Synthesis and characterization of gold nanoparticles stabilized by palladium(II) phosphine thiol

This work is focused on the synthesis of innovative hybrids made by linking gold nanoparticles to protected organometallic Pd(II) thiolate. The organometallic protected Pd(II) thiolate, i.e. trans-thioacetate-ethynylphenyl-bis(tributylphosphine)palladium(II) has been synthesized, in situ deprotected and linked to Au nanoparticles. In this way new hybrid, with a direct link between Pd(II) and Au nanoparticles through a single S bridge, has been isolated. The combination of the organometallic Pd(II) thiol with gold nanoparticles allows the enhancement and tailoring of electronic and optical properties of the new organic-inorganic nano-compound. Single-crystal gold nanoparticles, uniform in shape and size were obtained by applying a modified two-phase method (improved Brust-Schiffrin reaction). In addition, the chemical environment of the Au nanoparticles was investigated and a covalent bonding between Au nanoparticles and the organometallic thiols was observed.     

Colloidal metal nanoparticles as a component of designed catalyst

Recent advances in the synthesis of colloidal metal nanoparticles of controlled sizes and shapes that are relevant for catalyst design are reviewed. Three main methods, based on colloid chemistry techniques in solution, i.e., chemical reduction of metal salt precursors, electrochemical synthesis, and controlled decomposition of organometallic compounds and metal-surfactant complexes, are used to synthesize metal nanoparticles. Their catalytic activity and selectivity depend on the shape, size and composition of the metal nanoparticles, and the support effect, as shown for many reactions in quasi-homogeneous and heterogeneous catalysis. A specially designed type of thermally stable catalysts--"embedded" metal catalysts, in which metal nanoparticles are isolated by porous support shells so that metal sintering is effectively avoided at high temperatures, are also introduced. The utilization of pre-prepared colloidal metal nanoparticles with tuned size, shape and composition as components of designed catalysts opens up new field in catalysis.     

Synthesis of copper nanoparticles in the matrix of ethylene-propylene copolymer

Copper nanoparticles in the matrix of ethylene propylene copolymer were derived by a method of a high thermal decomposition of an organometallic precursor in a high shear. It was revealed that the decomposition temperature of the precursor increases significantly in the formation of nanoparticles in the polymer matrix. It was found by X-ray diffraction analysis and scanning electron microscopy that copper nanoparticles in shape close to spherical and of a wide particle size distribution are formed in the decomposition of copper formate dihydrate in an elastomeric matrix.     

Colloidal self-assemblies used as templates to control size,shape and self-organization of nanoparticles

In this paper we show that the use of colloidal assemblies as templates favors the control of the size and shape of nanoparticles. As expected theoretically, the change in size and shape of copper metal nanosized particles induces changes in their optical properties. Cylindrical copper metal particles having the same size and shape can be obtained in various regions of the phase diagram when the template is made of interconnected cylinders. Self-assembly of silver metal nanoparticles is reported. Monolayers of particles organized in a hexagonal network are formed over very large domains. Small or large aggregates can also be produced, and, in these aggregates, the particles are highly organized and form pseudo-crystals with a face-centered cubic structure for various particles sizes. The optical properties of the silver nanoparticles isolated in micellar solution or self-assembled in 2D or 3D supperlattices are reported. Syntheses of magnetic fluids differing in their particle size are presented. The magnetic properties differ with the particle size.     

Chemical and optical properties of CdSe and CdSe/ZnS nanocrystals investigated using high-performance liquid chromatography

We apply a variety of characterization tools, including dynamic light scattering (DLS), transmission electron microscopy (TEM), high-resolution size-exclusion chromatography (HRSEC), and X-ray fluorescence (XRF), to study CdSe and CdSe/ZnS semiconductor nanocrystals of various sizes. We compare the size monodispersity, composition, and optical properties such as absorbance, photoluminescence (PL), and photoluminescence excitation of samples synthesized by high-temperature organometallic decomposition methods to CdSe clusters synthesized in our laboratory using a room-temperature metathesis from ionic precursors in coordinating solvents. DLS revealed considerable aggregation in all the conventionally synthesized samples, while TEM showed significant size and shape polydispersity in the core/shell CdSe/ZnS nanoparticles. We demonstrate how HRSEC can be used to explore size and shape polydispersity in semiconductor nanocrystals by measurement of the spectral homogeneity of the PL and PLE of spectra obtained within cluster elution peaks observed by HRSEC. Using HRSEC, we show that size fractionation by solvent/nonsolvent precipitation is only partially effective in size selection and that discrete size populations are present in each fraction. HRSEC shows that our synthesis yields a single-size, blue-emitting, homogeneous population whose absorbance and PL correspond to those of the smallest-size fraction made by conventional synthesis. This suggests that especially stable discrete sizes are favored in both synthetic methods.     

One‐Step Synthesis of Hybrid Liquid–Crystal ZnO Nanoparticles: Existence of a Critical Temperature Associated with the Anisotropy of the Nanoparticles

Zinc oxide nanoparticles were obtained from the hydrolysis of an organometallic precursor in pure hexadecylamine. Interestingly, we demonstrate that the final (anisotropic or isotropic) shape of the nanoparticles is strongly correlated to the existence of a critical temperature. This suggests that the organization of the fatty amines is a paramount parameter in this synthesis. Moreover, the final hybrid ZnO materials systematically exhibit a liquid–crystal smectic phase, whereas no liquid–crystal phase was observed in the pristine reaction media. This simple process is, therefore, a direct and straightforward method to synthesize liquid–crystal hybrid materials.     

Facile phase transfer of large, water-soluble metal nanoparticles to nonpolar solvents

The facile phase-transfer of large, water-soluble metal nanoparticles to nonpolar solvent is reported here. Thiol-terminated polystyrene (PS-SH) is ligand-exchanged onto water-soluble metal nanoparticles in single-phase acetone/water mixtures, generating a precipitate. The solvent is then removed and the particles are redissolved in nonpolar solvent. This approach is demonstrated for nanoparticles of different metal (Au and Ag), size (3 to >100 nm), shape (spheres, rods, and wires, etc.), and leaving ligand (citrate, cetyltrimethylammonium bromide, poly(vinylpyrrolidone), and 4-dimethylaminopyridine. The resulting PS-SH-stabilized nanoparticles maintain their initial size and shape, and are highly stable. They are soluble in various organic solvents (toluene, benzene, chloroform, dichloromethane, and tetrahydrofuran), and can be readily dried, purified, and re-dissolved. This method makes possible the utilization of a full range of existing nanoparticle cores in nonpolar solvents with a single ligand. It provides access to numerous nanomaterials that cannot be obtained through direct synthesis in nonpolar solvent, and is expected to be of significant value in a number of applications.     

Photochemical synthesis of gold nanoparticles in N,N′-dimethylformamide via thiourea-derivatized polyoxometalate

In the present work, we report the photochemical synthesis of gold nanoparticles in N,N′-dimethylformamide by addition of a photocatalyst like thiourea-modified polyoxometalate (γ-SiW₁₂O₄₀). The polyoxometalate behaves as an electron relay. Reduction of the polyoxometalate takes place under UV irradiation followed by a transfer of electrons to the gold ions, leading to the formation of gold nanoparticles. The formation of the gold particles was monitored with time by UV–Vis spectrophotometry. The polyoxometalate also acts as a stabilizing agent and helps in controlling the size of the nanoparticles. The shape and size distribution was obtained from transmission electron microscopy studies. Spherical and monodisperse gold nanoparticles of ~10 nm size were obtained.     

Forces between surfaces across nanoparticle solutions: role of size, shape, and concentration

Using a surface force apparatus, we have measured the normal forces between mica surfaces across various types of nanoparticles consisting of ZnS cores coated with a monolayer of physisorbed surfactant, dispersed in organic solvents. We focused on the effects of nanoparticle size, shape, and concentration on the force-distance profiles. Forces were exponentially repulsive when the surfactant layers were strongly bound to the nanoparticles and were roughly linear when there was adhesion between the nanoparticle cores, i.e., when the surfactant layers detached from the nanoparticles. In both cases, the range and magnitude of the forces were dependent upon the particle size, shape, and solution concentration. Fine details in the otherwise smooth force-distance profiles indicate specific effects due to particle chemistry and geometry and the existence of first-order disorder-order phase transitions upon confinement. Small amounts of water in the (hydrophobic) organic solvents had dramatic effects on the measured forces. Understanding and controlling the effects of particle shape, size, and concentration and the presence of water (or other surface-active solutes) on particle-particle and particle-surface interactions are important for the processing of nanoparticles into ordered superstructured materials.     

Preparation of silver nanoparticles with controlled particle size

Silver colloids show different colors due to light absorption and scattering in the visible region based on plasmon resonance. The resonance wavelength depends on particle size and shape. Here we report chemical reduction methods for preparation of silver nanoparticles exhibiting multicolor in aqueous solutions. Depending on chemical conditions the obtained nanoparticles are different regarding size and morphology.In order to investigate the relationship between size, stability and color of silver colloids we obtained silver nanoparticles in aqueous solutions using different reducing agents. The effect of polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) on stabilization of obtained silver colloids was investigated. We have also studied the effect of silver precursor and its concentration on the formation of stable silver colloids.UV-VIS spectrum for silver colloids contains a strong plasmon band near 410 nm, which confirms silver ions reduction to Ag° in the aqueous phase. The formation of metal silver was also confirmed by powder X-ray diffraction (XRD) analysis. The diameter size of silver nanoparticles was in the range from 5 nm to 100 nm     

“Sweet” gold nanoparticles with oligosaccharide-modified poly(ethyleneimine)

This paper is focused on the use of oligosaccharide-modified hyperbranched poly(ethyleneimines) (PEI) as reducing and stabilizing agent for the formation of gold nanoparticles. The results show that the secondary amino groups of the PEI as linear units are responsible for the reduction process, and the primary amino groups as terminal units are of relevance for the particle stabilization. With regard to the final size and shape of the gold nanoparticles formed, the amount and type (maltose or maltotriose) of oligosaccharide units and structural parameters of the PEI samples are of importance. The smallest particle size of about 2 nm is obtained from a maltose-modified PEI with an excess of linear units. The size and shape of the polymer-stabilized nanoparticles can be further tuned by changing the solute concentration, the time of heating, as well as the pH value.     

Formation of nanocomposite platinum catalysts on porous silicon

Platinum nanoparticles supported on porous silicon were synthesized by radiation-chemical reduction in solutions of reverse micelles. The Pt nanoparticles obtained are electrondeficient. The degree of porosity, conductivity type, pore geometry of the silicon matrix, and precursor parameters affect the size, shape, and charge state of the platinum catalysts.     

Preparation,Characterization of Hydrophobic Drug in Combine Loaded Chitosan/Cyclodextrin/Trisodium Citrate Nanoparticles and in vitro Release Study

Chitosan/cyclodextrin/trisodium citrate(CS/CD/TSC) nanoparticles with ibuprofen(IBU) loaded were prepared via the ionic cross-linking method, with trisodium citrate selected as the cross-linking agent. The drug-loading capacity, particle size, zeta potential and surface morphology of the obtained nanoparticles were investigated. The results show a good drug-loading capacity. The prepared nanoparticles were spherical in shape with an average size of 293.7 nm and a zeta potential of +30.72 mV. The in vitro release studies show that the controlled release of IBU from the nanoparticles was followed. The drug release from CS/β-CD/TSC nanoparticles followed non-Fickian or anomalous diffusion.     

探索利用无机结合肽PT2(DRTSTWR)制备纳米铂晶体

实验中首先利用固定化于PET(聚对苯二甲酸己二醇酯)膜上无机结合肽PT2 (DRTSTWR)制备出铂微晶体. 然后用游离的PT2与PtCl₄在室温和pH中性环境中反应24 h, 所得产物用TEM观察, 其多数为1～2 nm呈方形和球形晶体, 经EDX分析显示晶体的元素组成中Pt远大于Cl的含量, 显然晶体不可能是PtCl₄或PtCl₂; 样品的XPS谱图中出现了结合能值为71.0 eV峰(Pt_4f标准值71.1 eV), 确认晶体为铂纳晶, 由此推断无机结合肽PT2在无细胞状态下能够作为模板仿生合成铂晶体. 继而在反应体系中加入不同浓度的壳聚糖和聚丙烯酸钠, 观察到纳米粒子的粒径和形貌随表面活性剂的加入发生了改变. 加入5倍的壳聚糖制备的铂晶体的直径在12～15.5 nm之间, 晶体排布似乎有成线状的趋势. 加入5倍的聚丙烯酸钠制备的铂晶体, 形貌更加规整, 以球形颗粒为主, 粒子直径在6～8 nm之间.     

Particle size, shape and activity for photocatalysis on titania anatase nanoparticles in aqueous surroundings

TiO(2) nanoparticles have been widely utilized in photocatalysis, but the atomic level understanding on their working mechanism falls much short of expectations. In particular, the correlation between the particle structure and the photocatalytic activity is not established yet, although it was observed that the activity is sensitive to the particle size and shape. This work, by investigating a series of TiO(2) anatase nanoparticles with different size and shape as the photocatalyst for water oxidation, correlates quantitatively the particle size and shape with the photocatalytic activity of the oxygen evolution reaction (OER). Extensive density functional theory (DFT) calculations combined with the periodic continuum solvation model have been utilized to compute the electronic structure of nanoparticles in aqueous solution and provide the reaction energetics for the key elementary reaction. We demonstrate that the equilibrium shape of nanoparticle is sensitive to its size from 1 to 30 nm, and the sharp crystals possess much higher activity than the flat crystals in OER, which in combination lead to the morphology dependence of photocatalytic activity. The conventionally regarded quantum size effect is excluded as the major cause. The physical origin for the shape-activity relationship is identified to be the unique spatial separation/localization of the frontier orbitals in the sharp nanoparticles, which benefits the adsorption of the key reaction intermediate (i.e., OH) in OER on the exposed five-coordinated Ti of {101} facet. The theoretical results here provide a firm basis for maximizing photocatalytic activity via nanostructure engineering and are also of significance for understanding photocatalysis on nanomaterials in general.     

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.     

Separation of nanorods by density gradient centrifugation

The experimental conditions necessary for the synthesis of well-defined nanoparticles are often difficult to control. There is thus a compelling need for post-synthesis separation of nanoparticles polydispersed in size and shape. We demonstrate here both theoretically and experimentally that gold nanorods with diverse aspect ratios can be separated using density gradient centrifugation. By analysing the force balance of a Brownian rod falling in a Stokes flow, we derive a rigorous and predictive model that reveals the quantitative dependency of the nanorod sedimentation rates on their mass and shape. The calculations show that while mass dependency is still the dominating factor during centrifugation, the shape factor is not insignificant. Relatively heavier but long and thin rods could sediment slower than certain size of lighter spheres, and some rods and spheres with different masses and shapes may never be separated. This mass and shape dependency is exploited to separate as-prepared gold nanorod colloids by sucrose gradient centrifugation. Two layers of nanorods with narrow aspect-ratio distributions are obtained.     

Controlled Synthesis of Water‐Dispersible Faceted Crystalline Copper Nanoparticles and Their Catalytic Properties

We report a solution‐phase synthetic route to copper nanoparticles with controllable size and shape. The synthesis of the nanoparticles is achieved by the reduction of copper(II) salt in aqueous solution with hydrazine under air atmosphere in the presence of poly(acrylic acid) (PAA) as capping agent. The results suggest that the pH plays a key role for the formation of pure copper nanoparticles, whereas the concentration of PAA is important for controlling the size and geometric shape of the nanoparticles. The average size of the copper nanoparticles can be varied from 30 to 80 nm, depending on the concentration of PAA. With a moderate amount of PAA, faceted crystalline copper nanoparticles are obtained. The as‐synthesized copper nanoparticles appear red in color and are stable for weeks, as confirmed by UV/Vis and X‐ray photoemission (XPS) spectroscopy. The faceted crystalline copper nanoparticles serve as an effective catalyst for N‐arylation of heterocycles, such as the C? N coupling reaction between p‐nitrobenzyl chloride and morpholine producing 4‐(4‐nitrophenyl)morpholine in an excellent yield under mild reaction conditions. Furthermore, the nanoparticles are proven to be versatile as they also effectively catalyze the three‐component, one‐pot Mannich reaction between p‐substituted benzaldehyde, aniline, and acetophenone affording a 100 % conversion of the limiting reactant (aniline).     

Optical absorbance of colloidal suspensions of silver polyhedral nanoparticles

The optical absorption of colloidal suspensions made of silver nanoparticles with polyhedral shapes is studied experimentally and theoretically. The influence of the shape on the optical response is investigated by comparing the measured absorbance with theoretical results for icosahedral, decahedral, and cuboctahedral silver nanoparticles. The theoretical spectra are obtained within the discrete dipole approximation. We find that colloidal suspensions of silver nanoparticles with a small dispersion of size distribution show very few structural shapes.     

Investigation of the formation of CuInS2 nanoparticles by the oleylamine route: comparison of microwave-assisted and conventional syntheses

The formation of copper indium disulfide nanoparticles via the oleylamine route using copper iodide, indium chloride, and elemental sulfur has been investigated by applying conventional thermal heating as well as microwave irradiation. Oleylamine thereby acts as a capping ligand as well as a solvent. In an initial set of experiments, the onset of the reaction was determined to be around 115 °C by an in situ X-ray study using Synchrotron radiation. Using comparatively low synthesis temperatures of 120 °C, it is already possible to obtain nanoparticles of 2-4 nm with both heating methods but with irregular shape and size distribution. By applying higher temperatures of 220 °C, more crystalline and larger nanoparticles were obtained with slight differences in crystallite size and size distribution depending on the synthesis route. The size of the nanoparticles is in the range of 3-10 nm depending on the heating time. Using microwave irradiation, it is possible to obtain nanoparticles in only 90 s of total synthesis time. Control experiments to probe a nonthermal microwave effect were carried out ensuring an identical experimental setup, including the heating profile, the stirring rate, and the volume and concentration of the solutions. These experiments clearly demonstrate that for the preparation of CuInS(2) nanoparticles described herein no differences between conventional and microwave heating could be observed when performed at the same temperature. The nanoparticles obtained by microwave and thermal methods have the same crystal phase, primary crystallite size, shape, and size distribution. In addition, they show no significant differences concerning their optical properties.