The relevance of shape and size of Au55 clusters

This critical review deals with the history of Au(55)(PPh(3))(12)Cl(6) and its derivatives from the very beginning in 1981 to date. Au(55) clusters obtain their special interest from their ultimate size and their ideal cuboctahedral structure. They are part of the family of so-called full-shell clusters, particles with perfectly completed geometries, also represented by icosahedral Au(13) clusters. Bare as well as ligand protected Au(55) clusters not only exhibit special chemical and physical stability, but draw their attention particularly from their unique electronic properties. Single electron switching at room temperature becomes possible, giving rise for development of applications in future nanoelectronic devices. A predominantly size-determined property of the 1.4 nm particles becomes obvious with respect of biological response. Au(55) clusters indicate an unusual cytotoxicity which seems to be caused by the unusually strong interaction between the 1.4 nm particles and the major grooves of DNA. Only marginally smaller or larger particles show drastically reduced toxicity, whereas significantly larger gold nanoparticles are completely non-toxic. Both, the electronic perspectives as well as the relevance in toxicology are at very early stages of development (75 references).     

利用壳层厚度调节核壳Au@Pd纳米粒子的SERS活性

设计合成了一种尺寸可控, 且外壳上无“针孔”的核壳钯包金(Au@Pd)纳米粒子, 通过改变核的尺寸和外壳的厚度来调控其光学性质, 并用TEM、HRTEM、UV-Vis和SERS等手段对其进行了表征. 通过研究Au@Pd纳米粒子的SERS活性随Pd壳层厚度变化的规律, 发现薄壳Au@Pd纳米粒子远远优于Pd金属本身的SERS活性, 其原因主要是内层金核电磁场增强的长程效应.     

Physical and Chemical Consequences of Size-Reduction of Gold: Bioresponse and Biodistribution

The article is dealing with the dependency of physical and chemical properties on size and coating of gold nanoparticles (Au NPs) and their potential in medicine. Full-shell clusters of the type Au₅₅(PR₃)₁₂Cl₆ are in the focal point due to their special properties. They act as quantum dots at room temperature and their stability is based on the perfect cuboctahedral structure. The bioresponse of the 1.4 nm Au₅₅ clusters is, compared with smaller and larger Au NPs, very special, indicated by high cytotoxicity. It is caused by oxidative stress in cells accompanied by direct interactions with DNA. Biodistribution in Wistar–Kyoto rats differs also characteristically from larger Au NPs. Larger Au NPs, intravenously injected, assemble almost quantitatively in the liver, whereas Au₅₅ clusters distribute over numerous other organs. All comparisons have been carried out by Au species with identical ligand molecules in order to have the same conditions concerning surface behaviour.     

An in situ quick XAFS spectroscopy study on the formation mechanism of small gold nanoparticles supported by porphyrin-cored tetradentate passivants

We previously reported that a porphyrin-cored tetradentate passivant, which has two disulfide straps over one face of the porphyrin plane, can produce monolayer-protected gold nanoparticles, 2-4 nm in size, by the one-pot reduction of HAuCl(4) in DMF. The resulting nanoparticles are smaller than those prepared using the same S/Au molar ratio of a monodentate passivant. To examine the formation mechanism of small gold nanoparticles, the formation of gold nanoparticles in the presence of porphyrin-cored tetradentate passivants or a structurally related monodentate passivant was studied by time-resolved quick X-ray absorption fine structure spectroscopy. The results demonstrated that all of Au ions in solution are reduced to compose small Au clusters, i.e. nuclei, just after the NaBH(4) reduction of HAuCl(4) in both cases, but their size varied with the initial S/Au molar ratios and structure of the passivants. Thus, the size of Au nuclei was kinetically controlled by the passivants. Interestingly, the porphyrin-cored tetradentate passivant could stabilize smaller gold nanoparticles, 2-4 nm in size, but it was less efficient in trapping the Au nuclei formed at a very early stage, in comparison to the monodentate passivant.     

Sub-nanometre sized metal clusters: from synthetic challenges to the unique property discoveries

Sub-nanometre sized metal clusters, with dimensions between metal atoms and nanoparticles, have attracted more and more attention due to their unique electronic structures and the subsequent unusual physical and chemical properties. However, the tiny size of the metal clusters brings the difficulty of their synthesis compared to the easier preparation of large nanoparticles. Up to now various synthetic techniques and routes have been successfully applied to the preparation of sub-nanometre clusters. Among the metals, gold clusters, especially the alkanethiolate monolayer protected clusters (MPCs), have been extensively investigated during the past decades. In recent years, silver and copper nanoclusters have also attracted enormous interest mainly due to their excellent photoluminescent properties. Meanwhile, more structural characteristics, particular optical, catalytic, electronic and magnetic properties and the related technical applications of the metal nanoclusters have been discovered in recent years. In this critical review, recent advances in sub-nanometre sized metal clusters (Au, Ag, Cu, etc.) including the synthetic techniques, structural characterizations, novel physical, chemical and optical properties and their potential applications are discussed in detail. We finally give a brief outlook on the future development of metal nanoclusters from the viewpoint of controlled synthesis and their potential applications.     

Linking the Gold Nanoparticles Formation Kinetics with Their Morphology

In this paper, we show that using different concentrations of reagents, it is possible to produce gold nanoparticles with different morphology (size, shape). The color of obtained colloidal gold change from pink, violet to blue, and it corresponds to the shape change. The pink color corresponds to spherical nanoparticles and the blue one to a star shape. The mixture of those two types of nanoparticles result in a violet tone. It was also shown that kinetics of nucleation and growth process is controlled by the reaction on the gold atoms surface, i.e., comproportionation of Au(III) and Au(0) to Au(I), which can be inhibited by varying precursor and reductant concentration.     

Au/Ag核一壳结构复合纳米粒子形成机制的研究

在已制备好的Au纳米粒子表面,通过化学还原的方法沉积生长Ag包覆层,通过 控制Au, Ag的比列,制备了粒度均匀且粒径可控的Au/Ag核-壳结构纳米粒子。利用 UV-vis吸收光谱和透射电子显微镜（TEM）对SAu, Ag摩尔比为1：10的复合纳米粒 子的光学性质和形态进行随时监测,直接观察了核-壳结构纳米粒子的生长过程： 一部分Ag+在Au核表面还原生长,溶液中其余Ag+还原形成银的纳米团簇向粒子表面 的继续沉积生长,壳层增厚。     

Hydrotalcite-supported gold catalyst for the oxidant-free dehydrogenation of benzyl alcohol: studies on support and gold size effects

Gold nanoparticles with uniform mean sizes (≈3 nm) loaded onto various supports have been prepared and studied for the oxidant-free dehydrogenation of benzyl alcohol to benzaldehyde and hydrogen. The use of hydrotalcite (HT), which possesses both strong acidity and strong basicity, provides the best catalytic performance. Au/HT catalysts with various mean Au particle sizes (2.1-21 nm) have been successfully prepared by a deposition-precipitation method under controlled conditions. Detailed catalytic reaction studies with these catalysts demonstrate that the Au-catalyzed dehydrogenation of benzyl alcohol is a structure-sensitive reaction. The turnover frequency (TOF) increases with decreasing Au mean particle size (from 12 to 2.1 nm). A steep rise in TOF occurs when the mean Au particle size becomes smaller than 4 nm. Our present work suggests that the acid-base properties of the support and the size of Au nanoparticles are two key factors controlling the alcohol dehydrogenation catalysis. A reaction mechanism is proposed to rationalize these results. It is assumed that the activation of the β-C-H bond of alcohol, which requires the coordinatively unsaturated Au atoms, is the rate-determining step.     

Electronic and chemical properties of supported Au nanoparticles

Oxidation and reduction behaviors of Au nanoparticles with different sizes on highly ordered pyrolytic graphite (HOPG) and silica were studied using X-ray photoelectron spectroscopy (XPS). For Au nanoparticles smaller than 6 nm in diameter, we found a novel oxygen species formed in Au nanoparticles, which is absent in larger particles and Au bulk crystals. This new oxygen species is attributed to the subsurface oxygen: for a complete understanding of the structures of catalytically active Au, the new oxygen species should be taken into account. In this context, it is worth mentioning that the subsurface oxygen species has been suggested to play an important role in heterogeneous catalysis. With decreasing Au particle size, a positive core level shift can be observed, which can be mostly attributed to the final state effects. Increase of the number of undercoordinated atoms with decreasing particle size is evidenced by a reduced splitting between 5d_3/2 and 5d_5/2 states and a band narrowing. Our results on electronic structures of Au nanoparticles on silica are compared to those on other substrates such as zirconia and titania to shed light onto the metal-support interactions.     

On the origin of the unique properties of supported Au nanoparticles

The unique catalytic activity of supported Au nanoparticles has been ascribed to various effects including thickness/shape, the metal oxidation state, and support effects. Previously, we reported the synthesis of ordered Au monolayers and bilayers on TiO(x), with the latter being significantly more active for CO oxidation than the former. In the present study, the electronic and chemical properties of ordered monolayer and bilayer Au films have been characterized by infrared reflection adsorption spectroscopy using CO as a probe and ultraviolet photoemission spectroscopy. The Au overlayers are found to be electron-rich and to have significantly different electronic properties compared with bulk Au. The common structural features of ordered Au bilayers and Au bilayer nanoparticles on TiO2(110) are described, and the exceptionally high catalytic activity of the Au bilayer structure related to its unique electronic properties.     

水溶液中碳纳米管的表面增强拉曼光谱研究

合成了碳纳米管和金纳米颗粒的复合物, 测量了水溶液相中复合物的表面增强拉曼光谱, 结果表明, 碳纳米管的巯基化修饰可以提高碳纳米管与金纳米颗粒复合的效率, 随着金纳米颗粒负载量的增加, 碳纳米管的拉曼信号逐渐增强. 加入己二胺分子可以减小金纳米颗粒之间的距离使表面增强效应更显著, 碳纳米管的拉曼光谱得到进一步的增强. 还可进一步在复合体系中加入对巯基苯胺和罗丹明B等小分子拉曼探针, 利用金纳米颗粒的表面增强效应, 这种多元复合体系有望作为多通道拉曼成像探针材料.     

Synthesis and electrochemical and spectroscopic characterization of biicosahedral Au25 clusters

The synthesis and electrochemical and spectroscopic characterization of biicosahedral Au(25) clusters with a composition of [Au(25)(PPh(3))(10)(thiolate)(5)Cl(2)](2+) are described. The biicosahedral Au(25) clusters protected with various types of thiol ligands including alkanethiols, 2-phenylethanethiol, 11-mercaptoundecanoic acid, and 11-mercapto-1-undecanol were synthesized in high yields using a one-step, one-phase procedure in which Au(PPh(3))Cl is reduced with tert-butylamine-borane in the presence of the thiol ligand in a 3:1 v/v chloroform/ethanol solution. All biicosahedral Au(25) clusters prepared exhibit characteristic optical absorption and photoluminescence properties. The emission energy is found to be substantially smaller than the optical absorption energy gap of 1.82 eV, indicating a subgap energy luminescence. The electrochemical HOMO-LUMO gap (~1.54 eV) of the clusters is also substantially smaller than the optical absorption energy gap but rather similar to the emission energy. These electrochemical and optical properties of the biicosahedral Au(25) clusters are distinctly different from those of the Au(25)(thiolate)(18) clusters.     

Rapid synthesis of highly monodisperse Au(x)Ag(1-x) alloy nanoparticles via a half-seeding approach

Gold-silver alloy Au(x)Ag(1-x) is an important class of functional materials promising new applications across a wide array of technological fields. In this paper, we report a fast and facile synthetic protocol for preparation of highly monodisperse Au(x)Ag(1-x) alloy nanoparticles in the size range of 3-6 nm. The precursors employed in this work are M(I)-alkanethiolates (M = Au and Ag), which can be easily prepared by mixing common chemicals such as HAuCl(4) or AgNO(3) with alkanethiols at room temperature. In this half-seeding approach, one of the M(I)-alkanethiolates is first heated and reduced in oleylamine solvent, and freshly formed metal clusters will then act as premature seeds on which both the first and second metals (from M(I)-alkanethiolates, M = Au and Ag) can grow accordingly without additional nucleation and thus achieve high monodispersity for product alloy nanoparticles. Unlike in other prevailing methods, both Au and Ag elements present in these solid precursors are in the same monovalent state and have identical supramolecular structures, which may lead to a more homogeneous reduction and complete interdiffusion at elevated reaction temperatures. When the M(I)-alkanethiolates are reduced to metallic forms, the detached alkanethiolate ligands will serve as capping agent to control the growth. More importantly, composition, particle size, and optical properties of Au(x)Ag(1-x) alloy nanoparticles can be conveniently tuned with this approach. The optical limiting properties of the prepared particles have also been investigated at 532 and 1064 nm using 7 ns laser pulses, which reveals that the as-prepared alloy nanoparticles exhibit outstanding broadband optical limiting properties with low thresholds.     

Fully ferrocenated hexanethiolate monolayer-protected gold clusters

The synthesis and compositional analysis of four different gold clusters with protecting monolayers comprised solely of ferrocene hexanethiolate ligands is described. The gold nanoparticles have average core diameters of 1.4, 1.6, 2.0, and 2.2 nm with estimated average atom counts of 55, 140, 225, and 314 Au atoms and average monolayer coverages of 37, 39, 43, and 58 ferrocenated ligands, respectively. The data show unequivocally that the number of ferrocene hexanethiolate ligands bound to each core size is constrained by the steric requirements of the ferrocene head group; the ligand numbers are significantly smaller than those for hexanethiolate ligands bonded to analogous-sized Au cores. Voltammetry of dilute solutions of these nanoparticles shows a large ferrocene oxidation wave and, at more negative potentials, smaller one-electron waves for the quantized double-layer charging of the Au cores. Together, the ferrocenes and core of the ferrocenated Au314 nanoparticle deliver 60 electrons at the ferrocene oxidation potential, which amounts to a very large volume charge capacity, 7x10(9) C/m3, for an undiluted nanoparticle sample.     

光化学合成Au核@Pd壳复合纳米粒子及其表征

在PEG-丙酮溶液体系中, 采用紫外光辐射还原Au(Ⅲ), Pd(Ⅱ)离子混合物和以Au晶种为核、紫外光辐射还原Pd(Ⅱ)使其沉积在Au晶种表面上这两种方法, 合成了Au核@Pd壳复合纳米粒子. 通过改变Au(Ⅲ)离子或Au晶种对Pd(Ⅱ)离子的摩尔比调节复合粒子的尺寸和Pd壳厚度, 分别获得了直径范围为5.6~4.6 nm和4.6~6.2 nm的复合粒子. 利用UV-Vis吸收光谱、TEM、HR-TEM和XPS等表征手段, 证明了合成的纳米粒子为核-壳复合结构. 研究了Au@Pd纳米粒子的直径随溶液中Au(Ⅲ)/Pd(Ⅱ)摩尔比的改变而变化的规律; 对Au核向Pd壳的供电子作用以及复合粒子的光化学形成机理进行了讨论.     

Biosynthesis of Au nanoparticles using olive leaf extract: 1st Nano Updates

The biological synthesis of gold nanoparticles (AuNPs) of various shapes (triangle, hexagonal, and spherical) using hot water olive leaf extracts as reducing agent is reported. The size and the shape of Au nanoparticles are modulated by varying the ratio of metal salt and extract in the reaction medium. Only 20 min were required for the conversion into gold nanoparticles at room temperature, suggesting a reaction rate higher or comparable to those of nanoparticles synthesis by chemical methods. The variation of the pH of the reaction medium gives AuNPs nanoparticles of different shapes. The nanoparticles obtained are characterized by UV–Vis spectroscopy, photoluminescence, transmission electron microscopy (TEM), X-ray diffraction (XRD), FTIR spectroscopy and thermogravimetric analysis. The TEM images showed that a mixture of shapes (triangular, hexagonal and spherical) structures was formed at lower leaf broth concentration and high pH, while smaller spherical shapes were obtained at higher leaf broth concentration and low pH.     

Preparation of Au/TiO2 nanocomposites and their catalytic activity for DPPH radical scavenging reaction

Au/TiO2 nanocomposites have been prepared by UV photolysis or chemical reduction of a Au(III) complex formed on a spherical or a rodlike TiO2 support, and their catalytic activity for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging reaction was investigated. The chemical reduction with dimethylamine borane (DMAB) provided smaller gold nanoparticles than those synthesized by UV photolysis. Type of the TiO2 also affected the size of gold particles; smaller gold particles were deposited on the spherical TiO2 support than on rodlike one. For the radical scavenging reaction, the Au/TiO2 nanocomposites prepared by chemical reduction exhibited a higher catalytic activity than those photochemically prepared, and rodlike TiO2 provided a higher activity than spherical one. The effects of preparation methods and type of TiO2 supports on the catalytic activity are discussed.     

Size-dependence of Fermi energy of gold nanoparticles loaded on titanium(iv) dioxide at photostationary state

TiO(2) particle-supported Au nanoparticles (NPs) with varying sizes and good contact (Au/TiO(2)) were prepared under a constant loading amount by the deposition-precipitation method. The Fermi energy of Au NPs loaded on TiO(2) at the photostationary state (E(F)') was determined in water by the use of S/S(2-) having specific interaction with Au as a redox probe. The E(F)' value goes up as the mean size of Au NPs (d) increases at 3.0 相似文献   

One-pot synthesis of Ag-Au bimetallic nanoparticles with Au shell and their high catalytic activity for aerobic glucose oxidation

PVP-protected Ag(core)/Au(shell) bimetallic nanoparticles of enough small size, i.e., 1.4nm in diameter were synthesized in one-vessel using simultaneous reduction of the corresponding ions with rapid injection of NaBH(4), and characterized by HR-TEM. The Ag(core)/Au(shell) bimetallic nanoparticles show a high and durable catalytic activity for the aerobic glucose oxidation, and the catalyst can be stably kept for more than 2months under ambient conditions. The highest activity (16,890mol-glucoseh(-1)mol-metal(-1)) was observed for the bimetallic nanoparticles with Ag/Au atomic ratio of 2/8, the TOF value of which is several times higher than that of Au nanoparticles with nearly the same particle size. The higher catalytic activity of the prepared bimetallic nanoparticles than the usual Au nanoparticles can be ascribed to: (1) the small average diameter, usually less than 2.0nm, and (2) the electronic charge transfer effect from adjacent Ag atoms and protecting PVP to Au active sites. In contrast, the Ag-Au alloy nanoparticles, synthesized by dropwise addition of NaBH(4) into the starting solution and having the large mean particle size, showed a low catalytic activity.     

Gold nanoparticle size controlled by polymeric Au(I) thiolate precursor size

We developed a method in preparing size-controllable gold nanoparticles (Au NPs, 2-6 nm) capped with glutathione by varying the pH (between 5.5 and 8.0) of the solution before reduction. This method is based on the formation of polymeric nanoparticle precursors, Au(I)-glutathione polymers, which change size and density depending on the pH. Dynamic light scattering, size exclusion chromatography, and UV-vis spectroscopy results suggest that lower pH values favor larger and denser polymeric precursors and higher pH values favor smaller and less dense precursors. Consequently, the larger precursors led to the formation of larger Au NPs, whereas smaller precursors led to the formation of smaller Au NPs. Using this strategy, Au NPs functionalized with nickel(II) nitriloacetate (Ni-NTA) group were prepared by a mixed-ligand approach. These Ni-NTA functionalized Au NPs exhibited specific binding to 6x-histidine-tagged Adenovirus serotype 12 knob proteins, demonstrating their utility in biomolecular labeling applications.