microspheres have been synthesized on silicon substrate in absence of any catalyst or template material. ZnO hexagonal nanocones have been synthesized on Si(100) substrates by directly evaporating zinc acetate dihydrate, at a low temperature of 400 degrees C, without using any carrier gas. The possible mechanism of formation of these structures has been discussed in brief. Chemical composition analysis by energy dispersive X-ray spectroscopy shows an O rich condition of ZnO nanocones and oxygen deficient condition of nanocombs.

Morphological Variation and Raman Spectroscopy of ZnO Hollow Microspheres Prepared by a Chemical Colloidal Process

The morphological variation of ZnO hollow miscrospheres was achieved via a two-step chemical colloidal process. The products were investigated by scanning electron microscopy, high-resolution transmission electron microscopy, Raman scattering spectroscopy, and photoluminescence spectroscopy. A possible evolution mechanism of the ZnO hollow microspheres was discussed. The lattice distortion of ZnO hollow microspheres was found on the edge of the surface. Raman spectra reveal that the E(2)(high) mode of ZnO hollow microspheres is observed at 432 cm(-1). A Raman shift of 5 cm(-1) had taken place compared with the original form of the ZnO microsphere. This study helps us to understand further the structural properties of ZnO hollow microspheres synthesized by a chemical colloidal process.

ZnO Nanobelts and Hollow Microspheres Grown on Cu Foil

ZnO nanobelts, hollow microspheres, and urchins have been prepared on copper foil via a simply low temperature evaporation route. The microstructure, morphologies, and photoluminescence of the ZnO nanostructures were studied with X-ray diffraction, Raman spectra, scanning electron microscopy and photoluminescence spectra. The width of the nanobelts was about 500 nm and the length was longer than 10 μm. The diameter of the hollow microspheres was between 5 and 10 μm. A possible growth mechanism of the nanobelts, microspheres and urchins was proposed. The photoluminescence spectrum exhibited strong deep level energy emissions and a weak near band edge emission. These ZnO nanostructures on a copper substrate have the advantages of naturally good adhesion and electrical connection between the ZnO nanostructures and the conductive substrate.

Investigation of Hydrogen Storage Capabilities of ZnO-Based Nanostructures

Hydrogen storage capabilities of controlled synthesized ZnO-based nanostructures have been investigated. The microscopic results reveal that the products consist of hollow ZnO microspheres composed of nanowires, hollow Sb-doped nanospheres, and Al-doped nanobelts. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) give evidence that Sb and Al dopants are successfully substituted into nanospheres and nanobelts, respectively. The photoluminescence (PL) spectra exhibit a strong green emission band due to defects in nanostructures which lead to a significant role in the hydrogen storage applications. The hydrogen storage characteristics prove that the defects in nanostructures are responsible for higher hydrogen absorption. Among the nanostructures the maximum hydrogen storage capacity of about 2.94 wt % is achieved under the pressure of 5 MPa for Al-doped ZnO nanobelts, and about 81.6% of the stored hydrogen can be released under ambient pressure at 373 K. The highly reversible absorption/desorption reactions exhibit that Al-doped nanobelts are promising material for hydrogen storage.

Using sonochemistry for the fabrication of hollow ZnO microspheres

Hollow ZnO microspheres assembled by nanoparticles have been prepared by a sonochemical synthesis at room temperature using carbon spheres as template. The growth process of the precursor was investigated. The prepared hollow spheres were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM). The diameter of the obtained hollow spheres is about 500 nm, and the walls are composed of numerous ZnO aggregate nanocrystallines with diameters of 90 nm. A possible growth mechanism for the formation of ZnO microspheres has been proposed, in which carbon spheres play a crucial role in the formation of the wurtzite hollow ZnO microspheres. The specific structure of the hollow spheres may find applications in nanoelectronics, nanophotonics and nanomedicine.

Synthesis and evolution of hollow ZnO microspheres assisted by Zn powder precursor

Hollow ZnO microspheres with nanowires grown on the inner and outer surfaces (HZMSnws) have been successfully synthesized by a simple two-step thermal process approach, where pre-deposited Zn powder particles on Si substrates act as temporary templates to form hollow ZnO sphere shells, while additional Zn powder acts as a Zn source to grow single crystal nanowires on the surfaces of spherical shells. SEM, XRD, TEM and HRTEM were used to characterize the morphology and crystalline structure of the samples. Photoluminescence (PL) measurement shows strong UV emission (380 nm) of HZMSnws samples. Lacking the need for the additional template removal is an important advantage of this approach over others and it therefore can be used to prepare hollow ZnO nano/microsphere shells (HZMSs) and HZMSnws at low cost and at large scale. These kinds of special high surface area hollow spherical structures may find potential applications in photocatalysis, light-weight composite fillers, acoustic insulation, UV nano/micro-optoemission devices and photoanodes of dye-sensitized solar cells.

Controlled growth surface morphology of ZnO hollow microspheres by growth temperature

The structural and optical properties of ZnO hollow spheres with club-shaped nanorods grown on the outer and inner surfaces were investigated by using Zn powder as precursor at 475 ∘ C . SEM, XRD, TEM and HRTEM were used to characterize the morphology and crystalline structure of the samples. Thus to realize the controlling of surface morphology, it is most essential to grow ZnO hollow spheres at different experimental conditions. Therefore, the effect of the growth temperature on surface morphology of ZnO hollow spheres should be scrutinized in detail. We grew ZnO hollow spheres by thermal evaporation at various temperatures in the range of 465– 520 ∘ C . We found that the increase in growth temperature transformed surface morphology from nanowires to club-shaped nanorods and nanograins. In addition, the increased growth temperature caused changes of optical qualities of the products.

Self-assembly of ZnO nanoparticles and subsequent formation of hollow microspheres

Nanostructure ZnO hollow microspheres with average crystallite size of about 15 nm, and average diameters of about 1 mu m, were successfully fabricated through a novel hydrothermal method. Hollow microspheres were formed due to self-assembly of ZnO oblong nanoparticles, which resulted in formation of a protrusive surface nanostructure. The obtained material was characterized with X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) investigations. The photoluminescence characterization of the nanostructure microspheres exhibited a UV irradiation at around 380 nm and a broad visible emission band centered at green region. (C) 2008 Elsevier B.V. All rights reserved.

Chemical strategy for tuning the surface microstructures of particles

Particles with tailored surface microstructures exhibit unique structure-dependent phenomena and subsequent utilization of them for the practical applications are of significant interest. In this work, we have developed some potential chemical strategies to tune the surface microstructures of functional materials, such as hollow ZnO microspheres, semiconductor films or arrays, LiNbO 3 spheres, and cubic phase Cu 2O particles. We describe their surface microstructure-guiding processes and illustrate the detailed key factors controlling their growth by examining various reaction parameters. The proposed surface structure-guiding mechanisms are presented and the important pioneering studies on the rational design and fabrication of particles with tunable surface microstructures are discussed. Current results demonstrate that our suggested chemical strategies for tuning surface microstructures of particles can be used as a versatile and effective route to the controllable synthesis of other inorganic functional materials.

Template-Free Synthesis of Zinc Oxide Hollow Microspheres in Aqueous Solution at Low Temperature

A novel template-free hydrothermal method is developed to prepare large-scale ZnO hollow microspheres. The key strategy for the successful realization is that we employ a high concentration of trisodium citrate to control the nucleation and growth rate of ZnO crystal forming microspheres with core/shell structures and the proper pH of an alkaline solution to remove the cores generating hollow microspheres. The morphology, structure, and composition of the microspheres have been investigated with field-emission scanning electron microscopy and high-resolution transmission electron microscopy for the growth mechanism. A series of controlled experiments have also been carried out to better understand the formation mechanism of ZnO hollow microspheres and the function of reactants used in the experiments. The infrared absorption spectra indicate that annealing can lead to the decomposition of impurity groups in the as-prepared sample. Both room-temperature Raman and photoluminescence results demonstrate that the annealed ZnO microspheres are of good crystalline wurtzite structure with high optical quality.

Hollow ZnO Microspheres with Complex Nanobuilding Units

A three-tiered organization of ZnO nanobuilding blocks into hollow spherical conformations has been developed. This self-assembly approach demonstrates new capacities of template-assisted synthesis in the architecture of hollow structures as well as in the construction of structurally complex nanomaterials.

Polyhedral construction of hollow ZnO microspheres by CO 2 bubble templates

A new type of complex ZnO hollow structures constructed by polyhedral particles has been prepared via a facile solution-phase route, in which ZnO precursors (ZnCO 3) are synthesized through the reaction between Zn(CH 3COOH) 2 and NH 4HCO 3 in aqueous solution. Similar morphology of hollow ZnO microspheres can be effectively obtained simply by the pyrolysis method. The formation mechanism of hollow microspheres is mainly via an oriented aggregation process. CO 2 bubble templates produced during the reaction to form the aggregation centers help the small particles to aggregate and form hollow microspheres. The surface morphology and size of these microspheres can be tuned by simply varying the reaction temperature. The hollow ZnO microspheres constructed by polyhedral particles may bring novel physical and chemical properties in the field of microscale electronics and photonics.

From Zn microspheres to hollow ZnO microspheres: A simple route to the growth of large scale metallic Zn microspheres and hollow ZnO microspheres

Large scale metallic Zn microspheres and hollow ZnO microspheres are synthesized by thermal evaporation and vapor transport by heating a ZnO/graphite mixture at 1000 °C. Firstly, metallic Zn microspheres are fabricated with diameters in the range of 1–10 μm. The Zn microspheres are then annealed at 600 °C in air, which form hollow semiconducting ZnO microspheres. EDX and XRD spectra reveal that the oxidized material is indeed ZnO. Room temperature photoluminescence spectra of the oxidized material show a sharp peak at ∼380 nm and a wider broad peak centered at ∼490 nm. This growth mechanism is discussed and further investigated for other metallic and metal oxide microstructures.

Morphosynthesis of Hierarchical Hydrozincite with Tunable Surface Architectures and Hollow Zinc Oxide

Hydrozincite (Zn5(CO3)2(OH)6) microspheres with a tunable surface architecture have been successfully synthesized via a homogeneous precipitation method under solvothermal conditions. For a smooth hydrozincite microsphere, various building blocks such as nanocubes, nanorods, and nanosheets are arranged to cover a spherical surface by concisely controlling reaction time and the volume of ethylene glycol. Hexagonal Zn5(CO3)2(OH)6 with nanostep structures are also prepared without any additives. The hollow ZnO microspheres with a porous surface have been successfully fabricated via a solution-based method by the room-temperature treatment of filled Zn5(CO3)2(OH)6 microspheres composed of nanocubes. A possible growth mechanism of these hollow ZnO microspheres is proposed. The similar filled ZnO microspheres can also be obtained by a direct pyrolysis of Zn5(CO3)2(OH)6 microspheres composed of nanocubes at 450 degrees C.

Synthesis of hollow ZnO microspheres by an integrated autoclave and pyrolysisprocess

Hollow zinc oxide microspheres have been synthesized from a microZnBr2·2H2O precursor obtained by an autoclave process in bromoform steam at220 °C /2.5 MPa. Field-emission scanning electron microscropy (FE-SEM) andtransmission electron microscopy (TEM) show that the products are about1.0 µm single crystal spherical particles with hollow interiors, partly open surfaces and wallsself-assembled by ZnO nanoparticles. X-ray diffraction (XRD) analysis shows that theas-prepared ZnO hollow spheres are of a hexagonal phase structure. A possible formationmechanism is suggested on the basis of the shape evolution of ZnO nanostructures observedby SEM and TEM. The room-temperature photoluminescence (PL) spectrumshows UV emission around 386 nm and weak green emission peaks indicatingthat there are few defects in the single crystal grains of the ZnO microspheres.

Fabrication of hollow ZnO microsphere with zinc powder precursor

A facile approach is reported for the preparation of hollow ZnO microspheres using Zn powders as raw materials. Firstly, Zn(OH) 2 was precipitated on the surface of Zn powder to form core/shell structure in solution, and subsequent calcination these core/shell composite particles at 650 °C in air would lead to the formation of ZnO hollow spheres whose diameter were determined by the dimension of the used Zn powder. XRD, TEM, SAED, EDS and UV–vis were used to characterize the as-prepared samples. A formation mechanism is proposed to be a process following the formation of Zn/Zn(OH) 2 core/shell particles, the decomposition of Zn(OH) 2 shell to ZnO, and the sublimation and oxidation of Zn core.