Hydrothermally grown ZnO NSs on Bi-Directional woven carbon fiber and effect of synthesis parameters on morphology

ZnO nanostructures on woven carbon fiber have been developed by hydrothermal technique under varying conditions of the process parameters. The impact of process parameters such as pH and molar concentration of precursor solution, growth duration and growth temperature on morphology and dimensions of ZnO nanostructures has been analyzed by Field Emission Gun-Scanning Electron Microscope, Energy Dispersive Spectroscopy (EDS) and UV-VIS-NIR spectroscopy. Different ZnO nanostructures of nanopallets-like, nanoflowers-like and nanoflakes-like were achieved at pH > 7 but nanorods-like and nanowires-like morphology were achieved at low pH. In addition, the impact of the chemical reactions, seeding and the growth process on ZnO nanostructures on woven carbon fibers has been discussed in the present work.     

On the control of carbon nanostructures for hydrogen storage applications

The storage of hydrogen in different carbon nanostructures has been investigated using classical Monte-Carlo simulations techniques. Very low hydrogen uptakes (?1% wt) have been calculated for single-walled and double-walled carbon nanotubes, as well as for graphite nanofibers at 293 K and 10 MPa. The amount of hydrogen uptake strongly depends on the porosity within the nanostructure network where optimal arrangements give rise to the formation of a well-defined two-dimensional adsorbed hydrogen layer. The presence of metallic impurities within single-walled nanotube bundles was modeled by disseminating atomic particles, characterized by a highly attractive potential, throughout the nanotube network. It has been found that the presence of metallic particles significantly enhances the hydrogen uptake, but not to a point where this could be considered a promising storage solution.     

Zinc oxide nanostructures and their applications

Zinc oxide (ZnO) has been known as the next most important material for the fabrication of efficient nanodevices and nanosystems because of its versatile properties such as semiconducting, piezoelectric, and pyroelectric multiple properties. In this review, the state-of-the-art technologies related to the synthesis and characterization, the selective growth of ZnO nanostructures, and their applications for nanodevices are discussed. A special concern is focused on the controlled selective growth of ZnO nanostructures on wanted areas of substrates, which is crucial factor for devices applications. The device applications of ZnO nanostructures include field effect transistors (FETs), field-emission devices, piezoelectric nanogenerators, biosensors, p-n heterjunction diodes such as light-emitting diodes and photovoltaic cells, and so on.     

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.     

Mechanistic aspects of molecular formation and crystallization of zinc oxide nanoparticles in benzyl alcohol

Zinc oxide nanostructures are known to exist in a great variety of morphologies. However, the underlying mechanisms leading to these architectures are far from being fully understood. Here, we present a time dependent study of the generation of zinc oxide nanorods, which arrange into bundles with a fan- or bouquet-like structure, using the benzyl alcohol route. The structural evolution of the nanoparticles was monitored by electron microscopy techniques, whereas the progress of the chemical reaction was followed by quantification of the organic by-products using gas chromatography. With this study we give a detailed insight into the formation of the zinc oxide structures, which involves a complex pathway based on many in parallel occurring processes such as crystallization of primary particles, their oriented attachment and surface reconstruction inside the nanoparticulate agglomerates. However, in spite of such an intricate growth behavior, the ZnO nanostructures are surprisingly uniform in size and shape.     

Controllable electrochemical synthesis of La/ZnO hierarchical nanostructures and their optical and magnetic properties

Here we presented a facile electrochemical deposition route for the controllable preparation of La³⁺/ZnO hierarchical nanostructures, such as flower-like nanostructures consisted of nanorods, flower bundles, and hexagonal nanorods with nests at the top. These prepared La³⁺/ZnO deposits were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectrophotometer, and photoluminescence spectroscopy. The formation process of La³⁺-doped ZnO and the growth mechanisms of La³⁺/ZnO hierarchical nanostructures were discussed. The UV and PL spectra measurements show that the surface morphologies of La³⁺/ZnO deposits have an obvious effect on their optical properties and we can easily adjust their optical properties as well as La³⁺/ZnO nanostructures by changing electrochemical deposition parameters. In addition, the magnetic properties of La³⁺/ZnO deposits were also investigated.     

Carbothermal Synthesis of the Nanostructures of Al2O3 and ZnO

Nanostructures of Al₂O₃ and ZnO have been synthesized by a carbothermal route involving the reaction of the metal or the metal oxide with carbon. In the case of Al₂O₃, nanowires and nanotubes are obtained starting with Al metal and active carbon or graphite. ZnO nanowires are obtained by the reaction of zinc oxalate or ZnO with active carbon or multiwalled carbon nanotubes. The Al₂O₃ and ZnO nanostructures obtained have been characterized by X-ray diffraction, electron microscopy and photoluminescence spectroscopy. These nanostructures are likely to be of use as catalyst supports and in other technological applications.     

Quantum Capacitance Extraction for Carbon Nanotube Interconnects

Electrical transport in metallic carbon nanotubes, especially the ones with diameters of the order of a few nanometers can be best described using the Tomanaga Luttinger liquid (TL) model. Recently, the TL model has been used to create a convenient transmission line like phenomenological model for carbon nanotubes. In this paper, we have characterized metallic nanotubes based on that model, quantifying the quantum capacitances of individual metallic single walled carbon nanotubes and crystalline bundles of single walled tubes of different diameters. Our calculations show that the quantum capacitances for both individual tubes and the bundles show a weak dependence on the diameters of their constituent tubes. The nanotube bundles exhibit a significantly large quantum capacitance due to enhancement of density of states at the Fermi level.     

Natural citric acid (lemon juice) assisted synthesis of ZnO nanostructures: Evaluation of phase composition,morphology, optical and thermal properties

In recent years, because of their excellent electrocatalytic action and applications in different fields, metal oxide nanostructures have received massive consideration from scientists. Zinc oxide nanostructures are useful materials for a range of sensing applications and possess admirable electrocatalytic properties and stability. The current research presents the natural citric acid assisted synthesis of ZnO nanostructures and their structural, optical, morphological and thermal properties. X-ray diffraction was studied for the phase assessment of as prepared (Z1) and annealed ZnO (Z2) nanostructures and the crystallite sizes of the Z1 and Z2 samples were also located in the range between 35 nm and 38 nm. FESEM and TEM experiments were carried out to explore the surface features of Z1 and Z2 samples. The polycrystalline existence of the samples is demonstrated by the hexagonal, cubic and spherical shaped ZnO nanostructures. The energy band gap of Z1 and Z2 samples was determined (3.16 eV for Z1 and 3.12 eV for Z2) from the UV spectrum. The impact of annealing treatment on the thermal stability of ZnO nanostructures was studied and the main peak was observed for the Z1 sample at ~249 °C and for the Z2 sample at ~289 °C.     

Surface characterization and properties of functionalized nonwoven

Nonwoven materials have been increasingly used in many industries. The surface properties of nonwoven materials are of importance in these applications. In this study, functional nonwoven materials were prepared by sputtering deposition of copper (Cu), zinc oxide (ZnO), and polytetrafluoroethylene (PTFE) on the surface of polypropylene (PP) fibers. Atomic Force Microscopy (AFM) and Environmental Scanning Electron Microscopy (ESEM) were employed to study the surface morphology and chemical compositions. The observations by AFM revealed the formation of functional nanostructures on the fibre surfaces and the ESEM examination confirmed the formation of functional compositions on the fiber surface. The metallic coating of Cu significantly improved the surface conductivity of the material. The transmittance analysis indicated that the ZnO coating obviously increased the ultra‐violet absorption of the material. The surface hydrophobicity of the nonwoven material was enhanced by the sputter coating of PTFE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Water induced protonation of amine-terminated micelles for direct syntheses of ZnO quantum dots and their cytotoxicity towards cancer

This work designs a new strategy for the direct synthesis of different zinc oxide (ZnO) nanostructures at low temperatures. Micelles of dodecylamine (DDA) assembled in an ethanol-water system have been explored as a template to direct the growth of the ZnO nanostructures. The key species for the formation of the ZnO nanostructures, OH(-), can be provided by the water-induced protonation of DDA. The pH of the reaction micro-environment can be regulated by changing the input amount of water and DDA. By controlling the reaction temperature and pH, various ZnO nanostructures, i.e. quantum dots with green or yellow-green emissions, have been prepared. The relationship of the optical properties and the synthetic conditions has been further discussed. This strategy realizes the convenient preparation of ZnO QDs, indicating the potential prospects in the nanotechnology field for their low-cost synthesis. Meanwhile, the cellular toxicity study of ZnO nanoparticles toward cancer cells, including leukemia K562 and K562/A02 cells as well as HepG2 cells, indicates a selective cytotoxic effect of ZnO QDs against a broad range of human cancer cell lines.     

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.     

Designing zinc oxide nanostructures (nanoworms,nanoflowers, nanowalls,and nanorods) by pulsed laser ablation technique for gas-sensing application

In this study, pulsed laser ablation technique, also known as pulsed laser deposition (PLD), is used to design and grow zinc oxide (ZnO) nanostructures (nanoworms, nanowalls, and nanorods) by template/seeding approach for gas-sensing applications. Conventionally, ZnO nanostructures used for gas-sensing have been usually prepared via chemical route, where the 3D/2D nanostructures are chemically synthesized and subsequently plated on an appropriate substrate. However, using pulsed laser ablation technique, the ZnO nanostructures are structurally designed and grown directly on a substrate using a two-step temperature-pressure seeding approach. This approach has been optimized to design various ZnO nanostructures by understanding the effect of substrate temperature in the 300-750°C range under O₂ gas pressure from 10-mTorr to 10 Torr. Using a thin ZnO seed layer as template that is deposited first at substrate temperature of ~300°C at background oxygen pressure of 10 mTorr on Si(100), ZnO nanostructures, such as nanoworms, nanowalls, and nanorods (with secondary flower-like growth) were grown at substrate temperatures and oxygen background pressures of (550°C and 2 Torr), (550°C and 0.5 Torr), and (650°C and 2 Torr), respectively. The morphology and the optical properties of ZnO nanostructures were examined by Scanning Electron Microscope (SEM-EDX), X-ray Diffraction (XRD), and photoluminescence (PL). The PLD-grown ZnO nanostructures are single-crystals and are highly oriented in the c-axis. The vapor-solid (VS) model is proposed to be responsible for the growth of ZnO nanostructures by PLD process. Furthermore, the ZnO nanowall structure is a very promising nanostructure due to its very high surface-to-volume ratio. Although ZnO nanowalls have been grown by other methods for sensor application, to this date, only a very few ZnO nanowalls have been grown by PLD for this purpose. In this regard, ZnO nanowall structures are deposited by PLD on an Al₂O₃ test sensor and assessed for their responses to CO and ethanol gases at 50 ppm, where good responses were observed at 350 and 400°C, respectively. The PLD-grown ZnO nanostructures are very excellent materials for potential applications such as in dye-sensitized solar cells, perovskite solar cells and biological and gas sensors.     

Synthesis of hybrid ZnO/CNTs nanoparticles and their reinforcement in nylon‐6 polymer fibers

In this investigation, in situ synthesis of zinc oxide nanoparticles in the presence of multiwalled carbon nanotubes (CNTs) have been carried out using a sonochemical technique. Zinc(II)acetate was used as a source of ZnO in the presence of ethylene glycol (EG) to obtain zinc oxide (ZnO) nanoparticles. The synthesized hybrid ZnO/CNTs nanoparticles were used as reinforcements to enhance the mechanical, thermal and UV absorbing properties of Nylon‐6 composite fibers. The polymer nanocomposites (PNC) were fabricated by dry mixing Nylon‐6 polymer powder with the ZnO/CNTs hybrid nanoparticles as the first step, then followed by the drying and melt extrusion process of fiber materials in a single‐screw extruder. The extruded fibers were stretched and stabilized using a godet set‐up and wound on a Wayne filament winder machine. The hybrid ZnO/CNTs infused Nylon‐6 composite fibers were compared with commercial ZnO, CNTs infused Nylon‐6 composite fibers and neat Nylon‐6 fibers for their structural and thermal properties. The morphological characteristics of ZnO/CNTs nanoparticles were carried out using X‐ray diffraction and transmission electron microscopy (TEM) techniques. The Nylon‐6 PNC fibers which were of ～80 μ size were tested mechanically. The tensile tests revealed that failure stress of the 1% infused ZnO/CNTs Nylon‐6 PNC fibers is about 73% higher than the neat extruded Nylon‐6 fiber and the improvement in the tensile modulus is 377.4%. The DSC results show an increase in the glass transition temperature and crystallization for ZnO/CNTs infused Nylon‐6 PNC fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Atomic Layer Deposition of ZnO on Multi-walled Carbon Nanotubes and Its Use for Synthesis of CNT–ZnO Heterostructures

In this article, direct coating of ZnO on PECVD-grown multi-walled carbon nanotubes (MWCNTs) is achieved using atomic layer deposition (ALD). Transmission electron microscopy investigation shows that the deposited ZnO shell is continuous and uniform, in contrast to the previously reported particle morphology. The ZnO layer has a good crystalline quality as indicated by Raman and photoluminescence (PL) measurements. We also show that such ZnO layer can be used as seed layer for subsequent hydrothermal growth of ZnO nanorods, resulting in branched CNT–inorganic hybrid nanostructures. Potentially, this method can also apply to the fabrication of ZnO-based hybrid nanostructures on other carbon nanomaterials.     

Characteristics of a dye-sensitized solar cell based on an anode combining ZnO nanostructures with vertically aligned carbon nanotubes

Electrical conductivity and a high surface area in the anode are of primary importance for the enhancement of photoelectric conversion efficiency (η) in dye-sensitized solar cells (DSSCs). This study reports on the fabrication of a DSSC anode using ZnO nanostructures. These ZnO nanostructures are coated on vertically aligned carbon nanotubes (CNTs) on stainless steel substrates using thermal chemical vapor deposition. The resulting CNTs provided a good electric connection between the ZnO overlayer and the stainless steel substrate. The photoelectric characteristics of the DSSCs were optimized with the immersion of dye for 15 hrs. Compared to the η of ZnO nanostructures on randomly distributed CNTs, the η of ZnO nanostructures on vertically aligned CNTs increased approximately 4-fold. This result showed that the vertically aligned CNTs coated with ZnO nanostructures had improved the performance of DSSC.     

Solution combustion synthesis of ZnO powders using CTAB as fuel

Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using cetyltrimethylammonium bromide (CTAB) as fuel. The effects of fuel to oxidant ratios (? = 0.5, 0.75, 1 and 1.5) on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy, and diffuse reflectance spectrometry techniques. The slow decomposition rate of CTAB guaranteed the direct formation of single phase and well-crystalline ZnO powders regardless of fuel content. The specific surface area of the as-combusted ZnO powders with platelet particles increased from 21 ± 1 to 35 ± 2?m²/g with fuel content. The band gap energy also increased from 2.99 to 3.13?eV due to the decrease of particle size. The as-combusted ZnO powders at ? = 1.5 exhibited the highest photodegradation (~69%) of methylene blue under ultraviolet light irradiation, due to their good crystallinity and smaller particle size.     

Nanostructured CNx (0 < x < 0.2) films grown by supersonic cluster beam deposition

Nanostructured CN_x thin films were prepared by supersonic cluster beam deposition (SCBD) and systematically characterized by transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The incorporation of nitrogen in the films (0 < x < 0.2) and the nanostructure were controlled by using different synthesis routes. Films containing bundles of well-ordered graphene multilayers, onions and nanotubes embedded in an amorphous matrix were grown alongside purely amorphous films by changing the deposition parameters. Graphitic nanostructures were synthesized without using metallic catalysts. The structural and electronic properties of the films have been studied by EELS. The role played by N in the carbon nanostructures has been deduced from XPS line-shape analysis.     

Facile synthesis of ZnO nanostructures and enhancement of their sinterability via short-time cryo-milling

Zinc oxide (ZnO), a wide band-gap semiconductor, has received a great interest due to its potential applications in various fields both as nanostructures and as sintered compacts. In this study, we report on the synthesis of the ZnO nanostructures and facilitation of their sintering for the production of fine-grained dense compacts. The facile synthesis of gram scale ZnO nanostructures was achieved by thermal decomposition of zinc acetate dihydrate (Zn(Ac)₂·2H₂O) or Zn(Ac)₂·2H₂O/graphite mixtures at 300 °C for 12 h. Thermal decomposition of Zn(Ac)₂ resulted in the formation of mostly ZnO nanoparticles with wurtzite structure along with ZnO nanorods, while the addition of graphite significantly promoted the growth of ZnO nanowires. Microstructural and phase properties of the obtained ZnO nanostructures were determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) techniques, all of which revealed the successful synthesis of high quality ZnO nanostructures. In addition to synthesis and characterization of the ZnO nanostructures, we report on the enhancement of their sinterability by a subsequent cryogenic milling for a short duration of 5 min. As a result of the applied cryo-milling, fabrication of highly dense (96.2%) sintered compacts with fine grain sizes (572 nm) could be achieved after pressureless sintering at 1000 °C for 2 h.     

氧化锌纳米棒阵列对芳纶的改性

利用湿化学方法在芳纶Ⅲ表面预制氧化锌(ZnO)晶种层,再在晶种膜的基础上制备出了垂直生长的ZnO纳米棒阵列。采用X射线衍射(XRD)、场发射扫描电镜(FE-SEM)和微脱黏试验对纤维表面的组成、形貌及复合材料的界面黏结性能进行了研究。结果表明:纤维表面生长的ZnO纳米棒阵列属于六方纤锌矿晶相,纳米棒垂直生长在纤维表面,增大了与基体的接触面积,能够使纤维更好地与环氧树脂基体间发生界面结合,进而有效改善芳纶Ⅲ-环氧复合材料的界面黏接强度。