Metal-Containing Poly(tetrafluoroethylene): A Novel Material

A method is described for preparing isolated Fe nanoparticles on the surface of poly(tetrafluoroethylene) (PTFE) nanogranules. The composition and atomic structure of the nanoparticles are investigated by transmission electron microscopy and EXAFS, x-ray emission, and Mössbauer spectroscopic techniques. The nanoparticles have a complex composition and structure and contain -Fe (15%). The majority phase in the nanoparticles is iron carbide (48%). On the surface of the PTFE nanogranules, the nanoparticles react with fluorine, forming Fe–F bonds (12% FeF₂). The free surface of the nanoparticles, noninteracting with fluorine, is oxidized by oxygen to form Fe₂O₃ (25%). A model for the structure of the nanoparticles is described.     

Fe-containing nanoparticles on the surface of silica microgranules

We have prepared nanomaterials consisting of SiO₂ microgranules and Fe-containing nanoparticles on their surface and determined the size and composition of the nanoparticles. The nanoparticles are shown to have a core-shell structure (α-Fe core and γ-Fe₂O₃ shell). The α-Fe core and Fe₂O₃ shell are responsible, respectively, for the broad and narrow lines in the EMR spectrum of the nanoparticles. The magnetic properties of larger nanoparticles are dominated by the core, while those of smaller nanoparticles are dominated by the oxide shell.     

Preparation and characteristics of core–shell structure cobalt/silica nanoparticles

The silica nanolayer with different thickness was coated on the spherical cobalt nanoparticles (an average diameter of 67 nm) to form core–shell structure by the controlled hydrolysis and condensation of tetraethyl orthosilicate (TEOS). This coating process was based on the use of silane coupling agent 3-mercaptopropyltrimethoxysilane (HS-(CH₂)₃Si(OCH₃)₃, MPTS) as a primer to render the cobalt surface vitreophilic, thus rendering cobalt surface compatible with silica. The control over the silica coating layer thickness can be achieved by varying the reaction time. The cobalt nanoparticles and the cobalt coated with silica shell were confirmed by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) was used to gain insight into the way in which the MPTS is bound to the surface of the cobalt nanoparticles. Result of the thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicate that the thermal stability of cobalt/silica is better than that of pure cobalt nanoparticles. Magnetic properties of these powders have been evaluated. These cobalt/silica core–shell nanoparticles can be utilized as precursors for making property-tunable magnetic nanoparticles, thin films, and multilayered core–shell structure nanocomposites.     

Thermal stability of graphite-Cobalt nanocomposite materials

Graphite-Co composites produced by intercalating potassium into graphite to give C₈K, followed by reaction with CoCl₂ and reduction of Co were characterized by x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and secondary ion mass spectrometry. The results indicate that the Co in the composites is present both between graphite layers, in the form of atomically dispersed metal (intercalated into graphite), and on the surface of the graphite support, in the form of nanoparticles. Heat treatment of the nanocomposites in several steps increases the amount of cobalt on the graphite surface relative to that between the graphite layers owing to the outdiffusion of cobalt atoms from the interlayer spaces. Heating markedly increases the magnetic susceptibility of the graphite-Co composites, also by virtue of the Co diffusion to the surface of the graphite particles and the formation of Co agglomerates.     

Role of Ni<Superscript>2+</Superscript> Ions in Magnetite Nano-particles Synthesized by Co-precipitation Method

In the present work, nickel-doped iron oxide (Ni_xFe_3?x O ₄) nanoparticles with different concentration of nickel (x = 0, 0.05, 0.1, and 0.15) have been prepared by co-precipitation method. These prepared nanoparticles have been characterized by using x-ray diffractometer, thermo gravimetric analysis and differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer, and UV-Visible spectroscopy to study their structural, thermal, morphological, magnetic, and optical properties, respectively. The x-ray diffraction confirms the formation of single-phase inverse spinel cubic structure of NiFe₃ O ₄ nanoparticles. Crystallite size has been estimated by the full width at half maximum of the most intense x-ray diffraction peak where vibrational and stretching modes of metal-oxygen bonds in 872 cm are shown in Fourier transform infrared spectra which confirms the formation of nanoparticles. The thermal analysis revealed that the transition temperature and stability increases with increasing Ni concentration. The surface morphology indicated that the particles are spherical in shape with some agglomeration. The magnetic measurement revealed that the coercivity and anisotropy increases with nickel doping in magnetite nanoparticles. The optical analysis revealed that direct and indirect both types of band gap increases when the particle size decreases because the absorption spectra shift toward smaller wavelength. The blue shift confirms the formation of nanoparticles.     

Hydroxyapatite-Carboxymethyl Cellulose Nanocomposite Biomaterial

An organic-mineral composite of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) nanoparticles and carboxymethyl cellulose (CMC) is synthesized via coprecipitation from a solution containing CaCl₂, aqueous ammonia, (NH₄)₂HPO₄, and CMC. The composition and microstructure of the composite and the lattice parameters and particle size of the hydroxyapatite are determined using x-ray diffraction, chemical analysis, IR spectroscopy, scanning and transmission electron microscopy techniques, electron diffraction, and x-ray microanalysis. The hydroxyapatite nanoparticles are shown to form agglomerates about 200 nm in size. The interaction between the nanoparticles and CMC macromolecules leads to the formation of a pore structure potentially attractive for biomedical applications.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 592–599.Original Russian Text Copyright © 2005 by Zakharov, Ezhova, Koval, Kalinnikov, Chalykh.     

Structural,optical and magnetic properties of cobalt-doped CdSe nanoparticles

Pure and Co-doped CdSe nanoparticles have been synthesized by hydrothermal technique. The synthesized nanoparticles have been characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–Visible), photoluminescence spectroscopy (PL), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID), at room temperature. From XRD analysis, pure and cobalt-doped CdSe nanoparticles have been found to be polycrystalline in nature and possess zinc blende phase having cubic structure. In addition to this, some peaks related to secondary phase or impurities such as cobalt diselenide (CoSe₂) have also been observed. The calculated average crystallite size of the nanoparticles lies in the range, 3–21 nm, which is consistent with the results obtained from TEM analysis. The decrease in average crystallite size and blue shift in the band gap has been observed with Co-doping into the host CdSe nanoparticles. The magnetic analysis shows the ferromagnetic behaviour up to 10% of Co-doping concentration. The increase of Co content beyond 10% doping concentration leads to antiferromagnetic interactions between the Co ions, which suppress the ferromagnetism.     

Synthesis of Co3 O4 /graphene nanocomposite using paraffin wax for adsorption of methyl violet in water

This study discusses the use of Co₃ O₄ impregnated graphene (CoOIG) as an efficient adsorbent for the removal of methyl violet (MV) dye from wastewater. CoOIG nanocomposites have been prepared by pyrolyzing paraffin wax with cobalt acetate. The synthesised nanocomposite was characterised by X‐ray diffraction, field emission scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscope, Raman spectroscopy, and Brunauer–Emmett–Teller isotherm studies. The above studies indicate that the composites have cobalt oxide nanoparticles of size 51–58 nm embedded in the graphene nanoparticles. The adsorption studies were conducted with various parameters, pH, temperature and initial dye concentration, adsorbent dosage and contact time by the batch method. The adsorption of MV dye by the adsorbent CoOIG was about 90% initially at 15 min and 98% dye removal at pH 5. The data were fitted in Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich and Sips isotherm models. Various thermodynamic parameters like Gibbs free energy, enthalpy, and entropy of the on‐going adsorption process have also been calculated.Inspec keywords: cobalt compounds, graphene, nanoparticles, nanocomposites, nanofabrication, adsorption, dyes, scanning electron microscopy, field emission electron microscopy, transmission electron microscopy, Raman spectra, Fourier transform infrared spectra, free energy, enthalpy, entropyOther keywords: nanocomposite, paraffin wax, adsorption, methyl violet dye, water, X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, Brunauer‐Emmett‐Teller isotherm, cobalt oxide nanoparticles, graphene nanoparticles, thermodynamic parameters, Gibbs free energy, enthalpy, entropy, Co₃ O₄ ‐C     

Synthesis and characterization of CoFe(2)O(4) ferrite nanoparticles obtained by an electrochemical method

Uniform size cobalt ferrite nanoparticles have been synthesized in one step using an electrochemical technique. Synthesis parameters such as the current density, temperature and stirring were optimized to produce pure cobalt ferrite. The nanoparticles have been investigated by means of magnetic measurements, M?ssbauer spectroscopy, x-ray powder diffraction and transmission electron microscopy. The average size of the electrosynthesized samples was controlled by the synthesis parameters and this showed a rather narrow size distribution. The x-ray analysis shows that the CoFe(2)O(4) obtained presents a totally inverse spinel structure. The magnetic properties of the stoichiometric nanoparticles show ferromagnetic behavior at room temperature with a coercivity up to 6386?Oe and a saturation magnetization of 85?emu?g(-1).     

Growth of MoS<Subscript>2</Subscript> layers on the surface of multiwalled carbon nanotubes

Molybdenum disulfide has been deposited on the surface of multiwalled carbon nanotubes synthesized through arc vaporization of graphite. As shown by transmission electron microscopy, extended MoS₂ layers have been formed on the surface of the carbon nanoparticles. According to x-ray diffraction results, the crystallinity of the MoS₂ layers in the composites improves with increasing annealing temperature. Free MoS₂ particles can be removed from the composites by centrifugation in bromoform.     

Study of preparation and magnetic properties of silica-coated cobalt ferrite nanocomposites

The structure and the magnetic properties of silica-coated cobalt ferrite nanoparticles (80 wt% CoFe₂O₄), prepared by sol–gel method and submitted to thermal treatments in the range 800–1,000 °C, were investigated through XRD, FT-IR, TEM and VSM. The effects of thermal treatment temperatures on the structure and magnetic properties of nanoparticles were examined. A silica shell thickness of about 5 nm was synthesized on top of cobalt ferrite nanoparticles. The non-crystalline silica confines the growth of cobalt ferrite nanoparticles, i.e., the particle sizes are almost independent of the thermal treatment. Saturation magnetization (Ms) was decreased slightly and coercivity (Hc) was increased, when the non-crystalline silica was coated on the surface of cobalt ferrite nanoparticles.     

Effect of sintering temperature on the phase composition and microhardness of WC-8 wt % Co cemented carbide

The effect of sintering temperature (800–1600°C) on the phase composition, density, and microhardness of WC-8 wt % Co cemented carbide has been studied using x-ray diffraction, scanning electron microscopy, optical microscopy, and density measurements. The results indicate that, during sintering of the starting powder mixture, containing not only WC and Co but also the lower carbide W₂C and free carbon, W₂C reacts with cobalt metal to form Co₃W. At sintering temperatures from 900 to 1200°C, the reaction intermediate is the ternary carbide phase Co₆W₆C. During sintering at 1300°C, this phase reacts with carbon to form Co₃W₃C. Sintering at 1000°C and higher temperatures is accompanied by the formation of a cubic solid solution of tungsten carbide in cobalt, β-Co(WC). The density and microhardness of the sintered samples have been measured as functions of sintering temperature, and the optimal sintering temperature has been determined.     

The interaction of cobalt with oxidized silicon surface

The initial stages of the growth of cobalt disilicide (CoSi₂) on a 2×1 reconstructed Si(100) surface in the presence of oxygen have been studied for the first time by method of high-resolution photoelectron spectroscopy. The evolution of the electron structure of the sample surface was traced in the course of silicon oxidation, cobalt deposition, and subsequent thermal annealing. It is established that cobalt atoms penetrate to the oxide-silicon interface even at room temperature. This phenomenon favors the formation of an epitaxial CoSi₂ layer with improved morphology.     

Various curing conditions for controlling PTFE micro/nano-fiber texture of a bionic superhydrophobic coating surface

A simple and conventional coating-curing process to fabricate superhydrophobic coating surface with both the micro-nano-scale binary structure (MNBS) roughness, and the lowest surface energy hydrophobic groups (?CF₃) on engineering materials of stainless steel or other metals was developed by control of curing conditions. Results show that higher temperature and longer cooling time resulted in longer crystallizing process, and the forming PTFE aggregates could slowly produce the crystallization and create the willow-leaf-like or wheat-haulm-leaf-like polymer micro/nano-fiber on the atop surface. The curing temperature dramatically influences the micro/nano-fiber texture of the PTFE/PPS superhydrophobic coating surface, leading to the excellent superhydrophobicity at higher temperature. An increase of the curing temperature is beneficial to fluorine gradient-distribution, PPS thermal-oxidative cross-linking and oxidative reaction, resulting in the enhancement of adhesive strength and mechanical properties of the PTFE/PPS superhydrophobic coatings. A bionic superhydrophobic surface with porous gel-like network and PTFE micro/nano-fiber textures could be created by natural cooling in air, whereas PTFE nano-sphere/-papillates textures could be fabricated by hardening in H₂O.     

Modeling of Silver Nanoparticle Synthesis in Ternary Reverse Microemulsion of Cyclohexane/Water/SDS

In the present study, a simple mathematical model has been developed for synthesis of silver nanoparticles. The silver nanoparticles have been synthesized in ternary reverse microemulsion of cyclohexane/water/sodium dodecyl sulfate (SDS). The silver nanoparticles were produced by reaction between silver nitrate in the water droplet core of one microemulsion and hydrazine as reducing agent in the water droplet core of another microemulsion. The dynamic behavior of process was modeled on mass balance equations which were solved using the finite difference method. The kinetic parameters of the critical number size (N _crit ), rate order of nucleation, and growth constants were estimated by minimizing the difference between the average particle size predicted by model and those obtained by experiments. The UV-Vis absorption spectra, transmission electron microscopy (TEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS) were used to analyze the structure and particle size distribution of silver nanoparticles.     

Investigation of Structural, Magnetic and Magnetotransport Properties of Electrodeposited Co–TiO2 Nanocomposite Films

Nanocomposite Co?CTiO₂ thin films were prepared by simultaneous electrodeposition of Co and TiO₂ on a Cu substrate from a solution based on Co sulfate in which TiO₂ nanoparticles were suspended by stirring. We investigated the influence of the TiO₂ nanoparticles concentration in the bath on the morphology, composition, magnetic and magnetotransport properties of the films. The Co?CTiO₂ thin films were characterized by using scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction analyses, and their magnetic properties were evaluated by using an induction type device with data acquisition system and a torque magnetometer. The current in-plane transport properties of the films have been investigated. The results showed that the films were composed of a Co metal matrix containing embedded TiO₂ nanoparticles and cobalt hydroxide which is formed simultaneously with cobalt metal deposition. The amount of TiO₂ in the film increases with the rising concentration of TiO₂ nanoparticles in the plating bath. This complex structure favored the increase of the magnetoresistance. The Co?CTiO₂ nanocomposite films (containing about 1.3 at.% Ti) exhibit a giant magnetoresistance contribution of 47.6 %. From the magnetic measurements, we have found that the saturation magnetization, the magnetic susceptibility, and the effective magnetic anisotropy constant decrease with the increasing content of TiO₂ in the thin layer. The easy magnetization axis direction changes from in-plane to almost perpendicular-to-plane, with increasing TiO₂ nanoparticles content in the film. The existence of a giant magnetoresistance effect in Co?CTiO₂ is very promising for potential applications in spintronics.     

Synthesis and characterization of calcium hydroxide nanoparticles by hydrogen plasma-metal reaction method

Ca(OH)₂ nanoparticles have been synthesized with high purity and yield using the hydrogen plasma-metal reaction method. They are spherical in shape with a mean particle size of approximately 100 nm. The morphology of nanoparticles is spongy with mesopores, mostly less than 10 nm. The pore volume and surface area of Ca(OH)₂ nanoparticles are 0.084 cm³/g and 28.7 m²/g, respectively. Both transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis demonstrated that these nanoparticles possess poly-nanocrystalline structure with an average grain size of about 10 nm. The formation mechanism of Ca(OH)₂ nanoparticles was discussed in terms of chemical reactions and coalescence during the processing.     

Characterization of platinum–iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation

Mesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum−iron catalysts Pt–Fe/RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0 wt.%, respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was + 3, as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H₂O₂ as the oxidant at phenol : H₂O₂ mole ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. The first three ratios produced only catechol and hydroquinone, whereas the 2 : 4 ratio also produced benzoquinone. The 2 : 3 ratio gave the highest phenol conversion of 47% at 70 °C. The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt/RH-MCM-41 and Fe/RH-MCM-41.     

The effect of humic acid on the stability and aggregation kinetics of WO3 nanoparticles

The physicochemical properties including size, hydrodynamic diameter, agglomeration rate, surface area, crystal structure, and surface charge were determined for WO₃ using x-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), UV-Vis spectrometer (DRS), and Zetasizer Nano ZS. The stability and aggregation behavior of WO₃ were investigated using dynamic light scattering (DLS) to monitor the hydrodynamic size and zeta potential. The effect of ionic strength was further studied using NaCl, MgCl_2. and CaCl₂ electrolytes at pH 5 as well as the effect of humic acid. WO₃ nanoparticles behaved similarly in deionized water suspensions and in the presence of NaCl electrolytes. The stability of nanoparticles was notable at low concentration (1?ppm) of humic acid particularly with NaCl electrolytes. Divalent cations enhanced agglomeration of nanoparticles even at the highest concentration of humic acid due to the formation of cation-humic acid bridges. The Derjaguin–Landau–Verwey–Overbeek theory was used to investigate the interaction energies, and it was found that van der Waals attraction forces are dominant in the presence of divalent cations.     

Biosynthesis and stabilization of Au and Au–Ag alloy nanoparticles by fungus,Fusarium semitectum

Abstract

Crystallized and spherical-shaped Au and Au–Ag alloy nanoparticles have been synthesized and stabilized using a fungus, F . semitectum in an aqueous system. Aqueous solutions of chloroaurate ions for Au and chloroaurate and Ag⁺ ions (1 : 1 ratio) for Au–Ag alloy were treated with an extracellular filtrate of F . semitectum biomass for the formation of Au nanoparticles (AuNP) and Au–Ag alloy nanoparticles (Au–AgNP). Analysis of the feasibility of the biosynthesized nanoparticles and core–shell alloy nanoparticles from fungal strains is particularly significant. The resultant colloidal suspensions are highly stable for many weeks. The obtained Au and Au–Ag alloy nanoparticles were characterized by the surface plasmon resonance (SPR) peaks using a UV-vis spectrophotometer, and the structure, morphology and size were determined by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and transmission electron microscopy (TEM). Possible optoelectronics and medical applications of these nanoparticles are envisaged.