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.     

Synthesis and Optical Properties of Ce-doped ZnO

ZnO nanorods were synthesized using the sol-gel method, and the effects of annealing temperature and Ce doping on the morphologies and optical properties of ZnO nanostructures were investigated in detail. The XRD measurements showed that the as-synthesized ZnO nanostructures had a hexagonal wurtzite structure. SEM images showed that uniform nanorods formed at 900 °C. Photoluminescence measurements showed an ultraviolet emission peak and a relatively broad visible light emission peak for the samples sintered at different temperatures. The UV emission peak bathochromically shifted when the annealing temperature rose from 850 to 1000 °C. Ce doping decreased the synthesized temperature of the ZnO nanorods to 500 °C, and the UV peaks hypsochromically shifted.     

Sb2S3纳米粒子修饰ZnO纳米片微纳分级结构的光电化学性能

采用恒电位方法,选择氯化钾和乙二胺(EDA)为添加剂,在氧化铟锡(ITO)导电玻璃上制备了高度有序的ZnO纳米片阵列,通过二次电沉积得到了ZnO纳米片上生长纳米棒的微纳分级结构.利用化学浴沉积法在ZnO基底上沉积Sb₂S₃纳米粒子制备出了Sb₂S₃/ZnO纳米片壳核结构和Sb₂S₃/ZnO微纳分级壳核结构.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、紫外-可见(UV-Vis)吸收光谱、瞬态光电流等对其形貌、结构组成和光电化学性能进行了表征和分析.结果表明, Sb₂S₃/ZnO纳米片上生长纳米棒分级壳核结构的光电流明显高于Sb₂S₃/ZnO纳米片壳核结构.在Sb₂S₃/ZnO纳米片壳核结构和Sb₂S₃/ZnO微纳分级壳核结构的基础上旋涂一层P3HT薄膜形成P3HT/Sb₂S₃/ZnO复合结构,以上述复合结构薄膜为光活性层组装成杂化太阳电池,其中, P3HT/Sb₂S₃/ZnO分级壳核结构杂化太阳电池的能量转换效率最高,达到了0.81%.     

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.     

不同形貌ZnO纳米结构的电子显微分析

控制实验合成条件,利用溶胶-凝胶法和化学溶液生长法制备出不同形貌的ZnO纳米结构。采用X射线衍射仪(XRD)、扫描电子显微镜( SEM) 以及透射电子显微镜(TEM)等多种测试手段对ZnO纳米结构的微观形态及晶相进行了分析。结果表明:3种ZnO纳米结构形貌虽不同,但均具有Z nO六方纤锌矿晶相结构。ZnO纳米棒和花状ZnO纳米结构为单晶,生长方向均沿(0001)方向。ZnO纳米球则为多晶。     

Morphology‐Dependent Gas‐Sensing Properties of ZnO Nanostructures for Chlorophenol

The crystal‐plane effect of ZnO nanostructures on the toxic 2‐chlorophenol gas‐sensing properties was examined. Three kinds of single‐crystalline ZnO nanostructures including nanoawls, nanorods, and nanodisks were synthesized by using different capping agents via simple hydrothermal routes. Different crystal surfaces were expected for these ZnO nanostructures. The sensing tests results showed that ZnO nanodisks exhibited the greatest sensitivity for the detection of toxic 2‐chlorophenol. The results revealed that the sensitivity of these ZnO samples was heavily dependent on their exposed surfaces. The polar (0001) planes were most reactive and could be considered as the critical factor for the gas‐sensing performance. In addition, calculations using density functional theory were employed to simulate the gas‐sensing reaction involving surface reconstruction and charge transfer both of which result in the change of electronic conductance of ZnO.     

Synthesis of variable-aspect-ratio, single-crystalline ZnO nanostructures

Variable-aspect-ratio (length/diameter), one-dimensional (1-D) ZnO nanostructures (nanorods and nanowires) were prepared in alcohol/water solution by reacting a Zn2+ precursor with an organic weak base, tetramethylammonium hydroxide (Me4NOH). The effect of the experimental parameters (temperature, base concentration, reaction time, and water content) on nucleation, growth, and the final morphology of the ZnO nanostructures was investigated. The low-temperature syntheses (75-150 degrees C) yielded aspect ratios of the 1-D ZnO nanostructures that depended on the water content. The individual ZnO nanorods and nanowires were determined to be perfect, single crystals with their c axes as the primary growth direction.     

Fine-tuning the synthesis of ZnO nanostructures by an alcohol thermal process

A simple and efficient alcohol thermal technique was applied to control the growth of the dimensions and morphology of ZnO nanostructures under mild conditions, where surfactant was not necessary. The size of ZnO nanocrystals increased with growth temperature and they transformed into nanorods with different aspect ratios through tuning the reaction time. The length of nanorods increased significantly with the reaction time, but their thickness only slightly increased. The as-prepared ZnO nanocrystals were monocrystalline and the growth orientation of ZnO nanorods was [001]. Photoluminescence measurements showed a blue shift in violet emission with a reduction in crystal size and revealed the quantum confinement effect. Electron irradiation induced structural damage was observed in the ZnO nanorods synthesized at 120 degrees C. Experimental results proved that the possible growth mechanism of ZnO nanostructures was oriented attachment.     

Selected-control synthesis of ZnO nanowires and nanorods via a PEG-assisted route

Long-chain polymer-assisted growth of one-dimensional (1D) nanostructures has been investigated in previous research. This kind mild method has lots of merits such as not requiring complex procedures, without template supporting etc. Can the short-chain polymer also be used to grow long nanowires? In the present work, a short-chain polymer (PEG400) was found to promote the formation of 1D ZnO nanostructures, which cannot be obtained by long-chain polymers (such as PEG10000). Moreover, nanowires and nanorods can be selectively synthesized by using short-chain polymers. The influence factors for the formation of 1D ZnO nanostructures were also investigated in detail. The XRD, Raman spectrum, XPS, SEM, TEM, ED, HRTEM, EDXA, and PL spectra have been provided for the characterization of the as-obtained nanowires and nanorods.     

Factors Affecting Laser-Excited Photoluminescence from ZnO Nanostructures

The role of defects on laser-excited photoluminescence of various ZnO nanostructures has been investigated. The study shows that defects present in ZnO nanostructures, specially Zn-related defects play a crucial role in determining the laser-excited photoluminescence intensity (LEI). ZnO nanoparticles as well as nanorods (NR) annealed in oxygen atmosphere exhibit remarkable enhancement in LEI. A similar enhancement is also shown by Al-doped ZnO NR.     

Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea

Silver coated ZnO nanorods and nanoflakes with different crystallographic orientations were synthesized by a combination of sputter deposition and solution growth process. Catalytic properties of morphology‐dependent Ag/ZnO nanostructures were then investigated for urea sensors without enzyme. Ag/ZnO nanorods on carbon electrodes exhibit a higher catalytic activity and an improved efficiency than Ag/ZnO nanoflakes on carbon electrodes. Ag/ZnO nanorod catalysts with more electrochemically surface area (169 cm² mg^?1) on carbon electrode facilitate urea electrooxidation due to easier electron transfer, which further promotes the urea electrolysis. The Ag/ZnO nanorod catalysts also show a significant reduction in the onset voltage (0.410 V vs. Ag/AgCl) and an increase in the current density (12.0 mA cm^?2 mg^?1) at 0.55 V vs Ag/AgCl. The results on urea electrooxidation show that Ag/ZnO nanostructures can be a potential catalyst for non‐enzymatic biosensors and fuel cells.     

Room temperature solution synthesis of monodispersed single-crystalline ZnO nanorods and derived hierarchical nanostructures

In this work, we report a room temperature wet-chemical approach to synthesize highly regulated, monodispersed ZnO nanorods and derived hierarchical nanostructures. In particular, ZnO has been prepared into single-crystalline conical or prismatic nanorods, and various hierarchical structures such as hexagonally branched, reversed umbrella-type, and cactus-like ZnO nanostructures comprising individual c-oriented nanorods. Depending on the synthetic conditions used, the diameter of nanorods can be controlled with a size down to 10-30 nm, while the aspect ratio can be controlled up to 50-100. Various preparative parameters, such as initial reactant concentrations, solvents, ligands, surfactants, precursor salts, and reaction time, have been systematically examined. Due to slow reactions at room temperature, excellent crystallinity and high morphological yield (100% in most cases) have been achieved via tuning the synthetic parameters. Our photoluminescence and UV measurements also confirm the attained crystal perfection and size uniformity.     

Fabrication of ZnO nanorods in ionic liquids and their photoluminescent properties

A novel and simple approach is reported to fabricate uniform single-crystal ZnO nanorods in ionic liq-uids. The as-obtained ZnO nanorods have been characterized by XRD,TEM,HRTEM,SAED,XPS,EDXA,PL and UV-vis absorption spectra. The rod diameters of the nanostructures can be controlled by tuning the amount of sodium hydroxide in the synthesis. Photoluminescence results show that the nanos-tructural ZnO exhibits better optical properties than bulk ZnO does and interestingly,the smaller the rod diameters are,the better optical property 1D nanostructural ZnO exhibits. The possible growth mechanism of ZnO nanorods is also investigated.     

以介孔氧化硅薄膜为模板电沉积合成新型纳米结构

首次以不同孔道结构的介孔氧化硅薄膜为模板,采用电化学沉积的方法,合成了金属铜和半导体氧化锌的纳米材料,并对其结构进行了表征．以六方孔道结构的介孔氧化硅模板获得了直径为7nm的金属铜纳米线阵列;以笼状体心立方孔道结构的模板获得了具有哑铃状形貌的铜单质纳米颗粒．对于氧化锌纳米结构,电化学沉积过程使得氧化锌完全填充氧化硅模板的孔道,分别得到了具有六方和体心立方介孔结构的Zn0/SiO2纳米复合物薄膜．     

Fabrication of hierarchical ZnO architectures and their superhydrophobic surfaces with strong adhesive force

Grid-structured ZnO microsphere arrays assembled by uniform ZnO nanorods were fabricated by noncatalytic chemical vapor deposition, taking advantage of morphologies of alumina nanowire pyramid substrates and ZnO oriented growth habits. Every ZnO microsphere (similar to the micropapilla on a lotus leaf surface) is assembled by over 200 various oriented ZnO nanorods (similar to the hairlike nanostructures on mircopapilla of a lotus leaf). This lotus-leaf-like ZnO micro-nanostructure films reveal superhydrophobicity and ultrastrong adhesive force to liquid. The realization of this hierarchical ZnO nanostructure film could be important for further understanding wettability of biological surfaces with micro-nanostructure and application in microfluidic devices.     

Controlling the morphology of ZnO nanostructures in a low-temperature hydrothermal process

ZnO nanostructures of different morphologies were grown in a controlled manner using a simple low-temperature hydrothermal technique. Controlling the content of ethylenediamine (soft surfactant) and the pH of the reaction mixture, nanoparticles, nanorods, and flowerlike ZnO structures could be synthesized at temperatures 80-100 degrees C with excellent reproducibility. High-resolution electron microscopy revealed the well crystalline nature of all the nanostructures with preferential growth along the [002] direction for linear structures. Photoluminescence spectra of the as-grown nanostructures revealed oxygen-vacancy-related defects in them, which could be reduced by air annealing at 250 degrees C. Possible mechanisms for the variation of morphology with synthesis parameters are discussed.     

Simple solvothermal route to synthesize ZnO nanosheets, nanonails, and well-aligned nanorod arrays

ZnO nanosheets, nanonails, and well-aligned nanorods were fabricated on Zn foils by a solvothermal approach using ethanol as the solvent. A lower synthesis temperature and a shorter time period favor the formation of nanosheets. By optimizing the synthesis temperature and time period, ZnO nanonails with a hexagonal cap and a long stem could be produced. A higher temperature was not favorable to produce uniform and smooth nanorods. Well-aligned ZnO nanorod arrays were produced with diameters within 100-250 nm and lengths up to approximately 6 microm when NaOH was added to the solvent. By optimizing the reaction parameters, the morphology, size, and orientation of the nanoforms could be tailored. The ZnO nanorods exhibit an excitonic strong UV emission and a defect-related broad green emission at room temperature. The defect-related green emission band decreased with the improvement of the degree of alignment of the nanorods.     

Passivation layer–dependent catalysis of zinc oxide nanostructures

Electrochemical and photoelectrochemical catalysis of surface-passivated zinc oxide (ZnO) nanostructures with three different metal oxides were investigated. Initially, vertically aligned ZnO nanorods structures were developed over conductive substrates by a two-step approach and then passivated with an ultrathin zinc hydroxide, that is, Zn(OH)₂, cobalt oxide, that is, CoO, and Zn(OH)₂/CoO as bilayer, by electrochemical deposition. Compared with the pristine ZnO structures, the surface-passivated nanostructures possess slightly rough surfaces, whereas their crystal structure remains unchanged. From electrochemical catalysis studies under dark and illumination, it is noticed that vertically aligned ZnO nanostructures passivated with narrow band-gap CoO layers have a predominant water oxidation performance than that of the structures passivated with other oxide materials. It is mainly attributed to the eradication of surface states present on ZnO nanorods. Interestingly, the structures passivated with bilayers, that is, Zn(OH)₂/CoO, showed significant stability and durability (～103% retention in current density@60^th min) with a continuous oxygen evolution reaction process for long durations.     

Formation and Dissolution of Twin ZnO Nanostructures Promoted by Water and Control over Their Emitting Properties

By using ZnO as a model system, the formation of twinned nanostructures has been investigated under microwave irradiation, exploiting experimental conditions ranging from purely solvothermal when N,N‐dimethylformamide was used, to purely hydrothermal when water was the solvent. A progressive increase in size, elongation and roughness of the surface was observed with increasing water content in the solvent mixture. Particular attention was paid to the reactivity of the ZnO surfaces towards dissolution. Our results show that the formation of twinned nanorods is a dynamic process and that the coupling interphase itself is highly reactive. Consequently, the twinned rods undergo a number of complex dissolution processes that are responsible for the appearance of a wide distribution of defects either on the surface or inside the structure. Poly(N‐vinyl pyrrolidone) influences the photoluminescent properties of the as‐synthesised materials and allows control of the ratio of the intensity of the UV and visible emission.     

Biomimetic arrays of oriented helical ZnO nanorods and columns

Extended helical or chiral nanostructures are usually associated with biomolecules but are mostly absent in synthetic materials. Here we report the first synthesis of unusual oriented and extended helical nanostructures in synthetic ceramics. Large arrays of oriented helical ZnO nanorods and columns are formed using simple citrate ions to control the growth habits of the ZnO crystal. This novel mechanism could lead to new approaches to control the orientation, the surface area, and the defect structure of synthetic materials that are critical for practical applications. The morphology generated in the helical ZnO nanostructure shows remarkable resemblance to the growth morphology of nacreous calcium carbonate and thus may shed new light on morphology and orientation control of biominerals.