Properties of polypropylene nanocomposites containing silver nanoparticles

Silver/polypropylene (PP) nanocomposites containing silver nanoparticles smaller than 10 nm were prepared using a new synthetic method. AgNO3 crystals were dissolved into hydrophilic domain of polyoxyethylene maleate-based surfactant (PEOM), which gives self-assembly nano-structures. The AgNO3 in the nano-domains of PEOM was reduced by NaBH4 to form nanoparticles. The colloidal solutions with silver nanoparticles were diluted with ethanol and were mixed with PP pellets. Silver nanocomposites were prepared by extrusion compounding process after drying the pellets. Contents of silver nanoparticles dispersed within PP resin were changed from 100 to 1000 ppm. Formation of silver nanoparticles within PP was confirmed by UV-Vis spectroscopy and TEM. Size and distribution of dispersed silver nanoparticles were also measured by TEM. Silver/PP nanocomposites films showed not only improved thermal stability but also increased mechanical properties compared to neat PP film. Tensile properties of PP nanocomposites were largely improved compared with neat PP resin, and elongation increased also by 175% for the nanocomposites containing 1000 ppm silver nanoparticles.     

基于毛竹半纤维素的银纳米粒子的绿色合成

直接以碱溶性毛竹半纤维素为稳定剂、葡萄糖为还原剂,在水介质中绿色合成银纳米粒子,讨论了合成条件对银纳米粒子的形成和储存稳定性的影响,表征了银纳米粒子-半纤维素复合物经热处理后获得的Ag-C复合物的物理化学特性,并讨论了银纳米粒子的可能形成机理。在恒定其他反应条件下,延长反应时间会有更多银纳米粒子生成,但过度延长反应时间会使银纳米粒子发生团聚而生成大颗粒的粒子;高的葡萄糖浓度、反应温度和初始半纤维素用量会加快银纳米粒子的生成。银纳米粒子的平均粒径和粒径分布范围均随半纤维素用量的增大而减小,而银纳米粒子在4℃的储存稳定性随半纤维素用量的增大而增强。银纳米粒子-半纤维素复合物在空气气氛中300℃热处理1h后获得的Ag-C复合物中同时存在金属态的银和氧化态的银。半纤维素中呈电负性的大量自由羟基和少量羧基可能对银纳米粒子的形成起至关重要的作用。     

前驱物和表面活性剂对等离子体电化学法制备银纳米颗粒的影响

利用等离子体电化学法成功制备出银纳米颗粒,并通过局域表面等离子共振效应对颗粒的生长过程进行实时监测,研究了表面活性剂的浓度、种类和前驱物浓度对银纳米颗粒制备的影响。研究结果表明:增大前驱物或表面活性剂浓度对Ag;还原均有促进作用;与聚乙烯吡络烷酮(PVP)和十六烷基三甲基溴化铵(CTAB)相比较,十二烷基硫酸钠(SDS)作为表面活性剂,在相同时间内,生成的银纳米颗粒数量更多,尺寸和形状分布更均匀。     

Polyelectrolyte assisted silver nanoparticles synthesis and thin film formation

Silver nanoparticles were prepared by the reduction of silver salts with sodium borohydride and capped with a copolymer of styrene sulfonate and maleic monomers. The synthesized nanoparticles were then deposited on a glass substrate using the layer-by-layer deposition technique in alternance with polycationic poly(diallyl-dimethylammonium chloride) PDADMAC. The synthesis of the silver nanoparticles as well as the layer-by-layer deposition with PDADMAC was easily monitored by UV–Vis spectroscopy due to the strong plasmon absorbance at 400 nm of the silver nanoparticles. Our study shows that increasing the concentration ration between the co-polyelectrolyte and silver nitrate has a negative effect on the size distribution of the resulting silver nanoparticles. For the layer-by-layer assembly, the PSS-co-Maleic was found to be a good capping agent since it allows later the formation of uniform thin films when deposited with PDADMAC. A linear increase in absorbance as a function of the number of deposited layers was observed.     

纳米银粒子在微乳液中的制备及其抗菌性能

在以二丁酸二异辛酯磺酸钠为表面活性剂、异辛烷为油相形成的W／O型微乳体系中,以AgNO3为银源、抗坏血酸为还原剂,讨论了AgNO3浓度、抗坏血酸浓度以及水核半径（W）对制备纳米银粒子的影响。利用紫外一可见光谱分析（UV-Vis）、透射电镜（TEM）和纳米粒度仪对制得的纳米银进行表征。结果表明,在AgNO3浓度为0．2mol／L,抗坏血酸浓度为0．2mol／L,W值为10的条件下,得到大小为10nm左右,单分散性好的均匀球状纳米银溶胶。抗菌性能测试表明,当纳米银粒子质量浓度为10μg／mL时,对大肠杆菌的杀菌率达98％以上。     

One-step synthesis of silver nanoparticles at the air-water interface using different methods

Silver nanoparticles were synthesized in a one-step process at the air-AgNO(3) aqueous solution interface under Langmuir monolayers of 5,10,15,20-tetra-4-oxy(2-stearic acid) phenyl porphyrin (TSPP) at room temperature by using different methods including UV-light irradiation, ambient light irradiation, and formaldehyde gas reduction. It was found that parallel aligned one-dimensional (1D) chains composed of discrete silver nanoparticles with the size of 3-5?nm were formed under UV-light irradiation for a short time, while large areas of uniform silver spherical nanoparticles were formed under natural daylight illumination for several days or by formaldehyde gas treatment for several hours. The average size of the spherical nanoparticles ranges from 6.88 ± 0.46 to 11.10 ± 1.47?nm, depending on the experimental conditions. The 1D chains formed under UV-light irradiation result from the templating effect of parallel aligned linear supramolecular arrays formed by TSPP at the air-water interface, and rapid nucleation and growth of the nanoparticles. The formation of the uniform silver nanoparticles under daylight illumination or by formaldehyde gas treatment, however, should be ascribed to a kinetically controlled growth process of the nanoparticles.     

Effect of biologically synthesised silver nanoparticles on Staphylococcus aureus biofilm quenching and prevention of biofilm formation

The development of green experimental processes for the synthesis of nanoparticles is a need in the field of nanotechnology. In the present study, the authors reported rapid synthesis of silver nanoparticles using fresh leaves extract of Cymbopogan citratus (lemongrass) with increased stability. The synthesised silver nanoparticles were found to be stable for several months. UV-visible spectrophotometric analysis was carried out to assess the synthesis of silver nanoparticles. The synthesised silver nanoparticles were further characterised by using nanoparticle tracking analyser (NTA), transmission electron microscope (TEM) and energy-dispersive x-ray spectra (EDX). The NTA results showed that the mean size was found to be 32?nm. Silver nanoparticles with controlled size and shape were observed under TEM micrograph. The EDX of the nanoparticles confirmed the presence of elemental silver. These silver nanoparticles showed enhanced quorum quenching activity against Staphylococcus aureus biofilm and prevention of biofilm formation which can be seen under inverted microscope (40X). In the near future, silver nanoparticles synthesised using green methods may be used in the treatment of infections caused by a highly antibiotic resistant biofilm.     

Synthesis of silver nanoparticles from carboxylate precursors under hydrogen pressure

A direct, high yield synthesis for preparing narrow-size silver nanoparticles by decomposition of silver carboxylate precursor under H₂ pressure (3 bars) in solution is reported. The method corresponds to that for nanoparticles synthesised by thermal decomposition of carboxylic acid silver salts, but is faster, reproducible, versatile, and easier to control. Most of carboxylate groups are reprotonated upon the presence of dihydrogen and subsequent reduction of Ag⁺ produces spherical particles of dimensions 4–6 nm. The IR studies indicate that aliphatic carboxylates chemisorb on the nanoparticle surface with the two oxygen atoms coordinated mostly symmetrically and forming bridging bidentate Ag–O bonds. This implies strong interactions between the surfactant and Ag nanoparticle and enhances the stability of Ag colloid. There are some sites yet, probably at vertex or facet atoms of the nanoparticle, which form linkages of chelating bidentate or ionic character. Silver particles can be additionally capped in situ either by aliphatic primary amines or thiols forming mixed carboxylate/amine or carboxylate/thiol protecting monolayer. It is demonstrated that coordination of the second ligand adjusts physicochemical properties of nanoparticles. In the dual passivating system both amine and thiol were found to be tightly bounded to the silver nanoparticle surface.     

PVP表面修饰不同形貌金银纳米粒子研究现状

聚乙烯吡咯烷酮(PVP)是一种重要的工业化大分子表面活性剂,由于其大分子结构的特殊性及生物适应性,使得PVP在制备金属纳米粒子过程中得到了广泛应用。近年来,有大量关于以PVP为大分子表面修饰剂制备不同形貌金属纳米粒子的文献报道。文中综述了以PVP为表面修饰剂,分别以乙二醇、乙醇、N,N-二甲基甲酰胺及水为溶剂,通过溶剂和PVP自身的还原作用,在不同反应条件下制备不同形貌金、银纳米粒子的研究现状,提出了不同溶剂体系中不同形貌金属纳米粒子的形成机理研究是未来该领域要解决的主要问题。     

Low-current resistance spot welding of pure copper using silver oxide paste

Silver oxide particles were used as an insert material to reduce the current necessary for resistance spot welding of pure copper plates. To form a conduction path for successful bonding, silver-oxide particles were reduced before bonding by preheating with a reducing solvent at 120 °C for 3 min to cover the particles with silver nanoparticles. At 2200 A, bonding could be achieved with silver-oxide particles, whereas bonding was not successful in welding experiments conducted without insert materials or with fine silver particles. Bonding was accomplished through the formation of a dense sintered layer. When such silver oxide particles are used for resistance spot welding, the joining is achieved by the high sinterability of the generated silver nanoparticles.     

A green method for synthesis of silver nanodendrites

A simple, green method was developed for the synthesis of silver nanodendrites by an aqueous chemical route. This method involves the reduction of silver nitrate with absolute alcohol using polyvinyl pyrrolidone (PVP) as the surfactant. UV–vis absorption spectra, X-ray diffraction patterns (XRD) and energy dispersive spectrometry (EDS) suggest the formation of Ag nanoparticles. Transmission electron microscopy (TEM) images show the shape and sizes of the nanoparticles. During the synthesis, it was found that the morphology and size distribution of the as-prepared silver nanoparticles varied with the concentration of the precursor metal salts, reaction time and surfactant ratios. The formation mechanism of Ag nanodendrites was determined based on the investigation of the above reaction parameters. Simple methods, nontoxic chemicals and environmentally benign solvents make this synthesis ideally suited for industrial production.     

Silver nanoparticles: Large scale solvothermal synthesis and optical properties

Silver nanoparticles have been successfully synthesized by a simple and modified solvothermal method at large scale using ethanol as the refluxing solvent and NaBH₄ as reducing agent. The nanopowder was investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), UV-visible and BET surface area studies. XRD studies reveal the monophasic nature of these highly crystalline silver nanoparticles. Transmission electron microscopic studies show the monodisperse and highly uniform nanoparticles of silver of the particle size of 5 nm, however, the size is found to be 7 nm using dynamic light scattering which is in good agreement with the TEM and X-ray line broadening studies. The surface area was found to be 34.5 m²/g. UV-visible studies show the absorption band at ∼425 nm due to surface plasmon resonance. The percentage yield of silver nanoparticles was found to be as high as 98.5%.     

Facile chemical synthesis of nano-silver powders for printable electronics applications

In this article, a simple and reproducible technique for the synthesis of silver nanoparticles in organic phase without using external reducing agents is reported. The organic phase contains silver acetate as precursor, oleic acid and oleyl amine as capping molecules and diphenyl ether as solvent. Monodispersed silver nanoparticles with an average size of 5?nm could be easily synthesised at large scale and it was possible to isolate the particles suitable for electronics applications. The formation of silver nanoparticles has been characterised in terms of optical absorption, transmission electron microscopy images and small-angle X-ray scattering. Recovered silver nanoparticles reveal X-ray diffraction of a well grown-up fcc-Ag lattice. Chemical and thermal characterisations of silver nanopowders were carried out using X-ray photoelectron spectroscopy and thermogravimetric analysis, respectively. For the latter purpose, concentrated dispersions of silver nanoparticles were prepared and used for depositing uniform thin layers. Thin films were sintered at low temperature to obtain conductive films and the films were characterised using scanning electron microscope. Electrical conductivity of the conductive films was in the range 2–3?×?10⁴?S?cm^?1.     

Synthesis, characterization, and antibacterial activity of silver-doped silica nanocomposite particles

Silver nanoparticles were adsorbed preferentially on silica surface to form composite particles using a reverse micelle process that stabilizes the silver particles by an anionic sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant in isooctane solvent together with the silica particles in which their surface being mediated by a cationic poly(allylamine hydrochloride) (PAH) polyelectrolyte. The heterogeneous adsorption was rendered by both electrostatic attraction and hydrophilic/hydrophobic interaction, and was carried out in multiple deposition cycles. The resulting nanocomposite particles were characterized by zeta-potential measurement, electron microscopy, X-ray diffractometry, field-emission electron spectroscopy for chemical analysis (ESCA), and inductively coupled plasma analysis, respectively. In addition, antibacterial activity of the composite particles was examined against Escherichia coli (E. coli) in aqueous environment.     

A versatile synthesis of highly bactericidal Myramistin® stabilized silver nanoparticles

Silver nanoparticles stabilized by a well-known antibacterial surfactant benzyldimethyl[3-(myristoylamino)propyl]ammonium chloride (Myramistin(?)) were produced for the first time by borohydride reduction of silver chloride sol in water. Stable aqueous dispersions of silver nanoparticles without evident precipitation for several months could be obtained. In vitro bactericidal tests showed that Myramistin(?) capped silver NPs exhibited notable activity against six different microorganisms-gram-positive and gram-negative bacteria, yeasts and fungi. The activity was up to 20 times higher (against E. coli) compared to Myramistin(?) at the same concentrations and on average 2 times higher if compared with citrate-stabilized NPs.     

Efficient synthesis and structural characterization of silver nanoparticle/ bis(o-phenolpropyl)silicone composites

Silver nanoparticle/bis(o-phenolpropyl)silicone composites have been synthesized by the reduction of silver nitrate with bis(o-phenolpropyl)silicone BPPS [(o-phenolpropyl)2(SiMe2O)n, n = 2, 3, 8, 236]. TEM and FE-SEM data clearly show that the silver nanoparticles with the size of < 20 nm are well dispersed throughout the BPPS matrix in the composites. XRD patterns are consistent with those for multicrystalline silver. The size of silver nanoparticles increased with increasing the relative molar concentration of silver salts added. It was found that in the absence of BPPS, most of the silver nanoparticles undergo macroscopic precipitation by agglomeration, indicating that BPPS is essential to stabilize the silver nanoparticles.     

银纳米线的溶剂热合成与表征

以聚乙烯吡咯烷酮(PVP)为表面活性剂、乙二醇为溶剂,通过简易的溶剂热方法合成了银纳米线.结果表明,在反应体系中乙二醇不仅能作为溶剂,而且还能起到还原剂的作用.用XRD、SEM对产物进行了表征.考察了乙二醇和PVP用量等对银纳米线合成的影响;找出了合成的较佳条件.对银纳米线的合成机理进行了初步探讨.     

Optical switch from silver nanocomposite thin films

Silver nanoparticles capped with sodium alginate were assembled into thin films by using the layer-by-layer dipping technique. Composite films were built by sequential dipping of a glass slide in either anionic alginate capped nanoparticles or cationic Poly(diallyldimethylammonium chloride) (PDADMAC). The growth of the film was characterized using UV-Vis spectroscopy by monitoring the increase in absorbance at 420 nm which correspond to the silver nanoparticles plasmon band. The final films formed onto glass slides displayed and interesting color shift upon exposure to water or to a less polar solvent such as ethanol. In this research, changes in spectral absorbance of the nanoparticles film were monitored as a function of ethanol content (0, 20, 40, 60, 80 and 100%) in water. The color shift from yellow to red color was explained by the changes in the dielectric constant of the silver nanoparticles surrounding medium which induce a shift in their plasmon band absorbance. These composite thin films displayed fast color change and could therefore be used in sensing application as well as for optical switches.     

Directly ultraviolet photochemical deposition of silver nanoparticles on silica spheres: Preparation and characterization

A simple method was developed to directly deposit silver nanoparticles on the surface of silica spheres. The photochemical reduction was carried out by ultraviolet irradiation in air atmosphere at room temperature. The [Ag(NH₃)₂]⁺was reduced to silver atoms upon ultraviolet irradiation. Silver atoms subsequently deposited on the surface of silica spheres and agglomerated into silver nanoparticles. Silica spheres with silver nanoparticles of different size and density can be simply controlled by adjusting the UV-light irradiation time. The silver nanoparticles deposited on silica spheres were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.     

Biological synthesis of gold and silver nanoparticles mediated by the bacteria Bacillus subtilis

Biological synthesis of gold and silver nanoparticles was carried out using the bacteria Bacillus subtilis. The reduction processes of chloroaurate and silver ions by B. subtilis were found to be different. Gold nanoparticles were synthesized both intra- and extracellularly, while silver nanoparticles were exclusively formed extracellularly. The gold nanoparticles were formed after 1 day of addition of chloroaurate ions, while the silver nanoparticles were formed after 7 days. The nanoparticles were characterized by X-ray diffraction, UV-vis spectra and transmission electron spectroscopy. X-ray diffraction revealed the formation of face-centered cubic (fcc) crystalline gold nanoparticles in the supernatant, broth solution and bacterial pellet. Silver nanoparticles also exhibited diffraction peaks corresponding to fcc metallic silver. UV-vis spectra showed surface plasmon vibrations for gold and silver nanoparticles centered at 530 and 456 nm, respectively. TEM micrographs depicted the formation of gold nanoparticles intra- and extracellularly, which had an average size of 7.6 +/- 1.8 and 7.3 +/- 2.3 nm, respectively, while silver nanoparticles were exclusively formed extracellularly, with an average size of 6.1 +/- 1.6 nm. The bacterial proteins were analyzed by sodium dodecyl sulfonate-polyacrylamide electrophoresis (SDS-PAGE) before and after the addition of metal ion solutions. We believe that proteins of a molecular weight between 25 and 66 kDa could be responsible for chloroaurate ions reduction, while the formation of silver nanoparticles can be attributed to proteins of a molecular weight between 66 and 116 kDa. We also believe that the nanoparticles were stabilized by the surface-active molecules i.e., surfactin or other biomolecules released into the solution by B. subtilis.