Formation and properties of the nanocluster structure of iron oxides

Nanostructures based on iron oxide clusters 1–300 nm in size were synthesized and studied. Thermodynamic models of nanocluster nucleation resulting in the formation of both primary nanoclusters and nanocluster aggregates with the sizes up to 70–80 nm were considered. Models of heat capacity of the nanoclusters were examined, and the twofold increase in the heat capacity of the iron oxide clusters 2–3 nm in size compared to that of the bulk iron oxide samples was found. The size of the primary nanoclusters and the intercluster interaction make it possible to vary the magnetic properties of the nanostructures in a wide range from paramagnetic to magnetically ordered α-Fe₂O₃-γ-Fe₂O₃ nanostructures with the first-order magnetic phase transitions, magnetic twinning, and a strong magnetic field (10 Oe) effect on the magnetization increase at low temperatures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1693–1704, October, 2006.     

Novel iron-decorated carbon nanorods from fullerene soot

A novel form of nano-sized carbon rods decorated with monodispersed iron particles in a size range of 30-50 nm on their surface is successfully synthesized by arcing discharge of composite electrodes made from iron particles and fullerene soot; this will be of potential as catalyst for hydrogenation reactions.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Nano-architecture platinum catalyst layer prepared by electrophoresis deposition for PEM fuel cells

A Pt-loaded carbon black electrode was prepared by pulsed electrophoresis deposition in a Pt colloid solution as a plating bath to overcome the growth problem of a Pt catalyst during deposition in an electrochemical process. This method is a promising technique for preparing Pt catalyst layers at the polymer electrolyte/electrode interface. The particle size of the Pt catalyst loaded by electrophoresis deposition was the same as that of Pt nanoparticles (3–4 nm) in a colloid and the particle size was maintained even during deposition. The loading of the Pt catalyst was controlled by the pH of the Pt colloid and deposition time. The Pt nanoparticles were deposited on a carbon black electrode to a depth of 2.5 μm.     

Effect of the Conditions the Reaction on the Formation of Iron Nanoparticles during the Reduction of Iron(III) Ions with Sodium Borohydride

Abstract—Iron nanoparticles are obtained by reducing iron(III) chloride with sodium borohydride in aqueous solutions at room temperature without using stabilizing agents. The obtained samples are characterized by X-ray diffraction analysis, low-temperature adsorption of argon, and transmission electron microscopy. The effect of the concentration of reagent solutions, the molar ratio of reagents, and exposure to ultrasound and inert atmosphere (Ar) on the size and composition of the resulting particles is found. Depending on the conditions of borohydride reduction of iron salts in an aqueous solution, both agglomerates of iron nanoparticles (5–50 nm) of 200 nm or larger and individual iron nanoparticles of 1 to 20 nm in size can be obtained. The presence and concentration of wustite and magnetite in the composition of the obtained particles mainly depend on the concentration of the reducing agent.     

New route to 3-methacryloxypropyltrimethoxysilane-base organic–inorganic hybrid film

A series of poly(3-methacryloxypropyltrimethoxysilane)/waterborne polyurethane (PMPS/WPU) composite latexes and organic–inorganic hybrid films with PMPS contents of 0, 10, 20, 30, 40 and 50 wt.% were prepared via seeded emulsion polymerization initiated by AIBN and hydrolysis–condensation process of PMPS during the evaporation of water, respectively. WPU, that is anionic polyurethane emulsion, was synthesized using isophorone diisocyanate, polytetramethylene ether glycol, dimethylol propionic acid, 1,4-butanediol, and triethylamine. An investigation of transmission electron microscopy confirmed the core–shell morphology of the composite latex particle which was composed of a PMPS core and a polyurethane shell. A dynamic light scattering analysis showed that the average particle size distributed in the range of 42–134 nm. The proposed novel preparation method included the use of polyurethane as macromolecular emulsifier and steric stabilizer, control of (3-methacryloxypropyltrimethoxysilane) (MPS) content less than 50 wt.%, slow addition of MPS and application of AIBN ensured the preparation of a stable PMPS/WPU composite latex. Formed PMPS/WPU organic–inorganic hybrid film with high PMPS content via sol-gel process had uniform transparency at visible band because of less crystalline and phase separation between organic and inorganic phases.     

Hydrogenation of fullerites in the presence of intermetallic compounds or metals

Fullerene hydrides containing 24–26 H atoms per fullerene molecule were obtained by hydrogenation of solid-phase mixtures of fullerenes with either intermetallic compounds LaNi₅, LaNi_4.65Mn_0.35, CeCo₃ or V and Pd metals with gaseous hydrogen at 1.0–2.5 MPa and 573–673 K. These fullerene hydrides decompose at 800 K with evolution of H₂. Upon subsequent heating to 1000 K, vanadium reacts with fullerene to yield a cubic phase of vanadium carbide. The intermetallic compounds react with fullerene with the formation of a metallic phase of the 3d-metal and destruction of fullerene. Palladium does not react with fullerene. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 679–683, April, 1997.     

Brewing MnWO<Subscript>4</Subscript> microspheres on the eggshell membrane at room temperature

Manganese tungstate microspheres were successfully fabricated using biomimetic process on living eggshell membrane (ESM) at room temperature. The microspheres were assembled by nanolamellar subunits, which are in the size with lengths of 1–2 nm, widths of 0.1–0.2 nm and thicknesses of 15–20 nm. The morphology and the size were governed mainly by the configuration and chemical functional residues of ESM. The functional groups such as amido groups and imido residues of ESM macromolecules could direct the formation of 15–20 nm thicknesses MnWO₄ nanolamellar subunits. The as-prepared microspheres exhibited similar structure with ESM, which would further illumination the potentials of bio-inspired manufactures in the field of synthesis inorganic materials. The article is published in the original.     

Particle Size Limit for Concomitant Tuning of Size and Shape of Platinum Nanoparticles

Based on a polyol process, one-step synthetic procedures were investigated for concomitant control of the shape and size of platinum nanoparticles (Pt NPs). Cubic and octahedral/tetrahedral particles of different sizes (5–10 nm) were synthesized using these procedures. Further attempts to control the shape of the NPs below 3–4 nm failed. It was found that 3–4 nm is the particle size limit for Pt NPs above which the particle size and shape can be concomitantly controlled.     

Synthesis and structure of composite fibers based on silicon and carbon obtained by electrospinning

Composite polymer fibers with a composition of Si-C-O obtained by electrospinning of precursors solution containing polycarbosilane or phenol formaldehyde resins with an admix of organic-silicon compounds were synthesized in order to find efficient new electrode materials for lithium ion batteries. The composition and structure of pyrolized composite fibers were studied by means of X-ray dispersive analysis and X-ray diffraction, Raman spectroscopy, and by AFM and SEM. It was shown that the composite fibers (with a diameter of 0.5–1.5 μm) were nanostructured materials with carbon and silicon-oxy-carbide areas about 2–5 nm in size. A model of the nanostructure of a skeleton for composite fibers synthesized is proposed.     

Chemical synthesis of tungsten-copper nanocomposite powder

In this study homogeneous powders of CuWO₄ and WO₃ was produced from ammonium para-tungstate (APT) and copper nitrate. Then, the product was used to prepare nano-sized W-Cu powder. Hence, a mixture of ammonium paratungstate and copper nitrate with predetermined weight proportion was made in distilled water, while the content of the beaker was being stirred at a certain speed to reach the desired composition of W-20 wt % Cu. Mixture was heated to 80–100°C for 6 h. Also, pH range was adjusted at about 3–4. The mixture was then evaporated and dried in the air. To reach W-Cu composite powder, the precursor powders burned out at 520°C for 2 h in the air to form W-Cu oxide powder and then were ball milled and reduced in H₂ atmosphere to convert it into W-Cu composite powder. The resulting powders were evaluated using scanning electron microscopy, X-ray diffraction, thermogravimetric analysis and differential thermal analysis techniques. The results showed that homogeneous powders of W-Cu with particle size of around 100 nm and a nearly spherical shape could be obtained by this process. Each particle include smaller parts with size of around 20–30 nm.     

Elucidation of the charge-discharge mechanism of lithium/polymer electrolyte/pyrite batteries

The purpose of this work is the elucidation of the charge-discharge mechanism in the all-solid-state lithium/composite polymer electrolyte/pyrite battery operating at 120–135 °C. The main focus is the explanation of the unexpected potential jump at 1.85 V during the charge process. Effects on the charge-discharge mechanism of particle size, pyrolysis, alumina addition and Zn doping of the pyrite-based cathode are addressed. Analysis of the experimental data, as well as the structure of the charge-discharge intermediates, diffusion of lithium and iron cations in the composite cathode, suggests that the sudden charge overpotential is associated with slow mass transport of iron(II) cations through the Li₂FeS₂ phase. Electronic Publication     

Effect of sol-gel preparation method on particle morphology in pure and nanocomposite PZT thin films

Double-scale composite lead zirconate titanate Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films of 360 nm thickness were prepared by a modified composite sol-gel method. PZT films were deposited from both the pure sol and the composite suspension on Pt/Al₂O₃ substrates by the spin-coating method and were sintered at 650°C. The composite suspension formed after ultrasonic mixing of the PZT nanopowder and PZT sol at the powder/sol mass concentration 0.5 g mL⁻¹. PZT nanopowder (≈ 40–70 nm) was prepared using the conventional sol-gel method and calcination at 500°C. Pure PZT sol was prepared by a modified sol-gel method using a propan-1-ol/propane-1,2-diol mixture as a stabilizing solution. X-ray diffraction (XRD) analysis indicated that the thin films possess a single perovskite phase after their sintering at 650°C. The results of scanning electron microscope (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses confirmed that the roughness of double-scale composite PZT films (≈ 17 nm) was significantly lower than that of PZT films prepared from pure sol (≈ 40 nm). The composite film consisted of nanosized PZT powder uniformly dispersed in the PZT matrix. In the surface micrograph of the film derived from sol, large round perovskite particles (≈ 100 nm) composed of small spherical individual nanoparticles (≈ 60 nm) were observed. The composite PZT film had a higher crystallinity degree and smoother surface morphology with necklace clusters of nanopowder particles in the sol-gel matrix compared to the pure PZT film. Microstructure of the composite PZT film can be characterized by a bimodal particle size distribution containing spherical perovskite particles from added PZT nanopowder and round perovskite particles from the sol-matrix, (≈ 30–50 nm and ≈ 100–120 nm), respectively. Effect of the PZT film preparation method on the morphology of pure and composite PZT thin films deposited on Pt/Al₂O₃ substrates was evaluated.     

Surfactant assisted preparation and characterization of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod like cation exchanger

Carboxymethyl cellulose Sn(IV) phosphate composite nano-rod like cation exchanger with diameter in the range of 20–40 nm, length in the range of 100–150 μm and particle size in the range of 21–38 nm have been successfully prepared by surfactant assisted sol–gel method. Scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, fourier transform infra red spectroscopy and thermogravimetric analysis-differential thermal analysis studies were carried out to study the structure and morphology of this composite nano-rod like cation exchanger. Freundlich adsorption isotherm is well fitted for the adsorption of pyridine on the surface of this composite nano-rod like cation exchanger. The thermodynamic parameters such as Freundlich constant, thermodynamic equilibrium constant (K ₀), standard free energy changes (ΔG ⁰), standard enthalpy changes (ΔH ⁰) and standard entropy changes (ΔS ⁰) have been evaluated. These parameters indicated that the adsorption of pyridine on the surface of composite nano-rod like cation exchanger was feasible, spontaneous and exothermic in nature which suggests for the potential application of pyridine removal from water.     

Structural evolution and magnetic properties of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers by electrospinning

The SrFe₁₂O₁₉/poly (vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol-gel assisted electrospinning with ferric nitrate, strontium nitrate and PVP as starting reagents. Subsequently, the M-type strontium ferrite (SrFe₁₂O₁₉) nanofibers were derived from calcination of these precursors at 750–1,000 °C.The composite precursors and strontium ferrite nanofibers were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The structural evolution process of strontium ferrite consists of the thermal decomposition and M-type strontium ferrite formation. After calcined at 750 °C for 2 h the single M-type strontium ferrite phase is formed by reactions of iron oxide and strontium oxide produced during the precursor decomposition process. The nanofiber morphology, diameter, crystallite size and grain morphology are mainly influenced by the calcination temperature and holding time. The SrFe₁₂O₁₉ nanofibers characterized with diameters of around 100 nm and a necklace-like structure obtained at 900 °C for 2 h, which is fabricated by nanosized particles about 60 nm with the plate-like morphology elongated in the preferred direction perpendicular to the c-axis, show the optimized magnetic property with saturation magnetization 59 A m² kg⁻¹ and coercivity 521 kA m⁻¹. It is found that the single domain critical size for these M-type strontium ferrite nanofibers is around 60 nm.     

Cu-particle-dispersed (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> composite thin films derived from sol–gel processing

Sol–gel processing of Cu-particle-dispersed (K_0.5Na_0.5)NbO₃ (Cu/KNN) thin films was studied in an attempt to develop a method producing piezoelectric composite films with good mechanical performance. The Cu/KNN films were prepared via crystallization annealing at 650–750 °C for 1 min in air, followed by reduction annealing at 400–500 °C for 1–2 h in a 5% H₂ and 95% Ar gas mixture. The resultant composite films consisted of perovskite KNN, metallic Cu, and Cu₄O₃. This suggests that the decomposition of Cu sources takes two different ways in this study. The Cu/KNN composite films containing Cu₄O₃ phases were produced by the crystallization annealing at 700 °C for 1 min followed by the reduction annealing at 500 °C for 1 h. Surface morphology observations reveal that these films have dense KNN matrix with a grain size of ~200 nm and uniformly dispersed Cu or Cu₄O₃ particles with a size of <500 nm.     

Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 10⁵ l mole^–1cm^–1 and 5.69 × 10⁴ l mole^–1cm^–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml^–1, a calibration sensitivity of 0.744 ml μg^–1 at 560 nm and 0.323 ml μg^–1 at 748 nm, and a detection limit of 15 ng ml^–1 and 44 ng ml^–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system. Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996     

Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 10⁵ l mole^–1cm^–1 and 5.69 × 10⁴ l mole^–1cm^–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml^–1, a calibration sensitivity of 0.744 ml μg^–1 at 560 nm and 0.323 ml μg^–1 at 748 nm, and a detection limit of 15 ng ml^–1 and 44 ng ml^–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system. Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996     

Poly(styrene-b-ethylene oxide) copolymers as stabilizers for the synthesis of silica–polystyrene core–shell particles

Following previous works [1, 2], silica–polystyrene core–shell particles have been synthesized by dispersion polymerization of styrene in an ethanol/water mixture in the presence of a poly(styrene-b-ethylene oxide) block copolymer as stabilizer. Besides the formation of composite core–shell particles, a large number of free latex particles that do not contain silica were also formed. This number decreases as the size of the silica beads decreases from 300 to 29 nm in diameter, and becomes very low compared to the number of composite particles for the smallest silica beads used. In every case, the composite particles could be easily separated from the free latex particles by centrifugation, providing a material made of regular core–shell composite particles. On the basis of the mechanisms involved in dispersion polymerization, hypotheses were formulated to account for the formation of the silica–polystyrene composite particles. Received: 6 May 1999 Accepted in revised form: 29 June 1999     

The nanoscale description of acid penetration to the gold colloids encapsulated in silica sol–gel matrix

Various sizes of gold nano colloidal particles ranging from 5 nm to 100 nm of size were encapsulated in a silica based sol–gel, and these surfaces were exposed to a pH 1 acid solution. This enabled us to observe the process of solvent intrusion and interaction with gold colloids by the absorption spectrum as a function of time. The rate was analyzed by a single exponential analytical function, and the maximum rate was found for gold colloid of 15 nm size. The least acid interaction and colour change was observed for the size of 60 nm. It was speculated that the surface of these gold colloids were homogeneously covered by the sodium tetra-borate buffer which insulated silica gel layer, thus avoiding direct contact of the acid with the surface of the gold colloid. This study confirmed that the nano scale dopant size affects the rate of solvent penetration into a sol–gel cavity.