Engineering ZnO nanowire surfaces via a chemical method

Quasi‐aligned porous ZnO nanowire arrays are promising architectures for potential applications in catalysts, gas sensors and solar cells. However, processes for conversion of ZnO nanowire arrays into porous ones have rarely been reported. Here, we report a facile chemical method for the synthesis of ZnO nanowire array with porous surface. The morphology and structure of the obtained products have been investigated with field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy. Time‐dependent experiments have also been carried out to better understand the formation process of porous structures on the nanowire surfaces. The obtained porous ZnO nanowire arrays may find potential applications in catalysts, solar cells and gas sensors due to the large surface area of the yielded products.     

用AAO模板法制备高度定向碳纳米管阵列的研究进展

用二步氧化法可以在草酸或硫酸中制备多孔氧化铝（AAO）模板,这种模板成本低,高度有序,六角排列。利用化学气相沉积技术可以制备高度定向生长的碳纳米管,这将有利于研究碳纳米管的性质和它在纳米电子器件及其他领域的应用。本文介绍了AAO模板的阳极氧化工艺,成膜机理以及不同电解液,氧化电流、电压等因素对纳米孔道的影响。讨论了催化剂和气相沉积温度对碳纳米管特性的影响,并指出这种制备碳纳米管的技术需要深入研究的问题。     

TiO_2纳米管阵列的制备及其光催化性能研究

采用阳极氧化法在钛箔上制备了TiO_2纳米管阵列,利用场发射扫描电子显微镜(FSEM)、X射线衍射仪(XRD)和紫外-可见分光光度计对TiO_2纳米管的形貌、结构和光学性能进行表征,详细考察了阳极氧化工艺参数对纳米管阵列形貌的影响,探讨了氧化钛纳米管阵列的形成机理,并对其光催化活性进行了测试,研究结果表明:在0.5 wt; HF和1 mol/L H3PO_4电解液中,控制氧化电压为20 V,反应60 min后,在钛箔表面可获得垂直导向的TiO_2纳米管阵列,管内径为60~80 nm,管壁厚约10 nm;600 ℃热处理后的TiO_2纳米管阵列薄膜对349.7 nm近紫外光和443.9 nm可见光有较强的吸收能力;煅烧温度对纳米管的晶型结构和光催化活性有显著影响.     

Synthesis and characterization of Bi3.15Nd0.85Ti3O12 nanotube arrays

Nd-substituted bismuth titanate (Bi_3.15Nd_0.85Ti₃O₁₂, BNT) nanotube arrays are fabricated by means of a sol–gel method utilizing porous anodic aluminum oxide (AAO) template. The morphologies and structures have been determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diameter and length of these nanotubes are about 200 nm and 60 μm, respectively, and their wall thickness is about 30 nm. The average grain size is around 40 nm. XRD data show that the BNT nanotubes possess bismuth-layered perovskite structure. High-resolution electron microscopy (HRTEM) image demonstrates that the BNT nanotubes are polycrystalline. Polarization–electric field (P–E) response curves of BNT nanotube arrays were measured, and a size induced polarization reduction phenomenon is observed.     

The thermal stability of anodic alumina membranes at high temperatures

Nano‐structured anodic alumina membranes are ideal templates and have wide applications. However, anodic alumina materials begin to curl up at high temperatures. To better understand and overcome this problem, the thermal stability of anodic alumina membranes was investigated. Anodic alumina membranes obtained in oxalic acid electrolyte were heat treated in air at different annealing temperatures up to 1200 °C. Our results show that the sub‐pores produced during the annealing process are responsible for the curling. The repulsive forces between neighboring pores caused by mechanical stress at the metal nucleus/oxide interface promote the formation of the sub‐pores. Annealing under a suitable pressure provided thermal stability to the membranes, because it avoided or minimized curling and cracking phenomena. Scanning electron microscopy images showed that the sub‐pores disappeared when annealed under a suitable pressure.     

Synthesis and photoluminescence properties of ZnO nanowire arrays

In this paper we report a chemical method named coordination reaction method to synthesize ZnO nanowire arreys. ZnO nanowires with the diameter about 80nm were successfully fabricated in the channels of the porous anodic alumina (PAA) template by the above coordination reaction method. The microstructures of ZnO/PAA assembly were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The results showed that the ZnO nanowires can be uniformly assembled into the nanochannels of PAA template. The growth mechanism of ZnO nanowires and the conditions of the coordination reaction are discussed. Photoluminescence (PL) measurement shows that the ZnO/PAA assembly system has a blue emission band caused by the various defects of ZnO. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile synthesis and characterization of hierarchical CuO nanoarchitectures by a simple solution route

The controlled synthesis of hierarchical CuO nanomaterials in a solution phase has been realized with high yield at low temperature using copper acetate hydrate and NaOH as starting materials with the assistance of surfactant under hydrothermal conditions. X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet‐visible spectroscopy (UV‐Vis) were used to characterize the products. It was shown that the hierarchical CuO nanoarchitectures were formed through aggregation of tiny single‐crystal CuO nanorods. Experiments demonstrated that the morphology of CuO products was significantly influenced by hydrothermal temperature and reaction time. A rational growth mechanism based on oriented attachment was proposed for the selective formation of the hierarchical CuO nanoarchitectures. Our work demonstrated the growth of hierarchical CuO nanoarchitectures built from one‐dimentional nanorods through a one‐step solution‐phase chemical route under controlled conditions. In addition, The UV‐Vis spectrum of the hierarchical CuO nanoarchitectures showed large blue shift because of the quantum size effect. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural control and magnetic properties of electrodeposited Co nanowires

Co nanowires with a preferred orientation were fabricated by direct current electrodeposition into the pores of porous anodic alumina membrane, and the structure of Co nanowires was studied by X-ray diffraction and high-resolution transmission electron microscopy with selected-area electron diffraction. It is found that the crystal structure of Co nanowires lies on the deposition potential. When electrodeposition is performed far from equilibrium conditions, i.e., at a high potential, face-centered cubic Co nanowires are deposited, while hexagonal close packing Co nanowires are formed at the low potential. The experimental results indicate that the orientation of the nanowires has effects on the coercivity for both hexagonal close packing (hcp) and face-centered cubic (fcc) Co.     

Characteristics of Dye-Sensitized Solar Cells Using TiO2 Nanotube Arrays with Large Surface Area by Spin-Coating Nanoparticle

Highly ordered TiO₂ nanotube arrays (TNAs) fabricated by anodization are very attractive for use in dye-sensitized solar cells (DSSCs), because of their superior charge percolation and slow charge recombination. Highly ordered, vertically aligned TNAs have been prepared by three-step anodic oxidation. In this work, we investigated such strategies for improving the efficiency of DSSCs. Based on one of these approaches, oxide semiconductors in the form of a TNA were used as a novel method for improving electron transport through a film. A solution containing an appropriate amount of TiO₂ nanoparticles was prepared, and the mixed slurry was spin-coated on a TNA film. The coated film provided a large surface area for dye adsorption. The DSSCs achieved a light-to-electric energy conversion efficiency of 5.91% under simulated solar irradiation at 100 mW/cm² (AM 1.5).     

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)     

Fabrication and photocatalytic property of CuO nanosheets via a facile solution route

Two‐dimensional (2D) CuO nanosheets were fabricated on Cu foils using a solution method. The method was novel, easy and can be completed at room temperature in the absence of any surfactant. The obtained materials were characterized by X‐ray diffraction (XRD), X‐ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM) and ultraviolet‐visible (UV‐Vis) spectroscopy. The effects of reaction time and temperature on the morphology and formation of CuO nanosheets were investigated, and a possible mechanism for the formation of CuO nanosheets was proposed. Experiments demonstrated that the formation of CuO nanosheets were significantly influenced by the growth time, and the reaction temperature was a key factor in determining the size of CuO nanosheets. Photocatalytic performance of CuO nanosheets was evaluated by measuring the decomposition rate of methyl orange solution. About 93% of the methyl orange was degraded after 150 min, which was much more efficient than that of CuO nanoparticles.     

Ce/TiO2纳米管阵列的制备及光催化性能的研究

采用电化学阳极氧化法在钛表面制备TiO2纳米管阵列,并用稀土铈对其修饰改性.以甲基橙为目标降解物,考察了Ce3+溶液浓度、甲基橙溶液的初始浓度和初始pH对铈改性的TiO2纳米管光催化活性的影响.结果表明:Ce3+溶液的浓度存在一个最佳值,当Ce3+溶液浓度为0.01 mol/L,在10 mg/L,pH =3的甲基橙溶液中光催化活性最好.光照4h后,甲基橙的降解率达83％.     

纳米微结构材料多孔氧化铝膜的制备及应用

本文简要地介绍了多孔氧化铝理论模型的发展历程,采用目前较为成熟的阳极氧化法制备有序多孔氧化铝薄膜.讨论了多孔氧化铝自身的物理性质,重点展示了如何充分利用多孔氧化铝作为模板制备纳米材料的美好前景,明确了今后的工作重点为开拓新的应用领域及对多孔氧化铝膜孔径大小及孔的形状进行有效控制.     

Morphology control of CuO micro‐particles using Zn2+ ion and ultrasonic treatment

Novel tomato‐shaped copper oxide crystals has been prepared by a simple hydrothermal method with the presence of Zn²⁺ ion. The ultrasonic pretreatment has proved to be the key factor during the synthesis process. Scanning electron microscope, energy dispersive X‐ray spectrometry and powder X‐ray diffraction were used to characterize the microstructure and morphology of the as‐prepared products. The obtained tomato‐shaped CuO particles were constructed by nanorods with the diameter of about 20 nm. The possible growth mechanism was proposed based on the experimental results. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Noncatalytic synthesis of carbon nanotubes by chemical vapor deposition

A new method is proposed to obtain uniform arrays of multiwall carbon nanotubes without catalysts. Nanotubes have been formed by carbon condensation from a hydrogen-methane gas mixture activated by a dc discharge. Structural and morphological investigations of the obtained material were performed by Raman spectroscopy, scanning and transmission electron microscopy, energy-dispersive X-ray analysis, and electron energy loss spectroscopy. It is shown that the obtained nanotubes contain no impurities that could act as catalysts. Based on these experimental data, it is concluded that the nanotube synthesis under study is noncatalytic. Possible mechanisms of this synthesis are considered.     

Leaf‐like copper oxide nanocrystals synthesized by a gas‐liquid diffusion method at room temperature

The leaf‐like copper oxide (CuO) nanocrystals have been synthesized by a gas‐liquid diffusion method in pure aqueous solution at room temperature. The structure, morphologies and related properties of the as‐prepared crystals were characterized with X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED) and thermogravimetric analysis (TG). The influence of copper concentration was investigated, which plays an important role in the formation of nanostructured CuO crystals. Only when the copper concentration was low enough (0.005 M) that the leaf‐like CuO could be obtained directly. Additionally, a growth mechanism of CuO was also proposed based on the observed results.     

Facile synthesis of low dimensional CuO nanostructures and their gas sensing applications

A simple and cost effective hydrothermal method has been employed to synthesis morphology controlled pure and Cr doped (4 and 8 at. %) CuO nanostructures. Crystalline purity and structure of the nanostructures were validated by X‐ray diffraction and Retvield analyses. Field emission scanning electron microscopy revealed the evolution of rod‐like, sheet‐like and boat‐like morphologies for pure, 4 and 8 at. % Cr doped CuO nanostructures respectively. The optical band gap estimated using the K‐M function plot from diffused reflectance spectroscopy showed a shift in band gap from 1.68 to 1.90 eV with respect to Cr concentration. The synthesized CuO nanostructures were investigated for the efficient room temperature gas sensing of ammonia, ethanol and methanol vapours under different concentrations (100‐600 ppm). The 8 at. % Cr doped CuO nano‐boats showed enhanced gas sensitivity than other CuO nanostructures owing to their typical morphology, larger surface area and related properties.     

Fabrication and photocatalytic property of ZnO/SrTiO3 core/shell nanorod arrays

ZnO/SrTiO₃ core/shell nanorod arrays were fabricated by a facile two‐step method. ZnO nanorod arrays were first hydrothermally grown on Si substrate. Then, using liquid phase deposition method, SrTiO₃ were deposited onto the ZnO nanorods to form core/shell nanorod structures. The morphologies and structures of the products were characterized by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The photocatalytic behavior of the nanorod arrays was also examined through the photodegradation of methylene blue solution under UV irradiation. It was found that the core/shell nanorod arrays with deposition time of 10 min showed higher photocatalytic activity than bare ZnO nanorod arrays. This enhancement was attributed to the efficient charge separation at the ZnO/SrTiO₃ interface.     

用热CVD法制备片状碳纳米材料的研究

采用阳极氧化法在草酸溶液中制备了孔径约为100nm的多孔氧化铝(AAO)模板。利用此模板在不负载任何催化剂的条件下,利用热CVD装置制备出片状碳纳米薄膜,并对此片状薄膜做了SEM,TEM显微观察和EDS能谱分析,对其形成条件和生长机理等方面做了探讨分析,为在氧化铝模板上生长包括管状、片状、棒状等形状的碳纳米材料提供了一定的借鉴意义。     

Structural analysis of anodic alumina films

Structures of amorphous anodic alumina films have been investigated by the X-ray radial distrubution function and the correlation method. The amorphous anodic alumina films are considered to contain AlO₅ coordination polyhedra as well as AlO₄ tetrahedra and AlO₆ octahedra. Two types of conformation are taken into account by the correlation method; one (model A) is the conformation in which the above coordination polyhedra are arranged in a similar way to that found in the crystalline modifications of γ-Al₂O₃ within a short range of r < 4.5 Å and the other (model B) is the conformation in which coordination polyhedra are randomly arranged. The final model formed by mixing these two conformations (model A and B) in 1 : 1 ratio describes quantitatively the observed scattering intensity curves of the amorphous anodic alumina films.