Improved dye-sensitized solar cell with a ZnO nanotree photoanode by hydrothermal method

This study investigated the influence of ZnO nanostructures on dye adsorption to increase the photovoltaic conversion efficiency of solar cells. ZnO nanostructures were grown in both tree-like and nanorod (NR) arrays on an AZO/FTO film structure by using a hydrothermal method. The results were observed in detail using X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), UV-visible spectrophotometry, electrochemical impedance spectroscopy, and solar simulation. The selective growth of tree-like ZnO was found to exhibit higher dye adsorption loading and conversion efficiency than ZnO NRs. The multiple ‘branches’ of ‘tree-like nanostructures’ increases the surface area for higher light harvesting and dye loading while reducing charge recombination. These improvements result in a 15% enhancement in power conversion. The objective of this study is to facilitate the development of a ZnO-based dye-sensitized solar cell.     

Synthesis of ZnO nanoparticles by an aerosol process

Spherical nano-sized zinc oxide (ZnO) particles were produced by a spray pyrolysis method using the aerosol technique described in this study. The effects of reaction temperatures of 600, 800 and 1000 °C and collection locations of the particles, such as the flask collector and the tube exit, on the morphology and crystal structure of the ZnO particles were investigated. X-ray diffraction (XRD) studies showed that the crystallinity of the particles was increased by increasing the reaction temperature from 600 °C to 1000 °C. Fourier transform infrared spectroscopy (FTIR) measurements revealed that the particles were pure and similar to each other. Scanning electron microscopy (SEM) revealed that the synthesized nanoparticles had sizes between 200 nm and 400 nm, with uniform morphologies. A computational fluid dynamics (CFD) model of the horizontally positioned tube reactor was developed. Simulation results provided information about the residence time and the temperature distribution along the tube, which were found to be correlated to the particle morphology.     

Morphology control of ZnO crystalline particles in aqueous solution

We developed an aqueous solution process to synthesize crystalline ZnO particles and control their morphology. ZnO crystals were prepared in an aqueous solution containing zinc acetate and ammonia at 50 °C with no additional phase. ZnO particles having long hexagonal cylinder, short hexagonal cylinder, rounded hexagonal cylinder, rounded ellipse, pointed ellipse or multi-needle shapes were homogeneously nucleated and precipitated in solution. Crystal growth and preferential growth faces were controlled by solution conditions. Morphological control techniques in this system will contribute to the development of solution chemistry for inorganic materials and future oxide devices.     

The NaxMnO2 materials prepared by a glycine-nitrate method as advanced cathode materials for aqueous sodium-ion rechargeable batteries

Cathodic material for sodium-ion rechargeable batteries based on Na_xMnO₂ were synthesized by glycine nitrate method and subsequent annealing at high temperatures. Different crystal structures with different morphologies were obtained depending on the annealing temperature: hexagonal layeredα-Na_0.7MnO_2.05 nanoplates were obtained at 850 °C, while 3-D tunnel structured Na_0·4MnO₂ and Na_0·44MnO₂, both with rod-like morphology, were obtained at 800 °C and 900 °C, respectively. The investigations of the electrochemical behavior of obtained cathodic materials in aqueous NaNO₃ solution have shown that Na_0·44MnO₂ obtained at 900 °C has shown the best battery performance. Its initial discharge capacities are 123.5 mA h/g, 113.2 mA h/g, and 102.0 mA h/g at the high current densities of 1000, 2000 and 5000 mA/g, respectively.     

Preparation of ZnO/Eu mixed films by electrochemical precipitation

The electrochemical preparation of europium doped zinc oxide and europium oxide/hydroxide as thin films is investigated. First, a thermodynamic study of the Eu-Cl-H₂O system has been carried out at 25 and 70 °C in order to predict the electrochemical behaviour of Eu(III) dissolved in aqueous solution containing chloride ions. A comparison of the Eu-Cl-H₂O and Zn-Cl-H₂O systems indicates the possible coprecipitation of ZnO and Eu(OH)₃ from deposition solutions containing well-adjusted Eu(III)/Zn(II) concentrations ratio. The thermodynamic predictions have been confirmed experimentally by the electrochemical co-deposition of ZnO/Eu thin films on conducting electrode substrates at −1.4 V versus MSE. The presence of europium in the film is detected for Eu(III)/Zn(II) concentration ratio at (0.6 mM/5 mM) which is lower than the predicted value. Increasing Eu(III) concentration leads to the rapid appearance of two phases: dispersed zinc oxide nanorods and, at the bottom of the rods, a covering layer containing Eu(OH)₃ and zinc. The density of ZnO rods decreases and the rod size increases with increasing Eu(III) concentration in the bath. Above 1 mM EuCl₃, a dramatic fall in the current density is observed with the formation of a less conducting ZnO/Eu mixed deposit.     

Controlled synthesis of defects-containing ZnO by the French process modified with pulsed injection and its luminescence properties

Zinc oxide (ZnO) nanoparticles containing oxygen vacancies were synthesized by the French process modified with pulsed injection of nitrogen. Zinc vapor was generated by evaporation of zinc foil and carried by a carrier gas to react with co-currently supplied air. During the reaction, nitrogen gas was injected in pulse, perpendicular to the flow direction of both zinc vapor and air. Low partial pressure of oxygen and turbulence caused by pulsed injection yielded uniform ZnO nanotetrapods that contained oxygen vacancies. The content of oxygen vacancies depended upon the characteristics of the pulse, i.e. flowing and non-flowing period of the gas, pulsing cycle time, and the supplied pressure of the injected gas. Strong correlation between the presence of oxygen vacancies and the intensity of green emission in the photoluminescence spectra of ZnO was also observed.     

Controllable synthesis of ZnO nanostructures on the Si substrate by a hydrothermal route

In this paper, controllable synthesis of various ZnO nanostructures was achieved via a simple and cost-effective hydrothermal process on the Si substrate. The morphology evolution of the ZnO nanostructures was well monitored by tuning hydrothermal growth parameters, such as the seed layer, solution concentration, reaction temperature, and surfactant. X-ray diffraction and photoluminescence measurements reveal that crystal quality and optical properties crucially depend on the morphology of the ZnO nanostructures. The ease of synthesis and convenience to tune morphology and optical properties bring this approach great potential for nanoscale applications.     

Ultra-rapid microwave-assisted synthesis of gallium doped zinc oxide for enhanced photocurrent generation

Ultra-rapid microwave-assisted hydrothermal synthesis was performed, zinc oxide nanoparticles were fabricated and doped with gallium. Different times (5, 15, and 30 min) and concentrations of doped Ga (1, 3, and 6%) were used to improve their characteristic properties. In addition, the relation between time/dopant was analyzed. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and UV–Vis diffuse reflectance spectroscopy. Photoluminescence (PL) to verify number of defects. SEM analysis showed the formation of nanorods morphology even with a short synthesis time. The X-ray diffractograms and Raman spectra suggest the successful insertion of Ga into the ZnO lattice. The crystallite size obtained by doping was between 36 and 50 nm. The lattice parameters determined by the Rietveld refinement confirmed the formation of a wurtzite hexagonal structure. The band gap range found was 3.12–3.22 eV, which increases the potential of ZnO for optical applications. The presence of defects as result of doping was confirmed by PL. The microstructural changes of the material are enhanced by doping, which causes the photocurrent to increase from 0,002 to 0.012 mA/cm² in doped ZnO. The synthesis time and Ga doping facilitated the production of ZnO nanoparticles with improved properties.     

Magnetic Properties of Ni-doped ZnO Nanocombs by CVD Approach

The search for above room temperature ferromagnetism in dilute magnetic semiconductors has been intense in recent year. Arrays of perpendicular ferromagnetic nanowire/rods have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple low-temperature chemical vapor deposition (CVD) to create self-assembled comb-like Ni-/undoped ZnO nanostructure arrays. The phases, compositions, and physical properties of the studied samples were analyzed by different techniques, including high-resolution X-ray diffraction/photoelectron spectroscopy/transmission electron microscopy, photoluminescence, and MPMS. In particular, the Ni-doped ZnO nanocombs (NCs) with ferromagnetic and superparamagnetic properties have been observed whereas undoped ZnO NCs disappear. The corresponding ferromagnetic source mechanism is discussed, in which defects such as O vacancies would play an important role.     

TEA协助层状LZH到ZnO纳米材料控制生长机制研究

三乙醇胺(TEA)协助下类水滑石氢氧化物碱式硝酸锌(LZH)结构到二维层状氧化锌纳米片(ZnO)转变及其性能研究相对较少。以Zn(NO₃)₂为锌源,借助于三乙醇胺/水体系,研究制备LZH和二维氧化锌纳米片工艺条件及影响合成层状LZH和氧化锌纳米材料的各种因素。利用X-射线粉末衍射(PXRD)、扫描电镜(SEM)、红外光谱(FT-IR)、荧光光谱(PL)等技术手段对其进行解析和表征,探讨层状碱式硝酸锌和氧化锌纳米材料之间的转变机制。结果表明:在研究范围内,温度和反应时间的改变不会影响产物的组成和结构,TEA用量直接影响到合成的目标产物。首先生成Zn(OH)₂,其次转化为Zn₅(OH)₈(NO₃)₂·2H₂O,过渡生成[Zn₅(OH)_10-x·2H₂O]^x+,最终自组装形成层状ZnO二维纳米材料,从而实现无需焙烧,通过控制TEA用...     

Determination of aerosol kinetics of thermal ZnO dissociation by thermogravimetry

The thermal decomposition of ZnO is the high temperature solar step in a two-step water splitting process for sustainable H₂ production. To optimize aerosol solar reactor design, it is desired to understand the forward kinetics of this reaction in an aerosol configuration. Non-isothermal thermogravimetric (TG) experiments were conducted to determine the applicability of TG kinetic data to aerosol reactor environments. It was found that the differentiating heat and mass transfer factors—initial loaded mass, particle size, and heating rate—had no statistically significant effect on the activation energy or pre-exponential factor. This allowed TG data to be applied to the aerosol case. Isothermal TG experiments were subsequently performed to determine the kinetic rate parameters. Using the model expression

     

Phase formation,microstructure development and thermoelectric properties of (ZnO)kIn2O3 ceramics

The (ZnO)_kIn₂O₃ system is interesting for applications in the fields of thermoelectrics and opto-electronics. In this study we resolve the complex homologous phase evolution with increasing temperature in polycrystalline ceramics for k = 5, 11 and 18 and its influence on the microstructural development and thermoelectric properties. The phase formation at temperatures above 1000 °C is influenced by the local ZnO-to-In₂O₃ ratio in the starting-powder mixture. While the Zn₅In₂O₈ equilibrium phase for k = 5 is formed directly after sintering at 1200 °C, the formation of the k = 11 and k = 18 equilibrium phases proceeds at higher temperatures by diffusion between the initially formed phases, the lower k Zn₅In₂O₈/Zn₇In₂O₁₀ and the higher k Zn_kIn₂O_k+3 (9 < k < ∞). Such phase formation affects the sintering and grain growth, and consequently, with the degree of structural and compositional homogeneity, also the thermoelectric characteristics of the (ZnO)_kIn₂O₃ ceramics.     

花形氧化锌光催化剂的制备

介绍了一种简单的由Na2CO3和ZnSO4·7H2O在无表面活性剂条件下,沉淀反应制备花形氧化锌的方法。用甲基橙作为模型化合物研究了产物在紫外灯下的光催化降解性能。使用扫描电镜、X-射线衍射、红外光谱和紫外光谱等手段对产物结构进行了表征。X-射线衍射结果表明制备的产物为氧化锌,扫描电镜的结果表明氧化锌的形貌是由纳米片组成的花形微米球。     

Synthesis, photocatalytic and antibacterial activities of ZnO particles modified by diblock copolymer

Various shapes of ZnO particles were synthesized through a precipitation method as a low cost technique. The morphological changes due to the use of poly(ethylene oxide)-b-poly(propylene oxide) copolymer as a stabilizer and precipitation from pH solutions of 8, 10 and 12 were investigated. The ZnO powder that was prepared from pH 10 showed the highest efficiency for degrading the dyes methylene blue, rhodamine B and reactive orange under backlight fluorescent tubes. This may be due to the highest surface area obtained from precipitation at this pH. These prepared ZnO particles also exhibited antibacterial effects that were stronger on Staphylococcus aureus than on Escherichia coli.     

Temperature effects on ZnO electrodeposition

A thermochemical study of the temperature effects on the Zn-Cl-H₂O system by means of potential-pH, solubility and species repartition diagrams is presented with the view to better understand the effect of temperature on the deposition mechanism and composition of zinc oxide thin films. These calculations have been completed by film preparation at different temperatures between room temperature and 90 °C. Below 34 °C, we observe the absence of continuous film growth and surface passivation. The oxide nucleation and film growth start above 34 °C, whereas the optimum film transparency and crystallinity is obtained from 40 °C. Above, the main effect of the temperature is to raise the film texturation with the c-axis perpendicular to the substrate surface.     

Thermodynamic analysis of ZnO nanoparticle formation by wire explosion process and characterization

Zinc Oxide (ZnO) nanoparticles were synthesized by wire explosion process through deposition of different levels of energy to the exploding conductor in oxygen ambience at different pressures. The produced nanoparticles were analyzed by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and by Brunauer-Emmett-Teller (BET) studies. Energy dependent formation reaction mechanisms were formulated based on Born-Haber cycle. The size dependent gas phase reaction energetics was analyzed by using Hess's diagram. Butler's multicomponent molten oxide model was adopted to predict the surface tension of ZnO. Thermodynamic modelling studies revealed that the amount of energy deposited has an impact on saturation ratio, activation free energy, and nucleation rate of nanoparticles. It is observed based on experimental and modelling studies that the amount of energy deposited to the current carrying conductor, ambient pressure of oxygen and the saturation ratio influence the size of nanoparticle formed.     

Anomalous luminescence phenomena of indium-doped ZnO nanostructures grown on Si substrates by the hydrothermal method

In recent years, zinc oxide (ZnO) has become one of the most popular research materials due to its unique properties and various applications. ZnO is an intrinsic semiconductor, with a wide bandgap (3.37 eV) and large exciton binding energy (60 meV) making it suitable for many optical applications. In this experiment, the simple hydrothermal method is used to grow indium-doped ZnO nanostructures on a silicon wafer, which are then annealed at different temperatures (400°C to 1,000°C) in an abundant oxygen atmosphere. This study discusses the surface structure and optical characteristic of ZnO nanomaterials. The structure of the ZnO nanostructures is analyzed by X-ray diffraction, the superficial state by scanning electron microscopy, and the optical measurements which are carried out using the temperature-dependent photoluminescence (PL) spectra. In this study, we discuss the broad peak energy of the yellow-orange emission which shows tendency towards a blueshift with the temperature increase in the PL spectra. This differs from other common semiconductors which have an increase in their peak energy of deep-level emission along with measurement temperature.     

Photoluminescence of hydrothermally epitaxied ZnO films

In this study, epitaxial ZnO films were grown hydrothermally on (1 1 1)-oriented single crystal MgAl₂O₄ substrates at 150 °C from aqueous precursor solutions. It was observed that the film morphology varied with the pH value of the precursor solution, giving pitted films at higher pH and smooth films at lower pH. The photoluminescence spectra of these ZnO films showed a strong near band-edge ultraviolet emission together with deep level emission bands comprised of green and orange-red luminescence. The green band centred around 500 nm was attributed to the presence of Zn vacancies, whereas the orange-red band centred around 650 nm could be related to the presence of oxygen interstitials.     

Interior-architectured ZnO nanostructure for enhanced electrical conductivity via stepwise fabrication process

Fabrication of ZnO nanostructure via direct patterning based on sol-gel process has advantages of low-cost, vacuum-free, and rapid process and producibility on flexible or non-uniform substrates. Recently, it has been applied in light-emitting devices and advanced nanopatterning. However, application as an electrically conducting layer processed at low temperature has been limited by its high resistivity due to interior structure. In this paper, we report interior-architecturing of sol-gel-based ZnO nanostructure for the enhanced electrical conductivity. Stepwise fabrication process combining the nanoimprint lithography (NIL) process with an additional growth process was newly applied. Changes in morphology, interior structure, and electrical characteristics of the fabricated ZnO nanolines were analyzed. It was shown that filling structural voids in ZnO nanolines with nanocrystalline ZnO contributed to reducing electrical resistivity. Both rigid and flexible substrates were adopted for the device implementation, and the robustness of ZnO nanostructure on flexible substrate was verified. Interior-architecturing of ZnO nanostructure lends itself well to the tunability of morphological, electrical, and optical characteristics of nanopatterned inorganic materials with the large-area, low-cost, and low-temperature producibility.     

One-step synthesis of ZnO nanosheets: a blue-white fluorophore

ABSTRACT: Zinc oxide is synthesised at low temperature (80[DEGREE SIGN]C) in nanosheet geometry using a substrate-free, single-step, wet-chemical method and is found to act as a blue-white fluorophore. Investigation by atomic force microscopy, electron microscopy, and X-ray diffraction confirms zinc oxide material of nanosheet morphology where the individual nanosheets are polycrystalline in nature with the crystalline structure being of wurtzite character. Raman spectroscopy indicates the presence of various defects, while photoluminescence measurements show intense green (centre wavelength approximately 515 nm) blue (approximately 450 nm), and less dominant red (approximately 640 nm) emissions due to a variety of vacancy and interstitial defects, mostly associated with surfaces or grain boundaries. The resulting colour coordinate on the CIE-1931 standard is (0.23, 0.33), demonstrating potential for use as a blue-white fluorescent coating in conjunction with ultraviolet emitting LEDs. Although the defects are often treated as draw-backs of ZnO, here we demonstrate useful broadband visible fluorescence properties in as-prepared ZnO.