Ultrasonic, chemical stability and preparation of self-assembled fullerene[C60]-gold nanoparticle films

C(60)-functionalized gold nanoparticle films were self-assembled on the reactive surface of glass slides functionalized with 3-aminopropyltrimethoxysilane. The functionalized glass slides were alternately soaked in the solutions containing unmodified C(60) and 4-aminothiophenoxide/hexane thiolate-protected gold nanoparticles. Organic reaction (amination) facilitated the layer-by-layer multilayer film assembly. C(60)-functionalized gold nanoparticle films have grown up to several layers (upto 5 layers were examined) depending on the immersion time. The assembled nanoparticle films were characterized using UV-vis spectroscopy. The chemical stability of C(60)-gold nanoparticle films was studied by monitoring the changes in absorbance after the immersion of the films in acidic solutions. The ultrasonic stability of these nanoparticle films was studied by exposing them to ultrasonic irradiated surrounding, which results in the aggregation of nanoparticles on solid surfaces.     

两种纳米粒子的自组装及表面增强拉曼光谱研究

在氨基硅烷化的单晶硅片表面通过静电自组装技术组装上金和金核铂壳两种纳米粒子,通过改变基底浸泡在溶胶中的时间控制基底上纳米粒子的密度。用扫描电子显微镜(SEM)对基底表面上的形貌进行表征,结果表明纳米粒子呈亚单层二维阵列分布。以吡啶(Py)为探针分子,用波长为632.8 nm的激发光作为激发光源,研究纯金和金铂复合基底上的表面增强拉曼光谱(SERS)行为。数据显示在金纳米粒子之间引入金核铂壳纳米粒子后,Py的两个特征峰的频率没有明显变化,但谱峰的强度却变弱了,其SERS信号衰减最大可至原来的24%。这是由于引入的铂的d态电子使金的等离子体激发猝灭,从而破坏了电磁场增强,使金的SERS信号衰减。     

Preparation of surfactant-stabilized gold nanoparticle–peptide nucleic acid conjugates

A simple, two-step method of producing stable and functional peptide nucleic acid (PNA)-conjugated gold nanoparticles using a surfactant stabilization step is presented. PNA are DNA analogs with superior chemical stability and target discrimination, but their use in metallic nanoparticle systems has been limited by the difficulty of producing stable colloids of nanoparticle–PNA conjugates. In this work, the nonionic surfactant Tween 20 (polyoxyethylene (20) sorbitan monolaurate) was used to sterically shield gold surfaces prior to the addition of thiolated PNA, producing conjugates which remain dispersed in solution and retain the ability to hybridize to complementary nucleic acid sequences. The conjugates were characterized using transmission electron microscopy, dynamic light scattering, and UV–visible absorbance spectroscopy. PNA attachment to gold nanoparticles was confirmed with an enzyme-linked immunoassay, while the ability of nanoparticle-bound PNA to hybridize to its complement was demonstrated using labeled DNA.     

Localization of the electromagnetic field in the vicinity of gold nanoparticles: Surface modification of different substrates

Theoretical predictions and experimental results for nanosized modification of metal (Au), semiconductor (Si), or dielectric (soda lime glass) substrates using near-electromagnetic field enhancement in the vicinity of gold nanoparticles are presented. The near field properties for the system consisting of an isolated gold nanoparticle or nanoparticle aggregate deposited on the substrates, which is irradiated by electromagnetic wave, are investigated using Finite Difference Time Domain Simulation technique. The influence of the substrate material on the near field distribution characteristics is predicted. The results reveal that the field on the substrate surface is enhanced in the three investigated cases, but its spatial distribution and magnitude depend on the substrate material. In the case of the metal and semiconductor substrate the enhanced near field is strongly localized in the vicinity of the contact point with the particle, in an area with diameter smaller than the particle's one. The intensity of the enhanced field on the glass is more than an order of magnitude lower than the case of using silicon substrate. The properties of the near field on the substrate surface also depend on the particle arrangement. For a two-dimensional gold nanoparticle array, when the particles are closely arrayed, the intensity of the enhanced field on the substrate surface is minimal. With the increase of the interparticle distance the near field intensity increases. The validity of the obtained theoretical results is confirmed experimentally.     

Optical Properties of CdS–PVA Nanocomposites

Semiconductor–polymer nanocomposites, with good control over the nanoparticle size and their dispersion within the polymer matrix, can have applications in many optical and luminescent display devices. Cadmium sulphide (CdS) is the most popular semiconductor nanoparticle exhibiting size dependent properties due to its large exciton binding energy and its suitability for large scale production. The nanoparticles need to be passivated against aggregation with suitable capping agents, without sacrificing the desirable properties like transparency and flexibility of the polymer. Cadmium sulphide nanoparticles capped with polyvinyl pyrrolidone (PVP) are synthesized using cadmium nitrate (Cd(NO₃)₂) and hydrogen sulphide (H₂S) as Cd²⁺ and S^2– sources, respectively. CdS particles with sizes in the range of 5–6 nm are prepared in methanol and the solvent is removed using a rotary evaporator. CdS powder is dispersed in polyvinyl alcohol (PVA) solution with dimethyl formamide (DMF) as solvent to get (PVP–CdS)–PVA nanocomposite film of about 0.2 mm thickness. This has been characterized by powder X-ray diffraction (XRD), optical absorption studies, transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and photoluminescence (PL). Particle size does not change due to incorporation in the polymer matrix and the polymer retains its transparency and flexibility. The nanocomposite shows good photoluminescence property with stronger band edge emission than defect related emission. The latter could be quenched completely by optimizing the PVP content. Irradiation of the nanocomposite with 8 MeV electrons at a dose of 100 kGy could effectively quench the defect related emission.     

电场辅助溶解法实现玻璃表面金纳米粒子的形貌控制

贵金属纳米粒子由于其非常独特的光学特性和表面活性, 在光子学、 催化和生物标识等方面都有非常重要的应用. 采用离子溅射和后续热处理相结合的方法在玻璃表面形成了尺寸大约为60-80 nm的单分散的球形金纳米粒子. 在适当的温度条件下, 采用步进式增加的强直流电场, 实现了金纳米粒子的电场辅助溶解过程. 在玻璃表面的不同颜色区域, 初始球形的金纳米粒子溶解成月蚀状形貌. 结合不同颜色区域内金纳米粒子的表面等离子体共振吸收性质和扫描电镜照片, 研究了实验条件对金纳米粒子性质的影响. 结合电场辅助溶解实验过程中的电流-电压特性, 分析了金纳米粒子在强直流电场辅助下溶解的物理过程: 金粒子中动出的电子向阳极的隧穿过程作为开始, 随后是金阳离子向玻璃基体中的传输过程和阴极提供的电子与带有正电荷的金粒子相结合的过程. 详细讨论了电场辅助溶解法实现金纳米粒子形貌控制的物理机制.     

Formation of structures from amorphous metallic nanoparticles by dispersing metal drops continuously charging in an electron beam

The formation of amorphous metal nanoparticles by the method of electrohydrodynamic dispersion is studied. In this method, fine liquid metal drops are generated, charged in an electron beam to an unstable state, and dispersed into nanometer droplets. Rapid cooling of these nanometer droplets results in the formation of amorphous metal nanoparticles. The chief problem in the formation of such particles is that it is difficult to charge molten metal drops to an unstable state, since the bombardment of the drop by an electron beam may cause intense emission of electrons. To overcome this difficulty, the drops are charged by a beam of slow electrons. Charging proceeds in such a way that the electron energy rises with the drop’s charge. It is shown that this method makes it possible to obtain granulated films made up of amorphous metal particles. Copper films with a nanoparticle mean size of 2 nm and a small dimensional variation are prepared.     

Optical characterization of the polymer embedded alloyed bimetallic nanoparticles

A theoretical approach for the calculation of the bimetallic nanoparticles absorption spectra has been developed as an extension of the Mie theory in which nanoparticle dielectric function is found by the weighted linear combination of the dielectric functions for particles made of the corresponding pure metals. In the frame work of the theoretical model an expression for the resonance light absorption frequency were derived taking into account the interband transitions in the dielectric functions. We propose a simple method for the on-line monitoring of the bimetallic nanoparticles composition based on the measurement of the absorption peak position. Elaborated theoretical approach was used to investigate the polymer embedded Ag/Au nanoparticles which were prepared by reducing gold and silver salts (HAuCl4 and AgNO3, respectively) by ethylene glycol in presence of poly(vinyl pyrrolidone) (PVP) at room temperature. Calculated absorption spectra for the Ag/Au nanoscopic systems showed good agreement with the experimental data. Temporal evolution of the Ag/Au nanoparticles has also been investigated by this approach.     

A Novel Ultraviolet Irradiation Technique for Fabrication of Polyacrylamide–metal (M = Au,Pd) Nanocomposites at Room Temperature

Polyacrylamide (PAM)–metal (M = gold, palladium) nanocomposites with metal nanoparticles homogeneously dispersed in the polymer matrix have been prepared via a novel ultraviolet irradiation technique at room temperature, which is based on the simultaneous occurrence of photo-reduction formation of the colloidal metal particles and photo-polymerization of the acrylamide (AM) monomer. The UV–vis absorption spectra and TEM were employed to characterize the M-PAM nanocomposites by different irradiation times. The average sizes of the colloidal gold and palladium particles dispersed in the nanocomposites were calculated by XRD patterns and TEM images. The present method may be extended to prepare other metal–polymer hybrid nanocomposite materials.     

Nanosphere dispersion on a large glass substrate by low dose ion implantation for localized surface plasmon resonance

Dispersing nanospheres on a large glass substrate is the key to fabricate noble metal nanostructures for localized surface plasmon resonance through dispersed nanosphere lithography. This article reports that by modifying the glass surface with low dose ion implantation and successively dip coating the surface with poly(diallyldimethyl ammonium chloride) (PDDA), polystyrene or silica nanospheres can be dispersed on a large glass substrate. Investigation shows that several kinds of ions, such as silicon, boron, argon, and arsenic, can improve the nanosphere dispersion on glass, attributed to the ion bombardment-caused silicon increment. Ion implantation imposes no surface roughness or optical loss to the glass substrate, thus this method is suitable for localized surface plasmon resonance application. Experiments show silicon ion implantation can best disperse the nanospheres. For the gold nanostructures obtained by obliquely evaporating 30 nm of gold film onto the polystyrene nanospheres, which are dispersed on a silicon ion implanted glass substrate, a localized surface plasmon resonance sensitivity of 242 nm/RIU is achieved.     

Preparation of silver-coated glass frit and its application in silicon solar cells

A simple electroless plating process was employed to prepare silver-coated glass frits for solar cells. The surface of the glass frits was modified with polyvinyl-pyrrolidone(PVP) before the electroless plating process. Infrared(IR) spectroscopy,field emission scanning electron microscopy(FESEM), and x-ray diffraction(XRD) were used to characterize the PVP modified glass frits and investigate the mechanism of the modification process. It was found that the PVP molecules adsorbed on the glass frit surface and reduced the silver ions to the silver nanoparticles. Through epitaxial growth, these nanoparticles were uniformly deposited onto the surface of the glass frit. Silicon solar cells with this novel silver coating exhibited a photoelectric conversion efficiency increase of 0.33%. Compared with the electroless plating processes, this method provides a simple route to prepare silver-coated glass frits without introducing impurity ions.     

Fabrication of nano-structured polythiophene nanoparticles in aqueous dispersion

The synthetic route of unsubstituted polythiophene (PT) nanoparticles was investigated in aqueous dispersion via Fe³⁺-catalyzed oxidative polymerization. With this new synthetic method, high conversion of thiophene monomers was obtained with only a trace of FeCl₃. The dispersion state showed that the PT nanoparticles were well dispersed in many polar solvents, compared to non-polar solvents, such as acetone, chloroform, hexane, and ethyl acetate. To compare the photoluminescence properties between PT nanoparticle dispersion and PT bulk polymers, the PL intensities were measured in the same measuring conditions. Further, core–shell poly(styrene/thiophene) (poly(St/Th)) latex particles were successfully prepared by Fe³⁺-catalyzed oxidative polymerization during emulsifier-free emulsion polymerization. The different polymerization rates of each monomer resulted in core–shell structure of the poly(St/Th) latex particles. The PL data of the only crumpled shells gave evidence that the shell component of core–shell poly(St/Th) latex particles is indeed PT, which was corroborated by SEM data. PL intensity of the core–shell poly(St/Th) nanoparticle dispersion was much higher than that of the PT nanoparticle dispersion, due to its thin shell layer morphology, which was explained by the self-absorption effect.     

Synthesis of core–shell nanoparticles with a Pt nanoparticle core and a silica shell

A method to prepare a core–shell structure consisting of a Pt metal core coated with a silica shell (Pt(in)SiO₂) is described herein. A silica shell was grown on poly(vinylpyrrolidone) (PVP)-stabilized Pt nanoparticles 2–3 nm in size through hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) in a water/ethanol mixture with ammonia as a catalyst. This process requires precise control of the reaction conditions to avoid the formation of silica particles containing multiple Pt cores and core-free silica. The length of PVP molecules, water content, concentration of ammonia and Pt nanoparticles in solution were found to significantly influence the core–shell structure. By optimizing these parameters, it was possible to prepare core–shell particles each containing a single Pt nanoparticle with a silica layer coating approximately 10 nm thick.     

Bimetallic Nanoparticles with Exotic Facet Structures via Iodide‐Assisted Reduction of Palladium

Iodide is arguably the most challenging halide to control as a shape‐directing additive in metal nanoparticle synthesis and the addition of iodide during bimetallic nanoparticle growth often leads to inhomogeneously stellated products. Through judicious control of low micromolar concentrations of iodide ions in solution in a seed‐mediated approach, alloyed gold–palladium tetradecapod nanoparticles have been synthesized with a mixture of both well‐defined convex and concave surfaces. Notably, these particles are uniform and symmetrical, and this unusual combination of convex and concave features in a single nanostructure is not simply an artifact of intersecting spikes, as would be the case with stellated particles. Further, an important new role for iodide in catalyzing the reduction of palladium ions is identified, particularly at the edge sites of the growing gold nanoparticles. This differs from the commonly accepted theory that iodide slows metal ion reduction, and thus opens up promising new routes to the synthesis of other bimetallic nanoparticles with exotic shapes and surface structures.     

Electrospinning method for the preparation of silver chloride nanoparticles in PVP nanofiber

It has been successfully developed by the electrospinning technology that AgCl nanoparticles were incorporated into polymer fiber. In this paper, we chose poly(vinyl pyrrolidone) (PVP) because it was not only a good material for electrospinning but also it was excellent capping reagent of various metal nanoparticles. The silver ions interacted with the carbonyl groups in the PVP molecules. The formation of AgCl nanoparticles inside the PVP were carried out via the reaction of silver ions and HCl. TEM proved that most of the AgCl nanoparticles were uniformly dispersed in the PVP fibers.     

Hybridization of surface-modified metal nanoparticles and a resin

Mercapto-terminated linear polymers, which were prepared by a reversible addition-fragmentation chain transfer (RAFT) technique, were used to modify metal nanoparticle surfaces. Au and Ag nanoparticles which are approximately 3–6 nm were used. This modification resulted in easy dispersion of the nanoparticles in polymer resins by simple mixing. The quality of the dispersion was confirmed by UV–Vis spectroscopy and transmission electron microscopy.     

Dispersion stability of nanoparticles in ecotoxicological investigations: the need for adequate measurement tools

One of the main challenges in nanoecotoxicological investigations is in the selection of the most suitable measurement methods and protocols for nanoparticle characterisation. Several parameters have been identified as being important as they govern nanotoxicological activity, with some parameters being better defined than others. For example, as a parameter, there is some ambiguity as to how to measure dispersion stability in the context of ecotoxicological investigations; indeed, there is disagreement over which are the best methods to measure nanoparticle dispersion stability. The purpose of this article is to use various commercially available tools to measure dispersion stability and to understand the information given by each tool. In this study, CeO₂ was dispersed in two different types of media: de-ionised water and electrolyte-containing fish medium. The DLS mean particle size of freshly dispersed sample in DI water was ~200 nm in diameter. A visual sedimentation experiment showed that nanoparticle dispersion made in the fish medium was less stable compared to corresponding dispersion in de-ionised water. Stability of these dispersions was monitored using various techniques, for a period of 3 days. Our findings have shown that dispersion stability can be suitably assessed by monitoring: (a) surface charge, (b) sedimentation events and (c) presence of agglomerates, through time. The majority of techniques employed here (zeta potential, particle size via DLS, fluorescence and UV–Vis spectroscopy and SEM) were shown to provide useful, complementary information on dispersion stability. Nanoparticle Tracking Analysis (NTA) provides useful, quantitative information on the concentration of nanoparticles in suspension, but is limited by its inability to accurately track the motion of large agglomerates found in the fish medium.     

Effects of iron oxide nanoparticles on polyvinyl alcohol: interfacial layer and bulk nanocomposites thin film

Iron oxide (α-phase) nanoparticles with coercivity larger than 300 Oe have been fabricated at a mild temperature by an environmentally benign method. The economic sodium chloride has been found to effectively serve as a solid spacer to disperse the iron precursor and to prevent the nanoparticles from agglomeration. Higher ratios of sodium chloride to iron nitrate result in smaller nanoparticles (19 nm for 20:1 and 14 nm for 50:1). The presence of polyvinyl alcohol (PVA) limits the particle growth (15 nm for 20:1 and 13 nm for 50:1) and favors nanoparticle dispersion in polymer matrices. Obvious physicochemical property changes have been observed with PVA attached to the nanoparticle surface. With PVA attached to the nanoparticle surface, the nanoparticles are found not only to increase the PVA cross-linking with an increase in melting temperature but also to enhance the thermal stability of the PVA. The nanoparticles are observed to be uniformly dispersed in the polymer matrix. Scanning electron microscopy (SEM) microstructure also shows an intermediate phase with a strong interaction between the nanoparticles and the polymer matrices, arising from the hydrogen bonding between the PVA and hydroxyl groups on the nanoparticle surface. The addition of nanoparticles favors the cross-linkage of the bulk PVA matrices, resulting in a higher melting temperature, and an enhanced thermal stability of the polymer matrix.     

Electrochemical and surface characterisation of gold nanoparticle decorated multi-walled carbon nanotubes

A novel type of gold nanoparticle/multi-walled carbon nanotube (AuNP/MWCNT) composite electrodes is presented. The electrochemical reduction of oxygen on these hybrid electrodes was studied using the rotating disk electrode (RDE) method. The AuNP/MWCNT nanocomposites were prepared by sputter deposition of gold in argon atmosphere on MWCNTs followed by heat-treatment of the catalyst at different temperatures. High-resolution scanning electron microscopy (HR-SEM), glancing incidence angle X-ray powder diffraction (GIXRD) and small-angle X-ray scattering (SAXS) techniques were employed to characterise the surface structure and morphology of catalyst materials. Au nanoparticles with diameter around 20 nm were dispersed at the tips and on the sidewalls of nanotubes. Electrochemical measurements were performed to demonstrate the electrocatalytic properties of the composite catalysts towards O₂ reduction in acid media. The successful preparation of AuNP/MWCNT nanocomposites by magnetron sputtering opens up the possibility of making an efficient dispersion of nanoparticles for electrocatalyst design.     

Preparation of silver nanoparticles by laser ablation in polyvinylpyrrolidone solutions

We performed laser ablation of a silver plate in polyvinylpyrrolidone (PVP) aqueous solutions to prepare silver nanoparticles. Secondary laser irradiation onto the prepared colloidal solutions was also carried out. It was revealed that the formation efficiency was increased by addition of PVP as well as the stability of nanoparticles. The result of shadowgraph measurements suggested that the increased ablation efficiency by PVP is attributable to increased secondary etching efficiency by the solvent-confined plasma toward the silver plate. On the other hand, the size decrease of the nanoparticles by addition of PVP was more remarkable during the secondary irradiation process than in the laser ablation (nanoparticle preparation) process. This result indicates that emitted materials interact less sufficiently with PVP molecules in the laser ablation process than in the secondary laser irradiation process.