Fabrication of nanorattles with passive shell

This investigation describes the formation of a metal nanorattle with a pure metal shell by varying experimental parameters. The galvanic replacement reaction between silver and chloroauric acid was adopted to prepare hollow metal nanoparticles. This approach is extended to produce nanorattles of Au cores and Au shells by starting with Au(core)Ag(shell) nanoparticles as templates. The effect of temperature on the nanostructure of the final product is also considered. The composition of the shell in nanorattles can be controlled by varying the reaction temperature (to form pure gold or gold-silver alloy, for example). X-ray absorption fine structure spectroscopy is conducted to elucidate the fine structure of these nanoparticles. Partial alloying between the Au core and the Ag shell is observed by extended X-ray absorption fine structure (EXAFS).     

Organosulfur-functionalized Au, Pd, and Au-Pd nanoparticles on 1D silicon nanowire substrates: preparation and XAFS studies

A hybrid preparative method was developed to prepare organosulfur-functionalized Au nanoparticles (NPs) on silicon nanowires (SiNWs) by reacting HAuCl(4) with SiNW in the presence of thiol. A number of organosulfur molecules-dodecanethiol, hexanethiol, 1,6-hexanedithiol, and tiopronin-were used to functionalize the Au surface. Size-selected NPs ranging from 1.6 to 7.5 nm were obtained by varying the S/Au ratio and the concentration of HAuCl(4). This method was further extended to the preparation Pd and Pd-Au bimetallic NPs on SiNWs. The morphology of the metal nanostructures was examined by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The local structure and bonding of the SiNW-supported metal nanostructures were studied using X-ray absorption fine structures (XAFS) [including both X-ray near-edge structures (XANES) and extended X-ray absorption fine structures (EXAFS)] at the Au L(3)-, Pd K-, S K-, and Si K-edges. It was also found that the annealing of the thiol-capped Au NPs up to 500 degrees C transforms the surface of the thiol-capped NPs to gold sulfide, as identified using Au L(3)- and S K-edge XANES. We also illustrate that this preparative approach can be used to form size-controllable Au NPs on carbon nanotubes.     

Aerosol assisted chemical vapor deposition using nanoparticle precursors: a route to nanocomposite thin films

Gold nanoparticle and gold/semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapor deposition (CVD). A preformed gold colloid in toluene was used as a precursor to deposit gold films onto silica glass. These nanoparticle films showed the characteristic plasmon absorption of Au nanoparticles at 537 nm, and scanning electron microscopic (SEM) imaging confirmed the presence of individual gold particles. Nanocomposite films were deposited from the colloid concurrently with conventional CVD precursors. A film of gold particles in a host tungsten oxide matrix resulted from co-deposition with [W(OPh)(6)], while gold particles in a host titania matrix resulted from co-deposition with [Ti(O(i)Pr)(4)]. The density of Au nanoparticles within the film could be varied by changing the Au colloid concentration in the original precursor solution. Titania/gold composite films were intensely colored and showed dichromism: blue in transmitted light and red in reflected light. They showed metal-like reflection spectra and plasmon absorption. X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis confirmed the presence of metallic gold, and SEM imaging showed individual Au nanoparticles embedded in the films. X-ray diffraction detected crystalline gold in the composite films. This CVD technique can be readily extended to produce other nanocomposite films by varying the colloids and precursors used, and it offers a rapid, convenient route to nanoparticle and nanocomposite thin films.     

以碳微球为核的金纳米壳球体的制备

通过水热合成法制备了单分散碳微球, 并以此单分散碳微球为核, 利用其表面修饰的银纳米粒子作为种子, 进一步还原制备了以碳微球为核、以金为壳的金纳米壳(Nanoshell)球体. 通过透射电子显微镜和紫外可见吸收光谱对其形态以及光谱性质进行了表征. 研究结果表明, 采用该种方法制备出来的碳微球具有良好的单分散性, 表面修饰简便快捷, 利用碳微球为核制备的金纳米壳球体尺寸可控, 在近红外范围内有强吸收. 实验结果证明该方法是制备金纳米壳球体的一种有效新方法.     

Assembly of metal nanoparticle-carbon nanotube composite materials at the liquid/liquid interface

Carbon nanotubes (CNTs)-mediated self-assembly of metal (Au and Ag) nanoparticles at the liquid/liquid interface in the form of a stable nanocomposite film is reported. The metallic luster results from the electronic coupling of nanoparticles, suggesting the formation of closely packed nanoparticle thin films. The interfacial film could be transferred to mica substrates and carbon-coated transmission electron microscopy (TEM) grids. The transferred films were very stable for a prolonged time. The samples were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), TEM, and X-ray photoelectron spectroscopy (XPS). SEM and TEM results show that the films formed at the liquid/liquid interface are indeed composite materials consisting of CNTs and nanoparticles. XPS measurements further indicate the presence of the interaction between nanoparticles and CNTs.     

A general thermal process for the one-step preparation of well-stable noble metal nanoparticles

Heating sodium 3-thiophenemalonic acid-noble metal salt aqueous solution at 100°C, without the extra step of introducing other reducing agents and protective agents, results in the formation of well-stable noble metal that includes Au, Ag, Pt, or Pd nanoparticles. As-formed colloidal solutions were characterized by UV-vis absorption spectra and transmission electron microscopy and the nanoparticle formation process was also traced by time-dependent UV-vis absorption spectra. The text was submitted in English by the author.     

Synthesis of Ag/Pd nanoparticles via reactive micelles as templates and its application to electroless copper deposition

Ag/Pd nanoparticles have been synthesized with a reactive alcohol-type surfactant, sodium dodecyl sulfate (SDS), without the presence of an external reducing agent. Both UV-vis absorption spectra and X-ray diffraction patterns for the bimetallic and physical mixtures of individual nanoparticles revealed the formation of a bimetallic structure. Based on this method, an ordered 3D grapelike nanostructure was formed, possibly due to transformation of the liquid crystal phase of the micelles. Data from the energy-dispersive X-ray analysis show that the composition of bimetallic nanoparticle is approximately equal to the feeing solution. Furthermore, the Ag/Pd nanoparticles exhibit distinct catalyst for electroless copper deposition and may be a substitute for the conventional palladium system, which is expensive and unstable in operation.     

Formation of Pd/Au nanostructures from Pd nanowires via galvanic replacement reaction

Bimetallic nanostructures with non-random metal atoms distribution are very important for various applications. To synthesize such structures via benign wet chemistry approach remains challenging. This paper reports a synthesis of a Au/Pd alloy nanostructure through the galvanic replacement reaction between Pd ultrathin nanowires (2.4 +/- 0.2 nm in width, over 30 nm in length) and AuCl3 in toluene. Both morphological and structural changes were monitored during the reaction up to 10 h. Continuous changes of chemical composition and crystalline structure from Pd nanowires to Pd68Au32 and Pd45Au55 alloys, and to Au nanoparticles were observed. More interestingly, by using combined techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), UV-vis absorption, and extended X-ray absorption fine structure (EXAFS) spectroscopy, we found the formation of Pd68Au32 non-random alloy with Au-rich core and Pd-rich shell, and random Pd45Au55 alloy with uniformly mixed Pd and Au atom inside the nanoparticles, respectively. Density functional theory (DFT) calculations indicated that alkylamine will strongly stabilize Pd to the surface, resulting in diffusion of Au atoms into the core region to form a non-random alloy. We believe such benign synthetic techniques can also enable the large scale preparation of various types of non-random alloys for several technically important catalysis applications.     

Au nanoparticle monolayers covered with sol-gel oxide thin films: optical and morphological study

In this work, we provide a detailed study of the influence of thermal annealing on submonolayer Au nanoparticle deposited on functionalized surfaces as standalone films and those that are coated with sol-gel NiO and TiO(2) thin films. The systems are characterized through the use of UV-vis absorption, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and spectroscopic ellipsometry. The surface plasmon resonance peak of the Au nanoparticles was found to red-shift and increase in intensity with increasing surface coverage, an observation that is directly correlated to the complex refractive index properties of Au nanoparticle layers. The standalone Au nanoparticles sinter at 200 °C, and a relationship between the optical properties and the annealing temperature is presented. When overcoated with sol-gel metal oxide films (NiO, TiO(2)), the optical properties of the Au nanoparticles are strongly affected by the metal oxide, resulting in an intense red shift and broadening of the plasmon band; moreover, the temperature-driven sintering is strongly limited by the metal oxide layer. Optical sensing tests for ethanol vapor are presented as one possible application, showing reversible sensing dynamics and confirming the effect of Au nanoparticles in increasing the sensitivity and in providing a wavelength dependent response, thus confirming the potential use of such materials as optical probes.     

Facile fabrication of Ag-Pd bimetallic nanoparticles in ultrathin TiO(2)-gel films: nanoparticle morphology and catalytic activity

Ag-Pd bimetallic nanoparticles were prepared directly in ultrathin TiO(2)-gel films by a stepwise ion-exchange/reduction approach. Ion-exchange sites were created in ultrathin films using Mg(2+) ions as template. Ag(+) ion was then incorporated by ion exchange, and converted into metallic nanoparticles by low-temperature H(2) plasma, regenerating ion-exchange sites. The same procedure was then carried out for Pd(2+) ion, producing Pd-on-Ag bimetallic nanoparticles, as TEM observation and plasmon resonance absorption indicate. By contrast, reversed metal incorporation procedure appeared to give a mixture of individual Ag and Pd nanoparticles, as confirmed by TEM, absorption spectroscopy and X-ray photoelectron spectroscopy. For hydrogenation of methyl acrylate, the catalytic activity of the Pd-on-Ag nanoparticle is 367 times as large as that of commercial Pd black and 1.6 times as large as that of Pd monometallic nanoparticle. The outstanding catalytic activity was explicable by the large fraction of the surface-exposed Pd atoms. The formation process of the bimetallic nanoparticle and their general morphological feature are discussed.     

水滑石层间阴离子为还原剂原位负载贵金属纳米颗粒

研究了以水滑石为载体原位负载贵金属纳米颗粒(Pd、Ag、Ru、Au)的方法,通过共沉淀合成甲酸根水滑石,以层间甲酸根为还原剂原位还原贵金属前驱体制得高分散水滑石(LDH)负载纳米颗粒。本方法无需载体预处理,操作方便、适用性强,阴离子前驱体(Au)和阳离子前驱体(Pd、Ag、Ru)均可顺利得到纳米颗粒。所得水滑石负载纳米颗粒系一种潜在的纳米催化剂,作为示例,Pd/LDH在Suzuki偶联反应中显示出较高催化活性。     

室温电子还原制备金纳米颗粒与琼脂糖复合膜的表征与应用

利用室温电子还原技术合成了一种金纳米颗粒与琼脂糖复合膜。合成过程采用氩气辉光放电为廉价电子源,方便快捷,绿色环保。通过紫外-可见(UV-Vis)分光光度计、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)仪、光电子能谱(XPS)等表征,发现可以通过改变氯金酸浓度调控复合膜中金纳米颗粒的分布,加入聚乙烯吡咯烷酮(PVP)可有效控制金纳米颗粒的形貌。由于复合膜具有金纳米颗粒密集排布的结构,可作为表面增强拉曼散射(SERS)活性基底。实验表明,以对氨基苯硫酚为探针,该复合膜作为SERS基底,SERS平均增强因子超过了106,检测限达到了10-12mol?L-1。除此之外,作为SERS基底,复合膜具有良好的均一性和稳定性。     

Synthesis of Au, Au/Ag, Au/Pt and Au/Pd nanoparticles using the microwave-polyol method

Gold, Au/Ag, Au/Pt and Au/Pd bimetallic nanoparticles with varying mol fractions were synthesized in ethylene glycol and glycerol, using the microwave technique in the presence of a stabilizer poly(N-vinylpyrrolidone) (PVP). It was found that bimetallic colloids of Au/Ag, Au/Pd and Au/Pt form an alloy either on co-reduction of respective metal ions or on mixing individual sols.     

Nano-titanium oxide doped with gold,silver, and palladium — synthesis and structural characterization

Nano-titania doped with noble metals (Au/TiO₂, Ag/TiO₂, Pd/TiO₂) has been synthesized by mild hydrolysis of the mixture of metal salts or complexes and titanium isopropoxide ((iPr-O)₄Ti). After thermal decomposition of the obtained precursors, nanomaterials were formed. Morphological characterization of the nanomaterials was provided by scanning electron microscopy (SEM) and stereological analysis, determining the BET specific surface area, and BJH nanoporosity (pore volume, pore size). It has been found that the structure of nanomaterials (size of nanoparticles and agglomerates) depended strongly on the method of the (iPr-O)₄Ti hydrolysis. A minor dependence on the kind of solvents and precursors of noble metals was observed. The presence of doping metal nanoparticles was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Nanomaterial phases were identified by X-ray diffraction (XRD). According to the XRD patterns, Ag/TiO₂ and Pd/TiO₂ products with doping metals in their oxidized form contain Ag-Ti and Pd-Ti phases. Peaks of the metal oxides Ag₂O and PdO are absent in the XRD patterns. The average size of TiO₂ nanoparticles is situated in the region of 20–60 nm, whereas metals are present as about 10–15 nm sized particles and fine nanoparticles.     

A general method for the rapid synthesis of hollow metallic or bimetallic nanoelectrocatalysts with urchinlike morphology

We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100 degrees C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile. Most importantly, the hollow bimetallic nanospheres (Au/Pt and Pd/Pt) obtained here exhibit an area of greater electrochemical activity than other Pt hollow or solid nanospheres. In addition, the approximately 6 nm hollow urchinlike Pt nanospheres can achieve a potential of up to 0.57 V for oxygen reduction, which is about 200 mV more positive than that obtained by using a approximately 6 nm Pt nanoparticle modified glassy carbon (GC) electrode. Rotating ring-disk electrode (RRDE) voltammetry demonstrates that approximately 6 nm hollow Pt nanospheres can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated H(2)SO(4) (0.5 M). Finally, compared to the approximately 6 nm Pt nanoparticle catalyst, the approximately 6 nm hollow urchinlike Pt nanosphere catalyst exhibits a superior electrocatalytic activity toward the methanol oxidation reaction at the same Pt loadings.     

Protein-sheathed SWNT as a versatile scaffold for nanoparticle assembly and superstructured nanowires

One dimensional (1D) nanostructures have many possible applications in electronic, optical, and sensing devices associated with their nanosized lateral dimensions. In this regard, a general and bottom-up strategy to synthesize 1D nanoparticle arrays and conductive nanowires with a facile structural/compositional control is highly desired. We herein report a protein-sheathed single walled carbon nanotube (SWNT) that satisfies the criteria for an ideal template to assemble micron-long gold nanoparticle (AuNP) linear arrays with high structural rigidity. The resulting AuNP array has minimized inter-particle gaps, which is especially useful to template the overgrowth of Ag, Pd, and Pd/Ag metals into continuous nanowires (Au@M, M=Ag, Pd, Ag/ Pd). Our method successfully overcomes the incompatibility between carbon and metal materials, and the resulting superstructured metal nanowires have a tunable diameter below 100 nm and a shape closely replicating a SWNT. The Ag nanowires are composed of coalesced Au@Ag coreshell nanoparticles, while the Pd and Pd/Ag nanowires are made of very fine Pd nanocrystallites around the AuNP cores. These unique structural features are pivotal to various applications including surface enhanced Raman scattering (SERS), electrocatalysis, and gas sensors.     

Homogeneous silver-coated nanoparticle substrates for enhanced fluorescence detection

A simple method has been developed for the deposition of uniform silver-coated nanoparticles on glass substrates, with a homogeneous distribution shown by scanning electron microscopy (SEM). UV-visible spectroscopy and energy-dispersive X-ray analysis (EDX) have been used to characterize both the optical density and elemental content of the deposited nanoparticles. The fluorescence enhancement was investigated using a monolayer of FITC-conjugated human serum albumin (FITC-HSA) and tested using laser scanning microscopy at 488 nm excitation wavelength. The enhancement factor was calculated from individual spectra recorded with a Fluorolog-Tau-3 spectrofluorometer. We identified the nanoparticle growth regime which led to fluorescence enhancement. Such enhancement is detectable when Au core-Ag shell nanoparticles increased their size to 47 nm, in agreement with theoretical estimates. The origin of this enhancement for appropriate size nanoparticles is attributed to the effect of an increased excitation rate from the local field enhanced by the interaction of incident light with the nanoparticles and/or higher quantum yield from an increase of the intrinsic decay rate of the fluorophore. We thus demonstrated that the Au core-Ag shell nanostructures on glass surfaces are promising substrates for fluorescence enhancement with outstanding macroscopic homogeneity. This important feature will pave the way for the application of our substrates in biotechnology and life sciences such as imaging and sensing of biomolecules in proteomics.     

Preparation and characterization of metal-chitosan nanocomposites

Various metal-chitosan nanocomposites were synthesized, including silver (Ag), gold (Au), platinum (Pt), and palladium (Pd) in aqueous solutions. Metal nanoparticles were formed by reduction of corresponding metal salts with NaBH4 in the presence of chitosan. And chitosan molecules adsorbing onto the surface of as-prepared metal nanoparticles formed the corresponding metal-chitosan nanocomposites. Transmission electron microscopy (TEM) images and UV-vis spectra of the nanocomposites revealed the presence of metal nanoparticles. Comparison of all the resulting particles size, it shows that silver nanoparticles are much larger than others (Au, Pt and Pd). In addition, the difference in particles size leads to develop different morphologies in the films cast from prepared metal-chitosan nanocomposites. Polarized optical microscopy (POM) images show a batonet-like structure for Ag-chitosan nanocomposites film, while for the films cast from other metal (Au, Pt, and Pd)-chitosan nanocomposites, some branched-like structures with a few differences among them were observed under POM observation.     

Metal-ion induced transition from multi- to single-bilayer tubes in histidine bearing lipids and formation of monodisperse Au nanoparticles

We report that a histidine based cationic lipid forms multi-bilayer nanotubes and the addition of metal ions such as Cu(2+) and Au(3+) induces transformation into single-bilayer nanotubes owing to coordination of the metal ions on the nanotube surface. The morphological transition was detected with X-ray scattering and electron microscopy. IR showed that the metal coordination is presumably the major driving force. The reduction of Au(3+) ions on the tube surface produced gold nanoparticles attached on the nanotube surface. The nanoparticle was almost monodisperse with the average diameter of 1.7 nm and the standard deviation σ of 0.29, which is remarkably narrower than that of previously reported lipid systems. The obtained particles were stable and no further aggregation and growth was observed after one week, providing a powerful and facile tool for producing nanoparticles in a wide range of applications.     

Tailored Synthesis of Various Nanomaterials by Using a Graphene‐Oxide‐Based Gel as a Nanoreactor and Nanohybrid‐Catalyzed CC Bond Formation

New graphene oxide (GO)‐based hydrogels that contain vitamin B₂/B₁₂ and vitamin C (ascorbic acid) have been synthesized in water (at neutral pH value). These gel‐based soft materials have been used to synthesize various metal nanoparticles, including Au, Ag, and Pd nanoparticles, as well as nanoparticle‐containing reduced graphene oxide (RGO)‐based nanohybrid systems. This result indicates that GO‐based gels can be used as versatile reactors for the synthesis of different nanomaterials and hybrid systems on the nanoscale. Moreover, the RGO‐based nanohybrid hydrogel with Pd nanoparticles was used as an efficient catalyst for C? C bond‐formation reactions with good yields and showed high recyclability in Suzuki–Miyaura coupling reactions.