Intrinsic magnetism in Fe doped SnO2 nanoparticles

Iron doped semiconducting nanoparticles Sn_1−xFe_xO₂ with x=0, 0.001, 0.002, 0.003, 0.004, 0.01 and 0.03 were prepared by a sol-gel method. The X-ray diffraction, Transmission Electron Microscopy measurements confirm the rutile structure with no impurity phase. The three characteristic lines of electron spin resonance (ESR) are observed in the doped samples for all compositions, which is a clear evidence for rhombic Fe³⁺ in rutile phase. The line width of ESR increases with increase in Fe concentration due to induced disorder. The spin-pumping effect is observed at temperatures below 250 K for the samples with x=0.01 and 0.03. However, based on the Curie-Weiss susceptibility, iron is in paramagnetic state and is subject to weak antiferromagnetic interaction. Blue shift in the optical band gap is observed with increase in the Fe content.     

Synthesis of silver nanoparticles using dl-alanine for ESR dosimetry applications

The potential use of alanine for the production of nanoparticles is presented here for the first time. Silver nanoparticles were synthesized using a simple green method, namely the thermal treatment of silver nitrate aqueous solutions with dl-alanine. The latter compound was employed both as a reducing and a capping agent. Particles with average size equal to 7.5 nm, face-centered cubic crystalline structure, narrow size distribution, and spherical shape were obtained. Interaction between the silver ions present on the surface of the nanoparticles and the amine group of the dl-alanine molecule seems to be responsible for reduction of the silver ions and for the stability of the colloid. The bio-hybrid nano-composite was used as an ESR dosimeter. The amount of silver nanoparticles in the nanocomposite was not sufficient to cause considerable loss of tissue equivalency. Moreover, the samples containing nanoparticles presented increased sensitivity and reduced energetic dependence as compared with pure dl-alanine, contributing to the construction of small-sized dosimeters.     

Hydrogen peroxide induced formation of peroxystannate nanoparticles

Stable, amorphous potassium peroxystannate nanoparticles of controlled average size—in the range 10–100 nm—and of controlled hydrogen peroxide content—in the range of 19–30 wt%—were synthesized by hydrogen peroxide induced polymerization in water–potassium hexahydroxostannate solutions. The sol phase and the precipitate were characterized by vibrational spectroscopies, ¹¹⁹Sn NMR, XPS and XRD using crystalline K₂Sn(OH)₆ and K₂Sn(OOH)₆ reference materials. This is the first study to show that peroxocoordination induces polymerization of a main group element. ¹¹⁹Sn NMR studies show that peroxotin coordination and polymerization took place already in the hydrogen peroxide–water phase. The high abundance of peroxotin bonds revealed by ¹¹⁹Sn MAS NMR, vibrational spectroscopy, and XPS suggests that the particles are predominantly made of peroxo bridged tin networks. Although the particles are highly stable in the dry phase as well as in alcohol solutions and do not lose hydrogen peroxide upon storage, they release their stored hydrogen peroxide content by exposure to water.     

Doping mechanism of C60 fullerene by sodium and potassium

ESR spectra of localized states of KC₆₀ and K₂C₆₀ and conducting electrons of K₃C₆₀ were recorded in the process of doping C₆₀ by potassium. The ESR spectra of K _x C₆₀ (x < 3) and Na _x C₆₀ correspond to the semiconductive state of the samples.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2190–2195, November, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4101). The work was performed under terms of the interindustry program Fullerenes and Atomic Clusters.     

Synthesis of Nanocrystalline TiO<Subscript>2</Subscript> Particles and Their Structural Characteristics

Controlled nanosized TiO₂ particles of 4–10 nm were synthesized by a simple hydrolysis method followed by calcination at different temperatures. These particles were investigated using X-ray diffraction (XRD), Photoacoustic/Fourier transform infrared (PA/FTIR) spectroscopy, Raman spectroscopy and electron spin resonance (ESR) spectroscopy to understand their structural properties. X-ray diffraction studies confirmed the anatase phase of the particles where as the PA/FTIR revealed the bands around 1,500 and 3,300 cm⁻¹ due to –OH bands. ESR spectroscopic investigations carried out from 5 to 300 K indicated the presence of an ESR line at g = 2.00 emerging from radical species. It is significant to note that the intensity of the ESR line decreased as the particle size increased.     

Doping silver nanoparticles in AOT lyotropic lamellar phases

The organic lyotropic liquid crystal with long-range structural order is used as template to assemble inorganic/organic hybrid by doping pre-fabricated Ag nanoparticles. The lamellar hybrid with both hydrophilic and hydrophobic particles doped simultaneously is realized for the first time. The change of template structure after doping and the stability origin of dual-doped system are characterized by small angle X-ray scattering and polarized optical microscopy. Results show that the interaction and space matching between surfactant bilayers and doped particles are key factors to obtain stable hybrid.     

Wrapping of nanoparticles by membranes

How nanoparticles interact with biomembranes is central for understanding their bioactivity. Biomembranes wrap around nanoparticles if the adhesive interaction between the nanoparticles and membranes is sufficiently strong to compensate for the cost of membrane bending. In this article, we review recent results from theory and simulations that provide new insights on the interplay of bending and adhesion energies during the wrapping of nanoparticles by membranes. These results indicate that the interplay of bending and adhesion during wrapping is strongly affected by the interaction range of the particle–membrane adhesion potential, by the shape of the nanoparticles, and by shape changes of membrane vesicles during wrapping. The interaction range of the particle–membrane adhesion potential is crucial both for the wrapping process of single nanoparticles and the cooperative wrapping of nanoparticles by membrane tubules.     

J-complexes of retinol formed within the nanoparticles prepared from microemulsions

Retinol nanoparticles have been obtained by direct precipitation of retinol in the inner water cores of AOT/heptane/water microemulsions. The retinol dissolved in chloroform was injected into the microemulsion. The diameter of the so-obtained nanoparticles was measured using transmission electron microscope pictures where the revelation was made thanks to adsorbed iodine on the nanoparticles. The size is ca 6.0 nm, and it is not dependent either on the size of the water droplets or the concentration of the retinol molecules. This phenomenon is explained by the thermodynamic stabilization of the nanoparticles at a certain size. UV-visible spectra of the nanoparticles show a new band the maximum of which has a bathochromic shift with respect to the absorption band of the retinol monomers. If the bathochromic shift is plotted as a function of the line width, a linear correlation is obtained, the line width is decreasing with increasing shift. This behavior is interpreted as being due to an excitonic transition of a J-complex. Quantum chemical calculations have been carried out to confirm the presence of J-complexes. Taking into account the various possible geometries, the results confirm the presence of J-complexes composed of three head-to-tail molecules on the average.     

Photoinduced magnetism in rubidium cobalt hexacyanoferrate Prussian blue analogue nanoparticles

Nanoparticles of rubidium cobalt hexacyanoferrate were synthesized using the organic ligand poly(vinylpyrrolidone) (PVP). The particles, with composition Rb_1.8Co₄[Fe(CN)₆]_3.2 · nH₂O determined from CHN combustion analysis and ICP-MS, have an average size of 10 nm ± 2 nm. Similar to bulk samples, the nanoparticles show evidence of ferrimagnetic ordering in DC magnetization below T_C ∼ 15 K, although the transition is broadened due to the small particle size and its dispersion. Upon illumination with white light at 5 K, the field-cooled DC magnetization of these particles increased 40%.     

Zirconium phosphate nanoparticles from water-in-oil microemulsions

Non-ionic water-in-oil (w/o) microemulsions of pentaoxyethylenenonylphenyl ether (Igepal-CO520)/cyclohexane/water at 25 °C have been used as reaction vessels to obtain zirconium hydrogen phosphate nanoparticles.     

Spontaneous formation of silver nanoparticles in aminosilica

We report a rapid and spontaneous metallization process associated with sol–gel reaction of aminosilane that can be utilized to synthesise silver embedded silica nanocomposite without involving additional reducing agents. The reduction reaction induced by bis[3-(trimethoxysilyl)propyl]ethylenediamine (enTMOS) involves amine functional moieties, which drive the reduction reaction with presence of water. Cyclic voltammetry was used to investigate the redox potential of enTMOS and its relation to chemical environment. It was found that the oxidation potential of enTMOS depending on the amount of water (water:enTMOS (v/v) = 8:1–0:1) ranges from 0.48 to 0.68 V versus Ag/AgCl electrode in methanol. The oxidation potential of aminosilane decreases with water content and becomes more negative than that of Ag, suggesting the aminosilane acts as a silver reducing agent while serving as a matrix to encapsulate silver nanoparticles after reacting with water. This process has been utilized to produce evenly dispersed silver nanoparticles with sizes ranging from 5 to 20 nm in both liquid and solid forms of aminosilane, allowing us to prepare silver nanoparticles doped silica nanocomposite that exhibits enhanced electrochemical properties.     

Nanobubbles and nanoparticles

Gas saturated solutions have attracted great attention in the past two decades with reports of stable nanobubbles in solutions. The fundamental interest focus arises from the surprising stability which opens up a wide range of potential applications where the interactions between particles and nanobubbles are important. Here, we review the current state of knowledge on systems involving both nanobubbles and nanoparticles. As nanoparticles and nanobubbles are found together in many circumstances, particularly those involving applications of nanobubbles, knowledge of these systems is important. This includes examining the formation of nanoparticles from nanobubbles, the nucleation of nanobubbles from nanoparticles, and the interactions between nanobubbles and nanoparticles. It is clear that further work is required to more fully understand these systems, in particular on the problem of nanobubble nucleation and nanobubble–nanoparticle interactions at the submicron scale.     

Morphology of supported nanoparticles

An short review of the shape of supported nanoparticles is presented. In the first part of this review the basic theoretical concepts governing the shape of crystals are given. The validity of the concepts of equilibrium shape for crystals with nanometer dimensions is discussed as well as the influence of the support. The effect of the growth kinetics on the particle shape is also discussed. In the second part, several examples of metal (Au and Pd) nanoparticles supported on MgO, mica and graphite substrates are given to demonstrate the utility of the main experimental techniques (TEM, STM, AFM, GISAXS) used to observe the morphology of nanocrystals.     

Electromagnetic properties of zinc–nickel ferrites in the frequency range of 0.05–10 GHz

Zn_x-1Ni_xFe₂O₄ samples have been synthesized by solid-state reactions. Data on the chemical composition and the surface morphology of the samples have been obtained using a scanning electron microscope. X-ray powder diffractometer has been used to establish the phase purity and to determine the unit cell parameters. It has been found that the obtained samples had the spinel structure with Fd-3m (No. 227) space group. The unit cell parameters decrease with increasing nickel concentration. The magnetic characteristics of the obtained samples are determined and discussed. The Curie point of obtained samples varies in the range of 803.5–572.7 K. The maximum spontaneous magnetization of ~74.6 emu/g at room temperature was fixed for the solid solution with x = 0.6. The maximum value of the μ^/real part of ~12 and μ^//imaginary part of 6 of the permeability in the frequency range of 50 MHz–10 GHz is observed for the composition with x = 0.3. The composite samples for microwave study were prepared by mixing the ferrite powders with molten paraffin wax. The largest value of the μ^/ real part of ~3 and μ^// imaginary part of 0.63 of permeability is found for the x = 0.4 composite. The formation of the composite significantly reduces permeability.     

Interaction of ozone with gold nanoparticles

Gold nanoparticles interact with aqueous ozone to produce a surface plasmon resonance shift without aggregation of the nanoparticles. Given ozone's destructive nature, the surprising finding was that the gold nanoparticles returned to their original color and were able to cycle between the wavelengths as ozone was introduced and removed. Gold islands were made and tested for a gaseous ozone response. Similarly to the aqueous system, the gold islands show a cycling effect. Potentially, this system would be useful as a sensor that identifies the presence of ozone in gaseous media.     

Preparation and characterization of cross-linked hyaluronan nanoparticles

The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on hyaluronic acid (HA). The diamine, 2,2′(ethylenedioxy)bis(ethylamine) was used for cross-linking of the HA linear chains. The condensation reaction of amino groups and pendant carboxyl groups of HA was performed in aqueous media at room temperature using water-soluble carbodiimide. The prepared nanosystems, aqueous solutions, or dispersions of nanoparticles were stable, transparent, or mildly opalescent systems depending on the ratio of cross-linking, findings consistent with values of transmittance above 77%. The structure of products was determined by nuclear magnetic resonance spectroscopy, and the particle size was identified by laser light scattering (DLS) and transmission electron microscopy (TEM) measurements. Particle size measured by TEM varied less than 130 nm; in the swollen state, the average size of the particles measured by DLS was in the range of 30–140 nm depending on the ratio of cross-linking and the molecular weight of HA. Formation of cross-linked nanoparticles results in a viscosity drop compared to the viscosity of the corresponding solution of the HA, and this trend becomes decreasingly appreciable as the molecular weight of HA decreases.     

Solid state synthesis of water-dispersible silicon nanoparticles from silica nanoparticles

A solid state synthesis for obtaining nanocrystalline silicon was performed by high temperature reduction of commercial amorphous nanosilica with magnesium powder. The obtained silicon powder contains crystalline silicon phase with lattice spacings characteristic of diamond cubic structure (according to high resolution TEM), and an amorphous phase. In ²⁹Si CP MAS NMR a broad multicomponent peak corresponding to silicon is located at −61.28 to −69.45 ppm, i.e. between the peaks characteristic of amorphous and crystalline Si. The powder has displayed red luminescence while excited under UV illumination, due to quantum confinement within the nanocrystals. The silicon nanopowder was successfully dispersed in water containing poly(vinyl alcohol) as a stabilizing agent. The obtained dispersion was also characterized by red photoluminescence with a band maximum at 710 nm, thus enabling future functional coating applications.     

The use of nanoparticles in electroanalysis: a review

Nanoparticles can display four unique advantages over macroelectrodes when used for electroanalysis: enhancement of mass transport, catalysis, high effective surface area and control over electrode microenvironment. Therefore, much work has been carried out into their formation, characterisation and employment for the detection of many electroactive species. This paper aims to give an overview of the investigations carried out in this field. Particular attention is paid to examples of the advantages and disadvantages nanoparticles show when compared to macroelectrodes and the advantages of one nanoparticle modification over another. Most work has been carried out using gold, silver and platinum metals. However, iron, nickel and copper are also reviewed with some examples of other metals such as iridium, ruthenium, cobalt, chromium and palladium. Some bimetallic nanoparticle modifications are also mentioned because they can cause unique catalysis through the mixing of the properties of both metals.     

Mini-review: Ferrite nanoparticles in the catalysis

Recent applications of ferrite nanoparticles as catalysts in organic processes are reviewed. Catalytic applications include the use of mainly cobalt, nickel, copper, and zinc ferrites, as well as their mixed-metal combinations with Cr, Cd, Mn and sometimes some lanthanides. Core–shell nanostructures with silica and titania are also used without loss of magnetic properties. The ferrite nanomaterials are obtained mainly by wet-chemical sol-gel or co-precipitation methods, more rarely by the sonochemical technique, mechanical high-energy ball milling, spark plasma sintering, microwave heating or hydrothermal route. Catalytic processes with application of ferrite nanoparticles include decomposition (in particular photocatalytic), reactions of dehydrogenation, oxidation, alkylation, C–C coupling, among other processes. Ferrite nano catalysts can be easily recovered from reaction systems and reused up to several runs almost without loss of catalytic activity.     

Bimetallic PdAu nanoparticles as hydrogenation catalysts in imidazolium ionic liquids

Metallic and bimetallic PdAu nanoparticles were solubilized in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid (IL) by a phase-transfer method using poly(vinylpyrrolidone) (PVP) as a stabilizer. Nanoparticles were characterized by UV–vis spectroscopy and transmission electron microscopy. The bimetallic PdAu nanoparticles in the IL-phase were examined as catalysts for hydrogenation reactions; both the activity and selectivity of the hydrogenation reactions could be tuned by varying the composition of the bimetallic nanoparticles, with maximum activities seen at 1:3 Au:Pd ratios. These nanoparticles/IL catalysts were recycled and then reused for further catalytic reactions with minimal loss in activity.