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.     

Morphology study of gold-chitosan nanocomposites

Gold nanoparticles were prepared in the presence of chitosan via reduction of HAuCl4 with sodium borohydride. The gold-chitosan nanocomposite was formed by adsorbing chitosan molecules onto the gold nanoparticle surfaces. The resulting gold nanoparticles were characterized by transmission electron microscopy and UV-vis spectroscopy. Morphology of gold-chitosan nanocomposite films was investigated by polarized optical microscopy. The morphology of chitosan crystal cast from the prepared nanocomposite was much different from that cast from chitosan solution due to the possible nucleation of gold nanoparticles. A branched-like structure or a cross-linked needle-like structure could be formed in nanocomposite films with different casting volumes.     

Aerosol assisted chemical vapor deposition using nanoparticle precursors: a route to nanocomposite thin films

Gold nanoparticle and gold/semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapor deposition (CVD). A preformed gold colloid in toluene was used as a precursor to deposit gold films onto silica glass. These nanoparticle films showed the characteristic plasmon absorption of Au nanoparticles at 537 nm, and scanning electron microscopic (SEM) imaging confirmed the presence of individual gold particles. Nanocomposite films were deposited from the colloid concurrently with conventional CVD precursors. A film of gold particles in a host tungsten oxide matrix resulted from co-deposition with [W(OPh)(6)], while gold particles in a host titania matrix resulted from co-deposition with [Ti(O(i)Pr)(4)]. The density of Au nanoparticles within the film could be varied by changing the Au colloid concentration in the original precursor solution. Titania/gold composite films were intensely colored and showed dichromism: blue in transmitted light and red in reflected light. They showed metal-like reflection spectra and plasmon absorption. X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis confirmed the presence of metallic gold, and SEM imaging showed individual Au nanoparticles embedded in the films. X-ray diffraction detected crystalline gold in the composite films. This CVD technique can be readily extended to produce other nanocomposite films by varying the colloids and precursors used, and it offers a rapid, convenient route to nanoparticle and nanocomposite thin films.     

Nanocomposite electrode materials based on poly(3,4-ethylenedioxythiophene) with incorporated gold and palladium: Preparation and morphology study

Chemical deposition of ultrafine gold and palladium particles into poly(3,4-ethylenedioxythiophene) matrix has yielded the metal-containing polymer composites. Their structure has been studied as affected by duration of reduced polymer immersion into the metal salts solution, and by concentration of the latter. Morphology features of the composite films (size and concentration of metal particles) have been elucidated by scanning and transmission electron microscopy. The mixed clusters have been formed predominantly in the course of preparation of bimetal composite films via sequential deposition of gold and palladium; the isolated palladium clusters nucleate slower due to the gold-palladium alloys formation. Longer deposition of the metals leads to increase in the nanoparticles size and their concentration in the composite. Properties of the prepared materials have been demonstrated using the model electrochemical reactions.     

Templated growth of smart nanocomposite thin films: Hybrid aerosol assisted and atmospheric pressure chemical vapour deposition of vanadyl acetylacetonate,auric acid and tetraoctyl ammonium bromide

Hybrid aerosol assisted and atmospheric pressure chemical vapour deposition methodology has been utilised to produce nanocomposite thin films of gold nanoparticles and vanadium dioxide from vanadyl acetylacetonate and auric acid. The addition of tetraoctyl ammonium bromide (TOAB) to the precursor solution gave control of the size and distribution of gold nanoparticles in the vanadium oxide matrix. These reactions led to vanadium dioxide films with reduced crystallite sizes and enhanced thermochromic properties. The films were analysed by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Their optical and thermochromic behaviour was also determined. This hybrid method shows great potential for the production of nanocomposite thin films with good physical properties.     

Aggregation of photolytic gold nanoparticles at the surface of chitosan films

Formation and aggregation of photolytic gold nanoparticles at the surface of chitosan (CTO) films have been investigated. When thin films of chloroauric acid salt of CTO were irradiated with UV light in wet air at room temperature for 10 min, gold nanoparticles of approximately 10 nm size are formed at the film surface. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize gold nanoparticles at the film surface. The shift of Au(4f) peak to the higher energy side and broadening of full width at half-maximum in the XPS spectrum are the direct evidence of the existence of gold atoms and small clusters in the early stage of photolysis. According to FE-SEM observation, growth in the particle diameter and aggregation of nanoparticles were observed after prolonged irradiation, and, finally, the film surface was densely covered with gold particles of 20-100-nm size. Gold atoms and clusters could move in the film and precipitate to the irradiated surface. Chemical composition analysis further suggests that gold particles at the surface are covered with an ultrathin CTO layer, which is partly oxidized by oxygen and chlorinated by chlorine during photochemical reactions.     

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene with microsphere sizes of 100, 300, 500, and 1410 nm under the action of monochromatic light with an excitation wavelength of 254 nm was studied. Preliminary irradiation of the polymer dispersion induces formation of gold particles under dark conditions. Dependences of gold nanoparticles formation on the duration of preliminary polymer irradiation and concentration of introduced HAuCl₄ aqueous solution were determined. A mechanism of the polystyrene-assisted formation of gold nanoparticles was proposed. The size and structure of gold nanoparticles were determined.     

Gold nanoparticle embedded, self-sustained chitosan films as substrates for surface-enhanced Raman scattering

In this work, self-sustained, biocompatible, biodegradable films containing gold nanostructures have been fabricated for potential application in nanobioscience and ultrasensitive chemical and biochemical analysis. We report a novel synthesis of gold nanoparticles mediated by the biopolymer chitosan. Self-supporting thin films are formed from the resultant gold-chitosan nanocomposite solutions and characterized by UV-visible surface plasmon absorption, transmission electron microscopy, atomic force microscopy, infrared absorption, and Raman scattering measurements. Results demonstrate control over the size and distribution of the nanoparticles produced, which is promising for several applications, including the development of biosensors. As a proof of principle, we demonstrate that gold-chitosan films can be employed in trace analysis using surface-enhanced Raman scattering.     

Lamellar multilayer hexadecylaniline-modified gold nanoparticle films deposited by the Langmuir-Blodgett technique

Organization of hexadecylaniline (HDA)-modified colloidal gold particles at the air-water interface and the formation thereafter of lamellar, multilayer films of gold nanoparticles by the Langmuir-Blodgett technique is described in this paper. Formation of HDA-capped gold nanoparticles is accomplished by a simple biphasic mixture experiment wherein the molecule hexadecylaniline present in the organic phase leads to electrostatic complexation and reduction of aqueous chloroaurate ions, capping of the gold nanoparticles thus formed and phase transfer of the now hydrophobic particles into the organic phase. Organization of gold nanoparticles at the air-water interface is followed by surface pressure—area isotherm measurements while the formation of multilayer films of the nanoparticles by the Langmuir-Blodgett technique is monitored by quartz crystal microgravimetry, UV-Vis spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy.     

Microwave-induced synthesis of highly dispersed gold nanoparticles within the pore channels of mesoporous silica

Highly dispersed gold nanoparticles have been incorporated into the pore channels of SBA-15 mesoporous silica through a newly developed strategy assisted by microwave radiation (MR). The sizes of gold are effectively controlled attributed to the rapid and homogeneous nucleation, simultaneous propagation and termination of gold precursor by MR. Diol moieties with high dielectric and dielectric loss constants, and hence a high microwave activation, were firstly introduced to the pore channels of SBA-15 by a simple addition reaction between amino group and glycidiol and subsequently served as the reduction centers for gold nanoparticles. Extraction of the entrapped gold from the nanocomposite resulted in milligram quantities of gold nanoparticles with low dispersity. The successful assembly process of diol groups and formation of gold nanoparticles were monitored and tracked by solid-state NMR and UV-vis measurements. Characterization by small angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the incorporation of gold nanoparticles would not breakup the structural integrity and long-range periodicity of SBA-15. The gold nanoparticles had a narrow size distribution with diameters in the size range of 5-10 nm through TEM observation. The average particles size is 7.9 nm via calculation by the Scherrer formula and TEM measurements. Nitrogen adsorption and desorption isotherms gave further evidence that the employed method was efficient and gold nanoparticles were successfully incorporated into the pore channels of SBA-15.     

Green synthesis of gold-chitosan nanocomposites for caffeic acid sensing

In this work, colloidal gold nanoparticles (AuNPs) stabilized into a chitosan matrix were prepared using a green route. The synthesis was carried out by reducing Au(III) to Au(0) in an aqueous solution of chitosan and different organic acids (i.e., acetic, malonic, or oxalic acid). We have demonstrated that by varying the nature of the acid it is possible to tune the reduction rate of the gold precursor (HAuCl(4)) and to modify the morphology of the resulting metal nanoparticles. The use of chitosan, a biocompatible and biodegradable polymer with a large number of amino and hydroxyl functional groups, enables the simultaneous synthesis and surface modification of AuNPs in one pot. Because of the excellent film-forming capability of this polymer, AuNPs-chitosan solutions were used to obtain hybrid nanocomposite films that combine highly conductive AuNPs with a large number of organic functional groups. Herein, Au-chitosan nanocomposites are successfully proposed as sensitive and selective electrochemical sensors for the determination of caffeic acid, an antioxidant that has recently attracted much attention because of its benefits to human health. A linear response was obtained over a wide range of concentration from 5.00 × 10(-8) M to 2.00 × 10(-3) M, and the limit of detection (LOD) was estimated to be 2.50 × 10(-8) M. Moreover, further analyses have demonstrated that a high selectivity toward caffeic acid can be achieved without interference from catechin or ascorbic acid (flavonoid and nonphenolic antioxidants, respectively). This novel synthesis approach and the high performances of Au-chitosan hybrid materials in the determination of caffeic acid open up new routes in the design of highly efficient sensors, which are of great interest for the analysis of complex matrices such as wine, soft drinks, and fruit beverages.     

Solvent effect on the structure of composite films obtained from chitosan solutions with a precursor of silver nanoparticles

The solvent effect on the structure of nanocomposite films cast from chitosan solutions with AgNO₃ as a precursor of silver nanoparticles was studied for the first time. The size and concentration of silver nanoparticles in the chitosan matrix can be controlled by varying the chitosan-dissolving ability of the solvent with carbonic acid.     

Preparation and characterization of metal-chitosan nanocomposites

Various metal-chitosan nanocomposites were synthesized, including silver (Ag), gold (Au), platinum (Pt), and palladium (Pd) in aqueous solutions. Metal nanoparticles were formed by reduction of corresponding metal salts with NaBH4 in the presence of chitosan. And chitosan molecules adsorbing onto the surface of as-prepared metal nanoparticles formed the corresponding metal-chitosan nanocomposites. Transmission electron microscopy (TEM) images and UV-vis spectra of the nanocomposites revealed the presence of metal nanoparticles. Comparison of all the resulting particles size, it shows that silver nanoparticles are much larger than others (Au, Pt and Pd). In addition, the difference in particles size leads to develop different morphologies in the films cast from prepared metal-chitosan nanocomposites. Polarized optical microscopy (POM) images show a batonet-like structure for Ag-chitosan nanocomposites film, while for the films cast from other metal (Au, Pt, and Pd)-chitosan nanocomposites, some branched-like structures with a few differences among them were observed under POM observation.     

乳液聚合法制备纳米金/聚苯乙烯复合粒子

以氯金酸为前驱体,十二烷基硫醇和硼氢化钠分别作为稳定剂和还原剂,采用相转移法制备了单分散的金纳米粒子.将金纳米粒子通过乳液聚合的方法制备了纳米金/聚苯乙烯复合粒子.通过紫外-可见吸收光谱(UV-Vis)研究了纳米金和纳米金/聚苯乙烯复合粒子的光吸收特性,使用傅立叶变换红外光谱(FT-IR)、X射线衍射(XRD)、透射电子显微镜(TEM)和动态光散射(DLS)对产物的组成、晶体结构、形貌、以及粒径进行了表征.结果表明,复合粒子为粒径分布较窄的球形,其中的金纳米粒子为面心立方结构.热失重分析(TGA)说明制备的纳米金/聚苯乙烯复合粒子具有很好的热稳定性.     

Gold nanoparticles fabricated by pulsed laser ablation in supercritical CO2

Nanosecond pulsed laser ablation (PLA) of gold plate with an excitation wavelength of 532?nm was carried out in supercritical CO₂ (scCO₂) to fabricate gold nanoparticles. Surface morphology of the gold plate after irradiation and the crater depth after PLA were observed by scanning electron microscopy and laser scanning microscopy, while extinction spectra of gold nanoparticles collected in the glass slide was measured by UV?CVis spectrophotometer. The gold plate was ablated at various scCO₂ densities and irradiation times at constant temperature of 40??C. The ablation was also conducted at atmospheric condition with air to evaluate the environmental dependence of ablation. Both surface morphology of the irradiated gold plate and crater depth formation were significantly affected by the changes in scCO₂ density, the surrounding environment, and irradiation time. As expected, the increasing scCO₂ density resulted in a deeper ablation crater, however, the deepest crater was obtained at a density of 0.63?g/cm³ or pressure of 10?MPa. Gold nanoparticles generated by PLA in scCO₂ have been confirmed at the spectra band near 530?nm.     

Effect of pressure on the structure of composite chitosan films obtained from solutions in carbonic acid

The effect of pressure in solutions of chitosan in carbonic acid with the AgNO₃ precursor on the structure of cast nanocomposite films with silver nanoparticles has been studied for the first time. The size of silver nanoparticles can be controlled by varying pressure in carbonic acid.     

Correcting for a density distribution: particle size analysis of core-shell nanocomposite particles using disk centrifuge photosedimentometry

Many types of colloidal particles possess a core-shell morphology. In this Article, we show that, if the core and shell densities differ, this morphology leads to an inherent density distribution for particles of finite polydispersity. If the shell is denser than the core, this density distribution implies an artificial narrowing of the particle size distribution as determined by disk centrifuge photosedimentometry (DCP). In the specific case of polystyrene/silica nanocomposite particles, which consist of a polystyrene core coated with a monolayer shell of silica nanoparticles, we demonstrate that the particle density distribution can be determined by analytical ultracentrifugation and introduce a mathematical method to account for this density distribution by reanalyzing the raw DCP data. Using the mean silica packing density calculated from small-angle X-ray scattering, the real particle density can be calculated for each data point. The corrected DCP particle size distribution is both broader and more consistent with particle size distributions reported for the same polystyrene/silica nanocomposite sample using other sizing techniques, such as electron microscopy, laser light diffraction, and dynamic light scattering. Artifactual narrowing of the size distribution is also likely to occur for many other polymer/inorganic nanocomposite particles comprising a low-density core of variable dimensions coated with a high-density shell of constant thickness, or for core-shell latexes where the shell is continuous rather than particulate in nature.     

Metal nanoparticle formation on layer silicate lamellae

Nanoparticles (Ag, Pd) were prepared by heterogeneous nucleation on the interlayer space of layered montmorillonite and kaolinite minerals in aquatic dispersion. Interlamellar incorporation of nanoparticles was monitored by X-ray diffraction and verified by transmission electron microscopy (TEM). After the reduction of adsorbed metal ions, a new Bragg reflection appeared, proving the formation of nanoparticles in the interlamellar space of clay mineral. Lamellar structure of layered silicates is partly destroyed by the particle formation. TEM images showed that larger nanoparticles were formed by UV irradiation and hydrazine hydrate than in the case of reduction by NaBH₄. Aqueous solutions of polyvinyl pyrrolidone and clay minerals were used for the stabilization of Pd° nanoparticles. The size of particles generated on the surface of clay minerals by heterogeneous nucleation increased with increasing metal concentration. When polymer is added to this system, particle size can be decreased by increasing polymer concentration. In this case, the particles are stabilized by the concerted action of the support and the macromolecule. The polymers promoted intercalation of nanoparticles into the clay mineral. In the absence of nanoparticles, the intercalation of polymers was significantly less extensive.     

Green synthesis of antibacterial chitosan films loaded with silver nanoparticles

An eco-friendly chemical reduction method was successfully used for the preparation of chitosan (CTS) composite films loaded with silver nanoparticles (AgNPs) by self assembly method using poly(ethylene glycol) as both reducing and stabilizing agent. UV-Vis spectra of the prepared chitosan loaded silver nanoparticles (CTSLAg) films reveal that full reduction of silver ions to silver nanoparticles takes place at 90 °C. The effect of reaction conditions on the silver nanoparticles formation was investigated using UV-Vis spectrophotometer. The morphology of the films was tested by scanning electron microscopy (SEM). The DSC curves showed that the CTSLAg film had a favorable compatibility and heat stability. AgNPs were confirmed by XRD and UV-Vis spectroscopy. The TEM findings revealed that the silver nanoparticles synthesized were spherical in shape with uniform dispersal, and by increasing CTS:PEG ratio larger silver nanoparticles could be obtained. The results of antibacterial study reveal that the prepared nanocomposite films exhibited potential inhibition.     

Synthesis and properties of polyimide/silver nanocomposite containing dibenzalacetone moiety in the main chain

A new thermally stable polyimide–silver nanocomposite containing dibenzalacetone moiety in the main chain was synthesized by a convenient ultraviolet irradiation technique. A precursor such as AgNO₃ was used as the source of the silver nanoparticles. Polyimide 6 as a source of polymer was prepared by polycondensation reaction of 2,5-bis(4-aminobenzylidene) cyclopentanone 4 with pyromellitic anhydride 5 in m-cresol solution and in the presence of iso-quinoline as a base. The resulting nanocomposite film was characterized by FTIR spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Thermal gravimetric analyses (TGA), differential gravimetric analyses (DTG) and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) confirmed the formation and dispersion of silver nanoparticles in polymer matrix having average size of ～20 nm. Incorporation of inorganic metal silver nanoparticles has improved the thermal behavior of the nanocomposite film as compared to pure polyimide film. Also 2,5-bis(4-aminobenzylidene) cyclopentanone 4 was synthesized by using a two-step reaction.