一步湿化学法合成超细金纳米线

以氯金酸(HAuCl₄)为前驱物, 油胺同时作为溶剂、表面稳定剂和还原剂, 通过简单的一步湿化学法合成超细金纳米线. 制备出的超细金纳米线不仅产量高、纯度高, 而且纵横比大, 纳米线平均直径~2 nm, 长度可达数十微米. 如果添加另一种还原剂油酸并调节油胺和油酸的体积比为1:1, 将生成直径为~9 nm的金纳米线. 通过改变反应温度和还原剂用量, 对该种超细金纳米结构的生长机制进行阐述说明: 以油胺为模板, 在油胺和一价金卤化物(AuCl)亲金键合形成的一维聚合链作用下, 被还原的金原子附着在已成核颗粒表面, 一维地生长成超细金纳米线.     

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.     

Ultrathin gold nanowires can be obtained by reducing polymeric strands of oleylamine-AuCl complexes formed via aurophilic interaction

This Communication describes a facile route to the preparation of ultrathin gold nanowires using linear chains formed from [(oleylamine)AuCl] complex via aurophilic interaction. The linear chains, with AuI...AuI bonds as the backbone and surrounded by oleylamines, can group together to form bundles of polymeric strands. When the AuI was reduced to Au0 by reacting with Ag nanoparticles in hexane, the polymeric strands functioned as both the source of Au and the template to mediate the nucleation and growth of Au nanowires. Using this method, we were able to produce Au nanowires with an average diameter of approximately 1.8 nm and an aspect ratio of >1000 in high yields (approximately 70%).     

多元醇还原法制备片状六边形Fe3O4纳米颗粒

在表面活性剂油酸和油胺,液相环境二苄醚体系中,利用多元醇还原法,采用1,2-十二烷二醇还原前驱体乙酰丙酮铁Fe(acac)3,通过表面活性剂、金属前驱体以及液相环境的共同作用,制备出了单分散片状六边形Fe3O4纳米颗粒。分析了表面活性剂以及还原剂多元醇对纳米颗粒尺寸及形貌的影响。TEM表征结果显示：与未使用表面活性剂的情况相比,油酸和油胺的加入抑制了颗粒的生长,使颗粒尺寸从24.2 nm降低到10.7 nm;颗粒形貌多样化,出现了片状六边形形貌的Fe3O4纳米颗粒。磁性能检测表明： Fe3O4纳米颗粒具有高饱和磁化强度（Ms=88 emu/g）和零剩磁的特点,有望作为磁标记材料应用在生物检测上     

Controllable Synthesis and Study on Morphology of Copper Nanowires

High‐purity, large‐aspect‐ratio, and well‐dispersed copper nanowires (CuNWs) with an average diameter of 45 nm and length >100 μm were successfully synthesized by reducing a Cu(II) salt with glucose, with oleylamine (OM) and oleic acid (OA) serving as dual capping agents, through hydrothermal reduction. A systematic study of the effects of the copper salt, capping agents, reductant, and temperature on the morphology of CuNWs has been conducted. Our results indicate that CuNWs with different diameters can be obtained using different copper salts. The diameter of the as‐prepared CuNWs decreases with increasing amounts of OM/OA and glucose but increases with the increasing temperature of the reaction. By adjusting the experimental parameters, we could achieve controlled synthesis of CuNWs and obtain high‐quality CuNWs with different diameters of 45, 76, 85, 90, 100, 112, 135, and 175 nm.     

Au Nanowires-MWCNTs修饰电极对葡萄糖的催化氧化

通过油胺(Oleylamine)还原法制备了金纳米线(Au nanowires),将其与酸化处理的多壁碳纳米管(MWCNTs)通过层层组装制备了Au nanowires-MWCNTs复合结构修饰的玻碳电极(Au nanowires-MWCNTs/GCE).电化学研究结果表明,与单纯Au nanowires或MWCNTs修饰电极相比,Au nanowires-MWCNTs/GCE对葡萄糖表现出更优良的电催化性能.以Au nanowires-MWCNTs/GCE为阳极,电沉积Pt膜电极(Pt/GCE)为阴极,构建了葡萄糖/O2燃料电池.测试结果表明,构建的燃料电池的开路电位(OCP)为0.57 V,在0.44 V下最大功率密度(Pmax)为0.28 m W/cm2.     

Synthesis of colloidal uranium-dioxide nanocrystals

In this paper, we have developed an organic-phase synthesis method for producing size-controlled, nearly monodispersed, colloidal uranium-dioxide nanocrystals. These UO2 nanocrystals are potentially important to applications such as nuclear fuel materials, catalysts, and thermopower materials. In addition, we have systematically mapped out the functions of the solvents (oleic acid, oleylamine, and 1-octadecene) in the synthesis, and we found that N-(cis-9-octadecenyl)oleamide-a product of the condensation of oleic acid and oleylamine-can substantially affect the formation of UO2 nanocrystals. Importantly, these results provide fundamental insight into the mechanisms of UO2 nanocrystal synthesis. Moreover, because a mixture of oleic acid and oleylamine has been widely used in synthesizing a variety of high-quality metal or metal-oxide nanocrystals, the results herein should also be important for understanding the detailed mechanisms of these syntheses.     

Mechanistic studies on the galvanic replacement reaction between multiply twinned particles of Ag and HAuCl4 in an organic medium

This article presents a mechanistic study on the galvanic replacement reaction between 11- and 14-nm multiply twinned particles (MTPs) of Ag and HAuCl4 in chloroform. We monitored both morphological and spectral changes as the molar ratio of HAuCl4 to Ag was increased. The details of reaction were different from previous observations on single-crystal Ag nanocubes and cuboctahedrons. Because Au and Ag form alloys rapidly within small MTPs rich in vacancy and grain boundary defects, a complete Au shell did not form on the surface of each individual Ag template. Instead, the replacement reaction resulted in the formation of alloy nanorings and nanocages from Ag MTPs of decahedral or icosahedral shape. For the nanorings and nanocages derived from 11-nm Ag MTPs, the surface plasmon resonance (SPR) peak can be continuously shifted from 400 to 616 nm. When the size of Ag MTPs was increased to 14 nm, the SPR peak can be further shifted to 740 nm, a wavelength sought by biomedical applications. We have also investigated the effects of capping ligands and AgCl precipitate on the replacement reaction. While hollow structures were routinely generated from oleylamine-capped Ag MTPs, we obtained very few hollow structures by using a stronger capping ligand such as oleic acid or tri-n-octylphosphine oxide (TOPO). Addition of extra oleylamine was found to be critical to the formation of well-controlled, uniform hollow structures free of AgCl contamination thanks to the formation of a soluble complex between AgCl and oleylamine.     

Water-based ferrofluids from FexPt1-x nanoparticles synthesized in organic media

This paper describes an effective method to transfer oleic acid/oleylamine-capped colloidal FePt nanoparticles dispersed in hexane into water, using tetramethylammonium hydroxide (TMAOH) as a phase transfer agent. FexPt1-x nanoparticles with different compositions (x = 0.32, 0.40, 0.48, 0.60, 0.66, 0.69) in the size range of 2-4 nm were synthesized by a high-temperature organometallic route with oleic acid and oleylamine as stabilizers. The surface of such nanoparticles was modified through removal of the organic, hydrophobic layer and adsorption of TMAOH, which provides the nanoparticles with sufficient surface charge so that an electrostatic double layer builds up, and the FePt nanoparticles can be fully redispersed in aqueous solution, even with high concentrations. The water-dispersible FePt nanoparticles were characterized by transmission electron microscopy, electrophoretic mobility, X-ray diffraction, and Fourier transform infrared spectroscopy.     

Inorganic nanocrystal self-assembly via the inclusion interaction of beta-cyclodextrins: toward 3D spherical magnetite

Synthesis and three-dimensional (3D) assembly of magnetite nanocrystals were realized by a one-pot procedure, in which Fe(acac)3 (acac = acetylacetonate) was partly reduced by hydrazine accompanied with ethylene glycol and spontaneously assembled into spherical nanostructures in the presence of surfactants including beta-cyclodextrin, oleic acid, and oleylamine. The size of the assembled spheres can coarsely be controlled in a limited range (100 nm to 2 microm) by changing the reaction temperature and the concentration of beta-cyclodextrin. X-ray diffraction and far Fourier transform infrared spectroscopy were employed to clarify the structures of magnetite in the assembled spheres. Electron diffraction pattern in a selected-area exhibits a high-crystallinity characteristic of cubic structure magnetite. We found that the formation of spherical magnetite aggregates highly depends on the presence of beta-cyclodextrin, while oleic acid and oleylamine improve the morphology of individual magnetite nanoparticles in the assembled spheres. In addition, the thermal gravimetric analysis and differential thermal analysis were applied to determine the content of magnetite in the products. Magnetic properties were also studied by using a superconducting quantum interference device magnetometer.     

Disproportionation for growing copper nanowires and their controlled self-assembly facilitated by ligand exchange

The coating makes the wire bundle: High-quality free-standing copper nanowires have been successfully produced by disproportionation of Cu(+) in oleylamine. This provides an effective way to prepare high-quality copper nanowires, but also enriches synthetic routes to other nanostructures. These copper nanowires can self-assemble by surface ligand exchange of oleylamine with trioctylphosphine.     

Large-scale synthesis of hexagonal pyramid-shaped ZnO nanocrystals from thermolysis of Zn-oleate complex

We report the large-scale synthesis of uniform-sized hexagonal pyramid-shaped ZnO nanocrystals by the thermolysis of Zn-oleate complex, which was prepared from the reaction of inexpensive and environmentally friendly reagents such as zinc chloride and sodium oleate. Under optimized reaction conditions, we were able to synthesize as much as 2.83 g using 300 mL of oleylamine and 90 mL (284 mmol) of oleic acid (OA) as both solvents and stabilizing surfactants. The UV-vis spectrum showed the absorption onset of 380 nm, and the photoluminescence spectrum showed a near band-edge emission at 387 nm and a broad blue-green emission band above 468 nm.     

Template synthesis of metal nanowires containing monolayer molecular junctions

Metal nanowires containing in-wire monolayer junctions of 16-mercaptohexanoic acid were made by replication of the pores of 70 nm diameter polycarbonate track etch membranes. Au was electrochemically deposited halfway through the 6 microm long pores and a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid was adsorbed on top. A thin layer of Au was then electrolessly grown to form a metal cap separated from the bottom part of the wire by the SAM. Electron micrographs showed that the bottom and top metal segments were separated by an approximately 2 nm thick organic monolayer. Current-voltage measurements of individual nanowires confirmed that the organic monolayer could be contacted electrically on the top and bottom by the metal nanowire segments without introducing electrical short circuits that penetrate the monolayer. The values of the electrical properties for zero-bias resistance, current density, and breakdown field strength were within the ranges expected for a well-ordered alkanethiol SAM of this thickness.     

Structural study of gold clusters

Density functional theory (DFT) calculations were carried out to study gold clusters of up to 55 atoms. Between the linear and zigzag monoatomic Au nanowires, the zigzag nanowires were found to be more stable. Furthermore, the linear Au nanowires of up to 2 nm are formed by slightly stretched Au dimers. These suggest that a substantial Peierls distortion exists in those structures. Planar geometries of Au clusters were found to be the global minima till the cluster size of 13. A quantitative correlation is provided between various properties of Au clusters and the structure and size. The relative stability of selected clusters was also estimated by the Sutton-Chen potential, and the result disagrees with that obtained from the DFT calculations. This suggests that a modification of the Sutton-Chen potential has to be made, such as obtaining new parameters, in order to use it to search the global minima for bigger Au clusters.     

Size-controlled synthesis of magnetite nanoparticles

Monodisperse magnetite nanoparticles have been synthesized by high-temperature solution-phase reaction of Fe(acac)3 in phenyl ether with alcohol, oleic acid, and oleylamine. Seed-mediated growth is used to control Fe3O4 nanoparticle size, and variously sized nanoparticles from 3 to 20 nm have been produced. The as-synthesized Fe3O4 nanoparticles have inverse spinel structure, and their assemblies can be transformed into gamma-Fe2O3 or alpha-Fe nanoparticle assemblies, depending on the annealing conditions. The reported procedure can be used as a general approach to various ferrite nanoparticles and nanoparticle superlattices.     

Understanding mercapto ligand exchange on the surface of FePt nanoparticles

Tailoring the surface of nanoparticles is essential for biological applications of magnetic nanoparticles. FePt nanoparticles are interesting candidates owing to their high magnetic moment. Established procedures to make FePt nanoparticles use oleic acid and oleylamine as the surfactants, which make them dispersed in nonpolar solvents such as hexane. As a model study to demonstrate the modification of the surface chemistry, stable aqueous dispersions of FePt nanoparticles were synthesized after ligand exchange with mercaptoalkanoic acids. This report focuses on understanding the surface chemistry of FePt upon ligand exchange with mercapto compounds by conducting X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies. It was found that the mercapto end displaces oleylamine on the Pt atoms and the carboxylic acid end displaces the oleic acid on the Fe atoms, thus exposing carboxylate and thiolate groups on the surface that provide the necessary electrostatic repulsion to form stable aqueous dispersions of FePt nanoparticles.     

油胺/油酸稳定的CdSe量子点的绿色合成

以液体石蜡为高温反应溶剂,油酸和油胺为混合稳定剂,利用高温热解法一步合成了高质量的CdSe量子点。通过紫外-可见吸收光谱、荧光发射光谱、红外光谱和X射线衍射等手段对量子点的光学性质和结构进行了表征。结果表明,油胺/油酸混合表面活性剂稳定的量子点吸收光谱峰形更尖锐,荧光发射光谱半峰宽更窄。反应温度和反应时间均对量子点的生长过程和光学性质有明显影响,220℃下反应15 min,荧光量子产率可达26%。得到的CdSe量子点为立方晶型,表面同时包覆了油酸和油胺,具有良好的光稳定性。该方法无需使用三烷基膦,价廉环保,且合成的CdSe量子点性质稳定、性能优越,有利于其在分析检测领域中的应用。     

Facile synthesis of gold nanoparticles with narrow size distribution by using AuCl or AuBr as the precursor

Gold(I) halides, including AuCl and AuBr, were employed for the first time as precursors in the synthesis of Au nanoparticles. The synthesis was accomplished by dissolving Au(I) halides in chloroform in the presence of alkylamines, followed by decomposition at 60 degrees C. The relative low stability of the Au(I) halides and there derivatives eliminated the need for a reducing agent, which is usually required for Au(III)-based precursors to generate Au nanoparticles. Controlled growth of Au nanoparticles with a narrow size distribution was achieved when AuCl and oleylamine were used for the synthesis. FTIR and mass spectra revealed that a complex, [AuCl(oleylamine)], was formed through coordination between oleylamine and AuCl. Thermolysis of the complex in chloroform led to the formation of dioleylamine and Au nanoparticles. When oleylamine was replaced with octadecylamine, much larger nanoparticles were obtained due to the lower stability of [AuCl(octadecylamine)] complex relative to [AuCl(oleylamine)]. Au nanoparticles can also be prepared from AuBr through thermolysis of the [AuBr(oleylamine)] complex. Due to the oxidative etching effect caused by Br(-), the nanoparticles obtained from AuBr exhibited an aspect ratio of 1.28, in contrast to 1.0 for the particles made from AuCl. Compared to the existing methods for preparing Au nanoparticles through the reduction of Au(III) compounds, this new approach based on Au(I) halides offers great flexibility in terms of size control.     

Structure and morphology of spinel MFe2O4 (M=Fe, Co, Ni) nanoparticles chemically synthesized from heterometallic complexes

We synthesized magnetic spinel ferrites from trimetallic single-source precursors. Fe(II), Co(II), and Ni(II) ferrite nanoparticles in the range of 9-25 nm were synthesized by solvothermal decomposition of trimetallic acetate complex precursors in benzyl ether in the presence of oleic acid and oleylamine, using 1,2-dodecanediol as the reducing agent. For comparison, spinel ferrite nanoparticles were synthesized by stoichiometric mixtures of metal acetate or acetylacetonate salts. The nanoparticles (NP) were characterized by TEM, DLS, powder XRD, and Raman spectroscopy; and their magnetic properties were characterized by ZFC-FC and M(H) measurements. The ferrite-NP were more homogeneous and had a narrower size distribution when trimetallic complexes were used as precursors. As a consequence, the magnetic properties of these ferrite-NP are closer to the aimed room temperature superparamagnetic behavior, than are those of other ferrites obtained by a mixture of salts.     

Controlled aging of PbS colloidal quantum dots under mild conditions

A new controlled aging methodology was developed for the synthesis of PbS colloidal quantum dots (QDs), applying larger PbS QDs as a starting material for smaller QDs by application of environmentally friendly oleic acid and oleylamine as reagents. This simple and mild procedure provides a possible strategy for tailoring the size-dependent properties of PbS QDs.