Toward monodispersed silver nanoparticles with unusual thermal stability

A novel in situ autoreduction route has been developed, by which monodispersed silver nanoparticles with tunable sizes could be easily fabricated on silica-based materials, especially inside the channels of mesoporous silica (MPS). 13C CP/MAS NMR spectroscopy was employed to monitor the whole assembly process. It was demonstrated that the amino groups of APTS (aminopropyltriethoxyl silane)-modified MPS can be used to anchor formaldehyde to form novel reducing species (NHCH2OH), on which Ag(NH3)2NO3 could be in situ reduced. Monodispersed silver nanoparticles were thus obtained. In situ XRD and in situ TEM experiments were used to investigate and compare the thermal stabilities of silver nanoparticles on the external surface of silica gels (unconfined) and those located inside the channels of SBA-15 (confined). It was observed that unconfined silver nanoparticles tended to agglomerate at low temperatures (i.e., lower than 773 K). The aggregation of silver nanoparticles became more serious at 773 K. However, for those confined silver nanoparticles, no coarsening process was observed at 773 K, much higher than its Tammann temperature (i.e., 617 K). Only when the treating temperature was higher than 873 K could the agglomeration of those confined silver nanoparticles happen with time-varying via the Ostwald ripening process. The confinement of mesopores played a key role in improving the thermal stabilities of silver nanoparticles (stable up to 773 K without any observable coarsening), which is essential to the further investigations on their chemical (e.g., catalytic) properties.     

Understanding the role of clay silicate nanoparticles with organic modifiers in thermal curing of cyanate ester resin

The catalytic effect of montmorillonite clay nanoparticles containing organic modifiers such as quaternary phosphonium salts on cure mechanism of cyanate ester resin (RS-9D) was studied by differential scanning calorimetry (DSC) measurements, FT-IR and NMR spectroscopy as well as mass-spectrometry. The results show that the net catalytic effect arises from the presence of moisture associated with nanoclay particles where organic modifiers act as moisture transport agents. Possible mechanisms for cure pathways are discussed.     

Enhanced thermal and mechanical properties and biostability of polyurethane containing silver nanoparticles

A polyether-type polyurethane (PU) containing silver (Ag) nanoparticles (4-7 nm, 1.51 × 10⁻³-1.13 × 10⁻² wt-%) was prepared by mixing the waterborne PU with the nanoparticle suspension, casting and drying at 60 °C. The Ag nanoparticles were found to be well dispersed in PU. A significant increase in the thermal stability and mechanical properties of the polymer was demonstrated in the nanocomposite PU films, which was believed a result of induced crystallization in the presence of Ag nanoparticles. The biostability was tested in a rat subcutaneous model. After 19 days of implantation, the PU containing Ag showed enhanced biostability and lowered foreign body reaction. The effect of Ag on the stability of the PU polymer was even more remarkable over a wider range of particle contents than that of the gold nanoparticles previously studied.     

High‐performance liquid chromatography separation of unsaturated organic compounds by a monolithic silica column embedded with silver nanoparticles

The optimization of a porous structure to ensure good separation performances is always a significant issue in high‐performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high‐performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high‐performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high‐performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36 000 m^?1. Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans‐stilbene with separation factor as 7 and theoretical plate number as 76 000 m^?1 for cis‐stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long‐ established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes.     

Graphene nanofl akes and hybrid nanocomposites with gold and silver nanoparticles: optical and thermal properties

Russian Chemical Bulletin - New technologies for the preparation of graphene nanofl akes (GNF) with noble metal nanoparticles (NPs), specifi cally Au and Ag, as well as hybrid nanocomposites...     

Structural properties of ultra-small thorium and uranium dioxide nanoparticles embedded in a covalent organic framework

We report the structural properties of ultra-small ThO₂ and UO₂ nanoparticles (NPs), which were synthesized without strong binding surface ligands by employing a covalent organic framework (COF-5) as an inert template. The resultant NPs were used to observe how structural properties are affected by decreasing grain size within bulk actinide oxides, which has implications for understanding the behavior of nuclear fuel materials. Through a comprehensive characterization strategy, we gain insight regarding how structure at the NP surface differs from the interior. Characterization using electron microscopy and small-angle X-ray scattering indicates that growth of the ThO₂ and UO₂ NPs was confined by the pores of the COF template, resulting in sub-3 nm particles. X-ray absorption fine structure spectroscopy results indicate that the NPs are best described as ThO₂ and UO₂ materials with unpassivated surfaces. The surface layers of these particles compensate for high surface energy by exhibiting a broader distribution of Th–O and U–O bond distances despite retaining average bond lengths that are characteristic of bulk ThO₂ and UO₂. The combined synthesis and physical characterization efforts provide a detailed picture of actinide oxide structure at the nanoscale, which remains highly underexplored compared to transition metal counterparts.

ThO₂ and UO₂ nanoparticles synthesized using a COF-5 template exhibit unpassivated surfaces and provide insight into nanoscale properties of actinides.     

Fabrication of optically active flexible polymer films with embedded chain-like arrays of silver nanoparticles

We report a straightforward method for preparation of freestanding transparent polymer film containing 2D silver nanoparticle arrays and possessing polarization-sensitive optical properties.     

Catalytic properties of silver nanoparticles supported on silica spheres

In this work, we investigate the catalytic properties of silver nanoparticles supported on silica spheres. The technique to support silver particles on silica spheres effectively avoids flocculation of nanosized colloidal metal particles during a catalytic process in the solution, which allows one to carry out the successful catalytic reduction of dyes. The effects of electrolytes and surfactants on the catalytic properties of silver particles on silica have been investigated. It is found that the presence of surfactants depresses the catalytic activity of the silver particles to some extent by inhibiting the adsorption of reactants onto the surface of the particles. Electrolytes either increase the migration rate of reactants in the solution resulting in an increase in the catalytic reaction rate or inhibit the adsorption of reactants onto the surface of the silver particles leading to a loss in the activity of the metal particles.     

A plasmonic photocatalyst consisting of silver nanoparticles embedded in titanium dioxide

Titanium dioxide (TiO2) displays photocatalytic behavior under near-ultraviolet (UV) illumination. In another scientific field, it is well understood that the excitation of localized plasmon polaritons on the surface of silver (Ag) nanoparticles (NPs) causes a tremendous increase of the near-field amplitude at well-defined wavelengths in the near UV. The exact resonance wavelength depends on the shape and the dielectric environment of the NPs. We expected that the photocatalytic behavior of TiO2 would be greatly boosted if it gets assisted by the enhanced near-field amplitudes of localized surface plasmon (LSP). Here we show that this is true indeed. We named this new phenomenon "plasmonic photocatalysis". The key to enable plasmonic photocatalysis is to deposit TiO2 on a NP comprising an Ag core covered with a silica (SiO2) shell to prevent oxidation of Ag by direct contact with TiO2. The most appropriate diameter for Ag NPs and thickness for the SiO2 shell giving rise to LSP in the near UV were estimated from Mie scattering theory. Upon implementing a device that took these design considerations into account, the measured photocatalytic activity under near UV illumination of such a plasmonic photocatalyst, monitored by decomposition of methylene blue, was enhanced by a factor of 7. The enhancement of the photocatalytic activity increases with a decreased thickness of the SiO2 shell. The plasmonic photocatalysis will be of use as a high performance photocatalyst in nearly all current applications but will be of particular importance for applications in locations of minimal light exposure.     

Preparation and evaluation of lauryl methacrylate monoliths with embedded silver nanoparticles for capillary electrochromatography

In this article, capillary columns constituted by lauryl methacrylate monoliths with embedded silver nanoparticles (AgNPs) were developed and tested. Two incorporation approaches of AgNPs in monoliths were explored. The AgNPs were either photogenerated in situ during polymerization of the monolith by UV irradiation, or incorporated to the polymerization mixture (ex situ). The influence of the AgNP concentration on the morphological and chromatographic properties of the polymer matrix was investigated, and both the in situ and ex situ approaches were comparatively discussed. The morphology of the monoliths was characterized by electron microscopic techniques, and their electrochromatographic performance was also evaluated with test mixtures of neutral compounds (sterols, fatty acid methyl esters, tocopherols, and polyaromatic hydrocarbons).     

Study of the thermal properties and some reactions of silver fluorides

The thermal properties of silver fluoride and silver subfluoride were studied by derivative thermal analysis and by X-ray analysis. From the results, conclusions were drawn on the decomposition mechanism.The thermal behaviour of silver fluoride-alkali halide systems was studied. It was established that silver fluorides react with the alkali halides.     

Chitosan and silver nanoparticles as pudding with raisins with antimicrobial properties

Chitosan nanoparticles (CS-NP) containing small silver nanoparticles are reported (Ag@CS-NP). CS-NP was synthesized using tripolyphosphate (TPP) as a polyanionic template. TPP also served to electrostatically attract Ag(+) inside CS-NP, where it was reduced by the terminal glucosamine units of the biopolymer. This procedure is environmental friendly, inexpensive, and permits the synthesis of very small AgNP (0.93-1.7 nm), with only a discrete dependence from the amount of silver nitrate used (5-200mg). The obtained hybrid nanocomposites Ag@CS-NP were characterized by DLS, HRTEM, and HAADF-STEM presenting a mean hydrodynamic diameter of 78 nm. The antimicrobial activity of Ag@CS-NP against Candida glabrata, Sacharomyces cerevisiae, Escherichia coli, Klebsiella pneumoniae, Salmonella, Staphylococcus aureus, and Bacillus cereus corresponded to MIC values lower than for AgNO(3).     

Optical and electrical behavior of organic/inorganic hybrid with embedded gold nanoparticles

Gold nanoparticles (AuNPs) with different diameters (from 4 up to 10 nm) were immobilized within a amine-alcohol-silicate matrix [AA(600)] by mixing a preformed Au nanoparticle colloidal solution with the precursors of amine-alcohol-silicate, prior to the sol–gel transition. The organic–inorganic hybrid (OIH) nanocomposites were synthetized by sol–gel method by reaction of amino-functionalized polyether and a siloxane functionalized with a terminal epoxy group. The obtained homogeneous, high transparent and stable materials exhibit enhanced optical and electrical properties derived from plasmonic effects associated with the size and form of the nanoparticle dopants which show to be preserved during the synthesis steps. Performed electrochemical impedance spectroscopy revealed that OIH gels doped with AuNPs exhibit low conductivity that shows to be slightly dependent on dispersed Au particle sizes. The characterization of this materials by current–voltage (I–V) measurements shows that these materials exhibit an electrical stability within an range of applied potential of about 5 V and suggests that charge transfer mechanism is strongly dependent on the potential applied across the OIH gel as observed by testing different charge transfer models: space-charge-limited current, Poole–Frenkel, Schottky emission and hopping conduction or the Schottky-Simmons. The results obtained from the characterization the electrochemical properties shows that the produced material to be relevant for the potential application of OIH embedded AuNPs nanocomposites in non-volatile organic memory devices.     

Hybrids of silver nanoparticles with amphiphilic hyperbranched macromolecules exhibiting antimicrobial properties

Hybrids of silver particles of 1 to 2 nm in size with highly branched amphiphilically modified polyethyleneimines adhere effectively to polar substrates providing environmentally friendly antimicrobial coatings.     

Characterization of silver sulfadiazine-loaded solid lipid nanoparticles by thermal analysis

The aim of this study is the solid-state characterization of solid lipid nanoparticles (SLN) based on Compritol^® 888 (C888) and Lutrol^® F68 (F68), loaded with silver sulfadiazine (AgSD), used to develop sponge-like dressings to treat chronic skin ulcers such as decubitis and leg ulcers. Silver compounds like AgSD, in fact, are used to prevent and/or to treat wound colonization that could impair healing, also in the case of antibiotic-resistant bacteria. Thermal analysis, with support from powder X-ray diffractometry and Fourier transform infrared spectroscopy, is used to characterize lipid and drug bulk, unloaded and drug-loaded SLN. In particular, differential scanning calorimetry is used to investigate the degree of crystallinity and the solid-state modification of lipid, two parameters correlated to drug incorporation and drug release rates. The solid-state characterization demonstrates AgSD entrapment in C888 as a core enclosed into F68 shell. AgSD SLN are also stored at different temperatures 25 and 37 °C, respectively, to study the effect of storage conditions, that induce an increase of the lipid crystallinity index correlated to drug release from the lipid matrix.     

Study on cyanobiphenyl nematic doped by silver nanoparticles

We study the effects of doped (1%wt and 2%wt) silver nanoparticles on material properties of nematic liquid crystal: 4-pentyl-4′-cyanobiphenyl. Using differential scanning calorimetry, electrical and dielectric measurements methods, we show that the doped NPs do not affect the nematic’s phase clearing point, lower the dielectric anisotropy, viscosity, switching-off time, and increase the threshold voltage and elasticity of the nematic. We report that the doped materials temperature behaviour of Frederick’s transition threshold voltage and switching-off time, deviates from the expected behaviour for pristine nematics. To explain this anomalous behaviour, we perform data analysis of the governing Frederick’s transition material parameters of studied samples. We show that the elastic parameter of doped samples is not following the predictions of Maier–Saupe theory, which is valid for conventional nematics. We report that the doped samples temperature behaviour of the elastic parameter follows the predictions of the Gelbart and Ben-Shaul theory.     

Evaluation of thermal properties of MMCp composites with silver alloy matrix

Journal of Thermal Analysis and Calorimetry - Silver, silver alloys, and composites with silver matrix are used mainly as electric contacts, circuit-breakers, and slide bearings. Contacts working...     

银/碳纳米管纳米复合物制备及性质研究

基于苯环与碳纳米管之间较强的π-π共轭效应和醛基对银氨溶液的还原作用,利用吸附在碳纳米管上的香草醛分子原位还原[Ag(NH3)2]+,成功获得了纳米银/碳纳米管(Ag-NPs/CNTs)复合纳米材料。紫外-可见吸收光谱和荧光光谱结果表明,碳纳米管对香草醛分子有较强的吸附作用及银纳米粒子的形成。透射电镜结果表明,碳纳米管表面形成了大小约5.0 nm银纳米颗粒。所制备的纳米复合材料表现出较明显的荧光特性,且对浓度为1.0×10-7～6.0×10-7 mol/L的H2O2表现出较好的电催化还原能力。     

Structural properties of palladium nanoparticles embedded in inverse microemulsions

Pd nanoparticles were synthesized by reduction of palladium acetate by ethanol in systems containing tetrahydrofuran (THF) as dispersion medium and tetradodecylammonium bromide (TDABr) surfactant as stabilizer. The polar phase (ethanol) acts at the same time as reducing agent. THF/TDABr/H₂O inverse microemulsions containing micelles of various sizes were also prepared, and the structure of complex liquids was studied by density measurements. Sols containing nanosize Pd⁰ particles were synthesized within the water droplets of this micellar system. The stabilized Pd⁰/surfactant system was characterized by density measurements, absorption spectroscopy, and transmission electron microscopy. The stabilizing surfactant layer adsorbed on the liquid/liquid interface and on the surface of the nanoparticles (i.e., the liquid/solid interface) significantly reduced the excess volume for the palladium nanodispersion in organic solvent. Received: 17 July 2000 Accepted: 5 October 2000