Synthesis of high concentration colloid solution of silica-coated AgI nanoparticles

Methods for high concentration silica-coated silver iodide (AgI/SiO2) particles, which could be practically used as X-ray contrast agent, were examined. The first was a single-step method, which was to prepare AgI nanoparticles at an AgI concentration of 5 x 10(-3) M and coat the AgI nanoparticles with silica shell by a St?ber method. The second was a multiple-step method, which was to repeat a step for preparing a AgI/SiO2 particle colloid solution with 10(-3) M AgI 5 times for adjusting a final AgI concentration to 5 x 10(-3) M. In the two methods, dominant particle aggregation took place, though core-shell particles were also produced. The third was a salting-out method, which was to salt out AgI/SiO2 particles in their colloid solution prepared at an AgI concentration of 10(-3) M, remove supernatant by decantation, and redisperse the particles in a fresh solvent. Consequently, AgI/SiO2 particles with an AgI concentration as high as 0.05 M were successfully prepared with the salting-out method, and their core-shell structure was not damaged during the salting-out.     

Synthesis and characterization of monodisperse ultra-thin silica-coated magnetic nanoparticles

A systematic study of the formation of silica-coated magnetite particles via a modified reverse microemulsion approach was investigated by using transmission electron microscopy (TEM), x-ray diffraction (XRD) and a superconducting quantum interference device (SQUID). The results show that the surfactant Igepal CO-520 played an important role in the reaction system, and the thickness of the silica shell could be controlled by the concentration of the reaction agents. The developed ultra-thin silica-coated magnetic particles with a ～2?nm thin silica shell have a high saturated magnetization around 15?emu?g(-1).     

Paramagnetic silica-coated gold nanoparticles

Water soluble gold nanoparticles, obtained by the reduction of the gold (III) chloride with sodium borohydride in the presence of citric acid or thioctic acid, were covered with a paramagnetic silica layer using the Stober method, yielding a hybrid metallic-inorganic nanomaterial (gold nanoparticles, with an average size of 5 nm, embedded into silica nanoparticles, with an average size of 100 nm). The paramagnetic silica layer was formed by copolymerization of a paramagnetic silica precursor (derived from 3-aminopropyltrimethoxysilane) with tetramethyorthosilicate. The paramagnetic silica precursor was obtained by coupling 3-aminopropyltrimethoxysilane with 3-carboxy-proxyl free radical. TEM pictures show that each silica nanoparticle of about 100 nm in size embedded about 10 gold nanoparticles. These hybrid nanoparticles are quite stable and exhibit the expected paramagnetic characteristics, as seen by electron paramagnetic resonance. The accessibility of methanol through the silica layer was also studied. Depending on the capping ligands of the gold nanoparticles (citric or thioctic acid), different silica networks are formed, as seen by the mobility of the spin-label inside the silica layer. The EPR spectra showed that the paramagnetic silica layer is very robust and the mobility of the spin-probe inside the silica layer is very little affected by methanol. However, if spin-labeled thioctic acid protected gold nanoparticles were used in the material synthesis, the mobility of the spins attached to the gold surface is quite high in the presence of methanol, while the spins embedded into the silica layer remains immobilized.     

Synthesis of silica-coated AgI nanoparticles and immobilization of proteins on them

This paper describes a method for preparing silica-coated silver iodide (AgI/SiO2) particles and immobilizing proteins on the AgI/SiO2 particles. Colloid solution of AgI particles was prepared by mixing AgClO4 aqueous solution and KI aqueous solution. Silica-coating of the AgI particles was performed by adding 3-mercaptopropyltrimethoxysilane, tetraethylorthosilicate/ethanol solution and NaOH aqueous solution successively to the AgI colloid solution. TEM observation revealed that the AgI nanoparticles were coated with uniform silica shell. The AgI/SiO2 particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by XPS measurement that amino group or carboxyl group was introduced onto the AgI/SiO2 particles. Protein-immobilization was performed in aqueous solution with bovine serum albumin (BSA) in the presence of the surface-modified AgI/SiO2 particles. UV-VIS absorption spectroscopy revealed that the BSA was adsorbed on the surface-modified particles.     

Effect of temperature in synthesis of silver nanoparticles in triblock copolymer micellar solution

Knowing that poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) in aqueous solution is thermoresponsive, the effect of temperature on formation and stabilisation of silver nanoparticles has been investigated systematically. Synthesis of silver nanoparticles was achieved from silver ammonia complex [Ag(NH₃)₂]⁺ in aqueous solution of hydroxyl terminated PEO–PPO–PEO at four different temperatures. A non-Arrhenius behaviour for the rate of silver reduction with temperature was observed. The hydrodynamic diameter of the composite coils suddenly increased at certain intermediate time indicating sudden agglomeration of individual micelles to form bigger network structures. The size and the distribution of the nanoparticles show a bimodal distribution at the lowest temperature. At intermediate temperature, particles of the smallest size with a narrow distribution was achieved. At the highest temperature, a bunch-like particle morphology was found. Chemical changes in polymer properties were observed at higher temperatures. The results suggest that at a lower temperature, a change in polymer morphology play an important role in controlling the particle size and their distribution, whereas at a higher temperature, this role is shifted to the chemical change of the polymer. At an intermediate temperature, a balance between the two effects provides the optimum condition for formation of silver nanoparticles of small size and narrow distribution.     

Synthesis and growth of germanium oxide nanoparticles in AOT reversed micelle

Germanium oxide (GeO₂) nanoparticles with a narrow size distribution have been synthesized by a reverse micelle technique. The cubic GeO₂ particles with particle size of 15 nm were obtained as the reaction solution was left standing for 24 h, the particle size and shape can be controlled by changing the molar ratio of surfactant/water (R_w) and the aging time. The effect of R_w and aging time on the particle size was discussed.     

Uptake of silica-coated nanoparticles by HeLa cells

Nanoparticles have seen wide applications in cellular research and development. One major issue that is unclear is the uptake of nanoparticles by cells. In this study, we have investigated the uptake of silica-coated nanoparticles by HeLa cells, employing rhoadime 6G isothiocyanate (RITC)-doped nanoparticles as a synchronous fluorescent signal indicator. These nanoparticles were synthesized with reverse microemulsion. A few factors, such as nanoparticle concentration, incubation time and temperature, and serum and inhibitors in culture medium were assessed on the nanoparticle's cellular uptake. The experimental results demonstrated that uptake was maximum after a 6 h incubation and was higher at 37 degrees C than that at 4 degrees C. Nanoparticle uptake depended on the nanoparticle concentration and was inhibited by hyperosmolarity, K+ depletion. In addition, serum in culture medium decreased the cellular uptake of nanoparticles. The results indicated that the uptake of silica-coated nanoparticles by HeLa cells was a concentration-, time-, and energy-dependent endocytic process. Silica-coated nanoparticles could be transported into HeLa cells in part through adsorptive endocytosis and in part through fluid-phase endocytosis.     

Preparation and characterization of ZnS nanoparticles synthesized from chitosan laurate micellar solution

Synthesis of ZnS nanostructured materials has been performed in the micellar solution system, containing chitosan laurate as the surfactant. The self-assembling of the surfactant molecules in water solution can form unique architecture that can be adopted as the reaction template for the formation of nanomaterials. The synthesized nanomaterials have been characterized by energy filter transmission electron microscopy (EFTEM), Energy Dispersive X-ray Analysis (EDAX), X-ray diffractometry (XRD) and UV–Visible absorption measurement in order to determine the size, morphology, composition, crystal structure and optical behavior of the products. The spectroscopic results showed that the synthesized nanoparticles exhibited strong quantum confinement effect as the optical band gap increased significantly as compared to the bulk materials. In addition, the size of the resulting nanoparticles is greatly affected by the surfactant concentration and range from 2 to 10 nm. It was found that the nanomaterials obtained existed in face-centered cubic structure and exhibited the characteristic line broadening feature in the XRD patterns.     

Synthesis process of gold nanoparticles in solution plasma

We describe the dynamics of the synthesis of gold nanoparticles by a glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. The initial [AuCl₄]⁻ ion concentration and the voltage applied between the electrodes were varied. The [AuCl₄]⁻ ion was reduced by the H radicals generated in the discharge. The reduction rates were calculated from the changes in the [AuCl₄]⁻ ion concentration during the discharge time. Dendrite-shaped nanoparticles of about 150 nm size were formed in discharge during 1 min. The pH of the solution decreased gradually with the increase of the discharge time. The decrease in pH led to the dissolution of gold nanoparticles. The reduction and the dissolution rates increased proportionately with the applied voltage. The size of the gold nanoparticles decreased at 20 nm after running the discharge during 45 min. Moreover gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon were also observed. The particles were confirmed to be as polycrystalline gold nanoparticles by electron diffraction patterns. In summary, when the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in size in the solution.     

Synthesis of Yb nanoparticles by laser ablation of ytterbium target in sodium bis(2-ethylhexyl)sulfosuccinate reverse micellar solution

Surfactant-coated ytterbium nanoparticles were produced by Nd:YAG laser ablation of a Yb bulk target immersed in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane micellar solution. In our experimental conditions, as highlighted by IR spectroscopy, AOT molecules are not decomposed by the intense laser pulses but play a pivotal role in the stabilisation of Yb nanoparticles. The formation of Yb nanoparticles in the liquid phase was monitored by UV-Vis spectroscopy whereas the Yb/AOT composites obtained by evaporation of the organic solvent were characterised by XPS and TEM. Data analysis consistently shows the presence of surfactant-coated, nearly spherical and non-interacting Yb nanoparticles of mean diameter of 3 nm.Moreover, the presence of bigger polycrystalline nanoparticles (about 30%) in coexistence with smaller mono crystalline ones indicates that, after the rapid formation of the pristine Yb nanoparticles from plume condensation, two processes effectively compete for their size distribution: nanoparticle agglomeration and surfactant adsorption.     

Nanoepitaxy using micellar nanoparticles

The shape of platinum and gold nanoparticles (NPs) synthesized via inverse micelle encapsulation and supported on TiO2(110) has been resolved by scanning tunneling microscopy. Annealing these systems at high temperature (～1000 °C) and subsequent cooling to room temperature produced ordered arrays of well-separated three-dimensional faceted NPs in their equilibrium state. The observed shapes differ from the kinetically limited shapes of conventional physical vapor deposited NPs, which normally form two-dimensional flat islands upon annealing at elevated temperatures. The initial NP volume was found to provide a means to control the final NP shape. Despite the liquid-phase ex situ synthesis of the micellar particles, the in situ removal of the encapsulating ligands and subsequent annealing consistently lead to the development of a well-defined epitaxial relationship of the metal NPs with the oxide support. The observed epitaxial relationships could be explained in terms of the best overlap between the interfacial Pt (or Au) and TiO2 lattices. In most cases, the ratio of {100}/{111} facets obtained for the NP shapes resolved clearly deviates from that of conventional bulklike Wulff structures.     

Growth of carbon nanofibers catalyzed by silica-coated copper nanoparticles

Silica-coated copper nanoparticles were synthesized by coating copper nanoparticles with a silica shell through microemulsion. The copper nanoparticles are 30–40 nm in diameter and the silica coating is 10 nm in thickness. After coating, copper nanoparticles were encapsulated in a silica matrix. These particles were used as a catalyst for the growth of carbon nanofibers in a tubular furnace. It is found that carbon nanofibers are mirror-symmetric growth and 100 nm in diameter. During growth, the copper nanoparticles moved out of the silica. As the experiment progressed, the interplanar spacing of copper (2 2 0) increased from 0.1288 nm to 0.1306 nm indicating that (2 2 0) plane exhibited high catalytic activity. The out-of-sync growth of different faces provides new evidence for the research of growth mode in carbon nanofibers.     

反胶团酶膜反应器研究进展

两亲分子溶入有机溶剂时可自组织形成球形聚集体，称作反胶团，酶能溶入反胶团的水池中以催化特定的反应文中对反胶团介质中的酶反应进行了介绍，并对膜反应器在反胶团酶反应中的应用进行了综述     

Radial anisotropic growth of rhodium nanoparticles

In this contribution, we report the synthesis of rhodium multipods that result from a homogeneous seeded growth mechanism. Small Rh nanocrystal seeds were synthesized by the reduction of RhCl3 in ethylene glycol in the presence of PVP. These seed particles could be subsequently used, without isolation, to form larger rhodium nanoparticles. A reaction temperature of 190 degrees C led to isotropic cubic Rh particles. Lowering the reaction temperature resulted in more anisotropic growth, which gave Rh cubes with horns at 140 degrees C, and Rh multipods at 90 degrees C. The anisotropic growth occurred in the (111) direction, as determined by high-resolution TEM (HRTEM). Anisotropic growth proceeds via a seeded growth mechanism, and not by oriented attachment.     

反相胶束法制备纳米ZrO2粉体

利用NA/煤油-n-C6-OH/NH3@H2O反胶束体系,制备了纳米ZrO2粉体.采用TG-DTA、TEM、XRD等手段对粉体及前驱体进行表征粉体粒度分布均匀,无硬团聚,平均粒度为20～40nm.并且研究了反相胶束中的溶水量对ZrO2粒径的影响以及pH值对ZrO2晶型的影响.并推测20～40nmZrO2的单斜晶(m)与四方晶(t)可能的相转变温度为723℃,比相应的体相材料降低了近450℃.     

Synthesis of a stable colloidal solution of PbS nanoparticles

A method has been proposed for the synthesis of stable colloidal solutions of lead sulfide nanoparticles from aqueous lead acetate and sodium sulfide solutions. The citrate ion and ethylenediaminetetraacetic acid were used as complexing agents to stabilize the solution. The solutions obtained were shown to remain stable at room temperature for at least 30 days from the instant of synthesis, depending on the initial reactant concentration. According to X-ray diffraction and dynamic light scattering data, the stability and coagulation of the nanoparticles in solution were influenced by the lead and sulfur concentration, the presence of complexing agents, and the quantitative relation between the lead and complexing agent ions in solution. Optical absorption measurements for the colloidal PbS nanoparticle solutions showed that their absorbance was a nonlinear function of reactant concentration.     

Characterization of silica-coated Ag nanoparticles synthesized using a water-soluble nanoparticle micelle

This article describes the synthesis of silica-coated Ag nanoparticles using a water-soluble nanoparticle micelle under basic conditions. Monodispersed Ag nanoparticles with a mean particle size of 7 nm were synthesized using AgNO₃ in the presence of ascorbic acid as a reducing agent. The Ag nanoparticles were easily re-dispersed into an aqueous solution by surface adsorption of surfactant molecules, indicating formation of water-soluble nanoparticle micelles. Silica-coated Ag nanoparticles ranging in size from 50 to 100 nm were obtained by controlling the surfactant, Ag nanoparticle and tetraethylortho silicate (TEOS) concentrations. Adsorbed surfactant monolayers on Ag nanoparticles were used as a template for the silica shell because of the hydrophobicity of TEOS. In all cases, the size of the resulting particles increased linearly as these concentrations increased. Based on transmission electron microscopy, all the Ag nanoparticles were completely covered with a silica shell. In most samples, however, Ag nanoparticle size increased from 7 to 50 nm due to evaporation of hexane by heating. Although mean particle size of silica-coated Ag nanoparticles was drastically altered, characteristic absorption peaks were observed at approximately 410 nm.