One-step synthesis of large-aspect-ratio single-crystalline gold nanorods by using CTPAB and CTBAB surfactants

Gold nanorods were prepared in high yields by using a one-step seed-mediated process in aqueous cetyltripropylammonium bromide (CTPAB) and cetyltributylammonium bromide (CTBAB) solutions in the presence of silver nitrate. The diameters of the nanorods range from 3 to 11 nm, their lengths are in the range of 15 to 350 nm, and their aspect ratios are in the range of 2 to 70. The diameters of the Au nanorods obtained from one growth batch in CTPAB solutions decrease as their lengths increase, and their volumes decrease as the aspect ratios increase. The diameters of the Au nanorods obtained from one growth batch in CTBAB solutions first decrease and then slightly increase as their lengths increase, and their volumes increase as the aspect ratios increase. These Au nanorods are single-crystalline and are seen to be oriented in either the [100] or [110] direction under transmission electron microscopy imaging, irrespective of their sizes. To the best of our knowledge, this is the first report of the preparation by using wet-chemistry methods of single-crystalline Au nanorods with aspect ratios larger than 15.     

反相微乳液法合成钛酸钡纳米棒

本文在W/O型反相微乳液(Reverse Microemulsion)体系中制得了BaTiO3纳米棒, 考察了ωo值、反应物浓度等因素对BaTiO3纳米棒尺寸及形貌的影响. 用TEM、XRD和电子衍射对材料进行了表征,并用ICP测试了产品中钡与钛的摩尔比.     

Ultrafast studies of gold, nickel, and palladium nanorods

Steady state and ultrafast transient absorption studies have been carried out for gold, nickel, and palladium high aspect ratio nanorods. For each metal, nanorods were fabricated by electrochemical deposition into approximately 6 microm thick polycarbonate templates. Two nominal pore diameters(10 and 30 nm, resulting in nanorod diameters of about 40 and 60 nm, respectively) were used, yielding nanorods with high aspect ratios (>25). Static spectra of nanorods of all three metals reveal both a longitudinal surface plasmon resonance (SPR(L)) band in the mid-infrared as well as a transverse band in the visible for the gold and larger diameter nickel and palladium nanorods. The appearance of SPR(L) bands in the infrared for high aspect ratio metal nanorods and the trends in their maxima for the different aspect ratios and metals are consistent with calculations based on the Gans theory. For the gold and nickel samples, time resolved studies were performed with a subpicosecond resolution using 400 nm excitation and a wide range of probe wavelengths from the visible to the mid-IR as well as for infrared excitation (near 2000 cm(-1)) probed at 800 nm. The dynamics observed for nanorods of both metals and both diameters include transients due to electron-phonon coupling and impulsively excited coherent acoustic breathing mode oscillations, which are similar to those previously reported for spherical and smaller rod-shaped gold nanoparticles. The dynamics we observe are the same within the experimental uncertainty for 400 nm and infrared (5 microm) excitation probed at 800 nm. The transient absorption using 400 nm excitation and 800 nm probe pulses of the palladium nanorods also reveal coherent acoustic oscillations. The results demonstrate that the dynamics for high aspect ratio metal nanorods are similar to those for smaller nanoparticles.     

Facile deposition of [60]fullerene and carbon nanotubes on ITO electrode by electrochemical oxidative polymerization of ethylenedioxythiophene

It was found that [60]fullerene encapsulated in p-sulfonatocalix[8]arene and single-walled carbon nanotubes (SWNTs) solubilized by sodium dodecylsulfate can be readily deposited on the ITO electrode by electrochemical oxidative polymerization of ethylenedioxythiophene (EDOT) without chemical modification of these carbon clusters. The driving force for the deposition is an electrostatic interaction between the anionic complexes and the cationic charges of poly(EDOT) formed in the oxidative polymerization process. The surface morphology was thoroughly characterized by scanning electron micrograph: the [60]fullerene/poly(EDOT) film is covered by nano-particles with 20-100 nm diameters whereas the SWNTs/poly(EDOT) film is covered by nanorods with several microm length and ca. 100 nm diameter. The results indicate that the anionic complexes act as nuclei for the polymer growth in the oxidation polymerization. Interestingly, when these modified ITO electrodes were photoirradiated, the appearance of a photocurrent wave was observed. The action spectra showed that the photoexcited energy of [60]fullerene or SWNTs is efficiently collected by the electroconductive poly(EDOT) film and transferred to the ITO electrode.     

Fabrication of Co3O4 nanorods by calcination of precursor powders prepared in a novel inverse microemulsion

Co3O4 nanorods were prepared by improving traditional molten salt synthesis; the length and diameters of the Co3O4 nanorods were about 10 microns and 40-100 nm, respectively; the mechanism of formation of the Co3O4 nanorods is discussed.     

Use of ionic liquids in the synthesis of nanocrystals and nanorods of semiconducting metal chalcogenides

We have synthesized nanoparticles of hexagonal CdS in the diameter range 3-13 nm by the reaction of cadmium acetate dihydrate with thioacetamide in imidazolium [BMIM]-based ionic liquids. We have obtained three different particle sizes of CdS by changing the anion of the ionic liquid. Addition of trioctylphosphine oxide (TOPO) to the reaction mixture causes greater monodispersity as well as smaller particle size, while addition of ethylenediamine produces nanorods of 7 nm average diameter. Hexagonal ZnS and cubic PbS nanoparticles with average diameters of 3 and 10 nm, respectively, have been prepared by the reaction of the metal acetates with thioacetamide in [BMIM][BF4]. Hexagonal CdSe nanoparticles with an average diameter 12 nm were obtained by the reaction of cadmium acetate dihydrate with dimethylselenourea in [BMIM][BF4]. In this case also we observe the same effect of the addition of TOPO as in the case of CdS. Addition of ethylenediamine to the reaction mixture gives rise to nanorods. ZnSe nanowires with a cubic structures, possible diameters in the range 70-100 nm by the reaction of zinc acetate dihydrate with dimethylselenourea in [BMIM][MeSO4]. The nanostructures obtained are single crystalline in all the cases. Most of the nanostructures show characteristic UV/Vis absorption and photoluminescence emission spectra. The thermodynamically most stable structures are generally produced in the synthesis carried out in ionic liquids.     

Nanorods versus nanovesicles from amphiphilic dendrofullerenes

Three new amphiphilic dendrofullerenes endowed with 4, 8, and 16 carboxylic groups have been efficiently prepared by using a click chemistry methodology. These amphiphilic fullerene derivatives aggregate forming micelles, nanorods, or hollow vesicles depending on the concentration and on the solid substrate.     

不同形貌ZnSe的制备及光电化学性能

采用水热法制备了ZnSe纳米棒和微球, 用XRD, TGA-DTA和SEM等技术对其进行了表征, 提出了解释ZnSe微球的形成新机理. 研究结果表明, 纳米棒直径为50~100 nm, 棒长约为200~300 nm, ZnSe微球直径为3~10 μm.; 纳米棒在反应温度为240 ℃时具有闪锌矿和纤维锌矿型混晶结构, 微球在反应温度为210 ℃时具有闪锌矿结构; 将ZnSe纳米棒和微球均匀地涂在导电玻璃的导电面上, 于380 ℃煅烧40 min后制成膜电极, 并进行了光电化学研究, 纳米棒膜结构电极最高单色光的光电转换效率(IPCE)可达到9.09%.     

Synthesis of single-crystalline perovskite nanorods composed of barium titanate and strontium titanate

We report the solution-based synthesis of single-crystalline nanorods composed of barium titanate (BaTiO3) and strontium titanate (SrTiO3), which yields well-isolated nanorods with diameters ranging from 5 to 60 nm and lengths reaching up to >10 mum. Electron microscopy and diffraction measurements show that these nanorods are composed of single-crystalline cubic perovskite BaTiO3 and SrTiO3 with a principal axis of the unit cell preferentially aligned along the wire length. These BaTiO3 and SrTiO3 nanorods should provide promising materials for fundamental investigations on nanoscale ferroelectricity, piezoelectricity, and paraelectricity.     

Synthesis of Nanorods of Crystalline Co3O4Using Carbon Nanotubes as Templates

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First crystallographic signature of an acyclic peptide nanorod: molecular mechanism of nanorod formation by a self-assembled tetrapeptide

A terminally protected acyclic tetrapeptide Boc-Aib-Val-Aib-beta-Ala-OMe 1 (Aib: alpha-aminoisobutyric acid, beta-Ala: beta-Alanine) self-assembles into a continuous hydrogen-bonded supramolecular helix with an average diameter of 10 A (1 nm) starting from a double bend molecular conformation in crystals and further self-assembly of this supramolecular architecture leads to the formation of polydisperse nanorods of diameters 10-40 nm.     

CeO2 nanorods and gold nanocrystals supported on CeO2 nanorods as catalyst

The formation mechanism of uniform CeO2 structure at the nanometer scale via a wet-chemical reaction is of great interest in fundamental study as well as a variety of applications. In this work, large-scale well-crystallized CeO2 nanorods with uniform diameters in the range of 20-30 nm and lengths up to tens of micrometers are first synthesized through a hydrothermal synthetic route in 5 M KOH solution at 180 degrees C for 45 h without any templates and surfactants. The nanorod formation involves dehydration of CeO2 nanoparticles and orientation growth along the 110 direction in KOH solution. Subsequently, gold nanoparticles with crystallite sizes between 10 and 20 nm are loaded on the surface of CeO2 nanorods using HAuCl4 solution as the gold source and NaBH4 solution as a reducing agent. The synthesized Au/CeO2 nanorods demonstrate a higher catalytic activity in CO oxidation than the pure CeO2 nanorods.     

Heterogeneous nucleation for synthesis of sub-20 nm ZnO nanopods and their application to optical humidity sensing

We present a novel method for colloidal synthesis of one-dimensional ZnO nanopods by heterogeneous nucleation on zero-dimensional ZnO nanoparticle ‘seeds’. Ultra-small ZnO nanopods, multi-legged structures with sub-20 nm individual leg diameters, can be synthesized by hydrolysis of a Zn2+ precursor growth solution in presence of ∼4 nm ZnO seeds under hydrothermal conditions via microwave-assisted heating in as little as 20 min of reaction time. One-dimensional ZnO nanorods are initially generated in the reaction mixture by heterogeneous nucleation and growth along the [0001] direction of the ZnO crystal. Growth of one-dimensional nanorods subsequently yields to an ‘attachment’ and size-focusing phase where individual nanorods fuse together to form multi-legged nanopods having diameters ∼15 nm. ZnO nanopods exhibit broad orange-red defect-related photoluminescence in addition to a near-band edge emission at 373 nm when excited above the band-gap at 350 nm. The defect-related photoluminescence of the ZnO nanopods has been applied towards reversible optical humidity sensing at room temperature. The sensors demonstrated a linear response between 22% and 70% relative humidity with a 0.4% increase in optical intensity per % change in relative humidity. Due to their ultra-small dimensions, ZnO nanopods exhibit a large dynamic range and enhanced sensitivity to changes in ambient humidity, thus showcasing their ability as a platform for optical environmental sensing.     

Large-scale synthesis of TiO2 nanorods via nonhydrolytic sol-gel ester elimination reaction and their application to photocatalytic inactivation of E. coli

A simple method of synthesizing a large quantity of TiO(2) nanorods was developed. A nonhydrolytic sol-gel reaction between titanium(IV) isopropoxide and oleic acid at 270 degrees C generated 3.4 nm (diameter) x 38 nm (length) sized TiO(2) nanocrystals. The transmission electron microscopic image showed that the particles have a uniform diameter distribution. X-ray diffraction and selected-area electron diffraction patterns combined with high-resolution transmission electron microscopic image showed that the TiO(2) nanorods are highly crystalline anatase crystal structure grown along the [001] direction. The diameters of the TiO(2) nanorods were controlled by adding 1-hexadecylamine to the reaction mixture as a cosurfactant. TiO(2) nanorods with average sizes of 2.7 nm x 28 nm, 2.2 nm x 32 nm, and 2.0 nm x 39 nm were obtained using 1, 5, and 10 mmol of 1-hexadecylamine, respectively. The optical absorption spectrum of the TiO(2) nanorods exhibited that the band gap of the nanorods was 3.33 eV at room temperature, which is 130 meV larger than that of bulk anatase (3.2 eV), demonstrating the quantum confinement effect. Oleic acid coordinated on the nanorod surface was removed by the reduction of the carboxyl group of oleic acid, and the Brunauer-Emmett-Teller surface area of the resulting naked TiO(2) nanorods was 198 m(2)/g. The naked TiO(2) nanorods exhibited higher photocatalytic activity than the P-25 photocatalyst for the photocatalytic inactivation of E. coli.     

Synthesis and optical properties of colloidal tungsten oxide nanorods

Thermal decomposition of W(CO)6 in oleylamine in the presence of mild oxidant Me3NO.2H2O produces tungsten oxide nanorods with diameters ranging from 3 to 6 nm. The size of nanorods can be easily varied by the employed surfactant ratio or reaction temperature. The prepared tungsten oxide nanorods exhibit strong photoluminescence (PL) peaks in 300-500 nm, which show a weak size dependency.     

The effect of hydrothermal growth temperature on preparation and photoelectrochemical performance of ZnO nanorod array films

Highly oriented ZnO nanorod arrays with controlled diameter and length, narrow size distribution and high orientation consistency have been successfully prepared on ITO substrates at different growth temperatures by using a simple hydrothermal method. XRD results indicate that the nanorods are high-quality single crystals growing along [001] direction with a high consistent orientation perpendicular to the substrate. SEM images show that the nanorods have average diameters of about 30-70 nm by changing growth temperature. The thin films consisting of ZnO nanorods with controlled orientation onto ITO substrates allow a more efficient transport and collection of photogenerated electrons through a designed path. For a sandwich-type cell, the relatively high overall solar energy conversion efficiency reaches about 2.4% when the growth temperature is at 95 °C.     

Synthesis of CeVO<Subscript>4</Subscript> Crystals with Different Sizes and Shapes

Tetragonal CeVO₄ was prepared through hydrothermal treatment and sonication method with the same precursor in the absence of any catalysts or templates, and the products were characterized by XRD, TEM and Raman. It is found that microrods, nanoparticles, nanorods and nanoplates have been obtained. The bigger nanorods produced through hydrothermal treatment have average diameters of 15–25 nm and lengths of 20–60 nm. The smaller nanorods prepared through ultrasound treatment have average diameters of 6–12 nm and lengths of 10–18 nm. Uniform nanoplates have been produced. The nanoplates produced through hydrothermal method are composed of CeVO₄ and CeO₂. The mechanism of shape changing has been discussed. And the existing vanadium which is sensitive to the pH value of synthesis solution may be a key factor for the resulted sizes and shapes of the obtained nanocrystals. The samples prepared through hydrothermal treatment and sonication method were used as the catalysts for the combustion of trichloroethylene to test their catalytic activity.     

Synthesis and gas sensitivities of SnO2 nanorods and hollow microspheres

SnO₂ urchin-like structures composed of nanorods with diameters of 10-15 nm and lengths of 50-70 nm have been hydrothermally synthesized via a H₂O₂-assisted route without any surfactant, using SnCl₂ as raw material. With the addition of methenamine (HMT), SnO₂ hollow microspheres with diameters of 2-3 μm and shell thickness of 60-140 nm were also prepared. The as-obtained products were examined using diverse techniques including X-ray powder diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-resolution TEM and photoluminescence spectra. The gas sensitivity experiments have demonstrated that the as-synthesized SnO₂ materials exhibit good sensitivity to alcohol vapors, which may offer potential applications in gas sensors.     

Gold Nanostructures Formed in Ionic Clusters of Perfluorinated Ionomer

Summary: Gold nanoparticles and nanorods have been synthesized in the ionic cluster network of Nafion using a liquid‐phase chemical impregnation/reduction process seemingly visualizing the phase‐separated hydrated cluster network of Nafion. The spherical shape of the hydrated clusters is clearly seen by the replicated gold nanoparticles with diameters of 5–6 nm. The gold nanoparticles grow through the Nafion cluster network to form gold nanorods with diameters of 5–6 nm and a characteristic length of 12–15 nm, which compare well to the previously reported small‐angle X‐ray scattering results. Tiny channels between adjacent spherical clusters are also observed, which expand to form a rod structure by a reorganization of ion exchange sites and an elastic deformation of Nafion polymer chains. The gold nanorods become interconnected in a cascadic feature, and a tripod‐shaped nanorod structure is one of the most commonly observed structures of the replicated gold. Although further study should be performed, the synthesized gold may be used to visualize the hydrated cluster and the network structure of Nafion, which could be used as important information in identifying the morphology and ion transport phenomena of Nafion.

Gold nanoparticles and nanorods growing through a hydrated Nafion cluster network.     

Magnetron sputtering of silver nanowires using anodic aluminum oxide template: a new active substrate of surface enhanced Raman scattering and an investigation of its enhanced mechanism

A high quality anodic aluminum oxide (AAO) template with ordered apertures about 50-80 nm was fabricated by anodizing aluminum in electrolytes through a two-step method, and silver nanowires with diameters from 40nm to 70nm were prepared on this AAO template by magnetron sputtering. On the glass covered with silver nanowires, high quality surface enhanced Raman scattering (SERS) spectra of sudan II (C₁₈H₁₆N₂O) with enhancement factors of 10⁵ were obtained. And comparison of SERS spectra on silver nanowires with the SERS spectra of silver colloids indicates that main enhanced mode is lightning rod effect of nanorods on the Sudan II/silver nanowires system.