Low temperature synthesis of spindle‐like ZnO nanostructures under microwave irradiation

A simple and general microwave route is developed to synthesize nanostructured ZnO using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single source precursor. The reaction time has a great influence on the morphology of the ZnO nanostructures and an interesting spindle‐like nanostructure is obtained. The microstructure and morphology of the synthesized materials are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that all of them with hexagonal wurtzite phase are of single crystalline structure in nature. Ultraviolet–visible (UV‐vis) absorption spectra of these ZnO nanostructures are investigated and a possible formation mechanism for the spindle‐like ZnO nanostructures is also proposed.     

Synthesis and growth mechanism of ZnO rod‐like nanostructures by a microwave‐assisted low‐temperature aqueous solution route

A zinc oxide (ZnO) nanoarray (rod‐like nanostructure) was successfully synthesized through a low‐temperature aqueous solution and microwave‐assisted synthesis using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (HMTA) as raw materials, and using FTO glass as substrate. The effects of parameters in the preparation process, such as solution concentration, reaction temperature and microwave power, on the morphology and microstructure of ZnO nanoarray were studied. Phase structure and morphology of the products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that hexagonal wurtzite structure ZnO nanoarray with good crystallization could be prepared through a low‐temperature solution method. When the concentration of the mixed solution was 0.05 M, the reaction temperature was 95 °C, and the reaction time was 4 h, high‐density ZnO regular nanorods of 200 nm diameter were obtained. A possible mechanism with different synthesis methods and the influence of microwave processing are also proposed in this paper.     

Photoluminescent hierarchical Zno micro‐flower and its surface wettability

The flower‐like ZnO with micro‐nano hierarchical structure is successfully obtained by a simple hydrothermal synthesis, using sodium dodecyl benzene sulfonate (SDBS) as a structure direct agent. The resulted ZnO micro‐flowers are very uniform in morphology with particle sizes around 1 µm. A number of techniques, including X‐ray diffraction (XRD), field emission scan electron microscopy (FESEM), energy‐dispersive spectroscopy (EDS), fourier transform infrared (FTIR) spectra and thermogravimetry analysis (TGA), are used to characterize the obtained ZnO. The self‐assemble of ZnO nano‐sheets under the direction of SDBS leads to the formation of ZnO micro‐flowers. The room temperature photoluminescence property of the obtained flower‐like ZnO exhibits a broad visible light emission. The surface of as‐made ZnO shows a very hydrophilic property, while the special micro‐nano hierarchical structure enables the ZnO micro‐flower a superhydrophobic surface after modification of fluoroalkylsilane.     

Electroless deposition of Cu dendrites decorated with ZnO rods

In this paper, copper dendrites decorated with ZnO rods have been electrolessly deposited on brass substrate by a simple galvanic replacement method. SEM images show that these copper dendrites possess a pronounced trunk and highly ordered branches distributed on both sides of the trunk. Meanwhile, both the trunk and branches are decorated with ZnO rods. The diffusion‐limited aggregation (DLA) model has been used to explain the fractal growth of Cu dendritic structures. This method provides a facile route to the synthesis of copper dendrites with ZnO, which can be extended to the preparation of other forms three‐dimensional (3‐D) metal structures or metal/ZnO composites by modifying electrolyte parameters such as composition, concentration, pH and temperature. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of radial‐like ZnO structure by hydrothermal method with ZnSO4·7H2O and Zn(CH3COO)2·2H2O as zinc sources

Radial‐like ZnO structures were prepared using zinc sulfate (ZnSO₄·7H₂O) and zinc acetate [Zn(CH₃COO)₂·2H₂O] as zinc sources by a facile template‐free hydrothermal method in this paper. Structural and optical properties of radial‐like ZnO structures are characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV‐vis spectrophotometer and photoluminescence measurement (PL). It has been found that the distinct surface morphologies of radial‐like ZnO structures grown by different zinc sources. Slim radial‐like ZnO with a hexagonal wurtzite structure is grown by using ZnSO₄·7H₂O as zinc sources, whereas coarse radial‐like ZnO with zincite structure is achieved by zinc acetate. The UV‐vis absorption spectra of them both display an obvious and significant absorption in the ultraviolet region. The room temperature PL spectra of ZnO structures grown by two different zinc sources possess a common feature that consists of a strong ultraviolet (UV) peak and visible emission band.     

Synthesis of flower‐like zinc oxide and polyaniline with worm‐like morphology and their applications in hybrid solar cells

ZnO with a “flower‐like” morphology was synthesized using a simple microwave assisted hydrothermal method and used as an acceptor material in hybrid solar cells. X‐Ray diffraction and Raman Spectroscopy confirmed the formation of a highly crystalline wurtzite ZnO structure. A highly crystalline and conductive polyaniline with “worm‐like” morphology was synthesized by chemical polymerization of aniline using KH(IO₃)₂ as an oxidant and was used as a donor material for solar cells. The morphology was probed by using scanning and transmission electron microscopy. Polyaniline with worm‐like morphology had a diameter of 160 nm and about 2 µm long. Solar cell device fabricated from PANI/ZnO active bilayer demonstrated a fill factor of about 22.8%. Upon blending PANI with ZnO the fill factor was improved to 25.6% and efficiency by almost 100 fold when PANI:ZnO 1:1 composite was used as an bulk heterogeneous active layer. The fill factor was further improved to 26.4% when device architecture was changed to diffused bilayer. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of flower‐like CdS prepared by a hydrothermal method with SDBS as surfactant

In this article, flower‐like CdS structures have been prepared by a hydrothermal method with SDBS as surfactant. The influences of different experimental conditions on the morphologies, UV‐Vis and fluorescence properties of CdS have been investigated. The performances of CdS have been analyzed by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet‐visible (UV–Vis) and room‐temperature photoluminescence (PL). The XRD result indicates that the flower‐like CdS structures are of hexagonal phase. The FESEM results indicate that the main role of SDBS is to make the CdS crystals assemble together to form the flower‐like structures. The UV–Vis results show CdS has a strong absorption in the ultraviolet region and visible‐light region. The PL results show CdS has two emission peaks, respectively at 461 nm and 553 nm. The growth mechanism for the formation of flower‐like CdS structures is also described.     

α‐Fe2O3 nanospindles loaded with ZnO nanocrystals: Synthesis and improved gas sensing performance

ZnO/α‐Fe₂O₃ nanocomposites were fabricated through a two‐step hydrothermal method. The morphology and composition of the as‐synthesized products were characterized by X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The gas sensing properties of the fabricated products were investigated towards ethanol, acetone, propanol, isopropanol, formaldehyde, chloroform and so on. The results demonstrated that the ZnO/α‐Fe₂O₃ nanocomposites exhibited excellent sensing properties and showed remarkably higher sensing responses and much lower optimum operating temperature compared to individual ZnO and α‐Fe₂O₃. In addition, the ZnO/α‐Fe₂O₃ nanocomposites have some selectivity for ethanol, propanol and isopropanol. The possible gas sensing mechanism was also proposed. Our studies demonstrate that our fabricated materials could be widely used in the future.     

Properties of InAs co‐doped ZnO thin films prepared by pulsed laser deposition

InAs co‐doped ZnO films were grown on sapphire substrates by pulsed laser deposition. The grown films have been characterized using X‐ray diffraction (XRD), Hall effect measurements, Atomic force microscope (AFM) and Field emission scanning electron microscope (FESEM) in order to investigate the structural, electrical, morphological and elemental properties of the films respectively. XRD analysis showed that all the films were highly orientated along the c‐axis. It was observed from Hall effect measurements that InAs co‐doped ZnO films were of n‐type conductivity. In addition, the presence of In and As has been confirmed by Energy dispersive X‐ray analysis. AFM images revealed that the surface roughness of the films was decreased upon the co‐doping. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology‐photocatalytic properties‐growth mechanism for ZnO nanostructures via microwave‐assisted hydrothermal synthesis

ZnO nanostructures with various morphologies including rod‐like, sheet‐like, needle‐like and flower‐like structures were successfully synthesized via a fast and facile microwave‐assisted hydrothermal process. Reaction temperature, reaction time and the addition of NaOH were adjusted to obtain ZnO with different morphologies. Scanning electron microscopy(SEM), transmission electron microscope(TEM), X‐ray diffraction (XRD) and ultraviolet spectrophotometer (UV) were used to observe the morphology, crystal structure, ultraviolet absorption and photocatalytic activity of the obtained ZnO. The results indicated that growth rate of ZnO nanostructure along [001] direction was more sensitive to temperature compared with those along [101] and [100] directions. The competition between anionic surfactant and OH⁻ played an important role in the formation of ZnO with various morphologies. Flower‐like ZnO had better ultraviolet absorption property and excellent photocatalytic activity than ZnO in the other morphologies. On the basis of the above results, a possible growth mechanism for the formation of ZnO nanostructures with different morphologies was described.     

Template‐free synthesis of hierarchical zinc oxide with improved photocatalytic properties

Novel hierarchical nano materials possess tremendous latent force in many applications. In this paper, hierarchical flower‐like, spherical and bowl‐like zinc oxide was successfully synthesized by altering solvent ratio (absolute ethanol and diethylene glycol) via a simple and template‐free solvothermal synthetic route. The solvent ratio also plays a vital role in deciding the structure, crystalline, band gap energy and specific surface area of the as‐synthesized samples. The preparation mechanism of ZnO in mixed alcohols was discussed. The obtained samples were characterized by energy dispersive spectroscopy(EDS), X‐ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), N2 adsorption‐desorption, UV–vis diffuse reflectance spectroscopy (DRS). Photocatalytic activity of the as‐prepared ZnO nanocrystals was evaluated by the degradation of MB under UV irradiation. Among, the most effective photocatalyst was synthesized when the diethylene glycol was 10 ml.     

Preparation of dendritic‐like CdS by hydrothermal method and its photocatalytic performance

In this article, dendritic‐like CdS has been prepared by a hydrothermal method using thiourea as the sulfur source, and the effects of experimental conditions on the morphologies of CdS have been investigated. The performances of CdS have been analyzed by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and the fluorescence and photodegradation properties of CdS have also been investigated. The XRD result indicates that the dendritic‐like CdS are of hexagonal phase and they are highly crystallized. Also, the FESEM results show that the ratio of raw material affects the yield of CdS, the reaction time affects the morphology of CdS. The best morphology of CdS is dendritic structures and the length is about 6 μm. The fluorescence spectrum shows three peaks at 470 nm, 513 nm and 547 nm, which indicates that the dendritic‐like CdS mainly emits green and blue fluorescence. Moreover, the dendritic‐like CdS exhibits good photocatalytic activity and its photodegradation rate to methylene blue can reach 92%. The growth mechanism for the formation of CdS with dendritic structure is also described.     

Large‐scale synthesis of submicron gallium oxide hydrate rods and their optical and electrochemical properties

Large‐scale submicron gallium oxide hydrate (GaOOH) rods have been synthesized by a simple hydrothermal process and their optical, electrochemical properties have been analyzed. The diameter of the GaOOH nanorods with good single crystalline structure is 80‐800 nm and length of less than 4 μm. The tips of the GaOOH structures are composed of nanorods with the diameter of less than 10 nm and length of more than 100 nm. Hydrothermal temperature, time and the Ga‐contained starting materials have important roles on the formation and growth of submicron GaOOH rods. The submicron GaOOH rods exhibit good UV‐vis absorption ability. The electrochemical analysis shows that the submicron GaOOH rods have good detecting ability for ascorbic acid and cysteine in PBS and NaCl solution exhibiting promising potential for electrochemical sensing application. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal conversion of ZnO2 to ZnO flowers: A mechanistic investigation and characterization

In this article, we report a novel but simple method for the phase transformation of ZnO₂ to flower‐like ZnO microstructures hydrothermally at 90 °C with and without the assistance of hexadecylamine as surfactant. The generation of zincate ion ZnO$^{2-}_{2}$ as a growth unit from the reaction between ZnO₂ and peroxide ion O$^{2-}_{2}$ in situ plays a key role in the phase transformation of ZnO₂ to ZnO. The morphology, structure, and composition of the products have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Powder X‐ray diffraction (PXRD) and energy dispersive X‐ray analysis (EDX). It has been demonstrated that the as‐fabricated ZnO flowers are composed of self‐assembled brooms and rods in the presence and absence of hexadecylamine respectively. On the basis of experimental results, a possible reaction mechanism and the growth processes involved in the formation of flower‐like ZnO microstructures are discussed.     

Solvothermal growth of highly oriented wurtzite‐structured ZnO nanotube arrays on zinc foil

ZnO nanotube arrays were synthesized on zinc foil by a simple solvothermal approach. In this approach, zinc foil was used not only as a substrate but also as a zinc‐ion source for the direct growth of ZnO nanotube arrays. X‐ray diffraction (XRD) analysis and Scanning electron microscope (SEM) images, indicated that the structure of the ZnO nanotube arrays on the zinc foil substrate was single‐crystalline with a wurtzite structure. The optical properties of the ZnO nanorod arrays were characterized by photoluminescence spectroscopies and Raman. Photoluminescence exhibited strong UV emission and a broad deep‐level (visible) emission emission at with 325 nm excitation. A possible mechanism is also proposed to account for the growth of the ZnO nanotube arrays. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of tunable 3D ZnO architectures assemblied with nanoplates

A simple hydrothermal method has been used to synthesize 3D ZnO architectures without any surfactants. The assemblies were composed of thin nanoplates with the thickness of about 35nm. X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) characterized the structure, morphology and optical property of products. The thickness of plates and assembly pattern can be controlled by adjusting the experimental parameters. Furthermore, these ZnO nanoplate assemblies exhibited enhanced photocatalytic activity in the degradation of methylene blue (MB). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of ZnO nanorods grown on Si substrates coated with NiCl2

ZnO nanorods were synthesized on NiCl₂‐coated Si substrates via a chemical vapor deposition (CVD) process. The as‐fabricated nanorods with diameters ranging from 150 nm to 200 nm and lengths up to several tens of micrometers grew preferentially arranged along [0001] direction, perpendicular to the (0002) plane. The clear lattice fringes in HRTEM image demonstrated the growth of good quality hexagonal single‐crystalline ZnO. Room temperature photoluminescence (PL) spectra illustrated that the ZnO nanorods exhibit strong UV emission peak and green emission peak, peak centers located at 388 nm and 506 nm. A possible growth mechanism based on the study of our X‐ray diffraction (XRD), electron microscopy and PL spectroscopy was proposed, emphasizing the effect of NiCl₂ solution (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anomalously Large Pockels Effect in ZnO‐F Single Crystalline Films Deposited on Bare Glass

Large linear electrooptics (the Pockels effect) of up to 17 pm/V for the wavelength 435 nm has been observed in ZnO films doped by fluorine and deposited on bare glass. In order to describe the phenomenon observed, a complex approach, including self‐consistent band structure calculations together with the appropriate molecular dynamics simulations of the interfaces, was applied. The origin of the effect observed is linked to substantial charge density non‐centrosymmetry between the wurtzitelike crystalline films and the bare glass substrate, as well as to additional charge density polarisation caused by the fluorine.     

Synthesis of ZnO nanorods by the thermal reduction process of a mixture of ZnO and Al powder

Single‐crystalline Zinc oxide (ZnO) nanorods were firstly synthesized on gold‐coated Si substrate via a simple thermal reduction method from the mixture of ZnO and Al powder. The growth process was carried out in a quartz tube at different temperature (550‐700 °C) and at different oxygen partial pressure. Their structure properties were investigated by X‐ray diffraction (XRD), scanning electron microscope (SEM), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The length of the as‐prepared ZnO nanorods was up to several micrometers and their diameters were about 130 nm. The X‐ray diffraction patterns, transmission electron microscopic images, and selective area electron diffraction patterns indicate that the one‐dimensional ZnO nanorods are a pure Single‐crystal and preferentially oriented in the [0001] direction. The reaction mechanism of ZnO nanorods was proposed on the basis of experimental data. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

梳子状ZnO纳米棒阵列的制备及表征

采用水热法在HTlc-ZnAlCO3纳米片上对称生长出平行排列的梳子状ZnO纳米棒.利用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)对得到的样品进行表征.揭示ZnO纳米棒的可控生长规律,在此基础上对其生长机理进行初步探讨.