Mechanism of formation of urchin-like ZnO

Thin films composed of ZnO nanowires (NWs) hierarchically organized with an urchin-like 3D morphology were obtained by combining the electrochemical deposition and sphere lithography methods. Deposited on a transparent conductive oxide substrate (TCO), a monolayer of carboxylate modified polystyrene spheres organized with a hexagonal closed-packed structure played the role of a template. The spheres were activated in a solution of zinc chloride by the formation of bonds between the carboxylate terminals and the Zn²⁺ ions and were used as a template for the electrodeposition of vertically aligned ZnO NWs around them. Without this treatment, ZnO NWs were deposited only on the TCO substrate between the PS spheres. To reach a density of nanowires high enough to obtain the urchin morphology, the concentration of ZnCl₂ had to be at least equal to 2 M. It was also found, as soon as small grains of ZnO started to be electrodeposited on the polystyrene spheres that the spheres were no longer close packed. The space created between them increased with the increase in the number of small ZnO grains and the increase in their length, allowing the further growth of the nanowires between the spheres. As a result the initial round shape of the spheres was modified and the urchin-like ZnO exhibited an ellipsoidal shape.     

Formation of dual-responsive polystyrene/polyaniline microspheres with sea urchin-like and core-shell morphologies

In the present work, a simple and effective approach has been employed to fabricate the polystyrene/polyaniline (PS/PANI) composite microspheres with various morphologies. PS/PANI composite microspheres exhibiting different structures such as sea-urchin like, core-shell structure, have been synthesized by seeded emulsion polymerization with polystyrene microspheres as seeds. In particular, the sea urchin-like PS/PANI composite microspheres, with radial array nanofibers on the surface, have demonstrated the switchable wettability between superhydrophilicity (0°) and superhydrophobicity (152°) under the response of either electrical potential or pH. This intelligible approach can produce sea urchin-like PS/PANI composite microspheres in bulk. The growth mechanism of sea urchin-like PS/PANI composite microspheres has also been elucidated. Following the dissolution of the PS template, the sea urchin-like polyaniline (PANI) hollow microspheres are obtained.     

Synthesis of carbon nanosheets from Kapton polyimide by microwave plasma treatment

Vertically-aligned carbon nanosheets (CNSs) have been fabricated on the Cu substrate from Kapton polyimide (PI) film under Ar/H₂ plasma irradiation. The high purity CNSs possess petal-like structures with many sharp edges, which are composed of few-layer graphene sheets. In addition, the irradiated Kapton PI film was covered by a layer of urchin-like carbon particles with about 4 μm in diameter, which also consist of few-layer graphene sheets along radial directions. Except for the morphologies, both the CNSs and urchin-like carbon particles demonstrate similar microstructures and chemical compositions.     

Enhanced optical confinement and lasing characteristics of individual urchin-like ZnO microstructures prepared by oxidation of metallic Zn

We prepared urchin-like micron-sized ZnO cavities with high optical quality by oxidizing metallic Zn and proposed the mechanism that resulted in the growth of the urchin-like microstructures. The photoluminescence spectra of the ZnO microstructures had a predominant excitonic emission at room temperature. The lasing properties of the urchin-like ZnO microstructures were investigated systematically through excitation power- and size-dependent photoluminescence measurements. The results showed that a low lasing threshold with high quality factors could be achieved because of the high reflectivity of the optical reflectors formed by the tapered nanowires. The unique optical characteristics may facilitate the development of high-efficiency random lasers.     

Optimization of mechanical and tribological properties of carbon fabric/resin composites via controlling ZnO nanorods morphology

The multi-scale reinforcements of ZnO nanorods/carbon fabric with different morphologies were obtained using a simple water bath method via controlling the concentration of growth solution for a new application in wet friction materials. The ZnO nanorods/carbon fabric were characterized via X-ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectra. As a result, the ZnO nanorods/carbon fabric/resin composite (sample CP3) possesses the maximum bending and tensile strength of 62.7?MPa and 170.0?MPa, which increases by 40.2% and 59.1% compared with that of bare carbon fabric/resin composite due to the best mechanical interlocking and chemical adhesion at the interfacial region of the composite. Meanwhile, the wear rate of the sample CP3 decreases obviously by 81.5% together with stable friction coefficient under various friction condition. From view point of material design, it is necessary to control the morphologies of ZnO nanorods to optimize mechanical and tribological properties of ZnO nanorods/carbon fabric/resin composites.     

MnO2 prepared by hydrothermal method and electrochemical performance as anode for lithium-ion battery

Two α-MnO₂ crystals with caddice-clew-like and urchin-like morphologies are prepared by the hydrothermal method, and their structure and electrochemical performance are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), galvanostatic cell cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The morphology of the MnO₂ prepared under acidic condition is urchin-like, while the one prepared under neutral condition is caddice-clew-like. The identical crystalline phase of MnO₂ crystals is essential to evaluate the relationship between electrochemical performances and morphologies for lithium-ion battery application. In this study, urchin-like α-MnO₂ crystals with compact structure have better electrochemical performance due to the higher specific capacity and lower impedance. We find that the relationship between electrochemical performance and morphology is different when MnO₂ material used as electrochemical supercapacitor or as anode of lithium-ion battery. For lithium-ion battery application, urchin-like MnO₂ material has better electrochemical performance.     

Fabrication of Porous SiC Ceramics with Special Morphologies by Sacrificing Template Method

Sacrificial template technique is widely used in producing porous materials with controlled morphologies and tailored properties. In this paper, unique templates such as filters, carbon nanotube, carbon fiber and silica were used to make porous SiC ceramic with special morphologies. Template derived porous ceramic plates, SiC nano-net, fiber-inverse and bead-inverse porous SiC ceramic were successfully prepared from the preceramic precursor, polymethylsilane (PMS). The synthesis procedures were involved with the infiltration of the templates with appropriate concentration of the preceramic polymer, their curing, pyrolysis and subsequent template removal. The synthesized porous SiC was characterized by SEM, TEM, XRD and BET methods.     

ZnO基复合材料的改性研究

通过恒温水浴法制备了ZnO纳米墙,以ZnO纳米墙为限域生长模板,通过化学气相沉积法将固态碳源(樟脑)气化沉积在ZnO纳米墙上形成石墨烯@ZnO纳米墙复合薄膜。制备的石墨烯@ZnO纳米墙复合薄膜结构比较稳定。与传统的ZnO/石墨烯材料相比,材料垂直生长,具有更大的比表面积,不易发生团聚等优点。     

Preparation and hydrophobicities of biomorphic ZnO based on carbon derived from indicalamus leaf template

Abstract

Some plant leaves possess a superhydrophobicity because of the exclusive structures on their surfaces. Many methods were developed to imitate the leaf structures in order to obtain the superhydrophobic ZnO. However, it is difficult to simulate the natural complex structures through the traditional methods. In the present study, we used an indicalamus leaf as a template to fabricate a superhydrophobic biomorphic ZnO on a carbon substrate (ZnO/C). First, a carbon substrate with a leaf microstructure was obtained by sintering an indicalamus leaf in argon. The biomorphic ZnO/C was then obtained by immersing this carbon substrate into a Zn(NO₃)₂ solution and again sintering it. This ZnO/C exhibited superhydrophobicity after it was modified with fluorine silane. The water contact angle of the resulting product was 163°, which is similar to that of the indicalamus leaf (159°) and is much higher than that of smooth carbon covered with the same fluorine silane (114°).     

Theoretical Computational Fluid Dynamics Study of the Chemical Vapor Deposition Process for the Manufacturing of a Highly Porous 3D Carbon Foam

Aerographite is a three‐dimensional carbon foam with a tetrapodal morphology. The manufacturing of aerographite is carried out in a chemical vapor deposition (CVD) process, based on a zinc oxide (ZnO) template, in which the morphology is replicated into a hollow carbon shell. During the replication process, the template is reduced by the simultaneous formation of the carbon structure. The CVD process is one of the most efficient methods for the manufacturing of various carbon nanostructures, such as graphene or carbon nanotubes (CNTs). Based on the growth mechanism of aerographite, a computational fluid dynamics model is presented for the fundamental investigations of the temperature and flow/microflow behavior during the replication process. This allows a deeper process understanding and further optimizations.     

采用高吸水树脂为模板制备新型纳米炭材料的研究

首先采用高吸水树脂为模板,制备了四重网络结构高吸水树脂,然后采用四重高吸水树脂为有机模板,蔗糖为炭源制备了新型纳米炭材料,研究了四重高吸水树脂的高分子网络结构及蔗糖溶液的浓度对新型纳米炭材料微观结构的影响。研究结果表明：采用四重高吸水树脂为模板可以制备出新型纳米炭颗粒,这些纳米炭颗粒可以自组装成不同的微观形貌。XRD和Raman的研究结果表明,蔗糖的浓度对新型炭材料的微观结构也有较大的影响。     

Growth and formation mechanism of sea urchin-like ZnO nanostructures on Si

Sea urchin-like nanostructures of ZnO consisting of ZnO nanowires with blunt faceted ends were grown on Si (100) substrates by oxidation of metallic Zn at 600 °C. ZnO nanowires having a diameter of 30–60 nm and length of 2–4 Μm were in similar shape with uniform diameter along its entire length with well faceted blunt ends. X-ray diffraction and transmission electron microscope analysis showed that the as-grown nanostructures were highly crystalline with wurtzite hexagonal structure having lattice constants of a=b=3.25 å and c=5.21 å. Room temperature photoluminescence (PL) measurements showed a weak near band-edge emission at 380 nm, but a strong green emission at 500–530 nm. A model for vapor-solid (VS) growth mechanism of ZnO nanowires was presented, in which nucleation of ZnO is crucial for the growth of the nanostructures.     

以碳球为模板的核壳型结构的制备与表征

利用表面具有羟基和羧基等活性机团的碳球和铜-碳核壳微球（Cu@C）作为模板,通过一个简单的过程合成各种ZnO的中空结构（包括氧化铜-氧化锌铃铛型中空结构）。该方法在合成氧化铜中空球时具有明显优势。     

Effects of etching parameters on ZnO nanotubes evolved from hydrothermally synthesized ZnO nanorods

This paper reports fabrication and characterization of ZnO nanotubes on Au cylindrical spirals. Highly oriented single-crystalline ZnO nanorods were hydrothermally synthesized on Au cylindrical spirals and were etched in NaOH solution to form nanotubes. Effects of etching parameters on the lengths, wall thicknesses and morphologies of the ZnO nanotubes were studied with the etching period, etching temperature and NaOH concentration regulated respectively. It turns out that the etching parameters affect significantly the morphologies of the ZnO nanotubes but negligibly the lengths and wall thicknesses. The surfaces of the ZnO nanotube-coated Au cylindrical spirals tend to be Gaussian rough ones as the etching parameters become larger. Adjusting the etching temperature readily gives rise to perfect ZnO nanotubes. The results are beneficial for large-scale preparation of ZnO nanotubes with controllable sizes and morphologies in nanodevices.     

Mesoporous carbon spheres grafted with carbon nanofibers for high-rate electric double layer capacitors

Carbon nanofibers were grafted onto mesoporous carbon spheres to produce “sea urchin-like” mesoporous carbon with a nanofiber content of 25 wt.%. Because of its combined features of high electronic conductivity and efficient electrolyte transport, the sea urchin-like mesoporous carbon assembled in electric double layer capacitors shows outstanding high-rate performance with a voltammetric scan rate as high as 3000 mV s⁻¹. Ac impedance analysis shows that this method of carbon nanofiber grafting promotes electronic percolation and ionic transportation in the carbon electrode, reducing the capacitive relaxation time to less than one fourth of its original value. Electrochemical oxidation in sea urchin-like mesoporous carbon produces a capacitance increase of ca. 200% while retaining high electronic and ionic conductivities in the electrode.     

Preparation of highly ordered ZnO nanowire arrays by paired-cell deposition

Highly ordered ZnO nanowire arrays were fabricated by paired cell method into nanoporous anodic alumina oxide (AAO) template. ZnO nanowires were uniformly assembled into the ordered channels of the AAO template. TEM and selected-area electron diffraction patterns indicated that the ZnO nanowires grow as a single crystal. The factors influencing the final filled density of ZnO nanowires, including the solution concentration and the diffusing temperature are discussed briefly. In addition, the possible mechanism is also proposed to account for the growth of the ZnO nanowires in the AAO template. This result has established that this paired cell method makes it possible to grow single-crystalline ZnO nanowires in the AAO template under appropriate conditions.     

不同醇溶剂中氧化锌纳米晶的可控制备

采用液相直接沉淀法,以醋酸锌和氢氧化钠为原料,在醇溶剂体系中成功制备出不同形貌的ZnO纳米晶,使用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和紫外-可见分光光度计(UV-vis)等检测方法对样品进行表征.结果表明,制备的ZnO均为六方纤锌矿结构,形貌受到溶剂种类、反应温度和反应时间等因素影响;在乙醇溶剂中,通过反应温度和反应时间控制可得到分散均匀、形貌均一纳米颗粒或纳米棒,并对不同形貌ZnO的生长机理进行了初步讨论.     

原子层沉积氧化锌功能化碳纳米管织物及其光催化特性

以二乙基锌和去离子水为前驱体,利用原子层沉积(ALD)在自支撑碳纳米管(CNT)织物上沉积氧化锌(ZnO)对其进行了功能化;考察了ALD沉积过程中功能化织物的微观形貌、晶型结构、表面性质及光催化性能.实验结果表明,ZnO最初在CNTs表面生长为纳米颗粒,随ALD循环次数的增加,逐渐形成包覆CNTs的保形生长层,改变AL...     

XPS and optical studies of different morphologies of ZnO nanostructures prepared by microwave methods

Zinc oxide (ZnO) nanostructures of various morphologies were prepared using a microwave-assisted aqueous solution method. Herein, a comparative study between three different morphologies of ZnO nanostructures, namely nanoparticles (NPs), nanoflowers (NFs) and nanorods (NRs) has been reviewed and presented. The morphologies of the prepared powders have been studied using field effect scanning electron microscopy (FESEM). X-ray diffraction (XRD) results prove that ZnO nanorods have biggest crystallite size compared with nanoflowers and nanoparticles. The texture coefficient (T_c) of three morphologies has been calculated. The T_c changed with varying morphology. A comparative study of surfaces of NPs, NFs and NRs were investigated using X-ray photoelectron spectroscopy (XPS). The possible growth mechanisms of ZnO NPs, NFs and NRs have been described. The optical properties of the ZnO nanostructures of various morphologies have been investigated and showed that the biggest crystallite size of ZnO nanostructures has lowest band gap energy. The obtained results are in agreement with experimental and theoretical data of other researchers.     

A CTAB-assisted hydrothermal and solvothermal synthesis of ZnO nanopowders

ZnO nanopowders were synthesized by hydrothermal and solvothermal method by using CTAB as surfactant, and the effects of CTAB on the morphologies of ZnO nanopowders were investigated. The results showed that the presence of CTAB could greatly vary the shape of the ZnO crystals. ZnO nanorods were prepared from the hydrothermal system without CTAB and flowers-like ZnO nanostructures were produced from hydrothermal system with 0.4 M and 0.5 M CTAB. Low concentration of CTAB in ethanol was conducive to the formation of ZnO nanorods, but the concentration continued to increase, the morphology of sample transformed into hexagonal bipyramid, and then transformed into spherical. The synthesis mechanism of ZnO powders with different morphologies has been presented.