Synthesis Of Flower-like ZnO Nanostructures Research Articles

A green approach to the microwave-assisted synthesis of flower-like ZnO nanostructures for reduction of Cr(VI)

Zinc oxide nanostructures with different morphologies were prepared via a microwave-assisted method and used as photocatalysts for reduction of chromium(VI) under ultraviolet-B illumination. X-ray diffraction revealed that as-made ZnO samples have wurtzite hexagonal structure. Scanning electron microscopy demonstrated that the morphology of the ZnO crystals could be easily modified from star-shaped to chrysanthemum flower-like structure by changing the ratio of zinc nitrate and sodium hydroxide. X-ray photoelectron spectroscopy and energy dispersive X-ray analysis confirmed the stoichiometry of pure ZnO. Its optical properties were also investigated by UV-Vis diffuse reflectance spectroscopy, which indicated that the prepared ZnO possessed a band gap value of 3.2 eV. Photocatalytic activity studies revealed that the ZnO (1:6) (1 × 10−3 mol zinc nitrate: 6 × 10−3 mol sodium hydroxide) catalyst exhibited a significantly faster reduction rate of Cr(VI) compared to ZnO (1:5) and ZnO (1:4). More than 95% of Cr(VI) at a concentration of 10 mg/L has been reduced to Cr(III).

Synthesis of flower-like ZnO nanostructures by sonochemical route and their photocatalytic activity

In this study, the flower-like ZnO nanostructures have been fabricated using zinc chloride and potassium hydroxide as precursors by sonochemical technique. The as-prepared ZnO nanostructures were characterized by SEM, XRD, Fourier Transform Infrared Spectroscopy (FTIR), Raman spectra and UV–vis spectroscopy. The results indicated that the synthesized zinc oxide posses a flower shape with diameters in the range of 4–6μm. Meanwhile, every single flower is composed of needle-like crystals of 200–300nm in diameter irradiated from the center. The morphologies of the obtained product at different sonochemical time were experimentally studied. The formation mechanism is discussed in detail. Additionally, photocatalytic activity of the prepared ZnO sample was evaluated by the degradation of methylene blue under UV irradiation.

Hydrothermal Synthesis of Flower-Like ZnO Nanostructures and their Optical Properties

Flower-like ZnO nanostructures have been synthesized using zinc nitrate hexahydrate and hexamethylenetetramine (HMT) by a low-temperature hydrothermal technique. The prepared ZnO nanostructures exhibit hexagonal wurtzite structure, well-defined flower-like morphology, and a strong blue emission photoluminescence. Flower-like ZnO nanostructures consisting of multilayered petals are formed with the length of about 1 μm. All the flower petals exhibit the tapering feature with the root size of 300-500 nm and tip size of 50-100 nm. The prepared ZnO sample has been studied using x-ray diffraction technique, energy dispersive x-ray analysis, scanning electron microscope and FTIR spectroscopy. The photoluminescence spectrum demonstrated two emission bands, a near band edge (NBE) emission in the UV region centering at 386 nm and a high intensity deep band emission (DBE) in the visible region centering at 483 nm.

Facile and fast synthesis of flower-like ZnO nanostructures

A fast and facile method has been developed to synthesise flower-like ZnO nanostructures at room temperature without using any capping agent. ZnO nanoflowers could be easily prepared by adding ethanol to the precursor solution having higher concentration of hydroxide ions. The amount of ethanol plays an important role in the formation of ZnO nanoflowers. The products were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The room-temperature photoluminescence (PL) spectrum of the sample consists of near-band edge emission at ∼385nm as well as a strong and broad green–yellow emission band due to the presence of defect states in the sample. A reasonable growth mechanism is also proposed for the formation of flower-like ZnO nanostructures.

Enhanced ammonia sensing performances of Pd-sensitized flowerlike ZnO nanostructure

We report the synthesis of flowerlike ZnO nanostructure using a facile hydrothermal process, and the investigation on the ammonia (NH 3)-sensing properties of the pure and palladium (Pd)-sensitized flowerlike ZnO nanostructure. The phase purity, morphology, and structure of the pure and Pd-sensitized ZnO nanostructure are investigated. The characterized results reveal that the flowerlike ZnO has a wurtzite structure and is composed of numerous aggregated single-crystalline ZnO nanorods with a diameter of about 60 nm. Having fabricated gas sensors based on the pure and Pd-sensitized flowerlike ZnO, we find that the Pd-sensitized sensor exhibits a response of 45.7–50 ppm NH 3 at 210 °C, which is about 8 times higher than that of pure ZnO at the optimal operating temperature of 350 °C. The enhanced NH 3-sensing performance demonstrates that the significant decrease in optimal operating temperature and the distinct increase in response are attributed to the sensitization effect of Pd.

Low temperature pH dependent synthesis of flower-like ZnO nanostructures with enhanced photocatalytic activity

In the present study we have synthesized flower-like ZnO nanostructures comprising of nanobelts of 20 nm width by template and surfactant free low-temperature (4 °C) aqueous solution route. The ZnO nanostructures exhibit flower-like morphology, having crystalline hexagonal wurtzite structure with (0 0 1) orientation. The flowers with size between 600 and 700 nm consist of ZnO units having crystallite size of ∼40 nm. Chemical and structural characterization reveals a significant role of precursor:ligand molar ratio, pH, and temperature in the formation of single-step flower-like ZnO at low temperature. Plausible growth mechanism for the formation of flower-like structure has been discussed in detail. Photoluminescence studies confirm formation of ZnO with the defects in crystal structure. The flower-like ZnO nanostructures exhibit enhanced photochemical degradation of methylene blue (MB) with the increased concentration of ligand, indicating attribution of structural features in the photocatalytic properties.

Flash synthesis of flower-like ZnO nanostructures by microwave-induced combustion process

Flower-like ZnO particles were fabricated from zinc nitrate and urea via the microwave-induced combustion technique (MICT). The structure and morphology of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The effects of growth conditions such as microwave power, radiation time, and molar ratio of urea/Zn 2+ were investigated. Results show that the morphologies and particle sizes of the final products depend on the molar ratio of urea/Zn 2+. The SEM images of ZnO flowers grown in different periods were employed to explain the formation mechanism. This study provides a simple and efficient approach for synthesizing flower-like ZnO heterostructures.

Large-scale synthesis of flowerlike ZnO nanostructure by a simple chemical solution route and its gas-sensing property

A large-scale flowerlike ZnO nanostructure is prepared using a very simple solution method at near room temperature. The flowerlike ZnO nanostructure is self-assembled by thin and uniform nanosheets with a thickness of approximately 18 nm. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to characterize the structure and morphology. The possible growth mechanism is carefully discussed based on the reaction process. The as-prepared ZnO nanoflowers exhibit a good response and reversibility to some organic gases, such as ethanol and n-butanol. The responses to 100 ppm ethanol and n-butanol are 25.4 and 24.1, respectively, at a working temperature of 320 °C. In addition, the sensors exhibit a good response to acetone, 2-propanol, and methanol. The relationship between the gas-sensing properties and the microstructure of the as-prepared ZnO nanoflowers is also investigated.

Low Temperature Synthesis of Flowerlike ZnO Nanostructures by Cetyltrimethylammonium Bromide-Assisted Hydrothermal Process

The flowerlike ZnO nanostructures, which consisted of swordlike ZnO nanorods, have been prepared by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process at low temperature (120 °C). The XRD pattern indicated that the flowerlike ZnO nanostructures were hexagonal. Furthermore, the SAED and HRTEM revealed that the swordlike ZnO nanorods were single crystal in nature and preferentially grew up along [001]. Finally, the mechanism for the CTAB-assisted hydrothermal synthesis of flowerlike ZnO nanostructures has been preliminarily explained by polar crystal growth theory and surfactant action theory.

Synthesis of flower-like ZnO nanostructures by an organic-free hydrothermal process

Flower-like ZnO nanostructures, which consisted of sword-like ZnO nanorods, have beenprepared by an organic-free hydrothermal process. The XRD pattern indicated thatthe flower-like ZnO nanostructures were hexagonal. The SAED and HRTEMexperiments implied that the sword-like ZnO nanorods were single crystal in nature andpreferentially grew up along the [001] direction. The effects of temperature, pH value andmineralizer on the morphology have been also investigated. It is considered thatpH value is the main factor to influence the morphology because of its effect onthe initial nuclei and growth environment of ZnO. Finally, the mechanism fororganic-free hydrothermal synthesis of the flower-like ZnO nanostructure is discussed.