联柱状ZnO微晶的微波合成及其光催化活性

以醋酸锌和六次甲基四胺为起始原料,表面活性剂CTAB和SDS为形貌控制剂,采用微波法合成了联柱状ZnO微晶,借助XRD、XPS、FT-IR、FT-Ra-man、TEM、SEM和UV-vis等测试技术对其进行了表征,并以甲基橙为模型污染物考察了样品的光催化活性.结果表明,所得样品均为六方纤锌矿ZnO;同时添加两种表面活性剂CTAB和SDS时所获样品形貌最佳,为六棱柱对接而成的联柱状结构,其在200～420nm波长范围内对光有较强吸收,对卷烟厂蒸叶车间废水的光降解表现出较高的催化活性,自然光照5h,废水COD去除率为84.7%;另外,对联柱状ZnO微晶的形成机理进行了初步探讨.     

Effect of Sn doping on microstructural and optical properties of ZnO nanoparticles synthesized by microwave irradiation method

Pure and Sn-doped ZnO nanostructures have been synthesized by the microwave irradiation method. The influence of Sn loading on the morphology and microstructure was evaluated by using field emission scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectrum analysis techniques, X-ray diffraction, and Fourier transform infrared spectroscopy. A change in the growth pattern, from needle-like particles for pure ZnO to agglomerated spherical crystallites for Sn-doped ZnO, has been observed. TEM observations indicated that the average particle size of the pure ZnO nano needles is in the range of 40–60 nm, whereas on addition of Sn spherical nanoassemblies size lies in the range of 10–21 nm. The pure ZnO and Sn-doped ZnO nanostructures were further characterized for their optical properties by UV–Vis reflectance spectra (DRS) and photoluminescence (PL) spectroscopy.     

Facile synthesis, optical and photoconductive properties of novel ZnO nanocones

Large-scale, uniform ZnO nanocones with tips about 200 nm and length about 50 μm have been synthesized by a facile hydrothermal method. The morphology and structures were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HR-TEM). The effects of reaction time and PEG-400 on the morphology of ZnO nanostructures were investigated, also an oriented attachment mechanism has been briefly proposed. The optical properties were investigated by lasing confocal microscope and photoluminescence spectrum, a strong near band edge emission peak centered at 387 nm from the ZnO nanocones was observed in photoluminescence spectrum. Finally, we have fabricated UV photodetector based on single ZnO nanocone, which present good switching properties by turning the UV light on and off.     

Structural and electrochemical studies of tungsten oxide (WO<Subscript>3</Subscript>) nanostructures prepared by microwave assisted wet-chemical technique for supercapacitor

Tungsten oxide (WO₃) nanostructures were synthesised using the microwave-assisted wet chemical method without any addition of surfactant for three different microwave irradiation times (10, 20 and 30 min). Then as-prepared nanostructures were characterised using various characterization techniques to know their structural, morphology and optical properties. The monoclinic and orthorhombic (WO₃) crystal structure was obtained from the as-prepared nanostructures by using X-ray diffraction analysis and its calculated crystalline size were found to be increased from 14 to 18 nm on increasing microwave irradiation time. The functional groups were investigated by using Fourier transform infrared spectroscopy analysis and the W–O chemical bonding nature was confirmed. The surface morphology was unclear using scanning electron microscope analysis, and a careful observation in high resolution transmission electron microscope studies shows that rod shaped structure. A blue-shifted optical absorption spectrum was observed by ultraviolet–visible spectroscopy analysis analysis and the bandgap energy value of WO₃ was calculated as approximately 3.62 eV. The emission behaviours were investigated by using photoluminescence spectrofluorometer analysis and an enhanced defect reduced emission was obtained. Finally, the electrochemical properties were analyzed by using cyclic voltammogram and galvanostatic charge–discharge analysis analyses. The maximum capacitance was recorded at 264 F/g which was declined to 149 F/g with the growth of WO₃ nanostructures size. Hence, the effect of microwave on structure and morphology, and consequent supercapacitor performances of WO₃ were discussed in details.     

ZnO microstructures and nanostructures prepared by sol-gel hydrothermal technique

Zinc oxide (ZnO) is an emerging material in large area electronic applications such as thin-film solar cells and transistors. We report on the fabrication and characterization of ZnO microstructures and nanostructures. The ZnO microstructures and nanostructures have been synthesized using sol-gel immerse technique on oxidized silicon substrates. Different precursor's concentrations ranging from 0.0001 M to 0.01 M (M=molarity) using zinc nitrate hexahydrate [Zn(NO3)2. 6H2O] and hexamethylenetetramine [C6H12N4] were employed in the synthesis of the ZnO structures. The surface morphologies were examined using scanning electron microscope (SEM) and atomic force microscope (AFM). In order to investigate the structural properties, the ZnO microstructures and nanostructures were measured using X-ray diffractometer (XRD). The optical properties of the ZnO structures were measured using photoluminescence (PL) and ultraviolet-visible (UV-Vis) spectroscopies.     

A comparative study on the NO2 gas sensing properties of ZnO thin films, nanowires and nanorods

ZnO thin films were fabricated using the spin coating method, ZnO nanowires by cathodically induced sol-gel deposition by the means of an anodic aluminum oxide (AAO) template, and ZnO nanorods with the hydrothermal technique. For thin film preparation, a clear, homogeneous and stable ZnO solution was prepared by the sol-gel method using zinc acetate (ZnAc) precursor which was then coated on a glass substrate with a spin coater. Vertically aligned ZnO nanowires which were approximately 65 nm in diameter and 10 μm in length were grown in an AAO template by applying a cathodic voltage in aqueous zinc nitrate solution at room temperature. For fabrication of the ZnO nanorods, the sol-gel ZnO solution was coated on glass substrate by spin coating as a seed layer. Then ZnO nanorods were grown in zinc nitrate and hexamthylenetetramine aqueous solution. The ZnO nanorods are approximately 30 nm in diameter and 500 nm in length. The ZnO thin film, ZnO nanowires and nanorods were characterized by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). The NO₂ gas sensing properties of ZnO thin films, nanowires and nanorods were investigated in a dark chamber at 200 °C in the concentration range of 100 ppb-10 ppm. It was found that the response times of both ZnO thin films and ZnO nanorods were approximately 30 s, and the sensor response was depended on shape and size of ZnO nanostructures and electrode configurations.     

Effect of solvents on the synthesis of nano-size zinc oxide and its properties

The effect of the solvents on particle size and morphology of ZnO is investigated. The optical properties of nano ZnO were studied extensively. During this study, zinc oxalate was prepared in aqueous and organic solvents using zinc acetate and oxalic acid as precursors. The thermo-gravimetric analysis (TGA/DTA) showed formation of ZnO at 400 °C. Nano-size zinc oxide was obtained by thermal decomposition of aqueous and organic mediated zinc oxalate at 450 °C. The phase purity was confirmed by XRD and crystal size determined from transmission electron microscopy (TEM) was found to be 22–25 nm for the aqueous and 14 –17 nm in organic mediated ZnO. Scanning electron microscope (SEM) also revealed different nature of surfaces and microstructures for zinc oxide obtained in aqueous and organic solvents. The UV absorption spectra showed sharp absorption peaks with a blue shift for organic mediated ZnO, due to monodispersity and lower particle size. Sharp peaks and absence of any impurity peaks in photoluminescence spectra (PLS) complement the above observations.     

Magnetic, optical and structural studies on Ag doped ZnO nanoparticles

The influences of annealing effects have been explored on the crystallinity, morphology, optical and magnetic properties of Ag–ZnO nanostructures prepared by a simple sol–gel method. X-ray powder diffraction, scanning electron microscope, high resolution transmission electron microscope (HRTEM), vibrating sample magnetometer and photoluminescence spectroscopy (PL) have been used to characterize the crystal structures, surface morphology, magnetic and optical properties of the pure ZnO and Ag–ZnO nanostructures respectively. The synthesized Ag–ZnO nanostructures are found to have hexagonal wurtzite crystal structures and their grain size increases while lattice strain decreases on annealing. From HRTEM observation, it is found that the annealed samples show nanorod like structures with Ag nanoparticles (NPs) embedded on the surface. Due to annealing effect, Ag–ZnO shows higher saturation magnetization at room temperature.     

Utilization of ZnO nanocones for the photocatalytic degradation of acridine orange

A facile aqueous solution process was used to synthesize well-crystalline ZnO nanocones at 60 degrees C by using zinc nitrate hexahydrate and sodium hydroxide. The morphological, structural and optical properties of the synthesized ZnO nanocones were investigated by using field emission scanning electron microscopy (FESEM) attached with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) equipped with high-resolution (HRTEM), X-ray diffraction (XRD) pattern, Fourier transform infrared (FTIR) spectroscopy and UV-Vis. spectroscopy measurements. The structural and optical properties of the as-synthesized nanocones confirmed a pure and well crystalline product possessing wurtzite hexagonal phase. The as-synthesized ZnO nanocones were used as photocatalyst for the efficient photocatalytic degradation of acridine orange. The acridine orange was almost completely degraded within 105 minutes. This research demonstrates that the simply synthesized ZnO nanostructures could be efficient photocatalyst for the photocatalytic degradation of various organic dyes and chemicals.     

Hybrid nanostructures of titanium-decorated ZnO nanowires

Hybrid nanostructures of titanium (Ti)-decorated zinc oxide (ZnO) nanowire were synthesized. Various thick Ti films (6 nm, 10 nm, and 20 nm) were coated to form a titanium oxide (TiO) coating layer around ZnO nanowires. Transmission electron microscope analysis was performed to verify the crystallinity and phases of the TiO layers according to the Ti-coating thickness. Under UV illumination, a bare ZnO nanowire showed a conventional n-type conducting performances. With a Ti coating on a ZnO nanowire, it was converted to a p-type conductor due to the existence of electron-captured oxygen molecules. It discusses the fabrication of Ti-decorated ZnO nanowires including the working mechanisms with respect to UV light.     

Synthesis and characterization of ZnO/SiO2 core/shell nanocomposites and hollow SiO2 nanostructures

In this paper, we prepared the ZnO nanoparticles by a simple hydrothermal method and fabricated the ZnO/SiO₂ core/shell nanostructures through a sol-gel chemistry process successfully. The hollow SiO₂ nanostructures were obtained by selective removal of the ZnO cores. The structure, morphology and composition of the products were determined by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the ZnO nanoparticles were sphere-like shape with the average size of 60 nm and belonged to hexagonal wurtzite crystal structure. With the coating of SiO₂, the vibration modes of Si-O-Si and Si-OH were found. Furthermore, the measurement results of optical properties showed that spectra of bare ZnO nanoparticles and ZnO/SiO₂ core/shell nanocomposites exhibited similar emission features, including a blue emission peak and an orange emission band.     

Fabrication of ordered flower-like ZnO nanostructures by a microwave and ultrasonic combined technique and their enhanced photocatalytic activity

Ordered flower-like zinc oxide (ZnO) nanostructures were fabricated via a facile microwave and ultrasonic combined technique. The product was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction pattern (SAED). The flower-like ZnO nanostructures were assembled by a central petal and six symmetrical petals which grew radially from the center. The flower-like ZnO sample showed an enhanced photocatalytic performance compared with the ZnO microrods for the methylene blue (MB) degradation, which could be attributed to its special structure feature. Au/ZnO and Ag/ZnO nanocomposites were also synthesized and exhibited enhanced photocatalytic efficiency after decorating noble metal nanoparticles on the surface of flower-like ZnO nanostructures.     

Structural properties and growth mechanism of flower-like ZnO structures obtained by simple solution method

Flower-shaped zinc oxide (ZnO) structures have been synthesized in the reaction of aqueous solution of zinc nitrate and NaOH at 90 °C. To examine the morphology of ZnO nanostructures, time-dependent experiments were carried out. Detailed structural observation showed that the flower-like structures consist of triangular-shaped leaves, having sharpened tips with wider bases. Photoluminescence spectrum measured at room temperature show a sharp UV emission at 381 nm and a strong and broad green emission at 480-750 nm attributed to structural defects. A possible growth mechanism for the formation of flower-shaped ZnO structures is discussed in detail.     

Preparation and characterization of vanadium-doped ZnO nanoparticles for environmental application

Vanadium-doped ZnO nanoparticles (ZnO:V) were prepared via flame spray pyrolysis (FSP) from a mixed aqueous solution of zinc hydroxide and vanadyl (IV) acetylacetonate. The morphological, structural and optical properties of the ZnO:V photocatalyst were characterized via transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and UV-visible diffused reflection spectrum (DRS). The photocatalytic activity of ZnO:V was evaluated via photocatalytic degradation of methylene blue (MB). The results showed that the hexagonal wurtzite-structured ZnO:V nanoparticles were successfully synthesized via FSP. The morphology of the as-prepared nanoparticles was polyhedral and non-hollow. The average diameter of ZnO:V, which was calculated from BET result, was 11.7 nm when the molar ratio of V/Zn was 0.1. The maximum decomposition of MB by the ZnO:V nanoparticles was 99.4% after 180 min under UV irradiation, whereas the decomposition of MB by the pure ZnO nanoparticles was 96.6%.     

Synthesis, characterization, UV and dielectric properties of hexagonal disklike ZnO particles embedded in polyimides

A series of novel ZnO/polyimide composite films with different ZnO contents was prepared through incorporation hexagonal disklike ZnO particles into poly(amic acid) of the pre polymer of the polyimide. The hexagonal disklike ZnO particles with a diameter of 300-500 nm were synthesized from zinc acetate and NaOH in water with citric acid. The prepared zinc oxide-polyimide composites were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy, scanning electron micrograph, X-ray diffraction and thermal analysis techniques. Thermal analyses show that the ZnO particles were successfully incorporated into the polymer matrix and these ZnO/polymer composites have a good thermal stability. Scanning electron microscopy studies indicate the ZnO particles were uniformly dispersed in the polymer and they remained at the original size (300-500 nm) before immobilization. All composite films with ZnO particle contents from 1 to 5 wt% show good transparency in the visible region and luminescent properties.     

ZnO nanoparticles: hydrothermal synthesis and 4-nitrophenol sensing property

In this paper reports a facile hydrothermal synthesis, characterization and sensing application of zinc oxide (ZnO) nanostructures. ZnO nanostructures were synthesized by mixing triethylamine (TEA) with zinc nitrate at 60?°C followed by calcination at 650?°C for 6 h. The detailed characterizations conformed the synthesized ZnO nanostructures. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectral analysis confirmed the formation of hexagonal ZnO. Band gap of the ZnO nanoparticles was determined by UV–visible absorption spectroscopy. Morphology and size of the sample was examined by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). It shows that the sample has rod and hexagonal morphology. Elemental composition was determined by energy dispersive X-ray (EDX) spectroscopy. The ZnO was coated on glassy carbon electrode (ZnO/GCE) and it was utilized as an electrochemical sensor for 4-nitrophenol (4-Np). Sensitivity and detection limit of ZnO/GCE towards 4-Np was found to be 0.04 µA/mM and 2.09?×?10^?5 M. The result suggests that ZnO has suitable sensor detection of 4-Np.     

Low temperature pH dependent synthesis of flower-like ZnO nanostructures with enhanced photocatalytic activity

In the present study we have synthesized flower-like ZnO nanostructures comprising of nanobelts of 20 nm width by template and surfactant free low-temperature (4 °C) aqueous solution route. The ZnO nanostructures exhibit flower-like morphology, having crystalline hexagonal wurtzite structure with (0 0 1) orientation. The flowers with size between 600 and 700 nm consist of ZnO units having crystallite size of ∼40 nm. Chemical and structural characterization reveals a significant role of precursor:ligand molar ratio, pH, and temperature in the formation of single-step flower-like ZnO at low temperature. Plausible growth mechanism for the formation of flower-like structure has been discussed in detail. Photoluminescence studies confirm formation of ZnO with the defects in crystal structure. The flower-like ZnO nanostructures exhibit enhanced photochemical degradation of methylene blue (MB) with the increased concentration of ligand, indicating attribution of structural features in the photocatalytic properties.     

Hollow CoNi alloy submicrospheres consisting of CoNi nanoplatelets: Facile synthesis and magnetic properties

Magnetic alloy micro/nanostructures with controllable size and morphology have drawn intensive attention due to their interesting physicochemical properties and potential applications in micro/nanodevices. In this letter, CoNi hollow submicrospheres consisting of CoNi nanoplatelets with a thickness of ca. 10 nm have been successfully synthesized via a facile wet-chemical approach free of any template or surfactant. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images indicate that the diameter and shell thickness of the as-prepared hollow submicrosphere are ca. 600 nm and 200 nm, respectively. Elemental maps demonstrate that Co and Ni elements are distributed homogeneously in the CoNi hollow submicrosphere. Magnetic measurement reveals that the hollow submicrospheres display ferromagnetic behaviour with a coercivity of 109.5 Oe.     

Tailor of ZnO morphology by heterogeneous nucleation in the aqueous solution

The umbrella-like ZnO nanostructures have been prepared by the morphological tailoring in the aqueous solution at 95 °C in the addition of heterogeneous seeds such as MnO₂ and CdS nanoparticles. The morphology and structure of as-synthesized umbrella-like ZnO nanostructures have been characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), electron energy loss spectroscopy (EELS), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The heterogeneous seeds play the critical role for the formation of umbrella-like ZnO nanostructures. Furthermore, the formation mechanism of the umbrella-like nanostructures has been phenomenally presented.     

ZnO micro and nanocrystals with enhanced visible light absorption

In this paper, we investigate the effect of the particle size and morphology on the optical properties of ZnO. A series of ZnO micro and nanocrystals were synthesized by the hydrothermal processing of zinc acetate dihydrate and sodium hydroxide as the starting materials, and polyvinylpyrrolidone (PVP) as the polymer surfactant. The particle size and morphology were tailored by adjusting the reactant molar ratios [Zn²⁺]/[OH⁻], while the reaction temperature and the time remained unchanged. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM) have shown that the micro and nanocrystals have a high crystalline pure wurtzite-type hexagonal structure with nanosized crystallites. The size and morphology of the ZnO micro and nanocrystals were investigated by field emission scanning electron microscopy (FE-SEM), which showed a modification from micro-rods via hexagonal-faceted prismatic morphology to nanospheres, caused by simple adjustment of the reactant molar ratio [Zn²⁺]/[OH⁻] from 1:1 to 1:5. The optical properties of the ZnO micro and nanocrystals, as well as their dependence on the particle size and morphology were investigated by Raman and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS). The UV–vis spectra showed that the modification of the particle size and morphology from nanospheres to micro-rods resulted in increased absorption, and a slight red-shift of the absorption edge (0.06 eV). Besides, the band gap energy of the synthesized ZnO micro and nanocrystals showed the red shift (∼0.20 eV) compared to bulk ZnO. According to the results of a Raman spectroscopy, the enhanced visible light absorption of the ZnO micro and nanocrystals is related to two phenomena: (1) the existence of lattice defects (oxygen vacancies and zinc interstitials), and (2) the particle surface sensitization by PVP.