Synthesis and characterization of bismuth single-crystalline nanowires and nanospheres

A facile solution-phase process has been demonstrated for the selective preparation of single-crystalline bismuth nanowires and nanospheres by reducing sodium bismuthate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) or acetone. Bismuth nanobelts and Bi/Bi(2)O(3) nanocables could be also obtained by changing some reaction parameters. Various techniques such as XRD, EDXA, SEM, TEM, HRTEM, and FT-IR have been used to investigate the physical characteristics of these low-dimensional bismuth nanostructures.     

Dispersibility, stabilization, and chemical stability of ultrathin tellurium nanowires in acetone: morphology change, crystallization, and transformation into TeO2 in different solvents

The dispersibility and stabilization of freshly synthesized ultrathin tellurium nanowires with diameters of 4-9 nm using poly(vinyl pyrrolidone) (PVP) as a capping agent can be well controlled through an easy acetone-addition process. Ultrathin Te nanowires synthesized by a hydrothermal method using PVP as a capping agent will aggregate in a water/acetone system, and their aggregation state strongly relies on the volume of water and acetone in this mixed solution. This phenomenon is due to the different solubility of PVP in water and acetone, which has significant influence on the dispersibility and stabilization of the nanowires. The results also demonstrate that the freshly prepared Te nanowires are not stable after being stored for a prolonged time in contact with air, ethanol, and water. Ultrathin Te nanowires can be oxidized easily with various final morphologies, which are core-shell structures in contact with air, amorphous nanoparticles and nanoplatelets in ethanol, and large square flakes in water. The entire conversion process from crystalline Te nanowires to amorphous TeO2 nanoparticles or single-crystal paratellurite (TeO2) at room temperature was carefully studied, implying that tellurium nanowires synthesized by other chemical methods and other nanomaterials after synthesis could also not be stable, and their storage methods require special attention.     

Shape control of single crystalline bismuth nanostructures

A synthesis approach for shape control of single crystalline Bi nanostructures has been developed. By controlling the molar ratio of PVP and Bi in a polyol process, Bi nanocubes with an edge length of approximately 60-80 nm, triangular nanoplates with an edge length of 200-500 nm, and nanospheres with an average diameter of 75 nm have been successfully synthesized. In the same synthetic process, Bi nanobelts with lengths of up to 80 microm and widths of up to 0.6 microm were synthesized in large quantities by introducing a trace amount of Fe3+ species into the reaction system. These single crystalline nanostructure Bi materials are expected to find potential applications in a variety of areas including high efficiency thermoelectric devices.     

基于AuCl(油胺)复合物合成形貌可控的金纳米结构

简要综述了使用一价金复合物AuCl(油胺)作为前驱物合成形貌可控的金纳米结构的相关工作. 通过改变有机溶剂、添加异质金属纳米粒子及控制反应温度等手段, 成功合成出球形的金纳米粒子(平均直径12.7 nm)、超细金纳米线(平均直径1.8 nm)及超细金纳米棒(平均直径2 nm); 并通过牺牲磁性纳米粒子模板的方法合成出枝状金纳米结构. 除了对合成方法和过程的介绍, 还简要讨论了每种纳米结构的形成机制.     

The role of oxidative etching in the synthesis of ultrathin single-crystalline Au nanowires

The fabrication of ultrathin single-crystal Au nanowires with high aspect ratio and that are stable in air is challenging. Recently, a simple wet-chemical approach using oleylamine has been reported for the synthesis of Au nanowires with micrometer length and 2 nm in diameter. Despite efforts to understand the mechanism of the reaction, an ultimate question about the role of oxygen (O(2)) during the synthesis remained unclear. Here we report that the synthesis of ultrathin Au nanowires employing oleylamine is strongly affected by the amount of O(2) absorbed in the reaction solution. Saturating the solution with O(2) leads to both a high-yield production of nanowires and an increase in their length. Nanowires with diameters of about 2 nm and lengths of 8 μm, which corresponds to an aspect ratio of approximately 4000, were produced. The role of oxygen is attributed to the enhanced oxidation of twin defects on Au nanoparticles formed in the first stage of the reaction. Understanding the role of oxidative etching is crucial to significantly increasing the yield and the length of ultrathin Au nanowires.     

Molecular Template Assisted Growth of Ultrathin Silicon Carbide Nanowires with Strong Green Light Emission and Excellent Field‐Emission Properties

A novel molecule template assisted chemical co‐reduction method has been successfully developed for the controlled synthesis of ultrathin β‐SiC single‐crystalline nanowires on a large scale. The ultrathin β‐SiC single‐crystalline nanowires are about 8 nm in diameter and 200–800 nm in length. The resulting thin β‐SiC single‐crystalline nanowire is new in the family of β‐SiC one‐dimensional (1D) nanostructures. A synergistic action of π‐stacking and steric hindrance result from the 1,10‐phenanthroline molecule template are proposed to explain the growth mechanism of the ultrathin β‐SiC single‐crystalline nanowires based on the experimental observation. Importantly, such ultrathin β‐SiC nanowire has shown a strong structure‐induced enhancement of photoluminescence properties and has exhibited a very strong green light emission, which can be seen by naked eye. Furthermore, the unique β‐SiC ultrathin nanowire structure exhibits a low turn‐on field (3.57 V μm^?1) and a large field‐emission current density (20 mA cm^?2). These results suggest that the ultrathin β‐SiC nanowires can be expected to find promising applications as field emitters and photoelectronic devices.     

Ultrathin gold nanoframes through surfactant-free templating of faceted pentagonal silver nanoparticles

Ultrathin gold nanoframes (up to 1.6 nm) were prepared via templating upon well-defined faceted silver morphologies. Starting with silver decahedra, small quantities of gold (1-10 mol% relative to the amount of silver) were selectively deposited on the nanoparticle edges under optimized reducing conditions. Silver dissolution in hydrogen peroxide yielded well-defined gold frames that retained their structural integrity in the ultrathin nanowire regime below 2 nm. The frame formation protocol was also successfully applied to other silver nanoparticle shapes featuring pentagonal twinning and (111) facets (e.g., pentagonal faceted rods and icosahedra). The demonstrated approach can be applied in the controlled preparation of ultrathin metal nanowires complementary to lithography and in the production of ultrafine noble-metal nanostructures for catalytic applications.     

Mn掺杂SnO_2一维纳米结构的制备、形貌及光学性质

用化学气相沉积(CVD)法制备了Mn掺杂的SnO2一维纳米结构(纳米线及纳米带),X射线衍射(XRD)显示样品为金红石型SnO2晶体,其生长机理可分别归结为气-液-固(VLS)和气-固(VS)机理,生长温度和气态原料浓度的差别是造成样品形貌及生长机理不同的主要原因.样品的拉曼谱出现了500、543、694和720cm-1四个新拉曼谱峰,分别是由活性的红外模和表面模引起的.纳米线及纳米带发光峰位于520nm处,发光强度随样品中氧空位的增减出现由强到弱的变化.     

Ultrathin Au nanowires and their transport properties

This paper presents a facile synthesis of single-crystalline Au nanowires by reduction of HAuCl4 in oleic acid and oleylamine. The diameter of these micron-meter-long Au nanowires is controlled to be 3 and 9 nm by volume ratio of oleylamine and oleic acid. When linked between two gold electrodes, the 9 nm Au nanowire shows good electron conductivity with its breakdown current density reaching 3.5 x 10(12) A/m2. This demonstrates that the chemically made ultrathin Au nanowires can be used as a molecular-scale interconnect for nanoelectronic applications.     

阳离子表面活性剂作用下制备一维纳米结构聚苯胺

在十六烷基三甲基溴化铵(CTAB)存在下, 以盐酸为质子酸, 过硫酸铵为氧化剂, 制备了平均直径为115 nm、具有分叉结构的聚苯胺纳米纤维和平均直径为75 nm的卷曲聚苯胺纳米线, 两者的结构产率高达90%和100%, 电导率分别为1.6×10-2和9.3×10-2 S/cm. 研究发现, 聚苯胺的一维纳米结构受盐酸浓度和苯胺与CTAB摩尔比的协同影响. 用TEM, SEM和FTIR对产物的形貌和化学结构进行了表征. 利用pH监测反应并结合SEM结果研究了聚苯胺纳米线的形成过程, 结果表明, CTAB阳离子与过硫酸根形成的絮状物的诱导作用是聚苯胺纳米纤维和纳米线形成的关键因素.     

Recycling Nanowire Templates for Multiplex Templating Synthesis: A Green and Sustainable Strategy

Template‐directed synthesis of nanostructures has been emerging as one of the most important synthetic methodologies. A pristine nanotemplate is usually chemically transformed into other compounds and sacrificed after templating or only acts as an inert physical template to support the new components. If a nanotemplate is costly or toxic as waste, to recycle such a nanotemplate becomes highly desirable. Recently, ultrathin tellurium nanowires (TeNWs) have been demonstrated as versatile chemical or physical templates for the synthesis of a diverse family of uniform 1D nanostructures. However, ultrathin TeNWs as template are usually costly and are discarded as toxic waste in ionic species after chemical reactions or erosion. To solve the above problem, we conceptually demonstrate that such a nanotemplate can be economically recycled from waste solutions and repeatedly used as template.     

静电纺丝技术制备LaCrO4和LaCrO3纳米带及其光催化性质

采用溶胶-凝胶法结合静电纺丝技术制备了PVP/[La(NO3)3|Cr(NO3)3]复合纳米带, 经热处理后得到LaCrO4纳米带和LaCrO3纳米带. 采用TG-DTA, XRD, SEM和EDS等测试手段对样品进行了表征. 结果表明, PVP/[La(NO3)3-Cr(NO3)3]复合纳米带表面光滑, 宽度为(9.1±1.9) μm, 厚度约385 nm; 经600 ℃焙烧后得到单斜独居石型LaCrO4纳米带, 宽度为(2.5±0.5) μm, 厚度约100 nm; 当焙烧温度为650~800 ℃时得到LaCrO3多孔纳米带, 属正交晶系, Pbnm空间群, 经650 ℃焙烧后得到的LaCrO3纳米带呈多孔结构, 带宽为(2.4±0.5) μm, 厚度约90 nm; 经800 ℃焙烧后得到的LaCrO3纳米带部分破碎形成LaCrO3纳米粒子, LaCrO3纳米带宽度约(1.3±0.4) μm, 厚度约90 nm, LaCrO3纳米粒子粒径约80 nm. 以罗丹明B为目标降解物, 研究了不同焙烧温度下产物的光催化性能, 其中800 ℃焙烧后得到的样品在紫外光照射下对罗丹明B的降解效果最好, 光照200 min后罗丹明B的降解率为94.6%.     

A vapor-solid strategy to silica sheathed metal nanostructures and microstructures via reactions of metal chlorides with silicon

A facile vapor-solid strategy has been developed to prepare silica-sheathed metal micro/nanostructures with controllable shapes. As examples, silica-sheathed nickel nanowires (diameter approximately 50 nm), microcubes (edge length 1-3 microm), nanocubes (edge length approximately 200 nm) with an epitaxial tail (diameter<100 nm), and 1D assembly structures of nanoparticles (particle diameter<100 nm) as well as silica-sheathed cobalt and copper micro/nanostructures are synthesized. The possible reaction and growth mechanisms of Ni/SiO2 structures are discussed. The method is expected to be applied to a wider range of metals.     

Surface-enhanced Raman scattering and polarized photoluminescence from catalytically grown CdSe nanobelts and sheets

We have successfully fabricated single-crystalline CdSe nanowires, nanobelts, and sheets by a chemical vapor deposition (CVD) method assisted with laser ablation. The synthesized CdSe nanostructures have hexagonal wurtzite phase as characterized by X-ray diffraction (XRD). CdSe nanobelts can range in length from several tens to a hundred micrometers, in thickness from 40 to 70 nm, and a tapered width which is approximately 3 microm at one end and tapers off to approximately 100 nm at a catalytic gold particle. Both selected area electron diffraction (SAED) and high-resolution transmission electron microscopic (HRTEM) measurements show that the single-crystalline hexagonal belts and sheets grew along the [0.1-1.0] direction with side surface of +/-(0 0 0 1) and top surface of +/-(2 -1 -1 0). While the growth mechanism of nanobelts complies with a combination of vapor-liquid-solid (VLS) and vapor-solid (VS) processes, the formation of sheets is primarily based on the VS mechanism. For comparison, the phonon modes of CdSe nanobelts and bulk powder have been measured by surface-enhanced Raman scattering (SERS) and normal Raman scattering (NRS) spectroscopies with off- and near-resonant excitations. A blue-shift of 2.4 cm(-1) for the longitudinal optical (LO) phonon of CdSe nanobelts, relative to bulk CdSe, is attributed to a lattice contraction in the belt structure, which is confirmed by the XRD measurement. Room-temperature microphotoluminescence (PL) at approximately 1.74 eV from single CdSe nanobelts shows a 3-fold enhancement compared to that from bulk CdSe powder and displays a partial polarization dependence of emission angles.     

Single-crystal nanowires of platinum can be synthesized by controlling the reaction rate of a polyol process

Platinum nanowires of approximately 100 nm in length and approximately 5 nm in diameter have been synthesized by reducing H(2)PtCl(6) with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Fe(3+) or Fe(2+). The wires were generated at the final stage of the synthesis, which involved the formation of several intermediate species. The Fe(3+) or Fe(2+) ions had dual functions in the synthesis: they induced aggregation of Pt nanoparticles into larger structures that served as the nucleation sites, and they greatly reduced the reaction rate and supersaturation level to induce anisotropic growth. The reaction mechanism was studied by X-ray photoelectron spectroscopy (XPS) and UV-vis spectral analysis. The Pt nanowires could be readily separated from the surfaces of the agglomerates by sonication and obtained as pure samples by centrifugation.     

A novel synthesis of ultrathin CoPt3 nanowires by dealloying larger diameter Co99Pt1 nanowires and subsequent stress-induced crack propagation

A novel approach to the fabrication of ultrathin CoPt₃ nanowires with a diameter of a few nanometers has been developed, by taking advantage of the volume shrinkage and formation of nanoporous structures upon dealloying electrodeposited Co₉₉Pt₁ nanowires (28 nm in diameter), followed by an ultrasonication treatment. The as-produced ultrathin CoPt₃ nanowires have an average diameter of 5 nm and lengths of up to 10 μm, and are found to be ferromagnetic at room temperature.     

Study on morphology of LaFeO3 nanofibers under different voltage connections

Continuous LaFeO₃ nanowires and nanobelts were successfully synthesized using a sol–gel assisted electrospinning method followed by calcination at 500°C in air. The thermal decomposition processes of LaFeO₃ are carefully investigated and the best calcining temperature was found to be 500°C. The two nanofibers obtained were characterized using X‐ray diffraction analysis, which shows single phase and the structure of nanobelts has higher crystallinity than that of the nanowires. The scanning electron microscopy reveals that the diameter of the obtained LaFeO₃ nanowires is 139.3 nm. And the thickness and width of the nanobelts are 80 and 459 nm. Moreover, the electrospun LaFeO₃ nanobelts are endowed with a higher specific surface area compared with the nanowires, which results from the regular one dimensional morphology without any detectable agglomeration and a rough surface.     

Preparation of gold-tellurium hybrid nanomaterials for surface-enhanced Raman spectroscopy

We report a simple method for preparing three different SERS-active substrates. Concentrated hydrazine solution as the reducing agent and tellurium dioxide as the precursor were used to prepare Te nanowires (NWs). The as-prepared Te NWs have an average length of 547.7 +/- 111.6 nm and an average width of 15.1 +/- 2.7 nm. Through the reaction of Te NWs with sodium tetrachloroaurate in the presence of hexadecyltrimethylammonium bromide (CTAB) over reaction times of 10, 20, and 60 min, gold-tellurium nanodumbbells, gold-tellurium nanopeapods, and gold pearl-necklace nanomaterials (Au PNNs) were obtained, respectively. By controlling the reaction time, the distance between adjacent gold nanoparticles (Au NPs) in each Te nanowire was tunable, allowing us to investigate its effect on the SERS signals. Having shorter distances among Au NPs (greater electromagnetic fields), the Au PNNs provided a reproducible enhancement factor of 5.6 x 10(9).     

Synthesis of Sub‐2 nm Iron‐Doped NiSe2 Nanowires and Their Surface‐Confined Oxidation for Oxygen Evolution Catalysis

Ultrathin nanostructures are attractive for diverse applications owing to their unique properties compared to their bulk materials. Transition‐metal chalcogenides are promising electrocatalysts, yet it remains difficult to make ultrathin structures (sub‐2 nm), and the realization of their chemical doping is even more challenging. Herein we describe a soft‐template mediated colloidal synthesis of Fe‐doped NiSe₂ ultrathin nanowires (UNWs) with diameter down to 1.7 nm. The synergistic interplay between oleylamine and 1‐dodecanethiol is crucial to yield these UNWs. The in situ formed amorphous hydroxide layers that is confined to the surface of the ultrathin scaffolds enable efficient oxygen evolution electrocatalysis. The UNWs exhibit a very low overpotential of 268 mV at 10 mA cm^?2 in 0.1 m KOH, as well as remarkable long‐term stability, representing one of the most efficient noble‐metal‐free catalysts.     

Ultrathin single crystal ZnS nanowires

A facile synthesis of ultrathin single crystal ZnS nanowires with an average diameter of 4.4 nm in high yield (close to 100%) was firstly reported through the pyrolysis of a single-source precursor (zinc diethyldithiocarbamate). The obtained ultrathin ZnS nanowires exhibit good optical properties and hold promise for future applications in nanodevices.