Poly(zinc dimethacrylate) as a precursor in the low-temperature formation of ZnO nanoparticles

We present a simple, low-temperature synthesis of pure ZnO nanoparticles and polymer-ZnO hybrid materials formed by the NaOH-mediated conversion of poly(zinc dimethacrylate) in 1-butanol. The polymer poly(zinc dimethacrylate) was used as a precursor to prepare neat ZnO particles. It has a double role in the ZnO formation process, acting as a template and simultaneously controlling the crystal growth. The obtained single-crystalline ZnO nanorods show a low tendency to aggregate. The reaction mechanism of ZnO formation was proposed on the basis of a model system of the base-mediated conversion of a monomer zinc dimethacrylate Zn(MA)(2).     

Effect of seeded substrates on hydrothermally grown ZnO nanorods

We report a study on the effect of seeding on glass substrates with zinc oxide nanocrystallites towards the hydrothermal growth of ZnO nanorods from a zinc nitrate hexahydrate and hexamethylenetetramine solution at 95 °C. The seeding was done with pre-synthesized ZnO nanoparticles in isopropanol with diameters of about 6–7 nm as well as the direct growth of ZnO nanocrystallites on the substrates by the hydrolysis of pre-deposited zinc acetate film. The nanorods grown on ZnO nanoparticle seeds show uniform dimensions throughout the substrate but were not homogenously aligned vertically from the substrate and appeared like nanoflowers with nanorod petals. Nanorods grown from the crystallites formed in situ on the substrates displayed wide variations in dimension depending upon the preheating and annealing conditions. Annealing the seed crystals below 350 °C led to scattered growth directions whereupon preferential orientation of the nanorods perpendicular to the substrates was observed. High surface to volume ratio which is vital for gas sensing applications can be achieved by this simple hydrothermal growth of nanorods and the rod height and rod morphology can be controlled through the growth parameters.     

Photocatalytic formation of porous CdS/ZnO nanospheres and CdS nanotubes

It was found that ZnO nanocrystals have photocatalytic activity in the formation of CdS during the reduction of sulfur in the presence of cadmium acetate. It was shown that mesoporous spheres measuring 150–170 nm and consisting of CdS/ZnO particles measuring 5–8 nm are formed during the irradiation of ZnO particles measuring 5.5 nm. During the photodeposition of CdS by the action of light on nanorods produced by ultrasonic treatment of microcrystalline zinc oxide nanotubes of CdS 0.5–0.8 μm in length and 15–110 nm in internal diameter are formed. A mechanism, in which they appear at the ends of the ZnO nanorods and grow on the surface of the CdS/ZnO heterojunction, is proposed for the formation of the CdS nanotubes. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 215–219, July–August, 2007.     

Spectroscopic characterization of zinc oxide nanorods synthesized by solid-state reaction

Well-crystallized zinc oxide nanorods have been fabricated by single step solid-state reaction using zinc acetate and sodium hydroxide, at room temperature. The sodium lauryl sulfate (SLS) stabilized zinc oxide nanorods were characterized by using X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and photoluminescence spectroscopy. The X-ray diffraction revealed the wurtzite structure of zinc oxide. The size estimation by XRD and TEM confirmed that the ZnO nanorods are made of single crystals. The growth of zinc oxide crystals into rod shape was found to be closely related to its hexagonal nature. The mass ratio of SLS:ZnO in the nanorods was found to be 1:10 based on the thermogravimetric analysis. Blue shift of photoluminescence emission was noticed in the ZnO nanorods when compared to that of ZnO bulk. FT-IR analysis confirmed the binding of SLS with ZnO nanorods. Apart from ease of preparation, this method has the advantage of eco-friendliness since the solvent and other harmful chemicals were eliminated in the synthesis protocol.     

A simple preparation technique for shape-controlled zinc oxide nanoparticles: Formation of narrow size-distributed nanorods using seeds in aqueous solutions

Various shapes of wurtzite-type ZnO nanoparticles were selectively produced in a simple aqueous system prepared by mixing ZnSO₄ and NaOH solutions. Ellipsoidal nanoparticles were obtained by the addition of an alkaline agent into an acidic zinc solution (acidic route), while nanorods were grown by mixing a zinc precursor into an alkaline solution (basic route). The aspect ratio and size distribution of the nanorods grown through the basic routes were controlled by the addition of nanoparticles prepared by the acidic route as seeds. On the other hand, micrometric branching rods were obtained by dilution of the reaction solution in the basic routes. The morphological variation of ZnO particles is ascribed to the balance of the nucleation and crystal growth depending on the degree of the supersaturation. We successfully prepared narrow size-distributed rods with a nanometric width and a submicrometric length using the seed particles, because the presence of the seeds suppressed additional nucleation and then controlled the degree of the supersaturation for steady growth of the crystalline particles.     

Towards high‐performance biopackaging: barrier and mechanical properties of dual‐action polycaprolactone/zinc oxide nanocomposites

The properties of nanocomposites of biodegradable polycaprolactone containing zinc oxide (ZnO) nanoparticles with diverse morphologies, that is, ZnO nanospheres, nanorods, and nanodisks are investigated. It is demonstrated for the first time that the dual action of the ZnO nanoparticles reduces the gas permeability of the nanocomposites via two mechanisms: first by the creation of a tortuous path and second by gas adsorption. Depending on the morphology of the particles, the oxygen permeability can be reduced by more than 60%. Tensile tests show that the nanocomposites remain very ductile. The nominal strain for all nanocomposites is higher than 500% before fracture occurs. The Young's modulus and tensile strength of the nanocomposites increase at higher ZnO concentrations. This behavior is more pronounced in the case of ZnO nanorods. As a result, the incorporation of ZnO nanoparticles into (bio)polymers provides an opportunity to manufacture polymer‐based nanocomposite materials, resulting in the production of high‐performance (bio)packaging. Copyright © 2011 John Wiley & Sons, Ltd.     

一种在固体基底上制备高度取向氧化锌纳米棒的新方法

采用廉价、低温的方法，在修饰过ZnO纳米粒子膜的ITO基底上成功制备出具有 高长径比、高度取向的ZnO纳米棒阵列，用扫描电子显微镜(SEM)，X射线衍射(XRD) ，高分辨透射电子显微镜(HRTEM)以及拉曼光谱对制备出的ZnO纳米棒的结构和形貌 进行了表征，测试结果表明，ZnO纳米棒是单晶，属于六方晶系，与基底直，上仍 沿(001)晶面择优生长的特征，并且ZnO纳米棒基本上无氧空位的存在，统计结果显 示，水热反应2h后90%以上的ZnO纳米棒直径为120～190nm，长度为4μm     

Fast synthesis of ZnO nanostructures by laser-induced decomposition of zinc acetylacetonate

A CO2 laser (lambda = 10.6 microm) was used to heat a solution of water and alcohol saturated by Zn(AcAc)2 on a fused quartz substrate in open air. After only a few seconds of irradiation, various zinc oxide (ZnO) nanostructures including nanorods and nanowires are formed near the center of the irradiated zone, surrounded by a porous thin film of ZnO nanoparticles. The type of structures produced and their localization on the substrate can be varied by selecting adequate irradiation time and laser power ranges. The deposits have been analyzed using SEM, TEM, EDS, XRD, and Raman spectroscopy, revealing that the nanorods (aspect ratio ~6) and nanowires (aspect ratio ~94) are single-crystalline structures which grow along the c axis of wurtzite ZnO. The nanoparticles are also single-crystalline and have an average diameter of 16 nm. A qualitative model for nanostructure growth is proposed, based on previous studies of aqueous solution and hydrothermal processing.     

Photoswitching in azobenzene self-assembled monolayers capped on zinc oxide: nanodots vs nanorods

We report the synthesis and spectroscopic characterization of nanohybrid structures consisting of an azobenzene compound grafted on the surface of zinc oxide nanoparticles. Characteristic bathochromic shifts indicate that the azobenzene photochromic molecules self-assemble onto the surface of the nanocrystals. The extent of packing is dependent on the shape of the nanoparticle. ZnO nanorods, with flat facets, enable a tighter organization of the molecules in the self-assembled monolayer than in the case of nanodots that display a more curvated shape. Consistently, the efficiency of photochromic switching of the self-assembled monolayer on ZnO nanoparticles is also shown to be strongly affected by nanoparticle shape.     

Synthesis, characterization and study of photocatalytic activity of surface modified ZnO nanoparticles by PEG capping

Nanoparticles of bare and PEG (Polyethylene glycol) capped zinc oxide (ZnO) were synthesized by precipitation method. The photocatalytic activity of bare and modified ZnO nanoparticles was studied by monitoring the degradation of Rhodamine B (RhB). The results show that PEG capped ZnO nanoparticles has reduced photocatalytic activity than the bare ZnO nanoparticles. The reduction in the chemical oxygen demand (COD) and total organic carbon (TOC) results also revealed the reduced photocatalytic activity of PEG capped ZnO. The UV-shielding property was evaluated by measuring the transmittance which shows that both bare and PEG capped ZnO nanoparticles possess good UV-shielding ability.     

Controlled growth of well-aligned ZnO nanorod array using a novel solution method

A simple method of synthesizing nanomaterials and the ability to control the size and position of them are crucial for fabricating nanodevices. In this work, we developed a novel ammonia aqueous solution method for growing well-aligned ZnO nanorod arrays on a silicon substrate. For ZnO nanorod growth, a thin zinc metal seed layer was deposited on a silicon substrate by thermal evaporation. Uniform ZnO nanorods were grown on the zinc-coated silicon substrate in aqueous solution containing zinc nitrate and ammonia water. The growth temperature was as low as 60-90 degrees C and a 4-in. wafer size scale up was possible. The morphology of a zinc metal seed layer, pH, growth temperature, and concentration of zinc salt in aqueous solution were important parameters to determine growth characteristics such as average diameters and lengths of ZnO nanorods. We could demonstrate the discrete controlled growth of ZnO nanorods using sequential, tailored growth steps. By combining our novel solution method and general photolithography, we selectively grew ZnO nanorod arrays on a patterned silicon substrate. Our concepts on controlled ZnO nanorod growth using a simple solution method would be applicable for various nanodevice fabrications.     

Improvement of the performance of dye sensitized solar cell using ZnO nanorods array deposited with Ag nanoparticles as photoanode

Well-aligned zinc oxide (ZnO) nanorods (NRs) arrays deposited with Ag nanoparticles (NPs) are prepared by a liquid phase epitaxial growth process followed by a reduction of Ag on the surface of the ZnO NRs. Transmission electron microscopy images show that most Ag NPs are deposited on the upper part of the ZnO NRs, and the overall optical absorption in the range of visible light can be enhanced due to the surface plasmon resonance of the Ag NPs. ZnO NRs with and without Ag NPs are used to assemble dye sensitized solar cells. Devices fabricated from the Ag NPs/ZnO NRs composite arrays exhibit a higher open voltage, short circuit current and fill factor than that fabricated from the bare ZnO NRs array, thus, the overall efficiency of the as-fabricated cell is increased from less than 0.5?% to 0.8?%. The main reason for the enhancement of the device performance may be ascribed to that the electron transfer back from ZnO to the dye and electrolyte is blocked by the Schottky barrier at the Ag/ZnO interface, resulting in a great increase of the electron density at the ZnO conduction band.     

Controlled reduction of the deleterious effects of photocatalytic activity of ZnO nanoparticles by PVA capping

Nanoparticles of uncapped and PVA (poly vinyl alcohol) capped zinc oxide were synthesized by precipitation method. The synthesized ZnO nanoparticles were characterized by fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric-differential thermal analysis. The photocatalytic activity of bare and modified ZnO nanoparticles was studied by monitoring the degradation of Rhodamine B. The results show that PVA capped ZnO nanoparticles has reduced photocatalytic activity than the bare ZnO nanoparticles. The reduction in the chemical oxygen demand and total organic carbon results also revealed the reduced photocatalytic activity of PVA capped ZnO. The UV-shielding property was evaluated by measuring the transmittance which shows that both bare and PVA capped ZnO nanoparticles possess good UV-shielding ability.     

Electrochemical synthesis of ZnO nanorods/porous silicon composites and their gas-sensing properties at room temperature

The zinc oxide (ZnO) nanorods with different aspect ratio (length/diameter) were grown directly on the porous silicon (PS) substrate through electrochemical synthesis. The obtained ZnO nanorods/PS products were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and gas-sensing test. Comparative study shows that the addition of nonionic polymer polyvinylpyrrolidone (PVP) into oxygenated zinc chloride electrolyte can modulate the crystal growth and the aspect ratio of ZnO nanorods from electrodeposition, thus, influence the gas-sensing properties of ZnO nanorods/PS composites. With appropriate amount of PVP in the electrolyte, the product possessing high-density and large aspect ratio ZnO nanorods has an obvious improvement of the NO₂-sensing performances with high sensitivity, fast response-recovery characteristic, and good repeatability and selectivity. The gas-sensing mechanism was discussed in the paper. The result indicated that the heterojunction effect of ZnO nanorods and PS may be responsible for the excellent gas-sensing properties.     

Pt纳米花/ZnO复合阵列的制备及对甲醇氧化催化的研究

利用调控ZnO纳米棒阵列的疏水、亲水性,由电化学方法制备了Pt纳米花/ZnO(PtNF/ZnO)复合阵列.该复合阵列排列规则、尺寸均一、方向一致.每一根ZnO纳米棒的顶端都覆盖着由Pt纳米颗粒构成的Pt纳米花,具有大的比表面积.与以亲水性的ZnO纳米棒制得的覆盖Pt纳米颗粒的ZnO复合阵列(PtNP/ZnO)以及单独的Pt颗粒相比,PtNF/ZnO复合阵列对甲醇氧化具有更高的电化学催化活性.     

Straight and thin ZnO nanorods: hectogram-scale synthesis at low temperature and cathodoluminescence

A novel seed-assisted chemical reaction at 95 degrees C has been employed to synthesize uniform, straight, thin, and single-crystalline ZnO nanorods on a hectogram scale. The molar ratio of ZnO seed and zinc source plays a critical role in the preparation of thin ZnO nanorods. At a low molar ratio of ZnO seed and zinc source, javelin-like ZnO nanorods consisting of thin ZnO nanorods with a diameter of 100 nm and thick ZnO nanorods with a diameter of 200 nm have been obtained. In contrast, straight ZnO nanorods with a diameter of about 20 nm have been prepared. Dispersants such as poly(vinyl alcohol) act spatial obstructors to control the length of ZnO nanorods. The morphology, structure, and optical property of the ZnO nanostructures prepared under different conditions have been characterized by transmission electron microscopy, field emission scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and cathodoluminescence. The formation mechanisms for the synthesized nanostructures with different morphologies have been phenomenologically presented.     

ZnO纳米粒子结构对光电量子限域特性的影响

Zn O作为一种宽禁带 (3 .3 6e V)高激子结合能 (60 me V)的半导体材料已引起人们的关注 .Zn O纳米粒子的比表面积较大 ,表面活性较高 ,对周围环境敏感 ,使其成为传感器制作中最有前途的材料[1] ,还在太阳能转换[2 ] 、发光材料[3] 、半导体表面修饰与敏化[4 ] 、纳米电子学以及分子电子学器件[5] 等领域显示出广阔的应用前景 .制约这些应用的关键是 Zn O纳米粒子表面和界面的电子结构和电荷转移行为 ,但有关此方面的报道较少 .本文用溶胶 -凝胶法制备了不同粒径的 Zn O纳米粒子 ,应用表面光电压谱 (SPS)和场诱导表面光电压谱 (FISPS…     

Sensitive,Fast, Solution‐Processed Ultraviolet Detectors Based on Passivated Zinc Oxide Nanorods

Solution‐processed ultraviolet photodetectors based on passivated and unpassivated zinc oxide (ZnO) nanorods, in which the ZnO nanoparticles are synthesized by a hydrothermal method, are demonstrated and characterized. Photoconductive photodetectors fabricated using simple solution processing have recently been shown to exhibit high gains and outstanding sensitivities. One ostensible disadvantage of exploiting photoconductive gain is that the temporal response is limited by the release of carriers from trap states. Herein, specific chemical species are introduced onto the surfaces of ZnO nanoparticles to produce desired trap states with a carefully selected lifetime. Compared with conventional photodetectors based on ZnO nanoparticles, the proposed UV photodetectors have much higher photoresponses and faster response times in the UV region. The photoconductive gain of the fabricated photodetectors varies from 26.83 to 2.32×10² for passivated samples, which indicates high gain. The best temporal response for the fabricated detectors is 34 ms rise time and 132 ms decay time for ZnO nanoparticles passivated by hexamethylenetetramine.     

Hierarchically Structured ZnO Nanorods as an Efficient Photoanode for Dye‐Sensitized Solar Cells

Hierarchical ZnO nanorods composed of interconnected nanoparticles, which were synthesized by controlling precursor concentrations in a solvothermally assisted process, were exploited as photoanodes in dye‐sensitized solar cells (DSCs). The as‐prepared hierarchical nanorods showed greatly enhanced light scattering compared to ZnO nanoparticles for boosting light harvesting while maintaining sufficient dye‐adsorption capability. The charge‐transfer characteristics were studied by electrochemical impedance measurements, and reduced electron recombination and longer electron lifetime were observed for the ZnO nanorods. Photovoltaic characterization demonstrated that DSCs utilizing the hierarchical nanorods significantly improved the overall conversion efficiency by 34 % compared to nanoparticle‐based DSCs.     

Hydrothermal Synthesis and Field Enhancement Behavior of ZnO Nanorods Pattern

We provide a new way to prepare ZnO nanorods pattern from the solution composed of hexamethylenetetramine (HMT) and Zn(NO₃)₂. The substrate is ITO substrate covered by well ordered Au islands. Since Au and the underneath ITO substrate have two different nucleation rates in the initial stage of heterogeneous nucleation process, the subsequent ZnO growth on the quick nucleating area takes place under diffusion control and is able to confine the synthesis of ZnO nanorods to specific locations. The concentrations of zinc nitrate and HMT are well adjusted to show the possibility of the new route for the patterning of the ZnO nanorods. Furthermore, the nanorods pattern was characterized by X-ray diffraction and photoluminescence and the performance of field emission property from ZnO nanorod patterns was investigated. The ZnO nanorods pattern with a good alignment also shows a good field enhancement behavior with a high value of the field enhancement factor.