Low-temperature growth of ZnO nanorods by chemical bath deposition

Aligned ZnO nanorod arrays were synthesized using a chemical bath deposition method at normal atmospheric pressure without any metal catalyst. A simple two-step process was developed for growing ZnO nanorods on a PET substrate at 90-95 degrees C. The ZnO seed precursor was prepared by a sol-gel reaction. ZnO nanorod arrays were fabricated on ZnO-seed-coated substrate. The ZnO seeds were indispensable for the aligned growth of ZnO nanorods. The ZnO nanorods had a length of 400-500 nm and a diameter of 25-50 nm. HR-TEM and XRD analysis confirmed that the ZnO nanorod is a single crystal with a wurtzite structure and its growth direction is [0001] (the c-axis). Photoluminescence measurements of ZnO nanorods revealed an intense ultraviolet peak at 378.3 nm (3.27 eV) at room temperature.     

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.     

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.     

Surface study of sintered alumina substrates using solution‐processed ZnO nanorods as a microscopic wettability indicator

Wettability and its distribution are crucial factors that indicate the surface conditions of substrates. We report a surface study of sintered alumina substrates using solution‐processed ZnO nanorods as a microscopic wettability indicator. The alumina substrates comprising of micrometer‐sized sintered grains were treated separately with ultraviolet/ozone (dry process) or ozone water (wet process), and their surface conditions were characterized by conventional surface analysis methods, such as water contact angle, X‐ray photoelectron spectroscopy and grazing angle attenuated total reflection Fourier transform infrared spectroscopy. The results showed that the alumina substrates treated with ultraviolet/ozone and ozone water had distinct clean surfaces compared to those without treatments, but no significant differences were noted between these two ozone‐based treatments. Then, as a wettability‐sensitive deposition technique, Pd‐catalyzed chemical deposition of ZnO nanorods was performed on the alumina substrates, which involved dip coating of Pd nanoparticles on the substrates in aqueous solutions, followed by the chemical solution growth of ZnO. Vertically aligned ZnO nanorods of ~85 nm in diameter were densely formed along a rough surface of the substrates. Morphological uniformity of the nanorods varied depending on the treatment condition; local surfaces with sufficient wettability provided uniform nanorods but those with insufficient wettability gave irregular nanorods, making the visualization of the microscopic surface wettability possible. Copyright © 2016 John Wiley & Sons, Ltd.     

籽晶层制备方式对氧化锌纳米棒阵列的影响

采用3种不同的方式制备ZnO薄膜籽晶层:旋涂、喷雾热解和脉冲激光沉积。对于每一种制备方式,其薄膜的晶体结构、形貌、表面粗糙度等性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)进行了表征。之后,通过水热合成方法,在3种籽晶层衬底上制备得到具有不同结构和形貌特征的ZnO纳米棒阵列。结果表明,ZnO纳米棒生长和籽晶层制备方式具有极强的相关性。最后,对两者相关性的生长机理进行了解释。     

From Zn-Al layered double hydroxide to ZnO nanostructure:Gradually etching by sodium hydroxide

Zn-Al layered double hydroxide(LDH) was used as precursor to produce ZnO nanostructures through dissolution of aluminum hydroxide in caustic soda.The Zn-Al LDH could transform into different nanostructures of ZnO on LDH nanosheets and even pure ZnO nanorods under various NaOH concentration.The formed ZnO nanorods vertically aligned on both LDH sides.UV-vis diverse reflectance spectra show that the obtained ZnO nanorods have a band gap of approximately 3.05 eV.Such ZnO/LDH nanostructures might be used as photocatalyst in the organic pollutant decomposition.     

基于柔性衬底的ZnO葡萄糖酶电极制备及特性

通过水热法在长有ZnO籽晶层的柔性聚酰亚胺(PI)衬底上生长了整齐的ZnO纳米棒,ZnO纳米棒的晶体结构和表面形貌通过X射线衍射(XRD)、扫描电子显微镜(SEM)等进行表征.通过静电吸附方式,将葡萄糖氧化酶(GOx)固定在其表面.分别对GOx及修饰前后的ZnO纳米棒进行了紫外-可见光谱表征,发现修饰后存在ZnO的吸收峰和GOx的特征吸收峰,表明GOx固定在ZnO表面.通过对修饰样品进行傅里叶变换红外(FTIR)光谱测试发现了与GOx相关的吸收峰,这进一步表明GOx仍保持生物活性.最后在循环伏安曲线的测试中,这种在柔性衬底上制备的生物酶电极表现出非常灵敏的电流响应,为制备柔性葡萄糖生物传感器奠定了实验基础.     

Electrochemical Sensitive Determination of Nanomolar Guanine from ZnO Nanorods Coated on Platinum Electrode

The crystalline ZnO nanorods, grown on Si‐substrate (100) at a low temperature using a hydrothermal process were used for modification of platinum electrode using PVC and THF for in order to test their chemosensor activity. The modified electrode can be used for selective nanomolar determination of guanine in aqueous media without any interference from other biomolecules. The prepared chemosensor has a lower detection limit of 40 nM for guanine, and a modification of the electrodes with ZnO nanorods increases the reproducibility by reducing the fouling effect caused by the oxidation of biomolecules on the electrode surface as the prepared electrode can be used for more than 30 consecutive scans and can be used for 5 days without any change in current intensity or sensitivity.     

Influence of different substrates on ZnO nanorod arrays properties

Zinc Oxide (ZnO) nanorod arrays were grown on different substrates by hydrothermal method. The crystallinity of ZnO nanorod was regularly investigated by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine morphology of the ZnO nanorods. The results indicate that the nanorods grow along [002] orientation. SEM and TEM images and XRD patterns show that the growth of ZnO nanorods on graphene/Quartz substrate is better than the other substrates due to the number and size of the nanorods which are highly affected through the properties of ZnO seed layers and it has lower defects than the other substrates. PL spectra ZnO would have a higher concentration of oxygen vacancy.     

Conversion of ZnO nanorod arrays into ZnO/ZnS nanocable and ZnS nanotube arrays via an in situ chemistry strategy

Vertically aligned ZnO nanorods with uniform diameter and length have been synthesized on a zinc foil substrate with ammonium persulfate as oxidant via a facile, larger scale production and inexpensively synthesized method without any templates or additives. SEM and XRD studies indicate that ZnO nanorods are well-oriented along the c-axis. The PL spectrum indicates that our as-synthesized ZnO nanorods with a stronger and wider green emission are promising candidates as electron nanoconductors in nano-optoelectronic devices. Furthermore, by an effective thioglycolic acid-assisted solution route, well-aligned ZnO/ZnS nanocable and ZnS nanotube arrays have been successfully synthesized. ZnS nanotubes show a perfect hexagonal and obvious tubular shape. Our present strategy shows mild growth conditions and good reproducibility.     

Dipole Field Guided Orientated Attachment of Nanocrystals to Twin‐Brush ZnO Mesocrystals

Mesocrystals of ZnO were synthesized hydrothermally by using gum arabic as a structure‐directing agent. Their hierarchical structure has a unique twin‐brush form consisting of vertically aligned nanorods in a single‐crystal‐like porous form. The formation mechanism of the twin‐brush ZnO was investigated by quenching a series of samples at different times and examining them by TEM, SEM, and XRD. The alignment of ZnO crystal units can be modulated by adding simple salts such as KCl to change the units from nanorods to nanoplates. This can be explained by screening the dipolar force of the polar crystal. Local cathodoluminescence of twin‐brush ZnO was used to follow the local structure changes.     

Synthesis and magnetic properties of hexagonally packed ZnO nanorods

Large-scale uniform aligned ZnO nanorods with a hexagonal tip were successfully synthesized via a facile process at low temperature of (～140 °C) without using any additives and substrate. The process is based on a simple reaction of zinc powder and de-ionized water. The results reveal that the as-prepared ZnO products have an average length of 10 μm and a diameter in the range of 50–260 nm, possessing a single crystal wurtzite structure. The structure and morphology of the ZnO products are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometer (EDX). The possible formation mechanism of nanorods is proposed in brief. The optical properties of grown products were characterized by room-temperature. The magnetic property was tested with a vibrating sample magnetometer at room temperature and revealed a high hysteresis loop indicating a strong ferromagnetic nature of as synthesized ZnO nanorods. The yield producing nanorods with this method includes ease, flexibility, fast being low cost and ineffective on environment free.     

Theoretical analysis of growth of ZnO nanorods on the amorphous surfaces

Semiconductor nanorod arrays on a substrate have a preferential alignment orientation that minimizes the excessive free energy of the system. In the case of wet chemically synthesized zinc oxide (ZnO) nanorod on the amorphous surfaces, the thermodynamic driving force determines the orientation to be normal to the surface. Among the various kinds of amorphous surfaces, the spherical seed layer composed of ZnO precursors gives isotropic radially aligned arrays. For other surfaces, such as wrinkled and planar ZnO precursor thin film, nanorod arrays are aligned to be perpendicular to the tangential line of the surface. The maximum value of the aspect ratio of the nanorod is determined by the thermodynamic relationship. The number density of nanorods per unit precursor particles decreases with increasing contact angle of the seed particles.     

Facile and large-scale production of ZnO/Zn-Al layered double hydroxide hierarchical heterostructures

ZnO/Zn-Al layered double hydroxide (ZnO/Zn-Al LDH) hierarchical architecture, a new type of ZnO-based heterostructure, has been synthesized directly on an Al substrate via a facile solution phase process. The firecracker-like heterostructures consist of uniform ZnO nanorods orderly standing at the edges of two-dimensional (2D) surfaces of Zn-Al LDH nanoplatelets. Experimental result obtained from the early growth stage indicates that the underlying Zn-Al LDH nanoplatelet arrays are well constructed with their (00l) planes perpendicular to the surface of Al substrate. We propose that the "edge effect" of Zn-Al LDH and the "lattice match" between ZnO and Zn-Al LDH are vital to the growth of such heterostructures. The effects of total solution volume and NH3.H2O concentration on the formation of heterostructures are investigated. It is found that other LDH-based complex structures can also be achieved controllably by varying the mentioned experimental factors. Our work is the first demonstration of fabricating intricate ZnO/Zn-Al LDH heterostructures as well as well-defined Zn-Al LDH arrays on an Al substrate, for which several promising applications such as optoelectronics, biosensors, and catalysis can be envisioned.     

Three‐Dimensional Structures of Nanoporous NiO/ZnO Nanoarray Films for Enhanced Electrochromic Performance

An electrochromic device with the as‐obtained nanoporous NiO /ZnO nanoarray as a working electrode was constructed and assembled. The nanoporous NiO/ZnO nanoarray film with a three‐dimensional structure was prepared on indium tin oxide (ITO) glass substrate through a two‐step route that combined chemical bath deposition method with a hydrothermal method. The nanoporous NiO/ZnO nanoarray electrode reveals a noticeable improvement in electrochromism compared with that of nanoporous NiO alone, including higher optical modulation (81 %), higher coloration efficiency (78.5 cm² C^?1), faster response times (2.6 and 9.7 s for coloring and bleaching, respectively), and favorable durability performance. Such enhancements are mainly attributed to the three‐dimensional structures of nanoporous NiO coated on ZnO nanoarray, namely, 1) the uniform hexagonal ZnO nanoarray loads more nanoporous NiO, 2) nanoporous NiO cross‐linked with ZnO nanorods provides a loose interspace morphology, 3) stronger adhesion between ZnO nanorods and ITO covered with ZnO seed, 4) core–shell and cross‐linked structures promote electrolyte infiltration, and 5) appropriate band gaps improve charge transfer.     

电沉积制备ZnO纳米棒修饰电极上氧化还原蛋白的电化学行为

采用恒电位阴极还原法在金电极表面一步修饰ZnO纳米棒, 制备成ZnO纳米棒修饰电极. 扫描电子显微镜(SEM)和X射线衍射(XRD)结果显示制得的ZnO为直径约100 nm的六棱柱状纤锌矿晶体纳米棒. 使用ZnO纳米棒修饰的金电极研究细胞色素c的直接电化学行为, 结果表明: ZnO纳米棒修饰的金电极能有效探测到细胞色素c的铁卟啉辅基在不同价态下的电化学行为; 细胞色素c吸附后, ZnO纳米棒修饰的金电极对过氧化氢的电流响应呈现良好的线性关系.     

Amplified Electrochemical Immunosensor for Calmodulin Detection Based on Gold‐Silver‐Graphene Hybrid Nanomaterials and Enhanced Gold Nanorods Labels

Calmodulin (CaM) is an important intracellular calcium‐binding protein. It plays a critical role in a variety of biological and biochemical processes. In this paper, a new electrochemical immunosensing protocol for sensitive detection of CaM was developed by using gold‐silver‐graphene (AuAgGP) hybrid nanomaterials as protein immobilization matrices and gold nanorods (GNRs) as enhanced electrochemical labels. Electrode was first modified with thionine‐chitosan film to provide an immobilization support for gold‐silver‐graphene hybrid nanomaterials. The hybrid materials formed an effective matrix for binding of CaM with high density and improved the electrochemical responses as well. Gold nanorods were prepared for the fabrication of enhanced labels (HRP‐Ab₂‐GNRs), which provided a large capacity for HRP‐Ab₂ immobilization and a facile pathway for electron transfer. With two‐step immunoassay format, the HRP‐Ab₂‐GNRs labels were introduced onto the electrode surface, and produced electrochemical responses by catalytic reaction of HRP toward enzyme substrate of hydrogen peroxide (H₂O₂) in the presence of thionine. The proposed immunosensor showed an excellent analytical performance for the detection of CaM ranging from 50 pg mL^?1 to 200 ng mL^?1 with a detection limit of 18 pg mL^?1. The immunosensor has also been successfully applied to the CaM analysis in two cancer cells (HepG2 and MCF‐7) with high sensitivity, which has shown great potency for improving clinic diagnosis and treatment for cancer study.     

Platinum‐Coated Porous Gold Nanorods in Methanol Electrooxidation: Dependence of Catalytic Activity on Ligament Size

Here we demonstrate that, in the dealloying process of Au–Ag nanorods, temperature is the key parameter for producing porous Au nanorods with tunable ligament sizes. The vertically aligned Au–Ag alloy nanorods were first synthesized by the electrochemical co‐deposition of Au and Ag onto anodic aluminum oxide (AAO) membrane templates. Porous Au nanorods were then obtained by selectively etching Ag away from the precursor Au–Ag alloy nanorods. Control of the ligament size was achieved by controlling the dealloying temperature. Pt deposited on the porous Au nanorods with smaller ligaments exhibited a higher catalytic activity during methanol electrooxidation than those deposited on nanorods with larger ligaments produced by dealloying at higher temperatures. The strong dependence of the catalytic activity on the ligament size of porous Au is principally due to different amounts of carbon monoxide (CO) generated during methanol electrooxidation. Less CO was generated as the ligament size decreased. This finding is of importance for developing highly efficient cathode materials for carrying out methanol electrooxidation in practical applications in which porous Au with a large surface area is used as a supporting substrate.     

Structural,optical and magnetic characterization of ZnO nanorods synthesized using hydrothermal technique at low temperature

Pure ZnO nanorods were grown from aqueous solutions at low temperature (90 °C) by hydrothermal growth technique on sapphire (0001) substrate coated with ZnO thin film. X-ray diffraction results show that these nanorods crystallize in the wurtzite structure having space group P6₃mc and that they are oriented along the c-axis. Raman and photo-luminescence studies show the presence of oxygen vacancies in the ZnO nanorods. The ZnO nanorods show room temperature ferromagnetism.     

Fabrication of ZnO Nanorods in Colloidal Systems Formed by PEO‐PPO‐PEO Block Copolymers

One‐dimensional (1‐D) ZnO nanorods with various sizes were synthesized in colloidal systems formed by PEO‐PPO‐PEO block copolymers. The experimental results revealed that the growth of ZnO nanorods was dependent on the molecular structure of polyether. It was known that L64 (EO₁₃PO₃₀EO₁₃) and F68 (EO₈₀PO₃₀EO₈₀) had the same size PPO block but different content of PEO. We concluded that the size of the ZnO products obtained in F68 was larger due to its longer PEO chain.