Preparation of sterically stabilized gold nanoparticles for plasmonic applications

Plasmonic nanoparticles such as those of gold or silver have been recently investigated as a possible way to improve light absorption in thin film solar cells. Here, a simple method for the preparation of spherical plasmonic gold nanoparticles in the form of a colloidal solution is presented. The nanoparticle diameter is controlled in the range from several nm to tens of nm depending on the synthesis parameters with the size dispersion down to 14 %. The synthesis is based on thermal decomposition and reduction of the chloroauric acid in the presence of a stabilizing capping agent (surfactant) that is very slowly injected into the hot solvent. The surfactant prevents uncontrolled nanoparticle aggregation during the growth process. The nanoparticle size and shape depend on the type of the stabilizing agent. Surfactants with different lengths of the hydrocarbon chains such as Z-octa-9-decenylamine (oleylamine) with AgNO₃ and polyvinylpyrrolidone with AgNO₃ were used for the steric stabilization. Hydrodynamic diameter of the gold nanoparticles in the colloidal solution was determined by dynamic light scattering while the size of the nanoparticle metallic core was found by small-angle X-ray scattering. The UV-VIS-NIR spectrophotometer measurements revealed a plasmon resonance absorption in the 500–600 nm range. Self-assembled nanoparticle arrays on a silicon substrate were prepared by drop casting followed by spontaneous evaporation of the solvent and by a modified Langmuir-Blodgett deposition. The degree of perfection of the self-assembled arrays was analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering. Homogeneous close-packed hexagonal ordering of the nanoparticles stretching over large areas was evidenced. These results document the viability of the proposed nanoparticle synthesis for the preparation of high-quality plasmonic templates for thin film solar cells with enhanced power conversion efficiency, surface enhanced Raman scattering, and other applications.     

Light-induced aggregation of colloidal gold nanoparticles capped by thymine derivatives

The colloid stability of thymine-coated gold nanoparticles under light irradiation as a function of particle size, surface charge, and exposure time was investigated in alkaline, aqueous solutions as well as in a 0.5 vol % of DMF in H(2)O mixture. With increasing exposure to light irradiation at 280 nm, more and more particles coagulated. Light-induced aggregation of colloidal gold nanoparticles was attributed to reorientation of thymine terminal groups tethered on gold particle surfaces. A smaller particle size and negatively charged surface reduced the rate of photodimerization or even inhibited the photoreaction. UV-vis and FTIR spectroscopy confirmed the photodimerization of terminal thymine molecules under 280 nm light irradiation. The reaction kinetics of thymine photodimerization appears to be a combination of first-order reactions, each having different rates, reflecting the inhomogeneity and high curvature of the gold nanoparticle surfaces.     

Size dependent catalysis with CTAB-stabilized gold nanoparticles

CTAB-stabilized gold nanoparticles were synthesized by applying the seeding-growth approach in order to gain information about the size dependence of the catalytic reduction of p-nitrophenol to p-aminophenol with sodium borohydride. Five different colloidal solutions of stabilized gold nanoparticles have been characterized by TEM, AFM, UV-Vis, SAXS, and DLS for their particle size distributions. Gold nanoparticles (mean sizes: 3.5, 10, 13, 28, 56 nm diameter) were tested for their catalytic efficiency. Kinetic data were acquired by UV-Vis spectroscopy at different temperatures between 25 and 45 °C. By studying the p-nitrophenol to p-aminophenol reaction kinetics we determined the nanoparticle size which is needed to gain the fastest conversion under ambient conditions in the liquid phase. Unexpectedly, CTAB-stabilized gold nanoparticles with a diameter of 13 nm are most efficient.     

Influence of dose on particle size of colloidal silver nanoparticles synthesized by gamma radiation

Colloidal silver nanoparticles were synthesized by γ-irradiation-induced reduction method of an aqueous solution containing silver nitrate as a precursor in various concentrations between 7.40×10^?4 and 1.84×10^?3 M, polyvinyl pyrrolidone for capping colloidal nanoparticles, isopropanol as radical scavenger of hydroxyl radicals and deionised water as a solvent. The irradiations were carried out in a ⁶⁰Co γ source chamber at doses up to 70 kGy. The optical absorption spectra were measured using UV–vis spectrophotometer and used to study the particle distribution and electronic structure of silver nanoparticles. As the radiation dose increases from 10 to 70 kGy, the absorption intensity increases with increasing dose. The absorption peak λ_max blue shifted from 410 to 403 nm correspond to the increase of absorption conduction electron energy from 3.02 to 3.08 eV, indicating the particle size decreases with increasing dose. The particle size was determined by photon cross correlation spectroscopy and the results showed that the particle diameter decreases exponentially with the increase of dose. The transmission electron microscopy images were taken at doses of 20 and 60 kGy and the results confirmed that as the dose increases the diameter of colloidal silver nanoparticle decreases and the particle distribution increases.     

Synthesis of colloidal dispersions of rhodium nanoparticles under high temperatures and high pressures

Colloidal dispersions of rhodium (Rh) nanoparticles have been synthesized by the reduction of Rh ions (III) in high-temperature and high-pressure water, ethanol, or water-ethanol mixture under the existence of the protective polymer of poly(N-vinyl-2-pyrrolidone). The possibility of the regulation of the particle size and size distribution has been tested under several solvents at various temperatures and pressures. At 473 K and 25 MPa, particularly, concentrated colloidal dispersions of Rh particles of 2.5+/-0.5 nm were synthesized from the ionic solution of ethanol ([Rh]=15 mM) within a few seconds. Dilute colloidal dispersions of Rh particles were also synthesized from the dilute ionic solution ([Rh]=1.5 mM) with a diameter of 2.0+/-0.4 nm. From the water solution, Rh particles tended to form aggregates, especially for the lower concentration solution. In the case of solutions in water and ethanol mixture, the average diameter of Rh particles tended to be larger than in ethanol solution, and their distribution became broad.     

Analysis of titanium nanoparticles created by laser irradiation under liquid environments

The results of studies of the formation of various titanium-based nanoparticles by laser ablation of a titanium rod in liquid environments comprised of water, ethanol, 2-propanol, and n-hexane are reported. The effect of fluence on nanoparticle characteristics was studied by ablation with a 532 nm Nd:YAG operating at 10 Hz, showing that mean particle size and the size distribution increase with increasing laser intensity. The solvent plays a crucial role in the nature of the nanoparticles, as solvent components are incorporated into the nanoparticles during formation. Titanium nanoparticles formed in oxygen-rich solvents incorporate oxygen, while those formed in a carbon-rich environment are found to contain carbon. The nanoparticles created in their respective liquid environments are very stable, maintain their character over time, and remain in solution for months after creation.     

Influence of intense pulsed laser irradiation on optical and morphological properties of gold nanoparticle aggregates produced by surface acid-base reactions

Gold nanoparticles were surface modified with an ionizable and pH-sensitive monolayer of thiobarbituric acid (TBA). By variation of the pH value of the solution, nanoparticle aggregates can be produced in a controlled way. The aggregates thus prepared were irradiated with an intense pulsed laser at 532 nm. The products in solution were examined by transmission electron microscopy (TEM) and optical absorption spectroscopy. The TEM images of the products revealed that the nanoparticle aggregates dissociate upon laser irradiation and form much smaller gold nanoparticles. The optical absorption spectra measured simultaneously show the gradual disappearance of the absorbance band of the aggregates at around 680 nm. Additionally, a blue shift (from 534 to 524 nm) of the resonance absorbance corresponding to isolated nanoparticles has been observed. All the observations suggest that the colloidal solution becomes more stable after laser irradiation. Both the reduced nanoparticle size and the stabilizing TBA ligands present on the particle surface contribute to the acquired stability of the colloidal solutions.     

Extinction coefficient of gold nanoparticles with different sizes and different capping ligands

Extinction coefficients of gold nanoparticles with core size ranging from approximately 4 to 40 nm were determined by high resolution transmission electron microscopy analysis and UV-vis absorption spectroscopic measurement. Three different types of gold nanoparticles were prepared and studied: citrate-stabilized nanoparticles in five different sizes; oleylamide-protected gold nanoparticles with a core diameter of 8 nm, and a decanethiol-protected nanoparticle with a diameter of around 4 nm. A linear relationship between the logarithms of extinction coefficients and core diameters of gold particles was found independent of the capping ligands on the particle surface and the solvents used to dissolve the nanoparticles. This linear relation may be used as a calibration curve to determine the concentration or average size of an unknown nanoparticle or nanoparticle-biomolecule conjugate sample.     

Thermodiffusion in model nanofluids by molecular dynamics simulations

In this work, a new algorithm is proposed to compute single particle (infinite dilution) thermodiffusion using nonequilibrium molecular dynamics simulations through the estimation of the thermophoretic force that applies on a solute particle. This scheme is shown to provide consistent results for model nanofluids in the liquid state (spherical nonmetallic nanoparticles+Lennard-Jones fluid) where it appears that thermodiffusion amplitude, as well as thermal conductivity, decreases with nanoparticle concentration. Then, by changing the nature of the nanoparticle (size, mass, and internal stiffness) and that of the solvent (quality and viscosity), various trends are exhibited. In all cases, the single particle thermodiffusion is positive, i.e., the nanoparticle tends to migrate toward the cold area. The single particle thermal diffusion coefficient is shown to be independent of the size of the nanoparticle (diameter of 0.8-4 nm), whereas it increases with the quality of the solvent and is inversely proportional to the viscosity of the fluid. In addition, this coefficient is shown to be independent of the mass of the nanoparticle and to increase with the stiffness of the nanoparticle internal bonds. Besides, for these configurations, the mass diffusion coefficient behavior appears to be consistent with a Stokes-Einstein-like law.     

纳米2,4-二羟基苯甲酸铅(Ⅱ)配合物的合成及其燃烧催化性能研究

采用液相分散沉淀法制备了纳米2,4-二羟基苯甲酸-Pb(Ⅱ)配合物粉体,并用TG,XRD,TEM,IR和元素分析对产物进行了表征.研究了反应条件对产物粒径和粒子形貌的影响.用DSC考察了产物对吸收药热分解的催化作用.结果表明,在水溶液中得到的产物为15nm×40nm的棒状粒子,而在乙醇溶液中得到的是粒径约为50nm的球形粒子.产物对吸收药热分解有显著的催化效果,使吸收药的分解峰温降低5.6℃,分解热增加918J/g.     

Tailoring the carbon nanostructures grown on the surface of Ni-Al bimetallic nanoparticles in the gas phase

A gas-phase, one-step method for producing various aerosol carbon nanostructures is described. The carbon nanostructures can be selectively tailored with either straight, coiled, or sea urchin-like structures by controlling the size of Ni-Al bimetallic nanoparticles and the reaction temperature. The carbon nanostructures were grown using both conventional spray pyrolysis and thermal chemical vapor deposition. Bimetallic nanoparticles with catalytic Ni (guest) and non-catalytic Al (host) matrix were reacted with acetylene and hydrogen gases. At the processing temperature range of 650-800 °C, high concentration straight carbon nanotubes (S-CNTs) with a small amount of coiled carbon nanotubes (C-CNTs) can be grown on the surface of seeded bimetallic nanoparticle size <100 nm, resulting from consumption of the melting Al matrix sites; sea urchin-like carbon nanotubes (SU-CNTs) of small diameter (～10±4 nm) can be grown on the bimetallic nanoparticle size >100 nm, resulting from the significant size reduction of the available Ni sites due to thermal expansion of molten Al matrix sites without consumption of Al matrix. However, at the processing temperature range of 500-650 °C, C-CNTs can be grown on the bimetallic nanoparticle size <100 nm due to the presence of Al matrix in the bimetallic nanoparticles; SU-CNTs of large diameter (～60±13 nm) can also be grown on the bimetallic nanoparticle size >100 nm due to the isolation of Ni sites in the Al matrix.     

Synthesis of spherical submicron-sized magnetite/silica nanocomposite particles

This paper describes a method for fabricating spherical submicron-sized silica particles that contained magnetite nanoparticles (magnetite/silica composite particles). The magnetite nanoparticles with a size of ca. 10 nm were prepared according to the Massart method, and were surface-modified with carboxyethylsilanetriol. The fabrication of magnetite/silica composite particles was performed in water/ethanol solution of tetraethoxyorthosilicate with ammonia catalyst in the presence of the surface-modified magnetite nanoparticles. The magnetite/silica composite particles with a size of ca. 100 nm were successfully prepared at 0.05 M TEOS, 15 M water, and 0.8 M ammonia with injection of the magnetite nanoparticle colloid at 2 min after the initiation of hydrolysis reaction of TEOS. Magnetite concentration in the composite particles could be raised to 17.3 wt.% by adjustment of the injected amount of the magnetite colloid, which brought about the saturation magnetization of 7.5 emu/g for the magnetite/silica composite particles.     

Preparation of nanoparticle colloids of methoxy poly(ethylene glycol)-<Emphasis Type="Italic">b</Emphasis>-poly(<Emphasis Type="SmallCaps">D</Emphasis>,<Emphasis Type="SmallCaps">L</Emphasis>-lactide): effects of surfactant and organic solvent

Nanoparticle colloids of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) diblock copolymer were prepared by a modified spontaneous emulsification solvent diffusion method using acetone/ethanol as the mixture organic solvents. The MPEG-b-PDLL was synthesized by ring-opening polymerization of D,L-lactide using stannous octoate and MPEG with molecular weight of 5,000 g/mol as the initiating system. The MPEG-b-PDLL obtained was an amorphous polymer with molecular weight of 73,600 g/mol. Influences of acetone/ethanol (v/v) ratios and Tween 80 surfactant concentrations on characteristics of the colloidal nanoparticles were investigated and discussed. Light-scattering analysis showed that average diameters of the surfactant-free colloidal nanoparticles were in the range of 86–124 nm. The nanoparticle sizes decreased as the ethanol ratio increased. The Tween 80 did not show the significant effect on the nanoparticle sizes. Scanning electron micrographs of dried nanoparticles that demonstrated the aggregation of most particles suggested they were the soft nanoparticles. However, the dried nanoparticle morphology can be observed from scanning electron microscopy as having a spherical shape and smooth surfaces.     

Long-Term Colloidally Stable Aqueous Dispersions of ≤5 nm Spinel Ferrite Nanoparticles

Applications in biomedicine and ferrofluids, for instance, require long-term colloidally stable, concentrated aqueous dispersions of magnetic, biocompatible nanoparticles. Iron oxide and related spinel ferrite nanoparticles stabilized with organic molecules allow fine-tuning of magnetic properties via cation substitution and water-dispersibility. Here, we synthesize≤5 nm iron oxide and spinel ferrite nanoparticles, capped with citrate, betaine and phosphocholine, in a one-pot strategy. We present a robust approach combining elemental (CHN) and thermal gravimetric analysis (TGA) to quantify the ratio of residual solvent molecules and organic stabilizers on the particle surface, being of particular accuracy for ligands with heteroatoms compared to the solvent. SAXS experiments demonstrate the long-term colloidal stability of our aqueous iron oxide and spinel ferrite nanoparticle dispersions for at least 3 months. By the use of SAXS we approved directly the colloidal stability of the nanoparticle dispersions for high concentrations up to 100 g L⁻¹.     

Hydrothermal growth of mesoporous SBA-15 silica in the presence of PVP-stabilized Pt nanoparticles: synthesis, characterization, and catalytic properties

A novel high surface area heterogeneous catalyst based on solution phase colloidal nanoparticle chemistry has been developed. Monodisperse platinum nanoparticles of 1.7-7.1 nm have been synthesized by alcohol reduction methods and incorporated into mesoporous SBA-15 silica during hydrothermal synthesis. Characterization of the Pt/SBA-15 catalysts suggests that Pt particles are located within the surfactant micelles during silica formation leading to their dispersion throughout the silica structure. After removal of the templating polymer from the nanoparticle surface, Pt particle sizes were determined from monolayer gas adsorption measurements. Infrared studies of CO adsorption revealed that CO exclusively adsorbs to atop sites and red-shifts as the particle size decreases suggesting surface roughness increases with decreasing particle size. Ethylene hydrogenation rates were invariant with particle size and consistent with a clean Pt surface. Ethane hydrogenolysis displayed significant structure sensitivity over the size range of 1-7 nm, while the apparent activation energy increased linearly up to a Pt particle size of approximately 4 nm and then remained constant. The observed rate dependence with particle size is attributed to a higher reactivity of coordinatively unsaturated surface atoms in small particles compared to low-index surface atoms prevalent in large particles. The most reactive of these unsaturated surface atoms are responsible for ethane decomposition to surface carbon. The ability to design catalytic structures with tunable properties by rational synthetic methods is a major advance in the field of catalyst synthesis and for the development of accurate structure-function relationships in heterogeneous reaction kinetics.     

Synthesis of platinum nanoparticles on substrates of various chemical natures using supercritical carbon dioxide

A method for synthesizing platinum nanoparticles on a dispersed substrate using supercritical carbon dioxide was applied on substrates of various chemical natures: silicon carbide, titanium nitride, and tin dioxide. On all the substrates, materials with narrow uniform platinum nanoparticle size distributions were obtained. The platinum nanoparticle size distribution on each of the substrates was studied. It was shown that the platinum particle sizes are within a narrow range with an average particle size of about 3 nm and scarcely dependent on the chemical nature of the substrate.     

Synthesis of pure colloidal silver nanoparticles with high electroconductivity for printed electronic circuits: the effect of amines on their formation in aqueous media

This paper describes a practical and convenient method to prepare stable colloidal silver nanoparticles for use in printed electronic circuits. The method uses a dispersant and two kinds of reducing agents including 2-(dimethylamino) ethanol (DMAE), which play important roles in the reduction of silver ions in an aqueous medium. The effect of DMAE and dispersant, as well as the factors affecting particle size and morphology are investigated. In the formation of the silver nanoparticles, reduction occurs rapidly at room temperature and the silver particles can be separated easily from the mixture in a short time. In addition, organic solvents are not used. Pure, small and relatively uniform particles with a diameter less than 10 nm can be obtained that exhibit high electroconductivity. The silver nanoparticles are stable, and can be isolated as a dried powder that can be fully redispersed in deionized water. This method of producing colloidal silver nanoparticles will find practical use in electronics applications.     

Self-assembly of organic monolayers on aerosolized silicon nanoparticles

A new method is described for surface functionalization of silicon nanocrystals. Organic monolayers were self-assembled via gas-phase adsorption of amines, alkenes, alkynes, and aldehydes onto the surfaces of aerosolized crystalline silicon nanoparticles of 12.2 nm diameter in an atmospheric pressure tube reactor. Assembly took place within 4 s at temperatures between 200 and 500 degrees C. The extent of adsorption was measured by using tandem differential mobility analysis (T-DMA), an on-line diagnostic method for measuring changes in particle size. Functionalized particles were further characterized by high-resolution transmission electron microscopy and diffuse reflectance Fourier transform infrared spectroscopy. The apparatus described in this work can be used for continuous mass production of functionalized silicon nanoparticles. Moreover, the overall strategy of using T-DMA for monitoring monolayer uptake could be generally applied to study surface processing of other aerosolized nanoparticle systems.     

Construction of simple gold nanoparticle aggregates with controlled plasmon–plasmon interactions

We have developed a colloidal assembly for the study of plasmon–plasmon interactions between gold nanoparticles. Colloidal aggregates of controlled size and interparticle spacing were synthesized on silica nanoparticle substrates. Following the immobilization of isolated gold nanoparticles onto silica nanoparticles, the surfaces of the adsorbed gold nanoparticles were functionalized with 4-aminobenzenethiol. This molecular linker attached additional gold nanoparticles to the ‘parent' gold nanoparticle, forming small nanoparticle aggregates. The optical absorption spectrum of these clusters differed from that of gold colloid in a manner consistent with plasmon–plasmon interactions between the gold nanoparticles.     

Synthesis of Silicon Nanoparticles in Nonthermal Capacitively-Coupled Flowing Plasmas: Processes and Transport

Control of the size and material properties of silicon nanoparticles plays a critical role in optimizing applications using those nanoparticles, such as photovoltaics and biomedical devices. While synthesis of silicon nanoparticles in low temperature plasmas has many attractive features, the basic mechanisms leading to formation of nanoparticles in these plasmas are poorly understood. A two-dimensional numerical model for synthesis of silicon nanoparticles (<5 nm in diameter) in radio frequency (RF) discharges was developed and used to investigate mechanisms for particle growth for Ar/He/SiH₄ gas mixtures. Algorithms for the kinetics of nanoparticle formation were self-consistently embedded into a plasma hydrodynamics simulation to account for nucleation, growth, charging, and transport of nanoparticles. We found that with RF excitation in narrow tubes at pressures of a few Torr, the electric field does not fully confine charged nanoparticles in the axial direction, which then results in a finite residence time of particles in the plasma. We found that because of the high neutral nanoparticle density, coagulation plays a significant role in growth. The model predicts the possibility of synthesizing crystalline silicon nanoparticles under these conditions. Trends in the growth of nanoparticles as a function of power are discussed.