Water-based wet chemical synthesis of (doped) ZnO nanostructures

Looking at its vast range of applications, nanostructured ZnO can be considered as a key technological material. Simple and ecological production techniques for this and other nanostructured materials can boost the detection of their unusual properties. In this context water-based wet chemical synthesis routes for nanostructured ZnO are explored in this study. The advantages and disadvantages of controlled double-jet precipitation, microemulsion preparation, hydrothermal synthesis and an aqueous solution-gel route are described for the formation of (doped) ZnO nanoparticles. The influence of the synthesis parameters on the particle size, size distribution and degree of agglomeration of the particles is reported. Thin films are prepared by chemical solution deposition from aqueous solution. The heat treatment profile and the precursor composition are seen to largely control the density, the grain size and the degree of preferential c-axis orientation.     

Facet-dependent electrochemiluminescence spectrum of nanostructured ZnO

A facet-dependent electrochemiluminescence (ECL) behavior was found for nanostructured ZnO with different dominant exposing planes.The ECL spectrum of nanostructured ZnO was recorded by the emission scan mode with a fluorescence spectrometer and applied to investigate the difference of surface state for different crystal planes.Electronic structure calculations based on density functional theory were used to study the effect of crystal plane on the band structure and density of states.It revealed that the ECL emission was originated primarily from the recombination of electrons from Zn 4s and the hole from O 2p,which could be utilized to study the physical and chemical properties of surface structures of as-prepared nanostructured ZnO.A physical model was suggested to elucidate the differences of ECL spectra.A concept was proposed that the energy released as photons during ECL process of nanocrystalline semiconductor materials will be correlated with the energy level of active sites located at different crystal planes.     

Enhanced super-hydrophobic and switching behavior of ZnO nanostructured surfaces prepared by simple solution--immersion successive ionic layer adsorption and reaction process

A simple and cost-effective successive ionic layer adsorption and reaction (SILAR) method was adopted to fabricate hydrophobic ZnO nanostructured surfaces on transparent indium-tin oxide (ITO), glass and polyethylene terephthalate (PET) substrates. ZnO films deposited on different substrates show hierarchical structures like spindle, flower and spherical shape with diameters ranging from 30 to 300 nm. The photo-induced switching behaviors of ZnO film surfaces between hydrophobic and hydrophilic states were examined by water contact angle and X-ray photoelectron spectroscopy (XPS) analysis. ZnO nanostructured films had contact angles of ~140° and 160°±2 on glass and PET substrates, respectively, exhibiting hydrophobic behavior without any surface modification or treatment. Upon exposure to ultraviolet (UV) illumination, the films showed hydrophilic behavior (contact angle: 15°±2), which upon low thermal stimuli revert back to its original hydrophobic nature. Such reversible and repeatable switching behaviors were observed upon cyclical exposure to ultraviolet radiation. These biomimetic ZnO surfaces exhibit good anti-reflective properties with lower reflectance of 9% for PET substrates. Thus, the present work is significant in terms of its potential application in switching devices, solar coatings and self-cleaning smart windows.     

Morphology effects on the biofunctionalization of nanostructured ZnO

A stepwise surface functionalization methodology was applied to nanostructured ZnO films grown by metal organic chemical vapor deposition (MOCVD) having three different surface morphologies (i.e., nanorod layers (ZnO films-N), rough surface films (ZnO films-R), and planar surface films (ZnO films-P). The films were grown on glass substrates and on the sensing area of a quartz crystal microbalance (nano-QCM). 16-(2-Pyridyldithiol)-hexadecanoic acid (PDHA) was bound to ZnO films-N, -R, and -P through the carboxylic acid unit, followed by a nucleophilic displacement of the 2-pyridyldithiol moiety by single-stranded DNA capped with a thiol group (SH-ssDNA). The resulting ssDNA-functionalized films were hybridized with complementary ssDNA tagged with fluorescein (ssDNA-Fl). In a selectivity control experiment, no hybridization occurred upon treatment with non complementary DNA. The ZnO films' surface functionalization, characterized by FT-IR-ATR and fluorescence spectroscopy and detected on the nano-QCM, was successful on films-N and -R but was barely detectable on the planar surface of films-P.     

Conductivity of ZnO nanowires, nanoparticles, and thin films using time-resolved terahertz spectroscopy

The terahertz absorption coefficient, index of refraction, and conductivity of nanostructured ZnO have been determined using time-resolved terahertz spectroscopy, a noncontact optical probe. ZnO properties were measured directly for thin films and were extracted from measurements of nanowire arrays and mesoporous nanoparticle films by applying Bruggeman effective medium theory to the composite samples. Annealing significantly reduces the intrinsic carrier concentration in the ZnO films and nanowires, which were grown by chemical bath deposition. The complex-valued, frequency-dependent photoconductivities for all morphologies were found to be similar at short pump-probe delay times. Fits using the Drude-Smith model show that films have the highest mobility, followed by nanowires and then nanoparticles, and that annealing the ZnO increases its mobility. Time constants for decay of photoinjected electron density in films are twice as long as those in nanowires and more than 5 times those for nanoparticles due to increased electron interaction with interfaces and grain boundaries in the smaller-grained materials. Implications for electron transport in dye-sensitized solar cells are discussed.     

三维分级结构ZnO的制备及光催化性能

以聚乙烯醇/醋酸锌复合纳米纤维为模板, 采用模板辅助共沉积技术制备了三维尖晶石型ZnO纳米线/纳米纤维分级结构, 并采用SEM, XRD对其形貌和晶型结构进行了表征. 在光催化降解乙醛性能实验中, 三维分级结构ZnO表现出比纳米粒子和纤维更好的光催化性能. 这主要归因于ZnO纳米线的次级结构和开放的三维网络结构更有利于乙醛分子和氧分子的扩散和传输, 从而提高了乙醛的光降解速率.     

Electrochemical deposition of mesoporous nickel hydroxide films from dilute surfactant solutions

A series of micelle-templated mesoporous nickel hydroxide films were prepared by electrochemical deposition from dilute surfactant solutions by using different types of template and by varying plating solvent composition. Lamellar mesostructured Ni(OH)2 films are obtained with only anionic surfactant sodium dodecyl sulfate (SDS) as the template. In particular, a unique cooperative assembly fashion, that is, the combination between Ni2+ and a complex composed of the primary template SDS and a cosurfactant, such as triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymers and poly(ethylene glycol), was explored, by which two-dimensional hexagonal mesoporous Ni(OH)2 films were electrodeposited. Meanwhile, the deposition medium also plays a crucial role in determining the mesostructure of Ni(OH)2 films. For the composite nickel hydroxide films deposited from aqueous solution or dilute aqueous solution of ethylene glycol (<20 wt %) in the presence of SDS or the SDS-poly(alkylene oxide) polymer complexes, a mixed lamellar phase with d(001) = 37.4 A and d(001) = 28.5 A was obtained. However, single lamellar phase with d(001) = 37.4 A was electrodeposited from concentrated aqueous solutions of ethylene glycol (> or = 20 wt %). Furthermore, such deposition baths have access to hexagonal mesoporous nickel hydroxide films with d(100) = 37.4 A at 70 degrees C with the SDS-poly(alkylene oxide) polymer complexes as the templates. Within the potential window for Ni(OH)2, the morphology and quality of mesostructured films are significantly dependent on the deposition potential, while the mesostructures of the composite films always remain unchanged.     

Structure and morphology of nanostructured zinc oxide thin films Prepared by dip-vs. spin-coating methods

In this study, we use dipping and spinning methods to coat glass slides with sol-gel ZnO thin films, composed of zinc acetate dihydrate, monoethanolamine (MEA), de-ionized water and isopropanol. The effect of the annealing temperature on the structural morphology and optical properties of these films is investigated. These ZnO films were preheated at 275 °C for 10 min and annealed either at 350, 450 or 550 °C for 60 min. As-deposited films, formed by amorphous zinc oxide-acetate submicron particles, are transformed into a highly-oriented ZnO after thermal treatment. The surface morphology, phase structure and optical properties of the thin films were investigated by scanning electron microscopy, X-ray diffraction (XRD) and optical transmittance. Both techniques produced nanostructured ZnO thin films with well-defined orientation. The annealed films were transparent in the visible range with an absorption edge at about 375 nm and a transmittance of ca 85–90% with an average diameter of 40 nm. XRD results show the film was composed of polycrystalline wurtzite, with a preferential c-axis orientation of (002) and a single sharp XRD peak at 34.40, corresponding to the hexagonal ZnO. The grain size is increased by the annealing temperature. Both coating techniques create sol-gel ZnO films with the potential for application as transparent electrodes in optic and electronic devices.     

氯醇盐溶胶-凝胶法纳米结构氧化钨薄膜的光谱学特性

由非离子型Gemini表面活性剂TMDD(HO(EO)xC14(EO)yOH)为结构导向模板, 改进EISA(挥发诱导自组装)镀膜工艺经300 ℃焙烧制得具有连续、均一和光学透明特点的蠕虫介孔纳米晶孔壁氧化钨薄膜. 采用SEM、TEM和Raman光谱对此种薄膜的介孔纳米结构进行了表征, 通过光谱电化学、XPS和椭偏谱等方法, 研究了该薄膜在电解质溶液中的电致变色行为. 结果表明, 所制备的纳米结构氧化钨薄膜在633 nm波长处的循环可逆透过率调制幅度可达75%以上, 并且其电致变色机理具有显著的双注入吸收调制特性.     

New insights on the doping of ZnO films with elements from group IIIA through electrochemical deposition

This study was focused in the electrodeposition of both compact and nanostructured extrinsic n-type doped ZnO films, which was achieved with aluminum, gallium, and indium. These elements were directly added into a Zn(II) rich electrolyte with molecular oxygen acting as an oxide precursor in aqueous perchlorate media. This way, the use of nitrate ions, whose by-products are accumulated in the aqueous electrolyte, and chloride ions, an electrically active element in ZnO, was therefore avoided. Speciation diagrams, conditional solubility diagrams and a potentiodynamic study were used to explain the way in which extrinsic n-type ZnO can be prepared by electrochemical deposition. Relatively compact films with a highly preferred orientation along the c-axis were suitable for impedance measurements, thus allowing the measurement of their doping levels. Al- and Ga-doped lamellar nanostructures were successfully prepared when the nature of the anion was changed from perchlorate to sulfate. Under specific conditions, the structure of these films changed from opened and isolated nanosheets to interconnected ones. Morphological, optical, and crystallographic properties of these films were also analyzed. Results and discussion presented here should provide a better understanding toward the study of alternative materials in fields such as photovoltaics and photocatalysis.     

Block Copolymer Directed Nanoporous Metal Thin Films

Porous metal thin films have high potential for use in applications such as catalysis, electrical contacts, plasmonics, as well as energy storage and conversion. Structuring metal thin films on the nanoscale to generate high surface areas poses an interesting challenge as metals have high surface energy. In this communication, we demonstrate direct access to nanostructured metal nanoparticle hybrid thin films with high nanoparticle loadings through spin coating of a mixture of block copolymer and ligand stabilized platinum and palladium nanoparticles. Plasma cleaning to remove the organics results in a conductive metal thin film. We expect that the methods described here can be generalized to other metals, mixtures of metal nanoparticles, and intermetallics.

     

Facile Synthesis of 3D Porous Flower-like ZnO Micro/nanostructure Films and Their Photocatalytic Performance

3D porous flower-like ZnO micro/nanostructure films grown on Ti substrates are synthesized via a very facile electrodeposition technique followed by heat treatment process. The ZnO architecture is assembled with ultra thin sheets, which consist of numbers of nanoparticles and pores, and the size of the nanoparticles can be controlled by adjusting the electrodepo-sition time or calcination temperature. It is worth noting that this synthetic method can provide an effective route for other porous metal oxide nanostructure films. Moreover, the photocatalytic performance shows the porous ZnO is an ideal photocatalyst.     

ZnO/Ag复合膜的制备及其润湿性转换研究

利用溶胶-凝胶技术制备了ZnO/Ag复合膜. 采用X射线粉末衍射和扫描电子显微镜对其物相组成、 晶型结构以及表面形貌进行了表征, 采用接触角测试仪对其润湿性进行了表征, 并研究了紫外光照射下Ag的掺杂量对ZnO薄膜润湿性的影响. 结果表明, 当Ag掺杂量(摩尔分数)为5%时, 所得膜的润湿性转换速率最快, 紫外光照3 h后, 其润湿性由超疏水性转换为亲水性, 黑暗中放置5 d后, 亲水性再次转换为超疏水, 实现了润湿性的可逆转换.     

Fabrication of surface-patterned ZnO thin films using sol–gel methods and nanoimprint lithography

Surface-patterned ZnO thin films were fabricated by direct imprinting on ZnO sol and subsequent annealing process. The polymer-based ZnO sols were deposited on various substrates for the nanoimprint lithography and converted to surface-patterned ZnO gel films during the thermal curing nanoimprint process. Finally, crystalline ZnO films were obtained by subsequent annealing of the patterned ZnO gel films. The optical characterization indicates that the surface patterning of ZnO thin films can lead to an enhanced transmittance. Large-scale ZnO thin films with different patterns can be fabricated by various easy-made ordered templates using this combination of sol–gel and nanoimprint lithography techniques.     

Liquid-liquid biphasic synthesis of layered zinc hydroxides intercalated with long-chain carboxylate ions and their conversion into ZnO nanostructures

A method for synthesizing layered zinc hydroxide compounds in high yields is developed using an immiscible liquid-liquid system in one pot. Long-chain carboxylate ions such as heptanoate, decanoate, and dodecanoate were successfully intercalated between zinc hydroxide layers in one process starting from a xylene-water system. Typically, a xylene phase dissolving the respective carboxylic acids was allowed to stand in contact with an aqueous phase dissolving zinc nitrate hexahydrate and urea. During keeping the resultant biphasic system at 80 °C, urea was thermo-hydrolyzed to supply OH(-) in the aqueous phase while the carboxylic acids were continuously transferred from the xylene phase under the distribution law. The aqueous phase was then supersaturated, and a solid phase of layered basic zinc carboxylate was precipitated as films on glass substrates through heterogeneous nucleation and subsequent two-dimensional crystal growth. Crystal structures and morphology of the films were modulated by the kind of the carboxylic acids employed. The layered basic zinc carboxylate films could be converted to nanostructured, mesoporous ZnO films by heating at 450 °C in air. The relationship between the initial solution compositions and the final solid products was systematically examined to discuss reaction mechanisms in the biphasic systems.     

水热法制备高度取向的氧化锌纳米棒阵列

氧化锌的激子结合能(60meV)及光增益系数(300cm^-1)比GaN的(25meV,100cm^-1)还高,这一特点使它成为紫外半导体激光发射材料的研究热点。最近,Yang等成功地观测到规则的ZnO纳米线阵列的激光发射现象,更加激起了人们合成一维高度有序ZnO纳米结构的热情,由于一维ZnO     

Zinc Oxide-Based Acetone Gas Sensors for Breath Analysis: A Review

Acetone is one of the toxic, explosive, and harmful gases. It may cause several health hazard issues such as narcosis and headache. Acetone is also regarded as a key biomarker to diagnose several diseases as well as monitor the disorders in human health. Based on clinical findings, acetone concentration in human breath is correlated with many diseases such as asthma, halitosis, lung cancer, and diabetes. Thus, its investigation can become a new approach for health monitoring. Better management at the early stages of such diseases has the potential not only to reduce deaths associated with the disease but also to reduce medical costs. ZnO−based sensors show great potential for acetone gas due to their high chemical stability, simple synthesis process, and low cost. The findings suggested that the acetone sensing performance of such sensors can be significantly improved by manipulating the microstructure (surface area, porosity, etc.), composition, and morphology of ZnO nanomaterials. This article provides a comprehensive review of the state-of-the-art research activities, published during the last five years (2016 to 2020), related to acetone gas sensing using nanostructured ZnO (nanowires, nanoparticles, nanorods, thin films, etc). It focuses on different types of nanostructured ZnO-based acetone gas sensors. Furthermore, several factors such as relative humidity, acetone concentrations, and operating temperature that affects the acetone gas sensing properties- sensitivity, long-term stability, selectivity as well as response and recovery time are discussed in this review. We hope that this work will inspire the development of high-performance acetone gas sensors using nanostructured materials.     

纳米结构ZnO/染料/聚吡咯光阳极的光电化学性质

用光电化学方法研究了染料RuL2 (NCS) 2 (L =2 ,2′ bipydine 4,4′ dicarboxylicacid) (简写为Dye)、聚吡咯 (PPy)敏化氧化锌 (ZnO)纳米晶电极以及用RuL2 (NCS) 2 和PPy复合敏化ZnO纳米晶膜电极的光电化学行为 .实验表明 ,ZnO/PPy纳米多孔膜电极为双层n 型半导体结构 .PPy和RuL2(NCS) 2 都可对ZnO纳米晶膜产生敏化作用 ,ZnO/RuL2 (NCS) 2 /PPy复合多孔膜电极产生的光电流远大于ZnO/PPy纳米多孔膜电极和ZnO/Dye多孔膜电极产生的光电流 .讨论了该电极的光生电子的机理 ,初步测定了ZnO/RuL2 (NCS) 2 /PPy电极作为光阳极的光电化学电池的工作特性曲线 ,测得该电池的光电转换效率为 1 .3% ,填充因子为 0 .75 .     

表面活性剂种类对纳米氧化锌形貌的影响

利用简单的水热法,以Zn(Ac)2.2H2O为锌源,通过调整表面活性剂的种类及碱源,制备了一系列不同形貌的纳米结构氧化锌;利用场发射扫描电子显微镜和X射线粉末衍射仪分析了产物的形貌和晶体结构,并探讨了多种表面活性剂和醋酸钠碱源对氧化锌纳米结构的影响.结果表明,以NaOH作为碱源时,在不添加任何表面活性剂的情况下,产物的形貌结构与氢氧化钠的加入量有关,当n(Zn2+)∶n(OH-)为1∶2.5、1∶10及1∶20时,分别得到片状、棒状及海胆状纳米结构的氧化锌;产物均为六方相氧化锌.     

Influence of rapid thermal annealing on structure and interfacial characteristic of ZnO thin films

Highly C‐axis oriented ZnO thin film was manufactured by radio‐frequency magnetron sputtering technique on Si (111) substrate. The main objective was to study the influence of rapid thermal annealing (RTA) temperature on the structure and interfacial characteristic of ZnO thin films. X‐ray diffraction results showed that the ZnO thin films annealed at 600 °C by RTA technique had a perfect C‐axis preferred orientation compared to the other ZnO thin films, and the full width at half maximum of ZnO (002) rocking curve measurements indicted that the RTA‐annealed ZnO thin films possessed better crystal structure. Atom force microscopy displayed that the grain size of RTA‐annealed ZnO thin films was fine and uniform compared with the as‐deposited ZnO thin films, although the grains grew in RTA process and the root meant square roughness was smaller than that of as‐deposited films. High‐resolution transmission electron microscopy showed that there was an obvious amorphous layer between ZnO thin films and Si substrate, but the RTA‐annealed ZnO thin films exhibited larger and denser columnar structure and a preferred orientation with highly c axis perpendicular to the amorphous layer. Copyright © 2012 John Wiley & Sons, Ltd.