用原位液体池透射电镜技术表征金属钯在球形金纳米颗粒表面的异质沉积

采用原位液体池透射电镜技术,在扫描透射电子显微镜(STEM)中,实时观察溶液中金属钯(Pd)在金(Au)纳米颗粒及团簇周围的异质沉积过程。通过对该动态过程的定量分析,结合高分辨透射电子显微镜(HRTEM)对样品进行形貌与结构表征,研究异质沉积的机理。结果表明,电子束辐照下Au-Pd异质结构纳米颗粒的形成存在两种主要机制:第一种机制中,Pd在Au纳米颗粒表面的生长是以岛状沉积开始,随着时间推移,出现Pd岛的结构弛豫和沿着Au颗粒表面的迁移扩展。伴随Pd的不断沉积和弛豫,Au-Pd复合颗粒的外接圆直径表现为震荡生长,而Au表面的Pd覆盖率显示出随时间单调增加的趋势。第二种机制中,由于Pd单体在Au纳米颗粒上的沉积位点有限,使部分被还原的Pd在Au颗粒以外区域进行同质形核与生长形成Pd团簇,之后再与Au颗粒上的Pd岛合并。进一步的结果分析显示,Au颗粒外围的Pd沉积体为多晶结构,由随机取向的Pd纳米晶粒构成。     

紫外光照射二氧化钛纳米管沉积纳米金颗粒应用于染料敏化太阳能电池

通过紫外光照射成功把金粒子沉积到二氧化钛纳米管的管壁中。通过扫描电镜、能谱和X射线衍射进行表征。沉积所得的金粒子为高度分散的纳米级粒子,并且金颗粒的粒径和密度可通过沉积时间控制。应用于染料敏化太阳电池中,由于金颗粒存在表面等离子增强效应,可提高电池的光电转换效率。然而随着沉积时间增长,沉积的金颗粒粒径会增大,所得电池的效率将会下降。     

微波法合成纳米金胶体颗粒的调控研究

用微波法制备高分子聚合物稳定的纳米金胶体颗粒, 制得的金纳米颗粒的平均粒径在5～120 nm之间. 考察了醇还原剂以及碱对金颗粒形成的影响, 使用透射电子显微镜、紫外可见分光光度计进行表征. 结果表明, 微波法制备的金胶体颗粒具有粒径小、分散性好的特点. 金颗粒的尺寸和形状随醇还原剂的种类及碱(NaOH)用量的不同而有明显的变化. 紫外可见吸收光谱表明, 在反应物中加入碱的体系, 金颗粒的形成速度明显加快, 且利于圆球形金颗粒的形成.     

Synthesis of gold nanoparticles from gold(I)-alkanethiolate complexes with supramolecular structures through electron beam irradiation in TEM

Monodisperse gold nanoparticles were prepared via electron beam irradiation of Au(I)-SR (R = -CnH2n+1) polymers with highly ordered supramolecular structures in transmission electron microscopy. The Au(I)-SR polymers were synthesized simply by mixing LiAuCl4 and an excess amount of alkanethiol in tetrahydrofuran. The sizes of the gold nanoparticles were controlled by changing the length of the alkyl group or by adjusting the energy of the electron beam.     

The Au(n) cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples. A 100-fold increase in the molecular ion yield was observed when the incident energy of Au(9) (+) was varied from 10 to 180 keV. Values of emission yields and damage cross-sections are presented as a function of cluster size and energy. The possibility to adjust both cluster size and energy, depending on the application, makes the analysis of biomolecules by secondary ion mass spectrometry an extremely powerful and flexible technique, particularly when combined with orthogonal time-of-flight mass spectrometry that then allows fast measurements using small primary ion beam currents.     

Bimodal Size Distribution of Gold Nanoparticles under Picosecond Laser Pulses

The evolution of size distributions of gold nanoparticles under pulsed laser irradiation (Nd:YAG, lambda = 355 nm, pulse width 30 ps) was carefully observed by transmission electron microscopy. Interestingly, the initial monomodal size distribution of gold nanoparticles turned into a bimodal one, with two peaks in the number of particles, one at 6 nm and the other at 16-24 nm. The sizes for small particles depended very little on the irradiated laser energy. This change is attributed to laser-induced size reduction of the initial gold nanoparticles followed by the formation of small particles. In our analysis, we extracted a characteristic value for the size-reduction rate per one pulse and revealed that laser-induced size reduction of gold nanoparticles occurred even below the boiling point. When laser energy is insufficient for the boiling of particles, formation of gold vapor around liquid gold drops is thought to cause the phenomenon. With enough laser energy for the boiling, the formation of gold vapor around and inside liquid gold drops is responsible for the phenomenon. We also observed particles with gold strings after one pulse irradiation with a laser energy of 43 mJ cm(-2) pulse(-1), which is sufficient energy for the boiling. It is considered that such particles with gold strings are formed by the projection of gaseous gold from liquid gold drops with some volume of liquid gold around the bubble. On the basis of comparison with previous work, picosecond laser pulses are thought to be the most efficient way to cause laser-induced size reduction of gold nanoparticles.     

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC₈) and of the cobalt octanoate (CoC₈). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained.     

Light Element Analysis of Individual Microparticles Using Thin-Window EPMA

 The determination of the concentration of light elements, such as carbon, nitrogen and oxygen, in e.g. atmospheric aerosol particles is important to study the chemical behaviour of atmospheric pollution. The knowledge of low-Z element concentrations gives us information on the speciation of nutrients (species having nutritional value for plants) and toxic heavy metals in the particles. The capability of the conventional energy-dispersive EPMA is strongly limited for the analysis of low-Z elements, mainly because the Be window in the EDX detector hinders the detection of characteristic X-rays of light elements such as C, N, O and Na. WDS is suitable for analysis of light elements, but the measurement of beam sensitive microparticles requires the minimisation of the beam current and the measurement time. A semi-quantitative analytical method based on EPMA using an ultra-thin window EDX detector was developed. It was found that the matrix and geometric effects that are important for low-energy X-rays can be reliably evaluated by Monte Carlo calculations. Therefore, the quantification part of the method contains reverse Monte Carlo calculation done by iterative simulations. The method was standardised and tested by measurements on single particles with known chemical compositions. Beam-sensitive particles such as ammonium-sulphate and ammonium-nitrate were analysed using a liquid nitrogen cooled sample stage. The shape and size of the particles, which are important for the simulations, were determined using a high-magnification secondary electron image. Individual marine aerosol particles collected over the North Sea by a nine-stage Berner cascade impactor were analysed using this new method. Preliminary results on five samples and 4500 particles show that the method can be used to study the modification of sea-salt particles in the troposphere.     

Nucleation of isotactic polypropylene crystallization by gold nanoparticles

Nucleation of isotactic polypropylene (iPP) crystallization by gold (Au) nanoparticles was studied. Regardless of their size, 4.3, 8.8, 28.3, and 84.5 nm, all particles were able to nucleate spherulites when deposited on the iPP surface. However, when added and melt‐mixed with iPP, only the smallest particles affected significantly the iPP bulk crystallization. Au nanoparticles larger than 4.3 nm, at the concentration of 0.001 wt %, did not influence the crystallization of iPP. Contrary to this, 0.001 and 0.005 wt % of Au nanoparticles having the size of 4.3 nm increased crystallization temperature of the iPP by 7–8 °C and decreased markedly the sizes of polycrystalline aggregates. Aggregation of Au nanoparticles in the polymer matrix was evidenced by electron microscopy and contributed to their decreased effectiveness in the nucleation of iPP crystallization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 469–478, 2010     

Study of Aggregation of Gold Nanoparticles in Chitosan

In this work it is reported the synthesis of gold nanoparticles supported in situ in chitosan by solvated metal atom dispersion technique in order to study the inclusion of Au nanoparticles in the biopolymer matrix. To study their aggregation along time and compare with the synthesis of Au/2-propanol colloid by chemical liquid deposition technique. Studies of Au nanoparticles aggregation along time, supported nanoparticles and colloidal nanoparticles morphology were also carried out. The characterization of Au nanoparticles was performed by transmission electron microscopy, field-emission and scanning electron microscopy, infrared spectroscopy, X-ray diffraction, light scattering and ultraviolet–visible spectroscopy. Metal colloid showed fractal agglomeration type and delay time after the synthesis, the agglomeration size increased to flocculate. Au nanoparticles supported in chitosan showed the same shape as colloids and fractal aggregation was mostly distributed on the matrix.     

Preparation of highly uniform Ag/TiO2 and Au/TiO2 supported nanoparticle catalysts by photodeposition

Photodeposition of Ag nanoparticles on commercial TiO2 particles and nanoparticles was performed in order to provide direct visualization of the spatial distribution of photoactive sites on sub-micrometer-scale and nanoscale TiO2 particle surfaces and to create materials for potential catalytic applications. HRTEM (high-resolution transmission electron microscopy) and HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) were used to characterize these materials. The size and spatial distributions of the Ag nanoparticles on the commercial TiO2 were not uniform; the concentration of Ag was higher on grain boundaries and at the edges of these submicrometer particles. In the case of TiO2 nanoparticles, the size distribution of the Ag nanoparticles deposited was relatively uniform and independent of irradiation time and photon energy. The amount of Ag deposited on TiO2 nanoparticles was at least 6 times higher than that on the commercial samples for comparable irradiation conditions. Compared to the case of Ag photodeposition, the difference in the amount of Au photodeposited on TiO2 particles and nanoparticles was even greater, especially at low precursor concentrations. Photodeposition on TiO2 nanoparticles is suggested as a potential method for the preparation of Au/TiO2 catalysts, as loadings in excess of 10 wt % of uniform 1 nm metal particles were achieved in this work.     

微波法制备3.5 G PAMAM树状大分子保护的金纳米粒子

以3.5 G PAMAM(3.5代聚酰胺-胺型)树状大分子为保护剂,利用微波法还原HAuCl₄溶液制备金纳米粒子.考察了当3.5 G PAMAM与HAuCl₄物质的量的比一定时,微波照射不同时间对金纳米粒子大小及形状的影响;以及同一照射条件下,3.5 G PAMAM与HAuCl₄不同的物质的量比值对金纳米粒子大小及形状的影响.利用紫外可见分光光度计、透射电子显微镜对其进行了表征.结果表明,当3.5 G PAMAM与HAuCl₄物质的量的比值一定时,金纳米粒子的形状和大小受微波照射时间长短的影响不大;适当延长照射时间,制得的金纳米粒子的分散性较好.在相同照射条件下,随着3.5 G PAMAM与HAu-Cl₄物质的量比值的减小,得到的金纳米粒子粒径逐渐变大,且分散性变差.     

蔡司GeminiSEM 300型场发射扫描电镜常见故障的预防、排除和磁性样品的测试方法

金属有机框架材料（MOFs）的形貌结构对其性能应用具有很大影响,但MOFs普遍存在导电性差且对电子束敏感等问题,在进行扫描电子显微镜（SEM）测试时容易损伤样品,发生荷电现象. 因此摸索合适的测试参数,对获得高质量的MOFs扫描电子显微镜图像具有重要意义. 以MIL-101(Cr)、Fe-MOF、Mn-MOF、ZIF-67(Co)这4种典型的MOFs为例,主要探究了加速电压、电子束流、工作距离、探头及喷金对其成像效果的影响. 结果表明,升高加速电压可有效提高图像分辨率,但同时电子束穿入深度增大,可能导致电荷击穿效应对其表面结构造成破坏. 适当增大束流可提高图像信噪比,但过大的束流会导致纳米颗粒边缘变钝,因此选用0.1~0.4 nA中等束流为佳. 在选择探头时需注意,艾弗哈特-索恩利探头（ETD）和透镜内二次电子（T2）探头所成图像立体感较好,透镜内背散射电子（T1）探头的立体感弱,但衬度较好,柱内二次电子（T3）探头分辨率最佳,但更容易荷电,显得颗粒扁平. 而喷金处理可有效提高样品的导电性. 以上结果对使用SEM探究MOFs形貌结构具有一定的借鉴作用.     

微波辐照制备无皂阳离子PMMA胶乳粒子

在微波辐照条件下 ,用偶氮二异丁基脒盐酸盐 (AIBA)引发甲基丙烯酸甲酯的均聚 ,制得窄分散的无皂阳离子胶乳粒子 .讨论了引发剂的浓度、单体的浓度、离子强度等对粒子大小、分散性和乳液稳定性的影响 .对微波辐照和水浴加热进行比较 ,发现微波辐照反应速度快、反应无恒速阶段 ,所得粒子的粒径小 ,粒子数目多 ,这为通过改变反应条件制备适宜的窄分散的胶乳粒子提供了一条途径 .     

Gold nanoparticles supported on ionic liquid‐modified cellulose as an efficient and recyclable catalyst for the oxidation of alcohols to aldehydes/ketones and reduction of nitroarenes

A novel catalyst of gold nanoparticles supported on cellulose fibres with the ionic liquid framework (Au NPs@CL‐IL) has been shown to be a highly active and recyclable catalyst for the oxidation of primary and secondary alcohols and reduction of nitroarenes in aqueous media. The reusability of this catalyst is high, and it can be reused ten times without a significant decrease in its catalytic activity. Furthermore, transmission electron micrographs of the recovered catalyst show the presence of well‐distributed Au NPs on the CL‐IL fibres without any aggregation.     

Effect of electron beam irradiation on the formation of active sites in the Pt/H pentasil catalyst

The influence of preirradiation with an electron beam from a linear resonance electron accelerator in flowing argon on the structure and properties of the 1% Pt/H pentasil catalyst was studied. The support structure was studied by x-ray diffraction and low-temperature nitrogen adsorption. No changes in the crystal structure and pentasil specific surface area were observed in the irradiation dose range from 120 to 900 Mrad at an average electron energy of 7.7 MeV. The electron beam treatment resulted in a considerable increase in the catalytic activity of the Pt/H pentasil in gas-phase toluene hydrogenation as a model reaction. The results obtained by IR spectroscopy of adsorbed CO and X-ray diffraction data suggested that the increase in the catalyst activity after electron beam irradiation is due to changes in the size and charge of the Pt particles.     

钾改性对Au/ZSM-5催化剂上正丁烷裂解性能的影响

采用负压沉积沉淀法制备了负载型Au/HZSM-5催化剂,采用X射线衍射（XRD）、透射电镜（TEM）、Ｘ射线光电子能谱（XPS）、NH3-TPD、紫外可见漫反射（UV-vis）等技术对催化剂进行了表征分析,并考察了催化剂对正丁烷裂解性能的影响。结果表明,Au金属成功负载到HZSM-5催化剂上,并且金颗粒的尺寸受负载量的影响,其中1.0%Au/HZSM-5催化剂中的金颗粒粒径最小,约为5～10nm。钾离子作为一种碱性离子可以调节载体酸性,随着K离子的引入xK-Au/HZSM-5催化剂的酸性逐渐降低,使Au0的电子结合能更高。相对于HZSM-5,2.0Au/HZSM-5催化剂对于正丁烷的转化率从13.1%提升到了37.5%,对丙烯的选择性从17.2%提升到了52.5%。随着K离子的引入,催化剂对于丁烯以及异丁烷的选择性有所提高,当K离子负荷为0.08%时,对丁烯的选择性从3.8%提高到36.9%,负荷为0.1%时,对异丁烷的选择性由2.8%提升到51.8%。但原料转化率低于2.0Au/HZSM-5,这可能与K的加入降低催化剂酸改性有关。此外通过研究Au/HZSM-5用K+修饰得知Au+离子是Au/HZSM-5催化剂转化正丁烷主要活性中心。     

Gold-polyaniline composites. Part II. Effects of nanometer sized particles

The amount of electronic charge transferred between gold particles and polyaniline depends not only on the electron affinity of the two materials but also on the size of the gold particles. As measured by X-ray photoelectron spectroscopy, for particles < approximately 5 nm the binding energy of the electrons is size dependent. This "nano-effect" has its origin in the electrostatics of particles. It is demonstrated as a measurable shift of the binding energy of the Au(4f7/2) photoelectrons emitted from Au particles embedded in a polyaniline matrix. Gold nanoparticle size was evaluated by high resolution transmission electron microscopy.     

The characterization of latex particles prepared by pulsed electron beam induced emulsion polymerization

The emulsion polymerization of styrene (St) and methyl methacrylate (MMA) induced by 10 MeV pulsed electron beams (PEB) was investigated. The monomer conversion of MMA and St was found to be very low so that the final prepared poly(methyl methacrylate) (P(MMA)) and polystyrene (PS) latex particles exhibit porous structures, as verified by TEM and SEM observations. The results of dynamic light scattering (DLS) and gel permeation chromatography (GPC) showed that both the particle size and the molecular weight of PS and PMMA latexes decrease with the increase of the absorbed dose. However, the molecular weights and the particle sizes of the PS and PMMA latexes change differently with the irradiation time. This work indicated that emulsion polymerization induced by high energy electron beam has an advantage over that induced by γ-ray or chemical initiators in the preparation of latex with a low molecular weight and porous structure.     

Sintering of passivated gold nanoparticles under the electron beam

Time-lapse studies of a film of passivated gold nanoparticles under electron beam irradiation have been performed using a transmission electron microscope, revealing the microscopic dynamics of the sintering process at the single nanoparticle level. It is found that the sintering of individual passivated gold nanoparticles under electron irradiation is local and mainly depends on the sensitivity of the passivating ligands to the electron beam. A multilayer film is less stable than monolayer film, consistent with the enhanced generation of secondary electrons. The observations also reveal a significant difference between the sintering of passivated nanoparticles and bare metal particles, especially regarding the size effect on the sintering rate. The formation of a neck between adjacent nanoparticles further indicates a mechanism driven by surface diffusion rather than Ostwald ripening at the initial sintering stage.