Low temperature synthesis of fluorescent ZnO nanoparticles

Fluorescent ZnO nanoparticles have been prepared by mixing aqueous solutions of zinc nitrate and ammonium carbonate in the presence of a non-ionic surfactant, Tween-80. Increased concentrations of the surfactant were found to affect both the morphology and purity of the synthesized ZnO nanoparticles. XRD, SEM, FTIR, TGA and Confocal laser scanning microscopy were employed to characterize the as-prepared samples. ZnO nanoparticles ranging in particle size from 11 to 15 nm were formed at the reaction temperature of 70-80 °C. The results of FTIR and TGA analysis indicate the self assembly of Tween molecules on the surface of ZnO nanoparticles. A bright emission in the visible region from the as-prepared ZnO nanoparticles was recorded using confocal laser scanning microscopy. This property of the as-prepared nanoparticles may find potential application in bio-imaging.     

Low temperature synthesis of ITO nanoparticles using polyol process

A low temperature synthesis technique to prepare indium tin oxide (ITO) nanoparticles by the polyol process is proposed. On examining the phase formation of ITO nanoparticles in polyols and alcohols such as ethylene glycol, trimethylene glycol, and 1-heptanol, it was found that ITO nanoparticles could be synthesized directly without any post--annealing treatments at 175 °C in 1-heptanol. The morphology of the particles is influenced by the type of polyol. The composition of Sn in the ITO system could be easily controlled by simply varying the In/Sn precursor ratio in 1-heptanol. The low temperature synthesis method has enabled the formation of highly crystalline ITO nanoparticles with diameters less than 25 nm even at annealing temperatures as high as 700 °C.     

Low temperature one-step synthesis of cobalt nanowires encapsulated in carbon

The one-step method of carbon nanotubes filled with continuous cobalt nanowires (CoF-CNT) synthesis is presented. Co/ZSM-5 (8 wt% Co) was used as catalyst for CoF-CNT production by methane decomposition at the temperature of 400 °C and 800 °C at atmospheric pressure in a conventional gas-flow system. The average diameter of the CoF-CNT is about 25 and 40 nm for products obtained at 400 °C and at 800 °C, respectively. The average size of coherently scattering domains along the normal to graphite layers L _c , the interlayer spacing d ₀₀₂, the graphitization degree of carbon, and the relative intensities of the G and D bands in Raman spectroscopy were determined to characterize the quality of carbon. It was proved that cobalt-filled carbon nanotubes can be produced by a simple method. The results of XRD, FE-SEM, and TEM show that CoF-CNT can be obtained even at 400 °C by catalytic decomposition of methane. On the basis of XRD, TEM, Raman spectroscopy was found that at a temperature of 800 °C, a better quality of carbon was produced.     

Density expansion of the viscosity of carbon dioxide near the critical temperature

We present a detailed experimental study of the viscosity of carbon dioxide as a function of density at a temperature near the critical temperature. Kinetic theory predicts the presence of a logarithmic term in the density expansion for the viscosity of gases. While it is difficult to prove the existence of such a term experimentally, the data are consistent with a possible logarithmic contribution of an order of magnitude estimated theoretically by Kan.     

Solid state synthesis and room temperature magnetic properties of iron phosphide nanoparticles

Room temperature magnetic properties have been achieved for nano-crystalline iron phosphide synthesized from the direct solid state reaction of iron chloride and tri-octylphosphine (TOP). The magnetization continuously increased with higher magnetic fields, indicating a super-paramagnetic behavior. It is observed that room temperature magnetism is possible for the material showing antiferromagnetic nature at low temperatures. In the present synthesis, TOP acted as a source of phosphorus as well as a surfactant. X-ray diffraction (XRD) studies revealed that the black powder is a mixture of FeP and Fe₂P. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed elongated as well spherical particles. Energy dispersion X-ray analysis (EDAX) confirmed a non-stoichiometric iron phosphide. Presence of TOP was confirmed by infra-red (IR) spectroscopy, and thermo-gravimetric analysis (TGA) indicated about 6% wt. loss due to presence of organics.     

Functionalization of carbon encapsulated iron nanoparticles

Carbon-encapsulated magnetic nanoparticles are a new class of materials where the core magnetic nanoparticle is protected from reactions with its environment by graphite shells. Having a structure similar to carbon nanotubes, these nanoparticles could be potentially functionalized using methods which are already applied to those structures. We present the effects of acidic treatments based on HCl, HNO₃, and H₂SO₄ on these nanoparticles highlighting the impact on their magnetic and surface properties. We show that acidic treatments based on HNO₃ can be successfully applied for the generation of carboxylic groups on the surface of the nanoparticles. Using methylamine as a model, we demonstrate that these functional groups can be used for further functionalization with amino-containing biomolecules via diimide-activated amidation.     

Fabrication of titanium dioxide nanofibers containing hydroxyapatite nanoparticles

In the present study, we introduce titanium dioxide (TiO₂) nanofibers that contain hydroxyapatite (HAp) nanoparticles (NPs) as a result of an electrospinning process. A simple method that does not depend on additional foreign chemicals has been employed to synthesize HAp NPs through calcination of bovine bones. Typically, a colloidal gel consisting of titanium isopropoxide/HAp was prepared to produce nanofibers embedded with solid NPs by electrospinning process. The SEM results confirmed well oriented nanofibers and good dispersion of HAp NPs over the nanofibers. XRD results demonstrated well crystalline feature of both TiO₂ and HAp. Physiochemical aspects of prepared nanofibers were characterized for TEM and TEM-EDS which confirmed nanofibers were well oriented and had good dispersion of HAp NPs. Accordingly, these results strongly recommend the use of obtained nanofiber mats as a future candidate for hard tissue engineering applications.     

Broadening peculiarities of vibrational bands in the spectrum of carbon dioxide close to the critical temperature

Carbon dioxide Fermi doublet 1388/1285 cm⁻¹ Q-band broadenings and shifts measured using coherent anti-Stokes Raman spectroscopy are presented. Measurements were performed over a wide density range (0.1ρ _c < ρ < 1.9ρ _c ) during compression in the gaseous and condensed states at temperatures close to critical (the reduced temperature values were T _r = 0.995, 1.000, and 1.006). At densities above the ρ _c critical value, the width of Q-bands did not increase as the density grew, and the low-frequency Q band considerably narrowed up to the density value 1.7ρ _c . The main reason for this anomalous behavior was progressing narrowing of the spectral contribution caused by the special features of rotational exchange in the condensed state and not related directly to the closeness to the critical point. The refined critical broadening value was about 10% of the width for the high-frequency Q-band and 15% of the width for the low-frequency Q-band.     

Controlled oxidation of iron nanoparticles in chemical vapour synthesis

Enteric-coated formulations can delay the release of drugs until they have passed through the stomach. However, high concentration of drugs caused by rapidly released in the small intestine leads to the intestinal damage, and frequent administration would increase the probability of missing medication and reduce the patient compliance. To solve the above-mentioned problems, aspirin-loaded enteric-coated sustained-release nanoparticles with core–shell structure were prepared via one-step method using coaxial electrospray in this study. Eudragit L100-55 as pH-sensitive polymer and Eudragit RS as sustained-release polymer were used for the outer coating and inner core of the nanoparticles, respectively. The maximum loading capacity of nanoparticles was 23.66 % by changing the flow rate ratio of outer/inner solutions, and the entrapment efficiency was nearly 100 %. Nanoparticles with core–shell structure were observed via fluorescence microscope and transmission electron microscope. And pH-sensitive and sustained drug release profiles were observed in the media with different pH values (1.2 and 6.8). In addition, mild cytotoxicity in vitro was detected, and the nanoparticles could be taken up by Caco-2 cells within 1.0 h in cellular uptake study. These results indicate that prepared enteric-coated sustained-release nanoparticles would be a more safety and effective carrier for oral drug delivery.     

Laser-driven synthesis and magnetic properties of iron nanoparticles

Nanoparticles of iron have been prepared by laser-driven decomposition of iron pentacarbonyl vapor. In this method, an infrared laser rapidly heats a dilute mixture of precursor vapors to decompose the precursor and initiate particle nucleation. It was found that when using SF₆ as a photosensitizer during the synthesis, ferrous fluoride (FeF₂) was produced as an undesired byproduct in the product powder. The particle size, composition, and crystalline structure have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS). Results of magnetization measurements for small iron nanoparticles (about 5 nm diameter) are also presented, showing superparamagnetic behavior at room temperature, and a blocking temperature near 125 K.     

Light scattering by polystyrene films containing carbon nanoparticles

Laser (λ = 0.63 μm) Mueller polarimetry at different angles of incidence and detection is used to measure the elements of the Mueller matrices of polystyrene films, as well as of polystyrene films modified by adding carbon nanoparticles (fullerenes or nanotubes). The complex index of refraction, depolarization index, and polarizance (degree of polarization) of the test samples are determined. It is shown that adding even a small amount (1.0–3.5 mass %) of fullerenes or carbon nanotubes changes the depolarization properties of the modified polystyrene films. Depending on the illumination and observational geometry, these films are found to have different depolarization properties.     

Low temperature magnetic structure of erbium iron garnet

The magnetic and crystallographic structure of erbium iron garnet {Er₃}[Fe₂](Fe₃)O₁₂ has been refined simultaneously from powder and single crystal neutron diffraction data. At 5 K the ferrimagnetic structure has a spin direction parallel to [100]. Magnetic moments of iron and erbium and canting angles for the erbium sublattices were derived in space groupI4₁/acd for 5 K<T<65 K. The magnetic moments of the two erbium sites are 6.9 _B and 4.3 _B at 5 K. An indication of further symmetry reduction of the magnetic structure from tetragonal to orthorhombic below 5 K is discussed.     

Low temperature conductivity of carbon nanotube aggregates

We compare, over wide temperature ranges, the transport properties of single-wall carbon nanotubes arranged in the form of aligned arrays or in the form of fibres. The experimental data show that both the forms of aggregates present a crossover in the transport mechanism from three-dimensional hopping of the electrons between localized states at high temperature to fluctuation-induced tunnelling across potential barriers at low temperature. The role of the junctions formed between the bundles in the array and between the nanotubes inside the fibres is discussed on the basis of the experimental results.     

Magnetic resonance of metallic nanoparticles in vitreous silicon dioxide implanted with iron ions

Silica glasses exposed to steady-state and pulsed irradiation with Fe⁺ ions are studied using magnetic resonance. The irradiation doses used in experiments are equal to 1 × 10¹⁵, 1 × 10¹⁶, and 1 × 10¹⁷ cm^?2. It is found that, under both steady-state and pulsed irradiation conditions, glass samples exposed at a dose of 1 × 10¹⁷ cm^?2 exhibit a broadband orientation-dependent signal. The shape of inclusions is evaluated under the assumption that the observed spectrum is caused by the ferromagnetic resonance induced in a new phase of metallic iron.     

Behaviour of shear viscosity near the critical point of carbon dioxide

Summary Accurate measurements of shear viscosity near the critical point of carbon dioxide, performed down to(T−T _c)/T_c∼-10⁻⁶ with an improved version of the vibrating-wire viscometer, are presented in this paper. Both density and viscosity can be measured at the same time, so that gravitational effects can be controlled. The experimental results, obtained at a vibrating frequency of 1600 Hz, suggest a finite value of the viscosity at the critical point. This result, in apparent contradiction with the theoretically predicted divergent behaviour may be explained qualitatively by a frequency effect on the measured viscosity.

---

Riassunto In questo lavoro si presentano misure accurate della viscosità di scorrimento attorno al punto critico dell'anidride carbonica, eseguite fino a(T−T _c)/T_c∼-10⁻⁶ con una versione perfezionata del viscosimetro a filo vibrante. Sia la densità che la viscosità possono essere misurate contemporaneasmente, così gli effetti gravitazionali possono essere controllati. I risultati sperimentali, ottenuti ad una frequenza di vibrazione di 1600 Hz, suggeriscono un valore finito della viscosità al punto critico. Questo risultato, in apparente contraddizione con un comportamento divergente previsto teoricamente, può essere spiegato qualitativamente con un effetto di frequenza sulla viscosità misurata.

---

Резюме Приводятся результаты точных измерений сдвиговой вязкости вблизи критической точки диоксида углерода, проведенные при (T−T _c)/T_c∼-10⁻⁶ с помощью улучшенного варианта вискозиметра с колеблющимся проводом. Одновременно могут быть измерены плотность и вязкость, так что можно контролировать гравитационные зффекты. Экспериментальные результаты, полученные при частоте 1600 Гц, предполагают конечную величину вязкости в критической точке. Этот результат, противоречащий теоретически предсказанному поведению, может быть качественно обьяснен, как влияние частоты на измеренную вязкость.

---

---

To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Low ambient temperature CVD growth of carbon nanotubes

We show that good quality single-walled and multi-walled carbon nanotubes can be grown on CMOS-compatible metal electrodes at ambient room temperature using highly localised catalyst heating at nanostructured electrodes. The method is relatively straightforward and allows considerable flexibility in the kinds of devices that can be fabricated as well as allowing CVD nanotube growth to take place in the close vicinity of temperature-sensitive materials and devices. PACS 81.07.-b; 81.07.De     

Electrochemical synthesis of magnetic iron oxide nanoparticles with controlled size

We present a novel and facile method enabling synthesis of iron oxide nanoparticles, which are composed mainly of maghemite according to X-ray diffraction (XRD) and Mössbauer spectroscopy studies. The proposed process is realized by anodic iron polarization in deaerated LiCl solutions containing both water and ethanol. Water seems to play an important role in the synthesis. Morphology of the product was studied by means of transmission electron microscopy and XRD. In the solution containing almost 100% of water a black suspension of round shaped maghemite nanoparticles of 20–40 nm size is obtained. Regulating water concentration allows to control nanoparticle size, which is reduced to 4–6 nm for 5% of water with a possibility to reach intermediate sizes. For 3% or lower water concentration nanoparticles are of a needle-like shape and form a reddish suspension. In this case phase determination is problematic due to a small particle size with the thickness of roughly 3 nm. However, XRD studies indicate the presence of ferrihydrite. Coercivities of the materials are similar to those reported for nanoparticle magnetite powders, whereas the saturation magnetization values are considerably smaller.     

Phase states and magnetic properties of iron nanoparticles in carbon nanotube channels

The structure, phase composition, and magnetic properties of carbon nanotubes filled with iron nanoparticles and obtained by thermolysis of a mixture of ferrocene and C₆₀ fullerene or ferrocene and orthoxylene at a temperature of 800°C are investigated. Electron microscopy, X-ray diffraction, and Mössbauer spectroscopy data lead to the conclusion that carbon nanotubes are multilayer systems partially filled with iron nanoparticles and/or nanorods. Metallic inclusions in nanotube channels form α-Fe, γ-Fe, and Fe₃C phases. The concentration of each phase in the samples is determined. It is shown that 10–20-nm iron clusters in nanotubes exhibit magnetic properties typical of bulk phases of iron. High elasticity of carbon nanotube walls facilitates stabilization of the high-temperature γ-Fe phase; the relative concentration of this phase in a sample can be increased by lowering the concentration of ferrocene in the initial reaction mixture.     

Solvothermal synthesis of green-fluorescent carbon nanoparticles and their application

A novel solvothermal approach to synthesize green-fluorescent carbon nanoparticles (CNPs) was developed using l-ascorbic acid as the carbon source, glycol and triple distilled water as the solvent. The CNPs emit strong green fluorescence under UV irradiation, and the fluorescence intensity showed a good linear relationship with pH value within a certain range. Direct yeast cell labeling was achieved through cell endocytosis of these CNPs.     

The synthesis of boron-containing nanoparticles inert at room temperature

Boron-containing (C₂B₄H₂) _n nanoparticles with size 6.7, 7.8, and 10.8 nm inert at room temperature were synthesized. The synthesis was performed by the pyrolysis of gaseous carborane C₂B₄H₆ at 1200–1280 K and the initial carborane pressure (5–25) × 10⁻³ MPa. An analytic dependence relating the size of nanoparticles to the temperature and initial carborane pressure was obtained.